EPA 440/1-78/085
DEVELOPMENT DOCUMENT FOR
PROPOSED EXISTING SOURCE
PRETREATMENT STANDARDS
FOR THE
ELECTROPLATING
POINT SOURCE CATEGORY
\
II ED STATES ENVIRONMENTAL PROTECTION AGENCY
FEBRUARY 1978
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DEVELOPMENT DOCUMENT
for
PROPOSED EXISTING SOURCE PRETREATMENT STANDARDS
for the
ELECTROPLATING
POINT SOURCE CATEGORY
Douglas M. Costle
Administrator
Thomas C. Jorling
Assistant Administrator for
Water and Hazardous Materials
Swep Davis
Deputy Assistant Administrator
for Water Planning and Standards
Robert B. Schaffer
Director, Effluent Guidelines Division
Devereaux Barnes, P.E.
Project Officer
February 1978
Effluent Guidelines Division
Office of Water and Hazardous Materials
U.S. Environmental Protection Agency
Washington, D.C. 20160
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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 Federal Water Pollution
Control Act, as amended (33 U. S.C. 1251, 1317 (b), 86 Stat.
816 et. seg) .
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.
111
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CONTENTS
Number Title
I. Conclusions 1
II. Recommendations 3
III. Introduction 5
Authority 5
Approach to Pretreatment Standards 5
Description of the Plating Segment 21
Description of the Metal Finishing Segment 41
Description of the Printed Board Segment 52
IV. Industry Categorization 77
Introduction 77
Categorization Basis 77
Effluent Limitation Base 83
V. Waste Characterization 95
Introduction 95
Characteristics of Wastes from the Plating Segment 95
Characteristics of Wastes from the Metal Finishing
Segment 107
Characteristics of Wastes from Printed Board
Manufacture Segment 113
VI. Selection of Pollutant Parameters 123
Introduction 123
Pollutant Parameters 123
VII. Control and Treatment Technology 147
Introduction 147
In-Plant Technology 150
Individual Treatment Technologies 171
End-of-Pipe Technology for Plating and Metal
Finishing 284
In-Line Technology for Plating and Metal
Finishing 287
End-of-Pipe Technology for Printed Board Manufacture 292
In-Line Technology for Printed Board Manufacture 299
VIII. Cost of Waste Water Control and Treatment 305
Introduction 305
Cost Estimates 305
IX. Best Practicable Control Technology Currently Available,
Guidelines and Limitations 365
X. Best Available Technology Economically Achievable,
Guidelines and Limitations 367
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XI. New Source Performance Standards 369
XII. Pretreatment 371
Introduction 371
Pass-Through, Interference and sludge Disposal
Considerations 371
Technical Approach 383
Treatment of Cyanide 384
Treatment of Hexavalent Chromium 399
Metals Removal Using Sedimentation 412
Metals Treatment Using Filtration 439
Metals Removal for Electroless Plating and Printed
Circuit Board Manufacturing 448
Surrogate Parameter Analysis 456
XIII. Acknowledgements 465
XIV. References 467
XV. Glossary 489
VI
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TABLES
Number Title
2-1 Recommended Pretreatment Standards 4
3-1 Data Source Summary 7
3-2 Characteristics of the Data Base 20
3-3 Common Chelating Agents - Marketers and
Manufacturers 39
3-4 Comparison of Basic Process Steps 54
4-1 Metal Finishing Subcategorization 88
4-2 Effect of Masking on Dragout 89
4-3 Effect of Holes on Dragout 89
4-4 Common and Precious Metals and Electroless
Plating Operations 90
4-5 Metal Finishing Operations 91
4-6 Operations in the Manufacture of Printed Boards 93
5-1 Analysis Methods 96
5-2 Chelate Analysis Methods 97
5-3 Composition of Raw Waste Streams from Common
Metals Plating 1C4
5-4 Composition of Raw Waste Streams from
Precious Metals Plating 105
5-5 Composition of Raw Waste Streams from
Electroless Plating 106
5-6 Chelating Agents in Electroless Plating 106
5-7 Composition of Raw Waste Streams from Anodizing 110
5-8 Composition of Raw Waste Streams from Coatings 111
5-9 Composition of Raw Waste Streams from
Chemical Milling and Etching 112
5-10 Characteristics of Raw Waste Streams
in the Printed Board Industry 122
6-1 Pollutant Parameter Occurrence 124
6-2 Parameters Not Selected for Regulation 125
7-1 Comparison of Wastewater at Plant ID 23061
Before and After Pumping of Settling Tank 149
7-2 Usage of Various Rinse Techniques by Companies 149
7-3 Electroplating Plants that Currently Employ
Chemical Reduction 176
7-4 Electroplating Plants that Currently Employ
pH Adjustment 179
7-5 Plants Currently using A System Including
Clarification 186
7-6 Electroplating Plants that Currently Employ
Oxidation by Chlorine 196
7-7 Relative Performance and Application
Characteristics of Solid/Liquid
Separation Equipment 205
7-8 Application of Ion Exchange to Electroplating
for Used Rinse Water Processing 208
7-9 Application of Evaporation to the Electroplating
Point Source Category 220
7-10 Electroplating Plants that Employ Evaporation 222
vii
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7-11 Application of Reverse Osmosis in the Electro-
plating Point Source Category 222
7-12 Typical Membrane Performance 229
7-13 Electroplating Plants that Currently Employ
Vacuum Filtration 265
7-14 Removal of Metals by Lime Precipitation -
Activated Carbon Combination 277
7-15 Removal of Metals by Ferric Chloride -
Activated Carbon Combination 278
7-16 Treatment of Waste Waters Containing Metals 281
7-17 Removal of Metal Cations from Water with
Insoluble Starch Xanthate 283
7-18 Removal of Metals from Dilute Solution
with Insoluble Starch Xanthate 283
7-19 Treatment System Elements for Various
Manufacturing Operations 286
7-20 In-Line Technology Applicability 289
7-21 Pollutant Discharge at an Example Plant 293
8-1 Index to Technology Cost Tables 306
8-2 Countercurrent Rinse (for other than
Recovery of Evaporative Plating Loss) 310
8-3 Countercurrent Rinse Used for Recovery
of Evaporative Plating Loss 311
8-4 Spray Rinse Used for Recovery of
Evaporative Plating Loss 313
8-5 Still Rinse Used for Recovery of
Evaporative Plating Loss 315
8-6 Clarification-Continuous Treatment
Settling Tank 317
8-7 Clarification-Batch Treatment Settling Tank 317
8-8 Chromium Reduction - Continuous Treatment 319
8-9 Chromium Reduction - Batch Treatment 319
8-10 Cyanide Oxidation - Continuous Treatment 321
8-11 Cyanide Oxidation - Batch Treatment 321
8-12 pH Adjustment 324
8-13 Diatomaceous Earth Filtration 324
8-14 Submerged Tube Evaporation - Single Effect 325
8-15 Submerged Tube Evaporation - Double Effect 325
8-16 Climbing Film Evaporation 327
8-17 Atmospheric Evaporation 327
8-18 Flash Evaporation 329
8-19 Ultrafiltration 329
8-20 Membrane Filtration 333
8-21 Ion Exchange - In-Plant Regeneration 333
8-22 Ion Exchange - Service Regeneration 335
8-23 Cyclic Ion Exchange 335
8-24 Reverse Osmosis 336
8-25 End-of-Pipe Treatment Without Chelated Wastes 341
8-26 End-of-Pipe Treatment With Chelated Wastes 342
8-27 Base Plant - Running Rinses 346
8-28 3-Stage Countercurrent Rinses 347
8-29 Plating Solution Recovery 348
8-30 Plating Solution Recovery with Base Plant
End-of-Pipe Treatment 351
Vlll
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8-31 Electroless Plating on Metals and Plastics
In-Line 352
8-32 Printed Board Manufacture In-Line 352
8-33 Cost Program Pollutant Parameters 355
8-34 Wastewater Sampling Frequency 359
8-35 Nonwater Quality Aspects of Wastewater Treatment 362
8-36 Nonwater Quality Aspects of Sludge and
Solids Handling 363
12-1 CN(A) Concentrations Observed in Effluent from
Plants with Cyanide Oxidation in Waste
Treatment System 386
12-2 CN(T) Concentrations Observed in Effluent from
Certain Plants with Cyanide Oxidation
in Waste Treatment System 388
12-3 Mean and Standard Deviation of the Logarithm
of Daily Observations of CN(A) Concentration 395
12-4 Mean and Standard Deviation of the Logarithm
of Daily Observations of CN(T) Concentration 396
12-5 Cr(6) Concentrations Observed in Effluent from
Plants with Cr Plating or Chromating
Operations 400
12-6 Mean and Standard Deviation of the Logarithm of
Daily Observations of Cr(6) Concentrations 406
12-7 Plants Used for Small Plater Amenable
Cyanide Analysis 398
12-8 Fit of Average Metal Species Discharged from 25
Plants with Clarifier Systems (Model 1) 414
12-9 Fit of Average Metal Species Discharged from 25
Plants with Clarifier Systems (Model 2) 415
12-10 Metal Concentrations Predicted by Equation (2)
and by "Best Fit" Equation at Average
Values of Independent Variables 416
12-11 Distribution of Fraction Metal in Raw Waste Load
Total Metals; and Predicted Average Metal
Concentration in Discharge for 47 Metal
Finishing Plants 429
12-12 Dependence of Xme on Number Metals Used
in Plating and Finishing 430
12-13 Predicted Average Metal Concentration in
Discharge from Plants with 25 mg/1 TSS 432
12-14 Estimated Daily C99/Average from Plant
Historical Data 437
12-15 TSS in Discharge from 5 Plants Using Filtration
for Primary solids Separation 440
12-16 Average Metal Concentrations in Discharge from 5
Plants Using Filtration for Primary Solids
Separation 442
12-17 TSS in Discharge from 5 Plants Using Polishing
Filter After Clarifiers 444
12-18 Average Metal Concentrations in Discharge from 5
Plants Using Polishing Filter After Clarifier 447
12-19 Metal Removal Efficiency of Treatment System of
10 Plants Depositing Cu by Electroless Plating '450
12-20 Metal Removal Efficiency of Treatment System of
IX
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7 Plants Depositing Ni by Electroless Plating 454
12-21 Comparison of Observed and Predicted Effluent Cu
Concentrations with Factors Potentially
Related to Waste Stream Concentrations
of Complexing Agent 455
12-22 Comparison of Observed and Predicted Effluent Ni
Concentrations with Factors Potentially
Related to Waste Stream Concentrations
of Complexing Agent 456
12-23 Percent Individual Metals in Total Metal
Discharge from 41 Plants 458
15-1 Metric Conversion Table 532
x
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FIGURES
Number Title
3-1 Telephone Interview Form 9
3-2 Data Collection Portfolio Forms 10
3-3 Detail Sampling Report Forms 13
3-4 On-Site, Local and Central Laboratory Result Forms 14
3-5 Pinse Analysis Form 16
3-6 Conceptual Arrangement of the Plating Process 23
3-7 Typical Electroplating Pretreatment Sequence 27
3-8 Typical Electroless Plating on Plastic -
Pretreatment Sequence 29
3-9 Typical Electroless Plating on Metals -
Pretreatment Sequence 30
3-10 Conceptual Arrangement of a Process Line 43
3-11 Typical Pretreatment Sequence for Anodizing
of Aluminum 44
3-12 Typical Pretreatment Sequence for Immersion
Plating of Copper on Steel Basis 46
3-13 Subtractive Process 55
3-14 Additive Process 57
3-15 Semi-Additive Process 59
3-16 Single Sided Board Production Sequence 60
3-17 Double Sided Board Production Sequence 62
3-18 Multi-Layer Board Production Sequence 63
3-19 Multi-Layer Hole Cleaning 64
3-20 Cleaning Sequence for Electrolass Copper 65
3-21 Catalyst Application and Electroless Copper
Deposition 68
3-22 Pattern Plating (Copper and Solder) 72
3-23 Tab Stripping and Plating (Nickel and Gold) 73
3-24 Immersion Tin Plating Line 74
3-25 Etching Line Process 75
5-1 Schematic Flow Chart for Water Flow in Chromium
Plating Zinc Die Castings, Decorative 99
5-2 Use of Rinse Water in Electroless Plating
of Nickel 100
5-3 Typical Printed Board Process Schematic 114
5-4 Surface Preparation S Catalyst Application
& Copper Electroless Plate 115
5-5 Copper & Solder Electroplate 116
5-6 Etching Operation 117
5-7 Tab Plating
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7-8 Mortified Printed Board Rack for
Dragout Control 165
7-9 Flow Diagram for Treatment of Hexavalent
Chromium Waste by Reduction with
Sulfur Dioxide 172
7-10 Effect of pH on Solubility of Trivalent
Chromium 175
7-11 Mechanical Gravity Thickener 183
7-12 Air/Solids Ratio 191
7-13 Flow Diagram for Treatment of Cyanide
Waste by Alkaline Chlorination Process 194
7-14 Typical Ozone Plant for Waste Treatment 198
7-15 Typical Pressure Filter 202
7-16 Chromic Acid Recovery by Cyclic Operation
Ion Exchange 210
7-17 Types of Evaporation Equipment 216
7-18 Application of Evaporation to Metal Finishing 219
7-19 Application of Reverse Osmosis Alone and
with Supplemental Evaporation 226
7-20 Application of Membrane Filtration to Metal
Finishing Wastewater 235
7-21 Extended Surface Electrolysis Cells 241
7-22 Application of Extended Surface Electrolysis 243
7-23 Effect of Concentration on Electrical
Efficiency in Metals Reduction 244
7-24 Simple Electrodialysis Cell 246
7-25 Mechanism of the Electrodialytic Process 247
7-26 Electrodialysis Recovery System 249
7-27 Electrolytic Recovery 251
7-28 Mechanical Gravity Thickening 253
7-29 Typical Pressure Filter 256
7-30 Feed Flow and Filtrate Drainage 257
7-31 Plan and Section of a Typical Sludge
Drying Bed 260
7-32 Vacuum Filtration System 263
7-33 Conveyor Type Sludge Dewatering Centrifuge 268
7-34 End-of-Pipe Treatment System 285
7-35 Typical In-Line Treatment System 291
7-36 End-of-Pipe System for Printed Board
Manufacturers (Single Waste Stream) 295
7-37 End-of-Pipe System for Printed Board
Manufacturers (Segregated Waste Streams) 296
7-38 End-of-Pipe System for Printed Board
Manufacturers (for Ammoniated Waste Waters) 298
7-39 In-Line Treatment System for Printed Board
Plants (Recovery of Electroless Plating
Solution) 300
7-40 In-Line Treatment System for Printed Board
Plants (End-of-Pipe Filtration) 301
8-1 Evaporation Investment Cost 330
8-2 Evaporation Total Annual Cost 331
8-3 End-of-Pipe Treatment System 339
12-1 Cumulative Plot of Average CN(A) in Discharges
from 85 Plants 387
xn
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12-2 Cumulative Plot of Average CN(T) in Discharges
from 58 Plants 389
12-3 Cumulative Distribution of 124 Daily CN(T) Dis-
charge Concentrations from Plant 20-17 391
12-4 Cumulative Distribution of 13 Daily CN (A) Dis-
charge Concentration from Plant 11-08 393
12-5 Cumulative Distribution for Average of Observed
Cr(6) Concentrations for 74 Sets of Plant Data 402
12-6 Cumulative Distribution of 53 Daily Cr (6) Dis-
charge Concentration from Plant 33-15 407
12-7 Cumulative Distribution of 119 Daily Cr(6) Dis-
charge Concentration from Plant 20-06 408
12-8 Cumulative Distribution of 116 Daily Cr(6) Dis-
charge Concentration from Plant 20-01 409
12-9 Cumulative Distribution of 45 Daily Cr (6) Dis-
charge Concentrations from Plant 1-16 410
12-10 Cumulative Distribution of 22 Daily Cr(6) Dis-
charge Concentrations from Plant 33-20 411
12-11 Contours of Constant Expected Discharge Metal
Concentration as a Function of TSS and Xme 420
12-12 Comparison of Observed Discharge Metal Concentra-
tion vs Cme = 1 mg/1 Contour 421
12-13 Comparison of Observed Metal Discharge vs Me = 25
mg/opm2 Contour 422
12-14 Daily Values of Total Cr Concentration Reported by
Metal Finishing Plant in Michigan During
Period 4/75 - 2/76 435
12-15 Cumulative Plot of Daily Cr Concentrations Reported
by Metal Plating Plant in Michigan 436
12-16 Total Metals out vs Total Metals in for 5 Plants
with Filtrations as Primary Means or Solids
Separation 443
12-17 Effluent Metal Concentration vs RWL Metal Concentra-
tions for 5 Plants with Filtration as Primary
Means or Metal Removal 446
12-18 Total Metals vs TSS in Discharge from 2 Plants with
Polishing Filters 449
12-19 Flow vs Area Processed for Printed Circuit Board,
Electrolessplating and Common Metal Plating
Plants 453
12-20 Plot of Average Total Metal Concentrations vs Average
TSS Concentrations for 29 Electroplaters Using
Clarifiers for Solid Separation 462
12-21 Likelihood that a Plant which Maintains a Given
Average TSS Concentration Experiences at Least
One Average Individual Metal Concentration
Exceeding m 463
12-22 Likelihood that a Plant which Maintains an Average
Total Metals Concentration of M* Experiences at
Least One Average Individual Metal Concentration
Exceeding m 464
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 thev
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represent an absolute control on pollution. In addition,
pretreatment standards can also be specified in terms of
concentration.
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. These limitations are expressed in concentration
levels for each parameter. Section XII details the
rationale for these pretreatment standards.
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TABLE 2-1
RECOMMENDED PRETREATMENT STANDARDS
Pollutant
or
Pollutant
Property
CN,A
CN,T
Cr,VI
Cu
Ni
Cr, Total
Zn
Pb
Cd
Total2'
Metals
Silver3'
TSS4'
PH4'
PRETREATMENT STANDARD
Maximum for Average of Daily
Any 1 Day Values for 30
Consecutive Days
Shall not Exceed
(mg/1)
0.20
0.64
0.25
4.6
3.6
4.2
0.08
0.24
0.09
2.0
1.8
1.6
3.4 : 1.5
0.8 0.4
1.0 , 0.5
7.5
1.0
15
3.9
0.34
10
Within the range 7.5 to 10.0
t
PR
Maximum
Any 1 Da
2.0
0.25
0.8
1.0
SMALL PLATER1'
PRETREATMENT STANDARD
Notes:
1)
2)
3)
4}
(mg/1)
Average of
Daily Values
For 30
Consecutive Days
Shall not Exceed
0.8
0.09
0.4
0.5
"Small plater" indicates plants discharging less than 38,000 liters
(10,000 gallons) per day of electroplating process waste water.
"Total metals" is defined as the sum of the concentration of copper,
nickel, total chromium and zinc.
The silver pretreatment standard applies only to Subpart B, precious
metals plating.
The TSS and pH pretreatment standards are part of an optional alternate
limitation which may be elected by the plant introducing treated process
waste water into a POTW. In the absence of strong chelating agents and
after neutralization using calcium oxide (or hydroxide), the alternate
limitations are for CN,A; CN,T; Cr,VI; Pb; Cd; TSS; and pH as tabulated
above under "PRETREATMENT STANDARD".
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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 segments within the point source category. This
analysis resulted in the division of the electroplating
category into three segments: plating of common and
precious metals; metal finishing; and electroless plating
and printed board manufacturing.
The electroplating industry was initially investigated to
determine pollutant discharge rates in each industry
segment. The Printed Board (PB) industry was known to have
somewhat different wastes than the remainder of the
electroplating industry and was subsequently investigaged to
compare pollutant discharge rates, composition, and water
uses in this industry segment to those from the remaining
electroplating segments. This comparison indicated that
there were higher pollutant discharges for some parameters
and higher water uses in PB manufacturing than in the
remaining electroplating industry segment. Thus, PB
manufacturing is considered a separate segment in the
electroplating point source category, and further
subdivision of PB manufacturing is not required. Once the
pollutant discharges were analyzed, the raw waste
characteristics for each industry segment 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 industry was then
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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 involved, the processes employed, the engineering
aspects of the application of various types of control tech-
nicques, process changes and non-water quality environmental
impact (including energy requirements) .
Details of the approach are described in the paragraphs that
follow.
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 detail in Section
XIV. The material researched covered manufacturing
processes used in the industry, water use and percent
recycling, waste treatment technology, pollutant characteri-
stics and economic data. This information provided con-
siderable insight into the plating industry, provided back-
ground against which to categorize the industry, and pro-
vided a list of some of the plants engaged in this
industrial area.
Federal and State Contacts - All Federal EPA regions 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 - A pollution abatement meeting
of the American Electroplater's Society was attended at
which various papers en plating technology and waste
treatment were presented by the industry and the EPA.
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Table 3-1
Data Source Summary
Data Source Plating
Literature Sources *
EPA Regional Offices 10
State and Territories
(contacted only
when regional
data was not
available) 11
Plating Materials
Suppliers 40
Companies (Plants)
Contacted
& Considered for
This Study 495
Companies Visited for
Data Verification 68
Seminars
Segment
Metal Printed
Finishing Boards
10
11
495
36
10
11
40
57
10
1
*Total of 224 literature sources were used for
plating, metal finishing, and-printed boards.
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A general meeting of the Institute cf 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 plated 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 (Figure 3-1 is an example of a form
used). Those that were involved in electroplating and whose
personnel were agreeable to filling out a data collection
portfolio were sent a portfolio. The final form of the
portfolio is detailed in Figure 3-2. 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 categories.
3. The plant must have adequate waste treatment
control technology in place.
U. The mix of plants visited should contain both
surface dischargers and sanitary sewer dischargers.
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M.P.,0, ,* .,.. F|L£ MEMORANDUM
fx] TELCON
Q MEETING
P E RSON(S)
CONTACTED
DATS
....
TIME
INITIATED BV
»L»CB
COMPANY ADDRK»*
CONTACTS* NAME
PHOMtr EHTCNBIOH
DYES D NO
HE1POI41I BL E PERSON
NAME
COMPANY 0« OEPT
Hamilton Standard is under contract to the U. S. Environmental Protection
Agency to evaluate the limitations set for a portion of the electroplating
industry and also the manufacture and plating of printed circuit boards*
1. Do you fall within the scope of our study? That is, do you manufacture
and plate:
printed circuit boards? nves
and/or do electroless plating? p~]yes
IF ANSWER TO BOTH IS NO; THANK YOU AND HANG UP
2. Do you keep records of the area you plate? Qyes
3. What type of parts or products do you plate?
Qno
Dno
4. For electroless plating what metal is plated on what base material?
Is this an in process operation? [Jfye
5. Do you treat your plating wastes? Dve
6. If yes, how? _
Fl
7. Are any wastes other than plating wastes treated in your plant?
D yes D no
8. If yes, what wastes?
9. Where does effluent go? [check (v/)]
sanitary sewer storm sewer
river, stream other (explain)
10. Would you be receptive to a visit from us to take samples which will help
us to recommend appropriate limitations for the printed circuit board and
electroless plating industry. Qyes E]no
11. Is it feasible to sample plating raw waste and plant effluent?
Qyes Qno
12. What type of masking material do you use in your plating operations
(specify name and type)?
Is it hydrophilic or hydrophobic?
13. Do you use chelating agents? Dyes |~| no
Where are the chelating agents used (what for)?
£] don't know
What kind [specify name, type and supplier)?
Inform Plant we are sending portfolio.
FIGURE 3-1. TELEPHONE INTERVIEW FORM
-------
Portfolio Number
1.0 MANUFACTURING ESTABLISHMENT DRTA
Total Number of Employees
Standard Industrial Classification Number(s)
Type of Shop (Job or Captive)
Type of Disch;
Rural or Urbai
Types of Parts or Products Plated
,1}
(Name) (Title)
2.0 SPECIFIC PRODUCTION PROCESSES EMPLOYED
Electroplating
1. Copper 10.
2. Nicfcel 11.
3.
Chr<
__Solder
_S liver
Gold
12.
_Anodizing
_Etching
_MUling
_Chromating
Phosphating
Principal Raw Materials Consumed and Amounts per Day (pertaii
to processes listed in paragraph 2.0 below)
__Copper
Nickel
20. Gold
21. Other
28. Stripping
25. Electropainting
27. Coloring
processes
30. Lead Electroplating
31. Bright Dip
32.
3.0 COMPLEXING RGENTS USED IH ELECTRQLESS PLATING
Quantity
(Ib/year)
Type of Metal
Complexed
HEDDA
HE IDA
GXutamic Acid
DHEG
Glycine
Citric Acid
_Gluconic Acid
"Glutaconic Acid
ic Acid
ic Acid
Pyrophoaphate
• Acid
cid
Acid
~~Succi i Acid
_Malic A id
Sodium ydroxy Acetate
""Rochell
_Other ( Specify)
What ii the relative efficiency of complexing agent* in improving
the adhesion of the electroless plate?
What is the effect of these complexing agents on your waste treat-
ment process?
Ars the complsxing agents themselves removed in
process?
raste treatment
4.0 HASTE MANAGEMENT PROCESSES
4.1A Mater Supply Source
A. River
B. Lake
C. Municipal
Portfolio ]
Avq CPU (during plant operation)
Type
A.Pretreatment before plating
B. Plating
D. Total Process
E. Sanitary
F. Cooling
G. Total Non-Process
Avq GPH (during plant operation)
Make-up Recycled Total
Water Water Water
4.2 Waste i
Outfall
(circle pertinen-
streams)
A. Cyanide Raw Haste
B. Cyanide Effluent
C. Chromium Raw Haste
D. Chromium Effluent
E. Raw Haste (combined)
F. Final Effluent
G. Concentrated Raw Haste (batch dumps)
H. Concentrated Effluent (batch dumps)
4.3 Description of the Plant's Current Effluent Requirements or
Regulations (county, city, town or federal.For NPDES permits,
indicate number and state office where filed and provide copy
of permit if available)
FIGURE 3-i" DATA COLLECTION PORTFOLIO FORMS
10
-------
Composit
each sti
of Streams (more than one set of data can be specified :
Stream Stream
Stream Type
(ie« para 4.2)
Sample Type
(composite or grab:
Analysis Type
Silver**
Aluminum
Gold"
Boron
Cadmium*
11. Cobalt
12. Carbonate _
13. COD _
14. Conductance^
(umho»/cm) ~
15. Kexavalent
Chromium* _
16. Total
Chromium* _
17. Copper*
18. iron*
*Teat Parameters
••Special Tests
20. Mercury
22. iridium**
23. Magnesium
25. Molybdenum
26. Nickel*
27. Oil t
Greaae
28. Osmium**
29. Phosphorus*
30. Lead*
31. Palladium*1
32. Platinum**
33. Rhodium**
34. Ruthenium*1
36. Tin*
37. Zinc*
38. Flow(gph)
39. pH*
40. Total
41. Total
suspended
solids*
43. Sulfates
44. Nitrates
45. Sulfides
46.Chlorinated
Hydrocarbons
•Test Parameters
"Special Tests
Portfolio Number
4.6a WASTE TREATMENT COST INFORMATION (conventional treatment)
Raw Hast** Hast*
Treatment Streams Reduction
System Date Capital operating Treated Accomplished
Identification Installed Costs Costs_t$/yr) (see para. 4.21 (t)
S.O WASTE TREATMENT SYSTEM DESCRIPTION
01 Batch
02 Continuous
03 integrated
4.7a WASTE TREATMENT COSTjNFORMATION (recycle systems)
Raw Wastes Wast*
Treatment Streams Reduction
System Date Capital Operating Treated Accomplished
Identification Installed Costs Costs(5/yrl (see para. 4.2) 1%)
Reverse Osmosis(RO)
Ion Exchange
Evaporation
Electrodialysis
Pfaudler
Lancey
Waatesaver
IB Ultrafiltration
b)
c)
4.8 Have you ever used or considered using an advanced waste treat-
ment technique [such as reverse osmosis, ultrafiltration, etc.)?
Qno
If so, are you stil
If you have dropped plans or equipment for such a system, why?
using one, how do you rate it?
20 Screening
21 Emulsion breaking
22 Skimming
23 Chemical oxidation (incl.
cyanide)
24 Chemical reduction (incl.
chromium)
25 Neutralisation
27 Flotation
28 Lagooning (for solids settling)
29 Clarification (with addition of coagulants)
30 Filtration
31 Ion exchange
32 Reverse o«mosis (R.O.)
33 Adsorption
34 Evaporation (distillation)
36 Lagooning (for biological decomposition)
SLUDGE DEWATERIMG OIL DISPOSAL MATER DISCHARGE
40 Thickening 60 incineration/Combuition 70 Sanitary sewer
SLUDGE DISPOSAL
50 Lagooning
51 Land fill
52 Incineration
53 Pyrolysis
62 Contractor i
_
72 Lake/pond
73 Deep well
74 Leach field
Circle if the following are
your waste treatment plant.
82 Boiler blowdoi
FIGURE 3-2. ( CONTINUED )
10(a)
-------
Portfolio Number
6.0 MATERIAL FINISHING LINE DESCRIPTIONS
Draw Schematic for Each Material Finishing Lin
chelating agents used in each line)
Portfolio Number
(identify any/all
Acid Pickling
Electrosonic
Neutralization
Degreasing
Catalyst Application
Acceleration
Other (Specify)
Rinse Technique
1 stage
2 series
3 series
»3 series
2 countercurrent
3 countercurrent
^•3 countercurrent
Spray
Fog
Other (Specify)
Electroplating
Copper
Nickel
Chromium
Cadmium
zinc
solder
Lead
Tin
Gold
Silver
Anodizing
Coloring
Phosphating
Chromating
Immersion plating
ECM
4B Polishing
49 Electropainting
50 Etching
51 Chemical Milling
52 Hon-aqueoua plating
53 Stripping
59 Combined
60 Bright Dip
Other
61 Other (Specify)
Note: ID numbers 20 through 61 used in these schematics are also to be
used on the plant data sheet {Table 1) as "lin* description num-
bers" . The number corresponding to the principle output of the
line should be used in first column in Table 1.
S5S.
11
.ll
o o +j
S! -6S
O -P n a.
FIGURE 3-2. ( CONCLUDED )
10(b)
-------
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.
A total data base of 151 electroplating facilities,
metal finishing facilities and 27 printed board facilities
were contacted. Data from some of the companies were
inadequate for complete analysis, leaving an analyzable data
base of 123 electroplating facilities, 91 metal finishing
facilities, and 14 printed board facilities. The companies
in each segment of the data base for the industry are not
mutually exclusive since some companies have operations in
more than one segment.
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 effluent limitations under which the plant
is operating and any difficulties in meeting them.
5. Particular pollution 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 beard plants:
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.
11
-------
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. The format of this sampling plan is shown in
Figure 3-3.
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. An example of a wastewater analysis
report used for each facility visited, showing a data
checklist and on-site, local and central laboratory analysis
results, is presented in Figure 3-4.
12
-------
DETAILED SAMPLING PLAN
DETAILED SAMPLING PLAN
(Continued)
I.D. Number
Week To Be Sampled
Contact
Plant Name
Address '_'_ ~
Telephone No. ^
All available data for above plant has been reviewed.
List Data.
Sketch of waste treatment facility showing individual process lines.
Identify planned sample points.
Flow Rate Description (approximate flow, steady or intermittent, how flo'
will be measured}
Point
Point
Point
Will system be running at time of visit?
Sample Collection
Batch or Continuous
Samples Per Day
Sampling Frequency
Minimum Sample Size
Point
Point
Point
Complete description of point of discharge where sample is to be taken
(sample point). Show whether flow is influent, intermediate, or effluent.
Describe the industrial process or waste treatment associated with the
sample point flow.
Local Lab
Address
No. of Samples to 'be Delivered
Data will be Forwarded By (DateT
Telephone No.
Contact
Telepho.
Special Parameter Analysis
Potential Problems:
FIGURE 3-3. DETAIL SAMPLING REPORT FORMS
13
-------
Plant ID No
Page 1 of
W/>TCJ' POLLLTION CONTROL MONITORING
TASK 1
WASTEWATER ANALYSIS REPORT
Composite Sample Results Consisting of:
1) Sample Visit Results
2) On-site Test Results Received
3) Local Lab Test Results Received
4) Central Lab Test Results Received
For
Address
City State Zip
Contact(s) Tel
Tel
Sampled By
Date
1. Sample Visit Results
Plant Name__ I.D
Dates Sampling Accomplished
Number of Samples Taken
Disposition of Samples: Local
Central
Data Reviewed and Returned (List Date Returned)
A) Portfolio^
B) NPDES Permit Copy and Associated Data
C) Process and Waste Treatment Layouts
D) Description of Rinsing Operations
E) Other (Specify)
Signed
2. composite Sample ON-SITE analysis report
Company . ____
Sample Point #_
DATE - TIME (38)FLOW'
1
Plant ID No._
Page of
SAMPLE SIZE {39}pH* (42JTEMPERATUPE*
GPH QTS pH UNITS °C
pH is measured with a Leeds (, Northrup pH meter. Model I7417-L2.
Temperature is measured with a centigrade thermometer. Describe
fully method used to measure flow. Use schematic diagram on re-
verse side if necessary. Show one sample flow calculation.
rd pH of composited sample and its temperature.
Temperature ___ _
3. Composite Sampi
Company
Local lab name
Address
City
Attn:
Telephone•
Sample analysis results
9. Cyanide Amenable to
10. Total Cyanide
Plant ID No.
Sample Point #
••*ASTM D2036 Colorimetric.
Minimum analysis level
0.005 mg/1. Sample water con-
with sufficient ION NaOH to
Phosphorus mg/1 EPA249 "SMSIS, Persulfate
Digestion, Vanadomolybdophosh-
ponc Colorimetric. Mini-
mum analysis level: 0.02 mg/1
Sample water contained in two
bottles marked "D" and refri-
served with 2ml/lH2SO4.
*SH: (standard methods) "Standard Methods for Examination of
ASTM: Annual Book of Standards, Pact 23, water, Atmosphere
Standards 1972. American Society for Testing and Materials.
Authority granted for_
'ater samples as described
above, at a vendor quoted price of
Hamilton Standard Purchase Order No.
Authorized by
Hamilton Standard, United Technologies Corp.
Telephone 203-623-1621, Extension 8321
FIGURE 3-4. ON-SITE, LOCAL AND CENTRAL LABORATORY RESULT FORMS
14
-------
In addition to the sampling and analysis described above,
special grab samples were obtained from a few select plants.
These samples were taken from the rinses in the pre-
treatment 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. The alkaline rinse samples were analyzed for
phosphorus, basis metal, oil and greaser total dissolved
solids, and total suspended solids. With the exception of
phosphorus, the acid rinse samples were analyzed for the
same constituents. An example of the analysis reporting
form is shown in Figure 3-5.
One of the principal areas of interest in the study of
printed board (PB) 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.
The wastewater analysis log sheets include the sample
results for chelating agents (reference Figure 3-4). In
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 pre-
treatment 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 sclids, 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 three segments of
the electroplating industry. These three segments are
15
-------
LOE Task 11
Pretreatment Rinse Analysis Report
Company
Local/Central Lab Name
Address
City
Attn:
Telephone:
Sample Analysis Results
Plant ID N0._
Page of
State
Zip_
Sample Point #
(Local) Phosphorus
mg/1
(Central) Base Metal
mg/1
Oil & Grease
Total Dissolved Solids
Total Suspended
EPA249 SM466*. Persulfate
Digestion, Vanadomolybdophosh-
poric Colorimetric. Mini-
mum analysis level: 0.02 mg/1
Sample water contained in two
bottles marked "D" and refri-
gerated to 4°c. Samples pre-
served with 2ml/lH2S04.
Method Bottle
Atomic Absorption A
Soxhlet Extraction D
Filtration,
Evaporation A
Glass Fiber
Filtration 0.1 A
*"Methods for Chemical Analysis of Water and Wastes",
EPA-625-16-74-003, U.S. Environmental Protection Agency, pg. 249.
*SM "Standard Methods for Examination of Water and Wastewater"
American Public Health Assoc. pg. 466.
Authority granted for__^
to perform chemical analysis of_
water samples as described
above, at a vendor quoted price of_
Hamilton Standard Purchase Order No,
Authorized by
SS297963NL (Local), SS297964NL (Central)
Date
Record local analysis results on this form in the spaces provided above
and return to:
Hamilton Standard, United Technologies Corp.
Windsor Locks, Connecticut 09096
Attn: A. Krivickas, 1A-2-4
203-623-1621 Ext. 8321
FIGURE 3-5 RINSE ANALYSIS FORM
16
-------
plating, metal finishing, and printed board manufacturing.
This subdivision is based on the fact that distinctly
different production processes are performed in each of the
three segments, even though these segments are not mutually
exclusinve subdivisions of the electroplating point source
category. These segment 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 Categori zation - Subdivision of the
segments to account for different types of operations is
required and 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. An operation-processed
area basis for limitations is selected following a review of
several industry 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 en 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 characteristization 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.
17
-------
section VII; Treatment Technology - Treatment technologies
observed during plant visits and described in the literature
are discussed in three main areas. The first describes in-
plant 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 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.
Sections IX, X, XI, and XIIt Effluent Limitations - Limita-
tions are discussed in detail in Sections IX, X, XI, and
XII. "Best Practicable Control Technology Currently Avail-
able" (BPT) is representative of the average of the best
waste treatment facilities (Section IX). "Best Available
Technology Economically Achievable" (BAT) represents the
very best practical waste treatment facility (Section X).
