EPA-440/1-73-003
Development Document for Proposed
Effluent Limitations Guidelines
and New Source Performance Standards
COPPER, NICKEL, CHROMIUM,
and ZINC
Segment of the Electroplating
Point Source Category
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
AUGUST 1973
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Publication Notice
This is a development document for proposed effluent
limitations guidelines and new source performance standards
As such, this report is subject to changes resulting from
comments received during the period of public comments of
the proposed regulations. This document in its final form
will be published at the time the regulations for this
industry are promulgated.
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DEVELOPMENT DOCUMENT
for
EFFLUENT LIMITATIONS GUIDELINES
and
NEW SOURCE PERFORMANCE STANDARDS
COPPER, NICKEL, CHROMIUM, AND ZINC
SEGMENT OF THE ELECTROPLATING
POINT SOURCE CATEGORY
John Quarles
Acting Administrator
Robert L. Sansom
Assistant Administrator for Air & Water Programs
Allen Cywin
Director, Effluent Guidelines Division
Harry M. Thron, Jr.
Project Officer
August 1973
Effluent Guidelines Division
Office of Air and Water Programs
U.S. Environmental Protection Agency
Washington, D.C. 20460
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BHVIRONMETTAL rT^w"HON AGENCY
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ABSTRACT
This document presents the findings of an extensive ^tudy of the
electroplating industry by the Environmental Protection Agency for the
purpose of developing effluent limitations guidelines, standards of per-
formance, and pretreatment standards for the industry to implement
Sections 304 (b) and 306 of the "Act."
Effluent limitations guidelines for the copper, nickel, chromium, and
zinc segment contained herein set forth the degree of effluent reduction
attainable through the application of the best practicable control
technology currently available and the degree of effluent reduction
attainable through the application of the best available technology
economically achievable which must be achieved by existing point sources
by July 1, 1977 and July 1, 1983, respectively. The standards of
performance for new souces contained herein set forth the degree of
effluent reduction which is achievable through the application of tlr?
best available demonstrated control technology, processes, operating
methods, or other alternatives. The proposed regulations for all thre-
levels of technology set forth above are presented in Section II,
RECOMMENDATIONS.
Supportive data and rationale for development of the proposed effluent
limitations guidelines and standards of performance are contained in
this report.
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CONTENTS
Section
I CONCLUSIONS 1
II RECOMMENDATIONS 3
Best Practicable Control Technology
Currently Available
Best Available Technology Economically
Achievable
New Source Performance Standards
III INTRODUCTION 8
Purpose and Authority
Summary of Methods Used for Development
of the Effluent Limitations Guidelines
and Standards of Performance
Information Sources
General Description of the
Electroplating Industry
IV INDUSTRY CATEGORIZATION 14
Introduction
Objectives of Categorization
The Relationship of Electroplating
and Metal Finishing
Profile of Production Processes
Materials Receiving Electroplates
Factors Considered in Categorization
V WASTE CHARACTERIZATION 31
Introduction
Specific Water Uses
Quantity of Wastes
Sources of Waste
VT SELECTION OF POLLUTANT PARAMETERS 51
Introduction
Metal Finishing Wastewater Constituents
Electroplating Wastewater Constituents
Wastewater constituents and Parameters
of Pollutional Significance
Rationale for the selection of
Wastewater Constituents and Parameters
Rationale for the Selection of Total
Metal as A Pollutant Parameter
Rationale for Rejection of Other
Wastewater Constituents as Pollutants
VTI CONTROL AND TREATMENT TECHNOLOGY 60
IX
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Page
Introduction
Chemical Treatment Technology
Process Principles and Equipment
Practical Operating Systems
Demonstration Status
Process Principles and Equipment
Water Conservation Through Control
Technology
Demonstration Status
Water Conservation
Extraction
Methods of Achieving No Discharge of
Pollutants
VIII COST, ENERGY, AND NONWATER QUALITY 116
ASPECTS
Introduction
Treatment and Control Costs
Cost Effectiveness and Treating
Procedures
Nonwater Quality Aspects
IX BEST PRACTICABLE CONTROL TECHNOLOGY 125
CURRENTLY AVAILABLE, GUIDELINES,
AND LIMITATIONS
Introduction
Industry Category and Subcategory
Covered
Identification of Best Practicable
Control Technology Currently Available
Rationale for Selecting the Best
Practicable Control Technology
Currently Available
Waste Management Techniques Considered
Normal Practice in the Electro-
plating Industry
Degree of Pollution Reduction Based
on Existing Performance by Plants
of Various, Sizes, Ages, and
Processes Using Various Control
and Treatment Technology
Determination of Effluent Limitations
Selection of Best Practicable
Additional Factors Considered in
Selection of Best Practicable
Control Technology Currently
Available
Effluent Limitations Based on the
Application of Best Practicable
Control Technology Currently
Available
Guidelines for the Application
111
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of Effluent Limitations
X BEST AVAILABLE TECHNOLOGY ECONOMICALLY 180
ACHIEVABLE, GUIDELINES AND LIMITATIONS
Introduction
Industry Category and Subcategory
Covered
Identification of Best Available
Technology Economically Achievable
Rationale for Selection of Best
Available Technology Economically
Achievable
Effluent Limitations Based on the
Application of Best Available
Technology Economically Achievable
Guidelines for the Application of
Effluent Limitations
XI NEW SOURCE PERFORMANCE STANDARDS 185
Introduction
Industry Category and Subcategory
Covered
Identification of Control and
Treatment Technology Applicable to
Performance Standards and Pre-
treatment Standards for New Sources
Rationale for Selection of Control
and Treatment Technology Applicable
to New source Performance Standards
Standards
New Sources
Guidelines for the Applications of
New Sources Performance Standards
XII ACKNOWLEDGEMENTS 189
XIII REFERENCES 190
XIV GLOSSARY 194
IV
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TABLES
Number Page
1 Recommended Effluent Limitations for 4
the Electroplating Industry to be
Achieved by July 1, 1977, based on
Best Practicable Control Technology
Currently Available (BPCTCA)
1A Recommended Standards of Performance 5
for the Electroplating Industry to
be Achieved by New Sources
2 Process for Plating on Steel 16
3 Processes for Plating on Zinc Die 17
Castings
H Processes for Plating on Brass 18
5 Processes for Plating on Aluminum 19
6 Processes for Plating on Plastics 19
7 Distribution of Electroplate According 22
to Type of Basis Material
8 Processing Sequences Decorative Copper- 24
Chromium Plating
9 Processing Sequences for Nickel Plating 25
10 Processing Sequences for Chromium Plating 25
11 Processing Sequences for Zinc Plating 26
12 Estimated Daily Raw Waste Load of 36
Principal Salts Used in Copper,
Nickel, Chromium, Zinc Plating and
Related Processes
13 Principal Wastewater Constituents in 33
Wastes From Processes for Plating on
Steel
14 Principal Wastewater Constituents in
Waste From Processes for Plating 39
on Zinc Die Castings
15 Principal Wastewater Constituents in 40
Waste From Processes for Plating on
Brass
16 Principal Wastewater Constituents in 41
v
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Number
Waste From Processes for Plating
on Aluminum
17 Principal Wastewater Constituents 42
in Waste From Processes for Plating
on Plastics
18 Approximate Concentrations of Waste- 53
Water Constituents Prior to Treatment
From a Typical Facility Electroplating
copper, Nickel, Chromium, and Zinc
(Plant 33-1)
19 concentrations of Heavy Metals and 7g
Cyanide Achievable by Chemical Treating
of Waste Created by Copper, Nickel,
Chromium and Zinc Plating and Zinc
Chromating Operations
20 Decomposition Products of Cyanide in 81
Rinse Water From a cyanide zinc
Electroplating Operation After
Treatment with Peroxygen
Compound
21 Estimated Costs for Small Electroplating 119
Facilities With No Waste Treatment
to Meet Effluent Limitations for
1977 and 1983
22 Geographical Distribution of Good 132
Electroplating Waste Treatment
Facilities Based on Initial Referrals,
Companies Contacted for Information,
and Representative Facilities Evaluated
in Detail
23 Classification by Size, Type of Facility, 134
and Effluent Discharge for 53 Electro-
plating facilities selected for
Evaluation
24 Classification of 53 Facilities 136
Evaluated By Mix of Plating Operations
and Type of Waste Treatment and
In-Process Controls
25 source of Information and Classification 137
by Size and Waste Treatment Method
26 Size of Plating Operations 140
27 Treated Effluent Data 147
VI
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Number
28 Comparison of Treated Effluent Data
Based on Total Amperage
29 Summary of Water Use Parameters for
Four Plants Based on copper. Nickel
Chromium or Zinc Plating and Ex-
cluding Nonpertinent Metal Finishing
Processes
30 Summary of Treated Effluent from 2.64
Copper, Nickel, Chromium or Zinc
Excluding Nonpertinent Plant
Metal Finishing Operations
31 Summary of Treated Effluent Based 165
on BCL Sampling and Analysis During
Second Round Visit for Comparison
with Table 2
32 Monthly Average Effluent Concentration 167
for Plant 33-1 Showing Improved
Results Obtained Over a 14-Month
Period
33 Comparison of Battelle Analytical 168
Results with EPA Reference Standards
34 Typical Current Efficiencies Assumed 17 8
for Calculation of Plated Area
Using Equation (2)
35 Comparison of Effluent Limitations for 179
BPCTCA (Table 1) in Terms of
Concentration for Various Effluent
With the Prior Interim Guideline
Concentrations
36 English/Metric Unit Conversion 206
VII
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FIGURES
Number
1 Relationship of Total Metal in 28
Treated Water Discharge to the
Production Capacity of Typical
Electroplating Plants Expressed
as Metal Deposited Per Hour
2 Schematic Flow Chart for Water Flow 33
in Chromium Plating Zinc Die Castings
Decorative
3 Alternative Methods of Rinsing after 34
a Processing Operation
4 Diagram of a Typical Continuous-Treatment 63
Plant
5 Integrated Treatment System 64
6 Solubility of Copper, Nickel, Chromium 65
and Zinc as a Function of Solution pH
7 Experimental Values - Solubility of 67
Metal Ions as a Function of pH
8 Batch Treatment of Cyanide Rinse Waters 80
by Combined Metal Precipitation and
Cyanide Destruction
9 Schematic Presentation of Ion-Exchange 90
Application for Plating-Effluent
Treatment (7,25)
10 schematic Presentation of Ion-Exchange 91
Operation at Plant 11-8
11 Representative closed-Loop System for 96
Recovery of Chemicals and Water with
a Single-Effect Evaporator
12 Representative Open-Loop Evaporative 97
Recovery System
13 Schematic Diagram of the Reverse-Osmosis 101
Process for Treating Plating Effluents
14 Closed-Loop System for Metal Finishing 103
Process Water at Rock Island Arsenal
15 Schematic Diagram of Freezing Process 105
Vlll
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for Recovery of Water and Chemicals
from Plating Rinses (37,38)
16 Schematic Diagram of Ion-Flotation '°9
Cell for Treatment of Plating Effluent
17 Flow Chart for Treatment of Waste Water 114
from Cleaner and Acid Dip When Plating
Operations Have separate stream
Treatment
18 Effective of Size of Plating Plant on 117
Investment Cost of Waste-Treatment
Facility
19 Cost Effectiveness of Treatments and 123
In-Process Water Conservation
Technigues
20 Employees Per Shift in Plating Versus 139
Cumulative Percentage of 53 Plants
21 Total Installed Current for Plating 142
Versus Cumulative Percentage of
53 Plants
22 Installed Rectifier Capacity in Amperes 143
for Electroplating Versus Number of
Employees Per Shift in Electroplating
for 53 Plant Sample (Ration of Amperes
Used To Amperes Installed is Typically
65 Percent)
23 Effluent Discharge Rate Versus 144
Cumulative Percentage of 53 Plants
24 Composite of Pollutant Parameters in 145
Treated Effluent Versus Cumulative
Percentage of Plants
25 Water Use Based on Total Installed 149
Current Versus Cumulative Percentage
of 53 Plants
26 Comparison of the Water Use for Plants 152
that Use In-Process Chemical Recovery
Systems on One or More Plating
Operations with the Water Use of Plants
that do not Use In-Process Recovery
27 Copper In Treated Effluent 153
From Electroplating
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28 Nickel In Treated Effluent From 154
Electroplating
29 Hexavalent Chromium In Treated 155
Effluent From Electroplating
30 Total Chromium In Treated Effluent 156
From Electroplating
31 Zinc In Treated Effluent From 157
Electroplating
32 Cyanide In Treated Effluent From 158
Electroplating
33 Suspended Solids In Treated 159
Effluent From Electroplating
34 Typical Variation in Concentration 169
of Pollutant Parameters From Analysis
of Daily Composite Over a 4-Month
Period Reported by Plant 11-8
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SECTION I
CONCLUSIONS
The electroplating of copper, nickel, chromium and zinc, on ferrous,
nonferrous, and plastic materials is a single subcategory of the
electroplating point source category for the purpose of establishing
effluent limitations guidelines and standards of performance. The
consideration of other factors such as the age of the plant, processes
employed, geographical location, wastes generated and wastewater
treatment and control techniques employed support this conclusion. The
similarities of the wastes produced by electroplating operations and the
control and treatment techniques available to reduce the discharge of
pollutants further substantiate the treatment of copper, nickel,
chromium and zinc electroplating as a single subcategory. However,
guidelines for the application of the effluent limitations and standards
of performance to specific facilities do take into account the size of
the electroplating facility and the mix of different electroplating
processes possible in a single plant.
Presently, over half of the 53 operating plants for which sufficient
data were available achieve low concentrations of pollutants in the
treated effluent using conventional chemical treatment systems. Over
half of the plants achieve low water use with such in-process controls
as needed to restrict the volume of treated effluent discharged to
surface waters. Therefore, it was concluded that all 53 plants could
achieve the recommended effluent limitations by practicing both good
water conservation and good chemical treatment.
It is estimated that only a small percentage of the raw waste being
generated by the electroplating industry is being discharged directly to
navigable waters without any treatment. It is concluded that ~he
remainder of the industry can achieve the reguirements as set forth
herein with a minimum investment cost of $50,000 and a minimum opera4-: nq
cost of $13,000/year. For larger plants plating over 100 sq m/hr (1076
sq ft/hr) the operating cost will be less than 5 percent of the pi.Vina
cost exclusive of waste treatment. The capital investment will be of
the order of $150,000 per 100 sq m/hr ($140,000 per 1000 sq ft/hr) of
plated area. It is further estimated that no discharge of pollutants,
when required, could be achieved with increased costs of about 10
percent of the total plating costs (including land and building).
capital investment will be of the order of $100,000 to $200,000 per 100
sq m/hr (93,000 to $186,000 per 1000 sq ft/hr).
The development of data and recommendations in this document for
effluent limitation guidelines and standards of performance for the
electroplating industry (Phase I) relate to rack and barrel
electroplating of copper, nickel, chromium, and zinc. This segment is
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estimated to contribute about two-thirds of the total amount of
chemicals added to wastewater in the electroplating industry and,
therefore, was selected for study first. The control and tr =atmep+-
technology identified in this report is broadly applicsible -^ +*rc>.<*
res-raining areas of study: (1) electroplating operations o*hf>r thv r - ~k
and barrel; (2) electroplating of metals other than copper, 'I'.'-"' """ ,
chromium, and zinc; and (3) other metal finishing processes. Efflupn-
limitations guidelines and standards of performance for the remaining
segments of the electroplating point source category might require a
greater or lesser degree of effluent reduction.
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SECTION II
RECOMMENDATIONS
Best Practicable^Control Technology
CurrentlY_Available
Recommended effluent limitations for the electroplating industry
applicable to existing sources discharging to navigable waters are
summarized in Table 1 and the specific effluent limitation guidelines
and rationale are discussed in greater detail in Section IX of this
report. Chemical treatment of wastewaters to destroy oxidizable cyanide
and remove all but small amounts of the heavy metal pollutants
represents the Best Practicable Control Technology Currently Available
for existing point sources.
The effluent limitations are based on achieving by July 1, 1977, at
least the pollution reduction attainable using this control and
treatment technology as presently practiced by the average of the best
plants in this category. Additional currently available in-process
control technology designed to recover and reuse process chemicals and
water and/or reduce water consumption may be required to meet the
effluent limitations depending on the kind of parts being electroplated
or the nature of available process facilities.
The technologies on which such limitations are based emphasize use
of end-of-process chemical treatment to remove pollutants to th°
greatest practical degree with simultaneous reduction of effluent
discharged using currently available in-process control technology and
directed towards eventual elimination of discharge of pollutants as
electroplating facility equipment is modified or replaced.
Best Ayailable^Technolpgy Economically
Achievable
For the electroplating industry, no discharge of process
waste water pollutants to navigable waters is recommenced as the
effluent limitation to be achieved by existing point sources by July 1,
1983.
This represents the degree of effluent reduction believed to be
attainable by existing point sources through the application of the Best
Available Technology Economically Achievable for recovery and reuse of
water.
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TABLE 1. RECOMMENDED EFFLUENT LIMITATIONS FOR THE ELECTRO-
PLATING INDUSTRY TO BE ACHIEVED BY JULY 1, 1977,
BASED ON BEST PRACTICABLE CONTROL TECHNOLOGY
CURRENTLY AVAILABLE (BPCTCA)
Effluent Limitations (a)
Single Day Maximum (k)
Parameter mg/sq m lb/10& sq ft
Copper (Cu) (d) 80 16.4
Nickel (Ni) (d) 80 16.4
Chromium
hexavalent
(Cr6+) (d) 8 1.6
Chromium, total
(CrT) ^) (e) 80 16.4
Zinc (Zn) (d) 80 16.4
Cyanide , oxi-
dizable (CN) (f) 8 1.6
Cyanide, total
(CN) w) 80 16.4
Total Suspended
Solids (TSS) (h) 2400 491.0
pH range 6 to
9.5 U)
30-Day Average ^c>
mg/sq m lb/106 sq ft
40 8.2
40 8.2
4 0.8
40 8.2
40 8.2
4 0.8
40 8.2
1200 245.5
See Footnotes on page 6
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TABLE 1A. RECOMMENDED STANDARDS OF PERFORMANCE FOR THE
ELECTROPLATING INDUSTRY TO BE ACHIEVED BY
NEW SOURCES
Standards of Performance (a)
Single Day Maximum (
D; 30-Day Average (c)
Parameter mg/sq m lb/10b sq ft mg/sq m lb/10
Copper (Cu) (d) 40 8.2
Nickel (Ni) (d) 40 8.2
Chromium,
hexavalent
(Cr6+) (d) (e) 4 0.8
Chromium, total
(CrT) (d) (e) 40 8.2
Zinc (Zn) (d) 40 8.2
Cyanide, oxi-
dizable (CN) (f) 4 0.8
Cyanide, total
(CN) (g) 40 8.2
Total Suspended
Solids (TSS) 00 1200 246
pH range 6 to
9.5 (I)
20 4
20 4
2 0
20 4
20 4
2 0
20 4
600 123
t> sq ft
.1
.1
.4
.1
.1
.4
.1
See Footnotes on page 6
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FOOTNOTES FOR TABLES 1 AND 1A
(a) The effluent limitations and standards of performance
are defined as the weight of pollutant in milligrams
discharged per square meter of total area plated.
The total area plated is the sum of the areas plated
in each copper, nickel, chromium and zinc plating
solution that requires a subsequent rinse.
(b) Single Day Maximum is the maximum value for any one day
(c) 30-Day Average is the maximum average of daily values
for any consecutive 30 days
(d) Total metal (soluble and insoluble) in sample. (4)
(e) Total chromium (Cri) is the sum of all ionic forms
(Cr3+ + Cr6+). (5)
(f) Oxidizable cyanide is defined as detectable cyanide
amenable to oxidation by chlorine according to standard
analytical procedures. (6)
(g) Total cyanide is defined as all detectable cyanide in
the sample following distillation according to standard
analytical procedures. (6)
(h) Total suspended solids retained by a 0.45 micron filter
according to standard analytical procedures. (5)
(i) A pH in the range of 8 to 9 is the best range for mini-
mizing the soluble metal-concentration during coprecipi-
tation, as discussed in Section VII.
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New Source PerfQrmance_Standards
Table 1A summarizes the recommended standards of performance for
discharge to navigable waters applicable to new sources in the
electroplating industry, the construction of which is commenced after
publication of proposed regulations prescribing a standard of
performance. The standards of performance are based on demonstrated low
water use currently being achieved in representative electroplating
process lines and the demonstrated low concentration of each pollutant
parameter in the treated effluent currently being achieved by over half
of the plants for which data were available. The recommended standard
of performance provides for the control of discharge of pollutants which
reflects the greatest degree of effluent reduction achievable through
application of the best available demonstrated control technology,
process, operating methods, or other alternatives.
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SECTION III
INTRODUCTION
Purgose_and^Authority
Section 301(b) of the Act requires the achievement by not later than
July 1, 1977, of effluent limitations for point sources, other than
publicly-owned treatment works, which are based on the application of
the best practicable control technology currently available as defined
by the Administrator pursuant to Section 304(b) of the Act. section
301 (b) also requires the achievement by not later than July 1, 1983, of
effluent limitations for point sources, other than publicly-owned
treatment works, which are based on the application of the best
available technology economically achievable which will result in
reasonable further progress toward the national goal of eliminating the
discharge of all pollutants, as determined in accordance with
regulations issued by the Administrator pursuant to Section 304 (b) to
the Act. Section 306 of the Act requires the achievement by new sources
of a Federal standard of performance providing for the control of the
discharge of pollutants which reflects the greatest degree of effluent
reduction which the Administrator determines to be achievable through
the application of the best available demonstrated control technology,
processes, operating methods, or other alternatives, including where
practicable, a standard permitting no discharge of pollutants.
Section 304 (b) of the Act requires the Administrator to publish within
one year of enactment, of the Act, regulations providing guidelines for
effluent limitations setting forth the degree of effluent reduction
attainable through the application of the best practicable control
technology currently available and the degree of effluent reduction
attainable through the application of the best control measures and
practices achievable including treatment techniques., process and
procedure innovations, operation methods and other alternatives. The
regulations proposed herein set forth effluent limitations guidelines
pursuant to Section 304 (b) of the Act for the electroplating subcategory
of the metal finishing source category.
section 306 of the Act requires the Administrator, within one year
after a category of sources is included in a list published pursuant to
section 306 (b) (1) (A) of the Act, to propose regulations establishing
Federal standards of performances for new sources within such
categories. The Administrator published in the Federal Register of
January 16, 1973 (38 FR 1624), a list of 27 source categories.
Publication of the list constituted announcement of the
Administrator's intention of establishing, under Section 306, standards
of performance applicable to new sources within the electroplating
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subcategory of the metal finishing industry which was included within
the list published January 16, 1973.
Summary of: Methods_Used_for Development .of the Effluent
Limitation Guide!ineg_and standards of,Performance
The effluent limitation guidelines and standards of performance
recommended herein were developed in the following manner. The point
source subcategory of electroplating was first categorized for the
purpose of whether separate limitations and standards would be
appropriate for different segments. Such subcategorization was based
upon raw material used, product produced, manufacturing process
employed, and other factors. The raw-waste characteristics for each
subcategory were then identified. This included an analyses of (1) the
source and volume of water used in the process employed and the sources
of waste and waste waters in representative plants; and (2) the
constituents of all waste waters including toxic constituents and other
constituents which result in taste, odor, and color in water or aquatic
organisms. The constitutents of waste waters which should be subject to
effluent limitation guidelines and standards of performance were
identified.
The full range of control and treatment technologies exisring within
each subcategory was identified. This included an identification of
each distinct control and treatment technology, including both in-plant
and endof-process technologies, which are existent or capable of being
designed for each subcategory. It also included an identification in
terms of the amount of constituents and the chemical, physical, and
biological characteristics of pollutants, of the effluent level
resulting from the application of each of the treatment and control
technologies. The problems, limitations and reliability of each
treatment and control technology were also identified.
In addition, the nonwater quality environmental impact, such as the
effects of the application of such technologies upon other pollution
problems, including air, solid waste, and noise were also identified.
The energy requirements of each of the control and treatment
technologies was identified 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 constituted the "best practicable
control technology currently available," "best available technology
economically achievable" and the "best available demonstrated control
technology, processes, operating methods, or other alternatives." In
identifying such technologies, various factors were considered. These
included the total cost of application of technology in relation to the
effluent reduction benefits to be achieved from such application, the
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age of equipment and facilities involved, the process employed, the
engineering aspects of the application of various types of control
techniques process changes, nonwater quality environmental impact
(including energy requirements) and other factors.
The data for identification and analysis were derived from several
sources and included EPA research information, published literature,
information from state water control agencies and trade literature.
Supplemental data were obtained by making on-site visits and
interviewing personnel at exemplary electroplating facilities.
References used during the development of the data in this report are
listed in Section XIII of this document.
Companies plating copper, nickel, chromium and zinc and reporting
low levels of pollutants in their waste discharge to EPA regional
offices or state authorities were contacted by telephone or letter to
develop quantitative data on volume of production (or direct current
use) , water flow rate and composition of waste water discharge. This
list of companies was supplemented by others suggested by trade
associations and several suppliers of waste treatment equipment. Prom
the information collected from more than 200 companies, data on plants
having a volume of effluent flow or discharge of pollutants that
reflected inferior treatment technology were excluded from the analysis
of pollutant reductions achievable by the application, of the best
practical control technology. Data from 53 companies oract icing good
waste treatment were expanded by 23 plant visits and analyzed to
identify the control and treatment technologies which became the basis
for the effluent limitations and standards of performance recommended in
Section II. This group of 53 companies included 12 independent job
shops employing as few as 16 to as many as 200 workers. Size in terms
of installed current capacity ranged from 6,000 to 263,000 amperes among
the independent shops and 3,000 to 450,000 amperes among the captive
facilities. Chemical waste treatment was practiced by all but two
companies, which used evaporators to recycle plating rinse water; 13
companies utilized integrated chemical treatment; 13 employed
evaporators to reduce the water flow rate from one, two or three plating
processees. Four utilized ion exchange units and two used reverse
osmosis for some plating processes. Two companies were using
counterflow rinses for reclaiming plating solution dragged into rinse
water. A total of 21 companies employed batch or continuous chemical
treatment exclusively.
Sources of information utilized for developing the data in this
document included the following:
(1) Published literature (References appear in Section XIII)
(2) Trade literature
10
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(3) Technology Transfer Program on Upgrading Metal Finishing
Facilities to Reduce Pollution, December 12-13, 1972, sponsored
by Environmental Pollution Agency
(4) Pollution Abatement Seminar, sponsored by the Metal Finishing
Suppliers Association, January 23,1973, Cleveland, Ohio
(5) Ten EPA regional offices and 32 state pollution abatement
offices
(6) Representatives of the American Electroplaters1 Society, (AES),
the Metal Finishing Suppliers' Association (MFSA) and the
National Association of Metal Finishers (NAMF)
(7) Representatives of 130 companies with facilities for
electroplating copper, nickel, chromium, or zinc, during
telephone conferences
(8) Representatives of seven companies during office conferences
(9) Representatives of 23 companies who visited by BCL staff
members for development of detailed data
(10) Analytical verification of effluent data for five plants
engaged in electroplating copper, nickel, zinc, and/or
chromium. These five companies included captive facilities and
job shops.
General Description of _the Elect ro p. 1 at ing_ Indus try
The electroplating industry, a subcategory of the metal finishing
activities included in standard industrial classification (SIC) 3471, is
defined for the purpose of this document as that segment of industry
applying metallic coatings on surfaces by electrodeposition and includes
both independent (job) platers and captive operations associated with
product fabrication and assembly. The annual dollars-added value by
electroplating exceeds $2,000,000,000. Approximately 20,000 companies
are engaged in electroplating; 3500 of these arejob shops supplying only
plating service. About 25 percent of this segment is concentrated in
the middle western states of Illinois, Michigan, and Ohio. Another 20
percent is concentrated in Eastern Pennsylvania and the Atlantic
Coastline states of Connecticut, Rhose Island, New York and New Jersey.
The location of captive plating facilities follows the same general
pattern.
The energy consumed annually by electroplating is estimated to be in
the range of 1 to 1.5 x 109 kilowatt hours. From 9 x 107 to 1 x 108 kg
(100,000 to 120,000 tons) of metal (principally copper, nickel, zinc,
and tin) is converted annually to electroplated coatings. These
coatings provide corrosion protection, wear or erosion resistance,
antifrictional characteristics, lubricity, electrical conductivity, heat
and light reflectivity or other special surface characteristics, which
enables industry to conserve several millions of tons of critical
metals, such as: cobalt, chromium, nickel, silver and gold.
Electroplated coating thickness usually ranges from 0.0006 to 0.004 cm
(0.00025 to 0.0015 inch), but thicker coatings to 0.025 or 0.04 cm
11
-------
(0.010 to 0.015 in.) are sometimes required for special engineering
purposes or for salvaging worn or mismachined parts.
An electroplating process includes cleaning, electroplating, rinsing
and drying. The cleaning operation consists of two or more steps that
are reguired for removing grease, oil, soil, and oxide films from the
basic metal surface and insuring good electroplate adhesion. Sequential
treatments in an alkaline solution and an acid solution with
intermediate rinsing are the minimum number customary for these
purposes. In the electroplating solution, metal ions in either acid,
alkaline or neutral solutions are reduced on cathode surfaces, which are
the work pieces being plated. The metal ions in solution are usually
replenished by the dissolution of metal from anodes in bar form or in
small pieces contained in inert wire or expanded metal baskets, but
replenishment with metal salts is sometimes 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 commerically, but only two or three types are utilized widely
for a single metal or alloy. Cyanide solutions are popular for copper,
zinc, and cadmium, for example, yet non-cyanide alkaline solutions
containing pyrophosphate or another chelating agent have been adopted
recently for zinc and copper. Acid sulfate solutions also are used for
zinc, copper, and several other metals, especially for plating
relatively simple shapes.
Barrel and rack operations are used respectively for small parts
that tumble freely in rotating barrels and larger parts that cannot be
tumbled without surface impingment. Perforated plastic barrels range in
diameter from 15 to 75 cm (6 to 30 in.), depending on part size and
shape. Direct current loads up to several hundred amperes are
distributed to the parts being plated in horizontal barrels through
danglers suspended from a current carrying bar located at the
longitudinal axis. In oblique barrels, a conductive button at the
bottom transmits the current.
Rack plating is required for perhaps 90 percent of the surface area
processed commercially; the parts are attached to plastic-coated copper
frames designed to carry current equitably 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 2 to 7
kg (5 to 15 pounds) of parts having a surface area of 0.5 to 1 sq meter
(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.
12
-------
Electroplating facilities vary greatly in size and character from
one plant to another. The size of a single facility expressed as
plating solution volume ranges from less than 400 liters (100 gallons)
to more than 190,000 liters (50,000 gallons). The area of the products
being electroplated 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 kilowatt hours/day to as much as 20,000 kilowatt-hours/day.
Products being plated vary in size from less than 65 sq cm (1 sq in.) to
more than 1 sq meter (10 sq ft) and in weight from less than 30 q (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 other specialize in just one or two.
Because of differences in character, size and processes, few or no
similar plants exist at the present time. Construction of facilities
has been tailored to the specific needs of each individual plant.
13
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SECTION IV
INDUSTRY_CATEGORIZATION
This section discusses in detail the scope of the metal finishing
industry and its subcategories that will be examined later. The
rationale is then developed for considering the Electroplating Industry
as a separate subcategory for the development of effluent limitation
guidelines and standards of performance. Further rationale is offered
for the selection of copper, nickel, chromium, and zinc electroplating
for study in Phase I on which this report is based and all other metal
electroplating in Phase II. The rationale is then developed to show why
further subcategorization of the electroplating industry is not required
for the purpose of developing effluent limitation guidelines and
standards of performance.
Ob ject ives_of Categori zat ion
A primary purpose of industry categorization is to develop quantitative
effluent limitations and standards of performance that are uniformly
applicable to a specific category or subcategory. This does not
preclude further classification within a category for the purpose of
monitoring to insure compliance.
The_RelationshiE_gf^Electroplating and Metal^Finishing
Electroplating is one of several processes in the broader category of
metal finishing, which includes anodizing, bright dipping, buffing,
coloring, conversion coating, descaling, electropolishing, galvanizing,
mechanical polishing, tumbling, and other finishing processes. One,
several, or all of the above processes may be performed in a single
facility. For example, electroplating and its attendent operations of
preparation for plating and post plating treatment may be the only
process performed.
As pointed out above, electroplating is one of several processes in the
broader category of metal finishing. Electroplating is an appropriate
subcategory of metal finishing because other subcategories of metal
finishing employ chemical processes exclusively.
Profile of Production Processes
-------
The electroplating industry utilizes chemical and electrochemical
operations to effect an improvement in the surface properties of metals
and other materials. In practice, the operations are put together in
sequences that become the processes which effect the improvement. Thus,
electroplating is both process and materials oriented.
In one segment of the industry, identified as No. 3471 in the Standard
Industrial Classification (SIC) Manual 1972, published by the Executive
Office of the President (Bureau of the Budget), processes are performed
on metals or other materials as products owned by someone else, i.e.:
The customer. Such work is done in job shops, also known as contract
shops. The same operations for electroplating are performed by
manufacturers classified by other SIC numbers, on their own metals,
materials, and products in captive shops under their own management.
Typical processes are the same for both types of facilities. Examples
are shown for copper, nickel, chromium, and zinc plating which is nhe
subject of this report according to basis metal or material and opera-
tions in Tables 2 to 6. Not shown in these tables are sequences for
electroplating cadmium, brass, gold, iron, lead, silver, tin, the
platinum metals, and other metals and alloys which are practiced by only
a few companies, relative to the much larger number engaged in
electroplating copper, nickel, chromium, and zinc. These less common
electroplating processes will be examined and analyzed later durina
Phase II of this program. Copper, nickel, chromium, and zinc plating
processes which is the subject of this report were selected first,
because a large proportion (about two thirds) of the waste generated by
electroplating processes are derived from those associated with copper,
nickel, chromium, and zinc. Furthermore, almost all facilities are
equipped for plating at least one of these common metals.
15
-------
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-------
TABLE 3. PROCESSES FOR PLATING ON ZINC DIE CASTINGS
Operation
Alkaline clean/
rinse
Acid dip /rinse
Copper strike/
rinse
Acid dip/rinse
Copper/rinse
Nickel/rinse
Nickel/ rinse
Anodic treat/
rinse
Chromium/ rinse
Chromate/ rinse
Decorative
Chromium
Plate
1
X
X
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
X
X
X
Protective
Finish
3
X
X
X
Protective
Finish
A
X
X
X
17
-------
TABLE 4. PROCESSES FOR PLATING ON BRASS
Operation
Alkaline clean/
rinse
Acid dip/rinse
Copper strike/
rinse
Acid dip/rinse
Copper/rinse
Nickel/rinse
Nickel/rinse
Anodic treat/
rinse
Chromium/rinse
Chromium
Plate
1
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
Decorative
Chromium
Plate
3
X
X
X
X
X
X
Protective
Nickel
Plate
A
X
X
X
X
X
18
-------
TABLE 5. PROCESSES FOR PLATING ON ALUMINUM
Operation
Alkaline
Clean/ rinse
Acid dip/rinse
Activate/rinse
Zinc strike/
rinse
Copper strike/
zinse
Copper/rinse
Nickel/rinse
Nickel/rinse
Chromium/rinse
Zinc/rinse
Chromate/rinse
Decorative
Chromium
Plate
1
X
X
X
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
X
X
X
X
Decorative
Chromium
Plate
3
X
X
X
X
Protective
Zinc
Plate
A
X
X
X
X
X
X
TABLE 6. PROCESSES FOR PLATING ON PLASTICS
Operation
Alkaline
Clean/rinse
Acid dip rinse
Activate rinse
Catalyze rinse
ElectrolcEs
Deposit/rinse
Copper strike/
rinse
Copper/rinse
Nickel/rinse
Nickel/rinee
Chromium/ rinse
Decorative
Chromium
Plate
1
X
X
X
X
X
X
X
X
X
Decorative
Chromium
Plate
2
X
X
X
X
X
X
X
X
X
Sasis
for
Coating
3
X
X
X
X
X
X
X
Basis for
Magnetic
Coating
4
X
X
.X
X
X
X
19
-------
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 the steps of
electroplating, copper, nickel, chromium, or zinc. These operating
solutions are the sources of pollutants which appear in the rinses
immediately following the concentrated solutions, in spills, and from
the discard of spent or contaminated solutions. The intermediate rinses
are essential for removing the processing solution from the workpieces
so as to avoid contaminating the next processing solution. The final
rinse assures a clean finished surface.
