oEPA
United States
Environmental Protection
Agency
Water and Waste Management
Effluent Guidelines Division
WH-552
Washington, DC 20460
Development
Document for
Existing Source
Pretreatment
Standards for the
Electroplating
EPA 440/1-79/003
August 1979
Final
Point Source Category
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DEVELOPMENT DOCUMENT
for
EXISTING SOURCE PRETREATMENT STANDARDS
for the
ELECTROPLATING
POINT SOURCE CATEGORY
Douglas M. Costle
Administrator
Swep Davis
Deputy Assistant Administrator
for Water Planning and Standards
Robert B. Schaffer
Director, Effluent Guidelines Division
Ernst P. Hall, P.E.
Chief, Metals and Machinery Branch
J. Bill Hanson, P.E.
Project Officer
August 1979
Effluent Guidelines Division
Office of Water and Hazardous Materials
U.S. Environmental Protection Agency
Washington, D.C. 20460
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11
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ABSTRACT
This report presents the findings of an extensive study of
electroplating processes for the purpose of developing pretreatment
standards for existing point sources discharging to publicly owned
treatment works (POTW) to implement Section 307(b) of the Clean Water
Act, as amended (33 U.S.C. 1317(b)), which requires the establishment
of pretreatment standards for pollutants introduced into publicly
owned treatment works (POTWs). This regulation is also being
promulgated in compliance with the Settlement Agreement in Natural
Resources Defense Council, Inc. v. Train, 8 ERC 2120 (D.D.C. 1976), as
modified March 9, 1979.
This study presents pretreatment standards for the entire
electroplating point source category for existing sources discharging
to municipal treatment systems. Pretreatment standards for existing
sources presented in this document describe the degree of effluent
reduction attainable through the application of the best practicable
control technology currently available and do not account for the
further incidental treatment to be performed by municipal treatment
systems.
These standards may be achieved by chemical treatment of the waste
waters to destroy oxidizable cyanide, reduce hexavalent chromium, and
removal of all but small amounts of metals using conventional solids
removal equipment. In-process control equipment such as ion exchange,
evaporation or reverse osmosis may also be used, either alone or in
conjunction with the end-of-pipe control equipment to achieve these
standards.
Pretreatment standards setting forth the degree of pollutant reduction
attainable through the application of the best available technology
economically achievable (BAT) will be published at a later date. The
standards of performance for new sources discharging to surface waters
or municipal treatment systems will also be published at a later date.
iii
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IV
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CONTENTS
Number Title Page
I. Conclusions 1
II. Recommendations 3
III. Introduction 9
Authority 9
Approach to Pretreatment Standards 9
Description of the Electroplating 17
IV. Industry Categorization 67
Introduction 67
Categorization Basis 67
Effluent Limitation Base 72
V. Waste Characterization 81
Introduction 81
Characteristics of Wastes from the Electro-
plating Point Source Category 81
VI. Selection of Pollutant Parameters 103
Introduction 103
Examples of Effect of Pretreatment on
Sludge Quality 105
Pollutant Parameters 106
Pollutant Parameters not Selected 116
VII. Control and Treatment Technology 117
Introduction 117
In-Plant Technology 120
Individual Treatment Technologies 139
End-of-Pipe Technology for Electroplating 248
In-Line Technology for Electroplating 251
End-of-Pipe Technology for Printed Board Manufacture 257
In-Line Technology for Printed Board Manufacture 261
VIII, Cost of Wastewater Control and Treatment 267
Introduction 267
Cost Estimates 267
Energy and Non-Water Quality Aspects 321
IX. Best Practicable Control Technology Currently Available,
Guidelines and Limitations 325
X. Best Available Technology Economically Achievable,
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Guidelines and Limitations 327
XI. New Source Performance Standards 329
XII. Pretreatment 331
Technical Approach 331
Statistical Methodology 332
Treatment of Cyanide 336
Amenable Cyanide Treatment for Small Platers 346
Treatment of Hexavalent Chromium 350
Metals Removal Using Sedimentation for the
Electroplating Category: Cr,T, Cu, Ni, Zn,
Cd, Pb, Ag 354
Estimation of Average Metal Concentrations 370
Metals Treatment Using Filtration 382
Metals Removal for Electroless Plating and Printed
Circuit Board Manufacturing 392
Overview of Concentration Based Pretreatment
Standards 396
Equivalent Mass-Based Pretreatment Standards 396
Total Suspended Solids as a Monitoring Alternative 404
Summary 411
Appendix XII 413
XIII. Acknowledgements 459
XIV. References 461
XV. Glossary 485
VI
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TABLES
Number Title Page
2-1 Recommended Pretreatment Standards 5
2-2 Optional Mass-Based Standards 6
2-3 Optional Pretreatment Standards 7
3-1 Data Source Summary 11
3-2 Characteristics of the Data Base 13
3-3 Common Chelating Agents - Marketers and
Manufacturers 31
3-4 Comparison of Basic Process Steps 44
4-1 Effect of Masking on Dragout 74
4-2 Effect of Holes on Dragout 74
4-3 Electroplating Operations 77
4-4 Operations in the Manufacture of Printed Boards 79
5-1 Analysis Methods 82
5-2 Chelate Analysis Methods 86
5-3 Composition of Raw Waste Streams from Common
Metals Plating 96
5-4 Composition of Raw Waste Streams from
Precious Metals Plating 97
5-5 Composition of Raw Waste Streams from Anodizing 97
5-6 Composition of Raw Waste Streams from Coatings 98
5-7 Composition of Raw Waste Streams from
Chemical Milling and Etching 99
5-8 Composition of Raw Waste Streams from
Electroless Plating 100
5-9 Chelating Agents in Electroplating 100
5-10 Characteristics of Raw Waste Streams
in the Printed Board Industry 101
6-1 Pollutant Parameter Occurrence 104
7-1 Comparison of Wastewater at Plant ID 23061
Before and After Pumping of Settling Tank 119
7-2 Usage of Various Rinse Techniques by Companies 119
7-3 Electroplating Plants that Currently Employ
Chemical Reduction 143
7-4 Electroplating Plants that Currently Employ
pH Adjustment 147
7-5 Plants Currently Using A System Including
Clarification 154
7-6 Electroplating Plants that Currently Employ
Oxidation by Chlorine 166
7-7 Relative Performance and Application
Characteristics of Solid/Liquid
Separation Equipment 173
7-8 Application of Ion Exchange to Electroplating
for Used Rinse Water Processing 176
VII
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7-9 Application of Evaporation to the Electroplating
Point Source Category 187
7-10 Electroplating Plants that Employ Evaporation 189
7-11 Application of Reverse Osmosis in the Electro-
plating Point Source Category 189
7-12 Typical Membrane Performance 196
7-13 Electroplating Plants that Currently Employ
Vacuum Filtration 230
7-14 Removal of Metals by Lime Precipitation -
Activated Carbon Combination 241
7-15 Removal of Metals by Ferric Chloride -
Activated Carbon Combination 242
7-16 Treatment of Wastewaters Containing Metals 245
7-17 Removal of Metal Cations from Water with
Insoluble Starch Xanthate 247
7-18 Removal of Metals from Dilute Solution
with Insoluble Starch Xanthate 247
7-19 Treatment System Elements for Various
Manufacturing Operations 250
7-20 In-Line Technology Applicability 253
7-21 Pollutant Discharge at an Example Plant 256
8-1 Index to Technology Cost Tables 268
8-2 Countercurrent Rinse (for other than
Recovery of Evaporative Plating Loss) 273
8-3 Countercurrent Rinse Used for Recovery
of Evaporative Plating Loss 274
8-4 Spray Rinse Used for Recovery of
Evaporative Plating Loss 275
8-5 Still Rinse Used for Recovery of
Evaporative Plating Loss 277
8-6 Clarification-Continuous Treatment
Settling Tank 279
8-7 Clarification-Batch Treatment Settling Tank 279
8-8 Chromium Reduction - Continuous Treatment 281
8-9 Chromium Reduction - Batch Treatment 281
8-10 Cyanide Oxidation - Continuous Treatment 284
8-11 Cyanide Oxidation - Batch Treatment 284
8-12 pH Adjustment 286
8-13 Diatomaceous Earth Filtration 286
8-14 Submerged Tube Evaporation - Single Effect 287
8-15 Submerged Tube Evaporation - Double Effect 287
8-16 Climbing Film Evaporation 289
8-17 Atmospheric Evaporation 289
8-18 Flash Evaporation 291
8-19 Ultrafiltration 291
8-20 Membrane Filtration 295
8-21 Ion Exchange - In-Plant Regeneration 295
8-22 Ion Exchange - Service Regeneration 296
8-23 Cyclic Ion Exchange 296
Vlll
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8-24 Reverse Osmosis 298
8-25 End-of-Pipe Treatment Without Chelated Wastes 302
8-26 End-of-Pipe Treatment With Chelated Wastes 303
8-27 Base Plant - Running Rinses 307
8-28 3-Stage Countercurrent Rinses 308
8-29 Plating Solution Recovery 309
8-30 Plating Solution Recovery with Base Plant
End-of-Pipe Treatment 312
8-31 Electroless Plating on Metals and Plastics
In-Line 313
8-32 Printed Board Manufacture In-Line 313
8-33 Cost Program Pollutant Parameters 315
8-34 Wastewater Sampling Frequency 319
8-35 Nonwater Quality Aspects of Wastewater Treatment 322
8-36 Nonwater Quality Aspects of Sludge and
Solids Handling 323
12-1 CN(A) Concentrations Observed in Effluent from
Plants with Cyanide Oxidation in Waste
Treatment System 338
12-2 CN(T) Concentrations Observed in Effluent from
Plants with Cyanide Oxidation
in Waste Treatment System 341
12-3 Plant Summary Statistics and Variability
Factors for CN(A) 347
12-4 Plant Summary Statistics and Variability
Factors for CN(T) 348
12-5 Clarifier Influent Concentrations Observed from
Plants Used in the Amenable Cyanide Analysis
for Smaller Platers 349
12-6 Cr(VI) Concentrations Observed in Effluent from
Plants with Cr Plating or Chromating
Operations 351
12-7 Plant Summary Statistics and Variability
Factors for Cr(VI) 355
12-8 Regression Fit of Average Metal Species Discharged
from 25 Plants with Clarifier Systems
Using Equation [5] 359
12-9 Regression Fit of Average Metal Species Discharged
from 25 Plants with Clarifier Systems
Using Equation [6] 360
12-10 Metal Concentrations Predicted by Equation [6]
and Equation [7] at Average Values of
TSS and Xme 361
12-11 Distribution of Fraction Metal in Raw Waste Load
Total Metals Discharged by 47 Metal
Finishing Plants 371
12-12 Dependence of Xme on Number Metals Used
in Plating and Finishing 373
12-13 Predicted Average Metal Concentration in
Discharge from Plants with 25 mg/1 TSS 374
IX
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12-14 Daily Variability Factors for Electroplating Category 379
12-15 Discharge and Raw Waste Silver Concentrations
Observed for Nine Plants 381
12-16 TSS in Discharge from Five Plants Using Filtration
for Primary Solids Separation 383
12-17 Average Metal Concentrations in Discharge from Five
Plants Using Filtration for Primary Solids
Separation 385
12-18 TSS in Discharge from Five Plants Using Polishing
Filter After Clarifiers 388
12-19 Average Metal Concentrations in Discharge from Five
Plants Using Polishing Filter After Clarifier 391
12-20 Metal Removal Efficiency of Treatment System of Ten
Plants Depositing Cu by Electroless Plating 394
12-21 Metal Removal Efficiency of Treatment System of Seven
Plants Depositing Ni by Electroless Plating 395
12-22 Summary of Long Term Averages, Variability
Factors and Daily and 30-Day Average
Maximum Limitations 397
12-23 Summary of Concentration-Based Pretreatment
Standards 398
12-24 Water Usage for the Electroplating Category
(l/op-m*) 400
12-25 Water Usage for the Electroless Plating
Subcategory (1/op-m2) 402
12-26 Water Usage for the Printed Circuit Board
Subcategory (l/op-m*) 403
12-27 Summary of Mass-Based Pretreatment Standards
for the Electroplating Category and
Electroless Plating Subcategory 405
12-28 Summary of Mass-Based Pretreatment Standards
for the Printed Circuit Board
Subcategory 406
12-29 Individual Metal Hydroxide Constants 408
12-30 Total Suspended Solids Hydroxide Equivalents 408
12-31 Observations with No Limitations Exceeded 409
12-32 Observations with at Least One Limitation
Exceeded 410
12-33 Summary of Concentration-Based Pretreatment
Standards and Equivalent Mass-Based
Pretreatment Standards 412
15-1 Conversion Table 526
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FIGURES
Number Title Page
3-1 Conceptual Arrangement of the Plating Process 19
3-2 Typical Electroplating Surface Preparation Sequence 23
3-3 Example of Electroless Plating on Plastic -
Surface Preparation Sequence 33
3-4 Example of Electroless Plating on Metals -
Surface Preparation Sequence 34
3-5 Example of Surface Preparation Sequence for Anodizing
of Aluminum 37
3-6 Subtractive Process 46
3-7 • Additive Process 48
3-8 Semi-Additive Process 49
3-9 Single Sided Board Production Sequence 50
3-10 Double Sided Board Production Sequence 51
3-11 Multi-Layer Board Production Sequence 53
3-12 Multi-Layer Hole Cleaning 54
3-13 Cleaning Sequence for Electroless Copper Deposition 55
3-14 Catalyst Application and Electroless Copper
Deposition 58
3-15 Pattern Plating (Copper and Solder) 61
3-16 Tab Stripping and Plating (Nickel and Gold) 62
3-17 Immersion Tin Plating Line 64
3-18 Etching Line Process 65
5-1 Schematic Flow Chart for Water Flow in Chromium
Plating Zinc Die Castings, Decorative 88
5-2 Use of Rinse Water in Electroless Plating
of Nickel 89
7-1 Single Rinse Tank 122
7-2 3-Stage Countercurrent Rinse 123
7-3 3-Stage Countercurrent Rinse with
Outboard Arrangement 124
7-4 Series Rinse Tanks 125
7-5 Spray Rinse 127
7-6 Closed Loop 3-Stage Countercurrent Rinse 129
7-7 Typical Printed Board Rack 133
7-8 Modified Printed Board Rack for
Dragout Control 134
7-9 Hexavalent Chromium Reduction with
Sulfur Dioxide 141
7-10 Effect of pH on Solubility of Trivalent
Chromium 145
7-11 Circular Clarifier 151
7-12 Air/Solids Ratio 159
7-13 Treatment of Cyanide Waste by Alkaline
Chlorination 161
XI
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7-14 Typical Ozone Plant for Waste Treatment 165
7-15 Typical Pressure Filter 170
7-16 Chromic Acid Recovery by Cyclic Operation
Ion Exchange 178
7-17 Types of Evaporation Equipment 184
7-18 Application of Evaporation to Metal Finishing 186
7-19 Application of Reverse Osmosis Alone and
with Supplemental Evaporation 193
7-20 Application of Membrane Filtration to Metal
Finishing Wastewater 202
7-21 Extended Surface Electrolysis Cells 207
7-22 Application of Extended Surface Electrolysis 209
7-23 Effect of Concentration on Electrical
Efficiency in Metals Reduction 210
7-24 Simple Electrodialysis Cell 212
7-25 Mechanism of the Electrodialytic Process 213
7-26 Electrodialysis Recovery System 215
7-27 Electrolytic Recovery 216
7-28 Mechanical Gravity Thickening 219
7-29 Typical Pressure Filter 221
7-30 Feed Flow and Filtrate Drainage 222
7-31 Plan and Section of a Typical Sludge
Drying Bed 225
7-32 Vacuum Filtration System 228
7-33 Conveyor Type Sludge Dewatering Centrifuge 232
7-34 End-of-Pipe Treatment System 249
7-35 Typical In-Line Treatment System 254
7-36 End-of-Pipe System for Printed Board
Manufacturers (Single Waste Stream) 258
7-37 End-of-Pipe System for Printed Board
Manufacturers (Segregated Waste Streams) 259
7-38 End-of-Pipe System for Printed Board
Manufacturers (for Ammoniated Waste Waters) 262
7-39 In-Line Treatment System for Printed Board
Plants (Recovery of Electroless Plating
Solution) 263
7-40 In-Line Treatment System for Printed Board
Plants (End-of-Pipe Filtration) 264
8-1 Evaporation Investment Cost 292
8-2 Evaporation Total Annual Cost 293
8-3 End-of-Pipe Treatment System 300
12-1 Cumulative Plot of Average CN(A) in Discharges
from 47 Plants 337
12-2 Cumulative Plot of Average CN(T) in Discharges
from 69 Plants 343
12-3 Cumulative Distribution of 24 Daily CN(T) Dis-
charge Concentrations from Plant 3320 344
12-4 Cumulative Distribution of 13 Daily CN(A) Dis-
charge Concentration from Plant 1108 345
xn
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12-5 Cumulative Plot of Average Cr(VI) 353
12-6 Cumulative Distribution of 45 Daily Cr(VI) Dis-
charge Concentration from Plant 116 356
12-7 Contours of Constant Expected Discharge Metal
Concentration as a Function of TSS and Xme 364
12-8 Comparison of Observed Discharge Metal Concentra-
tion vs Cine = 1 mg/1 Contour 365
12-9 230 Daily Values of Total Cr,T Concentration
for Plant 2080 377
12-10 Cumulative Distribution of 230 Daily Cr,T Concen-
trations for Plant 2080 378
12-11 Total Metals Out vs Total Metals In for Five Plants
with Filtrations as Primary Means or Solids
Separation 386
12-12 Effluent Metal Concentration vs RWL Metal Concentra-
tions for Five Plants with Filtration as Primary
Means or Metal Removal 387
12-13 Total Metals vs TSS in Discharge from Two Plants
with Polishing Filters 390
Xlll
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SECTION I
CONCLUSIONS
For the purpose of establishing pretreatment standards, the
electroplating point source category was divided into three segments:
plating, metal finishing and printed circuit board manufacture. The
plating category was then subdivided into common metal electroplating,
precious metal electroplating and electroless plating. The metal
finishing segment was subdivided into anodizing, coating, chemical
milling, and etching. The printed board manufacturing segment was not
subdivided like the plating and metal finishing segments because
printed board manufacturing is a unique mixture of operations and does
not require further subdivision. These subcategory selections were
based on a review of potential subcategory bases including: types of
processes, types of basis materials, raw materials used, size and age
of facilities, number of employees, geographic location, quantity of
work processed, waste characteristics, treatment technology, and water
use.
Of these potential subcategorization parameters, raw materials used
(plating baths) is the most suitable for the plating segment because
it focuses on the plating baths, and the dragout from these baths is
the major source of wastes in this industry segment. The value of
plating bath constituents dictates the type of treatment and recovery
practices for the plating wastes. The types of manufacturing
processes are the basis for subcategorization for the metal finishing
segment as they are the source of wastes from the plant and inherently
encompass the process baths used. Manufacturing processes also
provide a basis for subdividing the printed board industry. However,
because of the similarity in operations and wastes for printed board
plants, only one subcategory is selected for printed board
manufacture.
The pretreatment standards can be expressed in units of mass of
pollutant discharged per unit area processed for each plating or metal
finishing operation performed (mg/operation-sq m). For printed board
manufacture, area immersed is used in place of area processed. Area
immersed accounts for the dragout from the masked portion of the
board. The units in which the limitations are expressed directly
reflect the quantity of work performed by a plant and indirectly
relate to the number of parts processed, the size of the plant, and
the number of employees. These units are practical to derive, apply
and enforce, and they represent an absolute control on pollution. In
addition, pretreatment standards can also be specified in terms of
concentration.
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Pretreatment standards for electroplating were generally based on
actual performance by plants. This actual performance was determined
by plant visits and plant submitted data. Incidential pollutant
removal accomplished by municipal treatment systems was not considered
when determining these pretreatment standards.
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SECTION II
RECOMMENDATIONS
Proposed pretreatment standards for existing facilities discharging to
municipal treatment plants are summarized in Table 2-1. As shown in
the table, the limitations specified in this document are expressed in
terms of concentration (mg/1). Concentration limits are specified
primarily because of the ease of enforcing such regulations. Section
XII details the rationale for these standards as well as the optional
standards which follow. The table also shows a separate set of
regulations for smaller electroplating sources. These are defined as
plants discharging less than 38,000 liters (10,000 gallons) per day of
electroplating process water. This division was established in order
to minimize the economic impact to small sources caused by new
regulations. In future regulations, the Agency expects to define
small electroplating sources on the basis of the mass of pollutants
discharged as well as flow.
Table 2-2 presents an optional set of mass-based standards for plants
discharging more than 38,000 liters (10,000 gallons) per day of
electroplating process wastewater. These limitations may be used in
place of the concentration based standards upon prior agreement with
the publicly owned treatment works receiving the wastes. These
standards were designed as an equivalent to the concentration limits
for use by plants which recover process solutions and practice water
conservation. The link between the concentration standards and the
mass-based standards is a flow conversion factor (liters/square
meter). This flow conversion is the average production related flow
of the relevant plants in the data base (Reference Section XII).
Another optional set of limitations is the TSS monitoring alternate
(Table 2-3) in which TSS replaces Cu, Ni, Cr, and Zn as monitoring
parameters. The TSS monitoring alternate may be used with the
following stipulations:
No strong chelating agents are present in the waste, such as
cyanide, ammonia, EDTA, quadrol, HEDTA, NTA and DTPA (and
other amino polycarboxylic acid-type chelates).
Hexavalent chromium wastes are reduced.
All wastewaters are neutralized with calcium oxide (or
hydroxide).
These optional TSS regulations were developed in order to relieve the
monitoring burden from those plants who presently have a well operated
waste treatment system. The Agency believes that if the required
level of suspended solids is met, the individual metal and total metal
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concentrations of the effluent streams will not be greater than their
regulated concentrations.
Section XII explains the monitoring requirements and their
derivations. If regulated pollutants are found in concentrations less
than .10 mg/1 and the owner or operator of the plant attests that such
pollutants are not a part of his raw materials or processes, then
monitoring of these pollutants may be omitted for six months.
(Reference Section XII).
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Pollutant
or
Pollutant
Property
TABLE 2-1
RECOMMENDED PRETREATMENT STANDARDS
PRETREATMENT STANDARD
Maximum for
Any 1 Day
(mq/1)
Average of Dally
Values for 30
Consecutive Days
Shall Not Exceed
SMALL PLATER1)
PRETREATMENT STANDARD
Average of Daily
Values for 30
Maximum for Consecutive Days
Any 1 Day Shall Not Exceed
(mg/1)
CN, Amenable
CN, Total
Cu
Ni
Cr. Total
Zn
Pb
Cd ..
Total Metals2'
Silver-^)
0.8
4.5
4.1
7.0
4.2
0.6
1.2
10.5
0.23
1.8
1.8
2.5
1.8
0.3
0.5
5.0
5.0
0.6
1.2
1.5
0.3
0.5
Notes:
1) "Small plater" indicates plants discharging less than 38,000 liters (10,000 gallons)
per day of electroplating process waste water.
2) "Total metals" is defined as the sum of the concentration of copper, nickel, total
chromium, and zinc.
3) The silver pretreatment standard applies only to Subpart B, precious metals plating.
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Pollutant
or
Pollutant
Property
TABLE 2-2
OPTIONAL MASS-BASED PRETREATMENT STANDARDS
PRETREATMENT STANDARD
(mg/sq m-operati'on)
SUBCATEGORIES A, B, D, E, F, G PRINTED CIRCUIT BOARD MANUFACTURING
Maximum for
Any 1 Day
Average of Daily
Values for 30
Consecutive Days
Shall Not Exceed
Maximum for
Any 1 Day
Average of Daily
Values for 30
Consecutive Days
Shall Not Exceed
CN, Total
Cu
Ni
Cr
Zn
Pb
Cd ..
Total Metals1 '
Silver2^
29
176
160
273
164
23
47
410
47
9
70
70
98
70
12
20
195
20
67
401
365
623
374
53
107
935
20
160
160
223
160
27
45
445
NOTES:
1) "Total metals" is defined as the sum of the concentration of copper, nickel, total
chromium and zinc.
2) The silver pretreatment standard applies to Subpart B, precious metal plating.
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TABLE 2-3
OPTIONAL PRETREATMENT STANDARDS
PRETREATMENT STANDARD
(mg/1)
Pollutant Average of Daily
or Values for 30
Pollutant Maximum for Consecutive Days
Property Any 1 Day Shall Not Exceed
CN, Total 0.8 0.23
Pb 0.6 0.3
Cd 1.2 0.5
TSS 20.0 10.0
pH Within the range 7.5 to 10.0
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SECTION III
INTRODUCTION
AUTHORITY
Section 307(b) of the Act requires the administrator to establish
pretreatment standards for existing and new sources for incompatible
pollutants introduced into publicly owned treatment works (POTWs).
APPROACH TO PRETREATMENT STANDARDS
The standards proposed in this document were developed in the
following manner. The overall electroplating point source category
was first studied for the purpose of determining whether separate
standards were appropriate for different subcategories within the
point source category. This analysis resulted in the division of the
electroplating category into seven subcategories: electroplating of
common metals, electroplating of precious metals, anodizing, coatings,
chemical etching and milling, electroless plating and printed circuit
board manufacturing.
The electroplating category was initially investigated to determine
pollutant discharge rates in each subcategory. The printed circuit
board (sometimes called printed board) industry was known to have
somewhat different wastes than the remainder of the electroplating
category and was subsequently investigaged to compare pollutant
discharge rates, composition, and water uses in this subcategory to
those from the remaining electroplating subcategories. This
comparison indicated that there were higher pollutant discharges for
some parameters and higher water uses in printed circuit board
manufacturing than in the remaining electroplating subcategories.
Thus, printed circuit board manufacturing is considered a separate
subcategory in the electroplating category, and further subdivision of
printed circuit board manufacturing is not required. Once the
pollutant discharges were analyzed, the raw waste characteristics for
each subcategory were then identified. This included an analysis of
1) the source and volume of water used and the sources of wastes and
wastewaters, and 2) the constituents of all contact process
wastewaters including toxic constituents and other constituents which
result in taste, color and odor in water or affect aquatic organisms.
From this analysis, the constituents of wastewaters which should be
subjected to standards of performance were identified.
The full range of control and treatment technologies existing within
the electroplating category was then identified. In evaluating this
technology, various factors were considered. These included the total
cost of application of the technology in relation to the effluent
reduction benefits to be achieved, the age of equipment and facilities
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involved, the processes employed, the engineering aspects of the
application of various types of control techniques, process changes
and non-water quality environmental impact (including energy
requirements).
Sources of Industry Data
Data on electroplating and related processes were obtained from
literature studies and inquiries to federal and state environmental
agencies, plating materials suppliers, trade associations, and the
manufacturers themselves. These contacts are summarized in Table 3-1
and discussed below.
Literature Study - Published literature in the form of books,
periodicals, reports, papers, and promotional material was examined
and is presented in a detailed bibliography in Section XIV. The
material researched covered manufacturing processes used in the
industry, water use and percent recycling, waste treatment technology,
pollutant characteristics and economic data. This information
provided considerable insight into the plating industry, provided
background against which to categorize the industry, and provided a
list of some of the plants engaged in this industrial area.
Federal and State Contacts - All EPA regional offices and some state
environmental agencies were contacted to obtain permits and monitoring
data on plants contacted that were engaged in electroplating and
related processes.
Plating Materials Suppliers and Manufacturers - Two major plating
material suppliers and manufacturers were visited to gather
information on the chemistry of plating baths, the pollutional aspects
of the chemicals in baths, and the application of baths. In addition,
another 38 plating material suppliers and manufacturers were contacted
to obtain information on the chemicals in their baths.
Trade Association Contacts - Pollution abatement meetings of several
trade and professional associations were attended.
10
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Data Source
Table 3-1
Data Source Summary
Literature Sources 224
EPA Regional Offices 10
State and Territories
(contacted only
when regional
data was not
available) 11
Plating Materials
Suppliers 40
Companies (Plants)
Contacted 542
& Considered for
This Study
Companies Visited for
Data Verification 82
Seminars 1
11
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A general meeting of the Institute of Printed Circuits was attended at
which time the objectives of this program were outlined, and specific
effluent information from printed circuit manufacturers was solicited.
No significant response to this request was received.
Seminar - A seminar on printed circuits was attended. At this
seminar, state-of-the-art technology, particularly in the area of
additive and semi-additive circuitry, was presented.
Plant Survey and Evaluation - A number of sources were used to find
prospective companies to establish a data base for the electroplating
category. Among these sources were prior environmental studies done
on the subject, state and local agencies, literature studies, and
trade associations. Based on information from these sources, a total
of over 500 plants were contacted by telephone or letter.
All of the plants were initally contacted by telephone using standard
interview forms to guide the telephone conversation. Those that were
involved in electroplating and whose personnel were agreeable to
filling out a data collection portfolio were sent a portfolio. It has
sections for general plant data, specific production process data,
waste management process data, raw and treated wastewater data, waste
treatment cost information, material finishing line data, and
chelating agent information.
The criteria involved in selecting plants for sampling visits from the
telephone contacts were:
1. Electroplating or related manufacturing processes should
represent a large percentage of the plant's effluent
discharge.
2. The physical layout of plant plumbing should facilitate
segregation of the wastewater under study. This was
necessary to avoid interference of wastes from other
manufacturing operations.
3. The plant must have adequate waste treatment control
technology in place.
4. The mix of plants visited should contain both direct
dischargers and indirect dischargers.
5. The selected plants should provide a representative
geographical distribution to avoid a data base that
concentrates on a unique geographical condition.
6. The printed board plants visited should use a variety of
chelating agents.
12
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As stated, over 500 plants were contacted by telephone or letter.
Data from a large number of the companies were inadequate for complete
analysis, leaving an analyzable data base of 196 electroplating
facilities. A summary of the plant data base is presented in Table
3-2. The companies in each subcategory of the data base for the
industry are not mutually exclusive since some companies have
operations in more than one subcategory.
TABLE 3-2
CHARACTERISTICS OF THE DATA BASE
SUBCATEGORY NO. OF PLANTS
A. Electroplating of Common Metals 118
B. Electroplating of Precious Metals 39
D. Anodizing 26
E. Coatings 46
F. Chemical Etching and Milling 69
G. Electroless Plating 28
H. Printed Circuit Board Manufacture 14
The on-site evaluations consisted of two major activities; collection
of technical information and water sampling and testing. The
technical information gathering effort centered around a review and
completion of the data collection portfolio. In addition to this, the
following specific technical areas were studied during the visitation.
1. Rinsing operations and their effect on water use and waste
characteristics.
2. Water conservation techniques.
3. Overall performance of the waste treatment system and future
plans or changes anticipated.
4. Current discharge limitations under which the plant is
operating and any difficulties in meeting them.
5. Particular pollutant parameters which plant personnel feel
will be found in the waste stream.
6. Any problems or situations peculiar to the plant being
visited.
In addition, the following areas were reviewed during visits to
electroless plating and printed board plants:
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1. Chelating agents/ their applications and their effects on
waste treatment.
2. Masking and its effect on dragout.
3. Through-hole plating and its effect on dragout.
The wastewater collection at the visited plants consisted of a
composite sampling program done over two or three days. Prior to the
sampling visit, all available data, such as layouts and diagrams of
the selected plants' manufacturing processes and waste treatment
facilities, were reviewed. Representative sample points were selected
such as effluents from plating rinse tanks as well as total raw wastes
entering treatment systems and the final effluents. Finally a
detailed sampling plan showing the selected sample points and the
overall sampling procedure was generated and reviewed.
Composite samples were taken at each sample point for two or three
consecutive days. A minimum of four grab samples were obtained and
composited by flow proportioning over each eight-hour period. When
sampling large batch tanks with fill times greater than two hours,
well-mixed grab samples were taken at predetermined intervals.
Samples were subjected to three levels of analysis depending on the
stability of the parameters to be analyzed. These levels were: on-
site analysis, local laboratory analysis, and central laboratory
analysis. On-site analysis, performed by the sampler at the facility,
determined flow rate, pH, and temperature. Three liters of water from
each sample point were delivered to a laboratory in the area of the
subject plant and analyzed for total cyanide, cyanide amendable to
chlorination, and phosphorus. This analysis was performed by these
local laboratories within a 24 hour period after the composite sample
was prepared. The remainder of the wastewater was shipped to a
central laboratory where analysis was performed within seven days for
silver, gold, cadmium, hexavalent chromium, total chromium, copper,
iron, fluorides, nickel, lead, tin, zinc, total suspended solids, and
total dissolved solids as appropriate. Analysis for certain special
parameters such as palladium and rhodium was performed only if the
facility being sampled utilized such materials in their plating lines.
In addition, samples from electroless plating plants were also
analyzed for the chelating agents which were being used by the plant.
The acquisition, preservation, and analysis of the water samples was
performed in accordance with methods set forth in 40 CFR Part 136.
One of the principal areas of interest in the study of printed board
manufacture was the use of chelating agents in electroless plating
solutions. All available data concerning these chelating agents were
solicited from the facilities under study, and wastewater from the
sample points where chelating agents might be found was analyzed. In
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addition to the sampling and analysis described above, special samples
were obtained from a few select plants. These samples were taken from
the rinses in the surface preparation section of the plating lines.
Rinse samples were taken from the rinse immediately following the
first alkaline cleaning process and acid cleaning process in the line.
These samples were a one time grab type. The alkaline rinse sample
was analyzed for phosphorus, basis metal, oil and grease, total
dissolved solids, and total suspended solids. The acid rinse sample
was analyzed for the same constituents excluding phosphorus.
Finally, special tests were conducted at several plants to determine
the dragout characteristics in the printed board industry. Different
combinations of boards (with and without holes, and with and without
masking) were run through actual plating lines to determine the effect
of masking and holes upon dragout.
Utilization of. Industry Data
Data collected from the previously described sources were used
throughout this report. The following paragraphs discuss the
application of this information in Sections III through XII.
Section III: Introduction - Industry data are used in the last part
of this section to describe the seven regulated subcategories of the
electroplating industry. These subcategories are electroplating of
common metals, electroplating of precious metals, anodizing, coatings,
chemical etching and milling, electroless plating and printed board
manufacturing. This subdivision is based on the fact that distinctly
different production processes are performed in each of the
subcategories even though these subcategories are not mutually
exclusive subdivisions of the electroplating point source category.
These subcategory descriptions provide an overview of the industry in
the area of production processes and product descriptions. In
describing electroless plating, particular attention is focused on the
use of chelating agents in these plating baths since their property of
holding plating metals in solution during the plating process
inherently inhibits the precipitation of these metals in waste
treatment facilities.
Section IV; Industry Categorization - Seven subcategories are
established to cover the entire industry, one for common metals
electroplating, another for precious metals, a third for electroless
plating of common and precious metals, a fourth for anodizing, a fifth
for coatings, a sixth for chemical milling and etching, and a seventh
for printed board manufacture. Information used for selection is
derived from actual plant visits and from data collection portfolios
received from plants contacted but not visited. A concentration basis
for limitations, as well as an optional operation-processed area basis
for limitations, is selected following a review of several industry
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characteristics that potentially relate to pollutant discharges
including: processed area, number of employees, power consumed,
number of parts processed, and effluent discharge destination.
Section V: Waste Characterization - The raw waste loadings presented
are based entirely on an analysis of raw waste samples taken from
contacted plants because published data were fragmented and
incomplete. The raw waste data are based on an analysis of wastewater
samples taken downstream of manufacturing operations, and upstream of
any treatment. The waste characterization is common to both direct
and indirect discharge electroplating facilities since wastes are
dependent only upon the production processes performed.
Section VI; Pollutant Parameters - Based on analysis of both raw
waste data and effluent data collected from the contacted plants,
pollutant parameters requiring limitations were selected. This
selection required that two primary criteria be met: first, the
pollutant nature of the parameter must be significant; and second, it
must be discharged at a significant level.
Section VII; Treatment Technology - Treatment technologies observed
during plant visits and described in the literature are discussed in
three main areas. The first describes inplant techniques in the area
of rinsing, good housekeeping, chemical recovery, bath regeneration,
and bath recycling. The second presents the performance of individual
pieces of waste treatment equipment. The third section concerns the
system performance of groups of such equipment. Most of the equipment
descriptions were derived from the literature and supplemented by
plant data analysis. Where this information was inadequate, equipment
makers were contacted directly. End-of-pipe and in-line system
descriptions are based on an analysis of the treatment techniques
currently being used or installed as observed during the plant visits.
Section VIII; Economics - The wastewater economics data presented
were obtained from the waste treatment equipment manufacturing
industry and were applied with the aid of a computer. The basic
program logic allows the program user to vary both the types of unit
wastewater treatment processes to be used in the waste treatment
system and the manner in which the processes are interconnected. Each
unit process is described in a separate subroutine which sizes the
unit, calculates its performance, and estimates the total investment
and annual costs associated with the process. At the end of the
system iteration, process costs are summed, and auxiliary costs are
estimated. The computer cost estimates were compared to many actual
plant wastewater treatment installations and vendor quotes, and were
consistently within 20 percent of actual cost.
The technologies identified in Section VII were then input to a
computer to calculate costs and performance. Both single unit
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processes and typical end-of-pipe and in-line treatment systems were
described. The program was executed several times for each unit
process and overall system, each time utilizing a different raw
wastewater flow rate. These various flow rates provided a
relationship between plant production rate and estimated costs of
water pollution control.
Section XII; Effluent Limitations - The derivation and formulation of
pretreatment limitations are discussed in detail in Section XII.
DESCRIPTION OF THE ELECTROPLATING POINT SOURCE CATEGORY
The industrial operations covered by this document include those
subcategories of the electroplating category dealing with
electroplating of common and precious metals, anodizing, coating,
chemical etching and milling, electroless plating and printed board
manufacturing. It is estimated that a total of approximately 13,000
companies are engaged in metal plating in the United States with about
3400 of these companies being independent (job) platers. The majority
of the plating facilities are captive shops, i.e., facilities plating
their own work. Department of Commerce data indicate the annual value
added by job plating shops may exceed $2,000,000,000, and the annual
value added by the captive sector is estimated to be an additional
$10,000,000,000.
Electroplating facilities vary greatly in size and character from one
plant to another. A single facility for plating individual parts
formed by stamping, casting, and machining, may employ plating or
processing solutions (excluding water rinses) ranging in volume from
less than 400 liters (100 gallons) to more than 20,000 liters (5300
gallons). The area of the products being plated in these facilities
varies as much as three orders of magnitude, from less than 10 to more
than 1000 sq meters/day (100 to 10,000 sq ft/day). The power consumed
by a single facility varies from a few kwh/day to as much as 20,000
kwh/day. Products being plated vary in size from less than 6.5 sq cm
(1 sq in) to more than 1 sq m (10 sq ft) and in weight from less than
30 g (1 oz) to more than 9000 kg (10 tons). Continuous strip and wire
are plated in some plants on a 24-hour/day basis. Some companies have
capabilities for electroplating ten or twelve different metals and
alloys, but others specialize in just one or two. Because of
differences in character, size and processes, facilities are custom
tailored to the specific needs of each individual plant.
Electroplating applies a surface coating typically by
electrodeposition to provide corrosion protection, wear or erosion
resistance, anti-frictional characteristics or decorative purposes.
The electroplating of common metals includes the processes in which a
ferrous or nonferrous basis material is electroplated with copper,
nickel, chromium, zinc, tin, lead, cadmium, iron, aluminum or
17
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combinations thereof. Precious metals electroplating includes the
processes in which a ferrous or non-ferrous basis material is plated
with gold, silver, palladium, platinum, rhodium, or combinations
thereof.
Electroless plating on metals is an integral part of a number of
industries, such as, aircraft, shipbuilding, automotive and heavy
machinery. It is associated, in general, with industries whose
products have to withstand unfavorable conditions or significant wear
and abrasion. Electroless plating on plastics for both functional and
decorative purposes is most prevalent in some specific industries:
automotive, furniture, appliance and electronics.
Anodizing and coating processes (chromating, phosphating, metal
coloring) provide a surface coating on a metal substrate. These
surface coatings provide corrosion protection, wear or erosion
resistance, electrical conductivity, a pleasing appearance or other
special surface characteristics. Chemical etching and milling bring
about a specific amount of metal removal through chemical dissolution
of the basis material.
A plating line usually is a sequence of tanks in which one or more
coatings are applied or a basis material is removed. A process is the
accumulation of steps required to bring about a plating result. A
rinse is a step in a process used to remove dragout from the work
following immersion in a process bath. A rinse may consist of several
steps such as successive countercurrent rinsing or hot rinsing
followed by cold rinsing.
Conceptually, an electroplating line may be broken down into three
steps; surface preparation involving the conditioning of the basis
material for plating, actual application of the plate and the post-
treatment steps. This breakdown is presented in Figure 3-1. Each of
these steps are covered in the following pages. Also included is a
separate subsection on chelating agents which are an integral
component in electroless plating baths but which also have a uniquely
negative effect on waste treatment systems.
Electroplating
The electroplating processes apply a surface coating for functional or
decorative purposes. In electroplating, metal ions in either acid,
alkaline or neutral solutions are.reduced on cathodic surfaces, which
are the workpiece being plated. The metal ions in solution are
usually replenished by the dissolution of metal from anodes or small
pieces contained in inert wire or expanded metal baskets.
Replenishment with metal salts is also practiced, especially for
chromium plating. In this case, an inert material must be selected
for the anodes. Hundreds of different electroplating solutions have
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PARTS
SURFACE
PREPARATION
ELECTROLESS OR
ELECTROPLATING
PROCESS
POST-TREATMENT
PARTS
FIGURE 3-1 CONCEPTUAL ARRANGEMENT OF THE PLATING PROCESS
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been adopted commercially, but only two or three types are utilized
widely for any particular metal or alloy. Cyanide solutions are
popular for copper, zinc, brass, cadmium, silver and gold, for
example, yet non-cyanide alkaline solutions containing pyrophosphate
or another agent have come into use in recent years for zinc and
copper. Zinc, copper, tin and nickel are plated with acid sulfate
solutions, especially for plating relatively simple shapes. Cadmium
and zinc are sometimes electroplated from neutral or slightly acid
chloride solutions.
The electroplating process is basically an oxidation-reduction
reaction. Typically, the part to be plated is the cathode, and the
plating metal is the anode. Thus, to plate copper on zinc parts, the
zinc parts are the cathodes, and the anode is a copper bar. On the
application of electric power, the copper bar anode will be oxidized,
dissolving it in the electrolyte (which could be copper sulfate):
Cu = Cu+2 + 2e~
The resulting copper ions are reduced at the cathode (the zinc part)
to form a copper plate:
Cu+2 + 2e- = Cu
With some exceptions, notably chromium plating, all metals are usually
electroplated in a similar manner. In chromium plating, the typical
anode material is lead, and the chromium is supplied to the plating
baths as chromic acid.
The two most common methods for plating parts are in barrels or on
racks. Barrel plating is used for small parts that tumble freely in
rotating barrels. Direct current loads up to several hundred amperes
are distributed to the parts being plated. Parts may be rack plated
by attaching them to plastic coated copper frames designed to carry
current equally to a few hundred small parts, several medium-sized
shapes or just a few large products through spring-like rack tips
affixed to the rack splines. Racks fabricated for manual transfer
from cleaning, plating, and rinsing tanks usually hold workpieces
totaling 0.5 to 1 sq m (5 to 10 sq ft) in area. Larger racks for
holding heavier parts are constructed for use with mechanical hoist
and transfer systems. Mechanized transfer systems for both barrels
and racks, which range in cost from $50,000 to more than $1,000,000
are being utilized for high-volume production involving six to thirty
sequential operations. In some instances, dwell time and transfer
periods are programmed on magnetic tape or cards for complete
automation. Facilities for plating sheets will be in the higher end
of this cost range.
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Following are descriptions of the various surface preparation and
post-treatment steps involved with electroplating along with
description of the electroplating processes themselves.
Electroplating Processes - Techniques for electroplating aluminum,
cadmium, chromium, copper, gold, indium, iron, lead, palladium,
platinum, rhodium, ruthenium, silver, tin and zinc are described
below.
Surface Preparation
Surface preparation involves cleaning, descaling, degreasing, and
other processes which prepare the basis material for plating.
Cleaning involves the removal of oil, grease and dirt from the surface
of the basis material and may be accomplished in any of several ways.
These include solvent cleaning, alkaline cleaning (both non-
electrolytic and electrolytic alkaline cleaning), emulsion cleaning,
ultrasonic cleaning, and acid cleaning.
Solvent cleaning of metals is classified as either hot cleaning such
as vapor degreasing or cold cleaning, which covers all solvent
cleaning near room temperature. Vapor degreasing, which is performed
in specifically designed equipment that maintains a nonflammable
solvent at its boiling point, is used to clean metal parts and is very
effective in removing lubricants high in non-saponifiable oils or
sulfurized or chlorinated components as well as in flushing away
soluble soil. In cold cleaning, the solvent or mixture of solvents is
selected based on the type of soil to be removed. For some parts,
diphase cleaning provides the best method of cleaning where soil
removal requires the action of water and organic compounds. This
approach uses a two layer system of water soluble and water insoluble
organic solvents. Diphase cleaning is particularly useful where
solvent-soluble and water-soluble lubricants are used, where the part
cannot be heated and when heat tends to "set" the soil.
Alkaline cleaning is used to remove oily soils or solid soil from
workpieces. The detergent nature of the cleaning solution provides
most of the cleaning action with agitation of the solution and
movement of the workpiece being of secondary importance. Alkaline
cleaners are classified into three types: soak, spray, and
electrolytic. Soak cleaners are used on easily removed soil. This
type of cleaner is less efficient than spray or electrolytic cleaners.
Spray cleaners combine the detergent properties of the solution with
the .impact force of the spray which mechanically loosens the soil. A
difficulty with spray cleaning is that to be effective the spray must
reach all surfaces. Another problem is that the detergent
concentration is often lessened because of foaming. Electrolytic
cleaning produces the cleanest surfaces available from conventional
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methods of alkaline cleaning. The effectiveness of this method
results from the strong agitation of the solution by gas evolution and
oxidation-reduction reactions that occur during electrolysis. Also,
certain dirt particles become electrically charged and are repelled
from the surface. Direct current (cathodic) cleaning uses the
workpiece as the cathode, while for reverse current (anodic) cleaning
the workpiece is the anode. In periodic reverse current cleaning, the
current is periodically reversed from direct current to reverse
current. Periodic reverse cleaning gives improved smut removal,
accelerated cleaning and a more active surface for subsequent plating.
Emulsion cleaners consist of common organic solvents dispersed in an
aqueous medium by emulsifying agents. The various types of emulsion
cleaners are classified by the stability and number of phases. The
stable single phase cleaner requires no agitation to maintain the
dispersion of the discontinuous phase throughout the continuous phase.
The unstable single phase requires agitation to maintain a uniform
dispersion of the discontinuous phase.
Ultrasonic energy is finding increased use for the agitation of
cleaning solutions. Although it is more expensive to install, there
are substantial savings in labor and time. Ultrasonic cleaning is
used to remove difficult inorganic and organic soils from intricate
parts. Acid cleaning is used to remove oxides that are formed on the
metal surfaces prior to plating. The removal involves the dissolution
of the oxide in an acid. Sulfuric acid is the most common cleaning
acid with hydrochloric and phosphoric acids also being used. The
oxide removal rate is increased by an increase in temperature, acid
concentration and degree of agitation.
Salt Bath Descaling - Molten salt baths are used in a salt bath -
water quench - acid dip sequence to clean hard-to-remove oxides from
stainless steels and other corrosion-resistant alloys. The work is
immersed in the molten salt (temperature range from 400° C - 540° C),
water quenched, and then acid dipped. Oxidizing, reducing and
electrolytic baths are available and a particular selection is
dependent on the oxide to be removed.
A typical electroplating surface preparation sequence is shown in
Figure 3-2. The first step (alkaline soak) removes oil and grease
from the surface. The acid cleaning removes oxide and scale and is
followed by a rinse. The subsequent electrolytic alkaline cleaning
gives the cleanest surface obtainable from conventional alkaline
methods. The final acid dip removes light oxide films and activates
the surface prior to electroplating.
1. Aluminum Electroplating - Application of aluminum on a commercial
basis is limited. It has been used for coating uranium and steel
strip and electroforming.
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PARTS
SOLVENT
DECREASE
ALKALINE
CLEAN
(SOAK)
RINSE
ACID
CLEAN
RINSE
ANODIC
ALKALINE
CLEAN
RINSE
ACID
CLEAN
RINSE
ELECTROPLATE
AND RINSE
FIGURE 3-2 TYPICAL ELECTROPLATING SURFACE PREPARATION SEQUENCE
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Because it is more reactive than hydrogen, aluminum cannot be plated
from aqueous solutions or any solution containing acidic hydrogen.
Only plating from a hydride bath with the basic ingredients of diethyl
ether, aluminum chloride and lithium aluminum hydride has had any
commercial applications.
2. Cadmium Electroplating - Cadmium electroplating provides a
corrosion protection coating over the basis material. Iron and steel
are the most commonly used basis materials. Since cadmium is
relatively high priced, only thin coatings are applied. It is
sometimes used as an undercoating for zinc. Cadmium plating is often
used on parts consisting of two or more metals to minimize galvanic
corrosion. Cadmium cyanide baths are by far the most popular because
they cover completely and give a dense, fine-grained deposit which can
be made very lustrous by the use of stable brighteners.
3. Chromium Electroplating - Chromium electroplating solutions
contain chromic acid and silicate or fluoride ions. Three basis
materials account for the bulk of the chromium plated work: steel,
nickel-electroplated steel, and nickel-electroplated zinc. Solutions
containing 150 to 400 g/1 of chromic acid are the common baths for
electroplating 0.0002 mm to 0.10 mm (0.000008 to 0.00040 inch) of
decorative chromium or hard chromium (for resisting wear) on steel and
aluminum. Unlike the copper and nickel plating processes which
utilize soluble copper or nickel anodes to replenish the solution the
metal deposited on the work-pieces, chromium electroplating processes
always use insoluble lead alloy anodes. Thus, some portion of the
chromic acid added regularly for maintenance is consumed by reduction
to chromium metal at cathode surfaces.
4. Copper Electroplating - Copper is electroplated from several types
of baths. Among these baths are alkaline cyanide, acid sulfate,
pyrophosphate, and fluoborate, which are prepared with the
corresponding copper salt. The cyanide solutions contain sodium
carbonate and may also contain sodium hydroxide or sodium potassium
tartrate. All four types may also contain a small amount of an
organic chemical for refining the grain or brightening the plate.
Cyanide solutions are used extensively for copper electroplating but
acid copper solutions have been adopted for plating large numbers of
steel, plastic, and zinc alloy products. Steel and zinc are
customarily plated first in a cyanide strike bath to insure good
electroplate adhesion.
Alloyed forms of copper also find use in electroplating, the most
common being brass and bronze. Brass, a combination of copper and
zinc, is often used as a decorative plate on furniture hardware.
Several types of bronze solutions including copper-tin, copper-cadmium
and copper-zinc are utilized primarily as decorative finishes.
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5. Gold Electroplating - Gold electroplated surfaces not only provide
decorative finishes and corrosion protection, but are also important
in providing electrical contact surfaces, bonding surfaces and
electroformed conductors. Plating baths have been developed for each
of these uses. Four types of gold baths are used. Three of these are
cyanide baths - unbuffered alkaline with a pH range of 8.5 to 13, acid
buffered with a pH range of 3 to 6, and a neutral buffer with a pH
range of 6 to 8.5, The fourth is noncyanide.
6. Indium Electroplating - Indium electroplating is used in the
manufacture of aircraft engine bearings. Corrosion of the originally
plated cadmium-silver-copper bearings is reduced by an indium over-
layer and heat treating. Indium is often alloy plated with copper,
tin, lead, cadmium, nickel, bismuth or rhodium.
Initially, indium baths were composed of cyanide and sugar. Today the
sulfate bath is the most widely used along with alkaline, fluoborate,
sulfamate, chloride, perchlorate and tartrate baths.
7. Iron Electroplating - The electroplating of iron is used for
certain specialized purposes such as electroforming and buildup of
worn parts. Since iron does not alloy with solder, this has lead to
iron plating of soldering tips. While there are several difficulties
in the maintenance of an iron electroplating line, the iron
electroplating solutions are comparatively stable and simple to
operate. Special noncorrosive equipment is needed to heat and agitate
the plating bath. Also, care must be taken that the plating bath
does not oxidize. However, these disadvantages may be offset by the
great abundance of low cost iron. Iron may be deposited as a hard and
brittle or soft and ductile coat. Almost all iron is plated from
solutions of ferrous salts at low pH's. The most common baths contain
sulfate, chloride, fluoborate and sulfamate.
8. Lead Electroplating - Lead is most resistant to hydrofluoric and
sulfuric acids and is used for protective linings as well as coatings
on nuts and bolts, storage battery parts and bearings. Lead is often
an undercoat for indium plating. Lead-tin and lead-antimony alloys
are used. Solder plating is a 40/60 lead-tin alloy which is widely
used in the electronics field.
Fluosilicate and fluoborate baths are the most widely used. The
fluoborate bath is more expensive, but it gives finer grained denser
deposits, adheres better to steel and will not decompose as readily.
9. Nickel Electroplating - Nickel is electroplated from several
baths; among these are Watts (sulfate-chloride-boric acid), sulfamate,
all chloride, and fluoborate baths. Each type of solution is prepared
with the corresponding nickel salt, a buffer such as boric acid and a
small concentration of a wetting agent. A small amount of another
25
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organic chemical may be added to brighten the deposits or control
other properties. Nickel is extensively electroplated in a three-
metal composite coating of copper, nickel, and chromium. Nickel is
also electrodeposited on steel for decorative-protective finishes and
on other materials for electroforming. In these applications, nickel
electroplating is preceded by cleaning and activating operations in a
sequence selected for a specific basis material.
Organic agents that refine the grain size of the deposit and brighten
the plate are added to all nickel plating baths adopted for sequential
nickel-chromium plating. Proprietary agents are supplied by metal
finishing supply companies that have developed stable, effective
chemicals for insuring mirror-like, corrosion-protection deposits
requiring no buffing.
10. Platinum Metals Electroplating - Of the six metals in the platinum
group only platinum, rhodium, and palladium are electroplated to any
extent. Of these, rhodium is most often deposited. Decorative
coatings for silverware, jewelery, and watches are very thin (0.1 urn)
and are used to prevent tarnish and excessive wear of silver and to
enhance the color of gold and gold-filled products. When the basis
metal is not a silver or a gold alloy an undercoat of nickel is
generally used. Coatings 25 urn thick (0.001 inch) are used for wear
and corrosion resistance in the electronics industry and provide a
surface of high optical reflectivity.
Platinum is electroplated on titanium and similar metals which are
used as insoluble anodes in other plating operations (e.g. rhodium and
gold). Electroplated platinum is used as an undercoat for rhodium
plate. Ruthenium electroplating is used on high intensity electrodes
to improve electrical contact. Commercial electroplating of osmium
and iridium are believed to be non-existent.
Rhodium electroplating baths are supplied as phosphate or sulfate
concentrates. The only additions made to the diluted concentrate are
phosphoric and/or sulfuric acids at concentrations of 25 to 75 ml per
liter of plating bath. A rhodium conentration of 2.0 g/1 is used for
decorative coatings. Concentration is increased to 10 to 20 g/1 for
achieving thicker deposits.
The palladium content in plating solutions ranges from 2.5 to 10 g/1
in the form of an amino nitrite complex. Other constituents are 11
g/1 sodium nitrite and 40 ml/1 of concentrated ammonium hydroxide.
Palladium deposition has been accomplished from chloride or bromide
solutions and from a molten cyanide bath.
11. Silver Electroplating - The use of silver electroplating is
expanding in both the engineering and the decorative fields. Silver
is typically electroplated in two types of baths, a conventional low
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metal bath and the high speed bath with a much higher silver content.
Most baths are now based on potassium formulations because of high
plating speeds, better conductivity, increased tolerance to carbonates
and smoother deposits.
12. Tin E1e c tr op1ating - In terms of tonnage of product produced,
continuous tin electroplating of coil steel represents the largest
application of electroplating in the world. Tin is resistant to
corrosion and tarnish, solderable, soft and ductile. These properties
of tin make it excellent for food handling equipment, electronic
components and bearing surfaces where lubricity to prevent seizing and
scoring is desired.
Tin electroplate can provide a mat or bright deposit. The common
baths of alkaline stannate and acid fluorborate produce a mat finish
while the acid sulfate process can result in either type of deposit.
Commonly, mat finishes are brightened by a post-plating operation of
melting the deposit. This method is call "reflowing".
13. Zinc Electroplating - Zinc is electroplated in (a) cyanide
solutions containing sodium cyanide, zinc oxides or cyanide and sodium
hydroxide; (b) non-cyanide alkaline solutions prepared with zinc
pyrophosphate or another chelating agent such as tetrasodium
pyrophosphate, sodium citrate or the sodium salt of ethylenediamine
tetraacetic acid; (c) acid or neutral chloride baths prepared with
zinc chloride and a buffer salt such as ammonium chloride; or (d) acid
sulfate solutions containig zinc sulfate and a buffer salt such as
aluminum chloride or sulfate. A small concentration of an organic
compound such as glucose, licorice, or glycerin may be added to the
chloride or sulfate baths for brightening purposes.
Post-Treatment Processes - After a deposition of a metallic coating
either by electro or electroless techniques, an additional coating is
sometimes applied. The function of the additional coating is to
improve the metal surface for painting, lubricity, improved corrosion
protection or the application of a colored finish. These post-
treatment processes encompass chemical conversion coatings
(chromating, phosphating and metal coloring) which are discussed later
as treatment processes.
Electroless Plating
Electroless plating is a chemical reduction process which depends upon
the catalytic reduction of a metallic ion in an aqueous solution con-
taining a reducing agent, and the subsequent deposition of metal
without the use of external electrical energy. It has found
widespread use in industry due to several unique advantages over
conventional electroplating. Electroless plating provides a uniform
plating thickness on all areas of the part regardless of the
27
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configuration or geometry of the part. This makes it possible to
plate deep recesses and niches that electroplating cannot effectively
reach due to current distribution problems. An electroless plate on a
properly prepared surface is dense and virtually non-porous.
Furthermore, certain types of electroless platings provide better
hardness and corrosion protection than their electroplated
counterparts.
Copper and nickel electroless plating are the most common. Others
found on a smaller scale are iron, cobalt, gold, palladium, and
arsenic. Because of their widespread use, nickel and copper
electroless plates are described in the following paragraphs, and then
the application of these plates to both metals and plastics is
described.
The basic ingredients in an electroless plating solution are:
1. A source of metal, usually a salt.
2. A reducer to reduce the metal to its base state.
3. A chelating agent to hold the metal in solution (so the metal
will not plate out indiscriminately).
4. Various buffers and other chemicals designed to maintain bath
stability and increase bath life.
For electroless nickel plating baths, the source of nickel is a salt
such as nickel chloride or nickel sulfate and the reducer is sodium
hypophosphite. There are several chelating agents which can be used,
the most common ones being citric and glycolic acid.
The basic plating reactions proceed as follows:
The nickel salt is ionized in water.
NiS04 = Ni+z + S04-2
There is then a redox reaction with nickel and sodium
hypophosphite.
+ S04~2 + 2NaH2P02 + 2H20 = Ni + 2NaH2P03 + H2 + H2S04
The sodium hypophosphite also results in the following reaction:
2NaH2P2 + H2 = 4P + 2NaOH + 2H20
As can be seen in the equations above, both nickel and phosphorus are
produced, and the actual metal deposited is a nickel-phosphorus alloy.
28
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The phosphorus content can be manipulated to produce different
characteristics in the nickel plate.
Electroless copper plating is similar to electroless nickel plating.
The source of copper is one of a variety of salts such as cupric
chloride and copper sulfate. The reducer is one of a variety of
agents including formaldehyde, acetaldehyde, trioxane, hydrazine and
hypophosphite. Formaldehyde, however, is by far most commonly used.
The chelating agent in a copper bath is usually either a tartrate
(Rochelle salt) or a member of the amine family.
The copper salt is ionized in water,
CuS04 = Cu+2 + S04-2
There is then a redox reaction with the copper and the
formaldehyde to:
Cu + z + 2H2CO + 4 OH-* - Cu + 2HC02-1 + 2H20 + H2
The base metal copper now begins to plate out on a proper surface,
that is, on a less noble metal or on a surface which has been
sensitized with a catalyst. Electroless copper deposits quite readily
on certain metal surfaces, but a catalyst must be used to plate copper
on a non-metal.
Of particular interest among the constituents of electroless plating
baths are the chelating agents. Chelation is an equilibrium reaction
between a metal ion and a complexing agent characterized by the
formation of more than one bond between the metal and a molecule of
the complexing agent. This results in the formation of a ring
structure incorporating the metal ion and thus holding it in solution.
Chelating agents control metal ions by blocking the reactive sites of
the metal ion and preventing them from carrying out their normal (and
in many cases undesirable) reactions.
In the electroless plating processes, the purpose of the chelating
agent is to hold the metal in solution, to keep it from plating out
indiscriminately. Thus, the chelate can only be replaced by some
material capable of forming an even more stable complex, that is, the
part to be plated.
One of the drawbacks in the use of chelating agents is the difficulty.
in precipitating chelated metals out of wastewater during treatment.
Quite often, plants which are engaged in plating activities that make
use of chelating agents have treatment systems based on the
precipitation and the settling out of heavy metals. Unfortunately, in
the treatment system, the chelating agents continue to hold the metal
in solution, and cause the chelated metal to pass through the
29
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treatment system without precipitation and settling. In some
situations, particularly with the stronger chelates, special
consideration or treatment is necessary in order to remove the bound
metals. Proper treatment of chelates is discussed in the system
portion of Section VII.
The more common chelating agents currently being used in industry are
shown in Table 3-3 along with some of their marketers and
manufacturers. These chelates are divided into three main categories:
amino carboxylic acids, amines, and hydroxy acids. The amino
carboxylic acids and the amines are stronger, more aggressive chelates
that are more difficult to break away from the metal ion. The hydroxy
acids are fairly mild chelates whose bond with a metal can be broken
rather easily, if necessary. These hydroxy acids are biodegradable.
Surface Preparation for Electroless Plating on Plastics - Surface
preparation for electroless plating on plastics consists of cleaning
and roughening or etching. Roughening can be accomplished by
mechanical means such as tumbling or vapor blasting, or it can be done
by chemical means such as etching. Once the plastic surface is
roughened, a catalyst must be applied. All plastics which are plated
need the catalyst in order for the metal deposition to occur. The
catalyst application consists of deposition of a thin layer of
palladium on the surface of the part. Usually, it is a two step
process which is variously known as: "sensitizing", "activating",
"accelerating", and "catalyzing".
Two different catalyst application methods have been employed and both
are based on the interaction of stannous and palladium salts. One
method involves adsorbing stannous tin on the surface, then immersing
the part in palladium chloride. This reduces the palladium to the
metal form and oxidizes the tin from stannous to stannic. A molecular
layer of palladium metal is deposited on the surface of the part and
the tin remains in the solution. The other process used for.catalyst
application involves the application of a mixture of stannous and
palladous compounds on the part. This activator is adsorbed on the
part, and a reaction takes place when the part is exposed to a
solution that dissolves tin on the surface. After the catalyst is
applied, the part is immersed in the electroless bath and the desired
metal plates out on the palladium. After the initial layer of metal
is applied it becomes the catalyst for the remainder of the plating
process.
Surface preparation of plastic prior to electroless plating is shown
in Figure 3-3. The production process for electroless plating on
plastics is different from that used for electroless plating on
metals. After cleaning with an alkaline soak cleaner, the surface is
roughened or etched by an acid. Following neutralization a tin-
30
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Table 3-3.
Common Chelating Agents - Marketers and Manufacturers
JH
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AMINES
AMINOCARBOXYLIC
ACIDS
Glycolic Acid
Gluconic Acid
Citric Acid
Tartrates
tetren
trien
TBED
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Thiourea
TPA
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•HI
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en
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31
-------
palladium catalyst is applied. The acceleration step dissolves the
tin from the surface, allowing the part to be plated.
Surface Preparation for Electroless Plating on Metals - Surface
preparation for electroless plating on metal consists of the
conventional electroplating cleaning steps for metals with active
surfaces such as iron, cobalt, nickel, ruthenium, palladium, osmium,
iridium and platinum. In addition, the smoother the surface the
better the resulting plating finish. Therefore, the parts usually
undergo mechanical preparation such as honing, and chemical treatment
such as acid dipping and alkaline cleaning. However, not all metals
are active enough to accept electroless plating directly and,
consequently, require an activation step. Surface preparation for
stainless steels, aluminum base alloys, beryllium, and titanium alloys
typically consists of a flash deposit of nickel to catalyze the
surface for subsequent electroless deposition.
Certain materials need a galvanic initiation, normally an immersion
nickel deposit. Included in this group are copper, chromium,
selenium, and uranium. Material surfaces containing such metals as
lead, cadmium, zinc, tin and antimony (such as soldered components,
galvanized products or cadmium-zinc plated items) are not amenable to
electroless plating in that they interfere with all electroless
plating activity. Thus, when electroless plating these materials, it
is necessary to use a preplate of a material that is autocatalytic. A
copper strike is frequently used which then can be surface activated
and electroless plated.
Surface preparation of metals prior to electroless plating is shown in
Figure 3-4. The first two steps (vapor degrease and alkaline clean)
remove oil and grease from the surface. The acid cleaning removes
oxide and scale and is followed by a rinse. The subsequent alkaline
cleaning (electrolytic) gives the cleanest surface obtainable from
conventional methods. The final acid cleaning removes light oxide
films and activates the surface prior to flash electroplating. After
the electroplate, which acts as a catalyst, the part is electroless
plated.
Electroless Plating on Metals - Electroless plating on metal is
associated in general with products which have to withstand
unfavorable conditions or significant wear and abrasion. Electroless
nickel plating is the most widely used type of electroless plating in
industry. Its primary importance is its use in protecting against
corrosion and wear. Because of its corrosion protection, it is used
in such areas as ship components to resist the marine atmosphere,
filters, heat exchangers, pumps, holding tanks and oil field drilling
equipment. An electroless nickel plate can be heat treated to
hardness values not attainable with electroplated nickel and thus has
a tremendous resistance to wear and abrasion. This property is useful
32
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PARTS
MILD SOAK
CLEANER
COLD
RINSE
PPF— ETCH
ACID
ETCH
r^'Diir' ruiT
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/-»f\T r\ TJTMQP*
/"*f\T r\ TJTKICTr
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CATALYST
APPLICATION
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COLD RINSE
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COLD RINSE
COLD RINSE
ELECTROLESS
PLATE
FIGURE 3-3 EXAMPLE OF ELECTROLESS PLATING ON
PLASTIC-SURFACE PREPARATION SEQUENCE
-------
PARTS
VAPOR
DECREASE
ALKALINE
CLEAN
f*f\T T\ t>T*SCl?
CUUJ KIN fat
ACID
CLEAN
ALKALINE
CLEAN
fTMCl?
\~WJblJ £\X«o£i
ACID
CLEAN
NICKEL STRIKE
(ELECTROPLATE)
RINSE
TO ELEC1
FIGURE 3-4 EXAMPLE OF ELECTROLESS PLATING ON METALS-SURFACE PREPARATION SEQUENCE
-------
in coating hydraulic cylinders, valve inserts, friction rings,
linkages, pump and fan impellers, and ink cylinders.
Electroless Plating on Plastics - During the past decade, the plating
of plastics has increased significantly. Included in the industries
applying such platings are the automotive, appliance, cosmetic,
electrical, hardware, furniture, and plumbing industry.
Among the plastics most widely used for plating are acrylonitrile-
butadiene-styrene (ABS), polycarbonate, polypropylene, polysulfone,
and epoxies. ABS is a low cost, easily plated plastic which is used
in automotive grilles, appliance knobs, and plumbing. Polycarbonate,
whose best feature is its high impact strength, has found use in air-
craft parts. Polypropylene, which has been described as having a
unique blend of average properties, is the least expensive of the
plastics which are plated and is used for lamps and appliance parts.
Polysulfone which has good dimensional stability and high temperature
tolerance, is employed in household appliances and camera housings.
Epoxy resin type plastics are mostly used in the electronics industry,
particularly in the production of printed boards.
An electroless nickel plate has an active surface, making it very
receptive to a follow-up electroplate. Because of this, electroless
nickel is used as a base coating in the plating of plastics. A large
variety of follow-up electroplates and finishes are used including
bronze, satin copper, satin gold, silver, bright copper, brass and
black oxide. However, the usual procedure is to follow up the
electroless nickel plate with copper, nickel, and then chromium
electroplate. The procedure is widely used for decorative parts in
the automotive, furniture, and appliance industries.
Electroless copper plating was developed primarily for deposition of
copper on plastic printed boards and is still generally only used in
this industry. The chemistry of electroless copper plating is similar
to electroless nickel plating; only the chemicals are different.
Post-treatment Processes - The most common operation carried out after
electroless plating is electroplating. Virtually all of the
electroless plating done on plastics is followed by some form of
electroplating operation. Although an electroless plate has superior
hardness and corrosion protection characteristics, it may be covered
by some coating such as a lacquer.
Anodizing
Anodizing is an electrolytic oxidation process which converts the
surface of the metal to an insoluble oxide. These oxide coatings
provide corrosion protection, decorative surfaces, a base for painting
and other coating processes, and special electrical and engineering
35
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properties. Aluminum is the most frequently anodized material, while
some magnesium and limited amounts of zinc and titanium are also
anodized.
Surface Preparation - Surface preparation for anodizing can be minor
or extensive depending on the alloying elements in the basis material
and the amount of oil, grease, or oxide present on the part. Figure
3-5 presents a surface preparation sequence for either chromic or
sulfuric acid anodizing of aluminum. The vapor degreasing step is
usually required only if the amount of oil and grease on the part is
excessive. The next step is cleaning in an inhibited soak cleaner.
This is the principal cleaning step for most work. Following
cleaning, an oxide removal step is included only if a large amount of
oxide is present on the part. The etching step provides an active
surface for anodizing but also produces a smut on the surface when an
alloying agent (particularly copper) is present and the etch is an
alkaline type. For these situations a desmutting bath such as nitric
acid is used to remove the smut. The desmutting is followed by
anodizing. Preparation for anodizing of magnesium, zinc, and titanium
typically consists of cleaning in an inhibited alkaline cleaner with
only titanium requiring activation in a nitric- hydrofluoric acid
solution.
For aluminum parts, the formation of the oxide occurs when the parts
are made anodic in dilute sulfuric acid or dilute chromic acid
solutions. The oxide layer begins formation at the extreme outer
surface, and as the reaction proceeds, the oxide grows into the metal.
The last formed oxide, known as the boundary layer, is located at the
interface between the base metal and the oxide. The boundary is
extremely thin and nonporous. The sulfuric acid process is typically
used for all parts fabricated from aluminum alloys except for parts
subject to stress or containing recesses in which the sulfuric acid
solution may be retained and attack the aluminum.
Chromic acid anodic coatings are more protective than sulfuric acid
anodic coatings. This is partly due to the retention of chromic acid
in the coating and its relatively thick boundary layer. For these
reasons, a chromic acid bath is used if a complete rinsing of the part
cannot be achieved.
The characteristics of anodic coating on magnesium vary from thin
coatings to give good corrosion resistance to heavy coatings for
abrasion and corrosion resistance. Of the numerous anodizing
solutions available, only two are in widespread use. Of these
solutions, one is a combination of fluoride, phosphate, and chromic
acids, and the other is a mixture of potassium hydroxide, aluminum
hydroxide, and potassium fluoride.
36
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PARTS
VAPOR *
DECREASE
INHIBITED
ALKALINE
SOAK-CLEAN
RINSE
ACID
CLEAN
RINSE
ETCH*
(ACID OR
ALKALINE "TYPE)
OTMCp
ANODIZE
PARTS
* OPTIONAL DEPENDING ON BASIS MATERIAL
FIGURE 3-5 EXAMPLE OF SURFACE PREPARATION SEQUENCE FOR ANOD1ZI1MU OF ALUMINUM
-------
Coatings
This section deals with the chemical conversion coating of chromating
and phosphating, metal coloring and immersion platings. These
coatings are applied to previously deposited metal or basis material
for increased corrosion protection, lubricity, preparation of the
surface for additional coatings, or formulation of a special surface
appearance.
Surface Preparation - Surface preparation involves cleaning,
descaling, degreasing and other processes which prepare the basis
material for surface treatment. The number of surface preparation
steps required prior to additional surface treatment depends upon the
work flow sequences established in individual facilities. The surface
preparation processes for coating are identical to those described
earlier for electroplating. In addition to these operations,
polishing is often used to obtain the desired surface prior to
coloring. Mechanical polishing, electropolishing, and chemical
polishing are used to obtain specific surface finishes.
Chromating - Chromate conversion coatings are protective films formed
on the metal surfaces. During the process of chromating, a portion of
the base metal is converted to one of the components of the film by
reaction with aqueous solutions containing hexavalent chromium and
active organic or inorganic compounds. Chromate coatings are most
frequently applied to zinc, cadmium, aluminum, magnesium, copper,
brass, bronze, and silver. The chromating solutions are generally
acidic and contain chromic acid or its sodium or potassium salts, plus
organic or inorganic compounds such as activators, accelerators, or
catalysts. Although chromate conversion coatings can be applied by
chemical or electrochemical action, the bulk of the coatings are
usually applied by a chemical immersion, spray or brush treatment.
Most chromate treatments used in industry employ proprietary
solutions. With these processes, a wide variety of decorative and
protective films ranging from colorless to iridescent yellow, brass,
brown, and olive drab can be produced. The coating appearance will
depend on the basis metal and the processing procedures employed.
Additional coloring of the coatings can be achieved by dipping the
parts in organic dye baths to impart red, green, blue, and other
colors. Besides their use as protective or decorative films, chromate
conversion coatings are extensively employed to provide an excellent
base for paint and other organic finishes which do not adhere well to
untreated metal surfaces.
Phosphating - Phosphate conversion coatings produce a mildly
protective layer of insoluble crystalline phosphate on the surface of
a metal. Phosphate coatings are used to a) provide a good base for
paints and other organic coatings, b) condition the surfaces for cold
forming operations by providing a base for drawing compounds and
38
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lubricants, and c) impart corrosion resistance to the metal surface by
the coating itself or by providing a suitable base for rust-
preventative oils or waxes. Phosphate conversion coatings are formed
by the immersion of iron, steel, or zinc plated steel in a dilute
solution of phosphoric acid plus other reagents.
The method of applying the phosphate coating is dependent upon the
size and shape of the part to be coated; Small parts are coated in
barrels immersed in the phosphating solution. Large parts, such as
steel sheet and strip, are spray coated or continuously passed
through the phosphating solution. Supplemental oil or wax coatings
are usually applied after phosphating unless the part is to be
painted.
Coloring - Metal coloring by chemical conversion methods produces a
large group of decorative finishes. This section covers only chemical
methods of coloring in which the metal surface is converted into an
oxide or other insoluble metal compound. The most common colored
finishes are used on copper, steel, zinc, and cadmium.
Application of the color to the cleaned basis metal involves only a
brief immersion in a dilute aqueous solution. The colored films
produced on the metal surface are extremely thin and delicate.
Consequently, they lack resistance to handling and the atmosphere. A
clear lacquer is often used to protect the colored metal surface.
A large quantity of copper and brass is colored to yield a wide
variety of shades and colors. Shades of black, brown, gray, green,
and patina can be obtained on copper and brass by use of appropriate
coloring solutions. The most important colors for ferrous metals are
based on oxides which yield black, brown, or blue colors. A number of
colors can be developed on zinc depending on the length of immersion
in the coloring solution. For instance, in a solution of ammonium
chlorate the color sequence is yellow, brown, violet, deep blue, and
blue-black. Ammonium molybdate solutions give a gold to brown to
black color sequence. Although cadmium is not a structural metal, it
is used in decorative coloring as a protective deposit on ferrous
metal substrates. The most important surface treatment for cadmium is
chromate passivation which improves its resistance to the atmosphere
and to fingerprints as well as providing color. In most instances,
the color of chromate-passivated cadmium is yellow, bronze, or dark
green. Black and brown colors can also be produced on cadmium.
Silver, tin, and aluminum are also colored commercially. Silver is
given a gray color by immersion in a polysulfide solution such as
ammonium polysulfide. Tin can be darkened to produce an antique
finish of pewter by immersion in a solution of nitric acid and copper
sulfate. Because the colored layers on metal surfaces are so
delicate, they are usually protected by a coat of lacquer applied by
spraying or dipping.
39
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Immersion Plating - Immersion plating is a chemical plating process in
which a thin metal deposit is obtained by chemical displacement of the
basis metal. In immersion plating, a metal will displace from
solution any other metal that is below it in the electromotive series
of elements.
The lower (more noble) metal will be deposited from solution while the
more active metal (higher in the series) will be dissolved. A common
example of immersion plating is the deposition of copper on steel from
an acid copper solution.
The thickness of immersion deposits is usually of the order of 0.25 urn
(.00001 in) although a few processes produce deposits as thick as 2.5
to 5 urn (.0001-.0002 in). This thinness limits the usefulness of
immersion deposits as to applications other than corrosion protection,
such as decoration or preparation for further processing such as
painting or rubber bonding. The most widely used immersion plating
processes are, a) tin on brass, copper, steel, or aluminum, b) copper
on steel, c) gold on copper or brass, d) nickel on steel and e) zinc
on aluminum.
Immersion tin plating is used to "whiten" pins, hooks, eyelets,
screws, buttons, and other hardware items made of copper, brass, or
steel. In addition, aluminum alloy pistons for internal combustion
engines are immersion tin plated. All immersion tin plating baths for
copper, brass, and steel are based on stannous chloride solutions.
Immersion tin solutions contain, in addition to stannous chloride,
cream of tartar (potassium bitartrate), ammonium aluminum sulfate, or
sodium cyanide and sodium hydroxide.
Copper is immersion deposited on steel wire prior to drawing in order
to reduce wear on the dies. Copper is deposited from an acid copper
sulfate solution. A copper-tin alloy is obtained on steel wire by
adding tin salts to the copper sulfate solutions.
Gold is immersion deposited on copper and brass to gild inexpensive
items of jewelry. Typical immersion gold plating solutions contain
gold chloride and potassium cyanide or pyrophosphate.
Post-treatment Processes
The corrosion resistance of anodic coatings on aluminum and its alloys
is improved by immersion of the anodized surface into slightly
acidified hot water. The sealing process converts the amorphous
anhydrous aluminum oxide to the crystalline monohydrate (A1203.H20).
For chromic acid anodized parts, a slight amount of chromic acid is
added to the sealing bath. For sulfuric acid anodized parts 5 to 10%
by weight potassium dichromate is added. Parts are rinsed and dryed
after the sealing.
40
'o
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Anodic coatings on magnesium are sealed in ammonium acid fluoride and
sodium dichromate solutions. After sealing, the parts are water
rinsed and dried. This sealing neutralizes any alkali retained in the
coating and provides better corrosion protection and improved paint
adhesion.
Unsealed anodic coatings on aluminum are colored by immersion in a
solution of organic or inorganic dyes. The depth of dye absorption
depends on the thickness and porosity of the anodized surface. After
rinsing, the sealing of the dye is accomplished by immersion in a hot
solution of nickel or cobalt acetate.
Special surface characteristics can be imparted to chromate conversion
coatings by bleaching or dyeing. Clear bright finishes are obtained
by immersion in various mildly acidic or alkaline solutions.
Solutions such as sodium hydroxide, sodium carbonate, or phosphoric
acid are employed to eliminate the yellow coloring from the chromate
film. Dyed coatings can also be applied.
After the post phosphating water rinse, phosphated parts can be rinsed
in a weak chromic acid solution. The chromic acid solution
neutralizes any phosphoric acid remaining on the part and improves the
corrosion resistance. Following the acid rinse, parts are frequently
dipped in a suitable oil, wax, or other lubricant before drying in hot
air.
Chemical Milling and Etching
Chemical milling and etching processes are used to produce specific
design configuration and tolerances on metal parts by controlled
dissolution with chemical reagents or etchants. Included in this
general classification are the specific processes of chemical milling,
chemical etching, bright dipping, electropolishing, and electro-
chemical machining.
Surface Preparation - Surface preparation procedures for chemical
milling and etching are similar to those presented for electroplating.
Prior to the etch step, the basis material is usually alkaline or acid
cleaned. After removal of grease, dirt, oxide, or scale from the
metal surface by any of the applicable methods, parts to be chemically
milled or etched sometimes have a mask applied. Areas where no metal
removal is desired are masked off with an etch resistant material.
Masks are applied by dip, spray, brush, roll or flow-coating, silk-
screen techniques or photosensitive resists. Typically photographic
techniques are used for the blanking of small intricately shaped parts
or for the production of name plates, dials, and fine mesh screen.
After masking, parts may be dipped in acid to activate the surface
prior to chemical milling or etching.
41
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Chemical Milling - Chemical milling is similar to the etching
procedure used for decades by photoengravers, except that the rates
and depths of metal removal are usually much greater. Chemical
milling is especially suited for removing metal from shallow depths on
formed complex shaped parts (e.g., forgings, castings, extrusions)
from thin sections and from large areas.
The amount of metal removed or the depth of removal is controlled by
the immersion time in the milling solutions. The metal can be removed
from an entire part or restricted to selected areas by masking. Areas
where no metal removal is desired are masked off. Masks are applied
by dip, spray, brush, roll or flow-coating techniques. These
preparatory steps were discussed in the Surface Preparation section.
Typical solutions for chemical milling include ferric chloride, nitric
acid, ammonium persulfate, chromic acid, cupric chloride, hydrochloric
acid and combinations of these reagents. Aluminum is milled in ferric
chloride or hydrochloric acid or sodium hydroxide solutions. Copper
is milled in ferric chloride, cupric chloride, chromic acid, or
ammonium persulfate solutions.
Etching - Chemical etching is the same process as chemical milling
except relatively small amounts (1-5 mils) of metal are removed.
Bright dipping is a specialized example of the etching process.
Etching to produce a pattern for printed circuit boards is discussed
later in this development document in the description of the printed
board subcategory.
Bright dipping is used to remove oxide and tarnish from ferrous and
nonferrous materials. Bright dipping can produce a range of surface
appearance from bright clean to brilliant depending on the surface
smoothness desired in the finished part. A smoother surface results
in a more brillant appearance.
Bright dipping solutions usually involve mixtures of two or more of
sulfuric, chromic, phosphoric, nitric, and hydrochloric acids. The
rate of attack on the metal is controlled by the addition of
inhibiting materials. The quantity of these materials is dependent
upon the metals that are to be dipped. The type and quantity of the
parts to be bright dipped greatly influences the composition of the
bath. For parts with simple shapes which can be easily removed from
the dipping solution and quickly rinsed, fast-acting dips are used.
Slow-acting dips are used for bulk loads of parts and parts with
complex shapes.
Printed Board Manufacturing
Printed boards are fabricated from nonconductive board materials such
as plastic or glass on which a circuit pattern of conductive metal,
42
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usually copper, has been formed. The board not only provides a
surface for the application of a conductive wiring path but also gives
support and protection to the components it connects. As a means of
packing and interconnecting electronic devices, printed boards find
widespread use in such applications as business machines, computers,
communications, and home entertainment equipment.
The total market for printed boards is about one billion dollars
domestically and about two billion dollars world wide. The industry
in the U.S. consists of large facilities totally involved with printed
board manufacture, both large and small captive facilities, small job
shops doing contract work, and speciality shops which do low volume
and high precision type work. Total annual production is
approximately 150 million square feet of printed boards.
This section presents details on the production methods, types of
circuit boards, and the specific processes involved in producing
printed boards.
Production Methods - The earliest printed boards were produced by
brushing a specially formulated silver paint on a ceramic plate for
the required circuit pattern. This was followed by heating at high
temperatures to remove the paint vehicle and binder, leaving the
deposited silver electrically conductive. Over the years, several
different production methods have been employed as the overall science
evolved. Presently, the industry limits itself to three main
production methods (additive, semi-additive, and subtractive). Some
small production facilities use offshoots of these main processes as
well as some remaining processes from the past. Table 3-4 presents a
comparison of the three principal production methods. The following
paragraphs describe the general subtractive, additive, and semi-
additive processes.
43
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TABLE 3-4
COMPARISON OF BASIC PROCESS STEPS
Conventional
Subtractive
Process sequence
begins with copper
clad material
I - Fabricate holes
- Chemically clean
II - Sensitize
(Catalyze surface)
- Electroless copper
flash
III - Print reverse
pattern
IV - Electroplate copper
to desired thickness
- Over plate
- Strip mask
V - Etch
IV - Tab plate
Semi-Additive
Unclad
Process sequence
begins with
unclad material
Fabricate holes
Promote adhesion
Sensitize
(Catalyze surface)
Electroless copper
flash
Print reverse
pattern
Electroplate
copper to
desired
thickness
Over plate
Strip mask
Quick Etch
Tab plate
Fully Additive
Standard
Process sequence
begins with
unclad material
(already sensitized)
Fabricate holes
Print reverse
pattern
Electroless
deposit copper
to desired
thickness
Tab plate
I - Cleaning & Surface Preparation
II - Catalyst & Electroless Plating
III - Pattern Printing & Masking
IV - Electroplating
V - Etching
44
-------
The subtractive process derives its name from the large amount of
material that is removed in order to make the circuit. The simplest
of the subtractive techniques is the print and etch process which
begins with a board of nonconductive material, such as glass or
plastic, which is clad with a copper foil. The circuit pattern is
printed onto this foil in oil, cellulose, asphalt, vinyl, or resin
based ink and then the board goes through an etching operation in
which the area of the foil not covered by the ink is removed. Next,
the ink is stripped from the foil, leaving only the desired circuit of
copper on the board.
The conventional subtractive process shown in Figure 3-6 begins with a
laminate board composed of a nonconductive material such as glass
epoxy or phenolic paper. This board is then clad with a metallic
foil, usually copper, and drilled for mounting and through hole
connections. After appropriate cleaning and surface preparation, the
panel is plated entirely with electroless copper in order to deposit a
uniform conductive layer over the entire board, including the inside
surfaces of the holes.
At this point, the board can be handled in one of two ways. If it is
to be panel plated, the whole board is electroplated with copper.
Then a plating resist is applied in a form such that only the desired
circuit is left exposed (not covered by resist). This exposed area is
then electroplated (by immersing the entire board in the plating
solution) with an etch resist, usually solder. If it is to be pattern
plated, the plating resist is applied directly after the electroless
copper step, so only the circuit is copper electroplated and likewise
solder plated.
