&EPA
United States
Environmental Protection
Agency
Technology Transfer
EPA/625/5-85/016
September 1985
Revised
Environmental Pollution
Control Alternatives
Reducing Water Pollution
Control Costs in the
Electroplating Industry
t~
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Cover Photograph:
Exterior batch treatment tanks.
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Technology Transfer
EPA/625/5-85/016
Environmental Pollution
Control Alternatives
Reducing Water Pollution
Control Costs in the
Electroplating Industry
September 1985
This report was prepared jointly by
Industrial Technology Division
Office of Water Regulations and Standards
Office of Water
Washington, DC 20460
and
Center for Environmental Research Information
Office of Research Program Management
Office of Research and Development
Cincinnati, OH 45268
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From left to right, a lime slurry tank, flocculator feed tank, lamella solids separator, control panel, and sludge
storage tank for a 300 gal/min facility.
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Contents
1. Overview 1
2. Costs of Conventional Wastewater Treatment Systems 3
Capital Costs '.'.'.4
Wastewater Collection 4
Chromium Reduction 5
Cyanide Oxidation 3
Neutralization/Precipitation 9
Clarification \Q
Sludge Handling 11
Operating Costs 13
Sludge Disposal and Municipal Fees 14
Wastewater Treatment Chemical Costs 17
Total Facility Costs/An Example Calculation 21
3. Process Modifications to Reduce Costs 24
Reducing Rinse Water Use 26
Reducing Drag-Out Loss 29
Recovering Drag-Out from Rinse Tanks 30
Reducing Drag-Out from Plating Tanks 34
Example of Cost/Benefits Analysis 35
Materials Recovery Processes 33
Evaporation 40
Reverse Osmosis 44
Ion Exchange 47
Electrodialysis 59
Electrolytic Processes 52
Bibliography 55
Appendix A. Drag-Out Recovery Cost Reduction Worksheet 57
HI
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Illustrations
Figures
1. Conventional Wastewater Treatment System for Electroplating 4
2. Investment Cost for Chromium Reduction Units 7
3. Investment Cost for Cyanide Oxidation Units 8
4. Investment Cost for Continuous Single-Stage Neutralization/
Precipitation Units 9
5. Investment Cost for Flocculation/Clarification Units 10
6. Investment Cost for Sludge Storage/Thickening Units 12
7. Hardware Cost for Recessed Plate Filter Presses 12
8. Annual Sewer Fee as a Function of Clarifier Overflow Rate 14
9. Annual Cost for Industrial Sludge Disposal 15
10. Capital Cost Justification for Sludge Dewatering Equipment 16
11. Consumption and Cost Factors for Wastewater Treatment
Chemicals 18
12. Generation and Cost Factors for Sludge Disposal 19
13. Consumption and Cost Factors Using Lime for Wastewater
Treatment 20
14. Wastewater Treatment Flow Chart: Example System 21
15. Savings Resulting from Use of Spent HCI in Chrome Reduction
Treatment Process 25
16. Countercurrent Rinse Systems - 26
17. Estimating Rinse Ratios for Multiple-Tank Rinse Systems 27
18. Surface Evaporation Rate from Plating Baths with Aeration 30
19. Surface Evaporation Rate from Plating Baths without Aeration 31
20. Input Required with Heat Aeration of Plating Baths 32
21. Automated Rinse-and-Recycle System 33
22. Drag-Out Recovery Rate for Rinse-and-Recycle Systems 33
23. Nickel-Chrome Wastewater Flow Rates: Original System 36
24. Nickel-Chrome Wastewater Flow Rates: Modified System 37
25. Recovery Systems: (a) Closed Loop; (b) Open Loop 40
26. Recovery Potential for a Two-Stage Countercurrent Rinse System ... 41
27. Closed-Loop Evaporative Recovery System 42
28. Investment and Energy Costs for Evaporative Recovery Units 42
29. Reverse Osmosis System for Nickel Plating Drag-Out Recovery 44
30. Investment Cost for Reverse Osmosis Unit 45
31. Ion Exchange System for Chromic Acid Recovery 47
32. Operating Cycle for Reciprocating Flow Ion Exchange Unit 48
33. Electrodialysis Flow Schematic 50
34. Electrodialysis System for Nickel Plating Drag-Out Recovery 50
35. Investment Cost for Electrolytic Recovery Units 53
A-1. Worksheet Completion Procedure 58
A-2. Cost Reduction Worksheet 60
IV
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Tables
1. Prices of Electroplating Chemicals, Wastewater Treatment
Chemicals, and Utilities Used by the Electroplating Industry 2
2. Composition of Raw Waste Streams from Common Metals Plating ... 3
3. Costs for Wastewater Collection 5
4. Basis for Economic Evaluations 13
5. Cost Comparison of Common Alkaline Reagents 19
6. Wastewater Treatment Chemical and Sludge Disposal Costs:
Example System 22
7. Investment Costs for Wastewater Treatment: Example System 23
8. Total Annual Costs for Wastewater Treatment: Example System .... 23
9. Economic Consequences of Plating Chemicals Losses 29
10. Standard Nickel Solution Concentration Limits 35
11. Evaluation of Rinsing Options for Nickel Plating Operation 38
12. Evaluation of Rinsing Options for Chrome Plating Operation 38
13. Summary of Recovery Technology Applications 39
14. Economics of Evaporator System for Chromic Acid Recovery 43
15. Reverse Osmosis Operating Parameters 45
16. Economics of Reverse Osmosis System for Nickel Salt Recovery 46
17. Economics of Reciprocating Flow Ion Exchange System for
Chromic Acid Recovery 49
18. Economics of Electrodialysis System for Nickel Plating Solution
Recovery 50
19. Economics of Electrolytic Copper Recovery System 54
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Bath and rinse tanks for rack electroplating operation.
VI
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1. Overview
Under the Federal Water Pollution
Control Act Amendments of 1972,
the Environmental Protection
Agency (EPA) was directed to issue
effluent limitations and performance
standards for industrial dischargers
to waterways or publicly owned
treatment works (POTWs).
Subsequent legislation, the Clean
Water Act Amendments of 1977,
required that EPA adhere to a new
schedule for promulgating those
limitations and standards,
particularly with regard to a list of
toxic pollutants referred to as
"priority" pollutants. A number of
these pollutants are associated with
the electroplating industry.
Regulations under this Act appear as
the Effluent Guidelines and
Standards for Metal Finishing,
promulgated July 15,1983 in 48
Federal Register 32485, and in
subsequent amendments and
corrections. These are incorporated
into Title 40, Part 433 of the Code of
Federal Regulations. These
regulations apply to all new metal
finishing and electroplating facilities
and all captive and integrated
existing facilities. Regulations for
existing electroplating job shops that
discharge to POTWs appear in Part
413 of Title 40 of the Code of Federal
Regulations.
In addition to these effluent-related
requirements, electroplaters are also
affected by the requirements of the
Resource Conservation and
Recovery Act of 1976 (RCRA). Under
RCRA and the subsequent
amendments of 1984, EPA has
promulgated and will continue to
promulgate regulations controlling
the management and disposal of
industrial sludges, particularly those
containing hazardous materials.
Operating costs in the electroplating
industry have been affected by the
economic burden of meeting these
pollution control requirements, as
well as by steadily rising raw
material and utility costs. Table 1
illustratesjhe increase in unit prices
over a ^^year period for
electroplating chemicals,
wastewater treatment chemicals,
and utilities used in the industry.
Three significant features of the
electroplating chemicals listed in the
Table are worthy of mention:
• Cyanide, chromium, and cadmium
compounds are classified as toxic
substances on the EPA list of
priority pollutants.
• Almost all the chemicals listed are
typically present in the wastewater
from electroplating processes.
• The price of each has risen
dramatically since 1972.
As indicated in Table 1, prices of
wastewater treatment chemicals and
utility costs, including water and
sewer fees, have also risen sharply.
These rising costs of materials and
services, as well as increasingly
stringent EPA regulations, suggest
that all of these costs, and
particularly the costs of water
pollution control treatment for the
electroplating industry, need to be
reevaluated.
A review of the costs of conventional
treatment systems for electroplating
wastewater quickly comes to focus
on two factors:
• The volume of wastewater
passing through the system
• The concentration of pollutants in
the wastewater.
The capital and operating costs are
both directly dependent on these
factors. Consequently, costs of
complying with EPA regulations can
be reduced by using technologies
that minimize the volume of
wastewater generated, thereby
reducing the quantity of treatment
chemicals used as well as reducing a
firm's water, sewer, and sludge
removal expenses. Costs can be
further reduced by using
technologies which allow for the
recovery and reuse of valuable
plating materials and process
chemicals.
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This publication discusses the cost
tradeoffs of wastewater reduction
and materials recovery technologies
for the electroplating industry in the
context of the EPA regulations.
Although it discusses sludge briefly,
its primary focus is on wastewater
treatment. It is designed for those
who will be selecting an optimum
control system for their operation.
Chapter 2 presents a description and
capital costs for each of six
components of a conventional
treatment system. The chapter also
includes information on determining
the operating costs for the system.
Chapter 3 presents process
modifications technologies which
offer potential for cost savings by
minimizing water use or by reducing
drag-out loss. These include several
materials recovery processes. For
each, examples or worksheets are
provided to aid the user in
estimating costs or in making
cost/benefit assessments of
treatment technologies.
This publication is an update of a
1979 EPA publication:
Environmental Pollution Control
Alternatives: Economics of
Wastewater Treatment Alternatives
for the Electroplating Industry; EPA
publication number 625/5-79-016. It
has been revised to reflect changes
in technologies and prices and in the
EPA regulations that directly affect
costs in the electroplating industry.
A companion document,
Environmental Regulations and
Technology: The Electroplating
Industry, EPA publication number
625/10-85-001 a, gives detailed
information on water and waste
regulations, case histories, an
overview of control technologies for
both water and solid waste, financial
information, and sources for further
information.
Table 1.
Prices of Electroplating Chemicals, Wastewaster Treatment Chemicals, and
Utilities Used by the Electroplating Industry
Electroplating chemicals ($/lb):a'fi
Boric acid (H3B03)
Cadmium chloride (CdCI2)°
Chromic acid (H2CrO4)
Copper cyanide (Cu(CN}2)°
Copper sulfate (CuSO4)<:
Nickel chloride (NiCI2)c ,
Nickel sulfate (NiSO4)c
Sodium cyanide (NaCN)°
Zinc (metallic)0
Zinc cyanide (Zn(CN)2)c
Wastewater treatment chemicals ($/lb):a'b
Calcium hydroxide (Ca(OH)2)
Calcium oxide (CaO, quicklime)
Chlorine (CI2)
Ferrous sulfide (FeS)
Hydrochloric acid (28% HCI)
Sodium bisulfite (NaHSO3)
Sodium carbonate (58% Na2CO3)
Sodium hydroxide (98% NaOH equiv.)
Sodium hypochlorite (NaOCI)
Sodium sulfide (Na2S)
Sulfur dioxide (SO2)
Sulfuricacid (H2S04)
1972
0.069
—
0.37
1.05
0.47
0.67
0.50
0.21
0.18
0.64
0.010
0.009
0.038
—
0.0135
0.066
0.018
0.036
—
0.07
0.038
0.017
Price
1978
0.176
2.60
0.78
1.95
0.88
1.04
0.76
0.40
0.31
1.41
0.017
0.016
0.075
0.40
0.023
0.13
0.03
0.08
0.40
0.12
0.085
0.023
1984
0.30
3.73
1.18
2.62
0.88
1.05
1.19
0.68
0.51
2.00
0.025
0.02
0.09
, 0.50
0.35
0.30
0.06
0.13
0.60
0.22
0.14
0.05
Utilities:"
Electricity ($/kWhr)
Steam by energy source ($/MMBtu):
0.028
0.045
0.08
Natural gas
Oil
Water ($/1 ,000 gal):
Use fee
Sewer fee8
1.03
1.39
0.25
0.25
2.07
3.53
0.50
0.60
6.00
7.50
0.80
1.20
"Prices are for bulk shipments of chemicals; prices for smaller quantities or specially packaged
quantities may be 10% to 50% higher. Plating chemicals purchased with proprietary additives are
from 20% to 40% higher.
"Prices from Chemical Marketing Reporter, Oct. 30,1972; Feb. 20,1978; and Feb. 6,1984.
"Substance is on EPA list of priority pollutants.
"Average prices.
Typical of a metropolitan area.
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2. Costs of
Conventional
Wastewater
Treatment Systems
Certain wastewater treatment
technologies have become so widely
accepted in the electroplating
industry that they are usually
referred to as "conventional"
treatment technologies. These
include chromium reduction and
cyanide oxidation (as needed),
neutralization to precipitate
suspended solids followed by
clarification of the wastewater, and
thickening and filtration of the
resulting sludge. Figure 1 illustrates
a conventional treatment system for
wastes containing, among other
pollutants, chromium and cyanides.
Of course, the size and complexity of
a particular system can vary
significantly. Wastewater flow rate is
a major factor in determining the
initial cost of equipment, while both
flow rate and pollutant loading are
significant in determining the
operating cost of the system. System
design is also affected by wide
variations in pollutant loading often
found in electroplating waste
streams.
Table 2 lists the variability in
wastewater characteristics found by
EPA in a survey of the electroplating
industry. While no single waste
stream is expected to experience
such variability in all of its
components, it is essential that the
variations be understood, and that
the waste treatment system be sized
to handle variations that cannot be
eliminated. In addition, complex
plating systems or unusual
wastewater characteristics often
mean that laboratory- or pilot-scale
tests must be conducted to
determine whether a proposed
system will bring a waste stream into
compliance with regulations.
(Guidance on the design and sizing
of wastewater treatment systems is
available in several publications
listed in the Bibliography.)
This chapter discusses the factors
needed to estimate capital and
operating costs of the conventional
wastewater treatment systems.