Some generalizations will be encountered as process descriptions. For
example, decorative chromium plating refers to copper plus nickel plus
chromium plating and hard chromium plating refers to only chromium
(usually on steel), as seen in Table 2.
In some facilities, vapor degreasing with tri- or perchloroethylene may
be used to precede the alkaline cleaner. The only water associated with
this operation is for cooling. The cooling water effluent is usable for
rinsing after the alkaline cleaning. Therefore, no further mention is
made of vapor degreasing. However, it is a source of possible air
pollution.
For each typical electroplating operation, exemplified in Tables 2 to 7,
a variety of solutions can be selected. The choice is usually based on
personal knowledge and experience in a specific process for a specific
basis material. The selection of an alkaline cleaner for a specific
basis material could be made from at least five types. The number of
candidate solutions for other operations is as follows:
(1) Three to six acid dips each basis material
(2) Two to three copper strike solutions
(3) Four copper plating solutions
(U) Four nickel plating solutions
(5) Three chromium solutions
(6) Three zinc solutions.
Thus, the most appropriate solution for a particular operation will not
be the same in all electroplating facilities. Further evidence of the
complex character of the electroplating industry is seen in the size
range of less than 400 liters (100 gallons) to more than 190,000 liters
(50,000 gallons) of plating solutions in a single facility. The less
than 400 liter (100 gallon) installations involve parts either small in
size or guantity or are specialized as for electrodepositing chromium on
tools and custom parts in a captive shop. Installations of larger
gallonage process parts large in size (as bumpers for automobiles, sheet
and strip steel for prefab plating and/or large numbers of zinc die
castings and steel and brass stampings or castings).
20
-------
At the low and intermediate region of the size range are the
contract shops, representing approximately 3500 facilities of SIC 3471
classification. Larger facilities are in captive shops where logistics
and process control are more effectively geared to a high production
volume. Other SIC classification numbers cover the captive plating
facilities, estimated to be five to six times the number of contract or
job shops. About 90 percent of the volume of electroplating in dollars-
added value is supplied by companies doing their own electroplating on
their own products.
Unlike most of the captive plating operations, which process
approximately the same number of the same products each month, job shops
are required to handle a greater variety of shapes and different metal
substrates. Production volume for a specific type of product varies
appreciably from day to day. Thus, an individual job shop might be
generating a large amount of copper, nickel, and chromium waste and
little or no zinc waste during a limited, three- or four-week period at
the beginning of a new model-year season for automotive or appliance
hardware, or a much lesser amount of copper, nickel, and chromium waste
and a large amount of zinc waste near the end of a model-year run for
typical customer products. Day-to-day variations can be expected in the
amount and type of waste generated by a typical independent facility as
a result of meetina delivery schedules.
Because of the large variety of products handled by the independent job
shops, in-process controls for minimizing waste are less effective, in
comparison with the controls that can be exercised in a captive facility
always processing the same products and materials. As a result of this
situation, the advent of rigid waste-discharge enforcement is expected
to encourage some degree of specialization among the independent job-
shop establishments. Such a trend will reverse the tendency established
in the past by companies that have expanded in facilities with a larger
number of electroplating and finishing processes in order to provide
improved service to industry in a given geographical area.
Materials Receiying_Electrop-lates
Regardless of the size of facility for copper, nickel, chromium,
and/or zinc electroplating, it will process one or more of the commonly
used basis materials: steel, zinc die castings, brass, aluminum, and
plastic such as ABS and polypropylene as summarized in Tables 2 to 6.
The distribution of electroplating according to basis material is shown
in Table 7. More than half of all electroplating is done on steel as a
basis material. Zinc alloys as die castings comprise the next largest
category of basis materials. Reference to Tables 2 to 5 shows that
basis materials are first cleaned and acid dipped prior to the first
electroplating step.
21
-------
TABLE 7. DISTRIBUTION OF ELECTROPLATE ACCORDING
TO TYPE OF BASIS MATERIAL
Plate Steel Zinc Die Cast Brass Aluminum Plastics
Copper
Nickel
Chromium
Zinc
50
48
54
100
46
44.9
33.9
2
5
4
2
0.1 2
0.1 2
When the nature of the industry and the operations performed were
analyzed, consideration was given to the further categorization of
electroplating according to one or more of the following:
(1) Type of basis material
(2) Product design
(3) Raw materials used
(4) Size and age of facility
(5) Number of employees
(6) Geographic location
(7) Quantity of work processed
(8) Waste characteristics
(9) Treatability of wastes
(10) Rack plating versus barrel plating.
None of these is a basis for categorization for the reasons given below.
Type of Basis Material
The wastes produced by processing all common basis materials are
similar. A single facility can process all basis materials without
significant change in the raw materials consumed or the waste-treatment
technique adopted for control of end-of-pipe water discharge. Any
materials dissolved from the surface of the customary basis metals
during processing are removed from wastewater discharge by the treatment
processes adopted for removing copper, nickel, chromium and zinc, which
are described in section VII. Furthermore, the basis materials selected
for most consumer products frequently are interchanged from one model
22
-------
year to another. Therefore, the type of basis material does not
constitute a basis for subcategorization.
Product Design
Although complex shapes tend to generate more waste than simpler
ones, the premium in costs for fabricating and plating the complex
shapes far overshadows any small supplemental waste-treatment cost for
such products. Product design precepts for minimizing electroplating
costs also reduce wastes created by electroplating processes.(1)
Furthermore, the in-process controls and rinsing techniques described in
Section VII for minimizing the wastes generated by copper, nickel,
chromium, and zinc electroplating processes have been adopted for
canceling the effect of the shape factor. Therefore, product design
variance is not a basis for subcategorization.
Raw Materials Used
Raw materials do not provide a basis for subcategorization, because
practicable waste-treatment technology identified in Section VII is
equally applicable to all of the usual procedures and solutions
described previously for electroplating copper, nickel, chromium, and
zinc. In any facility carrying out one or more of the processes shown
in Tables 2 to 10, the same waste-treatment needs arise. Such varia-
tions as exist for each operation are not unique and do not affect the
waste-treatment technology and control.
23
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Size and Age of Facility
The nature of electroplating is the same in all facilities
regardless of size and age. For example, copper plating is technically
the same in 190 liters (50 gallons) as in 19,000 liters (5,000 gallons)
or larger installations. Technically, the age of the facility does not
alter this situation. Electroplating of nickel, chromium, and zinc
follows the same pattern. Thus, the characteristics of the waste will
be the same for plants of all ages and sizes. Only the quantity of
waste per unit time will differ. Yet, this factor is not a basis for
subcategorization, because waste discharge after treatment is directly
proportional to the size of the facility expressed as amount of metal
deposited, as shown in Figure 1. The amount of metal deposited in
typical facilities is directly related to the current consumed for
plating, the number of liters of installed plating solution, and the
volume of production. The guidelines recommended in this document
provide for variable production volume with no need to differentiate
plant capacity as a subcategory.
It is recognized that some small plating facilities may have
insufficient space for accommodating effective in-process controls for
minimizing water use and/or conventional chemical waste treatment
equipment. The capital investment/burden for installing good waste
control may be greater for such small companies relative to the burden
that can be amortized by larger companies. In such cases, heavy metal
pollutants can be absorbed on the resins in small ion-exchange units
available at relatively modest investment. At least one vendor of such
equipment will replace the resin beds, back wash the used beds in their
own facilities and regenerate the resins for reuse. Alternatively, both
local and regional organizations equipped with large tank trucks supply
a hauling and treating service in several areas. Costs depend on water
volume and the concentration of pollutants.
Number of Employees
The number of employees engaged in electroplating does not provide a
basis for subcategorization, because electroplating operations can be
carried out manually or in automatic machines which greatly conserve
labor. For example, an operation with 3,785-liter (1,000-gallon)
processing tanks may require six people if operated manually, whereas a
plant of the same tank size and carrying out the same operations in an
automatic machine would need only two people. The same amount of waste
would be generated in each case, if the products being plated were equal
in total area. Other examples could be cited to show that no basis
exists for relating the number of employees to the electroplating
operations carried out and/or to the waste that results from those
operations.
27
-------
Production Capacity, Lb Metal Deposited/Hour
20 40 60 80
100
I
I
I
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(H-8)
0.15
o
I
a
aJ
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(33-6)
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i
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o
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0.3 S
0.2
a>
O
o
in
in
i
O.I
10 20 30 40
Production Capacity, Kg Metal Deposited /Hour
FIGURE 1. RELATIONSHIP OF TOTAL METAL IN TREATED
WATER DISCHARGE TO THE PRODUCTION
CAPACITY OF TYPICAL ELECTROPLATING
PLANTS EXPRESSED AS METAL DEPOSITED
PER HOUR
-------
Geographic Location
Geographic location is not a basis for subcategorization. No
condition is known whereby the choice of electroplating operations is
affected by the physical location of the facility, except availability
of process water. If water is not available, no modification of
electroplating procedures can compensate for this lack. No
electroplating facilities would be installed at a water-deficient
location, because large amounts of water are required for replacing
water lost by evaporation. 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 rinsewater conservation
techniques described in Section VII can be adopted for minimizing the
land space required for the endof-process treating facility. A compact
unit can easily handle end-of-process waste if the best in-process
techniques are utilized to conserve raw materials and/or water
consumption.
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 process--1. The application of the guidelines provides for the
production of a particular facility.
Waste Characteristics
The physical and chemical characteristics of all wastes generated by
copper, nickel, chromium, and zinc electroplating processes are similar.
Specifically, all wastes are amenable to the conventional wasne-
treatment technology detailed in Section VII. The characteristics of
treated waste are the same througout the industry. Thus waste
characteristics do not constitute a basis for subcategorization.
Treatability of Wastes
As no special peculiarity exists between raw materials and waste
characteristics as a basis to separate facilities into subcategories,
none exists for treatability of wastes as a basis for subcategorization.
All of the principal treatment procedures and in-process controls are
technically applicable by choice for any given waste and all operations
generate the same type of raw waste regardless of the facility.
29
-------
Rack Plating Versus Barrel Plating
The choice of rack or barrel methods for plating is based on the
size and quantity of the parts to be processed per unit of time.
Neither of these conditions imposes a significant technical change in
the operations for electroplating. The selection is always based on
economic considerations because hand racking of small parts is usually
more costly than dumping them in a barrel for processing in bulk.
Technically, any plating operation can be done either by rack or by
barrel operations. Sometimes plating bath compositions will be modified
by altering the concentration of solution constituents. However, the
same types of salts, acids, and additives will be used. Thus, the
impact on waste characteristics is not changed. The volume of
wastewater (dragout) is frequently greater in barrel plating operations
but the final effluent quality is not a function of influent
concentration. Techniques are available to reduce the rinse water
volumes in barrel plating to the levels of rack plating. These techni-
ques are detailed in Section VTI. Therefore, rack plating and barrel
plating are not appropriate subcategories.
30
-------
SECTION V
WASTE CHARACTERIZATION
Introduction
Water flow and the nature and quantity of the wastes dissolved in the
water during copper, nickel, chromium, and zinc plating processes are
described in this section. Sources of waste are also discussed in this
section.
Water is a major material in the electroplating industry and is
associated with every operation. Yet, none of the water enters the
product and there is no payment for it as such.
5P.ec if i c _Water_Uses
Water is used in the following ways:
(1) Rinsing to remove films of processing solution from the surface
of work pieces at the site of each operation (2) Washing away spills in
the areas of the operations (3) Washing the air that passes through
ventilation ducts so as to remove spray from the air before it is
exhausted
(4) Dumps of operating solutions, mostly pretreatment and
posttreatment solutions
(5) Rinse water and dumps of solutions from auxiliary operations
such as rack stripping
(6) Washing of equipment (e.g., pumps, filters, tanks)
(7) Cooling water used in heat exchangers to cool solutions in
electroplating processes.
Rinsing
A large proportion (perhaps 90 percent) of the water usage is in the
rinsing operations. That used as cooling water usually does second duty
in rinsing steps. The water is used to rinse away the films of
processing solutions from the surface of the work pieces. In performing
this task, the water acquires the constituents of the operating
solutions and is not directly reusable. Thus, the cost of water is an
operating expense to which is added the cost of treating the water to
clean it up for reuse or for discard. Dilute water solutions result
from the raw waste from each operation. Therefore, the location of
rinse steps is important relative to the operations performed in the
electroplating process. The general outline of operations in the
processes was given in Tables 2 to 6.
31
-------
Figures 2 and 3 schematically illustrate flow charts for work pieces
being processed and show the sites of water usage for rinsing. Figure 2
shows the minimum number of operations and the water flow in the wide
practice of decorative chromium plating. However, there is no fixed
relation between water usage and amount of work processed. Some plants
use more water than the minimum required to maintain good quality work.
Charts for other processes shown in Tables 2 to 6 show analogous
water use for each operation of cleaning, acid dipping, plating, and
rinsing according to one of the schemes in Figure 3.
Spills and Air Scrubbing
The water from washing away spills and that from washing down
ventilation exhaust air is added to the chemically corresponding rinse
water for treatment.
Dumps
Operating solutions to be dumped are slowly trickled into rinse
water following the operation and prior to treatment. Alternatively,
the operating solutions, which are much more concentrated then the rinse
water, may be processed batch-wise in a treating facility. Subsequent
discussion of waste treatment of rinse water covers all the water in the
facility.
Water from Auxiliary operations
Auxiliary operations such as rack stripping utilize solutions
containing acids or cyanide for removing metal deposited on rack tips.
These solutions accumulate large concentrations of metals and are
decanted or dumped at regular intervals. They should be slowly trickled
into the appropriate rinse water stream that contains similar chemicals
for ultimate treatment.
32
-------
Work flow
Alkaline
clean
Precipitate
nickel and copper
FIGURE 2. SCHEMATIC FLOW CHART FOR WATER FLOW IN CHROMIUM
PLATING ZINC DIE CASTINGS, DECORATIVE
33
-------
Clean water
one or two rinses
Work flow
1
Sludge
a. One or Two (Series) Rinses
Effluent
water
Clean water
Work flow
Effluent water
Sludge
b. Two Counter-Flow Rinses
Clean water
Work flow1
c Three Counter-Flow Rinses
FIGURE 3 ALTERNATIVE METHODS OF RINSING AFTER A PROCESSING OPERATION
34
-------
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.
Cooling Water
As noted previously cooling water used in heat exchangers for
cooling electroplating solutions is usually routed to rinse tank's for
water conservation purposes. If this practice is not adopted, exit
water from cooling units should be checked for constituents of the
plating solution to guard against the discharge of pollutants in the
event of a leak into the cooling unit.
QuantitY_gf_Wastes
At least 95 percent of the products being electroplated (or
electroformed) to provide resistance to corrosion, wear, and other
destructive forces are processed in medium sized or large plants (4,000
to 5,000 in number), each deploying at least 11 kg/day (25 pounds/day)
of raw waste into rinse water. The potentially
toxic waste in -he ionu of heavy metal salts and cyanide salts from
these sources is approximately 340,000 kg/day (750,000 pounds/day (data
from a survey of chemicafs consumed by electroplating conducted by
Battelle's Columbus Laboratories in 1965, adjusted to reflect trends in
process modifications since 1965) equivalent to about 110,000 kg/day
(250,000 pounds/day) of heavy metal and cyanide ions. Of the total
salts, about two-thirds or 228,000 kg/day (505,000 pounds/day) is
contributed by copper, nickel, chromium, znd zinc plating operations, as
shown in Table 12.
Supplementing the chemicals listed in Table 12, at least 225,000
kg/day (500,000 pounds/day) of alkalies and 450,000 kg/day (1,000,000
pounds/day) of acids are contributed to the total waste by cleaning and
pickling operations that precede copper, nickel, chromium, and zinc
plating. The proportion of phosphates in alkaline cleaning chemicals is
unknown, but is believed to be 25 percent of the total alkalies.
35
-------
TABLE 12. ESTIMATED DAILY RAW WASTE LOAD OF PRINCIPAL SALTS
USED IN COPPER, NICKEL, CHROMIUM, ZINC PLATING
AND RELATED PROCESSES(a)
Operation
Principal Salts
Identity
kg/day pounds/day
Copper plating
Nickel plating
Chromium plating
Zinc plating
Copper cyanide, 54,000 120,000
sodium cyanide, and
copper sulfate
Nickel chloride and
nickel sulfate
Chromic acid
Zinc oxide, zinc
cyanide, sodium
cyanide, and
zinc sulfate
54,000 120,000
45,000 100,000
68,000 150,000
Percent of
Total Salts
Consumed by
Plating
(a) Data from a survey conducted by Battelle's Columbus
Laboratories in 1965.
13
17
13
23
Zinc chromating
Sodium chromate and
sodium dichromate
6,800
227,800
15,000
505,000
2
68
36
-------
Some of the alkaline solution waste and nearly all of the acid solution
waste contain heavy metals resulting from the dissolution of metal
products to be plated. Hence, the total amount of wastewater
constituents generated by copper, nickel, chromium, and zinc
electroplating probably exceeds 900,000 kg/day (2,000,000 pounds/day).
From the estimated plating salts in Table 12, the total metal and
cyanide load was estimated as follows:
Copper 11,000 kg/day ( 24,000 pounds/day) Nickel
12,000 kg/day ( 27,000 pounds/day) Chromium 25,000 kg/day
( 55,000 pounds/day) Zinc 19,000 kg/day ( 42,000
pounds/day) Cyanide _i*£tOOO kg/day (102A000 pounds/day)
TOTAL 113,000 kg/day (250,000 pounds/day)"
The estimated alkali load of 230,000 kg/day (500,000 pounds/day) and
acid load of 450,000 kg day (1,000,000 pounds/ day) are usually in about
the same ratio in most plants (i.e., combined acid/alkali wastewaters
are mostly acid). Assuming the alkalinity as sodium hydroxide (NaOH)
and acidity as sulfuric acid (H2SO4), combination/neutralization (about
0.9 kg NaOH/kg H2SO4) would indicate a total net acid load of 350,000
kg/day (750,000 pounds/day).
Sources_gf_Waste
In electroplating facilities the wastes are derived from the basis
materials receiving electroplates (discussed in Section IV) and the
contents of operating solutions used for electroplating processes. The
principal ionic constituents of wastewater from typical processes for
plating on five basis materials are listed in Tables 13 to 17. Wastes
associated with (1) preparation for plating, (2) electroplating, and (3)
postplating are combined in these tables. These operations are
discussed below in more detail.
Preparation for Plating
Wastewater constituents derived from the chemicals generally
utilized for maintaining preplate preparation solutions or from
reactions with the common basis materials processed in these solutions
are as follows:
37
-------
TABLE 13. PRINCIPAL WASTEWATER CONSTITUENTS IN
WASTES FROM PROCESSES FOR PLATING
ON STEELS*
Constituent
Iron, ferrous, Fe"*~2
Copper, cuprous, Cu
Copper, cupric, Cu+2
Nickel, Ni+2
Chromium, chr ornate, Cr"1""
Chromium, chromic, Cr"1"-^
Zinc, Zn+2
Cyanide, CN"1
Sulfate, S04"2
Chloride, Cl"1
Car b ona t e , C03 ~ 2
Silicate, Si03~2
Phosphate, P04~3
Fluoborate, BF6*1
Sulfamate, NI^SOs"1
Nitrate, N03*1
.Ammonium , NHA+^
Organics
1
X
2 3
X ' X
i
X X ,
X X
X i X ' X
x ; x x
J
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
4
X
X
X
X
X
X
X
X
X
X
5
X
X
X
X
X
X
X
X
6
X
X
X
X
X
X
X
X
X
7
X
X
X
X
X
X
X
X
X
X
8
X
X
X
X
X
X
X
X
* Process numbers correspond to those in Table 2.
38
-------
TABLE 14. PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTE FROM PROCESSES FOR PLATING
ON ZINC DIE CASTINGS*
Constituent
Fe+2
Cu+1
Cu+2
Ni+2
Cr+6
Cr+3
Zn+2
CN"1
SO^2
ri-1
Li
C03~2
Si03~2
PO^'3
BFg'1
NH2S03"1
NOT"-'-
il \S J
NH4+1
Organics
1
X
X
X
X
X
X
X
X
X
X
X
2
X
X
X
X
X
X
3
X
X
X
X
X
X
4
* Processes correspond to those in Table 3.
39
-------
TABLE 15. PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTE FROM PROCESSES FOR PLATING
ON BRASS*
Constituent
Fe+3
Cu+1
Cu+2
Ni+2
Cr+6
Cr+3
Zn+2
CN"1
S04'2
Cl"l
C03"2
Si03~2
P04'3
NH2S03*1
N03"1
Organics
1
X
X
X
X
X
X
X
X
X
X
X
X
2
X
X
X
X
X
X
X
X
X
X
X
3
X
X
X
X
X
X
X
X
X
X
X
X
4
X
X
X
X
X
X
X
X
X
* Processes correspond to those in Table 4.
40
-------
TABLE 16. PRINCIPAL WASTEWATER CONSTITUENTS IN
WASTE FROM PROCESSES FOR PLATING ON
ALUMINUM*
Constituent
Fe+3
Cu+1
Cu+2
Ni+2
Cr+6
Cr~*~3
Zn+2
Aluminum, AP"-^
CN"1
S04'2
Cl"1
C03~2
Si03"2
P04'3
BF6~-*-
NH2S03*1
NH3-1
Organics
1 2
X
X X
X , X
X ; X
y
X
X
X
X
X
y
X
X
X
X
3
X
X
X
X
X
X
X
A
5
* Processes correspond to those in Table 5.
41
-------
TABLE 17. PRINCIPAL WASTEWATER CONSTITUENTS
IN WASTE FROM PROCESSES FOR PLATING
ON PLASTICS*
Constituent
Tin,
Palladium,
Organics
Fe+3
Cu+1
Cu+2
Ni+2
Cr+6
Cr+3
Zn+2
Sn+2
Pd+2
CN"1
804" 1
cr1
0)3 ~2
Si03'2
P04"3
BF6
N03"1
NH3"1
1
X
X
X
X
X
X
X
X
X
2 3
X X
X X
X
X
X X
X
X
X
X
X
X
X
X
4
X
X
X
X
X
X
* Processes correspond to those in Table 6.
42
-------
Alkyl aryl oxyalcohols Nitric acid
Alkyl aryl sulfonates Phosphoric acid
Aluminum chloride Sodium bisulfate
Aluminum nitrate Sodium borate
Aluminum sulfate Sodium carbonate
Chromic acid Sodium hexametaphosphate
Copper chloride Sodium hydroxide
Copper fluoborate Sodium metosilicate
Copper nitrate Sodium orthosilicate
Copper sulfate sodium pyrophosphate
Ferric chloride Sodium sulfate
Ferric phosphate Sodium triphosphate
Ferric sulfate stannous chloride
Ferrous chloride Sulfamic acid
Ferrous phosphate Sulfuric acid
Ferrous sulfate Zinc chloride
Fluoboric acid Zinc sulfate
Hydrochloric acid
Solutions of all of the above chemicals containing acids and
alkalies must be neutralized prior to discharge into navigable waters.
All of the metals may be removed to varying degrees by thet treatment
techniques discussed in Section VII.
Alkaline Cleaners. Regardless of the material to be electroplated,
cleaners are made up with one or more of the following chemicals:
sodium hydroxide, sodium carbonate, sodium metasilicate, sodium
phosphate (di- or trisodium), sodium silicate, sodium tetraphosphate,
and a wetting agent. compositions for steel are more alkaline and
active than those for brass, zinc die castings, and aluminum. Soils to
be removed from basis materials by cleaners are unrelated chemically to
the metal and usually are the same general type. The need for variation
in cleaner composition is partly based on the nature of the soil and on
the chemical resistance of the material being prepared for plating.
In addition to the chemicals comprising the alkaline cleaners, rinses
and spills, wastes contain soaps from emulsification of certain greases
left on basis material surfaces from polishing and buffing that precede
electroplating. Also, emulsified oils are likely to be present. The
raw wastes from the basis materials and process solutions prior to
plating show up in the rinse waters, spills, dumps of concentrated
processing solution, wash waters from air-exhaust ducts, and leaky
heating and cooling coils and heat exchangers.
Acid_Dips. The nature of the basis material requires selectivity
for acid dips. Acid solutions are made up with one or more of the
following: hydrochloric acid, sulfuric acid, phosphoric acid, fluoboric
acid, chromic acid, and nitric acid. The solution- compositions vary
according to nature of any tarnish or scale, chemically related to the
-------
metal and to the resistance of the material to chemical reaction with
the acid solution. The acid-treating baths for preparing metal
substrates for plating usually have a relatively short finite life.
When used solutions are replaced with fresh solutions, large amounts of
chemicals must be treated or reclaimed. Water used for rinsing after
acid treating also collects heavy metal waste by dragout of solution
from the acid-treating tank.
Acid solutions used for pickling, acid dipping, or activating
accumulate appreciable amounts of heavy metals, as a result of metal
dissolution from metallic work pieces and/or uncoated areas of plating
racks that are recycled repeatedly through the cleaning, acid treating,
and elec<- roplating cycle. In barrel zinc-plating operations, the amount
of zinc dissolved in the acid-treating solution from the danglers used
to make electrical contact to the work pieces sometimes equals the
amount of zinc carried over into the water rinse solution following the
zinc-plating bath. The copper (and zinc) accumulated in acid bright dip
solutions used to prepare electrical copper and brass contacts for
plating can exceed in amount the metal contributed to rinse-water waste
by dragout from the plating bath.
The amount of waste contributed by preplate preparation steps varies
appreciably from one facility to another, depending on the substrate
material, the formulation of the solution adopted for cleaning or
activating the material, the solution temperature, the cycle time, and
other factors. The initial condition of the substrate material affects
the amount of waste generated during preplate treatment. A dense,
scalefree copper alloy article can be easily prepared for plating 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 insuring the complete removal
of any oxide, prior to plating.
Electroplating
Wastewater constituents derived from solutions generally used for
electroplating copper, nickel, chromium, and zinc are as follows:
Alkylaryl sulfonates Potassium hydroxide
Aluminum chloride Rochelle Salts
Aluminum sulfate Saccharin
Ammonium chloride Sodium bicarbonate
Boric acid Sodium carbonate
Chromic acid Sodium cyanide
Coumarin Sodium ethylene diamine
Copper cyanide tetraacetic acid
Copper sulfate Sodium fluosilicate
Fluoboric acid Sodium hydroxide
44
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Fluosilicic acid Sodium pyrophosphate
Hydrochloric acid Zinc chloride
Nickel chloride Zinc cyanide
Nickel fluoborate Zinc fluoborate
Nickel sulfamate Zinc oxide
Nickel sulfate Zinc sulfate
Potassium cyanide Sulfuric acid
Prior to end-of-process discharge, solutions containing alkalies and
acids (or acid salts) must be neutralized. All of the metals must be
removed by the technology detailed in Section VII.
Copper Plating. Copper is electroplated from four types of baths,
i.e., alkaline cyanide, acid sulfate, pyrophosphate, and fluoborate,
which are prepared with corresponding copper salt. The cyanide
solutions also 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. Typical compositions are cited in References (2)
and (3). Cyanide solutions are used extensively for copper plating, 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. Copper plating solutions are rarely dumped, so the principal
source of waste is the rinse water used to remove the solution that
remains on work surfaces (dragout) after copper-plated articles are
removed from the plating tank. Rinsing between cyanide copper striking
and plating in a concentrated cyanide bath is not reguired, so
facilities equipped with both kinds of solutions create just one source
of waste, in comparison with others eguipped with a cyanide strike and
an acid bath. Even so, some companies prefer the cyanide strike-acid
copper sequence for minimizing the amount of cyanide waste requiring
treatment by chemical oxidation (or for improving the quality of their
products).
A secondary source of waste in a typical copper plating facility is
associated with solution filtration. Filters, pumps, and pipes commonly
develop leaks, classified as spills. Not all of the solution is washed
back into the plating tank when filter cartridges or bags are exchanged
for new ones (or washed free of contaminating solids that reduce the
filtration rate). The high-concentration cyanide and acid copper
sulfate solutions are usually filtered continuously, in order to prevent
rough deposits.
A nickel strike for steel has been adopted by some companies
choosing to eliminate cyanide baths. The acid copper sulfate bath can
then be used over the nickel strike, in a sequence similar to that
adopted for copper plating on plastic which is first metallized by a
-------
thin film of electroless nickel. A satisfactory nickel shrike has not
been identified for zinc die castings, which are universally plated
first with a cyanide copper strike. Copper is extensively electroplated
in combination with nickel and chromium. About 75 percent of t.he copper
anode consumption (18,000,000 kg/year or 40,000,000 pounds/year) i?-,
expended for this purpose, but other applications aooour^- fov
significant quantities. For example, printed circuit boards are eof
plated to make through-hole electrical contacts between circuits o.
opposite sides of the boards. Another significant activity is copper
electroforming (including electrotyping) . Some facilities installed for
electroplating cabinet hardware (principally steel and zinc alloy die
castings) utilize copper plating as the only deposition step, to produce
colored finishes.
Nickel is electroplated from Watts (sulfate-
chloride-boric acid) ; sulfamate; all chloride; and fluoborate baths.
Each type of solution is prepared with the corresponding nickel salt, a
buffer such as boric acid and a small concentration of a wetting agent.
A small amount of another organic chemical may be added to brighten the
deposits or control another property. Nickel is extensively
electroplated in a three-metal composite coating of copper, nickel, and
chromium. In the best practice, nickel plating would follow copper
plating without drying as in Processes 1 and 2, Table 3. Nickel also is
electrodeposited on steel for decorative-protective finishes and on
other materials for electroforming. In these applications, nickel
plating is preceded by cleaning and activating operations in a sequence
selected for a specific basis material. Nickel electroplate is freshly
plated and rinsed without drying and directly chromium plotted according
to processes shown in Tables 2 through 6. Typical solution compositions
are given in References 2 and 3.
In addition to the constituents of new solutions, used solutions
contain small concentrations of other heavy metals, depending on the
kind of material being processed. For example, the? nickel bath
gradually picks up copper and zinc when copper-plated steel and copper-
plated zinc die castings are being nickel plated. Only periodic
analyses will reveal the amounts present.
Organic addition 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-protective deposits
requiring no buffing. Aryl polysulfonates, sulfonamides, and
sulfinimides such as napthylene disulfonic acid, p-toluene sulfonamide,
and saccharin are examples of one class of brightening agents frequently
combined with a sulfonated aryl aldehyde, ethylene sulfonamide, amine,
nitrile, imide, azo dye, or another special compound. These organic
chemicals and the surface active agents (typically sodium lauryl
46
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sulfate) customarily added to reduce surface tension and prevent pitting
contribute small concentrations that impose a small COD to the water
rinse step following nickel plating. Because the organic compounds are
customarily added to nickel plating baths in small concentrations (0.5
to 3 g/1), their total concentration in the untreated rinse water seldom
exceeds 4 mg/1.
Leakage from filters, pumps, and pipes is a secondary source of
nickel waste, although some filters are equipped to recover and recycle
leaks that occur from the pump and filter. Incomplete washing of filter
cartridges, bags, or plates during filter maintenance is another source
of waste. Continuous filtration of nickel solution is adopted for
preventing roughness by most of the companies engaged in nickel plating.
Filters sometimes are packed with activated carbon for removing organic
impurities that degrade the characteristics or properties of the
deposit.
The relatively high value of nickel has encouraged the adoption of
in-process controls for minimizing dragout into the rinse water
following nickel plating, which is the major source of waste. Because
of their relatively high value, nickel plating baths are rarely dumped.
Chromium Plating. All chromium plating solutions contain chromic
acid and a small amount of either sulfuric acid or a mixture of sulfuric
acid and fluosilicate or fluoride ions. The concentration of chromic
acid usually is two orders of magnitude higher than the concentration of
the other materials. Three basis materials account for the bulk of the
work: steel, nickel-electroplated steel, and nickel-electroplated zinc.
Solutions containing 150 to 400 g/1 of chromic acid are the common baths
for electroplating 0.2 to 1.0m (0.000008 to 0.00040 inch) of decorative
chromium or hard chromium on steel and aluminum for resisting wear.
Unlike the copper and nickel plating processes which utilize soluble
copper or nickel anodes to replenish in solution the metal deposited on
the work pieces, chromium plating 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. This proportion varies from only 10 to 20 percent in
decorative chromium plating facilities to the range of 25 to 90 percent
in hard chromium installations, depending on the in-process controls
adopted for reducing the dragout loss to the rinse water.
Dragout into rinse water is the major source of raw waste. Spray
carried from the solution by the hydrogen gas generated at cathode
surfaces and oxygen gas produced at anode surfaces is a significant
secondary source. Chromium plating process tanks are customarily vented
to protect workers from this spray, so an appreciable amount of chromic
acid is carried into air ducts in the form of aerosols released to the
atmosphere. Air scrubbers are incorporated in the exhaust systems
47
-------
installed in some plants to recover this source of waste and recycle it
to the chromium plating bath.
Zinc is electroplated in (a) cyanide solutions
containing sodium cyanide, zinc oxide or cyanide and sodium hydroxide;
(b) noncyanide alkaline solutions prepared with zinc pyrophosphate or
another chelating agent such as tetrasodium pyrophosphate, sodium
citrate or the sodium salt of ethylene diamine 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 containing
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. Formulations for these solutions are given in References (2)
and (3) .
In addition to dragout of solution into rinse water which is the
major source of waste, zinc waste is generated during continuous or
batch filtration. Air agitation and hydrogen gas evolution at cathode
surfaces create aerosol particles carried through exhaust systems into
the atmosphere, unless removed by wash water that is combined with the
rinse water for treatment.
Postplating Treatments
Postplating treatment is rare for nickel and chromiumplated
products, but a large proportion of zinc-plated steel and a smaller
proportion of copper-plated products are processed to impart a chromate
film or one of several alternative colored finishes. Chemicals utilized
for preparing postplating treatment solutions for copper and zinc
electroplates or derived by reactions with the electroplated metal
include the following:
Ammonium carbonate Nickel sulfate
Ammonium hydroxide Nitric acid
Ammonium molybdate Phosphoric acid
Ammonium persulfate Potassium chlorate
Barium sulfide Potassium nitrate
Chromic acid Potassium permanganate
Copper acetate sodium dichromate
Copper chloride Sodium hydroxide
Copper nitrate Sodium polysulfide
Copper ssulfate Sodium sulfide
Ferric chloride Sodium thiocyanate
Ferrous sulfate Sulfuric acid
Hydrochloric acid Zinc nitrate
Nickel chloride
-------
A dilute solution of nitric acid is an example of a bright dip bath
for zinc plate. A chromate solution for zinc is always acidic and
contains hexavalent chromium compounds, such as chromic acid, and
contains inorganic and organic compounds as activators or catalysts
known only to the suppliers. Both types of posttreatment solutions
accumulate dissolved zinc and require dumping and replacement at regular
intervals, thereby creating waste that must be treated prior to
discharge. Used chromate- filming solution also contributes both
trivalent and hexavalent chromium ions to wastewater. Of course, water
rinsing operations after bright dipping or chromating also are sources
for waste. Thus, the rinse water may be mixed with and treated the same
as rinse water from chromium plating.