Following the application of the solder plate by either method the
plating resist is stripped off, exposing the copper in areas where the
circuit is not required. This copper is then etched off, leaving only
the desired circuit which was etch protected by solder plate. The
tabs or fingers at the edges of the boards are now stripped of their
solder in preparation for subsequent plating. These tabs are
electroplated according to the specifications of the customer (in most
cases gold or nickel and gold). The solder plate in the circuit
pattern is now reflowed to completely seal the copper circuitry and
act as a corrosion preventative. The last step is the blanking and
cutting of boards to size and final inspection.
The additive process involves the deposition of plating material on
the board in the pattern dictated by the circuit, rather than removing
metal already deposited (as in the subtractive process). There have
been several "additive" methods for producing printed boards. The
original method consisted of depositing a thin layer of electroless
copper on a bare unclad board and following this up with the
conventional subtractive processing.
45
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CUT RAW
STOCK
DRILL HOLEb
c ZkKir"i
OAlNU
SURFACE
PREP
ELECTROLESS
COPPER PLATE
-»
COPPER
FLASH
IMAGE
TRANSFER
PATTERN
PLATE
SOLDER
PLATE
STRIP
RESIST
CPi
•^
ETCH
MASK FOR
SOLDER STRIP
(IN TAB
AREA)
SOLDER
STRIP
GOLD/NICKEL
PLATE .TABS
REMOVE
flASK
-*-
SOLDER
REFLOW
BLANK
AND
NOTCH
FINAL
INSPECT
FIGURE 3-6 SUBTRACTIVE PROCESS
-------
The additive process presently employed by some manufacturers is more
totally additive than the original method. The process, shown in
Figure 3-7, begins with a bare board which may or may not be
impregnated with a catalyst. Holes are then formed by drilling or
punching. The next step is an adhesion promotion operation where the
surface is roughened or etched in order to make it microporous. The
roughening or etching is required because of the large area that must
be electroless plated. If the board is not catalyst-impregnated, the
catalyst is applied after this roughening or etching operation.
Following this, the plating resist, describing the required circuit
pattern, is applied to the board in the non-circuit areas. The
accelerator step necessary for electroless plating is then carried
out, and the board goes into the electroless copper bath. Unlike the
subtractive process where the electroless copper is only used as a
base for copper electroplating, the electroless copper deposition is
used in the additive process, to build up the circuit. Since the
board does not initially have any copper in non-circuit areas and a
resist is applied to these areas prior to electroless plating, a
copper etching step is not necessary. Following the copper
deposition, the tabs are plated in the same manner as in the
subtractive process. At this point, different finishing steps may be
applied, such as the application of a protective coating to the board.
A recently developed additive method involves sensitizing the entire
board and then selectively activating the catalyst in the pattern of
the circuit by means of ultraviolet light.
A semi-additive production process is a compromise between the
additive and subtractive methods. The process sequence, shown in
Figure 3-8, begins with an unclad board which undergoes hole
fabrication (drilling or punching). An adhesion promotion operation
is performed on the board just as in the additive process, the board
being etched to obtain a microporous surface. At this point, the
sequence follows the subtractive process. The entire board is
catalyzed and activated, and electroless copper is applied to the
entire board including the inside surfaces of the holes. The circuit
pattern is then applied by conventional methods (screening or photo-
imaging). Copper electroplate is deposited to build up the circuit to
the desired thickness. The solder plate for etch masking is then
applied, and the plating mask is stripped from the noncircuit areas.
The subsequent etching operation is a quick etch (as compared with the
subtractive process etch) because only the electroless copper flash
has to be removed. In the subtractive process, the copper foil on the
board and the electroless copper have to be etched away, but this is
not required for the semi-additive process. Thus its advantage over
the subtractive process is a reduction in copper waste. After the
etch operation, the solder stripping, tab plating, and any final
fabrication processes are performed as in the conventional subtractive
47
-------
CUT RAW
STOCK
r\DT T T
UKl.L.b
APPLY
ADHESION
PROMOTER
ACTIVATE
TRANSFER
IMAGE
oo
-*•
ACCELERATE
ELECTROLESS
COPPERPLATE
RESIST
REMOVAL
(OPTIONAL)
TAB PLATE
FIGURE 3-7 ADDITIVE PROCESS
-------
CUT RAW
STOCK
ntJTT T
UK-L-Uj-i
SCRUB
APPLY
ADHESION
PROMOTER
ACTIVATION
-*•
ACCELERATE
ELECTROLESS
COPPER
TRANSFER
IMAGE
COPPER
ELECTRO
PLATE
OVE RPLATE
-**•
STRIP
RESIST
QUICK ETCH
SOLDER
STRIP
TAB PLATE
TO
FINAL
FABRICATION
FIGURE 3-8 SEMI-ADDITIVE PROCESS
-------
CIRCUIT LAYOUT
CIRCUIT
ARTWORK
en
O
CLEAN AND
APPLY RESIST
(COPPER CLAD
BOARD )
PRINT PATTERN
ETCH PATTERN
QTM^t/T? Ot?C fCf
KJbr'lUVc* KJbbJ-bl
CUT TO SIZE
TMCppf^
FIGURE 3-9 SINGLE SIDED BOARD PRODUCTION SEQUENCE
-------
DRILL HOLE
PATTERN
(COPPER CLAD
BOARDS)
CLEAN,
SENSITT7F t
ELECTROLESS
COPPER PLATE
ELECTROPLATE
COPPER
CLEAN
APPLY RESIST
PRINT PATTERN
WORKING
ARTWORK
CIRCUIT LAYOUT
PLATE EXTERNAL
PATTERN
REMOVE
PHOTORESIST
ETCH PATTERN
CUT TO SIZE
INSPECT
FIGURE 3-10 DOUBLE SIDED BOARD PRODUCTION SEQUENCE
-------
process. This semi-additive process is not used extensively at this
time.
Types of Boards - Printed boards can be classified into three basic
types: single-sided, double-sided, and multilayer. The type of board
used depends on such things as spatial and density demands and
intricacy of the circuits.
Single-sided boards (reference Figure 3-9 production sequence) are
used for relatively simple circuitry, where circuit types and speeds
do not place unusual demands on wiring electrical characteristics.
When density demands require more than one layer of wiring, circuits
are printed on both sides of the board (see Figure 3-10 production
sequence). The interconnection between the layers is accomplished by
going through the board rather than around it, and plated through
holes have come to be the conventional way of making such a
connection. The holes thus serve a dual purpose: providing an
electrical connection from one side of the board to the other and
accommodating a component lead. These are, of course, more difficult
to make than the single-sided boards because of the extra steps
involved (the drilling and the through hole plating).
The necessity for increased wiring density as required in many present
day electronic packaging applications can be met by the use of more
than two layers of wiring, i.e., a multilayer printed board. The
production sequence for multilayer printed boards is shown in Figure
3-11. A multilayer board is a series of individual circuit board
layers bonded together by an epoxy glass material to produce a thin,
monolithic assembly with the internal and external connections to each
level of the circuitry determined by the system wiring program.
Production Processes - Printed board production for all the above
board types can be broken down into the following operations: 1)
cleaning and surface preparation, 2) catalyst application and
electroless plating, 3) pattern printing and masking, 4)
electroplating, and 5) etching.
1. Cleaning and Surface Preparation - This is a crucial step in
printed board production. For a board to be plated correctly
without flaws, it must be cleaned and properly treated. In many
cases, the boards go through a mechanical scrubbing before they
reach the plating lines. In the case of multilayer boards, after
they are bonded or laminated, they go through an acid hole
cleaning operation, as shown in Figure 3-12, to remove any bonding
epoxy which spilled over the holes.
Once on the plating line, all types of boards are alkaline cleaned
(reference Figure 3-13) to remove any soil, fingerprints, smears
or other substances which cause plating flaws. A mild etch step
52
-------
CUT
EPQXY GLASS
TO SIZE
CONDITION AND
DRY GLASS
PASTS
PRINT INTERNAL
LAYER PATTERNS
FIGURE 3-11 MULTI-LAYER BOARD PRODUCTION SEQUENCE
-------
PARTS
ACID CLEAN
RINSE
SODIUM
BISULFITE
T3TMCT?
K_LrJO.Cj
_^_
ACID
RTNSE
—
RINSE
FIGURE 3-12 MULTI-LAYER HOLE CLEANING
-------
PARTS
SCRUB
ALKALINE CLEAN
RINSE
PERSULPATE
ETCH
RINSE
ACID fl.EAN
RINSE
ACID CLEAN
Ul
en
FIGURE 3-1 3 CLEANING SEQUENCE FOR ELECTROLESS COPPER DEPOSITION
-------
is then performed with ammonium or sodium persulfate to prepare
the copper foil surface (for copper clad boards) for subsequent
plating. The copper clad boards are then acid treated in order to
roughen the exposed plastic surfaces (inside area of holes) to
readily accept the catalyst. In the additive and semi-additive
production methods, the process sequence begins with an unclad
board. In order to get a good bond between the board and the
electroless plate, an adhesion promoter is applied and dried.
Then the board undergoes an etch (usually chromic acid or
chromic-sulfuric). This etch makes the surface of the board
microporous which allows for deep penetration of the catalyst and
subsequent strong bonding of the electroless copper plate.
2. Catalyst Application and Electroless Copper Plate - Electroless
copper deposits quite readily on a copper clad board, but for a
deposit to form on the exposed plastic or on a bare board (as in
the additive process or in through hole plating), a catalyst must
be involved for the copper plate on the nonmetal. The application
and activation of the catalyst is a two-step process. The
catalyst application consists of the deposition of a thin layer of
palladium on the surface of the part. This process goes under
several names: "sensitizing", "activating", "accelerating", and
"catalyzing".
Three different catalyst application methods have been employed,
and all are based on the interaction of stannous and palladium
salts. One method involves first adsorbing stannous tin on the
surface, then immersing the part in palladium chloride. This
reduces the palladium to the metal form and oxidizes the tin from
stannous to stannic. A molecular layer of palladium metal is
deposited on the surface of the part and the tin remains in the
solution. The overall chemistry of this reaction is as follows:
SnCl2 + H20 = SnO + 2HC1 (Sensitization Reaction)
SnO + Pd+2 + H20 = Sn02 + Pd + 2H+ (Activation Reaction)
Cu+2 + HCHO + OH-» = Cu + HCOO-i + H2 (Electroless
Deposition)
Another process used for catalyst application involves the
application of a mixture of stannous and palladious compounds on
the part. This activator is adsorbed on the part, and a reaction
takes place when the part is exposed to a solution that dissolves
tin, leaving only palladium on the surface. This step is commonly
referred to as "acceleration".
In a recently developed method, specifically for printed boards, a
catalyst is applied only to the area to be occupied by the
56
-------
circuit. Stannous chloride is adsorbed on the entire part's
surface. Then the surface is exposed to ultraviolet light shone
through a stencil. The light oxidizes the stannous tin to stannic
in the area not to be plated. This area, when exposed to
palladium chloride, undergoes no reaction, and no palladium is
deposited. Only the unexposed area receives a palladium deposit.
i
Once the catalyst is applied, the metal in the electroless bath
plates out on the palladium. After the initial layer of metal is
applied, it becomes the catalyst for the remainder of the plating
process.
After the boards have been catalyzed, they go into the electroless
copper solution (reference Figure 3-14) and are panel plated in
the subtractive and semi-additive processes or pattern plated in
the additive process. The electroless copper bath contains copper
salts (copper sulfate being most prevalent), formaldehyde as a
reducer, chelating agents to hold the copper in solution (in most
cases either a tartrate or an EDTA compound), sodium hydroxide as
a pH buffer, and various polymers and amines which serve as
brighteners and bath stabilizers. These chemicals vary according
to each bath supplier and his own "proprietary" formulas.
Of particular note among the constituents of electroless plating
baths are the chelating agents. Chelation is an equilibrium
reaction between a metal ion and a complexing agent characterized
by the formulation of more than one bond between the metal and a
molecule of the complexing agent and resulting in the formulation
of a ring structure incorporating the metal ion and thus holding
it in solution. Chelating agents control metal ions by blocking
the reactive sites of the metal ion and preventing them from
carrying out their normal (and in many cases undesirable)
reactions.
In the plating processes, especially electroless plating, the
purpose of the chelating agent is to hold the metal in solution,
to keep it from plating out indiscriminately. Thus, the chelate
can only be replaced by some material capable of forming an even
more stable complex, that is, the part to be plated.
One of the drawbacks in the use of chelating agents is the
difficulty in precipitating chelated metals out of wastewater
during treatment. Quite often, plants which are engaged in
plating activities that make use of chelating agents have
treatment systems based on the precipitation and settling out of
heavy metals. Unfortunately, in this type of treatment system,
the chelating agents continue to hold the metal in solution, and
cause the chelated metal to pass through the treatment system
without precipitating and settling. In some situations/
57
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PARTS
CATALYST
APPLICATION
RINSE
ACCELERATE
RINSE
-»•-
ELECTROLESS
COPPER PLATE
RINSE
RINSE
CJl
oo
FIGURE 3-14 CATALYST APPLICATION AND ELECTROLESS COPPER DEPOSITION
-------
particularly with the stronger chelates, special consideration or
treatment is necessary in order to remove the bound metals.
Proper treatment of chelates is discussed in the system portion of
Section VII.
The more common chelating agents currently being used in industry
were shown in Table 3-3 along with some of their marketers and
manufacturers. These chelates are divided into three main
categories: amino carboxylic acids, amines and hydroxy acids.
The amino carboxylic acids and the amines are stronger, more
aggresive chelates that are more difficult to break away from the
metal ion. The hydroxy acids are fairly mild chelates whose bond
with a metal can be broken rather easily, if necessary. These
hydroxy acids are biodegradable.
3. Pattern Printing and Masking - One of the key steps in the
manufacture of printed circuit boards is the pattern printing.
The precision of this artwork is crucial since the quality of the
final board can be no better than the image printed on it. There
are three principal methods in which the image or pattern is
applied to the board: screening, photosensitive resist techniques
and offset printing. All of the methods apply a resist material
to the board.
Screening consists of selectively applying resist material through
a stencil or screen. The screen material, which may be silk or
metal, is stretched tight over a metal frame. This is placed over
the work, and the ink or resist material is squeegeed through the
screen. Screening inks come in oil, cellulose, asphalt, vinyl, or
resin base. The screening method is highly acceptable for simple
low density circuits because its low cost allows for high volume
production.
Photosensitive resist is a light sensitive polymer which, after
curing, has a significant chemical resistance. After the board
has been cleaned and prepared, the polymer is applied by such
methods as dipping or rolling. A light source (usually
ultraviolet) is applied through a pattern onto the resist. The
light sensitive material hardens, and the unexposed resist is then
removed by various methods, usually a trichloroethylene degreaser.
This is followed by a baking or curing step after which the resist
is able to withstand plating solutions. This type of masking has
made possible the production of high density and intricate
circuits because of the precision obtainable with this method.
Offset printing is a high volume production technique which is
similar to the operation of a printing press. An etched plate
(the printing plate) serves as a master pattern. Ink is
transferred from an ink roller to the plate on a rubber cylinder.
59
-------
The ink image is then deposited on the copper covered board. By
making several passes, enough ink can be built up on the board to
form a plating or etching resist.
In the subtractive and semi-additive processes for making printed
boards, the pattern is applied after the board has been panel
plated with copper, and pattern plating directly follows the
application of the image. After the board has been solder plated,
the plating mask is stripped off, and the solder plate becomes the
mask (an etching mask).
In the additive process, the image is applied to the board before
it ever enters the electroless plating line. It is then used
solely as a plating mask in the electroless bath. After plating,
the stripping of the mask is optional, depending on subsequent
operations and customer demands.
Whether an additive, semi-additive, or subtractive process is
used, masking is applied when the tabs are being plated. The
simplest and most commonly used mask for such applications is a
water repellent tape which can be easily applied to or removed
from the board.
Electroplating - Electroplating is performed at several junctures
in the production of printed boards. It is employed in the actual
buildup of the circuit (in the subtractive and semi-additive
processes); it applies the etch resist and anti-corrosion layer to
the circuit; and it covers the tabs or fingers of all boards.
In order to build up the desired circuit in the subtractive and
semi-additive processes, copper electroplating is used followed by
solder electroplating (reference Figure 3-15). The copper bath
itself is usually one of four types: cyanide copper, fluoborate
copper, pyrophosphate copper, or sulfate copper. After the
application of the copper electroplate, solder electroplate is
applied. This serves a dual purpose. First, it acts as a mask
during the etching process and second, protects the copper circuit
from corrosion after final fabrication. This solder plate usually
consists of a 60-40 tin-lead electroplate, although tin-nickel and
gold are used in some instances.
The tabs or "fingers" of the printed circuit boards are elec-
troplated, as shown in Figure 3-16, for most applications
(additive, semi-additive or subtractive). In the subtractive and
semi-additive processes, there is a solder strip operation before
plating to ensure better adhesion, while this step is unnecessary
in the additive process. In most cases, nickel and gold or simply
gold is used.
60
-------
PARTS
APTD PT FAN
RINSE
PERSULFATE
ETCH
RINSE
-•*
ACID CLEAN
COPPER
ELECTROPLATE
pTVTCp
APTD CLEAN
-*•
RINSE
SOLDER
ELECTROPLATE
RINSE
—
FIGURE 3-15 PATTERN PLATING (COPPER AND SOLDER)
-------
PARTS
& TRI P *iOLDF R
RINSE
SCRUB
KINSE
— 9f~
ACID CLP AN
OTMCp
NICKEL PT.ATP
KlNoE
en
"•*
ACID DIP
"DTMCtT1
JrCXnoCi
miAT n t>r anrc1
vjwljL/ JrJb/ill!i
DRAG-OUT
RINSE
(ACID)
RINSE
FIGURE 3-16 TAB STRIPPING AND PLATING (NICKEL AND GOLD)
-------
Although it is not a type of electroplating, mention is made here
of tin immersion plating. This is a displacement type of plating
(reference Figure 3-17) in which a tin solution with a chelating
agent is employed. The tin displaces copper which goes into
solution. The chelating agent is used to tie up the copper going
into solution; the tin only complexes weakly. This is a process
almost universally found in printed board shops and is used mainly
for rework.
5. Etching - Etching is that process by which all the unwanted copper
(i.e., any copper other than in the circuit) is removed from the
board. This step, illustrated in Figure 3-18, follows, in
sequence, the pattern print and pattern plate. Most companies
make use of mechanical etchers which spray solutions from various
tanks (containing etch solutions, solder brighteners or
activators, and rinse waters) onto horizontally traveling boards.
The etch solutions include:
Ferric chloride base - This provides good uniform etching,
but removal of the residual acid from the work is difficult.
Cupric chloride - This is suitable for any resist and has the
advantage of continued regeneration through addition of
chemicals.
Chromic acid base - This is the most expensive etchant listed
here and requires special attention in waste treatment for
chromium reduction. It is also very effective.
Ammonium persulfate - This is clean and easy to handle, but
the solution can be somewhat unstable.
Etching is always used in the subtractive production method, while
an abbreviated etch is employed in the semi-additive process. The
etching operation is not a part of the additive process.
After etching, the boards are ready for solder stripping and the
electroplating of the tabs, which was described earlier.
63
-------
PARTS
A f* T F^ /"* T H* 7i M
/\CJ.U L.JjJt!j/lN
T3TKFCP1
rCJLINDlLr
IMMERSION TIN
PLATE
HOT RINSE
en
-Ca
FIGURE 3-17 IMMERSION TIN PLATING LINE
-------
PARTS __
ETfH
•prppo
SPRAY
RINSE
SPRAY
RINSE
SOLDER
nRTPHT
ENER
SPRAY
RINSE
cr>
en
FIGURE 3-18 ETCHING LINE PROCESS
-------
-------
SECTION IV
INDUSTRY CATEGORIZATION
INTRODUCTION
The primary purpose of industry categorization is to establish
groupings within the electroplating point source category such that
each group has a uniform set of effluent limitations. These
subcategories are not mutually exclusive subdivisions of the electro-
plating point source category, however, as plants often perform
operations in more than one subcategory. For the purposes of this
document, the printing and publishing industry (SIC 2700) and the iron
and steel industry (SIC 3300) are specifically excluded from this
subcategorization even though they do perform similar operations.
This section presents the subcategories established as well as the
rationale for this categorization. There are two main elements of
categorization: first, the selection of a basis upon which to divide
each industry subcategory; and second, the selection of a discharge
limiting parameter for each subcategory against which to quantify the
limitations. The subsections which follow deal with each of these
major considerations.
CATEGORIZATION BASIS
After considering the nature of the various segments of the
electroplating industry and the operations performed therein, the
following categorization bases were considered plausible:
1. Type of manufacturing process
2. Type of basis material
3. Process baths used
4. Waste characteristics
5. Size and age of facility
6. Number of employees
7. Geographic location
8. Quantity of work processed
9. Water use
10. Effluent discharge destination
11. Job shops vs. captive shops
Previous regulations for the electroplating point source category
subcategorized the industry on the basis of the processes employed.
Electroplating was separated from electroplating-related metal
finishing processes because electroplating always requires the action
of an electrical current to deposit a metallic coating on the basis
material. Electroplating-related metal finishing processes may not
require a current and may or may not deposit a metallic coat on the
67
-------
basis material. The processes of anodizing, conversion coating,
chemical etching and milling are different enough to warrant separate
subcategories. Anodizing, usually performed on aluminum, converts the
surface of the object to the metal oxide. Conversion coating refers
principally to chromating and phosphating. Each of these processes
chemically forms a thin protective coat on the treated object. An
electrical current may or may not be applied. Chemical etching and
milling involve the dissolution of the basis material.
In restudying the industry for the purpose of establishing
pretreatment regulations, the Agency decided that printed circuit
board manufacturing and electroless plating also warrant separate
subcategorization because of the unique mixture of electrolytic and
electroless plating operations found in these processes.
Additionally, these processes produce pollutants which may render
normal waste treatment techniques ineffective if proper safeguards are
ignored.
The following subsections present the rationale for the
categorizations and subsequent selection of subcategories.
Type of_ Manufacturing Process
The types of manufacturing processes are a natural candidate for
forming the anodizing, coatings, and chemical etching and milling
subcategories for the purpose of establishing effluent limitations.
Anodizing is an electrolytic oxidation process which is unique and
thus is a separate subcategory. The processes encompassing the
coating subcategory involve the displacement, conversion or covering
of the base metal, while the operations in the milling subcategory all
involve removal of the base or plated metal.
Manufacturing processes also provide a basis for subdividing the
printed board industry for the purpose of establishing effluent
limitations. The basic processes involved in the manufacture of
printed boards are cutting, drilling, screening, electroplating,
electroless plating and etching. The above processes involving
deposition or removal of metal use water. Although these water using
processes are distinctly different from one another, they are all
performed on the same product from plant to plant and thus the wastes
generated by each plant are similar for a given production level.
Because of the similarity in operations from plant to plant, only one
subcategory is selected for printed board manufacture. A convenience
of this approach is the fact that a printed board plant does not have
to classify its manufacturing processes to arrive at an allowable
discharge. All the processes performed are in the same subcategory
for determining compliance with effluent discharge limitations.
68
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Type of Basis Material
The wastes produced by plating different basis materials with the same
plating metal are similar. The distinguishing feature of these wastes
is the plating metal rather than the basis material.
Process Baths Used
Process baths (plating baths) provide a basis for subcategorization
because the major source of wastes are the dragout of the solutions
from the baths and the batch dumping of these baths. Thus the
characteristics of the wastes from this industry are dependent on the
constituents of the baths. The most significant distinguishing
characteristic among electroplating baths is whether common or
precious metal plating is performed. Precious metal plating has less
waste discharge than common metal plating because of the value of the
plating constituents. Plants tend to take greater care in recycling
or reclaiming precious metals dragged out from baths and thus the
quantity of precious metal contents in streams is significantly less
than the common metal contents in common metal plating waste streams.
Electroless plating baths are different than electroplating baths in
chemical makeup. The metal concentrations are lower and there are
more complexing and chelating agents which have a negative effect on
removal efficiency during treatment. Accordingly, three subcategories
are selected: common metal electroplating, precious metal
electroplating, and electroless plating. These subcategories are not
subdivided to account for plating of specific metals in each
subcategory because the recommended chemical treatment systems in
Section VII of this report effectively reduce all metals in each
subcategory regardless of the metal plated.
Process baths provide a basis for the subcategorization of anodizing,
coatings, and chemical etching and milling because a major source of
wastes in these operations is from the dragout of solutions from
process baths and thus the characteristics of the wastes from these
subcategories are dependent on the constituents of the process baths.
However, categorization by manufacturing process inherently
encompasses the process baths used because the different process
subcategories employ different process baths. While the various
processes within each subcategory might employ different process bath
constituents, the recommended chemical treatment systems in Section
VII of this report effectively reduce all pollutants in each
subcategory regardless of the specific operations in each subcategory.
Process baths do not provide a basis for printed board manufacture
subcategorization because practicable waste treatment technology
identified in Section VII is equally applicable to all of the usual
procedures and process solutions described in Section III for printed
69
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board manufacture. In any facility carrying out one or more of the
processes shown, the same waste treatment needs arise.
Size and Age of_ Facility
The nature of the processes for the various subcategories of the
electroplating industry is unrelated to size and age of the facility.
Size alone is not an adequate categorization parameter since the waste
characteristics of a plant per unit of production are essentially the
same for plants of all sizes.
The relative age of plants is important in considering the economic
impact of a guideline, but it is not an appropriate basis for grouping
the industry into specific subcategories because it does not consider
the significant parameters which affect the effluent discharged. The
constituents of plating baths have a much more significant impact on
the effluent discharge than the age of the plant.
Number of. Employees
The number of employees engaged in electroplating operations in a
plant does not directly provide a basis for subcategorization because
these operations can be carried out manually or in automatic machines
which greatly conserve labor. For example, an operation for a given
production level may require six people if operated manually, whereas
a plant of the same production level and carrying out the same
operation in an automatic machine may need only two people. The same
amount of waste could be generated in each case if all other factors
were the same.
Geographic Location
There is not a basis for subcategorization by geographic location
alone. Manufacturing processes are not affected by the physical
location of the facility, except for availability of useable process
water. The price of water may affect the amount of modification to
procedures employed in each plant. However, procedural changes can
affect the volume of pollutants discharged but not the characteristics
of the constituents. The waste treatment procedures described in
Section VII can be utilized in any geographical area. In the event of
a limitation in the availability of land space for constructing a
waste treatment facility, the in-process controls and rinse water
conservation techniques described in Section VII can be adopted to
minimize the land space required for the end-of-process treatment
facility. Often, a compact package unit can easily handle end-of-
process waste if good in-process techniques are utilized to conserve
raw materials and water.
70
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Quantity of Work Processed
Quantity of work processed is related to plant size. Therefore, the
discussion about plant size is equally applicable to the quantity of
work processed.
Waste Characteristics
The physical and chemical characteristics of wastes generated by
electroplating are inherently accounted for by subcategorization
according to process baths and manufacturing processes. The physical
and chemical characteristics of wastes generated by printed board
manufacturing processes are similar from one plant to another in that
all wastes are amenable to the conventional waste treatment technology
detailed in Section VII. Since the characteristics of treated waste
are the same throughout the industry, waste characteristics do not
constitute a basis for subcategorization.
The treatability of wastes from manufacturing operations is uniform
throughout each subcategory since all of the principal treatment
procedures and in-process controls are technically applicable, by
choice, for any given waste from each subcategory. Although the
chelates involved in electroless plating and printed board manufacture
have a uniquely negative effect on precipitation type waste treatment
systems, they can be treated effectively by chemical precipitation if
they are segregated from the other types of waste. In addition,
electroless plating with chelated baths is common to most printed
board manufacturers and thus does not constitute a peculiarity from
plant to plant.
Water Use
Water usage alone is not a comprehensive enough factor upon which to
subcategorize. While water use is a key element in the limitations
established, it does not inherently relate to the source of the waste.
Water usage must be related to some other factor to be an effective
subcategorization base. The other factor is the manufacturing process
utilizing the water since it dictates the water usage.
Effluent Discharge Destination
The effluent discharge destination (surface waters or municipal
treatment stream) is not an adequate basis for subcategorization. The
wastes produced are determined by the production processes regardless
of the effluent wastewater destination.
71
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Job Shops vs. Captive
A job shop/captive shop division is not a valid basis for
subcategorization. Although job shops on the average are much smaller
than captive shops, the two groups of plants employ similar types of
manufacturing processes and generate wastes with similar
characteristics.
EFFLUENT LIMITATION BASE
Having selected the appropriate categorization bases and having
established the subcategories, the next step is to establish a
quantitative parameter on which to base limitations. The possible
choices for this quantitative parameter were all considered in great
detail before the final selection was made. The primary limitations
specified in this document for plants discharging to publicly owned
treatment works (POTW) are expressed in terms of concentration.
Concentration limits are easier to report since pollutants are
normally measured in concentrations, and such a limitation is easier
to enforce by the monitoring authority. However, dilution may be a
problem in some instances. Where dilution is encountered and is of
concern, local authorities should consider the need for prohibitions
on dilution, inspection of pretreatment and industrial facilities, and
enforcement of mass limitations.
An optional mass-based standard is also presented in this document for
those plants which recover process materials and employ water
conservation techniques. A milligram per square meter (mg/sq m)
standard was selected as the most rational mass-based standard since
effluent discharge rates are a function of the level of production,
and this standard accounts for differences in the actual production
level from plant to plant. The following subsections deal with the
selection of this production related parameter and the application of
this parameter for discharge limitations.
Selection of_ Production Normalizing Parameter
The level of production activity in a particular plant can be
expressed quantitatively as the number of parts processed, processed
area, power consumed or number of employees. All of these parameters
have some relation to the level of production in a particular plant,
but area processed is more closely associated with the level of
activity relative to pollutant discharge than the other potential
parameters.
Number of_ Parts Processed - This parameter is a direct and readily
identifiable production related parameter. However, parts to be
processed or printed boards produced come in many different sizes and
since the pollution generation rate is dependent on the quantity of
72
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solution dragged out of process baths, different size parts drag out
different quantities of chemicals from the baths. Thus, the number of
parts processed is not sufficient for determining a quantitative
prediction of pollution discharge rate, but must be factored by the
plated area of these parts.
Area Processed - The direct relation of the pollution generation rate
to the quantity of dragout leads naturally to the selection of
processed area as a production related pollutant discharge rate
parameter. For the common metals electroplating, precious metals
electroplating and electroless plating subcategories, processed area
is area plated. For the anodizing, coatings and chemical etching and
milling subcategories, processed area is area finished. Although
masking (particularly hydrophilic masking) might contribute somewhat
to dragout, relatively little masking is used in these subcategories.
In addition, processed area for electroplating is readily obtainable
by measuring power consumption and determining the average plating
thickness. Thus, plated area is more easily measured for
electroplating operations than plated and masked area (total immersed
area).
For the printed board segment, the direct relation of the pollution
generation rate on the quantity of dragout leads naturally to
consideration of plated area as a production related pollutant
discharge rate parameter. The masked area of printed boards is
significant, but if the masked area of a printed board immersed in a
plating or treatment solution is hydrophobic, it should not drag out
any plating or treatment solution, and thus only the non-masked
(plated) area contributes to the dragout. However, controlled
experiments performed during a study of the industry indicate that
masking used on printed boards drags out as much of a plating bath as
the area plated. Table 4-1 presents this controlled experiment data
showing negligible difference (within expected measurement scatter) in
the amount of dragout from masked and unmasked boards. The actual
dragouts for each plant in Table 4-1 cannot be compared because
different boards were used at each plant. Since the sum of the area
plated and the area masked is the total area immersed, and since this
entire area immersed contributes to the dragout, total area is the
selected production related parameter for pollutant discharge for the
printed board manufacturing subcategory.
A unique characteristic of the printed board industry relative to
immersed area and associated process bath dragout is the effect of
through holes on dragout. To quantify the effect on dragout of
through hole plating, controlled experiments were performed. These
experiments involved immersing various boards (both with holes and
without) in an electroless copper plating bath and then rinsing these
boards and measuring the concentration of copper in the rinse tank.
The results of these experiments are shown in Table 4-2.
73
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TABLE 4-1
EFFECT OF MASKING ON DRAGOUT
COMPANY
ID
17061
36062
TEST TYPE OF MASK
II Photoresist
12 Photoresist
13 Screen
14 Photoresist
DRAGOUT
UNMASKED
280 mg/1
360.8 mg/1
0.377 mg/1-
in2
0.377 mg/1-
in
DRAGOUT
MASKED
250 mg/1
386.6 mg/1
0.33. mg/1-
in*
0.318 mg/1-
in
DIFFERENCE
-11%
+ 7%
- 2%
- 6%
TABLE 4-2
EFFECT OF HOLES ON DRAGOUT
COMPANY ID
4065
6067
36062
HOLE SIZE
0.077
0.031-0.040
0.031-0.040
0.045
0.037
0.045
0.037
0.045
0.037
DRAGOUT
WITHOUT HOLES
1.429 mg/1
4.429 mg/1
2.250 mg/1
0.337 mg/l-in*
0.337 mg/l-in2
0.938 mg/l-in*
0.038 mg/l-in*
0.331 mg/l-in*
0,318 mg/l-in*
DRAGOUT
WITH HOLES
1.786 mg/1
6.3 mg/1
2.921 mg/1
0.394 mg/l-in*
0.354 mg/l-in*
0.072 mg/l-in*
0.065 mg/l-in*
0.493 mg/l-in*
0.477 mg/l-in*
PERCENT
INCREASE
DRAGOUT
25%
42%
30%
17%
5%
92%
74%
49%
50%
74
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Based on these results, It is apparent that holes cause an increase in
dragout, but this increase is extremely variable and dependent on5
Plating bath characteristics (including viscosity, pH, and
chemical composition).
Physical handling of t
and agitation of parts).
the boards (types of racks, drip time,
Characteristics of holes (size and density).
Due to the complexity of calculating hole areas and volumes, no
significant data in this area were received from most plants
contacted. Therefore, the specific effect of holes on dragout cannot
be accounted for in establishing limitations. However, the provision
for a separate subcategory for printed boards relative to the overall
electroplating point source category negates the effect of holes since
many plants through hole plate and holes are, therefore, not a
distinguishing factor.
Power Consumption - Power consumption was also considered for a
production related parameter. For electroplating, this parameter can
be related by a coulombic equivalent to the quantity of metal
deposited on a part and if the average plating thickness is known, it
can be used to determine plated area. For anodizing, this parameter
is relatable to oxide buildup on a part and if the average oxide
thickness is known, it can be used to determine anodized area.
However, pollutant dragout is more closely related to area processed
rather than power since power varies as a function of the thickness of
the workpiece. Also this parameter is not applicable to electroless
plating, coatings, and chemical milling and etching.
Number of Employees - As discussed previously, some plants employ
automatic production lines while others have manual lines. Thus, for
the same production level, the work force at two plants might be
distinctly different. For this reason, the number of employees is not
an adequate production related parameter on which to base limitations.
Application of Production Normalizing Parameter
Basing limitations on processed area results in a milligram per square
meter limitation that is calculated from the concentration of
pollutants (mg/1) in a discharge multiplied by the discharge flow rate
(1/hr) and divided by the production rate (sq m/hr). However, the
mg/sq m term also requires definition of the number of manufacturing
operations since each manufacturing operation involves immersion in a
process tank with subsequent dragout of solution into rinse tanks. To
account for the different processing sequences found in different
electroplating plants, the limitation in terms of area processed must
75
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also be expressed in terms of operations performed (mg/operation-sq
m). Since dragout enters an effluent stream only when it is rinsed
from a part, only production steps which are immediately followed by a
rinse are counted as operations for the limitations.
Table 4-3 lists operatons applicable to the seven subcategories of the
electroplating category. Referring to Table 4-3, catalyst application
and acceleration are considered operations in electroless plating.
This is because these operations involve the deposition of palladium
and tin on the surface of a plastic part and are thus similar to
plating operations. In addition, the initial acid cleaning and
alkaline cleaning steps in a line are counted as operations if they
precede all electroplating processes (one alkaline cleaning step per
plating line). Sampling and analysis showed that basis metal and
surface contaminants are removed to a significant degree in the
initial cleaning steps of a plating line. Since the subsequent rinses
contribute metal to the waste stream, these initial cleaning steps are
regarded as operations. With the exception of catalyst application,
acceleration, and the initial cleaning steps, no other surface
preparation or post-treatment steps are considered plating operations.
These other surface preparation and post-treatment operations are
considered integral with subsequent plating type operations, and the
water used and wastes produced by these operations are intrinsically
included in the water use and pollutant discharge from the plating
operation. As such, the water use and pollutant discharge from
surface preparation and post-treatment operations are included in the
limitations which are established from overall plant discharges.
76
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TABLE 4-3
ELECTROPLATING OPERATIONS
Subpart A-Common Metals Plating
Aluminum Electroplating
Cadmium Electroplating
Copper Electroplating
Chromium Electroplating
Iron Electroplating
Nickel Electroplating
Tin Electroplating
Lead Electroplating
Zinc Electroplating
Electroplating of any combination of above
metals
Subpart B-Precious Metals Plating
Gold Electroplating
Indium Electroplating
Palladium Electroplating
Platinum Electroplating
Rhodium Electroplating
Silver Electroplating
Subpart D-Anodizing
Anodizing
Subpart E-Coatings
Coloring*
Chromating*
Phosphating*
Immersion Plating
Subpart F-Chemical Milling and Etching
Chemical Milling
Etching
Bright Dipping
Stripping (To salvage improperly coated
parts)**
Subpart G-Electroless Plating
Electroless Plating on Metals
77
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Electroless Plating on Plastics
Catalyst Application
Acceleration
All Subcateqories
Stripping (to salvage improperly plated parts)
Coloring**
Chromating**
Phosphating**
Acid Cleaning
Alkaline Cleaning
*Counted as a coating operation if not integral with a plating line.
If integral with plating line, it is counted as a plating operation.
**If integral within a plating line, it is counted as an operation of
that subcategory.
Table 4-4 lists operations applicable to printed board manufacture.
Referring to Table 4-4, both catalyst application and acceleration
steps are considered operations in the manufacture of printed boards.
This is because these operations involve the deposition of palladium
and tin onto the surface of the board and are thus similar to plating
operations. In addition, the initial acid cleaning and alkaline
cleaning steps in a line are counted as operations if they precede all
printed board operations. Sampling and anaylsis showed that basis
metal and surface contaminants are removed to a significant degree in
the initial cleaning steps of printed board process lines. Since
subsequent rinses contribute metal and other contaminants to the waste
stream, these initial cleaning steps are regarded as operations. No
other surface preparation or post-treatment type steps are considered
operations. These other surface preparation and post-treatment
operations are considered integral with the surface preceding or
subsequent plating type operations, and the water used and waste
produced by these operations are intrinsically included in the water
use and pollutant discharge from the plating operations.
78
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TABLE 4-4
OPERATIONS IN THE MANUFACTURE OF PRINTED CIRCUIT BOARDS
Catalyst Application
Acceleration
Copper Electroplating
Nickel Electroplating
Solder Electroplating
Tin Electroplating
Gold Electroplating
Silver Electroplating
Platinum Metals Electroplating
Electroplating of Any Combination of
Above Metals
Electroless Plating on Plastics
Electroless Plating on Metals
Immersion Plating
Etching
Stripping (To salvage Improperly Plated
Parts)
Acid Cleaning*
Alkaline Cleaning*
Conversion Coating
* Only the initial alkaline cleaning and acid cleaning steps in a
line are counted as operations. Therefore, any subsequent surface
preparation steps are not counted as operations.
Optional TSS Limitations
Another optional set of limitations established for indirect
dischargers is the total suspended solids (TSS) monitoring alternative
described in Section II. In this set of limitations, TSS replaces
copper, nickel, chromium, and zinc as monitoring parameters. TSS was
selected as a basis parameter because the Agency believes that if the
required level of TSS is met, the individual and total metal
concentrations of the effluent streams will not be greater than their
regulated concentrations.
79
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SECTION V
WASTE CHARACTERIZATION
INTRODUCTION
This section presents the waste constituents and quantities
originating from the Electroplating Point Source Category. The raw
waste data presented are derived from an analysis of samples taken
downstream of the manufacturing sources but prior to final treatment.
All parameters were measured as total material rather than dissolved.
A tabulation showing each parameter analyzed, the specific analysis
procedure employed, sample collection data, sample preservation data,
and the minimum detectable analysis limit is shown in Table 5-1.
Table 5-2 describes the analysis technique used to determine the
concentration of the chelates found in waste streams sampled. The
following section presents the characteristics of the wastes for the
common metals plating, precious metals plating, anodizing, chemical
conversion coating, etching and chemical milling, electroless plating
and printed circuit board subcategories of this point source category
because of the distinctly different operations performed in each
subcategory. These subcategories are not mutually exclusive
subdivisions of the electroplating point source category, however,
because plants often perform operations in more than one subcategory.
CHARACTERISTICS OF WASTES FROM THE ELECTROPLATING POINT SOURCE
CATEGORY
For the purposes of this document, electroplating process wastewater
is defined as all waters used for rinsing, alkaline cleaning, acid
pickling, plating and other metal finishing operations; it also
includes waters which come about from spills, batch dumps, and
scrubber blowdown. Cooling water which does not come in contact with
the produce or waste by-products is not included in this definition
unless the cooling water is subsequently used in an electroplating
process.
Wastewater from common and precious metals plating processes comes
from cleaning, surface preparation, plating, and related operations.
Wastewater from metal finishing processes comes from cleaning,
pickling, anodizing, coating, etching, and related operations.
Printed circuit board wastewater comes from cleaning, electroless
plating, etching, masking and electroplating. The wastewater from
electroless plating derives from etching, catalyst application,
acceleration and plating. The constituents in these wastewater
include the basis material being finished as well as the components in
the processing solutions. Predominant among the wastewater
constituents are copper, nickel, chromium, zinc, lead, tin, cadmium,
gold, silver, platinum metals, as well as ions that occur from
81
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PARAMETER
Silver
ON-SITE
TABLE 5-1
ANALYSIS METHODS
LOCAL LAB CENTRAL LAB
X
Gold
Cadmium
oo
no
Cyanide
Amenable to
Chlorination
Total Cyanide
SAMPLING AND ANALYSIS METHOD
EPA 146*, SM 301*. Atomic ab-
sorption. Sample collected in
polyethylene or glass bottles
and preserved with HNO3 to pH 2
maximum. Maximum holding per-
iod: 6 months. Minimum detec-
table limit: 0.001 mg/1.
Atomic Absorption. Sample col-
lected in glass bottle and pre-
served with HNO3^ to pH 2 maxi-
mum. Maximum holding time: 6
months. Minimum detectable
limit: 0.001 mg/1.
EPA 101, SM 301. Atomic absorp-
tion. Sample collected in poly-
ethylene or Pyrex bottles and pre-
served with HNO^3 to pH 2 maximum.
Maximum holding period: 6 months.
Minimum detectable limit: 0.001 mg/1
EPA 49, SM 376. Colorimetric.
Sample collected in polyethylene
bottles and preserved with suffi-
cient NaOH to maintain pH of 12
minimum. Sample refrigerated to
4 degrees C. Maximum holding
time: 24 hours. Minimum detec-
table limit: 0.001 mg/1.
EPA 40, SM 361. Distillation,
silver nitrate titration or
pyridine - pyrazolone colori-
metric. Sample collected and
preserved as in cyanide amenable
-------
PARAMETER
TABLE 5-1 (Continued)
ON-SITE LOCAL LAB CENTRAL LAB
Hexavalent
Chromium
Fluorides
CO
Nickel
Phosphorus
Tin
SAMPLING AND ANALYSIS METHOD
to chlorination described above.
Maximum holding time: 24 hours.
Minimum detectable limit: 0.001
mg/1.
SM 307B. Colorimetric. Diphenyl-
carbazide. Sample collected in
polyethylene or pyrex bottles and
preserved with HNO3_ to pH2 maximum.
Holding period: 6 months. Mini-
mum detectable limit: 0.005 mg/1.
EPA 59, SM 414. Distillation.
SPADNS. Sample collected in
polyethylene or glass bottle, and
refrigerated to 4 degrees C. Maxi-
mum holding time: 7 days. Mini-
mum detectable limit: 0.1 mg/1.
EPA 141, SM 301. Atomic absorp-
tion. Sample collected in poly-
ethylene or glass bottles and pre-
served with HNO_3 to pH 2 maximum.
Maximum holding period: 6 months.
Minimum detectable limit: 0.001 mg/1.
EPA 249, SM 425. Persulfate diges-
tion vanadomolybdo phosphoric colori-
metric. Plastic or glass container.
Sample refrigerated to 4 degrees C.
Max holding time: 24 hours. Mini-
mum detectable limit: 0.01 mg/1.
EPA 150, SM 301. Atomic absorption.
Sample collected in glass bottle
and preserved with HNO3_ to pH 2
maximum. Max holding time: 6 months.
Minimum detectable limit: 0.001
•9/1.
-------
PARAMETER
Zinc
TABLE 5-1 (Continued)
ON-SITE LOCAL LAB CENTRAL LAB
x
Flow
Lead
Palladium
00
Pho^ium
Total
Chromium
Copper
Iron
SAMPLING AND ANALYSIS METHOD
EPA 155, SM 301. Atomic absorp-
tion. Sample collected in poly-
ethylene or glass bottles and pre-
served with HN0.3 to pH 2 maximum.
Maximum holding period: 6 months.
Minimum detectable limit: 0.01 mg/1.
Measured with a flowmeter, measurable
restriction, elapsed tine meter or
container and stopwatch, as appli-
cable. Expressed in gallons per hour.
EPA 112, SM 301. Atomic absorption.
Sample handling and detection limits
same as cadmium.
Atomic absorption. Sample collected
in glass bottle and preserved with
HN03 to pH 2 maximum. Maximum
holding time: 6 months. Minimum
detectable limit: 0.001 mg/1.
Atomic absorption. Sample collected
in glass bottles and preserved with
HNO3 to pH 2 maximum. Maximum
holding time: 6 months. Minimum
detectable limit: 0.001 mg/1.
EPA 105, SM 301. Atomic absorption.
Sample handling and detection limits:
same as cadmium.
EPA 108, SM 301. Atomic absorption.
Sample handling and detection limits:
same as cadmium.
EPA 110, SM 301. Atomic absorption.
Sample handling and detection limits:
same as cadmium.
-------
PARAMETER
PH
Total
Dissolved
Solids
TABLE 5-1 (Continued)
ON-SITE LOCAL LAB CENTRAL LAB
X
Total
Suspended
Solids
00
01
Temperature
Oil and
Grease
SAMPLING AND ANALYSIS METHOD
EPA 239, SM 424. Measured with a
portable pH meter. Expressed in
pH units.
EPA 266, SM 208. Filtration, evapor-
ation. Sample collected in poly-
ethylene and pyrex bottles and refri-
gerated to 4 degrees C. Maximum
holding time: 7 days. Minimum det-
ectable limit: 0.1 mg/1.
EPA 268, SM 208. Filtration. Sample
collected in polyethylene or Pyrex
bottles and refrigerated to 4 degrees
C. Maximum holding time: 7 days.
Minimum detectable limit: 0.1 mg/1.
EPA 286, SM 212. Measured with a
thermometer or thermistor. Expressed
in centigrade degrees.
EPA 226, SM 502. Organic solvent ex-
traction. Sample collected in glass
and preserved with H2S04_ to pH 2 max.
Sample refrigerated to 4 degrees C.
Maximum holding period: 24 hours.
Minimum detectable limit: 0.1 mg/1.
*References
SM (Standard Methods)
"Standard Methods for the Examination of Water and Wastewater", 14th Ed. 1975.
American Public Health Association.
EPA
"Methods for Chemical Analysis of Water and Wastes", EPA-625/6-74-
003. U. S. Environmental Protection Agency, Washington, D. C., 1974.
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TABLE 5-2
CHELATING AGENT
EDTA
(Ethylenediamine-
tetraacetic Acid)
CO
Citric Acid
NTA
Tartrates
Tartaric Acid
Potassium Sodium
Tartrate
Thiourea
Gluconic Acid
Slycolic Acid
CHELATE ANALYSIS METHODS
CENTRAL LAB ANALYSIS METHOD
Preliminary screening by solubilizing copper with EDTA at
pH 10, followed by filtration and atomic absorption analysis
of soluble copper in the filtrate. Analysis of EDTA per-
formed by gas chromatographic analysis, flame ionization
detection. Minimum detectable limit: 0.5 mg/1.
Gas chromatographic analysis, flame ionization detection.
Minimum detectable limit: 0.1 mg/1.
Same as Citric Acid.
Screened by qualitative analysis, spot test using 1% resor-
cinol and H2SO£. Analysis performed by acid-base titration
as follows: Sample treated with potassium chloride and
acetic acid, then refrigerated to settle out potassium
bitartrate KHC4H40. Titrate with sodium hydroxide to
Phenolphthalein end point. Minimum detectable limit:
0.1 mg/1.
Colorimetric analysis procedure. Pentaammonium
Ferricyanide salts, 1% in water reagent. Minimum detectable
limit: 1.0 mg/1.
Gas chromatographic analysis, flame ionization detection.
Results inconclusive due to possible interference of other
wastewater constituents. Screening for gluconic acid using
excess copper and then analyzing the filtrate for copper
also was not conclusive for the same reason.
Gas chromatographic analysis, flame ionization detection.
Minimum detectable limit: 0.1 mg/1.
-------
cleaning, surface preparation, or processing baths such as phosphates,
chlorides, and various metal complexing agents. These constituents
are common to both direct and indirect discharge electroplating
facilities since they are dependent on the production processes
performed.
Water Usac
Water is used for rinsing work pieces, washing away spills, air
scrubbing, rinsing after auxiliary operations, preparing solutions,
and washing equipment. Descriptions of these uses follow.
Rinsing - A large proportion (approximately 90 percent) of the water
usage in plating is for rinsing. The water is used to remove the
process solution film from the surface of the work pieces. Ab a
result of this rinsing, the water becomes contaminated with the
constituents of the process solutions and is not directly reusable.
Dilute rinse water solutions of various process chemicals result from
each operation. Figure 5-1 illustrates rinse water flow in a typical
electroplating facility. Rinse water use for typical electroless
plating lines is diagrammed in Figure 5-2.
Spills and Air Scrubbing - The water from washing away and from
scrubbing ventilation exhaust air is normally added to the acid alkali
waste stream and then treated. This wastewater generally is
contaminated with constituents of the operating solutions.
Process Solution Preparation - As process baths become exhausted or
spent, new solutions have to be made up, with water a major
constituent of these baths. When a high temperature bath is being
used, water has to be added periodically to make up for evaporative
losses. Exhausted or spent process solutions to be dumped are often
slowly metered into rinse water following the operation and prior to
treatment. Alternatively, these solutions, which are much more
concentrated than the rinse water, may be processed batchwise in a
special treatment facility.
Rinsing after Auxiliary Operations - Water is used for rinsing after
auxiliary operations such as rack stripping in order to remove process
solution from the surface of the part, just as in rinsing after
plating operations.
Washing Equipment - Water used for washing filters, pumps, and tanks
picks up residues of concentrated solutions or salts and should be
routed to the appropriate rinse water stream for chemical treatment.
87
-------
CLEAN
WATER
NEUTRALIZE AND
PRECIPITATE
OXIDIZE
CYANIDE
PRECIPITATE
COPPER
SETTLE
SLUDGE
PRECIPITATE
NICKEL AND COPPER
REDUCE
CHROMIUM
PRECIPITATE
CHROMIUM
TREATED WATER
FIGURE 5-1 SCHEMATIC FLOW CHART FOR WATER FLOW IN
CHROMIUM PLATING ZINC DIE CASTINGS, DECORATIVE
88
-------
ELECTROLE
NICKEL
ON
PLASTIC
WATER
SOURCE
SS
WORK FLOW
1
CHROMIC
ETCH
C CU
RINS
RRENT
E
SPRAY
RINSE
NEUTRAL-
IZATION
RINSE
APPLY
CATALYST
RINSE
ACCELER-
ATION
RI1>
SPRAY
RINSE
ELECTRO-
LESS NI
Rlh
RIM
Cp
Cp
I
TO
CHROME
~~* REDUC-
TION
TO
— ^PRECIP-
ITATION
ELECTROLE
NICKEL
ON
METAL
WATER __»
SOURCE^
SS
P
WORK
j
FLOW
L
ALKALINE
CLEAN
RINSE
ACID
CLEAN
RINSE
NEUTRAL-
IZATION
RINSE
ELECTRO-
LESS NI
RI1<
RII
I
TCP
9
H
TO
. WASTE
~* TREAT
MENT
FIGURE 5-2
USE OF RINSE WATER IN ELECTROLESS PLATING OF NICKEL
89
-------
Sources of Waste
The following process solutions are the major waste sources during
normal plating operations.
Alkaline Cleaners - Cleaning solutions usually contain one or more of
the following chemicals: sodium hydroxide, sodium carbonate, sodium
metasilicate, sodium phosphate (di- or trisodium), sodium silicate,
sodium tetra phosphate, and a wetting agent. The specific content of
cleaners varies with the type of soil being removed. For example,
compositions for cleaning steel are more alkaline and active than
those for cleaning brass, zinc die castings, and aluminum. Waste
waters from cleaning operations contain not only the chemicals found
in the alkaline cleaners but also soaps from the saponification of
greases left on the surface by polishing and buffing operations. Some
oils and greases are not saponified but are, nevertheless, emulsified.
The raw wastes from cleaning process solutions and dissolution of
basis metals show up in the rinse waters, spills, dumps of
concentrated solutions, wash waters from air-exhaust ducts, and
leaking heating or cooling coils and heat exchangers. The
concentrations of dissolved basis metal in rinses following alkaline
cleaning are usually small relative to acid dip rinses.
Acid Cleaners - Solutions for pickling or acid cleaning usually
contain one or more of the following: hydrochloric acid (most
common), sulfuric acid, nitric acid, chromic acid, fluoboric acid, and
phosphoric acid. The solution compositions vary according to the
nature of the basis metals and the type of tarnish or scale to be
removed. These acid solutions accumulate appreciable amounts of metal
as a result of dissolution of metal from work pieces or uncoated areas
of plating racks that are recycled repeatedly through cleaning, acid
treating, and electroplating baths. As a result, the baths usually
have a relatively short life, and when they are dumped and replaced,
large amounts of chemicals must be treated or reclaimed. These
chemicals also enter the waste stream by way of dragout from the acid
solutions into rinse waters.
The amount of waste contributed by acid cleaners and alkaline cleaners
varies appreciably from one facility to another depending on the
substrate material, the formulation of the solution used for cleaning
or activating the material, the solution temperature, the cycle time,
and other factors. The initial condition of the substrate material
affects the amount of waste generated during treatment prior to
finishing. A dense, scalefree copper alloy part can be easily
prepared for finishing by using a mild hydrochloric acid solution that
dissolves little or no copper, whereas products with a heavy scale
require stronger and hotter solutions and longer treating periods for
ensuring the complete removal of any oxide prior to finishing.
90
-------
Catalyst Application and Acceleration - In electroless plating on
plastics, a catalyst must be applied to the plastic to initiate the
plating process. The catalyst consists of tin and palladium, and in
the acceleration process the tin is removed. A chromic acid surface
preparation of the plastic usually precedes the catalyst application.
Plating Operations and Post-treatment - Plating and post-treatment
baths contain metal salts, acids, alkalies, and various compounds used
for bath control. Common plating metals include copper, nickel,
chromium, zinc, cadmium, lead, iron, and tin. Precious plating metals
include silver, gold, palladium, platinum, and rhodium. In addition
to these metals ammonia, sodium and potassium are common cationic
constituents of plating baths. Anions most likely to be present in
plating and post-treatment baths are borate, cyanide, carbonate,
fluoride, fluoborate, phosphates, chloride, nitrate, sulfate, sulfide,
sulfamate, and tartrate.
Many plating solutions contain metallic, metallo-organic, and organic
additives to induce grain refining, leveling of the plating surface,
and deposit brightening. Arsenic, cobalt, molybdenum, and selenium
are used in this way, as are saccharin and various aldehydes. These
additives are generally present in a bath at concentrations of less
than one percent by volume or weight.
Complexing and chelating agents are important constituents of some
plating baths, especially electroless plating solutions. Most
electroless plating baths in commercial use are proprietary and
identification of complexing agents present is difficult. From a
wastewater standpoint, the prime importance of the agents lies in the
difficulties they present for effective metal removal since they
hinder precipitation of metal ions.
Chromium, aluminum, and manganese are the metal constituents most
common in anodizing baths; while ammonia, sulfate, fluoride,
phosphate, and various bases are the most important non-metal
constituents. Basis metal, usually aluminum, will also be present in
the bath. Posttreatment for anodized surfaces often consists only of
hot water rinsing. Occasionally, anodized parts are sealed with a
chromium salt solution or colored with organic or inorganic dyes.
Chromating baths are nearly all proprietary and little information
about their formulation is available. However, all baths have
chromate and a suitable activator (an organic or inorganic radical)
usually in an acid solution. Chromate conversions can be produced on
zinc, cadmium, aluminum, magnesium, copper and brass, and these metals
will dissolve into the chromating baths. Posttreatment of chromate
conversion coatings may include dipping in organic dips or sealing in
a hot water rinse.
91
-------
The phosphates of zinc, iron, manganese, and calcium are most often
used for phosphate coatings. Strontium and cadmium phosphates are
used in some baths, and the elements aluminum, chromium, fluorine,
boron, and silicon are also common bath constituents. Phosphoric acid
is used as the solvent in phosphating solutions. Phosphated parts may
be colored in a posttreatment step, or conditioned in very dilute
chromic or phosphoric acid.
Solutions for chemical milling, etching, and associated operations
contain dissolved or particulate basis metals and either chemical
agents for metal oxidation or electrolytes for electrical metal
removal (as in electrochemical machining). Bath constituents for
chemical removal of basis metals include mineral acids, acid
chlorides, alkaline ammonium solutions, nitroorganic compounds, and
such compounds as ammonium peroxysulfate. Common electrolytes are
sodium and ammonium chloride, sodium and ammonium nitrate, sodium
cyanide. Posttreatment baths for chemical milling or etching would
not contain significantly different constituents than those listed
above.
Immersion plating baths usually are simple formulations of metal
salts, alkalies, and complexing agents. The complexing agents are
typically cyanide or ammonia and are used to raise the deposition
potential of the plating metal. Parts plated by immersion are seldom
post-treated except in the case of zinc immersion plating of aluminum.
This process is used to form a base for subsequent electroplating,
usually copper.
Auxiliary Operations - Auxiliary operations such as rack stripping,
although essential to plant operation, are often neglected in
considering overall pollutant reduction. Stripping solutions using a
cyanide base can form compounds which are difficult to treat. One
such compound is nickel cyanide, in which the cyanide is not readily
amenable to chlorination. Frequent cleaning of stripping baths and
use of alternative chemicals can significantly reduce the pollutants
evolving from this type of source.
Waste Constituents And Quantities
The results of analysis of the specific constituents of raw waste
streams from the plating establishments in the data base are presented
in Tables 5-3 to 5-10. The following subcategories are represented:
Table 5-3 Common Metals Plating
Table 5-4 Precious Metals Plating
Table 5-5 Anodizing
Table 5-6 Coatings
Table 5-7 Chemical Milling and Etching
Table 5-8 Electroless Plating
92
-------
Table 5-10 Printed Circuit Boards
Data on the chelating agents used in the electroless plating
subcategory are presented in Table 5-9.
The values given for cyanide, hexavalent chromium, and total suspended
solids do not reflect actual raw waste concentrations. In a majority
of plants raw waste was sampled after cyanide oxidation, chrome
reduction, and pH adjustment, at a point just prior to clarification.
This was done since segregated waste streams were often very difficult
to sample, and, in the case of cyanide, potentially hazardous.
The numbers presented in Tables 5-3 through 5-10 are the range of
concentration values for each constituent. These values were deter-
mined by a statistical analysis of the raw waste streams for 82
visited plants in the data base. This analysis involved allocating
total pollutant raw waste masses to appropriate subcategories. No
allowance was made for alkaline or acid cleaning. Total raw waste
allocations for electroless plating were made to Subparts A and B.
Measured concentrations could not be used since nearly all plants
visited had wastes applicable to more than one subcategory. It should
also be noted that only plants which used a particular metal in their
process were used in averaging values for that metal.
Table 5-3 presents the range of pollutants found to a significant
degree in the common metals plating subcategory. The main
constituents of the waste streams are those parameters which are
ingredients of process solutions which have been dragged out into the
rinse waters. Included are cyanide and metals such as copper, nickel,
chromium, and zinc from plating solutions, fluorides from plating
solutions and acid cleaners, and phosphorus from cleaners.
The major constituents of wastewaters produced in the precious metals
subcategory are listed in Table 5-4. Just as with common metals
plating, the pollutants are a result of process solution dragout:
cyanide, silver, gold, palladium, platinum, rhodium and phosphorus.
Table 5-5 presents the pollutants found in the anodizing subcategory.
The high chromium levels are a result of chromic acid anodizing. The
phosphorous is contributed by cleaners and phosphoric acid and the
suspended solids are caused by the removal of soils and basis
material.
The concentration levels in Table 5-6 describe the raw wastes found in
the coating subcategory. The pollutants in these wastewaters are a
product of process solution dragout or basis material removal.
Chromium results from chromating and iron, zinc and phosphorous are
added by phosphating. Tin is contributed by immersion plating.
93
-------
Table 5-7 shows the composition of raw waste streams from the chemical
milling and etching subcategory. These pollutants originate in the
acid process solutions (chromium, fluoride and phosphorus from chromic
acid, hydrofluoric acid and phosphoric acid, respectively) or by basis
material removal (copper, zinc, iron, tin).
Tables 5-8 and 5-9 present the range of concentrations of pollutants
found in the electroless plating subcategory. As a rule, the metals
concentrations are lower than those found in common metals plating
streams due to more dilute plating solutions. Table 5-9 describes the
chelating agents which were present in those plants reporting their
use.
The results of an analysis of the constituents of raw waste streams
sampled from printed board manufacturers are shown in Table 5-10.
These figures are based on two or three day composite sampling visits
at ten printed board installations and represent the range of
concentrations from the visited printed board plants. Included in the
table are the results of an analysis for chelating agents, which are
particularly significant wastes from the printed board industry
because of their interference with effective waste treatment. The
information on chelates includes:
1. The number of plants out of the ten printed board instal-
lations sampled for chelating agents which reported use of a
specific agent.
2. The number of plants where that chelating agent was detected
above a minimum detectable limit.
3. The average concentrations of particular chelating agents
found.
The principal constituents of the waste streams from the printed board
industry are suspended solids, copper, fluorides, phosphorus, tin,
palladium and chelating agents. Low pH values are characteristic of
the wastes because of the acid cleaning and surface preparation
necessary. The suspended solids are comprised primarily of metals
from plating and etching operations and dirt which is removed during
the cleaning processes prior to plating. The large amount of copper
present in the waste stream comes from the electroless copper plating
as well as copper electroplating and etching operations. Fluorides
are primarily the result of cleaning and surface treatment processes
utilizing hydrofluoric and fluoboric acids. Phosphorus results from
the large amount of cleaning that is performed on the boards. Tin
results from operations involving catalyst application and solder
electroplating, and palladium is a waste constituent from catalyst
application. The chelating agents present are primarily from the
94
-------
electroless plating operations, although others may have been added by
the cleaning, immersion plating, and gold plating operations.
In order to figure the ranges of pollutant concentrations used above
to characterize the raw wastes of the different subcategories, all 82
sampled plants were used as a data base. However, not all of these
raw wastes were used in calculating effluent limitations. Plants were
selectively deleted from the data base used for analysis. Several
plants were screened out as having treatment systems which were
considered to be unrepresentative of the model pretreatment
technology. In addition to this, plants which had specific design or
operational problems as reported by sampling personnel were screened.
A- detailed description of effluent limitation derivation is presented
in Section XII.
95
-------
TABLE 5-3
COMPOSITION OF RAW WASTE STREAMS
FROM COMMON METALS PLATING
(mg/1)
Copper 0.032-272.5
Nickel 0.019-2954
Chromium, Total 0.088-525.9
Chromium, Hexavalent 0.005-334.5
Zinc 0.112-252.0
Cyanide, Total 0.005-150.0
Cyanide, Amenable to Chlorination 0.003-130.0
Fluoride 0.022-141.7
Cadmium 0.007-21.60
Lead 0.663-25.39
Iron 0.410-1482
Tin 0.060-103.4
Phosphorus 0.020-144.0
Total Suspended Solids 0.100-9970
96
-------
TABLE 5-4
COMPOSITION OF RAW WASTE STREAMS
FROM PRECIOUS METALS PLATING
(mg/1)
Silver 0.050-176.4
Gold 0.013-24.89
Cyanide, Total 0.005-9.970
Cyanide, Amenable to Chlorination 0.003-8.420
Palladium 0.038-2.207
Platinum 0.112-6.457
Rhodium 0.034*
Phosphorus 0.020-144.0
Total Suspended Solids 0.100-9970
*0nly 1 plant had a measurable level
of this pollutant.
TABLE 5-5
COMPOSITION OF RAW WASTE STREAMS
FROM ANODIZING
(mg/1)
Chromium, Total 0.268 - 79.20
Chromium, Hexavalent 0.005 - 5.000
Cyanide, Total 0.005 - 78.00
Cyanide, Amenable to Chlorination 0.004 - 67.56
Phosphorus 0.176 - 33.00
Total Suspended Solids 36.09 - 924.0
97
-------
TABLE 5-6
COMPOSITION OF RAW WASTE STREAMS
FROM COATINGS
(rag/1)
Chromium, Total 0.190 - 79.20
Chromium, Hexavalent 0.005 - 5.000
Zinc 0,138 - 200.0
Cyanide, Total 0.005 - 126.0
Cyanide, Amenable to Chlorination 0.004 - 67.56
Iron 0.410 - 168.0
Tin 0.102 - 6.569
Phosphorus 0.060 - 53.30
Total Suspended Solids 19.12 - 5275
98
-------
TABLE 5-7
COMPOSITION OF RAW WASTE STREAMS
FROM CHEMICAL MILLING AND ETCHING
(mg/1)
Copper 0.206 - 272.5
Chromium, Total 0.088 - 525.9
Chromium, Hexavalent 0.005 - 334.5
Zinc 0.112 - 200.0
Cyanide, Total 0.005 - 126.0
Cyanide, Amenable to Chlorination 0.005 - 101.3
Fluoride 0.022 - 141.7
Iron 0.075 - 263.0
Tin 0.068 - 103.4
Phosphorus 0.060 - 144.0
Total Suspended Solids 0.100 - 4340
99
-------
TABLE 5-8
COMPOSITION OF RAW WASTE STREAMS
FROM ELECTROLESS PLATING
(mg/1)
Copper
Nickel
Cyanide, Total
Cyanide, Amenable to Chlorination
Fluoride
Phosphorus
Total Suspended Solids
0.002-47.90
0.028-46.80
0.005-12.00
0.005-1.00
0.110-18.00
0.030-109.0
0.100-39.00
TABLE 5-9
CHELATING AGENTS
IN
ELECTROLESS PLATING
No. of Plants
Chelating No. of Plants Where Found
Agents Reporting Use
EDTA
NTA
Citric Acid
Glutaric
Acid
Lactic Acid
Tartrates
1
3
4
4
1
3
by-Analysis (range)
0
3
4
3
0
2
—
.1-89.9
.1-1213
.1-17.3
.1-7.66
(mea;
—
9.5
7.5
10.3
0.1
100
-------
TABLE 5-10
CHARACTERISTICS OF RAW WASTE STREAMS
IN THE PRINTED BOARD INDUSTRY
Constituent
Total Suspended Solids
Cyanide, Total
Cyanide, Amenable to Chlorination
Copper
Nickel
Lead
Chromium, Hexavalent
Chromium, Total
Fluorides
Phosphorus
Silver
Palladium
Gold
Range (mq/1)
0.998 -
0.002 -
0.005 -
1.582 -
0.027 -
0.044 -
0.004 -
0.005 -
0.648 -
0.075 -
0.036 -
0.008 -
0.007 -
408.7
5.333
4.645
535.7
8.440
9.701
3.543
38.52
680.0
33.80
0.202
0.097
0.190
CHELATING AGENTS
Chelating
Agent
EDTA
Citrate
Tartrate
Thiourea
NTA
Gluconic
Acid
No. of Plants
Reporting Use
of Particular
Chelating Agent
6
5
5
3
2
No. of Plants
Where Agent Was
Found by Analysis
2
4
4
0
2
Range
(mq/1)
15.8 - 35.8
0.9 - 1342
1.3 - 1108
47.6 - 810
101
-------
-------
SECTION VI
SELECTION OF POLLUTANT PARAMETERS
INTRODUCTION
The Electroplating Point Source Category wastewater constituents that
are significant pollutants are listed in Table 6-1. These parameters
are listed along with the range of raw waste concentrations in the
data base for each subcategory. These paramaters were selected from a
broad list of wastewater parameters using the following criteria for
selection:
1.
2.
3.
The characteristics of the pollutant require control in
effluent discharges.
The pollutant is commonly present in significant amounts in
the processing solutions used in the electroplating industry.
The pollutant can be controlled by practical technology
is currently available for wastewater treatment.
that
Wastewater from this industry comes from pretreatment and post
treatment operations as well as the actual metal finishing and
electroplating steps. The known significant pollutants and pollutant
properties from these operations include pH, total suspended solids,
cyanide, chromium, copper, nickel, zinc, cadmium, lead, aluminum, and
various precious metals and organic compounds. Many of these
pollutants may occur together with their individual concentrations
exceeding 100 mg/1.
Many of the pollutants which are generated are toxic pollutants which
have potential for environmental or POTW damage. Since none of the
metals are destroyed when introduced into a POTW, they either pass
through to the POTW effluent or concentrate in the POTW sludge.
Cyanide also can pass through a POTW, and both cyanide and the metals
can interfere with the POTW treatment processes.
All of the metals and cyanide are known to inhibit the operations of a
POTW at sufficiently high concentrations. Threshold process influent
concentrations for inhibition of activated sludge processes as given
in the Federal Guidelines for State and Local Pretreatment Programs
(EPA-430/9-76-017) are as follows:
Pollutant Cone, (mg/1)
Pollutant Cone, (mq/1)
Cd
CN,T
Cr,VI
10-100
0.1-5
1-10
Ag
Pb
Ni
5
0.1
1-2.5
103
-------
o
TABLE 6-1
POLLUTANT PARAMETER OCCUREHCE
SUBPART
Pollutant
Parameter
Copper
Nickel
Chromium, T
Chromium, VI
Zinc
Cyanide, T
Cyanide, A
Fluoride
Cadmium
Lead
Iron
Tin
Phosphorus
TSS
Silver
Gold
Palladium
Platinum
Rhodium*
Common Metals
Plating
0.032-272.5
0.019-2954
0.088-525,9
0.005-334.5
0.112-252.0
0.005-150.0
0.003-130.0
0.022-141.7
0.007-21.60
0.663-25.39
0.252-1482
0.060-103.4
0.020-144.0
.1-9970
Precious
Metals
Plating
0.005-9.970
0.003-8.420
0.020-144.0
.1-9970
0.050-176.4
0.013-24.89
0.027-0,625
0.112-6.457
0.034
. Eleetroless
Plating
0.002-47.90
0.028-46.80
0.005-12.00
0.005-1.00
0.110-18.00
0.060-90.0
0.030-109.0
.1-39.00
Anodizing
0.268-79.20
0.005-5.000
0.005-78.00
0.004-67.56
0.176-33.00
36.1-924.0
Coatings
0.190-79.20
0.005-5.000
0.138-200.0
0.005-126.0
0.004-67.56
0.410-168.0
0.102-6.569
0.060-53.30
19.1-5275
Chemical
Hilling 6
Etching
0.206-272.5
0.088-525.9
0.005-334.5
0.112-200.0
0.005-126.0
0.005-101.3
0.022-141.7
0.075-263.0
0.338-6.569
0.060-144.0
.1-4340
Printed
Circuit
Boards
0.203-535.7
0.027-13.30
0.005-47.8
0.005-4.4
0.005-10.80
0.005-9.38
0.280-680.0
0.010-10.2
0.060-54.0
0.051-53.6
1.0-611.0
0.001-0.478
0.006-0.107
0.005-0.234
*0nly 1 plant had a measurable level of this pollutant.
-------
Cr,III 50 Zn 0.08-10
Cu 1
For anaerobic digestion and nitrification processes, the threshold
inhibition concentrations differ. In the case of nitrification
processes especially, the threshold numbers are usually lower.
Since the metals are not destroyed, that fraction which does not pass
through the POTW is incorporated into sludge. Depending on sludge
disposal methods, these metals could contaminate and air, the water,
or in some cases enter the human food chain. In addition, sewage
sludge is a valuable soil conditioner with about 30 percent currently
being applied to land (about half of this amount to agricultural
cropland, the remainder to golf courses, nurseries, home lawns and
gardens, etc.). Land application is, in general, the least expensive
and most environmentally beneficial use of sludges. Metal
contamination of sludge can have various effects which limit the
amount of sludge which can be applied to cropland. These effects are
described below. Concentrations in sludge were taken from Appendix
VII, page 7, of "Municipal Sludge Management: Environmental Factors"
(EPA 430/9-77-004). Food and Drug Administration (FDA)
recommendations for cadmium and lead are summarized in Appendix IX of
the same reference. Unless noted otherwise, data on soil levels of
these metals and discussion of adverse effects on crops are based on
information contained in "Considerations Relating to Toxic Substances
in the Application of Municipal Sludge to Cropland and Pastureland"
(EPA 560/8-76-004) and "Application of Sewage Sludge to Cropland:
Appraisal of Potential Hazards of the Heavy Metals to Plants and
Animals" (EPA 430/9-76-013).
None of the pollutants are completely removed from wastewater by
average POTWs; part of the pollutant load passes through to the POTW
effluent and subsequently contaminates the receiving water. Pass
through data and some of the effects on receiving water are summarized
below. Data on pass through were calculated (as 100 percent minus
percent removal) from the removability data given on page 6-45 of
"Federal Guidelines: State and Local Pretreatment Programs" (EPA
430/9-76-017b). POTW effluent data were taken from pages 6-39 to 6-41
of the same reference.
EXAMPLES OF EFFECTS OF PRETREATMENT ON SLUDGE QUALITY.
Pretreatment programs have been effective in reducing metals
concentrations in sludge. Three examples are cited below.
Buffalo, New York;
Sludge concentration (mg/kg-dry basis)
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Pollutant Before Pretreatment After Pretreatment
(actual) (projected)
Cd 100 50
Cr 2540 1040
Cu 1570 330
Pb 1800 605
Ni 315 115
Zn 2275 364
Grand Rapids Michigan;
Sludge concentration (mg/kg-dry basis)
Pollutant Before Pretreatment After Pretreatment
(actual) (actual)
Cr 11000 2700
Cu 3000 2500
Ni 3000 1700
Zn 7000 5700
Muncie, Indiana;
Sludge concentration (mg/kg-dry basis)
Pollutant Before Pretreatment After Pretreatment
(actual) (actual)
(1972) (1978)
Cd 23 9.5
Cr 2000 675
Ni 8500 150
Zn 5800 2700
Pb 8500 1000
Cu 1750 700
POLLUTANT PARAMETERS
Copper (Cu)
Copper is an elemental metal that is sometimes found free in nature
and is found in many minerals such as cuprite, malachite, asurite,
chalcopyrite, and bornite. Copper is obtained from these ores by
smelting, leaching, and electrolysis. Significant industrial uses are
in the plating, electrical, plumbing, and heating equipment
industries. Copper is also commonly used with other minerals as an
insecticide and fungicide.
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In data from 156 POTWs, the median pass through was over 80 percent
for primary plants and about 40-50 percent for trickling filter and
activated sludge treatment plants. POTW effluent concentrations
(based on data from 192 plants) ranged from 0.003 to 1.8 mg/1 (mean =
0.126, standard deviation = 0.242).
The copper which passes through the POTW to the effluent is discharged
to ambient surface water. Copper is toxic to aquatic organisms at
levels typically observed in POTW effluents, for example:
o 48-hour LC50 for Daphnia Magna in soft water is 0.02 mg/1 (J.
Fish Res. Board Can., 29: 1972).
o 96-hour LC50 for the Chinook salmon is 0.017 mg/1 (Chapman,
G.A., 1975. Toxicity of Copper, Cadmium, and Zinc to Pacific
Northwest Salmonids. US EPA, Corvallis, OR).
o 96-hour TL50 for the fathead minnow is 0.023 mg/1 (Water
Pollut. Int. J. 10:453, 1966).
A study of 205 sewage sludges showed copper levels of 84 to 10,400
mg/kg, with 1210 mg/kg as the mean value and 850 as the median value.
These concentrations are significantly greater than those normally
found in soil, which usually range from 18-80 mg/kg. Copper toxicity
may develop in plants from application of sewage sludge contaminated
with copper. Livestock have been poisoned by eating plants
contaminated with copper.
Because of its toxicity, its tendency to pass through a POTW and its
wide use in the electroplating industry, copper has been eelected as a
pollutant parameter.
Nickel (Ni)
The uses of nickel are many and varied. It is machined and formed for
various products as both nickel and as an alloy with other metals.
Nickel is also used extensively as a plating metal primarily for a
protective coating for steel.
Data from 109 POTWs show that nickel pass through was greater than 90
percent for 82 percent of the primary treatment plants. Median pass
through for trickling filter and activated sludge plants was greater
than 80 percent. Data from 149 POTWs show POTW effluent
concentrations ranging from 0.003 to 40 mg/1 (mean = 0.411, standard
deviation = 3.279).
The nickel which passes through the POTW is discharged to ambient
surface water. Nickel is toxic to aquatic organisms at levels
typically observed in POTW effluents, for example:
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o 50 percent reproductive impairment of Daphnia magna at 0.095
mg/1 (J. Fish Res. Board Can., 29:1691, 1972).
o morphological abnormalities in developing eggs of Limnaea
palustris at 0.230 mg/1 (Bio. Bulletin 125:508, 1963).
o 50 percent growth inhibition of aquatic bacteria at 0.020
mg/1 (Curr. Sci. 45: 578-580, 1976).
Since surface water is often used as a drinking water source, nickel
passed through a POTW becomes a possible drinking water contaminant.
A study of 165 sludges showed nickel concentrations ranging from 2 to
3520 mg/kg (dry basis), with a mean of 320 mg/kg and a median of 82
mg/kg. Nickel toxicity may develop in plants from application of
sewage sludge on acid soils. Nickel reduces yields for a variety of
crops including oats, mustard, turnips, and cabbage.
Nickel is one of the most commonly used metals in the electroplating
industry. Due to its wide use and the deleterious effects outlined
above, nickel has been selected as a pollutant parameter.
Chromium (Cr)
Chromium is an elemental metal usually found naturally as a chromite
(FeCr204). The metal is normally processed by reducing the oxide with
aluminum.
Chromium and its compounds are used extensively throughout industry.
It is used to harden steel and as an ingredient in other useful
alloys. Chromium is also widely used in the electroplating industry
as an ornamental and corrosion resistant plating on steel, as a
conversion coating on a variety of metals, and can be used in pigments
and as a pickling acid (chromic acid).
The two most prevalent forms of chromium found in industry waste
waters are hexavalent and trivalent. Chromic acid used in industry is
a hexavalent chromium compound which is partially reduced to the
trivalent form during use. Chromium can exist as either trivalent or
hexavalent compounds in raw waste streams. Hexavalent chromium
treatment involves reduction to the trivalent form prior to removal of
chromium from the waste stream as a hydroxide precipitate.
The amount of chromium which passes through to the POTW effluent
depends on the type of treatment processes used by the POTW. Data
from 138 POTWs show that 56 percent of the primary plants allowed more
than 80 percent pass through to POTW effluent. More advanced
treatment reduces pass through, with median pass through values for
trickling filter and activated sludge treatments being about 60
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percent. Data from 179 POTWs show POTW effluent concentrations
ranging from 0.003 to 3.2 mg/1 total chromium (mean = 0.197, standard
deviation = 0.48), and from 0.002 to 0.1 mg/1 hexavalent chromium
(mean = 0.017, standard deviation = 0.020).
The chromium which passes through the POTW is discharged to ambient
surface water. Chromium is toxic to aquatic organisms at levels
observed in POTW effluents.
o trivalent chromium significantly impaired the reproduction of
Daphnia magna at levels of 0.3 to 0.5 mg/1 (J. Fish Res.
Board Can., 29: 1691, 1972).
o hexavalent chromium retards growth of Chinook salmon at
0.0002 mg/1 (Hanford Bio. Am. Rep., 1957)
Hexavalent chromium
sensitizer.
is also corrosive, and a potent human skin
Besides providing an environment for aquatic organisms, surface water
is often used as a source of drinking water. Because hexavalent
chromium can be reduced to trivalent chromium in the environment, and
trivalent chromium can possibly be oxidized to hexavalent chromium by
chlorine or other agents, the National Interim Primary Drinking Water
Standards are based on total chromium, the limit being 0.05 mg/1.
A study of 180 sewage sludges showed that sewage sludge contains 10 to
99,000 mg/kg (dry basis) of chromium (mean = 2620 mg/kg; median » 890
mg/kg). Most crops absorb relatively little chromium even when it is
present in high levels in soils, but chromium in sludge has been shown
to reduce crop yields in concentrations as low as 200 mg/kg.
Although chromium does not pass through the POTW to the same extent as
other metals, its relative abundance in electroplating wastewaters and
its toxicity to aquatic organisms justify its selection as a pollutant
parameter.
Zinc (Zn)
Occurring in rocks and ores, zinc is readily refined into a stable
pure metal and is used extensively as a metal, an alloy, and a plating
material. In addition, zinc salts are also used in paint pigments,
dyes, and insecticides. Many of these salts (for example, zinc
chloride and zinc sulfate) are highly soluble in water; hence, it is
expected that zinc might occur in many industrial wastes. On the
other hand, some zinc salts (e.g.zinc carbonate, zinc oxide, zinc
sulfide) are insoluble in water and, consequently, it is expected that
some zinc will precipitate and be removed readily in many natural
waters.
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Data from 148 POTWs show the median pass through values to be 70-80
percent for primary plants, 50-60 percent for trickling filter plants,
and 30-40 percent for activated sludge process plants. POTW effluent
concentrations of zinc (based on data from 198 POTWs) ranged from
0.009 to 3.6 mg/1 (mean = 0.330, standard deviation = 0.464).
The zinc which passes through the POTW to the effluent is discharged
to ambient surface water. Zinc is toxic to aquatic organisms in
concentrations typically observed in POTW effluents, for example:
96-hour LC50 for the cutthroat trout
Fishing Abstract 13665, 1971).
is 0.090 mg/1 (Sport
96-hour LC50 for the chinook salmon is 0.103 mg/1 (Chapman,
G.A., 1975. Toxicity of Copper, Cadmium and Zinc to Pacific
Northwest Salmonids. USEPA, Corvallis, Or).
48-hour LC50 for Daphnia magna is 0.100 mg/1
Board Can. 29:1691, 1972).
(J. Fish Res.
Jata from 208 sludges show a zinc range of 101 to 27,800 mg/kg (dry
basis), with a mean of 2790 mg/kg and a median of 1740 mg/kg.
These concentrations are significantly greater than those normally
found in soil, with observed values of 10 to 300 mg/kg, with 50 mg/kg
being the mean. Therefore, application of sewage sludge to soil will
generally increase the concentration of zinc in the soil. Zinc can be
toxic to plants, depending upon soil pH. Lettuce, tomatoes, turnips,
mustard, kale, and beets are especially sensitive to zinc
contamination.
Zinc has been selected as a pollutant parameter as a result of its
toxicity levels and its ability to pass through the POTW.
Cyanide
Cyanide is a compound that is widely used in industry primarily as
sodium cyanide (NaCN), potassium cyanide (KCN) or hydrocyanic acid
(HCN).. The major use of cyanides is in the electroplating industry
where cyanide baths are used to hold ions such as zinc and cadmium in
solution and to accelerate the plating process. Cyanides in various
compounds are also used in steel plants, chemical plants, photographic
processing, textile dying, and ore processing.
Of all the cyanides, hydrogen cyanide (HCN) is probably the most
acutely lethal compound. HCN dissociates in water to hydrogen ions
and cyanide ions in a pH dependent reaction. The cyanide ion is less
acutely lethal than HCN. The relationship of pH to HCN shows that as
the pH is lowered to below 7 there is less than 1 percent of the
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cyanide molecules in the form of the CN ion and the rest is present as
HCN. When the pH is increased to 8, 9, and 10, the percentage of
cyanide present as CN ion is 6.7, 42, and 87 percent, respectively.
The toxicity of cyanides is also increased by increases in temperature
and reductions in oxygen tensions. A temperature rise of 10°C
produces a two- to threefold increase in the rate of the lethal action
of cyanide.
Cyanide may theoretically be destroyed in a POTW, but data indicate
that much of it passes through to the POTW effluent. One primary
plant showed 100 percent c.anide pass through, and the mean pass
through for 14 biological plants was 71 percent. Data from 41 POTWs
indicate the effluent concentrations range from 0.002 to 100 mg/1
(mean = 2.518, standard deviation = 15.6). (If the plant with an
effluent of 100 mg/1 is removed from the data base as an outlier, the
mean becomes 0.081 mg/1 for 40 POTWs).
The cyanide which passes through to the POTW effluent is discharged
into ambient surface water. There is considerable evidence
documenting cyanide toxicity to aquatic organisms at levels at or
below those typically observed in POTW effluents.
Cyanides are more toxic to fish than to lower aquatic organisms such
as midge larve, crustaceans, and mussels. Toxicity to fish is a
function of chemical form and concentration, and is influenced by the
rate of metabolism (temperature), the level of dissolved oxygen, and
pH. In laboratory studies free cyanide concentrations ranging from
0.05 to 0.15 mg/1 have been proven fatal to sensitive fish species
including trout, bluegills, and fathead minnows (EPA 600/3-76-038).
Long term sublethal concentrations of cyanide as low as 0.01 mg/1 have
been shown to affect the ability of fish to function normally, e.g.
reproduce, grow, and move freely (G. Leduc, 1966, Ph.D Thesis, Oregon
State Univ., Corvallis).