Capital costs are described for each
of six components of a wastewater
treatment system:
Wastewater collection
Chromium reduction
Cyanide oxidation
Neutralization/precipitation
Clarification
Sludge handling.
Operating costs are described for
sludge disposal, municipal
wastewater treatment, and
wastewater treatment chemicals.
The chapter concludes with an
example that illustrates how total
costs can be estimated for a specific
facility.
Table 2.
Composition of Raw Waste Streams
from Common Metals Plating
Range (mg/J)
Copper
Nickel
Chromium:
Total
Hexavalent
Zinc
Cyanide:
Total
Amenable to chlorination
Fluoride
Cadmium
Lead
Iron
Tin
Phosphorus
Total suspended solids
0.032 - 272.5
0.019-2,954
0.088-525.9
0.005-334.5
0.112-252.0
0.005-150.0
0.003-130.0
0.022- 141.7
0.007-21.60
0.663 - 25.39
0.410- 1.482
0.060- 103.4
0.020-144.0
0.100-9,970
NOTE: All costs in this report relate to
1984.
SOURCE: U.S. Environmental Protection
Agency, Development Document for Proposed
Existing Source Pretreatment Standards for the
Electroplating Point Source Category, EPA
440/1-78-085, Feb. 1978.
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Add/alkali waste
Averaging
Filter cake
to approved
disposal
Polymer
3KTO&
fc'yia?
1
Wastewater
discharge
Flocculation
Clarification
Sludge
thickening
Filtration
Figure 1. Conventional Wastewater Treatment System for Electroplating
Capital Costs
The unit processes shown in Figure 1
are used extensively in the
electroplating industry, and as a
result their design has become
somewhat standard. The ability to
standardize has reduced the high
cost of site preparation and
construction through the
development of skidmounted
package systems, complete with all
hardware and auxiliaries. Installation
costs for package systems usually
range between 10 and 30 percent of
the purchase price of the equipment
compared with installation costs of
50 to 100 percent of purchase price
for component systems.
The costs presented in the following
sections assume the purchase of all
components of the individual
systems. Costs could be reduced by
using existing pumps, tanks, and
instrumentation, but these are rarely
available. Installation costs will
increase as a result of site-specific
requirements related to wastewater
collection systems, new building
space, structural modifications, or
the relocation of existing equipment.
Wastewater Collection. Wastewater
from individual plating operations
must be directed to the appropriate
treatment components, which often
entails separate wastewater
collection systems for chromium,
cyanide, and acid/alkali wastes.
Typically, a collection pipe system is
installed parallel to the plating line
so that spent rinse waters can be
drained to one or more treatment
sumps. Equipment washdown and
spilled materials are collected in a
trench which also leads to the
appropriate sump. The treatment
sump is equipped with a level-
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controlled pump that delivers the
wastewater to the treatment unit. In
addition, some provision must be
made for collecting the strong
cleaning and plating chemical
solutions which are usually bled at a
slow, constant rate into the
treatment system by way of an
averaging tank to avoid upsetting the
process.
Wastewater collection costs are
highly variable. A plant may have to
provide as many as five separate
collection/sump systems to handle
three different kinds of wastewater
plus spent cyanide and nohcyanide
chemical solutions. Cost
components for wastewater
collection are given in Table 3.
Larger sumps are used for chromium
and cyanide wastewater collection;
in fact, the sump itself may be used
as the treatment vessel (this practice
is rare). It should be pointed out that
custom-made concrete sumps are
considerably more expensive to
construct than the preformed sumps
indicated in Table 3.
Table 3.
Costs for Wastewater Collection
Collection conduit:"
Linear runs:
Each connection:
Each bend:
Collection sumps:6
4"-$1.50/ft
6"-$2.30/ft
4"-$200.00
6"-$350.00
4"-$200.00
6"-$300.00
100 gallons ... $2,000
300 gallons ... $2,500
500 gallons ... $3,000
1,000 gallons ... $3,500
"PVC pipe.
^Preformed PVC inground tank with sump
pump, level control and steel grating cover.
1984 data.
Chromium Reduction. Chromium is
usually present in electroplating
wastewater as trivalent chromium
(Cr+3) or as hexavalent chromium
(Cr+6). Although most heavy metals
are precipitated readily as insoluble
hydroxides in the neutralizer,
hexavalent chromium must first be
reduced to trivalent chromium.
Reduction is usually achieved by
reaction with gaseous sulfur dioxide
(SO2) or a bisulfite solution
(NaHSO3). Using sodium
metabisulfite (Na2S205), the net
reaction involves chromic acid and
sulfuric acid in the formation of
sodium sulfate, chromium sulfate,
and water:
3Na2S2O5
3Na2SO4
4H2CrO4 +
2Cr2(S04)3
7H2O
Because the reaction proceeds
rapidly at low pH, an acid is added to
maintain the chromic acid
wastewater between a pH of 2 and 3.
To prevent the release of sulfur
dioxide during the reaction,
maintaining the pH near 3 is advised.
In addition to the use of sulfur
dioxide or bisulfites to reduce
hexavalent chromium, there are
three commercially available
methods that use the reducing
potential of iron and/or iron salts.
Ferrous sulfate reduces hexavalent
chromium according to the following
equation:
3Fe
+2
Cr+3
The use of iron in this form adds
considerably to the volume of sludge
produced by the treatment system.
This method is rarely used except
where an effluent of high chromium
content is located close to a cheap
and abundant source of ferrous salts,
such as waste pickle liquor from a
steel mill.
Ferrous salts may also be generated
by a patented process employing an
electrolytic cell having iron anodes
and inert cathodes:
3Fe° + 6e~ -> 3Fe+2
As the iron anodes are dissolved in
the process, they must be replaced
with new ones. While this process
will also produce substantial
quantities of excess sludge, it
provides a convenient method of
continuously treating low
concentrations of hexavalent
chromium, such as might be found
in cooling tower blow-down waters
or in rinses from chromate
conversion coatings. With higher
chromium concentrations it is
difficult to economically, produce the
required ferrous ion concentrations
on a flow-through basis.
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Concentrated bath dump tank with oxidation and neutralization/flocculation units.
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50 (-
40
§
I 30
O
o
03
S!
20
10
10
20 30 40
FLOW RATE (gal/min)
50
60
Legend:
Total installed cost
Hardware cost
Notes:
Batch units:
Installed cost = 2 x hardware cost.
Unit consists of two 4-hour reaction tanks
with necessary auxiliaries.
Continuous units:
Installed cost = 1.25 x hardware cost.
Unit consists of equipment shown in Figure 1.
Figure 2. Investment Cost for Chromium Reduction Units
Iron, in the form of small pieces of
scrap steel, may also be used to
directly reduce hexavalent
chromium. This patented process is
controlled by adjusting the pH of the
influent according to its hexavalent
chromium content. A pH of 2.0 to 2.2
will usually accommodate chromium
loadings as high as 200 to 300 ppm.
Lower pH settings would be required
to treat higher chromium
concentrations. The following
equation represents the reduction
mechanism:
Fe°
Cr+s
Because the iron and chromium
react on a one-to-one basis, rather
than a three-to-one ratio-, the sludge
produced by this process is
significantly less than that generated
in the other processes using iron.
The low cost of scrap steel allows
this process to compete favorably
with the cost of sulfur dioxide
treatment, while eliminating the
potential of releasing hazardous gas.
Hardware and installation costs from
packaged continuous and batch
chromium reduction units are shown
in Figure 2. Costs include storage
and feed systems for the treatment
reagents, as well as the costs for
hardware, piping, instrumentation,
and utility connections. The
continuous unit costs are based on
using sodium metabisulfite as the
reducing agent and a wastewater
retention volume of 30 min. For very
small flows, simpler and less costly
batch systems are feasible. The
batch system costs include two
reaction tanks each sized to hold 4 h
of wastewater flow and equipped
with high level alarms, portable pH
and oxidation reduction potential
(ORP) meters, a portable mixer, and
storage tanks and feed pumps to add
sodium metabisulfite and sulfuric
acid to the reaction tanks.
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Cyanide Oxidation. Dilute cyanide
rinse streams resulting from plating
operations and cyanide dips must
also be treated separately to oxidize
the highly toxic cyanide, first to less
toxic cyanate, then to harmless
bicarbonates and nitrogen. The
oxidizing reagent is usually chlorine
gas (CI2) or sodium hypochlorite
(NaOCI). Using chlorine, the typical
reaction in the first stage involves
sodium cyanide (NaCN) and sodium
hydroxide (NaOH):
CI2 + NaCN + 2NaOH -H>
NaCNO + 2NaCI + H20
and in the second stage:
3CI2 + 2NaCNO
6NaCI + CO2 + N2
NaHCOs + 2H20
When sodium hypochlorite is used,
the typical reaction in the first stage
is:
NaOCI + NaCN -» NaCNO + NaCI
and in the second stage,
SNaOCI + 2NaCNO + H2O-»
SNaCI + N2 + 2NaHCO3
In most continuous systems, it is
preferable to conduct the operations
in two series-connected reaction
tanks rather than in stages in one
tank. In the first stage, the pH is
adjusted between 9 and 11 using an
alkali such as caustic soda or lime.
The pH in the second reaction
chamber is controlled to
approximately 8.5. Sodium
hypochlorite is added continuously
to both stages. Demand in each
stage is determined by measuring
ORP. The reaction time needed is
approximately 30 to 60 min in each
stage.
Figure 3 shows cost curves for
continuous and manual batch
cyanide oxidation units. The
continuous unit cost is for a unit
which uses sodium hypochlorite as
the oxidizing agent. The cost
includes storage and feed systems
for the treatment reagents. The batch
system cost is for a system with two
4 h reaction tanks and the auxiliaries
required to add sodium hypochlorite
and control pH.
Again, for very small flows, simpler
and less costly batch systems are
feasible. At wastewater flow rates
below 20 gal/min (76 l/min) batch
units appear to be more cost-
effective than continuous units.
50 i-
Legend:
TotalJ nstalled cost
Hardware cost
Notes:
Batch units:
Installed cost = 2x hardware cost.
Unit consists of two 4-hour reaction
tanks with necessary auxiliaries.
Continuous units:
Installed cost = 1.25X hardware cost.
Unit consists of equipment shown in
Figure 1.
FLOW RATE (gal/min)
Figure 3. Investment Cost for Cyanide Oxidation Units
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Neutralization/Precipitation. Waste
streams from each of the various
metal cleaning and plating
operations are combined in the
neutralizer with the effluent from the
chromium reduction and cyanide
oxidation units. Because the heavy
metals are only soluble under acidic
conditions, the pH is adjusted to a
range of 9.0 to 9.5, at which the
metals precipitate as hydroxides.
After the pH is adjusted, a small
amount (1 to 5 mg/l) of a coagulating
agent such as aluminum sulfate,
ferrous sulfate, or calcium chloride is
added to the wastewater to facilitate
precipitation.
Many types of neutralization
systems can be designed with
various degrees of automation and
controls, depending on the
magnitude and variability of the flow
and its pH. Because a change of 1 pH
unit represents a tenfold change in
hydrogen ion concentration and a
hundredfold change in solubility for
some metals, maintaining the pH in
the narrow range where maximum
removal of pollutants is realized is
critical, though difficult, especially
when the neutralizer feed is subject
to wide variation.
A single-stage, continuous
neutralizer, in which all the alkali
such as lime or caustic soda is fed
into a single reaction vessel, is
suitable for most electroplating
applications. If the wastewater is
subject to rapid changes in flow rate
or pH, however, a multistage
neutralizer is required. In the
multistage units, most of the alkali is
added in the first vessel to increase
the pH to 6. Final pH adjustments of
the wastewater are made in the
remaining reaction vessels to
promote precipitation and to
enhance the settling characteristics
of the metal hydroxides. To maintain
adequate pH control, the retention
time for typical neutralization is 15 to
30 min. The efficient use of lime
requires a minimum of 30 min
because lime reacts more slowly
than sodium hydroxide.
Figure 4 shows hardware and total
installed costs for a continuous
neutralization unit typically used in
the electroplating industry. This unit
is single stage with pH-controlled
addition of caustic soda and sulfuric
acid.
40
_ 30
8
8
CO
si
20
10
Total installed cost
20
40 60
FLOW RATE (gal/min)
80
100
Notes:
Installed cost = 1.25 x hardware cost.
Cost does not include flocculation system.
Figure 4. Investment Cost for Continuous Single-Stage Neutralization/
Precipitation Unit
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Clarification. Metal hydroxides and
other insoluble pollutants are
removed from the wastewater by
gravity settling and/or filtration. The
removal efficiency depends on the
settling rate of the suspended solids
in the wastewater feed. Typically,
some of these solids settle very
slowly because of their small size
and their slight density difference
compared with the water. Because
an economical design of the clarifier
limits the retention time in the
settling chamber, some level of
suspended solids will appear in the
overflow.
To enhance the settling
characteristics of the suspended
solids, a flocculating agent, usually
an organic polymer, is added in a
flocculator where the wastewater is
agitated gently to allow the solids to
agglomerate. The wastewater then
enters the clarifier where the solids
settle out. The solids in the
underflow can be discharged to a
holding tank for subsequent
dewatering.
The optimal doses of flocculating
agents, hardware specifications, and
solids removal efficiencies are
usually estimated based on
laboratory tests conducted by the
equipment vendor. Figure 5 shows
hardware and total installed costs for
flocculation and clarification units
typical of those used in the industry.
These costs are presented as a
function of volumetric flow rate; they
also reflect the effect on unit costs of
solids-settling rates and the level of
solids allowed in the effluent. The
units are assumed to have a separate
flocculation tank, a polymer feed
system, a "lamella" (or slant-tube
separator), and a zone in which
sludge collects before being
discharged. These units are more
widely used than simpler rectangular
settling chambers.