"New Source Performance Standard" (MSPS) represent the best
available demonstrated control technology, processes.
18
-------
operating methods, or other alternatives (Section XI).
11 Pretreatment Standards" represent the average of the best
waste treatment facilities discharging to publicly owned
treatment works (Section XII).
Effluent Limitation Derivation
The following sections summarize the formulation of effluent
discharge limitations in this industry segment and describe
the data analysis and computer programs used in this for-
mulation. A summary of the plant data base is presented in
Table 3-2.
Formulation of Effluent Discharge Limitations - Effluent
data from plants engaged in plating, metal finishing, and
printed board manufacture were analyzed. This analysis was
carried out to determine the achievable pollutant discharge
from plants employing proper waste treatment control
techniques and technology.
Data Analysis Computer Programs - Two computer programs were
designed to organize and analyze the data obtained from on-
site evaluations, sampling and portfolios. One program was
the "portfolio generator" program and the other, the
"limitations analysis" program.
The portfolio generator program accepted data from plants,
tested the data for consistency, and printed it out for each
plant. The input data included information on plating
processes, water use, raw and effluent wastes, waste
treatment methods, manufacturing line descriptions, areas
processed, and chelating agents.
The limitations analysis program used part of the portfolio
generator data to compute plant performance and provide
minimum, maximum, and mean effluent discharges for all
plants. To do this, the analysis program retrieved effluent
data, processed areas, and line description data from the
portfolio generator tapes. It then determined the discharge
from each plant per unit area processed and operations per-
formed. It did this for each pollutant parameter. The
manufacturing operation counter portion of the program was
based on the allowable operations. Data on each parameter
for each plant were then averaged, and the minimum and
maximum levels for each parameter were printed out. When
averaging each parameter, a check was made to assure that
each parameter was an applicable pollutant in the plant
where it was found (e.g., copper effluents were only
averaged from plants that plate copper or etch copper).
19
-------
Table 3-2
Characteristics of the Data Base
Common and Precious Metals Plating
Total Number of Plants 151
Number of Unanalyzable Plants 28
Number of Analyzable Plants
Total 123
Sufccategory A 118
Subcategory B 39
Subcategory G 28
Metal Finishing
Total Number of Plants 114
Number of Unanalyzable Plants 23
Number of Analyzable Plants
Total 91
Subcategory D 26
Subcategory E U6
Subcategory F 69
Printed Boards
Total Number of Plants 27
Number of Unanalyzable Plants 13
Number of Analyzable Plants 14
20
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DESCRIPTION OF THE PLATING SEGMENT
The industries covered by this section include those
segments of the Electroplating Point Source Category dealing
with electroplating of common and precious metals and
electroless plating on metals and plastics. A total of
approximately 10,000 companies are engaged in metal plating
in the United States with 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 indicates 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.
Plating facilities vary greatly in size and character from
one plant to another. A single facility for plating in-
dividual 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
kilowatthours/day to as much as 20,000 kilowatt hours/day.
Products being plated vary in size from less than 6.5 sq cm
(1 sq inch) to more than 1 sq meter (10 sq feet) 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
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.
21
-------
Electroless plating on metals is not a separate industry but
an integral part of a number of industries, such as, air-
craft, 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.
For the purpose of this document, a plating line is defined
as a sequence of tanks in which one or more coatings are
applied. 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 electroless or electroplating line may be
broken down into three steps; pretreatment involving the
preparation of the basis material for plating, actual app-
lication of the plate and the post-treatment steps. This
breakdown is presented in Figure 3-6. Each of these steps
are covered in the following pages. Also included is a
separate subsection on chealting agents which are an
integral component in electroless plating baths but which
also have a uniquely negative effect on waste treatment
systems.
Pretreatment Processes
Pretreatment steps involve cleaning, descaling, degreasing,
and other processes which prepare the basis material for
plating.
Cleaning - 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, ultra-
sonic 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
22
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PARTS
PRETREATMENT
ELECTROLESS OR
ELECTROPLATING
PROCESS
POST-TREATMENT
PARTS
FIGURE 3-6 CONCEPTUAL ARRANGEMENT OF THE PLATING PROCESS
23
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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 less-
ened because of foaming. Electrolytic cleaning produces the
cleanest surfaces available from conventional 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 electro-
lysis. 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
subseguent 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 UOO degrees C - 540 degrees 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.
Pretreatment for Electroless Plating On Plastics - Pre-
treatment 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 goes under several names:
"sensitizing11, "activating", "accelerating", and
"catalyzing".
Two different catalyst application methods have been em-
ployed 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
25
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plates out on the palladium. After the initial layer of
metal is applied it becomes the catalyst for the remainder
of the plating process.
Pretreatment for Electroless Plating on Metals
Pretreatment 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. Pretreatment for stainless steels,
aluminum base alloys, beryllium, and titanium alloys typi-
cally consists of a flash deposit of nickel to catalyze the
surface for subsequent electroless deposition.
Certain materials need a galvanic initiation, normally a
galvanic nickel deposit. Inlcuded 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 auto catalytic. A copper strike is
frequently used which then can be surface activated and
electroless plated.
Typical Pretreatment Processing Sequence - Electroless or
electroplating requires a cleaner surface than needed for
other processes such as painting or phosphating. The
pretreatment of metals typically consists of one or more of
the following: 1) solvent cleaning to remove most of the
soil, 2) alkaline cleaning, 3) electrocleaning to remove
traces of soil, 1) acid treatment tc remove light oxide
films formed during the cleaning process. In addition,
pickling or descaling is often required. The cleaning
sequence is similar for most basis metals, while the
descaling process is dependent on the basis metal. Typical
pretreatment sequences for electroplating on low carbon
steel, electroless plating on plastics, and electroless
plating on metals are discussed below.
A typical electroplating pretreatment sequence is shown in
Figure 3-7. The first step (alkaline soak) removes oil and
26
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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.
Pretreatment of plastic prior to electroless plating is
shown in Figure 3-8. 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-palladium catalyst
is applied. The acceleration step dissolves the tin from
the surface, allowing the part to be plated.
Pretreatment of metals prior to electroless plating is shown
in Figure 3-9. 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.
Electroplating and Electroless Plating Processs
As discussed previously, the electroplating or electroless
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 been adopted commercially, but only two or
three types are utilized widely for a 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 recently 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.
28
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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++ + 2e
The resulting copper ions are reduced at the cathode (the
zinc part) to form a copper plate:
Cu++ + 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 chro-
mium 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. Cirect 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 contain 0.5 to 1 sg m (5 to 10 sq ft). 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.
A description of the various techniques for electroplating
aluminum, cadmium, chromium, copper, gold, iridium, iron,
lead, palladium, platinum, rhodium, ruthenium, silver, tin,
and zinc follows.
Aluminum Electroplating - Application of aluminum on a
commercial basis is limited. It has been used for coating
uranium and steel strip, electrorefining and electroforming.
31
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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, aluirinum chloride and
lithium aluminum hydride has had any commercial appli-
cations.
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 comp-
letely and give a dense, fine-grained deposit which can be
made very lustrous by the use of stable brighteners.
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 UOO g/1 of
chromic acid are the common baths for electroplating 0.0002
mm to 0.10 mm (0.000008 to O.OOOUO 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.
Copper Electroplating - Copper is electroplated from several
types of baths. Among these baths are alkaline cyanide,
acid sulfate, pyrophosphate, and flucborate, 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.
Gold Electroplating - Gold electroplated surfaces not only
provide decorative finishes and ccrrcsion protection, but
32
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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 non-
cyanide.
Indium Electroplating - Indium electroplating is used
largely 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 treat-
ing. Indium is often alloy plated with copper, tinr 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, prechlorate and
tartrate baths.
Iron Electroplating - The electroplating of iron is used for
certain specialized purposes such as electr©forming 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.
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.
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.
Nickel Electroplating - Nickel is electroplated from several
baths, among these are Watts (sulfate-chloride-boric acid),
33
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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 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-pro-
tective 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.
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 refelctivity.
Platinum is electroplated on titanium and similar metals
which are used as insoluble anodes in other plating opera-
tions (e.g. rhodium and gold). Electroplated platinum is
used as an undercoat for rhodium plate. Ruthenium electro-
plating 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 10 ml/1 of con-
centrated ammonium hydroxide. Palladium deposition has been
accomplished from chloride or bromide solutions and from a
molten cyanide bath.
Silver Electropiating - The use of silver electroplating is
continuing to expand to the engineering as well as the
decorative fields. Silver is typically electroplated in two
types of baths, a conventional low 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.
Tin Electroplating -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 pro-
duce 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".
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.
Electroless Plating - Electroless plating is a chemical
reduction process which depends upon the catalytic reduction
of a metallic ion in an aqueous solution containing a
reducing agent, and the subsequent depostion of metal
35
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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 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 electro-
plating 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 fellows:
The nickel salt is ionized in water.
NiSO* = Ni + 2 + SOU- 2
There is then a redox reaction with nickel and sodium
hypo phosphate.
Ni+2 + SOU-2 + 2NaH2PO2 + 2H2O = Ni + 2NaH2PO3
36
-------
+ H2 + H2SOJI
The sodium hypophosphite also results in the following
reaction:
NaH2P2 + H = 2P + NaOH •»• H20
As can be seen in the equations above, both nickel and pho-
sphorus are produced, and the actual metal deposited is a
nickel-phosphorus alloy. 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 hypophosphate.
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.
CuSOU = Cu+2 + S04-2
There is then a redox reaction with the copper and the
formaldehyde to:
Cu+2 + 2H2CO + H OH-1 = Cu + 2HCO.2-1 * 2E2O + 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 and
resulting 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
37
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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 waste-
water during treatment. Quite often, plants which are
engaged in plating activities that make use of chelating
agents have treatment systems based en 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 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.
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 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
38
-------
Table 3-3.
Common Chelating Agents, - Marketers and Manufacturers
HYDROXY
ACIDS
AMINES
AMINOCARBOXYLIC
ACIDS
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Citric Acid
Tartrates
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automotive, appliance, cosmetic, electrical, hardware,
furniture, and plumbing industry.
Among the plastics most widely used for plating are acry-
lonintrile-butadiene-styrene (ABS), polycarbonate, poly-
propylene, 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, stain 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
After a deposition of a metallic coating either by electro
or electroless techniques, an additional coating is some-
times 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 as treatment processes in the following
section, Description of the Metal Finishing Segment.
-------
DESCRIPTION OF THE METAL FINISHING SEGMENT
This section includes those segments of the metal finishing
industry dealing with anodizing, chemical milling and
etching, chemical conversion coating, and immersion plating.
A total of 15,000 companies are engaged in metal finishing
with the industry composed of independent (job) shops and
captive shops, i.e., facilities finishing their own work.
Metal finishing facilities vary greatly in size and
character from one plant to another. A single facility for
finishing individual parts formed by stamping, casting, and
machining may employ processing solutions (excluding water
rinses) ranging in total volume from less than 380 liters
(100 gallons) to 18,900 liters (5,000 gallons). The area of
the products being finished in these facilities varies as
much as three orders of magnitude from less than 10 to more
than 1,000 square meters/day (100 to 10,000 square ft/day).
The power consumed by a single facility varies from a few
kilowatt-hours/day to as much as 20,000 kilowatt-hours/day.
Products being finished vary in size from less than 6.5
square cm (1 square inch) to more than 1 square meter (10
square feet) and in weight from less than 30 g (1 oz) to
more than 9,000 kg (10 tons). Some companies have
capabilities for finishing 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.
The metal finishing industries covered by this docv.nent
either provide a surface coating or remove metal by chemical
dissolution. The surface coating resulting from anodizing,
chromating, phosphating, and coloring provides corrosion
protection, wear or erosion resistance, electrical
conductivity, a pleasing appearance, or other special
surface characteristics. The removal of substantial amounts
of metals occurs during chemical milling, etching,
electrochemical machining, electropolishing, and bright
dipping.
The application of conversion coating or the removal of
metal by chemical milling occurs in a process line. For the
purposes of this doucment, a process line is defined as a
row of tanks in which a coating is applied or basis metal is
removed. A rinse is a step in a process line used to remove
bath dragout from the work following a process step. A
rinse may consist of several sequences such as successive
countercurrent rinsing or hot rinsing followed by cold
rinsing.
-------
Conceptually, a process line may be broken down into three
steps: pretreatment involving the preparation of the basis
material for a coating or milling, actual application of the
coating or removal of basis metal and the posttreatment
steps. This breakdown is presented in Figure 3-10. Each of
the steps will be discussed in detail below.
Pretreatment
Pretreatment steps involve cleaning, descaling, degreasing,
and other processes which prepare the basis material for
surface treatment or material removal. The number of
pretreatment steps required prior to additional surface
treatment depends on the work flow sequence established in
individual facilities. The cleaning and salt bath descaling
steps are identical to those discussed above for the plating
segment.
Masking and Activation of Parts Prior to Chemical Milling or
Etching - 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 tecnhiques or photosensitive resists. Typically
photographic techniques are used for the blanking of small
intricately shaped parts or for the production of name
plated, dials, and fine mesh screen. After masking, parts
may be dipped in acid to activate the surface prior to
chemical milling or etching.
Typical Pretreatment Processing Sequence - Pretreatment 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 3-11
presents a typical pretreatment 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 alsc 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.
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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.
A typical pretreatment sequence for immersion plating of
copper on steel is presented in Figure 3-12. The pretreat-
ment is very similar to the pretreatment process for
electroplating.
Pretreatment sequence procedures for chemical milling or
etching are similar to those for anodizing and immersion
plating. Prior to the chemical etching or milling, the
basis metal is alkaline and acid cleaned.
Material Coating and Treatment Processes
As discussed above, the anodizing, chromating, phosphating,
coloring, and immersion plating processes apply a surface
coating for specific functional or decorative purposes.
These processes as well as bright dipping, electrochemical
milling, electropolishing and chemical milling and etching
are covered in this section.
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
properties. Aluminum is the most frequently anodized
material, while some magnesium and limited amounts of zinc
and titanium are also treated.
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
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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.
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 de-
position cf copper on steel from an acid copper solution.
The thickness of immersion deposits is usually of the order
of 0.25 urn (10 micro inches) although a few processes
produce deposits as thick as 2.5 to 5 um (100 to 200 micro
inches). 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, and d) nickel on steel.
Immersion tin plating is used to "whiten" pins, hooks, eye-
lets, 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 in-
expensive items of jewelry. Typical immersion gold plating
solutions contain gold chloride and potassium cyanide or
pyrophosphate.
Coatings and Coloring - The following subsections deal with
the chemical conversion coating of chromating and
phosphating, and metal coloring. 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. 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 is generally acidic and contains
chromic acid or its sodium cr potassium salts, plus organic
or inorganic compounds 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.
Phosphate conversion coatings produce a mildly protective
layer of insoluble crystalline phosphate on the surface of a
metal. Phosphate coatings are used to e) 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 lubricants, and c) impart corrosion
resistance to the metal surface by the coating itself or by
providing a suitable base for rust-prevenatative 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 ether reagents.
48
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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.
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.
Preparation procedures for metal coloring are similar to
those used in the metal finishing processes, consisting of
alkaline and acid cleaning. 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. If mechanical polishing is used,
a degreasing operation must be included to remove the
polishing compound.
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 ircst important surface
treatment for cadmium is chrornate passivation which improves
its resistance to the atmosphere and tc 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 aluminun 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.
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 electrochemical machining.
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 Pretreatment section.
Typical solutions for chemical milling include ferric
chloride, nitric acid, ammonium persulfate, chromic acid,
cupric chloride, hydrochloride acids 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.
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 in the development document for
the printed board segment of the electroplating point source
category.
50
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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.
Posttreatment Process
Posttreatment processes include the sealing and coloring of
anodic coatings, bleaching or dyeing of chromate coatings,
chemical rinsing after phosphating, and removal of masking
materials used in chenr.ical milling processes. Each of these
posttreatment processes is covered in the following
paragraphs.
Sealing of Anodic Coatings - 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
(A12(^3.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.
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.
Coloring and sealing of Anodic Coatings - 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
51
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accomplished by immersion in a hot solution of nickel or
cobalt acetate.
Bleaching or Dying of Chromate Coatings - 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.
Chemical Rinsing After Phosphating - 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 oilr wax,
or other lubricant before drying in hot air.
DESCRIPTION OF THE PRINTED BOARC SEGMENT
The industry covered by this section includes that segment
of the electroplating point source category that produces
printed boards.
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.
Printed boards are fabricated from nonconductive board mate-
rials such as plastic or glass on which a circuit pattern of
conductive metal, 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 following subsections present details on the production
methods, types of circuit boards, and the specific processes
involved in producing printed boards. Also included is a
separate subsection on chelating agents which are an
integral component in electroless plating baths (a
-------
significant operation in the manufacture of printed boards)
but which also have a uniquely negative effect or waste
treatment systems.
Production Methods
The earliest printed boards were produced by brushing a spe-
cially 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 pro-
duction 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 sub-
tractive, additive, and semi-additive processes.
The subtrative 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 gees through an etching
operation in which the area of the fcil 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 shewn in Figure 3-13
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 fcil, 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.
53
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TABLE 3-4
COMPARISON OF BASIC PROCESS STEPS
Conventional
Subtractive
Process sequence
begins 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
Fully Additive
Standard
Process sequence
begins with
unclad material
(already sensitized)
Fabricate holes
Sensitize
(Catalyze surface)
Electrcless copper
flash
Print reverse
pattern
Electroplate
copper to
desired
thickness
Over plate
Strip mask
Quick Etch
Tab plate
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
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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
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.
The additive process presently employed by some
manufacturers is more totally additive than the original
method. The process, shown in Figure 3-14, 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 an
adhesive is applied, and the surface is roughened or etched
in order to make it microporous. The roughening of 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
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sub-tractive process where the electroless copper is only
used as a base for copper electroplating, in the additive
process, the electroless copper deposition is used 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 if Figure 3-15, 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, and the board is 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 non-
circuit 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 process. This semi-additive
process is not used extensively, and none of the plants in
this data base performed this process.
Types of Boards
Printed boards can be classified intc three basic types:
single-sided, double-sided, and multilayer. The type of
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board used depends on such things as spatial and density
demands and intricacy of the circuits.
Single-sided boards (reference Figure 3-16 production
sequence) are used for relatively simple circuitry, where
circuit types and speeds do not place unusual demands on
wiring electrical characterisitcs. When density demands
require more than one layer of wiring, circuits are printed
on both sides of the board (see Figure 3-17 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 singlesided 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 3-18. 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 boards types can
be broken down into the following categories: 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 Prepartions - 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 3-19, to remove
any bonding epcxy which spilled ever the holes.
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Once on the plating line, all types of boards are al-
kaline cleaned (reference Figure 3-20) to remove any
soil, fingerprints, smears cr ether substances which
cause plating flaws. A mild etch step 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 beard and the electroless
plate, an adhesion promoter is applied and dried. Then
the board undergoes an etch (usually chromic acid or
chromicsulfuric). 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 deposition 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:
H2O
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66
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Cu 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 the most recently developed method, specifically for
printed boards, a catalyst is applied only to the area
to be occupied by the 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.
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 3-21) 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 cf the metal ion and
preventing them from carrying out their normal (and in
many cases undesirable) reactions.
67
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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, 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 mere 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 tiodegradable.
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,
69
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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. tablishments employing
this technique in the data base are
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. 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.
70
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4. 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 3-22). 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/UO tin-lead electroplate, although tin-nickel
and gold are used in some instances.
The tabs or "fingers" of the printed circuit boards are
electroplated, as shown in Figure 3-23, 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.
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 3-24) 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 3-25, 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.
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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.
76
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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. This point source category was divided into
plating, metal finishing, and printed board manufacturing
segments because distinctly different operations are
performed in each segment. These segments are not mutually
exclusive subdivisions of the electroplating point source
category, however, as plants often perform operations in
more than one segment. This section presents the categories
established for each of these three segments 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 segment; 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 for each industry segment.
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
U. Size and age of facility
5. Number of employees
6. Geographic location
7. Quantity of work processed
8. Waste characteristics
9. Treatment technology
10. Water use
11. Effluent discharge destination
Of the possible categorization bases for the plating
segment, process baths used is the most appropriate for
establishing effluent limitations since it focuses on the
baths, and the dragout from these baths is the major source
77
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of wastes in this industry. On this basis, the
subcategories chosen for the plating segment are common
metals electroplating, precious metals electroplating, and
electroless plating. Since the value of plating bath
constituents may dictate the type of treatment or recovery
practiced for the plating wastes, the electroplating
processes are subcategorized into common metal plating and
precious metal plating. Because electroless plating baths
have different concentrations of metal than electroplating
baths and contain more chelating agents, electroless plating
is set apart as a third subcategory.
Similarly, the most applicable basis for categorization of
the metal finishing segment is the manufacturing process
performed. This categorization approach focuses on the
operations performed within a plant which are the effluent
sources. Following a review of the metal finishing
operations conducted by plants in this data base, it was
determined that all of these operations can be classified
into three main process subcategories; anodizing, coating,
and chemical milling and etching.
Finally, because of the unique mixture of electroplating and
electroless plating, the printed board industry has been
designated as a separate category. Since printed board
manufacture is a single product industry, with all the
operations involving this one product, there is no necessity
to subdivide this industry segment by the discrete
manufacturing processes that are involved in the production
of a printed board.
The following subsections present the rationale for the
categorizations and subsequent selection of subcategories.
Type of Manufacturing Process
Since the manufacturing processes performed in a plant are
the source of wastes from a plant, plating processes are a
natural candidate for subdividing the common and precious
metal plating industry segment for the purpose of
establishing effluent limitations. However, since this
industry segment involves only plating, the type of
manufacturing process is not a distinguishing factor.
Plating, whether electroplating or electroless plating,
involves the deposition of a metal on a part. The major
distinguishing feature of plating relative to waste
characteristics is the type of plating metal used.
Similar to the plating segment, the types of manufacturing
processes are a natural candidate for subdividing the metal
78
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finishing industry segment for the purpose of establishing
effluent limitations. Grouping according to their function
results in the subcategorization shewn in Table U-l.
Anodizing is an electrolytic oxidation process which is
unique and thus is a separate sutcategpry. 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, electroles plating and etching.
The above processes involving desposition 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 process to arrive at an allowable
discharge. All the processes performed are in the same
subcategory for determining compliance with effluent
discharge limitations.
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 is the
dragout of the solutions from the baths and 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
79
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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 metal finishing
subcategorization because a major source of wastes in metal
finishing operations is from the dragout of finishing
solutions from process baths and thus the characteristics of
the wastes from this industry segment 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 metal finishing sufccategory 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 metal finishing operation 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 board
manufacture. In any facility carrying cut 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 segments of the
electroplating industry is the same in all facilities
regardless of size and age. 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 segments
80
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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 and metal
finishing 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
would need only two people. The same amount of waste would
be generated in each case if all other factors were the
same.
Geographic Location
Geographic location is not a basis for subcategorization.
Manufacturing processes are not affected by the physical
location of the facility, except 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 endof-process treatment facility. Often, a
compact package unit can easily handle end-or-process waste
if good in-process techniques are utilized to conserve raw
materials and water.
Quantity of Work Processed
Quantity of work processed is analogous to plant size.
Therefore, the discussion about plant size is equally
applicable to the quantity of work processed and the
application of the limitations provides for the production
volume of a particular facility.
81
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Waste Characteristics
The physical and chemical characteristics of wastes
generated by plating and metal finishing are inherently
accounted for by subcategorization according to process
baths and manufacturing processes which reflect the waste
characteristics. 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.
Treatment Technology
The treatability of wastes from manufacturing operations is
uniform throughout each subcategcry 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 treat-
ment 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.
82
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Summary
Previous regulations for the electroplating point source
category were subcategorized on the basis of process
considerations. Electroplating was separated from metal
finishing processes because electroplating always requires
the action of an electrical current to deposit a metallic
coating on the basis material acting as an electrode. Metal
finishing processes may or may not require a current and may
or may not deposit a metallic coat on the basis meterial.
The processes of anodizing, coating, chemical etching and
milling are sufficiently different so as to warrant separate
subcategories.
In restudying the industry for the purpose of establishing
pretreatment regulations, it was determined that printed
board manufacturing and electroless plating also warrant
separate subcategorization because of the unique mixture of
electrolytic and electroless plating operations found in
these processes. In addition, these processes produce
pollutants which may render normal waste treatment
techniques ineffective if proper safeguards are ignored.
Finally, the foregoing subcategor^zation is consistent with
the existing structure of the industry, each subcategory
tending to be oriented toward individual processes or
identifiable markets which do not overlap significantly.
EFFLUENT LIMITATION BASE
Having selected the appropriate categorization bases and
establishing the subcategories for the various segments, the
next step is to establish a quantitative parameter on which
to base limitations. Since pollutants are measured in
concentration (mg/1), concentration is the obvious first
consideration for quantitative limitations. Concentration
alone, however, is not adequate since it is not
quantitative, and concentration effluent limitations can be
satisfied by dilution - particularly if a plant has no waste
treatment system. In order to preclude the possibility of
dilution, the concentration of pollutants in the discharge
must be multiplied by the discharge flow rate to provide a
mass limitation or standard for each pollutant (mg/hr).
Since effluent discharge rates are a function of the level
of production, this absolute standard requires still another
parameter to account for differences in the actual
production level from plant to plant. Such a parameter must
establish an effluent discharge rate relationship that
changes in proportion to the level of production activity
from plant to plant. The following subsections deal with
83
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the selection of this production related parameter and the
application of this parameter for discharge limitations.
The limitations specified in this document for plants
discharging to publicly owned treatment works (POTW) are
expressed in terms of concentration rather than in terms of
a mass based limitation. Concentration limits are specified
because of the ease of enforcing such limits. 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.
Selection of Production Related 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 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 cf 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 plating and
metal finishing segments, processed area is area plated and
area finished, respectively. Although masking (particularly
hydrophilic masking) might contribute somewhat to dragout,
relatively little masking is used for most plating and metal
finishing. Thus, area finished is selected for the metal
finishing segment. In addition, processed area for
electroplating is readily attainable 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 H-2
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 4-2 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 segment.
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 U-3. Based on these results, it is
apparent that holes cause an increase in dragout, but this
increase is extremely variable and dependent on:
Plating bath characteristics (including viscosity,
pH, and chemical composition).
Physical handling of the boards (types of racks,
drip time, and agitation of parts).
Characteristics of holes (size and density).
Due to the complexity of calculating hole areas and volumes,
no significant data in this area was received from most
plants contacted. Therefore, the specific effect of holes
85
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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 Related Parameter
Basing limitations on processed area results in a mg/sq m
limitation that is calculated from the concentration of
pollutants (mg/1) in a discharge multiplied by the discharge
flow rate (liters/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 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 liir.itations.
Table 4-4 lists operatons applicable to plating. Referring
to Table 4-4, catalyst application and acceleration are
considered operations in plating. This is because these
operations involve the deposition of palladium and tin on
86
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the surface of a plastic part and are thus similar to
plating operations. In addition, acid cleaning and
alkaline cleaning steps are counted as operations if they
precede all electroplating processes in a 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 pretreatment or
posttreatment steps are considered plating operations.
These other pre- and posttreatment 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 pre- and posttreatment
operations are included in the limitations which are
established from overall plant discharges.
Table 4-5 lists operations applicable to metal finishing in
each subcategory. Acid cleaning and alkaline cleaning step
are counted as operations if they precede all metal
finishing processes in a line. Sampling and analysis have
shown that basis metal and surface contaminants are removed
to a significant degree in the initial cleaning steps.
Since the subsequent rinse waters contribute metals and
other contaminants to the waste stream, they are regarded as
operations. Any other pre and post treatment operations are
considered integral with the preceding or subsequent
finishing type operations, and the water used and wastes
produced by these operations are intrinsically included in
the water use and pollutant discharge from the finishing
operation.
87
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TABLE 4-1
METAL FINISHING SUBCATEGORIZATION
Subcategory D - Anodizing
Subcategory E - coatings
Coloring
Chromating
Phosphating
Immersion Plating
Stripping (To salvage improperly coated
parts)
Subcategory F - Chemical Etching and Milling
Chemical Milling
Etching
Bright Dipping
88
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TABLE 4-2
EFFECT OF MASKING ON DRAGOUT
COMPANY
ID
17061
36062
TEST TYPE OF MASK
fl Photoresist
#2 Photoresist
#3 Screen
#4 Photoresist
DRAGODT
UNMASKED
280 mg/1
360.8 mg/1
0.377 mg/1-
in
0.377 mg/l-
in
DRASOUT
MASKED
250 mg/1
386.6 mg/1
0.33. mg/1-
in
0.318 mg/1-
in
DIFFERENCE
-11%
+ 7*
- 2%
- 6%
TABLE 4-3
EFFECT OF HOLES ON DRAGOUT
COMPANY ID
4065
6067
36062
HOLE SIZE
0.077
0.031-0.QUO
0.031-0.QUO
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-in2
0.337 mg/l-in*
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-in2
0.065 mg/l-in*
0.493 mg/l-in2
0.477 mg/l-in2
PERCENT
INCREASE IN
DRAGOUT
25*
42%
30%
17%
5%
92%
74%
49%
50%
89
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TABLE U-4
COMMON AND PRECIOUS METALS
AND ELECTROLESS PLATING OPERATIONS
Common Metals Plating (Subcategory A)
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
Precious Metals Plating (Subcategory B)
Gold Electroplating
Indium Electroplating
Palladium Electroplating
Platinum Electroplating
Rhodium Electroplating
Silver Electroplating
Electroless Plating (Subcategory G)
Electroless Plating on Metals
Electroless Plating on Plastics
Catalyst Application
Acceleration
All Subcategories
Stripping (to salvage improperly plated parts)
Coloring**
Chromating**
Phosphating**
Acid Cleaning
Alkaline Cleaning
**Counted as a plating operation only if an integral part of
a plating line. If not integral with plating, then it is a
metal finishing operation (Reference metal finishing segment
of Electroplating Point Source Category).
90
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TABLE 4-5
METAL FINISHING OPERATIONS
Suhcategory D - Anodizing
Anodizing
Acid Cleaning
Alkaline Cleaning
Sufccategory E - Coatings
Coloring*
Chromating*
Phosphating*
Stripping (To salvage improperly coated
parts)
Immersion Plating
Acid Cleaning
Alkaline Cleaning
Subcategory F - Chemical Milling and Etching
Chemical Milling
Etching
Bright Dipping
Acid Cleaning
Alkaline Cleaning
*Counted as a metal finishing operation if not integral with
a plating line. If integral with plating line, it is
counted as a plating operation (Reference Plating Segment of
Electroplating Point Source Category).
91
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Table H-6 lists operations applicable to printed board
manufacture. Referring to Table 4-6r both catalyst
application and acceleration steps are considered operations
in the manufacture of printed boards. This.is because these
operations involve the depostion of palladium and tin onto
the surface of the board and are thus similar to plating
operations. In addition, acid cleaning and alkaline
cleaning steps 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 conatminants to the waste stream, these
initial cleaning steps are regarded as operations. No other
pretreatment or posttreatment type steps are considered
operations. These other pre- and pcsttreatment operations
are considered integral with the 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.
92
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TABLE U-6
OPERATIONS IN THE MANUFACTURE OF PRINTED 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
93
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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 subsections present the
characteristics of the wastes for the plating, metal
finishing, and printed board manufacturing segments of this
point source category because of the distinctly different
operations performed in each segment. These segments are
not mutually exclusive subdivisions of the electroplating
point source category, however, because plants often perform
operations in more than one segment.
CHARACTERISTICS OF WASTES FROM THE PIATIKG SEGMENTS
Wastewater from plating processes comes from cleaning,
surface preparation, plating, and related operations. The
constituents in this 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 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 Usage
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
95
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97
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used to remove the process solution film from the surface of
the work pieces. As 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 platino 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 - 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.
Water from 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.
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.
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.
98
-------
WORK FLOW
CLEAN
WATER
ALKALINE
CLEAN
USE
ACID
DIP
RINSr
CYANIDE
COPPER STRIKE
RINSE
ACID
DIP
ACID
COPPER
PLATE
RK
NICKEL
RI1>
ISE
PLATE
SE
"* v
NEUTRALIZE AND
PRECIPITATE
OXIDIZE
CYANIDE
jf
PRECIPITATE
COPPER
1
SETTLE
T~
SLUDGE
PRECJPITATI
NICKEL AND COP
PER
REDUCE
CHROMIUM
*
T
PRECIPITATE
CHROMIUM
FIGURE 5-1 SCHEMATIC FLOW CHART FOR WATER FLOW \t-
CHROMIUM PLATING ZINC DIE CASTINGS, CF '~T R,\- I'.,
99
-------
ELECTROLESS
NICKEL
ON
PLASTIC
WORK FLOW
1
WATER
SOURCE'
CHROMIC
ETCH
C CURRENT
RINSE
SPRAY
RINSE
NEUTRAL-
IZATION
RINSE
APPLY
CATALYST
RINSE
ACCELER-
ATION
RINSE
SPRAY
RINSE
ELECTRO-
LESS NI
RINSE
RINSE
T
TO
CHROME
'REDUC-
TION
TO
—^PRECIP-
ITATION
ELECTROLESS
NICKEL
ON
METAL
WATER
SOURCE
h
WORK
J
FLOW
I
ALKALINE
CLEAN
RINSE
ACID
CLEAN
RINSE
NEUTRAL-
IZATION
RINSE
ELECTRO-
LESS NI
RINSE
RINSE
^
fc
P
TO
.WASTE
TREAT-
MENT
FIGURE 5-2
USE OF RINSE WATER IN ELECTROLESS PLATING OF NICKEL
ICO
-------
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 frcm 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 durina
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.
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
101
-------
process the tin is removed. A chromic acid pretreatment of
the plastic usually precedes the catalyst application.
Plating Operations and Posttreatment - Plating and
posttreatment 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 b
-------
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 and 5-H are the range of
concentration values for each constituent. These values
were determined by a statistical analysis of the raw waste
streams for 67 plants in the data base. This analysis
involved allocating total pollutant raw waste masses to
appropriate subcategories. Nc 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.
The range of values in Table 5-5 were actual concentrations
from segregated electroless plating rinse waters. These
data were obtained from visits to eight plants which
performed electroless nickel plating on metal or plastics.
Table 5-6 shows chelating agent data for five plants which
were sampled for chelating agent determinations.
103
-------
TABLE 5-3
COMPOSITION OF RAW WASTE STREAMS
FROM COMMON METALS PLATING
(mg/1)
Copper
Nickel
Chromium, Total
Chromium, Hexavalent
Zinc
Cyanide, Total
0.032-272.5
0.019-2954
0.088-525.9
0.005-334.5
0.112-252.0
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
104
-------
TABLE 5-4
COMPOSITION OF RAW WASTE STREAMS
FROM PRECIOUS METALS PLATING
(mg/1)
Silver
Gold
Cyanide, Total
Cyanide, Amenable to Chlorination
Palladium
Platinum
Rhodium
Phosphorus
Total Suspended Solids
*Only 1 plant had a measurable level
of this pollutant.
0.050-176.4
0.013-24.89
0.005-9.970
0.003-8.420
0.038-2.207
0.112-6.457
0.034*
0.020-144.0
0.100-9970
105
-------
TABLE 5-5
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 5-6
CHELATING AGENTS
IN
ELECTROLESS PLATING
No. of Plants
Chelating No. of Plants Where F<
Agents Reporting Use by-Analysis
EDTA
NTA
Citric Acid
Glutaric
Acid
Lactic Acid
Tartrates
1
3
4
4
1
3
0
3
4
3
0
2
jund Range
mg/1 mg/1
.1-89.9 9.5
.1-1213 7.5
.1-17.3 10.3
.1-7.66 0.1
106
-------
CHARACTERISTICS OF WASTES FROM METAL FINISHING SEGMENT
wastewater from metal finishing processes comes from
cleaning, pickling, anodizing, coating, etching, and related
operations. The constituents in this wastewater include the
basis material being finished as well as the components in
the processing solutions. Predominant among the wastewater
constituents are ions of copper, nickel, chromium, zinc,
lead, tin, cadmium, and ions that occur in cleaning,
pickling, or processing baths such as phosphates, chlorides,
and various metal complexing agents.
Water Usage
Water is used for rinsing workpieces, washing away spills,
air scrubbing, preparing solutions, and washing equipment.
Water usage for these purposes is identical to that
described for the plating segment above.
Sources of Waste
The following process solutions are the major waste sources
during normal metal finishing operations; alkaline cleaners,
acidy cleaners, and operations and posttreatment. The
discussion of alkaline cleaners and acid cleaners as sources
of wastes was presented above for the plating segment and
will not be repeated here.
Operations and Posttreatment - Baths used for anodizing,
coating and etching usually contain metal salts, acids,
bases, dissolved basis metals, complexing agents and other
deposition control agents. Each subcategory is discussed in
more detail below.
Chromium, aluminum, and maganese 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 consist only of hot water
rinsing. Occasionally, anodized parts are sealed with a
chromium salt solution cr 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
107
-------
into the chromating baths. As with anodizing and the other
coating processes, hot water rinsing is often the only post-
treatment for chromated parts. coloring of chromate
conversions is occasionally practiced.
The phosphates of zinc, iron, maganese, 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.
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 pcsttreated, except for
hot water rinsing.
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 cyanxide. Posttreatment baths for chemical
milling or etching would not contain significantly different
consitituents than those listed above.
Waste Constituents And Quantities
The results of analysis of the specific constituents of raw
waste streams from 50 metal finishing establishments in the
existing data base are presented in Tables 5-7 through 5-9.