Cyanide forms complexes with metal ions present in wastewater. All
these complexes exist in equilibrium with HCN. Therefore, the
concentration of free cyanide present is dependent on-the pH of the
water and the relative strength of the metal-cyanide complex. The
cyanide complexes of zinc, cadmium and copper may dissociate to
release free cyanide. Also, where these complexes occur together,
synergistic effects have been demonstrated. Zinc, copper, and cadmium
cyanide are more toxic than an equal concentration of sodium cyanide.
Another problem associated with cyanide pass through is possible
chlorination of cyanide to highly toxic cyanogen chloride, which is
subsequently released to the environment. This chlorination reaction
may occur as part of the POTW treatment, or subsequently as part of
the disinfection treatment for surface drinking water preparation.
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Data for Grand Rapids, Michigan, show a significant decline in cyanide
concentrations downstream from the POTW after pretreatment regulations
were enacted. Concentrations fell from 0.06 mg/1 before to 0.01 mg/1
after pretreatment was required.
As shown above, cyanide has a tendency to pass through the POTW. It
has been selected as a pollutant parameter because of its extensive
use and its high toxicity in a number of different forms.
Cadmium (Cd)
Cadmium is used primarily as a metal plating material and can be found
as an impurity in the secondary refining of zinc, lead, and copper.
Cadmium is also used in the manufacture of primary cells of batteries
and as a neutron adsorber in nuclear reactors. Other uses of cadmium
are in the production of pigments, phosphors, semi-conductors,
electrical contactors, and special purpose low temperature alloys.
Cadmium is an extremely dangerous cumulative toxicant, causing
insidious progressive chronic poisoning in mammals, fish and probably
other animals because the metal is not excreted. Cadmium could form
organic compounds which might lead to mutagenic or teratogenic
effects. Cadmium is known to have marked acute and chronic effects on
aquatic organisms also.
Data from 110 POTWs show that 75 percent of the primary plants, 57
percent of the trickling filter plants and 66 percent of the activated
sludge plants allowed over 90 percent of the influent cadmium to pass
through to the POTW effluent. Only 2 of the 110 POTWs allowed less
than 20 percent pass through, and none allowed less than 10 percent
pass through. Data from 145 POTWs show POTW effluent concentrations
ranged from 0.001 to 1.97 mg/1 (mean 0.028 mg/1, standard deviation
0.167).
The cadmium which passes through the POTW to the effluent is
discharged to ambient surface water. Cadmium is toxic to aquatic
organisms at levels typically observed in POTW effluents. For
example, the Cadmium Ambient Water Quality Criteria Document
(PB-292-423) cites:
o 96 hr LC50 for Chinook salmon is reported as 0.0018 mg/1,
o 96 hr LC50 for rainbow trout is reported as 0.0013 mg/1, and
o 48 hr. LC50 for the invertebrate cladoceran is reported as
0.007 mg/1.
Besides providing an,environment for aquatic organisms, surface water
is often used as a source of drinking water or irrigation water. For
states with drinking water or irrigation water standards, the most
common cadmium standard is 0.01 mg/1. Chronic ingestion of cadmium
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via drinking water and from use of contaminated irrigation water has
been documented as the cause of itai-itai disease in humans.
Cadmium has no known biological benefits for humans and is capable of
causing kidney damage when present in significant amounts; there is
suggestive evidence that cadmium may be a carcinogen. For these
reasons, it is prudent to restrict environmental sources of cadmium as
much as possible.
A study of 189 sewage sludges showed that sewage sludge contains 3 to
3410 mg/kg (dry basis) of cadmium (mean = 110 mg/kg; median = 16
mg/kg). These concentrations, are significantly greater than those
normally found in soil (0.01 to 7 mg/kg, with 0.06 mg/kg being the
mean). Data show that cadmium can be incorporated into crops,
including vegetables and grains, from contaminated soils. Although
the crops themselves show no adverse effects from soils with levels up
to 100 mg/kg cadmium, these contaminated crops could have a
significant impact on human health.
Three federal agencies have already recognized the potential adverse
human health effects posed by the use of sludge on cropland. The FDA
recommends that sludges containing cadmium concentrations over 20
mg/kg should not be used on agricultural land. The Department of
Agriculture (USDA) also recommends limitations on the total cadmium
from sludge that may be applied to land. Under Section 4004 of
Resource Conservation and Recovery Act (RCRA), the EPA will shortly
promulgate limits on the amount of sludge that can be landspread,
based on annual and cumulative cadmium application rates. Under
Section 405 of the Clean Water Act, additional restrictions will be
placed on sludge for home use, based on cadmium content. All these
federal restrictions are designed to prevent excessive cadmium
additions to the human diet.
Cadmium has been selected as a pollutant parameter due to its
extremely high toxicity to humans and aquatic organisms.
Lead (Pb>
Lead is used in various solid forms both as a pure metal and in
several compounds. Lead appears in some natural waters, especially in
those areas where mountain limestone and galena are found. Lead can
also be introduced into water from lead pipes by the action of the
water on the lead.
Lead is a toxic material that is foreign to humans and animals. The
most common form of lead poisoning is called plumbism. Lead can be
introduced into the body from an atmosphere containing lead or from
food and water. Lead cannot be easily excreted and is cumulative in
the body over long periods of time, eventually causing lead poisoning
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with the ingestion of an excess of 0.6 mg per day over a period of
years.
Data from 124 POTWs show median pass through values to be over 80
percent for primary plants. About half of the trickling filter and
activated sludge plants allow over 60 percent pass through. Lead
concentrations in POTW effluents (based on data from 157 POTWs) ranged
from 0.003 to 1.8 mg/1 (mean = 0.106, standard deviation <= 0.222).
The lead which passes through the POTW to the effluent is discharged
to ambient surface water. Lead is toxic to aquatic organisms at
levels typically observed in POTW effluents, for example:
o 48-hour LC50 for Daphnia magna is 0.45 mg/1 (J. Fish Res.
Board Can., 29:1691).
o 48-hour LC50 for rainbow trout is 0.9 mg/1 (Water Res.
2:723, 1968).
Besides providing an environment for aquatic organisms, surface water
is often used as a source of drinking water. The National Interim
Primary Drinking Water Regulation limit lead in drinking water to 0.05
mg/1.
The major risk of lead in drinking water is to small children, where
the water is one of several sources which result in a well documented,
serious problem of excess lead levels in the body. As a result of the
narrow range between the lead exposure of the average American in
everyday life and exposure which is considered excessive, (especially
in children) it is imperative that lead in water be maintained within
strict limits. Potential sources of exposure are diet, water, dust,
air, etc. Levels of lead in many urban children indicate
overexposure. High body levels of lead can result in serious
consequences (chronic brain or kidney damage, or acute brain damage);
therefore, lead in water should be limited to the lowest practicable
level.
A study of 189 sludges showed lead levels ranging from 13 to 19,700
mg/kg (dry basis) (mean = 1360 mg/kg; median = 500 mg/kg). Since the
normal range of lead content in soil is from 2 to 200 mg/kg,
application of contaminated sewage sludge to the soil will generally
increase the soil's lead content.
Data indicate that the application to cropland of sludge containing
excessive lead levels may increase the lead concentration in crops
grown on acid soils. Generally, roots accumulate more lead than do
plant tops. For above ground crops, significant impacts can occur
when sludge is applied as a surface dressing while crops are growing.
In light of the potential human health effects, the FDA has
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recommended that sludge containing more than 1000 mg/kg of lead should
not be used on agricultural land for crops used directly in the food
chain.
Lead has been found in electroplating wastes in amounts great enough
(as high as 25 mg/1) to warrant concern in light of its very high
degree of human toxicity. For this reason, lead has been chosen as a
pollutant parameter.
Silver (Ag_)
Silver is a soft lustrous white metal that is insoluble in water and
alkali. It is readily ionized by electrolysis and has a particular
affinity for sulfur and halogen elements. In nature, silver is found
in the elemental state and combined in ores such as argentite (Ag2S),
horn silver (AgCl), proustite (Ag,AsS3), and pyrargyrite (Ag3SbS,).
Silver is used extensively in electroplating, photographic processing,
electrical equipment manufacture, soldering and brazing and battery
manufacture. Of these, the two major sources of soluble silver wastes
are the photographic and electroplating industries with about 30
percent of U. S. industrial consumption of silver going into the
photographic industry. Silver is also used in its basic metal state
for such items as jewelry and electrical contacts.
Data from a recent EPA study of several POTWs show that silver
treatability is quite variable, but that a significant portion of the
influent silver (25 percent to 75 percent) is likely to pass through
to the POTW effluent.
The Silver Ambient Water Quality Criteria Document (PB-292-441)
provides the following information: The toxicity of silver to aquatic
organisms has long been recognized. Dosages of 0.000001 to 0.5 mg/1
of silver have been reported as sufficient to sterilize water.
Various toxic effects on aquatic life have been reported. For
example:
o 96-hr LC50 for rainbow trout has been reported as 6.5 ug/1 to 28.8
ug/1.
o 96 hr LC50 for the water flea (Daphnia Maqna) has been reported as
1.5 ug/1.
o Bioconcentration of silver up to 368 times has been reported.
Silver has been selected as a pollutant parameter because of the acute
sensitivity of aquatic systems to its presence.
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POLLUTANT PARAMETERS NOT SELECTED
The following pollutants were not selected for regulation:
Fluoride
Fluoride was not chosen for regulation as it would require platers to
install additional technology.
Iron
Iron is another pollutant which is removed from wastewater by the
POTW. The effects of iron pollution are generally more aesthetically
displeasing than they are toxic. Iron is sometimes added to
wastewater as a treatment chemical.
Tin
Tin is not generally present in electroplating wastewaters at high
concentration levels. In addition, tin has not been found to be
harmful to man when present in domestic water supplies. Tin is
ingested by humans on an almost daily basis (from canned foods) and
appears to have no detrimental health effects.
Phosphorus
Phosphorus (in the form of phosphates) generated by electroplating
operations does not comprise a large portion of the total phosphorus
received by the POTW. Phosphates are not particularly harmful to
humans although they do create nuisance conditions in aquatic systems.
Gold, Palladium, Platinum, Rhodium
These metals are not found in electroplating effluents at high
concentrations. Most platers make extensive efforts to recover them
prior to discharge because of economic considerations.
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SECTION VII
CONTROL AND TREATMENT TECHNOLOGY
INTRODUCTION
This section describes the treatment techniques currently used or
available to remove or recover wastewater pollutants normally
generated by plating, metal finishing and printed board manufacturing
processes. Following a discussion of in-plant technologies and then
invidividual treatment technologies for the overall electroplating
industry, this section presents system level descriptions of
conventional end-of-pipe treatment and advanced treatment. Advanced
treatment systems have greater pollutant reduction than conventional
treatment and/or stress conservation of raw materials by recycle and
reuse. The individual treatment technologies presented are applicable
to the entire electroplating industry for both direct and indirect
dischargers and reflect the entire electroplating data base. End-of-
Pipe and advanced systems are presented first for plating .and metal
finishing (combined) and then for printed board manufacture.
To minimize the total mass of pollutants discharged in electroplating,
a reduction in either concentration or flow or both is required.
Several techniques are being employed to effect a significant
reduction in total pollution. These techniques can be readily adapted
to other existing facilities and include:
1. Avoidance of unnecessary dilution. Diluting waste streams
with unpolluted water makes treatment more expensive (since
most equipment costs are directly related to volume of waste-
water flow) and more difficult (since concentrations may be
too low to treat effectively). Precipitated material may
also be redissolved by unpolluted water.
2. Reduction of flow to contaminating processes. Use of
countercurrent, spray, and fog rinses greatly reduces the
volume of water requiring treatment. After proper treatment,
the amount of a pollutant (based on maximum removal
efficiencies and the solubility of the pollutant) that
remains in the solution is a function of the volume of water.
Hence, less water, less pollutant discharged.
3. Treatment under proper conditions. The use of the proper pH
can greatly enhance pollutant precipitation. Since metallic
ions precipitate best at various pH levels, waste segregation
and proper treatment at the optimum pH will produce improved
results. The prior removal of compounds which increase the
solubility of waste materials will allow significanly more
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efficient treatment of the remaining material. An example is
the segregation of chelated wastes from wastewater containing
non-chelated metals. This will improve water discharge
quality since chelates form a highly soluble complex with
most metals.
4. Timely and proper disposal of wastes. Removal of sludges
from the treatment system as soon as possible in the
treatment process minimizes returning pollutants to the waste
stream through re-solubilization. One plant visited during
this program (ID#23061) utilized a settling tank in their
treatment system that required periodic cleaning. Such
cleaning had not been done for some time, and our analysis of
both their raw and treated wastes showed little difference.
Subsequent pumping out of this settling tank resulted in an
improved effluent (reference Table 7-1).
Once removed from the primary effluent stream, waste sludges
must be disposed of properly. If landfills are used for
sludge disposal, the landfill must be designed to prevent
material from leaching back into the water supply. Mixing of
waste sludges which might form soluble compounds should be
prevented. If sludge is disposed of by incinerating, the
burning must be carefully controlled to prevent air
pollution. A licensed scavenger may be substituted for plant
personnel to oversee disposal of the removed sludge.
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TABLE 7-1
COMPARISON OF WASTEWATER AT PLANT ID 23061
BEFORE AND AFTER PUMPING OF SETTLING TANK
Parameter
Concentration (mg/1)
Before Sludge Removal
Concentration (mg/1)
After Sludge Removal
Cyanide
Cyanide, Total
Phosphorus
Silver
Gold
Cadmium
Chromium,
Chromium
Copper
Iron
Fluoride
Nickel
Lead
Tin
Zinc
TSS
Solids
Total Raw
Waste
0.007
0.025
2.413
0.001
0.007
0.001
0.005
0.023
0.028
0.885
0.16
0.971
0.023
0.025
0.057
17.0
17.0
Treated
Effluent
0.001
0.035
2.675
0.001
0.010
0.006
0.105
0.394
0.500
3.667
0.62
1.445
0.034
0.040
0.185
36.00
36.00
Total Raw
Waste
0.005
0.005
14.32
0.002
0.005
0.005
0.005
0.010
0.127
2.883
0.94
0.378
0.007
0.121
0.040
67.00
67.00
Treated
Effluent
0.005
0.005
13.89
0.003
0.005
0.002
0.005
0.006
0.034
1.718
0.520
0.312
0.014
0.134
0.034
4.00
4.00
TABLE 7-2
USAGE OF VARIOUS RINSE TECHNIQUES BY COMPANIES
Type of Rinse
Techniques
Single running
Countercurrent
Series
Spray
Dead, Still, Reclaim
Number of Companies
Using Indicated
Rinse Techniques
157
98
69
89
115
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IN-PLANT TECHNOLOGY
The intent of in-plant technology for the overall electroplating point
source category is to reduce or eliminate the waste load requiring
end-of-pipe treatment and thereby improve the efficiency of waste
treatment. In-plant technology involves the selection of rinse tech-
niques (with the emphasis on closed loop rinsing), plating bath
conservation, good housekeeping practices, recovery and/or reuse of
plating and etch solutions, process modification and integrated waste
treatment. The sections which follow detail each of these in-plant
technologies describing the applicability and overall effect of each
in the electroplating industry.
Rinse Techniques
Reductions in the amount of water used in electroplating can be
realized through installation and use of efficient rinse techniques.
Cost savings associated with this water use reduction manifest
themselves in reduced operating costs in terms of lower cost for rinse
water and reduced chemical costs for wastewater treatment. An added
benefit is that the waste treatment efficiency is also improved. It
is estimated that rinse steps consume over 90 percent of the water
used by a typical plating facility. Consequently, the greatest water
use reductions can be anticipated to come from modifications of rinse
techniques.
Rinsing is essentially a dilution step which reduces the concentration
of contaminants on the work piece. The design of rinse systems for
minimum water use depends on the maximum level of contamination
allowed to remain on the work piece (without reducing acceptable
product quality or causing poisoning of a bath) as well as on the
efficiency or effectiveness of each rinse stream.
The following values have been reported as the maximum acceptable con-
centration in terms of total dissolved solids to prevent work quality
problems (staining, spotting, or peeling) for some plating and
cleaning operations. The concentrations shown are for the final rinse
on a finished product of medium quality. Higher concentrations can be
allowed following intermediate plating operations.
Maximum Total
Operation Dissolved Solids (mg/1)
Rinse after nickel or copper 37
Rinse after cyanide 37
Rinse after chromium 15
Rinse after acid dip or alkaline cleaner 750
Rinse after acid dip prior to chromium plate 15
Rinse after passivating 350-750
120
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Rinsing is particularly critical in electroless plating because of the
high degree of cleanliness required for electroless plating operations
as compared to electroplating. It is necessary to carefully and com-
pletely rinse parts to remove contaminants (particularly following
activation and sensitization steps in electroless plating of plastic)
before entering the plating bath. These contaminants may cause the
plating bath to seed out or to react excessively.
The sections which follow deal with rinsing efficiency, the primary
rinsing methods, various rinse systems, and the application and
control of rinse systems. Table 7-2 summarizes the usage of the
various rinse techniques by the 196 companies in this data base.
Rinsing Efficiency - A rinse system should be considered efficient if
the dissolved solids concentration is reduced just to the point where
no noticeable effects occur either as a quality problem or as
excessive dragin to the next process step. Operation of a rinse tank
or tanks which achieved a 10,000 to 1 reduction in concentration where
only a 1,000 to 1 reduction is required represents inefficient use of
water. Operating rinse tanks at or near their maximum acceptable
level of contamination provides the most efficient and economical form
of rinsing. Inefficient operation manifests itself in higher
operating costs not only from the purchase cost of water, but also
from the treatment of it.
Primary Modes gjf Rinsing - There are five primary modes of rinsing
presented below along with the advantages and applicability of each of
those modes.
1. Single Running Rinse - This arrangement (reference Figure 7-
1) requires a large volume of water to effect a large degree
of contaminant removal. Although in widespread use, single
running rinse tanks should be modified or replaced by a more
effective rinsing arrangement to reduce water use.
2. Countercurrent Rinse - The countercurrent rinse (reference
Figures 7-2 and 7-3) provides for the most efficient water
usage and thus, where possible, the countercurrent rinse
should be used. There is only one fresh water feed for the
entire set of tanks, and it is introduced in the last tank of
the arrangement. The overflow from each tank becomes the
feed for the tank preceding it. Thus, the concentration of
dissolved salts decreases rapidly from the first to the last
tank.
3. Series Rinse - The major advantage of the series rinse
(reference Figure 7-4) over the countercurrent system is that
the tanks of the series can be individually heated or level
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PARTS
r-o
r\3
r
TO WASTEWATER,
TREATMENT
1 «
I I
.RINSE WATER FEED
FIGURE 7-1. SINGLE RINSE TANK
-------
PARTS
• AIR
RINSL WATLR
FLED
TO WASTEWATER
TREATMENT
AIR AGITATION
FIGURE 7-2 3 STAGE COUNTER CURRENT RINSE
123
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PARTS
AIR
RINSE WATER
TO WASTEWATLR
TREATMENT
OVERFLOW PIPUS
FIGURE 7-3 3 STAGE COUNTERCURRENT RINSE WITH
OUTBOARD ARRANGEMENT
124
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PARTS
ro
en
r"ni~i r~.ni
_j
£511
_. I
RINSE WATER
FEED
TO WASTE
TREATMEN
FIGURE 7-4. SERIES RINSE TANKS
-------
controlled since each has a separate feed. Each tank reaches
its own equilibrium condition; the first rinse having the
highest concentration, and the last rinse having the lowest
concentration. This system uses water more efficiently than
the single running rinse, and the concentration of dissolved
salts decreases in each successive tank.
4. Spray Rinse - Spray rinsing (Figure 7-5) is considered the
most efficient of the various rinse techniques in continuous
dilution rinsing. The main concern encountered in use of
this mode is the efficiency of the spray (i.e., the volume of
water contacting the part and removing contamination compared
to the volume of water discharged). Spray rinsing is well
suited for flat sheets. The impact of the spray also
provides an effective mechanism for removing dragout from
recesses with a large width to depth ratio.
5. Dead, Still, or Reclaim Rinses - This form of rinsing is
particularly applicable for initial rinsing after metal
plating because the dead rinse allows for easier recovery of
the metal and lower water usage. The rinsing should then be
continued in a countercurrent or spray arrangement.
Combined Systems - By combining several rinsing arrangements, an effi-
cient rinse system for a particular application can be achieved. Five
systems that are most applicable to electroplating include:
1. Recirculating Spray - This arrangement combines the
advantages of the dead and spray rinse. Operating from a
captive reservoir (a dead tank), a pump transfers solution to
the spray. While not resulting in a final dilution (like all
dead rinses), the spray continuously dilutes the dragout on
the part, and because of the impact of the spray, contaminant
removal is improved.
2. Countercurrent Followed by Spray Rinsing - The feed for the
countercurrent tank is from the spray nozzles which are
mounted directly over the last countercurrent tank. This
provides for high pollutant removal and low water usage.
3. Dead Rinse Followed by_ Countercurrent Rinse - This
arrangement removes up to 80% of the contamination from a
part in the dead tank with the remainder being removed in the
countercurrent tank. (The removal rate of the dead tank is a
function of the frequency of the tank dump.) The dead tank
allows for the recovery of dragged out plating solution
(principally the metal constituents and chelating agents) and
for a lower feed rate of supply water for the countercurrent
tank.
126
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PARTS
TO WASTEWATER
TREATMENT
MANUAL OR FOOT
OPERATED VALVE
SPRAY RINSE
FEED
FIGURE 7-5 SPRAY RINSE
127
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4. Drip Station - Drip stations perform the same function as
dead tanks, but there is no water in the tank. Instead, the
parts are allowed to drain freely over the tank or may be hit
by a blast of air (such as from an air knife) or struck by a
mixture of air and water. The intent of this station is to
remove as much dragout as possible.
5. Closed Loop Countercurrent Rinses - Closed loop rinsing uses
the overflow rinse water to make up evaporative losses from
the plating bath, and thus, no rinse water is passed to any
waste treatment. A general schematic of such a system is
shown in Figure 7-6. A liquid level controller in the
plating bath senses the level of the bath and operates a
transfer pump between the rinse tank and the bath when the
liquid level drops below the set level. A liquid level
controller in the rinsing tank operates a solenoid valve on
the rinse tank water feed line opening the valve when the
liquid level drops due to solution pump-out to the plating
bath. Use of the system frequently requires several
countercurrent tanks and a sufficient evaporation rate from
the plating bath. There are numerous advantages to this type
of system. No wastewater treatment of overflow rinse waters
is required, a large percentage of plating solution drag out
is recovered and returned to the plating bath, and the liquid
level of the plating bath is automatically controlled
requiring no filling by the plating operator and, thus,
eliminating the possibility of overfilling the bath. This
rinse technique was observed at company ID 6072.
Factors Affecting the Application of_ Rinse Systems - There is no one
rinsing arrangement which provides maximum efficiency of water use for
all situations. Selection of the proper rinse arrangement depends
upon a number of factors described in the following sections.
1. Geometry of_ the Part - This partly determines the amount of
dragout contributed by a part and is one of the principal
determinants for the type of rinsing arrangement selected. A
flat sheet with holes is well suited for an impact spray
rinse rather than an immersion rinse, but for parts with cups
or recesses such as a jet fuel control, a spray rinse is
ineffective.
2. Kinematic Viscosity o_f the Plating Solution - The kinematic
viscosity is an important factor in determining plating bath
dragout. The effect of increasing kinematic viscosity is
that it increases the dragout volume in the withdrawal phase
and decreases the rate of draining during the drainage phase.
It is advantageous to decrease the dragout and increase the
drainage rate. Consequently, the plating solution kinematic
128
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f\>
to
LIQUID PARTS
LIQUID I "*" LEVEL -*""-
LEVEL I INDICATOR
CONTROLLER
EVAPORATION
I
PLATING BATH
AIR
RINSE WATER
FEED
SOLENOID
PUMP
— AIR AGITATION
FIGURE 7-€ CLOSED LOOP 3 STAGE COUNTER CURRENT RINSE
-------
viscosity should be as low as possible. Increasing the tem-
perature of the solution decreases its viscosity, thereby
reducing the volume of plating solution going to the rinse
tank. Care must be exercised in increasing bath temperature,
particularly with electroless baths, because the rate of bath
decomposition may increase significantly with temperature
increases.
3. Surface Tension of_ the Plating Solution - Surface tension is
a major factor that controls the removal of dragout during
the drainage phase. To remove a liquid film from a solid
surface, the gravitation force must overcome the adhesive
force between the liquid and the surface. The amount of work
required to remove the film is a function of the surface ten-
sion of the liquid and the contact angle. Lowering the
surface tension reduces the amount of work required to remove
the liquid and reduces the edge effect (the bead of liquid
adhering to the edges of the part). A secondary benefit of
lowering the surface tension is to increase the metal
uniformity in through-hole-metalization. Surface tension is
reduced by increasing the temperature of the plating solution
or more effectively, by use of a wetting agent.
4. Time of_ Withdrawal and Drainage - The withdrawal velocity of
a part from a solution has an effect similar to that of kine-
matic viscosity. Increasing the velocity or decreasing the
time of withdrawal increases the volume of solution that is
retained by the part. Since time is directly related to
production rate, it is more advantageous to reduce the drag-
out volume initially adhering to the part rather than attempt
to drain a large volume from the part.
5. Other Factors - There are other factors that enter into the
proper application of a particular rinsing arrangement.
These include:
A. Racking - Proper racking of parts is the most effective
way to reduce dragout. Parts should be arranged so that
no cup-like recesses are formed, the longest dimension
should be horizontal, the major surface vertical, and
each part should drain freely without dripping onto
another part. The racks themselves should be
periodically inspected to insure the integrity of the
rack coating. Loose coatings can contribute
significantly to dragout.
B. Barrel Operation - There are some significant
differences between rack and barrel operations as far as
subsequent rinsing is concerned. Typically, barrel
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plating solutions are more concentrated and have greater
dragout mass than rack operations. Another major
difficulty with barrel operations is the maintenance of
a well mixed solution between the overall rinse water
and the rinse water contained in the barrel. Rotation
of barrels in a rinse tank allows for more volume
changes of solution, thereby promoting better mixing and
rinsing. The depth of barrel immersion is a controlling
factor for the number of volume changes per revolution
of the barrel. It has been determined that greater
volume changes and, therefore, better rinsing occur at
more shallow immersion depths. Hence, the immersion
depth of a barrel will have a significant effect on
rinsing efficiency.
C. Rinse Tank Volume - This has no effect on the
equilibrium concentration in a tank. In steady state
or pseudosteady state conditions, the equilibrium
concentration is a function of dragin and dragout
volumes and the flow rate of fresh feed. Tank volume
does, however, determine how quickly the equilibrium
concentration is reached.
D. Agitation of Rinse Tank - Since rinsing is a dilution
process, greater efficiency results if the dragin is
diluted with all the water in the rinse tank. Thus, it
is advantageous to maintain a well mixed rinse tank.
Methods of providing complete mixing include air,
ultrasonic or mechanical agitation.
E. Manual or Automatic Plating Line - The type of plating
line operation - manual or automatic - may have a
significant impact on the cost of installing more
efficient rinsing systems. While it may be relatively
inexpensive to modify an existing manually operating
line, the cost to alter the arrangement of an automatic
plating line may be greater, unless existing unused or
nonessential tanks in the plating line can be converted
to rinse tanks. However, depending on the ingenuity and
flexibility of each plater, modifications to obtain more
efficient rinsing can be accomplished by: reducing the
withdrawal speed of the work pieces, decreasing the
surface tension of the plating solution, and installing
air-fog nozzles over the plating tank. These
modifications can be done without major capital outlays.
An advantage of automatic lines is that reproducible
results are obtained. This is of particular importance
with respect to the withdrawal speed and drainage time.
If the automatic machine is set up with dragout control
131
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and production rate in mind, the automatic line
typically provides better control over dragout than a
manual operation,
F, Rack Design - Physical or geometrical design of racks is
of primary concern for the control of dragout both from
the rack and the parts themselves. Orientation of parts
on a rack and the resulting dragout consideration have
been discussed previously. Dragout from the rack itself
can be minimized by designing it to drain freely such
that no pockets of plating solution can be retained.
For example, by changing the angle formed by side
members of a rack (reference Figures 7-7 and 7-8) from
90 degrees to something less than 90 degrees, the racks
will not retain excessive plating solution. This is
particularly true for printed board racks; plant ID
11068 changed vendor supplied racks by this type of
modification.
Controls Used on Rinse Tanks - There are several ways to control the
rinse water feed rate. For lines where production rates are
relatively constant, a fixed orifice may be used with good success to
control the fresh feed. This technique is inexpensive and has been
readily adapted to automatic plating machines. Other controls such as
conductivity controllers, liquid level controllers and manually
operated valves are better suited for operations with fluctuating
production rates or where parts have wide variance in dragout volume.
These various control techniques are described below.
1. Conductivity Controllers - Conductivity controllers provide
for efficient use and good control of the rinse process.
This controller utilizes a conductivity cell to measure the
conductance of the solution which , for an electrolyte, is
dependent upon the ionic concentration. The conductivity
cell is tied to a controller which will open or close a
solenoid on the makeup line. As the rinse becomes more
contaminated, its conductance increases until the set point
of the controller is reached, causing the solenoid to open
and allowing makeup to enter. Makeup will continue until the
conductance drops below the set point. The advantage of this
method of control is that water is flowing only when
required.
2- Liquid Level Controllers - These controllers find their
greatest use on closed loop rinsing systems. A typical
arrangement uses a liquid level sensor in both the plating
solution tank and in the first rinse tank, a pump to tranfer
solution from the first rinse tank and the plating tank, and
a solenoid on the rinse tank makeup water line. When the
132
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FIGURE 7-7 TYPICAL PRINTED BOARD RACK
133
-------
FIGURE 7-8 MODIFIED PRINTED BOARD RACK
FOR DRAGOUT CONTROL
134
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plating solution evaporates to below the level of the level
controller, the pump is activated, and solution is
transferred from the first tank to the plating tank. The
pump will remain active until the plating tank level
controller is satisfied. As the liquid level of the rinse
tank drops due to the pumpout, the rinse tank controller will
open the solenoid allowing fresh feed to enter.
3. Manually Operated Valves - Manually operated valves are
susceptible to misuse and should, therefore, be installed in
conjunction only with other devices. Orifices should be
installed in addition to the valve to limit the flow rate of
rinse water. For rinse stations that require manual movement
of work and require manual control of the rinse (possibly due
to low utilization), dead man valves should be installed in
addition to the orifice to limit the flow rate of rinse
water. They should be located so as to discourage jamming
them open.
4. Orifices or_ Flow Restrictors - These devices are usually
installed for rinse tanks that have a constant production
rate. The newer restrictors can maintain a constant flow
even if the water supply pressure fluctuates. Orifices are
not as efficient as conductivity or liquid level controllers,
but are far superior to manual valves.
Plating Bath Conservation
If the overflow water from a rinse tank can be reused, it does not
have to be treated, and additional water does not have to be
purchased. One approach currently in use is to replace the
evaporative losses from the plating bath with overflow from the rinse
station. This way a large percentage of plating solution normally
lost by dragout can be returned and reused. The usefulness of this
method depends on the rate of evaporation from the plating bath and
the overflow rate from the rinse tank. The evaporation from a bath is
a function of its temperature, surface area, and ventilation rate,
while the overflow rate is dependent on the dilution ratio, the
geometry of the part, and the dragout rates. If the rinse is
noncritical, i.e., where the part is going to another plating
operation, closing the loop (returning rinse overflow to the plating
tank) can be accomplished with far fewer rinse tanks than a critical
rinse (following the last plating operation). For example, if a
particular line is always used to plate base metals only, and
afterwards the work always goes to another process, then this permits
a lower flow rate with consequently higher buildup of pollutants in
the rinse. Under these conditions, an external concentrator, such as
an evaporator, is not required, and the rinse overflow can be used
directly for plating bath makeup. The reverse is often true with the
135
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rinse following the final finish plating step. The flow rate in this
instance may be high enough that it exceeds the bath evaporation rate
and some form of concentrator is required.
When using any rinse arrangement for makeup of evaporative losses from
a plating solution, the quality of the rinse water must be known and
carefully monitored. Naturally occurring dissolved solids such as
calcium and magnesium salts can slowly build up in the plating bath.
This can cause the process to go out of control. Even using softened
water can cause process control problems. For this reason, deionized
water is often used as a feed for rinsing arrangements which will be
used for evaporative makeup of plating solutions.
Closing the Loop With A Countercurrent Rinse - This particular
arrangement is well suited for use with heated plating baths. The
overflow from the countercurrent rinse becomes the evaporative makeup
for the plating bath. By installing the proper number of
countercurrent tanks, the fresh feed rate for a given dilution ratio
is sized to equal the bath's evaporative rate. This arrangement is
easily controlled by using liquid level controllers in both the
plating bath and rinse tank, a pump to transfer rinse solution to the
plating bath, and a solenoid valve on the fresh feed line for the
rinse tanks. Company ID 06072 uses this arrangement.
Closing The Loop With Spray Followed By_ Countercurrent Rinse - The
spray followed by countercurrent rinse is well suited for flat sheets
and parts without complex geometry. The spray is mounted over the
plating bath, and the work is fogged before moving to the
countercurrent rinse. A major advantage of this arrangement is that
the spray reduces concentration of the dragout on the part, returning
the removed portion to the plating tank. This provides for
evaporative makeup of the plating bath and a lower water usage and/or
number of tanks for the countercurrent rinse.
Closing The Loop With Countercurrent Rinsing Followed By Spray Rinsin
The countercurrent followed by spray rinsing approach can be use
when a very clean workpiece (and, therefore, final rinse) is required.
The spray is mounted above the last countercurrent rinse tank and
becomes the feed for the countercurrent rinse. Depending on the
evaporation rate of the plating solution, the evaporative makeup can
come from the first countercurrent tank.
Closing The Loop With Dead Rinse Followed By_ Countercurrent - The dead
followed by countercurrent rinse arrangement is particularly useful
with parts of a complex geometry. Evaporative losses from the
original solution tank can be made up from the dead rinse tank and the
required flow for the-countercurrent system can be greatly reduced.
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Closing The Loop With Recirculatory Spray - When the geometry of the
work permits, the recirculating spray offers an improved alternative
to the dead rinse. Operating with a captive supply of rinse solution,
the solution is sprayed onto the work. The advantage of this system
is that the impact of the spray is used to remove dragout,
particularly for work with holes in it. The basic equations for
concentration buildup hold but are modified by the removal efficiency
of the spray. The required flow rate of the spray is dependent on the
geometry of the parts, the production rate, and the solution
evaporation rate.
Good Housekeeping
Good housekeeping and proper maintenance of plating equipment are
required to reduce wastewater loads to the treatment systems.
Frequent inspection of racks for loose insulation prevents excessive
dragout of plating solutions. Also, periodic inspection of the
condition of tank liners and the tanks themselves reduces the chance
of a catastrophic failure which could overload the waste treatment
device, thereby allowing excessive pollutant discharges. Steps to
prevent the mixing of cyanide and iron or nickel wastes should be
taken. Proper tank linings in steel tanks prevent the formation of
untreatable wastes such as ferrocyanides. Likewise, anode selection
must also consider anode constituents to avoid the formation of
untreatable wastes. Periodic inspection should also be performed on
all auxiliary plating room equipment. This includes inspections of
pumps, filters, process piping, and immersion steam heating coils for
leaks. Filter replacement should be done in curbed areas or in a
manner such that solution retained by the filter is dumped to the
appropriate waste stream. Good housekeeping is also applicable to
chemical storage areas to preclude a catastrophic failure situation.
Storage areas should be isolated from high hazard fire areas and
arranged such that if a fire or explosion occurs in such areas, loss
of the stored chemicals due to deluge quantities of water would not
overwhelm the treatment facilities or cause excessive ground water
pollution. Good housekeeping practices also include the use of drain
boards between processing tanks. Bridging the gap between adjacent
tanks via drain boards allows for recovery of dragout that drips off
the parts while they are being transferred from one tank to another.
The board should be mounted in a fashion that drains this dragout back
into the tank from which it originated.
Chemical Recovery
There are a number of techniques that are utilized to recover and/or
reuse plating solutions or etchants. The incentive to recover or
reuse may be primarily economical, but the ecological impact of not
having to treat these concentrated solutions for discharge should also
be considered. The solutions can be reclaimed using any one of a
137
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number of techniques such as reverse osmosis, ion exchange, and
evaporation. Some processes include: reuse of spent etchant from a
subtractive printed circuit board process as a supply for an additive
electroless process bath; recovery of metal from spent plating baths;
and continuous regeneration of etchants. These techniques are briefly
described below.
Reuse of_ Spent Etchant - If a facility maintains both an additive and
a conventional subtractive line for the manufacturing of printed
boards, a two-fold incentive exists for reuse of spent copper etchant.
The copper etchant used in a conventional subtractive process is
normally dumped when the copper concentration reaches approximately
45,000 mg/1. However, by removing the iron and chromium from the
etchant, it can become an inexpensive source of copper for the
additive plating baths. This technique can be extended to recover the
copper bearing waters from copper etchant rinse tanks as well as from
the etch tank and is practiced at company ID 11065. Some type of
concentrating device, such as vacuum distillation, may be required to
reduce the volume of the rinse.
Recovery of_ Metal from Spent Plating Baths - Spent plating baths
contain a significant percentage of metal in solution. Recovery can
be effected by electrolizing the solution at low voltage or by
decomposing a hot bath with seed nuclei. The resultant material,
while pure, can be refined or sold to recover some of its original
value. The advantage of this type of treatment is that a large per-
centage of the metal is recovered and does not require treatment.
This type of metal recovery is performed by companies 17061 and 11065.
Regeneration o_f Etchants - Regeneration of etchants from a copper
etchant solution can be achieved by partially dumping the bath and
then adding make up fresh acid and water. If this is done, the
etchant life can be extended indefinitely. A method practiced for the
regeneration of chromic acid used in the electroless plating of
plastics is to oxidize the trivalent chromium back to the active
hexavalent chromium. The oxidization is done by an electrolytic cell.
Company 20064 regenerates its preplate etchants in this manner.
Again, use of this method reduces the amount of material requiring
waste treatment.
Process Modification
Process modifications can reduce the amount of water required for
rinsing and, thus, reduce the overall load on a waste treatment
facility. As an example, for electroless plating, a rinse step can be
eliminated by using a combined sensitization and activation solution
followed by a rinse instead of a process sequence of sensitization -
rinse, activation - rinse. Another potential process modification
would be to change from a high concentration plating bath to one with
138
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a lower concentration. Parts immersed in the lower concentration bath
require less rinsing (a dilution operation) and, thus, decrease the
water usage relative to high concentration baths. The use of non-
cyanide plating baths, and phosphate free and biodegradable cleaners,
where possible, are material substitutions which reduce the waste load
on an end-of-pipe treatment system.
Integrated Waste Treatment
Waste treatment itself can be accomplished on a small scale in the
plating room with constant recycling of the effluent. This process is
generally known as integrated waste treatment. Integrated treatment
uses a treatment rinse tank in the process line immediately following
a process tank (plating, chromating, etc.). Treatment solution
(usually caustic soda in excess) circulating through the rinse tank
reacts with the dragout to form a precipitate and removes it to a
clarifier. This clarifier is a small reservoir usually designed to
fit near the treatment rinse tank and be an integral part of water use
in the production process. Further treatment may take place in the
clarifier (cyanide oxidation, chrome reduction) or settling alone may
be used to separate the solids. Sludge is removed near the spillover
plate on the effluent side of the clarifier, and the effluent is
returned to the treatment rinse tank. Consequently, no pollutants are
directly discharged by the waste treatment process. Although further
rinsing of the parts is required to remove treatment chemicals, this
rinse will not contain pollutants from the original process tank, and
no further treatment is needed.
INDIVIDUAL TREATMENT TECHNOLOGIES
The following major headings provide descriptions of individual
treatment technologies that are used to varying degrees in the
electroplating industry. For each technology, a description of the
process, its advantages and limitations, its reliability and
maintenance requirements, and its demonstration status are discussed.
CHEMICAL REDUCTION OF HEXAVALENT CHROMIUM
Definition of the Process
Reduction is a chemical reaction in which one or more electrons are
transferred to the chemical being reduced from the chemical initiating
the transfer (reducing agent).
Sulfur dioxide, sodium bisulfite, sodium metabisulfite, and ferrous
sulfate form strong reducing agents in aqueous solution and are,
therefore, useful in industrial waste treatment facilities for the
reduction of hexavalent chromium to trivalent chromium. Reduction of
139
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chromium by ferrous sulfate is most effective at pH levels of less
than 3.0.
Description o_f the Process
The main application of chemical reduction to the treatment of
wastewater is in the reduction of hexavalent chromium to trivalent
chromium. The reduction enables the trivalent chromium to be
separated from solution in conjunction with other metallic salts by
alkaline precipitation. Gaseous sulfur dioxide is a reducing agent
widely employed for the process. The reactions involved may be
illustrated as follows:
3S02 + 3H20 = 3H2S03
3H2S03 + 2H2Cr04 = Cr2(S04)3 + 5H20
The above reaction is favored by low pH. A pH of from 2 to 3 is
normal for situations requiring complete reduction. At pH levels
above 5, the reduction rate is slow. Oxidizing agents such as
dissolved oxygen and ferric iron interfere with the reduction process
by consuming the reducing agent.
A typical wastewater treatment facility used to treat metal finishing
wastewaters containing chromates is presented in Figure 7-9. The
treatment consists of 45 minutes retention in a reaction tank. The
reaction tank is equipped with an electronic device which monitor and
control both pH and oxidation reduction potential (ORP). Gaseous
sulfur dioxide is metered to the reaction tank to maintain the ORP
within the range of 250 to 300 millivolts. Sulfuric acid is added to
maintain a pH level of from 1.8 to 2.0. The reaction tank is also
equipped with a propeller agitator designed to provide about one
turnover per minute. Following reduction of the hexavalent chromium,
the waste is combined with other waste streams for final
neutralization to a pH of 8 to remove chromium and other metals by
precipitation.
A common batch treatment system for chromium reduction has a
collection tank and a reaction tank with a four hour retention time.
The chromium is reduced by the addition of sodium bisulfite while the
pH is controlled by sulfuric acid addition.
Advantages and Limitations
Some advantages of chemical reduction in handling process effluent are
as follows:
1. Proven effectiveness within the industry.
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SUl.FURIC
ACID
SUUFUR
OIOXIOE
r~ —
PH CONTROUI.ER] I
I I 1
RAW WASTE
(HEXAVAUENT CHROMIUM)
1
OO
---D
ORP CONTROLUER
T
(TRIVAUENT CHROMIUM)
REACTION TANK
FIGURE 7-9
HEXAVALENT CHROMIUM REDUCTION WITH SULFUR DIOXIDE
-------
2. Processes, especially those using sulfur
suited to automatic control.
dioxide, are well
3. Operation at ambient conditions, i.e., 15.6 to 32.2 degrees C
(60 to 90 degrees F).
Some limitations of chemical reduction for treatment process effluents
are as follows:
1
Chemical
wastes.
interference is possible in the treatment of mixed
2. Careful pH control is required for effective hexavalent
chromium reduction.
3. A potentially hazardous situation
dioxide gas is stored and handled.
will exist when sulfur
Specific Performance
A study of an operational waste treatment facility chemically reducing
hexavalent chromium to trivalent chromium has shown that a 99.7%
reduction efficiency is possible.
Operational Factors
Reliability - High, assuming proper monitoring and control and
pretreatment to control interfering substances.
proper
Maintainability - Maintenance consists of periodic removal of sludge.
Collected Wastes - Pretreatment to eliminate substances which will
interfere with the process may be necessary. This process produces
trivalent chromium which can be controlled by further treatment.
There may, however, be small amounts of sludge collected due to minor
shifts in the solubility of the contaminants. This is processed in
the main sludge treatment equipment.
Demonstration Status
The reduction of chromium waste by sulfur dioxide is a classic process
and is found in use by numerous plants employing chromium compounds in
operations such as electroplating. One hundred and twenty plants in
the data base (196 plants) employed the chemical reduction process in
their treatment system and these plants are identified in Table 7-3.
142
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TABLE 7-3
ELECTROPLATING PLANTS THAT .CURRENTLY EMPLOY CHEMICAL REDUCTION
116
304
4031
4034
478
629
6051
6072
6076
6079
6085
6088
6731
1108
11065
1263
1902
19051
2001
2010
2025
20070
20078
20081
20084
20087
2307
2811
3007
3020
31020
3301
3311
3321
3330
33070
33074
36040
40062
4301
301
4003
4032
4035
5050
635
6053
6073
6077
6083
6086
6358
804
1113
1205
12065
1903
19063
2006
2015
20064
20073
20079
20082
20085
2103
23061
3001
3009
30050
31021
3303
3315
3324
3333
33071
3601
36041
4101
43003
303
4030
4033
4069
612
650
662
6074
6078
6084
6087
6381
902
1122
1208
15070
1924
19066
2007
2024
20069
20077
20080
20083
20086
2303
2501
3005
3019
30074
31050
3308
3320
3329
3335
33073
3612
40061
41041
44050
143
-------
p_H ADJUSTMENT
Definition of_ the Process
Wastewater pH is adjusted by addition of an acid or an alkali,
depending on the purpose of the adjustment. The most common purpose
of wastewater pH adjustment is precipitation of dissolved heavy
metals, as illustrated by Figure 7-10.
To accomplish this precipitation, an alkaline substance such as lime
is added to the wastewater to increase the pH to at least 8. This
decreases the solubility of the metal, which precipitates as a metal
hydroxide. The precipitated metal is then often removed from the
wastewater by clarification, which is described later in this section.
Adjustment of pH is sometimes used to neutralize wastewater before
discharge to either a stream or a sanitary sewer. This may involve
neutralization of alkaline wastewater with an acid, neutralization of
acid wastewater with an alkali, or neutralization of clarifier
overflow with an acid.
Description o£ the Process
Initial adjustment of pH is usually achieved simply by mixing alkaline
and acidic wastewaters. This may be carried out in a collection tank,
rapid mix tank, or equalization tank. However, the resulting pH is
seldom suitable as preparation either for clarification or sanitary
sewer discharge. Consequently, treatment chemicals are usually added.
A variety of treatment chemicals is used. The wastewater is generally
acidic, and the chemical most commonly used to increase pH is lime.
If substantial sulfur compounds are present in the wastewater, caustic
soda (sodium hydroxide) may be used in place of lime to prevent
precipitation of calcium sulfate, which increases sludge volume. Soda
ash (sodium carbonate) is also sometimes used. Sulfuric acid and
hydrochloric acid are used to decrease wastewater pH. Sulfuric acid
is less expensive and is used except when formation of sulfate sludge
is a problem.
Treatment chemicals for adjusting pH prior to clarification may be
added to a rapid mix tank, a mix box, or directly to the clarifier,
especially in batch clarification. If metals such as cadmium and
nickel are in the wastewater, a pH in excess of 10 is required for
effective precipitation. This pH, however, is unacceptable for dis-
charged wastewater, and the pH must therefore be reduced by adding
acid. The acid is usually added as the treated wastewater flows
through a small neutralization tank prior to discharge.
Advantages and Limitations
Some advantages of pH adjustment in treating process effluents are as
follows:
144
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I*4-0
2 3.0
o
-------
1. Proven effectiveness within the industry.
2. Processes are well suited to automatic control.
3. Often aided by necessary "in line" treatments.
4. Operation at ambient conditions, i.e., 15.5 to 32.2 degrees C
(60 to 90 degrees F).
Some limitations of pH adjustment for treatment of process effluents
are as follows:
1. Chemical interference is possible in the treatment of mixed
wastes.
2. Disposal of a substantial quantity of sludge is required.
Operational Factors
Reliability - High assuming proper monitoring and control and proper
pretreatment to control interfering substances.
Maintainability - Maintenance consists of assuring proper feeding of
treatment chemicals and operation of pH control instrumentation.
Collected Wastes - Precipitated solids must be subsequently removed
from the wastewater.
Demonstration Status
The pH adjustment of wastewater is a classic process, used by numerous
plants employing electroplating. One hundred and fifty-eight of the
plants in the data base used this process (Reference Table 7-4).
CLARIFICATION
Definition of the Process
Clarification is the separation of suspended solids, metal hydroxides,
and other settleable impurities that are heavier than water by
gravitational settling. This process has been in general industrial
use for many years and is currently the most commonly used technique
for the removal of settleable material from wastewater.
146
-------
116
02062
303
304
405
408
409
4045
4065
4069
4071
4077
478
4087
5020
5021
607
612
635
636
637
650
6051
6053
662
6065
6067
6072
6073
6074
6075
6076
6078
6079
6081
6083
6084
6085
6086
6087
6088
6089
TABLE 7-4
ELECTROPLATING PLANTS THAT CURRENTLY
EMPLOY £H ADJUSTMENT
1113 3008
11050 3009
11065 3019
11066 3021
1205 30050
1208 30074
1209 3116
12062 31020
1263 31021
12065 31050
1501 3301
15070 3302
17061 3305
1902 3306
1903 3308
1924 3309
19050 3311
19051 3315
19063 3320
19066 3322
2001 3323
2006 3324
2010 3327
2013 3329
2015 3330
2017 3335
2020 33050
2021 33065
2022 33070
2023 33071
2024 33073
2025 33074
20064 3601
20069 3602
20070 3612
20073 3613
20077 36040
20078 36041
20081 36062
20082 38050
20083 4004
20084 40061
147
-------
Table 7-4 (con't:
6358 20085 40062
6381 20086 4101
6731 20087 41041
804 2103 41067
805 2303 41069
808 2307 4301
902 2308 43003
907 23061 44050
9026 2501 44061
10020 2809 61001
1108 3007
148
-------
Description of the Process
Adjustment of pH, as described earlier, commonly precedes
clarification for electroplating wastes. Additionally, inorganic
coagulants or polyelectrolytic flocculants may be added to the waste
stream following pH adjustment and prior to gravitational separation.
These agents are used to enhance settling by coagulating small
suspended precipitates into large particles. Common coagulants are
aluminum sulfate, sodium aluminate, ferrous or ferric sulfate, and
ferric chloride. Organic polyelectrolytes vary in structure, but all
usually form larger floccules than coagulants used alone. Depending
on the particular application, coagulants and polyelectrolytes may be
used together.
A new process currently being employed by one electroplating plant
provides clarification and metal removal without prior chromium
reduction. In this process, sulfide precipitation, ferric chloride
and sodium sulfide are added to the wastewater. These chemicals act
as precipitants for phosphate, heavy metals, and suspended solids.
The massive floe created by these chemicals binds the chromium, either
hexavalent or trivalent, within the precipitate as a chromium iron
sulfide complex.
Following chemical treatment, wastewater is fed into a high volume
catchment for settling. This catchment may be a lagoon (where enough
land is available), a holding tank (for very small flows or batch
treatment), or a clarifier. If lagoons or holding tanks with high
retention times are used, coagulant addition may not be needed. This
type of treatment is referred to as simple sedimentation. Clarifiers,
however, are the most commonly used solids settling devices.
The clarifier tank may be circular or rectangular in design and
generally employs mechanical sludge collection equipment. Rectangular
clarifiers usually collect the sludge at the effluent end of the tank,
while circular clarifiers have a sloping funnel-shaped bottom for
sludge collection and withdrawal. Bottom slopes of at least 8.33 cm
per meter are required for bottom sludge withdrawal. The sludge
collection mechanism helps the sludge to overcome inertia and prevents
adherence to the bottom.
Once the sludge is collected, it may be pumped out or hydraulically
removed from the clarifier. Depending on the impurities present, the
retention time and the chemical treatment used, solids concentrations
of one to three percent are achievable in the sludge. Recycling of
metal hydroxide sludges back to the clarifier inlet results in
densification of the sludge.
A common type of clarifier is a circular tank in which the flow is
introduced at the center into a feed well which dissipates inlet
149
-------
velocities (Figure 7-11). The wastewater moves radially from the feed
well to the weir and overflow trough at the outside edge of the tank.
Settled solids are raked to a hopper near the tank center by arms
attached either to a drive unit at the center of the tank or a
traction unit operating on the tank wall. To expedite solids removal
from clarifiers, some equipment manufacturers have installed inlet
nozzles connected to hollow pipe arms instead of scrapers. These
nozzles sweep the entire tank bottom on a single revolution. This
method of sludge removal is referred to as hydraulic sludge removal.
Occasionally circular clarifiers use a surface blade to move floating
material to a skimmer.
Advantages and Limitations
The major advantage of simple sedimentation (settling without the aid
of coagulants) is the simplicity of the process itself - the
gravitational settling of solid particulate waste in a holding tank or
lagoon. It is also possible, with small sedimentation tanks, to use
hydraulic sludge removal techniques. A disadvantage of simple
sedimentation is that long retention times may be necessary to achieve
complete settling, especially if the specific gravity of the suspended
matter is close to that of water. Some materials cannot be
practically removed by sedimentation alone, and chemicals must be
added to achieve removal.
The major advantage of clarifiers is that they are effective in
removing slow settling suspended matter in a shorter time and in less
space than a simple sedimentation system. Improved performance is
obtained by an adjustment of the pH to 9 or higher. This increases
the rate of flocculation because of pollutant solubility
characteristics and, in many cases, improves effluent quality
noticeably. This rapid flocculation and removal may require flushing
or other maintenance to downstream equipment such as filters, pumps,
etc.
The major advantage of sulfide precipitation is that it provides
chromium removal without first requiring the reduction of hexavalent
chromium to the trivalent state. Chemical costs and sludge production
rates are fairly low. One limitation of the process is that hydrogen
sulfide gas results from the process. This is a noxious odor in very
small quantities and may be objectionable to downwind nearby
residential housing. Careful control of the sodium sulfide input can
minimize this problem.
Specific Performance - A properly operating clarification system is
capable of efficient removal of suspended solids, precipitated metal
hydroxides, and other impurities from wastewater. Effectiveness of
the process depends on a variety of factors, including the ratio of
organics to inorganics, effective charge on suspended particles, and
150
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CONDUIT
TO MOTOR
INFLUENT
CONDUIT TO
OVERLOAD
ALARM
COUNTERFLOW
INFLUENT WELL
OVERLOAD ALARM
EFFLUENT WEIR
DIRECTION OF ROTATION
EFFLUENT PIPE
EFFLUENT CHANNEL
PLAN
INFLUENT
TURNTABLE
BASE
HANDRAIL
CENTER COLUMN
CENTER CAGE
WEIR
STILTS
CENTER SCRAPER
SQUEEGEE
FIGURE 7-11 CIRCULAR CLARIFIER
151
-------
types of chemicals used in the treatment. Frequently, two or more
chemicals are used for treatment, and the proper quantities are
usually best determined by laboratory analysis.
The performance of a simple sedimentation process is a function of the
retention time for batch sedimentation, surface loading for
flow-through sedimentation, particle size and density, and
precipitation aids used, if any. The removal efficiency for a given
settling time requires consideration of the entire range of settling
velocities in the system. This may be accomplished by use of a
settling column or by use of sieve analyses and hydrometer tests, the
results of which must be analytically combined to obtain settling
velocities of each particle size. The average pollutant removal
performance for a group of typical plants visited during the project
is discussed in Sections IX and XII.
Operational Factors
The clarification process has been in general use for many years and
is currently the most commonly used technique for the removal of
settleable material from wastewater. This wide utilization has
resulted in high reliability. Corrosion due to caustic chemicals used
for pH adjustment may cause premature failures. Care must be taken to
minimize leakages of chemicals. Proper maintenance should also be
carried out to minimize failures.
Maintainability - When clarifiers are used, the associated system
utilized for chemical addition, stirring, and sludge dragout must be
maintained on a regular basis. Systems external to the clarifier tank
present minimal problems from a system operation viewpoint, while
systems within the clarifier may require emptying for maintenance to
be accomplished. Routine maintenance will generally consist of
lubrication, checking for excessive wear, and part replacement, as
required. When lagoons are used, maintenance problems similar to
those above exist for the chemical treatment aspect, but the lagoon
itself requires little maintenance other than periodic sludge-removal.
Collected Wastes - The sludge collected from clarification is usually
dewatered and then either buried in a landfill, incinerated, or hauled
away by a contractor.
Demonstration Status
Clarification and other solids settling techniques represent the
typical method of solids removal and were employed in 151 of the 196
plants in this data base. Table 7-5 identifies plants in the data
base already employing clarification. Clarifiers are the most
commonly used settling device because of their size advantage and
effectiveness for many wastewater constituents and have been in
152
-------
general use for many years. This is evidenced by the fact that over
two-thirds of the plants employing solids settling used clarifiers.
Lagooning was practiced in 60 of these plants (20 plants used both
clarifiers and lagoons).
DIATOMACEOUS EARTH FILTRATION
Definition o|_ the Process
Diatomaceous earth filtration, combined with pH adjustment and
precipitation, is a solids separation device which is an alternative
to settling for suspended solids removal. The diatomaceous earth
filter is used to remove metal hydroxides and other solids from the
wastewater and provides an effluent of high quality.
Description of_ the Process
A diatomaceous filter is comprised of a filter, a filter housing and
associated pumping equipment. The filter element consists of multiple
peat screens which are coated with diatomaceous earth. The size of
the filter is a function of flow rate and desired operating time
between filter cleanings.
153
-------
TABLE 7-5
PLANTS CURRENTLY USING A SYSTEM INCLUDING CLARIFICATION
2062
303
4003
4030
4032
4034
4045
4069
4077
5021
607
637
6053
6065
6073
6076
6078
6083
6085
6087
6358
804
902
1108
1208
12062
1302
17061
1924
301
304
408
4031
4033
4035
4065
4071
5020
5050
635
6051
662
6072
6075
6077
6081
6084
6086
6088
6381
808
10020
1122
11050
1209
1263
15070
1902
19050
19063
2007
2020
20070
20078
20080
20083
20085
20087
2811
3003
3008
3019
30050
31021
3311
3320
3322
3324
3329
33070
33073
3602
36040
4101
4301
2006
2010
20069
20073
20079
20082
20084
20086
23061
3001
3007
3009
3021
3116
3308
3315
3321
3323
3327
33050
33071
3601
3612
40061
41041
43003
154
-------
Normal operation of the system involves pumping
diatomaceous earth and water through the screen leaves.
the diatomaceous earth filter media on the screens and
for treatment of the waste v^ater. Once the screens
a mixture of
This deposits
prepares them
are completely
coated, the pH adjusted wastewater can be pumped through the filter
The pH adjustment and precipitation tank perform the same functions in
this system as in clarification, i.e. they transform dissolved metal
ions into suspended metal hydroxides. The metal hydroxides and other
suspended solids are removed from the effluent in the diatomaceous
earth filter. The buildup of solids in the filter increases the
pressure drop across the filter. At a certain pressure, the waste
water is stopped, the filter is cleaned and the cycle is restarted.
Advantages and Limitations
The principal advantage to using a diatomaceous earth filter is the
reduction in size of the waste treatment system compared to a system
using a clarifier. The filter system can be installed within an
existing plant structure even in cases where very little free floor
space is available. The filter system's performance is comparable
with that of a clarifier. One additional advantage is the sludge
removed from the filter is much drier than that removed from a
clarifier (approx. 50% solids). This high solids content can
significantly reduce the cost of hauling and landfill.
The major disadvantage to the use of a filter system is an increase in
operation and maintenance costs. In some cases this increase in 0 & M
costs is offset by the lower capital costs required when not investing
in land and outside construction.
Spej:ific Performance
A properly operating filter system has demonstrated the following
performance.
Total Suspended Solids
Zinc
Trivalent Chromium
Iron
Copper
Nickel
Removal
Percent
98%
99%
95%
96%
94%
98%
Raw
Waste
524
13.4
12.2
5,
7
2
81
53
57
Effluent
10
0.139
0.611
248
444
,044
0,
0,
0,
These figures are from an actual plant operating system visited and
sampled (ID 36041). Other plants visited, such as ID's 06731 and
09026, also had operating diatomaceous earth filters and similar
effluent levels.
155
-------
Demonstration Status
Filters with similar operating characteristics to that described above
are in common use throughout the electroplating industry. They are
employed by 5 plants in the data base.
The ID numbers of the plants using diatomaceous earth filtration are
listed below:
6731
9026
31020
33073
36041
FLOTATION
Definition o_f the Process
Flotation is the process of causing particles such as metal hydroxides
to float to the surface of a tank where they can be concentrated and
removed. This is accomplished by increasing the buoyancy of the solid
particles by releasing gas bubbles which attach to the solid particles
causing them to float. In principle, this process is the opposite of
sedimentation.
Flotation may be performed in several ways; froth, dispersed air,
dissolved air, gravity, and vacuum flotation are the most commonly
used techniques. Chemical additives may also be used to enhance the
performance of the flotation process.
Flotation is used primarily in the treatment of wastewater containing
large quantities of industrial wastes that carry heavy loads of finely
divided suspended solids and grease. Solids having a specific gravity
only slightly greater than 1.0, which would require abnormally long
sedimentation times, may be removed in much less time by flotation.
Description of_ the Process
The principal difference between types of flotation is the method of
generation of the minute gas bubbles, usually air, in a suspension of
water and small particles. The use of chemicals to improve the
efficiency may be employed with any of the basic methods. The
following paragraphs describe the different flotation techniques and
the method of bubble generation for each process.
Froth Flotation - Froth flotation is based on the utilization of
differences in the physiochemical properties in various particles.
156
-------
Wettability and surface properties affect the particles' ability to
attach themselves to gas bubbles in an aqueous medium. In froth
flotation, air is blown through the solution containing flotation
reagents. The particles in the solution, with water repellant
surfaces, stick to air bubbles as they rise and are brought to the
surface. A mineralized froth layer, with mineral particles attached
to air bubbles, is formed. Particles of other minerals which are
readily wetted by water do not stick to air bubbles and remain in
suspension.
Dispersed Air Flotation - In dispersed
generated by introducing the air
impellers or by spraying air through
flotation is used in the metallurgical
air flotation,
by mechanical
porous media.
industry.
gas bubbles are
agitation with
Dispersed air
Dissolved Air Flotation - In dissolved air flotation, bubbles are
produced as a result of the release of air from a supersaturated
solution. There are two types of contact between the gas bubbles and
particles. The first type is predominant in the flotation of
flocculated materials and involves the entrapment of rising gas
bubbles in the flocculated particles as they increase in size. The
bond between the bubble and particle is one of physical capture only.
The second type of contact is one of adhesion. Adhesion results from
the intermolecular attraction exerted at the interface between the
solid and gaseous phases.
Vacuum Flotation - This process consists of saturating the wastewater
with air either 1) directly in an aeration tank, or 2) by permitting
air to enter on the suction of a wastewater pump. A partial vacuum is
applied, which causes the dissolved air to come out of solution as
minute bubbles. The bubbles attach to solid particles and rise to the
surface to form a scum blanket, which is normally removed by a
skimming mechanism. Grit and other heavy solids that settle to the
bottom are generally raked to a central sludge pump for removal. A
typical vacuum flotation unit consists of a covered cylindrical tank
in which a partial vacuum is maintained. The tank is equipped with
scum and sludge removal mechanisms. The floating material is
continuously swept to the tank periphery, automatically discharged
into a scum trough, and removed from the unit by a pump also under
partial vacuum. Auxiliary equipment includes an aeration tank for
saturating the wastewater with air, a tank with a short retention time
for removal of large air bubbles, vacuum pumps, and sludge and scum
pumps.
Advantages and Limitations
Because flotation is dependent on the surface characteristics of the
particulate matter, laboratory and pilot plant tests must usually be
performed to yield the necessary design criteria. Factors that must
157
-------
be considered in the design of flotation units include the
concentration of particulate matter, quantity of air used, the
particulate rinse velocity, and the solids loading rate.
Specific Performance
The performance of a flotation system depends upon having sufficient
air bubbles present to float substantially all of the suspended
solids. An insufficient quantity of air will result in only partial
flotation of the solids, and excessive air will yield no improvement.
The performance of a flotation unit in terms of effluent quality and
solids concentration in the float can be related to an air/solids
ratio as shown in Figure 7-12. It should be noted that the shape of
the curve obtained will vary with the nature of the solids in the
feed.
The primary variables for flotation design are pressure, feed solids
concentration, and retention period. The effluent suspended solids
decrease, and the concentration of solids in the float increase with
increasing retention period. When the flotation process is used
primarily for clarification, a detention period of 20 to 30 minutes is
adequate for separation and concentration.
Operational Factors
Reliabi1ity - The reliability of a flotation system is normally high
and is governed by the sludge collector mechanism and by the motors
and pumps used for aeration.
Maintainability - Routine maintenance is required on the pumps and
motors. The sludge collector mechanism is subject to possible
corrosion or breakage and may require periodic replacement.
Collected Wastes - Chemicals are commonly used to aid the flotation
process. These chemicals, for the most part, function to create a
surface or a structure that can easily adsorb or entrap air bubbles.
Inorganic chemicals, such as the aluminum and ferric salts and
activated silica, can be used to bind the particulate matter together
and, in so doing, create a structure that can easily entrap air
bubbles. Various organic chemicals can be used to change the nature
of either the air-liquid interface or the solid-liquid interface, or
both. These compounds usually collect on the interface to bring about
the desired changes.
Demonstration Status
Flotation units are commonly used in industrial operations to remove
emulsified oils and grease as well as dissolved solids with a specific
158
-------
0.06
0.05
Q 0.04
8
0.03
0.02
0.01
I I
2 3
PERCENT SOLIDS
(A)
50 100 150
PPM EFFLUENT SUSPENDED SOLIDS
(B)
200
(A) THE RELATIONSHIP BETWEEN AIR/SOLIDS RATIO AND
FLOAT-SOUDS.CONCENTRATIONj
(B) THE RELATIONSHIP BETWEEN AIR/SOLIDS RATIO AND
EFFLUENT SUSPENDED SOLIDS.
FIGURE 7--I2
AIR/SOLIDS RATIO
159
-------
gravity close to water. In the 196 plant data base, this process was
employed by six plants (ID's 5050, 902, 2017, 2307, 4101, and 41041).
In addition, a Swedish company has developed a "micro flotation
system" which uses hydrostatic pressure to control the aeration step
by means of which suspended solids are swept to the surface. Several
plants are in operation with metal plating and pickling liquors,
chemicals, dye stuff, paper, glue, and sewage being treated with this
system. Solids removal is reported to be 90-99%. The most sig-
nificant factor in the operation of this system is that small bubbles,
typically 5-50 microns, are released very gradually, causing twice as
many bubbles with a higher affinity for solids, and the gradual
release is less disruptive to sludge formation.
OXIDATION BY CHLORINE
Definition of_ the Process
Oxidation is a chemical reaction in which one or more electrons are
transferred from the chemical being oxidized to the chemical
initiating the transfer (oxidizing agent).
Chlorine, in elemental or hypochlorite salt form, is a strong
oxidizing agent in aqueous solution and is used in industrial waste
treatment facilities primarily to oxidize cyanide.
Description of_ the Process
Cyanide Wastes - Chlorine as an oxidizing agent is primarily used in
industrial waste treatment to oxidize cyanide. This classic procedure
can be approximated by the following two step chemical reaction:
1. C12 + NaCN + 2NaOH = NaCNO + 2NaCl + B20
2. 3C12 + 6NaOH + 2NaCNO = 2NaHC03 + N2 + 6NaCl + 2H20
The reaction indicated by equation (1) represents the oxidation of
cyanides to cyanates. The oxidation of cyanides to cyanates is
accompanied by a marked reduction in volatility and a thousand fold
reduction in toxicity.
The reaction presented as equation (2) for the oxidation of cyanate is
the final step in the oxidation of cyanide to carbon dioxide and
nitrogen.
A typical wastewater treatment facility is shown in Figure 7-13 and
illustrates modern practice for treating electroplating wastewaters
containing cyanides. Continuous flow treatment facilities are
provided for cyanide-bearing wastes which are discharged from plating
160
-------
HAW W A t> T I
CADS I 1C
SODA
CONTNOl.l tH
-^~»»-^Lx->r
n
00
WATCH
CON 1 AINING
CYANATF
CHI. OH I ML!
HI AC I ION TANK
CHI. OH I NAT OH
CAUSTIC
9 On A
00
PH
CON I HOI LEK
HfACTION TANK
THCATEO
WASTE
FIGURE 7-13
TREATMENT OF CYANIDE WASTE BY ALKALINE CHLORINATION
-------
operations. In plating operations, copper, zinc, gold and cadmium may
be plated from cyanide baths.
The cyanide waste from these plating solutions is treated by the
alkaline chlorination process for oxidation of cyanides to carbon
dioxide and nitrogen. The treatment commonly consists of an
equalization tank followed by several reaction tanks connected in
series. Each retention tank has an electronic recorder-controller to
maintain required conditions with respect to pH and oxidation
reduction potential (ORP). In the first reaction tank, conditions are
adjusted to oxidize cyanides to cyanates. To effect the reaction,
chlorine is metered to the reaction tank as required to maintain the
ORP in the range of 350 to 400 millivolts, and 50% aqueous caustic
soda is added to maintain a pH range of 9.5 to 10. In the following
reaction tanks, conditions are maintained to oxidize cyanate to carbon
dioxide and nitrogen. The desirable ORP and pH for this reaction are
600 millivolts and 8.0, respectively. Each of the reaction tanks is
equipped with a propeller agitator designed to provide approximately
one turnover per minute.
Batch treatment is an alternative to the system comprised of the
equalization tank and several reaction tanks. In batch treatment, a
single tank holds the daily wastewater flow. The chemicals are added
at the end of daily operation and sufficient retention time to
accomplish the desired reaction is allowed before discharging the
wastewater.
Advantages and Limitations
Some advantages of chlorine oxidation for handling process effluents
are as follows:
1. Lowest cost and convenience of application.
2. Process is well suited to automatic control.
3. Operation at ambient environments, i.e., 15.5 to 32.2 degrees
C (60 to 90 degrees F).
Some limitations or disadvantages of chlorine oxidation for treatment
of process effluents are listed below.
1. Toxic, volatile intermediate reaction products must be
controlled by careful pH adjustment.
2. Chemical interference is possible in the treatment of mixed
wastes.
162
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3. A potentially hazardous situation exists when chlorine gas is
stored and handled.
f ic Performance
The following efficiency figures were generated by a study of an
operational waste treatment facility using chlorine as an oxidant.
Percentage
Parameter Reduction (1)
Cyanide 99.6
Phenol 100
Color 99
Turbidity 99.4 (2)
Odor 85
(1) Optimum conditions assumed
(2) Variable depending on exact
nature of contaminant.
Detailed analysis of cyanide reduction in electroplating plants is
contained in Section XII.
Operational Factors
Reliability - High, assuming proper monitoring and control and proper
pretreatment to control interfering substances.
Maintainability - Maintenance consists of periodic removal of sludge.
163
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Collected Wastes - Pretreatment to eliminate substances which will
interfere with the process may be necessary. Dewatering of sludge
generated in the chlorine oxidation process or in an "in line" process
may be desirable prior to contractor removal or disposal to a
landfill.
Demonstration Status
The oxidation of cyanide wastes by chlorine is a classic process and
is found in most plants using cyanides in electroplating operations.
Ninety companies in the data base employed this waste treatment
process (Reference Table 7-6).
OXIDATION BY OXYGEN
Oxygen, in a pure form or in its allotropic form (ozone), is an
oxidizing agent. Air and oxygen are not considered effective as
chemical agents in the treatment of industrial waste, i.e. cyanide
wastes are not oxidized to dischargeable concentrations. Ozone,
therefore, is the only oxygen form used extensively in industrial
chemical waste treatment. Ozone as an oxidizing agent is primarily
used to oxidize cyanide to cyanate and to oxidize phenols and
chromophores to a variety of colorless nontoxic products. The cyanide
oxidation can be illustrated by the following ionic equation:
CN(-l) + 03 = CNO (-1) + 02
The reaction indicated by the above equation represents the oxidation
of cyanides to cyanates.
Since ozone will not readily effect further oxidation, breakdown of
the cyanate waste is dependent on processes such as hydrolysis and
bio-oxidation.
A typical ozone plant for wastewater treatment is shown in Figure 7-
14.
Advantages and Limitations
Some advantages of ozone oxidation for handling process effluents are
as follows:
1. Reaction product (oxygen) is beneficial to receiving waters.
2. On site generation eliminates procurement and storage
problems.
3. Process is well suited to automatic control.
4. Operation at ambient conditions, i.e., 15.5 to 32.2 Degrees C
(60 to 90 Degrees F).
Some limitations or disadvantages of ozone oxidation for treatment of
process effluents are listed below.
1. High initial cost.
164
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Controls
1
Ozone
Mixing
Tank
® o
FIGURE 7-14
TYPICAL OZONE PLANT FOR WASTE TREATMENT
165
-------
TABLE 7-6
ELECTROPLATING PLANTS THAT CURRENTLY EMPLOY OXIDATION BY CHLORINE
116
304
4045
478
5021
607
629
635
637
650
6051
6053
662
6072
6073
6075
6077
6078
6079
6081
6084
6085
6087
6089
6358
6381
804
808
902
9026
10020
1108
1113
1203
1205
1208
1263
1302
1501
15070
1902
19050
19051
2001
2006
2007
2017
2021
20073
20077
20078
20079
20080
20081
20082
20084
20086
20087
2103
2303
23061
2501
2809
2811
3001
3003
3005
3007
3008
3021
31021
3301
3306
3311
3315
3320
3321
3324
3327
3330
33065
33070
33071
33073
3601
3612
36040
36041
4301
44061
166
-------
2. Chemical interference is possible in the treat-
ment of mixed wastes.
3. Cyanide is not effectively oxidized beyond the
cyanate level.
Specific Performance
Tests carried out in France on the effluent from a large
metal finishing factory showed that an ozone dose of 80 to
90 mg/liter could remove 25 mg/liter of cyanide. The
results of initial pilot tests are as follows:
Cyanide content of effluent before ozonation » 25 mg/liter
Cyanide content of effluent after ozonation « 0
Concentration of ozone in
air (q/cu m)
7 14. 20.
Total ozone applied 7.3 5.7 4.0
Ozone lost to atmosphere
(kg/kg cyanide) 3.8 2.5 0.0
Ozone used in destruction
of cyanide (kg/kg cyanide) 3.5 3.2 4.0
Operational Factors
Reliability - High, assuming proper monitoring and control and proper
pretreatment to control interfering substances.
Maintainability - Maintenance consists of periodic removal of sludge,
and periodic renewal of filter(s) and desiccator(s) required for the
input of clean dry air.
Collected Wastes - Pretreatment to eliminate substances which will
interfere with the process may be necessary. Dewatering of sludge
generated in the ozone oxidation process or in an "in line" process
may be desirable prior to contractor removal or disposal to a
landfill.
Demonstration Status
None of the plants in the electroplating data base employed this waste
treatment process. The first commercial size plant using ozone in the
treatment of cyanide waste was installed by a manufacturer of
167
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aircraft. This plant is capable of generating 54.4 kg (120 pounds) of
ozone per day. The amount of ozone used in the treatment is appro-
ximately 20 milligrams per liter. In this process, the cyanide is
first oxidized to cyanate, and the cyanate is then hydrolyzed to C02
and NH3. The final effluent from this treatment passes into a lagoon.
Because of an increase in the waste flow, the installation has been
expanded to produce 163.3 kg (360 pounds) of ozone per day.
DEEP BED FILTRATION
Definition of_ the Process
Suspended solids are commonly removed from wastewater streams by
filtering through a deep 0.3-0.9 m (1-3 feet) granular filter bed.
The porous bed formed by the granular media can be designed to remove
practically all suspended particles. Even colloidal suspensions
(roughly 1 to 100 microns) are adsorbed on the surface of the media
grains as they pass in close proximity in the narrow bed passages.
Description of_ the Process
Filtration is basic to water treatment technology, and experience with
the process dates back to the 1800's. Filtration occurs in nature as
the surface ground waters are purified by sand. Silica sand,
anthracite coal, and garnet are common filter media used in water
treatment plants. These are usually supported by gravel. The media
may be used singularly or in combinations. The multi-media filters
may be arranged to maintain relatively distinct layers (multi-layered)
by virtue of balancing the forces of gravity, flow, and buoyancy on
the individual particles. This is accomplished by selecting
appropriate filter flow rates (liters/min/sq meter (gpm/sq ft)), media
grain size, and density.
In recent years, vast improvements have been realized in filtration
efficiency by the use of mixed media filtration beds, wherein the
process water passes from coarse to fine bed characteristics. In
mixed media beds, the various media and operating parameters are
selected to achieve a natural mixing of the media which yields the
relatively continuous variation of bed characteristics desired.
Deep bed filtration process equipment can be further defined in terms
of other major operating characteristics. The most common filtration
approach is the conventional gravity filter which normally consists of
a deep bed granular media in an open top tank of concrete or steel.
The direction of flow through the filter is downward, and the flow
rate is dependent solely on hydrostatic pressure of the process water
above the bed.
168
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A variation of the gravity filter is commonly referred to as a
pressure filter (see Figure 7-15). In this case, the basic approach
is the same as the gravity filter, but it is enclosed in a steel tank
and pressurized. Other variations are commonly referred to as
uniflow, biflow, radial flow, and horizontal flow.
Additional characteristics used to classify the various deep bed
filters are the type(s) of filter media used (multilayered, mixed
media) and the flow rates (slow, rapid and fast). But these are all
deep bed filters which take advantage of certain economic or operating
characteristics for specific conditions in specific applications.
As wastewater is processed through a filter bed, the solids collect in
the spaces between the filter particles. Periodically, the filter
media must be cleaned. This is accomplished by backwashing the filter
(reversing the flow through the filter bed). The flow rate for
backwashing is adjusted such that the bed is expanded by lifting the
media particles a given amount. This expansion and subsequent motion
provides a scouring action which effectively dislodges the entrapped
solids from the media grain surfaces. The backwash water fills the
tank up to the level of a trough below the top lip of the tank wall.
The backwash is collected in the trough and fed to a storage tank and
recycled into the waste treatment stream. The backwash flow is
continued until the filter is clean.
Auxiliary filter cleaning is sometimes employed in the upper few
inches of filter beds. This is conventionally referred to as surface
wash and is in the form of water jets just below the surface of the
expanded bed during the backwash cycle. These jets enhance the
scouring action in the bed by increasing the agitation.
An important feature for successful filtration and backwashing is the
underdrain. This is the support structure for the media bed. The
underdrain provides an area for collection of the filtered water
without clogging from either the filtered solids or the media grains.
In addition, the underdrain prevents loss of the media with the water,
and during the backwash cycle, it provides even distribution of the
flow over the bed. Failure to dissipate the velocity head during the
filter or backwash cycle will result in bed upset and major repair.
Several standard approaches are employed for filter underdrains. The
simplest one consists of a parallel porous pipe imbedded under a layer
of coarse gravel and manifolded to a header pipe for effluent removal.
Other approaches to the underdrain system are known as the Leopold and
Wheeler filter bottoms. Both of these incorporate false concrete
bottoms with specific porosity configurations to provide for drainage
and velocity head dissipation.
169
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I
FINAL
POLISHING
ZONE
SOLIDS
STORAGE
INLET
OUTLET
FINE
GRADATION
MEDIUM
GRADATION
COARSE
GRADATION
FIGURE 7-15
TYPICAL PRESSURE FILTER
170
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Filter system operation may be manual or automatic. The filter
backwash cycle may be on a timed basis, a pressure drop basis with a
terminal value which triggers backwash, or a solids carry-over basis
from turbidity monitoring of the outlet stream. All of these schemes
have been successfully used.
The state-of-the-art in filter technology has progressed during the
last twenty-five years to produce improved performance and increased
understanding of the basic principles. However, it has not progressed
to the point where adequate sizing and performance predictions can be
made with confidence prior to testing. The use of pilot plant filters
for a specific application is a necessity as part of the engineering
design procedure.
Filters in wastewater treatment plants are often employed for
polishing following clarification, sedimentation, or other similar
operations. Chemical additives which enhance the upstream treatment
equipment may or may not be compatible with or enhance the filtration
process. It should be borne in mind that in the overall treatment
system, effectiveness and efficiency are the objectives, not the
performance of any single unit. The flow rates for various types of
filters are as follows:
Slow Sand 2.04- 5.30 Liters/Minute/Square Meter
Rapid Sand, Multi-layered 40.74-51.48 Liters/Minute/Square Meter
High Rate Mixed Media 81.48-122.22 Liters/Minute/Square Meter
Advantages and Limitations
The principal advantages of filtration are:
1. Low initial and operating costs.
2. Reduced land requirements over other methods to achieve the
same level of solids removal.
3. No chemical additions which add to the discharge stream.
4. Increased flow rates can be handled by paralleling added
filter(s).
Some disadvantages encountered with filters are:
1. Require pretreatment if solids level is high (from 100 to 150
mg/1).
2. Operator training is fairly high due to controls and periodic
backwashing.
171
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3. Capability limited to suspended solids and oils and greases.
4. Backwash must be stored and dewatered to be economically
disposed.
Specific Performance
Properly operating filters following some pretreatment should produce
water with less than 0.2 JTU (Jackson Turbidity Units), and mixed
media filters can process water having average turbidities as high as
50 JTU without pretreatment. Peaks as high as 200 can be tolerated.
Above these conditions, pretreatment, such as settling basins, may be
required.
Operational Factors
Reliability - The recent improvements in filter technology have
significantly improved filtration reliability. Control systems,
improved designs, and good operating procedures have made filtration a
highly reliable method of water treatment.
Collected Wastes - Table 7-7 presents a comparison of many of the
filtration techniques and their applicability. Those processes having
a rating under "Cake Dryness" are applicable to sludge filtering only.
Demonstration Status
Because of increased understanding, performance, and reliability
filtration is becoming a standard for water treatment plants in the
United States. More than 250 mixed media plants are in operation
producing over one billion gallons per day of municipal water.
Industries returning process water to municipal supplies should
consider filtration as part of their wastewater treatment. However,
none of the plants in the data base employ deep bed filtration as part
of their wastewater treatment.
ION EXCHANGE
Definition of_ the Process
Ion exchange is a process in which ions, which are held by electro-
static forces to charged functional groups on the surface of the ion
exchange resin, are exchanged for ions of similar charge in a solution
in which the resin is immersed. Ion exchange is classified as a
sorption process because the exchange occurs on the surface of the
solid, and the exchanging ion must undergo a phase transfer from
solution phase to surface phase.
172
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TABLE 7-7
Relative Performance and Application
Characteristics of Solid/Liquid Separation Equipment
Solids content* Relative Performance
Equipment for which effective Particle-size
(weight %) range* (microns)
Gravity filters
Drum
Flat bed
Rotating screen
Sand
Table/pan
Travelling screen
Vibrating screen
Compression filter
Automatic filter press
Press pan
Screw
Pressure filters
Cartridge
Drum
Edge
Filter press
Leaf, horizontal
Leaf, vertical
Sand
Strainers
Tubular element
0.08 to 0.8
0.05 to 5
0.009 to 0.1
0.002 to 0.01
5 to 70
0.009 to 0.1
0.1 to 1
0.2 to 40
10 to 60
10 to 70
0.002 to 0.2
0.7 to 8
0.002 to 0.1
0.002 to 30
0,002 to 0.06
0.008 to 0.04
0.002 to 0.02
0.002 to 0.02
0.002 to 0.1
50 to 6,000
1 to 90,000
100 to 10,000
0.1 to 50
50 to 80,000
100 to 10,000
30 to 100,000
1 to 200
1 to 200
1 to 200
0.6 to 50
5 to 200
1 to 200
1 to 100
1 to 100
1 to 110
0.2 to 60
4 to 600
0.5 to 100
Cake
dryness
r,
_
-
_
A-C
-
A
G
G
G
A
A-G
A
G
A
A-G
_
_
A
Cake
washing
-
G
-
-
V
-
A
G
G
-
G
G
G
G
V
A
_
-
G
Filtrate
clarity
G
V
G
V
G
G
G
G-V
G-V
-
G-V
G-V
G-V
G-V
V
G-V
G-V
G
G-V
* Approximate values.
A - average; B = below average; G = good; V - very good.
-------
Ion exchange is used extensively for water and wastewater treatment of
a variety of industrial wastes to allow for recovery of valuable waste
materials or by-products, particularly ionic forms of precious metals
such as silver, gold, and uranium.
In general, a synthetic ion-exchange resin consists of a network of
hydrocarbon radicals to which are attached soluble ionic functional
groups. The hydrocarbon molecules are linked in a three-dimensional
matrix to provide strength to the resin. The amount of crosslinking
determines the internal power structure of the resin and must allow
free movement of exchanging ions.
The behavior of the resin is determined by the ionic groups attached
to the resin. The total number of ionic groups per unit of resin
determines the exchange capacity, and the group type affects both the
equilbrium and the selectivity. Cation exchangers, those resins
carrying exchangeable cations, contain acid groups. The term
"strongly acidic" is used in reference to a cation exchange resin
containing ions from a strong acid such as H2S04, and "weakly acidic"
designates cation exchange resins made from a weak acid such as H2C03.
Anion resins containing certain ammonium compounds are referred to as
"strongly basic", and those with weak base amines are referred to as
"weakly basic".
majority of cation exchangers used in water and waste treatment
operations are strongly acidic, and they are able to exchange all
cations from the solution. Both types of anion exchangers are
employed. Strongly basic anion resins are capable of exchanging all
anions, including weakly ionized material such as silicates and
dissolved carbon dioxide, and weakly basic resins exchange only
strongly ionized anions such as chlorides and sulfates. Charac-
teristic selectivities of commercial resins are well-known and useful
for determining which resin is most suitable for a specific
application. Further, it is possible to construct a resin with high
selectivity for the polluting ions involved in a particular operation.
The rate at which an exchange reaction reaches equilbrium normally is
controlled by the rate of transport of the exchange ions in the
solution. In a well stirred batch system or in a normal flow-through
system, the exchange is generally determined by either the diffusion
of ions through the pores or the resin itself.
Description of the Process
Ion exchange is used in electroplating in four ways: to reduce the
salt concentrations in well or city water to be used for rinsing, to
purify plating baths, to recover rinse water or chemicals, and for
end-of-pipe treatment. Ion exchange should be extremely effective for
end-of-pipe removal of metal ions, but the economic attractiveness is
174
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questionable. Recovery of rinse water or chemicals is, therefore, of
greatest interest. It reduces pollution by eliminating the usual
wastewater stream.