60 r-
50
S 40
30
s
- 20
10
Total installed cost
20
40 60 80
FLOW RATE (gal/min)
100
120
Notes:
Installed cost = 1.25 x hardware cost.
Cost includes plate-type clarifier with flocculating
chamber and polymer feed system.
Figure 5. Investment Cost for Flocculation/Clarification Units
10
-------
Manually shifted low-pressure recessed-plate filter press with capabilities for filling disposal drums directly.
Sludge Handling. The solids from
clarifiers are typically discharged to
sludge holding tanks at solids
concentrations of 0.5 to 3%;
overflow from the tank is recycled to
the clarifier or to the flocculation
tank. Usually, metal hydroxide solids
will concentrate to approximately 3
to 5% solids in the sludge holding
tanks if sufficient retention time is
allowed. The tanks must also provide
adequate volume to store the sludge
before it is shipped to a disposal site
or transferred to another dewatering
stage. Figure 6 shows the investment
for sludge holding tanks as a
function of tank volume.
Further concentration of the
thickened sludge requires the use of
mechanical dewatering equipment.
Centrifuges, rotary vacuum filters,
belt filters, and filter presses have
been used to dewater metal
hydroxide sludge. The applicability
of a particular dewatering device for
a specific sludge, and the degree of
cake dryness the device will achieve,
can be determined by bench-scale
tests conducted by the vendor using
the intended feed material.
Figure 7 presents the unit costs for
recessed plate filter presses as a
function of the filter-cake volume of
the unit. The feed volume capacity of
the unit is also given, based on a
feed solids concentration of 2%, a
cake solids concentration of 20%,
and a press cycle of 8 h. The costs
shown in Figure 7 do not include
installation or auxiliary equipment
associated with the press, because
these costs are highly variable and
site-specific. Items that will
contribute to the cost of installation
include:
• High pressure feed pump(s) (often
quoted and supplied with the
filter)
• Sludge feed storage tanks
• Filtrate return lines (to clarifier)
• Cake solids handling equipment.
11
-------
30 I—
520
8
&
t» 10
ui
Total investment cost
Notes:
Based on carbon steel construction.
Costs include fiber-reinforced polyester
tank and diaphragm pump.
1000
2000 3000
VOLUME (gal)
4000
5000
Figure 6. Investment Cost for Sludge Storage/Thickening Units
400
=5 300
a
1
t
> 200
LU
^— *
O
£C
£
E 10°
/I
/
^^ .
/
J Automatic
- /
/
/
/
^f Manual _
/
S
^
1 1 1 1 I
500
375
.c .
"co
Dl
LU
250- 3
O Notes:
Q Cost includes carbon steel frame
LU propylene plates and filter cloths
poly-
"- Installation costs not included.
125 Cake volume based on 1 W thick sludge
cakes.
Feed volume capacity based on:
solids = 2%; cake solids = 20%;
time = 8 hours.
0 10 20 30 40 50 60
EQUIPMENT COST ($1,000)
feed
cycle
Rgure 7. Hardware Cost for Recessed Plate Filter Presses
12
-------
Operating Costs
Although the investment costs for
conventional wastewater treatment
systems depend principally on
wastewater flow rate, the operating
costs depend on the following
factors:
• Sludge disposal and municipal
sewer fees
• Wastewater treatment chemical
costs
• Operating and maintenance labor
costs
• Utility costs (primarily electricity
to operate pumps and agitators)
• Overhead costs and depreciation.
Of these, sludge disposal and
chemical costs offer the best
opportunities for reducing operating
costs since labor and utility
requirements are usually fixed. The
cost components of these and other
operating costs are described below;
Table 4 shows the assumptions for
these evaluations.
Table 4.
Basis for Economic Evaluations3
Basis
Annual operating costs:
Operating labor
Supervision
Maintenance
General plant overhead
Depreciation (10-year straight line)
Taxes and insurance
Utility charges:
Electricity
Cooling water (cooling tower)
Steam
Net operating savings ($/yr)
Net savings after taxes ($/yr)
Return on investment
Cash flow ($/yr)
Payback period (yr)
$9/h
$12/h
6% of investment
0.58 (operating + supervisory +
maintenance labor); maintenance labor
0.37 x (maintenance cost)
10% of investment
1% of investment
$0.08/kWhr
$0.25/1,000 gal
$6.00/1,000 Ib
Operating cost reduction resulting from
investment minus increase in fixed and
operating cost for new system
Net operating savings x 0.54 (assumes
46% tax rate)
Net savings after taxes •*• total installed
investment
Net savings after taxes + depreciation
Total installed investment •*• cash flow
"No interest on capital is included in the economic analyses.
13
-------
Sludge Disposal and Municipal Fees.
Installation of wastewater treatment
systems results in the discharge of
two streams: overflow from the
clarifier and sludge from the clarifier
or dewatering equipment. The costs
associated with these discharges are
site-specific, and depend on the
availability of local disposal sites to
receive the sludge and on municipal
sewer costs. These costs are
expected to escalate in the future as
new regulations are implemented.
For the overflow from the clarifier,
typical sewer fees for a major city as
presented in Table 1 are $1.20/1,000
gal. Figure 8 shows the direct
relationship of wastewater flow rates
and these sewer fees.
The cost of hauling the sludge to a
licensed hazardous waste landfill will
depend on the volume of sludge, the
distance hauled, and the sludge
composition. In most areas, the costs
of sludge disposal are currently in
the range of $.50 to $1.00/gal, but
there are cases where disposal costs
run as high as $2.00/gal. Figure 9
shows the annual disposal costs for
each 100 Ib. (45 kg) of solids
generated daily over a range of
sludge concentrations and disposal
costs. For example, if 100 Ib of solids
are generated daily at a
concentration of 6% and at a
disposal cost of $1.00/gal, the annual
cost for disposal will be $60,000
(point Aon Figure 9).
The disposal cost savings achievable
by thickening can also be estimated
by using Figure 9 to calculate the
difference between the disposal
costs at the present concentration
and at the projected final
concentration after thickening. For
example, a plant now disposes of
100 Ib/d (45.4 kg/d) of dry solids as a
sludge with a concentration of 6%
solids. From Figure 9, the disposal
cost of 100 Ib/d at $1.00/gal would be
$60,000 per year. If a filter press
performance test predicts a sludge
concentration of 25% solids, sludge
disposal costs would decrease to
$14,000. The disposal costs saved as
a result of greater dewatering of the
sludge (from 6 to 25% solids
concentration) would then be
$46,000 ($60,000 minus $14,000).
50 r
40
30
to
8 20
z>
•z.
<
10
246
CLARIFIER OVERFLOW RATE (1,000 gal/h)
10
Notes:
Operating 4800 h/yr.
Sewerfee = $1.20/1000 gal.
Water use fee not included.
Figure 8. Annual Sewer Fee as a Function of Clarifier Overflow Rate
14
-------
1000 r—
§
I100
8
_i
CO
O
Q_
co
Q
10
$2.00/gal sludge
disposal cost
$1.00/gal sludge
disposal cost
$0.50/gal sludge
disposal cost
0.1
1.0 10
CONCENTRATION SOLIDS IN SLUDGE (wt%)
100
Figure 9. Annual Cost for Disposal of Industrial Sludge
(per 100 Ib dry solids generated per day)
Filter press hopper with 40% solids filter cake.
15
-------
600 i—
$2.00/gal disposal cost
Notes:
Assumes 100 Ib/day dry solids generated.
Assumes 40% ROI (pretax).
ROI = (disposal cost savings - fixed cost)
•*• capital investment.
Fixed cost includes depreciation, taxes,
insurance and maintenance. Utility
and Igbor costs not included.
In a 2% solution, 100 Ib solids = 600 gal.
5% = 232 gal.
10% = 112 gal.
39% = 32 gal.
CONCENTRATION OF DEWATERED SLUDGE (% solids)
Figure 10. Capital Cost Justification for Sludge Dewatering Equipment
Mechanical dewatering of metal
hydroxide sludges can achieve
solids concentrations in the range of
15 to 50%. Figure 10 shows the
capital investment that could be
justified for dewatering equipment
to concentrate a sludge containing
only 2% solids. The cost reduction
used to calculate this return on
investment (ROI) did not take into
account variable operating costs,
such as utility costs and operating
labor, which for mechanical
dewatering devices could be
significant. These additional costs
would result in a lower ROI.
To illustrate the investment
justification for the mechanical
dewatering of a dilute sludge,
assume a plant generating 100 Ib/d
of dry solids was able to concentrate
its sludge from 2 to 20% solids with a
filter press. The annual disposal cost
would be reduced from $180,000 to
$16,000 based on a disposal cost of
$1.00/gal (Figure 9). The maximum
capital investment justified to
achieve this saving, using Figure 10,
is $270,000. Figure 7 shows the cost
of filter presses as a function of cake
volume and feed-processing
capacity. Using the feed-processing
capacity, the press feed rate would
equal:
100 Ib solids
gal sludge
8.34 Ib
x
Ib sludge
x
0.02 Ib solids
d _ 75 gal sludge
8h h
From Figure 7, the minimum size
commercial unit could dewater this
feed rate and would cost $16,000.
Assuming the total installed cost of
the system is twice the press cost, or
$32,000, the ROI would be well in
excess of the 40% used as a basis for
Figure 10.
16
-------
Wastewater Treatment Chemical
Costs. These chemical costs are
dependent on the concentration of
pollutants, the volumetric flow rate
of the waste stream, and the types of
chemicals chosen for wastewater
treatment. Because the addition of
chemicals involves a chemical
reaction with the pollutants, the
types of treatment chemicals
selected will produce different use
rates, volumes of sludge for
disposal, and removal efficiencies.
Each of these factors affect the
operating costs and must be
considered by the plater.
Common treatment reagents used in
the electroplating industry are
sodium bisulfite (NaHSO3) for
chromium reduction, sodium
hypochlorite (NaOCI) for cyanide
oxidation, and caustic soda for
neutralization/ precipitation. These
chemicals, and the chemical costs
given in Table 1, were used to
provide the cost model for
conventional wastewater treatment
shown in Figure 11. This model
enables the user to calculate the
consumption of treatment chemicals
(consumption factor) and the
associated cost (cost factor), based
on the volumetric flow rate of the
wastewater being treated and mass
flow of each pollutant. The sludge
disposal cost model (shown in
Figure 12) can be used to determine
the dry solids generated by
precipitation of the heavy metals
contained in the waste stream.
Figure 12 also indicates the disposal
cost for each pound of metal
precipitated, assuming the resulting
sludge is 20% solids and the disposal
cost is$1.00/gal.
Many treatment systems use
hydrated lime for neutralization
instead of sodium hydroxide; some
systems use soda ash. The selection
of neutralization chemicals is usually
based on convenience and price. The
choice of neutralization reagent will
affect the volume of sludge
generated, the costs of sludge
disposal, and the investment cost for
storage and handling for each
chemical. A cost comparison of the
various neutralizing reagents is
shown in Table 5. Lime requirements
and chemical and sludge disposal
costs can be estimated using the
model in Figure 13, which is similar
to the models developed in Figures
11 and 12 for caustic neutralization.
The cost models in Figures 11,12,
and 13 can be used to determine the
incremental costs associated with
removing each pound of pollutant
and treating each gallon of
wastewater entering the system.
These models can also be used to
predict the impact of water use
reduction programs, chemical
recycle systems, and other
modifications on the costs of
operating a wastewater treatment
system.
17
-------
Cyanide Waste Chromium Waste Acid/Alkali Waste
gal/min gal/min gal/min
IbCN" IbCr*6 Ib Metal"
Ib Metal' • ,
* * *
Oxidation (NaOCI)11 Reduction (NaHSO3, H2SO4)C
7.5lbNaOC!/ $450/|bCN 3 Ib NaHSOa/lb Cr"6 $1.00/lb Cr+6
0.2 Ib HaSOi/1000 gal
*
Neutralization (NaOH)d
1.5 IbNaOH/ 1000 gal $.20/1000 gal
*
Precipitation (NaOH)
2.0 Ib NaOH/lb Metal $.26/lb Metal
f
Flocculation (Polyelectrolyte)
0.1 lb/1000 gal $.20/1000 gal
t
_, ... . 1 ^ Wastewater
Clarification ^-^» Discharge
1
Sludge Storage
t
Dewatering
1
Disposal
Legend :
Process Step (Treatment Reagent)
Consumption Cost
Factor Factor °
Neutralization (NaOH)cl
1.0 IbNaOH/ 1000 gal $.13/1000 gal
Lb metal expressed as Ib of metal ion
Chromium reduction using S02 :
Reduction (SO2, H2SO4)
2 Ib S02/lb Cr+6 $.28/lb Cr+6
0.2lbSO2/1000gal $.07/1000 gal
0.2 Ib H2SO4/1000 gal
Cyanide oxidation using CI2 :
Oxidation (CI2, NaOH)
7lbCI2/lbCN tiR7/ihrM
8lbNaOH/lbCN »I-°/"U>,IM
Lime is also commonly used; a usage
model is presented in Section 3
Rgure 11. Consumption and Cost Factors for Wastewater Treatment Chemicals
-------
Cyanide Waste .^
Chromium Waste ^^
Acid/Alkali Waste ^
Notes:
Ib metal expressed as Ib of metal ion.
Disposal cost at $1.00/gal.
Precipitation (NaOH)
Ib dry solids generated
Cr 1.98
Ni 1.58
Cu 1.53
Cd 1.30
Fe 1.61
Zn 1 .52
Al 2.89
» Flocculationi*
Clarification '
Dewatering
420% Solids
Solid Waste Disposal Cos
($/lb of metal treated)
Cr $1.18
Ni 0.92
Cu 0.90
Cd 0.78
Fe 0.96
Zn 0.92
Al 1.72
t
<^ WactAwator
"^ Discharge
Figure 12. Generation and Cost Factors for Sludge Disposal
Table 5.