Copper (and brass) plated steel and zinc alloy products and zinc-
plated products are sometimes oxidized or otherwise treated in solutions
that produce attractive, desired colors such as those described in
Reference (3) . Some of these solutions are prepared with copper or
other heavy metal salts, others accumulate dissolved copper or zinc as
a result of use, some of which show up in rinse water associated with
the post treatment. Furthermore, all have a finite bath life and must
be replaced at intervals, like the bright-dip and chromate- filming
solutions used for treating zinc.
Decorative colors are applied on copper and zinc, after
electroplating. Operators frequently develop their own solution
compositions. The following formulation indicate the general nature of
such solutions.
P? own on copper j _
Potassium chlorate, KC1O3 - 40 g/1 (5.5 oz/gal)
Nickel sulfate, Ni2SO4.6H20 - 20 g/1 (2.75 oz/gal)
Copper sulfate, CUSO4.6H2O - 190 g/1 (24.0 oz/gal)
Li
-------
Ammonium molybdate, NH4MoO4 - 30 g/1 (4 oz/gal)
Ammonia, NH3 - 47 ml/1 (6 fluid oz/gal) or copper sulfate,
CUSO4.6H2O - 45 g/1 (6 oz/gal)
Potassium chloride, KCl - 45 g/1 (6 oz/gal)
Brown on zinc:
Double nickel salts, (NH4)2SO4.NiSO4 - 4 g/1 (0.5 oz/gal
Copper sulfate, CuSO4.6H2O - 4 g/1 (0.5 oz/gal)
Potassium chlorate, KC103 - 4 g/1 (0.5 oz/gal)
50
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SECTION VI
SELECTIQN_gF_POLLyTANT_PARAMETERS
Introduction
This section of the report reviews the waste characterization
detailed in Section V and identifies in terms of chemical, physical, and
biological constituents that which constitutes pollutants as defined in
the act. Rationales for the selection and, more particularly, the
rejection of wastewater constituents as pollutants is presented.
First, consideration was given to the broad range of chemicals used
in the metal finishing industry. Constituents associated with the
subcategory of electroplating and limited to copper, nickel, chromium
and zinc plating were considered next in detail. Those considered to be
potentially toxic pollutants are identified. Other constituents were
examined in the light of their probable concentration in untreated
wastewater in relation to water quality criteria for discharge, in order
to form a judgment on pollutants to be monitored.
Specific consideration is given in this section to defining the
physical form of heavy metals to be considered pollutants, as well as
definition of analytical technigues for reporting their concentrations
in the wastewater discharge.
Metal_Fini_shing Wastewater_Constituents
A large variety of chemicals are used in the metal finishing that
become wastewater constituents. The important wastewater constituents
for electroplating copper, nickel, chromium, and zinc were identified in
Section V. Not all of these constituents will be found in the
wastewaters from every facility since the number of metals plated in a
single facility varies as well as the number of basic metals pretreated
and types of posttreatment operations. Other metal finishing operations
than electroplating and other electroplating operations than copper,
nickel, chromium, and zinc would contribute other metal ions. When
present, these other metal ions are usually coprecipitated with copper,
nickel, chromium, and/or zinc unless they are heavy metal pollutants of
greater potential toxicity requiring special control and treatment
technology. The nonmetallic cations and anions from electroplating
copper, nickel, chromium, and zinc can be considered typical of the
metal finishing industry.
Electroplating_Wastewater Constituents
51
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The wastewater constituents from electroplating copper, nickel,
chromium, and zinc were identified qualitatively in Section V. Each
wastewater constituent is additive to the concentration of that
constituent in the raw water supply if the latter is not deionized.
Sometimes constituents in the effluent originate from the raw water
supply.
Table 18 shows approximate quantitative values for a typical
facility plating copper, nickel, chromium, and zinc (Plant 33-1) with no
other metal plating or metal finishing operations other than
electroplating. The values represent the combined raw waste effluent
assuming no treatment and include both chemicals in wastewater from
rinses and concentrated solution dumps collected and metered uniformly
into the wastewater. Good chemical treatment will oxidize over 99
percent of the cyanide and normally remove 85 to 99 percent of the heavy
metals. The other constituents in the raw waste having much higher
solubilities than metal hydroxides are usually not removed, and
contribute to the total dissolved solids of the treated effluent.
Some soluble constituents are adsorbed on the insoluble material and
removed during clarification. The concentration of total dissolved
solids and the concentration of each soluble constituent depend on the
degree of water conservation used in the facility. The concentrations
shown in Table 18 are considered representative of water use in the
average electroplating facility.
52
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TABLE 18. APPROXIMATE CONCENTRATIONS OF WASTEWATER CONSTITUENTS PRIOR TO
TREATMENT FROM A TYPICAL FACILITY ELECTROPLATING COPPER,
NICKEL, CHROMIUM, AND ZINC (PLANT 33-1)
Estimated Analysis of Water
Untreated Wastewater Treated Effluent Supply
Concentration, Concentration, Analysis,
Wastewater Constituent mg/1 mg/1 mg/1
Copper (Cu+) or Cu2+)
Nickel (Ni+2)
Chromium (Cr3*)
(Cr6+)
(CrT)
Zinc (Zn2+)
Cyanide (CN~)
Sodium (Na~*~)
Potassium (K )
Carbonate (C032~)
Orthophosphate (PO^3 )
Pyrophosphate (P207^~)
Silicate (Si032~)
Metaborate (BO?3")
Perborate (B033~)
Sulfate (S042~)
Bisulfate (HS04)
Fluoride (F~)
Fluosilicate (SiF62~)
Tartrate (C4H4062~)
Chloride (Cl~)
Nitrate (N03~)
Wetting agents (organic)
Sequestrants
Chelates
Additives (organic)
Proprietary acid salts
6.7 0.23
2.4 <0.20
0.05 0.15
17 <0.05
17 <0.20
32 0.1
50 0.21
465 20
2.4
57
47 3.0 <0.01
53
50
36
1.3
19 20
3.7
0.1 0.1
0.5
8.9
228 25
1.4
6.8
6.5
6.5
0.5
32
Total dissolved solids
1150.
53
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water conservation while the concentration of dissolved solids
containing more innocuous materials increases.
Wastewater Constituents_and^Pararr\eters_of_Pollutional Significance
The wastewater constituents of pollutional significance for this
segment of the electroplating industry include copper, nickel, chromium,
zinc, cyanide, suspended solids, and pH. It is recommended that copper,
nickel, chromium, zinc, and cyanide be the subject of effluent
limitations and standards of performance for the electroplating industry
regardless of the physical form (soluble or insoluble metal * 5) Or
chemical form (e.g., valence state of metal or type of cyanide complex).
All other heavy metals and chemical compounds in the wastewater that are
not yet specifically the subject of effluent limitations but which would
normally be precipitated during treatment for removal of copper, nickel,
chromium, and zinc are considered part of the suspended solids as well
as any chemical or biological material adsorbed or entrapped by the
suspended solids during clarification and separation. Thus, suspended
solids are a wastewater constituent of pollutional significance.
The pH is subject to effluent limitations because it affects the
solubility of metallic compounds such as zinc hydroxide and the soluble
metal content of the treated effluent.
Thus, the major chemical, physical, and biological wastewater
constituents and parameters of pollutional significance are as follows:
Copper
Nickel
Chromium, hexavalent
Chromium, total
Zinc
Cyanide, amenable to oxidation by chlorine 6
Cyanide, total *
Suspended solids
PH
Other wastewater constituents of secondary importance in the
electroplating industry that are not the subject of effluent limitations
or standards of performance are as follows:
Total dissolved solids
Chemical oxygen demand
Biochemical oxygen demand
Oil and grease
Turbidity
Color
Temperature
-------
Rationale for the^Selection^gf Wastewater Constituents and^Parameters
Copper
Copper may be present, in significant amounts in the was tewater from
this segment of the electroplating industry and is amenable to removal
by conventional chemical treatment techniques.
Nickel
Nickel may be present in significant amounts in the wastewater from
this segment of the electroplating industry and is amenable to removal
by conventional chemical treatment techniques.
Chromium, Hexavalent
Hexavalent chromium may be present in significant amounts in the
wastewater from this segment of the electroplating industry and is
amenable to removal by conventional chemical treatment techniques.
Hexavalent chromium also is an indicator of the effectiveness of an
important chemical reduction step to insure control of total chromium.
Chromium, Total
Total chromium may be present in significant amounts in the
wastewater from this segment of the electroplating industry and is
amenable to removal by conventional chemical treatment techniques.
Zinc
Zinc may be present in significant amounts in the wastewater from
this segment of the electroplating industry and is amenable to removal
by conventional chemical treatment techniques.
Cyanide, Amenable to Oxidation by Chlorine
Oxidizable cyanide may be present in significant amounts in the
wastewater from this segment of the electroplating industry and is
amenable to oxidation by chlorine under alkaline conditions.
55
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Cyanide, Total
Cyanide may be present in various forms and in significant amounts
in the wastewater from this segment of the electroplating industry.
Cyanide and all cyanide compounds have been proposed as toxic pollutants
pursuant to Section 307 of the Act. The relative difference in toxicity
between cyanide in various forms such as sodium cyanide, copper cyanide
complex, nickel cyanide complex, ferrocyanide ion, and cyanate ion
depends on the kinetics of dissociation under specified conditions which
cannot always be controlled after discharge of the effluent.
Suspended Solids
Suspended solids was selected as a parameter to insure that any
other metal or combination of metals than those subject to effluent
limitations that might be present in the wastewater from this segment
and are capable of being precipitated will be controlled. Suspended
solids also measures clarification efficiency.
PH
The pH was selected as a parameter to indirectly control the amount
of soluble metal relative to total metal in the effluent.
Rationale_for_the_ select ion_of
Total Metal_as_A_Pollutant Parameter
It is generally accepted that neutralization and precipitation of heavy
metals with no subseguent separation is insufficient treatment for
discharge to navigable waters. Removal of the insoluble metal
precipitate from the effluent is reguired by sedimentation,
clarification, or filtering prior to discharge of the liquid effluent to
streams. Apart from the adverse visible appearance of effluent with
large amounts of suspended metal hydroxides, there is evidence of
adverse effects on aquatic life such as clogging of gills of fish and
covering of food supply on the bed of streams. Also, large amounts of
metal hydroxides in the stream are further sources of metal ions if the
water later becomes acidic relative to the pH at which the metal
hydroxides were originally precipitated. Therefore, removal of
precipitated metal hydroxides by efficient clarification prior to
discharge of the effluent to navigable waters is assumed.
With removal of total suspended solids to levels of less than 50
mg/lr significant removal of metal hydroxides occurs. However, some
portion of the total suspended solids contains heavy metals either as
metal hydroxides or adsorbed metal ions. Regardless of the form, the
56
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heavy metal content of suspended solids represents a significant
pollutant in the water.
Heavy metals are considered pollutants regardless of form. The
standard method of analysis for total metal involves acidification of
the sample to analyze for total metal content (dissolved metal plus any
metal in suspended solids left from clarification). For the purpose of
establishing effluent limitations and standards of performance it is
herein specified, in the absence of any qualifying statement, that the
concentration of heavy metals in mg/liter means total metal, as
analytically determined by acid digestion prior to filtering.*
Rationale for Rejection ofBother
Wastewater Constituents_as Pollutants
Metals
The rationale for rejection of any metal other than copper, nickel,
chromium, and zinc as a pollutant is based on one or more of the
following reasons:
(1) They would not be expected to be present in
electroplating wastes from copper, nickel,
chromium, and zinc plating processed in
significant amounts (e.g., uranium,
mercury, arsenic), or
(2) They will be removed simultaneously by
coprecipitation and clarification along
with copper, nickel, chromium, and/or zinc
(e.g., iron) , or
(3) They will be the subject of effluent
limitations developed for other segments
of the electroplating point source category.
(e.g., electroplating of cadmium, tin,
lead, silver, gold, platinum, palladium,
iron, cobalt, and other metals and alloys)
or
(4) Insufficient data exists upon which to base
effluent limitations and standards
of performance.
Dissolved solids
57
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Dissolved solids is not a significant pollution parameter in
this industry. Although the concentration of total dissolved
solids will become higher as efforts are directed to reducing water use
and volume of effluent discharcred, the total quantity of dissolved
solids will remain unchanged.
Chemical Oxygen Demand
Chemical oxygen demand is not an important parameter in the
electroplating industry because cyanide is controlled independently and
the quantity of organic compounds or oxidizable inorganic compounds in
the wastewater is very low.
Biochemical Oxygen Demand
Biochemical oxygen demand is usually not an important pollution
parameter in the electroplating industry. An electroplating plant in a
suburban location not discharging to a publicly owned system must treat
its own sanitary sewage in a separate treatment facility. If the plant
chooses to mix the treated sanitary effluent with electroplating wastes
prior to treatment, BOD would be considered a major parameter.
Oil and Grease
Oil and grease is not normally a significant pollution parameter in
the electroplating industry because these materials are removed from
workpieces by nonaqueous solvents. Added pollution reduction is usually
achieved by the usual practice of installing oil and grease skimmers on
settling tanks. Where such control practices are absent, oil and grease
might be considered a parameter subject to control and treatment.
Turbidity
Turbidity is indirectly measured and controlled independently by the
limitation on suspended solids.
Color
Color is not usually significant in wastewater from electroplating
and is indirectly controlled by the effluent limitations on suspended
58
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solids and on total metal which controls the amount of colloidal metal
that could color the effluent.
Temperature
Temperature is not considered a significant pollution parameter in
the electroplating industry. However, cooling water used to cool
plating process tanks and/or evaporative recovery systems that are not
subsequently used for rinsing could contain pollutants from leaks in the
system.
59
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SECTION VII
CNTROLAND_TR EATMENT TECHNOLG Y
The control and -treatment technology for reducing the discharge of
pollutants from copper, nickel, chromium, and zinc electroplating
processes is discussed in this section.
The control of electroplating wastewaters includes process
modifications, material substitutions, good housekeeping practices, and
water conservation techniques, The in-plant control techniques
discussed are generally considered to be normal practice in this
industry.
The treatment of electroplating wastewaters includes all techniques
for the removal of pollutants and all techniques for the concentration
of pollutants in the wastewaters for subsequent removal by treatment.
Although all of the treatment technologies discussed have been applied
to electroplating wastewaters, some may not be considered normal
practice in this industry.
Chemical Treatment Technology is discussed first in this section
because treatment of all water waste generated by electroplating is
required, prior to water discharge into navigable streams, irrespective
of the in-plant controls adopted for reducing waste. Nevertheless, it
is emphasized that the amount of pollutants discharged to navigable
waters is directly proportional to the volume of water discharged.
The proper design, operation, and maintenance of all wastewater
control and treatment systems are considered essential to an effective
waste management program. The choice of an optimum wastewater control
and treatment strategy for a particular electroplating facility requires
an awareness of numerous factors affecting both the quantity of
wastewater produced and its amenability to treatment.
Chemical Treatment Technology
Applicability
Chemical treatment processes for waste water from electroplating
operations are based on chemical reactions utilized for 25 years or
more. A system has evolved that is capable of effectively treating
effluents from plants of any size and reducing metal ion concentrations
in the effluent to 1.0 mg/liter or less. Control procedures have been
devised to maintain the effectiveness of the process under a variety of
operating conditions.
60
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Processes
Sep.aration_of_ Streams. The rinse waters are usually se gated into three
streams prior to treatment, and consist of 1) those containing chromium
VI, 2) those containing cyanide, and 3) the remainder, constituting
water from acid dips, alkali cleaners, acid copper, nickel, and zinc
baths, etc. The cyanide is oxidized by chlorine and chromium VI is
reduced to chromium III with sulfur dioxide or other reducing agents.
The three streams are then combined and the metal hydroxides are
precipitated by adjustment of the pH. The hydroxides are allowed to
settle out, often with the help of coagulating agents, and the sludge is
hauled to a lagoon or filtered and used as land fill. The treatment
facilities may be engineered for batch, continuous, or integrated
operation. (7)
2§tch_Treatment The batch method is generally used for small or
medium- sized plants. Batch treatment is useful not only for rinse
waters but for process solutions containing high concentrations of
chemicals such as floor spills. Holding tanks collect the wastewater
and are large enough to provide ample time to treat, test, and drain a
tank while another is being filled. Analytical tests are made before
treatment to determine the amount of reagent to add and after treatment
to establish that the desired effluent concentrations have bean
obtained.
Tne chemical treatment process may be made
continuous by (1) sizing and baffling treatment tanks to provide
sufficient hold times to complete chemical reactions; (2) providing
continuous monitoring of pH and oxidation/reduction potentials and
controls for regulating reagent additions by means of these monitors;
and (3) providing a continuous-overflow settling tank that allows sludge
to be pumped off periodically through the bottom.
A diagram of a continuous-treatment plant operaing at maximum
capacity is shown in Figure 4. The dilute acid-alkali stream originates
from rinses associated with alkaline cleaners, acid dips, and baths
containing metal ions but no cyanide or hexavalent chromium. When
concentrated acid and alkali baths are to be discarded they are
transferred to a holding tank and added slowly to the dilute stream. In
this manner, sudden demands on the reagent additions and upsetting of
the treatment conditions are avoided. The dilute acid-alkali stream
first enters a surge tank to neutralize the wastewater and equalize the
composition entering the precipitation tank. The hexavalent chromium is
reduced at a pH of 3.5, and the addition of the SO2 and HC1 are
controlled by suitable monitors immersed in the well-agitated reduction
tank. Cyanide is destroyed in a large tank with compartments to allow a
two-stage reaction. Reaction time is about 3 hours.
61
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The treated chrome, cyanide, and neutralized acidalkali streams are
run into a common tank where pH is automatically adjusted to and held at
8.8. The stream then enters a solids contact unit where mixing,
coagulation, flocculation, recirculation, solid separation,
clarification, solids concentration, sludge collection, and sludge
removal are accomplished. Flocculants are continuously added to this
tank. Typically, residence time is 2 hours. The effluent from this
tank constitutes the discharge from the plant.
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Solution, pH
12
FIGURE 6. SOLUBILITY OF COPPER, NICKEL, CHROMIUM,
AND ZINC AS A FUNCTION OF SOLUTION pH
65
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Unit Operations
Precipitation. The effluent levels of metal ions attainable by chemical
treatment depend upon the insolubility of metal hydroxides in the
treated water and upon the ability to mechanically separate the
hydroxides from the process stream. Soluble concentrations of copper,
nickel, chromium, and zinc as a function of pH are shown in Figure 6,
taken from data published by Pourbaix.(8) At a pH of 9.5, the
solubility of all four metals is of the order of 0.1 mg/1, or less.
Experimental values of Schlegel (9) have been plotted In Figure 7 and
vary somewhat from the theoretical values of Figure 6. Nevertheless,
the need for fairly close pH control in order to avoid high
concentrations of dissolved metal in the effluent is evident. A pH of
8.5 to 9.0 is best for minimizing the solubility of copper and zinc, but
a pH of 9.5 to 10.0 is optimum for minimizing the solubility of nickel
and chromium. To limit the solubility of all four metals in a mixed
solution, a pH of 9.0 appears best.
The theoretical and experimental results do not always agree well
with results obtained in practice. Concentrations can be obtained that
are lower than the above experimental values, often at pH values that
are not optimum on the basis of the above considerations. Effects of
coprecipitation and adsorption on the flocculating agents added to aid
in settling the precipitate play a significant role in reducing the
concentration of the metal ions. Dissolved solids made up of noncommon
ions can increase the solubility of the metal hydroxides according to
the DebyeHuckel Theory. In a treated solution from a typical
electroplating plant, which contained 230 mg/1 of sodium sulfate and
1060 mg/1 of sodium chloride, the concentration of nickel was 1.63 times
its theoretical solubility in pure water. Therefore, salt
concentrations up to approximately 1000 ppm should not increase the
solubility more than 100 percent as compared to the solubility in pure
water. However, dissolved solids concentrations of several thousand ppm
could have a marked effect upon the solubility of the hydroxide.
when solubilizing complexing agents are present, the equilibrium
constant of the complexing reaction has to be taken into account in
determining theoretical solubility with the result that the solubility
of the metal is generally increased. Cyanide ions must be destroyed not
only because they are toxic but also because they prevent effective
precipitation of copper and zinc as hydroxides. If cyanide is replaced
in a plating bath by a nontoxic complexing agent such as EDTA (ethylene-
diamine-tetraacetic acid), the new complexing agent could have serious
consequences upon the removal of metal ions by precipitation.
§2ii
-------
O.I
Zinc
Legend
O Nickel
D Chromium
X Zinc
A Copper
Note : Values plotted as O.I mg/l
were reported as zero. The
O.lmg/X value is assumed
to be the detectable limit.
8 9 10
Solution , pH
12
13 14
FIGURE 7. EXPERIMENTAL VALUES - SOLUBILITY OF METAL IONS AS
A FUNCTION OF pH
67
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chromium.(10) Coagulation can also be aided by adding metal ions such as
ferric iron which forms ferric hydroxide and absorbs some of the other
hydroxide, forming a floe that will settle. Ferric iron has been used
for this purpose in sewage treatment for many years as has aluminum
sulfate. Ferric chloride is freguently added to the clarifier of
chemical waste-treatment plants in plating installations. Flocculat~on
and settling are further improved by use of polyelectrolytes, which "sr^
high molecular weight polymers containing several ionizable ions. DUP
to their ionic character they are capable of swelling in water and
adsorbing the metal hydroxide which they carry down during settling.
Settling is accomplished in the batch process in a stagnant tank,
and after a time the sludge may be emptied through the bottom and the
clear effluent drawn off through the side or top. The continuous system
uses a baffled tank such that the stream flows first to the bottom but
rises with a decreasing vertical velocity until the floe can settle in a
practically stagnant fluid.
Although the design of the clarifiers has been improved through many
years of experience, no settling technique or clarifier is 100 percent
effective; some of the floe is found in the effluent - typically 10 to
20 mg/liter. This floe could contain 2 to 10 mg/1 of metal. Polishing
filters or sand filters can be used on the effluent following
clarification but this is not commonly done. The effectiveness of such
filtering has not been ascertained.
Sludge _Disggsal. Clarifier underflow or "sludge" contains; typically 1
to 2 percent solids and can be carried to a lagoon. Run-off through
porous soil to ground-water is objectionable since precipitated metal
hydroxides tend to get into adjacent streams or lakes. Impervious
lagoons require evaporation into the atmosphere; however, the average
annual rainfall just about balances atmospheric evaporation.
Additionally, heavy rainfalls can fill and overflow the lagoon.
Lagooning can be avoided by dewatering the sludge to a semidry or dry
condition.
Several devices are available for dewatering sludge. Rotary vacuum
filters will concentrate sludge containing 4 to 8 percent solids to 20
to 25 percent solids. Since the effluent concentration of solids is
generally less than 4 percent a thickening tank is generally employed
between the clarifier and the filter. The filtrate will contain more
than the allowed amount of suspended solids, and must,, therefore, be
sent back to the clarifier.
Centrifuges will also thicken sludges to the above range of
consistency and have the advantage of using less floor space. The
effluent contains at least 10 percent solids and is returned to the
clarifier.
68
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Pressure filters may be used. In contrast to rotary filters and
centrifuges, pressure filters will produce a filtrate with less than 3
mq/1 of suspended solids so that return to the clarifier is not needed.
The filter cake contains approximately 20 to 25 percent solids.
Pressure filters are usually designed for a filtration rate of 2.04 to
2.44 liters/min/sq m (0.05 to 0.06 gpm/sg ft) of clarifier sludge.
Solids contents from 25 to 35 percent in filter cakes can be
achieved with semi-continuous tank filters rated at 10.19 to 13.44
liters/min/sg m (0.25 to 0.33 gpm/sq ft) surface. A solids content of
less than 3 mg/1 is normally accepted for direct effluent discharge.
The units require minimum floor space.
Plate and frame presses produce filter cakes with 40 to 50 percent
dry solids and a filtrate with less than 5 mg/1 total suspended solids.
Because automation of these presses is difficult, labor costs tend to be
high. The o#erating costs are partially off-set by low capital
equipment costs.
Automated tank type pressure filters are just now finding
application. The solids content of the cake can reach as high as 60
percent while the filtrate may have up to 5 mg/1 of total suspended
solids. The filtration rate is approximately 2.04 liters/min/sq m (0.05
gpm/sq ft) filter surface area. Pressure filters can also be used
directly for neutralized wastes containing from 300 to 500 mg/1
suspended solids at design rates of 4.88 to 6.52 liters/min/sq m (0.12
to 0.16 gpm/sq ft) and still maintain a low solids content in the
filtrate.
Filter cakes can easily be collected in solid waste containers and
hauled away to land fills. There may be situations, however, where the
metal in the filter cake could be redissolved if it came into contact
with acidic water. Careful consideration should be given to where such
a material is dumped.
Several companies have developed proprietary chemical fixation
processes which are being used to solidify sludges prior to land
disposal. In contrast to filtration, the amount of dried sludge to be
hauled away is increased. Claims are that the process produces
insoluble metal ions so that in leaching tests only a fraction of a part
per million is found in s61ution. However, much information is lacking
on the long term behavior of the "fixed" product, and potential leachate
problems which might arise. The leachate test data and historical
information to date indicate that the process has been successfully
applied in the disposal of polyvalent metal ions and it apparently does
have advantages in producing easier to handle materials and in
eliminating free water. Utilization of the chemical fixation process is
69
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felt to be an improvement over nu,ny of the environmentally unacceptable
disposal methods now in common usage by industry. Nevertheless,
chemically fixed wastes should be regarded as easier - to - handle
equivalents of the raw wastes and the same precautions and requirements
required for proper landfilling of raw waste sludges should be applied.
The possibility of recovering metal values from sludges containing
copper, nickel, chrome, and zinc has been considered(12) but such a
system appears to be uneconomic under present circumstances. It may be
profitable to recover metal values if 900 to 2300 kg (2,000 to 5,000
pounds) of dried sludge solids can be processed per day with a
thoroughly developed process. To attain this capacity would almost
certainly require that sludge from a large number of plants be brought
to a central processing station. The recovery would be simpler if the
metallic precipitates were segregated, but segregation would require
extensive modifications, investment, and increased operating expense for
precipitation and clarification. Laboratory experiments showed that
zinc could be leached from sludge with caustic after which copper,
nickel, and chromium were effectively dissolved with mineral acids.
Ammonium carbonate dissolved copper and nickel but not trivalent
chromium, thus giving a method of separation. Electrowinning of the
nickel and copper appeared to be a feasible method of recovering these
metals.
Practical-_Operating_Systems. Relatively few plating installations have
installed filters, although the problems of disposing of unfiltered
sludge should provide an impetus for use of more filters in the future.
Plant 12-8 has a large rotary filter in routine operation, and the
practicality of this unit has been well established. The Chemfix system
is in use at several plants.
Demonstratign_Status. Centrifuges are used for dewatering sludge in
the new waste treatment facility at Plant 11-22.
Cy_ani.de Oxidation. Cyanide in wastewaters is commonly destroyed by
oxidation with chlorine or hypochlorite prior to precipitation of the
metal hydroxides. The method is simple, effective, and economically
feasible even for small volume installations. A comprehensive study of
the method was made by Dodge and Zabban(10-13), the results of which
have been used to work out the practical processes. The following are
proposed reactions for chlorine oxidation:
(1) NaCN + C12>CNC1 + NaCl
70
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(2) CNCl « 2NaOH-»-NaCNO + NaCl + H2O
(3) 2NaCNO + 3C12 * 4NaOH-*-N2 + 2CO2 + 6NaCl * 2H2O.
Reaction (2) goes rapidly at pH 11.5, under which conditions, build
up of the toxic gas CNCl by Reaction (1) is avoided. Treatment of
dilute rather than concentrated solutions also minimizes its formation.
Oxidation to cyanate (NaCNO) is completed in 5 minutes or less.
Reaction (3) goes more slowly, requiring an hour in the preferred pH
range of 7.5 to 9.0, and a longer time at higher pH. After the
conversion to nitrogen and carbon dioxide, excess chlorine is destroyed
with sulfite or thiosulfate.
Sodium hypochlorite may be used in place of chlorine. Recent
technical innovations in electrochemical hypochlorite generators for on-
site use (17) raise the possibility of controlling the addition of
hypochlorite to the cyanide solution by controlling the current to the
electrochemical generator, using sodium chloride as the feed material.
Concentrated solutions, such as contaminated or spent baths, cyanide
dips, stripping solutions, and highly concentrated rinses, are normally
fed at a slow rate into a dilute cyanide stream and treated with
chlorine. However, concentrated solutions may also be destroyed by
electrolysis with conventional equipment available in the plating
shop.(18) In normal industrial practice the process is operated
batchwise, whereas the optimum system, from an operating standpoint,
would be a cascaded one in which successively larger tanks are operated
at successively lower current densities. This is the more effecient
system. In addition to the oxidation of cyanide at the anode, valuable
metal can be recovered at the cathode. The process becomes very
inefficient when the cyanide concentration reaches 10 ppm, but at this
point the solution can be fed into the process stream for chemical
destruction of cyanide to bring the concentration to the desired level.
The addition of chloride ions to the concentrated solutions, followed by
electrolysis, produces chlorine or hypochlorite in solution, which can
then destroy the cyanide to the same low levels as obtained by direct
chlorination. With the provision that chlorine or hypochlorite be
formed at a rate equal to the concentration of cyanide passing through
the system, the process can be operated continuously:
2NaCN + 2NaOCl^. 2NaCNO + 2NaCl
2NaCN + SNaOCl + H2O>- 2CO2+ N2 + 2NaOH + SNaCl.
71
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The Cynox process, based on the above principles, produces 1 kg of
active chlorine per 5,5 KwH.(19) Equipment needs are the same with the
exception that the tanks must be lined and graphite or platimized anodes
must be used.
Polysulfide-cyanide strip solutions containing copper and nickel do
not decompose as readily and as completely as do plating solutions.
Although the cyanide content can be reduced from 75,000 to 1000 nv.i/1
during two weeks of electrolysis anode scaling prevents further cyanide
decomposition unless anodes are replaced or freed from scale. Minimum
cyanide concentration attainable is about 10 mg/1 after which the
solution can be treated chemically.
The electrolysis of dilute cyanide solution can be improved by
increasing the electrode area. Area can be increased by filling the
space between flat electrodes with carbonaceous particles. (20) The
carbon particles accelerate the destruction process 1000 times, but flow
rate through the unit must be carefully adjusted, if used on a
continuous basis to achieve complete destruction (Plant 30-1).
Although cyanide can be destroyed by oxygen or air under suitable
conditions(21,22), cyanide concentrations in the effluent are reported
to be 1.3 to 2.2 mg/1, which is high for discharge to sewers or streams.
A catalytic oxidation unit using copper cyanide as a catalyst and
activated carbon as the reactive surface has been described for
oxidizing cyanide with air or oxygen (23) , and at least two units were
put in operation. The most recent information on these units is that
they are not operating and that at present the units are not being sold.
Ozone will oxidize cyanide (to cyanate) to below detectable limits
independent of the starting concentration or of the complex form of the
cyanide(24,25,26). The reaction can be completed even with the very
stable iron complexes if heat or ultraviolet light is used in conjunc-
tion with the ozone. The potential advantages of ozone oxidation are
enhanced by the efficiency and reliability of modern ozone generators,
and development work is continuing.
A method employing thermal decomposition for cyanide destruction has
been recently announced.(27) Cyanide solution is heated to 160 to 200 C
under pressure for 5 to 10 minutes. Ammonia and formate salts are
formed. No information is given on the final cyanide concentration.
One process destroys cyanides of
sodium, potassium, zinc, and cadmium and also precipitates zinc and
cadmium. The process is discussed later in this section,,
Precipitation of cyanide as ferrocyanide is restricted to
concentrated wastes. Ferrocyanide maybe less toxic than cyanide, but is
converted back to cyanide in sunlight. Treatment is accomplished by
72
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adding an amount in excess of stoichiometry (2.3 kg of Feso4 per kg of
cyanide). Large amounts of sludge are produced which add to the
pollution load. Complex cyanides do not break down readily and the
reaction stops when a concentration of 10 mg/1 of cyanide is reached.
No benefits can be foreseen in terms of reducing waste volume and
concentration.
Cyanide is also destroyed by reaction with polysulfides. Reasonable
reaction rates are obtained only if the solution is boiled. Since the
reaction does not destroy all of the cyanide further treatment is
necessary.
Reduction^of Hexayalent^Chromium. Hexavalent chromium (CrVI) is usually
reduced to trivalent chromium at a pH of 2 to 3 with sulfur dioxide
(SO2), sodium bisulfite, other sulfite-containing compounds, or ferrous
sulfate. The reduction makes possible the removal of chromium as the
trivalent hydroxide which precipitates under alkaline conditions.
Typical reactions for SO2 reduction are as follows:
SO 2 + H2O -*- H2SO3
2H2CnO4 + 3H2SO3 9- Cr2 (SO4) 3 + 5H2O.
Representative reactions for reduction of hexavalent chromium under
acidic conditions using sulfite chemicals instead of SO2 are shown
below:
(a) Using sodium metabisulfite with sulfuric acid:
HH2Cr04 + 3Na2S2O5 + 3H2SOi>-3Na2SO4 + 2Cr2 (S04) 3
+ 7H2O
(b) Using sodium bisulfite with sulfuric acid:
4H2CrOH + 6NaHSO3 + 3H2SO4 >-3Na2SOt» + 2Cr2 (SO4) 3
+ 10H20
(c) Using sodium sulfite with sulfuric acid:
2H2CrOU + 3Na2S03 + 3H2SO4»^3Na2SOU + Cr2(SOU)3
+ 5H2O.
73
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Reduction using sulfur dioxide is the most widely used method,
especially with larger installations. The overall reduction is readily
controlled by" automatic pH and ORP (oxidation-reduction potential)
instruments. Treatment can be carried out on either a continuous or
batch basis.
Hexavalent chromium can also be reduced to trivalent chromium in an
alkaline environment using sodium hydrosulfite as follows:
2H2Cr04 * 3Na S0 + 6NaOH-* 6NaS0 + 2Cr
As indicated in the above equation, the chromium is both reduced and
precipitated in this one-step operation. Results similar to those
obtained with sodium hydrosulfite can be achieved using hydrazine under
alkaline conditions.
2H2Cr04 + 3N2H2 Na2COj 2Cr (OH) 3 + 3N2 + 2H20.
Sodium hydrosulfite or hydrazine are frequently employed in the
precipitation step of the integrated system to insure the complete
reduction of any hexavalent chromium tha might have been brought over
from the prior reduction step employing sulfur dioxide or sodium
bisulfite. Where ferrous sulfate is readily available (e., g., from steel
pickling operations), it can be used for reduction of hexavalent
chromium; the reaction is as follows:
2Cr03 + 6FeSo4 7H2O + 6H2SO4 »~ 3Fe2 (SO4) 3 + Cr2(804)3
+ 48H20.