These represent the following subcategories:
Table 5-7 Anodizing
Table 5-8 Coatings
Table 5-9 Chemical Milling and Etching
The concentrations presented are the range of values for
each constituent. These values were determined by a
statistical analysis of the raw waste streams for 50 plants
in the data base. This analysis involved allocating total
pollutant raw waste masses to appropriate subcategories. No
108
-------
allowance was made for alkaline or acid cleaning. Measured
concentrations could not be used since nearly all plants
visited had wastes applicable to more than one subcategory.
It should be noted that only plants which used a particular
metal in their process were used in averaging values for
that metal.
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, chromium reduction, and pH
adjustment, at a point just prior to clarification.
109
-------
TABLE 5-7
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 0.001 - 67.56
Phosphorus 0.176 - 33.00
Total Suspended Solids 36.09 - 924.0
110
-------
TABLE 5-8
COMPOSITION OF RAW WASTE STREAMS
FROM COATINGS
(mg/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
111
-------
TABLE 5-9
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 tc 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
112
-------
CHARACTERISTICS OF WASTES FROM PRINTED BOARD MANUFACTURE SEGMENT
This section presents the waste characteristics of the
printed board (PB) industry. Included is a description of
not only the wastes, but also the sources of the wastes and
the water usage for printed board manufacturing.
Process Schematic And Waste Sources
Printed board manufacture involves several different
operations which use water. An overall process flow diagram
for a typical printed board plant is shewn in Figure 5-3.
Major waste producing steps are detailed in Figures 5-1
through 5-8. After the initial cutting, drilling and
sanding of the boards, the board surface is prepared for
plating electroless copper (reference Figure 5-4). This
surface preparation involves an etchback (removal of built-
up plastic around holes) and an acid and alkaline cleaning
to remove grime, oils, and fingerprints. The board is then
etched, and subsequent rinsing operations add copper to the
rinse waters. Following etching, the catalyst is applied,
and rinsing operations following catalyst application
contribute tin and palladium to the wastewater. The entire
board is then electroless copper plated and rinsed,
contributing copper and chelating agents to the wastewater
stream.
Following electroless copper plating, a plating resist is
applied in non-circuit areas. If a photoresist pattern is
used, silver might be added to the wastestream during the
development process. Following application of a resist, a
series of electroplates are applied (reference Figure 5-5).
First the circuit is copper plated, and the rinses directly
following this step contain significant amounts of copper.
A solder electroplate is applied next, and the rinse
following this operation contributes tin, lead and fluorides
to the wastewater. Fcr copper removal in non-circuit areas,
an etch step (Figure 5-6) is next. This releases more
copper to subsequent rinse waters. After the etch
operation, a variety of tab plating processes can be
utilized depending on the board design requirements. These
include nickel electroplating, gold electroplating
(reference Figure 5-7), rhodium electroplating and tin
immersion plating (reference Figure 5-8). Any or all of
these processes contribute specific metals to the rinse
waters and, in so doing, increase the total and suspended
solids levels as well as specific metals concentrations in
these waters.
113
-------
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119
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In addition to the above sources of wastewater from specific
processes, wastewater is also generated by the following:
1. Rinsing away spills
2. Air scrubbing water
3. Washing of equipment
4. Dumping spent process solutions
As is the case with rinsewaters, the wastewater from the
above sources contributes the specific metals and chemicals
used in the process baths to the overall waste stream. This
does not significantly alter the qualitative content of the
stream made up of rinse waters from the processes, but it
does increase the amount of each constituent over and above
that contained in the rinse water stream.
Water Usage
As discussed in the previous section and shown in Figures 5-
4 through 5-8, water is employed in the printed board
industry in the following manufacturing processes:
1. Surface preparation - The rinses following
scrubbing, alkaline cleaning, acid cleaning,
etchback, catalyst application and activation.
2. Electroless plating - Rinses following the
electroless plating step.
3. Pattern plating - Rinse following acid cleaning,
alkaline cleaning, copper plating and solder
plating.
4. Etching - Rinses following etching and solder
brightening.
5. Tab plating - Rinses following solder stripping,
scrubbing, acid cleaning, and nickel, gold or other
plating operations.
6. Immersion plating - Rinses following acid cleaning
and immersion tin plating.
Additionally, water may be used for subsidiary purposes such
as rinsing away spills, etc., as discussed previously.
The specific quantity of water used in each of the above
areas depends upon the amount and type of work processed and
the type of rinsing used.
120
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Waste Constituents And Quantities
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
installations 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 pretreatment 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 fluorboric 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 chealting agents
present are primarily from the electroless plating
operations, although others may have been added by the
cleaning, immersion plating, and gold plating operations.
121
-------
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 (mg/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
finer/11
15.8 - 35.
0.9 - 134
1.3 - 110
47.6 - 610
122
-------
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. The characteristics of the pollutant require
control in effluent discharges.
2. The pollutant is commonly present in significant
amounts in the processing solutions used in the
electroplating industry.
3. The pollutant can be controlled by practical
technology that is currently available for waste-
water treatment.
The following section discusses the characteristis of all
the pollutant parameters, regardless of whether they are
selected for regulations for the Electroplating Point Source
Category. Table 6-2 presents the list of pollutant
parameters and indicates whether they were selected as
pollutants for the Electroplating Point Source Category.
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.
123
-------
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TABLE 6-2
PARAMETERS NOT SELECTED FOP REGULATION
Pollutant Pretreatment
Parameter selection
Copper 1
Nickel 1
Chromium, total 1
Chromium, hexavalent 1
Zinc 1
Cyanide, total 1
Cyanide, amenable 1
Fluoride
Cadmium 1
Lead 1
Iron
Tin
Platinum Group Metals
Silver
Gold 1
Phosphorus
Total Suspended Solids
pH 1
Aluminium
Ammoni a
Biochemical Oxygen Demand
Boron
Chlorine
Oil and Grease
Legend
1 = selected as pretreatment parameter
2 = not selected because of limited occurrence
in Electroplating Point Source Category
3 = not selected because of removal accomplished
in POTW
125
-------
Traces of copper are found in all forms of plant and animal
life, and it is an essential trace element for nutrition.
Copper is not considered to be a cumulative systemic poison
for humans as it is readily excreted by the body, but it can
cause symptoms or gastroenteritis, with nausea and
intestinal irritations, at relatively low dosages. The
limiting factor in domestic water supplies is taste
Threshold concentrations for taste have been generally
reported in the range of 1.0-2.0 mg/1 of copper while
concentrations of 5.0 to 7.5 mg/1 have made water completely
undrinkable. It has been recommended that the copper in
public water supply sources not exceed 1 mg/1.
Copper salts cause undesirable color reactions in the food
industry and cause pitting when deposited on some other
metals such as aluminum and galvanized steel. The textile
industry is affected when copper salts are present in water
used for processing of fabrics. Irrigation waters
containing more than minute quantities of copper can be
detrimental to certain crops. The toxicity of copper to
aquatic organisms varies significantly, not only with the
species, but also with the physical and chemical
characteristics of the water, including temperature,
hardness, turbidity, and carbon dioxide content. In hard
water, the toxicity of copper salts may be reuduced by the
precipitation of copper carbonate or other insoluble
compounds. The sulfates of copper and zinc, and of copper
and cadmium are synergistic in their toxic effect on fish.
Copper concentrations less than 1 mg/1 have been reported to
be toxic, particularly in soft water, to many kinds of fish,
crustaceans, mollusks, insects, phytoplankton and
zooplankton. Concentrations of copper, for example, are
detrimental to some oysters above .1 ppm. Oysters cultured
in sea water containing 0.13-0.5 ppm of copper deposited
metal in their bodies and became unfit as a food substance.
Nickel (Ni)
Elemental nickel is seldom found in nature in the pure
state. Nickel is obtained commercially from pentlendite and
pyrrohotite. It is a relatively plentiful element and is
widely distributed throughout the earthfs crust. It occurs
in marine organisms and is found in the oceans. Depending
on the dose, the organism involved, and the type of compound
involved, nickel may be beneficial or toxic. Pure nickel is
not soluble in water but many of its salts are very soluble.
The uses of nickel are many and varied. It is machined and
formed for various products as both nickel and as an alloy
126
-------
with other metals. Nickel is also used extensively as a
plating metal primarily for a protective coating for steel.
The toxicity of nickel to man is believed to be very low and
systematic poisoning of human beings by nickel or nickel
salts is almost unknown. Nickel salts have caused the
inhibition of the biochemical oxidation of sewage. They
also caused a 50 percent reduction in the oxygen utilization
from synthetic sewage in concentrations of 3.6 mg/1 to 27
mg/1 of various nickel salts.
Nickel is exteremely toxic to citrus plants. It is found in
many soils in California, generally in insoluble form, but
excessive acidification of such soil may render it soluble,
causing severe injury to or the death of plants. Many
experiments with plants in solution cultures have shown that
nickel at 0.5 to 1.0 mg/1 is inhibitory to growth.
Nickel salts can kill fish at very low concentrations.
However, it has been found to be less toxic to some fish
than copper, zinc and iron. Data for the fathead minnow
show death occurring in the range of 5-43 mg/1 depending on
the alkalinity of the water.
Nickel is present in coastal and open ocean concentrations
in the range of 0.1 - 6.0 ug/1, although the most common
values are 2-3 ug/1. Marine animals contain up to 400
ug/1, and marine plants contain up to 3,000 ug/1. The
lethal limit of nickel to some marine fish has been reported
as low as 0.8 ppm. Concentrations of 13.1 mg/1 have been
reported to cause a 50 percent reduction of the
photosynthetic activity in the giant kelp (Macrocystis
pyrifera) in 96 hours, and a low concentration was found to
kill oyster eggs.
Chromium (Cr)
Chromium is an elemental metal usually found as a chromite
(FeCr20ft). 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 used in the
electroplating industry as an ornamental and corrosion
resistent plating on steel and can be used in pigments and
as a pickling acid (chromic acid).
The two most prevalent chromium forms found in industry
waste waters are hexavalent and trivalent chromium. Chromic
127
-------
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.
Chromium, in its various valence states, is hazardous to
man. It can produce lung tumors when inhaled and induces
skin sensitizations. Large doses of chromates have
corrosive effects on the intestinal tract and can cause
inflamation of the kidneys. Levels of chromate ions that
have no effect on man appear to be so low as to prohibit
determination to date. The recommendation for public water
supplies is that such supplies contain no more than 0.05
mg/1 total chromium.
The toxicity of chromium salts to fish and other aquatic
life varies widely with the species, temperature, pH,
valence of the chromium and synergistic or antagonistic
effects, especially that of hard water. Studies have shown
that trivalent chromium is more toxic to fish of some types
than hexavalent chromium. Other studies have shown opposite
effects. Fish food organisms and other lower forms of
aquatic life are extremely sensitive to chromium and it also
inhibits the growth of algae. Therefore, both hexavalent
and trivalent chromium must be considered harmful to
particular fish or organisms.
Zinc (Zn)
Occurring abundantly 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, seme zinc salts (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.
In soft water, concentrations of zinc ranging from 0.1 to
1.0 mg/1 have been reported to be lethal to fish. Zinc is
thought to exert its toxic action by forming insoluble
compounds with the mucous that covers the gills, by damage
to the gill epithelium, cr possibly by acting as an internal
poison. The sensitivity of fish to zinc varies with
128
-------
species, age, and condition, as well as with the physical
and chemical chracteristics of the water. Some
acclimatization to the presence of the zinc is possible. It
also has been observed that the effects of zinc poisoning
may not become apparent immediately so that fish removed
from zinc-contaminated to zinc-free water may die as long as
48 hours after the removal. The presence of copper in water
may increase the toxicity of zinc to aquatic organisms,
while the presence of calcium or hardness may decrease the
relative toxicity.
A complex relationship exists between zinc concentrations,
dissolved oxygen, pH, temperature, and calcium and magnesium
concentrations. Prediction of harmful effects has been less
than reliable and controlled studies have not been
extensively documented.
Concentrations of zinc in excess of 5 mg/1 in public water
supply sources cause an undesirable taste which persists
through conventional treatment. Zinc can have an adverse
effect on man and animals at high concentrations.
Observed values for the distribution of zinc in ocean waters
varies widely. The major concern with zinc compounds in
marine waters is not one of actute lethal effects, but
rather one of the long term sublethal effects of the
metallic compounds and complexes. From the point of view of
accute lethal effects, invertebrate marine animals seem to
be the most sensitive organisms tested.
A variety of freshwater plants tested manifested harmful
symptoms at concentrations of 10 mg/1. Zinc sulfate has
also been found to be lethal to many plants and it could
impair agricultural uses of the water.
Cyanide
Cyanide is a compound that is widely used in industry
primarily as sodium cyanide (NaCN) 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. 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
129
-------
below 7 there is less than 1 percent of the cyanide
molecules in the form of the CN ion and the rest is present
as HCN. When the pH is increased to 8r 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 produced a two-
to threefold increase in the rate of the lethal action of
cyanide.
In the body, the CN ion, except for a small portion exhaled,
is rapidly changed into a relatively non-toxic complex
(thiocyanate) in the liver and eliminated in the urine.
There is no evidence that the CN is stored in the body. The
safe ingested limit of cyanide has been estimated at
something less than 18 ing/day, part of which comes from
normal environment and industrial exposure. The average
fatal dose of HCN by ingestion by man is 50 to 60 mg. It
has been recommended that a limit of 0.2 mg/1 cyanide not be
exceeded in public water supply sources.
The harmful effects of the cyanides on aquatic life is
affected by the pH, temperature, dissolved oxygen content,
and the concentration of minerals in the water. The
biochemical degradation of cyanide is not affected by
temperature in the range of 10 degrees C to 35 degrees C
while the toxicity of HCN is increased at higher
temperatures.
On the lower forms of life and organisms, cyanide does not
seem to be as toxic as it is toward fish. The organisms
that digest BOD were found to be inhibited at 1.0 mg/1 and
at 60 mg/1 although the effect is more one of delay in
exertion of BOD than total reduction.
Certain metals such as nickel may complex with cyanide to
reduce lethality, especially at higher pH values. On the
other hand, zinc and cadmium cyanide complexes may be
exceedingly toxic.
Fluoride
Fluorine is the most reactive of the ncnmetals and is never
found free in nature. It is a constituent of fluorite or
fluorspar, calcium fluoride, cryolite, and sodium aluminum
fluoride. Due to their origins, fluorides in high
concentrations are not a common constituent of natural
surface waters; however, they may occur in hazardous
concentrations in ground waters.
130
-------
Fluoride can be found in plating rinses and in glass etching
rinse waters. Fluorides are also used as a flux in the
manufacture of steel, fcr preserving wood and mucilages, as
a disinfectant and in insecticides.
Fluorides in sufficient quantities are toxic to humans with
doses of 250 to 450 mg giving severe symptoms and 4.0 grams
causing death. A concentration of 0.5 g/kg of body weight
has been reported as a fatal dosage.
There are numerous articles describing the effects of
fluoride-bearing waters on dental enamel of children; these
studies lead to the generalization that water containing
less than 0.9 to 1.0 mg/1 of fluoride will seldom cause
mottled enamel in children, and for adults, concentrations
less than 3 or 4 mg/1 are not likely to cause endemic
cumulative fluorosis and skeletal effects. Abundant
literature is also available describing the advantages of
maintaining 0.8 to 1.5 mg/1 of fluoride ion in drinking
water to aid in the reduction of dental decay, especially
among children. The recommended maximum levels of floride
in public water supply sources range from 1.4 to 2.4 mg/1.
Fluorides may be harmful in certain industries, particularly
those involved in the production of food, beverages,
pharmaceutical, and medicines. Fluorides found in
irrigation waters in high concentrations (up to 360 mg/1)
have caused damage to certain plants exposed to these
waters. Chronic fluoride poisoning of livestock has been
observed in areas where water contained 10 to 15 mg/1
fluoride. Concentrations of 30 - 50 mg/1 of fluoride in the
total ration of dairy cows is considered the upper safe
limit. Fluoride from waters apparently does not accumulate
in soft tissue to a significant degree and it is transferred
to a very small extent into the milk and to somewhat greater
degree into eggs. Data for fresh water indicate that
fluorides are toxic to fish at concentrations higher than
1.5 mg/1.
Cadmium (Cd)
Cadmium is a relatively rare element that is seldom found in
sufficient quantities in a pure state to warrant mining or
extraction from the earth's surface. It is found in trace
amounts of about 1 ppm throughout the earth's crust.
Cadmium is, however, a valuable by-product of zinc
production.
Cadmium is used primarily as a metal plating material and
can be found as an impurity in the secondary refining of
131
-------
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.
Toxic effects of cadmium on man have been reported from
throughout the world. Cadmium is normally ingested by
humans through food and water and also by breathing air
contaminated by cadmium. Cadmium in drinking water supplies
is extremely hazardous to humans, and conventional
treatment, as practiced in the United States, does not
remove it. Cadmium is cumulative in the liver, kidney,
pancreas, and thyroid of humans and other animals. A severe
bone and kidney syndrome in Japan has been associated with
the ingestion of as little as 600 ug/day of cadmium. The
allowable cadmium concentration in drinking water is set as
low as 0.01 mg/1 in the U. S. and as high as 0.10 mg/1 in
Russia.
Cadmium acts synergistically with other metals. Copper and
zinc substanially increase its toxicity. Cadmium is
concentrated by marine organisms, particularly molluscs,
which accumulate cadmium in calcareous tissues and in the
viscera. A concentration factor of 1000 for cadmium in fish
muscle has been reported, as have concentration factors of
3000 in marine plants, and up to 29,600 in certain marine
animals. The eggs and larvae of fish are apparently more
sensitive than adult fish to poisoning by cadmium, and
crustaceans appear to be more sensitive than fish eggs and
larvae.
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.
132
-------
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 the
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 with
the ingestion of an excess of 0.6 mg per day over a period
of years. It has been recommended that 0.05 mg/1 lead not
be exceeded in public water supply sources.
Chronic lead poisoning has occurred among animals at levels
of 0.18 mg/1 of lead in soft water and by concentrations
under 2.4 mg/1 in hard water. Farm animals are poisoned by
lead more frequently than any other poison. Sources of this
occurrence include paint and water with the lead in solution
as well as in suspension. Each year thousands of wild water
fowl are poisoned from lead shot that is discharged over
feeding areas and ingested by the water fowl. The bacterial
decomposition of organic matter is inhibited by lead at
levels of 0.1 to 0.5 mg/1.
Fish and other marine life have had adverse effects from
lead and salts in their environment. Experiments have shown
that small concentrations of heavy metals, especially of
lead, have caused a film of coagulated mucus to form first
over the gills and then over the entire body probably
causing suffocation of the fish due to this obstructive
layer. Toxicity of lead is increased with a reduction of
dissolved oxygen concentration in the water.
Iron (Fe)
Iron is an abundant metal found in the earth's crust. The
most common iron ore is hematite from which iron is obtained
by reduction with carbon. Other forms of commercial ores
are magnetite and taconite. Pure iron is not often found in
commercial use, but it is usually alloyed with other metals
and minerals, the most common being carbon.
Iron is the basic element in the production of steel and
steel alloys, iron with carbon is used for casting of major
parts of machines and it can be machined, cast, formed, and
welded. Ferrous iron is used in paints, while powdered iron
can be sintered and used in powder metallurgy. Iron
compounds are also used to precipitate other metals and
undesirable minerals from industrial waste water streams.
Iron is chemically reactive and corrodes rapidly in the
presence of moist air and at elevated temperatures. In
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water and in the presence of oxygen, the resulting products
of iron corrosion may be pollutants in water.
Corrosion products of iron in water cause staining of
porcelain fixtures, and ferric iron combines with the tannin
to produce a dark violet color. The presence of excessive
iron in water discourages cows from drinking and, thus,
reduces milk production. High concentrations of ferric and
ferrous ions in water kill most fish introduced to the
solution within a few hours. The killing action is
attributed to coating of iron hydroxide precipitates on the
gills. Iron oxidizing bacteria are dependent on iron in
water growth. These bacteria form slimes that can affect
the esthetic values of bodies of water and cause stoppage of
flows in pipes.
Iron is an essential nutrient and micronutrient for all
forms of growth. Drinking water standards in the U. S. have
set a recommended limit of 9.3 mg/1 of iron in domestic
water supplies based not on the physiological
considerations, but rather on aesthetic and taste
considerations of iron in water.
Since iron is not severely toxic (except at very high
concentrations) , the fact that it does have a severe
nuisance value warrants its inclusion as a pollutant
parameter. It may be in fairly high concentrations in
plating wastes, and is removable by current treatment
practice.
Tin (Sn)
Tin is not present in natural water, but it may occur in
industrial wastes. Stannic and stannous chloride are used
as mordants for reviving colors, dyeing fabrics, weighting
silk, and tinning vessels. Stannic chromate is used in
decorating porcelain, and stannic oxide is used in glass
works, dye houses, and for fingernail polishes. Stannic
sulfide is used in some lacquers and varnishes. Tin
compounds are also used in fungicides, insecticides, and
anti-helminthics.
No reports have been uncovered to indicate that tin is
detrimental in domestic water supplies. Traces of tin occur
in the human diet from canned foods, and it has been
estimated that the average diet contains 17.1U mg of tin per
day. Man can apparently tolerate 850 to 1000 mg per day of
free tin in his diet.
13U
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On the basis of feeding experiments, it is unlikely that any
concentrations of tin that could occur in most natural
waters would be detrimental to livestock. Most species of
fish can withstand fairly large concentrations of tin;
however, tin is about ten times as toxic as copper to
certain marine organisms such as barnacles and tubeworms.
Platinum Group Metals
The platinum group metals of concern in electroplating are
palladium, platinum, and rhodium. Only limited data are
available, but toxicity of this group appears to be at the
same order of mangitude as that of gold. In one experiment,
lethal doses for fresh water fish were 14, 7, and 33 mg/1
for gold, palladium, and platinum salts, respectively.
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 (Ag3A S^) , and pyrargyrite (Ag_3SbS3) .
From these ores, silver ions may be leached into ground
waters and surface waters, but since many silver salts such
as the chloride, sulfide, phosphate, and arsenate are
insoluble, silver ions do not usually occur in significant
concentration in natural waters.
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.
While metallic silver itself is not considered to be
poisonous for humans, most of its salts are poisonous due to
anions present. silver compounds can be absorbed in the
circulatory system and reduced silver deposited in the
various tissues of the body. A condition known as argyria,
a permanent greyish pigmentation of the skin and mucous
membranes, can result. Concentrations in the range of O.U-1
mg/liter have caused pathologic changes in the kidneys,
liver and spleen of rats.
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Silver is recognized as a bactericide and doses as low as
0.000001 to 0.5 mg/1 have been reported as sufficient to
sterilize water.
Phosphorus
Phosphorus occurs in natural waters and in waste waters in
the form of various types of phosphates. These forms are
commonly classified into orthcphosphates, condensed
phosphates (pyro-, meta-, and polyphosphorus), and
organically bound phosphates. These may occur in the
soluble form, in particles of detritus or in the bodies of
aquatic organisms.
The various forms of phosphates find their way into waste
waters from a variety of industrial, residential, and
commerical sources. Small amounts of certain condensed
phosphates are added to some water supplies in the course of
potable water treatment. Large quantities of the same
compounds may be added when the water is used for laundering
or other cleaning since these materials are major
constituents or many commercial cleaning preparations.
Phosphate coating of metals is another major source of
phosphates in certain industrial effluents.
The increasing problem of the growth of algae in streams and
lakes appears to be associated with the increasing presence
of certain dissolved nutrients, chief among which is
phosphorus. Phosphorus is an element which is essential to
the growth of organisms and it can often be the nutrient
that limits the aquatic growth that a body of water can
support. In instances where phosphorus is a growth limiting
nutrient, the discharge of sewage, agricultural drainage or
certain industrial wastes to a receiving water may stimulate
the growth, in nuisance quantities, of photosynthetic
aquatic microorganisms and macroorganisms.
The increse in organic matter production by algae and plants
in a lake undergoing eutrophication has ramifications
throughout the aquatic ecosystem. Greater demand is placed
on the dissolved oxygen in the water as the organic matter
decomposes at the termination of the life cycles. Because
of this process, the deeper waters of the lake may become
entirely depleted of oxygen, thereby destroying fish habitat
and leading to the elimination of desirable species. Of
great importance is the fact that nutrients inadvertently
introduced to a lake are, for the most part, trapped there
and recycled in accelerated biological processes.
Consequently, the damage done to a lake in a relatively
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short time requires a many fold increase in time for
recovery of the lake.
When a plant population is stimulated in production and
attains a nuisance status, a large number of associated
liabilities are immediately apparent. Dense populations of
pond weeds make swimming dangerous. Boating and water
skiing and sometimes fishing may be eliminated because of
the mass of vegetation that serves as a physical impediment
to such activities. Plant populations have been associated
with stunted fish populations and with poor fishing. Plant
nuisances emit vile stenches, impart tastes and odors to
water supplies, reduce the efficiency of industrial and
municipal water treatment, impair aesthetic beauty, reduce
or restrict resort trade, lower waterfront property values,
cause skin rashes to man during water contact, and serve as
a desired substrate and breeding ground for flies.
Phosphorus in the elemental form is particularly toxic, and
subject to bioaccumulation in much the same way as mercury.
Colloidal elemental phosphorus will poison marine fish
(causing skin tissue breakdown and discoloration). Also,
phosphorus is capable of being concentrated and will
accumulate in organs and soft tissues. Experiments have
shown that marine fish will concentrate phosphorus from
water containing as little as 1 ug/1.
Total Suspended Solids (TSS)
Suspended solids include both organic and inorganic
materials. The inorganic compounds include sand, silt, and
clay. The organic fraction includes such materials as
grease, oil, tar, and animal and vegetable waste products.
These solids may settle out rapidly and bottom deposits are
often a mixture of both organic and inorganic solids.
Solids may be suspended in water for a time, and then settle
to the bed of the stream or lake. These solids discharged
with man's wastes may be inert, slowly biodegradable
materials, or rapidly decomposable substances. While in
suspension, they increase the turbidity of the water, reduce
light penetration and impair the photosynthetic activity of
aquatic plants.
Suspended solids in water interfere with many industrial
processes, cause foaming in toilers and incrustations on
equipment exposed to such water, especially as the
temperature rises. They are undesirable in process water
used in the manufacture of steel, in the textile industry,
in laundries, in dyeing, and in cooling systems.
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Solids in suspension are aesthetically displeasing. When
they settle to form sludge deposits on the stream or lake
bed, they are often damaging to the life in the water.
Solids, when transformed to sludge deposits, may do a
variety of damaging things, including blanketing the stream
or lake bed and thereby destroying the living spaces for
those benthic organisms that would otherwise occupy the
habitat. When of an organic nature, solids use a portion or
all of the dissolved oxygen available in the area. Organic
materials also serve as a food source for sludgeworms and
associated organisms.
Disregarding any toxic effect attributable to substances
leached out by water, suspended solids may kill fish and
shellfish by causing abrasive injuries and by clogging the
gills and respiratory passages of various aquatic fauna.
Indirectly, suspended solids are inimical to aquatic life
because they screen out light, and they promote and maintain
the development of noxious conditions through oxygen
depletion. This results in the killing of fish and fish
food organisms. Suspended solids also reduce the
recreational value of the water.
Although not a specific pollutant, pH is related to the
acidity or alkalinity of a waste water stream. It is not a
linear or direct measure of either; however, it may properly
be used as an indicator to control both excess acidity and
excess alkalinity in water. The term pH is used to describe
the hydrogen ion - hydroxyl ion balance in water.
Technically, pH is the hydrogen ion concentration or
activity present in a given solution. pH numbers are the
negative logarithm of the hydrogen ion concentration. A pH
of 7 generally indicates neutrality or a balance between
free hydrogen and free hydroxyl icns. Solutions with a pH
above 7 indicate that the solution is alkaline, while a pH
below 7 indicates that the solution is acid.
Knowledge of the pH of water or waste water is useful in
determining necessary measures for corrosion control,
pollution control, and disinfection. Waters with a pH below
6.0 are corrosive to water works structures, distribution
lines, and household plumbing fixtures and such corrosion
can add constituents to drinking water such as iron, copper,
zinc, cadmium, and lead. Low pH waters not only tend to
dissolve metals from structures and fixtures but also tend
to redissolve or leach metals from sludges and bottom
sediments. The hydrogen ion concentration can affect the
"taste" of the water and at a low pH, water tastes "sour".
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Extremes of pH or rapid pH changes can exert stress
conditions or kill aquatic life outright. Even moderate
changes from "acceptable" criteria limits of pH are
deleterious to some species. The relative toxicity to
aquatic life of many materials is increased by changes in
the water pH. For example, metalocyanide complexes can
increase a thousand-fold in toxicity with a drop of 1.5 pH
units. Similarly, the toxicity of ammonia is a function of
pH. The bacterial effect of chlorine in most cases is less
as the pH increases, and it is economically advantageous to
keep the pH close to 7.
Aluminum (Al)
Aluminum is an abundant metal fcund in the earth's crust
(8.1%), but is never found free in nature. Pure aluminum, a
silvery white metal, possesses many desirable
characteristics. It is light, has a pleasing appearance,
can easily be formed, machined, or cast, has a high thermal
conductivity, and it is non-magnetic and non-sparking and
stands second among metals in the scale of malleability and
sixth in ductility.
Although the metal itself is insoluble, some of its salts
are readily soluble. Other aluminum salts are quite
insoluble, however, and consequently aluminum is not likely
to occur for long in surface waters because its precipitates
and settles or is absorbed as aluminum hydroxide and
aluminum carbonate. Aluminum is also nontoxic and its salts
are used as coagulants in water treatment. Aluminum is
commonly used in cooking utensils and there is no known
physiological effect on man from low concentrations of this
metal in drinking waters.
Ammonia (NH3_)
Ammonia occurs in surface and ground waters as a result of
the decomposition of nitrogenous organic matter. It is one
of the constituents of the complex nitrogen cycle. It may
also result from the discharge of industrial wastes from
chemical or gas plants, from refrigeration plants, from
scouring and cleaning operations where "ammonia water" is
used from the processing of meat and poultry products, from
rendering operations, from leather tanning plants, and from
the manufacture of certain organic and inorganic chemicals.
Because ammonia may be indicative of pollution and because
it increases the chlorine demand, it is recommended that
ammonia nitrogen in public water supply sources not exceed
0.5 mg/1.
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Ammonia exists in its non-ionized form only at higher pH
levels and is most toxic in this state. The lower the pH
the more ionized ammonia is formed, and its toxicity
decreases. Ammonia, in the presence of dissolved oxygen, is
converted to nitrate (N
-------
anaerobic conditions and the production of undesirable gases
such as hydrogen sulfide and methane. The reduction of
dissolved oxygen can be detrimental to fish populations,
fish growth rate, and organisms used as fish food. A total
lack of oxygen due to the exertion of an excessive BOD can
result in the death of all aerobic aquatic inhabitants in
the affected area.
Water with a high BOD indicates the presence of decomposing
organic matter and associated increased bacterial
concentrations that degrade its quality and potential uses.
A by-product of high BOD concentrations can be increased
algal concentrations and blooms which result from
decomposition of the organic matter and which form the basis
of algal populations.
The BOD 5 (5-day BOD) test is used widely to estimate the
pollutional strength of domestic and industrial wastes in
terms of the oxygen that they will require if discharged
into receiving streams. The test is an important one in
water pollution control activities. It is used for
pollution control regulatory activities, to evaluate the
design and efficiencies of waste water treatment works, and
to indicate the state of purification or pollution of
receiving bodies of water.
Complete biochemical oxidation of a given waste may require
a period of incubation too long for practical analytical
test purposes. For this reason, the 5-day period has been
accepted as standard, and the test results have been
designated as BOD5. Specific chemical test methods are not
readily available for measuring the quantity of many
degradable substances and their reaction products. Reliance
in such cases is placed on the collective prarameter, BODJ5,
which measures the weight of dissolved oxygen utilized by
microorganisms as they oxidize or transform the gross
mixture of chemical compounds in the waste water. The
biochemical reactions involved in the oxidation of carbon
compounds are related to the period of incubation. The
five-day BOD normally measures only 60 to 80 percent of the
carbonaceous biochemical oxygen demand of the sample, and
for many purposes this is a reasonable parameter.
Additionally, it can be used to estimate the gross quantity
of oxidizable organic matter.
The BODJ5 test is essentially a fcioassay procedure which
provides an estimate of the oxygen consumed by
microorganisms utilizing the degradable matter present in a
waste under conditions that are representative of those that
are likely to occur in nature. Standard conditons of time.
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temperature, suggested microbial seed, and dilution water
for the wastes have been defined and are incorporated in the
standard analytical procedure. Through the use of this
procedure, the oxygen demand of diverse wastes can be
compared and evaluated for pollution potential and to some
extent for treatability by biological treatment processes.
Because the BOD test is a bioassay procedure, it is
important that the environmental conditions of the test be
suitable for the microorganisms to function in an
uninhibited manner at all times. This means that toxic
substances must be absent and that the necessary nutrients,
such as nitrogen, phosphorus, and trace elements, must be
present.
Boron (B)
Never found in nature in its elemental form, boron occurs as
sodium borate (borax) or as calcium borate (colemanite) in
mineral deposits and natural waters of Southern California
and Italy. Elemental boron is used in nuclear installations
as a shielding material (neutron absorber). It is also used
in metallurgy to harden other metals.
Boric acid and boron salts are used extensively in industry
for such purposes as weatherproofing wood, fireproofing
fabrics, manufacturing glass and porcelain and producing
leather, carpets, cosmetics and artificial gems. Boric acid
is used as a bactericide and fungicide and boron, in the
form of boron hydrides or borates, is used in high energy
fuels.
Boron is present in the ordinary human diet at about 10 to
20 mg/day, with fruits and vegetables being the largest
contributors. In food or in water, it is rapidy and
completely absorbed by the human system, but it is also
promptly excreted in urine. Boron in drinking water is not
generally regarded as a hazard to humans. It has been
reported that boron concentrations up to 30 mg/1 are not
harmful.
Chlorine (Cl)
Elemental chlorine is a greenish-yellow gas that is highly
soluble in water. It reacts readily with many inorganic
substances and all animal and plant tissues. Chlorine is
not found in a free state (HOCl, OCl, chloramines) in
natural waters but chlorides are common constituents of most
waters.
1U2
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Chlorine is not a natural constituent of water. Free
available chlorine (HOCl and OCl) and combined available
chlorine (mono- and di-chloramines) appear transiently in
surface or ground waters as a result of disinfection of
domestic sewage or from industrial processes that use
chlorine for bleaching operations or to control organisms
that grow in cooling water systems. Chlorine in the free
available form reacts readily with nitrogenous organic
materials to form chloramines. These compounds are harmful
to fish. Chloramines have been shown to be slightly less
harmful to fish than free chlorine, but their toxicity is
considered to be close enough to free chlorine that
differentiation is not warrented. Since the addition of
chlorine or hypochlorites to water containing nitrogenous
materials rapidly forms chloramines, toxicity in most waters
is related to the chloramine concentration. The toxicity to
aquatic life of chlorine will depend upon the concentration
of total residual chlorine, which is the relative amount of
free chlorine plus chloramines. The persistence of
chlorimines is dependent on the availability of material
with a lower oxidation-reduction potential. In most
receiving water, chloramines will combine with such
materials within a few days to form other compounds that may
have a toxic effect on fish.
In field studies in Maryland and Virginia it was observed
that, downstream from plants discharging chlorinated sewage
effluents, the total number of fish species were drastically
reduced with the stream bottom clear of the wastewater
organisms characteristically present in unchlorinated
wastewater discharges. No fish were found in water with a
chlorine residual above 0.37 mg/1 and the species diversity
index reached zero at 0.25 mg/1. A 50 percent reduction in
the species diversity index occurred at 0.10 mg/1. Of the
45 species of fish observed in the study areas, the brook
trout and the brown trout were the most sensitive and were
not found at residual chlorine levels above about 0.02 mg/1.
In studies of caged fish placed in waters downstream from
chlorinated wastewater discharge, it has been reported that
50 percent of the rainbow trout died within 96 hours at
residual chlorine concentrations of 0.014 to 0.029 mg/1.
Some fish died as far as 0.8 miles (1/3 km) downstream from
the outfall. Studies indicate that salmonoids are the most
sensitive fish to chlorine. A residual chlorine
concentration of 0.006 mg/1 was lethal to trout fry in two
days. The 7-day LC50 for rainbow trout was 0.08 mg/1 with
an estimated median period of survival of one year at 0.004
mg/1. Rainbow trout were shown to avoid a concentration of
0.001 mg/1. It has been demonstrated that brook trout had a
mean survival time of 9 hours at 0.35 mg/1, 18 hours at 0.08
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mg/1 and 48 hours at 0.04 mg/1, with mortality of 67 percent
after 4 days at 0.01 mg/1. A 50 percent brown trout
mortality has been observed at 0.02 mg/1 within 10.5 hours
and at 0.01 mg/1 within 43.5 hours.
The range of acutely lethal residual chlorine concentrations
is narrow for various species of warm water fish. 96 - hour
LC50 values have been determined for the walleye, black
bullhead, white sucker, yellow perch, largemouth bass, and
fathead minnow. The observed concentration range was 0.09
to 0.30 mg/1.