Cost Comparison of Common Alkaline Reagents
Agent
Sodium hydroxide
(caustic)
Sodium carbonate
(soda ash)
High calcium
hydrate (hydrated lime)
High calcium
lime (quicklime)
Chemical
formula
NaOH
Na2CO3
Ca(OH)2
CaO
Price
($/ton)
$260 (98%
NaOH
equivalent)
$120 (58%
Na2C03)
$50 (96%
pure)
$40 (96%
pure)
Ib/lb
H2S04
neutralized
0.826
1.90
0.788
0.595
Relative
cost
9.0
9.58
1.65
1.00
Process equipment required
and sequence for use
of reagents
Caustic storage -» Neutralizer
Soda ash storage-*
Slurry tank-* Neutralizer
Hydrated lime storage — >
Slurry tank — » Neutralizer
Quicklime storage — > Slaking — »
Slurry Tank — » Neutralizer
19
-------
Cyanide Oxidation
Ib Metal*)
Neutralization (Ca(O
Chromium Reduction
Effluent (gal/min, , ifc
IbCr*") *"~ 1.7 Ib Ca(OH)2/1000 gal $.
Acid/Alkali Waste ^
(gal/min, Ib Metal') -^ la|bCa(OHW1000gal $
Neutralization (Ca(C
Solids Generation Factors 0.1 Ib of dry solids generated
Ib of Ca(OH)2 consumed
Legend:
Process Step (Treatment Reagent)
Consumption Cost
Factor Factor
Basis :
Lime consumption of 20% in excess of
neutralization requirements.
10% of lime feed is insoluble.
H)2)
34/1000 gal
1 r
r
H)2) Precipitation (Ca(QH)2) i' M
o,,n™ ,**" 2.6lbCa(OH)2/lbCr $.07/lb Cr -»»~ To Clarification
03/1000 gal 2.2 Ib Ca(OH)2/lb Metal $.06/lb Metal
)H)2) -•;'. : -, Precipitation (Ca(OH)2) ;..-.' /
Disposal |b dry so|jds generated
Ib of metal precipitated
$.06
Cr 2.24
Ni 1.80
Cu 1.75
Cd 1.52
Fe+2 1.83
Zn 1.74
Al 3.11
Disposal
Cost0
$1.34
1.08
1.06
0.92
1.10
1.04
1.86
" Ib metals expressed as Ib of metal ions.
b per Ib Ca(OH)2 consumed @ 20% solids and $1.00/gal disposal fee,
c per Ib metal precipitated @ 20% solids and $1.00/gal disposal fee.
Figure 13. Consumption and Cost Factors Using Lime for Wastewater Treatment
20
-------
Total Facility Costs—An
Example Calculation
This section provides a sample
calculation of the investment and
operating costs of a hypothetical
conventional wastewater treatment
system. (A similar analysis can be
made at any plant once the
wastewater characteristics and flow
rates are known.) Figure 14
illustrates the hypothetical treatment
system, including the characteristics
and flow rates of the wastewater and
the required treatment steps. The
plant has chromium, cyanide, and a
mixed acid/heavy metals wastewater
entering the treatment system.
' "Cyanide Waste* ,' ,=f ;
20 gal/min
80 ppm CN~
60ppmZn+*
NaOCI 1 NaOH
1 * 1
* -.$%.<% .,-.
/electrolyte
1 ir
• * :'v; *| i !,,;• . :
Floccula'tipri ,f .• 's
.1 •.. i :. v : : '^ :
1
* -.. Clarification
'•' :: •'', •,"',, '':•
1
I «i . '''£'- *•»
^ •->T.iSJu.dge :- ••
•' '. •*- -r. .Storage ">-•••
i ; . ' "• '"• '' !> * :, -t •,
1
Filtering/ ' }
Dewatering •
1
.;• iSltfdge Disposal
| ;| (io% solids) : ,.
'.Acid/Alkali'Wast'e' . {,
60 gal/min
100 ppm Fe+2
80 ppm Ni+2
50ppmCu+2
___ 60 gal/min
^^^^^^ Wastewater
^^^^^^ Discharge
Figure 14. Wastewater Treatment Flow Chart: Example System
21
-------
Table 6.
Wastewater Treatment Chemical and Sludge Disposal Costs: Example Systema
Treatment chemicals
Treatment step
Rates
Waste streams (Ib/h)
Cost
($/h)
Sludge disposal
Dry solids
generated
(Ib/h)
Disposal
cost
($/h)
Total
annual
costs'*
($)
Chromium reduction
Cyanide oxidation
Neutralization
Chrome effluent
Cyanide effluent
Acid/alkali waste
Precipitation
Subtotal, precipitation
Flocculation
TOTALS
Treatment chemicals
Sludge disposal
30gal/min = 1,800 gal/hr
0.75 Ib/h Cr*6
0.15lb/hCr+3
20gal/min = 1,299 gal/h
0.80 Ib/h Cn-
0.60 Ib/h Zn+2
1,800 gal/h
1,200 gal/h
60 gal/min = 3,600 gal/h
0.90 Ib/h Cr+3
0.60 Ib/h Zn+2
3.01 Ib/h Fe+2
2.41 Ib/h Ni+2
1.51 Ib/hCu*2
110 gal/min = 6,600 gal/h
2.79 NaHSO3
1.86H2SO4
6.016 NaOCI
2.7 NaOH
b
3.6 NaOH
2.1 NaOH
1.2 NaOH
6.0 NaOH
4.8 NaOH
3.0 NaOH
17.1 NaOH
0.66 polyelectrolyte
2.8 NaHS03
1.9H2S04
6.0 NaOCI
29.8 NaOH
0.66 polyelectrolyte
0.93
3.60
0.35
b
0.47
0.27
0.16
0.78
0.62
0.39
2.22
1.32
8.89
1.80
0.91
4.83
3.80
2.30
13.64
1.06
0.55
2.89
2.22
1.36
8.08
13.64°
8.08
42,700
38,800
"System shown in Figure 14.
"pH adjustment not required.
cSludge volume at 20% solids ••
"4,800 Wyr.
8 gal/h; filter feed at 2% solids = 80 gal/h.
Table 6 presents the chemical
treatment and sludge disposal costs
using the factors presented in
Figures 11 and 12. Based on 4,800
h/yr operation (16 h/d, 300 d/yr),
costs are $42,700/yr for chemical
treatment and $38,800/yr for sludge
disposal. The required investment
for treatment hardware is calculated
in Table 7, using the equipment cost
data presented in this section. A cost
for engineering (10%) and
contingency (10%) were also added
to the estimate. The cost for
wastewater collection is based on
three wastewater conduits, each 60 ft
long with two bends and six rinse
connections. Each feeds a separate
collection sump. Table 8 expresses
these results as an annual cost
(using the basis defined in Table 4).
Including projected manpower
requirements and utility
consumption, the total annual cost is
$205,700.
22
-------
Table 7.
Investment Costs for Wastewater Treatment: Example System3
Cost ($)
Wastewater collection (3 systems: each 60' of 6" dia. pipe with 2
bends and 6 connections, from Table 3)
3sumps® 1,000gals (from Table3)
Chromium reduction unit (continuous system rated at 3O gal/min, from Figure 2)
Cyanide oxidation unit (continuous system rated at 20 gal/min, from Figure 3)
Neutralizer (single stage continuous system rated at 110 gal/min, from Figure 4)
Flocculation/clarification unit (system rated at 110 gal/min, from Figure 5}
Sludge storage tank (5,000 gal tank, from Figure 6)
Filter press (75 gal/hr, from Figure 7; installed cost is 2 x unit cost)
Total equipment and installation cost
Contingency"
Engineering6
Total installed cost
"System shown in Figure 14.
"10% of total equipment and installation cost.
8,500
10,500
28,000
36,000
38,000
55,000
22,000
36,000
234,000
23,000
23,000
280,000
Table 8.
Total Annual Cost for Wastewater Treatment:3 Example System6
Cost ($/yr)
Operating labor (based on 4 hr per shift)
Supervision
Maintenance
General plant overhead
Depreciation
Taxes and insurance
Chemical cost (Table 6)
Sludge disposal cost (Table 6)
Sewer fee (Figures)
Utilities (electricity; approximately
25 hp required)
Total annual cost"
21,600
C
16,800
16,100
28,000
2,800
42,700
38,800
31,700
7,200
205,700
"Based on Table 4.
^System shown in Figure 14.
cNone required.
^Excluding interest.
23
-------
3. Process
Modifications to
Reduce Costs
The capital and operating costs for
wastewater treatment systems were
shown in the preceding chapter to
depend primarily on the
concentration of pollutants in the
wastewater and on its volumetric
flow rate. Modifications to the design
and operation of plating baths and
rinse systems can significantly
reduce wastewater flow rates and
pollutant loading, thereby reducing
the amount of new plating chemicals
that must be added and reducing the
need for additional pollution control.
The two primary areas where such
cost reduction efforts are undertaken
involve reducing rinse water rates
and reducing drag-out losses. Rinse
water is the major contributor to the
total volumetric flow rate of most
electroplaters' wastewater treatment
systems. Drag-out (electroplating
chemicals inadvertently carried out
of the plating bath on a workpiece) is
the major contributor to the pollutant
loading in most electroplaters'
wastewater treatment systems, as
well as a significant contributor to
the need for replacement chemicals.
A number of ways to reduce rinse
water use and drag-out losses are
presented below, as is an example of
a cost/benefit calculation which
ordinarily precedes the decision to
implement such controls efforts.
Two additional areas where
wastewater treatment costs can be
readily reduced with little investment
in capital or operating funds are:
• Implementing a housekeeping
program
• Using spent reagents in
wastewater treatment.
Implementing a successful
housekeeping program, as a rule,
requires little or no capital
investment, yet can result in
significant savings, especially when
the loss of concentrated solutions of
plating chemicals is reduced or
prevented. The primary activities
involved in a housekeeping program
aimed at reducing costs are:
• Repairing leaks around processing
equipment (tanks, pipes, valves,
pump seals, heating coils). Losses
of 2 gal/h (7.6 l/h) can easily occur
through leaking pump seals alone.
« Installing antisiphon devices
equipped with self-closing valves
on inlet water lines where
required.
• Inspecting tanks and tank liners
periodically to avoid failures that
may overload the waste treatment
system.
« Inspecting plating racks frequently
for loose insulation that would
cause excessive drag-out of
plating solutions.
• Making provisions to ensure that
cyanide solutions do not mix with
compounds (iron, nickel) that
would form difficult-to-treat
wastes.
• Using dry cleanup, where
possible, instead of flooding with
water.
» Installing drip trays and splash
guards where required.
24
-------
Wastewater/ \30gal/min
30ppmCr+6
pH = 4
Chrome reduction tank
pH = 2
Amount
Chemical savings by using spent HC1 (Ib/h):
H2S04 (replaced by HCI) at 93% 9.2
Na2S2O5 (replaced by Fe*2 reduction) 0.04
NaOH (not needed to neutralize spent HCI) 7.5
Value of chemicals saved, at 3,600 h/yr ($/yr):
H2SO4 1,660
NaHSO4 40
NaOH 3,510
Total 5,210
Figure 15. Savings Resulting from Use of Spent HCI in Chrome Reduction Treatment Process
Substantial savings can be realized
through a housekeeping program,
but can be easily lost if the program
is allowed to lapse.
Using spent baths as treatment
reagents is a second possible cost-
reduction area. In many cases, the
processing solutions used in alkaline
or acid cleaning can easily be used
as pH adjustment reagents in the
waste treatment system. Typically,
cleaning solutions are either
dumped when the contaminant level
exceeds some acceptable
concentration, or bled off to waste
treatment and replaced with fresh
reagents. In either case, the solution
could instead be transferred to a
holding tank and subsequently used
to treat the wastewater.
Spent caustic soda solutions can be
used to adjust pH in the precipitation
tank. Spent sulphuric and
hydrochloric acid solutions can also
be used here as needed (though the
quantity used would be minimal
because waste streams are usually
acidic).
Waste acid solutions can also be
used for pH adjustment in chrome
reduction (Figure 15). A minor added
benefit in this case would be a
decreased demand for reducing
agents caused by the presence in the
acid of Fe+2 which reduces Cr"1"6.
Decreasing the demand for a
reducing agent can be further
achieved by dissolving scrap iron in
the spent acid, thus raising the
concentration of the Fe+2. However,
as suggested in Chapter 2,
substituting iron for sodium
bisulphite as the reducing agent
may drastically increase the amount
of hydroxide sludge generated.
Depending on the cost of sludge
disposal it may, in fact, cost more to
dispose of the additional solid waste
than will be saved by reducing
chemical consumption.
The impact of any additives in the
spent solutions on the waste
treatment process should be
considered before they are used as
treatment reagents.
25
-------
Reducing Rinse Water Use
The greatest potential for reducing
water use is in the rinse tanks that
follow many of the plating process
steps; these account for up to 90
percent of a plant's water demand.
Furthermore, if a plant is able to
reduce its process water discharge to
below 10,000 gal/d (37,850 l/d), it will
be classified as a "small plater" and
may be regulated by different
pretreatment standards. (This size
criterion only applies to plants
discharging to a POTW.)
Rinsing is used to dilute the
concentration of contaminants
adhering to the surface of a
workpiece to an acceptable level
before the workpiece passes on to
the next step in the plating
operation. The amount of water
required to dilute the rinse solution
depends on the quantity of chemical
drag-in from the upstream rinse or
plating tank, the concentration of
chemicals in the rinse water, and the
contacting efficiency between the
workpiece and the water.