Cr+6may be reduced at a pH as high as 8.5 with a proprietary
compound.(28) It is not necessary to segregate chrornate-containing
wastewaters from the acid-alkali stream, and the use of acid to lower pH
is eliminated in this case. Precipitation of chromic hydroxide occurs
simultaneously in this case with the reduction.
Cr+6 ions may be reduced electrochemically.(26) concentration of 100
mg/1 was reduced to less than 1 mg/1 with a power consumption of 1.2
kwh/1,000 liters. The carbon bed electrolytic process previously
described for cyanide (24) may also be used for chromate reduction in
acid solution and Plant 30-1 has achieved a Cr+6 concentration of .01
mg/1 using this method. Electrolysis may also be used to regenerate a
reducing agent. A process(27) has been described involving the
reduction of Fe(III) to Fe(II) electrochemically and the reduction of
74
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Cr (VI) by Fe(II). The method should be capable of achieving low Cr (VI)
levels.
The simultaneous reduction of Cr+6 and oxidative destruction of
cyanide finds limited application in waste-treatment practice. The
reaction requires mixing of Cr+6 and CM- in ratios between 2 and 3 using
Cu+2 as a catalyst in concentrations of 50 to 100 mg/1. The catalyst
introduces additional pollutant into the waste stream. Reaction rates
are generally slow, requiring from 6 to 24 hours for cyanide
concentrations ranging from 2,000 to less than 50 mg/1 at a solution pH
of 5. The slowness of the reaction and the high initial concentrations
of reactants required make the method unsuitable for treating rinse
waters. Its use is limited to batch treatment of concentrated
solutions. No benefits are obtained in terms of water volume and
pollution reduction. Destruction is not as complete as obtained by the
more common chemical methods.
Practical Operating Systems
Chemical treatment is used by every plant contacted during the
effluent guidelines study with the exception of those that are allowed
to discharge plating waste effluents into sewers or streams without
treatment.
The effectiveness of chemical treatment techniques depends on the
nature of the pollutant, the nature and concentration of interfering
ions, the procedure of adding the appropriate amount of chemicals (or
adjusting pH) , the
reaction time and temperature and the achievement of effective
separation of precipitated solids. The concentration of an individual
pollutant in the solution being treated has no effect on its final
concentration after treatment. On the other hand, effective removal of
heavy metal pollutants is inhibited by some types of chelating ions such
as tartrate or ethylene diamine tetracetate ions.
75
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The concentrations of heavy metals and cyanide achievable by the
chemical techniques employed for treating waste from copper, nickel,
chromium, and zinc electroplating and zinc chromating processes are
summarized in Table 19. concentrations lower than those listed as
maximum in Table 19 were reported by companies using all three
(continuous, batch, and integrated) treating systems. The data show
that the soluble concentration levels achieved in practice are near
those that would be expected based on solubility data discussed
previously.
Higher-than-normal concentrations of copper, nickel, chromium, and
zinc, when they occur, are usually caused by: (1) inaccurate pH
adjustment (sometimes due to faulty instrument calibration) ; (2)
insufficient reaction time: or (3) excessive concentrations of chelating
agents that complex the metal ions and prevent their reaction with
hydroxyl ions to form the insoluble metal hydrates. The causes for
higher -than-normal concentrations of cyanide are similar, but another
important factor must be added to the list of potential causes for
incomplete cyanide destruction. In this case, sodium hydroxide and
chlorine must be added conand provide sufficient reagent to complete the
reaction, which is normally monitored by an oxidation-reduction-
potential (ORP) recorder-controller. The maintenance of this system is
a critical factor affecting the effectiveness of chemical oxidation.
Solids. The suspended solids discharged after treatment and
clarification sometimes contribute more copper, chromium, and zinc than
the soluble metal concentrations, as shown in Table 19. For example,
the copper contribution from the total suspended solids determined for
four plants engaged in copper, nickel, chromium, and zinc electroplating
was in the range of 0.02 to 0.76 mg/1. Zinc contributions from
suspended solids ranged from 0.03 to 0.80 mg/1. The total copper,
nickel, chromium, and zinc content in suspended solids was equivalent to
as much as 2.04 mg/1, in comparison with a maximum of L.45 mg/1 for
these metals in the soluble form.
The concentration of total suspended solids in the endof-pipe
discharge from typical chemical treatment operations ranged from 20 to
24 mg/1. Maintaining conditions so as not to exceed these amounts
requires (1) a properly designed settling and/or clarifying facility,
76
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(2) effective use of flocculating agents, (3) careful removal of settled
solids, and (U) sufficient retention time for settling. Of course,
minimum retention time depends on the facility size and In practice,
this time ranges from about 2 to 8 hours for plants that are able to
reduce suspended solids to about 25 mg/1. Even so, this achievement
requires very good control of feeding flocculating agents.
Precipitation of Metal Sulfides
The sul fides of copper, nickel, and zinc are much less
soluble than their corresponding hydroxides. In neutral solution the
theoretical concentration of metal ions should be reduced by sulfide
precipitation as follows:
Copper 10~18 mg/1; Nickel 10"8 mg/1; Zinc 10~7 mg/1
Precipitation using hydrogen sulfide or soluble sulfides (Na2s) involves
toxicity problems with the excess reagent used. However, a system has
recently been developed that provides for sulfide precipitation without
the toxicity problems. (31) It should be applicable to treatment of
effluent from electroplating operations.
Process PrinciBles_and_Eguigmerit
Ferrous sulfide, which has a higher solubility than the sulfides of
the metals to be precipitated is used as the
precipitating reagent. However, the solubility of ferrous sulfide is
still so small (10-5 mg/1 of sulfide ion) that the toxicity problem is
eliminated. Freshly precipitated ferrous sulfide is most reactive and
is obtained by adding an excess of a soluble sulfide for precipitating
the metals to be removed from the effluent and then adding sufficient
soluble ferrous salt to precipitate all excess sulfide ion. The pH is
normally adjusted to the range of 7 to 8, prior to precipitation.
Hexavalent chromium that may be present is reduced to Cr(III) by the
ferrous iron and immediately precipitated as the hydroxide. Therefore,
no extra precipitation steps are necessary to remove the chromium. If
the extra ferrous ions in solution are considered undesirable they may
be oxidized to Fe (III) which will precipitate as the hydroxide.
However, removal of iron would not be possible until after the sulfide
precipitates had been separated from the liquid. In principle, it
should be possible to precipitate metallic sulfides from metal ion
complexes that are not amenable to chemical treatment by hydroxide
precipitation, due to the lower solubilities of the sulfides. It has
been demonstrated that copper can be effectively precipitated from the
ammonia complex.
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78
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Practical Operating Systems
No practical system is in operation.
Demonstration Statug
The process described is still being developed, and it is
anticipated that a demonstration plant will be built and operated in the
near future.
Combined Metal Precipitation and Cyanide Destruction
Applicability.. This process (32) is applicable to zinc and
cadmium cyanide solutions. The metal hydroxide is precipitated and
cyanide is decomposed. Applicability depends upon deciding whether the
products of cyanide decomposition are suitable for discharge or not.
The effluent is considered suitable for discharge to sewers
in some states and may be acceptable in certain areas for discharge to
streams. A modification of this process may be applicable to copper
cyanide.
Process_Princip_les_and_Eguip_inent
Cyanide in zinc and cadmium plating baths is destroyed by a mixture
of formalin and hydrogen peroxide according to the formula:
CN- + HCOH + H2O2 + H20 CNO- + NH4
+ H2C(OH)COHN2 glycolic acid amide.
The metal hydroxide is also precipitated. The hydrogen peroxide is
contained in the reagent (41%) which contains stabilizers and
additives to promote the reactions and help in settling the metal
hydroxide precipitate. The process may be carried out on a batch or
continuous basis, and is particularly convenient for the small shop.
Figure 8 shows the apparatus for batch treatment. To be economical the
rinse water should contain at least 55 ppm of cyanide, and sufficient
counter-flow rinses are normally installed to assure a sufficient
cyanide concentration. The typical treated effluent contains 0.1 mg/1
of cyanide and 1 to 2 mg/1 of zinc. Table 20 shows an analysis of the
products for decomposing 794 ppm of cyanide.
79
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FIGURE 8. BATCH TREATMENT OF CYANIDE RINSE WATERS BY
COMBINED METAL PRECIPITATION AND CYANIDE
DESTRUCTION
80
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TABLE 20. DECOMPOSITION PRODUCTS OF CYANIDE IN RINSE
WATER(1) FROM A CYANIDE ZINC ELECTROPLATING
OPERATION AFTER TREATMENT WITH
PEROXYGEN COMPOUND
Products Formed
by Treatment
Cyanate
Ammonia (free)
Dissolved
Volatilized
Combined Ammonia
Calc'd as NH3
Calti'd as glycolic
acid amide
Amount Formed
Actual
ppm
351
57
32
95
419
Cyanide Equivalent
ppm percent
265
164
91
274
33
21
11
35
794
100
* 'Analysis of water before treatment:
Cyanide 794 ppm
Cyanate^
Ammonia^
336 ppm
41 ppm.
Cyanide calculated as NaCN, cyanate as NaOCN, and
ammonia as NH
3*
81
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Practical Operating Sy_stems_. This process is being used in approxi-
mately 30 installations.
Water^cgnservation Through Control Teghnology
The volume of effluent is reduced if water is conserved during
rinsing operations. The solubility limit of effluent constituents is
essentially constant, so that a reduction in the effluent volume
accomplishes a reduction in the amount of effluent constituents
discharged. Water conservation can be accomplished by in-plant process
modifications requiring little capital or new equipment, materials
substitutions, and good housekeeping practice. Further water
conservation is obtained by installing counterflow rinse tanks and ion-
exchange, evaporative recovery, or reverse osmosis systems. Other
systems that may accomplish water conservation are freezing, electro-
dialysis, electrolytic stripping, carbon adsorption, and liquid-liquid
extraction.
Process Modifications
Wastes from electroplating operations can sometimes by reduced by
the following changes in electroplating processes:
(1) Elimination of copper prior to nickel and chromium plating,
especially for plating on steel.
(2) Elimination of copper by increasing the thickness of nickel.
(3) Substitution of a nickel strike for a copper strike and
replacing the highrate copper cyanide solution with a copper sulfate
bath.
(4) Substitution of low-concentration electroplating solutions for
highconcentration baths.
Metals remaining in solution after chemical treatment of the
effluent from a plant plating decorative copper, nickel, and chromium
can be reduced in amount by eliminating the copper. Some steel products
can be plated directly with nickel and chromium, especially when the
quality of the steel surface is improved. A better grade of steel or a
change in mechanical finishing methods to reduce surface roughness can
sometimes justify the elimination of copper without sacrificing high
specularity. To maintain good corrosion resistance on steel products
and eliminate copper, it may be necessary to increase the thickness of
the nickel or install duplex nickel in place of bright nickel, which is
much better than a single layer of bright nickel for providing maximum
82
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corrosion resistance. To maintain a high degree of specularity in the
absence of a copper plate, leveling nickel is recommended.
The substitution of a nickel strike for a copper strike has been
adopted in several plants plating nickel and chromium on steel. A
copper sulfate solution is then utilized after nickel striking in some
cases. This change avoids copper cyanide baths and the attendant need
for oxidizing cyanide in the treatment system and has been particularly
successful for steel products.
f Substitution of low-concentration electroplating solutions for high-
concentration baths has been adopted in recent years, principally for
reducing the cost of chemicals used for cyanide destruction. The dilute
solutions require less water for rinsing when electroplated parts are
transferred to rinse tanks. Assuming a 50 percent reduction in total
dissolved solids in the plating solution and two rinse tanks in series,
a 30 percent reduction in rinse water requirements is achieved.
Wastewater constituents requiring treatment are reduced by the same
amount. Adverse effects in terms of lower efficiency and reduced
productivity per unit facility may be encountered when dilution is
adopted to conserve rinse water and reduce wastewater constituents
requiring treatment, unless other factors affecting plating rate are
modified to adjust for the effects of dilution. Thus, dilution should
not be adopted before a complete analysis is made of all pertinent
factors.
The advent of effluent limitations is expected to encourage research
and development on other processes that will eliminate or reduce water
waste. A dry process for applying chromate coatings, which is currently
being developed, may prove useful for such a purpose, for example.
Chemical vapor deposition processes partially developed a few years ago
may be revived for plating hard chromium.
Materials Substitutions
Noncyanide solutions, which have been developed for copper and zinc
in place of cyanide solutions, reduce the costs of treatment by
eliminating cyanide destruction, but do not eliminate treatment to
precipitate and separate the metals. The chelating agents employed in
some noncyanide baths to keep the metal in soluble form are precipitated
when rinse water waste is treated with lime to precipitate the metals,
but other agents such as ethylene diamine tetraacetic acid inhibit the
precipitation of zinc and contribute organic matter to the treated water
waste. Thus, the applicability of the noncyanide solutions as
replacements for cyanide baths must be considered carefully in the light
of the effluent limitation guidelines recommended in this document.
Trivalent chromium baths have recently been introduced to the
electroplating industry. They eliminate the need for sulfur dioxide
83
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reduction of wastewater associated with chromium plating. The trivalent
chromium baths appear to have other advantages for decorative plating
such as better throwing power, current efficiency and plating rate. The
dark color of the deposits is cited as a disadvantage by some
purchasers, however. Nevertheless, this process modification may
ultimately prove to be significant for reducing waste treatment costs.
No details have been released on the treatment required for minimizing
the soluble chromium concentration in treated effluent, however.
Good Housekeeping Practices
Good housekeeping practices that reduce the waste generated in
electroplating facilities include the following:
(1) Maintain racks and rack coatings to prevent the transfer of
chemicals from one operation to another. (Loose rack coatings are
noteworthy as an example of poor practice.)
(2) Avoid overcrowding parts on a rack, which inhibits drainage when
parts are removed from a process solution. (3) Plug all floor exits to
the sewer and contain spills in segregated curbed areas or trenches,
which can be drained to direct the spills to rinse water effluent with
the same chemicals.
(3) Plug all floor exits to the sewer and contain spills in
segregated curbed areas or trenches, which can be drained to
direct the spills to rinse water effluent with the same
chemicals.
(H) Wash all filters, pumps and other auxiliary equipment in curbed
areas or trenches, which can be drained to direct the wash water to a
compatible holding tank or rinse water stream.
(5) Install anti-syphon devices on all inlet water lines to process
tanks.
(6) Inspect and maintain heating and cooling coils to avoid leaks.
(7) Inspect and maintain all piping installed for wastewater flow,
including piping from fume scrubbers.
Water Conservation by Reducing Dragout
Dragout. Dragout is defined as solution on the workpiece carried beyond
the edge of the plating tank. The dragout of concentrated solution from
the plating tank can vary over a wide range depending on the shape
-------
factor of the part. A value of 16.3 liters/1000 sq m (0.4 gal/1000 sq
ft)(33) is considered a minimum for vertical parts that are well
drained. The practical range for parts of various shapes that are well
drained is about 40 to 400 liters/sq m (1 to 10 gal/1000 sq ft).
Dragout Reduction. Water used for rinsing can be conserved by (1)
improving the racking procedure to improve drainage from surfaces over
the process tank, prior to transfer to the subsequent rinse tank, (2)
increasing the drainage time over the process tank, (3) reducing the
viscosity of the process solution by diluting it or increasing its
temperature, (4) adding a wetting agent to the process solution to
reduce surface tension, (5) installing fog nozzles above the process
tank to return a part of the solution remaining on work surfaces to the
process solution, and (6) installing a drip-save (reclaim) tank between
the process and rinse stations to collect dragout that is pumped back to
the process solution. A mixture of air and water is utilized in one
version of a fog nozzle claimed to be especially effective for removing
most of the solution from surfaces lifted above process tanks. With the
above techniques, the water needed for rinsing can be reduced as much as
50 to 60 percent. Detailed comments on these dragout reduction
techniques appear in Reference 34.
Reduction of dragout with the above methods is not without problems.
By returning chemicals to the plating tank, impurities tend to build up
in the plating solution. Therefore, purification systems, such as ion
exchange, batch-chemical treatments, and/or electrolytic purification
are required to control impurities. The purification systems create
some effluents which must be treated prior to end-of-pipe discharge.
Water Conservation During Rinsing
When effective chemical treatment exists, reduction in pollutional
load can be accomplished by reducing the water use in the facility. The
principal water use is for rinsing. Use of only that water needed for
effective rinsing based on dissolved solids would represent good
practice.
Water conservation procedures that are used after processed work is
transferred to a rinse tank include (1) adding a wetting agent to the
rinse water, (2) installing air or ultrasonic agitation and (3)
installing counterflow rinses whereby water exiting the last tank in the
rinsing operation becomes feed water for the preceding rinse. With two
counterflow rinses, water consumption is reduced 96 percent in
comparison with a single rinse, with equivalent rinsing effectiveness.
Use of conductivity meters in the final rinse provides automatic control
of water use according to need. Rinse water flow is shut off
85
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automatically when no work is being processed. Excessive use of water
can also be avoided by use of flow restrictors in the water feed lines.
Although multitank, counterflow rinsing imposes capital investment
costs for tanks, pumps, and floor space, these costs are compensated by
a savings in water (and sewer) charges. Further incentive is provided
when regulatory agencies reguire pollutional control. When
end-of-process chemical treatment is used, design of wastetreatment
facilities usually indicates the economic advantage of reducing rinse-
water flow by installing two or more counterflow rinses.
Because waste-treatment facilities are usually overdesigned to
handle future expansion in production, there is a tendency to use the
water flow capacity of the treatment facility whether or not it is
needed for effective rinsing. Furthermore, rinse water flows set by an
orifice are not always turned off when plating production is shut down.
In the case of an overdesigned installation, it is probably more
economical to reduce rinse water usage by use of good rinsing practice
than to increase water-treatment facilities in the event of an increase
in production.
Rinsing can be carried out beyond the point consistent with good
practice, even though there is an economic incentive to saive water. The
result is unnecessary pollution. Typical concentration levels permitted
in the rinses following various process tanks, should not be decreased
unless definite quality problems can be associated with the dissolved
solids concentrations listed below for representcitive rinsing
systems:(35)
Max Dissolved Solids
Process in Final Rinse,, mg/1
Alkaline cleaners 750
Acid cleaners, dips 750
Cyanide plating 37
Copper plating 37
Chromium plating 15
Nickel plating 37
Chromium bright dip 15
Chromate passivating 350-750
A Watts-type plating bath typically contains 270,000 mg/1 of total
dissolved solids. Obtaining 37 mg/1 in the final rinse requires 27,600
liters (7300 gallons) of rinse water if a single rinse tank is used, in
order to dilute 3.78 liters (1 gallon) of a Watts-type plating solution
containing 270 g/1 of dissolved solids. The same degree of dilution in
a final rinse tank may be obtained with less water by use of series and
86
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counterflow arrangement of two or more rinse tanks. If the tanks are
arranged in series and fresh water is fed in parallel to each tank in
equal volume, the ratio, r of rinse water to dragout is:
r = (CO/CF)n
where Co = concentration in the process solution CF = concentration in
last rinse tank and n = number of rinse tanks.
If the tanks are arranged in the same way but flow proceeds from the
last rinse tank to the first rinse tank (counterflow),
1
r = (CO/CF)
By feeding water to counterflow tanks instead of in series, the
reduction in water varies n-fold. Values of n calculated for several
rinsing combinations, using the Co and CF valuesgiven above for a nickel
bath are as follows:
Rinse_Combination Rinse^Ratio^ r
Single rinse 7300
Two rinses, parallel feed 171
Three rinses, parallel feed 58.3
Two rinses, counterflow feed 85.5
Three rinses, counterflow feed 19.5
There is a significant reduction in water use by addition of a
second rinse tank, and at least two rinse tanks can be considered normal
practice. These should best be fed in counterflow. Counterflow rinse
tanks increase the concentration of a metal or another constituent in
the first rinse tank following the plating or process bath. The water
in the first rinse tank can be used to supply make-up water for the
plating bath. As the concentration in the first rinse tank increases,
more of the drag-out from the plating bath can be returned to the bath
in the make-up water, and less will require treatment and/or disposal.
Therefore, the addition of countercurrent rinse tanks can decrease both
the volume of water to be treated and the amount of dissolved metal that
must be removed, at least in some cases.
The rate of evaporation from the plating bath is a factor in
determining how much make-up water must be added. Operating a bath at a
87
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higher temperature will allow more of the drag- out to be returned to the
bath because of the higher rate of evaporation. However, the
temperature at which a bath may be operated is sometimes limited because
of the decomposition of bath components. Progress has been made in
developing bath components that allow higher bath temperatures to be
used. For example, brighteners for zinc cyanide baths have been
developed (36) which allow bath operation at 50 C (120 F) as compared to
32 C (90 F) for baths using older aldehyde-type brighteners. Thus, the
new brighteners permit the return of more of the dragout to the plating
bath and a lessened load on the waste treatment system, in addition to
what other processing advantages they may offer.
Water Conservation by Ion Exchange
Ion exchange is currently a practical commercially
accepted method for the in-process treatment of (1) raw water, (2)
plating baths, and (3) rinse waters. Raw water is treated to provide
de-ionized water for both makeup and critical final rinsing operations.
Plating baths are treated to remove impurities, i.e., removal of nickel
ions from a chromic acid bath with a cation exchange resin. Rinse
waters are treated to provide water that can be returned to the process
solution. The concentrated regenerant can be chemically treated more
easily than the original volume of rinse water and in some cases the
chemicals can be recovered and returned to the bath. The in-process
treatment of chromium and nickel plating effluents by ion-exchange
techniques are the more economically attractive treatment operations
currently being carried out. Ion exchange also is beginning to find
increased use in combination with evaporative and reverse-osmosis
systems for the processing of electroplating rinse waters.
Advantages and __ Lim itat i oji s . Some advantages of ion exchange for
treatment of plating effluents are as follows:
(1) Ion exchange is an economically attractive method for the
removal of small amounts of metallic impurities from rinse
waters and/or the concentration for recovery of expensive
plating chemicals.
(2) Ion exchange permits the recirculation of a high-quality water
for reuse in the rinsing operations, thus saving on water
consumption.
(3) Ion exchange concentrates plating bath chemicals for easier
handling or treatment or subsequent recovery or disposal
operations.
88
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Some limitations or disadvantages of ion exchange for treatment of
plating effluents follow:
(1) The limited capacity of ion-exchange systems means that
relatively large installations are necessary to provide the exchange
capability needed between regeneration cycles.
(2) Ion-exchange systems require periodic regeneration with
expenditures for regenerant chemicals. Unless regeneration is carried
out systematically, leakage of undesirable components through the resin
bed may occur. In addition, the usual treatment methods must be
employed to dispose of the regenerated materials.
(3) Cyanide generally tends to deteriorate the resins, so that
processing of cyanide effluents (except for very dilute solutions) does
not appear practical at the present time.
(4) Resins slowly deteriorate with use and the products of
deterioration can contaminate the water.
Process_Princi.2les_and_Egui2S3ent. Ion exchange involves a reversible
interchange of ions between a solid phase and a liquid phase. There is
no permanent or substantial change in the structure of the solid resin
particles. The capacity of an ion-exchange material is equal to the
number of fixed ionic sites that can enter into an ion-exchange
reaction, and is usually expressed as milliequivalents per gram of
substance. Ion-exchange resins can perform several different operations
in the processing of wastewater, including:
(1) Transformation of ionic species
(2) Removal of ions
(3) Concentration of ions.
The performance of some of these functions is illustrated in Figure
9, which is a generalized schematic presentation of the application of
ion exchange to treatment of electroplating effluents.(37,38) In
practice, the solutions to be treated by ion exchange are generally
filtered to remove solids such as precipitated metals, soaps, etc.,
which could mechanically clog the resin bed. Oils, organic wetting
agents, brighteners, etc., which might foul the resins, are removed by
passage through carbon filters.
During processing, the granular ion-exchange resin in the column
exchanges one of its ions for one of those in the rinse water or other
solution being treated. This process continues until the solution being
89
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Cu-Ni-Cr
manual hoist
line
1
-^
y
Counter-
flow
rinses
Well
water
as needp'*
15 gpm
c
1
^
1
Cation
resin
Stevens
Ni-Cr
automatic
line
I
Counter-
flow
rinses
10 gpm
9 gpm
L '
\
Anion
resin
Hard-
chromium
plating
i
r
Counter-
flow
rinses
Cation
resin
r
Anion
resin
Deionized water
FIGURE 10. SCHEMATIC PRESENTATION OF ION-EXCHANGE OPERATION
AT PLANT 11-8
-------
treated exhausts the resin. When this happens, solution flow is
transferred to another column with fresh resin. Meanwhile, the
exhausted resin is regenerated by another chemical which replaces the
ions given up in the ion-exchange operation, thus converting the resin
back to its original composition. With a four-column installation
consisting of two parallel dual-bed units, as shown in Figure 9, the
ion-exchange process can be applied continuously by utilizing the
regenerated units while the exhausted units are being regenerated.
Practical Operating Systems. Figure 10 shows a schematic drawing of the
ion-exchange system used in Plant 11-7 to handle a flow ranging from
2,100 to 4,000 gph of chromium rinse water containing 30 to 250 ppm of
hexavalent chromium. The unit saves at least 150,000 liters/day (40,000
gpd) and provides a source of deionized water throughout the plant for
preparing plating solutions where good quality water is required. The
pure water recycled to the chromium rinse tanks is useful for avoiding
spotting of chromium-plated parts. Regenerated solution from the anion-
exchange unit is treated by reducing the chromium to Cr3+ and
precipitating it. Regenerated solution from the cation-exchange unit is
combined with the acid-alkali stream for treatment.
Cation-exchange resins are used widely throughout the industry for
removing nickel, trivalent chromium, and other impurities from chromium
plating baths. Cyanide may be absorbed on ion-exchange resins, but
there is danger of leakage of cyanide through the system. An improved
threebed system consists of strongly acidic, weakly basic, and strongly
basic layers. (39) In this system the weak base resin provides a high
capacity for cyanide adsorption and the strong base resin provides a
back up to take care of cyanide leakage.
Demonstratigr^Status^ An ion-exchange system utilizing a short 30
minute cycle, including a 3 to 4 minute back wash, to recover chronic
acid from rinse water has been in operation over a year. (40) The resin
undergoes very little deterioration since the chromic acid is not deeply
absorbed into the resin during such a short cycle.
Ion Exchange for Mixed Effluent. An installation for handling 6,300 gph
of wastewater containing nickel, chromates, chlorides and sulfates was
installed for recovering 96 percent of the water. (32) The cost saving
in water was more than three times the cost of operation.
Water Conservation by Evaporative Recovery
. When rinse water from one type of bath is distilled in
an evaporative unit, the concentrate may be returned to the plating bath
-------
and the distillate to the corresponding rinse tank, which is useful for
closing the loop on a single plating operation. The economics of
distillation, from the standpoint of either investment or operating
costs imposes a constraint on the size range of distillation equipment.
Units with a capacity of the order of 300 gph are used in practice.
Such a low rate of flow of rinse water is achieved in many plating
operations only by the use of at least three countercurrent rinses,
which by itself reduces the wastewater. Evaporative recovery units for
all of the rinse cycles would reduce the effluent to zero. So far,
recovery units have been installed on rinse tanks following plating
baths in order to recover plating chemicals and return them to the bath
and thereby reduce plating costs. The units have not been installed on
cleaner or acid dip lines because the cost of chemicals is not
sufficient to make recovery worthwhile.
Evaporation is a firmly established industrial procedure for
recovering plating chemicals and water from plating waste effluents.
Commercial units for handling zinc, copper, nickel, chromium, and other
metal plating baths have been operating successfully and economically
for periods of one to 10 years or longer. Packaged units for in-plant
treatment of plating wastes are available from many manufacturers.
Advantages and Limitations. The following are some of the advantages of
using evaporation for handling of plating waste effluents:
(1) Recovers expensive plating chemicals, which were either lost by
discharge to a sewer or stream or which had to be treated or
destroyed prior to disposal; chemicals concentrated to plating
strength can be returned to the plating tank.
(2) Recovers distilled water for reuse in the rinse operations, thus
lowering water and sewage costs.
(3) Eliminates or greatly minimizes the amount of sludge formed
during chemical treatment and eliminates or reduces the amount
requiring disposal by hauling or lagooning.
The use of vacuum allows evaporation to occur at relatively low
temperatures (e.g., 110 F) so that destruction of cyanides or other
heatsensitive materials is lessened.
(5) The technology of evaporators (conventional and vapor
recompression units) is firmly established, so their capabilities
are well known and their performances should be readily predictable
and adaptable to plating effluent handling.
Some of the limitations or disadvantages of evaporative recovery
systems are given below:
93
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(1) The rinse water saving [e.g., 1100 1/hr (300 gph) ] is rather
small, and by itself does not significantly reduce the rinse water load
on the
chemical treatment plant.
(2) Evaporative units have relatively high capital and operating
costs, especially for the vacuum units. Steam and coolant water
are required.
(3) The evaporative units are fairly complex and require highly
trained personnel to operate and maintain them.
Separate units are required for handling the waste effluent from
each line, as various solutions, such as zinc, nickel, copper,
chromium, cannot be mixed for chemical recovery.
The advantages offered by evaporative recovery outweigh the
disadvantages when existing chemical treatment facilities are not
available. Evaporative recovery is a promising and economical method
currently available for handling plating waste effluents and limiting
treatmentplant size. Where existing chemical treatment (cyanide
destruction, chromate reduction, and chemical precipitation) facilities
are operating at less than capacity, the economics and practicality of
installing new evaporative equipment must be closely evaluated.
small decrease in the rinse water effluent e.g., 1100 1/hr (300
by itself does not warrant the installation of an evaporative system.
The savings produced by the recovery of plating chemicals plays the
significant role in judging the overall merits of the evaporative system
for a specific operation.
Process __ Principles __ §nd_Eguip_ment . A representative closed loop system
for recovery of chemicals and water from a plating line with a single-
effect evaporator is shown in Figure 11. A single-effect evaporator
concentrates flow from the rinse water holding tank. The concentrated
rinse solution is returned to the plating bath, and distilled water is
returned to the final rinse tank. With the closedloop system, no
external rinse water is added except for make-up of atmospheric
evaporation losses. The system is designed for recovering 100 percent
of the chemicals, normally lost in dragout, for reuse in the plating
process.
Single , double and multiple-effect evaporators, and vapor-
recompression evaporator units are used for handling plating effluent.
Open-loop and combined evaporation (i.e., evaporation combined with ion-
exchange, reverse-osmosis, or other systems) are also employed for
handling plating effluent.
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A single-effect evaporator is preferred, if relatively
unsophisticated operating personnel are involved, or low initial capital
outlay is desired. ltfs the simplest in design and therefore the
easiest to operate. However, it is less economical than a double effect
or vapor-recompression unit with regard to utility costs.(41) A double-
effect evaporator should be considered when lower operating cost is
desired with a modest increase in capital investment.
A vapor-recompression evaporator should be considered if no steam or
cooling water is available. Where utilities for a conventional steam
evaporator are available, the highinitial cost of the vapor
recompression unit is not economically justified. Its operating cost is
the lowest of the three systems. Its dependence on an expensive and
complex mechanical compressor is the main disadvantage.
Some sources report considerable maintenance and down time and have
dispensed with use of evaporator units. Other sources report little or
no trouble and are very satisfied with the operation. It appears that
the units can perform very satisfactorily if the installation is
properly engineered, and if preventive maintenance and trouble-shooting
are carried out by knowledgable personnel.
In some instances, evaporation procedures must be used in
combination with chemical or other methods in order to handle small
amounts of impurity build-up (e.g., brighteners, carbonates, extraneous
metal ions, etc., in closed-loop operation) or for treatment of minor
bleed-off streams (open-loop).
Atmospheric evaporation, which uses air flow through packing media
in an evaporator, can concentrate plating solution such as chromic acid
up to 480 g/1 (4 Ib/gal)(42). One manufacturer(43) has introduced a new
concept for evaporative recovery. A glass shell and tube heat exchanger
is mounted vertically and the solution is fed through the bottom. The
boiling causes liquid surges that produce a "rising film" effect and an
improvement in heat transfer. Vapor and liquid overflow the top of the
tubes and are separated in a cyclone. Water with less than 0.05 ppm of
chromic acid has been produced from chromium plating rinse water.
Practical_OEerating_Sv.s_tems. Extensive use is made of evaporators in
Plant 20-14, where three~units with capacities of 380, 380, and 190 1/hr
(100, 100, and 50 gph) are used to completely close the copper cyanide,
nickel, and chromium rinse lines respectively. Only the cleaning and
acid pickling lines are open and it is roughly estimated that the
combined effluent volume from them may be of the order of 11,300 1/hr
(3000 gph). The alkali rinse is run directly to the sewer and the acid
line is neutralized and run to the sewer without clarification. Small
spills and washes are treated chemically. Rearrangement of cleaner and
acid dip rinse tanks to counterflow operation could reduce the volume of
-------
co«ecNT*ATE HOI.O TANK (M)
l fLATING »"OIIK TRAVEL
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FIGURE 11.
REPRESENTATIVE CLOSED-LOOP SYSTEM FOR RECOVERY
OF CHEMICALS AND WATER WITH A SINGLE-EFFECT
EVAPORATOR
96
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FIGURE 12. REPRESENTATIVE OPEN-LOOP EVAPORATIVE RECOVERY
SYSTEM(34)
97
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effluent to a very low level and installation of an evaporator would
reduce it further. In contrast to the plating tanks, the cleaners and
acids must be discarded periodically so that a completelyclosed loop on
these lines does not seem possible. However, there is no economic
incentive to change the present arrangement in this plant to reduce the
present effluent volume. One manufacturer has installed over 100
evaporative recovery systems in metal finishing shops.
Figure 12 illustrates an open-loop, partial recovery evaporation
system, which is suitable for plating installations where there is an
insufficient number (i.e., less than three) rinses. Although the
specific data shown in Figure 12 are for a cyanide plating line, the
general overall A small portion of the cyanide dragout that, accumulates
in the final rinse is not recirculated to the evaporator for
concentration. The circulation loop through the evaporator is opened by
creating another flow path for the cyanide. With only two rinse tanks,
the open-loop system can be operated economically, because only about 4
percent of the dragout is lost; this dragout must be treated by some
appropriate chemical method before disposal.
Demons tration_status
Atmospheric evaporators have been shown to be practical for
recovering chromic acid from spray mists collected in chromium plating
venting and scrubbing units. A cation exchanger is used to purify
concentrated chromic acid before it is recycled to the plating bath.
Several units of the glass "rising film" evaporator are being field
tested in applications involving chromic acid solutions.
Water Conservation by Reverse Osmosis
. Reverse osmosis uses a pressure differential across a
membrane to separate a solution into a concentrate and a more dilute
solution that may approach the purity of the solvent. It therefore
accomplishes the same type of separation as distillation and has been
applied in plating installations in the same manner. Small units under
300 gph have been installed to recover plating bath chemicals and make
closed-loop operation of a line possible. There are limitations on the
acidity and alkalinity of solutions suitable for treatment by reverse
osmosis that eliminate some alkaline baths and chromic acid baths
fromconsideration unless modifications are made to the solutions prior
to treatment. A recently designed system for Plant 11-22 offers promise
that large capacity reverse osmosis systems are possible and therefore
not subject to the size constraints of evaporative systems. If so, they
should play a key role in the design of plants that will have no liquid
effluent.