Using fathead minnows in a continuous bioassay technique, it
has been found that an average concentration of 0.16 to 0.21
mg/1 killed all of the test fish and that concentrations as
low as 0.07 mg/1 caused partial kills. A 50 percent
mortality has been demonstrated with smallmouth bass exposed
to 0.5 mg/1 within fifteeen hours. The mean 96-hour LC50
value for golden shiners was 0.19 mg/1. It has been found
for fathead minnows and the freshwater crustacean Gammarus
pseudolimnaeus in dilute wastewater that the 96-hour LC50 of
total residual chlorine for Gammarus was 0.22 mg/1 and that
all fathead minnows were dead after 72 hours at 0.15 mg/1.
At concentrations of 0.9 mg/1, all fish survived for seven
days, when the first death occurred. In exposure to 0.05
mg/1 residual chlorine, investigators found reduced survival
of Gammarus and at 0.0034 mg/1 there was reduced
reproduction. Growth and survival of fathead minnows after
21 weeks were not affected by contincus exposure to 0.043
mg/1 residual chlorine. The highest level showing no
significant effect was 0.016 mg/1. With secondary waste
water effluent, reproduction by Gammarus was reduced by
residual concentrations above 0.012 mg/1 residual chlorine.
In marine water, 0.05 mg/1 was the critical chlorine level
for young Pacific salmon exposed for 23 days. The lethal
threshold for Chinook salmon and coho salmon for a 72-hour
exposure was noted to be less than 0.01 mg/1 chlorine.
Studies on the effect of residual chlorine to marine
phytoplankton indicate that exposure to 0.10 mg/1 reduced
primary production by 70 percent while 0.2 mg/1 for 1.5
hours resulted in 25 percent of primary production.
Laboratory studies on ten species of marine phytoplankton
indicate that a 50 percent reduction in growth rate occurred
at chlorine concentrations of 0.075 to 0.250 mg/1 during a
24-hour exposure period. Oysters are sensitive to chlorine
concentrations of 0.01 to 0.05 mg/1 and react by reducing
pumping activity. At chlorine concentrations of 1.0 mg/1,
effective pumping could not be maintained.
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Oil and Grease
Because of widespread use, oil and grease occur often in
wastewater streams. These oily wastes may be classified as
follows:
1. Light Hydrocarbons - These include light fuels such
as gasoline, kerosene, and jet fuel, and
miscellaneous solvents used for industrial
processing, degreasing, or cleaning purposes. The
presence of these light hydrocarbons may make the
removal of other heavier oily wastes more
difficult.
2. Heavy Hydrocarbons, Fuels, and Tars - These include
the crude oils, diesel oils, #6 fuel oil, residual
oils, slop oils, and in some cases, asphalt and
road tar.
3. Lubricants and Cutting Fluids - These generally
fall into two classes: non-emulsifiable oils such
as lubricating oils and greases and emulsifiable
oils such as water soluble oils, rolling oils,
cutting oils, and drawing compounds. Emulsifiable
oils may contain fat soap or various other
additives.
H. Vegetable and Animal Fats and Oils - These
originate primarily from processing of foods and
natural products.
These compounds can settle or float and may exist as solids
or liquids depending upon factors such as method of use,
production process, and temperature cf waste water.
Oils and grease even in small quantities cause troublesome
taste and odor problems. Scum lines from these agents are
produced on water treatment basin walls and other
containers. Fish and water fowl are adversely affected by
oils in their habitat. Oil emulsions may adhere to the
gills of fish causing suffocation, and the flesh of fish is
tainted when microorganisms that were exposed to waste oil
are eaten. Deposition of oil in the bottom sediments of
water can serve to inhibit normal benthic growth. Oil and
grease exhibit an oxygen demand.
Levels of oil and grease which are toxic to aquatic
organisms vary greatly, depending on the type and the
species susceptibility. However, it has been reported that
crude oil in concentrations as low as 0.3 mg/1 is extremely
toxic to fresh-water fish. It has been recommended that
public water supply sources be essentially free from oil and
grease.
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Oil and grease in quantities of 100 1/sq km (10 gallons/sq
mile) show up as a sheen on the surface of a body of water.
The presence of oil slicks prevent the full aesthetic value
of a waterway.
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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 wastewater 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.
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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 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.
H. 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 (IDf23061) 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 tc 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 AFTEF PUMPING OF SETTLING TANK
Parameter
Concentration (mg/1)
Before Sludge Removal
Concentration (mg/1)
After Sludge Removal
Cyanide, Amen to
Chlor
Cyanide, Total
Phosphorus
Silver
Gold
Cadmium
Chromium,
Hexavalent
Chromium, Total
Copper
Iron
Fluoride
Nickel
Lead
Tin
Zinc
Total Suspended
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
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
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
Treated
Effluent
0.005
0.005
13.89
0.003
0.005
0.002
0
0
0
1
0
0
0
0
0
005
006
034
718
520
312
014
134
034
4.00
TABLE 7-2
USAGE OF VARIOUS PINSE 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
149
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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 techniques (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 waster 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 concentration 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
150
-------
Rinse after chromium 15
Rinse after acid dip or alkaline cleaner 750
Rinse after acid dip prior to chromium plate 15
Rinse after chromium passivating 350-750
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 completely
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 of 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.
151
-------
TO WASTEWATER.
TREATMENT
PARTS
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.RINSE WATER FEED
FIGURE 7-1. SINGLE RINSE TANK
152
-------
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153
-------
PARTS
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TO WASTEWATER
TREATMENT
OVERFLOW PIPES
FIGURE 7-3 3 STAGE COUNTERCURRENT RINSE WITH
OUTBOARD ARRANGEMENT
154
-------
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 th.e 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-U) over the
countercurrent system is that the tanks of the
series can be individually heated or level
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.
H. 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 efficient 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
155
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PARTS
TO WASTE WATER
TREATMENT
::A;;LAL OR FOOT
SPRAY RINSE
FEED
FIGURE 7-5 SPRAY RINSE
157
-------
on the part, and because cf 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.
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 rinsewater 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 overflew 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
158
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the plating operator and, thus, eliminating the
possibility of overfilling the bath. This rinse
technique was observed at company ID 06072.
Factors Affecting thg 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 totally ineffective.
2. Kinematic Viscosity of the Plating Solution - The
kinematic viscosity is an important factor in
determining plating bath dragcut. The effect of
increasing kinematic viscosity is that it increases
the dragout volume in the withdrawal phase and de-
creases 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 viscosity should be as
low as possible. Increasing the temperature 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 tension 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-hoie-
160
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metalization. Surface tension is reduced by
increasing the temperature of the plating solution
or more effectively, by use of a wetting agent.
U. Time of Withdrawal and Drainage - The withdrawal
velocity of a part from a solution has an effect
similar to that of kinematic 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 dragout volume initially adhering to the part
rather than attempt to drain a large volume from
the part.
5. Other Factors - There are ether factors that enter
into the proper application of a particular rinsing
arrangement. These include:
A. Packing - 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 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 cf a barrel will have a
significant effect on rinsing efficiency.
161
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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 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
162
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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 b.e 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. Orifices are not suited for
operations with fluctuating production rates or where parts
have wide variance in dragout volume. For these situations,
one of the following techniques may be used.
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 cf 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, vhen
the 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
163
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FIGURE 7-7 TYPICAL PRINTED BOARD RACK
164
-------
FIGURE 7-8 MODIFIED PRINTED BOARD RACK
FOR DRAGOUT CONTROL
165
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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.
**• 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 Path 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
166
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used directly for plating bath makeup. The reverse is often
true with the 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 arrangment 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 Rinsing - The countercurrent followed by spray rinsing
approach can be used 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.
167
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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.
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
168
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of dragout that drips off the parts while they are being
transferred from one tank tc 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 numter 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 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 bath
process; recovery of metal from spent plating baths; and
continuous regeneration of etachants. 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 electrclizing 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 percentage of the
metal is recovered and does not require treatment. This
type of metal recovery is performed by companies 17061 and
11065.
Regeneration of 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
169
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this is done, the etchant life can be extended indefinitely.
Another method practiced for the regeneration of etchants
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 2006U 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 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 treat-
ment. 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.
170
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INDIVIDUAL TREATMENT TECHNOLOGIES
The following major headings provide descriptions of indi-
vidual 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 aqeuous
solution and are, therefore, useful in industrial waste
treatment facilities for the reduction of hexavalent
chromium to trivalent chromium. Reduction of chromium by
ferrous sulfate is most effective at pH levels of less than
3.0
Description of 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:
3SOJ2 + 3H2O = 3H2SO.3
3H2S03 + 2H2Cr04 = Cr2(SOj»)3 + 5H2O
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 two hours retention
in an equalization tank followed by 45 minutes retention in
171
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each of two reaction tanks connected in series. Each
reaction tank has an electronic recorder-controller to
control process conditions with respect to pH and oxidation
reduction potential (ORP). Gaseous sulfur dioxide is
metered to the reaction tanks 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. Each of the
reaction tanks is 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.
Advantages and Limitations
Some advantages of chemical reduction in handling process
effluent are as follows:
1. Proven effectiveness within the industry.
2. Processes, especially those using sulfur dioxide,
are well suited to automatic control.
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 interference is possible in the treatment
of mixed wastes.
2. Careful pH control is required for effective
hexavalent chromium reduction.
3. A potentially hazardous situation will exist when
sulfur dioxide gas is stored and handled.
Specific Performance
A study of an operational waste treatment facility
chemically reducing hexavalent chromium to trivalent
chromium has shown that a 99.79? reduction efficiency is
possible.
Operational Factors
Reliability - High, assuming proper monitoring and control
and proper pretreatment to control interfering substances.
173
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Maintainability - Maintenance consists of periodic removal
of sludge.
Collected Wastes - Pretreatment tc 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 em-
ploying chromium compounds in operations such as electro-
plating. 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.
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 preci-
pitation 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 of 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
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6.0
7.0
8.0
9.0
10.0
11.0
FIGURE 7-10
EFFECT OF PH ON SOLUBILITY OF TRIVALENT CHROMIUM.
175
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TABLE 7-3
ELECTROPLATING PLANTS THAT CURRENTLY EMPLOY CHEMICAL REDUCTION
01016
03004
04031
04034
04078
06029
06051
06072
06076
06079
06085
06088
06731
11008
11065
12063
19002
19051
20001
20010
20025
20070
20078
20081
20084
20087
23007
28011
30007
30020
31020
33001
33011
33021
33030
33070
33074
36040
40062
43001
03001
04003
04032
04035
05050
06035
06053
06073
06077
06083
06086
06358
08004
11013
12005
12065
19003
19063
20006
20015
20064
20073
20079
20082
20085
21003
23061
30001
30009
30050
31021
33003
33015
33024
33033
33071
36001
36041
41001
43003
03003
04030
04033
04069
06012
06050
06062
06074
06078
06084
06087
06381
09002
11022
12008
15070
19024
19066
20007
20024
20069
20077
20080
20083
20086
23003
25001
30005
30019
30074
31050
33008
33020
33029
33035
33073
36012
40061
41041
44050
176
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preparation either for clarificaiton 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 discharged 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:
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.
177
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Specific Performance
The following reductions in dissolved metals were achieved
by a group of typical plants having successful waste treat-
ment processes. The plants were visited during this project
and employ pH adjustemnt for metal precipitation.
Parameter Seduction (%)
Copper 94.U
Nickel 83.6
Chromium 85.6
Zinc 91.1
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 th% 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.
178
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TABLE 7-4
ELECTROPLATING PLANTS THAT CURRENTLY
EMPLOY £H ADJUSTMENT
01016 11013 30008
02062 11050 30009
03003 11065 30019
03004 11066 30021
04005 12005 30050
04008 12008 30074
04009 12009 31016
04045 12062 31020
04065 12063 31021
04069 12065 31050
04071 15001 33001
04077 15070 33002
04078 17061 33005
04087 19002 33006
05020 19003 33008
05021 19024 33009
06007 19050 33011
06012 19051 33015
06035 19063 33020
06036 19066 33022
06037 20001 33023
06050 20006 33024
06051 20010 33027
06053 20013 33029
06062 20015 33030
06065 20017 33035
06067 20020 33050
06072 20021 33065
06073 20022 33070
06074 20023 33071
06075 20024 33073
06076 20025 33074
06078 20064 36001
06079 20069 36002
06081 20070 36012
06083 20073 36013
06084 20077 36040
06085 20078 36041
06086 20081 36062
06087 20082 38050
06088 20083 40004
06089 20084 40061
179
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Table 7-4 (con»t)
06358 20085 40062
06381 20086 41001
06731 20087 41041
08004 21003 41067
08005 23003 41069
08008 23007 43001
09002 23008 43003
09007 23061 44050
09026 25001 44061
10020 28009 61001
11008 30007
180
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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, sodium sulfide, 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
181
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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 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.
182
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DRAFT
INFLUENT PIPE
DRIVE MOTOR
OUTER WALL
FIGURE 7-11
MECHANICAL GRAVITY THK
:KENER
183
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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
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 te 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 ir.inimal problems from
a system operation viewpoint, while systems within the
clarifier may require emptying fcr maintenance to be accom-
plished. Routine maintenance will generally consist of
lubrication, checking for excessive wear, and part
184
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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 general use for many years. This is evidenced by the
fact that 111 of the 151 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 of thg 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.
185
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TABLE 7-5
PLANTS_CyRRENTLY USING A ^SYSTEM INCLUDING CLARIFICATION
2062
3003
4003
4030
4032
4034
4045
4069
4077
5021
6007
6037
6053
6065
6073
6076
6078
6083
6085
6087
6358
8004
9002
11088
12008
12062
13002
17061
19024
3001
3004
4088
4031
4033
4035
4065
4071
5020
5050
6035
6051
6062
6072
6075
6077
6081
6084
6086
6088
6381
8008
10020
11022
11050
12009
12063
15070
19002
19050
19063
20007
20020
20070
20078
20080
20083
20085
20087
28011
30003
30008
30019
30050
31021
33011
33020
33022
33024
33029
33070
33073
36002
36040
41001
43001
20006
20010
20069
20073
20079
20082
20084
20086
23061
30001
30007
30009
30021
31016
33008
33015
33021
33023
33027
33050
33071
36001
36012
40061
41041
43003
186
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Normal operation of the system involves pumping a mixture of
diatomaceous earth and water through the screen leaves.
This deposits the diatomaceous earth filter media on the
screens and prepares them for treatment of the waste water.
Once the screens 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 O & M costs is offset fcy the lower capital
costs reguired when not investing in land and outside
construction.
Specific Performance
A properly operating filter system has demonstrated the
following performance.
Total Suspended Solids
Zinc
Trivalent Chromium
Iron
Copper
Nickel
Pemoval
Percent
98*
991
95%
96*
Raw
Waste
524
13. <
12.
5,
7.
81
53
98"!?
2.57
Effluent.
10
0.139
0.611
0.248
0.444
0.044
187
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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.
Demonstration Status
Filters with similar operating characteristics to that
described above are in common use throughout the electro-
plating industry. They are employed by 5 plants in the data
base.
The ID numbers of the plants using diatomaceous earth
filtration are listed below:
06731
09026
31020
33073
36041
FLOTATION
Definition of 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.
188
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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. Wettability and surface properties
affect the particles1 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 air flotation, gas
bubbles are generated by introducing the air by mechanical
agitation with impellers or by spraying air through porous
media. Dispersed air flotation is used in the metallurgical
industry.
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 rinsing gas bubbles in the
flocculated particles as they increase in size. The bond
between the bubble and particle is cne 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 waste-
water 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
189
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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 charac-
teristics of the particulate matter, laboratory and pilot
plant tests must usually be performed to yield the necessary
design criteria. Factors that must 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 tc 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
Reliability - 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.
190
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0.06
0.05
01
D 0.04
0.03
0.02
0.01
I
I
1
2 3
PERCENT SOLIDS
(A)
50 100 150
PPM EFFLUENT SUSPENDED SOLIDS
(B)
200
(A) THE RELATIONSHIP BETWEEN AIR/SOLIDS RATIO AND
FLOAT-SO LJDS.CONCENTRATION,
(B) THE RELATIONSHIP BETWEEN AIR/SOLIDS RATIO AND
EFFLUENT SUSPENDED SOLIDS.
FIGURE 7-12
AIR/SOLIDS RATIO
191
-------
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-liguid 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 gravity close to water. In the 196
plant data base, this process was employed by six plants
(IDfs 05050, 09002, 20017, 23007, 41001, and UlOUl).
In addition, a Swedish company has developed a "micro flota-
tion 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 significant
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
192
-------
classic procedure can be approximated by the following two
step chemical reaction:
1. C12 + NaCN + 2NaOH = NaCNO + 2NaCl + H.2O
2. 3C12 + 6NaOH + 2NaCNO = 2NaHC(D3 + N2! + SNaCl * 2H2O
The reaction indicated by equation (1) represents the oxi-
dation of cyanides to cyanates. The oxidation of cyanides
to cyanate.5 is accompanied by a marked reduction in vola-
tility 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 electro-
plating wastewaters containing cyanides. Continuous flow
treatment facilities are provided fcr cyanide-bearing wastes
which are discharged from plating operations. In plating
operations, copper, zinc 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.
193
-------
OVERFLOW TO
PRESSURE
FILTER
ACID-ALKALI RINSES
CHROMATE WASTES
CAUSTIC PUMPS ARE pH CONTROLLED
CYANIDE RUNNINO
RINSE LINE
CYANIDE
DUMP LINE
CONTINUOUS
NEUTRALIZATION
TANK
CHEMICAL
PROPORTIONING PUMPS
H
H
CHLORINE FEEDERS
(OOP CONTROLLED)
TRANSFER
PUMP
OASEOU* CHLORINC
LIQUID CHLORINE
CHLORINE
EVAPORATOR
FIGURE 7-13
FLOW DIAGRAM FOR TREATMENT OF CYANIDE
WASTE BY ALKALINE CHLORINATION PROCESS
194
-------
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.
3. A potentially hazardous situation exists when
chlorine gas is stored and handled.
Specific 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 cf 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.
195
-------
TABLE 7-6
ELECTROPLATING PLANTS THAT CURRENTLY EMPLOY OXLDATLON BY CHLORI
01016
03004
04045
04078
05021
06007
06029
05035
06037
06050
06051
06053
06062
06072
06073
06075
06077
06078
06079
06081
06084
06085
06087
06089
06358
06381
08004
08008
09002
09026
10020
11008
11013
12003
12005
12008
12063
13002
15001
15070
19002
19050
19051
20001
20006
20007
20017
20021
20073
20077
20078
20079
20080
20081
20082
20084
20086
20087
21003
23003
2306
2500
2800
2801
3000
3000
3000
3000
3000
3002
3102
3300
330C
3301
3301
3302
3302
3302
2202
3303
330f
330:
330^
330-;
360C
360!
360*
360'
430C
4406
196
-------
Collected Wastes - Pretreatment to eliminate substances which
will interfere with the process may te 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 allctropic 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 eguation:
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.
U. Operation at ambient conditions, i.e., 15.5 to 32.2
Degrees C (60 to 90 Degrees F).
197
-------
Controls
Ozone
Dry Air
-*
n c:i "
11
Ozone
Mixing
Tank
-CX-
X
Settling
Tank
CN-
Acidic
Metals
FIGURE 7-14
TYPICAL OZONE PLANT FOR WASTE TREATMENT
198
-------
Some limitations or disadvantages of ozone oxidation for
treatment of process effluents are listed below.
1. High initial cost.
2. Chemical interference is possible in the treatment
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 ing/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 (g/cu m)
I 11 IP-
Total ozone applied 7.3 5.7 H.Q
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 1.0
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 fcr 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 linp" process may be desirable prior to
contractor removal or disposal to a landfill.
199
-------
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 aircraft. This plant is
capable of generating 5U.U kg (120 pounds) of ozone per day.
The amount of ozone used in the treatment is approximately
20 milligrams per liter. In this process, the cyanide is
first oxidized to cyanate, and the cyanate is then
hydrolized 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 ex-
perience with the process dates back to the 180O's. Fil-
tration 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 bouyancy 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.
200
-------
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.
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 (multi-
layered, 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. Perio-
dically, 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 back-
washing 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
201
-------
DRAFT
1
FINAL
POLISHING
ZONE
SOLIDS
STORAGE
INLET
OUTLET
FINE
GRADATION
MEDIUM
GRADATION
COARSE
GRADATION
FIGURE 7-15
TYPICAL PRESSURE FILTER
202
-------
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 cr backwash cycle will
result in bed upset and major repair.
Several standard approaches are employed for filter under-
drains. 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 fcr
drainage and velocity head dissipation.
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 net 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/Square Meter
Papid Sand, Multi-layered UO.74-51.48 Liters/Square Meter
High Rate Mixed Media 81.48-122.22 Liters/Square Meter
Advantages and Limitations
The principal advantages of filtration are:
1. Low initial and operating costs.
203
-------
2. Reduced land requirements over other methods to
achieve the same level of sclids removal.
3. No chemical additions which add to the discharge
stream.
U. 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.
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 re-
liability filtration is becoming a standard for water
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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 fil-
tration as part of their wastewater treatment. However,
none of the plants in the data base employ deep bed fil-
tration as part of their wastewater treatment.
ION EXCHANGE
Definition of the Process
Ion exchange is a process in which ions, which are held by
electrostatic 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 ex-
changing ion must undergo a phase transfer from solution
phase to surface phase.
Ion exchange is used extensively for water and wastewater
treatment of a variety of industrial wastes to allow for
recovery of valuable waste materials cr by-products, par-
ticularly 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
tc 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 equilfcrium 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 H2SC4, and "weakly acidic"
designates cation exchange resins made from a weak acid such
as H2!CO_3. Anion resins containing certain ammonium
compounds are referred to as "strongly basic", and those
with weak base amines are referred to as "weakly basic".
The majority of cation exchangers used in water and waste
treatment operations are strongly acidic, and they are able
206
-------
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
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 cf icn 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.
207
-------
TABLE 7-8
APPLICATION OF ION EXCHANGE TO ELECTROPLATING
FOR USED RINSE WATER PROCESSING
Number in Operation (Additional Units Orderec
Application
Chromic Acid
Recovery
Nickel Sulfate
Recovery
Gold/Silver
Recovery
Phosphatizing
Recovery
Mixed Plating
Wastes With Rinse
Water Reuse
Mixed Wastes,
End-of-Pipe
Replacement
Service
In-Place
Regeneration
At least 8
At least 20
At least 1
At least 1
At least 8
Cyclic
Operation
15 (5)
<* (1)
208
-------
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 per-
formed approximately every three months. One such regenera-
tion 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 electroplating plant (ID 11008) 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,
209
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wMch 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 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.
211
-------
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 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.
212
-------
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.
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, mq/1 Concentration, mg/1
Aluminum 5.60 0.24
Cadmium 1.05 0.00
Chromium 7.60 0.06
Copper 1.U5 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
213
-------
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 05050, 11008, 11065, 12065, 20017, 20021,
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.
Process Equipment
Atmospheric and vacuum evaporating equipment are described
below.
214
-------
Atmospheric Evaporation. Equipment for carrying out
atmospheric evaporation is quite similar from one
application to another. The major element is generally a
packed column with an accumulator bottom, as shown in Figure
7-17A. Accumulated wastewater is pumped from the base of
the column, through a heat exchanger, and back into the top
of the column, where it is sprayed into the packing. At the
same time, air drawn upward through the packing by a fan is
heated as it contacts the hot liquid, which partially
vaporizes and humidifies the air stream. The fan then blows
the hot, humid air to the outside atmosphere. A scrubber is
generally unnecessary because the packed column itself acts
as a scrubber.
- Vacuum Evaporation. Most vacuum evaporators equipment may
be classified as submerged tube, climbing film, or flash
evaporation units. The evaporated water is condensed in
each of these approaches, and either single or double effect
evaporation may be used.
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 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.
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out the top of the evaporator to the horizontal condenser,
while the condensate runs into an accumulator from which it
is pumped out of the system. A vacuum pump maintains the
reduced pressure in the system by withdrawing noncondensible
gases from the condenser. Concentrate is withdrawn from the
bottom of the evaporator.
A special type of evaporator is the wiped film evaporator.
It is used to evaporate mixed, treated wastewaters to near
dryness so that residue can be landfilled directly. These
units use a mechanical screw to force the drying residue
through a steam-jacketed pipe.
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.
217
-------
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 electroplating installations
(establishments 11008 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.
218
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TABLE 7-9
APPLICATION OF EVAPORATION
TO THE ELECTROPLATING POINT SOURCE CATEGOPY
Number in Operation {Additional Units Ordere
Application
Chromium Plating
Nickel Plating
Copper Plating
Cadmium Plating
Zinc Plating
Silver Plating
Brass or Bronze
Plating
Other Cyanide
Plating
Chromic Acid
Etching
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220
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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 antifearning 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 O.U mg/1 in the condensate.
Plant ID 33065 had U16 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 hew the various membrane
structures are mechanically designed and supported to take
the operating pressures.
221
-------
TABLE 7-10
ELECTROPLATING PLANTS THAT EMPLOY EVAPORATION
03001
03004
06037
06050
11008
19003
20024
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 Fibe
222
-------
Hollow fiber modules consist of polyamide fibers, each
having approximately 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
223
-------
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 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
recovery of salts and chemicals.
solutions for
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).
U. 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.H 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).
224
-------
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 suspended solids (such feed must be
amenable to solids separation before treatment by
reverse osmosis).
6. Inability to treat highly concentrated solutions
(some concentrated solutions may have initial
osmotic pressures which are so high that they
either exceed available operation pressures 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 return-' -1 to the plating bath, replacing evaporated water
and dragged out chemicals. The permeate goes to the last
rinse tank, providing water for the rinsing operatj.on.
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 concentr? '-...d 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.
225
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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
electroplating. 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, U-diisocyanate on a polysulfone support.
This membrane is claimed to 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)
227
-------
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) / (100/CAV)
where CAV may be approximated by (CF + CC) /2, and CF is the
concentration of the constituent in question in the feed, CC
is the concentration 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 + CC)/200
The concentration in the concentrate is estimated by making
a system maxerials balance assuming that all of the
constituent ends up in the concentrate.
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)7100 = 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 * CC)/2 - r(CF * CCJ/200 = (1,200 + 12,000)/2 -
99 (1,200 + 12,000)/200 = 66 mg/1
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
228
-------
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
Rejection
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 lon^ 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
229
-------
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 reverse osmosis (IDfs 08008, 11022, 12003, 13002,
33005, 33065, and 38050).
ULTRAFILTRATION
Definition of the Process
Ultrafiltration (OF) is a process using semipermeable
polymetric membranes to separate molecular or colloidal
materials dissolved or suspsended 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 mole-
cular 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 emul-
sified 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
230
-------
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 isr therefore, desirable to maximize flux.
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.
231
-------
Some limitations or disadvantages of ultrafiltration for
treatment of process effluents are:
1. Limited tmperature 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 re-
placement costs for 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.
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 ultrafiltration 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.
232
-------
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 ultrafiltration 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
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 (IDfs 09007 and 33034).
233
-------
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 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 recir dilating 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 ancl 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.
234
-------
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3. The sludge is highly stable in alkaline conditions.
U. Pemoval 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
Copper 0.1
Iron 0.1
Lead 0.05
Cyanide 0.02
Nickel 0.1
Zinc 0.1
These claims are largely substantiated by the following
analysis of composite samples taken during this project at
Company ID 19066:
Wastewater concentration, mq/1
Constituent Recirculation Tank Membrane Fill:
Influent Effluent
Cyanide, Total Less than 0.005 Less than 0.005
Phosphorus 0.158
Cadmium 0.007 Less than 0.005
Chromium, hexavalent O.U6 0.010
Chromium, total U.13 0.018
Copper 18.8 O.OU3
236
-------
Fluorides
Nickel
Lead
Tin
Zinc
Total Suspended Solids
22.0 22.0
9.56 0.017
0.652 Less than 0.01
0.333 0.200
2.09 0.046
632.0 Less than 0.01
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 consistintly below 0.5 mg/1 and usually
at 0.1 mg/1, even with a varying concentration of
copper in the feed.
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.
237
-------
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 cf 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
semipermeable 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 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.
238
-------
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 - Electro-
lytic 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.
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.
239
-------
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 flews 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++ + 2e- = Cu
and at the anode:
2 (OH-) = HJ2O + 1/2 O2
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 ether forms of treatment.
Performance of Advanced Electrolytic Recovery - Pollutants
recovered by the ESE modules are independent of
concentration levels. Under mass-transfer-limiting
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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
Unseated After 1 Cell After 2 Cells After 3 Cells After U_ Cell
20.0 8.2 3.a 1.3 0.6
45.5 15.5 5.a 2.1 0.9
15.5 5.6 2.8 1.7 0.7
With the addition of one more cell in all three cases, the
cell effluent level would be below 0.05 mg/1. The water can
then be recirculated back to the rinse tanks.
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 of 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
242
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such as acidified copper sulfate, performance of ESE
indicates it may be preferred for low concentrations (around
10 mg/1). However, for high concentrations (100 to 1000
mg/1), ion exchange appears to be the least costly techno-
logy.
Conventional Electrodialvsis
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 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
(K2SC4) into its components. Practical electrodialysis in-
stallations contain from ten to hundreds of compartments be-
tween one pair of electrodes. The application of an
electric charge draws the anions to the cathode and cations
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
electroldialysis 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
2U5
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CATION- ANION-
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246
-------
PURIFIED
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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. Chronic 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 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 20061
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 electro
dialysis system is used to oxidize trivalent chromium to
hexavalent chromium. Its design uses a circular, permeable
ar.ode, 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
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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,v 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 hexavalent chromium is pumped back into the
chromium 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 H20 - 3e~ = CrOU-2 + 8H3O+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 a widely practiced method of waste
treatment as yet. It is, however, a very efficient method
for waste treatment of chromium, 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
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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 fil-
tration, 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.
Description of thg 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 densify 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
sluge removal rate. These rates must be low enough not to
disturb the thickened sludge.
Specific 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.
252
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^THICKENING;
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SLUDGE PUMP
OVERFLOW
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PLANT
FIGURE 7-28
MECHANICAL GRAVITY THICKENING
253
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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 intai nab i1ity - 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.
De mons tr at i o n Status
Gravity sludge thickeners are used throughout industry to
reduce water content to a level where the sludge may be
efficiently handled. 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
254
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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.
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
255
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FEED FLOW AND FILTRATE DRAINAGE.
257
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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 process requirement.
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.
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 03003, 06050, 06077,
12009, 31021, 33021, 33022, and 33023). 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.
258
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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 reduce the water content of a variety of sludges
to the point where they are amenable to mechanical
collection and removal to landfill. These beds usually
consist of 15.24 to 45.72 cm (6 to 18 inches) of sand over a
30.48 cm (12 inch) deep gravel drain system made up of 3.175
to 6.35 mm (1/8 to 1/4 inch) graded gravel overlying drain
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 2CO 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.
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.
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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 eguilibrium 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.
Maintainabi1ity - 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 or 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 must be kept watertight.
Provision for drainage of lines in winter should be provided
to prevent damage from freezing. The partitions between
beds should be tight so that sludge will not flow from one
compartment to another. The outer walls or banks arour ^ the
beds should also be watertight.
261
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Collected Wastes - Dried sludge from sludge drying beds is
conventionally disposed of in landfills.
Demonstration Status
Sand bed drying of sludge is used by plants with a high
solids waste flow. It is used by three plants (ID'S 06051,
06073, and 20064) in this data base.
VACUUM FILTRATION
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.
Advantages and Limitations
Although the initial cost and area requirement of the vacuum
filtration system are higher than that of a centrifuge, the
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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 hiah in dissolved or
suspended solids may require further treatment prior to
discharge and is usually returned to the treatment facility
influent.
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
264
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TABLE 7-13
ELECTROPLATING PLANTS THAT CURRENTLY EMPLOY
VACUUM FILTRATION
02062 04071
06037 06074
06087 06088
09002 12008
12063 15070
20010 20020
20073 20077
20080 28011
31016 36040
41001 41041
43003
265
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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.
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.
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
266
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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 point where the
total moisture content of the dewatered sludge is in the
range of 65 to 70 percent.
Operationa1 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. Pretreatment requirements will vary depending
on the composition of the sludge and on the type of
centrifuge employed.
Maintainability - Maintenance consists of periodic
lubrication, cleaning, and inspection. The frequency and
degree of inspection required will vary depending on the
type of sludge solids being dewatered and the maintenance
service conditions. If the sludge is abrasive, it is
267
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-COVER
DIFFERENTIAL SPEED
GEAR Box
^ROTATING
CONVEYOR
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CENTRATE
DISCHARGE
SLUDGE CAKE
DISCHARGE
MAIN
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SHEAVE
-FEED PIPES
(SLUDGE a
CHEMICAL)
BEARING
BASE NOT SHOWN
FIGURE 7-33
CONVEYOR TYPE SLUDGE DEWATERING CENTRIFUGE
268
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recommended that the first inspection of the rotating
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.
Collected Wastes - Sludge dewatered in a centrifuge process
may be disposed of by direct application as landfill. The
clarified effluent (centrate), if high in dissolved or
suspended solids, may require further treatment prior to
discharge.
Demonstration Status
Twelve plants in the 196 plant electroplating data base
employ centrifugation (ID'S 06075, 06086, 11050, 12005,
19002, 19024, 20070, 20079, 33024, 25001, 33027, 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 fcy 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 laboratory setting. The processes
reviewed are: electrochemical treatment of chromium and
cyanide, extraction, adsorption, and a variety of heavy
metal chemical precipitation technigues.
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.
269
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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 invest-
ment, 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 en 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.
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.
270
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In addition to the electrochemical unit, the only equipment
required is a pump and a clarifier cr pond for settling. As
long as the pH of the entering stream is within the range of
6.0 to 9.0r no pH adjustment is necessary for either the in-
fluent 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 and thus no retention
time is required.
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.
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
271
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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 electrooxidation 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/sg 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 reguired, experiments have shown that the
current efficiency could drop as low as 49 percent.
High pH 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 waste-
water 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
complete. Complexing agents containing no carboxyl group
and only hydroxyl groups show no copper removal. The
272
-------
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 - NDA 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%
The high pH precipitation process is presently in the labor-
atory 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:
CM + HCHO + H2O = HOCH2CN + OH
The hydrogen peroxide converts cyanide to cyanate in a
single step:
CN + H2O2 = NCO + H2O
273
-------
The formaldehyde also acts as a reducer breaking zinc
and cadmium ions apart from the cyanide:
Zn(CN)4 + 4HCHO + 4H2O = 4HOCH2CN + ^OH + Zn
The metals subsequently react with the hydroxyl ions
formed and precipitate as hydroxides or oxides:
Zn2 + 2OH = ZnO + H2O
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 sig-
nificant 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
27U
-------
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.
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 adsorbtion 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.
Peactiviation 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.
275
-------
The activated carbon adsorption treatment process when used
on wastewaters following clarification or filtration is
applicable to plating 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 EOD, 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 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 preci-
pitates. 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
precipator 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 waste-
water 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.
276
-------
TABLE 7-14
REMOVAL OF METALS BY
LIME PRECIPITATION - ACTIVATED CARBON COMBINATION
Metal
Silver
Beryllium
Bismuth
Cobalt
Mercury
Antimony
Selenium
Tin
Titanium
Thallium
Vanadium
Manganese
Nickel
Zinc
Copper
Cadmium
Barium
Lead
Chromium
Arsenic
Mercury
Initial
Concentration
(mq/1)
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
277
-------
TABLE 7-15
REMOVAL OF METALS BY
FERRIC CHLORIDE
Metal
Silver
Beryllium
Bismuth
Cobalt
Mercury
Molybdenum
Antimony
Selenium
Tin
Titanium
Thallium
Vanadium
Manganese
Nickel
Zinc
Copper
Cadmium
Barium
Lead
Chromium
Arsenic
Mercury
Initial
Concentrat ion
(mq/1)
0.5
0.1
0.5
0.5
0.05
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
Pesidual
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
278
-------
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 ether 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. Pre-
cipitation 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
279
-------
clarifier to achieve very low effluent concentrations of
metals. The removal mechanism is chemisorption by the par-
ticles of peat. The peat is 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 con-
taining 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.
280
-------
TABLE 7-16
TREATMENT OF WASTE WATERS
CONTAINING METALS
ase No.
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
(mg/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
PeC13_/Na2S. Settl-
ing . Contacting
with peat.
Addition of FeSO4
and Na2S. Settling.
Contacting with
peat. Further
reduction of CN to
0.03 by aeration.
281
-------
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 secon-
dary 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 con-
taining 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 8.5r 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 ultravioler 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 cf 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.
282
-------
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,
g.
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
2.60
3.18
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
283
-------
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 PLATING AND METAL FINISHING
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, clarification 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
284
-------
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286
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•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 the sludge drying beds indicated or in a
vacuum filter, and contractor removal of sludge may
sometimes by replaced with landfilling en 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 PLATING AND METAL FINISHING
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
287
-------
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.
Applicabi1ity 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 1983 limitations.
288
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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 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, howeverf 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 ..he first rinse stage would be
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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 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.
292
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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
04069, and similar installations are under construction at
Plant ID'S 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.
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, 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
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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.
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 04061 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.
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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 7-10.
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 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 04065, 04069, 04071,
06065, 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
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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 chemicals are added to
cause flocculation. This wastewater and the flocculants are
302
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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.
303
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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 non-
water 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 obtained through discussions with waste
treatment equipment manufacturers. Another block of data
was derived from previous EPA projects which utilized data
from engineering firms experienced in the installation 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 individual 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.