Various techniques are used in the
electroplating industry to reduce the
volume of water needed to achieve
the required dilution including:
• Installing multiple rinse tanks
(including counterflow rinse tanks)
after a processing bath
• Using solenoids controlled by
conductivity cells or timers or
using flow regulators to control
water addition to rinse tanks and
avoid excessive dilution of the
rinse water
• Reusing contaminated rinse water
where feasible
• Subjecting the workpiece to a
spray rinse as it emerges from the
process tank
• Using air agitation or workpiece
agitation to improve plating
efficiency.
If multiple rinse tanks are installed so
that the rinse flows in a direction
counter to that of the parts
movement (Figure 16), the amount
of chemicals entering the final rinse
will be significantly less than the
amount that enters a single-tank
rinse system. The volume of rinse
water required for dilution will be
reduced accordingly. The volume for
each rinse step can be predicted by
using a model that assumes a
complete rinsing of the workpiece.
The ratio, r, of rinse water volume to
drag-out volume is approximated
by:
r = (Cp/Cnf/n
where
Cp = concentration in process
solution
Cn = required concentration in last
rinse tank
n = number of rinse tanks.
This model does not predict required
rinse rates accurately when the value
of r falls below 10. Also, complete
rinsing requires sufficient residence
time and agitation in the rinse tank.
Workpiece
_.
- _
!
.
.
. .,_
To wastewater treatment
Overflow pipes
Makeup water
No. of
rinse stages
Rinse ratio
Spent rinse water
concentration
(mg/1)
1,000
100
10
6
37
370
3,700
6,170
Required to maintain concentration in final rinse
at 37 mg/1 if the drag-out concentration equals
37,000 mg/1.
Figure 16. Countercurrent Rinse System
26
-------
100,000
10,000
1,000
100
10
n = 4
10
100 -• 1,000
RINSE RATIO
10,000
100,000
Notes:
Cn = concentration in final rinse
Cp = concentration in process bath
n = number of rinse tanks
Rinse ratio = gal rinse water/gal drag-out
This figure shows rinse ratios for counter-
current rinse systems. For series rinse
systems, multiply the rinse ratio for a
countercurrent arrangement with the
same number of tanks by the number of
tanks, e.g., two-stage countercurrent
rinse with Cp/Cn = 104 has a rinse ratio of
100 gal/gal. But with the two-stage series
the required rinse ratio is 200.
Figure 17. Estimating Rinse Ratios for Multiple-Tank Rinse Systems
Figure 17 shows the volume of rinse
water required as a function of initial
concentration in the plating bath,
required concentration in the final
rinse tank, and number of rinse
tanks. For example, a typical Watts-
type nickel plating solution contains
270,000 mg/l of total dissolved solids
(Cp), and the final rinse must contain
no more than 37 mg/l of dissolved
solids (Cn). The ratio of Cp/Cn, is
7,300; hence, 7,300 gal of rinse water
would be required for each gallon
(3.8 I) of process solution drag-in,
assuming a single-tank rinse system.
By installing a two-stage rinse
system, the same degree of dilution
is achieved with only 86 gal (326 I) of
water per gallon of process solution
drag-in, a reduction in rinse water
consumption of almost 99%. The
mass flow of pollutants leaving the
rinse system remains constant.
A three-stage countercurrent rinse
arrangement would further reduce
water consumption to 20 gal/h
(76 l/h). The resulting cost savings
by going from a one-stage to a
three-stage rinse system would
include reducing water use and
sewer fees by $14.56/h (based on
$2.00/1,000 gal combined water use
and sewer fees as shown in Table 1)
and reducing the size of the required
waste treatment systems. The
investment cost to add two
additional rinse tanks is highly site-
specific. For manual plating
operations, the major factor affecting
cost is the availability of space in the
process area. For automatic plating
machines, the cost of modifying the
unit to add additional stations may
be as high as $20,000 per station.
Rubber-lined steel open-top tanks
with appropriate weir plates and
nozzles cost anywhere from $1,000
to $3,000, depending on the cross-
sectional area required for the
workpiece.
A series rinse arrangement can also
be used with multiple rinse tanks. In
this case, each rinse tank receives a
fresh water feed and discharges the
overflow to waste treatment. The
rinse ratio required for a series rinse
arrangement is defined byr = n
(Cp/Cn)1/n. If the rate given in Figure
17 for a countercurrent rinse system
with the same number of rinse tanks
is multiplied by the number of rinse
tanks, the series rinse water rate can
be estimated. Rinse water rates are
significantly higher for series rinsing
than for countercurrent.
27
-------
Two-stage chrome reduction tank.
A conductivity probe is another
effective water-saving device used in
rinse systems. Except on highly
automated plating machines, the
frequency of rinse dips can vary
considerably. This means that
because the fresh rinse water usually
is fed continuously, there are periods
where considerably more water is
used than is needed for dilution. A
conductivity cell can measure the
level of dissolved solids in a rinse
water. When the level reaches a
preset minimum, the cell sends a
current to close a solenoid valve on
the fresh water feed. When the
concentration of dissolved solids
reaches the maximum desired level,
the solenoid valve is opened. These
units are generally reasonably
priced. A complete set, including a
probe, controller, and automatic
valve can be purchased and installed
for $300 to $1,000. A similar system
consisting of a solenoid operated by
a timer may be even less expensive.
A further water conservation step
uses flow regulators as a means of
controlling the fresh water feed rate
within a narrow range despite
variations in water pressure. These
devices, which cost from $10 to $40,
also eliminate the need to reset the
flow rate each time the valve is
opened. Some flow regulators are
designed to act as siphon breakers
and aerators (by the venturi effect).
Reusing rinse water is another
means of reducing water use. In
critical or final rinse operations, the
amount of contaminants remaining
on the workpiece must be extremely
small; for some intermediate rinse
steps, however, the level of
contaminants can be higher. Water
consumption can be reduced by
reusing the contaminated overflow
from the critical rinse in a less critical
rinse. Rinse water may also be
reused when the contaminants in it
do not affect the rinse water quality
required in a subsequent rinse. For
example, the overflow from an acid
dip rinse may be reused as the feed
to a rinse after an alkaline dip.
Interconnections between rinsing
systems might make operations
more complicated, but the cost
advantage they represent frequently
justifies the extra attention required.
28
-------
Reducing Drag-Out Loss
As a workpiece emerges from a
plating bath, it carries some of the
plating solution into the rinse. As
Table 9 shows, this carryover, known
as drag-out, can result in a
significant economic penalty for
each pound of plating chemicals lost
to the waste stream. Plant
modifications to minimize drag-out
are frequently cost-effective, due to
the high cost of replacing the raw
materials and treating and disposing
of the waste.
Drag-out losses can be minimized
either by reducing the amount of
plating solution which leaves the
plating bath, or by recycling plating
chemicals in the rinse water to the
plating bath. The cost-effectiveness
of each of these methods is
discussed below.
Assessing the potential economy of
drag-out recovery requires that the
quantity of plating chemicals lost to
the rinse system be determined. A
first approximation of this quantity
can be derived by multiplying the
quantity of plating chemicals added
to the bath by an assumed loss
factor. In chrome plating operations,
about 0.9 Ib of chrome is typically
lost as drag-out for every pound of
chrome added to the plating tank.
The loss factors for other plating
operations are between 50 and 90%.
If, as a result of a preliminary
assessment, chemical loss due to
drag-out represents a significant
cost, a more precise determination
can be undertaken to substantiate
the benefits of investing in drag-out
recovery modifications. The
following five steps constitute the
recommended analysis:
1. Fill the rinse station after the
process bath with a known volume
of water.
2. Using normal production
procedures, plate and rinse a
representative production unit.
3. Stir the rinse tank and collect a
sample of rinse water.
4. Plate and rinse several additional
production units and collect samples
of rinse water after each.
5. Find the concentration of plating
chemicals in the rinse water by
laboratory analysis.
Table 9.
Economic Consequences of Plating Chemicals Losses
Cost ($/lb)
Chemical
Replacement Treatment8 Disposal"
Total
Nickel:
As NiSO4
As NiCI2
Zinc cyanide as Zn(CN)2:
Using CI2 for cyanide
oxidation
Using NaOCI for cyanide
oxidation
Chromic acid as H2CrO4:
Using SO2 for chromium
reduction
Using NaHSO3 for
chromium reduction
Copper cyanide as Cu(CN)2:
Using CI2 for cyanide
oxidation
Using NaOCI for cyanide
oxidation
Copper sulfate as CuSO4
1.19
1.05
2.00
2.00
1.18
1.18
2.62
2.62
0.88
0.20
0.30
1.03
2.02
0.51
0.84
1.02
2.30
0.20
0.35
0.41
0.57
0.57
0.52
0.52
0.50
0.50
0.36
1.74
1.76
3.60
4.59
2.21
2.54
4.14
5.42
1.44
"Based on treatment model presented in Figure 12 at a concentration of 100 mg/l in wastewater.
"Based on Figure 14.
29
-------
Multiplying the volume of the rinse
tank by the concentration of each
chemical will determine the quantity
of chemical drag-out per production
unit. The volume of drag-out per
hour can be determined if the
production rate and the chemical
concentrations of the plating
solution are known.
Recovering Drag-Out from Rinse
Tanks. The drag-out lost from the
plating bath can be reduced
significantly by usually low-cost
modifications after other
modifications to reduce rinse water
use have been completed. One of
these new modifications is a
recycling system, including the
countercurrent rinse system, which
returns concentrated solutions of
dragged-out plating chemicals to the
plating bath to make up for water
lost by surface evaporation. The
amount of chemicals actually
recovered depends on the amount of
chemicals lost from the plating tank,
the number of rinse tanks used, the
concentration of chemicals
permitted in the final rinse tank, and
the rate at which rinse water can be
recycled to the plating tank.
Of these, the rate at which rinse
water can be recycled to the plating
tank is usually the most critical; it is
primarily dependent on the amount
of surface evaporation from the
plating tank.
High temperatures increase the
surface evaporation from the plating
baths. However, when the heat is
increased to get higher evaporation,
the increased temperature may
destroy heat-sensitive additives in
the bath. New additives that are not
as readily degraded have recently
been developed for many plating
applications, making these
operations possible at higher
temperatures, and thus facilitating
recycling techniques. Usually, the
increased energy cost to operate the
bath at a higher temperature is
justified by the value of the
recovered plating chemicals.
Surface evaporation can also be
increased by injecting air bubbles
into the bath (air agitation). The rate
of surface evaporation for plating
tanks with air agitators is shown in
Figure 18; the rate for those without
air agitators is shown in Figure 19. If
air agitators significantly increase
the evaporation rate, they will also
significantly increase the heat loss
from a plating tank and the energy
cost to maintain the bath
temperature. Figure 20 shows the
heat input required to compensate
for heat loss resulting from the use
of air agitators. Heat loss caused by
surface evaporation in a plating bath
without air agitators can be
calculated from: heat load (Btu/h) =
surface evaporation (gal/h) x 8,300
(Btu/gal).
100
50
30
1
3 20
cc
O 10
I
I 5
3
2.
10
100
AIR SPARGE RATE (SCFM)
1,000
Notes:
T = plating bath temperature.
Supply air at 75°F, 75% relative humidity.
Plating solution is 95% mole fraction H20.
Figure 18. Surface Evaporation Rate from Plating Baths with Aeration
30
-------
15.0 r
o
I
S-
100 120 140
BATH TEMPERATURE (°F)
Notes:
For 30 ft2 plating tank.
Ambient conditions are 75°F, 75% relative humidity.
Plating solution is 95% mole fraction H2O.
160
180
Figure 19. Surface Evaporation Rate from Plating Baths without Aeration
For example, two plating tanks, each
with a 30 ft2 (2.8 rrr) surface area, are
operated at 150°F (66°C). One uses
100 scfm (2.8 normal m3/min) air for
agitation; the second operates
without air agitation. The respective
surface evaporation rates are 9.8
gal/h (37.1 l/h) (Figure 18) and 4
gal/h (15.9 l/h) (Figure 19). The
respective heat inputs required are
107,500 Btu/hr (Figure 20) and 34,860
Btu/h using the formula above.
Using indirect steam heating to
compensate for the heat loss would
cost $0.64/h for the agitated bath
compared to $0.20/h for the bath
without air agitation, based on an
energy cost of $6/MMBtu.
If the evaporation rate can be
matched to the required rinse water
rate, the entire volume of rinse water
could be returned to the plating bath.
This set-up is referred to as a closed-
loop recovery system. In this case,
the reduction of drag-out loss can be
estimated by the following formula:
Percent recovery of drag-out =
1 - -^-x 100
where
Cp = concentration in plating bath
Cn = concentration in final rinse
tank.
In a closed-loop rinse water system
the only chemical loss is from the
drag-out after the last rinse tank,
which has a dilute concentration of
plating chemicals.
A closed-loop system may be
impractical when:
• A very low final rinse
concentration is required and only
achievable through a larger
number of rinse stages.
• Excessive drag-out is unavoidable.
• Plating tank surface evaporation is
minimal.
31
-------
1,000
500
300
200
I
100
a 50
I"
2 20
* 10
6.0
0.6
O
u
UJ
0.06
0.006
10
100
AIR SPARGE RATE (SCFM)
1,000
Notes:
T = plating bath temperature.
Supply air at 75°F, 75% relative humidity.
Plating solution is 95% mole fraction H2O.
Fuel cost to supply heat load based on energy supply at $6.00/MMBtu.
Figure 20. Input Required with Heat Aeration of Plating Baths
The low final concentration problem
can be overcome in many cases by
operating the final rinse as a free
(running) rinse, and using the
upstream tanks as a countercurrent
rinse-and-recycle system. Using this
approach, significant drag-out
recovery can be realized while
providing a final rinse with a low
level of contaminants. Figure 21
shows an automatic rinse-and-
recycle system with a running rinse.
Level-control devices in the plating
and rinse tanks control the flow of
rinse water through the system.