Table 7-8 indicates the application of ion exchange to metal finishing
operations for purification of waste rinse water. The number of "in-
place regeneration" units could not be accurately determined and the
number of "replacement service" units is limited because manufacturing
has only recently begun. Besides the applications listed in Table 7-
8, the technology for acid copper and acid zinc recovery is fully
developed. In addition, zinc chloride-ammonium chloride processing is
in the pilot plant stage, while phosphoric acid recovery has been
demonstrated in the laboratory.
Ion exchange resins are regenerated for metal recovery in at least
three different ways: by resin removal and replacement service, by
conventional in-place regeneration, and by rapid cyclic operation and
regeneration. Development of moving bed and fluidized bed approaches
is also underway.
175
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Application
Chromic Acid
Recovery
Nickel Sulfate
Recovery
Gold/Silver
Recovery
Phosphatizing
Recovery
Mixed Plating
Wastes With Rinse
Water Reuse
Mixed Wastes,
End-of-Pipe
TABLE 7-8
APPLICATION OF ION EXCHANGE TO ELECTROPLATING
FOR USED RINSE WATER PROCESSING
Number in Operation (Additional Units Ordered)
Replacement In-Place Cyclic
Service
Regeneration
At least 8
At least 20
At least 1
At least 1
At least 8
Operation
15 (5)
4 (1)
176
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Replacement Service - A regeneration service replaces the spent resin
with regenerated resin and regenerates the spent resin at its own
facility. This service is generally performed approximately every
three months. One such regeneration service designs the system,
fabricates it for purchase by the user, and then services it as
necessary.
In-Place Regeneration - Some establishments may find it less expensive
to do their own regeneration. This regeneration will result in one or
more waste streams which must either be hauled away by a contractor,
treated and discharged or reused. Regeneration will be performed as
required every few months. The wastes are essentially the same as
those described for the following system.
Cyclic Operation - A cyclic ion exchange system as used in an electro-
plating plant (ID 1108) is described in the following paragraphs. The
bed depth is only a few inches, and regeneration frequency is
typically twice an hour. To describe the recovery of chromic acid,
shown in Figure 7-16, it is convenient to divide the operating cycle
into four parts: dilute rinse purification, concentrated rinse
purification, regeneration, and flushing. The concentrated rinse
purification step may be omitted, but chromic acid recovery capacity
will be drastically reduced.
The major parts of the system are a filter, two cation resin beds, and
an anion resin bed. During the dilute rinse purification step, water
from the first countercurrent rinse stage {rinse No. 2 in Figure 7-16)
passes through the filter, the first cation bed, and the anion bed,
and then returns to the last countercurrent rinse stage (rinse No. 3).
Metallic impurities such as copper, iron, and trivalent chromium are
removed in the cation bed, while hexavalent chromium is retained on
the anion bed, leaving pure water to return for rinsing.
The concentrated rinse purification step is essentially the same,
except that the inlet water is withdrawn from a still rinse preceding
the countercurrent rinse, and the purified water returns to the same
still rinse. Thus, during these on-stream steps, dragged out
hexavalent chromium is recovered from the rinse water and retained on
the anion resin bed.
During the regeneration step, caustic is pumped through the anion bed,
carrying out the hexavalent chromium as sodium dichromate. This
sodium dichromate stream then passes through the second cation bed,
which is in the hydrogen form. This converts the sodium chromate to
chromic acid, which is concentrated by evaporation and returned to the
plating bath. Meanwhile, the first cation bed is regenerated with
sulfuric acid, resulting in a waste acid stream containing the
metallic impurities removed earlier. The second cation bed is
177
-------
CO
1 , IlilUTt HtMi.t H!l
I1IMMI PI.ATL
HI Mil
L.
FIGURE 7-16 CHROMIC ACID RECOVERY BY CYCLIC OPERATION ION EXCHANGE
-------
regenerated later, during the next rinse purification step, with
sulfuric acid. This results in a stream of waste sodium sulfate.
Flushing with water completes the cycle. Water is backflushed through
the second cation bed and then through the anion bed. This carries
excess caustic back into the caustic supply reservoir which is then
refilled with concentrated caustic. The first cation bed is flushed
separately to remove sulfuric acid as a waste stream. Thus, the rinse
water is purified, and chromic acid is recovered.
A similar approach is applied to nickel plating. Water from the first
stage of the countercurrent rinse is pumped through a cation bed, an
anion bed, and back to the final rinse stage as purified water. The
cation bed recovers nickel from the rinse water. The anion bed
removes organics, chlorides, bromides, and sulfates. During the
following regeneration step, sulfuric acid is passed through the
cation bed, and caustic is passed through the anion bed. The sulfuric
acid is supplied from a dilute acid reservoir and exchanges hydrogen
for nickel as it passes through the cation bed so that a mixture of
sulfuric acid and nickel sulfate emerges from the bed. Meanwhile, the
caustic flowing through the anion bed exchanges its hydroxyl group for
sodium so that the effluent from the bed contains sodium sulfate and
also any organics, chlorides, and bromides. The effluent, which
contains only traces of heavy metals is neutralized and discharged.
The nickel sulfate effluent resulting from regeneration of the cation
bed may possibly be returned directly to the plating bath, but it is
often too acidic because of the sulfuric acid in the mixture. If the
bed acidity is too high, it is processed through a second anion bed
which removes the sulfuric acid before being returned to the plating
bath. This second anion bed must later be regenerated with caustic,
resulting in additional waste sodium sulfate. The flushing step
follows regeneration. Both the cation and the anion beds are flushed
with water. Residual sulfuric acid in the cation bed is flushed back
into a reservoir to which concentrated sulfuric acid is adddd.
Residual caustic in the anion bed is flushed to waste treatment and
discharged. Thus, on an overall basis, the system recovers nickel
from the rinse water and returns it to the plating bath.
Other Approaches - Continous approaches to ion exchange are being
developed to avoid the complexity or inconvenience of cyclic systems.
In one of these, the resin is embedded in a fluid-transfusible,
polyester belt. The continuous belt passes through a compartmented
tank with adsorption, wash, and regeneration sections. Wastewater
flows in one end of the baffled adsorption section and out the other,
with the resin belt running through it in a generally countercurrent
direction. The belt is then spray washed before entering the
regeneration section, where it is sprayed with an appropriate liquid
regenerant as it passes through successive compartments. The
179
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serpentine path of the belt gives it maximum exposure to the
wastewater and regenerant.
The system can be used either for recovery of plating chemicals from
rinse water or for removal of impurities from plating solutions. In
one instance of the latter application, the following performance is
claimed for a hard chromium plating bath:
Concentration, mg/1
Impurity Inlet Outlet
Copper 100 0
Iron 3000 100
Trivalent
Chromium 5500 0
Fluidized bed ion exchange systems are under development in both the
United States and Canada, with the Canadian system targeted for
electroplating applications. However, information on this system was
not available for inclusion in this document.
Advantages and Limitations
Ion exchange systems are compact, relatively inexpensive, and can
often be installed with little or no production interruption.
However, treatment of wastes by ion exchange is complicated by the
presence of materials or conditions which may clog, attack, or foul
resins. Most current synthetic resins resist serious chemical or
thermal attack. High concentrations of oxidizing agents, such as
nitric acid, can attack these resins at vulnerable cross-links.
Regarding temperature stability, most resins are stable to 100 degrees
C or higher.
The selectivity characteristics of exchangers can often be exploited
by employing specially prepared resins. Even the separation of
similar ions has been achieved, notably the separation of the rare
earth metals by taking advantage of their dissimilar complexing
characteristics in solution. The major disadvantages of a high degree
of selectivity in an exchange reaction are the tight bonds formed and
poor regeneration characteristics.
Finally in a fixed bed packed column, excessive settleable or
suspended solids will cause a rapid and excessive pressure loss,
significantly reducing operating efficiency.
180
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Performance
Ion exchange is highly efficient at recovering plating chemicals, A
chromic acid recovery efficiency of 99.5 percent has been demonstrated
by the cyclic operation system. Company 32619 claims this has reduced
their chromic acid purchases by 75 percent (an annual saving of more
than $3,800 in chromic acid) and company 61001 claims a 90 percent
reduction (an annual saving of more than $20,000 in chromic acid). At
Company 61001, hexavalent chromium in the discharge regenerant from
the chromic acid recovery ion exchange system was nondetectable.
With regard to purification of the rinse water, the following data
have been reported for the "replacement service" system:
Raw Wastewater Treated Wastewater
Contaminant Concentration, mg/1 Concentration, mq/1
Aluminum 5.60 0.24
Cadmium 1.05 0.00
Chromium 7.60 0.06
Copper 4.45 0.09
Iron 3.70 0.10
Nickel 6.20 0.00
Silver 1.50 0.00
Tin 0.50 0.00
Cyanide 0.80 0.20
Sulfate 21.0 2.0
Phosphate 3.75 0.80
181
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Demonstration Status
Eleven of 196 plants in the electroplating data base employ ion
exchange as part of or all of their waste treatment system (ID's 5050,
1108, 11065, 12065, 2017, 2021, 31050, 33009, 40004, 40061, and
61001).
EVAPORATION
Definition of_ The Process
Evaporation is a concentration process. Water is evaporated from a
solution, increasing the concentration of solute in the remaining
solution. If the resulting water vapor is condensed back to liquid
water, the evaporation-condensation process is called distillation.
However, to be consistent with industry terminology, evaporation is
used in this report to describe both processes.
Both atmospheric and vacuum evaporation are used in the electroplating
industry. Atmospheric evaporation could be accomplished simply by
boiling the liquid. However, to lower the evaporation temperature,
the heated liquid is sprayed on an evaporation surface, and air is
blown over this surface and then released to the atmosphere. Thus,
evaporation occurs by humidification of the air stream, similar to a
drying process.
For vacuum evaporation, the evaporation pressure is lowered to cause
the liquid to boil at reduced temperature. All of the water vapor is
condensed and, to maintain the vacuum condition, noncondensible gases
(air in particular) are removed by a vacuum pump. Vacuum evaporation
may be either single or double effect. In double effect evaporation,
two evaporators are used, and the water vapor from the first
evaporator (which may be heated by steam) is used to supply heat to
the second evaporator, condensing as it does. Roughly equal
quantities of waste water are evaporated in each evaporator; thus, the
double effect system evaporates twice the water that a single effect
system evaporates, at nearly the same cost in energy but with added
capital cost and complexity. The double effect technique is
thermodynamically possible because the second evaporator is maintained
at lower pressure (higher vacuum) and, therefore, lower evaporation
temperature. Another means of increasing energy efficiency is vapor
recompression (thermal or mechanical), which enables heat to be
transferred from the condensing water vapor to the evaporating waste
water. Vacuum evaporating equipment may be classified as submerged
tube or climbing film.
In the most commonly used submerged tube evaporator, shown in Figure
7-17B, the heating and condensing coils are contained in a single
vessel to reduce capital cost. The vacuum in the vessel is maintained
182
-------
by an eductor-type pump, which creates the required vacuum by the flow
of the condenser cooling water through a venturi. Wastewater
accumulates in the bottom of the vessel, and it is evaporated by means
of submerged steam coils. The resulting water vapor condenses as it
contacts the condensing coils in the top of the vessel. The
condensate then drips off the condensing coils into a collection
trough that carries it out of the vessel. Concentrate is removed from
the bottom of the vessel.
The major elements of the climbing film evaporator are the evaporator,
the separator, the condenser, and the vacuum pump. As shown in Figure
7-17C, wastewater is "drawn" into the system by the vacuum so that a
constant liquid level is maintained in the separator. Liquid enters
the steam-jacketed evaporator tubes, and part of it evaporates so that
a mixture of vapor and liquid enters the separator. The design of the
separator is such that the liquid is continuously circulated from the
separator to the evaporator. The vapor entering the separator flows
out through a mesh entrainment separator to the condenser, where it is
condensed as it flows down through the condenser tubes. The
condensate, along with, any entrained air, is pumped out of the bottom
of the condenser by a liquid ring vacuum pump. Thus, the liquid seal
provided by the condensate keeps the vacuum in the system from being
broken.
Advantages and Limitations
Some advantages of the evaporation process are:
1. It permits recovery of a wide variety of plating and other
process chemicals.
2. The water recovered from the evaporation process is of high
purity. This process can be used to convert waste effluent
to pure or process water where other water supplies are
inadequate or nonexistent.
3. The evaporation process may be applicable for removal and/or
concentration of waste effluent which cannot be accomplished
by any other means.
Some limitations or disadvantages of the evaporation process are:
1. In general, the evaporation process consumes relatively large
amounts of energy for the evaporation of water. However, the
recovery of waste heat from many industrial processes (e.g.,
diesel generators, incinerators, boilers and furnaces) should
be considered as a source of this heat for a totally
integrated evaporation system.
183
-------
PACKED TOWiCH
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-------
2. For some applications, pretreatment may be required to remove
solids and/or bacteria which tend to cause fouling in the
condenser or evaporator.
3. The buildup of scale on the evaporator plates reduces the
heat transfer efficiency and may present a maintenance
problem or increase operating cost. However, it has been
demonstrated that fouling on the heat transfer surfaces can
be avoided or minimized for certain dissolved solids by
maintaining a seed slurry which provides preferential sites
for precipitate deposition. In addition, low temperature
differences in the evaporator will eliminate nucleate boiling
and supersaturation effects.
4. Steam distillable impurities in the process stream are
carried over with the product water and must be handled by
pre or post treatment if they cannot be tolerated,
Application to Electroplating
Evaporators are used primarily to concentrate and recover plating
solutions, as shown in Figure 7-18. Many of these evaporators also
recover water for rinsing. However, there are at least two electro-
plating installations (establishments 1108 and 30069) where the
evaporation system is designed to evaporate end-of-pipe wastewater to
near dryness.
Table 7-9 summarizes the application of evaporation to electroplating.
The tabulated values are based mainly on a survey of evaporator
manufacturers. The first flash evaporation unit was installed in
1949, and the data base for this project confirms that it is the most
common type.
There is no fundamental limitation on the applicability of
evaporation. There are, however, certain practical limitations for
most types. For example, climbing film evaporation is used for acid
copper plating solutions but not for cyanide copper because the
materials of construction in current use are appropriate only for
acidic conditions. However, both atmospheric and submerged tube
evaporators are used for cyanide copper, and there is no reason why
climbing film evaporation could not be used after a suitable change in
construction materials.
185
-------
OVERFLOW
PARTS
PLATING
BATH
FIRST
RINSE
LAST
RINSE
1 : f
1 j OVERFLOW
I 1
PARTS
CONCENTRATE
EVAPORATOR
HEAT SOURCE |
CO
CTs
WATER VAPOR ^
TO ATMOSPHERE
IF NONCONDENSING
SYSTEM
|
COOLING
WATER
CONDENSER
CONDENSATE
FK31H?E 7-18 APPLICATION OF EVAPORATION TO METAL FINISHING
-------
TABLE 7-9
APPLICATION OF EVAPORATION
TO THE ELECTROPLATING POINT SOURCE CATEGORY
Number in Operation (Additional Units Ordered)
Application
Chromium Plating
Nickel Plating
Copper Plating
Cadmium Plating
Zinc Plating
Silver Plating
Brass or Bronze
Plating
Other Cyanide
Plating
Chromic Acid
Etching
End-of-Pipe
Other, Unknown
Atmospheric
Submerged
Tube
21
6
2
(3)
(1)
(2)
14
9
5
4
6
7
- (1)
Climbing
Film
8
1
Flash
7_*
56*
Wiped
Film
4 (1)
1 (1)
14*
*Estimated by manufacturer
187
-------
Performance
In theory, evaporation should yield a concentrate and a deionized
condensate. Actually, carry-over has resulted in condensate metal
concentrations as high as 10 mg/1, although the usual level is less
than 3 mg/1, pure enough for most final rinses. The condensate may
also contain organic brighteners and antifoaming agents. These can be
removed with an activated carbon bed, if necessary. Samples from
plant ID 61001 showed 1,900 mg/1 zinc in the feed, 4,570 mg/1 in the
concentrate, and 0.4 mg/1 in the condensate. Plant ID 33065 had 416
mg/1 copper in the feed and 21,800 mg/1 in the concentrate. Chromium
analysis for the plant indicated 5,060 mg/1 in the feed and 27,500
mg/1 in the concentrate. Evaporators are available in a range of
capacities, typically from 15 to 75 gph. Units may be used in
parallel arrangements for higher rates.
Demonstration Status
Evaporation is used for treatment in 12 plants in the 196 plant data
base for this study (Reference Table 7-10).
REVERSE OSMOSIS
Definition of the Process
Osmosis is the passage, through a semipermeable membrane, of a liquid
from a dilute to a more concentrated solution. The transfer from one
side of the membrane to the other continues until the head (pressure)
is large enough to prevent any further transfer of water to the more
concentrated solution.
In reverse osmosis (RO), pressure is applied to the more concentrated
solution side of the semipermeable membrane causing the permeate to
diffuse through the membrane in the direction opposite to the osmotic
pressure. The concentrated solution of dissolved solids left behind
can be further treated or returned for reprocessing.
Process Equipment
In commercially available RO Systems, three basic modules are used:
the tubular configuration, the spiral-wound, and the hollow fiber.
Each, however, works on the same RO principle, the only difference is
how the various membrane structures are mechanically designed and
supported to take the operating pressures.
188
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TABLE 7-10
ELECTROPLATING PLANTS THAT EMPLOY EVAPORATION
301
304
637
6050
1108
1903
2024
20064
20069
20073
33065
38050
TABLE 7-11
APPLICATION OF REVERSE OSMOSIS
IN THE ELECTROPLATING POINT SOURCE CATEGORY
Application
Acid Nickel
Acid Zinc
Acid Copper
Palladium Chloride-
Ammonium Chloride
Mixed Plating Wastes
Number in Operation
(Additional Units Ordered)
Spiral Wound
68
3
3
1
Hollow Fiber
189
-------
Hollow fiber modules consist of polyamide fibers, each having approxi-
mately 0.0076 cm (3 mils) OD with about 0.0043 cm (1.7 mil) ID. A
typical RO module will contain several hundred thousand of these
fibers in a long tube. The fibers are wrapped around a flow screen
which is then rolled into a spiral. Each end of the roll is potted in
epoxy. The module consists of lengths of the fiber membrane bent into
a U - shape with their ends supported by the epoxy. Feed water, under
28.2 atm (400 psi), is brought into the center of the module through a
porous distributor tube where it flows through the membrane to the
inside of the fibers and from there to the end where it is collected.
The concentrate is returned to the process or to further treatment.
Tubular membrane systems use a cellulose acetate membrane-lined porous
tube. In a typical tube system, a length of 2.54 cm (1 in) diameter
tube is wound on a support spool and enclosed within a plastic shroud.
Feed water is driven into the tube at approximately 55.4 atm (800
psi). Permeate which passes through the walls of the coiled tube is
collected and drained off for use. Another type of system module
employs this principle in a straight tube within a housing.
Spiral-wound flat sheet membranes consist of a porous backing material
sandwiched between two membranes and glued along three edges. The
fourth edge of the "bag" is bonded to a product collection tube. A
spacer screen is placed on top of the bag, and the whole unit is
rolled around the central product collection tube. The spiraled unit
is then placed inside a pipe capable of supporting the feed water
pressure. In operation, the product water under pressure will
permeate the membrane and travel through the backing material to the
central product collection tube. The concentrate, containing
dissolved solids, is then drained, returned to the process, or fed to
further treatment facilities.
Advantages claimed for the hollow fiber and spiral-wound membranes
over the tubular-wound system include an ability to load a large
surface area of membrane into a relatively small volume. On the other
hand, with regard to fouling tendencies, the tubular system is less
susceptible to fouling than the others because of its larger flow
channel. Although all three systems theoretically can be chemically
regenerated, it can be very difficult to remove deposits from the
hollow fiber and spiral-wound membrane types. One manufacturer claims
that their helical tubular module can be physically wiped clean by
passing a soft porous polyurethane plug under pressure through the
module.
In selecting reverse osmosis devices for use in treatment of
wastewater, the effect of temperature on any reverse osmosis device is
significant. As water temperature increases, visocosity of water
decreases, and the semipermeable membrane passes more water,
approximately 3 percent per degree centrigrade. Therefore, the
190
-------
capacity is a straight line function of temperature. However,
pollutant permeability is also increased so that water quality remains
essentially constant. Membrane systems are usually rated at 20
degrees C (68 degrees F), and wastewater temperature should be
considered in sizing a RO unit.
Advantages and Limitations
Some advantages of reverse osmosis for handling process effluent are:
1. Ability to concentrate dilute solutions for recovery of salts
and chemicals.
2. Ability to sufficiently purify water for reuse.
3. Ability to operate under low power requirements (no latent
heat of vaporization or fusion is required for effecting
separations; the main energy requirement is for a high
pressure pump).
4. Operation at ambient temperature, i.e., about 15.5 to 32.2
degrees C (60 to 90 degrees F).
5. Relatively small floor space requirement for compact high
capacity units.
Some limitations or disadvantages of the reverse osmosis process for
treatment of process effluents are:
1. Limited temperature range for satisfactory operation. (For
cellulose acetate systems, the preferred limits are 18.3 to
29.4 degrees C (65 to 85 degrees F); higher temperature will
increase the rate of membrane hydrolysis and reduce system
life, while lower temperature will result in decreased fluxes
with no damage to the membrane).
2. Inability to handle certain solutions (strong oxidizing
agents, solvents, and other organic compounds can cause
dissolution of the membrane).
3. Poor rejection of some compounds (such as borates and
organics of low molecular weight exhibit poor rejection).
4. Fouling of membranes by slightly soluble components in
solution.
5. Fouling of membranes by feed waters with high levels of sus-
pended solids (such feed must be amenable to solids
separation before treatment by reverse osmosis).
191
-------
6. Inability to treat highly concentrated solutions (some con-
centrated solutions may have initial osmotic pressures which
are so high that they either exceed available operation pres-
sures or are uneconomical to treat).
7. Normally requires pretreatment to achieve adequate life.
Application to Electroplating
Reverse osmosis is used to close the loop as shown in Figure 7-19A.
Countercurrent rinsing is used to reduce the quantity of rinse water.
Overflow from the first rinse tank, contaminated with drag-out from
the plating bath, is pumped to the reverse osmosis unit. The reverse
osmosis unit separates the influent rinse water into two streams, one
containing a much higher concentration of dragged out plating
chemicals (the concentrate) and the other containing a much lower
concentration (the permeate). The concentrate is returned to the
plating bath, replacing evaporated water and dragged out chemicals.
The permeate goes to the last rinse tank, providing water for the
rinsing operation. Rinse water flows from the last rinse tank to the
first rinse tank, either directly or through intermediate rinsing
stages.
Reverse osmosis has limited concentrating ability and, therefore, the
system shown in Figure 7-19B may be required to reduce the concentrate
volume. In this approach, the reverse osmosis concentrate is further
concentrated by means of vacuum evaporation. The vapor may be vented
through a scrubber, condensed and returned to the last rinse tank, or
condensed, treated, and discharged. An alternative variation is to
increase plating bath evaporation rate, making room for the reverse
osmosis concentrate.
The cellulose acetate units have been applied mainly to nickel
plating, and their success in that application is proven. However,
the acetate membrane is limited to a relatively narrow pH range. The
polyamide has a broader pH tolerance, but it has been applied mainly
to mixed plating water and has, for the most part, failed due to
plugging in that application. Thus, use of reverse osmosis in other
applications is certainly possible but not thoroughly demonstrated.
Table 7-11 indicates the application of reverse osmosis to electro-
plating. The spiral wound membranes in current use are cellulose
acetate, which degrades under alkaline conditions. Hollow fiber
reverse osmosis may be used under the alkaline conditions in cyanide
plating baths, but consistent performance has not yet been
demonstrated. A totally new membrane now being tested for application
to cyanide plating baths shows great promise. Designated NS-100, the
membrane consists of polyethyleneimine crosslinked with tolylene-2, 4-
diisocyanate on a polysulfone support. This membrane is claimed to
192
-------
EVAPORATION
OVERFLOW
PARTS
FIGURE 7- 19 A
PARTS
EVAPOR
CONCENT
FIGURE 7-19 B
t f !
PLATING
EaTH
1
1
i
1
1
[CONCENTRATE
MINIMAL
EVAr. .RATION
PLAfING
BATH
FIRST
RINSE
LAST PA^L
"^ RINSE
1 A
1 OVERFLOW
f
REVERSE
OSMOSIS
SYSTEM
PERMEATE_ j
OVERFLOW
r* — - — ,
1 1
FIRST
RINSE
^ LAST . PA^r
RINSE
ATOR f | "
RATE 1 REVERSE i OVERFLOW
I OSMOSIS '
1 CONCENTRATE f
EVAPORATOR
1
1
T
VAPOR
i
REVERSE
OSMOSIS
SYSTEM
PERMEATE
FIGURE 7-19 APPLICATION OF REVERSE OSMOSIS ALONE AND
WITH SUPPLEMENTAL EVAPORATION
-------
exhibit excellent stability and excellent reverse osmosis performance
for feed solutions with the pH ranging from less than 1 to 13.
The overwhelming application of reverse osmosis is for the recovery of
nickel plating solutions. It appears to apply equally to other acid
metal baths and to mixed plating wastes if the pH is not too high.
Misapplication of RO can cause many failures and complete
dissatisfaction; however, proper application preceded by sufficient
testing has demonstrated the usefulness of RO under specific
conditions.
Performance
In considering reverse osmosis, the electroplater needs to estimate
how much of the feed water will emerge as concentrate and how pure the
permeate will be. These values may be determined from the "recovery"
and "percent ejection", which are two of the parameters customarily
used to describe reverse osmosis performance.
The recovery is the permeate flow rate expressed as a percentage of
the feed flow rate. Thus, if F is feed flow rate, P is permeate flow
rate, and R is recovery,
R = (P/F) x 100
and the concentrate flow, C, is
C = F-P = F - (FR/100)
Recoveries of 90 percent are usually attained, and 95 percent is
generally practical. Higher recoveries can often be achieved by
staging two reverse osmosis units.
Percent rejection is defined as
r = (CAV-CP) / (CAV/100)
where CAV may be approximated by (CF + CO /2, and CF is the concen-
tration of the constituent in question in the feed, CC is the concen-
tration in the concentrate, and CP is the concentration in the
effluent permeate. Substitution and rearrangement yields the
concentration of the constituent in the permeate.
CP = (CF + CO/2 - r (CF + CO/200
The concentration in the concentrate is estimated by making a system
materials balance assuming that all of the constituent ends up in the
concentrate.
194
-------
This procedure may be illustrated by considering a Watts nickel line
with a two-stage countercurrent rinse. The rinsing rate is 150 gpd,
and the concentration in the first rinse is 1,200 mg/1. Table 7-12
shows typical rejection values for reverse osmosis. Assuming a
recovery of 90 percent and a rejection for nickel from Table 7-12 of
99 percent, the foregoing equations can be solved. The result is a
concentrate rate of
C - F - FR/100 = 150 - (150)(90)/100 - 15 gpd
The concentration of nickel in the concentrate is then
approximately
C « 1,200 (150/15) = 12,000 mg/1
The concentration of nickel in the permeate is then
approximately
CP « (CF + CO/2 - r(CF + CO/200
99 (1,200 + 12,000)/200 - 66 mg/1
(1,200 + !2,000)/2 -
Permeate rate will be 150 - 15 « 135 gpd, and 15 gpd makeup rinse
water will, therefore, be required. The concentrate is strong enough
to return to the plating bath, the permeate is clean enough for
rinsing in an intermediate plating operation, and the evaporation rate
of 15 gpd is typical. For comparison, analysis of samples taken
during the survey
195
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TABLE 7-12
TYPICAL MEMBRANE PERFORMANCE
Ion
Aluminum
Ammonium
Cadmium
Calcium
Copper
Iron
Magnesium
Manganese
Mercury
Nickel
Potassium
Silver
Sodium
Zinc
Bicarbonate
Borate
Chloride
Chromate
Cyanide
Ferrocyanide
Fluoride
Nitrate
Phosphate
Sulfate
Sulfite
Thiosulfate
Percent
Reject ion
99 +
88-95
96-98
96-98
98-99
98-99
96-98
98-99
96-98
98-99
94-96
94-96
94-96
98-99
95-96
35-70
94-95
90-98
90-95
99 +
94-96
93-96
99 +
99 +
98-99
99 +
Maximum Concentrate
Concentration of the In
dicated Ion, Percent
5-10
3-4
8-10
*
8-10
*
*
*
-
10-12
3-4
*
3-4
10-12
5-8
-
3-4
8-12
4-12
8-14
3-4
3-4
10-14
8-12
8-12
10-14
*Depends on other ions present
196
-------
visit to Company 33065 showed 20,700 mg/1 of nickel in the concentrate
and 81 mg/1 in the permeate.
The preceding calculation approach determines the effect of
integrating a reverse osmosis unit into a plating line.
Demonstration Status
Seven electroplating plants in the data base of 196 plants employ
reversis (ID's 808, 1122, 1203, 1302, 3305, 33065, and 38050).
ULTRAFILTRATION
Definition o_f_ the Process
Ultrafiltration (UF) is a process using semipermeable polymetric
membranes to separate molecular or colloidal materials dissolved or
suspended in a liquid phase when the liquid is under pressure. The
membrane of an ultrafilter forms a molecular screen which separates
molecular particles based on their differences in size, shape, and
chemical structure. The membrane permits passage of solvents and
lower molecular weight solutes while barring dissolved or dispersed
molecules above a predetermined size. At present, an ultrafilter is
capable of separating materials with molecular weights in the range of
5,000 to 100,000.
Process Equipment
In an ultrafiltration process, the feed solution is pumped through a
tubular membrane unit. Water and some low molecular weight materials
pass through the membrane under the applied pressure. Emulsified oil
droplets and suspended particles are retained, concentrated, and
removed continuously. In contrast to ordinary filtration, retained
materials are washed off the membrane filter rather than held by the
filter.
The pore structure of the membrane acts as a filter, passing small
particles, such as salts, while blocking larger emulsified and
suspended matter. The pores of ultrafiltration membranes are much
smaller than the blocked particles. Therefore, these particles cannot
clog the membrane structure.
Once a membrane is chosen that provides maximum attainable removal of
the desired particles, the next most important design criterion is the
membrane capacity. Here the term flux is used. Flux is the volume of
water passed through the membrane area per unit time. The standard
units are cu m/day/sq m (gpd/sq ft). Both membrane equipment and
operating costs increase with the membrane area required. It is,
therefore, desirable to maximize flux.
197
-------
Membrane flux is normally dependent on operating pressure,
temperature, flux velocity, solids concentration (both total dissolved
solids and total suspended solids), membrane permeability, membrane
thickness, and fluid viscosity. Membrane flux is also affected by the
hydrophilic nature of the solution being processed. With a fixed
geometry, membrane flux will increase as the fluid velocity is
increased in the system. This increase in fluid velocity will require
greater pumping capacity and more horsepower. Less membrane area is,
therefore, required per unit of effluent to be treated with higher
fluid velocities so the membrane replacement and initial capital costs
decrease. Opposing these cost decreases is the increase in power and
its attendant cost.
Advantages and Limitations
Ultrafiltration is sometimes an attractive alternative to chemical
treatment because of the following major advantages:
1. Lower capital equipment, installation, and operating costs.
2. Insensitivity to the chemical nature of influent wastes.
3. Very high oil removal efficiency, independent of influent oil
content
4. No chemical additions required.
5. No oily sludge generated.
6. Little, if any, pretreatment required.
7. Concentrated waste can be incinerated and may be self
sustaining.
8. Very compact; utilizes small amount of floor space.
9. Provides a positive barrier beteeen oil and effluent. This
eliminates the possibility of oil discharge which might occur
due to operator error.
Some limitations or disadvantages of ultrafiltration for treatment of
process effluents are:
1. Limited temperature range (18 to 30 degrees C) for
satisfactory operation. Membrane life is decreased with
higher temperatures, but flux increases at elevated
temperatures. Therefore, surface area requirements are a
function of temperature and become a tradeoff between initial
costs and replacement costs for the membrane.
198
-------
2. Inability to handle certain solutions. Strong oxidizing
agents, solvents, and other organic compounds can cause
dissolution of the membrane.
3. Poor rejection of some compounds.
4. Fouling of membranes by slightly soluble components in
solution.
Application to Electroplating
There is an increasing acceptance of ultrafiltration as a proven
technique for the removal of oily or paint • contaminated wastes from
the process effluent stream. This permits reuse of both the permeate
and concentrate. Ultrafiltration of the effluent obtained from
electrocoating (electropainting) which has developed over the past
three years, provides an excellent example of this process. Most of
the automotive manufacturers and many other U.S. companies use
electropainting for priming purposes. In this application, the
ultrafiItration unit splits the electropainting rinse water
circulating through it into a permeate stream and paint concentrate
stream. The permeate is reused for rinsing, and the concentrate is
returned to the electropainting bath. Application to electropainting
has allowed many plants to increase solids to 15 percent from the
previous 8-10 percent levels.
Bleeding a small amount of the ultrafiltrate, which contains no
suspended solids and generally two or three percent of organic solids,
to the waste system enables ionic contaminants to be recovered from
the paint itself. Situations where tanks of 150,000 to 190,000 liters
(40,000 to 50,000 gallons) of paint were periodically dumped because
of contamination have now been eliminated by using ultrafiltration,
thus reducing effluent problems arising from this dumping process.
The economics of the recovery of high priced paint have allowed many
industrial ultrafiltration plants to be paid off in as little as six
to nine months, and this has fostered rapid acceptance of
ultrafiItration within the industry.
Performance
The most common applications of ultrafiltration demonstrate the
following performance:
Application Percent Removal Demonstrated
Removal of Paint Solids 100%
Removal of Cutting Oils and
199
-------
•o
Emulsified Oil Coolants 99%
Removal of Particulate Matter 100%
Removal of Detergents 99%
Removal of Inks and Dyes 100%
Removal of Total Solids 95%
pH and other conditions affect attainment of the removal percentages
shown.
The permeate or effluent from the ultrafiltration unit is normally of
a quality that can be reused in industrial applications or discharged
directly. The concentrate from the ultrafiltration unit can be
disposed of readily by incineration or by contract hauling. If
incineration is employed, additional fuel is not required because the
concentrated emulsion will support combustion. If contract hauling is
used, the cost is lowered because the waste volume is small, and a
usable product is available to the contractor.
Demonstration Status
Two plants in the 196 plant electroplating data base employed
ultrafiltration (ID's 907 and 3334).
MEMBRANE FILTRATION
Definition of_ the Process
The membrane filtration end-of-pipe treatment system is a combination
of a special chemical destruction technique and a special membrane
filter for effluent clarification. Thus, chromium reduction, cyanide
oxidation, and pH adjustment for precipitation are still required.
The first unique feature of this system is a proprietary chemical
added to the pH adjustment tank every few months. This chemical is
not consumed, but causes the metal hydroxide precipitate to be
nongelatinous, easily dewatered, and highly stable. The second
feature of the system is the membrane filter modules through which the
pH-adjusted water is pumped. These modules are similar to
ultrafiltration modules, but the membrane pores are larger. The water
that permeates these membranes is nearly free of the precipitate.
Process Equipment
Chromium reduction, cyanide oxidation, and pH adjustment equipment are
standard. Additional equipment consists of a pump, and a set of
filter modules. As shown in Figure 7-20, the contents of the tank are
200
-------
continuously recirculated through the filter module at 15 psig. Each
of these modules contains 13 tubular membranes. Purified water
permeates these membranes and is continuously withdrawn from the
system for discharge.
Thus, a wastewater-precipitate mixture is continuously added to the
system, and purified water is continuously withdrawn, resulting in a
steady increase in solids concentration in the recirculating
wastewater. When the solids content reaches about 15 percent, the
sludge valve at the discharge of the recirculating pump is opened, and
the contents of the recirculating tank are discharged for direct
landfill or dewatering and landfilling.
Advantages and Limitations
The four major advantages of the membrane filtration system are:
1. Installation can utilize most of a conventional end-of-pipe
system that is already in place.
2. Complexed metals can be removed with high efficiency.
3. The sludge is highly stable in alkaline conditions.
4. Removal efficiencies are excellent, even with widely varying
pollutant input rates.
The only disadvantage is that the cost of a membrane filter is
approximately 20 percent greater than a clarifier, which is the only
component of a conventional system that the membrane filter replaces.
Application to_ Electroplating
The membrane filtration system may be used in a new plant or it may be
used in an existing plant in place of the clarifier to reduce
pollutant discharge.
Performance
Flux for the membrane is 500 to 800 gallons per square foot per day.
The manufacturer claims the following effluent concentrations are
achievable regardless of influent concentration:
Wastewater Effluent
Constituent Concentration, mg/1
Aluminum 0.5
Chromium, hexavalent 0.03
Chromium, trivalent 0.02
201
-------
STANDARD BPT PRETREATMENT
CHROMIUM-
CONTAINING
WASTEWATER
OTHER
CHROME
'REDUCTION
WASTEWATER
CYANIDE-
CONTAINING
EQUALIZATION
TANK
WASTEWATER
L
CYANIDE
OXIDATION
pH
ADJUSTMENT
REAGENT
TANK
PERIODIC
REAGENT
ADDITION
ro
o
r\>
PURIFIED
_L
MEMBRANE
FILTER MODULES
WASTEWATER
RECIRCULATION
TANK
PERIODIC
•"—SLUDGE
WITHDRAWAL
FIGURE 7-20 APPLICATION OF MEMBRANE FILTRATION TO METAL
FINISHING WASTEWATER
-------
Copper
Iron
Lead
Cyanide
Nickel
Zinc
0.1
0.1
0.05
0.02
0.1
0.1
These claims are largely substantiated by the following analysis
composite samples taken during this project at Company ID 19066:
of
Wastewater
Constituent
Concentration,
Recirculation Tank
Influent
mg/1
Membrane Filter
Effluent
than 0.
0.
0.
4.
18.
22.
9.
0.
0.
2.
632.
005
007
46
13
8
0
56
652
333
09
0
Less
Less
Less
Less
than
than
than
than
0.
0.
0.
0.
0.
0.
22.
0.
0.
0.
0.
0.
005
158
005
010
018
043
0
017
01
200
046
01
Cyanide, Total Les
Phosphorus
Cadmium
Chromium, hexavalent
Chromium, total
Copper
Fluorides
Nickel
Lead
Tin
Zinc
Total Suspended Solids
In addition, tests carried out by one electroless plater show that the
system is also effective in the presence of strong chelating agents
such as EDTA, but continuous addition of the chemical reagent is
required. In particular, laboratory bench scale and pilot studies
have been conducted on several waste streams.
a. Tin and lead waste containing thiourea copper complexes were
tested on a pilot unit for over 200 hours with no flux
deterioration and with tin, lead and copper all less than 0.1
mg/1 in the process water.
b. Cupro-ammonia complex rinse from alkaline etching was treated
in the pilot unit for 400 hours with no flux deterioration
and with copper in the effluent less than 0.1 mg/1.
Based on this laboratory pilot study, a 1 gpm pilot test was
run in a printed circuit board manufacturing facility. Over
a 200 hour period, the flux was always in excess of 1.1 gpm.
The copper was consistently below 0.5 mg/1 and usually at 0.1
mg/1, even with a varying concentration of copper in the
feed.
203
-------
c. Preliminary runs with electroless copper rinse waters have
yielded product water in the range of 0.1 mg/1.
Another aspect of performance are leaching characteristics of the
sludge. The state of South Carolina approved the sludge for landfill
provided that an alkaline condition be maintained. This decision was
based on tests carried out by the state in which metals were extracted
from the sludge with nitric acid at various conditions of pH. Even at
the slightly acid pH of 6.5, leachate from a sludge containing 2,600
mg/1 of copper and 250 mg/1 of zinc contained only 0.9 mg/1 of copper
and 0.1 mg/1 of zinc.
Demonstrated Status
Only one plant (ID 19066) employed membrane filtration in the 196
plant electroplating data base for this study. However, there are a
total of 15 fully operational units, 6 of these are treating chelated
metal wastewaters with reportedly good performance.
ELECTROCHEMICAL RECOVERY
Two processes for electrochemical recovery ( electrolytic recovery and
electrodialysis) are discussed here. A conventional version and an
advanced version of each process is reviewed. Following the
Definition of Process Subsection, the four versions (conventional and
advanced electrolytic recovery and electrodialysis) are covered
individually.
Definition of the Process
Electrolytic recovery is a process in which there is electrochemical
reduction of metal ions at the cathode where these ions are reduced to
elemental metal. At the same time, there is evolution of oxygen at
the anode. Electrolytic recovery is used primarily to remove metal
ions from solutions.
Electrodialysis is a process in which dissolved colloidal species are
exchanged between two liquids through selective semipertneable
membranes. An electromotive force causes separation of the species
according to their charge, and the semipermeable membranes allow
passage of certain charged species while rejecting passage of
oppositely charged species. Electrodialysis is used primarily to
remove and concentrate dilute solutions of salt and other chemicals
from a waste stream, thereby providing purified water.
Conventional Electrolytic Recovery
Conventional Electrolytic Recovery Equipment - Equipment consists of a
drag-out recovery tank located in the plating line and an electrolytic
204
-------
recovery tank and recirculation pump, remote from the plating line. A
typical electrolytic recovery tank uses stainless steel cathodes of
approximately 15 cm. width upon which the recovered metal is
deposited. After the coating is sufficiently thick (0.6 cm.), the
metal deposited can be peeled off and returned to the refiner, or the
metal plated stainless steel can be used for anodes in the plating
bath.
To get high plating efficiencies, it is desirable that the solution be
reasonably well agitated in the electrolytic cell where the cathode
sheets are in use. The electrolytic recovery tank is designed to
produce high flow rates in a narrow channel.
To avoid buildup of harmful impurities in the recirculated solution,
approximately 20 percent of it should be dumped to waste treatment
each week.
Application of Conventional Electrolytic Recovery - Electrolytic
recovery is used to recover copper, tin, silver, and other metals from
plating and etching bath dragout. Because the electrolytic process
maintains a low concentration of metal in the drag-out recovery
process relative to that in the plating bath, metal drag-over into the
succeeding rinse tank is minimized. This, in turn, minimizes the load
on the waste treatment system and the eventual pollutant discharge
rate.
Performance of_ Conventional Electrolytic Recovery - Performance is
best illustrated by the actual examples tabulated below:
Parameter Tin Plating Silver Plating
Plating Bath Concentration, g/1 81 82
Drag-out Tank Concentration, g/1 1.2 0.2
Drag-out Rate, gph 1.2 0.8
Recovery Efficiency, % 97-99 99.8
Cathode Area, sq. ft. 45 35
Current Density, amp/sq. ft. 5-10 3-5
Current Efficiency, % 70 25-50
Current, amp 240 175
Advanced Electrolytic Recovery
Advanced Electrolytic Recovery Equipment - The extended surface
electrolysis recovery system (ESE) discussed here recovers metal
better at low concentrations than at high concentrations, whereas the
conventional electrolytic recovery system is only good for recovery of
metal at high concentrations. An extended surface electrolytic
recovery unit removes contaminant metals by electroplating them onto a
specially constructed flow-through electrode.
205
-------
The electrolytic processing technique involves reduction of the metal
ions at the cathode to form the elemental metal, with evolution of
oxygen at the anode.
Other cathodic reactions, such as the reduction of ions to produce
hydrogen gas, may also occur depending on the chemical composition of
the streams being treated.
The ESE spiral cell is of sandwich construction containing a fixed
"fluffy" cathode, a porous insulating separator, an anode of
screenlike material and another insulating separator. The anode and
cathode material may vary with the particular effluent stream to be
treated. Typically, cathode material is a fibrous woven stainless
steel mesh with a filament size of 2-5 mils. This sandwich structure
cathode, separator material, and anode are rolled into a spiral and
inserted into a pipe. This type of cell construction results in a
very open structure with a void volume of 93% to 95%, which provides a
low resistance to fluid flow.
A number of cells can be stacked as modules so that a large fraction
of contaminant metals can be recovered from an effluent. The solution
to be treated is pumped in at the top of the module and flows down
through the cells where the metals are plated out on the cathode.
Figure 7-21 shows that, as a copper-containing solution flows through
the cell stack, copper ions are attached to the cathode and deposited
as copper metal, hydroxyl ions are attracted to the anode, and
hydrogen and oxygen gas are given off. The following reactions take
place at the cathode:
Cu-n- + 2e- = Cu
and at the anode:
2(OH-) = H20 + 1/2 02
These reactions take place continuously as the fluid is pumped through
the various cells in the cell stack.
Application of_ Advanced Electrolytic Recovery - Extended surface
electrolysis cells are still in the pilot stage and will be used
commercially to plate out copper, lead, mercury, silver and gold.
This system should provide a very efficient means of removal because
of its low mass transfer requirements, larger electrode surface area
and, because of the construction of the electrodes, increased
electrical efficiency. This unit can be used in conjunction with
conventional electrodialysis or other forms of treatment.
Performance o_f_ Advanced Electrolytic Recovery - Pollutants recovered
by the ESE modules are independent of concentration levels. Under
206
-------
CD
--J
Cu++ + 2e--
•Cu°
DEPOSITED ,H2
COPPER }
/
A
02
"2
2(OH-)
+ 1/202
—
w
Q
O
33
E-i
-------
mass-transfer-limiting conditions, this device will operate as
efficiently at one mg/1 as at 1000 mg/1. The effluent concentration
decreases exponentially with the length of the module and its
available cathode area. Complexing of metals in solution is a problem
in some applications.
The following table shows the level of copper concentrations in waste
achievable, for three influent levels. The final concentrations for
all three cases are less than 1 mg/1.
Solution Concentration, mg/1
At Various Points in a Cell Stack
Untreated After 1 Cell After 2 Cells After 3 Cells After 4 Cells
20.0
45.5
15.5
8.2
15.5
5.6
3.4
5.4
2.8
1.3
2. 1
1.7
0.6
0.9
0.7
With the addition of one more cell in
effluent level would be below 0.05
recirculated back to the rinse tanks.
all three cases, the cell
mg/1. The water can then be
Flow to the ESE unit must be interrupted once a day for approximately
one hour so that the accumulated metals in the cell can be stripped
out by circulating an acidic cleaner through the cell. A schematic
diagram, Figure 7-22, shows how the cell is placed in a plating line.
The graph in Figure 7-23 compares the effect of electrical efficiency
in metals reduction for ESE and planar electrodes.
As indicated by the preceding table, a cell stack is at least 90
percent efficient in removal of metals from solution. A 200 1/min
waste stream containing 50 mg/1 copper requiring a 100:1 concentration
reduction could be treated in a 20 cm diameter ESE unit having 48
inches of active electrode length. The same waste stream treated by
conventional means would require a 120 cm diameter clarifier over 5
meters high. The electrical energy needed to treat this stream in an
ESE cell would approximate the energy expended to drive the rake on a
clarifier.
Cost gjf Advanced Electrolytic Recovery - The installation and
investment of the ESE unit is determined by three factors; the flow
rate of the stream to be treated, the reduction in metal
concentrations to be obtained and the degree to which the metal is
complexed in the solution. The operating costs of the unit depend on
cost of electricity to operate the cells and pumps and on manpower for
operation and maintenance. Comparing ESE with ion exchange on waste
such as acidified copper sulfate, performance of ESE indicates it may
be preferred for low concentrations (around 10 mg/1). However, for
203
-------
ro
O
DEIONIZED V?ATER
FOR REUSE
r
~i
INTERMITTENT CLEANING SYSTEM
ESE
UNIT
~r
I
I
I
^:=:H
D.C.
POWER
SUPPLY
n
WASTEWATER
WASTEVIATER,
HOLDING TANK
i i
,j L
; i
! I
r
i
LEACHATE
TANK
METAL •
FOR SALE!
RECOVERY UNIT
..j
FIGURE 7-22 APPLICATION OF EXTENDED SURFACE ELECTROLYSIS
-------
CATHODE: Cu++ 4- 2e~"
ro
»—*
O
CONVENTIONAL
(PLANAR)
TYPICAL "
ALLOWABLE
EFFLUENTS
TYPICAL
PLATING
BATH
COPPER CONCENTRATION, mg/1
FIGURE 7-23 EFFECT OF CONCENTRATION ON ELECTRICAL
EFFICIENCY IN METALS REDUCTION.
-------
high concentrations (100 to 1000 mg/1), ion exchange appears to be the
least costly technology,
Conventional Electrodi alys i s
Conventional Electrodialysis Process Equipment - Conventional
electrodialysis systems consist of an anode and a cathode separated by
an anion permeable membrane near the anode and a cation permeable
membrane near the cathode. This combination forms anode chamber,
cathode chamber, and center chamber. Upon application of an electric
charge, anions pass from the center chamber to the anode chamber and
cations pass from the center chamber to the cathode chamber. This
decreases concentration of salt in the center chamber.
Figure 7-24 shows the application of a simple electrodialysis cell to
separate potassium sulfate solution (K2S04) into its components.
Practical electrodialysis installations contain from ten to hundreds
of compartments between one pair of electrodes. The application of an
electric charge draws the cations to the cathode and anions to the
anode. Industrial wastewater containing metallic salts enters the
center cell, and the charge takes the positive ions to the cathode and
negative ions to the anode. The result is a significant reduction in
salt concentration in the center cell with an increase in solution
concentrations in the adjacent cells. Thus, the water from the center
of each of three adjacent cells is purified and metal ions are
concentrated in the cathode cell, with sulfates, chlorides, etc.,
concentrated in the anode cell. At the outlet end of the cell stack,
streams are drawn off from the individual cells either as the purified
water or as concentrate for recovery or for further treatment.
Figure 7-25 illustrates the operation of a seven chamber conventional
electrodialysis cell. In large electrodialysis installations, two or
more stacks are linked in series. The dilute effluent from the first
stage is passed through an identical second stage, and so forth, with
the effluent from the final stage reaching the desired concentration.
Application of_ Conventional Electrodialysis - Electrodialysis has been
shown to be an effective method for concentrating rinse waters to a
high percentage of bath strength. Nickel, copper, cyanide, chromic
acid, iron and zinc can be removed from plating wastes by
electrodialysis. The natural evaporation taking place in a plating
bath will often be sufficient to allow electrodialysis to be used to
close the loop without the addition of an evaporator. Electrodialysis
is used to treat spent chromic acid, copper, cyanide and other
solutions. Chromic acid solution containing trivalent chromium, iron,
zinc, copper, etc., enters the anode compartment of the
electrodialysis cell, where the application of an electrical potential
causes the copper, zinc, and trivalent chromium to pass through the
cation permeable membrane to the catholyte solution. At the same
211
-------
(CATHODE) _
I
CATION- ANION-
PERMEABLE PERMEABLE
MEMBRANE MEMBRANE
I
K2S04
i
(ANODE)
FIGURE 7-24 SIMPLE ELECTRODIALYSIS CELL
212
-------
PURIFIED
WATER
CONCENTRATED
f—J CATHODE
i
D^ffftZ
© © © ©
DP r ~
& &
D
v ?
©
iri
•WASTE WATER
ANODE
FIGURE 7-25
MECHANISM OF THE ELECTRODIALYTIC PROCESS.
213
-------
time, some of the trivalent chromium passes through the anion-
permeable membrane to the anode solution where it is oxidized to
hexavalent chromium at the anode. The result is a decreased
concentration of metal ions in the solution between the cation-
permeable membrane and the anion-permeable membrane.
Conventional electrodialysis is being used by plant ID 20064 as a
means of recovering various metals. Electrodialysis can be combined
with an existing treatment system for recovery of metals, or it can be
used with other treatment to effect recirculation of rinse water. The
possibilities that exist for electrodialysis are many, and with recent
developments in membrane materials and cathode design and increased
knowledge of their applications, it may become a major form of
treatment for metals.
Performance of_ Conventional Electrodialysis - Little information is
available on performance for treatment of chromic acid; however,
information is available on copper cyanide performance. Copper
cyanide rinse water is treated in an electrodialysis unit for return
of the concentrated chemicals to the plating bath. The copper cyanide
chemicals in the rinse water can be concentrated to slightly more than
70 percent of the bath strength. For most copper cyanide plating,
this concentration may be sufficient to permit the direct return of
all chemicals to the processing operation. Figure 7-26 shows an
electrodialysis recovery system.
Advanced Electrodialysis
Advanced Electrodialysis Equipment - This particular electrodialysis
system is used to regenerate chromic acid etchant by oxidizing
trivalent chromium to hexavalent chromium. Its design uses a
circular, permeable anode, separated from the cathode by a
perfluorosulfonic membrane. The anode material is a specially
designed lead alloy. The cathode is made from Hastelloy C tubing,
which is a nickel alloy. The cathode is located in the center of the
circular, permeable anode and has a catholyte (10 percent sulfuric
acid) which is circulating through it and surrounds the cathode. This
solution is used as a transfer solution. Figure 7-27 shows the
physical construction of this circular electrodialysis cell.
The etchant is pumped in at the bottom of the unit through the anode
so that it remains in the chamber between the anode and the
perfluorosulfonic membrane. No transfer of solution takes place
except for a small percentage of copper. Chromium in the trivalent
form is contained in the etchant and, when a current is passed through
this etchant solution, electrons are stripped from the trivalent
chromium causing oxidation of the trivalent chromium to hexavalent
chromium. The newly stripped electrons migrate through the
perfluorosulfonic membrane into the catholyte solution. Converted
214
-------
DRAG-OUT
DRAG-OUT
I 1
1 i
r
-OUT
PARTS
PLACING TANK
RINSE *1
RINSE */-
?W.
CONCENTRATE |
'
I
| ELECTRODIALYZER STACK |
-
I—$-.
FEED L
p
1
- 1
- J
—
t —
u _
— — —
hJ
FEED
J r»F TOTv r ^ "* * i"7> nT-TD
• — £. J- V_y L\ u. <.• jL * • •. V/*. I il I\
DEIONI ZED WATER
FIGURE 7-26 ELECTRODIALYSIS RECOVERY SYSTEM
-------
REGENERATED
CHROMIC ACID
ro
t—»
en
SPENT CHROMIC
PERMEABLE ANODE
PERFLUOROSULFONIC
MEMBRANE
CATHODE-
SPLNT CHROMIC
ACID
I*
•Ti
p«
vJ
Li
n
n
U
CATHOLYTIC
"INPUT
-CATHOLYTIC—|
OUTPUT
CATHOLYTE
STORAGE
IT
D
a
Q
D
a
a
a
D
D
n
TOP VIEW
SIDE VIEW
FIGURE 7-27 ELECTROLYTIC RECOVERY
-------
hexavalent chromium is pumped back into the chromic acid etch tank for
reuse, while at the same time the catholytic solution is being
recirculated. The reaction which occurs at the anode is as follows:
Cr + 3 + 12 HeO - 3e- = Cr04-2 + 8H30+1 + 6e~
This reaction is continually taking place as both the etchant and the
catholyte are circulated through the cell.
Application of_ Advanced Electrodialysis - Electrodialysis of chromium,
oxidizing trivalent chromium to hexavalent chromium, is not widely
practiced as yet. It is, however, a very efficient method for
regenerating spent chromic acid etchant and it is used at one company
visited (ID 20064). This electrodialysis cell closes the loop on
chromium so that there is no need to reduce hexavalent chromium. The
only application, current or predicted, for this electrodialysis cell
system is the oxidation of chromium wastes.
Performance of. Advanced Electrodialysis - The electrical efficiency of
the unit varies with the concentration of both hexavalent chromium and
trivalent chromium. The electrochemical efficiency of the unit is
generally between 50 and 90 percent, depending on the concentrations.
This corresponds to an energy consumption of 8 to 16 kwh/kg of chromic
acid from reduced chromium. The metal removal efficiency of the
electrodialysis unit is 90 percent for 8 mg/1 of trivalent chromium
and 95 percent for 12 mg/1.
SLUDGE DEWATERING
Several of the wastewater treatment concepts described in this
section, such as clarification and sedimentation, produce sludge.
Disposal of the sludge is usually accomplished by incineration,
contractor removal, or by landfilling. Disposal is usually
facilitated if the sludge is concentrated or dewatered, since
incineration energy requirements are lower, and bulk handling problems
are minimized if landfill or haulaway methods are employed.
Sludge is usually dewatered in one of the following ways; thickening,
gravity settling, centrifugation, vacuum filtration, sludge bed
drying, and pressure filtration.
GRAVITY SLUDGE THICKENING
Definition of_ the Process
Gravity sludge thickening is the concentrating of solids in a solid-
liquid system by gravitational force. As a waste treatment technique,
gravity thickening is employed to concentrate sludge prior to
dewatering.
217
-------
Description of the Process
In the gravity thickening process, dilute sludge is fed from a primary
settling tank to a thickening tank. Rakes stir the sludge gently to
density the sludge and to push the concentrated sludge to a central
collection well. The supernatant is returned to the primary settling
tank. The thickened sludge that collects on the bottom of the tank is
pumped to dewatering equipment or hauled away as required. Figure 7-
28 shows the design and construction of a gravity thickener.
Advantages and Limitations
The principle advantage of a gravity sludge thickening process is that
it facilitates further sludge processing. Other advantages are high
reliability and minimum maintenance requirements.
Limitations of the sludge thickening process are its sensitivity to
the flow rate through the thickener and the sludge removal rate.
These rates must be low enough not to disturb the thickened sludge.
Spec i f i c Performance
Primary sludges from sedimentation units of one to two percent solids
concentration can usually be gravity thickened to six to ten percent;
chemical sludges can be thickened to four to six percent.
Operational Factors
Reliability - Reliability is high assuming proper design and
operation. A gravity thickener is designed on the basis of square
feet per pound of solids per day, in which the required surface area
is related to the solids entering and leaving the unit. Thickener
area requirements are also expressed in terms of mass loading, grams
of solids per square meter per day (pounds per square foot per day).
Ma i n ta i nab i1i ty - Twice a year, a thickener must be shut down for
lubrication of the drive mechanisms. Occasionally, water must be
pumped back through the system in order to clear sludge pipes.
Collected Wastes - Thickened sludge from a gravity thickening process
will usually require dewatering prior to disposal, incineration, or
drying. The clear effluent may be recirculated in part, or it may be
subjected to further treatment prior to discharge.
Demonstration Status
Gravity sludge thickeners are used throughout industry to reduce water
content to a level where the sludge may be efficiently handled.
218
-------
CHICKENING;
•TANK:
SLUDGE PUMP
OVERFLOW
RECYCLED
THROUGH
PLANT
FIGURE 7-28
MECHANICAL GRAVITY THICKENIKG
219
-------
Further dewatering is usually practiced to minimize costs to approved
landfill areas.
FILTER PRESS
Definition of_ the Process
Pressure filtration is a sludge dewatering process which occurs by
pumping the liquid through a filter which is impenetrable to the solid
phase. The positive pressure exerted by the feed pump(s) or other
mechanical means provides the pressure differential and is the
principle driving force.
As a waste treatment procedure, pressure filtration is used to dewater
sludge. A typical filter press consists of a number of plates or
trays which are held together between a fixed and moving end.
Description of_ the Process
On the surface of each individual plate is mounted a filter cloth.
The sludge is pumped into the press and passes through feed holes in
the trays along the length of the press until the cavities or chambers
between the trays are completely filled. The sludge is then
entrapped, and a cake begins to form on the surface of the cloth. The
water passes through the fibers of the cloth, and the solids are
retained.
Drainage ports are at the bottom of the trays. The filtrate is
collected and discharged to a common drain. As the filter media
becomes coated with sludge cake, the flow of filtrate through the
pressure filter drops to near zero indicating that the capacity of the
filter has been exhausted. The filter is then vented and opened to
discharge the dewatered sludge to a hopper or conveyor. After
closing, the filter is ready for a new cycle. Figures 7-29 and 7-30
show the design and operation of a typical filter press.
Advantages and Limitations
The pressures which may be applied to a sludge for removal of water by
filter presses that are now available range from 5.1 atm to 13.2 atm.
In comparison, a centrifuge may provide forces at 239 atm and a vacuum
filter, 0.69 atm. As a result of these greater pressures, filter
presses offer the following advantages:
1. Filtration efficiency is improved, especially on materials
which are difficult to filter.
2. Requirements for chemical pretreatment are frequently
reduced.
220
-------
TRAVELLING END
OPERATING HANDLE
TWIN THRUST SCREWS
fflHHHHBHHHHHHHHtjQ
ELECTRIC
CLOSING GEAR
FIGURE 7-29
TYPICAL PRESSURE FILTER
-------
RttD END
FILTER CLOTHS
• mm
FILTRATE DRAIN HOLES
FIGURE 7-30
FEED FLOW AND FILTRATE DRAINAGE.
222
-------
3. Solids concentration in the final cake is increased.
4. Filter cakes are more easily accommodated by a material
handling system.
5. Filtrate quality as measured by suspended solids content is
improved.
6. Maintenance is minimal because very few moving parts are
involved.
Two disadvantages associated with past operations have been the short
life of filter cloths and lack of automation. New, synthetic fibers
have largely offset the first of these disadvantages as they have
increased cloth life up to 12-18 months. Units with automated feeding
and pressing cycles are also now available. It is only at the end of
the cycle that the process becomes semiautomatic as no foolproof
automatic method of discharging the filter cake is yet available.
Specific Performance
In a typical pressure filter, chemically preconditioned sludge held in
the pressure filter for one to three hours under pressures varying
from 5.1 to 13.2 atm (60 to 180 psig) exhibited final moisture
contents between 50 and 75 percent.
Operational Factors
Reliability - High, assuming proper design and control. Sludge
characteristics which will dictate design and control parameters are
listed below:
1. Size, shape, and electrical charge of the solid
particles.
2. Solids concentration and volatiles content.
3. Chemical composition.
4. Compressibility.
5. Viscosity.
Pretreatment such as screening or coagulant addition may be a
requirement.
process
Maintainability - Maintenance consists of periodic cleaning or
replacement of the filter media, drainage grids, drainage piping,
filter pans, and other parts of the equipment. Since the removal of
the dewatered sludge cake from the filter media is not a fully
automatic process, a manual scraping operation is also a maintenance
requirement.
223
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Collected Wastes - Sludge dewatered in a filter press may be heat
dried and/or directly applied as landfill. The clarified effluent may
require further treatment prior to discharge if it is high in
dissolved or suspended solids.
Demonstration Status
Eight plants in the 196 plant data base employed the use of a filter
press to dewater sludge (ID's 303, 6050, 6077, 1209 31021, 3321, 3322,
and 3323). In addition, it has been effectively employed on sludge
from domestic waste at the municipal treatment plant in Atlanta,
Georgia and at the Sobrante filter plant of the East Bay Municipal
System in the San Francisco Bay Area of California.
SLUDGE BED DRYING
Definition of the Process
Sludge bed drying is the process of reducing the water content in a
wet substance by spreading the substance on the surface of a sand bed
and allowing drainage and evaporation to the atmosphere to dry the
sludge. This process is used for the drying of sludge prior to
removal to a landfill.
Description of_ the Process
As a waste treatment procedure, sludge bed drying is employed to
the water content of a variety of sludges to the point where
amenable to mechanical collection and removal to landfill.
consist of 15.24 to 45.72 cm (6 to 18 inches) of
(12 inch) deep gravel drain system made up of
(1/8 to 1/4 inch) graded gravel overlying drain
reduce
they are
These beds usually
sand over a 30.48 cm
3.175 to 6.35 mm
tiles.
Drying beds are usually divided into sectional areas approximately
7.62 meters (25 feet) wide x 30.48 to 60.96 meters (100 to 200 feet)
long. The partitions may be earth embankments, but more often are
made of planks and supporting grooved posts. A typical sludge drying
bed is shown in Figure 7-31.
To apply liquid sludge to the sand bed, a closed conduit or a pressure
pipeline with valved outlets at each sand bed section is often
employed. Another method of application is by means of an open
channel with appropriately placed side openings which are controlled
by slide gates. With either type of delivery system, a concrete
splash slab should be provided to receive the falling sludge and
prevent erosion of the sand surface.
224
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SECTION A-A
FIGURE 7-31
PLAN AND SECTION OF A TYPICAL SLUDGE DRYING BED.
225
-------
Where it is necessary to dewater sludge continuously throughout the
year regardless of the weather, sludge beds may be covered with a
fiberglass reinforced plastic roof. Covered drying beds permit a
greater volume of sludge drying per year in most climates because of
the protection afforded from rain or snow and because of more
efficient control of temperature. Depending on the climate, a
combination of open and enclosed beds will provide maximum utilization
of the sludge bed drying facilities.
Advantages and Limitations
The main advantage of sand drying beds over other types of sludge
drying is the relatively low cost of construction, operation, and
maintenance.
Its disadvantages are the large area of land required and long drying
times that depend, to a great extent, on climate and weather.
Specific Performance
Dewatering of sludge on sand beds occurs by two mechanisms: filtration
of water through the bed, and evaporation of water as a result of
radiation and convection. Filtration is generally complete in one to
two days and may result in solids concentrations as high as 15 to 20
percent. The rate of filtration depends on the drainability of the
sludge.
The rate of air drying of sludge is related to temperature, relative
humidity, and air velocity. Evaporation will proceed at a constant
rate to a critical moisture content, then at a falling rate to an
equilibrium moisture content. The average evaporation rate for a
sludge is determined to be about 75 percent of that from a free water
surface.
Operational Factors
Reliability - High assuming favorable climatic conditions, proper bed
design, and care to avoid excessive or unequal sludge application. If
climatic conditions in a given area are not favorable for adequate
drying, a cover may be necessary.
Maintainability - Maintenance consists basically of periodic removal
of the dried sludge. Sand removed from the drying bed with the sludge
must be replaced and the sand layer resurfaced.
The resurfacing of sludge beds is the major expense item in sludge bed
maintenance, but there are other areas which may require attention.
Underdrains occasionally become clogged and have to be cleaned.
Valves or sludge gates that control the flow of sludge to the beds
226
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must be
should
between
compartment
kept watertight. Provision for drainage of lines in winter
be provided to prevent damage from freezing. The partitions
beds should be tight so that sludge will not flow from one
to another. The' outer walls or banks around the beds
should also be watertight.
Collected Wastes - Dried sludge from
ventionally disposed of in landfills.
sludge drying beds is con-
Demonstration Status
Sand bed drying
flow. It is used
data base.
VACUUM FILTRATION
of
by
sludge is used by plants with a high solids waste
three plants (ID's 6051, 6073, and 20064} in this
Definition of the Process
Vacuum filtration is a sludge dewatering process which occurs by
filtering the sludge phase through a mesh which prevents passage of
the solids. A pressure differential is obtained by drawing a vacuum
which is the principal driving force. As a waste treatment procedure,
vacuum filtration is used to dewater sludge.
Description of. the Process
In wastewater treatment plants, sludge dewatering by vacuum filtration
is an operation that is generally accomplished on cylindrical drum
filters. These drums have a filter medium which may be cloth made of
natural or synthetic fibers, coil springs, or a wire-mesh fabric. The
drum is suspended above and dips into a vat of sludge. As the drum
rotates slowly, part of its circumference is subject to an internal
vacuum that draws sludge to the filter medium. Water is drawn through
the porous filter cake to a discharge port, and the dewatered sludge,
loosened by compressed air, is scraped from the filter mesh. A
typical vacuum filter system is shown in Figure 7-32. Vacuum
filtration is a widely used technique since it requres less space than
a sludge drying bed.
Because the dewatering of sludge on vacuum filters is relatively
expensive per pound of water removed, the liquid sludge is frequently
thickened prior to processing. If coagulating agents are to be
employed in the thickening process, elution (washing) of the sludge to
remove soluble materials will reduce its chemical demand, thereby,
effecting a coagulant cost savings.
227
-------
Air inlet for
cake discharge
PO
IX)
CO
FIGURE 7-3Z
VACUUM FILTRATION SYSTEM.
-------
Advantages and Limitations
Although the initial cost and area requirement of the vacuum
filtration system are higher than that of a centrifuge, the operating
cost is lower, and no special provisions for sound and vibration
protection need be made.
The dewatered sludge from this process is in the form of a moist cake
and can be conveniently handled. A disadvantage of this process is
that its liquid effluent, although of higher purity than a liquid
effluent from a centrifuge may require treatment prior to discharge.
Specific Performance
The function of vacuum filtration is to reduce the water content of
sludge, so that the proportion of solids increases from the 5 to 10
percent range to about 30 percent. After dewatering the sludge is a
moist cake and is easily handled.
Operational Factors
Reliability - Maintenance consists of the cleaning or replacement of
the filter media, drainage grids, drainage piping, filter pans, and
other parts of the equipment. Experience in a number of vacuum filter
plants indicates that maintenance consumes approximately 5 to 15
percent of the total time. If carbonate buildup or other problems are
unusually severe, maintenance time may be as high as 20 percent. For
this reason, it is desirable in the selection of vacuum filters to
provide one or more spare units.
If intermittent operation is to be employed, the filter equipment
should be drained and washed each time it is taken out of service and
an allowance for wash time should be made in the selection of sludge
filtering schedules.
Collected Wastes - Sludge dewatered in the vacuum filtration process
may be disposed of by direct application as landfill. The filter
effluent, if high in dissolved or suspended solids may require
further treatment prior to discharge and is usually returned to the
treatment facility influent.
229
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Demonstration Status
Vacuum filter systems have been used successfully at many industrial
and municipal treatment facilities. Of the electroplating plants in
this data base, 21 employed vacuum filtration (Reference Table 7-13).
At present, the largest municipal installation with vacuum filters is
at the West Southwest wastewater treatment plant of Chicago, Illinois
where 96 large units have been in service for many years. At the
Milwaukee, Wisconsin treatment plant, the initial filters installed in
1925 functioned approximately 25 years and then were replaced with
larger units. Original vacuum filters at Minneapolis-St. Paul,
Minnesota now have over 28 years of continuous service, and Chicago
has some units with similar or greater service life.
TABLE 7-13
ELECTROPLATING PLANTS THAT CURRENTLY EMPLOY
VACUUM FILTRATION
2062 4071
6037 6074
6087 6088
902 1208
1263 15070
20010 2020
20073 20077
20080 2811
31016 36040
4101 41041
43003
CENTRIFUGATION
Definition of Process
Centrifugation is the use of centrifugal force to concentrate the
solids contained in a solid/liquid system. Centrifugal force is
effective because of the density differential between the insoluble
solids and the liquid in which they are contained.
As a waste treatment procedure, centrifugation is applied to the
dewatering of sewage and waste sludges.
Description of the Process
There are three common types of centrifuges applicable to waste
streams. These are the disc, basket, and conveyor type centrifuges.
All three operate by removing solids under the influence of a
centrifugal force. The fundamental difference between the three types
is the method by which solids are collected in and discharged from the
bowl.
230
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In the disc centrifuge, the sludge feed is distributed between narrow
channels that are present as spaces between stacked conical discs.
Suspended particles are collected and discharged continuously through
small orifices in the bowl wall. The clarified effluent is discharged
through an overflow weir.
A second type of centrifuge which is useful in dewatering waste
sludges is the basket centrifuge. In this type of centrifuge, the
sludge feed is introduced at the bottom of the basket, and solids
collect at the bowl wall while clarified effluent overflows the lip
ring at the top. Since the basket centrifuge does not have facilities
for continuous discharge of collected cake, operation requires
interruption of the feed for cake discharge for a minute or two in a
10 to 30 minute overall cycle.
The third type of centrifuge commonly used in sludge dewatering is the
conveyor type. In this type, sludge is fed through a stationary feed
pipe into a rotating bowl in which the solids are settled out against
the bowl wall by centrifugal force. From the bowl wall, they are
moved by a screw to the end of the machine, at which point thay are
discharged. The liquid effluent discharges out of effluent ports
after passing the length of the bowl under centrifugal force. Figure
7-33 shows the design and operation of a typical conveyor type
centrifuge.
Advantages and Limitations
Some of the advantages of sludge dewatering centrifuges are that they
have minimal space requirements, produce relatively dry cakes, and
show a high degree of effluent clarification. The operation is
simple, clean, and relatively inexpensive. The area required for a
centrifuge installation is less than that required for a vacuum filter
of equal capacity, and the initial cost is lower.
One limitation, however, of the centrifuge is that higher power costs
will partially offset the lower initial cost. Special consideration
must also be given to providing sturdy foundations and soundproofing
because of the vibration and noise that result from a centrifuge.
Adequate electrical power must also be provided since large motors are
required. Another difficulty encountered in the operation of
centrifuges has been the disposal of the concentrate which is
relatively high in suspended, nonsettling solids.
Specific Performance
The efficiency of the dewatering of sludge by centrifugation is
dependent on such factors as feed rate, rotational velocity of the
drum, and sludge composition and concentration. As a general rule,
assuming correct design and operation, moisture may be reduced to a
231
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•Coven
DIFFERENTIAL
GEAR Box
•MAIN
DRIVE
SHEAVE
» irMmiii ,
1 _ T2—-FEED PIPES
3 (SLUDGE ft
CHEMICAL)
ROTATING
CONVEYOR
CENTRATE
DISCHARGE
SLUDGE CAKE
DISCHARGE
BEARING
BASE NOT SHOWN
FIGURE 7-33
CONVEYOR TYPE SLUDGE DEWATERING CENTRIFUGE
232
-------
point where the total solids content of the dewatered sludge is in the
range of 30 to 35 percent.
Operational Factors
Reliability - High, assuming proper control of operational factors
such as sludge feed, consistency, and temperature. Pretreatment such
as grit removal and coagulant addition may be necessary
requirements will vary depending on the composition of
on the type of centrifuge employed.
Pretreatment
the sludge and
Maintainability - Maintenance consists of periodic
cleaning, and inspection. The frequency and degree
required will vary depending on the type of sludge
dewatered and the maintenance service conditions. If
abrasive, it is recommended that the first inspection of
assembly be made after approximately 1,000 hours of operation. If the
sludge is not abrasive or corrosive, then the initial inspection might
be delayed. Centrifuges not equipped with a continuous sludge
discharge system will require periodic shutdowns for manual sludge
cake removal.
lubrication,
of inspection
solids being
the sludge is
the rotating
Collected Wastes
"of
disposed
(centrate)
further treatment
- Sludge dewatered in a centrifuge process may be
by direct application as landfill. The clarified effluent
if high in dissolved or suspended solids, may require
prior to discharge.
Demonstration Status
Twelve plants in the 196 plant electroplating data base employ
centrifugation (ID's 6075, 6086, 11050, 1205, 1902, 1924, 20070,
20079, 3324, 2501, 3327, and 33071). The solid bowl conveyor
centrifuge is the machine most commonly used.
SLUDGE DISPOSAL
There are several methods of disposal of sludges from industrial
wastewater treatment. The two most common techniques are landfilling
by the company on its own property and removal by licensed contractor
to an outside landfill or reclamation point. Other disposal
techniques used for industrial waste include incineration, lagooning,
evaporative ponds, and pyrolysis. This latter technique produces a
dewatered ash or sludge which requires ultimate disposal by either
contractor hauling or on-site landfilling.
OTHER CONTROL AND TREATMENT PROCESSES
Additional control and treatment processes are in various stages of
development but were not observed either at the plants visited or in a
233
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laboratory setting. The processes reviewed are: electrochemical
treatment of chromium and cyanide, extraction, adsorption, and a
variety of heavy metal chemical precipitation techniques.
Electrolytic Oxidation
Electrolytic oxidation reduces free cyanide and cyanate levels in
industrial wastewaters to less than 1.0 mg/1. The process can also be
applied to the electrochemical oxidation of nitrite to nitrate. In
both cases the reduction is accomplished without the use of treatment
chemicals. However, if reaction time becomes a problem, the cycle can
be accelerated by augmenting the system with a chemical (hypochlorite)
treatment as long as the cyanide concentration level is less than 200
mg/1.
The process equipment consists of a reactor, a power supply, a storage
tank, and a pump. Maintenance is minimal since only the pump has
moving parts. The reactor is replaced at infrequent intervals and a
rebuilt reactor can be installed within a few hours.
This system has been used commercially only for heat treating
applications; however it should be equally appropriate for
electroplating wastes. Its application for electroplating is still in
the development stage.
Electrolytic oxidation has the following advantages:
1. Low operating costs with nominal capital investment, relative
to alternative processes.
2.
No requirement for chemicals, thereby eliminating both their
storage and control.
3. No need to dilute or pretreat the wastewater as the process
is most efficient at high cyanide concentration levels.
Performance has been demonstrated on a commercial scale and shown to
result in a reduction in the cyanide concentration level from 3500
mg/1 to less than 1.0 mg/1 in 160 hours. Process by-products are
nitrogen, carbon dioxide, and a trace of ammonia - all are vented to
the atmosphere, and there is no noticeable odor.
At the present time, the process is not in use at any of the plants in
the electroplating data base. However, there is currently a unit in
operation which is handling the cyanide bearing wastewater generated
by a heat treating operation.
234
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Electrolytic Reduction
This process has been developed for the removal of chromium from metal
finishing and chemical manufacturing wastewaters. It involves an
electrochemical reaction in which consumable iron electrodes in the
presence of an electrical current generate ferrous ions which react
with chromate ions in solution. The reaction produces chromic
hydroxides and ferric hydroxides that can be precipitated in a pond or
clarifier without the need for further chemical addition.
In addition to the electrochemical unit, the only equipment required
is a pump and a clarifier or pond for settling. As long as the pH of
the entering stream is within the range of 6.0 to 9.0, no pH
adjustment is necessary for either the influent or effluent streams.
Although the process was developed for removal of chromium and zinc
from cooling tower discharge, it has also been applied for treatment
of electroplating wastewaters. The best application of the process is
to low concentration, high volume wastewater streams.
The process is capable of removing hexavalent chromium from wastewater
to less than 0.05 mg/1 with input conditions of 8.0 mg/1 and 88 gpm.
In addition to chromium, laboratory tests have also shown the
capability of the process to remove nickel to 2.1 mg/1, copper to 0.2
mg/1, silver to 0.05 mg/1, and tin to less than 5 mg/1. Reaction time
is instantaneous at a pH of 7.0 to 8.0; thus retention time is
determined by reactor geometry and mixing time.
There are approximately 30 electrolytic reduction systems in operation
in a variety of industries. Three are in service at plants in the
electroplating industry at the present time.
Cyanide Extraction
This process of concentrating and recovering cyanides and metal
cyanides uses a continuous countercurrent solvent extraction technique
based on a quaternary amine solvent. The amine solvent is regenerated
by dilute sodium hydroxide stripping, and the metal and cyanides can
be recycled to the plating bath, or salvaged.
A bench scale plant has been designed and fabricated to evaluate the
process for treating cyanide wastes from the electroplating industry.
Free cyanide and zinc cyanide have been successfully removed,
concentrated, and recovered in a series of demonstration runs.
Testing has been done on a laboratory scale over a period of 3 1/2
years and is currently inactive.
235
-------
Electrochemical Chromium Regeneration
Chromic acid baths, which are used for electroplating, anodizing,
etching, chromating, and sealing, must be continuously discarded and
replenished to prevent buildup of trivalent chromium. This is
normally accomplished, at least in part, through dragout that is
converted to sludge by end-of-pipe treatment. An electrochemical
system employing a lead anode and nickel cathode has been developed to
recover chromium by converting the trivalent form to the hexavalent
form. In this electro-oxidation process, trivalent chromium is
converted to the hexavalent (dichromate) form at the lead anode.
Hydrogen is released at the nickel cathode. The reaction is carried
out at 68°C, a cell voltage of 4.5 volts, and anode current density of
21 mA/sq cm, and a cathode current density of 630 mA/sq cm.
The electro-oxidation process has been applied commercially (one
installation) to regeneration of a plastic etchant. In this
particular installation, chromic acid dragged out of the etching bath
into the first stage of a countercurrent rinse is concentrated by
evaporation and returned to the etching bath. This closed loop tends
to cause rapid buildup of trivalent chromium. However, the etchant is
recirculated through an electro-oxidation unit, where the trivalent
chromium is oxidized to the hexavalent form. The current efficiency
for this process is 80 percent at concentrations above 5 g/1. If a
trivalent chromium concentration of less than 5 g/1 were required, ex-
periments have shown that the current efficiency could drop as low as
49 percent.
High p_H Precipitation
The treatment of solutions of chelated copper with calcium hydroxide,
calcium oxide (lime), calcium chloride, or calcium sulfate at a pH of
11.6 - 12.5 will effectively remove copper from the solution as a
copper hydroxide. Flocculation of the copper hydroxide with an
anionic polyelectrolyte accelerates the settling of sludge. This
process works well with both concentrated baths and dilute rinse
baths.
The process equipment required for a high pH system includes holding
and treatment tanks if the operation is conducted on a batch basis.
Also needed are pumps to transfer the wastewater and a settling tank
to concentrate the precipitate.
Although results of lab tests have shown that the process is
applicable to removing copper from complexed copper solutions with
calcium ions at a high pH, the effectiveness of treatment is
determined by the structure of the complexing agent in the solution.
If the nitrogen in the complexing agent is completely substituted with
carboxyl groups, removal of copper by the calcium ion is almost
236
-------
complete. Complexing agents containing no carboxyl group and only
hydroxyl groups show no copper removal. The addition of small amounts
of sulfide ions or dithiocarbamates after the calcium ion treatment
aids in further removal of copper. Electroless nickel solutions were
also prepared under laboratory conditions and the results show the
calcium treatment at a high pH to be effective.
Removal effectiveness is dependent on the form of the metal in
solution. The following removal efficiencies are typical for copper:
Copper - NTA complex 99.9%
Copper - HEDTA complex - 97.0%
Copper - NBA complex - 95.0%
Copper - Tartrate complex - 60 to 85%
Copper - Citrate complex - 60 to 85%
Copper - Triethanol and Diethanol Amine complex - 0%
Commercial copper complexes - 99.9%
'o
The high pH precipitation process is presently in the laboratory stage
of development.
Hydrogen Peroxide Oxidation - Precipitation
The hydrogen peroxide oxidation - precipitation treatment process
treats both the cyanide and metals in cyanide wastewaters containing
zinc or cadmium. In this process, cyanide rinse waters are heated to
120 - 130 F (49 - 54 C) and the pH is adjusted to 10.5 - 11.8.
Formalin (37% formaldehyde) is added, while the tank is vigorously
agitated. After 2-5 minutes, a proprietary peroxygen compound (41%
hydrogen peroxide with a catalyst and additives) is likewise added.
After an hour of mixing, the reaction is complete. The cyanide is
converted to cyanate and the metals are precipitated as oxides or
hydroxides. The metals are removed from solution by either settling
or filtration.
The chemical reactions which take place are as follows:
The formaldehyde reacts with cyanide to form an organic
nitrite:
CN + HCHO + H20 = HOCH2CN + OH
The hydrogen peroxide converts cyanide to cyanate in a
single step:
CN + H202 = NCO + H20
The formaldehyde also acts as a reducer breaking zinc
and cadmium ions apart from the cyanide:
237
-------
Zn(CN)4 + 4HCHO + 4H20 = 4HOCH2CN + 40H + Zn
The metals subsequently react with the hydroxyl ions
formed and precipitate as hydroxides or oxides:
Zn2 + 20H = ZnO + H20
The main pieces of equipment required for this process are two holding
tanks. These tanks must be equipped with heaters and air spargers or
mechanical stirrers. These tanks may be used in a batch or continuous
fashion with one tank being used for treatment while the other is
being filled. A settling tank or a filter is needed to concentrate
the precipitate.
The hydrogen peroxide oxidation - precipitation process is applicable
to cyanide-bearing electroplating wastewaters, especially those from
cyanide zinc and cyanide cadmium electroplating. A disadvantage of
this process for treating wastewater being discharged to surface
waters is the BOD levels that result from the addition of
formaldehyde.
In terms of waste reduction performance, this process is capable of
reducing the cyanide ion level to less than 0.1 mg/1 and the zinc or
cadmium to less than 1.0 mg/1.
This treatment process was introduced in 1971 and is being used in
approximately forty individual facilities.
Oxalation
This process involves chemical treatment of mixed plating plant
sludges to separate and recover metals such as chromium, copper, and
nickel. Sludges are treated with oxalic acid, then ammonia, and
finally, sodium hydroxide. Bivalent copper, nickel, and zinc become
insoluble oxalates; trivalent chromium and iron are extracted and pH
adjusted. The remaining oxalates extract the other metals in the
sludge as hydroxides.
Because this is a chemical treatment process, the only significant
equipment required is a treatment tank and pumps for sludge and fluid
transfer.
The process has been demonstrated on various plating sludges.
Chromium, copper, nickel, iron and zinc have been recovered. Tests
show that chromium removal from the sludge is nearly complete.
This process was developed in Japan and is still in the laboratory
research stage.
238
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Activated Carbon Adsorption
Adsorption is defined as the adhesion of dissolved molecules to the
surface of solid bodies with which they are in contact. Those
molecules retained in the interior of any solid are subjected to equal
forces in all directions, whereas molecules on the surface are
subjected to unbalanced forces. This results in an inward force which
can only be satisfied if other molecules become attached to the
surface. Granular activated carbon particles have two properties
which make them effective and economical as adsorbents. First they
have a high surface area per unit volume which results in faster, more
complete adsorption and secondly they have a high hardness value which
lends itself to reactivation and repeated reuse.
The adsorption process typically uses preliminary filtration or
clarification to remove insolubles. Next, the wastewaters are placed
in contact with carbon so adsorption can take place. Normally two or
more beds are used so that adsorption can continue while a depleted
bed is reactivated. Reactiviation is accomplished by heating the
carbon to 1600 - 1800 Degrees F to volatize and oxidize the dissolved
contaminants. Oxygen in the furnace is normally controlled at less
than 1% to effect selective oxidation of contaminants. The
reactivated carbon has been found to have a slightly higher removal
efficiency of contaminants in wastewater than virgin carbon. This is
because the contaminants are adsorbed in the larger pores of the
carbon, and during reactivation many of the smaller pores are
fractured to create a higher proportion of larger pores per unit
weight of carbon.
The equipment necessary for an activated carbon adsorption treatment
system consists of the following: a preliminary clarification and/or
filtration unit to remove the bulk of the metallic solids; two or
three containers packed with activated carbon used for the actual
adsorption operation; a holding tank located between the adsorbers;
and pumps for transferral of liquid between the adosrbers. Unless a
reactivation service is utilized, a furnace and associated quench
tanks, spent carbon tank, and reactivated carbon tank are required for
reactivation.
The activated carbon adsorption treatment process when used on
wastewaters following clarification or filtration is applicable to
pl-ating wastes of all types. In addition to its ability to remove
metals, it also removes a large percentage of any organic contaminants
in the waste stream. This reduces the BOD, COD, and TOC
concentrations in the effluent.
Metals reduction in wastewaters by an activated carbon adsorption
system in conjunction with a clarification system is shown in Tables
7-14 and 7-15. Treatment is usually continuous and systems are
239
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designed for reactivation intervals of approximately one month. Loss
of carbon during reactivation can normally be held to 5% or less.