305
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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 Treatmen
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
8-21 Ion Exchange - In-Plant Regeneration
8-22 Ion Exchange - Service Regeneration
8-23 Cyclic Ion Exchange
8-24 Reverse Osmosis
306
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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 technologies. 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 contract, 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 regulations, 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
307
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were then verified by checking them against independent sets
of cost data. The specific assumptions 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 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 (H feet), length
of 1.22 meters (U 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 (H 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.
Pinse 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
308
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countercurrent Pinse - 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 (U 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 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 of 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 approximately 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 (U 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 (1
cfm/sq. ft.) at a discharge pressure of 1,538
309
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TABLE 8-2
COUNTERCURRENT RINSE (FOR OTHER THAN RECOVERY
OF EVAPORATIVE PLATING LOSS)
Number of Rinse Tanks 3 H 5
Investment $8,203 $10,553 $12,902
Annual Costs:
Capital Cost 523 673 823
Depreciation 1,641 2,111 2,580
Operation 5 Maintenance
Costs (Excluding Energy
6 Power Costs) 20 9 6
Energy & Power Costs 377 503 628
Total Annual Cost $2,561 $ 3,296 $ 4,038
310
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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 6 Maintenance
Costs (Excluding Energy
& Power Costs) 4 6 14
Energy 6 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.
311
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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-U 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 (H feet), and width of 1.22 meters
(1 feet) with 6 spray 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 (H feet) by 1.22 meters (H feet) by 0.91
meters (3 feet), the following costs are typical:
Investment ($) 3,350
Cost of Capital ($/Year) 21U
Depreciation ($/Year) 670
Operation and Maintenance
312
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TABLE 8-4
SPRAY RINSE USED FOR RECOVERY OF
EVAPORATIVE PLATING LOSS
Evaporative Rate
(Liters/Hr) 60.8 101.3 135.0
Investment $ 3,472 $ 3,472 $ 3,472
Annual Costs:
Capital Costs 221 221 221
Depreciation 694 694 694
Operation 6 Maintenance
Costs (Excluding Energy
& Power Costs) 16 27 36
Energy & Power Costs 0 00
Total Annual Cost $ 932 $ 943 $952
Note: Savings due to recovery of plating solution
are not presented in this table.
313
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(Less Energy 6 Power) ($/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,OU1 liter capacity. Investment
cost includes the tank, liquid level controller,
pump, and conversion of programmed hoist operation.
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 {U
feet) by 1.22 meters (4 feet) by 0.91 meters (3 feet), the
following costs are typical:
Investment ($) 2r907
Cost of Capital ($/Year) 185
Depreciation ($/Year) 581
Operation & Maintenance
(Less Energy S Power) ($/Year) 27
Energy & Power ($/Year) 0
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TABLE 8-5
STILL RINSE USED FOR RECOVERY OF
EVAPORATIVE PLATING LOSS
Evaporative Rate
(Liters/Hr) 29.7 59.5 99.1
Investment $ 2,971 $ 2,971 $ 2,971
Annual Costs:
Capital Costs 190 190 190
Depreciation 594 594 594
Operation & Maintenance
Costs (Excluding Energy
6 Power Costs) 8 16 27
Energy 6 Power Costs 000
Total Annual Costs $ 792 $ 800 $ 810
Note: Savings due to recovery of plating solution
are not presented in this table.
315
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Total Annual Costs 794
Clarification - Settling Tank - Settling tank clarification
costs are presented for continuous treatment in Table 8-6
and for batch treatment 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.U4 meters (8 feet), a thickness of 0.305
meters (1 foot), and an excess capacity factor of
1.2. A mixer is included in the flocculator.
C. The settling tank is sized for a hydraulic loading
of 1356.7 liters/hour per square meter (33.3
gallons/hour/ sq. ft.), a U hour retention time,
and an excess capacity factor of 1.2.
D. The two conical unlined carbon steel tanks are
designed for a H hour retention time in each tank.
E. 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.
F. Lime and sodium sulfide are added for metal and
solids removal. All power requirements are based
on data from a. major manufacturer.
G. 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.
H. Each tank is sized by an 8 hour retention time and
an excess capacity factor of 1.2. Each tank has a
316
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TABLE 8-6
CLARIFICATION-CONTINUOUS TREATMENT SETTLING TANK
Flow Rate
(Liters/Hr) 37,850 75,700 157,708
Investment $71,363 $91,575 $130,102
Annual Costs:
Capital Costs 4,552 5,842 8,301
Depreciation 14,273 18,315 26,020
Operation & Maintenance
Costs (Excluding Energy
6 Power Costs) 2,506 2,565 3,851
Energy & Power Costs 36 72 150
Total Annual Cost $21,367 $26,794 $ 38,322
TABLE 8-7
CLARIFICATION-BATCH TREATMENT SETTLING TANK
Flow Rate
(Liters/Hr) 1,893 3,785 18,925
Investment $25,551 $28,529 $38,032
Annual Costs:
Capital Costs 1,630 1,820 2,427
Depreciation 5,110 5,706 7,606
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 2,334 2,341 2,394
Energy & Power Costs 41 81 811
Total Annual Cost $ 9,155 $ 9,948 $13,238
317
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mixer that operates 1 hour for each 8 hours that
the tank is being used.
I. Manpower estimates for operation and maintenance
reflect the varying schemes for continuous and
batch treatment.
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.
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 regulato:
1 sulfuric acid pump
1 transfer pump for sulfur dioxide ejector
2 maintenance kits for electrodes, and mis-
cellaneous 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 U hour retention time, and an excess
318
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TABLE 8-8
CHROMIUM REDUCTION - CONTINUOUS TREATMENT
Flow Rate
(Liters/Hr) 3,785 7,570 18,925
Investment $20,416 $21,538 $24,003
Annual Costs:
Capital Costs 1,303 1,374 1,531
Depreciation 4,083 4,308 4,801
Operation 6 Maintenance
Costs (Excluding Energy
& Power Costs) 1,086 1,375 2,089
Energy 6 Power Costs 256 256 256
Total Annual Cost $ 6,728 $ 7,313 $ 8,677
TABLE 8-9
CHROMIUM REDUCTION - BATCH TREATMENT
Flow Rate
(liters/Hr) 189 379 1,893
Investment $8,493 $9,535 $14,405
Annual Costs:
Capital Costs 541 608 919
Depreciation 1,699 1,907 2,881
Operation 6 Maintenance
Costs (Excluding Energy
& Power Costs) 155 295 1,415
Energy & Power Costs 256 256 256
Total Annual Cost $2,651 $3,066 $ 5,471
319
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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 of 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. 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.
320
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TABLE 8-10
CYANIDE OXIDATION - CONTINUOUS TREATMENT
Flow Rate
(Liters/Hr) 3,785 5,678 7,570
Investment $47,808 $51,875 $55,556
Annual Costs:
Capital Costs 3,050 3,310 3,544
Depreciation 9,561 10,395 11,111
Operation 6 Maintenance
Costs (Excluding Energy
& Power Costs) 2,218 2,750 3,563
Energy & Power Costs 90 135 180
Total Annual Cost $14,920 $16,570 $18,098
TABLE 8-11
CYANIDE OXIDATION - BATCH TREATMENT
Flow Rate
(Liters/Hr) 189 757 1,893
Investment $10,325 $13,258 $17,069
Annual Costs:
Capital Costs 659 846 1,089
Depreciation 2,065 2,652 3,414
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 464 1,854 4,636
Energy & Power Costs 5 18 45
Total Annual Cost $ 3,192 $ 5,370 * 9,184
321
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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 OFF probes and transmitters
2 pH and ORP monitors
2 2-pen recorders
2 slow process controller
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.
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 pi pine
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 estavlishments, a completely manual
treatment system may be used. This system consists of flat
322
-------
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.
pH 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
reguirements, 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:
A. Unit size, power reguirements, 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.
323
-------
TABLE 8-12
pH ADJUSTMENT
Flow Rate
Flow Rate
(Liters/Hr) 492 4,921 49,205
Investment $1,452 $4,921 $18,855
Annual Costs:
Capital Costs 93 314 $ 1,203
Depreciation 290 984 3,771
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 286 1,036 3,758
Energy & Power Costs 8 79 1,503
Total Annual Cost $ 677 $2,413 $10,315
TABLE 8-13
DIATOMACEOUS EARTH FILTRATION
Flow Rate
(Liters/Hr) 189 4,731 47,313
Investment $8,823 $27,707 $62,819
Annual Costs:
Capital Costs 563 1,768 4,008
Depreciation 1,765 5,541 12,564
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 3,936 6,046 29,872
Energy & Power Costs 22 302 1,970
Total Annual Costs $6,286 $13,657 $48,414
324
-------
TABLE 8-14
SUBMERGED TUBE EVAPORATION - SINGLE EFFECT
Flow Rate
(Liters/Hr) 95 379 757
Investment $11,156 $23,486 $34,077
Annual Costs:
Capital Costs 712 1,498 2,174
Depreciation 2,231 4,697 6,815
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 1,678 6,713 13,427
Energy 6 Power Costs 6,048 20,117 37,815
Total Annual Cost $10,669 $33,026 $60,231
TABLE 8-15
SUBMERGED TUBE EVAPORATION - DOUBLE EFFECT
Flow Rate
(Liters/Hr) 189 568 1,136
Investment $19,424 $35,039 $50,841
Annual Costs:
Capital Costs 1,239 2,235 3,244
Depreciation 3,885 7,008 10,168
Operation S Maintenance
Costs (Excluding Energy
6 Power Costs) 1,678 5,035 10,070
Energy 6 Power Costs 6,048 15,844 29,270
Total Annual Costs $12,850 $30,123 $52,752
325
-------
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 manufacturers 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 manufacturer 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.
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.
326
-------
TABLE 8-16
CLIMBING FILM EVAPORATION
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
$27,559
1,758
5,512
0
5, 533
$12,803
795 4,731
$104,470 $600,090
6,665 38,285
20,894 120,018
0 0
37,106 220,522
$ 64,665 $378,825
TABLE 8-17
ATMOSPHERIC EVAPORATION
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance
Costs (Excluding Energy
& Power Costs)
Energy & Power Costs
Total Annual Cost
379 1,893
$20,430 $45,967
1,303
4,086
155
18,443
2,933
9,193
155
92,213
$23,987 $104,494
6,813
$143,008
9,124
28,602
155
331,968
$369,848
327
-------
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.
UltrafiItration - 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
328
-------
Flow Rate
(Liters/Hr)
Investment
Annual Costs:
Capital Costs
Depreciation
TABLE 8-18
FLASH EVAPORATION
189
$46,207
2,948
9,241
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 0
Energy & Power Costs 9,559
Total Annual Costs $21,749
TABLE 8-19
ULTRAFILTRATION
Flow Rate
(Liters/Hr) 95
Investment $9,843
Annual Costs:
Capital Costs 628
Depreciation 1,969
Operation 6 Maintenance
Costs (Excluding
Energy & Power Costs) 5,237
Energy & Power Costs 20
Total Annual Cost $7,854
568 1,136
$62,987 $76,585
4,018 4,886
12,597 15,317
0 0
26,649 52,284
$43,265 $72,487
4,731 9,463
$189,773 $379,546
12,107 24,214
37,955 75,909
28,662 44,360
1,025 2,050
$79,749 $146,533
329
-------
100,000
90,000
80,000
,000
60,000
W
H
50,000
40,000
30,000
20,000
10,000
0
0
352
1,333
704
2,666
1,057
4,000
1,409
5,333
1,761
6,666
2,113 (GP
8, 000 (LIT,
FLOW
FIGURE 8-1. EVAPORATION INVESTMENT COST
330
-------
225,000
200,000
175,000
150,000
125,000
.00,000
75,000
50,000
25,000
0 t.
0
0
352
1,333
704
2,666
1,057
4,000
1,409
5,333
1,761
6,666
FLOW
FIGURE 8-2. EVAPORATION TOTAL ANNUAL COST
2,113 (GPH)
8,000(LIT/HR)
331
-------
HP = meters x specific gravity x (liters/min rec:
<3r960 x 0.7)
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 filtration 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 are 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:
332
-------
TABLE 8-20
MEMBRANE FILTRATION
Flow Rate
(Liters/Hr) 3,407 6,813 10,220
Investment $42,136 $84,273 $126,409
Annual Costs:
Capital Costs 2,688 5,376 8,065
Depreciation 8,427 16,855 25,282
Operation 6 Maintenance
Costs (Excluding
Energy 6 Power Costs) 8,075 13,046 18,017
Energy & Power Costs 2,275 2,275 2,275
Total Annual Cost $21,465 $37,552 $ 53,639
TABLE 8-21
ION EXCHANGE - IN-PLANT REGENERATION
Flow Rate
(Liters/Hr) 95 4,731 9,463
Investment $2,789 $27,558 $42,660
Annual Costs:
Capital Costs 178 1,758 2,722
Depreciation 558 5,512 8,532
Operation & Maintenance
Costs (Excluding Energy
& Power Costs) 951 9,338 15,912
Energy & Power Costs 0 00
Total Annual Cost $1,687 $16,608 $27,166
333
-------
A. Unit sizes and pump power 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 manufacturer for a service charge.
C. Metalst 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 following mass equivalents are
maintained:
Chromium Mass
(kg/hour)
0.91
2.72
4.08
Nickel Mass
(kg/hour)
3.40
7.47
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 pre-
sented are for nickel removal.
334
-------
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
335
-------
TABLE 8-24
REVERSE OSMOSIS
Flow Rate
(Liters/Hr) 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 6 Maintenance
Costs (Excluding Energy
& Power Costs) 4,873 9,675 20,761
Energy 6 Power Costs 1,404 2,144 3,536
Total Annual Cost $12,906 $22,017 $40,275
336
-------
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 8-2U can
best be made by placing the treatment processes in the
following order:
1. Reverse osmosis
2. Ion exchange, which includes ion exchange with
service regeneration, ion exchange with in-plant
regeneration, and cyclic ion exchange
3. Ultrafiltration
4. Membrane filtration
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 exchange processes. The investment costs for both
of these are very similar. The next lowest investment
requirement is for membrane filtration 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
337
-------
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 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 (H 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
338
-------
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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.
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, 2U 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.
The actual costs of installing and operating an end-of-pipe
treatment system at a particular plant may be substantially
-------
TABLE 8-25
END-OF-PIPE TREATMENT WITHOUT CHELATED WASTES
Total Flow Rate (Liters/Hr)
Least Cost System
Investment Costs:
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Costs
Depreciation
Operation 6 Maintenance
Costs(Excluding Energy &
Power Costs)
Wastewater Treatment
Sludge Handling
Total O & M
Energy & Power Costs
Total Annual Costs
7,885 23,655 236,562
Batch Batch Continuous
$96,142 $145,166 $431,143
0 0 17,361
$96,142 $145,166 $448,504
6,134
19,228
7,555
0
7,555
627
$33,545
9,261
29,033
28,614
89,701
19,731 33,267
0 4,172
19,731 37,439
1,341 1,057
$ 59,367 $156,810
341
-------
TABLE 8-26
END-OF-PIPE TREATMENT WITH CHEIATED 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
Total O & M
Energy & Power Costs
Total Annual Costs
7,885 23,655 236,563
Batch Batch Continv
$129,269 $183,313 $516,802
0 0 17,284
$129,269 $183,313 $534,086
8,247
25,854
9,904
0
9,904
611
$ 44,615
11,695 34,074
36,663 106,817
22,122 36,041
0 4,197
22,122 40,238
1,291 1,057
71,770 $182,186
342
-------
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 cf contracting the work.
Equipment costs may be reduced by using or modifying
existing eqxiipment 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 cos-ts 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:
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
U. Peduction 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
3
-------
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 treatment. With approximately the same cyanide
mass as in the aforementioned batch treatment system and
with no wastewater flow segregation, this end-of-pipe
treatment requires an investment of approximately $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 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
344
-------
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 pretreatment 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 indentical 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 (EOF), the rinse techniques (Rinse),
and the combined EOF 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
categori es.
The various EOF investment costs assume that the EOF
treatment systems must be specially constructed and include
all subsidiary costs discussed under the cost Breakdown
Factors segment of this section. The 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
345
-------
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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 treatment 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 countercurrent rinse
with the final rinse waters going to a cyclic ion exchange
unit for plating solution recovery. The nickel plating
operation is followed by a three stage countercurrent rinse
with the final rinse water going to a reverse osmosis unit
to recover the plating solution and 95 percent of the rinse
water. The copper plating operation 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 stage running
rinses to a system to recover plating solutions and retains
the end-of-pipe treatment system that existed previously, no
3U9
-------
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 $39,81U 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 $63,515/ 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 l.t years
for the largest flow case (108.7 square meters per hour per
line).
In conjunction with the recovery costs presented in Table 8-
29r additional costs will be incurred to reduce the effluent
pollutant concentrations 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 electroless 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 countercurrent rinse after the
electroless plating process with the rinse overflow water
being treated by a single effect submerged tube evaporator.
The rinse tank sizes and rinsing ratio are the same as those
used in developing Table 8-31. The submerged tube
350
-------
TABLE 8-30
PLATING SOLUTION RECOVERY WITH
BASE PLANT END-OF-PIPE TREATMENT
Metal Plating
Production
(sq. meters/hour/line)
Investment Cost:
Wastewater Treatment
Sludge Handling
Total Investment
Annual Costs:
Capital Cost
Depreciation
Operation & Maintenance Costs
(Excluding Energy 6 Power costs)
Wastewater Treatment
Sludge Handling
Total O&M
Energy & Power Costs
Total Annual Costs
EOP
0
0
$ 0
72.5
Rinse
39814
0
$39814
Total
39814
0
$39814
9260
29028
•
7294
6618
13912
352
$52552
2540
7963
-23391
0
-23391
1818
$-11070
11800
36991
-16097
6618
-9479
2170
$41482
Note: Costs are for a plant that has 3 plating lines,
351
-------
TABLE 8-31
ELECTROLESS PLATING ON METALS AND PLASTICS IN-LINE
Dragout
Flow Rate (Liters/Hour)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation 6 Maintenance Costs
(Excluding Energy & Power Costs)
Energy & Power Costs
Total Annual Cost
TABLE 8-32
Dragout
Flow Rate (Liters/Hour)
Investment
Annual Costs:
Capital Costs
Depreciation
Operation & Maintenance Costs
(Excluding Energy 6 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
2
TURE IN-LINE
1.17
$19359
1235
3872
305
2917
$8328
2.35
$19359
1235
3872
609
3681
$9397
3.52
$19359
1235
3872
914
4445
$10466
352
-------
evaporator is a standard size unit of 94.6 liters per hour
(25.0 gallons per hour) capacity. Fuel oil is burned
specifically to feed the evaporation device. Costing
assumptions for the submerged tube evaporator and the
countercurrent rinse were discussed under "Technology Costs
and Assumptions", above.
System Cost Computation - A computer program was developed
to calculate 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 derived from cost data obtained from several sources
listed under the "Cost Estimates" 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 crder 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 (H) 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, id 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 separatii? of streams. Also included
were certain other industrial wastewater treatment
353
-------
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 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 concentrations 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 Industry 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
Pecovery Costs, Debt-Equity Ratio, and Subsidiary Costs.
Dollar Base - A. dollar base of January 1976 was used for all
costs.
354
-------
TABLE 8-33
COST PROGRAM POLLUTANT PARAMETERS
• Units
Flow, MGD
pH, pH units
Turbidity, Jackson units
Temperature, degree C
Dissolved Oxygen, mg/1
Residual Chlorine, mg/1
Acidity, mg/1 CaCO3
Alkalinity, mg/1 CaCO3
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
355
-------
Investment cost Adjustment - Investment costs were adjusted
to the aforementioned dollar base by use of the Sewage
Treatment Plant Construction Cost Index. This cost index is
published monthly by the EPA Division of Facilities
Construction and Operation. The national average 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 factor 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 obtained 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
maintenance cost.
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 calculated directly within each process. Estimated
costs were then determined 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
356
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operation would be satisfied by an existing electrical
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 percent annual interest rate for a period
of five years. The five year depreciation period was
consistent with the faster write-off (financial 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 (CFP) is normally used in
industry to help allocate the initial investment and the
interest to the total operating cost of the facility. The
CFR 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 CFR. 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
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:
357
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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 constructing 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 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 8-3U.
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).
358
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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
359
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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 1U 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 maintenance
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 construction of wastewater treatment facilities and
include such items as preparation of legal documents,
preparation of construction contracts, acquisition of land,
etc. 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, 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.
360
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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 water rate should be minimized by
all means possible. For example, an upstream reverse
osmosis or ultrafiltration unit can drastically reduce 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.
Incineration of sludges or solids can, however, cause
significant air pollution. In fact, efforts to reduce this
air pollution by scrubbing can result in water pollution.
Noise pollution disturbs equipment operators even more than
the surrounding community. However, none of the wastewater
treatment processes causes objectionable noise in either
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
361
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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 leachat.es is advisable. Where appropriate, the
location of solid hazardous materials disposal sites should
be permanently recorded in the appropriate office of legal
jurisdiction.
36U
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SECTION IX
BEST PPACTICAELE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE, GUIDELINES AND LIMITATIONS
These limitations will be developed at a later date.
365
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLE, GUIDELINES AND LIMITATIONS
These limitations will be developed at a later date.
-------
SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
These limitations will be developed at a latf»r date.
369
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SECTION XII
PRETREATMENT
Introduction
Approximately 80 percent of the plants in the electroplating
industry discharge to publicly owned treatment works (POTW).
These plants discharge to POTW of all sizes but are
concentrated in urban areas which are served by relatively
large POTW. Over 50 percent of electroplating facilities
are in cities with populations of 100,000 or more and more
than 75 percent of these urban plants are in cities of
20,000 people or more(2). It is estimated that
electroplating plants discharge approximately one billion
gallons of process water each day to POTW and an additional
21 million gallons per day directly to surface waters(1).
Most POTW consist of primary or secondary treatment systems
which are designed to treat domestic wastes. Many of the
pollutants contained in electroplating wastes are not
biodegradable and are ineffectively treated by such systems.
Further, these wastes have been known to interfere with the
normal operations of these systems.
Following is a discussion of the problems associated with
the uncontrolled release of these pollutants to POTW and an
analysis of the pretreatment control technology which is
appropriate for treating these wastes.
Pa ss-Through, Interference and Sludge Disposal
Considerations
Electroplating wastes discharged to POTW pose significant
problems for the POTW itself, as well as the surface waters
to which the POTW discharges. The toxic pollutants present
in electroplating wastes may interfere with the operation of
the POTW by killing the biota and reducing POTW efficiency.
Additionally, since POTW are not designed to treat these
wastes, a substantial fraction passes through the POTW
untreated and may cause serious environmental problems in
the receiving water. Finally, that fraction of these wastes
that is removed in the POTW is concentrated in the POTW
sludge. The presence of these pollutants in the sludge may
seriously impact sludge disposal utilization options.
Sludge containing excessive amounts of toxic pollutants may
not be suitable for spreading on agricultural land, a
practice currently employed to handle nearly 25 percent of
the POTW sludge(3). Other common practices such as
incineration (35 percent of POTW sludge) and landfill (25
371
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percent) may also be impacted since these pollutants may
exacerbate air pollution problems associated with
incineration and leach into aquifers from land disposal
sites under certain conditions.
Following is a more specific discussion of the problems
related to the individual regulated pollutant parameters.
Cadmium
Cadmium is not destroyed when introduced into a POTW, and
will either pass through to the POTW effluent or be
incorporated into the POTW sludge. It can interfere with
the POTW treatment process and can also limit the usefulness
of municipal sludge. It causes toxic effects in a wide
variety of organisms, including aquatic species and humans.
Threshold concentrations for inhibition by cadmium in a POTW
are 10 to 100 mg/1 for activated sludge processes and 0.02
mg/1 for anaerobic digestion processes. Other metals,
including zinc and magnesium, are synergistic for cadmium
inhibition.
In a recent study of 189 POTW's, 75 percent of the primary
plants, 57 percent of the trickling filter plants, 66
percent of the activated sludge plants and 62 percent of the
biological plants allowed over 90 percent of the influent
cadmium to pass through to the POTW effluent. Only 2 of the
189 POTWfs allowed less than 20 percent pass through, and
none less than 10 percent pass through. POTW effluent
concentrations ranged from 0.001 to 1.97 mg/1 (mean 0.028
mg/1, standard deviation 0.167 mg/1).
The cadmium which passes through the POTW to the effluent
will usually be discharged to ambient surface water.
Cadmium is toxic to aquatic organisms at levels typically
observed in POTW effluents; for example:
96 hr LC-50 for Chinook salmon is reported as 0.002
mg/1.
96 hr LC-50 for steelhead trout is reported as
0.0009 mg/1.
Reproductive decrease in flagfish and brook trout
at 0.0081 and 0.003H mg/1, respectively.
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 via drinking
372
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water and from use of contaminated irrigation water has been
documented as the cause of itai-itai disease in humans.
Cadmium not passed through the POTW will be retained in the
sludge, where it is likely to build up in concentration.
Sewage sludge is recognized as being a valuable resource for
soil conditioning, with about 25 percent being applied to
land (20 percent to cropland, 5 percent to golf courses,
etc.)- Cadmium contamination of sewage sludge limits its
use on land since it increases the level of cadmium in the
soil. Moreover, plant uptake results in contaminated crops.
Sewage sludge contains 3 to 3000 mg/kg (dry basis) of
cadmium (mean = 106 mg/kg; median = 16 mg/kg). These
concentrations, for the most part, are significantly greater
than those normally found in soil (0.017 to 7 mg/kg, with
0.06 mg/kg being a common level). Data show that cadmium
can be incorporated into crops, including vegetables and
grains, from contaminated soils. Since 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.
Cadmium may be a factor in the development of such human
pathological conditions as kidney disease, testicular
tumors, hypertension, arteriosclerosis, growth inhibition,
chronic disease of old age, and cancer. Cadmium which
enters a POTW will either be discharged to ambient water,
where it becomes a possible drinking water contaminant, or
be incorporated into sewage sludge, where it becomes a
possible human food contaminant via crop uptake.
Two 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 over
20 mg/kg should not be used on agricultural land. The USDA
also recommends placing limits on the total cadmium from
sludge that may be applied to land.
Pretreatment of electroplating discharges substantially
reduces the concentration of cadmium in sludge. In Buffalo,
New York, for example, pretreatment of electroplating waste
resulted in a decrease of cadmium concentrations in the
sludge from 100 to 50 mg/kg.
The Agency estimates that if the proposed regulation is
promulgated approximately 200,000 pounds per year of cadmium
will be removed from effluent entering POTW.
373
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Chromium
Chromium exists in the environment primarily in two
oxidation states, hexavalent chromium and trivalent
chromium. Chromium is not destroyed when treated by a POTW
(although the oxidation state may change), and will either
pass through to the POTW effluent or be incorporated into
the POTW sludge. Both oxidation states can cause POTW
treatment inhibition and can also limit the usefulness of
municipal sludge. Hexavalent and trivalent chromium both
cause toxic effects in a wide variety of organisms including
aquatic species and humans. Chromium which passes through a
POTW becomes a potential drinking and bathing water
contaminant. Hexavalent chromium is a known human
carcinogen, and is generally the more toxic of the two
oxidation states.
Hexavalent chromium threshold concentrations for POTW
treatment process inhibition are 1 to 10 mg/1 for activated
sludge, 5 to 50 mg/1 for anaerobic digestion, and 0.25 mg/1
for nitrification processes. Trivalent chromium threshold
concentrations are 50 mg/1 for activated sludge and 50 to
500 mg/1 for anaerobic digestion processes. Chromium can
also interfere with sludge settling in concentrations as low
as 7 mg/1.
The amount of chromium which passes through to the POTW
effluent depends on the type of treatment processes used by
the POTW. In a recent study of 240 POTW*s 56 percent of the
primary plants allowed more than 80 percent pass-throuqh to
POTW effluent. More advanced treatment results in less
pass-through, with median values for trickling filter,
activated sludge, and biological treatments all being near
about 60 percent pass-through. POTW effluent concentrations
ranged 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 will usually be
discharged to ambient surface water. Chromium is toxic to
aquatic organisms at levels observed in POTW effluents, for
example:
o
trivalent chromium showed a significant
impairment in reproduction of Daphnia
magna at levels of 0.3 to 0.5 mg/1.
hexavalent chromium retards growth
chinook salmon at 0.0002 mg/1.
of
374
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o hexavalent chromium is chronically toxic
at levels as low as 0.010 mg/lr affecting
the ability of several aquatic species to
grow or reproduce.
Hexavalent chromium is also corrosive, and a potent human
skin sensitizer.
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 .05
mg/1.
Chromium not passed through the POTW will be retained in the
sludge, where it is likely to build up in concentration.
Sludge concentrations of total chromium of over 20rOOO mg/kg
(dry basis) have been observed. Sewage sludge is recognized
as being a valuable resource for soil conditioning, with
about 25 percent currently being applied to land (20 percent
to cropland, 5 percent to golf courses, etc.). Most crops
absorb relatively little chromium, even when it is present
in high levels in soils, but hexavalent chromium has been
shown to reduce some crop yields in concentrations as low as
200 mg/kg.
Pretreatment of electroplating discharges substantially
reduces the concentration of chromium in sludge. In
Buffalo, New York, for example, pretreatment of
electroplating waste resulted in a decrease in chromium
concentrations in sludge form 2,510 to 1rOUO mg/kg. A
similar reduction occurred in Grand Rapids, Michigan where
the chromium concentration in the sludge decreased from
11,000 to 2,700 mg/kg.
The Agency estimates that if the proposed regulation is
promulgated approximately 10,000,000 pounds per year of
chromium will be removed from effluent entering POTW.
Copper
Copper is not destroyed when treated by a POTW, and will
either pass through to the POTW effluent or be retained in
the POTW sludge. It can interfere with the POTW treatment
processes and can limit the usefulness of municipal sludge.
It causes toxic effects in a wide variety of organisms,
including aquatic species.
375
-------
Threshold concentrations for inhibition by copper in a POTW
are 1.0 mg/1 in activated sludge and anaerobic digestion
processes, and 0.005 to 0.5 mg/1 for nitrification
processes, depending on POTW conditions. In a recent study
of 268 POTW's, the median pass through was over 80 percent
for primary plants and 40 to 50 percent for trickling
filter, activated sludge and biological treatment plants.
POTW effluent concentrations of copper 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
will be discharged to ambient surface water. Copper is
toxic to aquatic organisms at levels typically observed in
POTW effluents, for example:
o 96-hour LC-50 for the rainbow trout is 0.02 mg/1.
o 96-hour LC-50 for the Chinook salmon is 0.031 mg/1.
o 96-hour TL-50 for the fathead minnow is 0.023 mg/1.
Copper which does not pass through the POTW will be retained
in the sludge, where it is likely to build up in
concentration. The presence of excessive levels of copper
in sludge may limit its use on cropland. Sewage sludge
contains up to 16,000 mg/kg of copper, with 730 mg/kg as the
mean value. These concentrations are significantly greater
than those normally found in soil, which usaully range from
18 to 80 mg/kg. Copper toxicity may develop in plants from
application of sewage sludge contaminated with copper.
Yield reductions have been reported as low as 100 mg/kg with
legumes being more sensitive than cereals. In one study,
copper decreased beet yields by 74 percent at 80 mg/kg and
90 percent at 160 mg/kg.
Pretreatment of electroplating wastes in Buffalo, New York,
resulted in a decrease in copper concentration in sludge
from 1,570 to 330 mg/kg. In Grand Rapids, Michigan, the
sludge copper concentration decreased from 3,000 to 2,5000
mg/kg.
The Agency estimates that if the proposed regulation is
promulgated approximately 6,000,000 pounds per year of
copper will be removed from effluent entering POTW.
376
-------
Lead
Lead is not destroyed when treated in a POTW, but will
either pass through to the POTW effluent or be retained in
the POTW sludge. It can interfere with the POTW treatment
process and can also limit the usefulness of municipal
sludge. It causes toxic effects in a wide variety of
organisms, including aquatic species and humans,
particularly children.
Threshold concentrations for lead inhibition of POTW
treatment processes are 0.1 mg/1 for activated sludge
processes and 0.5 mg/1 for nitrification processes.
In a recent study of 21U POTW's, median pass through values
were over 80 percent for primary plants and over 60 percent
for trickling filter, activated sludge, and biological
process plants. Lead concentrations in POTW effluents
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 will
be discharged to ambient surface water. Lead is toxic to
aquatic organisms at levels typically observed in POTW
effluents, for example:
o 96-hour LC-50 for the coho salmon is 0.52 mg/1.
o 50 percent reproductive decrease in Daphina magna
at 0.1 mg/1.
o Chronic detrimental effects on rainbow trout, brook
trout, and sticklebacks at concentrations of 0.1
mg/1.
Besides providing an environment for aquatic organisms,
surface water is often used as a source of drinking water.
The National Interim Primary Drinking Water Regulations
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. According to the above regulations, 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. The
estimated maximum safe level of lead intake is 600 ug/day.
Potential sources of exposure are diet, water, dust, air,
etc. Levels of lead in many urban children indicate
377
-------
overexposure (chronic brain or kidney damage, or acute brain
damage), the levels of lead in water should be limited to as
low as is practicable.
Lead which does not pass through the POTW will be retained
in the sludge, where it is likely to build up in
concentration. Municipal sludge is recognized as a valuable
resource, with about 25 percent currently being applied to
land (20 percent crop uses, 5 percent golf courses, etc.).
In a recent two year study of eight cities, the median lead
content ranged from 546 mg/kg to 8,466 mg/kg, with a maximum
observed content of 11,897 mg/kg. Since the normal range of
lead content in soil is from 3 to 70 mg/kg, application of
contaminated sewage sludge to the soil will generally
increase the soil's lead content.
Data indicate that the application of sludge containing
excessive levels of lead to cropland may increase the lead
concentration in crops if grown on acid soils. Generally,
roots accumulate more lead than do plant tops. For above
ground crops, significant impacts on lead concentration 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 recommended that sludge containing more
than 1,000 mg/kg of lead should not be used on agricultural
land for crops used directly in the food chain.
Pretreatment of electroplating wastes in Buffalo, New York,
resulted in a decrease in lead concentrations in sludge from
1,800 to 605 mg/kg.
The Agency estimates that if the proposed regulation is
promulgated approximately 200,000 pounds per year of lead
will be removed from effluent entering POTW.
Nickel
Nickel is not destroyed when treated in a POTW, but will
either pass through to the POTW effluent or be retained in
the POTW sludge. It can interfere with POTW treatment
processes and can also limit the usefulness of municipal
sludge. Nickel causes toxic effects in a wide variety of
organisms, including aquatic species and humans. It is a
human carcinogen.
Threshold concentrations for POTW treatment process
inhibition are 1 to 2.5 mg/1 for activated sludge, 2 mg/1
for anaerobic digestion, and 0.53 mg/1 for nitrification
processes.
378
-------
In a recent study of 190 POTV^s, nickel pass through was
greater than 90 percent for 82 percent of the primary
plants. Median pass through for trickling filter, activated
sludge, and biological process plants was greater than 80
percent. POTW effluent concentrations ranged from 0.002 to
10 mg/1 (mean = O.U10, standard deviation = 3.279).
The nickel which passes through the POTW is usually
discharged to ambient surface water. Nickel is toxic to
aquatic organisms at levels typically observed in POTW
effluents, for example:
o 50 percent reproductive impairment of Daphnia magna
at 0.095 mg/1.
o 3 week LC-50 of 0.130 mg/1 for Daphnia magna.
o Morphological abnormalities in developing eggs of
Limnaea palustris at 0.23 mg/1.
o 50 percent growth inhibition of aquatic bacteria at
0.020 mg/1.
Since surface water is often used as a drinking water
source, nickel passed through a POTW becomes a possible
drinking water contaminant.
Nickel not passed through the POTW will be incorporated into
the sludge. Sewage sludge is recognized as being a valuable
resource, with 25 percent currently being applied to land
(20 percent to cropland, with 5 percent to golf courses,
etc.). In a recent two year study of eight cities, four of
the cities had median nickel concentrations of over 350
mg/kg, and two were over 1,000 mg/kg. The maximum nickel
concentration observed was 4,016 mg/kg.
Nickel toxicity may develop in plants from application of
sewage sludge on acid soils. Nickel has caused reduction of
yields for a variety of crops including oats, mustard,
turnips, and cabbage. For example, in one study, nickel
decreased the yields of oats by 16 percent at 50 mg/kg, and
70 percent at 100 mg/kg.
Pretreatment of electroplating wastes in Buffalo resulted in
a decrease in nickel concentration in sludge from 315 to 115
mg/kg. A similar decrease occurred in Grand Rapids,
Michigan, where the sludge nickel concentrations went from
3,000 to 1,700 mg/kg.
379
-------
The Agency estimates that if the proposed regulation is
promulgated approximately 12,000,000 pounds per year of
nickel will be removed from effluent entering POTW.
Zinc
Zinc is not destroyed when treated by a POTW, but will
either pass through to the POTW effluent or be retained in
the POTW sludge. It can interfere with treatment processes
in the POTW and can also limit the use of municipal sludge.
It causes toxic effects in a wide variety of organisms,
including aquatic species.
Threshold concentrations for POTW treatment process
inhibition are 0.3 mg/1 for activated sludge, 5 mg/1 for
anaerobic digestion, and 0.08 to 0.5 mg/1 for nitrification
processes. Other metals can cause synergistic effects.