Figure 22 shows the percent
recovery of drag-out for such a
system as a function of the recycle
ratio, defined as the volume of
recycled rinse divided by the volume
of drag-out in a given time. In Figure
22, the recycle rate is assumed to be
equal to the evaporation rate.
For example, a nickel plating
operation has these operating
characteristics: a drag-out rate of 0.5
gal/h (1.9 i/h), a surface evaporation
rate of 5 gal/h (19 I/h), and a final
rinse concentration of 40 mg/l.
Therefore, the recycle rinse ratio
could be set at 10. As seen in Figure
22, a one-stage recovery rinse and
recycle system would reclaim 91% of
the drag-out (point A). At this
recovery rate, the concentration ratio
is 0.09 (100% - 91%)-;-100%.
Assuming an initial plating tank
concentration of 270,000 mg/l, the
concentration entering the final rinse
is 0.09 x 270,000, or 24,300 mg/l. The
makeup water requirements in the
final rinse would be reduced by the
same level as drag-out losses, when
compared with the required rinse
rates for a single-tank rinse system.
• The rinse water required in the final
rinse tank to achieve 40 mg/l is 300
gal/h (1,150 I/h).
32
-------
The data presented in Figure 22 is
based on the assumption that make-
up water is added continuously to
the rinse tanks as surface
evaporation occurs. Typically,
recycled water is added in
increments rather than continuously,
in which case one would see cyclical
movement along the same curves
shown in Figure 22. The longer the
time interval between additions, the
greater the variation in the recovery
of the drag-out realized. Particularly
at low recycle rates where the
recovery potential is very sensitive to
changes in the recycle ratio,
minimizing the time between
additions will significantly increase
the amount of drag-out recovered. A
level-control device will approach
the potential of continuous water
addition and is recommended if the
recycle ratio is in the range of 3 or
less. These control devices cost from
$700 to $1,500.
In any of these recycling systems,
deionized water is specified for any
rinse stream that is recirculated to
the plating bath in order to avoid the
progressive buildup of contaminants
in the bath.
100 I—
2468
RECYCLE RINSE RATIO (r)
Notes:
n = number of counterflow rinse tanks in recovery use.
r = recycle rinse (gal/h) •*• drag-out (gal/h).
Recycle rinse set equal to surface evaporation from batch.
10
Figure 22. Drag-Out Recovery Rate for Rinse-and-RecycIe Systems
Makeup water"
. LC|
Surface
evaporation e
•: I
Workplace
Plating bath
LC = Level Control
"~l::.!lT
Figure 21. Automated Rinse-and-Recycle System
33
-------
Four-stage chelated treatment unit (red) with clarifier (blue).
Reducing Drag-Out from Plating
Tanks. There are three effective
methods of reducing the
concentration or amount of plating
solution lost from plating tanks:
spray rinses, air knives, and
minimizing plating bath
concentrations.
Spray rinses are ideal for reducing
drag-out from plating tanks on
automated lines. As the workpiece is
mechanically withdrawn from the
plating solution, a spray of water
automatically washes the workpiece,
returning as much as 75% of the
drag-out chemicals back to the
plating tank. Spray rinsing is best
suited for flat parts, but will reduce
drag-out effectively on any plated
part. The volume of spray rinse
cannot exceed the volume of surface
evaporation from the plating tank.
The savings are calculated in terms
of the concentration change in the
drag-out. For example, if the
concentration of the drag-out was
100,000 mg/l and a spray rinse
reduced the concentration to 50,000
mg/l, the chemical losses would be
reduced by 50%.
An air knife reduces drag-out in
much the same way as a spray rinse,
and is particularly useful when the
surface evaporation rate in the
plating bath is low. Air knives reduce
the volume of drag-out adhering to
the workpiece by subjecting the
workpiece to a high-velocity stream
of air. The drag-out is returned to the
plating bath without changing its
concentration.
A third means of reducing chemical
losses from drag-out is by reducing
the concentration of the plating bath,
since the amount of loss is
determined both by the volume of
the drag-out and its concentration.
Typically, the target operating
concentration is the midpoint of a
range of acceptable operating
concentrations. This practice is
sound unless the savings in chemical
replacement costs are exceeded by
the costs of controls needed to
maintain the target operating
concentrations.
34
-------
An example of how to calculate the
savings from not having to replace
the additional chemicals involves a
standard nickel plating solution
having the concentration limits
shown in Table 10. The plating shop
operates at an average of 12 h/d, 250
d/yr, and processes 600 ft2/h (56
irr/h). Drag-out losses are estimated
at 2,700 gal/yr (10,220 l/yr), based on
a drag-out rate of 1.5 gal/1,000 ft2 (61
1/1,000 m2). Modifying the operating
conditions to the minimum values
indicated in Table 10 would save this
shop 390 Ib (177 kg) of nickel sulfate
and 150 Ib (68 kg) of nickel chloride
annually. The money saved in
replacement chemicals, treatment
costs, and sludge disposal (as shown
in Table 9) would amount to $940/yr.
Example of Cost/Benefit Analysis.
The following example illustrates
how to calculate the potential
savings in water and chemicals that
result from the application of the
modifications discussed in this
chapter to a typical nickel-chromium
plating operation. The worksheet
provided in Appendix A can be used
to develop a similar analysis for
most plating shops.
The shop plates approximately 600
ft2/h (56 mah) in its nickel-chromium
operation, operating an average of
10 h/d, 300 d/yr. Figure 23 shows the
original processing sequence and
water use rates for the operation.
This processing sequence used two-
stage countercurrent rinse systems
after the nickel and chromium plate
tanks. As shown in Figure 24, in-
plant modifications were made at six
locations (Station 2 and Stations 4
through 8) to reduce raw material
losses and waste treatment costs.
For the alkaline rinse (Station 2) and
pickling rinse (Station 4), testing
indicated that with air agitation the
rinse rate for each station could be
reduced from 360 to 180 gal/h (1,363
to 681 l/h) with adequate rinsing
efficiency. This reduction was
accomplished by installing a venturi-
style water flow regulator that also
provided air agitation. In addition,
the overflow from the acid rinse was
fed to a suction pump and was used
as the feed to the alkaline rinse.
These modifications reduced
process water demand at these two
stations from 720 to 180 gal/h (2,725
to 680 l/h). Costs for the
modifications came to $2,500:
• Pump and foundation, $1,600
• Flow regulators, piping, valves,
and electrical connections, $300
• Labor, $600.
In the nickel plating and rinse
stations (5 and 6), the plating bath
operates at 150°F (66°C) and has the
following chemical composition:
• NiSO4-6H2O @ 45 oz/gal (337 g/l)
or NiSO4 @ 1.65 Ib/gal (0.2 kg/I)
• NiCI2-6H2O @ 10 oz/gal (75 g/l), or
NiCI2 @ 0.34 Ib/gal (0.04 kg/I)
• H3BO3 @ 6 oz/gal (45 g/l), or 0.38
Ib/gal (0.045 kg/I)
• Specific Gravity = 1.2.5
The plating tank has a surface area of
30 ft2 (2.8 m2) and drag-out is
determined by testing to equal 1.5
gal/1,000 ft2 (61 1/1,000 m2) of work
plated, or 0.9 gal/h (3.41 l/h) drag-out
at 600 ft2/h (56 m2/h) plated. The tank
is aerated at a rate of 60 scfm (1.7
normal m3/min). From Figure 18, the
evaporative rate in the plating tank is
5.85 gal/h (22.14 l/h).
Table 10.
Standard Nickel Solution Concentration Limits
Chemical
Concentration
range
(oz/gal)
Operating
condition
(oz/gal)
Modified
operating
condition
(oz/gal)
Nickel sulfate:
NiS04,6H20
As NiS04
Nickel chloride:
NiCI2.6H20
As NiCI2
Boric acid (H3BO3)
40-50
8-12
6-6.5
45.0
26.5
10.0
5.5
6.25
41.0
24.2
8.5
4.6
6.1
35
-------
The plant decided to reduce drag-out
losses with a rinse-and-recycle
system similar to that in Figure 21.
Using the existing two-stage,
countercurrent rinse as a single-
stage recovery (recycled) rinse
followed by a running rinse, drag-out
losses could be reduced by 85
percent. This can be seen in Figure
17 based on a recovery rinse ratio of
(5.85 gai/h)/(0.9 gal/h) = 6.5. If a third
rinse tank was installed, allowing a
two-stage recovery rinse before the
single-stage final rinse, the recovery
system would reclaim 98 percent of
the current drag-out losses. The
economy of adding the third rinse
tank was analyzed.
Table 11 summarizes the results.
Case 1 represents the current
operating practice. Case 2 represents
a single-stage recovery rinse
followed by a running rinse using the
two existing rinse tanks. Case 3
represents adding a third rinse tank
and operating a two-stage recovery
rinse followed by a running rinse.
The additional $3,000 investment for
a third rinse tank further reduced
operating costs by $4,400 per year
(Case 3). Because of this excellent
return on investment, a third rinse
tank was installed.
In the chrome plating and rinse
stations (7 and 8), the plating tank
has a surface area of 30 ft2 (2.8 m2)
and drag-out averages 1.5 gal/1,000
ft2 (61 1/1,000 m2) of work plated, or
0.9 gal/h (3.4 l/h) drag-out at 600 ft2/h
(56 m2/h) plated. This tank is also
aerated at a rate of 60 scfm (1.7
m3/min). The plating solution
contains 50 oz/gal (375 g/l) chromic
acid (H2CrO4), has a specific gravity
of 1.25, and is maintained at 125°F
(52°C). From Figure 18, the surface
evaporation rate is 2.4 gal/h (9.1 l/h).
360 gal/h
Process
water ""
360 gal/h
90 gal/h
90 gal/h_
Work flow
IJT (600ft2/h)
Alkaline
clean ,<~\
t
Alkaline
rinse s^.
t
Acid dip
(pickling) ^^^
t
Pickling
rinse f^\
t
Nickel
plate /-TN
t
Two-stage
counterflow
rinse /"X
t
Chrome
plate /^\
t
Two-stage
counterflow
rinse /— s
09
i
Hot
water
rinse /Ov
1
36pga
•™JB"
360
gal/h
1
90
gal/h
90
gal/hu
10
gal/h
/h
-H
j
i
t_
Neutralization
^ and
f, precipitation
920 gal/h
1 '
Clarification
k
i r
Wastewater
discharge
t
90 gal/h j
|^> Chrome
reduction
Figure 23. Nickel-Chrome Wastewater Flow Rates: Original System
36
-------
Workflow
Alkaline
clean
©
180
gal/h
Process water
5 gal/h
Alkaline
rinse /^\
t
Acid dip
(pickling) ^-^
*
Pickling
rinse /£N
— *
Nickel
plate x->.
I 5 J
*
Two-stage
recovery tank
Rinse (e)
-H
inn
Chrome
plate
Recovery tank
Two-stage
rinse
Hot water
rinse
A rinse-and-recycle system, as
shown in Figure 21, would operate at
a rinse ratio of (2.4 gal/h)/(0.9 gal/h)
= 2.66. If an additional rinse tank
was installed and a two-stage
recovery rinse was operated, 90
percent of the drag-out would be
recycled (Figure 22). A one-stage
recovery rinse could recover 72
percent of the current losses. The
plant decided to add a third rinse
tank and ah analysis was performed
to determine whether it would be
more advantageous to operate the
three rinse tanks as a two-stage
recovery rinse followed by a single-
stage final rinse or as a single-stage
recovery rinse followed by a two-
stage final rinse. Table 12
summarizes the results. Case 1
represents the current operating
practice. Case 2 represents the two-
stage final rinse. Case 3 represents
the two-stage recovery rinse.
The two investment options (Cases 2
and 3) entail equal capital costs and
reduce operating costs by almost
equal amounts. However, Case 3
would result in an almost tenfold
increase in wastewater flow to the
chromium reduction waste
treatment system, from 81 gal/h to
730 gal/h (307 to 2,763 l/h). This
volume increase would exceed the
capacity of the unit and would
reduce the efficiency of downstream
waste treatment equipment. When
the additional criteria were
considered. Case 2 represented the
most attractive option and these
modifications were incorporated into
the operation.
Figure 24. Nickel-Chrome Wastewater Flow Rates: Modified System
37
-------
The total cost of the modifications
selected was $1 5,000. The cost
assumes that the plating baths
already have purification systems
that would control any contaminant
buildup resulting from drag-out
recycling. The benefits from the
modifications include:
• An operating cost reduction of
$8,500/yr for the nickel plating
bath.
• An operating cost reduction of
$13,000/yrforthe chrome plating
bath.
• A reduction in the baseline flow to
waste treatment from 920 gal/h to
333 gal/h (3,445 to 1,250 l/h) (see
Figures 23 and 24). The total shop
discharge rate may now be below
10,000 gal/d (37,854 l/d), putting
the plater in an industry category
with less stringent treatment
regulations under the proposed
pretreatment standards.
• A reduced quantity of pollutants
discharged in the wastewater
effluent in direct proportion to the
reduced effluent volume.
Table 11.
Evaluation of Rinsing
Required modifications
Cost of modifications
Drag-out recovery
Drag-out losses8
Rinse water required6
Water use cost (at
$1.80/1 ,000 gal)
Annual operating cost0
Annual savings
aFrnm Tahlo Q
Options for Nickel
Case 1
(present 2-stage
countercurrent rinse)
—
0
$9,360/yr
70 gal/h
$380/yr
$9,740
—
Plating Operation
Case 2
(proposed 1 -stage
recovery rinse)
Level control
rinse feed.
repiping
$2,000
85%
$1,400/yr
735 gal/h
$4,000/yr
$5,600
$4,140
Case 3
(proposed 2-stage
recovery rinse)
Level control
rinse feed.
repiping,
additional
rinse tank
$5,000
98%
$190/yr
100 gal/h
$540/yr
$1,230
$8,510
nrom i ODIS 3.