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Most of the development work and commercial utilization of the
reverse osmosis process especially for desalination and water treatment
and recovery has occurred during the past 10 years. There is a steadily
growing number of commercial installations in plants for concentration
and recovery of plating chemicals along with recovery of water under
essentially closed-loop conditions. Most of the existing commercial
installations are for treatment of nickel plating solutions, since
reverse osmosis is especially suited for handling nickel solutions and
also because of the favorable economics associated with recovery and
reuse of expensive nickel chemicals. Commercial reverse osmosis units
for handling acid zinc and acid copper processes also have been
installed, however. Laboratory and pilot-plant studies directed at
handling cyanide and chromium-type effluents are under way.
Reverse osmosis is especially useful for treating rinse water
containing costly metals and other plating salts or materials.
Generally, the purified water is recycled to the rinse, and the
concentrated salts to the plating bath. In instances where the
concentrated salts cannot be rerecycled to the plating tank,
considerable savings will be achieved because of the reduced amount of
waste-containing water to be treated.
Advantages and Limitations. Some advantages of reverse osmosis for
handling plating effluents are as follows:
(1) Ability to concentrate dilute solutions for recovery of plating
salts and chemicals
(2) Ability to recover purified water for reuse
(3) Ability to operate under low power requirements (no latent heat
of vaporization or fusion is required for effecting separa
tions; the main energy requirement is for a high-pressure pump).
(4) Operation at ambient temperatures (e.g., about 60 to 90 F)
(5) Relative small floor space requirement for compact high-capacity
units.
Some limitations or disadvantages of the reversed osmosis process
for treatment of plating effluents are listed below:
(1) Limited temperature range for satisfactory operation. (For
cellulose acetate systems the preferred limits are 65 to 85 F; higher
temperatures will increase the rate of membrane hydrolysis, while lower
temperature will result in decreased fluxes but not damage the
membrane) .
99
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(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 (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 feeds high in suspended solids (such
feeds 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 operating pressures or are
uneconomical to treat).
Process Principles and Equipment. Water transport in reverse osmosis
(RO) is opposite to the water transport that occurs in normal osmosis,
where water flows from a less concentrated solution to a more
concentrated solution. In reverse osmosis, the more concentrated
solution is put under pressure considerably greater than the osmotic
pressure to drive water across the membrane to the dilute stream while
leaving behind most of the dissolved salts. Salts in plating baths such
as nickel sulfate or copper sulfate can be concentrated to solutions
containing up to 15 percent of the salt, by weight. (44,45)
Membrane materials for reverse osmosis are fairly limited and the
bulk of the development work has been with specially prepared cellulose
acetate membranes, which can operate in a pH range of 3 to 8 and are
therefore useful for solutions that are not strongly acid or alkaline,
i.e., rinses from Watts nickel baths. More recently, polyamide
membranes have been developed that will operate up to a pH of 12, and
several of these units are operating in plants for the treatment of
cyanide rinse waters.
Figure 13 is a schematic presentation of the reverse osmosis process
for treating plating-line effluent. The rinse solution from a
countercurrent rinse line is pumped through a filter, where any
suspended solids that could damage or foul the membrane are removed.
The rinse solution is then raised to the operating pressure by a high-
pressure pump and introduced into the reverse osmosis unit. The
concentrated salt stream is returned to the plating tank, while the
dilute permeate stream is returned to the second rinse tank. Currently,
several different configurations of membrane support systems are in use
in commercial reverse osmosis units. These include plate and frame,
tubular, spiral wound, and hollow fine fiber designs.
100
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Sy sterns. Plant 13-2 has installed a reverse osmosis
unit on the rinse line of a 6800 liter (ISOOgal) bright nickel solution.
Solution from a dragout tank immediately following the plating bath is
returned directly to the plating bath. Water in the succeeding rinse
tanks, containing approximately 25 ppm of nickel, is pumped through a 50-
micron prefilter and six reverse osmosis modules at the rate of 450 1/hr
(120 gph) . Concentrate, at the rate of 23 1/hr (6 gph) , is returned to
the plating tank and 445 1/hr (118 gph) of water are returned to rinse
tanks. The unit is reverse flushed once every two weeks, which produces
23 liters (6 gallons) of waste that is sent to a sludge holding tank.
Otherwise the system operates as a closed loop. Life of the modules is
estimated to be 2-1/2 years. This system is typical of the systems that
have been installed until recently.
A waste-treatment plant designed to produce no liquid effluent has
been recently installed at Plant 11-22. Key
components in the process are two reverse osmosis units operating in
parallel and capable of handling 26,000 1/hr (6800 gph) of effluent.
This flow rate is typical for a medium-large plating installation, so
that reverse osmosis should be capable of treating total wastewater
rather than being used for chemical recovery on individual lines where
water volume is much lower. Plant 11-22 had no treatment facilities
prior to installation of the new unit. Dilution of plating plant
effluent by other effluents at the site reduced concentrations of
pollutants to very low levels. The waste-treatment system could
therefore be designed from scratch rather than as an add-on to an
existing system. The system that was chosen uses chemical treatment
followed by reverse osmosis. The flow diagram in Figure 14 describes
Plant 11-22 's zero effluent system. The small amount of cyanide is
pretreated before being combined with streams from the chromium, acid,
alkali, acid copper and nickel baths.
102
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103
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Hexavalent chromium is reduced in the neutralizer tank at pH 8.5.
Metal oxides are precipitated at the same time. Effluent from the
clarifier goes through a reverse osmosis system. Each of the parallel
assemblies contain 26 units that are operated so that 18 units operate
in parallel, followed by 6 units in parallel, followed by 2 units in
parallel. Thus, these three parallel systems operate in series with
each other.
A smaller reverse osmosis unit is used in the plating plant to
recover chromium dragout. The acidity of the rinse water is reduced
somewhat to prevent deterioration of the reverse osmosis membrane. A
deionizer is then used to remove salts formed by the partial
neutralization, after which the chromium concentrate can be returned to
the plating tank.
Water Conservation by Freezing
Tne freezing process would be capable of recovering
metal and water values from plating rinse water to permit essentially
closed-loop-type operation if fully developed. The feasibility of using
freezing for treatment of plating rinse waters was demonstrated on a
laboratory scale using a mixed synthetic solution containing about 100
mg/1 each of nickel, cadmium, chromium, and zinc, along with 30,000 mg/1
of sodium chloride. Greater than 99.5 percent removal of the metallic
ions was achieved in the experiments, with the purified water product
containing less than 0.5 mg/1 each of the individual plating metals.
The separation tests were carried out using the 9500 1/hr (2500-gpd)
pilot-plant unit at Avco Systems Division, Wilmington, Massachusetts.
Process __ PEinc.ip.les __ and __ Eguip.ro.ej2i- The basic freezing process for
concentration and recovery of water from plating effluents is similar to
that used for recovery of fresh water from the sea. A schematic diagram
of the treatment of plating rinses by the freezing process is shown in
Figure 15. (46,47) The contaminated reuse water is pumped through a heat
exchanger (where it is cooled by melted product water) and into a
freezer. An immiscible refrigerant (e.g., Freon) is mixesd with the
reuse water. As the refrigerant evaporates, a slurry of ice and
concentrated solution is formed. The refrigerant vapor is pumped out of
the freezer with a compressor. The slurry is pumped from the freezer to
a count erwasher, where the concentrated solution adhering to the ice
crystals is washed off. The counterwasher is a vertical vessel with a
screened outlet located midway between top and bottom. Upon entering
the bottom, the slurry forms a porous plug. The solution flows upward
through the plug and leaves the counterwasher through the screen. A
small fraction of the purified product water (less than 5 percent) flows
10 4
-------
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W
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105
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countercurrervtly to the ice plug to wash off concentrated solution
adhering to the ice. The ice is pumped to a condenser and melted by the
release of heat from the refrigerant vapor which had been originally
evaporated to produce the ice, and which had been heated by compression
to a saturation temperature higher than the melting point of the ice.
Because of the pump work, compressor work, and incomplete heat
exchange, a greater amount of refrigerant is vaporized than can be
condensed by the melting ice. Consequently, a heat-removal system is
needed to maintain thermal equilibrium. This system consists of a
compressor which raises the temperature and pressure of the excess vapor
to a point where it will condense on contact with ambient cooling water.
The freezing process offers several advantages over some other
techniques. Because concentration takes place by freezing of the water
in direct contact with the refrigerant, there is no heat-transfer
surface (as in evaporation) or membrane (as in reverse osmosis) to be
fouled by the concentrate or other contaminants. Suspended solids do
not affect the freezing process and are removed only as required by the
end use to be made of the recovered products.
The heat of crystallization is about 1/7 the heat of vaporization,
so that considerably less energy is transferred for freezing than for a
comparable evaporation operation. Because freezing is a low-temperature
process, there will be less of a corrosion problem than with
evaporation, and less expensive materials of construction can be
employed. The freezing process requires only electrical power, as
opposed to the evaporation process which also requires steam generating
equipment. The cost of the freezing method may be only 1/3 that for
evaporative recovery,
Practical_O2erating_SY§tems. No commercial utilization of freezing for
treatment of waste water from metal finishing is known in the United
States. Practical systems may exist in Japan, however.
Demonstration Status. No demonstrations are in progress in metal
finishing plants. However, a 9500 liters/day (2500 gpd) unit is in
operation to demonstrate desalination of water.
Water Conservation by Electrodialysis
Applicability. Electrodialysis removes both cations and anions from
solution and is most effective with multi-valent ions.(48) Therefore,
it is capable of reducing the concentration of copper, chromium, nickel,
106
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and zinc ions from solution whether these metallic ions are complexed or
not. Chromate and cyanide ions may also be removed.
Process Principles and Equipment. The simplest electrodialysis system
consists of an insoluble anode and an insoluble cathode separated by an
anion permeable membrane near the anode and a cation permeable membrane
near the cathode. An anode chamber, cathode chamber, and middle chamber
are thereby formed. Upon electrolysis anions pass from the middle
chamber to the anode compartment and cations pass from the middle
chamber to the cathode compartment. The concentration of salt in the
central compartment is thereby decreased. By employing several anion
and cation permeable membranes between the electrodes several chambers
are created. A stream may then be run through several of these chambers
in such a pattern that the concentration is reduced in each successive
chamber. Another stream is run through chambers in which the
concentration is successively increased. The net effect is similar to
that of a continuous moving bed ion-exchange column with electrical
energy used for regeneration rather than chemicals.
Practical Operating Systems. No practical operating systems have been
reported. However, development has resulted in several demonstrations,
discussed below.
Demonstration Status. Several demonstrations have shown that
electrodialysis is a promising method. Further development and use of
the method may be expected. Copper cyanide rinse water may be
concentrated sufficiently to be returned to the bath by using two units
on a double counterflow rinse system, i.e., between the first and second
rinse tank and between the bath and first rinse tank.
Water Conservation by Ion-Flotation Techniques
Ion-flotation techniques have not been developed for
application to plating rinse water effluents. If successfully developed
into a practical method for plating effluent treatment, ion flotation
offers possibilities of reducing the amount of water discharged by 60 to
90 percent for some plating operations. These savings are based on
results of small-scale laboratory studies on solutions containing
cyanides or hexavalent chromium.
Process __ Principles __ and __ Eguip_ment. Separation of ions from aqueous
solutions by a flotation principle is a relatively new concept, first
107
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recognized about 25 to 30 years ago. In the ion-flotation operation a
surface active ion with charge opposite to that of the ion to be
concentrated is added to the solution and bubbles of air or other gas
are introduced into the solution to form a froth of the surface-active
material. The foam is separated and collapses to form a scum containing
an ion-concentrate. Ion flotation combines the technologies of mineral
flotation and ion-exchange. A schematic diagram of an ion-flotatior,
cell is shown in Figure 16.
Experimental results indicate that 90 percent of the hexavalent
chromium in a 10 to 100 ppm solution can be removed with primary amine
surface active agents. (49) However, the amine suffered deterioration
when regenerated for re-use, since the removal efficiency dropped to 60
percent after two regenerations of the amine.
Grieves, et al.,(50) have demonstrated the feasibility of using ion
flotation on dichromate solutions with a cationic surfactant
(ethylhexadecyldimethylammonium bromide). A continuous operation with a
retention time of 150 minutes was devised. The feed stream contained 50
mg/1 of dichromate. Approximately 10 percent of the feed stream was
foamed off to produce a solution containing 450 mg/1 of dichromate,
while the stripped solution contained 15 mg/1.
Cyanides have been removed from dilute solutions with mixed results.
The extraction efficiency from a cadmium cyanide solution containing 10
ppm of cyanide was 57 percent, using primary, tertiary, and quaternary
ammonium compounds as collectors. Extraction efficiencies for nickel
and iron cyanide solutions were approximately 90 percent.
ating_Sy.st ems. There are no practical operating systems.
Demonstration __ Status. The process has not been demonstrated in an
operating plant.
Water Conservation by Electrolytic Stripping
Electrolytic stripping is not in general use for copper,
nickel, chromium or zinc, although some procedures have been employed
for recovering precious metals. Recent technical developments suggest
that they can be used to reduce heavy metal concentrations in the
effluent to very low values as well as provide for recovery of the
metals.
108
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TREATMENT OF PLATING EFFLUENT
109
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Process_Princi2les_and_Egui221§Ilt' In order to strip a solution by
electrodeposition it is necessary that the metallic ions in a dilute
solution reach the cathode surface at a sufficient rate so that
essentially all of the ions can be deposited in a reasonable time.
Surfleet and Crowle(51) have discussed several methods of accomplishing
this. One method called the "integrated" system uses baffles in a tank
to create a very long path through which the water may be recirculated
at a high velocity. The method is suitable only for metals having a
relatively high limiting current density for dilute solutions, such as
gold, silver, tin. The fluidized bed electrode is a bed of metal
spheres or metal-coated glass spheres that is fluidized by pumping the
dilute solution through it and causing an expansion of 5 to 10 percent.
With spheres of 100 to 300 microns in diameter, a total geometric area
of 75 cm2/cm3 is obtained. Thus, the current density is very low and
the flow of electrolyte through the bed provides the forced convection
to support high currents. Another system employs electrodes made of
expanded metal and the turbulence around this structure enhances the
rate of deposition of metal when solution is pumped past it. Turbulence
and an increase in the rate of deposition at a plane electrode may also
be promoted by filling the space between electrodes with a woven plastic
screen, glass beads, etc.
In another system(52) the electrolyte is introduced into a narrow
gap between two porous carbon electrodes.The bulk of the solution (99%)
is forced through the cathode where copper is deposited out. Pre-
deposited copper on the anodic electrode is dissolved into the one
percent of the electrolyte that permeates through this electrode and a
copper concentrate is produced. The two electrodes are periodically
reversed so that copper deposited from a large volume of solution is
dissolved into a small volume of electrolyte. Copper in solution has
been reduced from 670 ing/1 to 0.55 mg/1 in the cathode stream and
concentrated to 44 g/1 in the anode stream. A similar system has been
used for depositing metallic impurities from strong caustic
solutions. (53)
Practical Operating Systems. There are no practical operating systems
in the electroplating industry, although the caustic purification system
is in use in the chlor-alkali industry.
Demonstration^Status. The porous electrode system(52) is still under
development at The University of California and has been scaled up to
handle 250 gpd of copper sulfate solution.
Water conservation by Carbon Adsorption
110
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Applicability. Activated carbon has been used for the adsorption of
various materials from solution, including metal ions. Experimental
data show that up to 98 percent of chromium can be removed from waste
water. (49) The treated water can be recycled to the rinse tanks.
Process ___ Principles ___ and __ Equipment. The process relies upon the
adsorption of metal ions on specific types of activated carbon. In the
case of chromium VI, a partial regeneration of the carbon can be
accomplished with caustic solution followed by an acid wash treatment to
remove residual caustic and condition the carbon bed for subsequent
adsorption cycles. The equipment consists of holding tanks for the raw
waste, pumps and piping to circulate the waste through adsorption
columns similar to those used for ion-exchange.
Practical Operating Systems . systems based on adsorption and desorption
are still under laboratory development and no practical operating
systems are known.
Demonstration __ Status. Pilot plant equipment has been operated
successfully in an electroplating plant treating chromium rinses at a
flow rate of 19 liters/min (5 gpm) at concentrations from 100 to 820
mg/1 hexavalent chromium. Adsorption was continued until the effluent
reached acceptable concentrations of chromium VI.
Water Congeryati.on_bY_Liguid-Liguid Extraction
Liquid-liquid extraction has been used on an
experimental basis only for the extraction of hexavaconcentrate
impurities in a smaller volume, which in turn will have to be treated by
other means or suitably disposed of. The fully extracted aqueous phase
may be recycled to the rinse tanks. Water savings from 50 to 73 percent
appear to be possible.
Process __ Principles __ and __ Eguipjnent. The metal-ion pollutant is reacted
with an organic phase in acid solution, which separates readily from the
aqueous phase. Metal is subsequently stripped from the organic phase
with an alkaline solution. Hexavalent chromium, for example, has been
extracted from wastewater at pH 2 with tertiary and secondary amines
dissolved in kerosene. After the reaction of the chromium with the
amine and phase separation, the chromium is stripped with alkaline
solution from the organic phase restoring the amine to its original
composition. For liquid-liquid extraction to be feasible the following
conditions would have to be met:
111
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(1) The extraction of chromium should be virtually complete.
(2) Reagent recovery by stripping would be efficient.
(3) The stripping operation should produce a greatly concentrated
solution.
(H) The treated effluent solution should be essentially free from
organic solvents.
(5) Capital and operating costs should be reasonable.
The equipment required consists basically of mechanically
agitated mixing and settling tanks, in which the phases are intimately
dispersed in one vessel y agitation and then permitted to flow by
gravity to a settling vessel for separation. Holding tanks for
extractant and stripper and circulating pumps for these solutions as
well as the purified waste water are necessary. Equipment for liquid-
liquid extraction would also include horizontal and vertical columns,
pulsed columns and centrifuges.
Practical_0p.erating_Sy.stems. Liquid-liquid extraction systems are not
known to be operating for treatment of electroplating wastes.
D§!DO!l§tration Status. Experimental evidence exists indicating that up
to 99 percent of chromium can be successfully extracted from rinse
waters containing 10 to 1000 mg/1 of Cr6+. With 10 ppm of Cr6+ in the
rinse water, the treated effluent contained as little as 0.1 mg/1 of the
ion; with 100 ppm in rinse water concentration was reduced to O.U mg/1.
Stripping was effective as long as the amines were not allowed in
contact with the chromium for a prolonged period of time which would
allow oxidation by Cr6+ ions. The effluent, however, contained from 200
to 500 mg/1 of kerosene, which is undesirable.
Methods_of_Achieying_No Discharge of Pollutants
Although chemical methods of treating electroplating waste waters
are achieving the low effluent discharges suggested in this report, they
are not improvable to the point of achieving zero discharge of
pollutants. The preceding discussion of water conservation [ion
exchange, evaporation, and reverse osmosis (RO) ] indicates procedures
for achieving no discharge of water. With closed-loop treatment of
rinse water in separate streams from each electroplating bath,
evaporation or RO can be used to return concentrate directly to the
corresponding plating bath.
112
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Impurities in an electroplating bath are increased in concentration
when pollutants in rinse waters are recycled and returned to the
solution. High concentrations of impurities ultimately affect the
quality of the electroplates. Thus, impurity removal becomes necessary.
Methods for removing impurities usually contribute pollutants that must
be disposed of by chemical treatment. For example, the removal of
carbonates from cyanide solutions by precipitation with calcium
hydroxide or by freezing involves the occlusion of cyanide and heavy
metals, which must be subjected to chemical treatment. Activated carbon
for removing organic impurities should be washed before disposal as a
solid and the wash water treated to destroy cyanide and/or precipitate
heavy metals. Spills that cannot be returned to the segregated recovery
cycles must be treated chemically to avoid pollution. These sources of
pollutants can be combined with waste water flows from alkaline
cleaners, acid dips and other preplating and post plating solutions;
from which chemicals cannot be recovered and returned to the process.
These preplating and post plating solutions are either changed
irreversibly during use or become too contaminated for economic
recovery. Replacement or makeup is unavoidable if the solutions are to
perform their proper function. Although rinse water can be recycled, a
sludge is inevitable in connection with recovering most of the water by
chemical treatment. This operation is best performed after mixing the
rinse waters from the cleaner and acid dips.
The acid in acid dip solutions gradually becomes neutralized by
reaction with the basis metal being processed, and the concentration of
the metal increases. Ion exchange can be used in a separate stream of
waste rinse water to recycle the water to rinsing. However, the
regenerant must be disposed because it contains the dissolved metals
that are not recyclable in the acid dipping operation. Most commonly
this will be done by chemical precipitation, after mixing with the rinse
waters.
A preferred procedure (A) for eliminating discharge of pollutants
into navigable streams omits the ion exchange step and concentrates the
rinse waters to recycle some of the water and minimize the chemical
treatment load as shown in Figure 17. Wash water from spills is fed
into either the alkali or acid rinse water holding tank. Obviously
dumps of concentrated cleaners and acid dips can be trickled into the
respective rinse water holding tank. Rinse water containing post
plating pollutants also can be treated by directing it to holding tanks
prior to treatment by evaporation or RO and ultimate chemical treatment
and precipitation of heavy metal pollutants.
Another procedure (B) for recycling water to rinse tanks and
achieving no discharge of pollutants includes chemical treatment of the
combined waste from all preplating, plating and post plating operations
and separation of solids as discussed on pages 61-79, followed by
further treatment of the effluent by evaporation or reverse osmosis to
113
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W
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114
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recover high-quality water suitable for rinsing. This water recovery
system is used with an RO unit at plant 11-22. (Figure 14). The
concentrate from the RO unit (or an evaporator) is evaporated to dryness
and disposed of as a granulated salt. When this method for achieving
zero discharge of pollutants into navigable streams is adopted with no
provision for recovering chemicals reusable in electroplating baths,
costs will be greater than the costs incurred for recycling
electroplating chemicals in segregated streams and combining preplating
and post plating rinse water for chemical treatment and subseguent
evaporation or RO for water recovery.
A possible future development may be direct treatment of the waste
water stream by evaporation or reverse osmosis without prior
precipitation of the heavy metals. The waste water would need
adjustment to a low enough pH to preclude any precipitation which could
cause corrosion problems or membrane deterioration. The method would
have the obvious merit of reducing the cost of chemical treatment and
limiting it to that required for cyanide destruction and chromate
reduction. However, the solid residue from evaporation may contain
soluble heavy metal salts that would require further treatment before
being used as land fill.
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SECTION VIII
CQST^ ENERGYf AND NONWATER QUALITY ASPECTS
Introduction
In this section, costs associated with the degree of effluent
reduction that can be achieved by exemplary treatment methods are
discussed. Costs also are estimated for evaporation and reverse osmosis
technologies that can achieve a further improvement in removing waste
water constituents. The nonwater quality aspects concerning disposal of
solid waste and the energy impact of the inprocess control and waste
treatment technologies also are discussed.
Treatment and control Costs
Chemical Treatment to Achieve Low Levels of Pollutants
BPCTCA Limitations .(Table !)_._ Costs associated with control technology
consistent with the exemplary practice of chemical treatment averaged
$10.24/100 sq m (9.52/1000 sq ft) for eight medium-sized and large
plants that supplied detailed cost data. The standard deviation for
this value was $6.31/100 sq m ($5.86/1000 sq ft) indicating considerable
spread from the average value. The operating cost of waste treatment,
as a percent of cost of plating was 3.80% with a standard deviation of
2.37%. Plating costs were assumed to be $2.70/sq m (0.25/sq ft) for
each deposit applied. (Copper, nickel, chrome on the same part
corresponds to three deposits.) The minimum investment cost for a
chemical treatment plant is of the order of $50,000 regardless of the
size of the plating installation. For plants with a plating capacity of
107 sq m/hr (1000 sq ft/hr), or larger, the investment cost is estimated
at approximately $150,000/100 sq m/hr ($140,000/1000 sq ft/hr) of
capacity (Figure 18) .
The control and treatment technology on which the above costs are
based will reduce the discharge of waste water constituents to only 0.1
to 1.0 percent of the amount that would be discharged in the absence of
chemical treatment.
The costs of waste treatment in smaller plants was estimated using a
model that included chemical treatment consisting of cyanide destruction
and hexavalent chromium reduction and precipitation and separation of
heavy metals from the combined waste water from preplating, plating, and
postplating operations.
A minimum capital investment of $50,000 was assumed for the chemical
treatment facility in any small plant. Only 2,000 hours of operation
per year (8 hr/day 5 days/week, 50 weeks/yr) was assumed for the small
116
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EFFECT OF SIZE OF PLATING PLANT ON
INVESTMENT COST OF WASTE-TREATMENT
FACILITY
117
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plants in place of 2,625 hours per year for medium- si zed Plant 33-1,
becuase many small plants confine their operations to only one, 8-hour
shift. As a result, of this assumption, fixed charges and operating
costs, based on area plated, are higher for the small plants.
Table 21 shows that estimated costs for meeting the 1977 BPCTCA
effluent limitations by chemical treatment are greater for small plants
plating less than 33 sq m/hr (360 sq ft/hr) in comparison with the costs
for meeting 1977 BPCTCA limitations by larger plants. The figures in
Table 21 reflect the fixed costs for capital investment depreciation,
interest on the investment and variable costs for chemical treatment.
The variable costs for chemical treatment were based on cost data
supplied by Plant 33-1. These variable costs at Plant 33-1 were as
follows:
Chemicals $28,439/yr
Sludge disposal 5,144/yr
Labor 23,433/yr
Equipment repair 3,889/yr
Power 3,887/yr
Total $64,792/yr
Plant 33-1 operates 2,625 hr/yr and has a plating rate of 4,560 sq ft/hr
(12,000,000 sq f t/yr) . The above cost is about $5.70/100 sq m
($5.30/1000 sq ft), which is about the average cost calculated for 6
other plants. The cost is about $2/1000 gal (assuming 2.5 gal/sq ft)
and is typical of values reported for chemical treatment.
According to the estimates in Table 21, the costs for chemical
treatment in a small plant with 6 to 10 employees are approximately 7
percent of the total plating costs, assuming that plating -costs are
$2.70/sq m ($0.25/sq ft). In comparison, costs for chemical treatment
in a plant with 2 employees are approximately 18 percent of the plating
costs.
As noted previously, the estimates in Table 21 are based on a
capital investment of $150,000/100 sq/hr ($140, OOO/ 1000 sq ft/hr). Any
plant capable of designing and constructing a chemical waste treatment
facility at a lower cost will have a lower waste treatment cost per unit
area plated. The eight larger plants cited on page 122 obviously were
able to reduce their capital investment appreciably because operating
costs at these plants averaged only $10.24/100 sq m ($9.52/1000 sq ft) ,
which is only about one half of the estimated cost in Table 21 for small
plants with 6 to 20 employees.
Source Performance Standards INSPSXi New sources that are required
to meet the standards of performance recommended in Table IA have the
opportunity of designing and building plants that reduce water flow.
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Such a reduction can be accomplished by installing counterflow rinsing
for each preplating and postplating operation. The capital investment
cost for installing a supplemental rinse tank for each operation in a
plant plating copper, nickel, chromium and zinc will be approximately
$20,000, The impact of this supplemental capital investment on waste
treatment costs for small companies is reflected in Table 21. Estimated
costs for a 6 to 20 employee plant plating 33 to 167 sq m/hr (360 to 800
sq ft/hr) amount to approximately 9 percent of the total plating costs,
assuming that plating costs are approximately $2.70/sq m ($0.25/sq ft).
Large companies plating more tha 167 sq m/hr (1800 sq ft/hr) will
incur costs of no more than $19.30/100 sq m ($17.9/1000 sq ft) to meet
new source performance standards. The level of costs for meeting NSPS
might be lower if investment costs for chemical treatment are lower than
$150,000/100 sq m/hr ($140,000/1000 sq ft/hr).
No Discharge of Pollutants
The elimination of waste water discharge pollutants can be
accomplished by water recovery by evaporation-condensation or reverse
osmosis in combination with chemical treatment and filtration for
acid/alkali waste. Ion exchange is useful for waste water conservation,
but is not practical for eliminating waste water constituents in the
end-of-process, point source discharge. The preferred mode of operation
is to conserve all plating bath chemicals and return them to the plating
bath, and concentrate all other chemicals (from preplate and postplate
operations) for chemical treatment and disposal in a solid state.
The cost for eliminating waste water pollution using evaporation
(and no chemical treatment) in a plant with a plating capaicity of 370 sq
m/hr ( 4000 sq ft/hr) is estimated to range from $5.40 to $17.20/100 sq
m ($5.00 to $16.00/1000 sq ft) or 2 to 6.5 percent of the plating costs.
The lower figure is associated with the use of a vapor compression
system for combined, preplating and postplating waste and individual
single stage evaporators for recovering plating solution from rinse
water following plating operations. The higher figure* is associated
with single effect units employing steam and cooling water for each
preplating, plating, and postplating operation. The capital investment
estimates for these evaporation systems are $68,659 and $164,000/100 sq
m ($63,810 and $153,000/1000 sq ft) for the vapor compression and single
effect evaporation system, respectively.
Costs incurred by a large plant for eliminating waste water
pollutants by chemical treatment followed by reverse osmosis are
estimated to be of the order of $8.60/100 sg m ($8.00/1000 sq ft) or
less, equivalent to about 3 percent of the plating cost. The capital
investment estimate for this system is $110,000/100 sq m/hr
($102,100/1000 sq ft/hr). Waste water pollution will be eliminated in
120
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this case but small amounts of both soluble and insoluble solid wastes
will be produced.
The incremental cost for achieving zero discharge of pollutants by
1983 by a large facility plating at least 370 sg m/hr (4000 sg ft/hr),
which is now eguipped for meeting 1977 new source standards or 1977
existing source limitations via chemical treatment is estimated to be
$3.39/100 sq m ($3.15/1000 sg ft). This incremental cost assumes that
effluent osmosis to recover water and that concentrate from the RO unit
will be evaporated to a granulated salt.
Estimated costs for eliminating waste water pollution from small
plants that recover no plating solution via evaporation or reverse
osmosis are much higher than the costs for achieving zero discharge of
pollutants in plants that use evaporation or reverse osmosis to recover
plating solution dragged into rinse water tanks. The estimates in Table
21 show the higher costs associated with chemical treatment of combined
waste water from all preplating, plating, and postplating operations
plus reverse osmosis (to recover water) plus evaporation of the
concentrate to granulated salt. These estimates vary with the size of
the plating facility. Costs increase appreciably as plant size is
reduced from 20 to 2 employees. At the 20 employee level, costs for
achieving zero discharge of pollutants with no recovery of plating
solution amount to approximately 10 percent of the total plating costs
(assuming plating costs are approximately $2.70/sg m ($0.25/sq ft)). In
comparison a plant with only two employees would entail costs eguivalent
to about 28 percent of plating costs to achieve the same standard.,
The incremental cost for achieving zero discharge of pollutants by
1983 for a small facility plating no more than 167 sg m/hr (1800 sg
ft/hr), which is initially equipped for meeting 1977 new source
standards via chemical treatment can be estimated from data in Table 21.
This increment will vary from $13.40/100 sq m ($12.45/100 sq ft) for a 2
employee plant to $2.40/100 sq m ($2.34/1000 sq ft) for a 20 employee
plant.
Cost_Effectiyeness^andjrreating Procedures
From an analysis of untreated rinse water and effluent in Plant 33-1
which corresponds to a medium-sized plant (50,000 amperes) with 38
employees, it was possible to calculate the amount of copper, chromium,
nickel, zinc, and cyanide removed from the rinse water and determine the
amount discharged with the effluent. The volume of discharge for
various rinse-tank arrangements and the costs associated with these
arrangements were also known. The costs of applying increasingly
effective treatment techniques to Plant 33-1 were estimated for the
following systems:
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(1) A single rinse tank for each rinsing operation; no wastewater
treatment
(2) A single rinse tank for each rinsing operation; chemical
treatment
(3) Two series rinses for each rinsing operation; chemical
treatment
(4) Three counterflow rinses for each rinsing operation; chemical
treatment
(5) Single-stage evaporation for each process bath plus 3
counterflow rinses, cleaners and acid dips included, which
requires a total of 21 evaporators. All rinse water would be
recycled and plating process rinse water would be returned to
the plating bath. Thus, no chemical treatment was included
(6) A single-stage evaporator for each process bath and counterflow
rinse, except for acid and alkaline preplating and postplating
rinses. A large vapor compression unit was assumed for the
acid-alkali and postplating stream. Effluent volume reduced to
approximately 37.8 1pd (10 gpd). No provision was made for
evaporating this very small volume to dryness.
(7) Process lines as they now exist in Plant 33-1. Chemical
treatment is used, followed by reverse osmosis on the effluent
from the chemical treatment. No provision was made for
evaporating the small volume of concentrate from the R.O unit.
From these data sources, a cost effectiveness curve was plotted, as
shown in Figure 19. The volume of water required for rinsing in single
rinse tanks is so large that no precipitation occurs during chemical
treatment and the weight of discharged water constituents is not
affected by the treatment. The lowest cost on the curve is that now
incurred by Plant 33-1 using their present system. The options listed
for eliminating discharge of wastewater constituents are associated with
costs ranging from $5.40 to $17.20/100 sq m ($5.00 to $16.00/1,000 sq
ft).
Nonwater Quality Aspects
Energy Requirements
Chemical_Treatment. The electric power used for plating consumes about
0.06 percent of the nation's electrical energy (1.7 x 1012 kilowatt
hours). The power required for chemical treatment is approximately 3.2
122
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percent of the power needed for plating, based on data developed from a
sample of eight plants with reliable records.
No Pis charge of Pollutants. Exclusive use of single or double effect
evaporators for reducing rinse water volume requires steam at a cost
that can be one to four times the cost of power for plating, depending
upon the degree of rinse water reduction achieved. Use of vapor
compression units in part or in whole will reduce the cost of energy
requirements to about the same as the cost of electrical energy for
electroplating or probably less, and eliminate discharge of pollutants
when combined with chemical treatment. Reverse osmosis will achieve the
same effluent limitation (when combined with chemical treatment) using
27 percent of the power required for electroplating.
Solids Disposal
The cost of lagooning sludge from a clarifier cifter chemical
treatment has not been considered, because the method is finding less
and less favor as a means of disposal. The volume generated by the
domestic plating industry is estimated to be about 200,000 cu yd/yr.
It is recommended that metal sludges be disposed of in a "specially
designated landfill," where "specially designated landfill" means a land-
fill at which protection is provided for the quality of surface and sub-
surface waters from heavy metal pollutants. Such sites should be located
an^ engineered to avoir! rlirent hvciraulic continuity with surface an^ sub-
surface waters, and any leachate or subsurface flow into the disposal area
should be contained within the site unless treatment is provided. Pre-
cautions to insure the continued insolubility of the metal sludges should
be taken, such as placing layers of lime and clay underneath the landfill.
Additional guidelines for the proper disposal are stated in the EPA Guide-
lines for Landfilling of Solid Waste. The location of the disposal site
should be permanently recorded in appropriate office of legal jurisdiction
124
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SECTION IX
BEST PgACTICABLE CONTROL TECHNOLOGY CURRENTLY
AVAILABLE, GUIDELINES, AND LIMITATIONS
Introduction
The effluent limitations which must be achieved July 1, 1977, are to
specify the degree of effluent reduction attainable through the
application of the Best Practicable Control Technology Currently
Available. Best Practicable Control Technology Currently Available is
generally based upon the average of the best existing performance by
plants of various sizes, ages, and unit processes within the industrial
category and/or subcategory. This average is not based upon a broad
range of plants within the metal finishing industry, but based upon
performance levels achieved by exemplary plants.