In a recent study of 258 POTWfs, the median pass through
values were 70 to 80 percent for primary plants, 50 to 60
percent for trickling filter and biological process plants,
and 30-10 percent for activated sludge process plants. POTW
effluent concentrations of zinc ranged from 0.003 to 3.6
mg/1 (mean = 0.330, standard deviation = 0.46U).
The zinc which passes through the POTW to the effluent will
be discharged to ambient surface water. Zinc is toxic to
aquatic organisms in concentrations typically observed in
POTW effluents, for example:
o 96-hour LC-50 for the cutthroat trout is 0.090
mg/1.
o 96-hour LC-50 for the Chinook salmon is 0.103 mg/1.
o Growth retardation in the minnow at 0.13 mg/1 and
abnormal swimming behavior at O.OU mg/1.
The zinc which does not pass through the POTW will be
retained in the sludge. Municipal sludge is recognized as a
valuable resource, with 20 percent currently being applied
to cropland as a soil conditioner. The presence of zinc in
sludge may limit its use on cropland. Sewage sludge
contains 72 to over 30,000 mg/kg of zinc, with 3,366 mg/kg
as the mean value. These concentrations are significantly
greater than those normally found in soil, which range from
0 to 195 mg/kg, with 94 mg/kg being a common level.
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.
380
-------
Lettuce, tomatoes, turnips, mustard, kale, and beets are
especially sensitive to zinc contamination.
Pretreatment of electroplating waste in Buffalo, New York,
resulted in a decrease in zinc concentrations in sludge from
2,275 to 364 mg/kg. The zinc content in the sludge of Grand
Rapids, Michigan, also decreased from 7,000 to 5,700 mg/kg
as a result of pretreatment.
Cyanide
Cyanides are widely used in the electroplating industry and
are among the most toxic of pollutants commonly observed in
industrial waste waters. Cyanides can interfere with the
treatment processes in a POTW, or pass through to ambient
waters. Cyanide also enhances the toxicity of metals
commonly found in POTW effluents.
Threshold cyanide concentrations for POTW treatment process
inhibition are 0.1 to 5 mg/1 for activated sludge, 4 mg/1
for anaerobic digestion, and 0.34 mg/1 for nitrification
processes.
Cyanide may be destroyed in a POTW, but data indicate that
much of it passes through to the POTW effluent. One primary
plant showed 100 percent cyanide pass through, and the mean
pass through for 14 biological plants was 71 percent. In a
recent study of 11 POTW's the effluent concentrations ranged
from 0.002 to 100 mg/1 (mean = 2.518, standard deviation =
15.6).
The cyanide which passes through to the POTW effluent will
usually be discharged into ambient surface water. There is
a considerable amount of data documenting cyanide toxicity
to aguatic 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 to be fatal to sensitive
fish species including trout, bluegills, and fathead
minnows. Levels above 0.2 mg/1 are rapidly fatal for many
species. Long term sublethal concentrations of cyanide as
low as 0.01 mg/1 have been shown to affect the ability cf
fish to function normally, e.g. reproduce, grow, and move
freely.
381
-------
Cyanide may exist as free cyanide (CN anion), hydrogen
cyanide (HCN), or as a complex with metals. In the absence
of metals, free cyanide and hydrogen cyanide are in an
equilibrium which is highly dependent upon pH. AT pH values
below 7.0, over 99 percent of the cyanide is present as HCN.
At pH values of 8.0, 9.0, and 10.0 the HCN percentage
decreases to 93.3 percent, 58 percent and 13 percent,
respectively. Since HCN is the most toxic form of cyanide,
it is clear that decreasing pH (increasing acidity) results
in greater toxicity. Temperature increase also results in
increased toxicity (2-3 fold over 10°C), as does reduction
in dissolved oxygen content.
Cyanide forms complexes with metal ions present in waste
water. 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.
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.
Silver
There is no available literature on the incidental removal
of silver by POTW. An incidental removal of about 50
percent is assumed as being representative as this is the
highest average incidental removal of any metal for which
data is available (Copper has been indicated to have a
median incidential removal rate of U9 percent).
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. The
threshold toxicity level ot other lower aquatic organisms
382
-------
has been reported at 30 to 50 ug/1. The toxic threshold of
silver nitrat0 for stickelbacks is reported as 4.8 ug/1 as
silver.
Bioaccumulation and concentration of silver from sewage
sludge has not been studied to any great degree. There is
some indication that silver could be bioaccumulated in
mushrooms to the extent that there could be an adverse
physiological effect on humans if they consumed large
quantities of mushrooms grown in silver enriched soil. The
effect, however, would tend to be unpleasant rather than
fatal. No data has been accumulated on the remainder of the
metals.
There is little summary data available on the quantity of
silver discharged to POTW. Presumably because of its high
intrinsic value there would be a tendency to limit its
discharge from a manufacturing facility. Pretreatment
requirements will limit the discharge of silver from those
establishments that allow or may allow them to discharge
freely.
Technical Approach
The pretreatment standards were developed in the following
manner: The point source category was first studied for the
purpose of determining whether separate standards are
appropriate for different segments within the category. The
raw waste characteristics for each such 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
then considered. Waste water constituents posing
pass-through or interference problems for POTW were
identified.
The control and treatment technologies existing within each
segment were identified. This included identification of
each distinct control and treatment technology, including
both in-plant and end-of-process technologies, which exist
or are capable of being designed for each segment. It also
included identification of 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. The problems,
limitations, and reliability of each treatment and control
technology were also identified. In addition, the nonwater
383
-------
quality environmental impact, such as the effects of the
application of such technologies upon other pollution
problems, including air, solid waste, noise, and radiation
were identified. 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 in
order to determine what levels of technology reflected the
application of appropriate pretreatment technologies. In
identifying such technologies, various factors were
considered. These included the total cost of application of
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, nonwatar quality environmental impact (including
energy requirements) and other factors.
The data upon which the analysis was performed included EPA
permit applications, EPA sampling and inspections,
consultant reports, and industry submissions.
Following is a detailed description of the analysis
performed by the Agency for this point source category.
Treatment of Cyanide
The distinction between CN,A and 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
the 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. Cyanide complexes with Ni,
which can be formed if cyanide rinses are not segregated
from Ni plating rinses before treatment, are destroyed
somewhat less rapidly but still should be largely removed
during first stage treatment. 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 which were discussed earlier.
The available technologies for treating cyanide were
described in detail in chapter VII.
381
-------
Attainable Levels of Control for CN,A
The destruction of CN,A by alkaline chlorination is a
kinetically rapid reaction, and a plant with an adequately
sized and controlled treatment unit should experience little
difficulty in bringing about substantially complete removal
of CN,A. That this is the case can be seen from the data in
Table 12-1. Of the 58 plants whose data are summarized in
this table, 19 (33%) reduced the average CM,A to 0.01 mg/1,
which is close to the limit of analytical measurability.
The plants described in Table 12-1 are those which: plate
Cu, Cd, Zn or precious metals; have an oxidation system to
treat their CN wastes; and have CM,A concentration data. An
effort has been made to make Table 12-1 as complete as
possible, by including all available CN,A data from plants
plating the appropriate metals and with oxidation treatment,
regardless of the quality of their waste management or
treatment systems.* Thus, all of the plants in this table
are not to be considered as necessarily exemplary in either
design or operation.
Figure 12-1 is a cumulative plot of the average CN,A
concentrations experienced by the 58 plants. The plot shows
that 33% of the plants removed essentially all amenable
cyanide (down to CN,A < 0.01 mg/1), and also shows that many
of the remaining plants, although not reaching the minimum
level, remove CNrA down to quite low levels. Some 55% of
all plants reported (or were found to have on sampling) CN,A
average levels of 0.04 mg/1 or less.
In some instances, the cause of the elevated CN,A levels
experienced by certain of the plants appears to be poor
design or control of the system. For instance, sampling
personnel -i It hough not specifically instructed to evaluate
the design or operation of plant treatment systems during
sampling visits, have for certain plants noted potential
design flaws (4045, 10020, 20084), a history of chlorine
feed malfunctions (6073), or spillage to streams of CN-
bearing solutions without treatment (20086).
Attainable Levels of Control for CN,T (Long Term Average)
Table 12-2 presents comparable data for 85 plants with
cyanide wastes, oxidation treatment, and which :: ,L.ort CN,T.
Figure 12-2 is a cumulative plot of the average CN,T's for
iThree plants (6078, 19002, 33071) were excluded from the
data base because of cyanide dc^truct systems which were not
operating properly or which were partially by-passed.
385
-------
TABLE 12-1
CN(A) CONCENTRATIONS OBSERVED IN EFFLUENT FROM PLANTS
WITH CYANIDE OXIDATION IN WASTE TREATMENT SYSTEM
Plant
4
6
7
e
15
19
316
478
€52
804
1108
1113
1924
2001
2007
2103
3301
3320
3601
4001
4045
50? 1
6037
6051
6050*
6053**
6072
6073
6075
6077**
6079
6081
6084
6085
6087
6069
6358**
€381
Oata*
Source
1
1
1
1
1
1
2
2
2
3
1
1
3
3
1
3
1
1
1
1
4
4
4
A
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
l\
3
3
3
1
1
1
2
3
2
3
3
3
1
3
1
3
2
3
Median
0.04 mg/1
-.32
.25
.80
.50
Concentration CN(A)
Avg
Max
.01
.06
.01
.01
.49
,04
,03
.04
.02
01
.01
,02
.01
.25
1.00
,01
.41
.01
.01
till
.01
1.46
,01
.01
.01
,02
J.97
,56
.04
.29
.01
.10
0.04 nig/1
,32
.25
.60
1.31
.56
.01
,06
,01
.02
.62
,16
.07
.04
,02
,01
.02
.02
.01
.25
1.15
.01
4.04
,01
.01
nil
.01
2.24
,01
.01
,01
,03
1.97
.57
,04
.53
,0>
.31
0.05
.32
.25
1.00
7.90
1.40
.01
.08
.01
.15
1.90
.68
.17
.06
.03
.03
.03
.02
.01
.45
2.20
,01
11.60
,01
,01
nil
,01
3.98
.01
.01
-01
.04
1.97
1.09
.04
1.14
.01
.75
386
-------
Data* Number Concentration CN(A)
Source Obs: Median Avg Max
$026 4 3 .01 .€2 .03
10020 4 3 4.40 5.30 7.30
15070 4 3 .01 .01 .02
19050 4 1 nil nil nil
19051 4 1 nil nil nil
20073 4 € -01 .02 .05
20077 4 € .39 .98 3.00
20078 4 6 .01 .01 iOl
20079 4 6 -01 .01 .01
20080 4 4 -01 ,03 .10
20081 4 7 .02 .13 .49
20082 4 6 ,79 ,96 3.00
20084 4 2 1.25 1.25 2.50
20086 4 3 ,36 1.87 5.25
20087 4 3 ,66 .49 .80
31021 4 3 .05 .05 .05
33024 344 3 ,04 .05 ,08
33073 4 2 ,02 ,02 .03
36040 4 3 ,01 .01 .01
36041 4 3 .10 ,20 .40
*1 = Data from reports by Yost et al, and Safranek et al
2 = Battelle
3 = Plant
4 = Hamilton Standard
**Integrated or Lancey System
386(a)
-------
in
«o
Ul
o
tK
se
Si
ui
UJ
0£
UJ
Afssnsav >• ssmvA HUM sssvo
387
do
-------
TABLE 12-2
CN(T) CONCENTRATIONS OBSERVED IN EFFLUENT FROM CERTAIN
PLANTS WITH CYANIDE OXIDATION IN WASTE TREATMENT SYSTEM
Plant Data Number Concentration CN(T)
ID Source Obs: Median Avg Max
41 2 .25 .25 .38
61 2 16.72 16.72 31.80
71 2 .45 .45 .59
B 1 2 14.00 14.00 16.00
15 1 11 1.30 2.65 12.00
19 1 11 .78 .80 1.60
116 3 37 ,01 .12 2.22
478 2 3 ,25 ,31 .61
607 243 3 .12 .11 .16
529 2 1 .07 .07 ,07
€37 243 8 .48 .52 1.00
€50 3 17(m) .01 .01 .03
652 2 1 .01 .01 ,01
662 3 7(n) .30 .36 .96
689 3 6 .08 .37 1.30
605 243 21 nil fill .05
902 3 6 nil nil nil
1108 .1 13 1.00 1.38 4.00
1113 1 9 .05 ,21 .78
1165 2 2 .09 ,09 ,12
1208 3 37 .10 .15 .92
1209 2 1 .03 .03 .03
1263 2 1 .01 .01 ,01
1302 2 1 1.00 1.00 1.00
1924 3 5 .01 .84 3.20
2006 2 7 .02 .02 .08
2007 1 2 .02 .02 .03
2017 3 124 .02 ,02 .07
2103 3 44 ,02 .02 .04
2303 2 1 ,20 .20 .20
2501 3 13 nil fill .03
2809 2 1 .01 .01 .01
2811 3 6 .10 .22 .40
3003 2 1 .01 -01 .01
3005 2 1 ,05 .05 .05
3021 3 7 ,03 .03 .07
3121 3 € ,01 ,t)2 .04
3301 1*3 21 .04 .05 .12
3311 3 25 till .07 1.60
3315 243 7(m) 4.30 4.26 9.90
3320 243 £6 .01 ,02 .16
388
-------
CN(T) CONCENTRATIONS OBSERVED IN EFFLUENT FROM CERTAIN
PLANTS WITH CYANIDE OXIDATION IN WASTE TREATMENT SYSTEM
Plant Data
ID Source
3321
3601
3612
4001
4045
4301
5021
6037
€050**
6051
6053**
6072
6073
6075
6077**
6079
6081
6084
6085
6087
6089
6358**
6381
9026
10020
15070
19050
19051
20073
20077
20078
20079
20080
20081
20082
20084
20086
20087
310?1
33024
33070
33073
36040
36041
2&3
1&3
3
1
4
3
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
344
-4
4
-4
4
Number
Obs;
7
2
89
2
3
1
3
3
1
1
1
2
3
3
3
3
3
3
3
3
3
3
3
3
3
3
1
1
6
6
6
€
6
7
£
2
3
3
3
15
3
3
3
3
Median
.10
.03
.02
.21
8.70
.01
.01
i59
.01
.01
.01
.01
3.08
.01
,01
.02
.10
.44
.96
.08
.43
.06
.04
.03
5.30
.03
,.01
.01
,08
2.20
-.01
.01
,01
,07
,83
34.70
1.13
3.50
.16
nil
~07
.13
,01
,40
Concentration CN(T)
Avg Max
.12
,03
.02
.31
10.10
.01
.01
4.57
.01
.€1
.01
.01
3.29
.01
.07
.02
.12
1.09
1.23
.10
1.04
.05
.38
.04
5.70
,11
.01
.01
.12
1.90
,01
3.51
.23
,87
1.47
34.70
2.37
18.36
.26
,01
-07
-13
.06
^42
.32
.03
,02
.52
15.20
.01
.01
12.60
.01
.01
.01
.01
5.18
,01
.20
.02
.19
2.80
1.80
.12
2.42
.06
.98
.08
7.40
.29
,01
.01
.37
3.00
.04
21.00
1.23
3.82
3.31
50.50
5.25
50.00
.35
.08
.10
.25
,16
.60
«n « monthly average data
388(a)
-------
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389
-------
these plants. Comparison of Figure 12-1 and 12-2 show them
to be similar in form. In both cases, a substantial
fraction of the plants achieved nearly complete cyanide
removal-36 percent of the Figure 12-2 plants experienced
average CN,T < 0.04 mg/1, with the median of the average
CN,T«s being 0.11 mg/1.
Variability Factor
As Tables 12-1 and 12-2 show, even plants which are
achieving good cyanide removal occasionally experience a day
of above average cyanide discharge. These high days may
reflect temporary imbalances in the treatment system caused
by fluctuations in flow, in raw waste cyanide loading, in
chemical feed, or in mixing flows within the tanks.
Allowance for the random variability of the discharge of a
well designed and operated plant may be made by applying a
"variability factor" to the expected long term average. The
expected long term average is then multiplied by the
variability factor. For purposes of establishing
regulations under the FWPCA, the variability factor is
generally set at a level such that 95 to 99 percent of the
normally-occurring fluctuations fall within the limit.
Based on the cyanide data, the variability of daily
composite samples was found to be 5.0 for CN,A and 5.8 for
CN,T. The variability of the monthly averages was found to
be 1.8 for CN,A and 2.2 for CN,T.
The formulation of an appropriate variability factor given
below is based upon observed discharge data from operating
plants. The plants with low average discharge
concentrations are likely to be most representative of the
performance of well controlled and well designed treatment
systems. However, the data base for variability factor
given below is based upon observed discharge data from
operating plants. It was found that the latter did not
experience variabilities that were significantly different
from those of the first group. In ether words, as in other
industries, the variability factor for this industry has
been found to be relatively insensitive to the plant's
average performance.
The calculation of the expected variability was based on the
observation that in this industry, as in many industries,
the discharge concentrations of metal and cyanide conform
closely to a standard lognormal statistical distribution.
Figure 12-3 shows a cumulative plot on a log probability
scale, of 123 daily observations of CN,T, which ranged over
one and a half orders of magnitude, from plant number 20-17.
The data fall nearly along a straight line (the deviations
390
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391
-------
being statistically insignificant), indicating that the
distribution of the observations from this plant is indeed
consistent with lognormality. Figure 12-'4 is a cumulative
plot of the CN,A data furnished for plant 11-08. The points
in this figure again fall along a straight line, indicating
that this sample also conforms to lognormality.
For a lognormal population, the relationship between the
percentile of the distribution (C) and the average (A) is
given by
log (C/A) = Z (SIGMA) - 1.513 SIG.MA2 [1]
where Z is the statistic for the percentile, and SIGMA is
the standard deviation of the logarithms of the
concentration. The "variability factor11 is C/A. It can be
seen from equation [1 ] that the C/A is dependent only on:
o The Z, which is a factor chosen by the Agency as
representative of the appropriate tradeoff between
the risk of setting a limit so low that a well-
designed and operated plant frequently exceeds the
limit and the risk of setting the limit so high
that proper operation of a treatment system becomes
unnecessary. The Agency believes a Z = 2.326 for
this category is appropriate for derivation of the
variability factor. Use of this number means that
the likelihood that a well-designed and operated
treatment system will exceed estimated upper
variability will be less than 1 percent.
o The SIGMA, which is determined from the data and
which is considered to be a characteristic of the
particular pollutant - treatment system combination
under study, was calculated by pooling the estimate
of the SIGMA's from a series of plants.
392
-------
»r.
10 IS 20
30
PERCENTAGE
40 SO 60
70
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FIGURE 12-4
--^3=fu=}_ CUMULATIVE DISTRIBUTION OF 13 DAILY
DISCHARGE CONCENTRATION FROM
PLANT 11-08
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For the data base of Tables 12-1 and 12-2, the plants
selected for variability factor analysis were those which:
had 10 or more daily observations; had nonzero standard
deviations; and did not have a large proportion of reported
zero cyanide effluent concentrations. For these plants.
Table 12-3 and Table 12-4 present the mean and standard
deviation of the logarithms of the observed daily CN,A and
CN,T concentrations, respectively.2
Variability of Daily Composite Samples
The pooled estimate of SIGMA characteristic of the discharge
from plants reporting CN,A was 0.413. Entry of this value
into Equation [1] (using Z = 2.326) yields an estimated
variability factor from daily data of 5.0. Thus, a plant
which maintains a long term CN,A average concentration of
0.04 mg/1 or less should experience a fluctuation of five
times this value (0.20 mg/1) with no more than 1%
likelihood.
The pooled estimate of SIGMA from systems reporting CN,T was
0.479. Entry of this value into Equation [1] yields an
estimated variability factor of 5.8. A plant which achieves
an average concentration of 0.11 mg/1 CN,T or less should
experience a fluctuation of 5.8 times this value (0.64 mg/1)
with no more than 1% likelihood.
Variability of Monthly Average
Because comparatively few of the plants of Tables 12-1 and
12-2 were sampled over a multi-month period, it is difficult
to use the above-described procedures to determine
variability factors for monthly average concentrations. The
month-to-month variations can, however, be estimated from
the daily variability through a procedure known as Monte
Carlo simulation. A large array of random-lognormal numbers
of mean = 0.04 and standard deviation of the logarithm =
zIt can be seen from these tables that the means and
standard deviations are independent. Hence, for these
plants the variability is more or less independent of the
plant's attained average, so that, as indicated above, we
can include in the estimation of the data from plants (such
as 11-08) which did not on the average achieve cyanide
levels as low as the levels achieved by most of the plants
in the data base. If these poorer-than-average plants are
excluded from calculation of the pooled SIGMA, the overall
results do not change markedly.
394
-------
TABLE 12-3
Mean and standard deviation of the logarithm of daily observations
»f CN(A) -concentration
Plant Mean Std. Dev.
ID LOG C LOG C
35 -0.26 .590
.19 -0.38 .362
304 -2.36 .€03
1108 -0.34 .369
2001 -1.40 .106
2103 -1.87 .176
*MS Avg. .413
395
-------
TABLE 12-4
Mean and standard deviation of the logarithm of daily observations
of CfKD concentration
Mean Std. Dev.
JOG C LOG C
15 €.22 -410
39 -0.15 .240
116 -2.10 1.033
1108 0.09 .330
1208 -0.96 -291
2017 -1.83 ^361
2103 -1.86 .250
3301 -1.43 -388
3320 -2.05 .486
JWS Avg -479
396
-------
0.413 (simulating the daily CN,A data) was generated. A
month's worth of these simulated daily samples were drawn
from this array and averaged - to obtain an estimate of one
month's average value. A large number of such monthly
average values was constructed, and the 99th percent!le of
the resulting distribution of monthly averages determined.
The value of the monthly variability factor so determined
was found to be 1.8. Thus, a plant which maintains a long
term CN,A average concentration of 0.04 mg/1 or less should
experience a 30-day average concentration of 1.8 times their
value (0.08 mg/1) with no more than 1 percent likelihood.
A similar calculation was made of the expected variability
of monthly samples drawn from a simulated lognormal daily
population having mean =0.11 and standard deviation of the
logarithm = 0.479 (representative of the CN,T case). The
resulting variability factor for the monthly average was
2.2. Thus, a plant which maintains a long term average CN,T
concentration of 0.11 mg/1 or less should experience a 30-
day average concentration of 2.2 times this value (0.24
mg/1) with no more than 1 percent likelihood.
Based on available treatment technologies, the following
levels of control can be attained:
Long-term Avg. 30 Day Avg. Daily Max.
CN,T 0.11 0.24 0.64
CN,A 0.04 0.08 0.20
Cyanide Treatment for Small Platers
Plants discharging less than 10,000 gal/day of
electroplating process waste water are not required to meet
limitations on copper, nickel, chromium and zinc.
Consequently, solids removal equipment, such as clarifiers
or filters, may not be utilized at these plants. Several
commenters 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 was analyzed.
This data was taken after cyanide oxidation but prior to
metals removal. The plants used in this analysis are given
in Table 12-7.
397
-------
TABLE 12-7
PLANTS USED FOR SMALL
PLATER AMENABLE CYANIDE ANALYSIS
04045 05021 06037
06051 06072 06073
06075 06079 06081
06084 06085 06087
06089 06381 09026
10020 15070 19050
19051 20073 20077
20078 20079 20080
20081 20082 20084
20086 20087 31021
33024 33070 33073
36040 36041
398
-------
The median or long term average of this data was 0.4 mg/1.
This is substantially higher than the long term average
found for the same plants utilizing data taken after metals
removal. The mechanism for this effect is unknown although
several theories have been suggested. However, the effect
is significant, and since 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.
Using the long term average of 0.4 mg/1 and the variability
factors found previously, the following limits for small
platers are proposed:
Long-term Avq. 30 Day Avq. Daily Max.
CN,A 0.4 0.8 2.0
Treatment of Hexavalent Chromium
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 removal of Cr,VI involves reduction of the
chromium to its trivalent state by addition of SO2 or
bisulfite. These chemical agents are capable, under
properly controlled conditions, of consistent and rapid
removal of Cr, VI down to an almost undetectable residual.
Available technologies for treating chromium were described
in detail in chapter VII.
Attainable Levels of Control for CrfVI (Long Term Average)
The observed concentrations of Cr,VI in the effluent from 73
plants which have either chromium plating or chromatinq
operations and which treat their chromium wastes by
reduction were included in the data base. An effort was
made to include in this data base, which is summarized in
Table 12-5, all of the appropriate plants for which data are
available, including both the 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
bypassed (e.g. plants 1902 and 33021) or because the
available raw waste data indicated an average Cr,T
concentration into the reduction unit of less than 1 mg/1
(e.g. plant 804).
399
-------
TABLE12-5
Cr(6) Concentrations Observed 1n Effluent from
Plants with Cr Plating or Chromatlng Operations
Plant
ID •
16
17
19
21
116
«35
805
1108-a
1108-b
1113
1209
1924
2001
2006
2007
2013
2024
2103
2501
2811
3009
3301
3306
3311
3315
3320
3601
4301
€051
6053**
€073
6074
6076
€078
€079
€083
€084
€085
€086
€358**
€381
€731
12065
15070
Data*
Source
1
1
1
I
3
2
2
1
3
142
2
3
3
3
1 4 3
2
2
3
2 ft 3
2
2
1 4 3
2
3
3
3
3
2
4
4
4
4
4
4
4
4
4
4
4
4
4
A
314
4
Number
Obs:
11
11
€
11
45
6
19
11
133
10
8
9
116
119
3
5
6
13
14
7
1
18
7
25
53
22
3
2
1
8
1
3
3
2
3
3
3
3
3
1
3
1
11
3
Concentration Cr(6)
Median to Wax
O.OSWn o.OS"19'1 o.05m
-02 ,02 .02
•05 .05 .05
-Of -05 lol
-31 .46 2.10
-06 .05 .07
-04 ,09 .38
-02 .18 1.40
nil .01 .04
•05 .05 .08
-06 .07 .10
-05 .05 ,05
-07 .07 .12
-02 ,04 .30
-05 -04 .05
J" *n mi
•11 -11 ,21
-10 .09 ,13
•02 .03 .15
•JO .40 .60
•01 .01 .01
•Si -05 ,15
-05 .05 .05
-08 .!3 ,60
•JJ -17 .37
•14 .17 .53
•06 .05 .08
.08 .08 .11
•01 ,01 .01
•01 ,01 .01
-17 .17 .17
-01 .01 ,01
-0 .01 ,02
-01 .01 ,01
•7* .77 .B3
•0 ,01 .01
•0 ,01 .01
•31 .€6 1.42
-03 ,22 ,63
-01 ,01 .01
-08 .08 .13
*13 .13 .13
-02 .05 .18
2.34 2.92 3.S3
400
-------
Data*
Source
Number
Obs:
Concentration Cr(6)
Median Avg
Max
'.9063 4
20010 4
20064 4
20069 4
20070 4
20073 4
20077 4
20078 4
20079 4
20080 4
20081 4
20082 4
20083 4
20084 4
20085 4
20086 4
20087 4
30050 4
31020 4
31021 4
31050 4
33024 3
33070 4
33073 4
33074** 4
36040 4
36041 4
40061 4
40062 4
43003 4
*1 « Data from reports
2 = Batten e
3 « Plant
4 * Hamilton Standard
3
6
2
1
7
6
5
6
€
7
7
6
€
1
3
3
1
1
1
3
1
14
3
3
3
3
3
2
2
1
by Yost et al,
.01
.01
.01
1.29
.30
.10
.03
.01
.01
.01
.03
.08
2.85
.05
.01
.42
1.07
f\+
.01
.01
,07
.01
nil
.17
.01
.01
.01
.01
.10
.34
.11
and Saf ranek et
.01
.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
.01
.07
.10
.34
.11
.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
.01
.02
.21
.19
.53
.11
** Integrated or Lancey System.
400(a)
-------
Figure 12-5 is a cumulative plot of the average Cr,VT
effluent concentrations experienced by the 73 plants. It
can be seen that more than half (55 percent) of these plants
reported average Cr,VI levels less than or equal to 0.05
mg/1. This demonstrates that a large proportion of plants
have found it possible to bring Cr,VI concentrations, if not
to the theoretical limit, at least down to the 0.05 mg/1
level, and that this level is in practice attainable under
normal conditions.
It should be emphasized that the averages plotted in Figure
5 include data from all plants, not just those with
exemplary treatment. The reduction of Cr,VT is a chemical
process, and no noncontrollable 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.
Variability Factor
Even with a properly designed and controlled treatment
system, small excursions above and below the average
concentration, perhaps as a consequence of fluctuations in
operating procedure, chemical feed, or chromium raw waste
load, can be anticipated. The high Cr,VI excursions to some
extent reflect inadequate operating control, as, for
example, is evidenced by the occurrence in a plant1s record
of daily data of one or two high values against a background
of low ones (e.g. plants 805 and 1108). For these cases, as
Table 12-5 shows, the median concentration is markedly lower
than the average.
Allowance for the random variability of the discharge of a
well designed and operated plant is normally made by
applying a "variability factor" to the expected long term
average. The expected long term average is then multiplied
by the variability factor. The variability factor in
establishing regulations under the FWPCA has generally been
set at a level such that 95 to 99 percent of the normally-
occurring fluctuations fall within the limit.
The variability factor is usually derived by determination
of the form of the distribution of the daily observations of
discharge concentration. Although for certain industries
and pollutants the observed concentrations appear to conform
to the traditional normal distribution, for the majority of
cases the daily observations conform rather closely to
U01
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402
-------
another standard statistical distribution called the
lognormal. In this industry, for example, the distribution
of cyanide concentrations has been found to be nearly
lognormal. For data which conform to either the normal or
lognormal distribution, the computation of variability
factors is comparatively straightforward.
For a lognormal population, the relationship between the
percentile of the distribution (C) and the average (A) is
given by
log (C/A) = Z (SIGMA) - 1.513 SIGMA* [2]
where Z is the statistic for the percentile, and SIGMA is
the standard deviation of the logarithms of the
concentration. The "variability factor" is C/A. It can be
seen from equation [2] that the C/A is dependent only on:
o The z, which is a factor chosen by the Agency as
representative of the appropriate tradeoff between
the risk of setting a limit so low that a well-
designed and operated plant frequently exceeds the
limit and the risk of setting the limit so high
that proper operation of a treatment system becomes
unnecessary. The Agency considers a Z = 2.326 as
appropriate for derivation of the variability
factor. Use of this number means that the
likelihood that a well-designed and operated
treatment system will exceed estimated upper
variability will be less than 1 percent.
o The SIGMA, which is determined from the data and
which is considered to be a characteristic of the
particular pollutant - treatment system combination
under study, was calculated by pooling the estimate
of the SIGMA1s from a series of plants.
403
-------
The variability factor for Cr,VI reduction was calculated
from equation [2], using Z = 2.326 and determining SIGMA
from the observed daily discharge concentrations reported
from 12 plants. Table 12-6 presents, for these plants, the
mean and standard deviation of the logarithms of the
observed daily Cr,vi concentrations.3 The root mean square
average SIGMA for these plants was 0.41.
Entry of SIGMA of 0.41 into equation [1] yields an estimated
variability factor of 5.0. A plant which achieves an
average Cr,VI discharge concentration of 0.05 mg/1 or less
should experience a fluctuation of five times this value
(0.25 mg/1) with no more than 1 percent likelihood.
Magnitude of Overestimate of Variability Factor
In point of fact, the well run plant should achieve a daily
variability less than five times the average. As indicated
above, there is implicit in the use of equation [2], and the
use of SIGMA*s based on the standard deviation of the
logarithm of the daily concentrations, the assumption that
the discharge concentrations of a typical plant will be
lognormally distributed. For many of the plants summarized
in Table 12-6, however, the daily Cr,VI data appear to
deviate from lognormality by having fewer than the expected
number of high Cr,VI values. The consequence of assuming
that the population of fluctuations in daily concentrations
is lognormal, if in fact it is of a form intermediate
between normal and lognormal, will be to cause the estimated
variability factor to err on the high side. Judging from
the individual plant distributions, the use of the lognormal
assumption can result in an overestimate of the 99th
percentile ranging from as high as a factor of two (Figures
12-6 to 12-8) down to nil (Figure 12-9 to 12-10).
To estimate the significance of the potential overestimate
of C/A from use of equation [2], an alternative procedure
for estimation of this variability factor was applied. This
approach estimates, from the maximum value and average value
data of Table 12-5, the apparent dependence of the ratio of
the maximum to average as a function of the number of
3The plants selected for this table were those which: had
10 or more daily observations; had nonzero standard
deviations; and did not have a large proportion of reported
zero Cr,VI concentrations. Table 2 presents 13 groups of
data; plant 1108 was divided into twc groups, corresponding
to the two different sources reporting data.
404
-------
observations. It can be expected that the ratio of the
number of observations - the likelihood of one "wild" value
increasing with the number of values observed. This effect
was observed, as is discussed below. First, all plants with
5 or fewer observations were deleted from the data to remove
the large number of cases with very few observations.
Second, the remaining data were fitted by regression to the
model:
Maximum/Average = A + B x (no. obs.) * 2 [3]
The fit to this model was significant (F = 7.1 for 31 d.f.),
with the fitting coefficients being: A = 1.18; B = 0.357.
Application of Equation [3] with these coefficients leads to
an estimate that the expected Maximum/Average for 100
observations = 4.75. If this number is used as a
variability factor with which to estimate the Daily Maximum
limit, and if the attainable long term average of a properly
operated chromium reduction unit is taken to be 0.05 mg/1,
the resulting Daily Maximum cr,VI concentration limit
becomes 0.24 mg Cr,vi/l. This is in approximate agreement
with the value determined by Equation (1] using the
lognormal distributional assumption.
Variability Factor for 30-Day Average
The C99/A variability factor for the Monthly Average limit
was determined by Monte Carlo simulation assuming: (1) 22
random independent samples per month (one per weekday); (2)
the population of daily observations of Cr,VI concentration
was lognormal with average = 0.05 mg Cr,VI/l and with
standard deviation of log concentration - 0.41. This
simulation indicates the monthly C99/A to be 1.7, and the
corresponding Monthly Average limit becomes 0.05 x 1.7 =
0.085 mg Cr,VI/l.
Based on available treatment technologies, the following
levels of control can be attained:
Long-term Avg. 30 Day Avg. Daily Max.
Cr,VI 0.05 mg/1 0.08 mg/1 0.25 mg/1
405
-------
Table 12-6
MEAN AND STANDARD DEVIATION OF THE LOGARITHM
OF DAILY OBSERVATIONS OF Cr{6) CONCENTRATIONS
MEAN STD. DEV.
LOG C LOG C
116 -0.52 .439
805 -1.19 .354
1108-a -1.37 .636
1108-b -2.04 .326
1113 -1.59 .269
2001 -1.23 .280
2006 -1.78 ,685
2103 -1.03 .112
2501 -1.70 .367
3301 -1.42 .329
3311 -1.04 .400
3315 -0.92 .402
3320 -.0.92 .394
RMS Avg .410
406
-------
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411
-------
Metals Removal Using Sedimentation
This analysis is based upon data from a subset of 25 plants
visited and samples by the Agency.* The results of this
analysis indicate that the variability in observed metal
concentration in clarifier discharges is substantially
related to:
1. The amount of TSS discharged from the system.
2. The composition of the raw waste load (RWL) into
the treatment system.
Factors influencing Individual Metal Effluent Concentratio
To determine which attributes of the plant and its treatment
system might influence the concentration of particular
metals in the clarifier discharge/ a series of exploratory
analyses was carried out. The data used in the analysis
were average values for each plant so that each plant*s
performance was given equal weight. When a particular metal
was under consideration, only those plants which are known
to use that metal were included. The metals discharges
which were studied in this way were Cr(III), Cu, Nir ZN, and
Ag.
The analyses of the relationships between discharge metal
concentrations and the characteristics of the effluent and
raw waste streams were made using the method of multiple
regression. The regressions showed that the concentration
of a metal in the clarifier discharge is significantly
related to three variables: the concentration of TSS in the
clarifier discharge; the concentration of the metal in the
raw waste load; and the total concentration in the raw waste
load of all metals which will precipitate as hydroxides at a
pH greater than 7.5.
Specifically, the following model adequately describes the
relationships which were found to exist:
Log Me = A + B Log TSS + c Log Me° + D Log Me0 [3]
where
Me ~ the amount (mg/1 or mg/opm2) of metal in the discharc
TSS = the amount (same units) of TSS in the discharge
*The sample include those electroplating and metal finishing
plants which used precipitation and setting for solids
separation and which did not have electroless plating
operations.
-------
Me0 = the amount (same units) of the given metal in the
raw waste load
Me0 = the amount (same units) of total precipitatable metal
in the raw waste load.
Because of the orders-of-magnitude range of the variables
studied, the regressions were performed on the logarithm of
the variables; this also had the effect of making the
residuals (the difference between the observed and the
predicted values of the dependent variable) more nearly
normally distributed.
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 (III) , Cu, Ni, Zn) are set forth in Table 12-8. This
table also gives the R2 for each regression (the fraction of
the total variance in the data accounted for by the
regression).