6From Figure 16, Cn = 37 mg/l.
"Depreciation at 10-year straight line.
Table 12.
Materials Recovery
Processes
The high cost of replacing and
treating the plating chemicals lost to
the waste stream has resulted in the
development of chemical separation
processes to reclaim these materials
for reuse. What all of these
processes have in common is that
they separate the spent rinse water
into a purified stream which is
returned to the rinse system, and a
stream of plating chemicals
concentrated to the point that the
solution can be returned to the
plating bath.
Evaluation of Rinsing Options for Chrome Plating Operation
Required modifications
Cost of modifications
Drag-out recovery
Drag-out losses8
Rinse water required"
Water use cost (at
($1.80/1 ,000 gal)
Annual operating cost0
Annual savings
'From Table 9.
"From Figure 17, Cn = 37 mg/l.
Case 1
(present 2-stage
countercurrent
rinse)
—
—
0
$18,800/yr
81 gal/h
$440/yr
$19,240
—
Case 2
(proposed 1 -stage
recovery rinse.
2-stage
final rinse)
LeVel control
rinse feed.
conductivity
controller.
repiping,
additional
rinse tank
$7,000
72%
$5,300/yr
43 gal/h
$230/yr
$6,230
$13,010
CaseS
(proposed 2-stage
recovery rinse,
1 -stage
final rinse)
Level control
rinse feed,
conductivity
controller.
repiping,
additional
rinse tank
$7,000
90%
$1,800/yr
730 gal/h
$3,940/yr
$6,530
$12,720
"Depreciation at 10-year straight line.
38
-------
Table 13.
Summary of Recovery Technology Applications
Plating Bath
Decorative Hard
Chromium Chromium
Nickel
Electroless Cadmium Zinc
Nickel (CN) (CN)
Zinc
(CD
Copper
(CN)
Tin
(BF4)
Silver
Evaporation
Electrodialysis
Reverse osmosis
Ion exchange
Electrolytic
Recovery processes, which include
evaporation, reverse osmosis, ion
exchange, electrodialysis and
electrolytic processes, should be
considered when low-cost plating
line modifications or rinse-and-
recycle modifications are not
available. However, the type of
purification system needed in a
given situation depends, among
other things, on the type of plating
chemicals being recovered. Table 13
presents the range of applications
for each of the recovery systems.
Each of the recovery processes can
be used either as a closed-loop
system or as an open-loop system. A
closed-loop system is one in which
the purified effluent from the
recovery unit provides the feed for
the final rinse tank (Figure 25a). In
this case very little rinse water is sent
to wastewater treatment, although
purge streams from the recovery
unit are almost always necessary.
Where rinse waters require separate
waste treatment systems (chromium
and cyanide are examples), closing
the loop around the plating
operation with a recovery system
can avert the need for the separate
wastewater treatment system. In
cases where the high quality of the
final rinse is more important than
closing the loop, the quality of the
final rinse can be ensured by using
an open-loop system (Figure 25b).
With this approach, the final rinse is
set up as a running rinse; its influent
is fresh water and its effluent is sent
directly to wastewater treatment.
The purified effluent from the
recovery unit is sent to the next-to-
final rinse.
Using a recovery unit requires first
reducing the rate of rinse water use
to a level that can be processed
economically. The use of a
multistage countercurrent rinse
system is, therefore, critical. Some
means of bath purification is also
needed to control the buildup of
contaminants in the closed-loop
system resulting from return of the
drag-out to the process bath. In an
open-loop system, the drag-out acts
as a bleed stream and serves to
control the buildup of contaminants.
39
-------
Workpiece
_J
,
Chemical
recycle
Plating
bath
Bath
purification
r
rn
L_Jll
i—
i ____ i
Rinse tanks
Recovery
Makeup
water
Rinse recycle
(a) Closed Loop
Workpiece
1
u
Rinse
"" water
•M ...... ^Ta-
(b) Open Loop
To waste
treatment
Makeup
water
Rgure 25. Recovery Systems: (a) Closed Loop; (b) Open Loop
Recovery is accomplished by boiling
off sufficient water from the
collected rinse stream to allow the
concentrate to be returned to the
plating bath. The condensed vapor is
recycled for use as rinse water in the
rinse tanks. The boil-off rate, or
evaporative duty, is set to maintain
the water balance of the plating bath.
The evaporation usually is
performed under vacuum to prevent
thermal degradation of additives in
the plating solution.
Figure 27 illustrates a closed-loop
evaporative recovery system used
on a chromium plating bath with a
three-stage, countercurrent rinse
system. This system includes a
cation exchange column which is
necessary in order to prevent the
buildup of metallic impurities
(primarily dissolved metals from the
processed work plus excess trivalent
chromium). The losses of plating
chemicals from the plating bath have
been minimized. Only the amount of
chromium plate on the finished
product must be replaced in the
plating tank. Water consumption is
reduced to the water lost to surface
evaporation.
The potential of a recovery system to
recover chemicals is shown in Figure
26 as a function of rinse ratio. The
curve is the same as that developed
for the recovery potential of a two-
stage rinse-and-recycle system in
Figure 22. In this case, however, the
recovery rinse rate is determined by
the capacity of the recovery unit, not
by the surface evaporation rate of
the plating bath.
This chapter examines the operating
parameters and costs of the different
recovery systems used in the
electroplating industry. This
information will enable the
electroplater, after assessing specific
loss factors, to determine the site-
specific economics of installing one
or more recovery units.
Evaporation. Evaporation was the
first separation process used to
recover plating chemicals lost to
rinse streams. The process has been
demonstrated successfully on
virtually all types of plating baths,
and several hundred units are
currently being operated.
40
-------
Note:
r = recovery rinse (gal/h)
RINSE RATIO (r)
• drag-out (gal/h).
Figure 26. Recovery Potential for a Two-Stage Countercurrent Rinse System
Total installed investment and
operating costs for a 20 gal/h (76 l/h)
evaporator such as the one shown in
Figure 27 are given in Table 14. Of
the total annual cost of operation
($20,100), steam and depreciation,
are the major portions. The annual
savings from the recovery of plating
chemicals and the reduction in
wastewater treatment costs total
$38,000. The before-tax annual
savings for this system is
approximately $18,000 and yields a
short payback period of 3.3 years.
The cost of the steam needed and
the installed cost for the evaporator
depend on the evaporative capacity
needed (Figure 28); for rinse
recovery systems, this is equal to the
required rinse water flow rate. To
minimize the rinse rate, such
methods as countercurrent rinse
systems are usually cost-effective, as
discussed in Chapter 3. A 50%
savings in the amount of steam
needed can be achieved with double-
effect evaporators; however, the
capital costs are considerably higher
and their operation is more
complicated. As a rule, at
evaporation rates below 150 gal/h,
(568 l/h), the additional investment
for double-effect evaporators is not
justified.
Because of the high initial
investment of an evaporative
recovery system, the decision to
acquire it depends largely on the
quantity of plating chemicals
available for recovery in the rinse
water. For example, if the 20 gal/h
(76 l/h) evaporator discussed in
Table 14 were fed a stream with 50%
less plating chemicals, the annual
savings for treatment and recovery
would decrease by 50% to
approximately $19,000 (38,200 x 0.5),
or slightly less than the annual
operating cost of the unit.
41
-------
Workpiece
Makeup water •
Air
Steam
Figure 27. Closed-Loop Evaporative Recovery System
125
100
8
C£
5>
75
<_>
in
50
25
Legend:
A highly corrosive duty, borosilicate
glass body and tubes
B highly corrosive duty, fiberglass-
reinforced plastic body with tan-
talum tubes
C corrosive duty, fiberglass-reinforced
plastic body with titanium tubes
D mild duty, carbon steel body
with stainless steel tubes
Notes:
Based on $6/MMBtu, the steam cost will
equal $7/hr per 100 gal/h of water
evaporated.
Cost includes vacuum evaporator, product
and rinse water feed tanks, condensate and
product return pumps, rinse filter, all pip-
ing, electrical work and installation.
25
50 75 100
EVAPORATIVE CAPACITY (gal/h)
125
150
Figure 28. Investment and Energy Costs for Evaporative Recovery Units
42
-------
Table 14.
Economics of Evaporator System for Chromic Acid Recovery3
Cost
INSTALLED COST, 20-gal/h evaporator ($):
Equipment:
Evaporator
Tanks
Pumps
Cation exchanger
Piping
Miscellaneous
Subtotal
Installation, labor and materials ($):
Site preparation
Plumbing
Electrical
Equipment erection
Miscellaneous
Subtotal
Total installed cost
ANNUAL COSTS ($/yr):
Operating:
Labor, 100 h/yr at $10/h
Supervision
Maintenance, 6% of investment
General plant overhead
Raw materials, cation exchanger:
H2S04,3,500 Ib/hr at $0.05/lb
NaOH, 3,000 Ib/yr at $0.13/lb
Utilities:
Electricity ($0.08/kWhr)
Cooling water,
1,000 gal/h x $0.10/1,000 gal
Steam, $6.00/MM6tu
Total annual operating cost
Fixed:
Depreciation, 10% of investment
Taxes and insurance, 1% of investment
Total annual fixed cost
Total annual cost of operation ($/yr)
ANNUAL SAVINGS ($/yr):°
Recovered plating chemicals,
(3.0 Ib/h H2CrO4)
Water treatment chemicals
Sludge disposal
Water use, 13 gal/h at 1.80/1,000 gal
Total annual savings
NET SAVINGS = annual savings-
(annual operating cost + annual fixed
cost) ($/yr)
NET SAVINGS AFTER TAXES, 48% tax rate ($/yr)d
AVERAGE ROI = (net savings after taxes/
total investment) x 100 (%)
CASH FLOW FROM INVESTMENT = net savings
after taxes + depreciation ($/yr)
PAYBACK PERIOD = total investment/
cash flow (yr)
24,000
2,000
1,000
9,000
3,500
500
500
4,000
1,500
500
500
1,000
b
2,800
1,200
200
400
2,500
500
6,300
4,700
500
17,700
12,600
7,800
100
18,100
9,400
20
14,100
3.3
40,000
7,000
47,000
14,900
5,200
20,100
38,200
"Operating 5,000 h/yr. No interest on capital is included.
"None required.
"From Table 9.
dThe analysis beginning with this line is based on tax law as it existed at the time of the installation.
43
-------
Workpi
Surface evaporation
(5 gal/h)
see 1 Drag-out (1 gal/h)
" i T r^"i r-
tit i i
••a" !4gHla^tes i j
1 I
I 1
Plating bath
(270,000 mg/l
solids)
100 gal/h
'
(
Activated
filter
1 ^~ r
_ i a
(3
m
>
Makeup water
5 gal/h 10 gal/h
1 1 — ** 1 | **
. .. I -1 H-
1 J
•*
Rinse tanks
,000 (333
g/l) mg/l)
Filter
*
1
L__J
1 Running rinse
• tank (37 mg/l),
L..m.i ^p. To waste
treatment
95 gal/h (10 gal/h)
RO unit
5 gal/h, 59,400 mg/l solids
Note:
Chemical recovery = 99%; Flux rate = 0.3 gal/h/ft2;
Rejection = 98%; Permeate/feed ratio = 0.95.
Rgure 29. Reverse Osmosis System for Nickel Plating Drag-Out Recovery
Reverse Osmosis. Reverse osmosis
(RO) is a pressure-driven membrane
separation process. The feed is
separated underpressure (400to 800
psig) through the microscopic pores
of a semipermeable membrane into
a purified "permeate" stream and a
concentrate stream. Commercial RO
units have proven successful in
concentrating and recycling rinse
streams in metal plating operations
for a number of years. The primary
area of application is in the
concentration of rinse waters from
mild pH nickel plating baths.
Figure 29 illustrates a typical RO
installation for recovering drag-out
from an acid nickel plating operation.
The system uses a 50 p,m filter to
prevent blinding of the membrane
by solid particles. The preassembled
RO unit consists of a high pressure
centrifugal pump and six membrane
modules, and installation requires
only piping and electrical
connections. An activated carbon
filter is used to avoid organic
contaminant buildup in the plating
bath.
The performance of RO units is
defined by flux (the rate of passage
of purified rinse water through the
membrane per unit of surface area)
and the percent rejection of a
dissolved constituent in the rinse
water, which relates to the
membrane's ability to restrict that
constituent from entering the
permeate stream. Percent rejection
is defined by:
Cf-Cp x100
Percent rejection = —
where
Cf = concentration in feed stream
Cp = concentration in permeate
stream.
The major limitation of commercial
RO systems has been their inability
to maintain membrane performance,
though in recent years two-year
warranties from vendors have
become common. Fouling and
gradual deterioration of membranes
can reduce the processing capacity
of the unit and necessitate frequent
membrane replacements. Currently,
feed solutions must be in a pH range
between 2.5 and 11 to ensure
maximum life of the membrane.
Another limitation of RO is that the
membranes are not suitable for
treating solutions having a high
oxidation potential, such as chromic
acid. Furthermore, the membrane
does not completely reject certain
species, such as nonionized organic
wetting agents.
Table 15 lists typical maximum
concentrations reached by RO units
in commercial applications. Because
of these limits, further concentration
of the stream by a small evaporator
may be required for ambient
temperature baths where there is
minimal surface evaporation.
Therefore, acid nickel plating baths,
which experience considerable
surface evaporation, are the primary
applications for RO.
44
-------
Table 15.
Reverse Osmosis Operating Parameters
Maximum
concentration
of concentrate
stream (%)
Percent
rejection
Ni+2
Cu+2
Cd+2
Cr04-2
CN-
Zn+2
Low molecular weight organics
10-20
10-20
10-20
10-12
4-12
10-20
b
98-99
98-99
96-98
90-98a
90-95"
98-99
"Performance depends greatly on pH of solution.