Consideration must also be given to:
(a) the total cost of application of technology
in relation to the effluent reduction benefits
to be achieved from such application;
(b) the size and age of equipment and facilities
involved;
(c) the processes employed;
(d) the engineering aspects of the application of
various types of control techniques;
(e) process changes;
(f) non-water quality environmental impact
(including energy requirements) .
The Best Practicable Control Technology Currently Available emphasizes
treatment facilities at the end of a manufacturing process but includes
the control technologies within the process itself when the latter are
considered to be normal practice within an industry.
A further consideration is the degree of economic and engineering
reliability which must be established for the technology to be
"currently available." As a result of demonstration projects, pilot
plants and general use, there must exist a high degree of confidence in
the engineering and economic practicability of the technology at the
time of commencement of construction or installation of the control
facilities.
125
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Industry Category^andT subcategory covered
The pertinent industry category is the electroplating industry which is
part of the metal finishing industry. This category includes plants
using electroplating processes as defined by SIC 3471 (1972) and
includes all electroplating processes and their associated pretreatment
and post-treatment operations if used in an electroplating process. All
other processes and operations defined by SIC 3U71 that are not part of
processes containing at least one electroplating operation are excluded
from this category.
The identification of Best Practicable Control Technology Currently
Available and recommended effluent limitations presented in this section
cover the subcategory of electroplating based on rack and barrel
electroplating of copper, nickel, chromium, and zinc, estimated to
contribute about two-thirds of the amount of waste in the electroplating
industry. Effluent limitations are not specified as yet for all metals;
all electroplating operations, or all metal finishing processes.,
However, the control and treatment technology identified is broadly
applicable in three other areas: (1) electroplating operations other
than rack and barrel; (2) electroplating of metals other than copper,
nickel, chromium, and zinc; and (3) other metal finishing processes than
electroplating yet to be considered. Recommended effluent limitations
applicable to these other subcategories might require a greater or
lesser degree of effluent reduction.
Identification of_Best_Practicable Control
Technology CurrentlY_Available
Best Practicable Control Technology Currently Available for the
electroplating industry subcategory of rack and barrel electroplating of
copper, nickel, chromium, and zinc is the use of chemical methods of
treatment of wastewater at the end of the process combined with the best
practical in-process control technology to conserve rinse water and
reduce the amount of treated wastewater discharged.
Chemical treatment methods are exemplified by destruction of cyanide by
oxidation reduction of hexavalent chromium to the trivalent form,
neutralization and coprecipitation of heavy metals as hydroxides or
hydrated oxides with settling and clarification to remove suspended
solids prior to discharge or prior to dilution with other
nonelectroplating process water before discharge. The above technology
has been widely practiced by many plants for over 25 years. However the
above technology cannot achieve zero discharge of heavy metals because
of finite solubility of the metals. In addition, it is not practicable
to achieve 100 percent clarification and some small amount of metal is
contained in the suspended solids. By optimum choice of pH and
efficient clarification in the heavy metal pollutional load such that
less than 1 mg of total metal (soluble plus insoluble) is discharged for
126
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each kilogram of metal electroplated on products. This degree of
pollution reduction is often achieved if the concentrations of all
metals is high in the raw waste.
No generalization regarding degree of heavy metal pollution reduction is
possible because of the mix of electroplating processes possible in a
single plant and a variety of metals in the raw waste of most plants.
Because of this fact and the high cost of in-plant segregation of all
waste streams according to metal, coprecipitation of metals is the
general practice. There is an optimum pH for precipitating each metal
that results in the greatest removal by clarification. The optimum pH
for removing all metals cannot be utilized for coprecipitation so the pH
selected for a mixture of metals is a compromise.
There are several advanced plating bath recovery methods available for
closing up the rinse water cycle on individual plating operations.
These methods (evaporation, ion exchange, reverse osmosis,
countercurrent rinsing) have not yet been applied to rinse waters from
pretreatment and posttreatment operations. The corresponding rinse
waters plus concentrated solution dumps and floor spills may contain one
or all of the pertinent metals (copper, nickel, chromium, and zinc) in
significant amounts reguiring chemical treatments. Thus, chemical
treatment of at least the typical acid/alkali stream from pretreatment
and posttreatment operations represents the best practicable control
technology currently available to achieve the effluent limitations
recommended.
Having identified the technology for end-of-process treatment and
recognizing the technical and practical limitations on removal of heavy
metals by this technology (metal solubility and clarification
efficiency), further reduction in the quantity of metal pollutants
discharged must be achieved by reduction in the volume of treated water
discharged. There are many in-process controls designed to reduce the
volume of wastewater which is principally that resulting from rinsing.
Some of these controls designed to minimize dragout of concentrated
plating solution or reclaim as much dragout as practical can be
considered normal practice within the industry. It can be assumed
according to good practice that reclaim tansk and/or still rinses are
being used and that all evaporation losses are made up with the
reclaimed solution. Dragout reclaimed does not contribute to the raw
waste load normally discharged from remaining rinses. There is economic
incentive to reduce the chemicals purchased for bath makeup and the
added economic incentive to reduce the cost of treatment chemicals
required for end-of-process treatment. Reduction of dragout leads to
reduction in water requirements for rinsing.
Further reduction in rinse water use can be achieved by multiple tank
countercurrent rinsing. Unless the rinse water can be used to make up
evaporation losses of the bath, there is little reduction in treatment
127
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chemical cost and no economic incentive to add more rinse tanks purely
for water conservation. However, the use of advanced recovery
techniques (evaporation, ion exchange, and reverse osmosis) which
concentrate the rinse water sufficiently to allow reclaim of the
valuable plating solution provides the economic incentive to use this
technology and justifies the cost of recovery equipment plus the cost of
installing multitank countercurrent rinsing. However, it should be
recognized that the major water reduction occurs because of the
installation and use of multitank countercurrent rinsing. The
additional reduction in volume of wastewater by recovery of all the
rinse water following a plating operation in lieu of chemical treatment
usually has limited impact on the total water use in the plant. This is
because the volume of rinse waters from pretreatment and posttreatment
operations (e.g., the acid/alkali wastewater stream) is often several
times larger than the volume of rinses from plating operations.
In the past there has been little economic incentive to reduce water use
for rinsing after pretreatment and posttreatment operations. For one
reason, the chemicals used in these solutions are not expensive compared
to plating solution chemicals and thus they are not purified for reuse.
These concentrated solutions are dumped at frequent intervals and there
is usually little concern for reducing dragout since the dragout reduces
the rate of buildup of impurities and extends the life of the
concentrated solution and requires less frequent dumping. Thus, for
pretreatment and posttreatment solutions that are dumped frequently
(e.g., once a week), dragout does not influence the quantity of material
in the wastewater requiring treatment. However, dragout from these
solutions does influence the amount of water required for adequate
rinsing.
While sufficient economic incentive is presently lacking to achieve
reduction in the volume of the rinse water from pre- and posttreatment
operations, there is an opportunity for significant reduction in
pollution. The above factors are taken into account in recommending the
effluent limitations. Even in plants currently achieving good waste-
treatment results, there are further opportunities for reduction in
volume of effluent discharged provided there is an economic incentive
related to achieving pollution reduction.
Rationale for Selecting^the Best Practicable^Contrgl
T§chnglggy_Currently_jwailable
General Approach
In determining what constitutes the Best Practicable Control Technology
Currently Available, it was necessary to establish the waste management
techniques that can be considered normal practice within the
electroplating industry. Then, waste-management techniques based on
advanced technology currently available for in-process control and end-
128
-------
of-process treatment were evaluated to determine what further reduction
in pollution might be achieved considering all the important factors
that would influence the determination of best practicable and currently
available.
Waste_Management Techniques Considered
Normal Practice in the Electroplating Industry
For that portion of the electroplating industry that discharges to
navigable waters it is estimated that a large proportion are currently
using chemical treatment for endof-process pollution reduction. some of
these waste-treatment facilities have been in operation for over 25
years with a continual upgrading of performance to achieve greater
pollution abatement. Because of the potentially toxic nature of the
chemicals used in the electroplating industry, there is a relatively
high degree of sophistication in its water pollution abatement
practices. For example, the accidental release of concentrated
solutions without treatment to navigable waters is believed to be a rare
occurrence today. This is because adequate safety features are
incorporated in the design of end-of-process waste treatment facilities
in conjunction with good housekeeping within the electroplating
facility. This example and other waste management techniques were
considered as examples of normal practice within the electroplating
industry in determining the Best Practicable Control Technology
Currently Available. Other examples of normal practice include:
(1) Manufacturing process controls to minimize dragout from
concentrated plating solutions such as
(a) proper racking of parts for eary drainage
(b) slow withdrawal of parts from the solution
(c) adequate drip time of dwell time over the plating tank
(d) use of drip collection devices.
(2) Effective use of water to reduce the volume of effluents such
as
(a) use of rinse water for makeup of evaporation losses from
plating solutions
(b) use of cooling water for noncritical rinses after cleaning
(c) use of treated wastewater for preparing solutions of
waste-treatment chemicals.
(3) Recovery and/or reuse of wastewater constituents such as
(a) use of reclaim tanks after plating operations to recover
concentrated solutions for return to the plating tank to
make up evaporation losses
129
-------
(b) reduction in wastewater volume by the use of at least two
series flow rinse tanks after each plating operation with
return of as much rinse water as possible to the plating
tank.
Other waste-management techniques not considered normal practice but
currently in use in one or more plants were evaluated on the basis of
reduction in the quantity of pollution in the effluent discharged.
Degree of Pollution Reduction Based on
Existing Performance by Plants of Various,
yarious_Cgntrgl_andmTreatment Technology
Identification of Best Waste Treatment Facilities
There are about 20,000 facilities for electroplating and metal
finishing in the United States and identification of the best plants
within the short period of this study required a rational screening
approach as follows. The initial effort was directed toward identifying
those companies which satisfied two criteria:
1. Engaged in rack and barrel plating of copper, nickel, chromium
and/or zinc
2. Achieving good waste treatment.
The 309 companies identified based on referrals by cognizant people
associated with the industry (EPA regional representatives, state
pollution control authorities, trade associations, equipment suppliers)
and review of permit applications were distributed geographically as
shown in Table 22. About 90 percent of the companies were in the three
principal regions expected to have high concentrations of electroplating
industry: 38 percent in the Northeast (principally EPA Regions I, II
and III; 28 percent in the Midwest (EPA Region V); 25 percent in the
Southeast (Region IV) .
Of these leads, the 129 companies initially contacted by telephone
were primarily in the principal electroplating regions (40 percent in
the Northeast; 28 percent in the Midwest; 22 percent in the southeast).
The telephone was to verify the existence of adequate waste treatment
facilities and the type of plating operations pertinent to Phase I.
Sufficient information was obtained to characterize the facility and if
pertinent to the scope of coverage desired operational data were
obtained.
These telephone contacts were continued until 53 plants were
identified that provided broad coverage of the industry pertinent to
Phase I. Because of the need to achieve variety in electroplating and
waste treatment operations, for this study no claim is made that the 53-
130
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TABLE 22. GEOGRAPHICAL DISTRIBUTION OF GOOD ELECTROPLATING
WASTE TREATMENT FACILITIES BASED ON INITIAL
REFERRALS, COMPANIES CONTACTED FOR INFORMATION,
AND REPRESENTATIVE FACILITIES EVALUATED IN
DETAIL
Area
EPA Region I
Connecticut
Massachusetts
New Hampshire
Rhode Island
Maine
Vermont
EPA Region II
Delaware
New Jersey
New York
EPA Region III
Maryland
Pennsylvania
Virginia
West Virginia
EPA Region IV
Alabama
Florida
Georgia
Kentucky
Mississippi
North Carolina
South Carolina
Tennessee
Referral
32
26
2
1
2
3
3
11
18
7
7
3
2
16
14
5
4
5
15
11
8
Contact
12
2
2
1
2
13
4
4
7
4
2
2
1
1
7
Evaluated
3
2
1
2
4
2
1
2
1
2
(Continued)
131
-------
TABLE 22.GEOGRAPHICAL DISTRIBUTION OF GOOD ELECTROPLATING
WASTE TREATMENT FACILITIES BASED ON INITIAL
REFERRALS, COMPANIES CONTACTED FOR INFORMATION,
AND REPRESENTATIVE FACILITIES EVALUATED IN
DETAIL
(Continued)
Area
Referral
Contact
Evaluated
EPA Region V
Illinois
Indiana
Michigan
Minnesota
Ohio
Wisconsin
EPA Region VI
Arkansas
EPA Region VII
Iowa
Kansas
Missouri
Nebraska
EPA Region VIII
Utah
EPA Region IX
California
EPA Region X
Washington
22
14
18
4
21
8
10
1
6
1
1
3
1
10
6
13
1
19
2
2
1
4
1
3
6
7
1
11
1
1
132 .
-------
plant sample includes all process combinations in the electroplating
industry. However, since the sample selection procedure emphasized good
waste treatment practice, the sample illustrates that good waste
treatment can be achieved by a variety of plants, job and captive, large
and small, few and many different plating processes, in various
geographic locations discharging to municipal systems or directly to or
navigable waters.
As shown in Table 23 the 53 plants consisted of 39 captive
facilities and 1U job shops; 28 of these plants discharged treated
effluent directly to streams and the other 25 discharged to municipal
systems. The relative size of the plants in terms of plating capability
and raw waste load to be treated is best indicated by the installed
amperes for plating. Most electroplaters readily knew their installed
rectifier capacity in amperes which represented their potential
production capability. A lesser number readily knew their production
capacity in area plated per unit time or production rate of parts
processed through the facility.
133
-------
TABLE 23. CLASSIFICATION BY SIZE, TYPE OF FACILITY,
AND EFFLUENT DISCHARGE FOR 53 ELECTRO-
PLATING FACILITIES SELECTED FOR
EVALUATION
Captive
Relative
Size
Very large
Large
Medium
Small
Very small
Amperes
Installed
over 200,000
50,000-200,000
10,000-50,000
1,000-10,000
less than 1,000
Munic-
ipal
--
7
4
7
--
Stream
1
2
11
6
1
Job
Munic-
ipal
--
1
5
1
--
Stream
1
2
3
1
--
134
-------
Classification of 53-Plant Sample
Table 24 shows the scope of coverage for the 53 plants in terms of
the mix of possible plating operations and variety of control and
treatment technologies. Most plants (32) are equipped for decorative
plating of copper-nickel-chromium and of these about half (14) also
plate zinc. About 75 percent of the plants in the sample that plate
zinc also use a subsequent chromate conversion. The remaining 21 plants
provide most of the expected process combinations of copper, nickel,
chromium and/or zinc plating that might be found in the industry. The
53 plants in the industry sample include the variety of control and
treatment combinations to be found. Most plants (38) used some type of
chemical treatment such as continous, (C) batch, (B) and/or integrated
to treat the metals and cyanide associated with the plating operation.
A few plants use electrolytic treatment (L) and one uses reclaim tanks
for recovery (R). The other 15 plants included examples of a variety of
advanced in-process controls combination of evaporation (E) , ion
exchange (D) and reverse osmosis (O). Most of the plants used end-of-
pipe chemical treatment (continuous or batch) for at least the
acid/alkali wastewater stream.
The classification of the 53 plants by size (based on amperes),
number of employees in plating for all shifts and waste-treatment method
is shown in Table 25. Figure 20 shows that more than half of these
plants had fewer than 20 employees per shift.
Of the 53 plants, 26 were visited for on-site inspection and
verification of information. The data on rated or installed current
capacity are shown in Table 26. Figure 21 shows the same data for total
installed current capacity and indicates that 50 percent of the plants
had less than 18,000 amperes. The normal use of installed current
capacity was 67 percent based on the 23-plant average of the fraction of
total rated capacity used shown in Table 26. Thus, it was estimated
that 50 percent of the plants used less than 12,000 amperes.
Figure 22 shows the relation of installed rectifier capacity to
number of employees per shift in electroplating for the 53-plant sample.
The average value calculated is about 1000 amperes installed/ employee.
Based on an estimated typical 65 percent use of installed capacity, the
average value would be 650 amperes used/employee per shift. The large
amperage per employee for automatic plating machines (over 5000
amperes/employee) would be exprected to result in considerable spread in
the data. Thus, number of employees per se, is not a definitive indicator
of plant size in terms of pollutional potential. Amperes as related
to area plated is a more definitive measure of plant size and raw waste
load.
135
-------
TABLE 2 4.CLASSIFICATION OF 53 FACILITIES EVALUATED
BY MIX OF PLATING OPERATIONS AND TYPE OF
WASTE TREATMENT AND IN-PROCESS CONTROLS
Waste
Treatment (a) Cu Cu
and Control Cu Ni Cr Zn Ni Cr
C
B 1111
CB
CBR
LC
I 1
1C
IB
IR
El 2
EC
EB 11
EDC
EDB
E 2
D
OB
OIC
Metals Electroplated
Cu
Cu Cu Ni Cu Ni
Cu Ni Ni Cr Ni Ni Cr Ni Cr
Zn Cr Zn Zn Cr Zn Zn Zn Zn Totals
2 161 6 16
111 7
3 3
1 1
2 2
12 15
2 2
1 1
1 1
1 3
1 1
2
1 1
1 1
1 3
2 2
1 1
1 1
Totals 01262023 01 18 310 14
(a) See Footnote (e) Table 25 for definition of symbols.
136
-------
TABLE 25. SOURCE OF INFORMATION AND CLASSIFICATION BY
SIZE AND WASTE-TREATMENT METHOD
Size of Facility
Company
Code No. ^a'
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Reference^))
S
13
13, L
11
S, 12
S, 13
32
S
S
S, 13, L
S
33, L
15
S
S
S
S
S
L
13
18
1. 21
S
S
S
L, 18
5, 17, L
5
5
S
7, 11
7, S
S
2
14
2
19
19
16, 5, S
S
13
13
17, L
5
S
S
S
S
5
L
32
5
S
Data
Obtained(c>
T
P
P
P
P
P
T
T
T
P
T
P
P
T
T
P
T
T
T
T
T
P
P
T
P
T
P
T
T
T
T
T
T
T
P
T
T
P
P
T
P
P
P
P
P
P
P
P
T
P
P
T
T
Employees
in Plating
10
19
31
40
6
54
20
12
50
165
18
90
25
120 ._
100
25
70
20
6
70
30
7
80
25
250
6-10
13
50
16
200
69
15
25
52
30
15
24
38
10
1
5
100
3
16
12
20
12
18
25
13
40
2
Relative
M
M
M
M
S
M
S
S
S
L
M
L
M
M
VL
L
M
L
M
S
M
M
S
L
M
L
M
S
L
S
L
L
M
L
M
M
M
M
L
S
S
S
M
VS
S
M
VL
S
L
M
S
M
S
Classification*-6'
C/S/CCC-CC
C/S/--BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/BII--B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/I./CCC-CC
J/S/CCDECC
J/S/CCC-CC
C/M/000-BC
J/M/NEENNC
J/M/CCCCAC
J/S/DDE-BB
C/M/CCCCCC
C/S/IRI-IC
C/M/---EE-
C/M/COI-CC
C/M/---EE-
J/S/LCLLLC
J/S/--I--C
C/S/C-CCCC
C/S/CCB-BC
C/S/CCBCBC
C/M/-II--C
c/s/icmc
C/M/-BB--B
C/S/CCCCCC
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/L/-B--BB
C/M/CCCCCC
J/M/LCLLLC
C/S/IIIIIC
C/S/III-IC
C/M/--NBBB
J/S/CCCCCC
C/S/BNN-NB
C/M/--IEEC
C/M/--IEEC
J/M/CCC--C
C/S/--B B
J/M/NDD-NC
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/--CCCC
C/S/BBBBBB
C/M/INI-IB
C/S/ODD C
C/S/RCRBBB
Footnotes appear on the following page.
137
-------
FOOTNOTES FOR TABLE 25
(a) Company identification by number for this report.
(b) Source of lead to company.
(c) Information from telephone call (T) or first-round
visit (P).
(d) Relative size based on total installed rectifier
capacity in amperes for plating:
VL = very large, >200,000 amperes
L = large, 50,000 to 200,000 amperes
M = medium, 10,000 to 50,000 amperes
S = small, 1,000 to 10,000 amperes
VS = very small, >1,000 amperes.
(e) Classification by type of facility (1st letter):
J = job shop or independent
C = captive plating facility,
where the treated effluent is discharged,
S = stream (or storm sewer to stream)
M = municipal sanitary treatment system,
L = liquid effluent disposed of on land
and the following coded waste treatment or in-process
control used for each constituent of the final effluent
considered in the order; copper, nickel, chromium, zinc,
cyanide, acid/alkali:
A - adsorption
B = batch chemical treatment
C = continuous chemical treatment
D = ion exchange
E = evaporation
I = integrated
L = electrolytic
N = no treatment beyond pH adjustment
0 = reverse osmosis
R = reclaim rinsing techniques.
13&
-------
100
20
30 40 50 60 70
Cumulative Percent
80 90
100
FIGURE 20. EMPLOYEES PER SHIFT IN PLATING VERSUS
CUMULATIVE PERCENTAGE OF 53 PLANTS
-------
TABLE
26.
SIZE OF PLATING OPERATIONS (RATED AND USED)
Company
Code No.
1-16
3-1
3-3
3-4
6-3 .
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3*
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8*
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Fraction of Rated
Capacity Used
1
5
1
1
8
3
4
80
6
1
6
2
13
5
1
27
20
2
35
6
3
2
3
7
1
3
63
3
4
8
1
Cu
,500
800
,000
600
,500
,000
,150
,000
500
600
,000
,000
,150
,000
,000
,000
300
,000
,000
,400
,000
750
,000
,650
,100
,750
,300
,000
,000
400
,000
,000
,000
,000
,000
,500
250
,000
,500
Ni
9,000
10,000
12,000
2,500
5,000
1,500
200
2,300
25,150
8,000
1,000
17,000
2,000
120,000
9,250
16,000
5,000
11,000
23,000
20,000
45,000
4,000
8,650
43,500
600
10,000
3,000
6,000
62,000
8,000
4,000
10,000
23,000
350
8,500
4,000
273,000
200
4,500
1,500
8,100
3,000
Cr
6,000
25,000
3,000
3,000
1,500
1,000
23,150
8,000
72,000
8,000
8,000
63,000
15,600
16,000
4,000
2,000
44,250
16,000
7,500
30,000
3,000
250
50,000
750
10,000
20,000
25,000
6,000
1,500
8,000
8,500
10,000
250
4,500
118,000
20,000
1,500
10,000
1,500
Zn
10,000
5,825
20,000
1,000
27,150
10,000
32,500
133,000
6,000
9,000
3,200
2,500
9,000
35,000
48,650
12,500
450
1,200
15,000
15,250
7,000
7,000
12,000
3,000
32,600
6,000
1,500
Total
16,500
10,000
40,825
12,800
5,500
35,000(a>
6,100
3,200
f\. \
8,160(b>
94,600(0
19,000
73,500
35,600
14,000
263,000
63,500
33,000
15,000
6,000
24,000
44,250
3,700
57,000
32,500
75,000
10,900
8,900
129,500
2,100
75,000
74,300
21,700(e>
134,600
21,200
10,000
20,000
15,000
49,750
1,250(0
7,000
7,000
25,500
250
9,500
15,000
454,000
6,200
52,600
16,000
3,650
26,100
7,500
Cu
0.8
0.3
0.04
0.3
1.0
0.3
1.0
1.0
0.8
0.5
0.4
0.2
0.7
0.4
1.0
0.9
Ni
0.8
0.8
0.05
0.6
0.4
0.8
0.4
0.5
1.0
0.9
0.6
0.4
0.2
0.7
0.4
0.3
0.9
0.1
Cr
1.0
0.2
0.5
0.5
0.9
0.3
1.0
1.0
1.0
0.7
0.9
0.7
0.5
0.7
0.8
0.2
0.3
0.9
0.4
2n
0.7
0.5
0.3
1.0
0.5
0.8
1.0
0.8
1.0
0.3
0.7
0.8
0.8
0.6
0.9
0.4
lotal
0.9
0.7
0.1
0.5
0.6
0.9
0.4
0.8
0.8
1.0
0.9
0.7
1.0
0.6
0.5
0.8
0.5
0.7
0.6
0.6
0.3
0.9
0.7
Footnotes appear on the following
140
-------
FOOTNOTES FOR TABLE 26
(a) Includes an additional 5,000 amperes for Cd.
(b) Includes an additional 1,000 amperes for Cd; 2,825 amperes for Ag; 35 amperes for Au.
(c) Includes an additional 11,000 amperes for Cd.
(d) Includes an additional 100 amperes for Cd and 100 amperes for Sn.
(e) Includes an additional 5,700 amperes for Ag and 10,000 amperes for Sn.
(f) Includes an additional 300 amperes for Cd and 200 amperes for Ag.
(g) Includes an additional 1000 amperes for anodizing.
(h) Includes an additional 400 amperes for Cd.
141
-------
1,000,000
500,000
200,000
g 100,000
Q.
E
o
£ 50,000
o>
20,000
2 10,000
5000
2000
1000
1 I I I T
1 I
I I
I I I I
10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 21. TOTAL INSTALLED CURRENT FOR PLATING
VERSUS CUMULATIVE PERCENTAGE OF
53 PLANTS
142
-------
500,000
200,000
100,000
50,000
(A
0)
£ 20,000
Q.
E
o
£ 10,000
"o
o
O
-o 5000
5 2000
1000
500
200
100
r | i i i i
i i i i
5 10 20 50
Number of Employees per Shift
100
FIGURE 22. INSTALLED RECTIFIER CAPACITY IN AMPERES FOR
ELECTROPLATING VERSUS NUMBER OF EMPLOYEES
PER SHIFT IN ELECTROPLATING FOR 53 PLANT
SAMPLE (RATIO OF AMPERES USED TO AMPERES IN-
STALLED IS TYPICALLY 65 PERCENT)
-------
200
100
1 1 1 1 1 1 1 1 1 1
0
10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 23. EFFLUENT DISCHARGE RATE VERSUS
CUMULATIVE PERCENTAGE OF 53 PLANTS
144
-------
E
Q.
Q.
C
O)
UJ
0)
0.05
0.02
0.01
0.005
0.002
0.001
10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 24. COMPOSITE OF POLLUTANT PARAMETERS IN TREATED
EFFLUENT VERSUS CUMULATIVE PERCENTAGE OF
PLANTS
i 45
-------
Waste Treatment Results
Table 27 shows the treated effluent data and plant effluent
discharge rate (average hourly rate in 1/hr). Figure 23 shows that 50
percent of the 53 plants evaluated have an effluent of less than 34,000
1/hr. most plants analyze for total metal and oxidizable cyanide
(rather than total cyanide). These concentration values reported by the
companies are typical average values (monthly period or longer). Figure
24 shows the range of concentration of heavy metals and cyanide
(oxidizable) typically achieved by those plants which report that
pollution parameter. The results are representative of chemical
treatment. Figure 24 shows that 50 percent of the plants have values
less than the following:
Cu 0.2 mg/1
Ni 0.5 mg/1
Cr« + 0.055 mg/1
CrT 0.3 mg/1
Zn 0.3 mg/1
CN 0.04 mg/1.
From the limited data on total suspended solids in Table 27 about half
the plants can achieve less than 15 mg/1.
Table 28 provides a comparison of the waste treatment results for
all 53 plants on the basis of total installed amperage. The total plant
effluent (1/hr) in Table 27 was divided by the total installed current
capacity (amperes) in Table 26 to obtain the plant water use (kg/AH
which is numerically equivalent to 1/AH) shown in Table 28.. The water
use multiplied by the concentrations (mg/1) of each constituent in the
treated effluent shown in Table 27 gave the waste discharged (mg/AH)
shown in Table 28. Table 28 provides an approximate intercomparison of
the waste treatment results for various plants for several pollutant
parameters over a wide range of plant sizes. The data have been
normalized by the use of total current. However, in order to draw valid
conclusions for direct comparison of two plants in Table 28 additional
information is needed on any unusual differences in thickness of deposit
(e.g., the two extreme cases of thick chromium plating are noted) or the
fraction of the rated current that is normally used (Table 26).
Figure 25 shows that 50 percent of the 53 plants can achieve a water
use of less than 1.35 1/AH (or kg/AH) based on total installed current.
The water used would be about 2.0 1/AH based on the assumption of 67
percent of the rated capacity normally used as indicated previously.
Since the latter water use (1/AH) is independent of the concentration
values (mg/1) achieved in chemical treatment, it is possible to multiply
the median water use and median concentrations to estimate the waste
discharge (mg/AH) which should be achievable for most plants:
146
-------
TABLE 2 7. TREATED EFFLUENT DATA
Company
Code
No.
1-16
3-1
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
]2-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3
20-1
20-6
20-7
20-10
20-13
20-15
20-17
21-3
23-3
25-1
28-9
28-11
30-1
30-5
30-7
30-8
33-1
33-2
33-3F
33-3U
33-6
33-8
33-9
33-11
33-15
33-20
35-21
36-1
3G-2
40-4
43-1
Treated Effluent, m?/l
Classification
C/S/CCC-CC
C/S/--BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/BII--B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/L/CCC-CC
J/S/CCDECC
J/S/CCC-CC
C/M/000-BC
J/M/NEENNC
J/M/CCCCAC
J/S/DDE-BB
C/M/CCCCCC
C/S/IRI-IC
C/M/---EE-
C/M/COI-CC
C/M/---EE-
J/S/LCLLLC
J/S/--I--C
C/S/C-CCCC
C/S/CCB-BC
C/S/CCBCBC
C/M/-II--C
C/S/ICIIIC
C/M/-BB--B
C/S/CCCCCC
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/L/-B--BB
C/M/CCCCCC
J/M/LCLLLC
C/S/II1IIC
C/S/III-IC
C/M/--NBBB
J/S/CCCCCC
C/S/BNN-NB
C/M/--IEEC
C/M/--IEEC
J/M/CCC--C
C/S/--B--B
J/M/NDD-NC
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/--CCCC
C/S/BBBBBB
C/M/INI-1B
C/S/DDD--C
C/S/KCRBBB
TSS Cu
0.5
0.018
0.08
3.4 0.08
0.53
0.1
0.03
0.1
0.3
<0.5
2.4
1.0
0.7
<1.0
3
0.15
13 0.18
0.096
25 <0.1
<0.1
21 0.41
0.2
1.75
<0.07
<10.0
15 0.41
0.2
<0.2
<3.5
0.2
9.5 1.47
S.5 <0.1
9.5 0.13
3.1
20 0.2
0.21
106 0.12
<0.01
0.16
<2
0.29
Ni
1.0
0.002
0.48
0.6
19.6
0.6
0.06
0.16
0.00
1.5
2.2
1.0
0.2
<1.0
2.5
<0.20
0.39
<0.7
2
0.3
<1.0
0.48
0.25
0.8
0.5
7.0
<0.2
0.3
1.0
<0.05
1.6
0.42
0.3
39,700
34,000
15,400
1,100
6,800
9,100
18,900
47,300
94,600*
123,000
28,000
401,000
55,300
28,000*
78,700
68,000
39,700
47,300
11,000
3,800
28,400
3,100
42,600
44,700
68,000
39,400
34,000
68,000
250,000
12,000
473,000*
55,300
2,800*
170,000
30,000
91,000
8,700
62,500
32,500
42,600*
11,200
8,100
21,600
32,500
3,800
11,400
295,000
11,500
129,000
36,000
8,700
17,000
620*
(a) \r. usterick after the total flow means an assumed 8-hour work day; values could be lower by a factor of 3 if
liters per day was based on 24-hour work day.
147
-------
TABLE 28 COMPARISON OF TREATED EFFLUENT DATA BASED ON TOTAL AMPERAGE
Company
Code No.
1-16
3-1,
3-3
3-4
6-3
6-12
6-29
8-4
8-5
11-8
11-13
11-22
12-3
12-5
12-6
12-8
12-9
12-12
13-2
15-1
19-2
19-3
33-9
33-11
33-15
33-20
33-21
36-1
36-2
40-4
43-1
Classification
C/S/CCC-CC
C/S/--BEE-
C/S/-IEI-B
C/S/EB--BB
C/S/BII--B
C/M/ENCEEN
J/S/CCICIC
C/M/CCC-CC
C/L/CCC-CC
J/S/CCDECC
J/S/CCC-CC
C/M/000-BC
J/M/NEENNC
J/M/CCCCAC
J/S/DDE-BB
C/M/CCCCCC
C/S/IRI-IC
C/M/---EE-
C/H/COI-CC
C/M/EE-
J/S/LCLLLC
J/S/--I--C
C/S/C-CCCC
C/S/CCB-BC
C/S/CCBCSC
C/M/-II--C
C/S/ICIIIC
C/M/-B3--B
C/S/CCCCCC
C/S/BBBBBB
J/M/CCC-CC
C/M/CCCCCC
J/L/-B BB
C/M/CCCCCC
J/M/LCLLLC
C/S/I1IIIC
C/S/III-IC
C/M/--NBBB
J/S/CCCCCC
C/S/BNN-NB
C/M/--IEEC
C/M/--IEEC
J/M/CCC--C
C/S/--B--B
J/M/NDD-NC
C/M/C-CCCC
C/S/CCB-BC
C/M/CCCCCC
C/M/--CCCC
C/S/BBBBBB
C/M/INI-IB
C/S/DDD--C
C/S/RCRBBB
Water
Use,
kg/AH
2.4
3.4
0.38
0.09
1.2
0.27
3.1 ,
15.0
12.0*
1.3
1.5
5.5 -
1.5
2.0*
0.30
1.1
1.2
0.35
0.77
0.64
1.2
0.07
12.0
0.77
2.1
0.55
3.1
7.7
2.0
5.9
6.4*
0.73
0.14*
1.3
1.5
9.1
0.44
4.2
0.65
34*
1.6
1.1
0.86
132
0.40
0.77
0.64
1.9
2.5
2.3
2.4
0.64
0.08
Waste Discharge, tnp; per AH
TSS Cu
1.1
0.007
0.007
4.2 0.098
0.14
1.5
0.026
0.15
1.7
0.75
4.8
0.30
26 0.77
1.2
2.3
0.01
156 2.2
0.074
53 0.21
0.31
42 0.82
1.2
11.0
0.051
1.4
20 0.53
0.30
1.8
1.5
14 0.13
323 50
7.3 0.086
3.8 0.052
2.4
13 0.13
0.40
265 0.30
0.023
0.38
1.3
0.023
Ni
2.4
0.0003
0.043
0.74
5.3
1.9
0.90
0.21
0.05
2.3
4.4
0.30
0.22
1.2
*-
1.9
0.01
0.30
1.5
1.1
0.93
7.7
0.96
1.5
0.58
0.65
11
1.8
0.20
34
0.043
0.64
0.27
0.75
0.023
18
3.2
0.028
Cr+6
0.22
0.022
0.012
0.014
0.93
0.75
0.013
0.015
0.55
1.5
0.015
0.036
0.028
0.36
0.12
0.021
0.10
0.20
0.015
0.41
0.039
0.51
0.43
0.15
0.46
0.026
0.37
0.10
0.072
CrT
3.6
0.17
0.061
0.17
O./A
4.2
12.0
0.026
2.6
2.3
8.2
0.30
0.66
0.06
0.38
0.046
0.77
0.42
1.1
0.31
7.7
0.66
1.2
64.0
O.il
1.6
7.5
6.8
4.2
0.20
4.8
0.08
0.06
6.6
0.21
1.4
0.15
0.52
0.28
0.1.4
0.072
0.64
0.024
Zn
0.51
0.32
5.0
0.16
0.55
0.80
0.66
1.2
0.22
3.2
0.008
15.6
0.53
0.62
0.16
0.18
13.0
0.64
0.50
12
4.1
21
0.52
0.08
0.06
0.39
0.06
0.95
2.1
0.32
0.31
CN
0.22
0.12
0.30
0.22
0.15
0.12
0.013
0.015
9.8
19.8
0.06
0.11
0.03
0.35
0.77
1.9
1.2
0.72
0.008
0.021
0.31
0.003
0.059
1.3
0.022
0.0014
0.065
0.53
0.46
0.17
O.OS5
19
0.21
0.14
0.0077
0.016
0.015
0. 13
0.023
0.043
0.0008
(a) An asterisk after the water use means that calculations were based on an assumed 8-hour work day.