Activated carbon adsorption systems have been in full scale commercial
use for years, but its application for metals removal is relatively
new.
Sulfide Precipitation
In this process heavy metals are removed as sulfide precipitates.
Sulfide is supplied by addition of very slightly soluble metal sulfide
which has a solubility somewhat greater than that of the sulfide of
the metal to be removed. Normally, iron (ferrous) sulfide is used.
It is fed into a precipitator where excess sulfide is retained in a
sludge blanket that acts both as a reservoir of available sulfide and
as a medium to capture colloidal particles.
The process equipment required includes a pH adjustment tank, a
precipitator, a filter, and pumps to transport the wastewater. The
filter is optional and may be a standard, dual media pressure filter.
The process is applicable for treatment of all heavy metals. It
offers a distinct advantage in the treatment of wastewater containing
hexavalent chromium. The ferrous sulfide acts as a reducing agent at
a pH of 8.0 to 9.0 and this reduces the hexavalent chromium and then
precipitates it as a hydroxide in one step without pH adjustment.
Therefore, hexavalent chromium wastes do not have to be isolated and
pretreated by reduction to the trivalent form. All metals other than
chromium are removed as sulfides.
240
-------
TABLE 7-14
REMOVAL OF METALS BY
LIME PRECIPITATION - ACTIVATED CARBON COMBINATION
Initial
Metal Concentration
(mq/1)
Silver
Beryllium
Bismuth
Cobalt
Mercury
Antimony
Selenium
Tin
Titanium
Thallium
Vanadium
Manganese
Nickel
Zinc
Copper
Cadmium
Barium
Lead
Chromium
Arsenic
Mercury
0.5
0.1
0.6
0.5
0.5
0.6
0.5
0.5
0.5
0.5
0.5
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.5
Percent
Removal
98.0
99.5
96.0
95.0
91.0
52.0
95.0
92.0
95.3
72.0
91.0
98.2
99.5
76.0
90.0
99.6
81.0
99.4
98.2
84.0
92.0
Residual
Metal (mg/1)
0.010
0.001
0.024
0.025
0.045
0.288
0.025
0.040
0.024
0.140
0.045
0.090
0.025
1.200
0.500
0.020
0.950
0.030
0.090
0.800
0.040
241
-------
TABLE 7-15
REMOVAL OF METALS BY
Metal
Silver
Beryllium
Bismuth
Cobalt
Mercury
Molybdenum
Antimony
Selenium
Tin
Titanium
Thallium
Vanadium
Manganese
Nickel
Zinc
Copper
Cadmium
Barium
Lead
Chromium
Arsenic
Mercury
FERRIC CHLORIDE
Initial
Concentration
(mq/1)
0.5
i 0.1
0,5
0,5
0.05
im 0.6
0.5
0.1
0.5
0.5
0.6
0.5
! 5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.5
ACTIVATED CARBON
Percent
Removal
99.1
98.9
96.2
30.0
99.0
80.0
72.0
80.0
98.5
90.0
45.0
97.8
17.0
37.0
94.0
96.0
98.6
95.6
99.1
99.3
97.1
98.0
COMBINATION
Residual
Metal (mg/1)
0.005
0.001
0.009
0.350
0.001
0.120
0.140
0.020
0.008
0.050
0.330
0.011
4.150
3.150
0.300
0.200
0.070
0.220
0.045'
0.035
0.145
0.010
242
-------
Data on the performance of this process show that concentrations of
less than 0.05 mg/1 have been achieved for most metals, with levels
down to ppb for some. Sludges are much less subject to leaching than
landfilled hydroxide sludges. This removal efficiency was
demonstrated by the sulfide precipitation unit employed at plant
27045.
Full size commercial units are presently produced by two manufacturers
and are in operation at several installations. These units are
essentially the same, except that one operates at an alkaline pH and
the other runs under acid conditions.
Soluble Sorbent Clarification
Soluble sorbent clarification is a treatment process which utilizes a
reagent added to the wastewater to adsorb and precipitate various
metals within a clarifier. Precipitation occurs at one pH level
rather than at different pH levels as is normal for a clarification
process. In its soluble form the reagent acts as an adsorbent for
metal ions in solution. The pH of the solution is raised to 8.5 - 9.0
by addition of sodium hydroxide or lime. In this pH range, the
reagent is insoluble and precipitates with the metals. The
supernatant in the clarifier is discharged, and the solids are pH
adjusted with acid. This resolubilizes the adsorbent which is
recycled for reuse. The heavy metal sludges are isolated and
dewatered for disposal.
The equipment necessary for the soluble sorbent clarification process
consists of a precipitation tank for pH adjustment of the wastewater,
a clarifier for solids settling, and pumps for transferral of water
and sludges.
The soluble sorbent clarification process is applicable to all types
of plating wastewaters containing all combinations of the common
metals - copper, nickel, chromium, cadmium, and zinc.
Pilot scale evaluation has been completed, and the process is now
ready for commercial application. Pilot scale tests have proven that
the system is capable of reducing copper, nickel, zinc, and cadmium to
0.02 - 0.05 mg/1 and chromium to 0.1 mg/1. The process also minimizes
suspended solids in the effluent.
Peat Adsorption
Peat adsorption is a polishing process that may be added to a
wastewater treatment system following a conventional clarifier to
achieve very low effluent concentrations of metals. The removal
mechanism is chemisorption by the particles of peat. The peat is
243
-------
supported on a stainless steel mesh belt, which is configured such
that there are two wastewater passes through the peat mat.
The contacting of wastewaters with peat is accomplished with the
following equipment: a mat generator, a contacting device, and a
system for peat disposal. Also required is a pump to transfer the
water and a dewatering device such as a filter press. Generation of a
mat of peat is achieved by continuous feed of peat to a wetting tank
where it is slurried and deposited on the metal mesh belt. After use,
the peat can be burned or used for landfill.
The use of peat moss in the treatment of wastewater is applicable to
waters containing metals such as mercury, cadmium, zinc, copper, iron,
nickel, chromium, lead, and organic matter such as oil and detergents.
Solutions containing hexavalent chromium require a special technique
for such treatment. Chromium bearing wastewater must first be treated
with ferric chloride and sodium sulfide at a pH in the range of 5.0 to
7.0. A precipitate is formed which settles easily. Contacting the
pretreated water with peat then reduces the remaining chromium below a
detectable level.
For initial concentrations of metals at 1.0 mg/1 or higher,
preliminary precipitation is required. For solutions with a
concentration lower than 1.0 mg/1, a simple pH adjustment to a level
between 6.0 and 8.0 followed by contact with the peat produces an
effective treatment. Table 7-16 contains the results obtained on a
pilot plant with a 20,000 gpd capacity.
The process is not in use at any of the plants in the electroplating
data base, although it is in operation at a dye making plant.
Starch Xanthate
Insoluble starch xanthate, when added to wastewater, exchanges sodium
ions for other metal ions and appears to be effective at varying
pollutant concentration levels. It can be added in the solid form or
in the form of a slurry and has proved to be effective over a pH range
of 3.0 to 11.0 with maximum effectiveness above 7.0. The resulting
metal precipitates may be removed by settling, centrifugation or
filtration.
244
-------
TABLE 7-16
TREATMENT OF WASTE WATERS
CONTAINING METALS
Case No.
1
Before Treatment
(mg/1)
Pb
Sb
Cu
Zn
Ni
PH
Cu
Ni
Zn
pH
Cu
Ni
Zn
pH
20
2.5
1.0
1.5
2.5
1.6
250
67.5
7.5
2.5
26,400
5,000
10
0.1
Cr + 6 36,000
pH 1.5
Cu
Zn
Fe
Ni
CN
pH
5.0
4.6
1.0
13.5
36.0
7.75
After Treatment
(mq/1)
0.025
0.90
0.2
0.25
0.07
7.1
0.24
0.5
0.08
7.2
0.24
0.5
0.16
7.2
0.04
7.0
0.25
0.10
0.05
0.6
0.7
8.0
Treatment
Adjustment of pH
in the range of
8.0 with lime.
Settling. Contact-
ing with peat.
As above.
As above.
Adjustment of pH
at 7.0 with lime.
Treatment with
FeCl3/Na2S. Settl-
ing. Contacting
with peat.
Addition of FeS04
and Na2S. Settling,
Contacting with
peat. Further
reduction of CN to
0.03 by aeration.
245
-------
When used in batch treatment operations the metal-xanthate sludge
settles rapidly. With a continuous flow stream, a clarifier,
centrifuge or a filter should be used.
The process offers a new way to recover metals dissolved in water.
Recovering these metals permits reuse. The use of starch xanthate is
effective in removal of metals from wastewaters that have
concentrations of less than 100 mg/1. If initial metal concentrations
exceed this limit, other treatment processes would be required for
initial control. The starch xanthate process could then be used as a
secondary treatment to further lower metal concentrations. Insoluble
starch xanthate (ISX) has been shown to be effective as a filter
precoat, and is in use at one plating facility to remove nickel,
copper , tin, and lead. ISX-metal sludge settles rapidly and dewaters
to 50 - 90% solids content after filtration or centrifugation.
Laboratory tests were performed on 1000 ml solutions containing
specific metals at known concentrations and the results of these tests
are found in Tables 7-17 and 7-18. The pH of the ISX in Table 7-17
was 3.7 and the pH in Table 7-18 was 3.5. Both solutions were treated
to a final pH of 8.9. After treatment, the effluent contains only
sodium and magnesium ions from the product. At a pH above 8.5, the
metal bearing products precipitate, leaving a clear effluent. The
sludge can also be incinerated to recover the metal oxides. If the
sludge is landfilled, the metal is bound fairly strongly and would
have less chance to be leached out than with a hydroxide sludge.
The starch xanthate process is in the laboratory stage of development;
however, at least one electroplater currently uses this process in
polishing his wastewater effluent. Several other electroplaters are
investigating full scale use of the process.
Oxyphotolysis
Oxyphotolysis uses the oxidizing powers of ozone combined with the
bondbreaking energies of ultraviolet light. Ozone is commonly
employed for the oxidation of cyanide wastes (refer to text on
oxidation by oxygen) for the purpose of freeing metallic ions for
removal in a subsequent treatment process. The addition of an
ultraviolet light decomposes strongly bound compounds, notably iron
cyanide and nickel cyanide. The ultraviolet light frees the cyanide,
allowing it to react with the ozone.
246
-------
TABLE 7-17
REMOVAL OF METAL CATIONS FROM WATER WITH
INSOLUBLE STARCH XANTHATE
Initial Cone.,
Metal mg./liter
Ag 53.94
Au 30.00
Cd 56.20
Co 29.48
Cr 26.00
Cu 31.77
Fe 27.92
Hg 100.00
Mn 27.47
Ni 29.35
Pb 103.60
Zn 32.69
ISX,
0.32
0.50
0.64
0.64
0.64
0.32
0.32
0.64
0.64
0.64
0.64
0.32
Residual Cone.,
mg./liter
0.016
0.010
0.012
0.090
0.024
0.008
0.015
0.001
0.015
0.160
0.035
0.294
Metal
Cd
Co
Cr
Cu
Fe
Hg
Mn
Ni
Pb
Zn
TABLE 7-18
REMOVAL OF METALS FROM DILUTE
SOLUTION WITH INSOLUBLE STARCH XANTHATE
Initial Cone.,
mg./liter
5.62
2.95
60
18
2,
3
2
79
10.00
2.75
2.93
10.36
3.27
Residual Cone.,
mg./liter
0.001
0.010
0.026
0.005
0.001
0.0007
0.010
0.050
0.031
0.007
247
-------
In this process, the cyanide wastewater is pumped to a mixing tank
where ozone is added and the ultraviolet light is provided by standard
germicidal lamps. The free cyanide is destroyed as quickly as ozone
is added to the solution; the metal-complexed cyanides require a
longer reaction time. The ultraviolet light speeds up the reaction
time more effectively and more economically than raising the
wastewater temperature. The intermediate oxidation product, cyanate,
is also destroyed in the process. In addition, the use of extra
reactor stages results in more complete destruction of the metal
cyanides. Once the cyanide has been destroyed, the metallic oxides
formed can be removed from solution by another type of waste
treatment, typically an alkaline precipitation system.
The equipment necessary for an oxyphotolysis treatment system is as
follows; an ozone generator to produce ozone from air; lamps to
provide ultraviolet light; pumps to transport the wastewater; and a
metal removal unit such as a settling tank or a filter.
Oxyphotolysis is applicable for treatment of wastewaters containing
cyanide and is especially useful for electroplating rinsewaters
containing iron cyanide and nickel cyanide. In addition to its use
for cyanides and heavy metals, oxyphotolysis is applicable for toxic
organic substances and for disinfection of secondary effluents and
source waters.
The oxyphotolysis treatment system has demonstrated a capability to
destroy cyanides completely, and, coupled with a metal removal system,
is capable of attaining discharge concentrations as low as 0.1 mg/1.
Presently there is one commercial installation treating electroplating
wastes though full size commercial units are available.
END-OF-PIPE TECHNOLOGY FOR ELECTROPLATING
The individual treatment technologies discussed in this section can be
combined to form systems which are tailored for the specific needs and
wastes of an individual plant. Figure 7-34 is a schematic diagram of
a system combining chromium reduction, cyanide oxidation, clari-
fication and sludge drying.
Table 7-19 indicates the system elements needed for various plating
and metal finishing operations. The exact nature of the system
depends on the types of wastewater that must be treated. Chromium
reduction and cyanide oxidation are used only if the wastewater
contains chromium or cyanide. Clarification includes pH adjustment,
precipitation, flocculation, and sedimentation, which may be carried
out in one or more vessels or pits. Chelated wastes, if present,
should be clarified separately to prevent the chelates from tying up
metals in other waste streams. Sludge drying may be carried out in
248
-------
CHROMIUM
WASTES
1 CHROMIUM
"| REDUCTION
(OPTIONAL) I
CYANIDE
WASTES
CYANIDP
OXIDATION
, 1
ro
I (OPTIONAL) I
CLEANING AND
OTHER WASTES
CHELATED
WASTES
o
K
n
f
w
CLARIFICATION
•N . CLARIFICATION
~y* (OPTIONAL)
SLUDGE
DRYING BEDS
CONTRACTOR REMOVAL
OF SLUDGE
DISCHARGE
FIGURE 7-34 END-OF-PIPE TREATMENT SYSTEM
-------
TABLE 7-19
TREATMENT SYSTEM ELEMENTS
FOR VARIOUS MANUFACTURING OPERATIONS
01
O
Manufacturing
Operation
Common Metals
Plating
Precious Metals
Plating
Electroless
Plating
Stripping
Catalyst
Deposition
Anodizing
Chromating
Phosphating
Immersion
Plating
Etching and
Milling
APPLICABLE WASTE TREATMENT SYSTEM ELEMENTS
Cyanide Chromium Clarification Segregated Sludge
Oxidation Reduction Clarification Drying
For Chelated
Metals
XXX - X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
-------
the sludge drying beds indicated or in a vacuum filter, and contractor
removal of sludge may sometimes by replaced with landfilling on
company property. Addition of a sludge thickening step following
clarification is often desirable. In addition, final neutralization
(pH adjustment) of the wastewater before discharge may be needed to
meet the pH limitation, particularly if nickel salts are removed
effectively by clarification at a relatively high pH.
The system shown schematically in Figure 7-34 is not the only approach
possible. Many alternative techniques have been encountered in the
field. These alternatives range from the use of a settling lagoon to
replace the clarifier to the use of reverse osmosis, ion exchange,
membrane filtration, diatomaceous earth filtration, and multiple stage
rinsing to reduce discharge of pollutants. Although not found as
commonly as clarification, most of the individual technologies
described earlier are in general use throughout this industry. The
use of any particular component or system will depend on the wastes to
be treated, space constraints, funding availability, and other factors
which involve management judgement.
Many system combinations are capable of adequate performance..
However, inadequate control, careless operation or maintenance, or
overloading due to inputs of large slugs of concentrated wastes can
produce upset conditions that will result in the discharge exceeding
the limitations. Concentrated slugs should be metered into the
treatment system to preclude overloading. Continuing management
attention to operation should be exercised to insure proper
performance.
IN-LINE TECHNOLOGY FOR ELECTROPLATING
The individual technologies discussed in the first part of this
section may be used singly or in combinations to reduce pollutants
sufficiently to meet very stringent requirements. In-line treatment
systems may have greater pollutant reduction than conventional end-of-
pipe treatment and/or stress conservation of raw materials by recycle
and reuse. Those in-line treatment systems designed to reduce rinse
water consumption while also recovering plating chemicals reduce cost
and provide high pollutant removal efficiencies.
The combinations of various techniques to form an in-line treatment
system will vary from plant to plant. No single combination can be
recommended for all treatment applications. The following paragraphs
present the applicability of individual technologies to various
operations, and describe a typical treatment system for a model plant.
251
-------
Applicability of_ In-line Technologies
Table 7-20 provides a general summary of the applicability of in-line
technology to the specific electroplating operations discussed earlier
in this section. Current development work is likely to extend the
indicated applicability.
Where recovery of plating chemicals and rinse water can be achieved by
multistage closed loop rinsing, this is a logical choice. The
alternative technologies are generally more complex, more expensive,
and more costly to operate compared to -closed loop rinsing. In
situations where the choice is between reverse osmosis, evaporation,
and ion exchange, the relative attractiveness of evaporation is
limited by the cost and availability of energy. Reverse osmosis for
nickel recovery or ion exchange for nickel or chromium (or other
applications) is likely to be a better choice than evaporation.
Nevertheless, use of evaporation where appropriate may still represent
a significant cost saving (such as results from recovering plating
chemicals) compared with end of pipe chemical destruction treatment.
A choice between ultrafiltration and ion exchange will be based on the
particular rinse water constituent to be recovered.
Many of the currently common treatment techniques can be modified to
meet more stringent regulations. In-plant recovery techniques may be
employed, thus reducing flow to the clarifier which increases
residence time and improves settling. Polishing with starch xanthate
can reduce clarifier pollutant discharge levels significantly.
Adaptation of the current clarifier to use the membrane filtration
system will produce improved results. All of these approaches allow a
plant to make maximum use of the currently installed equipment and by
this they reduce the cost impact of the more stringent BAT level
limitations.
Typical In-line Treatment System
Based on the preceding review of advanced technology applicability,
treatment requirements depend strongly on what plating and metal
finishing operations are used by an establishment, and there is no
single, universal system. An example of the development of a typical
treatment system is therefore presented in this subsection.
The example company, presented in Figure 7-35, employs an automatic
copper-nickel-chromium plating line. The plating operations are
preceded by an alkaline cleaning section. In addition, there is a
rack stripping step. Prior to treatment modifications, the company
used two series rinses after each plating operation, and the overflow
from each rinse tank was directed to a conventional end-of-pipe
treatment system. This conventional system consisted of chromium
252
-------
TABLE 7-20
IN-LINE TECHNOLOGY APPLICABILITY
Application
Acid Metal Plating
Recovery
Cyanide Metal Plating
Recovery
Precious f'.etal Platir«
Recovery
Phosphating Recovery
Mixed Plating Waste
Treatment
Electrocoating
Etching Pecovery
Chremating Rr>eo"ery
Reverse
Osmosis
X
-
-
-
X
-
X
-
Evaporation
X
X
X
-
X
-
X
X
ion
Exchange
X
_
X
X
X
-
-
X
Electrolytic
Recovery
X
X
X
-
_
-
X
-
Ultrafiltration
-
_
_
X
_
X
-
-
Membrane
Filtration
-
_
_
-
X
-
-
-
Advanced Rinsing
Techniques
X
X
X
-
..
-
-
-
-------
EVAPORATION
I
OVERFLOW 1
r
MAKE UP WATER
ro
en
PAR
TS
-»•-
PRECLEANINO
AND RINSING
COPPER
PLATE
4 ST
AGE COUNTERCURRENT RINSE
3 STAGE
COUNTERCURRENT RINSE
*••
NICKEL
PLATE
1 OVERFL
1
1
1
1
ow'
t
I
*
CHROME
PLATE
i
PERMEATE
REVERSE
OSMOSIS
coui
RECOVERED CHROMIC ACID
1 STAC
TERCU
RINSI
OV
s
!E 1
RRENT , r
= I I
1 !
ERFLOWl |
1 PUR:
1 MR'
1
1
PARTS 1
1
A i
_ _ j i
CHROMIC
ACID
SUPPLY
tFIED TANK
,CpNCENTRATE |
RACKS
RACK
STRIPPING
CAUSTIC
r
ION
EXCHANGE
(CHROMIC
I ACID
|
WASTEWATER
SULFURIC
ACID
-J
IWASTEWATER
WASTEWATER
FROM PRECLEANING_
AND RINSING
SPILLS
CONVENTIONAL
END-OF-PIPE
BPT TREATMENT
^-DISCHARGE
FIGURE 7-35 TYPICAL IN-LINE TREATMENT SYSTEM
^. SLUDGE
'I'O ^ArtUFI
-------
reduction, cyanide oxidation, pH adjustment for precipitation,
clarification, and final neutralization before discharge.
The first step the company took was a rinse water reduction study.
The study showed that replacement of the two-stage series rinses with
three-stage countercurrent rinses would reduce the water rate to those
rinses by nearly 90 percent. Discussions with a plating line
manufacturer determined that each pair of old rinse tanks could easily
be replaced with modern three-stage countercurrent rinses, with room
to spare. Because of the low flow rates required, the new tanks would
be air-agitated to assure adequate mixing. Adjustment of the
automatic system to accomodate these changes was also practical.
The projected rinse water changes alone would have resulted in a
significant reduction in both water costs and treatment chemical costs
for pH adjustment and neutralization. These reductions, however, did
not meet company cost reduction objectives. The company therefore
decided to install equipment to recover plating chemicals. At first,
evaporation appeared to be the only choice for recovery of copper
cyanide, but the 160 degrees F operating temperature of the "high
efficiency" plating bath suggested that a closed loop rinse with a
reasonable number of stages was feasible and would incur much lower
capital and operating costs. In fact, calculations showed that for a
four-stage rinse, the required rinse water flow rate would just
balance evaporative losses from the plating tank. Thus, water should
be added to the fourth rinse stage at this required rate, and overflow
from the first rinse stage would be returned to the plating bath to
replace dragged out plating chemicals and make up for evaporation
losses.
Evaporation, ion exchange or reverse osmosis could be used for the
nickel plating operation. Evaporation would have resulted in a cost
saving, but it was ruled out because of the relatively high energy
cost. Spiral wound reverse osmosis and cylic ion exchange were
equally competitive from a cost standpoint, but reverse osmosis was
finally selected because of its widespread use for nickel salt
recovery.
Both evaporative and cyclic ion exchange were investigated for chromic
acid recovery. Despite the relative newness of cyclic ion exchange,
the company decided to use it because the capital and operating costs
for evaporative recovery were much higher.
The cleaning and rack stripping steps were left unchanged, and
wastewater from these steps (as well as from spills) continues to be
handled by the existing end-of-pipe treatment system. Table 7-21
shows the current pollutant discharge as well as the original
pollutant discharge before conversion and the discharge that would
have resulted from conversion to countercurrent rinsing only. As
255
-------
TABLE 7-21
POLLUTANT DISCHARGE AT AN EXAMPLE PLANT
END-OF-PIPE COUNTERCURRENT IN-LINE TREATMENT
SYSTEM RINSING ONLY SYSTEM
PARAMETER (mn/1) (mg/on-m?) (mq/1) (mg/on-m?) (mo/1) (mg/oo-m2)
Chromium 0.54 24 0.61 23 0.02 0.8
Conner 0.49 21 0.56 21 0.02 0.8
Nickel 0.99 43 1.13 43 0.02 7.5
Cyanide 0.01 0.4 0.01 0.4 ND ND
Fluoride 2.0 87 2.0 76 2.0 75
Total SUSD.
Solids 15.0 655 16.5 622 16.7 628
Note: ND is Nondetectable
-------
shown in Section VIII, the company achieved a significant cost
reduction and concomitantly a drastic reduction in copper, nickel,
chromium and cyanide discharge.
END-OF-PIPE TECHNOLOGY FOR PRINTED BOARD MANUFACTURE
The individual treatment technologies discussed in a previous part of
this section describe the components available for application in
treatment systems for the overall electroplating industry
manufacturing wastes. Several combinations of these technologies are
used in the treatment systems of the printed board plants surveyed.
The systems presented in this subsection represent a range of commonly
encountered end-of-pipe systems.
The overall end-of-pipe treatment system for printed board
manufacturing shops involves precipitation followed by clarification
and ranges from treatment of all process wastes together to
segregation of wastes into separate streams and the subsequent
individual treatment of each stream. The recommended system is the
one that involves segregation and separate treatment of discrete waste
streams. The combined waste systems are presented merely to show the
range of treatment encountered during the course of this study.
The process flow schematic of a treatment system for printed board
manufacturing wastes involving a single waste stream (wastes not
segregated) is shown in Figure 7-36. Plant ID 04065 is a printed
board manufacturer with a treatment system similar to this type. All
of the process wastewater flows into a flocculation tank where
chlorine is added for the oxidation of cyanides. Lime is also added
to raise the pH for both the cyanide oxidation processes and the
precipitation of metals.
The water is pumped to a clarifier for settling out of metals as
hydroxides and other solids. After a sufficient retention time the
water is discharged. The sludge from the clarifier is hauled away
periodically and sent to an on-site landfill or removed by a
contractor.
The process flow schematic of the recommended system employing
segregation of waste streams for the printed board industry is
illustrated in Figure 7-37. A treatment system similar to this type
is currently in operation at plant ID's 4069, 17061, and 19063. The
waste streams requiring treatment are:
1. Cyanide bearing wastes - This stream is composed of rinses
following any operation where cyanides are employed: cyanide
copper plating, cyanide gold plating and cyanide gold
stripping.
257
-------
CH
1
ALL
PROCESS
WASTE
LORINE
| |LIME|
" iT
FLOCCULATION
TANK
CLARTFTFR
DISCHARGE
ro
en
CO
SLUDGE
FIGURE 7-36 END-OF-PIPE SYSTEM FOR PRINTED BOARD MANUFACTURERS
(SINGLE WASTE STREAM)
-------
SODIUM
HYPOCHLORITE
CYANIDE
ro
ui
CYANIDE
OXIDATION
COMMON
CHELATED
WASTES
LIME I
FLOCCULATOR
FLOCCULATOR
SETTLING
TANK
SLUDGE
SETTLING TANK
SLUDGE
DRYING BEDS
RECYCLE
DISCHARGE
SLUDGE
FIGURE 7-37 END-OF-PIPE SYSTEM FOR PRINTED BOARD MANUFACTURERS
(SEGREGRATED WASTE STREAMS)
-------
2. Acid-Alkali and non-chelated metals stream - This stream
consists of rinse waters following several operations: acid
and alkali cleaners in all process lines, non-chromium and
non-ammoniated etches, catalyst application, acceleration,
non-cyanide and non-chelated plating baths. This stream
generally contains metals such as tin, palladium, lead,
nickel and copper.
3. Chelated wastes stream - This stream consists of rinses
following operations where chelating agents are present.
Included in this group are electroless plating rinses. These
wastes must be kept separate from other metal bearing wastes.
4. Chromium bearing wastes - This stream contains hexavalent
chromium from chromic acid etch rinses if such etching is
used. This is usually not found in the printed board
industry. However, if such a stream exists, the hexavalent
chromium must first be reduced to the trivalent form before
being introduced to the flocculation tank. Because of the
limited use of chromic acid etches in the printed board
industry, the chromium stream is not included in the end-of-
pipe treatment system in Figure 7-37.
Referring to Figure 7-37, the wastewaters containing cyanide are
isolated for pretreatment and flow into a tank where they are oxidized
by the addition of sodium hypochlorite. The chlorine in the
hypochlorite oxidizes the cyanides to cyanates, reducing their
volatility and toxicity. Sodium hydroxide is also added to maintain
the proper pH level (approximately 11) for the reaction. After
oxidation, the treated cyanide stream joins the common cleaners and
metals stream.
The combined streams (stream 1 & 2) and the chelated waste stream flow
in parallel lines through similar treatments. First, they flow into
separate flocculation tanks where lime is added for the precipitation
of metals, including tin, copper, lead, and palladium. After a forty-
five minute retention time, the segregated waste streams pass into
separate settling tanks for further precipitation and settling. The
retention time in these settling tanks is approximately two hours.
This flocculation and settling removes ninety-five to ninety-eight
percent of the metals, depending on the type of metals in the waste
streams.
Following clarification, the chelated waste stream and the acid-alkali
and non-chelated metals streams are mixed together and then
discharged. The sludges formed in the flocculating and settling tanks
are pumped into one line and sent to a sludge dewatering unit. The
dewatered sludge is then disposed of by means of on-site landfill or
sent back to the clarifier inlet for further treatment.
260
-------
If a plant has a significant amount of ammonia in its wastewaters due
to the use of ammonia base etchants, the recommmended end-of-pipe
system involves segregation of the ammonia stream also. Such a system
is illustrated in Figure 7-38 and was seen at plant ID's 4061 and
36062. Using non-ammonia base etchants would be an alternative to
segregation of the ammonia stream.
The ammonia waste stream is segregated and sent to a batch treatment
tank. When enough water has been collected, caustic is added to raise
the pH, and live steam is injected. The effect of these two steps is
the precipitation of some metals and the dispersal of ammonia as a
gas.
The treated ammonia batch is emptied to a flocculation tank where the
acid-alkali and non-chelated stream is also collected. Lime is added
to raise the pH and cause metal precipitation. This combined waste
stream is then pumped to a settling tank.
After a two hour retention period in the settling tank, the wastewater
is pumped through a pressure filter for further removal of metals and
other solids. Following filtration, the wastewater enters an
equalization tank, from which it can be returned to the settling tank
for further treatment or discharged if it is properly treated. The
sludge from the settling tank is dewatered and then sent to an on-site
landfill or removed by a contractor.
IN-LINE TECHNOLOGY FOR PRINTED BOARD MANUFACTURE
This segment describes the commonly encountered in-line technology for
reducing pollution from processes involved with the printed board
industry. The technology reduces pollution by reducing the
concentration of pollutants, by reducing the quantity of polluted
water discharged, by reclaiming valuable potential pollutants for
reuse, and by reusing the water itself.
In-line technology reduces the volume of wastewater by use of water
conservation techniques such as countercurrent rinsing, fog rinsing,
and automatic shut-off equipment for rinse tanks. Use of recovery
techniques such as reverse osmosis, distillation, ion exchange, and
electrochemical recovery enables a plant to recover plating chemicals
and thus reduce pollutant discharge.
Typical in-line treatment systems for wastewaters in the printed board
industry are shown in Figures 7-39 and 7-40. An installation which
produces boards using the subtractive process was chosen as an example
since a large majority of printed boards are made in this fashion.
The boards are electroless plated with copper following the necessary
cleaning and surface treatment. Then they are successively
electroplated with copper and solder. Unwanted copper is then etched
261
-------
LIVE
STEAM
CAUSTIC
AMMONIA
WASTES
AMMONIA
BATCH
TREATMENT
COMMON
WASTES
SODIUM
HYPOCHLORITE
en
ro
CYANIDE
WASTES
CYANIDE
OXIDATION
FLOCCULATOR
SETTLING
TANK
SLUDGE
DISCHARGE
CHELATED
WASTES
FLOCCULATOR
SLUDGE
SETTLING
TANK
DRYING BEDS
RECYCLE
LANDFILL
FIGURE 7-38 END-OF-PIPE SYSTEM FOR PRINTED BOARD MANUFACTURERS
(FOR AMMONIATED WASTE WATERS)
-------
WASTE WATER FLOW
PARTS PLOW
CTl
00
PARTS
PRECLEANING gpRAY
AND FTNSING ™ . •. ArTTV»TTON ». - •» ACCELERATION
RINSE
(COUNTER
pr - ...-_.-
_
CLEANING ANE COPPER 4 STAGE CLEAN AND
RINSING DTUCP
(COUNTER ELECTROPLATE * CO ^SlWENT (COUNTER
CURRENT) r- LUJUU1NT ^ - CURRENT
1 1
1 1 ' '
1 L _i '
1 DISTILLATION | 1
L ~" "' 1
1
L
_
SPRAY SOLDER SPRAY CLEAN AND
FTCHTHG ^^ _^ ^ta _^MI RIMSE
•• RINSE •• STRIP * _ •" COUNTER
^. RINSE CURRENT
f ' '
L 1 R.O. tmiTjj 1 1
I
L
PARTS
L_
GOLD 3 STAGE
ELECTROPLATE CURRENT ^,
!
' [ION EXCHANGE fc 1
CLEAN t RINSE IMMERSION 3 STAGE PARTS
CURRENT TIN PIATING CURRENT
1 • ~l _
s
R
PRAY ELECTROLESS
lHstl COPPER PLATING
J SOLUTION T
SALVA
SOLDER
3
1 "" COU
j J~ (
I
ION EXCHANGE 1—
3
f-
OR i
t_y
1 — |_J>IS1
STAGE
rURRENT ^
I
j
NICKEL 3 STAGE
«. COWTKP
ELECTROPLATE CURRENT
r1
i
DISTILLATION |"
STAGE
CURRENT «- ,
1
1
riLLATION I
SLUDGE TO
LANDFILL
r
i
i
1
-
r-
BPT
CLARIFICATION DISCHA^E_
SYSTEM
FIGURE 7-39 IN-LINE TREATMENT SYSTEM FOR PRINTED BOARD PLANTS
(RECOVERY OF ELECTROLESS PLATING SOLUTION)
-------
WASTE WATER FLOW
PARTS FLOW
PARTS
PRECLEANING
AND RINSING
(COUNTER
J
ACTIVATION
SPRAY
RINSE
1
SPRAY
RINSE
1
ELECTROLESS
COPPER PLATING
3 STAGE
CURRENT
1
i
4 STAGE
COUNTER
CURRENT
CLEAN AND
RINSE
COUNTER
CURRENT
T
L
ETCHING
r-
SPRJ
RINE
[""R.O. 'UNIT l_J
L
ARTS
•»
GOLD
ELECTROPLATE
L
lY
E "" *•
r~
SOLDER
STRIP
3 STAGE
COUNTER
CURRENT
poN EXCHANGE 1
CLEAN « RINSE
!( COUNTER
CURRENT)
J_
IMMERSION
TIN PLATING
SPRAY
RIHSE
CLEAN AND H
RINSE
COUNTER ELE<
CURRENT
I
J J
PARTS^
1
1
3 STAGE
COUNTER
CURRENT
[•" pH ADJUSTMENT
PARTS ,
1
J- «. 1
ICKEL 3 STAGE
;TROPLATE CURRENT
1 — "^
* !
hi
SLUDGE TO
LANDFILL
PIL ^ DISCHAfiGE
-^ — •*'
TRATION
FIGURE 7-40 IN-LINE TREATMENT SYSTEM fOR PRINTED BOARD PLANTS
(EHD-OF-PIPE FILTRATION}
-------
away. Following a solder strip, the tabs of the boards are nickel and
gold electroplated. Some of the boards are then immersion tin plated.
A process sequence of this sort was found in plant ID's 4065, 4069,
4071, 6065, 17061, and 19063.
The in-line treatment systems for the printed board industry are based
upon two principles: reduction of water consumption and the recovery
of plating and etching solutions. Reduction of water used can be
accomplished by the application of countercurrent rinsing, spray
rinsing, and fog rinsing. Wherever applicable, a closed loop rinsing
system is best. By cutting back the volume of the water used, end-of-
pipe treatment is easier, less expensive, and more efficient.
There are several metal recovery techniques available for both of the
treatment systems presented, including reverse osmosis, distillation,
ion exchange, electrolytic recovery, and membrane filtration. For
copper electroplating, a distillation unit can be utilized with a
countercurrent rinse station. Water from the last stage of the rinse
goes to the distillation unit; the copper is separated out and
returned to the plating solution, and the water is returned to the
first station of the countercurrent rinse. If cyanide copper is used,
there is an added advantage of distillation treatment. The cyanide is
removed from the rinsewater and returned to the solution, thereby
eliminating the need for a cyanide oxidation system in the end-of-pipe
treatment.
Other electroplating solutions, such as solder, gold, and nickel can
be handled in a similar manner, using a recovery system in conjunction
with a rinsing system. These recovery units can be distillation
units, ion exchange units or reverse osmosis units, depending upon the
particular solution to be recovered and economic aspects.
In the system presented in Figure 7-39, there is a recovery unit on
the rinse station following the electroless copper operation. This
unit, a distillation unit, extracts the plating solution dragout from
the rinsewater. The water is returned to the first station of the
countercurrent rinse for reuse and the plating solution is stored
separately. This plating solution can be broken down and reused if
the plant makes up its own baths or it can be sold to a supplier or a
scavenger for reuse.
All the wastewater goes to a clarification system similar to the end-
of-pipe treatment system. This wastewater undergoes flocculation and
settling before discharge. The sludge in this system is periodically
collected, dewatered and sent to landfill.
In the system pictured in Figure 7-40, the rinsewaters from the
electroless plating operation join all the other wastewaters and are
collected in a neutralization tank. Here the water is pH adjusted and
265
-------
chemicals are added to cause flocculation. This wastewater and the
flocculants are pumped through a membrane filtration unit which can
effectively handle combined chelated and non-chelated waste streams.
The membrane filtration unit removes sufficient amounts of metals and
solids to allow discharge of the treated water. The sludge from the
unit is collected and sent to on-site landfill or hauled away by a
contractor.
There is another recovery technique which can be employed in a printed
board plant which has both additive and subtractive production
methods. This involves use of spent etchant from the subtractive
facility as plating bath make-up for additive plating. This technique
solves two problems: spent etchant disposal and the need for a high
purity copper salt for use in the electroless copper bath used in an
additive process. Printed board plant ID's 11065 and 30525 employ
such a system.
266
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SECTION VIII
COST OF WASTEWATER CONTROL AND TREATMENT
INTRODUCTION
This section presents the cost of implementing the major rinse and
treatment technologies described in Section VII. These rinse and
treatment costs as well as the costs of entire systems representing
conventional end-of-pipe treatment and in-line treatment and recovery
were determined by developing system costing logic and utilizing a
computer system for the required cost calculations. A discussion is
also presented to show that investment in rinse and treatment
techniques designed to recover plating solutions can result in
significant reductions in plant investment and operating costs. In
addition, the description of each control and treatment technology
presented in Section VII is extended to define non-water
characteristics. These nonwater characteristics include energy
requirements and an indication of the degree to which the technology
impacts air pollution, noise pollution, solid waste, and radiation.
COST ESTIMATES
Cost correlations and estimates are presented for individual waste
treatment and rinse technologies and for typical wastewater treatment
systems. Cost breakdown factors used in preparing these estimates are
discussed, assumptions are listed, system cost computations are
reviewed, and the computer techniques used are summarized.
The basic cost data came from a number of primary sources. Some of
the data were obtained during on-site surveys. Other data were ob-
tained through discussions with waste treatment equipment manufactur-
ers. Another block of data was derived from previous EPA projects
which utilized data from engineering firms experienced in the in-
stallation of waste treatment systems.
Technology Cost Estimates
Table 8-1 presents the list of individual wastewater treatment and
rinse technologies used in the electroplating industry. The individ-
ual process costs for these technologies are presented in Tables 8-2
through 8-24. These costs represent only the individual process costs
and do not include the subsidiary costs associated with system
construction. Therefore, addition of various process costs as
presented in Tables 8-2 through 8-24 to model a complete treatment
system will not yield an accurate treatment system cost estimate.
->67
-------
TABLE 8-1
INDEX TO TECHNOLOGY COST TABLES
Table Waste Treatment or Rinse Technology
8-2 Countercurrent Rinse (for other than Recovery
of Evaporative Plating Loss)
8-3 Countercurrent Rinse Used for Recovery of
Evaporative Plating Loss
8-4 Spray Rinse Used for Recovery of Evaporative
Plating Loss
8-5 Still Rinse Used for Recovery of Evaporative
Plating Loss
8-6 Clarification - Settling Tank; Continuous Treatment
8-7 Clarification - Settling Tank; Batch Treatment
8-8 Chromium Reduction - Continuous Treatment
8-9 Chromium Reduction - Batch Treatment
8-10 Cyanide Oxidation - Continuous Treatment
8-11 Cyanide Oxidation - Batch Treatment
8-12 pH Adjustment
8-13 Diatomaceous Earth Filtration
8-14 Submerged Tube Evaporation - Single Effect
8-15 Submerged Tube Evaporation - Double Effect
8-16 Climbing Film Evaporation
8-17 Atmospheric Evaporation
8-18 Flash Evaporation
8-19 Ultrafiltration
8-20 Membrane Filtration
268
-------
TABLE 8-1 (cont.)
8-21 Ion Exchange - In-Plant Regeneration
i
8-22 Ion Exchange - Service Regeneration
8-23 Cyclic Ion Exchange
8-24 Reverse Osmosis
269
-------
In general, the tables show costs for investment, total annual cost,
depreciation, cost of capital, operation and maintenance (less energy
and power), and energy and power. These costs are defined under the
subheadings to follow. Not all of these costs pertain to all tech-
nologies. Energy costs are often negligible, and some techniques such
as rinsing have no maintenance costs beyond what is already required
for the plating line.
Investment - Investment is the capital expenditure required to bring
the technology into operation. If the installation is a package con-
tract, the investment is the purchase price of the installed
equipment. Otherwise, it includes the equipment cost, cost of
freight, insurance and taxes, and installation costs.
Total Annual Cost - Total annual cost is the sum of annual costs for
depreciation, capital, operation and maintenance (less energy and
power) and energy and power (as a separate function).
Depreciation - Depreciation is an allowance, based on tax regula-
tions, for the recovery of fixed capital from an investment to be
considered as a noncash annual expense. It may be regarded as the
decline in value of a capital asset due to wear and obsolescence.
Capital - The annual cost of capital is the cost, to the plant, of
obtaining capital, expressed as an interest rate. It is equal to
the capital recovery cost (see the following section on cost
factors) less depreciation.
Operation and Maintenance - Operation and maintenance cost is the
annual cost of running the wastewater treatment or rinse
equipment. It includes labor and materials such as waste
treatment chemicals. As presented on the tables, operation and
maintenance cost does not include energy (power or fuel) costs
because these costs are shown separately.
Energy and Power - The annual cost of power and fuel is shown
separately, although it is commonly included as part of operation
and maintenance cost. Energy and power cost has been shown
separately because of its importance to the nation's economy.
Technology Costs and Assumptions
Specific cost data were generalized to obtain the cost correlations by
means of certain assumptions. Correlations were then verified by
checking them against independent sets of cost data. The specific as-
sumptions for each wastewater treatment process and rinse technique
are listed under the subheadings to follow. Costs are presented as a
function of process influent water flow rate except where noted
differently in the process assumptions. For all rinse techniques, a
270
-------
programmed hoist operation was assumed, and line conversion costs were
included. For operations of the cycle elevator conveyor type, line
conversion costs to incorporate rinse techniques are approximately 10
times the conversion cost of programmed hoist operations.
Single Stage Running Rinse - The costs of single stage running rinses
are discussed below. Costing assumptions are:
A. Unit cost is based on one open top stainless steel tank with
a depth of 1.22 meters (4 feet), length of 1.22 meters (4
feet), and width of 0.91 meters (3 feet). Investment cost
includes all water and air piping, a blower for agitation,
and conversion costs for programmed hoist operation.
B. Operation and maintenance costs include an electrical charge
for the blowers based on a capacity of 1,219 liters/min/sq.
meter of tank surface area (4 cfm/sq. ft.) at a discharge
pressure of 1,538 kg/sq. meter of tank depth (1 psi/18 in.).
Fan efficiency is assumed to be 60 percent. A rinse water
charge is also included. Rinse maintenance charges are
assumed to be negligible when compared to normal plating line
maintenance and are ignored.
For a dragin flow rate (i.e., plating tank dragout flow rate) of 22
liters/hour and a rinse ratio (plating solution concentration/final
rinse effluent concentration) of 363, the following typical costs are
incurred:
Investment ($) 3,505
Cost of Capital ($/Year) 224
Depreciation ($/Year) 701
Operation and Maintenance 2,156
(Less Energy and Power) ($/Year)
Energy and Power ($/Year) 126
Total Annual Cost ($/Year) 3,206
Countercurrent Rinse - The costs of countercurrent rinsing without
using the first stage for evaporative loss recovery are presented in
Table 8-2 as a function of the number of rinse tanks utilized.
Costing assumptions are:
A. Unit cost is based on open top stainless steel tanks with a
depth of 1.22 meters (4 feet), length of 1.22 meters (4
feet), and width of 0.91 meters (3 feet). Investment cost
271
-------
includes all water and air piping, a blower on each rinse
tank for agitation, and programmed hoist line conversions.
B. Operation and maintainance costs include a cost for
electricity for the blowers based on a capacity of 1,219
liters/min./sq. meter of tank surface area (4 cfm/sq. ft.)
at a discharge pressure of 1,538 kg/sq. meter/meter of tank
depth (1 psi/18 in.). Fan efficiency is assumed to be 60
percent. A water charge based on a rinse ratio of 8,180 is
also included. Rinse maintenance charges are assumed to be
negligible when compared to normal plating line maintenance
and are ignored.
Countercurrent Rinse Used for Recovery o_f Evaporative Plating Loss -
The costs of countercurrent rinsing with a rinse flow rate sufficient
to replace plating tank evaporative losses are presented in Table 8-3.
The results are tabulated for various evaporative rates which are
equal to the rinse water flow rates. Costing assumptions are:
A. Unit cost is based on a sufficient number of rinse stages to
replace the evaporative loss from a plating bath at approxi-
mately 60 degrees C while also maintaining a rinse ratio of
8,180.
B. Investment costs include open top stainless steel tanks with
a depth of 0.91 meters (3 feet), length of 1.22 meters (4
feet), and width of 1.22 meters (4 feet). All water and air
piping, a blower on each rinse tank for agitation, a liquid
level controller, solenoid, and pump are also included in the
investment cost. Operation is assumed to be programmed hoist
and line conversion costs are included.
C. Operation and maintenance costs include a cost for
electricity for the blowers based on a capacity of 1,219
liters/min/sq. meter of tank surface area (4 cfm/sq. ft.) at
a discharge pressure of 1,538 kg/sq. meter/meter of tank
depth (1 psi/18 in.). A fan efficiency of 60 percent is
assumed. A water charge is also included. Rinse maintenance
charges are assumed to be negligible when compared to normal
plating line maintenance and are ignored.
Spray Rinse - The costs of spray rinsing with a rinse flow rate
sufficient to replace plating tank evaporative losses are presented in
Table 8-4 as a function of the plating tank evaporative loss which is
equal to the rinse water flow rate. Costing assumptions are:
A. Unit cost is based on one open top stainless steel tank with
a depth of 0.91 meters (3 feet), length of 1.22 meters (4
feet), and width of 1.22 meters (4 feet) with 6 spray
272
-------
TABLE 8-2
COUNTERCURRENT RINSE (FOR OTHER THAN RECOVERY
OF EVAPORATIVE PLATING LOSS)
Number of Rinse Tanks 345
Investment $8,203 $10,553 $12,902
Annual Costs:
Capital Cost 523 673 823
Depreciation 1,641 2,111 2,580
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 20 9 6
Energy & Power Costs 377 503 628
Total Annual Cost $2,561 $ 3,296 $ 4,038
273
-------
TABLE 8-3
COUNTERCURRENT RINSE USED FOR RECOVERY OF
EVAPORATIVE PLATING LOSS
Evaporative Rate
(Liters/Hr) 15.3 24.0 50.8
Investment $13,753 $11,352 $ 8,951
Annual Costs:
Capital Costs 877 724 571
Depreciation 2,751 2,270 1,790
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 4 6 14
Energy & Power Costs 628 503 377
Total Annual Cost $ 4,261 $ 3,504 $ 2,752
Note: Savings due to recovery of plating solution
are not presented in this table.
274
-------
TABLE 8-4
SPRAY RINSE USED FOR RECOVERY OF
EVAPORATIVE PLATING LOSS
Evaporative Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
$
60.8
3,472
221
694
101.3
$ 3,472
221
694
135.0
$ 3,472
221
694
16
0
932
27
0
$ 943
36
0
$ 952
Note: Savings due to recovery of plating solution
are not presented in this table.
275
-------
nozzles. Investment cost includes the tank, spray nozzles,
conductivity meter controller, pump, solenoid, piping, and
conversion of programmed hoist operation.
B. Operation and maintenance cost is the rinse water charge
based on replacing the plating tank evaporative losses. A
combined spray efficiency of 50 percent is assumed. The
combined spray efficiency accounts for the amount of spray
water hitting the part and the amount of the part that can be
hit by the spray. Power, filter replacement, and maintenance
costs are negligible when compared to normal plating line
operation and maintenance and are ignored.
For spray rinsing without evaporative recovery, the only variation in
unit cost for various dragin flow rates is a variation in the rinse
water charge. Items included in non-recovery spray rinsing investment
costs are identical to those items included in recovery spray rinsing
except that the pump is omitted.
For a dragin flow rate of 15.1 liters/hour, rinse ratio of 8,108,
spray efficiency of 50 percent, and tank dimensions of 1.22 meters (4
feet) by 1.22 meters (4 feet) by 0.91 meters (3 feet), the following
costs are typical:
Investment ($) 3,350
Cost of Capital ($/Year) 214
Depreciation ($/Year) 670
Operation and Maintenance
(Less Energy & Power) ($/Year) 73
Energy and Power ($/Year) 0
Total Annual Costs ($/Year) 957
Still Rinse - The costs of still rinsing with a return from the rinse
tank sufficient to replace plating tank evaporative losses are
presented in Table 8-5 as a function of the plating tank evaporative
rate. Costing assumptions are:
A. Unit cost is based on one open top stainless steel tank with
a depth of 0.91 meters (3 feet), length of 1.07 meters (3.5
feet), and width of 1.07 meters (3.5 feet) with 1,041 liter
capacity. Investment cost includes the tank, liquid level
controller, pump, and conversion of programmed hoist
operation.
276
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TABLE 8-5
STILL RINSE USED FOR RECOVERY OF
EVAPORATIVE PLATING LOSS
Evaporative Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Costs $
Notes
$
29.7
2,971
190
594
59.5
$ 2,971
190
594
99.1
$ 2,971
190
594
8
0
792
16
0
$ 800 $
27
0
810
Savings due to recovery of plating solution
are not presented in this table.
277
-------
B. The operation and maintenance cost is the rinse water charge
based on replacing the plating tank evaporative losses and
maintaining the effluent rinse concentration less than or
equal to 30 percent of the influent concentration (i.e.,
plating tank dragout). The still rinse tank is assumed to be
hose filled and dumped to the plating
tank. Maintenance and power costs are negligible when
compared to normal plating line maintenance and power costs
and are ignored.
For still rinsing without evaporative recovery, only the cost of the
tank and conversion of programmed hoist operation are included in the
investment cost. The only variation in costs for various dragin flow
rates is a variation in the rinse water charge. For a dragin flow
rate of 36 liters/hour (55.2 square meters of various shaped parts
plated per hour) and tank dimensions of 1.22 meters (4 feet) by 1.22
meters (4 feet) by 0.91 meters (3 feet), the following costs are
typical:
Investment ($) 2,907
Cost of Capital ($/¥ear) 185
Depreciation ($/Year) 581
Operation & Maintenance
(Less Energy & Power) ($/Year) 27
Energy & Power ($/¥ear) 0
Total Annual Costs 794
Clarification - Settling Tank - Settling tank clarification costs are
presented for continuous treatment in Table 8-6 and for batch treat-
ment in Table 8-7. Costing assumptions are:
A. For continuous clarification with an influent flow rate
greater than or equal to 9857 liters per hour (2600
gallons/hour), costs include a concrete flocculator and its
excavation, a concrete settling tank with skimmer and its
excavation, and two centrifugal sludge pumps. For continuous
clarification with influent flows less than 9857 liters/hour
(2600 gallons/hour), costs include two above ground conical
unlined carbon steel tanks and two centrifugal sludge pumps.
B. The flocculator size is based on a 45 minute retention time,
a length to width ratio of 5, a depth of 2.44 meters (8
feet), a thickness of 0.305 meters (1 foot), and an excess
278
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CLARIFICATION-CON'! 1N=.
Flow Rate
(Liters/Hr)
Investment ~'7'
Annual Costs:
Capital Costs I
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 2
Energy & Power Costs
Total Annual Cost I2"1
CLARIFICATICN-EA'ICH T:
Flow Rate
(Liters/Hr) i H'
Investment $25,5
Annual Costs:
Capital Costs '• ';
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost * ';
-------
capacity factor of 1.2.
flocculator.
A mixer is included in the
C.
D.
E.
F.
G.
H.
I.
The settling tank is sized for a hydraulic loading of 1356.7
liters/hour per square meter (33.3 gallons/hour/ sq. ft.), a
4 hour retention time, and an excess capacity factor of 1.2.
The two conical unlined carbon steel tanks are designed for a
4 hour retention time in each tank.
The sludge pumps are assumed operational one hour for each 12
hours of production and have 20 percent excess pumping
capacity. Costs include motors, starters, alternators, and
necessary piping.
Lime and sodium sulfide are added for metal and solids
removal. All power requirements are based on data from a
major manufacturer.
For batch clarification, the dual centrifugal sludge pumps
and the chemical demands are identical to continuous
clarification. However, the flocculator and settling tank
are replaced with dual above ground cylindrical carbon steel
tanks.
Each tank is sized by an 8 hour retention time and an excess
capacity factor of 1.2. Each tank has a mixer that operates
1 hour for each 8 hours that the tank is being used.
Manpower estimates for operation and maintenance reflect
varying schemes for continuous and batch treatment.
the
Chromium Reduction - Chromium reduction costs are presented in Table
8-8 for continuous treatment and in Table 8-9 for batch treatment.
Costing assumptions are:
A. For both continuous and batch treatment, sulfuric acid is
added for pH control. A 90 day supply is stored in the 25
percent aqueous form in an above-ground, covered concrete
tank, 0.305 meters (1 foot) thick.
B. For continuous chromium reduction, the single chromium
reduction tank is sized as an above-ground cylindrical
concrete tank with a 0.305 meter (1 foot) wall thickness, a
45 minute retention time, and an excess capacity factor of
1.2. Sulfur dioxide is added to convert the influent
hexavalent chromium to the trivalent form.
280
-------
TABLE 8-8
CHROMIUM REDUCTION - CONTINUOUS TREATMENT
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
3,785
$20,416
1,303
4,083
1,086
256
$ 6,728
TABLE
CHROMIUM REDUCTION
Flow Rate
( liter s/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
189
$8,493
541
1,699
155
256
$2,651
7,570
$21,538
1,374
4,308
1,375
256
$ 7,313
8-9
18,925
$24,003
1,531
4,801
2,089
256
$ 8,677
- BATCH TREATMENT
379
$9,535
608
1,907
295
256
$3,066
1,893
$14,405
919
2,881
1,415
256
$ 5,471
281
-------
C. The control system for continuous chromium reduction consists
of:
1 immersion pH probe and transmitter
1 immersion ORP probe and transmitter
1 pH and ORP monitor
2 slow process controllers
1 sulfonator and associated pressure regulator
1 sulfuric acid pump
1 transfer pump for sulfur dioxide ejector
2 maintenance kits for electrodes, and miscellaneous
electrical equipment and piping.
D. For batch chromium reduction, the dual chromium reduction
tanks are sized as above-ground cylindrical concrete tanks,
0.305 meters (1 foot) thick, with a 4 hour retention time,
and an excess capacity factor of 1.2. Sodium bisulfite is
added to reduce the hexavalent chromium.
E. A completely manual system is provided for batch operation.
Subsidiary equipment includes:
1 sodium bisulfite mixing and feed tank
1 metal stand and agitator collector
1 sodium bisulfite mixer with disconnects
1 sulfuric acid pump
1 sulfuric acid mixer with disconnects
2 immersion pH probes
1 pH monitor, and miscellaneous piping.
F. Manpower estimates for operation and maintenance reflect the
varying schemes for continuous and batch operation.
G. A constant power requirement cf 2 horsepower is assumed for
chemical mixing.
For very small plating establishments, treatment may also be
accomplished with a completely manual system. With this approach,
flat bottom, open top, standard resin fiberglass tanks hold the daily
flow and chemicals are added manually at the end of each shift.
282
-------
Equipment costs range from $329 to $5,100 for daily flow rates from
1,893 to 37,850 liters per day.
Cyanide Oxidation - Cyanide oxidation costs are shown in Table 8-10
for continuous treatment and in Table 8-11 for batch treatment.
Costing assumptions are:
A. For both continuous and batch treatment, the cyanide
oxidation tank is sized as an above ground cylindrical tank
with a retention time of 4 hours based on the process flow.
Cyanide oxidation is normally done on a batch basis;
therefore, two identical tanks are employed.
B. Cyanide removal is accomplished by the addition of sodium
hypochlorite. Sodium hydroxide is added to maintain the
proper pH level. A 60 day supply of sodium hypochlorite is
stored in an in-ground covered concrete tank, 0.305 meters (1
foot) thick. A 90 day supply of sodium hydroxide is also
stored in an in-ground covered concrete tank, 0.305 meters (1
foot) thick.
C. Mixer power requirements for both continuous and batch
treatment are based on 2 horsepower for every 3,000 gallons
of tank volume. The mixer is assumed to be operational 25
percent of the time that the treatment system is operating.
D. A continuous control system is costed for the continuous
treatment alternative. This system includes:
2 immersion pH probes and transmitters
2 immersion ORP probes and transmitters
2 pH and ORP monitors
2 2-pen recorders
2 slow process controllers
2 proportional sodium hypochlorite pumps
2 proportional sodium hydroxide pumps
2 mixers
3 transfer pumps
1 maintenance kit
2 liquid level controllers and alarms, and
miscellaneous electrical equipment and
piping.
283
-------
TABLE 8-10
CYANIDE OXIDATION - CONTINUOUS TREATMENT
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
3,785 5,
$47,808 $51,
3,050 3,
9,561 10,
2,218 2,
90
$14,920 $16,
TABLE 8-11
CYANIDE OXIDATION - BATCH
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
189
$10,325 $13,
659
2,065 2,
464 1,
5
$ 3,192 $ 5,
678
875
310
395
750
135
570
7,570
$55,556
3,544
11,111
3,563
180
$18,098
TREATMENT
757
258
846
652
854
18
370
1,893
$17,069
1,089
3,414
4,636
45
$ 9,184
284
-------
E. A complete manual control system is costed for the
batch treatment alternative. This system includes:
2 pH probes and monitors
1 mixer
1 liquid level controller and horn
1 proportional sodium hypochlorite pump
1 on-off sodium hydroxide pump and PVC piping
from the chemical storage tanks.
F. Manpower estimates for operation and maintenance reflect the
varying schemes for continuous and batch operation.
For very small plating establishments, a completely manual treatment
system may be used. This system consists of flat bottom, open top,
standard resin fiberglass tanks that hold the daily flow. Chemicals
are added manually at the end of each shift. For daily flow rates of
1,893 to 37,850 liters per day, equipment costs range from $329 to
$5,100.
p_H Adjustment - pH adjustment costs are presented in Table 8-12.
Costing assumptions are:
A. The pH adjustment tank is an in-ground concrete tank with a
45 minute retention time. The tank has a length to width
ratio of 5, a depth of 2.44 meters (8 feet), a thickness of
0.305 meters (1 foot), and an excess capacity factor of 1.2.
A mixer and tank excavation are included in the costs.
B. Lime is added to obtain the desired effluent pH. Mixer power
is based on a representative installation with 1 turnover per
minute.
Diatomaceous Earth Filtration - Diatomaceous earth filtration costs
are presented in Table 8-13. Costing assumptions are:
A. Unit cost is based on one filter station comprised of one
filter, one mix tank, two pumps, and associated valving. The
unit is shut down one hour each day of operation for cleaning
and filter precoating.
B. Diatomaceous earth addition rates, power requirements, and
manpower requirements are based on manufacturer's data.
Submerged Tube Evaporation - Submerged tube evaporation costs are
shown for single effect units in Table 8-14 and for double effect
units in Table 8-15. Costing assumptions are:
285
-------
Flow Rate
(Liters/Mr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
TABLE 8-12
pH ADJUSTMENT
Flow Rate
492 4,921
$1,452 $4,921
49,205
$18,855
$
93
290
286
8
677
314
984
1,036
79
$2,413
$ 1,203
3,771
3,758
1,503
$10,315
TABLE 8-13
DIATOMACEOUS EARTH FILTRATION
Flow Rate
(Liters/Hr) 189
Investment $8,823
Annual Costs:
Capital Costs 563
Depreciation 1,765
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 3,936
Energy & Power Costs 22
Total Annual Costs $6,286
4,731 47,313
$27,707 $62,819
1,768 4,008
5,541 12,564
6,046 29,872
302 1,970
$13,657 $48,414
286
-------
TABLE 8-14
SUBMERGED TUBE EVAPORATION - SINGLE EFFECT
Flow Rate
(Liters/Mr)
Investment
Annual Costs?
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
SUBMERGED TUBE
Flow Rate
(Liters/Mr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs {Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Costs
95
$11,156
712
2,231
1,678
6,048
$10,669
TABLE 8-1
379
$23,486
1,498
4,697
6,713
20,117
$33,026
5
EVAPORATION - DOUBLE
189
$19,424
1,239
3,885
1,678
6,048
$12,850
568
$35,039
2,235
7,008
5,035
15,844
$30,123
757
$34,077
2,174
6,815
13,427
37,815
$60,231
EFFECT
1,136
$50,841
3,244
10,168
10,070
29,270
$52,752
287
-------
A. Unit size, power requirements, and operational expenses (less
energy and power) are based on data supplied by the
manufacturer for standard size units.
B. Investment cost includes the basic evaporator and bath
purification device.
C. Evaporative heat of 583 cal/gram of wastewater is required
for single effect units, and 292 cal/gram
is required for double effect units. The heating value of
fuel is assumed to be 10,140 cal/gram (Lower Heating Value
(LHV), API of 30) with a heat recovery of 85 percent.
D. A cooling water charge is not included in the operation and
maintenance cost. A cooling water circuit is assumed to
already exist for the plant.
E. The condensate is assumed to be pure with the percentage of
condensate and concentrate flow split based on the manu-
facturer's operational manual.
Climbing Film Evaporation - Climbing film evaporation costs are
presented in Table 8-16. Costing assumptions are:
A. Unit sizes and costs are based on data supplied by the manu-
facturer for unit capacities of 114 to 284 liters/hour.
Multiple units are used as needed.
B. Investment cost includes the basic evaporator and a bath
purification device.
C. Evaporative heat of 583 cal/gram of wastewater is required.
The heating value of fuel is assumed to be 10,140 cal/gram
(LHV, API of 30) with a heat recovery of 85 percent.
D. The electrical requirement is based on three pump horsepower
per evaporation unit.
E. A cooling water charge is not included. A cooling water
circuit is assumed to already exist for the plant.
F. The condensate is assumed to be pure.
Atmospheric Evaporation - Atmospheric evaporation costs are presented
in Table 8-17. Costing assumptions are:
A. Unit sizes are based on data supplied by the manufacturer for
standard unit capacities of 379 to 3,407 liters/hr. Two
units provide a capacity to 6,814 liters per hour, maximum.
B. Investment costs include the basic evaporator with mid-range
corrosion protection applied to the equipment and with bath
purification.
288
-------
TABLE 8-16
CLIMBING FILM EVAPORATION
Flow Rate
(Liters/Hr) 114 795 4,731
Investment $27,559 $104,470 $600,090
Annual Costs:
Capital Costs 1,758 6,665 38,285
Depreciation 5,512 20,894 120,018
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 000
Energy & Power Costs 5,533 37,106 220,522
Total Annual Cost $12,803 $ 64,665 $378,825
TABLE 8-17
ATMOSPHERIC EVAPORATION
Flow Rate
(Liters/Hr) 379 1,893 6,813
Investment $20,430 $45,967 $143,008
Annual Costs:
Capital Costs 1,303 2,933 9,124
Depreciation 4,086 9,193 28,602
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 155 155 155
Energy & Power Costs 18,443 92,213 331,968
Total Annual Cost $23,987 $104,494 $369,848
289
-------
C. Evaporative heat of 583 cal/gram of wastewater is required.
The heating value of fuel is assumed to be 10,140 cal/gram
(LHV, API of 30) with a heat recovery of 85 percent.
D. The electrical requirement is based on a fan system power
requirement of 10 horsepower per 379 liters per hour.
E. A cooling water circuit is assumed to already exist for the
plant, and the cost of cooling water is not included.
F. The condensate is assumed to be pure.
Flash Evaporation - The costs for flash evaporation are presented in
Table 8-18. Costing assumptions are:
A. Unit cost is based on a chromic acid influent requiring
fiberglass vessels and tantalum heat exchangers. Investment
cost includes the basic evaporator and bath purification and
is based on data supplied by the manufacturer.
B. Operation and maintenance cost includes the fuel requirements
for the evaporator and electrical requirements for the pumps.
C. Evaporative heat of 583 cal/gram of wastewater is required.
The fuel requirements are based on a heating value of 10,140
cal/gram (LHV, API of 30) and a heat recovery of 85 percent.
D. The electrical requirement is based on a constant six
kilowatts for the pumps.
E. A cooling water circuit is assumed to already exist for the
plant, and the cost of cooling water is not included.
F. The condensate is assumed to be pure.
Evaporative Cost Comparison - Figure 8-1 presents, for comparison
purposes, the relative investment cost of the four different types of
evaporation studied. Figure 8-2 presents the relative total annual
costs for these evaporation processes. These costs are based on the
various manufacturers' standard equipment sizes.
Ultrafiltration - Ultrafiltration costs are presented in Table 8-19.
Costing assumptions are:
A. The unit is sized by a hydraulic loading of 1,430 liters per
day per square meter of surface area and an excess capacity
factor of 1.2.
B. Power is based on 30.48 meters of pump head from the equation
HP = meters x specific gravity x (liters/min recirc) /
(3,960 x 0.7)
290
-------
TABLE 8-18
FLASH EVAPORATION
Flew Rate
(Liters/Hr) 189 568 1,136
Investment $46,207 $62,987 $76,585
Annual Costs:
Capital Costs 2,948 4,018 4,886
Depreciation 9,241 12,597 15,317
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 000
Energy & Power Costs 9,559 26,649 52,284
Total Annual Costs $21,749 $43,265 $72,487
TABLE 8-19
ULTRAFILTRATION
Flow Rate
(Liters/Hr) 95 4,731 9,463
Investment $9,843 $189,773 $379,546
Annual Costs:
Capital Costs 628 12,107 24,214
Depreciation 1,969 37,955 75,909
Operation & Maintenance
Costs (Excluding
Energy & Power Costs) 5,237 28,662 44,360
Energy & Power Costs 20 1,025 2,050
Total Annual Cost $7,854 $79,749 $146,533
291
-------
100,000
90,000
80,000 -
70,000 -
60,000 •
•to
W
50,000
40,000
30,000
20,000
10,000
1
0
0
1
352
1,333
i
704
2,666
i
1,057
4,000
i
1,409
5,333
i
1,761
6,666
i
2,11:
8,00(
FLOW
FIGURE 8-1. EVAPORATION INVESTMENT COST
292
-------
225,000
200,000
175,000
150,000
E-i
125,000
D
Z
100,000
75,000
50,000
25,000
0
0
0
352
1,333
704
2,666
1,057
4,000
FLOW
1,409
5,333
1,761
6,666
2,113 (GPH)
8,000(LIT/HR)
FIGURE 8-2. EVAPORATION TOTAL ANNUAL COST
293
-------
where: liters/min recirc =' 35
specific gravity = 1
HP = the horsepower
requirements for every 18,925 liters/day.
Membrane Filtration - The costs of membrane filtration are presented
in Table 8-20. Costing assumptions are:
A. Investment cost includes the complete membrane filtration
module and installation and.is based on data supplied by the
manufacturer.
B. Sodium hydroxide (NaOH) is added to precipitate the heavy
metals as hydroxides.
C. Operation and maintenance cost includes maintenance labor,
chemicals and electrical power to operate the membrane fil-
tration module pump, mixers, and sump pumps.
D. The effluent sludge stream is assumed to be 15 percent
solids.
Ion Exchange - In-Plant Regeneration - Ion exchange costs with in-
plant regeneration are presented in Table 8-21. Costing assumptions
are:
A. The unit size is based on two columns to allow both cation
and anion exchangers of sodium and chloride, rather than
hydrogen. An average resin life of seven years is assumed.
B. Regeneration is performed with a 10 percent aqueous solution
of sulfuric acid. 2.0 kg of sulfuric acid is required for
each 1.0 kg of removed contaminants. Regeneration
requirements ure based on typical influent values for
chromium, cadmium, and nickel.
C. Heavy metals removal is assumed to be complete.
Ion Exchange - Service Regeneration - Ion exchange costs with service
regeneration are presented in Table 8-22. Costing assumptions are:
A. Unit sizes and pump powe'r requirements are based on data
supplied by the manufacturer for standard system flow
capacities.
B. Replacement units are installed in place of exhausted units
every two months. Regeneration is performed by the manufac-
turer for a service charge.
294
-------
TABLE 8-20
MEMBRANE FILTRATION
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding
Energy & Power Costs)
Energy & Power Costs
Total Annual Cost
ION EXCHANGE
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
3,407
$42,136
2,688
8,427
8,075
2,275
$21,465
TABLE
6,813 10
$84,273 $126
5,376 8
16,855 25
13,046 18
2,275 2
$37,552 $ 53
8-21
,220
,409
,065
,282
,017
,275
,639
- IN-PLANT REGENERATION
95
$2,789
178
558
951
0
$1,687
4,731 9,
$27,558 $42,
1,758 2,
5,512 8,
9,338 15,
0
$16,608 $27,
463
660
722
532
912
0
166
295
-------
TABLE 8-22
ION EXCHANGE - SERVICE REGENERATION
Flow Rate
(Liters/Hr) 795
Investment $5,040
Annual Costs:
Capital Costs 345
Depreciation 1,080
Operation & Maintenance
Costs (Excluding Energy
& Power costs) 1,737
Energy & Power Costs 68
Total Annual Cost $3,230
4,731 9,463
$16,372 $21,840
1,044 1,393
3,274 4,368
6,241 10,258
203 406
$10,762 $16,425
TABLE 8-23
CYCLIC ION EXCHANGE
Influent Chromium Mass (Kg/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
0.91 2.72 4.08
$13,695 $27,034 $34,748
874 1,725 2,217
2,739 5,407 6,950
2,690 8,278 12,503
203 401 515
$ 6,506 $15,811 $22,185
296
-------
C. Metals, cyanide, and sulfates are removed to levels specified
by the manufacturer.
Cyclic Ion Exchange - The costs for cyclic ion exchange are presented
in Table 8-23 as a function of influent chromium mass. The same costs
can be generated with nickel as the critical influent mass if the fol-
lowing mass equivalents are maintained:
Chromium Mass Nickel Mass
(kg/hour) (kg/hour)
0.91 3.40
2.72 7.47
4.08 9.98
Costing assumptions are:
A. Unit cost is determined by the influent chromium or nickel
mass. Investment cost includes the skid mounted ion exchange
system and start-up servicing. An auxiliary evaporator is
not generally recommended by the manufacturer, and costs for
this device are not included.
B. Operation, maintenance, and utility costs are included. The
utility cost is an electrical charge for pump operation.
Reverse Osmosis - The costs of a spiral wound cellulose acetate
reverse osmosis system are presented in Table 8-24. Costing
assumptions are:
A. Unit investment, power, and operation and maintenance costs
are based on permeate recovery of 95 percent as applied to
manufacturers' cost data in gal/hr of permeate recovery.
Unit cost can vary depending on whether the unit is designed
for chromium or nickel removal. The unit costs presented are
for nickel removal.
B. Installation cost is considered negligible when compared to
equipment cost and is not included in investment cost,
C. Total operation and maintenance cost includes system and pump
maintenance, pump reconditioning, and a membrane replacement
cost based on membrane life of 1 1/2 years.
Comparison of Various In-Line and End-of-Pipe Process Costs
A comparison of the wastewater treatment process investment and annual
costs presented in Tables 8-14 through 8-24 can best be made by
placing the treatment processes in the following order:
297
-------
TABLE 8-24
REVERSE OSMOSIS
Flow Rate
(Liters/Mr) 2,366 4,731 9,462
Investment $25,129 $38,658 $60,569
Annual Costs:
Capital Costs 1,603 2,466 3,864
Depreciation 5,026 7,732 12,114
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 4,873 9,675 20,761
Energy & Power Costs 1,404 2,144 3,536
Total Annual Cost $12,906 $22,017 $40,275
298
-------
1. Reverse osmosis
2. Ion exchange, which includes ion exchange with service
regeneration, ion exchange with in-plant regeneration, and
cyclic ion exchange
3. Membrane filtration
4. Ultrafiltration
5. Atmospheric evaporation
6. Vacuum evaporation, consisting of submerged tube, climbing
film, and flash modes of vacuum evaporation
The lowest required investment is for the reverse osmosis and ion ex-
change processes. The investment costs for both of these are very
similar. The next lowest investment requirement is for membrane fil-
tration which, in turn, is cheaper than atmospheric evaporation. The
most expensive treatment processes are the ultrafiltration and vacuum
evaporation processes both of which have similar investment
requirements.
When comparing total annual costs of the wastewater treatment
processes, reverse osmosis and ion exchange remain the least
expensive, closely followed by membrane filtration. These three are
followed by ultrafiltration which has total annual costs approximately
midway between the lowest and highest processes. The most expensive
in terms of total annual costs are atmospheric and vacuum evaporation,
which have similar total annual cost levels. The high annual cost for
the evaporation processes is caused by the fuel required to provide
the heat to vaporize the wastewater. For the purpose of these cost
comparisons, it was assumed that fuel must be burned specifically to
feed the evaporation devices. If, in fact, a plant already has waste
heat available, it is possible to significantly lower the fuel
requirement, and, thus, the total annual cost of the evaporation
processes.
System Cost Estimates (End-Of-Pipe Treatment)
This section presents the system cost estimates of the end-of-pipe
chemical destruct treatment systems. A wide range of flow rates is
presented to model a wide spectrum of plant sizes.
A representative end-of-pipe treatment system is schematically
depicted in Figure 8-3. The chemical oxidation of cyanide, the
chemical reduction of chromium, and the segregated chelated waste
clarifier are shown as optional treatment processes. The use of any
of these treatment processes is determined by the production processes
299
-------
o
o
*l
H
G
00
I
u>
W
I
o
HI
31
W
25
CO
K
cn
^
W
CHROMIUM
WASTES
CHROMIUM
REDUCTION
1 (OPTIONAL)
CYANIDE r '
WASTES 1 CYANIDE ,
- — — . — - - n Y T n A T T nttf »
1 (OPTIONAL) '
L . ,. . J
CLEANING AND
OTHER WASTES
~_ .... . — fc.
RECYCLE 1
'
CLARIFICATION
N ' CLARIFICATION
J \ (OPTIONAL)
L J
DIS<
' f "
CHELATED
WASTES
SLUDGE
DRYING BEDS
CONTRACTOR REMOVAL
OF SLUDGE
-------
being employed at the plant. For example, electroless plating on
plastics requires the chromium reduction process because of typical
production processes of chromic acid pre-etching and etching. Cyanide
oxidation is required if cyanide is used in the process baths at the
plant. A separate clarifier is required for metal removal if a
chelated waste stream is generated at the plant. For the purposes of
the end-of-pipe treatment system cost estimates, chromium reduction
and cyanide oxidation are assumed to be required treatment processes.
The costing assumptions for the chromium reduction, cyanide oxidation,
and clarifier wastewater treatment processes were discussed above in
"Technology Costs and Assumptions". In addition to these processes,
sludge drying beds and contractor removal are also required for end-
of-pipe treatment.
Sludge drying beds are used for sludge dewatering. The dewatered
sludge is removed by a contractor and deposited in a secure landfill.
A sludge bed loading of 0.318 liters per hour per square meter (0.0078
gallons per hour per square foot) with a bed excavated to a depth of
1.2 meters (4 feet) and an excess capacity factor of 1.5 are used to
calculate the required drying bed area. This unit is not sized for
any influent flow rate less than 189 liters per day (50 gallons per
day) as the bed area becomes too small to warrant construction.
Separated water is recycled to the clarifier inlet. Since this volume
flow is so low, it is ignored when calculating the clarification
costs.
Table 8-25 presents costs for the end-of-pipe treatment system for
various treatment system influent flow rates for a plant with no
electroless plating operations. A plant with electroless plating
operations would require a separate clarifier for the segregated
chelated waste stream. The basic cost elements used in preparing this
table are the same as those presented for the individual technologies:
investment, annual capital cost, annual depreciation, annual operation
and maintenance cost (less energy and power cost), energy and power
cost, and total annual cost. These elements were discussed in detail
earlier in this section. Investment and annual operation and
maintenance cost (less energy and power cost) are divided into
wastewater treatment and sludge handling categories. Table 8-26
presents end-of-pipe treatment system costs where the separate
clarifier is required for the segregated chelated waste stream.
For the cost computation, a "least cost" treatment system selection is
performed. This procedure calculates the costs for a batch treatment
system, a continuous treatment system, and haulaway of the complete
wastewater flow over a 10 year comparison period and selects the
cheapest system. A typical "least cost" treatment system is indicated
on Tables 8-25 and 8-26 for the conditions outlined below.
301
-------
TABLE 8-25
END-OF-PIPE TREATMENT WITHOUT CHELATED WASTES
Total Flow Rate (Liters/Mr)
Least Cost System
Investment Costs:
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs(Excluding Energy &
Power Costs)
Wastewater Treatment
Sludge Handling 0 & M
Total 0 & M
Sludge Hauling
Energy & Power Costs
Total Annual Costs
7,885 23,655 236,562
Batch Batch Continuous
$ 96,142 $145,166 $431,143
22,600 39,000 247,000
$118,742 $184,166 $678,143
7,576
23,748
11,750
36,833
43,266
135,628
7,555
4,278
11,833
1,557
19,731
4,278
24,009
4,680
33,267
63,000
46,267
46,800
627 1,341 1,057
$ 45,341 $ 78,613 $273,018
302
-------
TABLE 8-26
END-OF-PIPE TREATMENT WITH CHELATED WASTES
Total Flow Rate (Liters/Hr)
Least Cost System
Investment Costs:
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs(Excluding Energy &
Power Costs)
Wastewater Treatment
Sludge Handling 0 & M
Total 0 & M
Sludge Hauling
Energy & Power Costs
Total Annual Costs
7,885
Batch
$129,269
22,600
$151,869
9,689
30,734
9,904
4,278
14,182
1,557
611
$ 56,413
23,655 236,563
Batch Continuous
$183,313 $516,802
39,000 247,000
$222,313 $763,802
14,183
44,463
48,731
52,760
22,122 36,041
4,278 13,000
26,400 49,041
4,680 46,800
1,291 1,057
$ 91,017 $2.98,389
303
-------
The various investment costs assume that the treatment system must be
specially constructed and include all subsidiary costs discussed under
the Cost Breakdown Factors
segment of this section. Operation and maintenance costs assume
continuous operation, 24 hours a day, 5 days per week, for 52 weeks
per year. The typical waste loads and treatment system influent flow
rates were based on the results of detailed waste and production
analyses of the plants surveyed. Chromium and cyanide bearing wastes
are each approximately 10 percent of the total plant wastewater
discharge. When chelated wastes are present, they may amount to
approximately 10 percent of the raw waste loading. The remainder of
the wastewater flow appears as the common acid - alkaline stream. The
total wastewater flow rates presented on Tables 8-25 and 8-26 are
identical. However, chelated wastes have different parameter
concentrations than the other waste streams. Therefore, a mass
balance does not exist between Tables 8-25 and 8-26, and the costs in
these two tables are not directly comparable.
Trie actual costs of installing and operating an end-of-pipe treatment
system at a particular plant may be substantially below the tabulated
values. Reductions in investment and operating costs are possible in
several areas. Design and installation costs may be reduced by using
plant engineering and maintenance personnel instead of contracting the
work. Equipment costs may be reduced by using or modifying existing
equipment instead of purchasing all new equipment. Application of an
excess capacity factor, which increases the size of most equipment to
compensate for shutdowns, may be unnecessary. Excavation and
foundations costs could be reduced if an existing concrete pad or
floor can be utilized. Equipment size requirements may be reduced by
the ease of treatment (for example, shorter retention time) of
particular waste streams. Substantial reductions in both investment
and operating cost could be realized if a plant reduced its water use
rate by various in-plant techniques. Then, to estimate its costs from
the tables, the plant would use the projected flow rate rather than
the current flow rate. If a plant has lower raw waste concentrations
than those indicated in Section V, investment and, in particular,
operating costs will be lower. The tabulated costs are based on
around-the-clock operation 260 days per year. Thus, if a plant
operates one or two shifts per day or has an annual shutdown period
operation costs would be significantly lower. In some parts of the
country, operating costs would be lower because of wage rates lower
than the value used in the computations. Reductions in labor cost by
using operating and maintenance personnel on a shared (part time)
basis may also be practical.
Of the aforementioned cost reduction techniques, several were observed
at plants visited during this study. The observed cost reduction
techniques were;
304
-------
1. System design and installation performed by plant engineering
and maintenance personnel rather than by a contractor
2. Modification of existing wastewater treatment equipment,
rather than purchase of new equipment, to improve wastewater
treatment control
3. Utilization of existing concrete pads and flooring
4. Reduction in water use rate by in-plant production process
modifications
5. Non-continuous plant operation
Cost estimates were also generated for an end-of-pipe batch treatment
system for a small plating shop utilizing in-plant wastewater control
techniques. The plating shop was assumed to operate eight hours per
day, five days per week with a plating production rate of 75 square
meters per hour and a water rate of 32 liters per square meter plated.
This same system is applicable to a plating shop plating 150 square
meters per hour with a water use rate of 16 liters per square meter.
Approximately twenty-five percent of the water was assumed to be
cyanide bearing and segregated from the remainder of the wastewater.
System costs are based on a small plater treatment system consisting
of batch cyanide oxidation and pH adjustment. The process assumptions
for both cyanide oxidation and pH adjustment were discussed above in
"Technology Costs and Assumptions".
To install this end-of-pipe treatment system requires an investment of
approximately $20,000. This investment cost includes line segregation
charges. The annual operation and maintenance costs (including energy
and power costs) are estimated as approximately $l,190/year.
This shop was also analyzed with only a batch cyanide oxidation treat-
ment. With approximately the same cyanide mass as in the afore-
mentioned batch treatment system and with no wastewater flow segre-
gation, this end-of-pipe treatment requires an investment of approxi-
mately $19,000. The annual operation and maintenance costs (including
energy and power costs) are estimated as approximately $l,260/year.
Small plating shops may also utilize a completely manual treatment
system to treat cyanide or chromium wastes. In this system, the total
daily flow is held in fiberglass or metal wall, lined tanks.
Chemicals are added manually at the end of each day before discharging
the water.
The results of the cost program executions are estimated to be
nominally accurate to +_ 12 percent. Comparison by an independent
contractor of the cost program output to actual plant data for
305
-------
comparable wastewater treatment equipment indicates that this range of
accuracy is being obtained.
System Cost Estimates (In-Line Processes)
System cost estimates of the effects of improved rinsing and recovery
techniques on wastewater treatment and control costs have also been
developed. These system cost estimates are an evolution of costs for
a plant to go from series rinsing to countercurrent rinsing to plating
solution recovery. It is shown that significant savings in plating
solution and treatment system costs result from the installation of
plating solution recovery units. These savings are sufficient to pay
for the investments in advanced techniques in a short period of time.
A typical model plant was studied over a range of production plating
rates. This typical plant was assumed to consist of a chromium
plating line, a nickel plating line, and a copper plating line. Each
plating line was assumed to have the required surface preparation and
cleaning steps. While not an actual plant in the data base, this
model was used to generate representative costs. System costs were
surveyed over a range of plating rates from 18.1 square meters per
hour (195 square feet per hour) to 108.7 square meters per hour (1,170
square feet per hour) for each plating line. It was assumed that
constant plating tank surface areas would be applicable for this range
of plating rates.
The overall treatment costs consist of rinsing and recovery costs and
end-of-pipe treatment system costs. The end-of-pipe treatment system
without plating solution recovery was applied to the chromium, copper,
nickel, and cleaning rinse waters. This end-of-pipe treatment system
is identical to the system presented in Figure 8-3, except the
segregated chelated waste stream clarifier is omitted.
The system cost estimates for the various rinse techniques and end-of-
pipe treatment systems are presented in Tables 8-27 through 8-29.
Each table presents costs for the end-of-pipe treatment system (EOP),
the rinse techniques (Rinse), and the combined EOP and Rinse costs
(Total) for various plating production rates. The basic cost elements
used in preparing these tables are the same as those presented for the
individual technologies: investment, annual capital cost, annual
depreciation, annual operation and maintenance cost (less energy and
power cost), energy and power cost, and total annual cost. These
elements were discussed in detail earlier in this section. Investment
and annual operation and maintenance cost (less energy and power cost)
are divided into wastewater treatment and sludge handling categories.
The various EOP investment costs assume that the EOP treatment systems
must be specially constructed and include all subsidiary costs dis-
cussed under the Cost Breakdown Factors segment of this section. The
306
-------
TABLE 8-27
BASE PLANT - RUNNING RINSES
Total no* Kdte
( 1 1 ters/hour )
Plating Production
(•q. mtrs/hr/lin«)
Investment Costs:
Wastevater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Cost
Depreciation
Operation t
Maintenance Costs
(Excluding Energy
4 Power Cost)
Wastewater Treatment
Sludge Handling- 0 i M
Total O fc M
SI udge Haul i n
-------
ft-?fi
COUNTf RCUOSfNT RINSE";
Total flo* Rate
(littrs/hour)
Plating Production
(»q. mtr»/hr/line)
Investment Costs:
Sludge Handling
Total Investment
Annual Costs:
Capital Cost*
Deprec i a t i on
Operation t
Maintenance Costs
(Excluding Energy
i. Power Costs)
Wastewater Treatment
Sludge Handling-0 t H
Total O i H
Sludge Haul ing
Energy 6 Power Costs
Total Annual Cost
BOP
c * a f\f\r\
> t> ouuu
25210
$93210
5947
18642
S218
4249
10118
3255
315
$37626
2080
18.1
Rinse
e •) e f\£ a
> 4. -JUOtt
0
S25068
1599
5013
9
0
9
0
1131
S7752
Total
$9 3068
25210
$118278
7546
23655
S227
4249
10127
32Si
1446
$453/8
EOF
$7496 9
34853
S109822
7006
21964
5998
4318
11619
6il5
450
$46252
4159
36.2
Rinse
$ 25068
0
S25068
1599
5013
19
0
19
0
1131
$7762
Total
$ 100037
348S3
S134890
8605
26977
6017
4318
11638
6M$
1581
$54014
EOP
S8 3864
53086
S136950
8737
27390
9720
4600
16925
13025
630
$64102
8318
72.5
Rime
$25068
0
S25068
1599
5013
39
0
39
0
1131
$7782
Total
$108932
53086
5162018
10366
32403
9759
4600
16964
13025
1761
$?1884
EOF
$90248
70582
$160830
10261
32166
11153
H26
20796
19540
810
$?965i
12477
108.7
Rins*
$25068
0
$25068
1599
5013
57
.0
57
0
1131
7800
Total
$115316
70582
$185898
11680
37179
11210
5726
20853
19540
1941
$8/455
CO
O
CO
Note: Costs are for a plant that has 3 plating lines.