Equation [3], above, can be simplified as Equation [H], below:
Log Me = A + E Log TSS + C Log Xme [ 1 ]
where
Xme = Me0/ Me0
The values for the coefficients A, B, and C which provide
the best fit are given in Table 12-9. The effect of making
this change is small because the coefficients C and D in
equation [ 3] are of approximately the same magnitude but of
opposite sign (see Table 12-8). Thus, the fit to the data
of the model expressed as equation £t] is nearly as close as
for the first equation. This can be seen by comparing the
P2 values in Tables 12-8 and 12-9.5 Table 12-10 shows that
for the TSS and Xme ranges of practical interest, the
regression models on the individual metals yield estimates
of discharge metal concentration which are roughly
comparable for all metals. Accordingly, a "group average"
fit was also constructed for the Me, TSS and Xme
observations of all of the four metals grouped into a single
matrix. The corresponding average equations are:
sspecifically, Cu + Ni + CR(III) + ZN
413
-------
TABLE 12-8
Fit of Average Metal Species Discharged from 25
Plants with Clarifier Systems
Model (1): Log Me = A + B Log TSS + C Log Me + D Log Me *
Metal
Species
Cr III
Cu
Ni
Zn
Cr III
Cu
Ni
Zn
Coefficients of Best Fit
Units
mg/1
mg/1
mg/1
mg/1
mg/opm
mg/opm
mg/opm
mg/opm
A
-.18
-.36
-.39
-.16
-.45
+.13
-.60
-.73
£
.58
.79
.85
.25
.74
.78
.97
.64
C
.79
.58
.29
.69
.78
.65
.25
.65
J)
-.90
-.73
-.55
-.58
-.73
-.76
-.39
-.45
R_
.55
.67
.45
.44
.67
.74
.65
.56
*Me = Sum of all RWL Metallic Species (excluding Al for which no
data)
-------
TABLE 12-9
Fit of Average Metal Species Discharged from 25
Plants with Clarifier Systems
Model (2): Log Me = A + B Log TSS + C Log Xme
Metal
Coefficients of Best Fit
Species Units
Cr III
Cu
Ni
Zn
Group
Cr III
Cu
Ni
Zn
mg/1
mg/1
mg/1
mg/1
Average
mg/opm
mg/opm
mg/opm
mg/opm
A
-.35
-.52
-.77
-.01
-.41
-.40
-.09
-.71
-.49
B
.54
.71
.73
.29
.58
.79
.73
.84
.79
C.
.78
.60
.26
.68
.61
.78
.65
.25
.60
R_
.54
.66
.40
.43
.50
.67
.74
.64
.54
Group Average -.44 .80 .61 .64
U15
-------
TABLE 12-10
METAL CONCENTRATIONS PREDICTED BY EQUATION (2) AND BY
"BEST FIT" EQUATION AT AVERAGE VALUES OF INDEPENDENT VARIABLES
Observed Predicted* Concentrations
Mediam
(mg/1) Eg. (2) "Best Fit"
Cr(III) 0.54 0.77 0.57
Cu 0.49 0.48 0.56
Ni 1.10 0.90 1.18
Zn 0.72 0.84 0.74
*Discharge concentrations were predicted for the average values of
the dependent variables. These averages were:
Log TSS Log Xme
Cr(III) 1.400 - .835
Cu 1.316 -1.090
Ni 1.414 - .736
Zn 1.440 .786
U16
-------
Log Me = -0.41 + 0.58 log TSS * 0.61 log Xme [5]
for metal concentrations expressed in mg/1; and
Log Me = -0.44 + 0.80 log TSS + 0.61 log Xme [6]
for amounts expressed in mg/op m2.
The results of the regression analyses, i.e., that the
amount of a given metal in the discharge is found to be a
strong function of the amount of TSS and also of the
fraction of the given metal in the metals entering the
clarifier have a reasonable physical explanation. A plant
discharge will normally contain metals both as the dissolved
species and as a component of the TSS. If a particular
metal is predominantly in solution, the concentration might
be a strong function of the fraction of metal in the
precipitate derived from the RWL, if the precipitate has the
form of a solid solution of mixed metal hydroxides.
Alternatively, if the effluent metals are predominantly as
TSS precipitate, we would expect the amount of a given metal
discharged to be a strong function of both the amount of TSS
and of the fraction of given metal in the total metals
entering the TSS. As Table 12-9 shows, the amount of metal
in the discharge is in fact a strong function of the amount
of TSS for every metal except possibly Zn, implying that
under the conditions of most of the sampled plants much of
the metal enters the discharge via TSS spillover.
Total Metals
The implication of Equations [5] and [6 ] is that the amount
of any specific metal discharged from a clarifier-based
treatment system will increase, probably at about the 0.6
power, with the fraction of the metal in the RWL. This
fraction varies between plants for any specific metal, with
a concomitant variation in the predicted concentration of
the metal.
This variability can be stabilized if the combined total of
several metals in the clarifier discharge is considered as a
single variable. It is, of course, a consequence of the
algebra defining Xme that the sum of the Xme's for all
metals equals one. The fraction in the RWL of a smaller
cluster of metals, say the total of Cr, Cu, Ni, and Zn, will
show some small variability between plants, but the
variability of this fraction, Xm, will be small compared to
that of the fractions for the individual metals in the RWL.
417
-------
The sum of these metals in the clarifier discharge, M,*
shows a functional dependence on TSS and on the Xm which is
similar to that found for the individual metals.
Application of a regression model of the form of equation
[4] to the sum of metals data from the 25 plants yields:
log M = -0.19 + 0.59 log TSS +0.67 log Xm [7]
for metal concentrations expressed in mg/1; and
log M = -0.29 + 0.83 log TSS +0.50 log Xm [8]
for amounts expressed in mg/opm2. The RZ'S observed for
Equations [7] and [8] were 0.34 and 0.62, respectively.
Validity of Regressions
Before the above equations can be used with confidence,
several tests of their validity and stability must be made:
o Are the apparent positive correlations between Me
and TSS and Xme an artifact of the use of the
regression methodology?
o Do they depend on the presence in the data base of
one or two (possibly atypical) plants?
o Do the equations fit the data?
o Are the results sensitive to any other factors?
To resolve the first of these issues nonparametric tests for
correlation between effluent metal concentration and TSS and
Xme were made. Such tests are independent of the
distributional assumptions inherent in the use of the
multiple regression equations. The Spearman's Rho, a
measure of correlation based on the ranking of the
observations rather than their actual values, showed
positive correlations between Me and TSS and between Me and
Xme for each of the four metals as well as for total
regulated metal. Thus, the positive correlations determined
by the multiple regression methodology are confirmed by the
results of nonparametric determinations.
'M = Cr + Cu + Mi + Zn will be referred to below as total
regulated metal.
-------
Stability of Regressions
The stability of the regression predictions with respect to
the 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 plants when removed from the regression, was
found to have a dramatic impact on the predicted Me. Plants
20010 and 33021 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 2U
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). The small size of this effect
shows that the predictions of discharge metal concentration
are stable and do not depend on the observations from any
one or two plants.
Tests of Fit
Figure 12-11 displays, for Equation [5], contours of
constant expected metal concentration as a function of
discharge TSS and of Xme. The area to the left of each of
the curved lines in this figure represents the region of
clarifier TSS discharge and of RWL metal fraction where the
concentration of metal should be less then the line's value.
Thus, for example, Figure 12-11 indicates that the
concentration of a metal discharged from a clarifier with 25
mg/1 TSS and a Xme = 0.2 in the RWL should be expected to be
slightly less than 1 mg/1.
It is instructive to compare the observed metal
concentrations discharged by the 25 plants with the
predicted envelopes. Figure 12-12 is a plot of the same
form as Figure 12-11, but only the 1 mg/1 contour is shown.
The points on this figure represent the TSS and Xme
conditions 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. 85
percent of those cases with actual discharge metal
concentration < 1 mg/1 fall, as predicted, below the curve,
while 70 percent of those cases with actual discharge metals
concentration > 1 mg/1 fall above the curve.
Figure 12-13 is a similar comparison of the observed metal
discharges, expressed in mg/opm2, with a constant expected
metal discharge contour derived from Equation [6]. In this
figure the contour represents those conditions for which
U19
-------
110-
100-
90-
80-
E 70-
r
r
u
E 60-
N
T
50-
M 40-
G
X
30-
20-
10-
0-
0.0
FIGURE 12-11
CONTOURS OF CONSTANT EXPECTED DISCHARGE
METAL CONCENTRATION AS A FUNCTION OF TSS
AND Xme
I
0.1
I
I I
O.E 0.3 O.H 0.5
FPftCTIQN METRU IN RNl. MET«l_S
0.6
o.:
l
o.s
420
-------
110-
100-
30-
E
r
F
L
U
E
N
T
T
S
£
M
6
FIGURE 12-12
COMPARISON OF OBSERVED DISCHARGE METAL
CONCENTRATION vs Cine = 1 mg/1 CONTOUR
o - observed CmeAl mg/1
* - observed Cnie^-1 mg/1
I
O.E 0.3 0.»4 0.5
FRACTION METftL. IN RWU METftUS
I
0.6
0.',
I
o.e
421
-------
5.00-
A*
4.50-
FIGURE 12-13
COMPARISON OF OBSERVED METAL DISCHARGE
vs Me « 25 mg/opm2 CONTOUR
o - observed Me-^25 mg/opm^
* - observed Mey25 mg/opnr
4.00-
0
15
E
F
F
L
U
E
N
T
T
S
S
M
G
/
a
p
M
S
a
3.50-
3.00-
I
0.£ U.3 0.4 0.5
FRACTION MET«L IN RWl. METfll_S
0.6
0.7
KJRMHL < PRINT '> NOFILE O UPRISHT
ftXES FIXED •> COLUMN E •;> SYMBOLCOL 3
ORDINl=lTE LDK LIMIT 1.5
fieSCIiirt LOW LIMIT 0
nrr. »...-. T- IIT.-.J , r,,TT C-
422
-------
Equation [6] predicts a metal discharge of 25 mg/opm2. As
in Figure 2, the points on the figure represent the TSS
(shown in log units to reduce the range of the scale) and
Xme conditions of each discharged metal. Again the
agreement between prediction and observation is rather good:
71 percent of those plants which discharge metals at < 25
mg/opm2 fall below the line; 81 percent of those plants
which discharge metals at > 25 mg/opm2 fall above the
predicted contour.
Sensitivity of Results to Other Variables
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 seemed to be associated with significantly
lower effluent metal concentrations. For the seven (7)
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 are observed for
the individual metals, with the apparent drop in effluent
concentration being most pronounced for Ni and Cu. The
seven (7) plants using lime appear otherwise typical of the
plants in the data base, having similar values of effluent
flow, TSS, RWL metal concentration, and area plated.
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 flow show above-average total regulated metal
concentrations, the data presented below show that there is
little evidence of any consistent overall relationship
between flow and concentration.
Number Median Median
Plants M (mq/1) Flow (GPH)
3 20.8 230
7 2.3 2100
7 1.5 3100
6 5.8 6000
2 3.2 19000
Plant Size. Two measures of plant size have been
considered: the total number of employees; and the plating
rate (opm2/hr). No consistent trend in total regulated
metal concentration was noted for either case.
U23
-------
pH. Of the 25 plants considered, 6 have average pH values <
8.5. At pH»s this low, the theoretical solubility of Ni
above its pure hydroxide exceeds 10 mg/1. Accordingly, the
discharge from a clarifier at pH < 8.5 might be expected to
contain comparatively high concentrations of Ni, if the
solubility of the pure hydroxide limits metal removal. This
does not appear to be the case. There are 5 plants which
plated Ni and which discharged at average pH < 8.5; H of
these had RWL Ni concentrations in excess of 5 mg/1. The
average effluent Ni concentration for these U plants was
only 1.1 mg/1, a value which is less than the median of all
Ni plating plants in the sample.
The failure of these plating plants to discharge Ni at
levels approximating the equilibrium solubility of the
hydroxide would indicate that some other factor controls the
solubility of this metal. It is possible that the metal is
precipitated in a less soluble form, possibly carbonate, or
that the nickel hydroxide is in solid solution with other
hydroxides and has a lowered activity.
If the pH is entered as a dependent variable in the
regression equations for the individual metals, or for the
total regulated metals, no significant effect on the
predicted metal concentration is found.
RWL Cu. In comments to EPA, one commenter has reported th«
results of his laboratory studies on the apparent solubility
of Cu above alkaline solutions which were derived frc
copper plating baths and which had been treated to remove
cyanide. He reported that the apparent Cu solubility
increased markedly with the initial Cu concentration of th»
treated solution. He also reported that Zn and N:
solubilities were increased if their solutions were mixec
with treated Cu plating solution.
The data indicated that, for the solutions and the treatmen'
procedures used, the apparent Cu solubility increased as th
1.5 to 2 power of the initial Cu concentration, for initia
Cu concentrations in the range 50 to 1,000 mg/1. Variou
explanations have been advanced to account for such
dramatic increase in apparent Cu solubility at high Cu
levels and for the reported increases in Zn and N
solubility; the presence of an unspecified complexing agent
stable to the experiments cyanide removal procedures, i
the Cu plating bath studied would seem to explain much o
the phenomenon. Complete data on the compositions of thes
baths were not furnished to EPA.
-------
It has proven difficult to confirm or deny the reality of
this laboratory effect. The minimum Cu° studied was 50
mg/1; and the effects reported were most noticeable at Cuols
in excess of 200 mg/1. These concentrations are well above
those normally encountered; only 3 plants of our sample
reported average Cu°'s greater than 50 mg/lr and the maximum
average Cu° was 125 mg/1.
Addition of a log Cu° term to the regressions of equation
[2] yielded no significant increase in explanatory power (in
fact, for 3 of the H metals the coefficient was negative,
indicating a negative correlation of discharge concentration
with Cu°) . Furthermore, no significant differences were
found between the observed Cu concentrations of the 7 daily
observations with Cu° > 50 mg/1 and the predicted Cu
concentrations derived from the regression equation of Table
12-9. In summary, it appears that under the operating
conditions of our sample plants the RWL Cu concentration
affects the discharged metal concentration only insofar as
it affects Xme.
Derivation of Limitations
To summarize the above, equations of the form of equation
[ 4 ] have been found to describe the dependence of the
average metal concentrations on TSS and Xme. The
coefficients of equation £4] that best describe the behavior
of the individual metals are summarized in Table 12-9.
Equation [5], of the same form as [4], is derived to give an
overall fit to the average concentration data of all
individual metals without regard to species. Equation [7]
describes the dependence of the average concentration of the
sum of all regulated metals.
These equations can be used to determine guideline
limitations on average effluent metal concentrations,
providing that levels of TSS and of Xme can be specified
that are technically attainable by a metal finisher who
properly controls his wastes and who employs a well designed
and operated clarification system. The following sections
of this analysis will discuss four factors in the
determination of guideline limitations; these are: TSS
concentrations; attainable Xme; the application of the
appropriate equations for estimation cf long term average
metal concentrations; and factors to allow for daily
variability about the average concentration.
425
-------
Variation in TSS
The average TSS concentrations discharged from the 25
sampled plants range 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 or
operating procedures. The clarification systems employed by
the 25 plants include lamella clarifiers (plant 3102), tube
settlers (20082), and settling tanks or clarifiers. The
retention times, a design parameter denoting the average
time available for a solid particle to settle out, vary from
0.8 hr. (6037) to 48 hr. (20084). It should be borne in
mind that the plants of this study were not selected as
necessarily representative of exemplary clarifier operation
and design; in fact, for certain of the plants the retention
time might be inadequate for satisfactory settling.
Operating procedures and controls will also impact the level
and stability of clarifier performance. Such procedures
could include the careful selection and addition of
polymeric coagulants and copreciptating metals (Fe or Al)
before clarification, and the recycling of aged sludge to
the precipitation tank to serve as a nucleating agent.
Control factors would include the equalization of flow, RWL
metal, or temperature surges in the clarifier influent and
the avoidance of oily wastes. Because many of the above
factors are not reported, the data base is not well designed
for determination of practically attainable TSS levels. It
does serve to indicate, however, that an average TSS
limitation of 20 to 25 mg/1 is reasonable. The data can be
divided into two approximately equal groups, those with some
evidence of inadequate design or plant control, and those
without this evidence.7 The median 1SS concentration for the
7Three measures of clarifier design and operation have been
considered. These are:
o Retention time, as indicative of clarifier design.
The median retention time of the 19 plants which
reported the parameter was six hours.
o 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.
(Continued)
426
-------
former is 47 mg/lr the median for the latter is 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. The average TSS concentrations observed for 11 of
the sampled plants were less than 25 mg/1.
Variations in Fraction in RWL of a Metal
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
increase in Xme for another.
A uniform reduction of all Xme 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.
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. These
latter plants, although not suitable for analysis of
effluent metal concentrations (because of incomplete cyanide
oxidation, use of filters, etc), were felt to have raw waste
load metal loadings representative of the industry. Table
12-11 summarizes the distribution of Xme's encountered in
(Continued)
o 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 < 3 hr.,
effluent oil and grease > 20 mg/1, or RWL
temperature more than -2° warmer than effluent
temperature were considered to have evidence of
inadequate design or operational control.
-------
the raw waste load of the combined *»7 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 Xmefs for the individual metals
vary over a wide range. Much of this variation reflects the
diversity of plant practices. However, the Xme appears also
to be related to the number of metals planted 8 within the
plant. If, for example, a plant plates only two metals, it
will be more difficult to bring the average Xme for these
two metals down to a low limit than would be the case if the
plant were to plate four metals. That the average observed
Xme for all metals is related 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 "typical" plant
plates 3.3 different metals and has an average Xme of 0.26.
Estimation of Average Metal Concentration
Equation [4 ] has been shown to provide an estimate of the
average effluent metal concentrations for various values of
TSS and Xme. The coefficients for this equation that give
the best fits for the individual metals Cr(9l), Cu, Ni and
Zn are cited in Table 12-9. Accordingly, Equation [1], with
Table 9 coefficients, will be used to derive average limits
for each of the individual metals. Equation [7] was
similarly derived 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 [5] is found to predict with reasonable accuracy
(see Table 12-10 and Figure 12-12) discharge concentrations
of the metals for which adequate data were available, and it
is reasonable that this equation can be used to derive
average Cd and Pb limits as well.9
The above equations all express the expected average metal
concentration in terms of the independent variables, TSS
8Include such non-plating operations as chromating.
'Equation [3], 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 3 Pb-
discharging plants; the average overprediction is about 65
percent.
H28
-------
TABLE 12-11
Distribution of Fraction Metal in Raw Waste Load Total Metals;
and Predicted Average Metal Concentration in Discharge
for 47 Metal Finishing Plants
Plants Fraction Metal
Metal Using Median75%-ile Maximum
Cd 8 .05 .06 .10
Cr 37 .12 .52 .82
Cu 39 .14 .27 .72
Ni 40 .16 .40 .79
Pb 11 .004 .015 .21
Zn 32 .21 .43 .71
Total Regulated 47 .91 .96 1.000
*Plants with more than 0.5 1 mg/1 Pb in RWL
429
-------
TABLE 12-12
Dependence of Xme on Number Metals Used in Plating and Finishing
Number Number Average
Metals* Plants Xme
1 2 .61
2 11 .31
3 11 .28
4 16 .21
5 7 .13
*From Appendix A, Table A-3 and A-4.
U30
-------
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 with the number of metals plated.
There would appear to be two alternative approaches to
setting Xme's for individual metals. First, the Xme
distribution data of Table 12-11 can be considered as
representative of the attainable Xme's for the individual
metals. A point on the distribution can be chosen which is
sufficiently 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 and independent of which metals are actually used.
The Xme values used would be the demonstrated average Xme's
of Table 12-12.
Table 12-13 summarizes the values of average metal
concentration expected for each metal using these two
approaches. The table shows that metal concentrations based
on a 75 percentile are usually somewhat in excess of those
based on a plant using two or more metals in its plating and
finishing processes, but that the 75 percentile value is
less than that for a plant using a single metal. Either of
these two alternatives appear to give average metal
concentrations which can be achieved by all plants using
more than a single metal. The Table 12-13 average metal
concentrations based on the two metal plating plants will be
used below in calculations of the Daily Maximum and 30 Day
Average limits for Cr(III) , Cu, Nif and Zn.
The above procedures for determining average metal
concentrations have two disadvantages. First, both
procedures depend on the evaluation of an attainable Xme for
each metal. Additionally, the concentrations calculated on
the basis of either the two metal average or the 75
percentile will be too high for most plants, which, on the
average, plate more than two metals and which experience
most Xme's near the observed medians.
An additional limitation, based on total regulated metals,
compensates for these problems. The value of the fraction
of total regulated metals in the raw waste metals, Xm, can
be expected to be almost independent of the number of metals
431
-------
TABLE 12-13
Predicted Average Metal Concentration in Discharge
from Plants with 25 mg/1 TSS
Number Metals Used
Pred.* Metal Cone.
Cd
Cr(III)
Cu
Ni
Pb
Zn
Basis for Attainable Xme
Average In
Table V
1
1.0
1.4
1.3
0.9
1.4
1.3
1.8 1.1 1.0
75%-ile of
Table IV
Avg.
0.5 mg/1
1.5
1.3
1.4
0.2
1.4
*Based on Equation (3) for Cd + Pb.
II coefficients for Cr(III), Cu, Ni,
Total Regulated.
Based on Equation (2) with Table
Zn. Based on Equation (5) for
432
-------
plated. Additionally, the Xm varies so little between the
median observed values and the maximum observed value (from
Xm = 0.91 to Xm = 1.0), that it makes little difference what
precentile is chosen as the basis for calculation. The
estimated total regulated metal concentrations, using
Equation [5] and assuming that TSS = 25 mg/1 and Xm = 0.96,
is 3.0 mg/1. This value will be used below in calculations
of the Daily Maximum and 30 Day Average Limits.
A total metals limitation alone, however, is insufficient
because it does not prohibit a for continuous discharge by a
plant of one metal (e.g., Cu) at concentrations above the
limitation for that individual metal. Such might be the
case for a plant whose waste contains only one or two
metals, or for a plant which has difficulty controlling
waste generation from one specific line.
Allowance for Fluctuations About the Average Concentration
Some degree of fluctuation in the concentration and quantity
of pollutant discharged from even a well equipped and
operated treatment system appears tc be unavoidable. Such
fluctuations are often in part controllable by the
discharger; they may reflect temporary imbalances in the
treatment system caused by variations in flow, in raw waste
loading, in temperature, in mixing patterns within tanks, or
in feed of treatment chemicals. Even so, for most
industries and pollutants there is a residual of essentially
uncontrollable day-to-day variations about the average
attainable discharge. This variability is reflected in the
Daily Maximum limit.
The attached figures illustration the day-to-day variability
usually observed in the output of a plant which discharges
metals in its wastes. Figure 12-14 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 comprised Zn plating of steel wire, followed
by a chromate conversion coating. The chromium wastes were
treated by reduction of Cr(6) to Cr(3), alkaline
precipitation, and clarification. The average Cr discharge
concentration over this period was 0.52 mg/1.
It can be seen that there is considerable, apparently
random, scatter of the points in Figure 12-14. Figure 12-15
is a probability plot, on a logarithmic probability scale,
of the data of Figure 12-14. The nearly linear form of this
plot implies that the data conform well to a commonly-
observed probability distribution called the lognormal.
The extreme values, both high and low, are close to the
straight line fitting the overall data, implying that these
433
-------
extremes possibly just represent the tails of an underlying
random statistical distribution rather than providing
evidence of unusually poor or good treatment system
operation.
The foregoing data have shown that day-to-day variability,
sometimes of a considerable magnitude, is typical of the
discharges from metal finishing plants. This apparently
random statistical variation about the average is taken into
account in deriving limitations by the Daily Maximum Limit
appreciably above the expected long term average. The ratio
of the Daily Maximum Limit to the long term average is
commonly known as the Variability Factor (V.F.) i.e.
V. F. = Daily Maximum Limit/Long Term Average
The determination of the separation between the Daily
Maximum Limit and the long term average represents a
judgmental tradeoff. On the one hand it is desirable to
have this separation large, with the Daily Maximum well
above the average, to minimize the risk, of false alarms
(reporting normally operating plants in violation solely
because of a statistical fluctuation). On the other hand a
high Daily Maximum increases the risk of missing an
improperly operating plant and perhaps of environmental
damage. Daily Maximum limitations have been frequently set
on the basis of =0.01, i.e., so that there is a 99
percent confidence that a plant whose day's observation
exceeds the limitation is in fact operating improperly.
The 0.01 limit of the population of effluent concentrations
will correspond to the 99 percentile of the distribution of
these concentrations (C99). If the Daily Maximum Limit is
set to correspond to the 99 percentile, the variability
factor can be written as C99/Average.
Estimates of the C99/Average ratio to be considered
appropriate for a well operated plant can be derived from
samples of observed data from individual plants. Table 12-
14 presents the estimated C99/Average ratios derived from
observed data for 21 individual plants. These ratios are
seen to fluctuate somewhat from plant to plant. Much of
this fluctuation in the C99/Average values is probably
statistical in nautre; to the extent that certain of the
plants might be high because they utilized poorer than
desired control over daily variations in effluent equality,
the median C99/Average values at the bottom line of Table
12-14 might overestimate the fluctuations in metal
concentrations from a well operated plant. It is felt that
this overestimate, which will result in a somewhat loosened
limitations, is not great.
434
-------
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TABLE 12-14
Estimated Daily C99/Average From Plant Historical Data
13
14
1016
6037
8004
11008
12008
15070
19024
20001
20070
20080
20081
20088
25001
33001
33011
33015
33020
33024
ledi an
Number
Observed
10
13
48
66
14
133
37
82
11
116
34
230
187
65
14
22
25
53
24
14
3.0
3.2
5.4
3.7
3.0
3.3
3.7
4.3
2.4
3.3
2.6
3.8
2.6
8.7
2.6
2.2
3.6
2.5
2.3
5.8
5.9
6.5
4.2
3.0
1.8
2.5
2.4
2.6
4.5
2.5
8.2
Cr
6.2
9.7
4.1
4.0
4.2
3.7
2.3
Zn
2.5
4.1
2.8
2.9
2.4
2.9
1.4
Other
2.4
3.6
2.7
2.6
2.8
2.6
3.2
2.1
2.5
4.8
6.0
5.3
3.7
4.7
2.9
4.4
1.7
3.7
6.0
15.9
5.3
3.2
3.0 4.0 37T
7.5
6.1
278
Total Regulated
2.5
2.3
2.6
3.3
3.1
2.5
2.4
1.8
2.1
1.4
2.8
1.9
1.9
3.8
7.9
2.7
1.9
3.6
2.5
*For Cu, Zn, Ag and Pb, the data used in calculation of the C99 were
those daily observations with CN(A) or CN(T) concentration less than
1 mg/1. For Cr(T) all daily observations were used except for those
with Cr(6) 0.25 mg/1 and with Cr(6)/Cr(T) - 0.25.
If number observations 100; C99/Average computed assuming observations
are sample from a lognormal population.
If number observations _ 100; C99/Average computed by dividing 99th
percentile of ranked data by average value
**Ag, Cd, or Pb
437
-------
The 30-day average concentration will also show some
variations about the long term average, but these variations
will be comparatively small because of the damping effect of
combining and averaging a month of daily observations.
Monthly variability factors for each of the metals were
determined by Monte Carlo simulation.8 The resulting
Monthly V.F.«s were: 1.3 for Total Regulated Metals; l.U
for Cu, Ni and Zn; 1.6 for Cd, Cr, and Pb.
Proposed Limitations
Daily Maximum and 30-Day Average limitations are derived by
multiplying the Variability Factors by the appropriate long
term average concentrations.»o
30-Day Daily
Metal Average Maximum
Cd 0.5 mg/1 1.0 mg/1
Cr, Total 1.6 H.2
Cu 2.0 4.6
Ni 1.8 3.6
Pb O.U 0.8
Zn 1.5 3.4
Total Regulated 3.9 7.5
Silver Analysis
The Agency data file contains 9 plants which carried out
silver plating operations during the time of the sampling
program. The silver concentrations observed in the
effluents of these plants during the period of sampling are
listed in Table 12-15.
If the data in Table 12-8 (excluding the two filter plants
as possibly having an unrepresentative Ag - TSS
relationship) are fitted by the regression expression
previously used for other metals, there results:
log Ag = 0.269 + 0.538 log TSS - 0.762 log XAg with R2 = 0.9
lounder the assumptions that the distribution of daily data
were random lognormal; the standard deviation of the
logarithms of the daily observations were such as to yield
the median Daily C99/Average values of Tables 12-m and 12-
20 observations per month.
H38
-------
The median XAg for the seven plants used in deriving
equation [9] was 0.0033; the estimated 75 percentile of
these XAg's was 0.011. If values of TSS = 25 mg/1 and XAg =
0.011 are entered into Equation [1] there results an
estimated value of the average attainable effluent Ag
concentration of 0.34 mg/1. This number, when multiplied by
a daily variability factor of 2.8, indicates a daily maximum
limitation of 1 mg Ag/1 is attainable.
Is an estimated average attainable silver discharge of 0.31
mg/1 reasonable in the light of the data of Table 12-8 This
table contains data from 4 plants which might be acceptable
for determining a functional relationship such as Equation
[9], but which are probably not typical of normal, good
operations by Ag platers. Plants 6073, 6081, and 6085 plate
only a small quantity of Ag in comparison with their other
operations, and their RWL Ag concentrations are
correspondingly quite small. Plant 6037, on the other hand,
is a major Ag plater but has a discharge CN(A) level so high
that very little of its RWL Ag is removed by waste
treatment.
If these 4 plants are excluded, the average Ag
concentrations of the remaining 5 plants are: 0.135; 0.135;
0.42; 0.56; 0.8 mgAg/1. The median of these 5 discharges is
0.42 mg Ag/lf slightly but not significantly higher than the
predicted 0.34 mg/1.
Metals Treatment Using Filtration
Filtration systems provide an alternative to the use of
clarifiers for 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. Five of these plants used filters as the
primary means of solids separation in their waste system;
the other 5 plants used filtration as a polishing step after
clarification. Because the two groups of plants experience
quite different input metal loadings to the filters, they
will be 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 indicate any significant
difference, either in effluent metal content or in
separation efficiency, between the two filter types.
439
-------
TABLE 12-15
TSS In Discharge From 5 Plants Using Filtration For Primary Solids Separ
DAILY TSS CONC.*
Plant ID
6079
6731
9026
36041
38050
MIN
MED
MAX
1
1
11
5
21
4
15
10
142
31
6
67
32
Average
Total M<
2.3
2.9
4.9
3.2
2.0
Concentrations are in mg/1. Total Metal concentration includes Fe and
440
-------
TSS. None of the filtration systems yielded a completely
clear effluent. As Table 12-16 shows, the TSS
concentrations in the discharges from the 5 plants ranged
from a low of 1 mg/1 to a high of 112 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 is no correlation between metal concentration and TSS
concentration, indicating that although some metal
hydroxides might have bypassed or gone through the filters,
metal pass-through is not sufficient to account for much of
the TSS. Possibly, the TSS is largely composed of suspended
filter aids which entered the waste during precoating and
backwashing stages; if so, an elevated TSS level is not in
itself an indicator of ineffective metals removal.*»
Metals. The average concentrations observed downstream of
the filter are reported in Table 12-17. It can be seen that
the median effluent concentrations of 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 9028, the observed metal concentrations
achieved by the filter was no greater than, and usually much
less than, the average concentrations assumed in setting the
limitations for clarifier-based systems.»*
Effect of Raw Waste Concentrations. The metal
concentrations discharged from the filter systems show a
small, but statistically significant increase with raw waste
concentrations. As Figure 12-16 shows:
Total Metals Out (Total Metals In) 0.3
It is difficult to be certain, based on data from 5 plants,
whether this relationship between effluent and raw waste
metal concentration is real. The data seem to show that any
dependence of effluent concentration upon raw waste
concentration which there may be is small.
i»The high observed TSS of 112 mg/1 from plant 38050 is
possibly associated with the addition to the plating wastes,
upstream of the filter, of an oily (677 mg oil/1) stream
from a tumbling operation. The discharge from the filter
averaged 62.5 mg oil/1.
*2See page 11 and Table VI of "Interim Report-Some Factors
Bearing on the Metal Concentration Discharged from
Electroplating plants which Use Clarification for Solid
Separation."
-------
TABLE 12-16
Average Metal Concentrations in Discharge from 5 Plants Using
Filtration for Primary Solids Separation
AVG. METAL CONC.*
PLANT ID
6079
6731
9026
36041
38050
Cr(III)
0.7
0.5
Cu
0.5
2.9
1.1
Ni
1.0
1.3
0.3
0.4
Zn
0.7
1.5
0.5
Total Me.
2.3
2.9
4.9
3.2
2.0
Median
0.6
1.1
0.6
0.7
2.9
*Concentrations are in mg/1. Discharge cones are given for
individual metals if RWL cones of these metals exceed 1 mg/1.
Total Metal concentration includes Fe and Sn.
442
-------
FIGURE 12-16
TOTAL METALS OUT VS. TOTAL METALS IN
FOR 5 PLANTS WITH FILTRATIONS AS PRIMARY
MEANS OR SOLIDS SEPARTION
IQ
4->
2
TOTAL RAW WASTE METALS mg/1
443
-------
TABLE 12-17
TSS in Discharge From 5 Plants Using Polishing Filter After Clarifien
Daily TSS Cone.*
Plant ID Min Med
Max
20077
31021
31020
33070
33073
9
7
1
4
11
18
16
13
32
26
21
82
42
Average
Total Metals
6.2
3.8
1.6
1.1
6.6**
Concentrations are in mg/1. Total Metals includes Fe and Sn.
**Includes 5.3 mg/1 Fe and Sn
444
-------
The same conclusion appears to hold for the individual
metals. Figure 12-17 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 of discharge concentration with input
concentration is seen to be small.
Polishing Filters
Six plants in the data base use clarifiers as the primary
means of solids removal, but also filter the effluent from
these clarifiers before final discharge. One of these six
plants (6076) was reported as experiencing 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 5 plants are of 3 types:
o Polyester felt cartridge (20077)
o Multi-media bed (31021)
o Diatomaceous earth on a precoat (31020,
33070, 33073)
TSS. As was the case for the 5 plants which used filtration
as the primary means of solids separation, the 5 plants
which use polishing filters discharge 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.
The 3 plants which used diatomaceous earth polishing
filters, and the 2 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 metals
concentrations than the other filters. The median of 7
daily values of total metals observed 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 differ with respect to the
relationship between TSS and metal concentrations. The
diatomaceous earth polishing filters exhibited no
significant correlation between TSS and total metal
concentrations; this parallels the results observed when
diatomaceous earth filters are used for primary solids
separation. The two plants (2007 and 31021) using polishing
filters of other kinds did, however, show s significant
increase in total metal concentration with increasing TSS.
HH5
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TABLE 12-18
Average Metal Concentrations in Discharge From 5 Plants
Using Polishing Filter After Clarifier
Average Metal Concentration'
Plant
Id
20077
31021
31020
33070
33073
Cr(III)
0.5
0.1
0.1
0.5
0.9
Cu
0.5
1.2
1.0
0.1**
0.1
Ni
1.1
1.1**
0.1**
0.2
Zn
2.7
0.9
0.1**
0.1**
0.1**
Total
Metals
6.2
3.8
1.6
1.1
6 . 6***
medium 0.5 0.5 0.5 0.1 3.8
Concentrations are in mg/1. Discharge concentrations are given for
individual metals if RWL concentrations of these metals exceed 1 mg/1.
Total metal conclusions including Fe and Sn.
**Ratio of RWL concentration of given metal to RWL total metal concen-
tration is less than 0.1.
***Includes 5.3 mg/1 Fe and Sn.
447
-------
The daily observations from the effluent of these two plants
are plotted in Figure 12-18.
Metals. The average metals concentrations observed
downstream of 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 3120, which
discharged an average Cu concentration of 1 mg/1, had a RWL
Cu concentration of 108 mg/1. It thus achieved a more than
99% removal of this metal.
The clarification-filtration systems of plants 20011 and
31021 were not quite so effective in achieving low discharge
metals concentrations, although only the Zn discharge of
20077 was much above the 1 mg/1 level.
Summary
In summary, the above data indicate that electroplating
waste treatment systems which use filtration as either the
primary means of solids separation or as an adjunct to
clarification can attain average concentrations of CR, Cu,
Ni or Zn of about 1 mg/1 or less. The median TSS
concentration in the 29 samples of daily discharge from 10
filtration plants was 17 mg TSS/1. For those 7 plants which
used diatomaceous earth to assist filtration the TSS
concentrations did not appear to be correlated with metal
concentration, implying that, for these plants at least,
measurement of TSS discharge concentration cannot serve as a
reliable surrogate for measurement of the individual metal
concentrations.
Metals Pemoyal for Electroless Plating And Printed Circuit
Board Manufacturing
The Electroless and printed circuit board manufacturing
processes both utilize electroless plating operations. The
chemical chelating agents which are used in these operations
pose serious potential problems for treating the wastes fron
these processes by chelating bonding tenaciously to metals
and forming complexes which are difficult to decompose under
normal treatment conditions.
Differences Between Su be ateg or i e s
The two subcategories differ primarily in the metal
deposited - electroless Cu in the Printed Circuit,
electroless Ni in the Electroless Plating subcategories. Ir
the data base (c.f. Appendix A) there was almost a complete
4U8
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TABLE 12-19
Metal Removal Efficiency of Treatment System of
10 Plants Depositing Cu by Electroless Plating
Effluent % RWL Effluent % RWL
Cu (Mg/1) Removed Ni (Mg/1 ) Removed
2062 1.52 NA
4065 0.64 88 (1) (1) (2)
4069 0.75 88
(1) 9.3
4065 0.64 88
. .23 92 9.5
5020 0.98 90
26
73
75
. 74 0.11 95 7.3
30050 39.61 97
.