(b) Hard chromium only; multiply nuvibers by 50. No chromium was expected in effluent.
(c) '.lard chromium only; multiply numbers by 50. Large water addition prior to treatment.
48
-------
too
0.02
0.01
0 10 20 30 40 50 60 70 80 90 100
Cumulative Percent
FIGURE 25. WATER USE BASED ON TOTAL INSTALLED CURRENT
VERSUS CUMULATIVE PERCENTAGE OF 53 PLANTS
349
-------
Cu 0.4 mg/AH
Ni 1.0 mg/AH
Cr6+ 0.11 mg/AH
CrT 0.6 mg/AH
Zn 0.6 mg/AH
CN(oxid) 0.08 mg/AH.
A comparison of the above values with those in Table 28 shows that many
plants attain lower values for a single pollution parameter. However,
for all pollution parameters (all heavy metals and cyanide) the above
values are attained by only 11 plants in Table 28 (3-1, 3-3, 3-4, 11-8,
12-6, 19-3, 25-1, 33-1, 33-15, 36-1, and 43-1).
150
-------
Excepting plant 19-3 which has hard chromium plating, the first five
plants listed use some type of in-process control for chemical recovery
whereas, the last five plants listed do not use any such systems. Thus,
there is no present evidence that use of chemical recovery systems
results in less discharge of pollutants. However, there is evidence
that water use can be reduced.
Figure 26 shows that those plants (15) that are using some
combination of in-process control for chemical recovery (evaporation,
ion exchange, reverse osmosis) in one or more plating operations have
lower water use than those plants (38) that do not use such in-process
controls. The apparent two to three-fold reduction in water use in
probably indicative of the general use of multitank countercurrent
rinsing and other water conservation practices in these plants.
Figures 27 through 33 show the data of Table 28 on performance being
obtained by various plants separately for each parameter: copper,
nickel, hexavalent chromium, total chromium (Cr3+ + Cr6+), zinc, cyanide
(amenable to oxidation by chlorine) and suspended solids. For a general
estimate, a value of 40 to 80 AH/scr m can be used to convert waste
discharged from mg/AH to mg/sg m and water use from kg/AH (or 1/AH) to
kg/sa m (or 1/sq m) . The various waste management technologies were
identified by symbols in Figures 27 through 33. The appropriar- symbol
is used for each parameter to show whether a reduction in guantity of
waste discharged was achieved as the result of using the particular
technology.
151
-------
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Continuous (flow through) chemical treatment is the baseline
technology for reference with inplant segregation of chromium and
cyanide streams for separate treatment prior to recombination with the
remaining waste streams (acid/ alkali and others) for final separation
of precipitated metals. The use of this technology provides the best
overall results for all parameters because its use insures complete
treatment of the acid/alkali stream to remove precipitated metal.
Complete batch chemical treatment of all segregated streams;, is an
alternative to continuous chemical treatment that can provide equivalent
pollution reduction. Batch chemical treatment of only the hexavalent
chromium and cyanide streams (Figure 18 and 21) combined with continuous
chemical treatment for metal removal does not provide significantly
greater -pollution reduction (Figures 16, 17, 19, and 20) .
All other technologies currently in use for in-proce>ss treatment
after one or more plating process such as integrated chemical treatment,
are combined with end-of-process continuous or batch treatment of at
least the acid/alkali stream for removal of metals. Where there is no
treatment prior to discharge beyond pH adjustment, the effluent may
contain a high level of pollutants. There was no evidence from plant
data that any in-process treatment achieved greater pollution reduction
than that which can be achieved by end-of-process chemical treatment.
In-process controls used after plating operations for recovery of
chemicals such as evaporation, ion exchange, reclaim rinses, and reverse
osmosis and/or reduction of water use are combined with >nd-of-process
chemical treatment. Otherwise, the effluent may contain a high level of
pollutants. Thus, there is presently no evidence that greatter pollution
reduction than by chemical treatment can be achieved by use of these
technologies. Closing up one or all plating operations by evaporative
technology does not presently succeed in eliminating the pollution
parameter from the final effluent. In general, the present use of the
above in-process controls does not lead to a significant reduction in
pollution for the total electroplating facility which includes rinse
water after pretreatment and posttreatment operations.
The above conclusions based on the degree of pollution reduction
achieved by existing sources indicates that end-ofprocess chemical
treatment in combination with in-process controls for water conservation
is the Best Practicable Control Technology Currently Available for
existing sources in the electroplating industry.
In using the term chemical treatment no distinction is made between
continuous chemical treatment, batch chemical treatment, integrated
chemical treatment or other in-process treatments or combinations
provided that the effluent limitations are achieved. No distinction is
made in the specific chemicals used, specific chemical reactions, or
specific processes employed for destruction of cyanide, reduction of
160
-------
hexavalent chromium, or removal of metals provided -the effluent
limitations are achieved. In using the term in-process controls, no
distinction is made between the various methods of recovery of chemicals
or water conservation. Effluent limitations can be achieved by either
reduction in water use or reduction in concentration of pollutant after
final treatment or both. It is recognized that the results attainable
with any wastemanagement technology are dependent on correct operation
of the process, the maintenance of control instrumentation, and the
quality and capability of operating and supervisory personnel.
Detailed Analysis of Plant Data
From the above analysis of data from 53 plants, 5 plants were
selected for additional on-site detailed analysis of plating operations
for correlation with in-porcess controls for water conservation and
waste treatment results including sampling to verify effluent data
reported. One of the plants selected (19-3) had only hard chromium
plating operations which is a special situation because of the thick
deposit. The other four plants (11-8, 12-8, 33-1, and 36-1) were
selected as representative of the average of the best plants involved in
rack and barrel electroplating of copper, nickel, chromium and zinc.
The data obtained from each of the four second round plant visits
were analyzed with respect to the various pertinent process lines of
rack and barrel plating of copper, nickel, chromium, and/or zinc. Non-
pertinent process lines (e.g., and anodizing, bright dipping, cadmium
plating, or other than rack and barrel plating) were not included as
well as certain pertinent process lines not in use or for which
insufficient data were available. The composite of the pertinent lines
was also analyzed. The purpose of the analysis was to study water use.
The various factors based on the composite of process lines are
shown in Table 29. The monthly average concentration of each pollutant
parameter reported by the plant multiplied by the specific water use
(1/AH) or effluent factor (1/sq m) yields the waste discharge in mg/AH
or mg/sq m respectively as shown in Table 30. The values can be
compared to the recommended 1977 effluent limitations for existing
sources for copper, nickel, chromium (total), zinc, and total cyanide
(40 mg/sq m) and for hexavalent chromium and oxidizable cyanide (4 mg/sq
m) and for suspended solids (1200 mg/sq m) .
For comparison, the corresponding data using the results of BCL
sampling and analysis on the day of the plant visit and the appropriate
water use factors from Table 29 are shown in Table 31.
For plants required to analyze daily composite samples for monthly
reporting to authorities, the monthly averages over a prior period of 6
to 12 months were used to determine typical average concentrations of
pollutants. In general, the latter value is more representative of
161
-------
TABLE 29. SUMMARY OF WATER USE PARAMETERS FOR FOUR
PLANTS BASED ON COPPER, NICKEL CHROMIUM
OR ZINC PLATING AND EXCLUDING NON-
PERTINENT METAL FINISHING PROCESSES
Company
No.
Specific
Water Use,
I/AH
Effluent
Factor,
1/sq m
Coulombic
Equivalent Factor,
AH/sq m
11-8
12-8
33-1
36-1
average
2.44
1.77
1.34
1.08
1.66
170.3
95.5
77.3
114.0
114.3
69.7
53.7
57.6
105.6
71.7
162
-------
waste treatment results than samples obtained over a short period during
a plant visit. However, for Plant 33-1, the average results for 1972
were considerably higher than those obtained after about June 1972, as
shown in Table 32. A significant reduction in concentration of heavy
metals occurred coincident with reduction of suspended solids
concentration as a result of improved clarification. The concentrations
currently as achieved in 1973 are lower than the average values used
previously in Table 30 to determine mg/AH and mg/sq m for each pollutant
parameter.
One purpose of the sampling during plant visits was to verify the
accuracy of the analytical results for the plant effluent reported by
the plants. The accuracy of the analytical procedures used at Battelle
was verified by analysis of standard EPA reference samples provided by
the EPA Analytical Quality Control Laboratory, Cincinnati, Ohio. The
subsequent comparison of Battelle results with values for the standard
reference samples provided later by EPA are shown in Table 33. The
agreement in results was very good. In the range of concentrations of
interest (Samples 2 and 3), the percent deviation of Battelle results
was 2 to 12 percent.
Daily variations in concentrations of metals and cyanide in treated
effluent compared to the monthly average are to be expected. Figure 34
shows the typical variation in analysis of daily composits over a 4-
month period for Plant 11-8. Because of the low concentrations being
measured, daily concentrations are at times twice the monthly average
concentration. One factor is analytical accuracy. For example, in the
measurement of copper (1 mg/1) , chromium (0.05 mg/1) and zinc (0.5 mg/1)
by atomic absorbtion methods the relative standard deviation is 11, 26,
and 8 percent respectively (4). Another factor is that daily composite
samples are usually analyzed the day following collection. Thus, there
is a 24-hour time lag in detection of slight changes in waste treatment
performance before corrective action is taken. In view of the above
factors and determination of plated area, effluent limitations should be
based on cumulative 30-day averages with an allowance for daily maximums
exceeding the 30-day average by a factor of 2.
163
-------
TABLE 30. SUMMARY OF TREATED EFFLUENT FROM COPPER, NICKEL,
CHROMIUM OR ZINC EXCLUDING NON-PERTINENT PLANT
METAL FINISHING OPERATIONS
Pollutant
Parameter
Cu
mg/1
rag/AH
mg/sq m
Ni
mg/1
mg/AH
mg/sq m
Cr (Hex)
mg/1
mg/AH
mg/sq m
Cr(Tot)
mg/1
mg/AH
mg/sq m
Zn
mg/1
mg/AH
mg/sq m
CN(Ox)
mg/1
mg/AH
mg/sq m
Plant
11-8
.03
.07
5.1
.16
.39
27.2
.01
.02
1.7
.02
.05
3.4
.12
.29
20.4
.01
.02
1.7
Plant
12-8
.70
1.24
66.8
.20
.35
19.1
--
.60
1.06
57.3
.60
1.06
57.3
.10
.18
9.6
Plant
33-1
.20
.27
15.5
.30
.40
23.2
.06
.08
4.6
.31
.42
24.0
.80
1.07
61.9
.13
.17
10.0
Plant
36-1
.03
.03
3.4
.02
.02
2.3
.01
.01
1.7
.06
.06
6.8
.14
.15
16.0
.01
.01
1.1
Average
.24
.40
22.7
.17
.29
18.0
.03
.04
2.7
.25
.40
22.9
.41
0.64
38.9
.06
.10
5.6
164
-------
TABLE 33. SUMMARY OF TREATED EFFLUENT BASED ON BCL
SAMPLING AND ANALYSIS DURING SECOND
ROUND VISIT FOR COMPARISON WITH TABLE 2
Pollutant
Parameter
Cu
mg/1
mg/AH
mg/sq m
Ni
mg/1
mg/AH
mg/sq m
Cr (Hex)
mg/1
mg/AH
mg/sq m
Cr (Tot)
mg/1
mg/AH
mg/sq m
Zn
mg/i
mg/AH
mg/sq m
CN(Tot)
mg/1
mg/AH
mg/sq m
SS
mg/1
mg/AH
mg/sq m
Plant
11-8
.07
.17
12
.54
1.32
92
.15
.37
25
.33
.80
56
.49
1.20
83
.78
4.64
133
Plant
12-8
.33
.58
31
.17
.30
16
.65
1.15
62
1.33
2.35
127
.42
.74
40
.22
.39
21
24
42
2292
Plant
33-1
.46
.62
36
.22
.29
17
«
.05
.07
4
.20
.27
15
.90
1.21
70
.21
.28
16
22
29
1701
Plant
36-1
3.16
3.41
360
.44
.47
50
.05
.05
6
.28
.30
32
.66
.71
75
.13
.14
15
20
22
2280
Average
.29
.46
26
.34
.60
44
.22
.41
24
.54
.93
57
.62
.96
67
.33
1.36
46
22
31
2091
165
-------
Ef fluentLimitations
The quantitative effluent limitations based on Best Practicable
Control Technology Currently Available for existing sources discharging
to navigable waters to be achieved by 1977 were listed in Table 1. The
quantitative values were based on determination of what can be achieved
by the average of the best plants in the electroplating category. The
values are based on technical consideration of what concentrations of
pollutants in the treated effluent can be achieved by chemical treatment
and technical consideration of what reduction in water use for rinsing
can be achieved by normal practice by existing sources in the
electroplating industry. The basis for the 30- day effluent limitations
will be reviewed first considering the heavy metal pollutants.
For copper, nickel, total chromium, and zinc it is possible to
achieve 40 mg/sq m as was shown for the average of four plants analyzed
in detail. In addition, the average of the median values for copper,
nickel, chromium, and zinc for 53 plants is about 0.3 mg/1. Thus, the
effluent limitations can be met with an effluent factor as high as 120
1/sq m. The median water use of 53 plants was shown to be about 1.3
1/AH based on rated current or about 2 1/AH based on typical current
used. Thus, a coulombic factor of 60 AH/sq m based on typical deposit
thicknesses indicates an effluent factor of 120 1/sq m.
Water use less than 120 1/sq m can be achieved using good rinsing
practice.
For example, an automatic copper, nickel, chromium rack plating
operation achieved 22 1/sq m and two different zinc platers (with chromate
conversion) achieved 45 1/sq m. The above values were attainable by use
of good in-process control without the use of any advanced recovery
techniques.
Allowing for the fact that all existing sources may not be able to
use optimum water conservation because of space limitation for
additional rinse tanks, a value of 80 1/sq m appeared to be broadly
applicable. Two of the plants studied in detail achieve this value.
Thus, the combination of an effluent factor 80 1/sq m and a
concentration of 0.5 mg/1 for copper, nickel, total chromium and zinc
appeared to be technically achievable by over 50 percent of the 53
plants studied. This was the basis for the effluent limitations to be
achieved by 1977. From the study of plant operations, it was evident
that there are many process lines on which significant reduction in
water use for rinsing could be achieved by normal electroplating
practice provided there was an incentive. For those existing sources
that can reduce their water use sufficiently to achieve 40 1/sq m, it
will be sufficient to reduce the total metal concentration below 1 mg/1
to achieve an effluent limitation of UO mg/sq m.
166
-------
TABLE 32. MONTHLY AVERAGE EFFLUENT CONCENTRATION
FOR PLANT 33-1 SHOWING IMPROVED RESULTS
OBTAINED OVER A 14-MONTH PERIOD
Chromium
Year Month
1972 Jan.
Feb.
Mar.
Apr.
May
June
July
Aug.
Sept.
Oct.
Nov.
Dec.
1973 Jan.
Feb.
Mar.
Apr.
Cd
0.31
0.28
0.26
0.54
0.15
0.03
0.07
0.03
0.03
0.01
0.01
0.18
0.05
0.05
0.05
0.09
Cr0^
0.08
0.15
0.12
0.05
0.05
0.04
0.04
0.04
0.05
0.03
0.05
0.03
0.01
0.02
0.01
0.02
Crj+
1.07
1.45
0.08
0.70
0.30
0.16
0.16
0.26
0.15
0.07
0.05
0.05
0.06
0.10
0.02
0.03
1
0
1
1
1
1
0
0
0
0
0
0
0
0
0
0
Cu Fe Ni
.6
.80
.3
. 30
.10
.0
.30 0.30 0.30
.60 0.20 0.60
.80 0.20 0.60
.20 0.10 0.80
.20 0.30 0.70
.15 0.20 0.20
.10 0.20 0.20
.03 0.08 0.10
.09 0.09 0.10
.07 0.20 0.06
Zn
5
16
24
8
2
0
0
0
0
0
0
0
0
0
0
0
.6
.0
.0
.50
.40
.2
.20
.20
.20
.10
.20
.20
.10
.09
.03
.20
CN
0.08
0.08
0.09
0.06
0.06
0.12
0.10
0.11
0.10
0.10
0.02
0.02
0.02
0.01
0.01
0.02
S.
18
32
52
27
12
8
10
10
10
15
11
12
11
8
11
11
S.
.9
.50
.0
.0
.0
.0
.0
.4
.1
.9
.0
.6
pH
7.5
7.6
7.2
8.3
8.4
8.9
8.4
8.1
8.9
8.8
8.5
7.9
7.6
7.8
7.9
7.7
(1) Averaged concentrations for each month are in mg/1 for daily composite
analysis of waste water.
167:
-------
TABLE 33. COMPARISON OF BATTELLE ANALYTICAL RESULTS
WITH EPA REFERENCE STANDARDS
Concentration, mg/1
Cadmium
Chromium
Copper
Iron
Lead
Manganese
Zinc
Sample No.
Standard
0.0018
0.0092
0.009
0.018
0.028
0.013
0.010
1
BCL
0.002
0.014
0.012
0.016
0.027
0.015
0.014
Sample
Standard
0.016
0.083
0.067
0.402
0.092
0.096
0.079
No. 1
BCL
0.018
0.089
0.071
0.410
0.094
0.100
0.081
Sample
Standard
0.073
0.406
0.314
0.769
0.350
0.449
0.367
No. 1
BCL
0.064
0.385
0.300
0.740
0.337
0.438
0.384
168
-------
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5 10 15 20 25 5 10 15 20 25 5 10 15 20 25 5 10 15 20 25
January February March April
FIGURE 34. TYPICAL VARIATION IN CONCENTRATION OF POLLUTANT
PARAMETERS FROM ANALYSIS OF DAILY COMPOSITE OVER
A 4-MONTH PERIOD REPORTED BY PLANT 11-8
169
-------
The effluent, limitations for hexavalent chromium and oxidizable
cyanide were determined to be 4 mg/sq m. For example, an effluent
factor of 80 1/sq m and a concentration of 0.05 mg/1 in the treated
effluent are both technically achievable. Several of the plants studied
in detail could achieve lower than 4 mg/sq m for these peirameters; the
average for the four plants was close to this value. The median values
achieved by 53 plants studied was about 0.05 mg/1. Since both
hexavalent chromium and cyanide are normally chemically treated in
segregated streams there is more latitude in achieving optimum
treatment. Also, the treated effluent streams are subsequently diluted
with other electroplating waste streams which further reduces the
concentration in the final plant effluent. The concentration level of
hexavalent chromium and oxidizable cyanide are not dependent on
clarification efficiency as with metals that are removed by
precipitation.
The effluent limitation for total cyanide of 40 mg/sq m was based on
a concentration of 0.5 mg/1 combined with an effluent factor of 80 1/sq
m. Some plants may analyze for total cyanide and report the value
simply as cyanide meaning maximum oxidizable as well as total cyanide.
However, some plants report oxidizable cyanide only. The average value
determined by Battelle analysis of samples from the four plants studied
in detail was less than 0.5 mg/1 total cyanide. Three of the four
plants had 20 mg/m2 or less.
The effluent limitation for total suspended solids of 1200 mg/sq m
was based on an effluent factor of 80 1/sq m combined with a
concentration 15 mg/1 achieved by over half of the plants for which data
was available. The value for three plants during visits was 22 to 24
mg/1 representative of a single day.
A 9-month average value of about 10 mg/1 achieved by one of these
plants was considered representative.
The above values used in determining effluent limitations are
summarized in Table 35 in terms of concentration of the pollutant
parameter in mg/1 for selected effluent factors in 1/sq m, the product
of which corresponds to the effluent limitations of Table 1 in mg/sq m.
The concentrations of Schedule A and B in the interim guidelines for the
electroplating industry as shown for comparison. In general, the
concentration values of Schedule A are similar to those for an assumed
effluent factor of 80 1/sq m. The latter values on which effluent
limitations are based represent what is technically achievable; the
desired values in Schedule A were derived with consideration of water
quality and stream standards.
The effluent limitations for BPCTCA in Table 1 are based on total
metal rather than dissolved metal for several reasons, but principally
170
-------
because insoluble metal hydroxides can redissolve depending on the pH of
the receiving body of water. The need to limit insoluble metal in the
effluent has been recognized for a long time (e.g., the limit of l/i'g/1
for insoluble metal for ru, Ni, Zn and 1.25 mg/1 for Cr in schedule A).
Good clarification and separation of suspended
solids prior to stream discharge has been practiced for many years.
Since the plant effluent is usually discharged at the same pH that
clarification occurs, the soluble metal concentration will usually be
significantly less than the total metal concentration. Analysis for
total metal only reduces the expense of plant monitoring of the effluent
discharge.
Additional^Fgctgrg_Considered_in_Selection
of_Best_Practicable_Control_TechnglogY
Currently Available
Total Cost of Application of Technology in Relation to
Effluent Reduction Benefits
Based upon information contained in section VIII of the report, the
average cost of chemical treatment prior to discharge of effluent to
surface waters from medium sized and large plants, is $10.70/100 sq m.
($9.9/1,000 sq ft). This cost averages 4 percent of the plating cost and
normally will be less than 5 percent of the plating cost for most
plants. The application of this technology can achieve an 85 to 99
percent reduction in pollutants in the effluent discharged to surface
waters.
Cost of chemical treatment in small plants are greater than
$10.70/100 sq m ($9.91/1000 sq ft) as indicated in Table 21.
Cost for small plants increase as size decreases because there is a
minimum capital investment ($50,000) for a chemical waste treatment
facility.
Size and Age of Equipment and Facilities
The size of the electroplating facility in terms of surface area
plated or the ampere-hours used does not affect the raw waste load
concentration and the degree of pollution reduction attainable by
application of the waste-treatment technology. The cost of applying the
technology is not significantly different when expressed as percentage
of plating costs for a wide range of plant sizes with the exception of
the very small plants discussed above.
Age of waste-treatment facilities is a factor that will affect the
capital cost outlay. This will be greatest for those plants not
presently treating waste prior to discharge to surface waters. Modest
investments will be required to update some existing treatment
171
-------
facilities to meet the effluent limitations. Recently constructed or
updated facilities might not require any further capital investment.
Some small increase in operating costs may be reguired to achieve the
effluent limitations but the total cost of application of the technology
would not exceed that based on the average of the best plants.
Some existing sources have a large investment in automatic plating
machines which are difficult or expensive to modify for installation of
additional rinse tanks after pretreatment and posttreatment operations.
For other existing sources where space is at a premium it might be
expensive and sometimes impractical to redesign existing plating lines
or redesign the entire plating facility to accommodate additional rinse
tanks for optimum water conservation on all operations. For these
reasons, extending in-plant controls for water conservation to closed-
loop operation and/or multitank rinsing following alkaline cleaners and
acid dips was not considered practicable for all existing sources.
Without such currently available in-process controls to reduce rinse
water usage, other advanced technology designed to close up the plant
with complete reuse of water to achieve no discharge of pollutants
cannot be considered for existing sources except in special situations.
It should be noted that limitations of space for sufficient rinse tanks
would not apply to design of a new plating facility. Also, the
limitations of space within existing automatic machines as older
eqiupment if retired over the future years. Thus, age of eqiupment and
facilities is a factor that influences what is practical to accomplish
over the years.
Because of the above factors, Best Practicable Control Technology
Currently Available for existing electroplating facilities in the
industry would not achieve the elimination of the discharge of process
waste water pollutants.
Processes Employed
The possible variations in electroplating processes within a single
existing facility were also considered. Complete segregation of single-
metal waste streams was not considered practical, based on available
technology. Stream integration dilutes one process wastewater with one
or more other and might result in little or no removal of certain metals
in concentrations below the solubility limit.
In defining the Best Practicable Control Technology, no special
allowance was made for variations in product design or shape factor. If
the shape of the parts being plated requires the use of inprocess
controls such as countercurrent rinsing, evaporation, or other advanced
recovery systems for achieving reduced water use to counteract the
effect of unusually high dragout, any supplemental cost may be added
to the cost of plating. Any such incremental increase in the cost of
plating will direct attention to the design of parts that drain more
easily to reduce dragout.
172
-------
Engineering Aspects of the Application of Various Types of Control
Technology
Advanced in-process controls for recovery of plating chemicals are
rapidly gaining acceptance and often show a net cost savings compared to
chemical treatment. However, the applicability of these in-process
controls is dependent on first achieving reduction in water use by
multitank countercurrent rinsing. Such installation is not practical in
all, cases depending on the age of equipment discussed above.
Process Changes
Process changes are not currently available for the electroplating
industry that would lead to greater pollution reduction than can be
achieved by the recommended effluent limitations. Some possible process
changes such as use of noncyanide plating baths may eliminate one
pollution parameter, but do not eliminate all. They may be useful in
some facilities for reducing the cost of meeting the effluent
limitations recommended in this document.
Nonwater Quality Enviromental Impact
As discussed in Section VIII of this report, the principal nonwater
quality aspect of electroplating waste treatment is in the area of solid
waste disposal. Disposal of sludges resulting from metal removal by
chemical treatment is a current problem in many states that have a high
concentration of electroplating facilities. The problem would be
partially alleviated by disposal of drier sludge. Such added costs for
removal of water from sludge would be imposed by the requirements for
solid waste disposal and does not directly result from the requriement
for water-pollution reduction.
173
-------
The use of advanced technology to recover metal plating chemicals
from rinse water rather than chemical treatment which adds to the sludge
is being applied in areas where the sludge-disposal problem is greatest.
Further impetus in the direction of recovery rather than disposal is
expected to be provided by authorities responsible for solid waste
disposal. This will have an overall beneficial effect on water
pollution because of the concurrent requirements for water conservation
for economic application of recovery techniques.
It is estimated that many of existing electroplating sources
discharging to navigable waters are already using chemical treatment
methods with a high percentage removal of metals. This is particularly
true in geographic areas where water pollution reduction has been
emphasized and the sludge-disposal problem is most evident. Achieving
the effluent limitations by application of chemicaltreatment technology
will have little impact in total quantity of sludge where solid waste
disposal is a problem.
There will be no direct effect on ai r quality as a result of the
application of recommended technology for water-pollution reduction.
Indirect effects related to increased energy use will be minor. Energy
requirements (mainly electrical) for chemical treatment are estimated to
be 3.2 percent of the power needed for electroplating.
l-f f luent_Limitations_Bgsed_on_the
Application_of^Best Practicable
Control TechnologY Currently Available
The recommended effluent limitations to be achieved by the
application of Best Practicable Control Technology Currently Available
were shown previously in Table 1 of Section II of this report.
Expressing effluent limitations in weight per unit of plated area (mg/sq
m) is a new concept that required careful interpretation. For example,
one square metal of surface that is consecutively plated with layers of
copper, nickel, and chromium constitutes three square meteirs of plated
area. The rationals for choice of units is discussed below in relation
to guidelines for application.
Guidelines for_the Application
of_Effluent_Limitations
Selection of Production Unit
Effluent limitations are intended to specify the maximum quantity of
pollutants which may be contained in the discharged treated effluent
from a point source. This quantity must be related to a unit of
production so that the effluent limitations can be applied broadly to
various plants in the same category regardless of their production
capacity. For example, an effluent limitation for a particular
174
-------
wastewater constituent in mg/unit times the production rate in units/hr
equals the maximum amount of that constituent that can be discharged in
mg/hr. Thus, for any production unit:
mg X Unit = mg X 1__
Unit hr 1 hr
The right-hand side of the above equation represents the normal
method of monitoring based on analysis of concentration of individual
pollutants in the effluent in mg/1 and measurement of the effluent
discharge rate in 1/hr. Expressing the effluent limitation as a
function of a production unit compensates for change in production rate,
which changes the effluent discharge rate. The effluent rate in the
electroplating industry is closely related to the rinse water rate which
is in turn related to the production rate of electroplated parts.
The effluent discharge rate as volume per day is commonly reported
by electroplating and other industrial sources. Because many plants do
not work on a 24-hour-day basis at all times, it would be preferable to
use the next smaller unit of time, which is an hour. This avoids the
uncertainty associated with the daily unit which often requires further
defintion as to the number of shifts worked per day and the hours per
shift.
The most appropriate production unit in some industries is either
the weight of product produced or the weight of raw materials purchased.
Neither a unit quantity of product produced nor a unit quantity of raw
material use is appropriate for the electroplating industry, because the
quantity of product expressed as the weight of products plated does not
bear any relation to raw waste produced. Electroplating is a surface
process that is not influenced by the volume or density of the part
plated. The raw waste load is related to surface area (not volume) of
electroplated parts which determines the concentrated solution dragout,
rinse water use, and ultimately the degree of pollution reduction
achievable. While it is common in barrel plating of small parts to
weigh the plated parts as a control measure for basket loading, the
optimum weight of parts was originally determined by trial and error
plating or precalculation of the part per unit weight in order to
achieve the correct total area for optimum plating current density.
Regardless of the method of controlling the plating operation, the
dragout is related to the total area of parts plated and not the weight.
Solution adhering to the surface of small parts causes dragout.
Although some cup-shape parts that are difficult to drain or rinse may
cause high dragout not directly related to area, weight would not be a
good unit quantity applicable to both rack and barrel plating.
Although the amount of raw material used or chemicals purchased was
considered as a possible unit quantity related to production, neither
unit appeared suitable as a reliable measure of production. The weight
175
-------
of material purchased and used as soluble anodes ends up on the parts
plated, but this weight must be divided by the thickness plated to
obtain a correlation with production rate in area plated per unit time
which is the true determinant of raw waste load. In the. case of
chemicals purchased for bath make up and particularly for chromium salts
purchased for plating with insoluble anodes,, there is a further
complication. A material balance will show that the difference between
the chromium purchased and the chromium on the plated parts produced
equals the chromium in the precipitated sludge minus the small amount of
chromium discharged with the treated effluent. Thus, chromium in
chromium salts purchased in excess of that on plated parts reflects
dragout and increased sludge but not necessarily increased water
pollution. The same reasoning applies to all other metal-containing
chemicals purchased for bath make up which primarily end up as
precipitated and separated sludge. Although the amount of chemicals
purchased indicates total dissolved salts in the treated effluent, total
dissolved solids is not considered an important pollutant parameter in
the electroplating industry.
Consideration of the above factors led to the conclusion that the
unit of production most applicable to the electroplating industry is
surface area. The surface area withdrawn from a concentrated solution
in a plating operation is the paramount factor influencing dragout of
solution constituents, some portion of which ends up in the waste water
and treated effluent. Surface area influencing dragout includes not
only the surface area receiving an electroplate but also the surface
area of nonsignificant surfaces receiving little or no electrodeposit
plus the surface area of racks or barrels which hold the parts.
The total surface area is rarely known and impractical to measure in
some cases in the electroplating industry. In this case, the plated
area is the alternative logical unit of production. Even so, plated
area requires precise definition and is not the type of information that
is readily available from all plants. Alternative units of production
based on amperes and water use, which are more easily measured, were
developed and correlated with plated area and ultimately to the total
surface area in establishing effluent limitations.
Plated Area Unit of Production
The plated area is the primary unit of production on which the
effluent limitations in Table 1 are based. Plated area is defined with
reference to Faraday's Law of electrolysis by the following equation:
S = BIT
100 Kt
where S = area, sq m (sq ft)
E = cathode current efficiency, percent
176
-------
I = current used, amperes
T = time, hours
t = average thickness of deposit, mm (mil)
k = a constant for each metal plated based on
the electrochemical equivalent for metal
deposition, amp-hr/mm-sq m (amp-hr/mil-sq ft).
The numerical product of current and time (IT) is the value that would
be measured by an ampere-hour meter. Values of the constant k based on
the valence of the metal deposited and the typical current efficiencies
for various electroplating operations are shown in Table 34.
Average thickness can be approximated by averaging thickness
measurements at several points on a single plated part, to establish the
ratio of average to minimum thickness. Minimum thickness is customarily
monitored to meet the specifications of purchasers of electroplated
parts, based on service requirements.
This equation was used in this study to determine the plated areas
per uni^. time in each plating operation when the only available
information was the current used and the average thickness of deposit.
Equation (2) was also used as a check on estimates of surface area
plated provided by the plants contacted.
To calculate the total plated area on which the effluent limitations
are based for a specific plant, it was necessary to sum up the area for
each electroplating process line using Equation (2). For process lines
containing two or more electroplating operations (such as in copper-
nickel-chromium decorative plating) the plated area is calculated by
the equation for each plating operation in the process. The results
should be the same, since the same parts are processed through each
operation. However, if the calculated plated area differed for each
plating operation in a single process line, the average of the
calculated plated areas for the operations was used. The sum of the
plated areas for each process line is the total plated area for the
plant.
Small discrepencies in the above calculation for two or more plating
operations in the same process line might be related to a difference in
the actual current efficiencies from those in Table 35 which are to be
used for the calculation. However, experience with data from several
plants indicated that the more likely cause of the discrepancy is the
accuracy of the reported values of average plate thickness.
The use of ampere-hour on rectifiers might have value for monitoring
or record keeping for some plants in lieu of measuring the area of the
parts plated provided the average thickness plated is known or
determined.
177
-------
TABLE 34. TYPICAL CURRENT EFFICIENCIES ASSUMED
FOR CALCULATION OF PLATED AREA
USING EQUATION (2)
Typical
Current
Type of Efficiency, Constant (k)
Plating Operation percent amp-hr/mm-sq m amp-hr/mil-sq ft
Cyanide copper
Noncyanide copper
Nickel
Chromium
Cyanide zinc
Noncyanide zinc
50
100
100
13
60
100
3
7
8
21
5
5
.75
.49
.05
.95
.80
.80
X
X
X
X
X
X
10
10
10
10
10
10
3
3
3
3
3
3
8.
17,
19.
51.
13.
13.
84
68
00
80
70
70
Records of plating voltage and ampere-hours on each rectifier (or
watt-hours) plus thickness deposited might be correlated with watt-hours
of electricity consumed per day or month with allowance for other
electricity uses (lighting, pumps, etc) to estimate total plated area
per day or month. The total effluent could be approximated by the plant
water purchases if mainly for electroplating. Thus, the information on
electric power consumption and water consumption from monthly bills for
these services might be used in an approximation of daily plated area
for a cross check against plated area determined by more direct means.
In practice, it should be possible for electroplaters to readily
adapt to keeping records of plated area for reporting purposes. The
fact that many platers do not presently know their production rate in
terms of surface area plated is not a valid consideration since there
has been no prior requirement to keep such records. Determining plated
area should not be difficult for platers whose process operation is
dependent on use of the correct current density for optimum plating
results.
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TABLE 3 5 COMPARISON OF EFFLUENT LIMITATIONS FOR BPCTCA (TABLE I) IN TERMS
OF CONCENTRATION FOR VARIOUS EFFLUENT FACTORS WITH THE PRIOR
INTERIM GUIDELINE CONCENTRATIONS
Concentration , mg/1
Effluent Factor^,
1/sq m ,
Parameter
Cu
Ni
Cr6+
CrT
Zn
CN, oxid.