-------
TABLE 1-29
PIATING SOLUTION RECOVERY
Total Flow Rate
(liters /hour)
Plating Production
(sq. mtrs/hr/line)
Investment Costs:
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Costs
Depreciation
Operation t
Maintenance Costs
(Excluding Energy
t Power Costs)
Wastewater Treatment
Sludge Handling-0 S f
Total O I M
SI udge Hau1 i nc;
Energy t Power Costs
Total Annual Cost
2044
18.0
EOF
$40500
24040
$64540
4118
12908
4607
4239
9419
2865
44
J28781
Rinse
$29958
0
$29958
1911
5991
-5586
0
-5586
0
1434
$3750
Total
$70458
24040
$94498
6029
18899
-979
4239
3833
2865
1478
J32531
4088
36.2
EOF
$44637
32132
$76769
4898
15354
4785
4299
10230
5730
176
S35241
Rinse
$34366
0
$34366
2192
6873
-11495
0
-11495
0
1615
$-815
Total
$79003
32132
$111135
7090
22227
-6710
4299
-1265
5730
1791
J3442b
8176
72.5
EOP
$49452
47478
$96930
6184
19386
7294
«327
13912
11455
352
J48999
Rinse
$39814
0
$39814
2540
7963
-23391
0
-23391
0
1818
$- 11070
Total
$89266
47478
$136744
8724
27349
-16097
4327
-9479
11455
2170
J37929
12263
108.7
EOP
$52655
62129
$114784
7323
22957
7516
5340
16293
17185
528
$60849
Rinse
$47078
0
$47078
3003
9416
-35288
0
-35288
0
2130
$-20739
Total
$99733
62129
$161862
10326
32373
-27772
534C
-18955
17185
2658
J40110
Note: Costs are for a plant that has 3, plating lines.
Negative entries under "Rinse" and "Total" result from savings in plating
solution costs, made possible by installation of in-line rinse technology.
-------
various rinse investment costs assume that the plating line is a pro-
grammed hoist operation and include line conversion costs as discussed
previously under "Technology Cost Assumptions".
Operation and maintenance costs for both EOF and Rinse assume
continuous operation, 24 hours per day, 5 days per week, 52 weeks per
year. The Rinse operation and maintenance costs include a rinse water
charge based on an average of in-plant process and municipal water
charges.
Table 8-27 presents the costs of the base plant with two single stage
running rinses following every plating operation. The resulting
plating rinse waters and cleaning rinses- then go to the end-of-pipe
treatment system.
Table 8-28 presents the costs of replacing the single stage rinses
with three stage countercurrent rinsing after each plating operation.
This reduces the plating rinse water flows going to the end-of-pipe
treatment system. Even though the precleaning rinse water flow rates
were assumed to be unchanged, the total end-of-pipe treatment system
influent flow rate is reduced because of the improved plating rinse
techniques. This slightly lowers the costs of the end-of-pipe treat-
ment system.
Table 8-29 presents the costs of implementing recovery after each
plating operation. The end-of-pipe treatment system cost is for the
system depicted in Figure 8-3 with chromium reduction, cyanide
oxidation, and the segregated chelated waste stream clarifier omitted.
The chromium plating operation is followed by a three stage counter-
current rinse with the final rinse waters going to a cyclic ion ex-
change unit for plating solution recovery. The nickel plating oper-
ation is followed by a three stage countercurrent rinse with the final
rinse water going to a reverse osmosis unit to recover the plating so-
lution and 95 percent of the rinse water. The copper plating opera-
tion is followed by a multi-stage countercurrent rinse with a rinse
water flow rate sufficient to make up the plating tank evaporative
loss. This also recovers the plating solution for reuse.
The savings in plating solution cost are depicted by a negative
operation and maintenance cost in the "Rinse" columns of Table 8-29.
The plating solution savings do not assume complete plating solution
recovery but rather account for the fact that some of the plating
solution will remain on the plated part after the final rinse.
Typical plating solution recoveries are greater than 99.5 percent.
While Table 8-29 presents the costs of the new EOF treatment system,
the effects of Implementing recovery while maintaining the base plant
EOF treatment system can also be determined. For example, if a plant
plates 72.5 square meters per hour per line and converts from two
310
-------
stage running rinses to a system to recover plating solutions and
retains the end-of-pipe treatment system that existed previously, no
new investment is required. The cost of capital and depreciation for
EOF remains unchanged from that presented in Table 8-27. New
operation and maintenance costs result due to lower flow rates into
the EOF treatment system. The actual cost tabulation for this case is
presented in Table 8-30. This table shows that investing $39,814 in
recovery equipment results in a new total annual cost of $41,482/year.
This is a reduction of $22,033/year from the plant's previous annual
cost of $63,5157 year with two series running rinses as presented in
Table 8-27 at a plating production rate of 72.5 square meters per hour
per line. In this example, the savings in total annual costs pays for
the recovery equipment in approximately two years. Payback periods
range from 7.6 years for the smallest flow cases (18.1 square meters
per hour per line) to 1.4 years for the largest flow case (108.7
square meters per hour per line).
In conjunction with the recovery costs presented in Table 8-29, addi-
tional costs will be incurred to reduce the effluent pollutant concen-
trations from an electroless plating process. At present, this
chelated solution from an electroless plating process cannot be
reused; however, specific wastewater treatment is required to reduce
effluent concentrations to advanced treatment levels.
Table 8-31 presents the additional in-line treatment costs required to
treat the chelated electroless nickel solution dragout from an elec-
troless plating on metals or plastics process in other than a printed
circuit board manufacturing plant. The costs represent three-stage
countercurrent rinse after the electroless plating process with the
rinse overflow water being treated by a spiral wound cellulose acetate
reverse osmosis unit. Each rinse tank is an open top stainless steel
tank with a depth of 1.22 meters (4 feet), length of 1.22 meters (4
feet), and width of 0.91 meters (3 feet). Rinse water flow rate
calculations are based on a rinsing ratio of 3,000. The reverse
osmosis and countercurrent rinse costing assumptions are the same as
those discussed under "Technology Costs and Assumptions" above.
Table 8-32 presents the additional in-line treatment costs required to
treat the chelated solution drag-out from an electroless plating
process in a printed board plant. The costs represent 3-stage count-
ercurrent rinse after the electroless plating process with the rinse
overflow water being treated by a single effect submerged tube ev?.por-
ator. The rinse tank sizes and rinsing ratio are the same as those
used in developing Table 8-31. The submerged tube evaporator is a
standard size unit of 94.6 liters per hour (25.0 gallons per hour) ca-
pacity. Fuel oil is burned specifically to feed the evaporation de-
vice. Costing assumptions for the submerged tube evaporator and the
countercurrent rinse were discussed under "Technology Costs and
Assumptions", above.
311
-------
TABLE 8-30
PLATING SOLUTION RECOVERY WITH
BASE PLANT END-OF-PIPE TREATMENT
Metal Plating
Production
(sq, meters/hour/line)
EOP
0
0
$ 0
9260
29028
Investment Costs
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Cost
Depreciation
Operation & Maintenance Costs
(Excluding Energy & Power costs);
Wastewater Treatment 7294
Sludge Handling O&M 4327
Total O&M 13912
Sludge Hauling 11455
Energy & Power Costs 352
Total Annual Costs $61716
72.5
Rinse
39814
0
$39814
2540
7963
-23391
0
-23391
0
1818
$-11070
Total
39814
0
$39814
11800
36991
-16097
4327
-9479
11455
2170
$50646
Note: Costs are for a plant that has 3 plating lines.
312
-------
TABLE 8-31
ELECTROLESS PLATING ON METALS AND PLASTICS IN-LINE
Dragout
Flow Rate (Liters/Hour)
Investment
Annual Costs?
Capital Costs
Depreciation
Operation & Maintenance Costs
(Excluding Energy & Power Costs
Energy & Power Costs
Total Annual Cost
1,17
$10066
642
2013
) 473
654
$3782
2.35
$10770
687
2154
528
692
$4061
3.52
$11318
722
2264
577
720
$4282
TABLE 8-32
PRINTED BOARD
Dragout
Flow Rate (Liters/Hour)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance Costs
(Excluding Energy & Power Costs
Energy & Power Costs
Total Annual Cost
MANUFACTURE
1.17
$19359
1235
3872
} 305
2917
$8328
IN-LINE
2.35
$19359
1235
3872
609
3681
$9397
3.52
$19359
1235
3872
914
4445
$10466
313
-------
System Cost Computation - A computer program was developed to calcu-
late the system costs listed in the cost tables. A mathematical model
or set of correlations was developed for
each individual wastewater treatment technology. In general, these
correlations related equipment size to influent flow rate and
pollutant concentrations and, in turn, related cost to equipment size.
The computer was programmed to combine specified individual treatment
technologies in a specified arrangement forming a system. Using this
arrangement, the computer then determined flow rates and
concentrations at all points in the specified system, determined
equipment sizes, determined equipment costs, and added these costs to
arrive at a total system cost.
The correlations used for computing equipment size and cost were de-
rived from cost data obtained from several sources listed under the
"Technology Costs and Assumptions" heading. The data for wastewater
flow rate, corresponding equipment size, and corresponding cost were
related to form the correlations by means of a separate computer
program. This program was developed to correlate the data by
regression analysis, utilizing first order arithmetic equations, first
order logarithmic equations, and multiple order equations, as
appropriate.
Each cost estimation computer run involved several inputs and outputs.
Specifically, to compute system costs, the computer required as input:
(1) identification of system components (such as clarifier and cyanide
oxidation), (2) a definition of how these components were
schematically arranged, (3) raw wastewater flow rate, and (4) raw
waste pollutant concentrations. The computer output consisted of a
system cost breakdown. Investment cost was listed, and total annual
cost was broken down to yield operation and maintenance cost, energy
cost, depreciation, and cost of capital.
The program was developed to accept any of the components (up to 25 in
a particular system) listed in Table 8-1. In addition, "mixers" and
"splitters" were incorporated to represent merging or separating of
streams. Also included were certain other industrial wastewater
treatment processes. The schematic arrangement of these components
that could be input to the computer was entirely flexible, permitting
simulation and costing of many variations. Care was taken to assure
reasonable results for large as well as small plants.
The program was designed to handle the wastewater parameters listed in
Table 8-33. The program used standard values for certain factors such
as depreciation rate, but different values could be input if desired.
Computer Techniques - The cost estimating computer program consists of
a main routine which accepts the system input cards and accesses all
other routines, a series of subroutines which compute the performance
314
-------
TABLE 8-33
COST PROGRAM POLLUTANT PARAMETERS
Parameter, Units
Flow, MGD
pH, pH units
Turbidity, Jackson units
Temperature, degree C
Dissolved Oxygen, mg/1
Residual Chlorine, mg/1
Acidity, mg/1 CaC03
Alkalinity, mg/1 CaC03
Ammonia, mg/1
Biochemical Oxygen Demand, mg/1
Color, Chloroplatinate units
Sulfide, mg/1
Cyanides, mg/1
Kjeldahl Nitrogen, mg/1
Phenols, mg/1
Conductance, micromho/cm
Total Solids, mg/1
Total Suspended Solids, mg/1
Settleable Solids, ml/1
Aluminum, mg/1
Barium, mg/1
Cadmium, mg/1
Calcium, mg/1
Chromium, Total, mg/1
Copper, mg/1
Fluoride, mg/1
Iron, Total, mg/1
Lead, mg/1
Magnesium, mg/1
Molybdenum, mg/1
Total Volatile Solids, mg/1
Parameter, Units
Oil, Grease, mg/1
Hardness, mg/1 CaCo3
Chemical Oxygen Demand, mg/1
Algicides, mg/1
Total Phosphates, mg/1
Polychlorobiphenyls, mg/1
Potassium, mg/1
Silica, mg/1
Sodium, mg/1
Sulfate, mg/1
Sulfite, mg/1
Titanium, mg/1
Zinc, mg/1
Arsenic, mg/1
Boron, mg/1
Iron, Dissolved, mg/1
Mercury, mg/1
Nickel, mg/1
Nitrate, mg/1
Selenium, mg/1
Silver, mg/1
Strontium, mg/1
Beryllium, mg/1
Surfactants, mg/1
Plasticizers, mg/1
Antimony, mg/1
Bromide, mg/1
Cobalt, mg/1
Thallium, mg/1
Tin, mg/1
Chromium, Hexavalent, mg/1
315
-------
and cost of each of the unit processes, a cost routine, and a routine
for
printing the results. The main routine performs a system iteration
for recycle systems until a mass balance has been established. The
mass balance is established when the pollutant parameter concentra-
tions in all the process streams differ from the values in the process
streams in the previous iteration by less than one part in one hundred
thousand or by 0.1 mg/1, whichever is larger.
The program was based on earlier work done by the EPA to compute costs
of municipal treatment plants and a cost estimating computer program
developed for the Machinery and Mechanical Products Manufacturing In-
dustry and Electroplating Industry Effluent Limitations Guidelines.
These earlier programs were analyzed, revised, and expanded to develop
the present program. Further revisions and modifications were also
incorporated during the course of the electroplating economic impact
analysis wastewater treatment system cost estimation activities. The
electroplating wastewater treatment cost estimating program was
written in FORTRAN IV for an IBM 370-168 computer system.
Cost Breakdown Factors
The factors used to compute the values of the cost elements for the
individual technologies and entire systems are defined and discussed
under the following subheadings. They are Dollar Base, Investment
Cost Adjustment, Supply Cost Adjustment, Cost of Labor, Cost of Energy
and Power, Capital Recovery Costs, Debt-Equity Ratio, and Subsidiary
Costs.
Dollar Base - A dollar base of January 1976 was used for all costs.
Investment Cost Adjustment - Investment costs were adjusted to the
aforementioned dollar base by use of the Sewage Treatment Plant Con-
struction Cost Index. This cost index is published monthly by the EPA
Division of Facilities Construction and Operation. The national aver-
age of the Construction Cost Index for January 1976 was 256.7. Within
each process, the investment cost was usually defined as some function
of the unit size capacity. Where applicable, an excess capacity fac-
tor was used when obtaining the cost-determining size or capacity.
This excess capacity factor is a multiplier on the size of the process
to account for shutdown for cleaning and maintenance.
Supply Cost Adjustment - Supply costs such as chemicals were related
to the dollar base by the Wholesale Price Index. This figure was ob-
tained from the U.S. Department of Labor, Bureau of Labor Statistics,
"Monthly Labor Review". For January 1976 the "Industrial Commodities"
Wholesale Price Index was 177.3. Process supply and replacement costs
were included in the estimate of the total process operating and main-
tenance cost.
316
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Cost of Labor - To relate the operating and maintenance labor costs,
the hourly wage rate for non-supervisory workers in water, steam, and
sanitary systems was used from the U. S. Department of Labor, Bureau
of Labor Statistics Monthly publication, "Employment and Earnings".
For January 1976, this wage rate was $5,19 per hour. This wage rate
was then applied to estimates of operational and maintenance man-hours
within each process to obtain process direct labor charges. To
account for indirect labor charges, 15 percent of the direct labor
costs was added to the direct labor charge to yield estimated total
labor costs. Such items as Social Security, employer contributions to
pension or retirement funds, and employer-paid premiums to various
forms of insurance programs were considered indirect labor costs.
Cost of. Energy and Power - Energy and power requirements were calcu-
lated directly within each process. Estimated costs were then deter-
mined by applying either typical fuel costs of approximately 35 cents
per gallon or, in the case of electrical requirements, a rate of
approximately 2,7 cents per kilowatt hour.
The electrical charge for January 1976, was corroborated through
consultation with the Energy Consulting Services Department of the
Connecticut Light and Power Company. This electrical charge was
determined by assuming that any electrical needs of a waste treatment
facility or rinse operation would be satisfied by an existing elec-
trical distribution system; i.e., no new meter would be required.
This eliminated the formation of any new demand load base for the
electrical charge, thus minimizing the electrical rates applied.
Capital Recovery Costs - Capital recovery costs were divided into
straight line five-year depreciation and cost of capital at a ten per-
cent annual interest rate for a period of five years. The five year
depreciation period was consistent with the faster write-off (finan-
cial life) allowed for these facilities even though the equipment life
is in the range of 20 to 25 years. The annual cost of capital was
calculated by using the capital recovery factor approach.
The capital recovery factor (CRF) is normally used in industry to help
allocate the initial investment and the interest to the total operat-
ing cost of the facility. The CRF is equal to the interest rate plus
the interest rate divided by A-l. A is equal to the quantity 1 plus
the interest rate raised to the Nth power, where N is the number of
years the interest is applied. The annual capital recovery (ANR) was
obtained by multiplying the initial investment by the CRF. The annual
depreciation (D) of the capital investment was calculated by dividing
the initial investment by the depreciation period N, which was assumed
to be five years. The annual cost of capital was then equal to the
annual capital recovery (ANR) minus the depreciation (D).
317
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Debt-Equity Ratio - Limitations on new borrowings assume that debt may
not exceed a set percentage of the shareholders equity. This defines
the breakdown of the capital investment between debt and equity
charges. However, due to the lack of information about the financial
status of various plants, it was not feasible to estimate typical
shareholders equity to obtain debt financing limitations. For these
reasons, no attempt was made to break down the capital cost into debt
and equity charges. Rather, the annual cost of capital was calculated
via the procedure outlined in the Capital Recovery Costs section
above.
Subsidiary Costs - The costs presented in Tables 8-25 through 8-30 for
end-of-pipe and advanced wastewater control and treatment systems
include all subsidiary costs associated with system construction and
operation. These subsidiary cost functions include:
administrative and laboratory facilities
garage and shop facilities
line segregation
yardwork
land
engineering
legal, fiscal, and administrative
interest during construction
Administrative and laboratory facility investment is the cost of con-
structing space for administration, laboratory, and service functions
for the wastewater treatment system. For these cost computations, it
was assumed that there was already an existing building and space for
administration, laboratory, and service functions. Therefore, there
was no investment cost for this item.
For laboratory operations, an analytical fee of $80 (January 1976
dollars) was charged for each wastewater sample, regardless of whether
the laboratory work was done on or off site. This lab fee estimate
includes the analysis of hexavalent chromium and cyanide amenable to
chlorination, as well as the regulated pollutants for platers
discharging more than 10,000 gallons per day of electroplating process
wastewater. This analytical fee is typical of the charges experienced
during the past several years of sampling programs. The frequency of
wastewater sampling is a function of wastewater discharge flow and is
presented in Table 8-34.
318
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TABLE 8-34
WASTEWATER SAMPLING FREQUENCY
Wastewater Discharge Sampling Frequency
(liters per day)
0 - 37,850 once per month
37,850 - 189,250 twice per month
189,250 - 378,500 once per week
378,500 - 946,250 twice per week
946,250 + thrice per week
319
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For the industrial waste treatment facilities being costed, no garage
and shop investment cost was included. This cost item was assumed to
be part of the normal plant costs and was not allocated to the
wastewater treatment system.
Line segregation investment costs account for plant modifications to
segregate wastes. The investment costs of line segregation included
placing a trench in the existing plant floor and installing the lines
in this trench. The same trench was used for all pipes and a gravity
feed to the treatment system was assumed. The pipe was assumed to run
from the center of the floor to a corner. Plant floor area was
related to discharge flow by the results of an analysis of 300 plants
visited for which flow and floor area were available. This data
indicated that 2.04 liters per hour of wastewater is discharged per
square meter of floor area (0.05 gallons per hour per square foot).
The yardwork investment cost item includes the cost of general site
clearing, intercomponent piping, valves, overhead and underground
electrical wiring, cable, lighting, control structures, manholes,
tunnels, conduits, and general site items outside the structural
confines of particular individual plant components. This cost is
typically 9 to 18 percent of the installed components investment
costs. For these cost estimates, an average of 14 percent was
utilized. Annual yardwork operation and maintenance costs are
considered a part of normal plant maintenance and were not included in
these cost estimates.
No new land purchases were required. It was assumed that the land
required for the end-of-pipe treatment system was already available at
the plant.
Engineering costs include both basic and special services. Basic
services include preliminary design reports, detailed design, and
certain office and field engineering services during construction of
projects. Special services include improvements studies, resident
engineering, soils investigations and surveys, operation and main-
tenance manuals, and other miscellaneous services. Engineering cost
is a function of process installed and yardwork investment costs.
Legal, fiscal and administrative costs relate to planning and con-
struction of wastewater treatment facilities and include such items as
preparation of legal documents, preparation of construction contracts
acquisition of land. These costs are a function of process installed,
yardwork, engineering, and land investment costs.
Interest cost during construction is the interest cost accrued on
funds from the time payment is made to the contractor to the end of
the construction period. The total of all other project investment
costs (processes installed; yardwork; land; engineering; and legal,
320
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fiscal, and administrative) and the applied interest affect this cost.
An interest rate of 10 percent was used to determine the interest cost
for these estimates.
For the rinse process costs, line conversion costs and rinse water
charges based on an average of typical in-plant process and municipal
water charges were included. It was assumed that a rinse water source
was available within three meters of the rinse tanks so minimum pipe
charges were included.
ENERGY AND NON-WATER QUALITY ASPECTS
Energy and non-water quality aspects of the wastewater treatment
technologies described in Section VII are summarized in Tables 8-35
and 8-36. Energy requirements are listed, the impact on air and noise
pollution is noted, and solid waste generation characteristics are
summarized. The treatment processes are divided into two groups,
wastewater treatment processes on Table 8-35 and sludge and solids
handling processes on Table 8-36.
Energy Aspects
Energy aspects of the wastewater treatment processes are important
because of the impact of energy use on our natural resources and on
the economy. Electrical power and fuel requirements (coal, oil, or
gas) are listed in units of kilowatt hours per ton of dry solids for
sludge and solids handling. Specific energy uses are noted in the
"Remarks" column.
Energy requirements are generally low, although evaporation can be an
exception if no waste heat is available at the plant. Thus, if
evaporation is used to avoid discharge of pollutants, the influent wa-
ter rate should be minimized by all means possible. For example, an
upstream reverse osmosis or ultrafiltration unit can drastically re-
duce the flow rate of wastewater to an evaporation device.
Non-water Quality Aspects
It is important to consider the impact of each treatment process on
air, noise, and radiation pollution of the environment to preclude the
development of a more adverse environmental impact.
None of the liquid handling processes causes air pollution. Incinera-
tion of sludges or solids can, however, cause significant air pollu-
tion. In fact, efforts to reduce this air pollution by scrubbing can
result in water pollution. Noise pollution disturbs equipment opera-
tors even more than the surrounding community. However, none of the
wastewater treatment processes causes objectionable noise in either
321
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TABLE
NONWATER QUALITY ASPECTS
»-35
OF WASTEWATER TREATMENT
no
ro
PROCESS
Neutralization
Chemical
Reduction
Clarification
Flotation
Chemical
Oxidation
By Chlorine
Oxidation
*3f Oxygen
Chemical
Precipitation
Sedimentation
Deep Bed
Filtration
Ion Exchange
Evapo rat ion n
Reverse
Osmosis
Ultrafiltration
Membrane
Filtration
Elect rodialysis
ENERGY
Power
Fuel
kw/1000 liter,«min
6-8.7
4.4-9,0
0.1-3.2
36
4.4-96
4.4-9.0
1.02
0.1-3.2
0.02
30
130-390
2.5-26
2.5-26
79.5
__.
2,500,000
....
Energy
Use
Mixing
Mixing
Sludge
Collector
Drive
Recirculation
Pump, Com-
pressor, Skim
Mixing
Mixing
Flocculation
Paddles
Sludge
Collector
Drive
Head, Back-
wash Pumps
Pumps
Evaporate
Hater
High
Pressure
Pump
High
Pressure
Pump
High
Pressure
Pump
Ion
Transport
NONWATER QUALITY IMPACT
Air
Pollution
Impact
Hone
None
None
None
None
None
None
None
None
None
None
None
None
None
Hone
Noise
Pollution
Impact
None
None
None
None
None
None
None
None
None
Not
Objectionable
Hone
Not
Objectionable
Not
Objectionable
Not
Objectionable
None
Solid
Waste
None
None
Concentrated
Concentrated
None
None
Concentrated
Concentrated
Concentrated
None
Concentrated/
Dewatered
Dilute
Concentrate
Dilute
Concentrate
Dilute
Concentrate
Dilute
Concentrate
Solid Haste
Concentration
% Dry Solids
— —
1-10
3-5
3-10
1-3
Variable
N/A
50-100
1-40
1-40
1-40
1-5
Solid
Waste
Disposal
Technique
N/A
N/A
Thicken, Dry i
Landfill or
Incinerate
Skim, Dry,
Landfill or
Incinerate
N/A
N/A
Devater, Landfill
Devater i
Landfill or
Incinerate
Backwash to
Settling
N/A
Landfill or
Incinerate
Distill i
Incinerate,
Landfill
Distill (.
Incinerate,
Landfill
Distill
Incinerate,
Landfill
Distill,
Landfill
-------
TABLE 8-r16.
NONWATER QUALITY ASPECTS OF SLUDGE AND SOLIDS HANDLING
PROCESS
Sludge
Thickening
Pressure
Filtration
Sand Bed
Drying
Vacuum
Fi Iter
Centrifugal ion
Landfill
Laqoon i ng
Incineration
Pyroly sis
ENERGY
Power
Fuel
kwh/ton dry solids
29-930
Zl
16.7-
66.8
0.2-
98.5
38
35
20-980
36
— — - —
27-127
Energy
use
Skimmer ,
Sludge Rake
Drive
High
Pressure
Pumps
Removal
Equipment
Vacuum Pump,
Rotation
Rotation
Haul, Land-
fill 1-10
Mile Trip
Remova 1
Equipment
Rakes ,
Cooling Fan
(Feed Com-
bustible)
Air Supply,
Gas Handl-
ing, Feed
NONWATER QUALITY IMPACT
Air
Pollution
Impact
None
None
None
None
None
None
None
Signifi-
cant
(Dust)
Minor
(Dust,
Odor,
Flammable)
Hoise
Pollution
Impact
None
None
None
Not
Objectionable
Not
Objectionable
None
None
Not
Objectionable
None
Solid
Haste
Concentrated
Dewatered
Oewatered
Dewatered
Dewatered
Oewatered
Dewatered
Dewatered/
Scrubber
Water
Dewatered
Solid Waste
Concentr at ion
% Dry Solids
4-27
25-50
15-40
20-40
15-50
N/A
3-5
100 I
Scrubber
100
Solid
Waste
Disposal
Technique
Dewater t
Landfill or
Incinerate
Landfill or
Incinerate
Landfill
Landfill or
Incinerate
Landfill or
Incinerate
H/A
Dewater t
Landfill
Landfill Ash/
Return
Scrubber
Landfill or
Byproduct
Recovery
oo
r\j
-------
respect. None of the treatment processes has any potential for
radioactive radiation hazards.
The solid waste impact of each wastewater treatment process is
indicated in three columns on the table. The first column shows
whether effluent solids are to be expected and, if so, the solids
content in qualitative terms. The second column lists typical values
of percent solids of the sludge or residue. The third column
indicates the usual method of solids disposal associated with the
process.
The processes for treating the wastewaters from this category produce
considerable volumes of sludges. In order to ensure long-term
protection of the environment from harmful sludge constituents,
special consideration of disposal sites should be made. All landfill
sites should be selected to prevent horizontal and vertical migration
of these contaminants to ground or surface waters. In cases where
geological conditions may not be expected to prevent this, adequate
mechanical precautions (e.g., impervious liners) should be used for
long-term protection of the environment. A program of routine
periodic sampling and analysis of leachates is advisable. Where
appropriate, the location of solid hazardous materials disposal sites
should be permanently recorded in the appropriate office of legal
jurisdiction.
324
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SECTION IX
PRACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE, GUIDELINES AND LIMITATIONS
These limitations will be developed at a later date.
325
-------
-------
SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE, GUIDELINES AND LIMITATIONS
These limitations will be developed at a later date.
327
-------
-------
SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
These limitations will be developed at a later date,
329
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-------
SECTION XII
PRETREATMENT
TECHNICAL APPROACH
Pretreatment standards for electroplating were developed in the
following manner. The point source category was first studied for the
purpose of determining whether separate standards were appropriate for
different segments within the category. The raw waste characteristics
of each segment were then identified. This included an analysis of
the source, flow, and volume of water used in the process employed;
the sources of waste and waste waters in the operation, and; the
constituents of all waste water. The compatibility of each raw waste
characteristic with municipal treatment works was considered. Waste
water constituents posing pass-through or interference problems for
POTWs were identified.
The control and treatment technologies appropriate to each segment
were also identified, including both existing in-plant and end-of-
process technologies as well as those capable of_ being designed for
each segment. The effluent level resulting from the application of
each of the technologies, in terms of the amount of constituents and
the chemical, physical, and biological characteristics of pollutants,
was also identified. The problems, limitations, and reliability of
each treatment and control technology were determined next. In
addition, the nonwater quality environmental impact, such as the
effects of the application of such technologies upon other pollution
problems (ie., air, solid waste, noise, and radiation) were evaluated.
Finally, the energy requirements of each control and treatment
technology were determined, as well as the cost of the application of
such technologies.
The information, as outlined above, was then evaluated to find the
appropriate level of effluent pretreatment given the total cost of
application of the technology, the age of equipment and facilities
involved, the process employed, the engineering aspects of_ the
application of various types of control techniques, process changes,
nonwater quality environmental impact (including energy requirements),
and other factors.
The data upon which the above analyses were performed included EPA
permit applications, EPA sampling and inspections, consultant reports,
and industry submissions.
331
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STATISTICAL METHODOLOGY
This section provides an overview of statistical methodologies
employed to determine pretreatment standards for the electroplating
industry. The methodology consisted essentially of determining long
term average pollutant discharges, expected from a well designed and
operated pretreatment system, and multiplying these long term averages
by variability factors designed to allow for random fluctuations in
treatment system performance. The resulting products yielded daily
and 30-day-average maximum limitations for each pollutant. A simple,
approximate equation was employed to obtain N-day-average maximum
limitations for N = 2, 3,...29. Modifications of this procedure were
made to accommodate mass-based and TSS options. The general sta-
tistical derivation of long term averages, variability factors, and
the resulting limitations follows.
Determination of Long Term Average
The long term average (LTA) is the expected discharge concentration of
a pollutant in mg/1 from an electroplating plant having a well
designed, maintained, and operated pretreatment system. The long term
average was determined for each pollutant to be regulated, and used to
obtain corresponding limitations for that pollutant. It is not
intended as a limitation itself, but rather as a specification which
the pretreatment system should be designed to attain over the long
term.
For the analyses on hexavalent chromium and cyanide and the metals
plated in the Electroless and Printed Circuit Board subcategories, the
long term average was calculated as the median of the plant averages
for each of these pollutants.
Determination o_f Variability Factors
Even plants that are achieving good pollutant removal experience
fluctuations in the discharge pollutant concentrations from their
pretreatment system. These fluctuations may reflect temporary
imbalances in the treatment system caused by fluctuations in flow, raw
waste load of a particular pollutant, chemical feed, mixing flows
within tasks, or a variety of other factors.
Allowance for the day-to-day variability in the concentration of a
pollutant discharged from a well designed and operated treatment
system is incorporated into the standards by the use of a "variability
factor." The theoretical derivation of the variability factor is
presented in Appendix XII-A.l. Under certain assumptions, discussed
below, the application of_ a variability factor allows the calculation
of an upper bound for the concentration of a particular pollutant such
that in expectation 99 percent of the randomly observed daily values
332
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from a pretreatment system discharging this pollutant at a known mean
concentration will fall below this bound.
The theoretical derivation of the variability factor is based on the
assumption that the daily pollutant concentrations follow a lognormal
distribution. This assumption is supported by test statistics (Kuiper
and Kolmogorov-Smirnov, not reported here), plots of the cumulative
distribution of observed concentrations for various pollutants (as
shown later), and comparisons of variability factors estimated from
plant data by two theoretically equivalent formulas (Appendix
XII-A.3).
The variability factor is estimated by the equation derived in
Appendix XII-A.l, which is:
log (VF) = Z(Sigma) - 1.15(Sigma)2 [l]
where
VF is the variability factor
2 is 2.326, which is the 99 percentile of the standard normal
distribution, and
Sigma is the standard deviation of the logarithms
(base 10) of the concentrations.
The accuracy of the variability factor is a function of the accuracy
of Sigma, the standard deviation of the logarithm of the observations
of a well designed and well operated plant. Important considerations
for assessing the accuracy of Sigma include:
1. the randomness of the concentrations sampled for each plant,
2. the number and accuracy of the daily samples per plant,
3. the number and appropriateness of the plants included in the
sample, and
4. the assumption that the daily pollutant concentrations follow
a lognormal distribution.
The last consideration has been discussed above. The methodology for
obtaining Sigma, and thus VF, takes into consideration the first three
factors.
The estimated single-day variability factor of a pollutant from a well
designed and operated plant was calculated in the following manner:
333
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1. For each plant1 with 10 or more but less than 100
observations and a small number of 0 values2 for the
pollutant, Sigma was calculated according to the standard
statistical formula3 ar\d was then substituted into Equation
[1] to find the VF.
2. For those plants with over 100 observations, the VF was
estimated directly by dividing the 99th percentile of
observed sample values by the average of the observations.
3. The VF for each pollutant was then calculated to be the
median of the plant variability factors for that pollutant.
Allowance for the variability of the average of a random sample of N
daily observations about the mean value of a pollutant discharged from
a well designed and operated pretreatment system was obtained by use
of a theoretically derived term (Appendix XII-A.2) called the "N-day-
1Plants with both high and low average concentrations fulfilling the
stated conditions were included in the data base to calculate the
variability factors. This was done since Appendix XII-A.4 showed that
the sample means and standard deviations of the logarithms of the
concentrations of a specific pollutant for each plant were not
significantly correlated across plants, i.e., standard deviations from
plants with high average concentration were not significantly larger
than standard deviations from plants with low average concentrations
for each pollutant. This is consistent with the assumption of
lognormality.
20nly 7 of 68 cases observed effluent concentrations of 0 and these
never represented more than 25% of the observations. Since log(O) is
undefined, the 0 values were set equal to one-half the next lowest
pollutant concentration. This was found to have little effect on the
results and in six of the above seven cases, the individual varia-
bility factors were greater than the median variability factor.
3 (X - X)2
n-1
where
x is the log of observation i
x is the average of the observations
n is the number of observations
334
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average variability factor." This term allows the calculation of an
upper bound for the concentration of a particular pollutant (under the
same assumptions stated above) such that in expectation 99 per cent of
the randomly observed N-day average values from a pretreatment system
discharging the pollutant at a known mean concentration will fall
below this bound. Thirty-day average variability factors are reported
in all analyses.
The N-day-average variability factor was estimated by a theoretically
based equation (Appendix XII-A.2).
log(VF ) = Z(Sigma ) - 1.15(Sigma )* [2]
where
VF is the N-day-average variability factor
Z is 2.326, which is the 99th percentile of the standard normal
distribution, and
Sigma is a function of Sigma and N.
Sigma can be obtained from the estimate of the (daily) variability
factor, VF, as outlined in Appendix XII-A.2. This is a departure from
the Monte Carlo simulation used to calculate this term in the previous
Development Document for proposed electroplating pretreatment
regulations.
Determination of Limitations
Daily maximum and 30-day-average maximum limitations (L and L30,
respectively) were calculated for each pollutant from the long term
average (LTA), the daily variability factor (VF), and the 30-day-
average variability factor (VF30) for that pollutant by the following
equations:
L = VF x LTA [3]
LJO s VF30 x LTA [4]
The daily maximum limitation calculated for each pollutant is a value
which is not to be exceeded on any one day by a plant discharging that
pollutant. The 30-day-average maximum limitation is a value which is
not to be exceeded by the average of any 30 single-day observations
for the regulated pollutant.
335
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TREATMENT OF CYANIDE
The distinction between amenable cyanide (CN,A) and total cyanide
(CN,T) stems from the chemical form of the cyanide in the waste
stream. Much of the cyanide-containing waste enters the treatment
system as a free ion, or in the form of complexes with Cu, Zn, Cd, or
Pb. Such cyanide is rapidly oxidized to cyanate in the first stage of
an alkaline chlorination treatment system, and falls into the
category, CN,A. Under some circumstances, a portion of the cyanide
may be present as iron or other heavy metal cyanide complexes. Since
these compounds are much more difficult to oxidize than free cyanide,
their formation should be avoided or minimized by careful attention to
proper housekeeping practices previously discussed.
Technologies for treating cyanide were described in detail in Chapter
VII.
Calculation of_ the Long Term Average for Amenable Cyanide (_C_NfA)
The destruction of CN,A by alkaline chlorination is a kinetically
rapid reaction. A plant with an adequately sized and controlled
treatment unit followed by pH adjustment and settling should achieve
nearly complete removal of CN,A. This can be seen from the data in
Table 12-1. Of the 46 plants with data summarized in this table, 15
(32%) reduced the average CN,A to 0.02 mg/1 or less.
The plants described in Table 12-1 are those which: (a) plate Cu, Cd,
Zn, or precious metals; (b) have an oxidation system to treat their CN
wastes; and (c) have CN,A concentration data. An effort has been made
to make Table 12-1 as complete as possible, by including all
appropriate CN,A data (from the data base compiled for analysis by
this Agency) from those plants plating the appropriate metals and
having oxidation treatment.
However, certain plants were found inappropriate and were thus
eliminated from the data base for CN,A long-term calculations. Among
these were: (a) three plants (6078, 19002, 33071) with cyanide
destruct systems which were not operating properly or which were
partially bypassed; (b) six plants (6050, 6053, 6077, 6087, 6358,
19051) with Lancy or Integrated pretreatment systems, and; (c) five
plants (6051, 6079, 6081, 19050, 36040) specified as having low
cyanide bearing wastes.
Figure 12-1 is a cumulative plot of the average CN,A concentrations in
the effluent from the 46 plants shown in Table 12-1. The plot shows
that 21% of the plants removed essentially all amenable cyanide (down
to CN,A less than or equal to 0,01 mg/1), and also shows that many of
the remaining plants, although not reaching this low level, still
336
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100
80
CO
GO
i
o
o
o
VI
52
§
60
40
20
I
I
I
I
.01
.02
.03
.05
.1 .2 .3 .5
Average CN, A Concentration (mg/l)
FIGURE 12-1
CUMULATIVE PLOT OF AVERAGE CN.A IN DISCHARGES FROM 47 PLANTS
-------
TABLE 12-1
CN,A CONCENTRATIONS OBSERVED IN THE FINAL EFFLUENT FROM PLANTS
WITH CYANIDE OXIDATION IN WASTE TREATMENT SYSTEM
Plant
ID
4
6
7
8
15
19
116
478
652
804
1108
1113
1924
2001
2007
2103
3301
3320
3601
4045
5021
6037
6072
6073
6075
6084
6085
6089
6381
9026
10020
15070
20073
20077
20078
20079
20080
20081
Data*
Source
1
1
1
1
1
1
2
2
2
3
1
1
3
3
1
3
1
1
1
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
Number
Obs.
1
1
2
2
11
11
1
2
1
11
13
9
3
114
2
13
4
2
1
3
3
3
2
3
2
1
3
3
3
3
3
3
6
6
6
6
7
6
Concentration CN,A
Median
0.04 mg/1
.32
.25
.80
.50
.42
.01
.06
.01
.01
.49
.04
.03
.04
.02
.01
.01
.02
.01
1.00
.01
.41
.01
1.46
.01
1.97
.56
.29
.10
.01
4.40
.01
.01
.39
.01
.01
.01
.02
Ay.8.--
0.04 mg/1
.32
.25
.80
1.31
.56
.01
.06
.01
.02
.62
.16
.07
.04
.02
.01
.02
.02
.01
1.15
.01
4.04
.01
2.24
.01
1.97
.57
.53
.31
.02
5.30
.01
.02
.98
.01
.01
.03
.13
Max.
0.05 mg/1
.32
.25
1.00
7.90
1.40
.01
.08
.01
.15
1.90
.68
.17
.06
.03
.03
.03
.02
.01
2.20
.01
11.60
.01
3.98
.01
1.97
1.09
1.14
.75
.03
7.30
.02
.05
3.00
.01
.01
.10
.49
Tcbntinued on next page)
338
-------
TABLE 12-1 (Continued)
20082
20084
20086
20087
31021
33024
33073
36041
Data*
Sourc e
4
4
4
1
4
3 & 4
4
4
Numbe r
Obs.
2
3
3
3
3
3
3
3
Concentration CN,A
Median
Max.
.79 rag/1
1.25
.36
.66
.05
.04
.02
.10
.96 mg/1
1.25
1.87
.49
.05
.05
.02
.20
3.00
2.50
5.25
.80
.05
.08
.03
.40
mg/1
*1 = Data from reports by Yost et al., and Safranek et al.
2 - Battelle
3 = Plant
4 = Hamilton Standard.
339
-------
achieved fairly good CN,A removal. The median or long term average
value for CN,A was .07 mg/1.
In some plants, the cause of high effluent CN,A concentrations
appeared to be poor design or control of the treatment system. For
instance, sampling personnel, although not specifically instructed to
evaluate the design or operation of plant treatment systems during
sampling visits, noted potential design flaws (4045, 10020, 20084), a
history of chlorine feed malfunctions (6073), and spillage to streams
of untreated cyanide bearing solutions (20086).
Calculation of_ the Long Term Average for Total Cyanide (CN,T)
Table 12-2 presents comparable data for 65 plants with cyanide wastes,
oxidation treatment, and CN,T measurements. Figure 12-2 is a
cumulative plot of the average CN,T values for these plants. A
comparison of Figure 12-1 and 12-2 shows them to be similar in form.
In both cases, a substantial fraction of the plants achieved
nearly complete cyanide removal: 34 percent of the Figure 12-2
plants experienced average CN,T effluent concentrations of less than
0.04 mg/1, with the median value or long term average being 0.15 mg/1.
The plants deleted from the CN,A analysis were also eliminated from
the CN,T analysis for the same reasons given above. Also, three
plants (2017, 2811, 3321) were eliminated from the analysis in Table
12-2 because they combined waste waters from other types of
operations. Additionally, the reported data from plants 689, 3301,
and 4301 were deleted as suggested by industry commenters due to
nonstandard analytical techniques.
Calculation of the Variability Factors
As Tables 12-1 and 12-2 show, even plants achieving good cyanide
removal occasionally experience a day of higher than usual cyanide
discharge. To allow for these fluctuations, variability factors, were
calculated as outlined in the section on statistical methodology^ The
calculation of this variability was based on the observation that in
this industry, as in many industries, the discharge concentrations of
metal and cyanide follow a standard lognormal statistical
distribution. Figure 12-3 shows a cumulative plot, on a log
probability scale, of 24 daily observations of CN,T from plant number
3320. The data fall nearly along a straight line, indicating that the
distribution of observations from this plant may indeed be assumed
consistent with lognormality. Figure 12-4 is a cumulative plot of the
CM,A data furnished for plant 1108. The points in this figure again
fall along a straight line, indicating that this sample also conforms
to lognormality.
340
-------
TABLE 12-2
CN,T CONCENTRATIONS OBSERVED IN THE FINAL EFFLUENT FROM
PLANTS WITH CYANIDE OXIDATION IN WASTE TREATMENT SYSTEMS
Plant
ID
4
6
7
8
15
19
116
478
607
629
652
662
805
902
1108
1113
1165
1208
1209
1263
1302
1924
2006
2007
2103
2303
2501
2809
3003
3005
3021
3301
3311
Data*
Source
1
1
1
1
1
1
3
2
2 & 3
2
2
3
2 & 3
3
1
1
2
3
2
2
2
3
2
1
3
2
3
2
2
2
3
1
3
Number
Obs:
2
2
2
2
11
11
37
3
3
1
1
7(m)
21
6
13
9
2
37
1
1
1
5
7
2
44
1
13
1
1
1
7
6
25
Concentration CN,T
Median
.25 mg/1
16.72
.45
14.00
1.30
.78
.01
.25
.12
.07
.01
.30
nil
nil
1.00
.05
.06
.10
.03
.01
1.00
.01
.02
.02
.02
.20
nil
.01
.01
.05
.03
.03
nil
Avg.
.25 mg/1
16.72
.45
14.00
2.65
.80
.12
.31
.11
.07
.01
.36
nil
nil
1.38
.21
.06
.15
.03
.01
1.00
.84
.02
.02
.02
.20
nil
.01
.01
.05
.03
.03
.07
Max.
.38 mg/1
31.80
.59
16.00
12.00
1.60
2.22
.61
.16
.07
.01
.96
.05
nil
4.00
.78
.12
.92
.03
.01
1.00
3.20
.08
.03
.04
.20
.03
.01
.01
.05
.07
.04
1.60
Tcontinued on next page)
341
-------
TABLE 12-2 (Continued)
Plane
ID
3315
3320
3601
3612
4045
5021
6037
6072
6073
6075
6084
6085
6089
6381
9026
10020
15070
20073
20077
20078
20079
20080
20081
20082
20084
20086
20087
31021
33024
33070
33073
36041
Data*
Source
2 & 3
2 & 3
1 & 3
3
4
4
2,3,& 4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
3 & 4
4
4
4
Number
Obs:
7(m)
26
2
39
3
3
11
2
3
3
3
3
3
3
3
3
3
6
6
6
6
6
7
6
2
3
3
3
15
3
3
3
Concentration CN,T
Median
4.30 mg/1
.01
.03
.02
8.70
.01
.53
.01
3.08
.01
.44
.96
.43
.04
.03
5.30
.03
.08
2.20
.01
.01
.01
.07
.83
34.70
1.13
3.50
.16
nil
.07
.13
.40
Avg.
4.26 mg/1
02
.03
.02
10.10
.01
1.62
.01
3.29
.01
1.09
1.23
1.04
.38
.04
5.70
.11
.12
1.90
.01
3.51
.23
.87
1.47
34.70
2.37
18.36
.26
.01
.07
.13
.42
Max.
9.90 mg/1
.16
.03
.02
15.20
.01
12.60
.01
5.18
.01
2.80
1.80
2.42
.98
.08
7.40
.29
.37
3.00
.04
21.00
1.23
3.82
3.31
50.50
5.25
50.00
.35
.08
.10
.25
.60
*1 = Data from reports by Yost et al., and Safranek et al.
2 = Batelle
3 = Plant
4 = Hamilton Standard
m = Monthly average data.
342
-------
100
80
o
e
o
O
o
VI
c
—
CL
H—
O
»*
I
60
40
20
0
.01
I
I
.02
.03
.05
.1 .2 .3 .5
Average CN, T Concentration (mgll)
FIGURE 12-2
CUMULATIVE PLOT OF AVERAGE CN J IN DISCHARGES FROM 69 PLANTS
-------
.10
.09
.08
.07
.06
.05
.04
.03
.02
.01
.009
.008
.007
.006
.DOS
.004
.003
.002
,001
/
y
/
/
/
>
/
j
Y
/
/
/
*
0.01 O.OS 01 0.2 0.5 1
90
95 98 99
10 20 I 30 40 50 60 70 80
Peromt of OfaMrv*tioiM
-------
9
8
7
6
5
4
3
2
1
.9
.8
.7
.6
.5
! 3
o .2
z"
u
.1
.09
.08
.07
.06
.05
.04
.03
.02
.01
X
x
x
x^
^x
V
^x
^
>^
,
_^
• >x^
x^
r
/
/
5 10 15 20 30 40 50 60 70 80 85 90 95 98
Percent of Observation £ CN,A Concentration
FIGURE 12-4
CUMULATIVE DISTRIBUTION OF 13 DAILY CN, A DISCHARGE CONCENTRATIONS
FROM PLANT 1108
345
-------
The individual plant Sigmas and variability factors for CN,A and CN,T
are listed in Table 12-3 and Table 12-4, respectively. The daily
variability f_actors for both CN,A and CN,T were found to be 5.0. The
30-day-average variability factors were calculated to be 1.5 for both
CN,A and CN,T, using the daily variability factor above, Equation [2],
and Appendix XII-A.2.
Calculation o_f the Limitations
Multiplying the long term averages of 0.15 mg/1 for CN,T and 0.07 mg/1
for CN,A by the appropriate variability factors above gives the
resulting limitations:
30-Day-Avg. Daily Max.
CN,T 0.23 0.78
CN,A 0.11 0.35
A plant maintaining average CN,A concentrations less than or equal to
the above long term averages would be expected to exceed these
limitations less than one percent of the time.
AMENABLE CYANIDE (CN,A) TREATMENT FOR SMALL PLATERS
Plants discharging less than 10,000 gal./day (i.e., small platers) of
electroplating process waste water are not subject to limitations on
copper, nickel, chromium, and zinc. Consequently, solids removal
equipment such as clarifiers or filters may not be used at these
plants. Several commenters to the proposed regulations have claimed
that solids removal equipment, if present, may enhance the apparent
performance of cyanide treatment by incidently removing cyanide along
with the metals.
To study this effect, clarifier influent data for a subset of the
plants used in the cyanide analysis were analyzed. The data in this
subset, listed in Table 12-5, were taken after cyanide oxidation but
prior to metals removal. Lancy or Integrated plants (6087, 19051) and
plants designated by NAMF (6051, 6079, 6081, 19050, 36040) which were
used in this analysis in the Development Document for proposed
regulations, were removed for reasons specified in the previous
section. Also, four plants (6072, 20081, 20087, and 33073) were
removed because the data were insufficient to determine CN,A
concentration after cyanide oxidation.
The median or long term average CN,A concentration of these data
is 1.0 mg/1, substantially higher than the long term average
calculated for the same plants with data taken after metals removal.
The mechanism for this effect is unknown, although several theories
have been suggested; however, the effect is significant. Since
346
-------
TABLE 12-3
PLANT SUMMARY STATISTICS AND VARIABILITY FACTORS
FOR CN,A
Plant No. of Mean Std. Dev,
IDm Obs^ _ Log C* Log C VF**
15 11 -0.26 .590 9.4
19 11 -0,38 .362 4.9
804 14 -2.15 .856 14.1
1108 13 -0.34 .369 5.0
2001 114 -1.40 .101 1.4+
2103 13 -1.87 .176 2.4
Median .366 5.0
Concentration of CN,A in mg/1.
**Variability factor for each plant calculated using Equation [1],
except as noted below,
+Variability factor determined empirically, i.e., using 99th percentile
of observations divided by the mean.
347
-------
TABLE 12-4
PLANT SUMMARY STATISTICS AND VARIABILITY FACTORS
FOR CN,T
11
11
37
13
37
44
24
Mean
Log C*
0.22
-0.15
-2.10
0.01
-0.96
-1.86
-2.05
Std. Dev.
Log C
VF**
5.8
3.1
15.0
5.0
3.8
3.2
Median
.366
7.2
5.0
Concentration of CN,A in mg/1.
**Variability factor for each plant calculated using Equation [1]
348
-------
TABLE 12-5
CLARIFIER INFLUENT CONCENTRATIONS OBSERVED FROM PLANTS
USED IN THE AMENABLE CYANIDE ANALYSIS FOR SMALL PLATERS
Plant
ID
4045
5021
6037
6073
6075
6084
6085
6089
6381
9026
10020
15070
20073
20077
20078
20079
20080
20082
20084
20086
31021
33024
33070
36041
Number
Obs.
3
3
2
3
2
1
3
3
4
3
3
3
6
6
6
6
2
6
2
3
3
1
2
3
Concentration CN .
Median
6.40 mg/1
.45
4.54
2.56
.01
1.16
2.36
.59
.42
.60
7.69
5.70
.12
.60
.01
1.50
.25
.81
3.25
65.00
.06
1.05
.14
.10
A v g .
7.23 mg/1
.71
4.54
2.81
.01
1.16
1.92
.68
.42
.63
5.22
5.80
.12
1.50
.01
2.03
.25
.96
3.25
69.33
.30
1.05
.14
.15
,A
Max.
9.80 mg/1
1.62
8.42
4.95
.01
1.16
2.52
1.16
.64
1.00
7.80
7.25
.30
5.77
.04
5.00
.50
3.00
5.50
130.00
.80
1.05
.27
.25
349
-------
smaller plants may not have to install metals removal technology, the
proposed cyanide limit for small platers should not reflect the effect
of metals removal systems used by large plants.
Use of the daily and 30-day-average variability factors calculated
previously for CN,A (5.0 and 1.5, respectively) along with the above
long-term average of 1.0 mg/1, yields the following CN,A limitations
for small platers: daily maximum, 5.0 mg/1; 30-day-average maximum,
1.5 mg/1.
TREATMENT OF HEXAVALENT CHROMIUM (CR,VI)
Chromium in its hexavalent state is commonly present in the discharge
from chromium plating, chromating, or from certain other surface
finishing operations. A commonly used technology for the removal of
Cr,VI involves the reduction of the chromium to its trivalent state by
the addition of sulfur dioxide or bisulfite. These chemical agents
are capable, under properly controlled conditions, of consistent and
rapid removal of Cr,VI to an almost undetectable residual.
Technologies for treating chromium were detailed in chapter VII.
Calculation of_ the Long Term Average for Hexavalent Chromium
(Cr,VI)
Observed concentrations of Cr,VI in the effluent of 70 plants having
either chromium plating or chromating operations and treating their
chromium wastes by reduction, were included in the data base. An
effort was made to include in Table 12-6 all of the appropriate plants
for which data were available. The data base included those plants
visited during the recent EPA study effort, earlier plant information
collected by the Agency, and other sources. A few plants were
deliberately excluded, either because their treatment systems appeared
to be functioning erratically or were being bypassed (e.g., plants
1902 and 33021), or because the available raw waste data indicated an
average total chromium (Cr,T) concentration flowing into the reduction
unit of less than 1 mg/1 (e.g., plant 804). Lancy and Integrated
plants (6053, 6358, 33074) and one plant with combined wastes (2811)
were also excluded from the analysis of the Cr,VI limitations.
Figure 12-5 is a cumulative plot of the average Cr,VI eff_luent
concentrations of the 70 plants of Table 12-6. It can be seen that
more than half (54 percent) of these plants reported average Cr,VI
levels less than or equal to 0.05 mg/1, and the median or long term
average for Cr,VI is, in fact, 0.05 mg/1.
It should be emphasized that the averages plotted in Figure 12-5
include data from all plants, not just those with exemplary treatment.
The reduction of Cr,VI is a chemical process, and no uncontrollable
350
-------
TABLE 12-6
Cr.VI CONCENTRATIONS OBSERVED IN EFFLUENT FROM
PLANTS WITH Cr PLATING OR CHROMATING OPERATIONS
Plant
ID
16
17
19
21
116
635
805
11 08- a**
1108-b
1113
1209
1924
2001
2006
2007
2013
2024
2103
2501
3009
3301
3306
3311
3315
3320
3601
4301
6051
6073
6074
6076
6078
6079
6083
6084
6085
6086
6381
6731
12065
15070
Data
Source*
1
1
1
1
3
2
2
1
3
1&2
2
3
3
3
1&3
2
2
3
2&3
2
1&3
2
3
3
3
3
2
4
4
4
4
4
4
4
4
4
4
4
4
3&4
4
Number
Obs.
11
11
6
11
45
6
19
11
133
10
8
9
116
119
3
5
6
13
14
1
18
7
25
53
22
3
2
1
1
3
3
2
3
3
3
3
3
3
1
11
3
Concentration Cr,
Median
0.05 mg/1
.02
.05
.05
.31
.06
.04
.02
nil
.05
.06
.05
.07
.02
.05
nil
.11
.10
.02
.01
.04
.05
.08
.14
.14
.06
.08
.01
.17
.01
.01
.01
.74
.01
.01
.31
.03
.08
.13
.02
2.34
Avg.
0.05 mg/1
.02
.05
.05
.46
.05
.09
.18
.01
.05
.07
.05
.07
.04
.04
nil
.11
.09
.03
.01
.05
.05
.13
.17
.17
.05
.08
.01
.17
.01
.01
.01
.77
.01
.01
.66
.22
.08
.13
.05
2.92
VI
Max.
0.05
.02
.05
.05
2.10
.07
.38
1.40
.04
.08
.10
.05
.12
.30
.05
nil
.21
.13
.15
.01
.15
.05
.60
.37
.53
.08
.11
.01
.17
.01
.02
.01
.83
.01
.01
1.42
.63
.13
.13
.18
3.63
mg/1
(continued on next page)
351
-------
TABLE 12-6 (Continued)
Plant
ID
19063
20010
20064
20069
20070
20073
20077
20078
20079
20080
20081
20082
20083
20084
20085
20086
20087
30050
31020
31021
31050
33024
33070
33073
36040
36041
40061
40062
43003
Data
Source*
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
3
4
4
4
4
4
4
4
Number
Obs.
3
6
2
1
7
6
5
6
6
7
7
6
6
1
3
3
1
1
1
3
1
14
3
3
3
3
2
2
1
Concentration Cr,VI
Median
.01 mg/1
.01
.01
1.29
.30
.10
.03
.01
.01
.01
.03
.08
2.85
.05
.01
.42
1.07
.01
.01
.07
.01
nil
.17
.01
.01
.01
.10
.34
.11
Avg.
.01 mg/1
.01
.01
1.29
.22
.10
.02
.03
.01
.01
.25
.11
5.35
.05
.11
.43
1.07
.01
.01
.05
.01
nil
.13
.01
.01
.07
.10
.34
.11
Max.
.01
.01
.01
1.29
.44
.17
.04
.08
.01
.03
.96
.24
14.10
.05
.33
.77
1.07
.01
.01
.08
.01
.01
.21
.01
.02
.21
.19
.53
.11
mg/1
*1 = Data from reports by Yost et al., and Safranek et al.
2 = Battelle
3 = Plant
4 = Hamilton Standard.
**Plant 1108 was divided into two groups due to the large number of
observations and the two different sources reporting data.
352
-------
100
80
o
u
> 60
U
VI
c
S.
oj o
en *•
"I
£
40
20
0
.01
.02
.03.
.05
.2
.3
.5
Average Cr.VI Concentration (mg/l)
FIGURE 125
CUMULATIVE PLOT OF AVERAGE Cr.VI
IN DISCHARGES FROM 70 PLANTS
-------
sources of interference with the completion of this reaction have been
brought to our attention. Those plants in the data base whose average
Cr,VI concentrations exceed 0.05 mg/1 do not appear to have
characteristics distinguishing them from the majority. No significant
differences were found between job and captive shops or between direct
and indirect dischargers.
Calculation of the Variability Factor
To allow for fluctuations in hexavalent chromium removal, variability
factors were calculated as explained previously, based on the
observation that the discharge concentrations of metals follow a
standard lognormal distribution. Figure 12-6 shows a cumulative plot,
on a log probability scale, of 45 daily observations of Cr,VI
from plant 116. The data were nearly linear, indicating that the
distribution of observations from this plant may be assumed consistent
with lognormality.
The individual plant Sigmas and variability factors for Cr,VI are
listed in Table 12-7. The median variability factor is 5.2. The 30-
day variability factor, calculated from the median variability factor,
Equation [2], and Appendix XII-A.2, is 1.5.
Calculation ojE the Limitations
Multiplying the long term average of 0.05 mg/1 by the variability
factors above gives daily and 30-day-average maximum limitations for
Cr,VI of 0.26 and 0.08 mg/1, respectively.
METALS REMOVAL USING SEDIMENTATION FOR THE ELECTROPLATING CATEGORY;
CU, NI, ZN, CD, PB, AG
This analysis is based on data from a subset of 25 plants sampled by
the Agency.4 The results of the statistical analysis of the analytical
sample demonstrate that the variability in metal concentration in
clarifier discharges is related to:
1. the amount of TSS discharged from the treatment system, and
4The sample includes those electroplating and metal finishing plants
that used precipitation and settling for solids separation, and those
that did not have electroless plating operations. For a listing of
plant identification numbers and metals which they plate, see Exhibit
B.I in Appendix XII-B.
354
-------
TABLE 12-7
PLANT SUMMARY STATISTICS AND VARIABILITY FACTORS
FOR Cr.VI
116
805
1108-a
1108-b
1113
2001
2006
2103
3301
3311
3315
3320
Mean
Log _C*
-0.52
-1.19
-1.39
-2.04
-1.59
-1.24
-1.78
-1.04
-1.48
-1.04
-0.92
-0.92
St. Dev,
Log C*
.439
.354
.584
.326
.269
.280
.685
.112
.361
.400
.402
.394
Median
VF**
6.3
4.8
9.2
4.3
3.5
1.8
6.2
1.8
4.9
5.6
5.6
5.5
5.2
*Concentration~TragYl) .
**Variability factor calculated using Equation [1] for those plants with
less than 100 observations or using the 99th percentile over the
observed average for those plants with 100 or more observations.
355
-------
o>
I
g
u
§
U
>
.1
.09
.08
.07
.06
.OS
.04
.03
.02
.01
10 15 20 30 40 50 60 70 80 85 90 95
Percent of Observations 5" Cr.VI Concentration
FIGURE 12-6
CUMULATIVE DISTRIBUTION OF 45 DAILY Cr, VI
DISCHARGE CONCENTRATIONS FROM PLANT 116
98
356
-------
2. the ratio of the metal to the total metals in the
load which goes to the pretreatment system.
raw waste
Factors Influencing Individual Metal Effluent Concentrations
A series of exploratory statistical analyses were conducted to
determine which measured attributes of the plant and treatment systems
influenced the concentration of particular metals in the clarifier
discharge. The data used in the analyses were average values for each
plant; thus, each plant's performance was given equal weight. When a
particular metal was under consideration, only those plants that were
known to use that metal were included. The metal discharges studied
in this way were Cr,T, Cu, Ni, Zn, Cd, and Pb.
The analyses of the relationships between discharge metal
concentrations and the effluent and raw waste streams were made using
the method of multiple regression. The regressions showed that the
concentration of a given metal in the clarifier discharge is
significantly related to three variables: the concentration of TSS in
the clarifier discharge (effluent); the concentration of the same
metal in the raw waste load (RWL); and the total concentration in the
RWL of all metals which would precipitate as hydroxides at a pH
greater than 7.5.
The following model describes this relationship:
Log Me = A + B Log TSS + C Log Me0 + D Log PM [5]
where
Me = the concentration (mg/1) of a specific metal in the discharge
TSS = the concentration (mg/1) of TSS in the discharge
Me0 = the concentration (mg/1) of the specific metal in the raw
waste load
PM = the concentration (mg/1) of total precipitable metal in the
raw waste load.5
The regressions were performed on the logarithm of the variables.
This made the distribution of the residuals (the difference between
the observed and the predicted values of the dependent variable) more
normal than would result from use of raw data values.
5Cu + Cr,T
Ni
Pb + Cd + Ag + Hg + Sn + Fe.
357
-------
The values for the coefficients A, B, C, and D which provide the best
fit for the data on each of the individual metals (Cr,T, Cu, Ni, Zn),
are shown in Table 12-8. This table also gives the coefficient of
multiple determination (R2) for each regression (the fraction of the
total variance in the data accounted for by the regression).
Equation [5], above, can be simplified to Equation [6], below:
Log Me = A + B Log TSS + C Log Xme [6]
where
Xme = Me°/PM.
The values for the new coefficients A, B, and C, which provide the
best fit, are given in Table 12-9. The effect of making the change
from Equation [5] to Equation [6] is small because the coefficients C
and D in Equation [5] are approximately the same magnitude, but of
opposite sign. (See Table 12-8.) Thus, the fit to the data of the
second model (Equation [6]) is nearly as close as for the first model
(Equation [5]), as can be seen by comparing the R2 values* in Tables
12-8 and 12-9. A "group average" fit was also constructed for the Me,
TSS, and Xme observations of all four metals combined into a single
group of 80 observations. The corresponding average equation is:
Log Me = -0.33 + 0.55 log TSS +0.65 log Xme [7]
This equation is for metal and TSS concentrations expressed in mg/1.
Table 12-10 shows that for average values of the logarithms of TSS and
Xme for each of the four metals, the regression models of Equations
[6] and [7] yield estimates of metal discharge concentrations that are
roughly comparable and generally greater than the observed median
concentration for the plants plating these metals.
There is a physical explanation for the concentration of a given metal
in the discharge being a statistical function of the amount of TSS and
the ratio of the given metal to total precipitable metals entering the
clarifier. A plant discharge will normally contain metals both as the
dissolved species and as a component of the TSS. When a particular
metal is predominantly in solution and the precipitate has the form of
a solid solution of mixed metal hydroxides, one might expect its
concentration to depend on the fraction of metal in the precipitate
derived from the RWL. Alternately, if the effluent metals are
predominantly TSS precipitate, one might expect the amount of a given
•Specifically those for Cu, Ni, Cr,T, Zn,
358
-------
TABLE 12-8
REGRESSION FIT OF AVERAGE METAL SPECIES DISCHARGED (mg/1)
FROM 25 PLANTS WITH CLARIFIER SYSTEMS USING EQUATION [5]
Model (1): Log Me = A + B Log TSS + C Log Me° + D Log PM
Metal
Species
Cr,T
Cu
Ni
Zn
No. of
Plants
22
19
21
18
Coefficients of Best Fit
A
-.04
-.35
-.39
-.15
B
.50
.78
.85
.23
C
.80
.59
.29
.68
D
-.88
-.74
-.55
-.57
7
ir
.55
.67
.45
.43
Me = Average concentration (mg/1) of given metal in the
effluent.
TSS = Average total suspended solids (mg/1) in the effluent.
Me = Average concentration (mg/1) of given metal in the raw
waste load.
PM = Cu + Cr,T + Zn + Ni + Pb + Cd + Ag + Hg + Sn + Fe.
A,B,C,D = Regression coefficients.
2
R = Square of multiple correlation coefficient.
359
-------
TABLE 12-9
REGRESSION FIT OF AVERAGE METAL SPECIES DISCHARGED (mg/1)
FROM 25 PLANTS WITH CLARIFIER SYSTEMS USING EQUATION [6]
Model (2): Log Me = A + B Log TSS + C Log Xme
Metal
Species
Cr,T
Cu
Ni
Zn
Group Ave.*
TRM**
No. of
Plants
22
19
21
18
80
25
Coefficients
A
-.20
-.41
-.76
-.02
-.33
-.18
of
B
50
66
73
29
55
59
Best Fit
C
.81
.66
.27
.67
.65
.69
2
R
.55
.67
.40
.42
.51
.33
Me = Concentration (mg/1) of given metal in the effluent.
TSS = Total suspended solids (mg/1) in the effluent.
Xme = Ratio of the given metal to total metals (PM) in the raw
waste load.
A,B,C = Regression coefficients.
2
R = Square of multiple correlation coefficient.
*A regression performed on the four metals combined into a single group,
**TRM (Total Regulated Metals) = Cr,T + Cu + Ni + Zn.
360
-------
TABLE 12-10
METAL CONCENTRATIONS PREDICTED BY EQUATION [6]
AND EQUATION [7] AT AVERAGE
VALUES OF TSS AND Xme
Predicted Concentrations
(mg/1)
Metal Equation [6]*
Cr,T .69
Cu .82
Ni 1.19
Zn .74
Equation [7]
.81
.72
.94
.90
Observed
Median**
(mg/1)
.70
.48
1.10
.75
For the following average values of the logarithms of TSS
(mg/1) and Xme for each plant.
Log TSS Log Xme
Cr,T 1.40 -.82
Cu 1.32 -.83
Ni 1.41 -.73
Zn 1.44 -.78
*With coefficients for the respective metals shown in
Table 12-9.
**Median of the observed plants plating the given metal.
361
-------
metal discharged to depend strongly on both the amount of TSS and of
the fraction of given metal in the total metals entering the TSS.
Total Regulated Metals
The sum of copper, total chromium, nickel, and zinc in the clarifier
discharge, designated by "TRM", or total regulated metals, also shows
a functional dependence on TSS and on a new variable Xm (the sum of
the Xme's of the four metals), which is similar to that found for the
individual metals. Application of a regression model of the form of
Equation [6] to the sum of metals data from the 25 plants yields:
log TRM * -0.18 + 0.59 log TSS +0.69 log Xm [8]
This equation is for metal concentrations expressed in mg/1, with the
square of the multiple correlation coefficient (R2) equal to 0.33.
Validity of_ Regressions
Before the above equations can be used with confidence, several tests
of their validity and stability must be made. Major points to be
considered are:
1. Are the apparent positive correlations between Me and TSS and
Xme {and between TRM and TSS and Xm) an artifact of the use
of the regression methodology?
2. Do they depend on the presence in the data base of one or two
(possibly atypical) plants, i.e., are regression results
stable?
3. Do the equations fit the data?
4. Are the results sensitive to any other factors?
Correlations Between Variables. To resolve the first of these
questions, nonparametric tests for correlation between effluent metal
concentration and TSS and Xme were made. The tests were independent
of the distributional assumptions inherent in the use of the multiple
regression equations. The Spearmen's Rho, a measure of correlation
based on the ranking of the observations, showed positive correlations
between Me and TSS and between Me and Xme, for each of the four metals
as well as for total regulated metals.
Stability of Regressions. The stability of the regression predictions
over the combination of plants selected for consideration was
investigated by systematically removing all possible pairs of plants
from the data base, and observing whether the predicted metal
concentrations (for a given TSS and Xme) changed markedly. No pair of
362
-------
plants, when removed from the regression, was tound to have a dramatic
impact on the predicted Me. Plants 20010 and 33024 had among the
highest impacts on the predictions for all metals. Even so, deletion
of these plants from the data base brought about only an 8 to 24
percent increase (depending on the specific metal under consideration)
in the predicted effluent metal concentrations (predicted for TSS = 25
mg/1 and Xme * the median value for each metal). This small effect
shows that the predictions of discharge metal concentration are stable
and do not depend strongly on the observations from any pair of
plants.
Test of Fit. Figure 12-7 displays, for Equation [7], contours of
constant expected metal concentration, Cme, as a function of discharge
TSS and of Xme. These contours are plots of the TSS and Xme values
obtained by holding Me in Equation [7] constant for each of the Cme
values indicated in Figure 12-7. The region under any given curved
line is the region of clarifier TSS discharge and of RWL metal
fraction for which the concentration of metal discharge is expected to
be less than the line's value. For example, Figure 12-7 illustrates
that the concentration of a metal discharged from a clarifier with 25
mg/1 TSS and Xme = 0.2 in the RWL is expected to be slightly less than
1 mg/1.
The observed metal concentrations discharged by the 25 plants should
be compared with those predicted in Figure 12-7. Figure 12-8 is a
plot of the same form as Figure 12-7, with only the 1 mg/1 contour
shown. The points on this figure are the TSS and Xme of each metal
discharged by the 25 plants. It can be seen that most of the
observations fall in the appropriate areas, relative to the
predicted 1 mg/1 line. Eighty-five (85) percent of those cases with
actual discharge metal concentration less than or equal to 1 mg/1
fall, as predicted, below the curve, while 70 percent of those cases
with actual discharge metal concentration greater than 1 mg/1 fall
above the curve.
Sensitivity ojf Results to Neutralization Agent. As a general
practice, either lime or caustic is added to the waste stream to
precipitate metals before clarification. In the plants in the data
base, the choice of lime was associated with significantly lower
effluent metal concentrations. For the seven plants using lime, the
median concentration of total regulated metal was 2 mg/1. For the
remaining 18 plants, the median was 5.1 mg/1. Similar effects were
observed for individual metals, with the apparent drop in effluent
concentration most pronounced for Ni and Cu. The seven plants using
lime appeared otherwise typical of the plants in the data base, having
similar values of effluent flow, TSS, RWL metal concentration, and
area plated.
363
-------
110
OB
O5
h-
e
«
3
100
90-
80-
70-
60
50-
40
30-
20-
10-
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Fraction of Matal in RWL MetaJj
FIGURE 12-7
CONTOURS OF CONSTANT EXPECTED DISCHARGE
METAL CONCENTRATION (Cme) AS A FUNCTION OF
TSS AND Xme
364
-------
110
ta
ta
3
£
LU
100
90
80
70
50.
40
30
20, *.
• — observed discharge ^ 1 mg/l
* — observed discharge > 1 mg/l
Cm* — constant expected discharge
metal concentration (mg/1)
10
* •
* *
• *
I
I
0.0 0.1 0.2 0.3 0.4 0.5
Fraction of Metal in RWL Metals
0.6
0.7
FIGURE 12-8
COMPARISON OF OBSERVED DISCHARGE METAL
CONCENTRATION VS Cme = 1 mg/I CONTOUR
365
-------
Sensitivity of Results to Flow. Since the quantity, in pounds/day, of
metal discharged to the sewer is dependent on the effluent flow, it is
important to determine whether flow and discharge concentration are
related. Although the three plants with the lowest flows have above-
average total regulated metal concentrations, the data presented below
show that there is little evidence of any consistent relationship
between flow and concentration.
Number Median Median
Plants TRM(mq/l) Flow(qal./hr.)
3 20.8 230
7 2.3 2100
7 1.5 3100
6 5.8 6000
2 3.2 19000
Sensitivity of_ Results to Plant Size. Two measures of plant size have
been considered: the total number of employees, and the plating rate
(op-m2/hr). No consistent trend in total regulated metal
concentration was noted for either case.
Sensitivity of_ Results to pH. Of the 25 plants considered, 6 had
average pH values less than or equal to 8.5. At a pH below this
value, the solubility of Ni exceeds that of its pure hydroxide by
irore than 10 mg/1. Accordingly, the discharge from a clarifier at a
pH less than or equal to 8.5 might contain comparatively high
concentrations of Ni, if the relative insolubility of the pure
hydroxide limits metal removal. However, this did not appear to be
the case. There were five plants which plated Ni and which discharged
at an average pH not greater than 8.5; four of these had RWL Ni
concentrations in excess of 5 mg/1. However, the average effluent Ni
concentration for these four plants was only 1.1 mg/1, a value less
than the median of all Ni plating plants in the sample.
The failure of these plating plants to discharge Ni at levels approx-
imating the equilibrium solubility of the hydroxide indicates that
some other factor controlled the solubility of the metal (e.g.,
presence of other metals). It is possible that the metal was
precipitated in a less soluble form, such as carbonate, or that the
nickel hydroxide was in solid solution with other hydroxides and had a
lowered activity.
It was found that pH entered as a dependent variable in the regression
equations for the individual metals or total regulated metals did not
add a statistically significant contribution to the correlation
coefficient.
366
-------
Sensitivity of Results to RWL Cu. In comments to EPA, one respondent
reported the results of his laboratory studies on the solubility of Cu
in alkaline solutions, which were derived from copper plating baths
and which had been treated to remove cyanide. He reported that the
apparent Cu solubility increased markedly with higher initial Cu
concentrations in the treated solution. He also stated that Zn and Ni
solubilities increased in solutions mixed with treated Cu plating
solution.
The data indicated that, for the solutions and the treatment
procedures used, the apparent Cu solubility increased as the 1.5 to 2
power of the initial Cu concentration, for initial Cu concentrations
in the range of 50 to 1,000 mg/1. There have been various
explanations to account for such a dramatic increase in apparent Cu
solubility at high initial Cu levels and for the reported increases in
Zn and Ni solubility; the presence of an unspecified complexing agent,
stable to the experiment's cyanide removal procedures in the Cu
plating baths studied, would seem to explain much of the phenomenon.
Complete data on the compositions of these baths were not furnished to
EPA.
The Agency has not been able to verify this laboratory effect with
available data. The minimum initial Cu studied was 50 mg/1, and the
effects reported were most noticeable at initial Cu's in excess of 200
mg/1. These concentrations were well above those normally
encountered; only three plants of our sample reported average raw
waste load Cu's greater than 50 mg/1, and the maximum average RWL Cu
was 125 mg/1.
The addition of a log RWL Cu term to the regressions of
yielded no significant increase in explanatory power.
three of the four metals, the coefficient was negative,
negative correlation of discharge concentration
Furthermore, no significant differences were
observed Cu concentrations of the seven daily observations with RWL Cu
greater than 50 mg/1 and the predicted Cu concentrations
the regression equation of Table 12-9. Thus, it appears
the operating conditions of the sample plants,
concentration affects the discharged metal concentration only insofar
as it affects Xme.
Equation [6]
(In fact, for
indicating a
with RWL Cu.)
found between the
with !
derived from
that under
the RWL Cu
Derivation of Limitations
To summarize, models of the form of Equation [6] have been found to
describe the dependence of the average effluent metal concentrations
on TSS and Xme. The coefficients of Equation [6] that best describe
the behavior of the individual metals are summarized in Table 12-9
(above). Equation [7], of the same form as [6], is derived to give an
overall fit to the average concentration data of all individual metals
367
-------
without regard to species. Equation [8] describes the dependence of
the average concentration of the Total Regulated Metals on TSS and Xm.
These equations can be used to determine guideline limitations on
average effluent metal concentrations, provided that levels of TSS and
Xme which are technically attainable by a metal finisher can be
specified. The metal finisher must properly control his wastes and
employ a well-designed and operated clarification system. The
following sections of this analysis will discuss four factors in the
determination
concentrations,
equations for
and factors to
concentration.
of guideline limitations.
Xme values, the application
estimation of long term average
allow for daily variability about
They are: TSS
of the appropriate
metal concentrations,
the long term average
Variation in TSS
The average TSS concentrations discharged from the 25 sampled plants
ranged from 2 to 120 mg/1, with a median of 28 mg/1. This wide range
of average TSS concentrations reflects a corresponding diversity in
clarifier design and operating procedures. The clarification systems
employed by the 25 plants included lamella clarifiers (plant 3102),
tube settlers (20082), and settling tanks or clarifiers. The
retention times, design parameters denoting the average time available
for a solid particle to settle out, varied from 0.8 hr. (6037) to 48
hrs. (20084). It should be remembered that the plants of this study
were not selected for exemplary clarifier operation and design; in
fact, for some of the plants, the retention operating procedures and
controls also impacted the level and stability of clarifier
performance. Such procedures could include the careful selection and
addition of polymeric coagulants and co-precipitating metals (Fe or
Al) before clarification, and the recycling of aged sludge to the
precipitation tank to serve as a nucleating agent. Control factors
important to clarifier operation could include equalization of flow,
RWL metal, and temperature in the clarifier influent and the avoidance
of oily wastes. Though many of the above factors were not reported,
the data base does indicate that an average TSS limitation of 20 to 25
mg/1 is reasonable.
The data can be divided into two groups, those with some evidence of
inadequate design or plant control, and those without this evidence.7
7Three measures of clarifier design and
considered. They are:
operation have been
(Continued)
368
-------
The median TSS concentration for the former was 47 mg/1, the median
for the latter was 18 mg/1. TSS separation by clarification is widely
practiced in many industries, with levels of 20 to 30 mg/1 being
readily attained. A level of 25 mg/1 appears reasonable for the metal
finishing industry, and this TSS concentration will be used as the
basis for estimating average attainable metal limits.
Variations iji a Metal's Fraction in the RWL
The Xme for an individual metal in the waste from a plant can be
controlled by reduction of the amount of the metal discharged to the
RWL. This reduction of Xme can be accomplished by such management
practices as dead rinses, fog-rinses, and adequate draining of the
finished material before rinsing. However, with such practices, the
reduction of the Xme for one metal is accomplished at the expense of
an increase in Xme for another.
A uniform reduction of Xme's for the regulated metals can be obtained
by the addition of an unregulated metal (such as Fe or Al) either
deliberately or by solution of the basis metal during cleaning steps.
Addition of such a metal should bring about some reduction in the
discharge concentration of regulated metals, particularly if the added
metal also serves as a coagulant for the precipitated TSS solids.
(Continued)
1. Retention time, as indicative of clarifier design. The median
retention time of the 19 plants that reported the parameter
was six hours.
2. Oil and grease effluent concentration, as indicative of a
problem which is at least partially controllable by plant
practices. Oil concentrations can be reduced by segregation
or by emulsion breaking followed by separation (plant 6074).
The median effluent oil and grease concentration of the 23
plants with data was under 3 mg/1.
3. Temperature differential between the clarifier discharge and
its influent can result in convective stirring and reduction
in clarifier settling efficiency, particularly if the
entering stream is warmer than the body of liquid in the
clarifier tank. Those plants which had retention times less
than or equal to 3 hours, effluent oil and grease greater
than or equal to 20 mg/1, or RWL temperature more than 2°C
warmer than effluent temperature, were considered to have
evidence of inadequate design or operational control.
369
-------
To determine the range of Xme values typically encountered in the raw
waste load of metal plating and finishing plants, the data base of 25
plants used in the previous analysis was supplemented by data from 22
additional plants (Appendix XII.B, Exhibit B.2). These latter plants,
although not suitable for analysis of effluent metal concentrations
(because of incomplete cyanide oxidation, use of filters, etc.) can
be used for analysis of raw waste load metal loadings. Table 12-11
summarizes the distribution of Xme's encountered in the raw waste load
of the combined 47 plant sample. The table also summarizes the
distribution of the fraction Xm, as discussed above under total
regulated metals.
As Table 12-11 shows, the Xme's for the individual metals vary over a
wide range. Much of this variation probably reflects the diversity of
plant practices. However, the Xme is also related to the number of
metals plated within the plant.8 For example, a plant which plates two
metals will generally have a higher average Xme for these metals than
a plant which plates four metals, simply because the two metals it
plates generally make up a larger fraction of all the metals in the
raw waste load. The relation of the average observed Xme for all
metals to the number of metals plated can clearly be seen in Table
12-12. This table shows the average Xme attained by plants using a
single metal to be 0.61, while the average Xme for plants plating or
finishing with five different metals was 0.13. The 47 plants plated
an average of 3.3 different metals and had an average Xme of 0.26.
ESTIMATION OF AVERAGE METAL CONCENTRATION
Equation [6] provides an estimate of the average effluent metal
concentrations expressed as a function of TSS and Xme. The
coefficients for this equation that give the best fit for the
individual metals Cr,T, Cu, Ni, and Zn, are listed in Table 12-9.
Accordingly, Equation [6], with Table 12-9 coefficients, will be used
to derive average limits for each of the individual metals. Equation
[8] was similarly constructed to fit the concentration of total
regulated metals, and this equation was used to derive average limits
for this total. Because of the small number of plants plating Cd or
discharging Pb, it is not feasible to develop best fit equations for
these metals. However, Equation [7] predicts, quite well (see Table
12-10 and Figure 12-7), the discharge concentrations of the metals for
"Includes such nonplating operations as chromating,
370
-------
TABLE 12-11
DISTRIBUTION OF THE FRACTION OF METAL IN THE
RAW WASTE LOAD TOTAL METALS DISCHARGED
BY 47 METAL FINISHING PLANTS
Plants Fraction metal (Xrae)
Metal Using Median 75 percentile Maximum
Cd 8 .05 .06 .10
Cr.T 37 .12 .52 .82
Cu 39 .14 .27 .72
Ni 40 .16 .40 .79
Pb* 11 .004 .015 .21
Zn 31 .21 .43 .71
TRM 47 .91 .96 1.000
*Plants with more than 0.5 mg/1 Pb in RWL.
371
-------
which adequate data were available. Therefore, this equation is used
to derive average Cd and Pb limits as well.9
The above equations all express the given metal concentration in terms
of the independent variables, TSS concentration and Xme. As discussed
earlier, average TSS concentrations of 25 mg/1 or less appear readily
attainable by waste stream clarification. The choice of appropriate
values of Xme to use for determination of metal limits is somewhat
more complex because of the variation of attainable Xme's with the
number of metals plated.
There appear to be two alternative approaches to setting Xme's for
individual metals. First, the Xme distribution data of Table 12-11
can be used to find a point on the distribution which is far enough
above the median to be attainable by most platers, regardless of the
number of metals plated. Such a point could be the 75 percentile,
which covers most cases, with the possible exception of plants plating
a single metal.
The second approach is to consider the attainable levels of Xme for
Cr, Cu, Ni, and Zn to be dependent only on the number of metals used
in plating and finishing operations by the plant, independent of which
metals are actually used. The Xme values derived would then be the
demonstrated average Xme's of Table 12-12.
Table 12-13 summarizes the values of the average metal concentration
excted for each metal using the two approaches. The table shows that
metal concentrations based on a 75 percentile are usually greater than
those based on a plant's using two or more metals in its plating and
finishing processes but less than those based on a plant using a
single metal. Either of these two alternative approaches appear to
give average metal concentrations that can be achieved by all plants
plating more than a single metal. The Table 12-13 long term average
metal concentrations, based on the 75 percentile Xme values, will be
used below in calculations of the daily maximum and 30-day-average
limits for Cr,T, Cu, Ni, and Zn.
The above procedures for determining average metal concentrations have
the following disadvantage. Since both procedures depend on the
'Equation [7], if applied to the three plants plating Cd, tends to
overpredict the observed average Cd discharge concentration with an
average error of 10 percent. The tendency of this equation to
overpredict the observed concentrations is more marked in the case of
the three Pb discharging plants; the average overprediction is
about 65 percent.
372
-------
TABLE 12-12
DEPENDENCE OF Xme ON THE NUMBER OF METALS USED
IN PLATING AND FINISHING
Number Number Average
Metals* P1 an t s Xme
1 2 .61
2 11 .31
3 11 .28
4 16 .21
5 7 .13
*Number of metals plated. For plants plating a specific
number of metals, see Exhibits B.I and B.2 in Appendix
XII-B.
373
-------
TABLE 12-13
PREDICTED AVERAGE METAL CONCENTRATION*
IN DISCHARGE FROM PLANTS WITH 25 mg/1 TSS
Using Average Xme's of Using 75 Percentile Xme's of
Table 12-12 Table 12-11**
Number Metals
Plated
Cd
Cr,T
Cu
Ni
Pb
Zn
-
2.1 mg/1
2.3
1.6
-
1.7
-
1.2 mg/1
1.5
1.3
-
1.1
-
1.1 mg/1
1.4
1.3
-
1.0
0.4 mg/1
1.9
1.4
1.4
0.2
1.4
*Based on Equation [7] for Cd and Pb. Based on Equation [6] with
Table 12-9 coefficients for Cr,T, Cu, Ni, Zn.