. 90 0.44 95 7.9
5021 2.25 26
73
. 75 (1) (1) 6.8
19063 3.15 74
.
. 26 0.85 82 7.6
6081 0.75 73 (1) (1) 8.5
17061 1.52 75
. .1 99 6.8
36062 0.29 100 Q.58 92 8.2
Median 1.2 88 0.3 95
(1) Not meaningful figure, since RWL Ni < 1 mg/1
(2) Not meaningful figure, since pH reduced after clarification
450
-------
correspondence; no Printed Circuit manufacturer deposited
significant amounts of electroless metal other than Cu; all
but one Electroless Plating plant electrolessly deposited
only Ni.
Plants in the two subcategories differed in other important
respects. The preparation and manufacture of printed
circuit boards is technically demanding, and the companies
that do this as the major portion of their business tend to
have treatment systems which are more sophisticated than
those of the other electroless platers. Thus, for example,
of the 9 printed circuit board manufacturers in the data
base 7 (78 percent) have a treatment system adapted in some
major way to the characteristics of the electroless waste.13 14 15
In contrast, of the 15 electroless platers, only 3 (20%)
have a system more complex than that typical for treatment
of normal metal plating wastes. There were also significant
differences between the Printed Circuit and Electroless
subcategories with respect to the concentration of the
electroless metal in the raw waste load. Thus, 9 plants
which deposited electroless Cu had a median Cu concentration
in the RWL of 6 mg/1; 13 plants which deposited electroless
Ni had a median RWL Ni of 31 mg/1. This difference in RWL
potentially impacts 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 importantly, in the
absence of any specific treatment systems for isolating and
destroying complexing wastes a higher RWL of the electroless
metal translates to a higher effluent concentration of
chelate, which will increase the difficulty of reaching low
effluent metal concentrations.
The Printed Circuit Board manufacturers in the data base
tended • to be smaller, in terms of area processed per hour,
and to use more water per unit area processed than the
Electroless Plating plants.
adaptations are: separate treatment of chelate waste
stream (5 plants); stripping of NH3-bearing wastes (3
plants); polishing filter after clarification (1 plant).
»*These cases are: separate treatment of chelate waste
stream <1 plant); some recycle of CrCW wastes (2 plants).
15These effects can be noted in the discharge from plant
30050 (see Table 12-19), which experienced a very high RWL
Cu concentration during the reporting period and which
discharged dissolved Cu at about UO mg/1.
451
-------
Median Area and Flow
Plant Sq. Ft./hr Gal/Sq.
8 Printed Circuit Board 330 9. 3
15 Electroless Plating 1030 5.5
25 Common Metal Plating 880 3.6
To some extent the higher water use is related to the
smaller area processed; as Figure 12-19, a plot of hourly
flow vs area, shows the Printed Circuit Board plants seem to
show about the same flow vs area dependence as is
characteristic of the Common Metal Platers.
Effluent Concentrations
As is shown in Table 12-19, the median discharge Cu
concentration achieved by 10 plants which plated electroless
Cu was 1.2 mg/1. There are two plants included in Table 12-
20 which are possibly atypical (6081 with only about 5
percent of production by an electroless process; 30050 with
an abnormal raw waste concentration). Removal of these two
cases from the data does not affect the median observed
effluent Cu concentration, although it reduces the scatter
about this median.
A similar range of discharge Cu concentrations was observed
for the 7 plants of 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.
It is not clear from the data that the presence of
complexing agents in the waste played a significant role in
determining the effluent Cu concentration. Table 12-22
presents two measures of effluent Cu concentration: the
average observed concentration of Cu from each plant; and
the difference between this observed concentration and an
expected concentration predicted by a previously-developed
empirical equation. Two potential surrogates for the
concentration of complexing agent are also presented: The
RVJL concentration of the metal which was electrolessly
deposited (since dragout of this metal from the electroless
bath will also drag out chelating agent); and the ratio of
the waste flow from the electroless bath to the total plant
discharge flow.
If indeed the concentration of complexing agent increases
with either (or both) of the surrogates, and if the presence
of complexing agent is significantly influencing the
discharge concentration of Cu, then it would be expected
452
-------
ill
— m
— o
m
m"
— o
(0
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il.
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Q
y
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LLI a:
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453
j a 3 "2
-------
TABLE 12-20
Metal Removal Efficiency of Treatment System of
7 Plants Depositing Ni by Electroless Plating
Plant
ID
6381
12065
20064
20070
20073
20083
20085
Median
Effluent
Cu (Mg/1)
3.75
3.98
0.82
0.56
1.74
1.03
0.18
1.0
% RWL
Removed
92
16
99
99
98
98
99
95
Effluent
Ni (Mg/1)
4.90
9 23
J • C.O
2.80
0 38
W • wJJ
1.13
1 * I ^
2.30
w * w V
1.11
17T
% RWL
Removed
l*Wlllw V CU
84
w~
1 1
1 J
95
QQ
yy
QQ
JO
ftfl
oo
99
95
£H
7.5
7.3
9.2
9.1
7.8
9.3
9.0
454
-------
Table 12-21
Comparison of Observed and Predicted Effluent Cu Concentrations
with Factors Potentially Related to Waste Stream Concentrations
of Complexing Agent
RWL Cone. Flow from
Effluent Obs.-Pred.* El'Less El'less Line
Cu(mg/l) Cu(mg/l) Metal 4Total Flow
4065 0.64 -1.90 5 .52
17061 1.52 .88 6 .28
6081 0.75 .52 3 NA
6381 3.75 2.31 31 .01
12065 3.98 2.82 11 NA
20064 0.82 -2.08 58 .37
20073 1.74 .18 74 .39
20083 1.03 - .25 106 .88
20085 0.18 -1.39 156 .4?
* Predicted Effluent Cu Concentration
log Cu = -.52 + .71 x log TSS + .60 x log XCu
where
TSS = Average discharge TSS in mg/1
XCU = Average RWL concentration Cu £ j£j>recipitatabie RWL metals
<*55
-------
Table 12-22
Comparison of Observed and Predicted Effluent Ni Concentrations
With Factors Potentially Related to Waste Stream Concentrations
of Complexing Agent
RWL Cone. Flow from
Effluent Obs.-Pred.* El'less El'less Line
Ni(mg/l) Ni(mg/1) Metal -yTotal Flow
6381 4.9 3.6 31 .01
12065 9.2 7.8 11 NA
20064 2.8 .3 58 .37
20073 1.1 -.2 74 .39
20083 2.3 .2 106 .88
20085 1.1 -.3 156 .43
* Predicted Effluent Ni Concentration
log Ni = -.77 + .73 x log TSS + .26 x log XNi
where
TSS = Average Discharge TSS in mg/1
XNi = Average RWL concentration Ni ££j)recipitatable RWL metals
456
-------
that either this Cu concentration (or the deviation of this
concentration from the predicted value) would increase with
increasing values of the surrogate. Table 12-22 shows that
such a correlation is not observed. Thus the evidence of
Table 12-22 does not support a contention that effluent Cu
is being significantly passed through the clarifier as a
soluble complex.
Table 12-23 is a similar presentation of the observed
effluent Ni concentrations from 7 electroless Ni platers who
do not separately treat chelated wastes. The conclusion
from this table is the same as that reached above, i.e., the
data do not indicate that the comparatively high
concentrations of effluent Ni are associated with
complexing.
Some of the high effluent Ni concentrations observed in
Tables 12-21 and 12-22 might be attributable to inadequate
operating controls. The two plants highest in effluent Ni
(6381 and 12065) both discharged at pH's < 7.5, and the
solubility of Ni at these low pH's can be expected to be
above average. In addition, plants 20061 and 20083, which
discharged Ni at concentrations exceeding 2 mg/1, also had
effluent TSS concentrations of 50-70 mg/1, more than a
factor of two higher than the TSS levels considered
characteristic of effective clarification.
Conclusions
The Printed Circuit and Electroless Plating Subcategory
plants discharged Cu at a median concentration of about 1
mg/1. Those Electroless Plating plants with effluent pH
levels above 7.5 and with TSS levels of about 30 mg/1 or
less discharged Ni at a median concentration of about 1
mg/1. These concentrations are close to the 1.3-1.4 mg/1
average concentrations previously recommended as providing
the basis for Cu and Ni limitations for the Common Metal
Plating subcategory. Since the data do not provide evidence
of substantial complexing of Cu or Ni by chelating agent, it
is recommended that the Cu and Ni limitations for both
Printed Circuit and Electroless Plating subcategory be set
equal to those of the Common Metal Plating subcategory.
Surrogate Parameter Analysis
For those plants which plate common metals and which treat
their wastes using conventional solids removal technology, *
the discharge concentrations of each of the metals are
»'CN oxidation, Cr (6) destruct, alkaline precipitation, and
solids separation by clarification.
457
-------
TABLE 12-23
PERCENT INDIVIDUAL METALS IN TOTAL METAL*
DISCHARGE FROM 41 PLANTS
PLANT
ID
13
14
6037
6074
6075
6081
6063
6085
6086
6087
15070
£0010
£0077
£0078
£0079
£0080
£0061
£00 6E
£0084
£0086
310E1
330 £4
33050
33073
36040
1016
SO 04
11008
1E008
£0088
£5001
33001
33011
33015
330 £0
6079
6731
90 £6
36041
38050
£0017
ft'.'ERRGE
STD DEV
TOTAL
METAL
(Ma/1)
3.E
1.6
7.6
0.9
6.6
1.0
3.0
10.7
E0.8
11.7
4.8
0.4
4.6
1.6
EE.5
l.E
1.5
6.0
10.6
E.E
5.4
1.3
1.0
6.3
E.O
3.4
O.E
0.4
£.0
£.3
0.3
3.1
£.7
0.5
3.E
1.9
£.5
4.5
£.4
1.4
0.3
TSS
(Mg/1 )
7.0
10.5
40,5
31.0
19.3
1.7
79.0
£8.0
90.0
50.7
19.3
49.5
17.8
38.7
10E.4
IE. 4
7.9
39.5
44.0
£7.0
££.7
4E.O
1E.O
50.7
11.0
10.5
l.E
-9.0
-9.0
-9.0
-9.0
£.5
-9.0
5.E
-9.0
-9.0
-9.0
-9.0
"9.0
-9.0
-9.0
PERCENT
Cr
59
3£
0
4£
IL
13
£9
14
67
0
46
7
7
6E
18
36
8
10
37
40
3
5
0
31
£6
ES
46
11
£7
~'*T
s
13
10
31
15
40
1
0
c.Q
?5
HP.
^4
Jt9
OF TOTAL
Cu
16
9
68
3
43
7E
7
39
1
E7
0
5
11
19
E
17
6
49
4
16
39
IE
15
48
3
10
41
6
31
18
!•!•
£6
90
19
58
3
EO
63
48
11
~9
£5
£3
METALS
M
17
43
31
5£
4£
9
56
40
3E
61
1
60
£4
16
70
7
45
37
8
14
£5
1
6
15
69
IE
11
E5
ic.
34
39
E3
"9
50
6.
53
5£
£
13
£5
58
30~
El
FROM
Zn
8
16
1
E
14
6
8
6
1
11
5E
£9
58
£
10
40
39
5
51
30
33
6£
79
6
1
46
~9
58
£9
11
36
38
"9
"9
EE
4
£7
34
19
9
~9
£5
££
Comment
1
1
1
l
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
£
£
E
£
£
E
£
£
E
E
3
3
3
3
I:
^
*Total Metal concentration 1$ defined as the sum of Cr, Cu, NI and Zn
Concentration.
Comment 1 » Plants visited by NAMF consultant or by Hamilton Standard;
clar1f1cattph;used for sol Ids.'separation*
Comment 2 » Data from self monitorina reoorts; clarification or settling
for solids separation.
Comment 3 « Plants, using some other procedure than clarification for
solids separation. . .
458
-------
related to two factors: the effluent concentrations of TSS;
and the ratio of the raw waste (RWL) metal concentration to
the sum of all RWL metal concentrations. Earlier analyses
suggested limitations appropriate for metals based on the
observed relationships and on attainable levels of effluent
TSS and RWL metals ratio.
It has been suggested that TSS concentrations with certain
additional limitations on discharge pH and on the presence
of complexing agents in the waste stream could be used as a
surrogate control parameter.
The extent to which limitations on TSS would substitute for
the metals limitations will be discussed below.
Rules for Surrogates
A series of general criteria have been laid down which
should be met before a limitation on one pollutant can be
considered as an adequate surrogate for individual
limitations on other pollutants. These criteria are: IT
1. Compliance with the limitations on the surrogate
pollutant will remove the pollutants to the levels
achievable if they were individually limited3;
2. The rulemaking record contains data sufficient to
establish that the technologies installed to comply
with the surrogate limitation will achieve the
desired limitation of the consent decree
pollutants;
3. The data must show that the discharger is not
likely to use a treatment process which controls
the surrogate while evading control of the other
pollutants.
Use of either of the two proposed surrogate pollutants,
total metals or TSS, would allow the discharger to meet the
surrogate limitations while having a comparatively high
concentration of one metal (a concentration greater than
that metal's individual limitation), while at the same time
discharging correspondingly lower concentrations of other
metals. Thus, problems with the first criterion listed
above are raised. The magnitude of these problems should be
considered and weighed against the desirability and
simplicity of the surrogate measure.
*7May 31, 1977 memo by Ridgeway M. Hall, Jr., "Use of
'Surrogate1 Limitations under the BAT/Toxics Consent
Decree."
459
-------
TSS
The measurement, of TSS is simple, inexpensive, and can be
readily carried out by municipal enforcement authorities.
There could be a considerable increase in convenience and
reduction in cost to plants and monitoring authorities if a
TSS limitation could be established as an acceptable
surrogate for individual and total metals limit.
Several problems in the use of TSS as a measure of total
metals are apparent, however. Three are:
1. The relationship between TSS concentration and
total metals concentration shows scatter, even at high
concentrations of both where it is likely that most of the
metal exists in precipitate form.
2. A limitation of only TSS would not encourage
certain treatment practices which might reduce the total
metals concentration without reducing TSS. The use of lime
as a neutralizing agent, and the addition of Fe or Al to the
raw waste, are examples.
3. Total metals exist in two forms, solid and
dissolved. The latter clearly bears no relationship to TSS,
and, in fact, it might be to the advantage of a TSS-
regulated discharger to increase the proportion of dissolved
metal (e.g., by poor pH control, by the addition of
complexing agents or by the use of plating baths containing
complexes) so as to reduce the amount of TSS-associated
solid metal hydroxide precipitates.
The scatter within the relaionship between TSS and total
metals can be estimated from the data of Table 12-23, and
will be discussed below.
Figure 12-20 presents a log plot, for the 29 plants of Table
12-23 with TSS data, of the observed total metals
concentration vs the observed TSS concentration. The
straight line is the least squares fit to 27 of these data
points, 18 and is of the form
Log Metals = -0.539 + 0.792 x Log TSS [10]
with correlation coefficient = 0.75 and Std. error = 0.335.
i8Plants 20010 and 33001, although plotted (checked points
of Figure 12-20) were omitted from Equation [10] and from
the variability calculations.
460
-------
It is possible to combine Equation [10] with the curves of
Figure 12-20 to reach an estimate of the probability of
discharging a high concentration of a consent decree metal.
The results of such a computation 19 are shown in Figure 12-
21.
Figure 12-21 is of the same general type as Figure 12-20,
i.e., a plot of the likelihood that a "typical" plant, which
discharges a surrogate pollutant at some average
concentration, will discharge one or more metals at a
concentration exceeding m. It can be seen, however, that
the form of Figure 12-21 differs considerably from that of
Figure 12-20, because of the statistical scatter in the
relationship between metals and suspended solids.
In the discussion of total metals, it was suggested that 3
mg/1 total metals would provide satisfactory control of
individual metal concentrations, based upon a prediction
that at this level of total metals no more than 15% of
plants would be likely to discharge a metal at more than 2
mg/1 average concentration. Based upon the relationships of
Figure 12-21 it would appear that 10 mg/1 TSS would also
meet this same criterion (i.e., 15 percent likelihood of
consent decree metal discharge above 2 mg/1) and might also
be a satisfactory surrogate for individual metals.
However, the use of TSS as a surrogate raises questions
which are not presented by the use of total metals. By
following bad practices such as poor control of pH or adding
complexing agents, a discharger might achieve the TSS limit
without controlling the concentration of individual metals
discharged. The 15 percent prediction given above assumes
these practices are not followed; therefore for TSS to be
used as a surrogate, additional constraints e.g. for
controlling pH and the use of complexing agents such as
ammonia or EDTA, need to be imposed.
»9The curves of Figure 12-22 are treated as conditional
probabilities, given M. The distribution of log M, for a
given TSS, is assumed to be normal, with as indicated by
Equation [10] and = 0.335.
461
-------
si
o
J 3 B h 3
o
1
j r u (- c j w
S B \ J
'1
o
462
-------
FIGURE 12-21
LIKELIHOOD THAT A PLANT WHICH MAINTAINS A GIVEN AVERAGE TSS CONCENTRATION
EXPERIENCES AT LEAST ONE AVERAGE INDIVIDUAL METAL CONCENTRATION EXCEEDING m
60 .
40
A
«
OJ
0)
o
520
I/I
4J
10
AVERAGE TSS CONCENTRATION
(mg/1)
30
463
-------
FIGURE 12-22
LIKELIHOOD THAT A PLANT WHICH MAINTAINS AN AVERAGE
TOTAL METALS CONCENTRATION OF M* EXPERIENCES AT LEAST
ONE AVERAGE INDIVIDUAL METAL CONCENTRATION EXCEEDING m
100 r-
E
A
1C
•M
Ol
O
i.
O
o>
O
tf>
c
«o
0
M = Average Concentration Total Metals (mg/1)
* Total Metals =Zo+Cu+Ni+Zn
464
-------
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 Standard1s effort was managed by Mr. Daniel J.
Lizdas and Mr. Walter M. Drake and included significant
contributions by Messrs. Eric Auerbach, Robert Blase r,
Jeffrey Wehner, Richard Kearns, Robert Lewis, William
Starkel, Robert Pacocha, Jeffrey Robert and Robert Patulak.
Mr. Devereaux Barnes of the EPA's Effluent Guidelines
Division served as Project Officer during the development of
limitations and the preparation of this document. Mr.
Robert Schaeffer, Director Effluent Guidelines Division, Mr.
Ernst P. Hall, Branch Chief, Effluent Guidelines Division,
and Mr. Harold E. Coughlin, Branch Chief, Effluent
Guidelines Implementation, offered guidance and suggestions
during this project.
Acknowledgement and appreciation is also given to Ms. Kaye
Starr and Ms. Carol Swann 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.
465
-------
SECTION XIV
REFERENCES
1. Agrawal, J. P., and Sourirajanr S., "Reverse
Osmosis Separation of Some Inorganic Salts in
Agueous Solution Containing Mixed solutes With a
Common Ion", Pub. in Ind. Eng. Chem. Process
Design and Development, National Research Council
of Canada Ottawa (Ontario) Div of Chemistry,
November 1968.
2. Allen, J. B., Clapham, T. M., Joyce, R. S., and
Sukenid, V. A., "Use of Granular Regenerable
Carbon for Treatment of Secondary Effluent,
Engineering Design and Economic Evaluation"* Final
Rept., Pittsburg Activated Carbon Co., Pa., October
1964.
3. Allen, T. A., Processing Prototype PC Boards at
Sandia Laboratories, Alburguergue, Report No. (SC-
DS-70-4807) , (Sandia Labs., Alburqueque, N. Mex.),
(nd), 9p.
4. Alonzo, William Lawrence, "Design of Wastewater
Treatment Systems to Satisfy Effluent Quality
Requirements Based on Intended Use ", Technical
Rept., Cornell Univ., Ithaca, N. Y. Water
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152. Oh, C. B., and Hartley, H. S., "Recycling Plating
Wastes by Vapor Recompression", Products Finishing
36 (8), 90-96, May 1972.
153. Oliver, G. D., (inventor to NASA), Scanning Nozzle
Plating System, Application date June 28, 1972, SN-
266913.
154. "Operation of the Multi-stage Flash Distillation
Plant, San Diego, Calif.", Semi-annual Rept. No. 3,
Catalytic Construction Co., Philadelphia, Pa., July
1970-December 1970.
155. "Operation of the Multi-Effect Multi-stage Flash
Distillation Plant (Clair Engle), San Diego,
Calif", Annual Rept, No. 2, Catalytic Construciton
Co. Philadelphia, Pa., June 1963-May 1969.
156. Othmer, K., Cgmplexing Agents Energy of Chemical
Technology, Published by Interscience.
157. "Overflow", Chemical Week, 111 (24), 47, December
1972.
481
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158. Oyler, R. W. Disposal of Waste Cyanides by
Electrolytic Oxidation", Plating, 36, (4), 341-342,
April 1949.
159. Parent, R. G., and Arnold, J.W., "Field Test
Evaluation of the High Temperature Elecgrodialysis
Process At Webster South Dakota", Research and
Development Progress Rept., lonies. Inc.,
Watertovm, Mass., January 1974.
160. Parthasaradhy, N. V., "survey of Methods for
Treatment of Effluents in Electroplating Industry",
Environ. Health, October 1969.
161. Pearlstein, F., and Weightman, R. F., "Electroless
Copper Plating Using Dimethvlamine Borane",
Technical Resparch Article, February 1973, pp. 7,
Frankford Arsenal, Philadelphia, Pa., Research and
Development Directorate FA-A73-1.
162. Pearlstein, F., and Weightman, R. F., "Electroless
Copper Plating Using Dimethylamine Borane",
Plating, May 1973, pp. 474-476.
163. Pearlstein, F., and Weigntman, R. F., "Electroless
Palladium Deposition", Report No. FA-A69-10, 1969.
164. PF Staff Report, "Developments in Additive
Circuits", Products Finishing, February 1975, pp.
74-78.
165. Phasey, N. W., "Experiences With Ion Exchange
Resins for Effluent Treatment", Prod. Finish
(Lond.), Oxford, Engl. British Leyland (Austin
Morris) Ltd., November 1972.
166. "Planning Development and Management of Waste Water
Treatment Facilities, Training Manual",
Environmental Protection Agency, Washington, D.C.,
Office of Water Programs, July 1971.
167. Plummer, C. W., Enos, J., LaConti, A. B., and
Boyack, J. R., Electrodialysis and/or Transport
Depletion", Research and ".Evaluation of Newly
Developed Ion-Exchange Membranes for
Electrodialvsis and/or Transprot Depletion",
Research and Development Progress Rept., General
Electric Co., Lynn, Mass., December 1969.
482
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168. Podobaev, N. I., "Electrolysis", Report No. ESTC-
HT-232011-72, April 23, 1974, pp. 19, Trans, of
Khimiya V Shkole (USSR) n3, pp. 7-18, 1971.
169. Porter, J. Winston., and Cherney, Si. "An Economic
and Engineering Analysis of the Electrodialysis
Process", Research and Development Progress Rept.,
Bechtel Corp., San Francisco, Calif., August 1969.
170. Pourbais, Marcel, "Atlas of Electrochemical
Eguilibria in Aqueous Solutions, Perfamon Press,
New York, 1966.
171. Pressman, Marice., "Prototype Reverse Osmosis
Wastewater Purification Unit", Final Rept., Army
Mobility Equipment Research and Development Center
Fort Belvoir Va., September 1973.
172. Price, W. L., "Plated Polyproplene", Plating,
February 1971, pp. 111-114.
173. Pajan, S., "Application of Inorganic Ion-Exchange
Membranes to Electrodialysis", Research and
Development Progress Rept., LIT Research Inst.,
Chicago, 111., November 1966.
174. Rauch, F. C., and Luciw, F. W., "Passivation of
Metal Aircraft Surfaces", Final Rept., January 1 -
June 30, 1970, American Cyanandd Co., Stamford,
Conn., Central Research Div., July 1970, pp. 27.
175. Reid, G. W., et al., "Effects of Metallic Ions on
Biological Waste Treatment Processes", Water & Sew.
Works, Vol. 115, No. 7, 1968, pp. 320.
176. "Reverse Osmosis and Electroplating", Anon., Ind
Finish, July 1974.
177. Rich. T. R., and Mix, T. W., "Development of an
Improved Membrane for a Vapor Diffusion Water
Recovery Process Final Report", August 1974, pp.
80.
178. Richardson, J. L., Segovin, G., Mason, J. W., and
Subcasky, W. J., "Advanced Reverse Osmosis-Membrane
Module Systems", Research and Development Progress
Rept., Philco-Ford Corp., Newport Beach, Calif.,
Aeronautics Dib., May 1971.
483
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179. Pigling, W. s., "Multilayer Printed Wiring Board
Design Standards", Final Report, October 2 -
December 5, 1970, Report No. OR-11035, August 1971,
pp. 32.
180. Robinson, L. C. R., "Printed Circuit
Manufacturing", SM/TN/B/1585, British Steel Corp.,
Sheffield, (England) Information Services, October
1973, pp. 6.
181. Rozell, Lee T., "Ultrathin Membranes for Treating
Metal Finishing Effluents by Reverse Osmosis",
North Star Research and Development Inst.,
Minneapolis, Minn., November 1971.
182. Rozelle, L. T., Kopp, C. V. Jr., Cadotte, J. E.,
and Cobian, K. E., "SN-100 Membranes for Reverse
Osmosis Applications", North Star Institute,
Minneapolis, Minn., July - August 1974.
183. 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.
184. Salyer, L. O., Kirkland, E. V., and Eilken, P. H.,
"Improved Avionic Membranes for Electrodialysis",
Research and Development Progress Rept., Monsanto
Research Corp., Dayton, Ohio, December 1968.
185. 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.
186. Silman, H., "Treatment of Rinse Water from
Electrochemical Processes", Efco Ltd., Surray,
England, June 1971.
187. Sinclair, R. G.r Biological Abstracts, Inc.,
Battelle, Columbus, Ohio, 1974.
188. Smookler, S., and Cannizzaro, J., "The Status of
Additive Circuits Today", Photocircuits Division of
Kollmorgen Corporation, No. 21/1.
189. Smolyakov, V., Water Filtration Purification and
Distillation (Opresenitelnaya Ustanovka), October
484
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1967, pp. 8 Contracts DA-44-009-AMC 1563 (T) n 6,
pp. 34-56, 1965, Distribution Limitation now
removed.
190. Sondak, N. E., and Dodge, B. F., "The Oxidation of
Cyanide Bearing Plating Wastes by Ozone. Part I",
Plating, 48 (2) 173-180, February, 1961.
191. Sondak, N. E., and Dodge, B. F., "The Oxidation of
Cyanide Bearing Plating Wastes by Ozone. Part II",
Plating: _48 (3) , 280-28196, March.
192. Snoevink, Vernon, L., Kin, Cyung R., Hinrichs,
Richard 1., and Jennings, Paul A., "Synthetic
Resins and Activated Carbon for Waste Water
Treatment", Final Rept., Illinois University
Urbana, June 1974.
193. Sorber, C. A., Malina, J. F., Jr., and Sagik, B.
P., "Virus Relection by the Reverse Osmosis
Ultrafiltration Processes", Report Nos. CRWR-82,
EHE-71-9, 1971, pp. 100.
194. Spatz, D. D., "Industrial Waste Processing With
Reverse Osmosis", Osmonics, Inc., Hopkins,
Minnesota, August 1, 1971.
195. Spatz, D. D., "Electroplating Waste Water
Processing With Reverse osmosis". Products
Finishing, 36 (11), 79-89, August, 1972.
196. 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. 38-44.
197. Stannett, T., and Hopgenberg, H. B., "Research on
Advanced Membranes for Reverse Osmosis", Research
and Development Progress Rept., March 1974.
198. Strickland, G. R., "Electroplating Techniques and
Equipment in Printed Circuit Manufacture",
Electroplating and Metal Finishing, July 1971.
199. "Studies on the Toxicity of Heavy Metals to Aquatic
Animals and the Factors to Decrease the Toxicity",
Bulletin of Total Regional Fisheries Research
Laboratory, No. 58., May 1969, pp. 233-241, 255-
264.
485
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200. Sussman, Donald L,, "Chemical and Physical Factors
in the Flocculation of Metal Plating Wastes with
Polyelectrolytes", Completion Report, Rhode Island
Univ., Kingston, Water Resources Center, June 1972.
201. Sussman, Donald L., "Flocculation of Chrome Plating
Wastes with Polyelectrolytes", Plenum Press (Polym
Sci. and Technol. V2), New York, August 1972.
202. Takano, O., and Ono, K., "Acoustic Emission During
Electro and Electroless Plating", Report No. UCLA
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Los Angeles School of Engineering and Applied
Science.
203. Titus, Joan, B., "Reverse Osmosis Bibliography;
Abstract and Indexed", Bibliography, Plastics
Technical Evaluation Center Dover, N.J., June 1973.
204. Toledo, E., and Sprague, D. R., "Nickel Plating of
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205. Ushakov, N. N., "Multilayered Printed-Circuit
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206. Viklung, H. I., and Jha, A. D., "High Temperature
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B. Letiz, Accomazzo, M. A., June 1974.
207. "Waste Treatment; Upgrading Metal Finishing
Facilities to Reduce Pollution", Report on
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208. "Wastewater Reclamation ", Sub-Council Rept.
National Industrial Pollution Control Council,
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209. "Waste Water Treatment and Reuse in a Metal
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486
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210. "Water Purification and Decontamination", Report
Bibliography, Defense Documentation Center
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212. "Water Reuse ", Office of Water Research and
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214. Watson, M. R.,. "Pollution Control in Metal
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215. Werbicki, J. J., Jr., "Practical Electroless and
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216. "Where to Buy Electroplating Services", Modern
Metals, 28 (6), P. 71, July 1972.
217. Wilson, G. C., "The Use of Tin When Alloyed With
Nickel or Lead as a Printed Circuit Finish",
Electroplating & Metal Finishing, December 1970,
pp. 15-25.
218. Wilson, J. V., "Systems Analysis of Distillation
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219. Winget, Oscar J., and Lindstrom Ronald E.,
"Separation of Rare Earth Elements by Ion
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220. Wirth L., Jr., "Trouble with Layered Beds",
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221. Wu, yung-Chir and Hamer, Walter J., "Osmotic
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487
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224. Zlatkis, A., Burening, W. , and Bayer, E.,
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225. P5S
226. Fed PT Guidelines, Vol, II
227. EPA, Nov. 1976
228. EPA, 1976
229. Chaney 6 Hornick
230. Jelinek, et al
231. FDA
232. Letter Hile to Breidenbach
233. Letter to Hezir, OMB
234. Cox & Rains
488
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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.)r as distinguished 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.
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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.
Admin i stra tor
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 of 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.
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Air Flotation
See Flotation
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 (NHJ3) 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.
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Anaerobic Waste Treatment
(Sludge Processing) Waste stabilization brought about
through the action of microorganisms in the absence of air
or elemental oxygen.
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 Eecovery 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.
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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.
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
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 micro-
organisms; specifically, the rate at which compounds may be
chemically broken down by bacteria and/or natural
environmental factors.
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Slowdown
The minimum discharge of recxrc-ulating 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.
Capi tal 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 low-
temperature 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.
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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.
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.
Centri fugation
(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 Agent
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
495
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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.
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
496
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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.
Chromati zing
To treat or impregnate with a chromate (salt of ester of
chromic acid) or dichromate, especially with potassium
dichromate.
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.
497
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Cleaning
See: Vapor Degreasing Sct-'ent Cleaning Acid Cleaning
Emulation 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 rinse water without the introduction of
additional makeup water.
Coagulation
A chemical reaction in which polyvalent ions neutralize the
repulsive charges surrounding colloidal particles.
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.
498
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Conductive Surface
A surface that can transfer hrr.t 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 flow-
through 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.
Copper Flash
Quick preliminary deposition of copper for making surface
acceptable for subsequent plating.
Coprecipitatipn of Metals
Precipitation of a metal with another metal.
Cost of capital
Capital recovery costs minus the depreciation.
499
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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.
Decarboxylat e
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.
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.
500
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Deprec i ati on
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.
Dewaterinq
(Sludge Processing) Removing water from sludge.
Diazotiz ation
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.
Distillation
Vaporization of a liquid followed by condensation of the
vapor.
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Distillation-Silver Nitrate Titration
A standard method of measurin3 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 workpiece 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 ir
order to allow the excessive dragout to drain off.
Drying Beds
Areas for dewatering of sludge by evaporation and seepage.
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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
reciprocal of the resistance in ohms measured between
opposite faces of a centimeter 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.
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Electroplating
The production of a thin coating of one metal on another by
electrodeposition.
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.
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Equalization
(Continuous Flow) Holding tank is used to give a continuous
flow for a system that has widely varying inflow rates.
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.
Fehling * 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.
Benedictfs modification is a one solution preparation. For
details, see Book of Methods, Association of Official
Analytical Chemists.
Fe rmen ta ti on
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.
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Ferrous
Relating to or containing iron.
Filtrate
Liquid after passing through a filter.
Filtration
Removal of solid particles from liquid or particles from air
or gas stream by means of a permeable membrane.
Types: Gravity
Pressure
Microstraining
Oltrafiltration
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.
Fog
A type of rinse consisting of a fine spray.
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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.
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. NH^CH2COOH,
Good Housekeeping
(In-Plant Technology) Good and proper maintenance minimizing
spills and upsets.
GPP
Gallons per day.
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Grab SajripJ.e
A single sample of wastewater taken without regard to time
or flow.
Gravimetric 103-105C
A standard method of measuring total solids in aqueous
solutions.
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*
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Heavy 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.
Hexadentat e
Pertaining to structure, having member connections in six
positions.
Hydrofluoric Acid
Hydrogen fluoride in aqueous solution.
Hydrogen Embrittlement
Embrittlement of a metal or alloy caused by absorption of
hydrogen during a pickling, cleaning, or plating process.
Hydrophilic
A surface having a strong affinity for water or being
readily wettable.
Hydrophobic
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 cf 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 metal displaces another from solution, for
example:
Fe + Cu(+2) = Cu + Fe( + 2)
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\
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.
Industrial User
Any industry that introduces pollutants into public sewer
systems and whose wastes are treated by a publicly-owned
treatment facility.
Industri al 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.
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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
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.
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.
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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 (cin2/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.
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 Fi eld
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.
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Level I
BPT technology or effluent limitations.
Level II
BAT technology or effluent limitations.
Level III
New Source Performance Standards.
Liqands
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) .
Manual Plating
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
514
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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 icn 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.
Mi crostr ai n i nq
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.
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.
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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 ether purposes.
Neutrali zation
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.
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.
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NPDES
See National Pollutant Discharge Elimination System.
Operation arid 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.
Passivation
The changing of the chemically active surface of a metal to
a much less reactive state by means of an acid dip.
ES
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.
ES Buffer
A substance used to stabilize the acidity or alkalinity in a
solution.
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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
porcelaini zing.
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.
Pickle
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 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.
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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.
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.
519
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Polyelectrolyte
A high polymer substance, either natural or synthetic, con-
taining 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.
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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.
P.ecirculating Spray
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.
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Re duel ng
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: KNacaHjtO_6. HH2O.
Running Rinse
A rinse tank in which water continually flows in and out.
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 eguivalent (e.g., and
radical). Example:
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HCL + NaOH = NaCL * H2O
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
The supply of water used for sewage transport and the
continuation of such effluents to disposal.
Sanitary Sewer
Pipes and conveyances for sewage transport.
Save Rinse
See Dead P.inse.
Scale
Oxide and metallic residues.
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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.
Series Rinse
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.
Settling Ponds
A large shallow body of water into which industrial
wastewaters are discharged. Suspended solids settle from
the wastewaters due to the larcre retention time of water in
the pond.
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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/^0 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.
Solution
Homogeneous mixture of two or more components such as a
liquid or a solid in a liquid.
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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.
Spray 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 tc
Section 306 of the Act on quantities, rates anc
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 01
the ocean.
Stannous Salt
Tin based compound used in the acceleration process.
Usually stannous chloride.
Still Rinse
See Dead Rinse.
Strike
A thin coating of metal (usually less than 0.0001 inch i
thickness) to be followed by other coatings.
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Stripping
The removal of coatings from metal.
Subcategory or 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.
Thickener
A device or system wherein the solid contents of slurries or
suspensions are increased by gravity settling and mechanical
527
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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.
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
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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
mi croagitation.
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 compartments. As the drum rotates,
sludge accumulates on the filter surface, and the vacuum
removes water.
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Vapor Degreasing
Eemoval 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 tc 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 sonw 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 under-
ground water source by plant facilities or obtained from
some source external to the plant.
Wet Air 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 whole-
sale 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 in
degree Fahrenheit °F
feet ft
gallon gal
gallon/minute gpm
horsepower hp
inches in
inches of mercury in Hg
pounds Ib
million gallons/day mgd
mile mi
pound/square
inch (gauge) psig
square feet sq ft
square inches sq in
ton (short) ton
yard yd
0.405
1233.5
0.252
ha
cu m
kg cal
0.555
0.028
1.7
0.028
28.32
16.39
0.555(«F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
kg cal /kg
cu m/min
cu m/min
cu m
1
cu cm
°C
m
1
I/sec
kw
cm
atm
kg
cu m/day
km
(0.06805 psig +1)* atm
0.0929 sq m
6.452 sq cm
0.907 kkg
0.9144 m
* Actual conversion, not a multiplier
hectares
cubic meters
kilogram - calories
kilogram calories/kilo*
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
killowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric ton (1000 kiloc
meter
* U.S. GOVERNMENT PRINTING OFFICE. 1978-258-461:6069
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