CN, total
TSS
40 80
1 0.5
1 0.5
0.1 0.05
1 0.5
1 0.5
0.1 0.05
1 0.5
30 15
160
0.25
0.25
0.025
0.25
0.25
0.025
0.25
7.5
Schedule A^c'
1.2 (0.2)
2.0 (1.0)
0.05
0.25 (0.1)
1.5 (0.5)
0.03
0.5
10
Schedule B
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SECTION X
BEST AVAILABLE TECHNOLOGY ECONOMICALLY
ACHIEVABLEJL_GUIpELINEi_AND_LIMITATigNS
The effluent limitations which must be achieved July 1, 1983 are to
specify the degree of effluent reduction attainable through the
application of the Best Available Technology Economically Achievable.
This technology can be based on the very best control and treatment
technology employed by a specific point source within the industry
category and/or subcategory or technology that is readily transferable
from one industry process to another. A specific finding must be made
as to the availability of control measures and practices to eliminate
the discharge of pollutants, taking into account the cost of such
elimination.
Consideration must also be given to:
(a) the age of the equipment and facilities involved;
(b) the process employed;
(c) the engineering aspects of the application of various types of
control technologies;
(d) process changes;
(e) cost of achieving the effluent reduction resulting from the
technology;
(f) nonwater quality environmental impact (including energy
requirements) .
The Best Available Technology Economically Achievable also assesses
the availability in all cases of in-process controls as well as the
control or additional treatment techniques employed at the end of a
production process.
A further consideration is the availability of processes and control
technology at the pilot plant, semi-works, or other levels, which have
demonstrated both technological performances and economic viability at a
level sufficient to reasonably justify investing in such facilities.
Best Available Technology Economically Achievable is the highest degree
of control technology that has been achieved or has been demonstrated to
be capable of being designed for plant scale operation up to and
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including no discharge of pollutants. Although economic factors are
considered, the costs for this level of control are intended to be top-
of-the-line of current technology subject to limitations imposed by
economic and engineering feasibility. However, Best Available
Technology Economically Achievable may be characterized by some
technical risk with respect to performance and with respect to certainty
of costs and thus may necessitate some industrially sponsored
development work prior to its application.
Industry Category and Subcategory Covered
The pertinent industry category is the electroplating industry as
defined previously in Section IX.
Identification of^Best_Ayailable_Technology
EconomicallY_Achievable
The Best Available Technology Economically Achievable is the use of
in-process and end-of-process control and treatment to achieve no
discharge of pollutants. By the use of inprocess controls to reduce the
volume of wastewater, it becomes economical to use end-of-process
treatment designed to recover water and reuse the water within the plant
thus avoiding any discharge of effluent to navigable waters. Solid
constituents in the wastewater are disposed of to landfill or otherwise.
As discussed in sections VTI and VIII one such type of treatment system
that has been designed and is currently in operation supplements
conventional chemical treatment with the use of reverse osmosis to
recover water from the treated waste stream. Additional water is
recovered for reuse by evaporation and distillation of the concentrated
waste stream from the reverse osmosis unit. The concentrated wastewater
solution from the evaporator is dry salt. It is expected that other
methods will be developed during the next five years to avoid discharge
of effluent to navigable waters and thus achieve no discharge of
pollutants in an economical manner.
Rationale_for_Selection_of_Best_Available
Technology Economically Achievablg
Time Available for Achieving Effluent Limitations
As noted previously, the effluent limitations selected for the Best
Available Technology Economically Achievable for existing sources do not
have to be achieved before July 1, 1983. This longer-range limitation
allows sufficient time for retirement and replacement of existing
electroplating and waste-treatment facilities as needed. Not all of
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these necessary changes can be expected by July 1, 1977 without placing
an unjustifiable economic burden on those plants which are currently
practicing pollution abatement.
Age of Equipment and Facilities
Replacement of older electroplating equipment and facilities will
permit the installation of modern multitank countercurrent rinsinq
systems after each operation in each process line with conservation of
water use for rinsing. The use of reclaim and recovery systems after
each plating operation should be possible. Use of in-process controls
to the maximum extent will reduce the volume of effluent such that
recovery and reuse of water is economically attractive.
Process Employed
The application of the technology for end-of-process recovery and
reuse of water to the maximum extent possible is not dependent on any
significant change in the processes now used in the electroplating
industry. Most water recovery technology can produce a higher quality
of water than normally available from public or private water supplies.
High purity water for the final rinse after plating is desirable to
improve the quality of the electroplated product.
Engineering Aspects of the Application of Various Types of Control
Techniques
Many plants are successfully using evaporative recovery systems
after one or more plating operations with a net savings compared to
chemical treatment. Evaporative systems are in current use after
copper, nickel, chromium and zinc plating operations some plants have
succeeded in using recovery systems after all plating operations in
their facility. The engineering feasibility of in-process controls for
recovery of chemicals and reuse of water are sufficiently well esta-
blished. Sufficient operational use has been accumulated to reduce the
technical risk with regard to performance and any uncertainty with
respect to costs.
The technical feasibility of end-of-process water recovery systems
has been established by extensive development of the recovery of pure
water in many related industrial processes. Although some uncertainty
may remain concerning the overall costs when applied to electroplating
wastewaters, such uncertainty primarily relates to the volume of water
that must be processed for recycling and reuse. The fact that the
technology as applied to the electroplating industry has progressed
beyond the pilot plant stage and has been designed and is being built
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for full-scale operational use indicates that the technology is
available and probably economical.
Process Changes
Application of the technology is not dependent on any process
changes. However, process changes and improvements are anticipated to
be a natural consequence of meeting the effluent limitations in the most
economic manner.
Cost of Achieving the Effluent Reduction
The costs of achieving no discharge of pollutants from large
facilities electroplating copper, nickel, chromium, and zinc are
expected to be no greater than $17.20/100 sq m ($16.00/1,000 sq ft) as
discussed in section VIII. With lower cost techniques, the cost for
achieving no discharge of pollutants may be about the same as the cost
for conventional chemical treatment, which averages about $10.70/100 sq
m ($9.91/1,000 sq ft). The cost range for achieving no discharge of
pollutants is expected to be only U to 6.5 percent of the plating costs.
It may be possible to recover and reuse sufficient chemicals and water
to offset the costs of achieving no discharge of pollutants in some
plants.
Cost for small plants of achieving zero discharge of pollutants to
navigable waters are greater than $17.20/sq ft ($16.00/1,000 sq ft) as
indicated in Table 21. Costs for small plants increase as size
decreases because there is a minimum capital investment for equipment
required to achieve reuse of water.
Nonwater Quality Environmental Impact
Application of technology to achieve no discharge of pollutants to
navigable waters by July 1, 1983, will have little impact on the solid
waste disposal problem with regard to metal removal as sludge beyond
that envisioned to meet effluent limitations recommended for July 1,
1977.
In general, it is anticipated that the technology will be applied in
a manner such that no discharge of effluent to surface waters occurs.
Thus, all of the dissolved solids in the effluent which are primarily
innocuous salts would be disposed of on land with suitable precaution to
avoid any ground water contamination. Because these salts are not large
in amount and can be dewatered to dry solids (by incineration if
necessary) very little additional impact on the solid waste disposal
problem is anticipated.
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No impact on air pollution is expected as the result of. achieving no
discharge of pollutanzs to surface water. The available technology
creates no air pollutants.
Energy requirements will increase with the achievement of no
discharge of pollutants to surface water. The amount will vary from
about 27 percent of the energy consumed by electroplating sources to as
much as four times the energy needed for plating, depending on the
specific process controls adopted in individual plants for achieving no
discharge of pollutants.
Effluent ^imitationg Bgsed^on the Application
of_Best_Available_TechnologY Economically Achievable
The recommended effluent limitations to be achieved by July 1, 1983
for existing sources based on the application of BJSt Available
Technology Economically Achievable is no discharge of process waste
water pollutants to navigable waters.
Gu i del i n es for_the Applic at i on of
Effluent Limitations
Achieving the effluent limitations of no discharge of pollutants by
achieving no discharge of effluent to surface waters is the most direct
method that eliminates the need for sampling and analysis. If there is
other effluent discharge to surface waters from the plant riot associated
with electroplating, a determination is required that no wastewaters
originating from electroplating processes are admixed with this other
plant effluent.
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SECTION XI
NEW SOURCE PERFORMANCE STANDARDS
Introduction
The standards of performance which must be achieved by new sources
are to specify the degree of effluent reduction attainable through the
application of the best available demonstrated control technology, pro-
cesses, operating methods, or other alternatives.
The added consideration for new sources is the degree of
effluent reduction attainable through the use of improved production
processes and/or treatment techniques. The term "new source" is defined
by the Act to mean "any source, the construction of which is commenced
after publication of proposed regulations prescribing a standard of
performance".
New Source Performance Standards are based on the best in-nlan^ and
end-of-process technology identified.
Additional considerations
applicable to new source performance standards take into account
techniques for reducing the level of effluent by changing the production
process itself or adopting alternative processes, operating methods, or
other alternatives. The end result will be the identification of
effluent standards which reflect levels of control achievable through
the use of improved production processes (as well as control
technology), rather than prescribing a particular type of process or
technology which must be employed. A further determination must be made
as to whether a standard permitting no discharge of pollutants is
practicable.
Consideration must also be given to:
(a) the type of process employed and process changes
(b) operating methods
(c) batch as opposed to continuous operations
(d) use of alternative raw materials and mixes of raw
materials
(e) use of dry rather than wet processes (including
substitution of recoverable solvents for water)
(f) recovery of pollutants as by-products.
Standards of Performance for New Sources are based on applicable
technology and related effluent limitations covering discharges directly
into waterways.
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Consideration must also be given to the fact that Standards of
Performance for New Sources could require compliance about three years
sooner than the effluent limitations to be achieved by existing sources
by July 1, 1977. However, new sources should achieve the same effluent
limitations as existing sources by July 1, 1983.
Industry category and Subcategorv Covered
The recommended new source performance standards apply to the
electroplating industry category as previously defined in Section IX.
Identification of Control and Treatment
TectoQlo^Y-Applic^ble to Performance
Standards and Pretreatment Standards for_New_sources
The technology previously identified in Section IX as Best
Practicable Control Technology Currently Available is also applicable to
New Sources, In addition a New Source can utilize
the best practice in multitank rinsing after each operation in the
process as required to meet the effluent limitations at the time of
construction. Thus, with no practical restrictions on rinsewater
conservation after each operation by multitank rinsing, there are fewer
restrictions on the use of advanced techniques for recovery of plating
bath chemicals and reduction of wastewater from rinsing after pre-
treatment and posttreatment. Maximum use of combinations of
evaporative, reverse osmosis, and ion exchange systems for inprocess
control currently available should be investigated. A small end-of-pipe
chemical treatment system can be used to treat spills, concentrated
solution dumps, and any other water flows not economically amenable to
in-process water and chemical recovery.
Rationale for Selection of Control and
Treatment Technology Applicable to
New Source s
The rationale for the selection of the above technology as
applicable to new sources discharging to navigable waters is as follows:
(1) In contrast to an existing source, a new source
has complete freedom to choose the most advan-
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tageous electroplating equipment and facility
design to maximize water conservation by use of
as many multitank rinsing operations as necessary.
This, in turn, allows for economic use of in-
process controls for chemical and water recovery
and reuse.
(2) In contrast to an existing source which may have at
present a large capital investment in waste treat-
ment facilities to meet effluent limitations by
July 1, 1977, a new source has complete freedom in
the selection of the Best Available Technology
Economically Achievable in the design of new waste
treatment facilities.
(3) In contrast to an existing source, a new source has
freedom of choice with regard to geographic location
in seeking any economic advantage relative to power
cost or land cost.
Standardsof_Perfornianc
The recommended Standards of Performance to be achieved by new
sources discharging to navigable waters was shown previously in Table 1A
of section II.
The quantitative values for the 30-day average standard for each
parameter in mg/sq m (lb/106 sq ft) is based on a effluent
factor of 40 1/sq m (1 gal/sq ft) combined with the concentrations
achievable by chemical treatment as previously shown in Table 33 of
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Section IX for existing sources based on an effluent factor of 80 1/sq
m. For example, 0.5 mg/1 for copper, nickel, total chromium, zinc, and
total cyanide, 0.05 mg/1 for hexavalent chromium and oxidizable cyanide,
15 mg/1 for suspended solids, when combined with an effluent factor of
40 1/sq m are the basis for the 30-day average standards of performance
in Table 1A.
In effect, Standards of Performance for New Sources Table 1A are 1/2
the values of the Effluent Limitations for existing sources to achieve
by July 1, 1977, as shown in Table 1. The rationale for selection of
Standards of Performance is based on the technical feasibility of
achieving greater reduction in water use by multitank rinsing at the
time of construction of new facilities in contrast to the present
limitations for some existing sources. For example, if an existing
source can achieve an effluent factor of 80 1/sq m, a new source should
be able to design a new facility to achieve an effluent factor of 40
1/sq m. As discussed previously in Section IX, the Standard of
Performance in mg/sq m is the product of the plant effluent factor in
1/sq m and the concentration of the parameter in the treated effluent in
mg/1. The choice of whether to reduce concentration by emphasis on
optimum chemical treatment and clarification or whether to reduce
effluent volume by water conservation or a combination of both
approaches is left to the discretion of the new source.
The rationale for establishing the daily maximum value of Standards
of Performance at twice the 30-day average is based on the limitations
in accuracy of analytical methods for measuring small concentrations,
the usual 24-time lag after analysis for corrective action, the accuracy
of measurement of effluent flow, and plated areas as discussed
previously in Section IX.
Guidelines_f.or^the Application of
New Source 3Perfgrmance_Standards
The recommended guidelines for the application of Standards of
Performance for New Sources discharging to navigable waters are the same
as those in Section IX relating to existing sources based on use of the
Best Practicable Control Technology Currently Available and those in
Section X based on use of Best Available Technology Economically
Achievable.
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SECTION XII
ACKNOWLEDGEMENTS
The following organizations associated with the electroplating
industry provided information on waste treatment technology:
American Electroplaters1 society. East Orange, New Jersey E. I. du
Pont de Nemours & Company, Wilmington, Delaware Heil Process Equipment
Corporation, Cleveland, Ohio
Industrial Filter 5 Pump Manufacturing Co., Cicero, Illinois Ionic
International, Incorporated, Detroit, Michigan Lancy Laboratories,
Zelienople, Pennsylvania M & T Chemicals, Incorporated, Matawan, New
Jersey
Metal Finishing Suppliers' Association, Incorporated, Birmingham,
Michigan National Association of Metal Finishers, Upper Montclair,
New Jersey Osmonics, Incorporated, Minneapolis, Minnesota Oxy Metal
Finishing Corporation, Warren, Michigan The Permutit Company,
Paramus, New Jersey Pfaudler Sybron Corporation, Rochester, New York
The assistance of personnel of all the EPA Regional Centers and the
many State agencies that were contacted to obtain assi stance in
identifying those plants in the electroplating industry achieving
effective waste treatment.
Acknowledgement is made of the cooperation of personnel in many
plants in the electroplating industry that were contacted and who
voluntarily provided plating operations data in addition to effluent
data. Special acknowledgement is made of those plant personnel and
company officers that cooperated in providing detailed plant operating
data and cost data to support this study of waste-treatment technology.
Acknowledgement also is made of the assistance provided by Walter
Hunt, Edward Dulaney, Murray Strier, John Ciancia, Hugh Durham, Lew
Felleison, Tom Gross, Tim Field, Alan Eckert, and Swep Davis and others
who provided helpful suggestions and comments.
Finally, the assistance of Linda Rose was invaluable in the timely
preparation of this report.
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SECTION XIII
REFERENCES
(1) Safranek, W. H., "The Role of Design in Better Plating", Metal
Progress, pp 67-70 (June 1968) .
(2) Modern Electrop.lating, Edited by F. A. Lowenheim, Second Edition,
John Wiley~and~Sons (1963), Chapter 7, pp 154-205.
(3) Metal Finishing Guidebook §_nd__pirectory, Metals and Plastics
Publications, Inc. (1973).
(4) "Methods for Chemical Analysis of Water and Wastes", Environmental
Protection Agency, Water Quality Office, Cincinnati,, Ohio (July
1971).
(5) Standard Methods for the Examination of Water_and Wastewater/
Thirteenth Edition (1971).
(6) ASTM Designation 2036-72.
(7) Ceresa, M., and Lancy, L. E., "Metal Finishing Waste Disposal.
Part One", Metal Finishing, 66 (4), 56-62 (April 1968).
(8) Pourbaix, Marcel, Atlas_of_Electrochemical_Eguilibria in Aqueous
Solutions , Pergamon Press, New York (1966) .
(9) Marquardt, Kurt, "Erfahrungen mit lonensautauschern als
Endreinungsstufe nach Entgiftung- und Neutralisationsanlagen aller Art",
Metalloberflache Angew. Elektrochemie 26 (11), 434 (1972).
(10) Personal communication from Dr. Coleman, Western Electric Company,
Indianapolis, Indiana.
(11) Environmental Sciences, Inc., "Ultimate Disposal of Liquid Wastes
by Chemical Fixation".
(12) Tripler, A. B., Cherry, R. H., Smithson, G. Ray, Summary Repbrt on
the Reclamation of Metal Values from Metal Finishing Waste Treatment
Sludges", Battelle Columbus Laboratories report to Metal Finisher's
Foundation, July 6, 1973.
(13) Dodge, B. F., and Zabban, W., "Disposal of Plating Room Wastes.
III. Cyanide Wastes: Treatment with Hypochlorites and Removal of
Cyanates", Plating, 38 (6), 561-586 (June 1951).
190
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(14) Dodge, B. F., and Zabban, W., "Disposal of Plating Room Wastes.
III. Cyanide Wastes: Treatment with Hypochlorites and Removal of
Cyanates. Addendum", Plating, 39 (4), 385 (April 1952).
(15) Dodge, B. F., and Zabban, W., "Disposal of Plating Room Wastes.
IV. Batch Volatilization of Hydrogen Cyanide
From Aqueous Solutions of Cyanides", Plating, 39 (10), 1133-1139
(October 1952) .
(16) Dodge, B. .F., and Zabban, W., "Disposal of Plating Room Wastes.
IV. Batch #olatilization of Hydrogen Cyanide From Aqueous Solutions
of Cyanides. Continuation", Plating, 39 (11), 1235-1244 (November
1952).
(17 Overflow", Chemical Week, 111 (24), 47 (December 13, 1972) .
(18) Oyler, R. W., "Disposal of Waste Cyanides by Electrolytic
Oxidation", Plating, 36 (4), 341-342 (April 1949).
(19) Kurz, H., and Weber, W., "Electrolytic Cyanide Detoxication by the
CYNOX Process", Galvanotechnik and Oberflaechenschutz, 3, 92-97
(1962) .
(20) "Electrolysis Speeds Up Waste Treatment", Environmental
Science and Technology", 4 (3) , 201 (March 1970) .
(21) Thiele, H., "Detoxification of Cyanide-Containing Waste Water by
Catalytic Oxidation and Adsorption Process", Fortschritte
Wasserchemie Ihrer Grenzgebiete, 9, 109120 (1968): CA, 70, 4054
(1969) .
(22) Bucksteeg, W., "Decomposition of Cyanide Wastes by Methods of
Catalytic Oxidation Absorption", Proceedings of the 21st Industrial
Waste Conference, Purdue University Engineering Extension Series,
688-695 (1966) .
(23) "Destroy Free Cyanide in Compact, continuous Unit", Calgon
Corporation advertisement, Finishers' Management, 18 (2) , 14
(February 1973) .
(24) 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).
(25) Sonday, N. E., and Dodge, B. F., "The Oxidation of Cyanide Bearing
Plating Wastes by Ozone. Part II", Plating, 48 (3), 280-284 (March
1961).
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(26) Rice, Rip G., letter from Effluent Discharge Effects committee to
Mr. Allen Cywin, Effluent Guidelines Division, July 9, 1973.
(27) "Cyanide Wastes Might Be Destroyed at One-Tenth the Conventional
Cost", Chemical Engineering, 79 (29), 20 (December 25, 1972).
(28) Manufacturers' Literature, DMP Corporation, Charlotte, North
Carolina (1973) .
(29) Ible, N., and Frei, A. M., "Electrolytic Reduction of Chrome in
Waste Water", Galvanotechnik und Oberflaechenschutz, 5 (6), 117-122
(1964) .
(30) Schulze, G., "Electrochemical Reduction of Chromic Acid-Containing
Waste Water", Galvanotechnik, 58 (7) , 475-480 (1967) : CA, 68,
15876t (1968).
(31) Anderson, J. R., and Weiss, Charles O., "Method for Precipitation
of Heavy Metal Sulfides", u. S. Patent No. 3,740,331, June 19, 1973.
(32) Lancy, L. E., and Rice, R. L., "Upgrading Metal Finishing
Facilities to Reduce Pollution", paper presented at the EPA
Technology Transfer Seminar, New York, N.Y. (December 1972) .
(33) ElectroBllting_Erigineering_Handbook, Edited by A. K. Graham,
Third Edition, Van Nostrand Reinhold Company, New York (1971).
(34) Olsen, A. E., "Upgrading Metal Finishing Facilities to Reduce
Pollution; In-Process Pollution Abatement Practices", paper
presented at the EPA Technology Transfer Seminar, New York, N. Y.
(December, 1972).
(35) Novotny, C. J. , "Water Use and Recovery", Finishers' Management,
18 (2) , 43-46 + 50 (February 1973) .
(36) Rushmere, J. D., "Process for Brightening Zinc and Cadmium
Electroplates Using an Inner Salt of a Quaternary Pyridine
Carboxylic Acid and Composition Containing the Same", U. S. Patent
3,411,996, November 19, 1968.
(37) Ceresa, M. , and Lancy, L. E. , "Metal Finishing Waste Disposal.
Part Two", Metal Finishing, 66 (5), 60-65 (May 1968).
(38) Ceresa, M. , and Lancy, L. E., "Metal Finishing Waste Disposal.
Part Three", Metal Finishing, 66 (6), 112118 (June 1968).
192
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(40) Brown, C. J., et al., "Plating Waste Recovery by Reciprocating-
Flow Ion Exchange", Technical conference of The American
Electroplaters1 Society, Minneapolis, Minnesota, June 18, 1973.
(41) Oh, C. B., and Hartley, H. S., "Recycling Plating Wastes by Vapor
Recompression", Products Finishing, 36 (8), 90-96 (May 1972).
(42) Kolesat, T. J., "Employment of Atmospheric Evaporative ##wers in
the Electroplating Industry as a Means of Recycle and Waste
Elimination", Technical Conference of The American Electroplaters'
Society, Minneapolis, Minnesota, June 18, 1973.
(43) McLay, W. J., Corning Glass Company, Personal Communication.
(44) Spatz, D. D., "Industrial Waste Processing With Reverse Osmosis",
Osmonics, Inc., Hopkins, Minnesota (August 1, 1971).
(45) Spatz, D. D., "Electroplating Waste water Processing Wirh Revers^
Osmosis", Products Finishing, 36 (11), 79-89 (August 1972).
(46) Campbell, R. J., and Emmerman, D. K., "Recycling of Water From
Metal Finishing Wastes by Freezing Processes", ASME Paper 72-PID-7
(March 1972) .
(47) Campbell, R. J., and Emmerman, D. K., "Freezing and Recycling of
Plating Rinsewater", Industrial Water Engineering, 9 (4), 38-39
(June/July 1972) .
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SECTION XIV
GLOSSARY
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 concentration of acid ions expressed as pH for a solution.
Act
The Federal Water Pollution Control Act Amendments of 1972.
Activator
Chemical substance, usually stannous chloride, that triggers the
electroless deposition process on a nonconducting surface.
Addition^Agent
Substance, usually an organic material, added to an electroplating
solution to improve the properties of the electroplate.
Alkalinity
The concentration of base ions expressed as pH for a solution.
Allowable ..Water Use
The sum of water used for each plating process or the sum of water used
for each necessary rinsing operation.
Ampere
Unit of electricity, amount of which is the current that will deposit
silver at the rate of 0.0011180 gram per second.
Ampere-hours
Product of amperes of electricity being used and time of that use.
Anions
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The negative charge ions in the solution, i.e., hydroxyl.
Anode
The electrode that takes electrons from the anions in solution (is
connected to the positive terminal of the direct current source).
Automatic_Plating
(1) full - plating in which the cathodes are automatically conveyed
through successive cleaning and plating tanks.
(2) semi - plating in which the cathodes are conveyed automatically
through only one plating tank.
Ba rr el _Plating
Electroplating of workpieces in barrels (bulk) .
S§§i§_Metal_or_Material
That substance of which the workpieces are made and that receives the
electroplate and the treatments in preparation for plating.
Best Available Technology Economically Achievable
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.
Best Practicable^Contrgl Technology Currently Available
Level of technology applicable to effluent limitations to be achieved by
July 1, 1977, for industrial discharges to surface waters as defined by
Section 301 (b) (1) (A) of the act.
BOD
Biochemical oxygen demand.
BrjLght_pip_
A solution used to produce a bright surface on a metal.
Cagital_Cgsts
Financial charges which are computed as the cost of capital times the
capital expenditures for pollution control. The
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cost of capital is based upon a weighed average of the separa## costs of
debt and equity.
Ca]3tive_O]3eratiQn
Electroplating facility owned and operated by the same organization that
manufactures the workpieces.
Cagtivexpiating Shops
Companies engaged in product fabrication and/or assembly and normally
process approximately the same number of the same products per month.
The volume of toxic wastes created by captive operations is expected to
be more or less constant.
Carbon_Bed_Catalytic^Destruction
A nonelectrolytic process for the catalytic oxidation of cyanide wastes
using trickling filters filled with low-temperature coke.
Chemical substance, usually palladium chloride, in a dip solution to
cause electroless deposition of a metal on a nonconducting surface.
Category,and^Subcategory
Divisions of a particular industry which possess different traits which
affect waste treatability and would require different effluent
limitations.
Cathode
The electrode (the workpieces in electroplating) that transfers
electrons to the cations in the solution.
Cations
The positive-charge ions in the solution, i.e., the metal to be
electrodeposited, hydrogen, copper, nickel, etc.
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 compound capable of forming a chelate compound with a metal ion.
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Chemical^RecQvery Systems
Chemical treatment of electroplating wastes utilizing (1) batch methods,
(2) continuous methods, or (3) integrated procedures.
Chromium^CatalYSt
Plating bath constituent that in small amounts makes possible the
continuing capability to electrodeposit chromium. Usually fluoride,
fluorosilicate and/or sulfate.
Cleaner
Usually an alkaline solution pretreatment to remove surface soil such as
oils, greases, and substrates chemically unrelated to the basis
material.
Closed-Loop Evaporation System
A system used for the recovery of chemicals and water from a plating
line. An evaporator concentrates flow from the rinse water holding
tank. The concentrated rinse solution is returned to the plating bath,
and distilled water is returned to the final rinse tank. The system is
designed for recovering 100 percent of the chemicals, normally lost in
dragout, for reuse in the plating process.
COD
Chemical oxygen demand.
Comgatible^Pgllutgnts
Those pollutants which can be adeguately treated in publicly owned
treatment works without harm to such works.
Continuous_Treatment
Chemical waste treatment operating uninterruptedly as opposed to batch
treatment; sometimes referred to as flow through treatment.
Conyersion_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.
Coulomb
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Product of current in amperes and time in seconds. Thus, one coulomb is
1 ampere-second.
Coulombic
A term used to denote a relationship based in. coulombs and
electrochemical equivalents according to Faraday's Law.
Count erf 1 ow_Ri n s i n g
Series of rinses; usually three, in which water flow is from last to
first rinse, thus counterflow to direction work loads move through the
rinses.
d-c Power source
Direct Current power source.
Refers to the multilayer electroplate of copper + nickel + chromium in
that order, on the basis material to provide the bright decorative
appearance.
Deposit
The material formed on the electrode or workpiece surface, i.e., a metal
in electroplating.
Accounting charges reflecting the deterioration of a capital asset over
its useful life.
Dracfout
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.
Dual Nickel Plate
Two layers of nickel electroplate with different properties to enhance
corrosion resistance and appearance under chromium electroplate.
Requires two different nickel plating baths.
Effluent
The waste water discharged from a point source to navigable waters.
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Ef fluent^Lirnitation
A maximum amount, per unit of production of each specific constituent of
the effluent that is subject to limitation in the discharge from a point
source.
Electrochemical_Eguivalent
The weight of metal electrodeposited (or other substance changed
chemically by reduction or oxidation) per unit of time and unit of
current; i.e., pound per ampere-hour, grams per ampere-second.
Electrode
Conducting material for passing the electric current out of a solution
by taking up or into it by giving up electrons from or to ions in the
solution.
Electrodeposition
The transfer of electrons from the cathode to metal ions at its surface
to produce the metal on the cathode surface.
El ectr g forming
The production or reproduction of articles by electrodeposition upon a
mandrel or mold that is subsequently separated from the deposit.
Electroless Plating
Deposition of a metallic coating by a controlled chemical reduction that
is catalyzed by the metal or alloy being deposited.
Electrolysis
The passage of current through an electrolyte bringing about chemical
reactions.
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
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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.
The electrodeposition of an adherent metallic coating upon the basis
metal or material for the purpose of securing a surface with properties
or dimensions different from those of the basis metal or material.
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 workpieces, and
drying.
Exhaust Wash
Water used to trap droplets and solubles from air passed to remove
spray, vapor, and gasses from electroplating and process tanks.
The number of coulombs (96,490) required for an electrochemical reaction
involving one chemical equivalent.
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.
Hard_Chrome
Chromium electroplate applied for nondecorative use such as wear
resistance in engineering applications.
Immersion Plate
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A metallic deposit produced by a displacement reaction in which one
metal displaces another from solution, for example:
Fe + Cu-n- T Cu + Fe+ +
Incomp_atible_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
owned by the customer.
Integrated Chemical Treatment
workpieces
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.
Jnvestment_ Costs
The capital expenditures required to bring the treatment or control
technology into operation. These include the traditional expenditures
such as design; purchase of land and materials; etc.; plus any
additional expenses required to bring the technology into operation
including expenditures to establish related necessary solid waste
disposal.
Treatment in publicly owned treatment works of combined municipal
wastewaters of domestic origin and wastewaters from other sources.
Mandrel
A form used as a cathode in electro forming; a mold or matrix.
N§w_Source
Any building, structure, facility, or installation from which there is
or may be a discharge of pollutants and whose construction is commenced
after the publication of the proposed regulations.
New Source Performance Standards
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Performance standards for the industry and applicable new sources as
defined by Section 306 of the Act.
ohm
The unit of electrical resistance. The resistance at OC of a column of
mercury of uniform cross section, having a length of 106.300 cm and a
mass of 14. 4521 gm.
Ogen-Logp Evaporation System
A system used for the partial recovery of chemicals and water from a
plating line using less than 3 rinses. The circulation loop through the
evaporator is opened by creating another flow path resulting in
wastewater. A small percentage (4-5 percent) of the dragout that
accumulates in the final rinse is not recirculated to the evaporator and
must be treated by a chemical method before disposal.
ORP_Recprderg
Oxidation- reduction potential recorders.
Oxidizable_Cy_anide
Cyanide amenable to oxidation by chlorine according to standard
analytical methods.
A unit for measuring acidity or alkalinity of water, based on 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 1, a
solution is alkaline.
Pickle
An acid solution used to remove oxides or other compounds related to the
basis metal from its surface of a metal by chemical or electrochemical
action.
Pickling
The removal of oxides or other compounds related to the basis metal from
its surface by immersion in a pickle.
Plated_Area
The area of the workpiece receiving an elect rodeposit. The thickness of
deposit usually varies over the plated area.
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Plating_Barrel
Container in which parts are placed loosely, so they can tumble as the
barrel rotates in the plating or processing solution.
Fixture that permits moving one or more workpieces in and out of a
treating or plating tank and transferring electric current to the
workpieces when in .the tank.
Point Source
A single source of water discharge such as an individual plant.
Preplating Treatment Waste
Waste contributed by preplating treatments is affected by the basis
materials, any surface soil on the workpieces, formulation of solutions
used for cleaning or activating the materials, solution temperatures,
and cycling times.
Treatment performed in wastewaters from any source prior to introduction
for joint treatment in publicly owned treatment works.
Electroplating of workpieces on racks.
Re cla j m^Ri ns es
Reclaim rinses are used as the first step following a plating process to
retain as much of the chemicals as possible and to allow return of the
dragout solution to the plating tank.
Rectifier
A device which converts ac into dc by virtue of a characteristic
permitting appreciable flow of current in only one direction.
Reverse Osmosis
A recovery process in which the more concentrated solution is put under
a pressure greater than the osmotic pressure to drive water across the
membrane to the dilute stream while leaving behind the dissolved salts.
Rinse
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Water for removal of dragout by dipping, spraying, fogging, etc.
Rochelle_Salt
Sodium potassium tartrate: KNaC4Ht»06.4H20.
Running Rinse
A rinse tank in which water continually flows in and out.
Saye_Rinse
Same as reclaim rinse.
Still_Rinse
Does not have water flowing in and out as a running rinsej and may be a
reclaim rinse or dumped periodically to wastewater.
Standard of Performance
A maximum weight discharged per unit of production for each constituent
that is subject to limitation and applicable to new sources as opposed
to existing sources which are subject to effluent limitations.
Strike
(1) noun - a thin coating of metal (usually less than 0.0001 inch in
thickness) to be followed by other coatings.
(2) noun - a solution used to deposit a strike.
(3) verb - to plate for a short time, usually at a high initial current
density.
Tank
Term for vessel that contains the solution and auxiliary equipment for
carrying out the electroplating or other operational step.
T.ank_Current
Total amperage required to electroplate all the workpieces of a tank
load.
Tank_Load
Total number of workpieces being processed simultaneously in the tank.
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Total_Chromijrri
Total chromium (CrT) is the sum of chromium in all valences
Cyanide
The total content of cyanide expressed as the radical CN-, or 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.
Total_Metal
Total metal is the sum of the metal content in both soluble and
insoluble form.
ynit_OE§ ration
A single, discrete process as part of an overall sequence, e.g.,
precipitation, settling, filtration.
y§ed_current
Current that is used in electroplating operations and related to (1) the
area being pla##d for a particular deposit thickness and (2) the
processing time (area per unit time) .
Volt
The voltage which will produce a current of one ampere through a
resistance of one ohm.
Watt
An energy rate of one joule per second, or the power of an electric
current of one ampere with an intensity of one volt.
Workpiece
The item to be electroplated.
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TABLE 36
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 lb
million gallons/day mgd
mile mi
pound/square
inch (gauge) psig
square feet sq ft
square inches sq in
tons (short) t on
yard y d
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)1
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3,785
1.609
(0.06805 psig +1)1
0.0929
6.452
0.907
0.9144
ha hectares
cu m cubic meters
kg cal kilogram - calories
kg cal/kg kilogram calories/kilogra
cu m/min cubic meters/minute
cu m/min cubic meters/minute
cu m cubic meters
1 liters
cu cm cubic centimeters
°C degree Centigrade
m meters
1 liters
I/sec liters/second
kw killowatts
cm centimeters
atm atmospheres
kg kilograms
cu m/day cubic meters/day
km kilometer
atm atmospheres (absolute)
sq m square meters
sq cm square centimeters
kkg metric tons (1000 kilogr;
m meters
1 Actual conversion, not a multiplier
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