**These values are the Long Term Averages (LTA) of the respective
metals.
374
-------
evaluation of an attainable Xme for each metal, the concentrations
calculated on the basis of either the two-metal average or the 75
percentile will be too high (lenient) for most plants, which, on the
average, plate more than two metals and for which most Xme's fall near
the observed medians.
An additional limitation, based on total regulated metals, compensates
for this problem. The value of the fraction of total regulated metals
in the raw waste metals, Xm, is less dependent on the number of metals
plated than are the individual Xme's. Additionally, Xm varies much
less than the Xme's between the median observed value and the maximum
observed value (from Xm = 0.91 to Xm = 1.0). As a result the
percentile chosen has less influence on the calculation of TRM. The
estimated long term average for total regulated metal concentration,
using Equation [8] and assuming that TSS = 25 mg/1 and Xm = 0.96,
is 4.2 mg/1. This value will be used in calculations of the daily and
30-day-average maximum limits for TRM.
A total regulated metals limitation alone is insufficient because it
does not prohibit continuous discharge by a plant plating only one
metal (e.g., Cu) at concentrations above the limitation for that
individual metal. This might be the case for a plant which plates
only one or two metals, or for a plant which has difficulty
controlling waste generation from one specific line. Therefore, each
plant will be required to meet limitations on both the individual
metals and on TRM.
Plants which plate only a single metal have been predicted by the
preceeding analysis to have typically higher Xme values and hence
higher effluent metal concentrations than plants which plate more than
one metal. This prediction does not demonstrate, however, that a
single-metal plater cannot meet the final regulations for the metal it
plates.
First, the Agency has conducted an analysis which shows that EPA data-
base plants with large Xme values (plants plating primarily a single
metal) met the limitations for the metals they plated with
approximately the same frequency as did other plants in the data
base. However, this analysis should not be interpreted as a statement
that the regression model does not apply. Specifically the model,
which is a function of only two ariables, has been used to describe
certain interactions among variables over a large range of
circumstances. It is a representation of a norm which is an aggregate
approximation in that the model does not fit any single case exactly.
Single metal platers and those with excessively high metal rates are
at the fringes of the region to which the model applies. In these
circumstances there are other important factors, such as those cited
below, which are not incorporated into the model directly. This
consideration and other analyses described here indicate that the
375
-------
model's predictive power is less accurate for single metal platers.
The Agency used the model by evaluating it at specific combinations of
the two independent variables resulting in appropriate standards for
all platers.
Second, the Agency has found that of the nine Printed Circuit Board
plants in the data base, none of which plated significant amounts of
metals other than Cu, only two10 failed to meet the daily limitation
on Cu set for the Electroplating category.
Finally, engineering measures may be undertaken to improve metals
removal whenever there is a relatively large amount of one metal in
the waste stream. For example, the pH of the wastewater in a plant
plating only one metal can be adjusted to optimize the treatment
system for removal of that metal—an adjustment which cannot be easily
made when more than one metal is involved.
Calculation of_ the Variability Factors
Some degree of fluctuation in the daily concentration and quantity of
pollutants discharged from even a well equipped and operated treatment
system appears to be unavoidable. The following two figures
illustrate the day-to-day fluctuations usually observed in the output
of a plant that discharges metals in its wastes. Figure 12-9 is a
plot of the daily concentrations of total chromium reported over an 11
month period from the metal finishing operations of plant 20080.
The operations consisted of Zn plating of steel wire, followed by
chromate conversion coating. The chromium wastes were treated by
reduction of Cr,VI to Cr,III, alkaline precipitation, and
clarification. The average Cr,T discharge concentration over this
period was 0.52 mg/1.
Figure 12-10 is a probability plot, on a logarithmic probability
scale, of the data of Figure 12-9. The nearly linear form of this
plot supports the assumption made earlier that the plant metal
concentrations follow a lognormal distribution. The derivation of the
variability factor equation is based on this assumption. Appendix
XII-A.3 provides more data which tend to support the good fit of_ the
lognormal distribution to the daily Cr,T, Cr, Ni, and Zn effluent
values from a plant. Using the methodology and assumptions discussed
earlier, the variability factors in Table 12-14 were calculated. The
statistics for each plant and individual metal necessary to
calculate VF are in Exhibit A.3 of Appendix XII-A.3. The 30-day-
l°Plant 19063 failed on only 1 of 6 observations by less than 10%,
376
-------
§
i
i
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
I
I
I
40 80 120 160 200
Day Number (Zero - 4/1/75)
240
280
320
FIGURE 12-9
230 DAILY VALUES OF TOTAL
CHROMIUM (CRT) CONCENTRATION FOR PLANT 2080
377
-------
CO
-~j
CO
10—
g
g
7
6
5_
4
3
5 2
E
I
6 i
E 9
8 8
3 7
t-
.•! 6
5
4
3
2
.1
0.
4
11 00501 0
s
.2 0
X
X>
•
*
J
M^
^
512 51
^
X
•
X
) 20 30 <
Pefccm of Obwn
^
0 1
ction
s*
S
^JL
_x
X.-
.*
f
s
•c
—• 1
•/
• •
X
0 60 70 80 90 95 98 i
i < Ci.T Concentration
*
X
»
9 9!
M>
f
.8 i
X
9.9 99
FIGURE 12 10
CUMULATIVE DISTRIBUTION OF 230
DAILY CHROMIUM (Cr,T| CONCENTRATIONS FOR PLANT 208O
-------
TABLE 12-14
DAILY VARIABILITY FACTORS FOR ELECTROPLATING CATEGORY
Plant
ID
13
14
116
637
804
804
1108
1208
1570
1924
2001
2070
2080
2081
2088
2501
3301
3311
3315
3320
3324
No. of
Obs.
10
13
48
66
14
14
133
37
82
11
116
34
230
187
65
14
22
25
53
24
14
Cu
3.03
4.88
5.91
3.54
2.99
—
2.38
3.61
—
4.21
2.26
3.28
—
2.59
3.69
2.57
7.23
2.81
2.15
3.60
2.45
Ni
2.26
5.23
5.81
6.15
4.50
—
2.93
—
—
1.77
—
—
—
2.48
2.40
2.58
4.39
—
2.52
7.36
—
Zn
2.49
3.05
—
—
—
—
2.64
2.90
2.36
3.02
1.40
—
4.11
1.70
3.60
6.13
13.34
—
—
5.14
3.51
Cr,T
5.48
7.84
3.31
—
4.97
—
3.97
3.57
2.26
—
—
—
2.87
2.13
2.49
5.00
5.99
7.07
3.83
4.99
2.82
Other*
„
4.48
—
4.90
2.86
2.08
2.64
—
—
2.80
2.55
—
—
—
—
—
7.49
—
—
5.36
—
TRM**
2.45
5.34
2.62
3.32
3.08
—
2.19
2.37
1.84
2.04
1.38
—
2.80
1.78
1.90
3.86
7.98
2.89
1.87
3.52
—
Median
3.2
2.9
3.0
3.9
2.9
2.5
*0ther - Ag, Cd, Pb.
**TRM - Total Regulated Metals = Cu + Cr,T + Ni + Zn.
For Cu, Zn, Ag, Cd and Pb, the data used in the above calculations were
those with daily observations of CN,A or CN,T concentration less than
1 mg/1. For Cr,T, all daily observations were used except for those
with Cr,VI greater than 0.25 mg/1 and with Cr,VI/Cr,T greater than or
equal to 0.25.
If the number of observations is less than 100, the plant VF is computed
using Equation [1].
If the number of observations is greater than or equal to 100, the plant
VF is computed by dividing the 99th percentile of ranked data by the
average value.
379
-------
average variability factors were: 1.4 for Cr,T; 1.3 for Cu, Ni, Zn,
Cd, Pb, and Ag; and 1.2 for Total Regulated Metals.
Silver Analysis
The Agency data file contains nine plants that carried out silver
plating operations during the time of the sampling program. The
observed silver concentrations in the effluents of these plants are
listed in Table 12-15.
Of the nine plants listed in Table 12-15, three plants (6073, 6081,
6085) plated only a small quantity of Ag in comparison with their
other operations, and thus, their RWL Ag concentrations were
correspondingly quite small. Plant 6037, on the other hand, is a
major Ag plater but had a CN,A level so high that very little of its
RWL Ag was removed by waste treatment. The remaining five plants had
Ag effluent concentrations of 0.14, 0.14, 0.42, 0.56, and 0.8 mg/1,
respectively. Thus, the median or long term average for these Ag
platers was 0.4 mg/1.
The variability factor of 2.8 for Ag comes from the column headed
"Other" in Table 12-14. The 30-day-average variability factor of 1.2
was obtained using the variability factor of 2.8, Equation [2] and
Appendix XII-A.2. Multiplying these variability factors by a long
term average of 0.4 mg/1 gives daily and 30-day-average maximum limits
for Ag of 1.2 and 0.5 mg/1, respectively.
Calculation of_ Limitations
The following daily and 30-day-average maximum limitations were
derived by multiplying the variability factors by the appropriate long
term average concentrations.
Daily 30-Day- Long Term
Metal Max. Average Max. Average
Ag 1.2 mg/1 0.5 mg/1 0.4 mg/1
Cd 1.2 0.5 mg/1 0.4 mg/1
Cr,T 7.0 2.5 1.8
Cu 4.5 1.8 1.4
Ni 4.1 1.8 1.4
Pb 0.6 0.3 0.2
Zn 4.2 1.8 1.4
TRM 10.5 5.0 4.2
380
-------
6073
6081
6088
6087
6085
6076
6381
6089
6037
TABLE 12-15
DISCHARGE AND RAW WASTE SILVER CONCENTRATIONS
OBSERVED FOR NINE PLANTS
Avg.
Disch .
Ag.
.014
.045
.135
.135
.140
.420
.564
.848
1.463
Avg.
RWL
Ag.
.01
.05
.82
.16
.17
.89
1.33
1.71
1.59
Avg.
Disch.
TSS
23
2
116
51
29
213*
31
20*
44
Avg.
Disch,
CN(A)
1.3
nil
.6
nil
.6
.2
.3
.5
4.0
Fract. Ag.
In RWL Me
XAg
.003
.0059
.0019
.0010
.0033
.0041
.0070
.0371
.0776
*Filter used for solids separation.
381
-------
METALS TREATMENT USING FILTRATION
Filtration systems provide an alternative to the use of clarifiers for
the separation of precipitated metals from electroplating wastes.
Following is an analysis of the performance of filters in 10 plants
visited and sampled by the Agency.11 Accompanying data for those 10
plants are presented in Exhibit C.2 of Appendix XII-C. Five of the
plants used filters as the primary means of solids separation in their
waste treatment system; the other five plants used filtration as a
polishing step after clarification. Because the two groups of plants
experienced quite different input metal loadings to the filters, they
were considered separately.
Filters for Primary Solids Separation
Five plants in the data base separated the precipitated metals from
the treated waste stream by filtration. Four of these plants used
diatomaceous earth filters; the fifth (plant 6079) employed vertical,
cloth-covered filter plates. The data do not appear to indicate any
major difference, in either effluent metal content or in separation
efficiency between the two filter types.
TSS. None of the filtration systems yielded a totally clear effluent.
As shown in Table 12-16, the TSS concentrations in the discharges from
the five plants ranged from a low of 1 mg/1 to a high of 142 mg/1.
Even within a given plant, the discharge TSS concentrations were found
to vary considerably from day to day. The median TSS of the 13 daily
observations was 11 mg/1.
There appeared to be no correlation between metal concentration and
TSS concentration in the discharge, indicating that even though some
metal hydroxides might have bypassed or gone through the filters,
metal pass-through was not sufficient to account for much of the TSS.
Possibly, the TSS was largely composed of suspended filter aids which
entered the waste during precoating and backwashing stages; if so, an
elevated TSS level was not in itself an indicator of ineffective
metals removal.12
lxExhibit C.I in Appendix XII-C presents the metals
additional descriptive information for those plants using
separation of solids from the effluent stream.
plated
filters
and
for
12The highest observed TSS value, 142 mg/1 from plant 38050, is
possibly associated with the addition to the plating wastes, upstream
from the filter, of an oily (677 mg oil/1) discharge from a tumbling
operation. The effluent from the filter averaged 62.5 mg oil/1.
382
-------
TABLE 12-16
TSS IN DISCHARGE FROM FIVE PLANTS USING FILTRATION
FOR PRIMARY SOLIDS SEPARATION
Daily TSS Concentration* Average
Miii. Med.Max. Total Metals**
6079 1 21 31 2.3
6731 146 2.9
9026 11 15 67 4.9
36041 5 10 32 3.2
38050 - 142 - 2.0
Concentrations are in mg/1.
**Total metals concentration includes Cr,III, Cu, Ni, Zn,
Cd, Ag, Pb, Hg, Sn, and Fe.
383
-------
Metals. The average concentrations observed downstream from the filter
are reported in Table 12-17, It can be seen that the median effluent
concentrations of trivalent chromium (Cr,III), Ni, and Zn were less
than 1 mg/1. The median Cu concentration was only modestly higher, at
1.1 mg/1,
For every plant, with the exception of 9026, the observed metal
concentrations achieved by the filter were no greater than, and
usually much less than, the long term average concentrations (Table
12-13) assumed in setting the limitations for clarifier-based systems.
Effect of_ Raw Waste Cp_nc_e_ntr a t i ons. The metal concentrations
discharged from the filter systems show a small increase with raw
waste concentrations as shown in Figure 12-11,
It is difficult to ascertain, based on data from only five plants,
whether this relationship between effluent and raw waste metal concen-
tration is real. The data gathered, however, indicate that any
existing dependence of effluent concentration on raw waste
concentration is likely to be small.
The same conclusion appears to hold for the individual metals. Figure
12-12 plots average effluent concentrations of Cr,III, Cu, Ni, and Zn
against their respective average raw waste concentrations {where the
latter exceed 1 mg/1). Again, the increase in discharge concentration
with input concentration is small.
Polishing Filters
Six plants in the data base used clarifiers as the primary means of
solids removal, but also filtered the effluent from these clarifiers
before f_inal discharge. One of these six plants, 6076 was reported to
be expeFiencing problems with filter plugging and bypassing during the
period of data collection; it was deleted from the data base. The
filtration systems of the remaining five plants were of three types?
1. Polyester felt cartridge (20077)
2. Multimedia bed (31021)
3. Diatomaceous earth on a precoat (31020, 33070, 33073).
TSg. As was the case for the five plants that used filtration as the
primary means of solids separation, the five plants that used
polishing filters discharged appreciable concentrations of TSS. As
shown in Table 12-18, the effluent TSS concentrations ranged from 1
mg/1 to 82 mg/1. The median daily concentration was 16 mg/1.
384
-------
TABLE 12-17
AVERAGE METAL CONCENTRATIONS IN DISCHARGE FROM
FIVE PLANTS USING FILTRATION FOR
PRIMARY SOLIDS SEPARATION
Plant Average Metal Concentration* Total
ID Cr.III £u Ni_ _Zn Metal
6079 0.7 - 1.0 - 2.3
6731 - 0.5 1.3 0.7 2.9
9026 - 2.9 - 1.5 4.9
36041 0.5 1.1 0.3 0.5 3.2
38050 - - 0.4 - 2.0
Median 0.6 1.1 0.7 0.7 2.9
Concentrations are in mg/1. Discharge concentrations are given for
individual metals if average RWL concentrations of these metals exceed
1 mg/1.
385
-------
10.
9.
8_
7_
6.
5.
it
LU
IS
O
GO
CO
Ol
3.
2.5.
1.5-
10
20
30 40 50 60 80 100
200 300 400 500
800
Total Raw Waste Metals !mg/0
FIGURE 12 11
TOTAL METALS OUT VS. TOTAL METALS IN
FOR FIVE PLANTS WITH FILTRATION AS PRIMARY
MEANS OF SOLIDS SEPARATION
-------
CO
03
--J
0.60
0.25
0.00
1 -0.26
—0.60
I —0.75
1
—1.00
—1.26
— 1.SO
C-Cu
N-Ni
R - Cr, III
Z<* Zn
JL
JL
-0.75 -0.50 -0.25
-0.00 0,25 0.50 0.75 1.00
Log RWL Mittl Conc*ntf»tion (m«/l)
1.2S
15O
1.7S
2JM
FIGURE 12-12
EFFLUENT METAL CONCENTRATION VS. RWL
METAL CONCENTRATION! FOR FIVE PLANTS
WITH FILTRATION AS PRIMARY MEANS OF
METAL REMOVAL
-------
TABLE 12-18
20077
31021
31020
33070
33073
TSS IN DISCHARGE FROM FIVE PLANTS USING
POLISHING FILTERS AFTER CLARIFIERS
Daily TSS Concentrations*
Min.
9
7
-
0.1
A
Med.
1A
18
16
13
32
Max.
26
21
-
82
A2
Total
Metals
6.2
3.8
1.6
1.1
6.6**
*Concentratfons are in mg/1.
**Includes 5.3 mg/1 Fe and Sn.
-------
The three plants which used diatomaceous earth polishing filters, and
the two plants using polishing filters of other design, achieved about
the same discharge TSS concentrations. However, the diatomaceous
earth filters appeared somewhat more effective at achieving low
discharge metal concentrations than the other filters. The median
value of seven daily observations of total metals in the discharges of
the diatomaceous earth plants was 1.6 mg/1; this is roughly one-third
of the 4,9 mg/1 median observed for the polyester or multimedia
filters.
The two types of filters also differed with respect to the
relationship between TSS and metal concentrations. The diatomaceous
earth polishing filters exhibited no significant correlation between
TSS and total metals concentrations; this parallels the results
observed when diatomaceous earth filters were used for primary solids
separation. The two plants (20077 and 31021) using polishing filters
of other kinds did, however, show a significant increase in total
metals concentration with increasing TSS. The daily observations from
the effluent of these two plants are plotted in Figure 12-13.
Metals. The average metal concentrations observed downstream from the
polishing filters are reported in Table 12-19. It is apparent that
the combination of a clarifier and a diatomaceous earth filter (31020,
33070, 33073) was successful in reducing individual effluent metal
concentrations to 1 mg/1 or below. Plant 31020, which discharged Cu
at an average concentration of 1 mg/1, had a RWL Cu
concentration of 108 mg/1. It thus achieved more than 99% removal of
this metal. The clarification-filtration systems of plants 20077 and
31021 were not quite as effective in achieving low discharge metal
concentrations, although only the Zn discharge of 20077 was much above
the 1 mg/1 level.
Summary
The above data indicate that waste treatment systems for
electroplating which use filtration as either the primary means of
solids separation or as an adjunct to clarification can attain average
concentrations of Cr,III, Cu, Ni, and Zn of about 1 mg/1 or less. The
median TSS concentration in the average daily discharge from 10
filtration plants (29 samples) was 17 mg/1. For those seven plants
that used diatomaceous earth to assist filtration, the TSS
concentrations did not appear to be correlated with metal
concentrations, implying that, for these plants, measurement of TSS
discharge concentration cannot serve as a reliable substitute for
measurement of the individual metal concentrations.
389
-------
1.0
• - Plant 20077 - Polyester Felt Cartridge
* - Plant 31021 - Multimedia Bed
CO
u>
o
D)
£
_o
'ff
I
-------
20077
31021
31020
33070
33073
TABLE 12-19
AVERAGE METAL CONCENTRATIONS IN DISCHARGES
FROM FIVE PLANTS USING POLISHING
FILTERS AFTER CLARIFIER
Average Metal Concentrations*
Cr.III
0.5
0.1
0.0
0.5
0.9
Cu
0.5
1.3
1.0
0.1**
0.1
Ni
1.1
1.1**
0.1**
-
0.2
Zn
2.7
0.9
0.0**
0.1**
0.0**
Total
Metals
6.2
3.8
1.6
1.1
6.6***
Median
0.5
0.5
0.2
0.1
3.8
*Concentrations are in mg/1. Discharge concentrations are given for in-
dividual metals if the average RWL concentrations of these metals exceed
1 mg/1. Total metals concentrations include Fe and Sn.
**The RWL concentration of this metal is less than 10% of total RWL metal
concentration.
***Includes 5.3 mg/1 Fe and Sn.
391
-------
METALS REMOVAL FOR ELSCTROLESS PLATING AND PRINTED CIRCUIT BOARD
MANUFACTURING
The electroless plating and printed circuit board manufacturing
processes both utilize electroless plating operations. The nature of
these processes is different because the chemical chelating agents
used in these operations bond to the metals and form complexes which
are difficult to decompose under normal treatment conditions.
Differences Between Subcategories
The primary difference between the two Subcategories is in the type of
manufacturing processes performed. The electroless plating
subcategory contains several similar plating processes whose only
differences are metal deposited. The printed circuit board
subcategory includes all of the manufacturing processes involved in
the manufacturing of printed circuit boards. This includes
electroless plating, as well as such processes as cutting, drilling,
screening, electroplating and etching. This variety of manufacturing
processes produces a much more complex combination of raw wastes than
are produced in the electroless plating subcategory. Because of this,
the companies in the data base which manufactured printed circuit
boards as the major portion of their business tended to have treatment
systems which were more sophisticated than those of the other
electroless platers. Of the nine printed circuit board
manufacturers in the data base, seven (78%) had a treatment system
adapted in some major way to the characteristics of the electroless
waste. In contrast, of the 15 electroless platers, only 3 (20%) had
a system more effective than that typical for treatment of normal
metal plating wastes.
There were also significant differences between the Printed Circuit
and Electroless Plating Subcategories in the concentration of the
electroless metal in the raw waste load.13 For example, 9 of 10 plants
that deposited electroless Cu had a median Cu concentration in the RWL
of 6 mg/1,* 13 of 15 plants that deposited electroless Ni had a median
RWL of 31 mg/1. This difference in RWL potentially affects the
attainable effluent concentration in two ways: first, a higher RWL
concentration requires a greater proportion of metal removal to
achieve an effluent limitation; second, and possibly more important,
in the absence of any specific treatment systems for isolating and
destroying complex ing wastes, a higher RWL concentration of the
13Plants and data are listed in Appendix XII-D. Electroless plating
plant 6081 deposited Cu. Raw waste load data were not available for
printed circuit board plant 2062 or electroless plant 41067.
392
-------
electroless metal translates to a higher effluent concentration of
chelate, possibly increasing the difficulty of reaching low effluent
metal concentrations.
Effluent Concentrations
As shown in Table 12-20, the median discharge Cu concentration
achieved by 10 plants that plated electroless Cu was 1.2 mg/1. Plant
6081 performed only about 5 percent of production by an electroless
process and plant 30050 had a raw waste Cu concentration of 1200 mg/1.
Removal of these two cases from the data did not affect the median
observed effluent Cu concentration, although it reduced the scatter
about this median. Removal of plant 17061, with a pH of 6.8, reduced
the median from 1.2 to 1.0 mg/1.
A similar range of discharge Cu concentrations was observed for the
seven plants in Table 12-21. These plants, which deposited
electroless Ni, also electroplated Cu. With the exception of plant
20070, the electroless Ni rinse wastes were combined without separate
treatment with the Cu wastes. It is possible that in these combined
wastes, some Cu complexing could have occurred. The four plants with
a pH greater than 7.5 had a median Cu effluent of about 1.0 mg/1.
Before the analysis of observed effluent concentrations, the 14 plants
of Exhibit D.I in Appendix XII-D that deposited electroless Ni (plant
6081 deposited electroless Cu) were screened to delete those plants
without solids separation in their treatment system (4077, 30074,
41069), and those plants with less than 1 mg/1 raw waste load
concentration of electroless nickel (6051, 23061, 41069). Two
additional plants were omitted from the analysis of electroless
plating performance. Plant 41067 had incomplete descriptive
information concerning its processes, treatment system, and RWL
concentration; the trip report for plant 20069 indicated that at the
time of the sampling its treatment system was hydraulically
overloaded.
Of the remaining seven plants shown in Table 12-21 as plating nickel
electrolessly, five had a pH greater than 7.5. These five plants had
a median effluent concentration of about 1,1 mg/1 of nickel.
Conclusion
The Printed Circuit and Electroless Plating subcategory plants with
effluent pH levels above 7.5 discharged Cu and Ni at a median of about
1 mg/1. These concentrations are less than the 1.4 mg/1 average
concentration previously recommended as providing the basis for Cu and
Ni limitations for the Electroplating category. The Agency,
therefore, has set the Cu and Ni limitations for the Printed Circuit
393
-------
TABLE 12-20
METAL REMOVAL EFFICIENCY OF TREATMENT SYSTEM OF
10 PLANTS DEPOSITING Cu BY ELECTROLESS PLATING
Effluent
Cu (mg/1)
2062
4065
4069
5020
5021
6081
17061
19063
30050
36062
% RWL
Removed
NA
88
88
90
26
73
75
74
97
100
Effluent
Ni (mg/1)
% RWL
Removed
*
*
92
95
82
*
*
95
99
92
pH
9.3
**
9.5
7.9
7.6
8.5
6.8
7.3
6.8
8.2
Median
1.2
88
0.4
94
* RWL Ni less than 1 mg/1.
** Inappropriate figure, since pH is reduced after clarification,
NA - Raw waste load data not available.
394
-------
TABLE 12-21
METAL REMOVAL EFFICIENCY OF TREATMENT SYSTEM OF
SEVEN PLANTS DEPOSITING Ni BY ELECTROLESS PLATING
Plant
ID
6381
12065
20064
20070
20073
20083
20085
Effluent
Cu (mg/1)
3.75
3.98
0.82
0.56
1.74
1.03
0.18
% RWL
Removed
92
16
.99
99
98
98
99
Effluent
Ni (mg/1)
4.90
9.23
2.80
0.38
1.13
2.30
1.11
% RWL
Removed
84
13
95
99
98
88
99
PH
7.5
7.3
9.2
9.1
7.8
9.3
9.0
Median 1.0 98 2.3 95
395
-------
Board and Electroless Plating subcategories equal to those of the
Electroplating category.
OVERVIEW OF CONCENTRATION-BASED PRETREATMENT STANDARDS
Following are concentration-based limitations, in mg/1, for those
regulated pollutants discharged by the electroplating industry. Table
12-22 presents the long term averages (LTA), daily and 30-day-average
variability factors (VF and VF30), and daily and 30-day-average
maximum limitations (L and L30) for the Electroplating category and
Electroless Plating and Printed Circuit Board subcategories. These
limitations are calculated as shown in Equations [3] and [4] in the
section on statistical methodology. Table 12-23 gives N-day-average
maximum limitations (L ) for each pollutant listed in Table 12-22.
The limitations have been calculated for each pollutant using
the following equation.
L = L30 + K (L, - L30) [9]
where
K is a set of constants given in Table 12-23.
This equation with these constants was shown in Appendix XII-A.5 to
provide excellent approximations to corresponding limitations
calculated using the N-day-average variability factors developed in
Appendix XII-A.2. Equation [9] was used to obtain N-day-average
limitations for N = 2, 3,...29 because of its simplicity and accuracy.
The resulting N-day-average maximum limitations for a given pollutant
are not to be exceeded by the average of any set of N, randomly
selected single-day observations of that pollutant. The limitations
for the pollutants total cyanide (CN,T), copper (Cu), total chromium
(Cr,T), nickel (Ni), zinc (Zn), total regulated metals (TRM), and
silver (Ag), apply only to large platers, defined as those plants
having a flow of more than 10,000 gallons per day. The limitations
for amenable cyanide apply only to small platers, or those plants
which have a flow of less than 10,000 gallons per day. The
limitations for lead (Pb) and cadmium (Cd) apply to all platers.
EQUIVALENT MASS-BASED PRETREATMENT STANDARDS
Even though plants may have pretreatment systems which are well-
designed, operated, and maintained, the effluent concentrations of the
individual metals or pollutants may exceed the concentration-based
limitations due to water conservation practices that reduce plant
flow. In order to avoid penalizing these plants or discouraging their
water conservation practices, mass-based limitations are calculated
below, as an alternative to the concentration-based limitations.
396
-------
TABLE 12-22
SUMMARY OF LONG TERM AVERAGES, VARIABILITY FACTORS
AND DAILY AND 30-DAY-AVERAGE MAXIMUM LIMITATIONS*
Daily Max.
Pollutant**
(1)
(2)
(3)
CN,T
Cu
Cr,T
Ni
En
TRM
Ag
CN,A
Cd
Pb
LTA***
0.15
1.4
1.8
1.4
1.4
4.2
0.4
1.0
0.4
0.2
VF
5.0
3.2
3.9
2.9
3.0
2.5
2.9
5.0
2,9
2.9
L
0.75
4.5
7.0
4.1
4.2
10.5
1.2
5.0
1.2
0.6
30-Day-Avg. Max.
VF
30
1.5
1.3
1.4
1.3
1.3
1.2
1.3
1.5
1.3
1.3
L
30
0.23
1.8
2.5
1.8
1.8
5.0
0.5
1.5
0.5
0.3
*For the Electroplating category, Electroless Plating subcategory,
and Printed Circuit Board subcategory.
**Limitations in pollutant group (1) apply to large platers (over
10,000 gal./day) only.
Limitations in group (2) apply to small platers (under 10,000
gal./day) only.
Limitations in group (3) apply to all platers.
***The Long Term Average (LTA) is not a limitation.
397
-------
TABLE 12-23
SUMMARY OF CONCENTRATION-BASED PRETREATMENT STANDARDS*
N Day-Average Maximum Pollutant Limitation** * (mo/I)
CO
U3
CO
N
1
2
3
4
s
6
7
S
9
10
1 2
20
30
Constant
KIM
1 . «) 0 0
. 31J 7
.430
. 333
.223
. 1 o 7
.12?
.033
.000
CN. T
.75
.54
.'*5
.35
. 33
.32
. 30
. 3.0
. 2:i
.25
. 23
Cu
4 .
3.
3.
2.
2.
2.
2.
2.
2.
2.
2.
1 .
1 .
Cr, T
5
4
0
7
5
*t
3
3
2
1
•>
.2
.')
.9
.S
,7
.'»
.2
.0
Afl
1 .2
.9
.«
.7
,7
.7
. o
. S
.6
.r,
. s
. 5
.5
Cd
1 .2
.9
.7
.7
.7
.&
Pb CN, A
, o
,5
, '-t
, n
,4
,4
, 4
, 4
,3
, 3
. 3
,3
, 3
5.0
3..i
3.0
2.7
2.4
2. 3
2.2
2.1
2.0
1 .'J
1 .7
1 .6
1.5
-------
For example, a plant may have installed new technology or developed
new practices which significantly reduced the flow of water. Though
individual and total pollutant loads remained the same or even
decreased, the effluent pollutant concentrations would have increased
due to the reduced flow of waste water. Thus, limitations based on
the mass of pollutant discharged per unit of production, rather than
volume of water, were calculated as an option for these plants. These
limitations were calculated specifically to benefit a plant achieving
water usage (i.e., volume of water per unit of production) lower than
the median plant water usage for its plating category (Electroplating,
Electroless Plating or Printed Circuit Board).
Calculation of_ Mass-Based Constants
The mass-based limitations were obtained by calculating the median
water usage for each of the three categories: Electroplating,
Electroless, and Printed Circuit Board. These were, in turn,
multiplied by the appropriate concentration-based limitations to
obtain equivalent mass-based limitations.
The data used by the Agency in this analysis are in Appendix XII-E.
The water usage for a plant in 1/op-m2 (liters per each square meter
plated for each plating operation) was calculated by the following
equation:
Water Usage = Flow x Conversion Factor [10]
Area
where
Water Usage = (1/op-m2) liters of water used for each
square meter plated for each plating operation
Flow = flow of plant in (gal./hr.)
Conversion Factor = 40.74 (1 x ft.2)/(gal. x m2)
= conversion from ft.2 to m2 and gal. to 1.
Area = sum of area plated (ft.2/hr.) for each plating operation.
The values for the hourly area plated and flow (Appendix XII-E) were
substituted into Equation [10] to determine the water usage for that
day, and then averaged over all sampled days f_or each plant (Tables
12-24 through 12-26). The medians of the average plant water usage in
1/op-m2 for each category were as follows: Electroplating, 39.0;
Electroless, 36.7; and Printed Circuit Board, 89.0.
399
-------
TABLE 12-24
WATER USAGE FOR THE ELECTROPLATING CATEGORY (1/op-m2)
Plant ID Water Usage Rank
20084 1.1 1
20079 2.0 2
6086 3.3 3
20080 3.9 4
6087 4.8 5
9026 9.9 6
20010 14.9 7
19051 17.9 8
6089 18.1 9
40062 19.2 10
20077 19.5 11
6079 21.4 12
6077 22.3 13
15070 23.7 14
20086 26.8 15
33071 28.0 16
20078 28.2 17
31050 30.2 18
40061 32.8 19
33073 33.3 20
6088 37.5 21
20082 37.9 22
33070 38.7 23
11050 39.0 24
31021 40.6 25
6084 40.8 26
13 41.1 27
36041 42.1 28
6037 43.5 29
4045 43.7 30
31020 46.3 31
38050 49.4 32
6085 58.3 33
6073 59.6 34
6036 60.4 35
6081 65.0 36
6075 66.3 37
10020 76.8 38
6074 88.0 39
6053 97.1 40
19050 106.6 41
14 108.1 42
400
-------
TABLE 12-24 (Continued)
Plant ID Water Usage Remlk
20081 110,0 43
6731 170.5 44
5050 253.9 45
6076 407.8 46
6083 1046.0 47
Median 39.0
401
-------
TABLE 12-25
WATER USAGE FOR THE ELECTROLESS
PLATING SUBCATEGORY (1/op-m )
Plant ID Water Usage Rank
20085 8.8 1
20064 9.9 2
30074 17.7 3
20073 22.9 4
20069 23.5 5
20083 24.8 6
6381 30.5 7
20070 36.7 8
6081 65.1 9
12065 74.1 10
41067 108.3 11
6051 113.9 12
4077 118.7 13
41069 141.1 14
23061 2108.1 15
Median 36.7
402
-------
TABLE 12-26
WATER USAGE FOR THE PRINTED CIRCUIT BOARD
SUBCATEGORY (1/op-m )
Plant ID
5020
19063
2062
4069
36062
5021
4065
17061
Water Usage
48.5
56.0
71.
85,
92.9
107.6
142.5
282.7
Rank
1
2
3
4
5
Median 89.0
Note: Plant 30050 has no data on area plated,
403
-------
Calculation of Equivalent Mass-Based Limitations
Table 12-27 lists the N-day-average maximum mass-based pretreatment
standards (mg/op-m2) for the Electroplating category and Electroless
Plating subcategory. These limitations were obtained by multiplying
the N-day-average maximum concentration-based limits (mg/1) of Table
12-23 by a water usage of 39 1/op-m2 (median of Table 12-24). Table
12-28 lists the N-day-average maximum mass-based standards for the
Printed Circuit Board subcategory. These were obtained by multiplying
the concentration-based limits of Table 12-23 by a median water usage
of 89 1/op-m* (Table 12-6).
TOTAL SUSPENDED SOLIDS (TSS) AS A MONITORING ALTERNATIVE
For those plants that plate common metals and treat their wastes using
conventional solids removal technology14 the discharge concentrations
of each of the metals are related to two factors: (1) the effluent
concentrations of TSS; and (2) the ratio of the raw waste load (RWL)
metal concentration to the sum of all RWL metal concentrations.
Earlier analyses estimated limitations appropriate for individual
metals based on the observed relationships and on attainable levels of
effluent TSS and RWL metals ratio.
The previous edition of this document noted the desirability of
monitoring alternatives. Chief among these was TSS concentration with
certain restrictions on discharge pH and on the presence of complexing
agents in the waste stream.
In view of comments received regarding the analysis of TSS in the
previous document, the agency has conducted additional analyses. The
combined analyses and resulting conclusions are reported below,
beginning with a disucssion of metal hydroxide equivalents and the
analysis of available data, and concluding with engineering
considerations.
Metal Hydroxide Equivalents
One of the commenters on the document suggested an alternative
approach to attain TSS limitations which would ensure that the
individual and total metals limitations are met. This approach is
based on the use of metal hydroxide equivalents to caclulate TSS as a
function of the individual and total metals limitations.
14CN oxidation, Cr,VI reduction, alkaline preciptiation, and solids
separation by clarification.
404
-------
o
en
TABLE 12-27
SUMMARY OF MASS-BASED PRETREATMENT STANDARDS FOR THE
ELECTROPLATING CATEGORY AND ELECTROLESS PLATING SUBCATEGORY
N-Day-Average Maximum Pollutant Limitations (mg/op-m )
N
1
2
3
4
5
0
7
d
9
10
IS
20
30
CN. T
29
21
Id
13
14
13
13
12
12
12
10
10
9
Cu
170
133
1 1 :">
1 J5
93
94
90
8 3
d5
34
77
74
70
Cr.T
273
202
173
156
1 4 4
137
130
127
122
120
109
103
98
Ni
160
124
109
100
94
90
H7
3 5
33
32
76
73
70
Zn
164
1 2 '->
1 10
102
35
91
83
86
33
a 2
76
73
70
TRM
410
323
2U7
2(i7
252
243
235
231
225
222
209
202
195
Ag
47
36
31
29
27
26
25
24
23
23
21
20
20
Cd
47
36
31
29
27
2o
25
24
23
23
21
20
20
Pb
23
19
17
15
15
14
14
14
13
13
12
12
12
CN. A
195
1-»Q
1 17
104
95
39
A 4
31
7 a
76
67
53
S<)
-------
TABLE 12-28
SUMMARY OF MASS-BASED PRETREATMENT STANDARDS
FOR THE PRINTED CIRCUIT BOARD SUBCATEGORY
N-Day-Avarage Maximum Pollutant Limitations (mg/op m )
CN, T Cu Cr T Ni Zn i HM «g Cd Pb CN, A
J7 401 523 365 37'* 935 1J7 137 53 '-I H 5
2 '43 SOU i, 5 2 2«2 283 737 82 32 «i 3 31'.)
3 '»0 26'4 395 2'4 a 252 655 71 71 38 267
-P. '» 36 2"4l 357 229 232 609 65 55 36 238
§ 5 33 22'* 329 215 217 575 61 51 3-'4 216
Cr. T
523
'»62
395
357
329
312
2Q7
2b9
279
273
2'»3
233
223
Mi
365
2«2
2 '* a
229
215
206
198
19i+
ItJ'j
186
173
157
150
Zn
37'*
283
252
232
217
208
2oa
196
190
187
17't
187
160
TRM
935
737
655
60'J
575
S5H
536
S27
sm
5D7
'*7S
H61
«+'*5
*£
1 J7
B2
71
65
61
58
5G
55
53
52
148
<»7
<45
6 31 21-4 312 206 208 S5H 58 5B 33 203
/ 29 205 2Q7 198 20i) 536 5G 56 32 191
A 23 200 2«9 19<4 196 S27 55 55 31 136
J 27 19H 279 ItJ'j 190 S1 <» 53 53 30 ,177
10 26 191 273 186 187 507 52 52 30 173
15 23 175 2'»3 173 17'» '*7S 148 <»8 2« 153
20 22 Ijb 233 157 187 H61 i»7 H7 28 l'4't
JO 20 160 223 150 160 «4'4 5 H 5 '45 27 13»i
-------
Theoretically, a dissolved metal concentration could be measured as
TSS in its metal hydroxide form if all of the metal assumed this form.
To obtain a value for the metal hydroxide concentration, the dissolved
metal concentration is multiplied by its individual metal hydroxide
constant (C ), which is the ratio of the molecular weight of a metal
hydroxide molecule to the atomic weight of the metal. If TSS were
calculated by multiplying each individual metal limitation by its
hydroxide constant and summing over all regulated metals, as suggested
by the commenter, our TSS value would overestimate an equivalent TSS
value for total metals.
A modification of this approach was constructed utilizing a weighted
hydroxide constant (WHO, calculated as follows:
WHC =
= (.31 x 1.54) + (.23 x 1.52) + (.23 x 1.58) + (.23 x 1.98}
= 1.68
where M = Cu, Cr,T, Ni, In.
The long term averages (LTA), as previously calculated, and the
fraction LTA/ LTA are shown in Table 12-29. This weighted hydroxide
constant of 1.68 is, in turn, multiplied by daily and 30-day-average
maximum total regulated metals (TRM) limitations previously given to
obtain TSS hydroxide equivalents. These are 17.8 and 8.5 mg/1,
respectively, as shown in Table 12-30.
However, Table 12-11 shows that the median ratio of total regulated
metals to the total metals in the raw waste load is .91. To reflect
the presence of the other metals in the waste stream, the alternative
TSS daily and 30-day average maximum limitations have been set at 20
and 10 mg/1, respectively,
Analysis ojf 2J> Plants ir\ Electroplatin g Category
Beginning with these hydroxide equivalents, an analysis of 25 plants
(92 observations) was conducted on plants listed in Exhibit B.I of
Appendix XII-B and previously employed to calculate the limitations
for individual and total regulated metals in the Common Metals
subcategory. The observed concentrations for Cr,T, Cu, Ni, Zn, TRM
and TSS, as extracted from the data base, are listed in Tables 12-31
and 12-32. Table 12-31 presents those observations for which none of
the observed metal concentrations exceeded the corresponding daily
maximum limitation, ranked according to TSS concentration. Note that
of the entire 92 observations:
1. 43 (47%) were < 18 mg/1
407
-------
Metal
Total
TABLE 12-29
INDIVIDUAL METAL HYDROXIDE CONSTANTS
LTA*
6.1
LTA/ELTA
1.00
**
OH
Cr
Cu
Ni
Zn
1.9 mg/1
1.4
1.4
1.4
.31
.23
.23
.23
1.54
1.52
1.58
1.98
*Long Term Average (mg/1)
**Hydroxide Constants
TABLE 12-30
TOTAL SUSPENDED SOLIDS HYDROXIDE EQUIVALENTS (mg/1)
TRM* Limitations
TSS Equivalents**
LTA
4.2
7.0
Daily Max.
10.6
17.8
30-Day Avg.
5.1
8.5
*Total Regulated Metals (mg/1)
**TSS Equivalents (rag/1) = TRM x WHC = TRM x 1.68
408
-------
TABLE 12-31
OBSERVATIONS* WITH NO LIMITATIONS** EXCEEDED
Plant
IE,
20G8U
608 1
20081
20041
U
14
dUdl
14
14
20081
20081
13
14
14
14
14
AOB1
2000U
20081
16040
U
U
}*>U4U
U
A075
15070
33050
20010
20081
2008U
11
11021
36U40
20010
20078
20077
6085
20077
2QOdU
20U8U
20080
20077
20UBO
t.075
6074
15U7Q
20077
20U86
11021
6081
o074
6075
33073
2U010
200"7d
20081
20oa<>
31021
20082
20082
20o7a
20078
J3J2,
4U74
200d2
200 IU
2007J
20004
2007*
2U07-*
203 10
14
33U71
21)07*
2U01U
"083
Ca
16
7SJ
29
27
180
40
d50
340
110
26
2b
890
330
120
1uO
190
650
28
24
oO
40u
3oO
7b
770
22 3U
20
1*7
29
70(1
tit)
560
1680
71
22
307
3Il>
3290
SO 2
647
470
71
625
106
2210
35
20
474
25u
1740
147
1u
4U60
301
9
247
42
464
2440
214*
3159
172
400
tou
44
20<>
19
4UU
765
4UU
11j
Id
70
1 llg
147
12
in
SL
50
«
70
!2d
250
3au
10S
79U
9oa
125
120
100
17UO
74U
HO
S4U
JO
1H
>U
1560
oJO
17U
77a
920
2B40
50
55
17i
Jdd
IdO
•J20
112U
17BO
230
144
750
2000
lOd'J
50
50
dO
U10
140
«7u
600
40
1250
2rfb
87S
2270
SJI
1SOO
132
200
106
J5UO
J57
212U
901
5JO
427
3d1
H
J04
6012
422
262
1440
4
iuao
Cf.T
ltd
1>0
2«9
so
1300
37o
1U2
230
'HO
t>*
215
JSOO
1500
1UO
boO
37o
1S5
195
4J
33J
1500
UOO
333
17QU
444
4250
12
17
783
783
1400
128
733
20
4UO
415
1630
166
396
100
JJ9
7d
609
101
143
3750
7J9
944
200
556
714
243
1110
50
500
1J50
(720
2)0
od7
79tf
2faUO
164J
'<;
33J
526
41
ia*u
125
d26
11)00
30
12'JJ
212U
U7u
27
1220
Z£
331
do
W3
uo7
IdU
17U
4)
320
400
600
400
340
100
140
250
160
52
J75
iuo
24
250
230
U
100
722
I3JO
77 t
Id!
600
iUU
240
1000
16
Ai
29
:=)00
258
3240
500
542
700
2760
5UO
433
21
3120
3000
470
1190
16°
14
1170
40
T3»
13
750
ddi
1130
aid
237
S3
4U
1'j^a
14
112
194
24
auo
32
2250
5U
150
311
2250
20
Jill
TRM
Db7
10^5
971
»02
2410
960
1100
ladU
2400
d!5
981
5U30
3630
1380
1CJ90
17B0
937
ijl.)
657
2177
2750
27UO
1200
3»-JO
6276
5650
985
402
2471
1573
3120
J928
2bUU
JS4
t)«0
3301
717»
-jOi'd
1S93
U62
1590
477j
1355
7034
799
69 1J
S463
19SU
4005
3139
1315
097 3
1<*23
4 IK
-------
TABLE 12-32
OBSERVATIONS* WITH AT LEAST ONE LIMITATION** EXCEEDED
Plant
ID
15070
20U84
6087
200H2
6037
33073
6085
6037
6086
6087
6087
20079
6086
6086
20079
20079
Cu
16
35
2630
6160
5930
7680
5130
4490
118
1940
5000
824
150
127
470
412
_Nj
45
212
6390
1406
1380
1620
6670
2770
4280
7300
7720
63750
12500
3130
6130
5250
CfJ
7370
7760
52
838
16
2630
1950
16
7610
59
75
2300
21000
13600
4370
9920
Zn
3000
10000
1120
121
88
533
106U
62
166
1000
1750
1250
120
134
2820
2730
TRM
10431
18057
10192
8525
7914
12463
14810
7338
12174
10299
14545
63124
33770
16991
13790
13312
TSS
25000
33000
34000
36000
39000
39000
40000
42000
42UOO
44000
74000
73000
108000
120000
130000
132000
Rank
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
•Ranked by TSS
*Tha metal» (maximum daily limitation in paranthmas for which th« observed effluent
lavali war* compared to th« limitations ware Cu (4.S), Ni (4.1), Cr, Total (7.4),
Zn (4.21, and Total Regulated Metals (10.5).
410
-------
2. 36 (39%) were < 15 mg/1
3. 22 (24%) were < 10 mg/1.
Also note that of the entire 25 plants:
1. All observations for 6 plants (24%) were < 18 mg/1. (Total 21
observations)
2. All observations for 4 plants (16%) were < 15 mg/1. (Total 13
observations)
3. All observations for 1 plant (4%) were < 10 mg/1. (Total 3
observations)
Table 12-32, also ordered by TSS concentration,
observations where at least one individual metal
exceeded. As shown in this table, the lowest
exceeding at least one limitation was 25 mg/1.
SUMMARY
contains those
limitation was
value of a plant
This chapter has reviewed the need for pretreatment of pollutant
discharges by the electroplating industry, the major technologies
available within the industry for pretreatment of pollutant
discharges, and statistical analyses and modeling studies conducted to
evaluate the effectiveness of these technologies. Statistical methods
employed for each pollutant included the calculation of the long term
average which is the expected discharge from a plant with a well-
designed and operated pretreatment system, and the derivation of
variability factors which allow for random fluctuations in operation
of pretreatment systems. The long term averages and variability
factors were used to calculate pollutant limitations which the
discharge of a plant will not be permitted to exceed.
Table 12-33 lists the daily and 30-day-average maximum concentration-
based (mg/1) limitations and mass-based (mg/op-m2) alternative
pretreatment standards for the Electroplating category, and the
Electroless and Printed Circuit Board subcategories. The main body of
this section also presents N-day-average maximum limitations for
N = 2, 3,...,29. Applicability of the limitations for each regulated
than 10,000 gal./day), small platers
or all platers is specified in Table
maximum limitations are not to be
or any average of 30 single-day
pollutant to large platers (more
(less than 10,000 gal./day),
12-33. Daily and 30-day-average
exceeded by any single-day
observations, respectively.
The equivalent mass-based standards were provided as an alternative to
the concentration-based standards for plants employing water
conservation technologies. Also, daily and 30-day-average maximum
limitations on the concentration of total suspended solids of 15 and
10 mg/1, respectively, are provided as an alternative to limitations
on Cu, Cr,T, Ni, Zn and total regulated metals to reduce monitoring
costs for plants demonstrating exceptional pollutant removal.
411
-------
TABLE 12-33
SUMMARY OF CONCENTRATION-BASED PRETREATMENT STANDARDS
AND EQUIVALENT MASS-BASED PRETREATMENT STANDARDS
Pollutant*
(1) CN,T
Cu
Cr,T
Ni
Zn
TRM
Ag
(2) CN,A
(3) Cd
Pb
Cone. -Based-t-
(mg/1)
L ** _L3Q***
0.75
4.5
7.0
4.1
4.2
10.5
1.2
0.23
1.8
2.5
1.8
1.8
5.0
0.5
5.0
1.2
0.6
1.5
0.5
0.3
Mass-Based++
(mg/op-m )
L
29
176
273
160
164
410
47
^30
9
70
98
70
70
195
20
195
47
23
59
20
12
Mass-Based+++
(mg/op-m )
L L,
67
401
623
365
374
935
107
445
107
53
-30
20
160
223
160
160
445
45
134
45
27
+ Applies to Electroplating category and Electroless Plating and
Printed Circuit Board subcategories.
++ Applies to Electroplating category and Electroless Plating
subcategory.
+++ Applies to Printed Circuit Board subcategory.
* Limitations in pollutant group
(1) apply to large platers (over 10,000 gal./day) only
(2) apply to small platers (under 10,000 gal./day) only
(3) apply to all platers.
** Daily maximum limitations.
*** 30-day-average maximum limitations.
412
-------
APPENDIX XII-A
DERIVATION OF VARIABILITY FACTOR EQUATIONS AND
FURTHER ANALYSIS OF THE LOGNORMALITY ASSUMPTION
413
-------
APPENDIX XII-A
DERIVATION OF VARIABILITY FACTOR EQUATIONS AND
FURTHER ANALYSIS OF THE LOGNORMALITY ASSUMPTION
Appendix XII-A.1 and XII-A.2 develop the derivation of the daily and
N-day-average variability factor equations (Equations [1] and [2] of
Chapter XII, respectively). Appendix XII-A.3 provides additional
support for the assumption that the daily concentration of a pollutant
follows a lognormal distribution. Appendix XII-A.4 presents sample
correlation coefficients between the sample plant means and standard
deviations of the log of the concentration for each pollutant. These
nonsignificant correlation coefficients support the use of plants with
both high and low mean pollutant concentrations in the calculation of
the variability factors. Appendix XII-A.5 presents a justification of
the approximation used to calculated N-day-average maximum limitations.
414
-------
APPENDIX XII-A.l
DERIVATION OF DAILY VARIABILITY FACTOR EQUATION
The daily concentration of a plant's metal or pollutant discharge is
assumed to be random arid was found to closely follow the lognormal
distribution (Chapter XII and Appendix XII-A.3). The variability factor
is a measure of the daily fluctuation of the effluent pollutant concen-
tration and is measured by the ratio of concentration to its long-term
average. Given the lognormality of the discharge concentration, the
equation to calculate the variability factor (Equation (1) of Chapter
XII) is
log(VF) = Z(Sigma) - l.lS(Sigma)2 (1)
where VF = the variability factor
Z = 2.326 (99th percentile of the standard normal distribution)
Sigma = the standard deviation of the log of the observations
The derivation of this equation is set out below.
C = concentration of metal or pollutant in discharge
A = average of concentration
= y (C)
0 = standard deviation of the logarithm of C
= a (log C)
u = average of the logarithm of C
- V (log C)
Z = standard normal variable.
415
-------
In the following calculations, the use of "log" or the subscript "10" refers
to common logarithms (base 10). When y and a do not appear with a subscript,
they refer to the mean and standard deviation of ln(C) (i.e., the natural
logarithm of C).
It is assumed that C follows a lognormal distribution. Therefore, log C
is normally distributed. Thus:
log C - U
2 . i!i (
or
log C = y + ZC7 (3)
*
According to Aitchison and Brown :
(y -t- 0.502} (4)
A = e
This equation follows directly from lognormal properties. Equation (4)
is now conveniently converted to the common logarithm (base 10).
log A = y + 1.15a2 (since ln(y) = log(y) x 2.3026) (5)
Substituting (3) and (5) into
log (C/A) = log C - log A (6)
gives
log (C/A) = zaiQ - 1.15a210 (7)
* Aitchison, J. and Brown, J.A.C., The Lognormal Distribution,
Cambridge University Press, London, Page 8, 1969.
416
-------
Finally, replacing C/A and a with their sample estimates, VF and Sigma,
respectively, and Z by 2.326 (99th percentile of standard normal distri-
bution) , in Equation (7) results in the variability factor equation,
Equation (1).
417
-------
APPENDIX XI I -A, 2
DERIVATION OF THE N-DAY -AVERAGE VARIRABILITY FACTOR
The variability factor for the N-day-average for N greater than or
equal to two was estimated from the following equation:
log (C./A) = ZO* - 1.150* 2 (1)
N N N
where
C = average concentration of N daily observations
A = average of concentration
CT* = adjusted standard deviation for the logarithm of the
concentrations used for the N-day-average (derived below)
Z = 2.326 (99th percentile of the standard normal distribution).
Assume X, concentration of a pollutant in the discharge, to be
lognormal with u and a as the mean and standard deviation of ln(X).
Then, based on lognormal properties:
M + |02 (2)
E(X) - e
Var(X) - e2U + * ( - 1} (3)
For the N-day-average, XVT, where each X is independent:
N
E (5T) = E (X) (4)
N
-------
It was then assumed that X follows a lognormal distribution with
N
parameters y ' and a' . The assumption, though theoretically invalid
N N
(since distribution of X is unknown), was made in order to approximate
the true distribution of X in the upper tail of the distribution and,
based on this approximation, to obtain estimates of the standard devia-
tion, variability factor and limitation of the N-day-average. The
validity of this assumption was examined later by comparing the 99th
percentile of the empirical distribution of X with the 99th percentile
based on the lognormality assumption and Equation (1).
Since X is assumed to be lognormal, E (X ) and Var (X ) are given by:
E (XN) = e (6)
(2p' + a' 2) - 2
Var (XN) = e W (e N - 1) (7)
Using equations (2), (3), (4), (5), (6), and (7),
^ and Q' are derived in terms of y and a as:
N N
2 a2
•ln
419
-------
where 0 is the standard deviation of the natural logarithm of the
observations. Finally, a"
by the following expression,
observations. Finally, a" is transformed back to the log (base 10)
CT*M * °'M x -> ic (since ln(y) = log(y) x 2.3026) (10)
IN N /, .
This parameter 0* , the assumption of lognormality stated above, and
N
the theory in Appendix XII-A.l result in Equation (1).
Calculation of the N-Day-Average Variability Factor
The N-day-average variability factor, VF , is an estimate of
C /A and is obtained from:
N
log (VFN) = Z SigmaN - 1.15 (Signup) 2 (11)
where Sigma is an estimate of o* Sigma can be obtained indirectly
from the variability factor, VF, calculated in Equation (1) of
Appendix XII-A.l. Sigma can be found by substituting VF into this
equation. This, in turn, can be transformed into the estimate of
0, the standard deviation of the natural logarithm of the observations,
using the relation:
ln(y) = log(y) x 2.3026 (12)
This estimate is substituted in Equation (9) to obtain an estimate of
a' . Applying Equation (12) to the last estimate gives the desired
value, Sigma,,,
N
420
-------
Accuracy of the Approximation Used to Derive the N-Day-Average
Variability Factor
In the derivation of Equation (1), the average concentration of N daily
samples (N-day-average) was assumed to follow a lognormal distribution,
given that the daily concentration also followed a lognormal distribution.
This assumption was made in order to approximate the 99th percentile of
the true and unknown distribution of the N-day-average. This assump-
tion is justified for a given mean and variance if the 99th percentile
of an empirically derived distribution of the N-day-average is not
significantly different from the 99th percentile based on Equation (1).
A description of such a comparison and its results are given below.
Note that the conclusions are valid only within the range of the values
of the parameters tested and only in the upper tail (specifically the
99th percentile) of the distribution.
The validity of the lognormality assumption and thus of Equation (1)
was checked by generating large sets of random lognormal numbers with
given u and a (mean and standard deviation of the logarithm of the ob-
servations) and calculating the 99 percent limits of N-day-averages based
on these empirical distributions. Fifteen samples for N=2, 5, and 30, of
size 1,000, 400, and 70, respectively, were generated. For two different
sets of parameter values the 99 percent limits derived from these samples
were then compared with the 99 percent limits calculated from Equation (1).
These parameters were the extremes of the values for the long term averages
(LTA) and sigmas used in the calculation of pollutant limitations. For each
of the 15 samples corresponding to each value of N (2, 5, and 30), the
proportion of empirically generated N-day averages greater than or equal
to the 99 percent limits directly estimated from Equation (1) was calculated.
The means and standard deviations of the proportions for the 2, 5, and 30-day
averages were also calculated (Exhibit A.2.). Since the 99th percentile
based on Equation (1) is identical with the 99th percentile derived empirically
421
-------
if the above proportion has the value 0.01, the means of the proportions
for the three N-day sizes of both cases were tested for significant
departure from 0.01. In all cases the t-values or indicators of departure
were observed to be insignificant. These figures are reported in
Exhibit A.2. This analysis, therefore, indicates that Equation (1) is
suitable for estimating variability factors and N-day-average limitations.
422
-------
EXHIBIT A.2.
PROPORTION OF EMPIRICAL N-DAY-AVERAGES GREATER THAN OR
EQUAL TO THE 99 PERCENT LIMITATION BASED ON EQUATION (1)
Parameter Values:
10
LTA
0.19
4.2
CASE I
N = 2
30
Mean
Standard Deviation
t Value
a*
0.0106
0.0037
0.62
0.6
0.0100
0.0055
0
1.0
CASE II
0.0086
0.0118
-0.99
0.4
Parameter Values:
o + = 0.377
LTA =0.15
N = 2
-t- Standard deviation of the logarithm of the concentrations.
* Approximate level of significance.
N
30
Mean
Standard Deviation
t Value
a*
0.0099
0.0025
-0.15
0.9
0.0087
0.0060
-0.84
0.4
0.0114
0.0134
0.40
0.7
423
-------
APPENDIX XII-A.3
FURTHER VERIFICATION OF THE LOGNORMALITY
ASSUMPTION AND THE VARIABILITY FACTOR EQUATION
The assumption of lognormality was central, to derivation of the
variability factor used in the calculation of the pollutant limitations.
Other than applying standard tests such as Kolmogorov-Smirnov and Kuiper
tests, the appropriateness of the lognormal distribution has also been
examined through a useful analytical procedure.
Let:
C = concentration of metal
A = average of concentration
= U (C)
a = standard deviation of the logarithm of C
= a (log C)
U = average of the logarithm of C
= u (log C)
Z = 2.326 (99th percentile of the standard normal distribution).
Based on the assumption of the lognormality of C, and using distributional
properties, two theoretical formulas for determining variability factors are:
10 exp(y + ZO )
(C/A') •• i2 i2_
log (C/A*) = Z010 - 1.150102 (2)
where
C, A, and Z are given above
U , a = mean and standard
of the concentrations, respectively.
U , a = mean and standard deviation of the logarithms (base 10)
424
-------
If lognormality holds, the two formulas are equivalent, i.e., will give
identical results. However, actual pollutant discharges will only
approximate lognormality, and the closeness of such approximation will
be reflected in the discrepancy between VF^ and VF*, estimates of (C/A')
and (C/A*), respectively. The smaller this discrepancy, the better the
approximation. A comparison of VF'and VF* can therefore be used as an
indicator of the appropriateness of the lognormality assumption.
The above procedure has been applied on discharges of common metals for
various plants, and the results are summarized in Exhibit A.3. A compar-
ison of VF^and VF* values reveals that they are quite close for most of
the plants (e.g., 89 percent of the plants had absolute difference between
VF' and VF* less than 0.5). This suggests that the lognormality assump-
tion and the variability factor equations, based on this assumption, are
reasonable. In light of this evidence, the assumption of lognormality
used in the derivation of the variability factor equations is reasonable.
425
-------
EXHIBIT A.3
COMPARISON OF TWO DIFFERENT ESTIMATES OF THE VARIABILITY FACTORS
Plant
ID
13
13
13
13
14
14
14
14
14
116
116
116
637
637
637
804
804
804
804
804
1208
1208
1208
1570
1570
1924
1924
1924
Metal
Cu
Ni
Zn
Cr
Cu
Ni
Zn
Cr
Cd
Cu
Ni
Cr
Cu
Ni
Ag
Cu
Ni
Cr
Cd
Pb
Cu
Zn
Cr
Zn
Cr
CU
Ni
Zn
A+
0.20
0.27
0.41
1.11
0.14
0.65
0.30
0.53
0.13
0.32
0.35
0.98
4.92
2.00
1.60
0.06
0.03
0.13
0.01
0.03
0.66
0.59
0.54
0.67
0.71
1.46
0.12
0.14
V
-0.76
-0.60
-0.42
-0.08
-0.98
-0.30
-0.58
-0.49
-0.99
-0.71
-0.65
-0.08
0.60
0.11
0.06
-1.27
-1.73
-1.06
-2.28
-1.50
-0.26
-0.29
-0.33
-0.20
-0.17
0.05
-0.92
-0.92
A
°10+
0.23
0.17
0.19
0.39
0.36
0.38
0.24
0.52
0.34
0.42
0.41
0.26
0.27
0.43
0.36
0.23
0.34
0.37
0.22
0.15
0.28
0.22
0.28
0.18
0.17
0.32
0.11
0.23
VF'
3.03
2.28
2.52
6.21
5.22
5.86
3.08
9.75
4.77
5.82
5.88
3.34
3.53
6.55
4.95
2.91
4. 15
4.86
2.80
2.09
3.68
2.90
3.72
2.40
2.29
4.26
1.77
2.88
VF*
3.03
2.26
2.49
5.48
4.88
5.23
3.05
7.84
4.48
5.91
5.81
3.31
3.54
6.15
4.90
2.99
4.50
4.97
2.86
2.08
3.61
2.90
3.57
2.36
2.26
4.21
1.77
3.02
(continued on next page)
426
-------
EXHIBIT A.3 (Continued)
Plant
ID
1924
2070
2088
2088
2088
2088
2501
2501
2501
2501
3301
3301
3301
3301
3301
3311
3311
3315
3315
3315
3320
3320
3320
3320
3320
3324
3324
3324
+ A A
A, /11Q
Metal
Pb
Cu
Cu
Ni
Zn
Cr
Cu
Ni
Zn
Cr
Cu
Ni
Zn
Cr
Cd
Cu
Cr
Cu
Ni
Cr
Cu
Ni
Zn
Cr
Cd
Cu
Zn
Cr
A
and
-------
APPENDIX XII-A.4
SAMPLE CORRELATION COEFFICIENTS TO SUPPORT
INCLUSION OF PLANTS IN THE ESTIMATION
OF THE VARIABILITY FACTORS
In estimating the variability factors of pollutants, plants that did
not, on the average, achieve levels as low as those achieved by most of
the plants in the data base were included. This is justified since the
average and standard deviation of the logarithm of the concentrations
are not significantly correlated for those plants used in the analysis
of the variability factor for each pollutant. Thus, including or
excluding poorer-than-average plants should not affect the results.
Exhibit A.4 presents sample correlations between the mean and standard
deviations of the logarithm of the concentrations for regulated
pollutants, based on the plants included for estimating the variability
factors. It can be seen from Exhibit A.4 that none of the pollutants
showed significant correlations based on a two tailed test with a
significance level of .10. These results support the inclusion of
plants with high average concentrations for estimating the variability
factors.
428
-------
EXHIBIT A.4
SAMPLE CORRELATIONS BETWEEN THE PLANT AVERAGE AND STANDARD
DEVIATION OF THE LOGARITHM OF THE DAILY CONCENTRATIONS
Pollutant
CN,A
CN.T
Cr.VI
Cu
Zti
Ni
Cr,T
Other
Data Source*
Table 12-4
Table 12-3
Table 12-6
Ex.A.3
Ex.A.3
Ex.A.3
Ex.A.3
Ex.A.3
No. of
Obs.
6
8
12
18
14
13
16
9
Sample
Correlation
-0.093
-0.444
-0.432
0.192
0.030
0.016
-0.341
0.272
Upper 5%
Critical Value
0.621
0.549
0.457
0.412
0.497
0.476
0.441
0.582
*Tables in chapter XII or exhibits in Appendix XII.
429
-------
APPENDIX XII-A.5
PRESENTATION AND JUSTIFICATION OF A SIMPLIFIED METHOD
FOR OBTAINING N-DAY-AVERAGE MAXIMUM LIMITATIONS
N-day-average maximum limitations (L ) can be obtained by multiplying
the N-day-average variability factor (VF ), derived in Appendix XII-A.2,
by the long term average (LTA). However, this approach requires lengthy
calculations. In order to simplify these calculations, the following
equation was used.
LN - L30 + *N (L - V
where
L and L,n are daily and 30-day-average maximum limitations derived
in the section on Statistical Methodology in Chapter XII, and
K are constants determined empirically from Exhibit A. 5.
Exhibit A. 5 lists N-day-average limitations obtained by equation [2].
LN' ' LTA x VFN [2]
for each of the 10 regulated pollutants and for N » 1, 2, 3, .... 30.
From this table, K^ values were calculated and substituted into Equation
[1] to obtain the limitations of Table 12-23 in Chapter XII. Note that
in comparing Exhibit A. 5 with this table, of the 110 limitations
(for N * 2, 3,... 29) a large majority (72%) are the same and only the
two limitations marked by an asterisk differ by an absolute value of 2
in the last significant digit.
430
-------
EXHIBIT A.5
SUMMARY OF LIMITATIONS^ALCULATED USING EQUATION [2]
N Day Average Maximum Pollutant Limitations mp/1
way
(N)
1
2
3
'-I
5
6
7
d
9
10
IS
20
30
CM, T
.75
.55
. <4'5
. '»!
.36
.35
. 34
.32
.31
.30
.27
.25
.23
Cu
H
3
3
2
2
2
2
2
2
2
2
1
1
.5
.4
.0
.7
. 6
.U.
. 3
.3
. 2
.2
.0
. 9
. «
Cr. T Ni^
7
5
4
4
3
3
3
3
3
3
2
2
2
.0
.2
.5
.0
.7
.5
. 4
.3
.2
.1
.8
.7
.5
,,
3
2
2
2
2
2
2
2
2
1
1
1
. 1
.2
.3
. b
. i}
.3
.2
.2
. 1
. I
.9
.9
.d
Zn
•4
3
2
2
2
2
2
2
2
2
1
1
1
.2
.2
.8
. 0
. 4
.3
.2
.2
. 1
. 1
.0
.9
.3
TRM
13
3
7
li
0
&
6
6
S
5
5
5
5
.5
.3
.4
.9
.6
.U
.2*
.0'
.9
. 8
.5
.3
.0
Aj
1 .2
.0
.8
.7
.7
.6
. b
.6
. b
.6
.b
.5
.5
Cd
1 .2
.9
.8
.7
.7
.6
. t,
.6
. b
.0
.5
.5
.5
Pb
.6
li
(l
.14
.3
.3
. 3
.3
.3
.3
.3
.3
.3
CH.t
5.0
3.7
3. I
2.8
2.5
O i|
2.2
2.1
2. 1
2 .0
1 » tt
1 .7
1.5
•Last significant figura differs by an absolute value of 2 from corresponding values
Table 12-23.
tFor purposes of comparison with limitations in Table 12-23 in chapter VII only, and not to be used for
purposes of regulation.
-------
APPENDIX XII-B
DATA BASE OF THE
ELECTROPLATING CATEGORY
432
-------
APPENDIX XII-B
DATA BASE OF THE
ELECTROPLATING CATEGORY
Appendix XII-B provides information necessary to replicate the
regression equations of Table 12-8, which are used in the analysis of
the limitations for Cu, Cr,T, Ni, Zn, Cd and Pb. Exhibit B.I presents
the Hamilton Standard plants used in the calculation of the regression
coefficients, and the specific metals each plant plated. Exhibit B.2
presents the additional 22 Hamilton Standard plants used to obtain the
75 percentile Xme in order to calculate the limitations for these
metals, and the metals plated by each plant. Exhibit B.3 presents the
data necessary to replicate the regression equations which are used to
calculate the limitations for the metals listed above. A list of
units and abbreviations for Exhibits XII-B.3 is at the. end of
Appendix XII.
433
-------
EXHIBIT B.I
PLANTS USED IN CALCULATION OF
REGRESSION EQUATIONS OF TABLE 12-8
Operations Generating
£r Cu Nl Zn TRM
13 + + + +
14 + + + + +
6037 + + +
6074 + + +
6075 + + + •• +
6081 + + + ( +
6083 + + + +
6085 + + + + +
6086 + + +
6087 + + + + +
15070 + + + +
20010 + + +
20077 + + + + +
20078 + + + + +
20079 + + + + +
20080 + + +
20081 + + + + +
20082 + + + + +
20084 + + + +
20086 + + + + +
31021 + + + + +
33024 + + + +
33050 + + +
33073 + + + + +
36040 + + + +
22 19 21 18 25
434
-------
EXHIBIT B.2
ADDITIONAL PLANTS USED IN THE CALCULATION OF
THE 75 PERCENTILE Xme
Operations Generating
Plant
ID Cr_ Cu N_i Zn TRM
4045 + + + + +
6073 + + + + +
6076 + + + + +
6078 + + + + +
6079 + + +
6084 + + + + +
6088 + -I- + + +
6089 + + +
6731 + + + + +
9026 + + +
10020 + + + +
11050 + +
19050 + +
19051 + + +
31020 + + + + +
33070 + + -I- -I- +
33071 + + + + +
36041 + + + + +
38050 + + +
40061 + + + +
40062 + + + +
44050 +_ +_ +_
15 20 19 13 22
435
-------
EXHIBIT B.3.1
COPPER RAW DATA IN ug/\
Plant
IE
6037
6037
SOTS
6075
$075
6081
6081
6081
6085
6085
6097
6087
6087
15070
15070
15070
20077
20077
20077
20077
20082
20082
20082
20082
20086
20086
31021
31021
31021
33021
33050
33073
33073
33073
360*0
38010
36000
200T8
20978
20078
20078
20078
20078
20079
20079
20079
20079
20079
20081
20031
20081
20031
20081
20081
20081
13
13
13
13
13
13
11
11
11
11
IK
11
11
11
Date
770216
770217
761102
7(1103
76U01
761020
761021
761022
770209
770210
770216
770217
770218
761102
7SU03
761101
760811
760»12
760915
760916
760*26
76092(
760929
760930
770119
770120
761211
781215
761216
7S0200
750300
7S1012
7(1013
761011
76110»
7S1110
761111
760117
760618
760»19
760921
760922
760923
760817
76081*
760819
760901
760902
760818
760817
760119
750421
760922
760923
760921
750527
750528
750529
750530
750709
750711
750602
750803
75060»
750605
750606
750708
750710
750801
_Cu
1190
5930
2230
1060
2230
750
6SO
150
5130
3290
1910
5000
2630
20
20
16
625
562
171
316
206
6160
2119
39S9
250
"69
1G10
2910
17*0
160
117
301
76(0
1110
60
71
76
307
217
372
100
100
100
• 21
170
112
IIS
117
29
S7
12
26
21
26
700
770
560
100
300
890
290
330
190
310
120
100
70
HO
»0
Effluent
TSS
12000
39000
20000
26000
12000
100
1000
1000
10000
16000
11000
71000
31000
12000
21000
25000
18000
17000
21000
1SOOO
19600
36000
36100
36100
21000
33000
11000
33000
21000
12000
12000
2*000
39000
85000
1000
11000
11000
11000
32000
37000
56000
55000
38000
78000
130000
132000
76000
96000
100
!00
32000
2000
7000
2000
12000
11000
13000
8009
• 000
2000
200
2000
3000
1000
2000
2000
82300
1000
100
eH
1000
890
1010
1010
1030
• 50
850
850
1150
1190
1180
830
920
990
860
970
970
950
975
960
950
910
920
930
1030
1030
790
820
910
850
1000
1130
1120
1170
900
910
920
1010
1030
1160
1180
1090
1070
930
960
910
960
950
810
930
810
760
790
860
880
890
920
920
900
830
820
850
820
320
820
820
920
820
890
Flow
6360
6360
1851
6380
6600
3120
3720
1500
3600
1039
2706
3682
2966
2739
1980
2260
23100
21360
29160
19110
SSll
5375
5375
5917
1600
1600
6601
6129
6375
3336
5908
2017
2716
2185
1050
12SO
1250
2102
1690
1722
1995
2200
2069
176
619
789
198
555
2010
9208
3900
1110
1110
5280
3180
2500
2500
2500
2500
2500
2500
17261
152T7
11359
19315
160H
12696
:2733
19172
Si
1219
7S89
20609
20609
19109
1893
1611
1812
6129
12509
19309
98209
80009
59
17
11
17109
7239
2839
2339
2351
8705
1563
5359
91809
107009
213009
101009
60009
1620
286
20009
17709
3219
1399
10209
6219
7699
7699
8319
12109
11109
8169
1539
S3«
1359
11«'S
1069
31118
17520
17520
3621
17520
17520
17520
9609
9909
669
36009
»39
169
1909
1109
3709
8709
2909
1109
2109
5609
Raw Watte
TS§
32000
72000
92000
111000
116000
2392
333
333
101000
291000
3HCOO
320000
392000
920000
901000
501000
100000
17000
150000
132000
206566
217811
1975*1
281871
2768000
3500000
1912000
971000
711000
251500
5270000
266000
111000
132000
15000
191000
66000
21000
9000
1*000
38000
10000
2000
3120000
3236000
2801000
2180000
2176000
61911
37035
3703S
9126
37035
37035
37035
SOOOOO
1)6000
191000
S17
356
306000
89000
91000
H6000
192000
102000
175000
136000
»76000
Load
EH
910
950
980
1010
970
132
126
105
USD
1170
mo
780
990
930
1050
1000
7*0
6SO
915
910
931
at7
913
895
1070
1110
150
830
930
850
910
810
100
960
670
720
700
260
270
250
110
3(0
280
1010
1000
910
1000
1030
666
578
S7«
1)9
578
578
578
920
920
930
910
770
770
850
870
910
170
860
950
850
980
EM
16993
12938
35517
39178
61111
1151
6584
12613
33531
61101
119025
212681
179861
309251
200371
101155
69139
65893
12985
36906
31796
13711
36239
10162
129110
159231
171015
211670
13»687
16853
20216
10767S
201665
111138
169870
1S0801
H1738
215176
208803
20911S
193211
215561
166365
892123
29313
771878
651380
650219
91595
95312
95312
99081
95312
95312
95312
129275
110205
113755
18068S
125275
1 15725
21951
28651
81051
19251
27851
56951
13961
65151
SM l*tt p«g* of Appendix for abbreviations and units.
436
-------
EXHIBIT B.3.2
CHROMIUM RAW DATA IN ug/l
Plant
IS
6071
6071
6011
6081
6081
609}
608]
608S
6086
6086
SOI6
6087
6087
1507C
1S070
20077
20077
20080
20080
20080
20C80
20080
20082
20082
20082
20086
20086
31021
31021
31021
33021
33073
33073
360iO
36010
36040
20010
20013
20010
20010
20010
20010
20078
20078
20078
20078
20078
20078
20079
20079
20079
20081
20081
20081
20011
20011
20081
20081
1)
13
13
13
S3
1*
11
11
11
11
11
11
Data
761026
761027
761020
761021
761022
770101
77010S
770209
77010S
770106
770107
770216
770217
761102
76110*
76081!
760916
760817
7608 19
760820
760915
760916
7608 26
760929
760930
770119
770120
7612H
761215
761216
750200
761012
76101.
761109
761110
761111
760810
760811
760812
760811
760901
760902
760817
760818
760921
760922
760923
760817
7608 18
760902
760818
760817
760819
760921
760923
760921
761105
7S0527
^50528
750529
750530
750709
750602
750601
7S060S
750606
750708
750710
75080!
Cr
333
143
:7o
155
102
1220
556
1950
7613
1 3 6 C 0
21000
59
1250
7370
166
US
195
396
300
609
783
S26
687
'98
911
1720
129
230
203
70
1110
212C
S33
733
333
SO
20
4 i
30
27
400
SOO
826
1390
1610
2300
1370
1870
289
ao
1050
61
235
783
7760
1700
1100
1500
1800
3500
1500
230
180
660
1 200
99C
370
Effluen
TSS
46000
21000
100
+ 000
1000
136000
22000
40000
-2000
120000
108000
HOCC
71000
12000
25000
17000
1JCOO
sooo
17000
18300
'. 30CO
49600
36100
36400
21000
33000
liOOO
21000
12'JOO
28000
85COO
8000
: i o o o
11000
28000
HOOO
530CO
80000
12000
1 100CO
UOOO
32300
S50CO
38000
78000
130000
96000
100
130
32000
2000
1200C
33000
11000
13000
SOOO
8000
2COO
2000
1000
2000
2000
82000
1000
100
t
EH
890
890
850
850
850
SOO
830
1150
mo
1 190
1060
1180
830
390
970
950
960
970
960
960
910
960
953
920
930
1030
1030
790
850
1130
1170
90".
910
920
: 172
1170
1170
1150
1 110
1120
1310
1030
1090
107;
930
960
960
950
813
830
810
760
380
1100
890
920
920
900
830
850
820
320
e;o
120
323
890
Flow
2100
2100
3120
3720
1500
3287
2626
3600
226
264
202
2706
1632
2739
2260
21360
ISliO
4336
2262
2262
3053
2850
5511
5375
591'
1600
1500
6801
3336
2017
;i 85
1350
1250
1250
4765
6128
7C89
5817
5989
6060
2102
1690
22CO
2C69
475
519
i98
555
20-0
2208
3900
3180
60
2500
2500
2500
2500
726:
1359
9345
60H
2696
2733
9172
Cr
98009
55309
379
679
S37
8083
'.2209
4889
i».:-9
16409
1*409
362
16 2
1 9 5 0 r- 9
50609
n 8 •: ?
2959
H2009
133535
200009
110009
210009
'.7732
231 = 0
26111
6S509
73509
155C9
3i5
63909
62309
25309
29.09
t-709
1S209
10609
13909
14709
12609
11609
117009
117009
106039
76709
.69009
316C09
295009
5843
197i7
•.9747
19747
H19
= 3009
53009
36001
70009
36009
4609
11009
5909
5i09
5109
7509
8409
Raw Wa
IS
3 9 ' 0 0 0 ~:
441-OOC
2392
133
333
•-72COO
1-3000
'2000
7 'i 0 0 "
132030
344000
12or,co
52:000
-------
EXHIBIT B.3.3
NICKEL RAW DATA IN /ug/\
Plant
ID
6037
6037
G07o
6071
607»
6075
6075
6075
6081
6081
5081
6083
6083
6C8S
6085
6086
6086
6086
6087
6087
6087
2C077
20077
20077
20077
20082
20082
20082
20082
20086
20086
31021
31021
31021
33073
330^3
33073
36000
36000
36000
20010
20010
20010
20010
20010
2C010
20073
20078
20078
20078
20078
20078
20079
20079
20079
20079
20079
2008!
20081
20081
20081
20081
20081
20081
20080
20080
3
3
3
3
3
3
4
It
0
0
0
0
•4
10
Data
770216
770217
761026
761027
761028
761102
761103
761100
761020
7610J1
761022
770100
770105
770209
770210
770105
770106
770107
770216
770217
770218
760811
760812
760915
760916
760826
760928
760929
760930
770119
770120
761210
761215
761216
761012
761013
761010
761109
761110
761111
760810
76081 1
760812
760831
760901
760902
760817
760818
760819
760921
760922
760923
760817
760818
760819
760901
76C902
760818
760817
760819
760921
760922
760923
760920
761001
761105
750527
7SCS28
7S0529
750S30
750709
750711
750602
7S0603
750600
75060S
750606
75C70S
750710
750801
JS!
2770
1880
300
600
571
2170
1SOO
2870
95
80
105
1080
2270
6670
2000
0280
3130
12500
7300
7720
6390
1310
1080
1250
750
6032
1006
901
530
286
357
1120
2120
875
332
1620
96»
1560
1780
778
200
230
022
237
175
156
loo
106
027
o89
262
381
63750
6130
5250
2120
2000
70
128
3500
125
90
320
388
1000
212
920
920
600
370
300
250
1700
800
790
700
80
000
903
380
Effluent
TSS
02000
39000
•46000
21000
26000
20000
26000
12000
100
• 000
1000
136000
22000
00000
16000
02000
120000
108000
ooOOO
70000
30000
18000
17000
21000
15000
09600
36000
36100
36000
21000
33000
10000
33000
21000
28000
39000
85000
8000
loOOO
11000
28000
10000
53000
30000
12000
110000
10000
32000
37000
56000
55000
38000
78000
130000
132000
76000
96000
:oo
100
32000
2000
7000
2000
12000
55000
33000
11300
13000
8000
3000
2000
200
2000
3000
1000
2000
2000
82000
1000
000
PH
1000
890
(90
890
1060
1010
1000
1030
850
850
850
800
830
1150
1190
1 100
1190
1060
: 180
330
920
970
950
975
960
950
9oO
920
530
1030
1030
790
820
900
1130
1:20
1170
900
910
920
1172
1170
1170
1150
1100
1120
1010
1030
1160
1180
1090
1070
930
960
910
960
950
8140
330
800
760
790
860
880
1000
1100
890
920
920
900
830
820
350
320
820
820
320
820
820
890
Flow
6360
6360
2100
2100
2100
1850
6360
6600
3120
3720
0500
3287
2626
3600
0039
226
260
202
2706
3682
2966
23000
21360
29160
19OOO
5511
5375
5375
5917
1600
1600
6801
6829
6375
2007
2706
2185
10SO
1250
1250
0765
6128
7089
5817
5989
6060
2102
1690
1722
1995
2200
2069
o76
619
789
098
555
2000
2208
3900
1010
10140
5280
3180
70
60
2500
2500
2500
2500
2500
2500
17261
15277
11359
1930S
16C01
12696
12733
19072
Hi
S7»9
2079
167009
9 U309
128009
7859
10809
37009
95
218
256
7229
9339
12S09
21009
8169
o»19
10009
50009
81009
73009
16509
10209
6269
8009
8o6k
3066
3002
2670
37809
01109
82809
30009
12509
10309
16809
20909
1»2009
108009
108009
100009
103009
91009
100009
310009
96009
85309
78709
78709
82009
92309
76909
90309
6139
120009
180009
130009
00765
09031
09031
53297
09031
09031
09031
3129
321
05009
02009
51009
50009
30009
35009
3709
0009
6109
5709
5509
7109
5909
0509
Raw Wa*
TSS
82000
72000
9970000
oolOOOO
8300000
92000
110000
106000
2J92
333
333
300000
072000
101000
298000
72000
79000
132000
300000
320000
392000
100000
07000
150000
132000
206566
217810
197581
260870
2768000
3500000
1912000
970000
708000
266000
108000
032000
05000
190000
66000
2000
8000
13000
20000
28000
• 2000
21000
9000
16000
38000
10000
2000
3020000
3236000
2800000
2180000
2 176000
60900
37035
37035
9126
37035
37035
37035
206000
53000
500000
036000
090000
517
356
306000
89000
90000
136000
192000
102000
175000
136000
076000
• Load
£H
910
850
10»0
930
1080
980
1010
970
112
126
105
790
820
1150
1170
1080
1130
1000
1100
780
990
700
650
985
900
938
897
913
895
1070
1100
850
830
930
810
800
960
670
720
700
110
110
110
210
190
190
260
270
250
010
380
:«o
1010
1000
910
1000
1030
S66
578
578
089
578
578
578
1000
1100
920
920
930
910
770
770
850
870
910
870
860
850
850
980
PM
16993
12938
1897153
709036
1216765
35517
39078
61111
<4050
6580
12603
126717
189108
33530
60001
25275
22156
27917
119025
212680
179868
69039
6589)
02985
36906
31796
03711
36239
00062
029110
059230
071015
2U670
130667
107675
201665
110036
169870
150108
111738
160231
116081
137110
190566
3SGS96
136330
215176
208803
209006
193281
215561
16636S
892123
29313
771878
650380
650219
91595
95312
95302
99081
95312
95312
91302
65779
101075
129275
110205
113755
160685
125275
115725
21950
28651
88051
09250
27851
66951
03960
65150
S*a last paga of Appendix for abbreviations and units.
438
-------
EXHIBIT B.3.4
ZINC RAW DATA IN ug/l
Plant
12.
6075
6075
6075
6083
6083
6085
6085
6087
6087
6087
15070
15070
15070
20077
20077
20077
20077
20080
20080
20080
20080
20080
20080
20080
20082
20082
20082
20082
20086
20086
31021
31021
31021
33021
33050
33073
33073
33073
20078
20078
20078
20078
20078
20078
20079
20079
20079
20079
20079
20081
20081
20081
20081
20081
20081
20081
20081
20081
11
11
11
11
11
11
li*
11
Date
761102
761103
761101
770101
770105
770209
770210
770216
770217
770218
761102
761103
761101
760811
760812
760915
760916
760817
760818
760819
760820
760911
760915
760916
760826
760928
760929
760930
770119
770120
761211
761215
761216
750200
750300
761012
761013
761011
760817
760818
760819
760921
760922
760923
760817
760818
760819
760901
760902
760818
760817
760819
760921
760922
760923
760921
761001
761105
750602
750603
750601
750605
750606
750708
750710
750801
iQ
833
1170
722
303
166
1060
258
1000
1750
1120
1330
3120
3000
2760
3210
3000
1800
375
333
500
512
700
500
500
112
121
618
257
170
882
1000
3130
1190
1090
771
80
533
533
29
33
83
32
21
10
1250
2820
2730
2250
2250
583
667
750
600
500
100
600
800
10000
100
360
320
310
250
150
100
170
Effluent
!§s
20000
26000
12000
136000
22000
10000
16000
11000
71000
31000
12000
21000
25000
13000
17000
21000
15000
5000
10
17000
17000
17000
18000
13000
19600
36000
36100
36100
21000
33000
11000
33000
21000
12000
12000
28000
39000
85000
11000
32000
37000
56000
55000
38000
78000
130000
132000
76000
96000
100
100
32000
2000
7000
2000
12000
55000
33000
2000
3000
1000
2000
2000
82000
1000
100
Raw Waste Load
etj
1010
1010
1030
800
830
1150
1190
1180
830
920
890
860
970
970
950
975
960
970
910
960
960
930
910
960
950
910
920
930
1030
1030
790
820
910
850
1000
1130
1120
1170
1010
1030
1160
1180
1090
1070
930
960
910
960
950
810
830
810
760
790
860
880
1000
1100
350
820
820
820
820
820
820
890
Flow
1851
6360
6600
3287
2626
3600
1039
2706
3682
2966
2739
1980
2260
23100
21360
29160
19110
1038
2262
2262
2262
2900
3050
2850
5511
5375
5375
5917
1600
1600
6801
6829
6375
3336
5908
2017
2716
2185
2102
1690
1722
1995
2200
2069
176
619
789
198
555
2010
2208
3900
1110
1110
5280
3180
71
60
17261
15277
11359
19315
16011
12696
12733
19172
Zn
5719
6009
1799
2329
3719
2259
1219
11209
22509
17509
103009
100009
12609
29009
33009
23509
19109
59109
60673
71507
82809
75109
61309
101009
1157
1120
5379
1968
192009
197009
131009
63809
17109
11989
9037
6579
11609
8529
1679
1899
1899
3899
5229
1119
252009
1919
158009
112009
191009
931
2978
2978
5021
2978
2978
2978
5119
61109
6109
11009
31009
21009
7609
28009
21009
36009
IS
92000
111000
116000
310000
172000
108000
298000
311000
320000
392000
920000
901000
501000
100000
17000
150000
132000
10000
876370
1015653
1596000
1628000
1111000
2181000
206566
217811
197581
261871
2768000
3500000
1912000
971000
718000
251500
5270000
266000
118000
132000
21000
9000
16000
38000
10000
2000
3120000
3236000
2801000
2180000
2176000
61911
37035
37035
9126
37035
37035
37035
206000
53000
89000
91000
186000
192000
102000
175000
136000
176000
etl
980
1010
970
790
820
1150
1170
1110
780
990
930
1050
1000
710
650
985
910
690
508
628
970
1010
1020
990
938
897
913
395
1070
1110
850
830
930
850
910
810
800
960
260
270
250
110
380
280
1010
1000
910
1000
1030
666
578
578
189
578
579
578
1000
1100
850
870
910
370
860
850
850
980
PM
35517
39178
61111
126717
189108
33531
61101
119025
212681
179868
309251
200379
101155
69139
65893
12985
36906
206669
250358
296830
299115
218111
252229
133988
31796
13711
36239
10162
129110
159231
171015
218670
131667
16853
20216
107675
201665
111136
215176
208803
209116
193281
215561
166365
892123
29313
771878
651380
650219
91595
95312
9S312
99081
95312
95312
95312
65779
101075
21951
28651
88051
19251
27851
669S1
13961
65151
See last page of Appendix for abbreviations and units.
439
-------
EXHIBIT B.3.5
TOTAL REGULATED METALS RAW DATA IN
Plant
JP.
6037
6037
6074
6074
6074
6075
6075
6075
6081
608 1
6081
6083
6033
6085
6085
6086
6086
6086
6087
6087
6087
15070
15070
15070
20077
20077
20077
20077
20080
20080
20080
20080
20080
20080
20080
20082
20082
20032
20082
20086
20086
31021
31021
31021
33024
33050
Data
770216
770217
761026
761027
761023
761102
761103
761104
761020
761021
761022
770 104
770105
770209
770210
770105
770106
770107
770216
770217
7702 Id
761102
761103
761104
760811
760812
760915
760916
760817
760818
7608 19
760820
760914
760915
76091G
760826
76092B
760929
760930
770119
770120
761214
761215
761216
750200
750300
TRM
7333
7914
715
799
1315
7034
6973
6276
1095
937
1 100
2900
3139
14810
717«
12174
16991
33770
10299
14545
10192
5650
6930
10431
4773
5048
5463
3301
616
567
1593
1362
1590
1355
1573
6876
8525
4355
4944
1950
3428
3923
3420
4005
1339
985
Effluent
ISS.
42000
39000
46000
21000
26000
20000
26000
12000
100
4000
1000
136000
22000
40000
16000
42000
120000
108000
44000
74000
34000
12000
21000
25000
18000
17000
21000
15000
5000
10
17000
17000
17000
18000
13000
49600
36000
36100
36400
21000
33000
14000
33000
21000
42000
12000
fiH
1000
390
390
390
1060
1010
1040
1030
850
350
350
800
830
1 150
1190
1140
1190
1060
1 180
830
920
890
360
970
970
950
975
960
970
940
960
960
930
940
960
950
940
920
930
1030
1030
790
320
940
350
1000
Flow
6360
6360
2100
2100
2100
4854
6360
6600
3120
3720
4500
3287
2626
3600
4039
226
264
202
2706
3682
2966
2739
1980
2260
23400
21360
29160
19440
4038
2262
2262
2262
2900
3050
2850
5511
5375
5375
5917
1600
1600
6801
6329
6375
3336
590B
TRM
14127
10325
266366
130586
233214
34297
37992
62459
3275
2747
5980
18433
25473
26386
45546
23955
21075
26769
110839
202489
171133
293166
188154
93318
63618
61266
37406
32416
202059
155041
209629
285076
209524
205424
342900
33007
42572
33144
39142
390136
423636
445336
204436
126916
14059
94H3
Raw Watt*
TSS
82000
72000
9970000
4410000
8340000
92000
114000
146000
2392
333
333
340000
472000
108000
298000
72000
79000
132000
344000
320000
392000
920000
904000
504000
100000
47000
150000
132000
10000
876370
1015653
1596000
1628000
1 144000
2484000
206566
217314
197581
264874
2768000
3500000
1912000
974000
748000
251500
5270000
Load
EH
910
350
1040
930
1080
980
1010
970
132
126
105
790
320
1150
1 170
1080
1130
1040
1140
780
990
930
1050
1000
740
650
985
940
690
508
623
970
1010
1020
990
933
897
913
895
1070
1140
350
830
930
850
910
PM
16993
12938
1697153
749036
1216765
35517
39478
64111
4454
6584
12643
126717
189108
33534
64401
25275
22156
27917
1 19025
212684
179868
309254
200379
101155
69439
65893
42985
36906
206669
250358
296830
299115
21841 1
252229
433988
34796
43711
36239
40462
429110
459234
471015
218670
134667
16853
20246
(continued on next page)
440
-------
EXHIBIT B.3.5 (Continued)
Plant
IP
33073
33073
33073
36040
36040
36Q4U
20010
20010
20010
20010
20010
20010
20078
20Q7U
20078
20078
20078
20078
20079
20079
20079
20079
20079
20081
20081
20081
20081
20081
20081
20081
20034
20084
13
13
13
13
13
U
14
14
14
14
14
14
14
14
Date
761012
7(>1013
761014
751109
761110
761111
760810
76081 1
760812
760831
76090 1
760902
760817
760819
760819
760921
760922
760923
760817
7603 IS
760819
760901
760902
760818
760817
760819
760921
760922
760923
760924
761001
761105
750527
75052B
750529
750530
750709
750711
750602
750603
750604
750605
750606
750708
750710
750801
IBM
1323
12463
4727
2177
2600
1200
418
354
676
335
402
215
380
886
3482
1747
1776
2461
68124
13790
18312
6085
6267
971
902
5342
315
657
981
2471
3130
18057
3690
3120
2750
2700
5030
2410
3630
176U
168U
1380
1090
1820
2400
960
Effluent
!§§.
23000
39000
85000
aooo
14000
11000
28000
I4UOO
53000
30000
12000
110000
14000
32000
37000
56000
55000
38000
78000
130000
132000
76000
96000
100
100
32000
2000
7000
2000
12000
55000
33000
11000
13000
3000
3000
2000
200
2000
3000
1000
2000
2000
•32000
1000
400
eii
1130
1120
1170
900
910
920
1 172
1170
1170
1150
1140
1120
1010
1030
1160
11SO
1090
1070
930
960
910
960
950
340
830
340
760
790
860
380
1000
1100
890
920
920
900
930
(120
850
820
B20
d20
820
820
820
890
Flow
2047
2746
2185
1050
1250
1250
4765
6128
7089
5817
5939
6060
2102
1690
1722
1995
2200
2069
476
en
799
493
555
2040
2208
3900
1440
1440
5280
3180
74
60
2500
2500
2500
2500
2500
2500
17261
15277
11359
19345
16041
12690
12733
19472
TRM
104806
199136
94996
169459
148756
139813
119298
1 14152
105856
156381
324608
108753
214696
208316
208936
192726
214955
165906
316866
16575
718386
&09216
617096
82960
39276
89276
95589
99276
89276
8927S
18610
66649
12H636
109736
143296
160136
124766
114896
16336
22H36
54836
39236
21436
4*5336
36536
54536
Raw Waste
TSS
266000
143000
432000
45000
194000
66000
2000
3000
13000
24000
28UOQ
42000
21000
9000
16000
38000
10000
2000
3420000
3236000
2304000
21
-------
EXHIBIT B.3.6
CADMIUM RAW DATA IN «g/l
Plant
ML.
6081
6081
6081
6087
6087
6087
It
14
It
It
It
It
Peg*
761020
761021
761022
770216
770217
770218
750602
750603
75060t
750605
750606
750708
750710
750801
M
214
190
190
It
13
13
80
180
220
250
170
30
120
50
Effluent
m
100
tooo
1000
ttooo
7tOOO
3tOOO
2000
3000
1000
2000
2000
82000
1000
too
R«w Wait! Load
ea
850
850
850
1180
830
920
850
820
820
820
820
820
820
890
Flow
3120
3720
tsoo
2706
3682
2966
17261
15277
11359
193t5
16041
12696
12733
19472
.Si
t2t
373
1557
39
31
31
1309
2109
5209
2209
2409
2609
919
1409
is
2392
333
333
344000
320000
392000
89000
gtooo
186000
192000
102000
175000
136000
t75000
fitt
132
126
105
lltO
780
990
850
870
910
870
860
850
850
980
PM
ttst
6"58t
12643
119025
21268t
179868
21954
28654
88054
t9254
27854
6695t
t3964
65154
EXHIBIT B.3.7
LEAD RAW DATA IN ,ug/l
Effluent
Raw Waste Load
Plant
112
6083
6083
6087
6087
6087
20079
20079
20079
20079
20079
Pat?
770104
770105
770216
770217
770218
760817
760818
760819
760901
760902
Pb
280
160
85
151
65
62
38
SO
85
80
IS
136000
22000
44000
74000
34000
78000
130000
132000
76000
96000
EH
800
830
1180
830
920
930
960
910
960
950
Flow
3287
2626
2706
3632
2966
476
619
789
498
555
Pb
2189
2509
1009
1509
1129
1259
59
40
1209
1109
IS
340000
472000
344000
3JOOOO
392000
3420000
3236000
2804000
2180000
2176000
ee
790
820
114Q
780
990
1010
1000
910
1000
1030
£M
126717
189108
119025
212684
179868
892423
29343
771878
654380
650249
S
-------
APPENDIX XII-C
DATA BASE FOR PLANTS
USING FILTERS FUR SEPARATION
OF SOLIDS FROM EFFLUENT STREAM
443
-------
APPENDIX XII-C
DATA BASE FOR PLANTS
USING FILTERS FOR SEPARATION
OF SOLIDS FROM EFFLUENT STREAM
Exhibit C.1 presents the plants visited and sampled by the Agency that
use filtration systems for separation of precipitated metals from
electroplating wastes, as well as the metals plated and any additional
waste treatment processes operated by each of these plants. The data
for the 10 plants used in the analysis of the performance of
filtration systems are listed in Exhibit C.2. A list of units and
abbreviations of Exhibit C.2 is at the end of Appendix XII.
444
-------
EXHIBIT C.1
PLANTS USING FILTERS FOR SEPARATION
OF SOLIDS FROM EFFLUENT STREAM
Plant Operations Generating Additional
ID Cr_ £u ]U Zn Waste Treatment
5050 (a) Ion Exchange
6076 + + + + Clarification
6077 + + + Lancy
6079 + + +
6089 (b) + + Lagoon;Lancy
6731 + + + +
9026 + +
11050 (c) +
19051 (d) + + Lancy
20077 + + + + Clarification
31020 + + + + Pptn tank clarifier
31021 + + + + Clarification
33070 + + + + Clarification
33073 + + + + Clarification
33074 + + + Lancy
36041 + + + +
36062 (e) + + Evaporation
38050 + +
40061 + + + Ion Exchange
40062 + + + Lagoon; Evaporation of Cr
(a) Filter used on floor spill sludge.
(b) Lancy followed by filter for stripping line wastes;
others to lagoon.
(c) Bright dip only. Filter used on floor spill sludge.
(d) Performs chemical milling only.
(e) Printed Circuit subcategory.
445
-------
EXHIBIT C.2
DATA FOR ANALYSIS OF METALS TREATMENT USING FILTRATION IN /xg/l
Effluent
Raw Waste Load
Plant
1C
6079
ft079
6079
6731
6731
6731
9026
t>026
9026
20077
20077
20077
20077
20077
20077
31020
31021
31021
31021
33070
33070
33070
33073
33073
33073
36041
36041
36041
38050
Date
701130
761201
761202
761117
761118
761119
761207
761208
761209
760810
760811
760812
760914
760915
760916
761214
761214
761215
761216
761019
761020
761021
761012
761013
761014
770118
770119
770120
750200
Cr. Ill
930
734
542
42
0
2B
3
5
7
313
95
161
1145
6SU
410
13
81
83
91
439
462
549
939
323
939
460
606
323
769
Cu
93
40
36
647
258
588
22SO
4170
2200
375
875
250
789
473
316
1000
300
1420
1580
58
131
84
12
317
91
1890
444
1060
158
Ni.
389
133J
733
1110
1000
1890
116
102
107
346
1620
692
1500
1250
875
120
1000
1620
750
95
120
80
235
256
150
320
44
571
350
Zn
1 10
78
40
304
889
889
3060
706
482
2470
3300
1760
3600
2800
2000
13
375
1380
1060
95
108
105
48
43
48
765
139
430
121
PM
2658
2536
1852
2391
2387
3798
5737
5278
3804
5382
7875
4419
3463
6189
4613
1554
2661
4912
391 1
1024
1372
1023
4747
2494
12653
4179
1662
3625
1969
ts§
10UO
31000
21000
6000
1000
4000
11000
15000
67000
11000
23000
9000
26000
17000
11000
16000
7000
18000
21000
13000
32000
100
32000
4000
42000
32000
10000
5000
142500
Cr, III
18832
16740
13540
132
954
359
73
31
81
6277
662
10787
7329
4753
2928
115995
7855
7630
4755
26995
29995
22913
63895
122995
62295
28595
12195
24979
577
Cu
587
300
210
647
941
1650
52400
63300
63800
6400
17400
7230
6280
2830
2330
103000
20400
12700
12300
1000
2420
1580
20000
47700
3240
26500
7530
9560
167
Ni
19600
21300
20900
1440
2220
3890
299
341
377
8440
16500
10200
5000
6260
3000
27500
2000
1000
1000
400
332
406
14300
16800
20900
5000
2570
4490
7062
Zn
13d
393
144
5070
9910
19200
22400
27600
30600
29000
29000
33000
16100
23500
19100
13800
8000
9820
13600
1850
2230
1920
6570
1 1600
8520
18700
13400
14300
138
EM
42577
43442
44010
11940
18164
32981
190331
258980
220020
54595
69347
65803
38981
42836
36812
534259
40121
33083
33592
31636
36794
28573
107598
201508
114359
91818
43683
100263
15975
See (aft page of Appendix for abbreviations and units.
446
-------
APPENDIX XII-D
DATA BASE OF THE ELECTROLESS PLATING AND
PRINTED CIRCUIT BOARD SUBCATEGORIES
447
-------
APPENDIX XII-D
DATA BASE OF THE ELECTROLESS PLATING AND
PRINTED CIRCUIT BOARD SUBCATEGORIES
Exhibit D. I presents the data prepared by Hamilton Standard, which were
used for the analysis of nickel within the Electroless subcategory.
Exhibit D.2 presents the data prepared by Hamilton Standard, which were
used for the analysis of copper within the Printed Circuit Board
subcategory. A list of units and abbreviations for Exhibits D.I and D.2
is ac the end of Appendix XII.
443
-------
EXHIBIT D.1
DATA FOR NICKEL PLATED IN ELECTROLESS SUBCATEGORY IN ug/l
gffluant
Raw Wait* Load
Plant
12
i»077
i*077
6051
6081
6081
6081
6381
6381
6381
12065
12065
20061*
2006 H
20069
20070
20070
20070
20070
20070
20070
20070
20073
20073
20073
20073
20073
20073
20083
20083
20083
20083
20083
20083
20085
20085
20085
23061
23061
30071*
3007).
i»1067
i*1069
1.1069
Data
760201*
760205
0
761020
761021
761022
761026
761027
761028
603730
6037HO
751008
751009
760219
760831
760901
760921
760922
760923
760205
760206
760821*
760825
760826
760911*
760915
760916
76082>*
760825
760826
760928
760929
760930
761116
761117
761118
751021
751022
760210
760211
7U12
76020>*
760205
Ni
2 <*500
21000
67
95
80
105
3330
5120
5240
9230
9230
2386
3216
18W06
327
750
533
889
53
65
36
2250
1*1*8
i*78
1380
1120
1120
5130
907
767
808
i*62
4750
1330
1330
667
312
1 11*
1*8700
i»8700
930
160
162
Tg
50000
162000
9000
100
i*000
1000
11000
26000
56000
23000
23000
108000
26000
138779
9000
18000
6000
7000
i*000
6000
17000
i*3000
11000
1UOOO
i*i*000
38000
33000
1W5000
3i*000
27000
9000
6000
97000
29000
32000
21000
i*000
15000
29000
21000
31000
100
17000
EH
770
750
0
850
850
850
752
750
760
700
760
920
910
11"*0
950
9i*0
920
890
890
890
885
820
790
810
850
930
U50
960
915
920
990
850
950
920
870
900
710
735
i*10
370
900
270
870
Flow
9600
9480
22000
3120
3720
i*SOO
13900
11690
12680
20833
20833
5917
5385
11028
35UO
3720
3225
3i*20
35i*0
3568
3678
13300
15i*25
18168
18769
17363
18305
i*i*16
3153
i*2"*5
i*833
i*780
4658
1*500
"»200
3900
US'*
115i*
2288
2288
375
828
828
lii
2U500
23800
192
86
209
247
32200
3UUOO
25600
9650
11500
71360
U5120
U9S87
30000
28000
28900
36400
36UOO
53UOO
38600
65200
53800
52500
102000
78200
89700
103000
153000
82800
97100
111000
87100
193000
li*7000
127000
378
737
27595
294U1
0
162
211
TSS
38000
23000
131000
2392
333
333
228000
452000
96000
U8000
80000
1552000
2UOOOO
i*i*272
675000
736000
592000
72>*000
720000
13000
17000
632000
702000
712000
300000
53000
12i»000
2UOOO
18000
15000
16000
3000
10000
661*000
768000
1122000
67000
201000
16727
130U5
0
11000
100
EH
550
5UO
0
132
126
105
7i»6
750
75C
650
730
U85
525
665
880
910
9UO
890
880
230
250
510
570
550
U80
U90
860
265
280
230
250
250
250
730
650
1100
720
750
290
303
0
270
680
SM lait page of Appendix for abbreviations and units.
449
-------
EXHIBIT D.2
RAW DATA FOR COPPER PLATED IN THE PRINTED CIRCUIT BOARD SUBCATEGORY IN ug/i
Plant
ID
2U62
20o2
4U65
4Jo5
4 Do-)
4J>J9
5020
5u2u
5020
502U
502'J
5U20
5021
5021
5U21
17061
17061
1-JQ63
19U63
19t>63
19063
19063
19053
30050
36062
360.32
Date
751007
751008
500711
500721
751001
751002
761116
761117
76111a
77011 1
770112
770113
76 1 1 30
761201
761202
750916
750917
761130
761130
761201
761201
761202
761202
750200
750924
750925
Cu.
1455
1591
898
300
727
776
206
147u
165
1850
900
1300
3820
1740
1200
1d33
1197
4880
2780
2210
2160
3590
3230
39614
479
101
Effluont
IS.
50000
3 1000
16000
27000
15000
4000
58000
234000
5000
340UO
24000
15000
24000
20000
24000
1000
6000
34000
6000
14000
10000
6000
16000
100
53000
58000
Raw Waste Load
ea.
900
950
69U
635
960
940
460
920
dOO
760
690
700
760
680
d40
620
730
690
710
710
800
690
800
680
385
760
Flow
2100
1500
1200
1200
13920
15340
1818
1620
1380
165d
16U1
1406
4800
4820
4020
8000
8000
3993
979
3996
940
3980
964
23520
2058
2050
SSL
0
0
6423
4549
4352
8437
9530
14700
7670
2859
19473
2625
4620
1580
289U
8197
3714
17700
3650
16200
8150
17900
8460
1202029
535700
382900
TSS
0
0
38000
59000
44606
55263
10000
54000
26000
4473
1 1473
1Q595
7000
5000
1000
14000
23000
50000
12000
86000
100000
152000
36000
43463
360000
263000
Efi.
0
0
835
700
572
843
270
960
760
352
344
407
940
310
470
640
640
1230
230
1230
220
1200
190
606
385
820
I art pag* of Appendix for abbreviations and units.
450
-------
APPENDIX XII-E
DATA BASE USED TO OBTAIN
MASS-BASED PRETREATMENT STANDARDS
451
-------
APPENDIX XII-E
DATA BASE USED TO OBTAIN
MASS-BASED PRETREATMENT STANDARDS
Exhibits E.I, E.2, and E.3 present the data prepared by Hamilton
Standard, that are needed to calculate the median water usage for the
Electroplating Category and Electroless Plating and Printed Circuit
Board subcategories, respectively. A list of units and abbreviations
for Exhibits E.I, E,2, and E.3 are at the end of Appendix XII.
452
-------
EXHIBIT E.I
DATA FROM ELECTROPLATING CATEGORY
FOR MASS BASED LIMITATIONS
Flint
JD.
6037
6037
6037
6074
6074
6074
6075
6075
6075
6081
6081
6081
6083
6083
6083
6084
6084
6084
6085
6085
6085
6086
6086
6086
6087
6087
6087
6088
6088
6088
10020
10020
Pat*
770215
770216
770217
761026
761027
761028
761102
761103
761104
761020
761021
761022
770104
770105
770106
770104
770105
770106
770209
770210
77021!
770105
770106
770107
770216
770217
770218
770126
770127
770128
770201
770202
Flow
6350
6360
6360
2100
2100
2100
4854
6360
6600
3120
3720
4500
3287
2626
2174
3200
2450
2190
3600
4039
3769
226
264
202
2706
3682
2966
430
530
530
6722
5689
Area
6530
5884
5512
972
972
972
3284
3913
3703
2291
2284
2498
105
105
105
2639
2613
2565
2469
3105
2448
2774
2774
2774
26263
25775
26047
449
686
511
4851
1896
Pt«nt
ID
10020
15070
15070
15070
19050
20077
20077
20077
20077
20077
20077
20080
20080
20080
20080
20080
20080
20080
20082
20082
20082
20082
20082
20082
20086
20086
20086
31021
31021
31021
31050
33024
Data
770203
761102
761103
761104
750200
760810
760811
760812
760914
760915
760916
760817
750818
760819
760820
760914
760915
760916
760824
760825
760826
760928
760929
760930
770118
770119
770120
761214
761215
761216
750200
750200
Flow
7295
2739
1980
2260
2702
17700
23400
21360
29160
29160
19440
4038
2262
2262
2262
2900
3050
2850
4725
5583
5511
5375
5375
5917
1600
1600
1600
6801
6829
6375
575
3336
Are*
5730
3653
4863
3839
1032
43856
40348
46527
53512
57735
50335
43167
41111
39055
44808
21583
20556
19528
5182
5516
5283
6600
6129
6357
2485
2005
2989
6173
7262
6722
775
6983
(continued on nmt paga)
453
-------
EXHIBIT E.1 (Continued)
Plant
IS
33050
33073
33073
33073
36040
36040
36040
44050
4045
4045
4045
6073
6073
6073
6073
6078
20010
20010
20010
20010
20010
20010
20078
20078
20078
20078
20078
20078
20079
20079
20079
20079
Data
750300
761012
761013
751014
761109
761110
761111
750300
770111
770112
770113
761019
761020
761021
761207
761208
760810
760811
760812
760831
760901
760902
760817
760818
760819
760921
760922
760923
760817
760818
760819
760831
Plow
5908
2047
2746
2185
1050
1250
1250
14220
6000
6000
6000
2472
1932
1752
5947
6339
4765
6123
7089
5817
5989
6060
2102
1690
1722
1995
2200
2069
476
619
789
606
AfM
6840
3185
2593
2889
1199
1199
1199
40
4711
9626
4535
1547
1116
1645
0
0
14377
18932
14585
16796
17161
16796
3278
2112
2058
3230
3233
3515
11782
12129
11957
11105
Plant
JD
20079
20079
20081
20081
20081
20081
20081
20081
20081
20084
20084
20084
33071
33071
33071
13
13
13
13
13
13
14
14
14
14
14
14
14
14
14
14
14
Date
760901
760902
760818
760817
760819
760921
760922
760923
760924
761001
761022
761105
761019
761020
761021
750527
750528
750529
750530
750709
750711
750602
750603
750604
750605
750606
750708
750710
750725
750723
750730
750801
Flow
498
555
2040
2208
3900
1440
1440
5280
3180
74
46
60
1498
2449
1745
2500
2500
2500
2500
2500
2500
17261
15277
11359
19345
16041
12696
12733
13106
13732
17475
19472
Area
10514
13708
1121
1121
1121
975
975
975
975
2613
1491
2608
2897
2720
2696
4227
1610
2800
3442
2394
1993
7013
8277
7725
4352
6332
11137
9602
4332
2803
5727
5901
$** last page of Appendix for abbreviations and units.
454
-------
EXHIBIT E.2
DATA FROM ELECTROLESS SUBCATEGORY
FOR MASS BASED LIMITATIONS
Flint
ID
4077
4077
6051
6081
6081
6081
6381
fi381
6331
12065
12065
20064
20064
20069
20070
20070
20070
20070
20070
20070
20070
20073
20073
20073
20073
20073
20073
20083
20083
20083
20083
20083
20083
20085
20085
20085
23061
23061
30074
30074
41067
41069
41069
Date
760204
760205
0
761020
761021
761022
761026
761027
761028
603730
603740
751008
751009
760219
760831
760901
760921
760922
760923
760205
760206
760824
760825
760826
760914
760915
760916
760824
760825
760826
760928
760929
760930
761116
761117
761118
751021
751022
760210
760211
7412
760204
7&0205
Flow
96UO
9480
22000
3120
3720
4500
13900
11690
12680
20833
20833
5917
5385
11028
3540
3720
3225
3420
3540
3568
3678
18300
16425
18168
18769
17363
18305
4416
3153
4245
4833
4780
4658
4500
4200
3900
1154
1154
2238
2288
375
828
328
Area
3275
3275
7865
229 1
2284
2498
18408
16338
16338
11451
11451
23208
23388
19060
4366
3737
3688
3804
3746
4063
4063
31434
30600
28322
39703
29353
33563
7574
7968
7448
7025
6274
7056
19920
19056
19488
19
27
5263
5263
141
239
239
$** last peg* of Appendix for abbreviations and units.
455
-------
EXHIBIT E.3
DATA FROM PRINTED CIRCUIT BOARD SUBCATEGORY
FOR MASS BASED LIMITATIONS
Pltnt
10
Oats
Flow
Ar*a
2062
2062
4065
4065
4069
4069
5020
5020
5020
5020
5020
5020
5021
5021
5021
17061
17061
19063
19063
19063
19063
19063
19063
30050
36062
36062
751007
751008
500711
500721
751001
751002
761116
761117
761118
770111
770112
770113
761130
761201
761202
750916
750917
761130
761130
761201
761201
761202
761202
750200
750924
750925
2100
1500
1200
1200
13920
15840
1818
1620
1330
1658
1681
1406
4800
4820
4020
8000
8000
3993
979
3996
940
3980
964
23520
2058
2050
1032
1032
343
343
7116
7116
1159
1159
1159
1589
1589
1589
2633
2537
957
1153
1153
1811
1811
1811
1811
1811
1311
0
716
1217
S*t lait p«gt of Appendix for abbreviations and units.
456
-------
ABBREVIATIONS AND UNITS
1.0. Identification Number of Plants
Date Date Sampled (example: 760618 - 6/18/76 - June 18, 1976)
TSS Total Suspended Solids (/xg/1)
Flow Flow in Gallons per Hour
pH pH of Waste Scream x 100
PM Precipitable Metals* (/ig/1)
TRM Total Regulated Metals (/ig/1)
- Cu + Ni + Cr.T + Zn
Area Area Plated in Square Feet per Hour.
*Precipitable Metals is the sum of (Cu + Cr,T + Zn + Ni -f- Cd + Pb + Ag + Hg +
Fe + Sn) in the Raw Waste Load.
457
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-------
SECTION XIII
ACKNOWLEDGEMENTS
The Environmental Protection Agency was aided in the preparation of
this Development Document by Hamilton Standard, Division of United
Technologies Corporation. Hamilton Standard's effort was managed by
Mr. Daniel J. Lizdas and Mr. Walter M. Drake and included significant
contributions by Messrs. Eric Auerbach, Robert Blaser, Jeffrey Wehner,
Richard Kearns, Robert Lewis, Joel Parker, William Starkel, Robert
Pacocha, Jeffrey Robert and Robert Patulak.
Mr. DevereauK Barnes and Mr. Bill Hanson of the EPA's Effluent
Guidelines Division served as Project Officers during the development
of limitations and the preparation of this document. Mr. Robert
Schaeffer, Director Effluent Guidelines Division, Mr. Ernst P. Hall,
Branch Chief, Metals and Machinery Branch, and Mr. Harold B. Coughlin,
Branch Chief, Effluent Guidelines Implementation, offered guidance and
suggestions during this project.
Acknowledgement and appreciation is also given to Ms. Kaye Starr, Ms.
Carol Swann and Ms. Nancy Zrubek of the word processing staff, Ms.
Helena Pohorylo and Ms. Diane Boucher of Hamilton Standard, and those
of the secretarial and administrative staff of the Effluent Guidelines
Division who worked so diligently to prepare, edit, publish and
distribute the manuscript.
Finally, appreciation is also extended to those plating, metal
finishing and printed board industry associations and plants that
participated in and contributed data for the formulation of this
document.
459
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-------
SECTION XIV
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471
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133. Lancy, L.E., and Steward, F.A., "Disposal of Metal Finishing
Sludges - The Segregated Landfill Concept", Plating and
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134. Lansdale, H. K., Milstead, C. E., Cross, B. P., and Braber,
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135. Larson, T. J., and Gibbons, B. C., "Reverse Osmosis Membrane
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June 1969.
472
-------
136. Lawes, B.C. and Stevens, W.F., "Treatment of Cyanide and
Chromate Rinses", AES Illustrated Lecture Series, American
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137. Lee, E. S., and Lee, P., "Nonlinear Boundary Value Problems
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138. Lefevre, L. J., "How to Ion Exchange Efficiently", Prod.
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139. Lehmann, Richard B., "Treatment of_ Electroplating Wastes by_
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140. Light, T. S., "Ion Selective Electrodes Industrial
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141. Logozzo, Arthur W., "Hard Chromium Plating", AES Illustrated
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142. Lordi, G., (Digital Equipment Corp., Maynard Mass.),
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143. Lowder, L.R., "Modifications Improve Treatment of Plating
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144. Lower, W. A., Eckefeldt, E., "Sodium Ion Monitoring", Indus.
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145. M&T Chemicals Inc., "Decorative Chromium Plating", AES
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146. MacDermid, Inc., "Chromate Conversion Coatings", AES
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147. Machinery and Mechanical Products Manufacturing, Hamilton
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473
-------
148. Manahan, E., Smith, M. J., Jones, D. , Harlan, S., and Kunkel,
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149. Mansen, R. A., and Dytrt, F., Method of Electroless Nickel
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150. Martell, A. E., "Chelation and Olation Reactions of_ Metal
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151. Martell, A. E., Chemistry of. Metal Chelate Compounds,
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152. Mazzeo, D.A., "Energy Conservation In Plating and Surface
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153. McDermott, J., Plating of_ Plastics With Metals , Noyes Data
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154. McDermott, G. N., Moore, W. A., Post, M. A., and Ettinger, M.
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155. McDonough, W. P., "Use o_f the Integrated Waste Treatment
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156. McGarr, H. J., and others, "Cost of Copper: Solvent
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157. McNutt, J.E., and Swalheim, D.A., "Recovery and Re-use of
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158. McRae, W. A., "Potable Water From Seawater By_ High
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474
-------
159. Metal Finishing Segment of Electroplating Development
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160. Metal Finishing, "Recycling Etchant for Printed Circuits",
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161. Metals Handbook, American Society for Metals, 8th Ed. 1964.
162. Metzger, C. A., Herald, A. B., McMullen, B., and Schelle, M.
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163. Michaels, A. S., Bixler, H. J., Cross, R. A., Cleveland, D.
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164. Mills, A. B., "Reverse Osmosis for Purification of_ Water",
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165. Missel, L. "Gold Plating of PC Boards and Wire", Metal
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167. Mohler, J. B., "Chromic-Sulfuric Etchants for Printed Circuit
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168. Mohler, J.B., "The Art and Science of Rinsing", AES
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169. Montgomery, D.C., "The Coloration of Anodic Coatings for
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475
-------
171. Morris, D. P., "Effect of Chelation on Toxicity of Copper",
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172. Murski, K., "Practical Electroless Nickel Plating", Metal
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173. Mytelka, A. I., et al., "Heavy Metals in Wastewater and
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476
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184. "Operation of. the Multi-Effect Multi-Stage Flash Distillation
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185. Ostraw, R. and Kessler, R.B., "A Technical and Economic
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192. Pearlstein, F., and Weightman, R. F., "Electroless Palladium
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194. Pearlstein, F. et al, "Testing and Evaluation of Deposits",
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477
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203. Pourbais, Marcel, "Atlas of_ Electrochemical Equilibria ir±
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204. Pressman, Marice., "Prototype Reverse Osmosis Wastewater
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205. Price, W. L., "Plated Polypropylene", Plating, February 1971,
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206. Rajagopal, I., and Rajam, K.S., "A New Addition Agent for
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207. Rajan, S., "Application of_ Inorganic Ion-Exchange Membranes
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478
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209. Read, H.J., "Principles of Corrosion", AES Illustrated
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210. "Recycling Etchant for Printed Circuits", Metal Finishing,
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211. Reid, G. W., et al., "Effects of Metallic Ions on Biological
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212. "Reverse Osmosis and Electroplating", Anon., Ind Finish, July
1974.
213. Rich. T. R., and Mix, T. W., "Development of_ an Improved
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214. Richardson, J. L., Segovin, G., Mason, J. W., and Subcasky,
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215. Rigling, W. S. , "Multilayer Printed Wiring Board Design
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216. Robinson, G.T., "Powder Coating Replaces Zinc Plating for
Pulleys", Products Finishing, Gardner Publications Inc.,
Cincinnati, Ohio, Feb. 1974, pp. 79-81.
217. Robinson, L. C. R., "Printed Circuit Manufacturing",
SM/TN/B/1585, British Steel Corp., Sheffield, (England)
Information Services, October 1973, pp. 6.
218. Rodzewich, Edward A., "Theory and Practice of Phosphating",
AES Illustrated Lecture Series, American Electroplaters
Society, Inc., Winter Park, FL. 1974.
219. Rozell, Lee T., "Ultrathin Membranes for Treating Metal
Finishing Effluents by Reverse Osmosis", North Star Research
and Development Inst., Minneapolis, Minn., November 1971.
220. Rozelle, L. T., Kopp, C. V. Jr., Cadotte, J. E., and Cobian,
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North Star Institute, Minneapolis, Minn., July - August 1974.
479
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221. Rozelle, L. T., Cadotte, J. E., Nelson, B. R., and Kopp, C.
V., "Ultrathin Membranes for Treatment of Waste Effluent by
Reverse Osmosis", North Star Research and Development
Institute, Minneapolis, Minn., 1973.
222. Sachs, T.R., "Diversified Finisher Handles Complex Waste
Treatment Problem" Plating and Surface Finishing, American
Electroplaters Society, E. Orange, NJ, Vol. 65, Dec. 1978, p.
36.
223. Salyer, L. 0., Kirkland, E. V., and Eilken, P. H., "Improved
Avionic Membranes for Electrodialysis", Research and
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224. "Semiconductor Technique Now to Plate Auto Parts", Machine
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225. Sephton, Hugo H., "An Investigation of Vertical Tube
Evaporation Utilizing the Septhon Flash Tube", Research and
Development Progress Rept., California Univ. Berkeley, Sea
Water Conversion Lab, June 1968.
226. Silman, H., "Treatment of. Rinse Water from Electrochemical
Processes", Efco Ltd., Surray, England, June 1971.
227. Sinclair, R. G., Biological Abstracts, Inc., Battelle,
Columbus, Ohio, 1974.
228. Smookler, S., and Cannizzaro, J., "The Status of_ Additive
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Corporation, No. 21/1.
229. Smolyakov, V., Water Filtration Purification and Distillation
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230. Sondak, N. E., and Dodge, B. F., "The Oxidation of Cyanide
Bearing Plating Wastes by Ozone. Part I", Plating, 48 (2)
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231. Sondak, N. E., and Dodge, B. F., "The .Oxidation of Cyanide
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232. Snoevink, Vernon, L., Kin, Cyung R., Hinrichs, Richard 1.,
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480
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for Waste Water Treatment", Final Rept., Illinois University
Urbana, June 1974.
233. Sorber, C. A., Malina, J. F., Jr., and Sagik, B. P., "Virus
Rejection by the Reverse Osmosis Ultraf iItrat ion Processes",
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234. Spatz, D. D., "Industrial Waste Processing With Reverse
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235. Spatz, D. D., "Electroplating Waste Water Processing With
Reverse Osmosis", Products Finishing, 36_ (11), 79-89, August,
1972.
236. Spencer, L. F., "Electroless Nickel Plating - A Review",
Metal Finishing , 4 parts, October 1974, pp. 35-45; November
1974, pp. 50-54, December 1974, pp. 58-64; January 1975, pp.
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237. Spooner, R.C., "Sulfuric Acid Anodizing of Aluminum and Its
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238. Staebler, C.J. and Simpers, B.F., "Corrosion Resistant
Coatings with Low Water Pollution Potential", Presented at
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239. Stannett, T., and Hopgenberg, H. B., "Research on Advanced
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240. Strickland, G. R., "Electroplating Techniques and Equipment
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241. "Studies ori the Toxicity of_ Heavy Metals to Aquatic Animals
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242. Sussman, Donald L., "Chemical and Physical Factors in the
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481
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243. Sussman, Donald L., "Flocculation of_ Chrome Plating Wastes
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244. Swalheim, D.A. et al, "Cyanide Copper Plating", AES
Illustrated Lecture Series, American Electroplaters Society,
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245. Swalheim, D.A. et al, "Zinc and Cadmium Plating", AES
Illustrated Lecture Series, American Electroplaters Society,
Inc., Winter Park, FL.
246. Takano, 0., and Ono, K., "Acoustic Emission During Electro
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247. "The Condensed Chemical Dictionary", Ninth Edition, revised
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248. "The Electrochemical Removal of Trace Metals for Metal Wastes
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249. Titus, Joan, B., "Reverse Osmosis Bibliography; Abstract and
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250. Toledo, E., and Sprague, D. R., "Nickel Plating of_ Copper
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251. Udylite Corporation, "Bright Acid Sulfate Copper Plating",
AES Illustrated Lecture Series, American Electroplaters
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252. Ushakov, N. N., "Multilayered Printed-Circuit Assembly",
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253. Viklung, H. I., and Jha, A. D., "High Temperature
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482
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264. Wilson, G. C., "The Use of Tin When Alloyed With Nickel or
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483
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266. Winget, Oscar J., and Lindstrom Ronald E., "Separation of
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267. Wirth L., Jr., "Trouble with Layered Beds", Combustion,
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484
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SECTION XV
GLOSSARY
Abrasive Blasting
(Surface treatment and cleaning.) Using dry or wet abrasive particles
under air pressure for short durations of time to clean a metal
surface.
Acceleration
See Activation.
Acetic Acid
(Ethanoic acid, vinegar acid, methanecarboxylic acid) CH3COOH.
Glacial acetic acid is the pure compound (99.8% min.), as dis-
tinguished from the usual water solutions known as acetic acid.
Vinegar is a dilute acetic acid.
Acid Dip
Using any acid for the purpose of cleaning any material. Some methods
of acid cleaning are pickling and oxidizing.
Acid Dip
An acidic solution for activating the workpiece surface prior to
electroplating in an acidic solution, especially after the workpiece
has been processed in an alkaline solution.
Acidity
The quantitative capacity of aqueous solutions to react with hydroxyl
ions. It is measured by titration with a standard solution of a base
to a specified end point. Usually expressed as milligrams per liter
of calcium carbonate.
Act
The Federal Water Pollution Control Act Amendments of 1972.
Activitated Sludge Process
Removes organic matter from sewage by saturating it with air and
biological active sludge.
485
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Activation
The process of treating a substance by heat, radiation or the presence
of another substance so that the first mentioned substance will
undergo chemical or physical change more rapidly or completely.
Additive Circuitry
1. Full - Circuitry produced by the buildup of an electroless copper
pattern upon an unclad board.
2. Semi - Circuitry produced by the selective "quick" etch of an
electroless layer; this copper layer was previously deposited on
an unclad board.
Administrator
Means the Administrator of the United States Environmental Protection
Agency.
Adsorption
The adhesion in an extremely thin layer of molecules (as of gases,
solids or liquids) to the surface of solid bodies or liquids with
which they are in contact.
Aerobic
Living, active, or occurring only in the presence of oxygen.
Aerobic Biological Oxidation
Any waste treatment process utilizing organisms in the presence of air
or oxygen to reduce the pollution load or oxygen demand of organic
substances in water.
Agitation o_f Parts
The irregular movement given to parts when they have been submerged in
a plating or rinse solution.
Air Agitation
The agitation of a liquid medium through the use of air pressure
injected into the liquid.
•^
Air Flotation
See Flotation
486
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Air-Liquid Interface
The boundary layer between the air and the liquid in which mass
transfer is diffusion controlled.
Aldehydes Group
A group of various highly reactive compounds typified by acetaldehyde
and characterized by the group CHO.
Alkaline Cleaning
A process for cleaning steel where mineral and animal fats and oils
must be removed from the surface. Solutions at high temperatures
containing caustic soda, soda ash, alkaline silicates and alkaline
phosphates are commonly used.
Alkalinity
The capacity of water to neutralize acids, a property imparted by the
water's content of carbonates, bicarbonates, hydroxides, and
occasionally borates, silicates, and phosphates.
Amines
A class of organic compounds of nitrogen that may be considered as
derived from ammonia (NH3) by replacing one or more of the hydrogen
atoms by organic radicals, such as CH3 or C6H5., as in methylamine and
aniline. The former is a gas at ordinary temperature and pressure,
but other amines are liquids or solids. All amines are basic in
nature and usually combine readily with hydrochloric or other strong
acids to form salts.
Anaerobic Biological Treatment
Any waste treatment process utilizing anaerobic or facultative
organisms in the absence of air to reduce the organic matter in water.
Anaerobic Digestion
The process of allowing sludges to decompose naturally in heated tanks
without a supply of oxygen.
Anaerobic Waste Treatment
(Sludge Processing) Waste stabilization brought about through the
action of microorganisms in the absence of air or elemental oxygen.
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Anions
The negatively charged ions in solution, e.g., hydroxyl.
Anode
The positively charged electrode in an electrochemical process.
Anodizing
The production of a protective oxide film on aluminum or other light
metal by passing a high voltage electric current through a bath in
which the metal is suspended.
Annual Capital Recovery Cost
Allocates the initial investment and the interest to the total
operating cost. The capital recovery cost is equal to the initial
investment multiplied by the capital recovery factor.
Aquifer
Water bearing stratum.
Atmospheric Evaporation
Evaporation utilizing a tower filled with packing material. Air is
drawn in from the bottom of the tower and evaporates feed material
entering from the top. There is no recovery of the vapors.
Atomic Absorption
Quantitative chemical instrumentation used for the analysis of
elemental constituents.
Automatic Plating
1. Full - Plating in which the workpieces are automatically conveyed
through successive cleaning and plating tanks.
2. Semi - Plating in which the workpieces are conveyed automatically
through only one plating tank.
Barrel Finishing
Improving the surface finish of metal objects or parts by processing
them in rotating equipment along with abrasive particles which may be
suspended in a liquid.
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Barrel Plating
Electroplating of workpieces in barrels (bulk).
Basis Metal or_ Material
That substance of which the workpieces are made and that receives the
electroplate and the treatments in preparation for plating.
Batch Treatment
A waste treatment method where wastewater is collected over a period
of time and then treated prior to discharge.
Best Available Technology Economically Available (BAT)
Level of technology applicable to effluent limitations to be achieved
by July 1, 1983 for industrial discharges to surface waters as defined
by Section 301(b) (2) (A) of the Act.
Level of technology applicable to effluent limitations to be achieved
by July 1, 1977 for industrial discharages to surface waters as
defined by Section 301 (b) (1) (A) of the Act.
Bidentate
Pertaining to structure, having member connections in two positions.
Biodegradability
The susceptibility of a substance to decomposition by microorganisms;
specifically, the rate at which compounds may be chemically broken
down by bacteria and/or natural environmental factors.
Slowdown
The minimum discharge of recirculating water for the purpose of
discharging materials contained in the water, the further buildup of
which would cause concentration in amounts exceeding limits
established by best engineering practice.
Bromine Water
A nonmetallic halogen element; normally a deep red corrosive toxic
liquid used as an oxidizing agent.
Bright Dipping
Using acidic solutions to produce a bright surface on metal.
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Capital Recovery Factor
Capital Recovery Factor is defined as:
i + i/(a - 1) where i = interest rate
a = (1 + i) to the power n n = interest period in years
Carbon Bed Catalytic Destruction
A non-electrolytic process for the catalytic oxidation of cyanide
wastes using trickling filters filled with lowtemperature coke.
Captive Operation
A manufacturing operation carried out in a facility to support
subsequent manufacturing, fabrication, or assembly operations.
Carcinogen
Substance which causes cancerous growth.
Catalytic Bath
A bath containing a substance used to accelerate the rate of chemical
reaction.
Category
Also point source category. A segment of industry for which a set of
effluent limitations has been established.
Cathode
The negatively charge electrode in an electrochemical process.
Cations
The positively charged ions in a solution.
Caustic
Capable of destroying or eating away by chemical action. Applied to
strong bases and characterized by the presence of hydroxyl ions in
solution.
Caustic Soda
Sodium hydroxide, NaOH, whose solution in water is strongly alkaline.
490
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Cementation
The electrochemical reduction of metal ions by contact with a metal of
higher oxidation potential. It is usually used for the simultaneous
recovery of copper and reduction of hexavalent chromium with the aid
of scrap iron.
Centrifugation
(Sludge Dewatering) The removal of water in a sludge and water slurry
by introducing the water and sludge slurry into a centrifuge. The
sludge is driven outward with the water remaining near the center.
The water is withdrawn, and the dewatered sludge is usually
landfilled.
Centrifuge
A device having a rotating container in which centrifugal force
separates substances of differing densities.
Chelate Compound
A compound in which the metal is contained as an integral part of a
ring structure and is not readily ionized.
Chelating
A coordinate compound in which a central atom (usually a metal) is
joined by covalent bonds to two or more other molecules or ions
(called ligands) so that heterocyclic rings are formed with the
central (metal) atom as part of each ring. Thus, the compound is
suspending the metal in solution.
Chemical Brightening
Process utilizing an addition agent that leads to the formation of a
bright plate or that improves the brightness of the deposit.
Chemical Deposition
Process used to deposit a metal oxide on a substrate. The film is
formed by hydrolysis of a mixture of chlorides at the hot surface of
the substrate. Careful control of the water mixture insures that the
oxide is formed on the substrate surface.
Chemical Machining
Production of derived shapes and dimensions through selective or
overall removal of metal by controlled chemical attack or etching.
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Chemical Metal Coloring
The production of desired colors on metal surfaces by appropriate
chemical or electrochemical action.
Chemical Milling
Removing large amounts of stock by etching selected areas of complex
workpieces. This process entails cleaning, masking, etching, and
demasking.
Chemical Oxidation
(Including Cyanide) The addition of chemical agents to wastewater for
the purpose of oxidizing pollutant material.
Chemical Polishing
Use of a chemical solution to put a smooth finish on a metallic
surface.
Chemical Precipitation
A chemical process in which a chemical in solution reacts with another
chemical introduced to that solution to form a third substance which
is partially or mainly insoluble and, therefore, appears as a solid.
Chemical Recovery Systems
Chemical treatment to remove metals or other materials from wastewater
for later reuse.
Chemical Reduction
A chemical reaction in which one or more electrons are transferred to
the chemical being reduced from the chemical initiating the transfer
(reducing agent).
Chromate Conversion Coating
Formed by immersing metal in an aqueous acidified chromate solution
consisting substantially of chromic acid or water soluble salts of
chromic acid together with various catalysts or activators.
Chromatizing ;
To treat or impregnate with a chromate (salt of ester of chromic acid)
or dichromate, especially with potassium dichromate.
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Chrome-Pickle Process
Forming a corrosion-resistant oxide film on the surface of magnesium
base metals by immersion in a bath of an alkali bichromate.
Chromophores
Chemical grouping which, when present in an aromatic coumpound, gives
color to the compound by causing a displacement of, or appearance of,
absorbent bands in the visible spectrum.
Clarification
The composite wastewater treatment process consisting of flash mixing
of coagulants, pH adjusting chemicals, and/or polyelectrolytes),
flocculation, and sedimentation.
Clarifier
A unit which provides for settling and removal or solids from
wastewater.
Cleaning
See: Vapor Degreasing Solvent Cleaning Acid Cleaning Emulstion
Cleaning Alkaline Cleaning Salt Bath Descaling Pickling Passivate
Abrasive Blast Cleaning Ultrasonic Cleaning
Evaporation using vertical steam-heated tubes.
Closed-Loop Evaporation System
A system used for the recovery of chemicals and water from a chemical
finishing process. An evaporator concentrates flow from the rinse
water holding tank. The concentrated rinse solution is returned to
the bath, and distilled water is returned to the final rinse tank.
The system is designed for recovering 100 percent of chemicals
normally lost in dragout for reuse in the process.
Closed Loop Rinsing
The recirculation of
additional makeup water.
Coagulation
A chemical reaction in which polyvalent ions neutralize the
charges surrounding colloidal particles.
rinse water without the introduction of
repulsive
493
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Coating
See: Aluminum Coating, Hot Dip Coating, Ceramic Coating, Phosphate
Coating, Chrome Conversion Coating, Rust-Preventive Compounds,
Porcelain Enameling Common Metals
Copper, nickel, chromium, zinc, tin, lead, cadmium, iron, aluminum, or
any combination thereof.
Compatible Pollutants
Those pollutants which can be adequately treated in publiclyowned
treatment works without upsetting the treatment process.
Conductance
See Electrical Conductivity.
Conductive Surface
A surface that can transfer heat or electricity.
Conductivity Meter
An instrument which displays a quantitative indication of conductance.
Contact Water
See Process Wastewater.
Contamination
Intrusion of undesirable elements.
Continuous Treatment
Treatment of waste streams operating without interruption as opposed
to batch treatment: sometimes referred to as flowthrough treatment.
Contractor Removal
Disposal of oils, spent solutions, or sludge by a scavenger service.
Conversion Coating
A coating produced by chemical or electrochemical treatment of a
metallic surface that gives a superficial layer containing a compound
of the metal. For example, chromate coatings on zinc and cadmium,
oxide coatings on steel.
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Copper Flash
Quick preliminary deposition of copper for making surface acceptable
for subsequent plating.
Coprecipitation of_ Metals
Precipitation of a metal with another metal.
Cost of_ Capital
Capital recovery costs minus the depreciation.
Countercurrent Rinsing
Rinsing of parts in such a manner that the rinse water is removed from
tank to tank counter to the flow of parts being rinsed.
Crystalline Solid
A substance with an ordered structure, such as a crystal.
Crystallization
1. Process used to manufacture semiconductors in the electronics
industry.
2. A means of concentrating pollutants in wastewaters by
crystallizing out pure water.
Dead Rinse
A rinse step in which water is not replenished or discharged.
Decarboxylate
Dissociation of carboxylic acid group.
Deep Bed Filtration
The common removal of suspended solids from wastewater streams by
filtering through a relatively deep 0.3-0.9 m granular bed. The
porous bed formed by the granular media can be designed to remove
partically all suspended particles by physical-chemical effects.
Degradable
That which can be reduced, broken down or chemically separated.
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Denitrification (Biological)
The reduction of nitrates to nitrogen gas by bacteria.
Deoxidizing
The removal of an oxide film from an alloy such as aluminum oxide.
Depreciation
Decline in value of a capital asset caused either by use or by
obsolescence.
Descaling
The removal of scale and metallic oxides from the surface of a metal
by mechanical or chemical means. The former includes the use of
steam, scale-breakers and chipping tools, the latter method includes
pickling in acid solutions.
Desiccator
A container which contains a hydroscopic substance such as silica gel
to provide a dry atmosphere.
Dewatering
(Sludge Processing) Removing water from sludge.
Diazotization
A standard method of measuring the concentration of nitrite a
solution.
Dibasic Acid
An acid capable of donating two protons (hydrogen ions).
Discharge of_ Pollutant(s)
1. The addition of any pollutant to navigable waters from any point
source.
2. Any addition of any pollutant to the waters of the continguous
zone or the ocean from any point source, other than from a vessel
or other floating craft. The term "discharge" includes either the
discharge of a single pollutant or the discharge of multiple
pollutants.
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Distillation
Vaporization of a liquid followed by condensation of the vapor.
Distillation-Silver Nitrate Titration
A standard method of measuring the concentration of cyanides in a
solution.
Distillation-SPADNS
A standard method of measuring the concetration of fluoride in a
solution.
Dollar Base
A period in time in which all costs are related. Investment costs are
related by the Sewage Treatment Plant Construction Cost Index. Supply
costs are related by the "Industrial Commodities" Wholesale Price
Index.
Drag-in
Water or solution carried into another solution by the work and the
associated handling equipment.
Dragout
The solution that adheres to the objects removed from a bath, more
precisely defined as that solution which is carried past the edge of
the tank.
Drainage Phase
Period in which the excess plating solution adhering to the part or
workplace is allowed to drain off.
Drip Station
Empty tank over which parts are allowed to drain freely to decrease
end dragout.
Drip Time
The period during which a part is suspended over baths in order to
allow the excessive dragout to drain off.
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Drying Beds
Areas for dewatering of sludge by evaporation and seepage.
EDTA Titration
EDTA - ethylenediamine tetraacetic acid (or its salts). A standard
method of measuring the hardness of a solution.
Effluent
The quantities, rates, and concentrations of chemical, physical,
biological, and other constituents which are discharged from point
sources.
Effluent Limitation
Any restriction (including schedules of compliance) established by a
state or EPA on quantities, rates, and concentrations of chemical,
physical, biological, and other constituents which are discharged from
point sources into navigable waters, the waters of the contiguous
zone, or the ocean.
Electrical Conductivity
The property of a solution which allows an electric current to flow
when a potential difference is applied. It is the reciprocal0of the
resistance in ohms measured between opposite faces of a ceittimeter
cube of an aqueous solution at a specified temperature. It is
expressed as microohms per centimeter at temperature degrees Celsius.
Electrobrightening
A process of reversed electro-deposition which results in anodic metal
taking a high polish.
Electrode
Conducting material for passing electric current out of a solution by
taking up electrons or passing electric current into it by giving up
electrons from or to ions in the solution.
Electrodialysis
A treatment process that uses electrical current and an arrangement of
permeable membranes to separate soluble minerals from water. Often
used to desalinate salt or brackish water.
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Electroless Plating
Deposition of a metallic coating by a controlled chemical reduction
that is catalyzed by the metal or alloy being deposited.
Electrolysis
The chemical decomposition by an electric current of a substance in a
dissolved or molten state.
Electrolyte
A liquid, most often a solution, that will conduct an electric
current.
Electrolytic Cell
A unit apparatus in which electrochemical reactions are produced by
applying electrical energy or which supplies electrical energy as a
result of chemical reactions and which includes two or more electrodes
and one or more electrolytes contained in a suitable vessel.
Electrolytic Decomposition
An electrochemical treatment used for the oxidation of cyanides. The
method is practical and economical when applied to concentrated
solutions such as contaminated baths, cyanide dips, stripping
solutions, and concentrated rinses. Electrolysis is carried out at a
current density of 35 amp/sq. ft. at the anode and 70 amp/sq. ft. at
the cathode. Metal is deposited at the cathode and can be reclaimed.
Electrolytic Oxidation
A reaction by an electrolyte in which there is an increase in valence
resulting from a loss of electrons.
Electrolytic Reduction
A reaction in which there is a decrease in valence resulting from a
gain in electrons.
Electrometric Titration
A standard method of measuring the alkalinity of a solution.
Electroplating
The production of a thin coating of one metal on another by
electrodeposition.
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Electroplating Process
An electroplating process includes a succession of operations starting
with cleaning in alkaline solutions, acid dipping to neutralize or
acidify the wet surface of the parts, followed by electroplating,
rinsing to remove the processing solution from the workpiece, and
drying.
Electropolishing
Electrolytic corrosion process that increases the percentage of
specular reflectance from a metallic surface.
Emulsifying Agent
A material that increases the stability of a dispersion of one liquid
in another.
Emulsion Breaking
Decreasing the stability of dispersion of one liquid in another.
Emulsion Cleaning
Organic solvents dispersed in an aqueous medium with the aid of an
emulsifying agent. .
End-of-Pipe Treatment
The reduction and/or removal of pollutants by chemical treatment just
prior to actual discharge.
Environmental Protection Agency
The United States Environmental Protection Agency.
EPA
See Environmental Protection Agency.
Equalibrium Concentration
A state at. which the concentration of chemicals in a solution remain
in a constant proportion to one another.
Equalization
(Continuous Flow) Holding tank is used to give a continuous flow for a
system that has widely varying inflow rates.
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Ester
An organic compound corresponding in structure to a salt in inorganic
chemistry. Esters are considered as derived from the acids by the
exchange of the replaceable hydrogen of the latter for an organic
alkyl radical. Esters are not ionic compounds, but salts usually are.
Etchant
An agent used to remove material by means of a chemical action.
Etchback
The chemical process of removing glass fibers and epoxy between
neighboring conductor layers of a PC board for a given distance.
Etching
A process where material is removed by chemical action.
Evaporation Ponds
Liquid waste disposal areas that allow the liquid to vaporize to cool
discharge water temperatures or to thicken sludge.
Fehlinq's Solution
A reagent used as a test for sugars, aldehydes, etc. It consists of
two solutions, one of copper sulfate, the other of alkaline tartrate,
which are mixed just before use. Benedict's modification is a one
solution preparation. For details, see Book of Methods, Association
of Official Analytical Chemists.
Fermentation
A chemical change to break down biodegradable waste. The change is
induced by a living organism or enzyme, specifically bacteria or
microorganisms occurring in unicellular plants such as yeast, molds,
or fungi.
Ferrous
Relating to or containing iron.
Filtrate
Liquid after passing through a filter.
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Filtration
Removal of solid particles from liquid or particles from air or gas
stream by means of a permeable membrane.
Types: Gravity
Pressure
Microstraining
Ultrafiltration
Reverse Osmosis (Hyperfiltration)
Flameless Atomic Absorption
A method of measuring the mercury concentration of a solution.
Flash Evaporation
Evaporation using steam heated tubes with feed material under high
vacuum. Feed material "flashes off" when it enters the evaporation
chamber.
Flocculation
The process of separating suspended solids from wastewater by chemical
creation of clumps or floes.
Flotation
The process of removing finely divided particles from a liquid
suspension by attaching gas bubbles to the particles, increasing their
buoyancy, and thus concentrating them at the surface of the liquid
medium.
A type of rinse consisting of a fine spray.
Free Cyanide
1. True - the actual concentration of cyanide radical or equivalent
alkali cyanide not combined in complex ions with metals in
solutions.
2. Calculated - the concentration of cyanide or alkali cyanide
present in solution in excess of that calculated as necessary to
form a specified complex ion with a metal or metals present in
solution.
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3. Analytical - the free cyanide content of a solution as determined
by a specified analytical method.
Freezing/Crystallization
The solidification of a liquid into aggregations of regular geometric
forms (crystals) accomplished by subtraction of heat from the liquid.
This process can be used for removal of solids, oils, greases, and
heavy metals from industrial wastewater.
Gas Chromotagrophy
Chemical analytical instrumentation generally used for quantitative
organic analysis.
Gas Phase Separation
The process of separating volatile constituents from water by the
application of selective gas permeable membranes.
Glass Fiber Filtration
A standard method of measuring total suspended solids.
Glycine
Aminoacetic acid. The only amino acid lacking an asymmetric center.
NH2CH^COOH.
Good Housekeeping
(In-Plant Technology) Good and proper'maintenance minimizing spills
and upsets.
GPP
Gallons per day.
Grab Sample
A single sample of wastewater taken without regard to time or flow.
Gravimetric 1Q3-1Q5C
A standard method of measuring total solids in aqueous solutions.
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Gravimetric 550C
A standard method of measuring total volatile solids in aqueous
solutions.
Gravity Filtration
Settling of heavier and rising of. lighter constituents within a
solution.
Gravity Flotation
The separation of water and low density contaminants such as oil or
grease by reduction of the wastewater flow velocity and turbulence for
a sufficient time to permit separation due to difference in specific
gravity. The floated material is removed by some skimming technique.
Hardness
A characteristic of water, imparted by salts of calcium, magnesium and
iron such as bicarbonates, carbonates, sulfates, chlorides and
nitrates, that cause curdling of soap, deposition of scale, damage in
some industrial processes and sometimes objectionable taste. It may
be determined by a standard laboratory procedure or computed from the
amounts of calcium and magnesium as well as iron, aluminum, manganese,
barium, strontium, and zinc and is expressed as equivalent calcium
carbonate.
Heat Treatment
The addition of heat to a substance to effect a temperature increase
in that substance which results in its permanent physical or chemical
alteration.
Metals
Metals which can be precipitated by hydrogen sulfide in acid solution,
e.q., lead, silver, gold, mercury, bismuth, copper, neckel, iron,
chromium, zinc, cadmium, and tin.
Hexadentate
Pertaining to structure, having member connections in six positions.
Hydrofluoric Acid
Hydrogen fluoride in aqueous solution.
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Hydrogen Embrittlemen t
Embrittlement of a metal or alloy caused by absorption of hydrogen
during a pickling, cleaning, or plating process,
Hydrophlllc
A surface having a strong affinity for water or being readily
wettable.
HydrophQbic
A surface which is non-wettable or not readily wettable.
Hydrostatic Pressure
The force per unit area measured in terms of the height of a column of
water under the influence of gravity.
Immersed Area
Total area wetted by the solution or plated area plus masked area.
Immersion Plate
A metallic deposit produced by a displacement reaction in which one
metaf displaces another from solution, for example:
Fe + Cu(+2) = Cu + Fe(+2)
Incineration
(Sludge Disposal) The combustion (by burning) of organic matter in
wastewater sludge solids after water evaporation from the solids.
Incompatible Pollutants
Those pollutants which would cause harm to, adversely affect the
performance of, or be inadequately treated in publicly-owned treatment
works.
Independent Operation
Job shop or contract shop in which electroplating is done on
workpieces owned by the customer.
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Industrial User
Any industry that introduces pollutants into public sewer systems and
whose wastes are treated by a publicly-owned treatment facility.
Industrial Wastes
The liquid wastes from industrial processes, as distinct from domestic
or sanitary wastes.
Inhibition
The slowing down or stoppage of chemical or biological reactions by
certain compounds or ions.
In-Process Control Technology
The regulation and the conservation of chemicals and rinse water
throughout the operations as opposed to end-of-pipe treatment.
Inspection
A checking or testing of something against standards or specification.
Intake Water
Gross water minus reused water.
Integrated Chemical Treatment
A waste treatment method in which a chemical rinse tank is inserted in
the plating line between the process tank and the water rinse tank.
The chemical rinse solution is continuously circulated through the
tank and removes the dragout while reacting chemicals with it.
Integrated Circuit (1C)
1. A combination of interconnected circuit elements inseparably
associated on or within a continuous substrate.
2. Any electronic device in which both active and passive elements
are contained in a single package. Methods of making an
integrated circuit are by masking process, screening and chemical
deposition.
Investment Costs
The capital expenditures required to bring the treatment or control
technology into operation.
506
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Ion Exchange
A reversible chemical reaction between a solid (ion exchanger) and a
fluid (usually a water solution) by means of which ions may be
interchanged from one substance to another. The superficial physical
structure of the solid is not affected.
Ion Exchange Resins
Synthetic resins containing active groups (usually sulfonic,
carboxylic, phenol, or substituted amino groups) that give the resin
the property of combining with or exchanging ions between the resin
and a solution.
Ion-Flotation Technique
Treatment for electroplating rinse waters (containing chromium and
cyanide) in which ions are separated from solutions by flotation.
Iridite Dip Process
Dipping process for zinc or zinc-coated objects that deposits
protective film that is a chromium gel, chromium oxide, or hydrated
chromium oxide.
Isolation
Segregation of a waste for separate treatment and/or disposal.
Jackson Units
The standard unit for measuring turbidity.
Kinematic Viscosity
The viscosity of a fluid divided by its density. The C.G.S. unit is
the stoke (cm2/sec).
Lagoon
A man-made pond or lake for holding wastewater for the removal of
suspended solids. Lagoons are also used as retention ponds after
chemical clarification to polish the effluent and to safeguard against
upsets in the clarifier: for stabilization of organic matter by
biological oxidation; for storage of sludge; and for cooling of water.
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Laminate
1. A composite metal, usually in form of sheet or bar, composed of
two or more metal layers so bonded that the composite metal forms
a structural member.
2. To form a metallic product of two or more bonded layers.
Landfill
Disposal of inert, insoluble waste solids by dumping at an approved
site and covering the earth.
Leach Field
An area of ground to which wastewater is discharged. Not considered
an acceptable treatment method for industrial wastes.
Leaching
Dissolving out by the action of a percolating liquid, such as water,
seeping through a sanitary landfill.
Level !_
BPT technology or effluent limitations.
Level I_I.
BAT technology or effluent limitations.
Level III
New Source Performance Standards.
Ligands
The molecules attached to the central atom by coordinate covalent
bonds.
Liquid/Liquid Extraction
A process of extracting or removing contaminant(s) from a liquid by
mixing contaminated liquid with another liquid which is immiscible and
which has a higher affinity for the contaminating substance(s).
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Manual Plat ing
Plating in which the workpieces are conveyed manually through
successive cleaning and plating tanks.
Masking
The application of a substance to a surface for the prevention of
plating to said area.
Mechanical Agitation
The agitation of a liquid medium through the use of mechanical such as
impellers or paddles.
Membrane
A thin sheet of synthetic polymer through the apertures of which small
molecules can pass, while larger ones are retained.
Membrane Filtration
Filtration at pressures ranging from 50 to 100 psig with the use of
membranes or thin films. The membranes have accurately controlled
pore sites and typically low flux rates.
Mercuric Nitrate Titration
A standard method of measuring chloride.
Metal Ion
An atom or radical that has lost or gained one or more electrons and
has thus acquired an electric charge. Positively charged ions are
cations, and those having a negative charge are anions. An ion often
has entirely different properties from the element (atom) from which
it was formed.
Methylene Blue Method
A standard method of measuring surfactants in aqueous solutions.
Microstraininq
A process for removing solids from water, which consists of passing
the water stream through a microscreen with the solids being retained
on the screen.
509
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Molecule
Chemical units composed of one or more atoms.
Monitoring
The measurement, sometimes continuous, of water quality.
Multi-Effect Evaporator
A series of evaporations and condensations with the individual units
set up in series and the latent heat of vaporization from one unit
used to supply energy for the next.
National Pollutant Discharge Elimination System (NPDES)
The federal mechanism for regulating point source discharge by means
of permits.
Navigable Waters
All navigable waters of the United States; tributaries of navigable
waters of the United States; interstate waters, intrastate lakes,
rivers and streams which are utilized for recreational or other
purposes.
Neutralization
Chemical addition of either acid or base to a solution such that the
pH is adjusted to 7.
New Source
Any building, structure, facility, or installation from which there is
or may be the discharge of pollutants, the construction of which is
commenced after the publication of proposed regulations prescribing a
standard of performance under Section 306 of the Act which will be
applicable to such source if such standard is thereafter promulgated
in accordance with Section 306 of the Act.
New Source Performance Standards (NSPS)
Performance standards for the industry and applicable new sources as
defined by Section 306 of the act.
Nitrification (Biological)
The oxidation of nitrogenous matter into nitrates by bacteria.
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Noncontact Cooling Water
Water used for cooling which does not come into direct contact with
any raw material, intermediate product, waste product, or finished
product.
Nonferrous
No iron content.
Non-Water Quality Environmental Impact
The ecological impact as a result of solid, air, or thermal pollution
due to the application of various wastewater technoligies to achieve
the effluent guidelines limitations. Associated with the non-water
quality aspect is the energy impact of wastewater treatment.
NPDES
See National Pollutant Discharge Elimination System.
Operation and Maintenance Costs
The cost of running the wastewater treatment equipment. This includes
labor costs, material and supply costs, and energy and power costs.
Organic Compound
Any substance that contains the element carbon, with the exception of
carbon dioxide and various carbonates.
Oxidants
Those substances which aid in the formation of oxides.
Oxidizable Cyanide
Cyanide amenable to oxidation by chlorine.
Oxidizing
Combining the material concerned with oxygen.
Parameter
A characteristic element of constant factor.
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Pas si vat ion
The changing of the chemically active surface of a metal to a much
less reactive state by means of an acid dip,
A unit for measuring hydrogen ion concentrations. A ph of 7 indicates
a "neutral" water or solution. At pH lower than 7, a solution is
acidic. At pH higher than 7, a solution is alkaline.
p_H Buffer
A substance used to stabilize the acidity or alkalinity in a solution.
Phenols
A group of aromatic compounds having the hydroxyl group directly
attached to the benzene ring. Phenols can be a contaminant in a waste
stream from a manufacturing process.
Phosphate Coating
Process of forming a conversion coating on iron or steel by immersing
in a hot solution of manganese, iron or zince phosphate,
Phosphates
Salts or esters of phosphoric acid. Often used in phosphating a metal
part prior to painting or porcelainizing.
Photoresists
Thin coatings produced from organic solutions which when exposed to
light of the proper wave length are chemically changed in their
solubility to certain solvents (developers). This substance is placed
over a surface which is to be protected during processing such as in
the etching of printed circuit boards.
P i ck 1 e
An acid solution used to remove oxides or other compounds related to
the basis metal from the surface of a metal by chemical or
electrochemical action.
Pickling
The process of removing scale, oxide, or foreign matter from the
surface of metal by immersing it in a bath containing a suitable
512
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chemical reagent which will attack the oxide or scale but will not
appreciably act upon the metal during the period of pickling.
Frequently it is necessary to immerse the metals in a detergent
solution or to degrease in a vapor before pickling.
Plant Effluent or Discharge After Treatment
The wastewater discharged from the industrial plant. In this
definition, any waste treatment device (pond, trickling filter, etc.)
is considered part of the industrial plant.
Plated Area
Surface upon which an adherent layer of metal is deposited.
Plating
Forming an adherent layer of metal upon an object.
Point Source
Any discernible, confined, and discrete conveyance including, but not
limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete
fissure, container, rolling stock, concentrated animal feeding
operation, or vessel or other floating craft from which pollutants are
or may be discharged.
Point Source Category
See Category.
Pollutant
Dredged spoil, solid waste, incinerator residue, sewage, garbage,
sewage sludge, munitions, chemical wastes, biological materials,
radioactive materials, heat, wrecked or discarded equipment, rock,
sand, cellar dirt and industrial, municipal and agricultural waste
discharged into water. It does not mean (1) sewage from vessels or
(2) water, gas, or other material which is injected into a well to
facilitate production of oil or gas, or water derived in association
with oil or gas production and disposed of in a well, if the well,
used either to facilitate production or for disposal purposes, is
approved by authority of the State in which the well is located, and
if such State determines that such injection or disposal will not
result in degradation of ground or surface water resources.
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Pollutant Parameters
Those constituents of wastewater determined to be detrimental and,
therefore, requiring control.
Pollution
The man-made or man-induced alteration of the chemical, physical,
biological, and radiological integrity of water.
Polyelectrolyte
A high polymer substance, either natural or synthetic, containing
ionic constituents; they may be either cationic or anionic.
Precious Metals
Gold, silver, iridium, palladium, platinum, rhodium, ruthenium, or
combination thereof.
Precipitate
The discrete particles of material rejected from a liquid solution.
Precipitation Hardening Metals
Certain metal compositions which respond to precipitation hardening or
aging treatment.
Pressure Filtration
The process of solid/liquid phase separation effected by passing the
more permeable liquid phase through a mesh which is impenetrable to
the solid phase.
Pretreatment
Treatment of wastewaters from sources before introduction into
municipal treatment works.
Primary Settling
The first treatment for the removal of settleable solids from
wastewater which is passed through a treatment works.
Primary Treatment
-------
The first stage in wastewater treatment in which floating or
settleable solids are mechanically removed by screening and
sedimentation.
Printed Circuit Boards
A circuit in which the interconnecting wires have been replaced by
conductive strips printed, etched, etc., onto an insulating board.
Methods of fabrication include etched circuit, electroplating, and
stamping.
Printing
A process whereby a design or pattern in ink or types of pigments are
impressed onto the surface of a part.
Process Modification
(In-Plant Technology) Reduction of water pollution by basic changes in
a manufacturing process.
Process Wastewater
Any water which, during manufacturing or processing, comes into direct
contact with or results from the production or use of any raw
material, intermediate product, finished product, byproduct, or waste
product.
Pyrolysis
(Sludge Removal) Decomposition of materials by the application of heat
in an oxygen-deficient atmosphere.
Pyrazolone-Colorimetric
A standard method of measuring cyanides in aqueous solutions.
Racking
The placement of parts on an apparatus for the purpose of plating.
Rack Plating
Electroplating of workpieces on racks.
Receiving Waters
Rivers, lakes, oceans, or other water courses that receive treated or
untreated wastewaters.
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Recirculating £»/ray
A spray rinse in which the drainage is pumped up to the spray and is
continually recirculated.
Recycle Lagoon
A pond that collects treated wastewater, most of which is recycled as
process water.
Reducing
Destroying a wastewater constituent by means of a reducing agent such
as sulfur dioxide.
Reduction
A reaction in which there is a decrease in valance resulting from a
gain in electrons.
Redox
A term used to abbreviate a reduction-oxidation reaction.
Residual Chlorine
The amount of chlorine left in the treated water that is available to
oxidize contaminants.
Reverse Osmosis
The application of pressure to the surface of solution, thus forcing
pure water to pass from the solution through a semipermeable membrane
that is too dense to permit passage of the solute, leaving behind the
dissolved solids (concentrate).
Rinse
Water for removal of dragout by dipping, spraying, fogging, etc.
Rochelle Salt
Sodium potassium tartrate: KNaC4H406>. 4H20.
Running Rinse
A rinse tank in which water continually flows in and out.
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Rust Prevention Compounds
Coatings used to protect iron and steel surfaces, against corrosive
environments during fabrication, storage, or use.
Salt
1. The compound formed when the hydrogen of an acid is replaced by a
metal or its equivalent (e.g., and NH4 radical). Example:
HCL + NaOH = NaCL + H20
This is typical of the general rule that the reaction of an acid and a
base yields a salt and water; Most salts ionize in water solutions.
2. Common salt, sodium chloride, occurs widely in nature, both as
deposits left by ancient seas and in the ocean, where its average
concentration is about 3%.
Salt Bath Descaling
Removing the layer of oxides formed on some metals at elevated
temperatures in a salt solution.
See: Reducing Oxidizing Electrolytic
Sand Bed Drying
The process of reducing the water content in a wet substance by
transferring that substance to the surface of a sand bed and allowing
the processes of drainage through the sand and evaporation to effect
the required water separation.
Sand Filtration
A process of filtering wastewater through sand. The wastewater is
trickled over the bed of sand where air and bacteria decompose the
wastes. The clean water flows out through drains in the bottom of the
bed. The sludge accumulating at the surface must be removed from the
bed periodically.
Sanitary Water
The supply of water used for sewage transport and the continuation of
such effluents to disposal.
Sanitary Sewer
Pipes and conveyances for sewage transport.
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Save Rinse
See Dead Rinse.
Scale
Oxide and metallic residues.
Screening
Selectively applying a resist material to a surface to be plated.
Secondary Treatment
The second step in most sanitary waste treatment plants in which
bacteria consume the organic portions of the waste. This removal is
accomplished by trickling filters, an activated sludge unit, or other
processes.
Sedimentation
The process of subsidence and deposition of suspended matter carried
by water, wastewater, or other liquids by gravity. It is usually
accomplished by reducing the velocity of the liquid below the point at
which it can transport the suspended material. Also called settling.
Sensitization
The process in which a substance other than the catalyst is present to
facilitate the start of a catalytic reaction.
Sequestering Agent
An agent (usually a chemical compound) that "sequesters" or holds a
substance in suspension.
A series of tanks which can be individually heated or level
controlled.
Settleable Solids
That matter in wastewater which will not stay in suspension during a
preselected settling period, such as one hour, but either settles to
the bottom or floats to the top.
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Settling Ponds
A large shallow body of water into which industrial wastewaters are
discharged. Suspended solids settle from the wastewaters due to the
large retention time of water in the pond.
Skimming
The process of removing floating solid or liquid wastes from a
wastewater stream by means of a special tank and skimming mechanism
prior to treatment of the water.
Slaking
The process of reacting lime with water to yield a hydrated product.
Sludge
Residue produced in a waste treatment process.
Slug Dose
A discharge in which the concentration of a material is significantly
higher than the average concentration. This discharge exists only
over a short period of time before the concentration returns to its
average value.
Slurry
A watery suspension of solid materials.
Solder Electroplate
60/40 tin/lead alloy used as etching resist.
Solid-Liquid Interface
The boundary layer between the solid and the liquid in which mass
transfer is diffusion controlled.
Solids
(Plant Waste) Residue material that has been completely dewatered.
Solute
A dissolved substance.
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Solution
Homogeneous mixture of two or more components such as a liquid or a
solid in a liquid.
Solvent
A liquid used to dissolve materials. In dilute solutions the
component present in large excess is called the solvent, and the
dissolved substance is called the solute.
Solvent Cleaning
Removal of oxides, soils, oils, fats, waxes, greases, etc. by
solvents.
Specific Conductance
The property of a solution which allows an electric current to flow
when a potential difference is applied.
Spectrophotometry
A method of analyzing a wastewater sample by means of the spectra
emitted by its constituents under exposure to light.
Rinse
A process which utilizes the expulsion of water through a nozzle as a
means of rinsing.
Standard of. Performance
Any restriction established by the Administrator pursuant to Section
306 of the Act on quantities, rates and concentrations of chemical,
physical, biological, and other constituents which are or may be
discharged from new sources into navigable waters, the waters of the
contiguous zone or the ocean.
Stannous Salt
Tin based compound used in the acceleration process. Usually stannous
chloride.
Still Rinse
See Dead Rinse.
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Strike
A thin coating of metal (usually less than 0.0001 inch in thickness)
to be followed by other coatings 1
Stripping
The removal of coatings from metal.
Subcateqory gjr Subpart
A segment of a point source category for which specific effluent
limitations have been established.
Submerged Tube Evaporation
Evaporation of feed material using horizontal steam-heat tubes
submerged in solution. Vapors are driven off and condensed while
concentrated solution is bled off.
Subtractive Circuitry
Circuitry produced by the selective etching of a previously deposited
copper layer.
Surface Tension
A measure of the force opposing the spread of a thin film of liquid,
Surface Waters
Any visible stream or body of water.
Surfactants
Surface active chemicals which tend to lower the surface tension
between liquids, such as between acid and water.
A sudden rise to an excessive value, such as flow, pressure,
temperature.
Testing
An examination, observation, or evaluation to determine that article
under inspection is in accordance with required specifications.
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Thickener
A device or system wherein the solid contents of slurries or
suspensions are increased by gravity settling and mechanical
separation of the phases, or by flotation and mechanical separation of
the phases.
Thickening
(Sludge Dewatering) Thickening or concentration is the process of
removing water form sludge after the initial separation of the sludge
from wastewater. The basic objective of thickening is to reduce the
volume of liquid sludge to be handled in subsequent sludge disposal
processes.
Threshold Toxicity
Limit upon which a substance becomes toxic or poisonous to a
particular organism.
Through Hole Plating
The plating of the inner surfaces of holes in a PC board.
Titration
1. A method of measuring acidity or alkalinity.
2. The determination of a constituent in a known volume of solution
by the measured addition of a solution of known
strength for completion of the reaction as signaled by observation of
an end point.
Total Chromium
The sum of chromium in all valences.
Total Cyanide
The total content of cyanide expressed as the radical CNor alkali
cyanide whether present as simple or complex ions. The sum of both
the combined and free cyanide content of a plating solution. In
analytical terminology, total cyanide is the sum of cyanide amenable
to oxidation by chlorine and that which is not according to standard
analytical methods.
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Trickling Filters
A filter consisting of an artificial bed of coarse material, such as
broken stone, clinkers, slate, slats, or brush over which an effluent
is distributed and applied in drops, films, or spray from troughs,
drippers, moving distributors, or fixed nozzles and through which it
trickles to the underdrains giving opportunity for the formation of
zoological slimes which clarify and oxidize the effluent.
Tridentate
Pertaining to structure, having member connections in three positions.
Turbidimeter
An instrument for measurement of turbidity in which a standard
suspension is usually used for reference.
Turbidity
1. A condition in water or wastewater caused by the presence of
suspended matter resulting in the scattering and absorption of light
rays.
2. A measure of fine suspended matter in liquids.
3. An analytical quantity usually reported in arbitrary turbidity
units determined by measurements of light diffraction.
Ultrafiltration
A process using semipermeable polymeric membranes to separate
molecular or colloidal materials dissolved or suspended in a liquid
phase when the liquid is under pressure.
Ultrasonic Agitation
The agitation of a liquid medium through the use of ultrasonic waves.
Ultrasonic Cleaning
Immersion cleaning aided by ultrasonic waves which cause
microagitation.
Vacuum Filtration
A sludge dewatering process in which sludge passes over a drum with a
filter medium, and a vacuum is applied to the inside of the drum
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compartments. As the drum rotates, sludge accumulate? on the filter
surface, and the vacuum removes water.
Vapor Degreasing
Removal of soil and grease by a boiling liquid solvent, the vapor
being considerably heavier than air. At least one constituent of the
soil must be soluble in the solvent.
Vapor Blasting
A method of roughing plastic surfaces in preparation for plating.
Viscosity
The resistance offered by a real fluid to a shear stress.
Volatile Substances
Material that is readily vaporizable at a relatively low temperature.
Volumetric Method
A standard method of measuring settleable solids in an aqueous
solution.
Waste Discharged
The amount (usually expressed as weight) of some residual substance
which is suspended or dissolved in the plant effluent.
Wastewater Constituents
Those materials which are carried by or dissolved in a water stream
for disposal.
Wastewater
Any water that has been released from the purpose for which is was
intended to be used.
Water Recirculation or Recycling
The volume of water already used for some purpose in the plant which
is returned with or without treatment to be used again in the same or
another process.
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Water Use
The total volume of water applied to various uses in the plant. It is
the sum of water recirculation and water withdrawal.
Water Withdrawal or_ Intake
The volume of fresh water removed from a surface or underground water
source by plant facilities or obtained from some source external to
the plant.
Wet Aijr Oxidation
(Sludge Disposal) This process oxidizes the sludge in the liquid phase
without mechanical dewatering. High-pressure high-temperature air is
brought into contact with the waste material in a pressurized reactor.
Oxidation occurs at 300 to 500 degrees F and from several hundred to
3,000 psig.
Wholesale Price Index
A measure of the fluctuation of the wholesale price of goods and
services with time. The base period to which all wholesale-*prices are
related is 1967 (index = 100).
Withdrawal Phase
Period for the part or workpiece from an immersion tank.
Workpiece
The item to be processed.
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TABLE 15-1
METRIC TABLE
CONVERSION TABLE
MULTIPLY (ENGLISH UNITS) by TO OBTAIN (METRIC UNITS)
ENGLISH UNIT ABBREVIATION CONVERSION ABBREVIATION METRIC UNIT
acre ac
acre - feet ac ft
British Thermal
Unit BTU
British Thermal
Unit/pound BTU/lb
cubic feet/minute cfm
cubic feet/second cfs
cubic feet cu ft
cubic feet cu ft
cubic Inches cu 1n
degree Fahrenheit °F
feet ft
gallon gal
gallon/minute gpm
horsepower hp
Inches 1n
Inches of mercury 1n Hg
pounds Ib
million gallons/day mgd
mile ml
pound/square
Inch (gauge) pslg
square feet sq ft
square Inches sq 1n
ton (short) ton
yard yd
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
Q.555(»F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
ha
cu m
kg cal
kg cal/kg
cu m/m1n
cu m/min
cu m
1
cu cm
•C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 pslg +1)* atm
0.0929 sq m
6.452 sq cm
0.907 kkg
0.9144 m
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
11ters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric ton (1000 kilograms)
meter
* Actual conversion, not a multiplier
GOVERNMENT PRINTING OFFICE: !980-3 I t• I 3!/ 1 65
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