'These compounds are concentrated in permeate stream because of selective passage through
membrane.
30 r-
o 25
20
^ 16
10
0 200 400 600 800
MEMBRANE SURFACE AREA (ft2)
Note:
Unit includes feed pump, filter, and membrane modules,
p reassembled, requiring only utility connections.
1000
1200
These limitations must be weighed
when RO applications are
considered. Where well chosen,
however, RO is an inexpensive,
automated process for recovery of
plating chemicals.
Figure 30 presents the investment
cost of RO units as a function of
membrane surface area. A
determination of the flux rate for a
specific application, and thus of the
necessary membrane surface area,
usually requires testing by the
vendor. As an approximate tool, the
flux rate of 0.3 gal/h/ft2 (12.2 l/h/m2)
(indicated in Figure 29 for a nickel
plating bath plating bath with a feed
concentration of 3,000 mg/l and a
permeate/feed ratio of 0.95) can be
used to determine membrane
surface area requirements. The flux
rate will decrease as the feed
concentration increases. Higher
permeate/feed ratios also will
decrease the flux rate. Experience
has shown that doubling the feed
concentration or reducing the
concentrate volume by 50%
(increasing the permeate/feed ratio
from 0.85 to 0.975) will decrease the
flux rate by 25%. For example, if the
RO system shown in Figure 29 was
to concentrate the drag-out into 2.5
gal/h (9.5 l/h) of concentrate instead
of the 5 gal/h (19 l/h) shown, the
membrane surface area
requirements would increase from
317 to 422 ft2 (29.5 to 39.2 m2).
The cost of the system, shown in
Figure 29 and itemized in Table 16, is
$27,500. Theoretically, the system
would recover 99% of the plating
chemicals lost to the rinse tank.
However, Table 16 presents the
operating cost reduction that would
be achieved if the unit operated 90%
of the time. The system has a
payback period of 4.6 years.
Figure 30. Investment Cost for Reverse Osmosis Unit
45
-------
Table 16.
Economics of Reverse Osmosis System for Nickel Salt Recovery*5
Cost
INSTALLED COST, 330 ft2 unit ($):
Equipment:
RO module including 50 |im filter,
pump and 6 membrane modules at 55 ft2
per module
Activated carbon filter
Piping
Miscellaneous
Subtotal
Installation, labor and material:
Site preparation
Plumbing
Electrical
Miscellaneous
Subtotal
Total installed cost
ANNUAL COSTS ($/yr):
Operating:
Labor, 100 h/yr at $10/h
Supervision
Maintenance
General plant overhead
Raw materials:
Module replacement, 2-yr life
(6 x $500)(module x 0.5/yr)
Resin for carbon filter
Utilities, electricity
($0.08/kWhr)
Total annual operating cost
Rxed:
Depreciation, 10% of investment
Taxes and insurance, 1% of investment
Total annual fixed cost
Total annual cost of operation ($/yr)
ANNUAL SAVINGS ($/yr):c
Plating chemicals:
1.65 Ib/h NiS04
0.34 Ib/h NiCl2
Water treatment chemicals
Sludge disposal cost
Water use (no saving)
Total annual savings
NET SAVINGS = annual savings -
(annual operating cost + annual fixed cost)
($/yr)
NET SAVINGS AFTER TAXES, 48% tax rate,
6,100 x 0.52 ($/yr)"'
AVERAGE ROI = (net savings after taxes/
total investment) x 100 (%)
CASH FLOW FROM INVESTMENT = net savings
after taxes ; depreciation ($/yr)
PAYBACK PERIOD = total investment/
cash flow (yr)
20,000
3,000
1,000
1,000
400
500
700
900
25,000
2,500
27,500
1,000
b
1,700
900
1,500
700
900
2,800
300
6,700
3,100
9,800
8,500
1,600
2,200
3,600
6,100
3,200
12
6,000
4.6
15,900
•Operating 5,000 h/yr. No interest on capital is included.
''None required.
cFrom Table 9, based on a 90% operating factor.
"The analysis beginning with this line is based on tax law as it existed at the time of the installation
46
-------
Ion Exchange. In ion exchange, a
chemical solution is passed through
a resin bed which selectively
removes charged particles (ions).
Either the positively charged cations
(e.g., Cu+2, Fe+2) or the negatively
charged anions (e.g., SO4~2, CN~)
are removed from the solution by the
exchange of an ion on the surface of
a resin particle for a similarly
charged ion in the solution. Ion
exchange is used in the
electroplating industry to remove
trace pollutants from wastewater
after a conventional treatment
process, or to recover plating
solution drag-out from rinse water
and to return the purified water for
reuse.
Unlike other recovery systems
whose operating costs are inversely
proportional to the chemical
concentration, ion exchange is
ideally suited for dilute solutions.
The treated water is of high purity.
As with most recovery systems,
however, the capital cost is'
proportional to flow rate.
A major drawback of ion exchange is
that the resin must be regenerated
after it has exhausted its exchange
capacity. This problem complicates
the operation of the system
considerably and results in
significant volumes of regenerant
and wash solutions, which add to the
wastewater treatment loading.
Figure 31 shows a fixed-bed ion
exchange system used to recover
chromic acid from rinse waters.
Initially, water passes in series
through a cation column and two
anion columns. The cation column is
Workpiece
Legend:
«__ primarily ion exchange circuit
___ secondary ion exchange circuit
— regeneration circuit
Figure 31. Ion Exchange System for Chromic Acid Recovery
47
-------
ON STREAM (LOADING)
Cation
T
Exhaust
(to waste
treatment)
Product
Rinse water is pumped from the chromium
plating rinse tanks through the prefilter to
remove any solids, then through the first
cation bed where cationic contaminants (e.g.,
Fe+3, Cr+3) are removed by the resin. The
rinse water then passes through the anion
bed where the chromate ions are removed.
The purified rinse is returned to the rinse
system. While the unit is on stream, the sec-
ond cation bed is regenerated..
1
REGENERATION
Exhaust
(to waste
treatment)
Cation
After a preset period of time, the unit goes
off stream. The first cation bed is regenerat-
ed with sulfuric acid and washed with
water. The anion bed is regenerated with
sodium hydroxide and the effluent is passed
through the second cation bed; the concen-
trated chromic acid solution resulting is
returned to the plating tank.
NaOH
WASHING
Water
1
Cation
Exhaust
(to waste
treatment)
Concentrated T
NaOH , I
1 Water
The three beds are then washed with water;
as the product from the anion bed contains
the excess caustic acid used in the regen-
eration step, it is mixed with concentrated
NaOH and used in the next regeneration cy-
cle. The unit then goes back on stream.
Rgure 32. Operating Cycle for Reciprocating Flow Ion Exchange Unit
used to remove any heavy metal
contaminants. The anion columns
remove the hexavalent chromium
from the rinse water. When the
upstream anion column has
exhausted its exchange capacity, it is
taken off stream and regenerated
with a caustic solution. This column
is then returned to service as the
downstream anion column. The
product of the anion column
regeneration is sodium chromate
and any excess caustic used; it is
passed directly to a second cation
column where the sodium ions are
exchanged for hydrogen ions,
yielding chromic acid and water.
This solution can be returned to the
plating bath. The cation columns are
regenerated with an acid solution
when saturated. The spent
regeneration solutions are ordinarily
treated by the wastewater treatment
plant.
The reciprocating flow ion
exchanger (Figure 32) was
developed to simplify the operation
of units processing large-volume
solutions such as the rinse overflow
from an electroplater's rinse tank.
The unit operates on the principle
that during the short period of time
the unit goes off stream for
regeneration, the buildup of
contaminants in the rinse system is
negligible. Several reciprocating
units with various column
configurations are being used to
reclaim plating chemicals from rinse
streams and to remove metal
impurities from various acid baths.
Table 17 presents the total
investment and operating costs for
and the annual savings realized by
installing a reciprocating flow ion
exchanger to recover drag-out from
a chromium plating operation. The
payback period for the initial
investment is estimated at 3.6 years.
48
-------
Table 17.
Economics of Reciprocating Flow Ion Exchange System for Chromic Acid
Recovery3
Cost
INSTALLED COST ($):
Equipment:
Reciprocating flow ion exchanger,
including cartridge filter and
three ion exchange beds
Piping
Miscellaneous
Subtotal
Installation, labor and material:
Site preparation
Plumbing
Electrical
Miscellaneous
Subtotal
Total installed cost
ANNUAL COSTS ($/yr):
Operating:
Labor, 100 h/yr at $10/h
Supervision
Maintenance
General plant overhead
Raw materials:
Replacement resin
Regeneration chemicals:
NaOH
H2S04
Utilities, compressed air
Fixed:
Total annual operating cost
Depreciation, 10% of investment
Taxes and insurance, 1% of investment
Total annual fixed cost
Total annual cost of operation
ANNUAL SAVINGS ($/yr):<:
Plating chemicals, 2 Ib/hr H2Cr04
Water treatment chemicals
Sludge disposal
Water use, 18 gal/h at $1.80/1,000 gal
Total annual savings
NET SAVINGS = annual savings-
(annual operating cost + annual fixed
cost) ($/yr)
NET SAVINGS AFTER TAXES, 48% tax rate
<$/yr)d
AVERAGE ROI = (net savings after taxes/
total investment) x 100 (%)
CASH FLOW FROM INVESTMENT = net savings
after taxes + depreciation ($/yr)
PAYBACK PERIOD = total investment/
cash flow (yr)
34,000
1,000
1,000
300
500
700
500
1,000
jb
2,300
1,100
1,000
1,100
1,500
300
3,800
400
11,800
8,400
5,200
160
13,100
6,800
18
10,600
3.6
36.000
2,000
38,000
8,300
4,200
12,500
25,600
"Operating 5,000 h/yr. No interest on capital is included.
°None required.
cFrom Table 9.
"The analysis beginning with this line is based on tax law as it existed at the time of the installation.
49
-------
Electrodialysis. Electrodialysis
concentrates ionic species contained
in a water solution. The process is
well established for purifying
brackish water and recently has been
demonstrated for recovering metal
salts from plating rinse. Compact
units suitable for this application
have been recovering metal values
successfully from rinse streams for a
number of years. In addition, a
recent EPA demonstration project
confirmed the applicability of
electrodialysis for plating solutions.
In electrodialysis, a water solution is
passed through alternately placed
cation-permeable and anion-
permeable membranes stacked
parallel to the direction of flow (see
Figure 33). An electric potential is
applied across the stack to induce
the ions to migrate across the
membranes. The selectivity of the
membranes results in the
concentration of ions in alternating
channels of the stack. Alternating
channels are hydraulically linked into
two primary hydraulic circuits — one
ion depleted, the other ion
concentrated. The water flow rate
through each of these circuits can be
set to achieve the high level of
concentration required for returning
the plating chemicals to the plating
bath. The degree of purification
achieved in the ion depleted circuit is
set by the electrical potential passed
across the membrane. Because ion
migration decreases as the diluting
circuit increases in purity, a cost
optimization is necessary to arrive at
the best design.
An EPA demonstration project tested
the applicability of an electrodialysis
unit to recover nickel from rinse
waters for reuse in a plating bath.
The system diagrammed in Figure 34
was tested for nine months with no
significant operating problems.
Electrodialysis units patterned after
the model described are being
marketed to reclaim metal values
from rinse streams. The units are
skid-mounted and require only
piping and electrical connections.
They cost in the range of $25,000 to
$30,000.
Table 18 itemizes the cost of the
demonstration unit and the
operating advantages attributable to
the unit. The payback period for the
unit, as shown in Table 18, is
estimated at 2.2 years.
Purified stream
(to rinse tanks)
Concentrated stream
(to plating bath)
Cathode
III
I
Contaminated
rinse water
Legend:
M* = cations
X" = anions
cation-selective membrane
anion-selective membrane
Figure 33. Electrodialysis Flow Schematic
Workpiece
Makeup water
r
U '-i
1
Plating
b"h
F^
1 __ ,-_J
Rinse tanks
Q—
Chemical
recycle
Filter
r
V-
L
Treated water
To waste
treatment
Electrodialysis
unit
Electrode
rinse
Figure 34. Electrodialysis System for Nickel Plating Drag-Out Recovery
50
-------
Table 18.
Economics of Electrodialysis System for Nickel Plating Solution Recovery3
Cost
INSTALLED COST ($):
Equipment:
Electrodialysis unit, complete with
cartridge filter strainer and
electrode rinse system
Piping
Miscellaneous
Subtotal
Installation, labor and material:
Site preparation
Plumbing
Electrical
Miscellaneous
Subtotal
Total installed cost
ANNUAL COSTS ($/yr):
Operating:
Labor, 100 h/yr at $10/h
Supervisor
Maintenance
General plant overhead
Raw materials:
Filter cartridges
Replacement membranes
Utilities, electricity ($0.08/kWhr)
Total annual operating cost
Fixed cost:
Depreciation, 10% of investment
Taxes and insurance, 1% of investment
Total annual fixed costs
Total annual cost of operation ($/yr)
ANNUAL SAVINGS ($/yr):c
Plating chemicals, 3.8 Ib/h NiS04
Water treatment chemicals
Sludge disposal cost
Water use (no saving)
Total annual savings
NET SAVINGS = annual savings-
(annual operating cost + annual fixed
cost)($/yr)
NET SAVINGS AFTER TAXES, 48% tax rate ($/yr)d
AVERAGE ROI = (net savings after taxes/
total investment) x 100(%)
CASH FLOW FROM INVESTMENT = net savings
after taxes + depreciation ($/yr)
PAYBACK PERIOD = total investment/
cash flow (yr)
30,000
1,000
1,000
300
500
700
500
1,000
b
2,000
1,000
1,000
500
400
3,400
300
22,600
3,800
6,600
23,400
12,200
36
15,600
2.2
32,000
2,000
34,000
5,900
3,700
9,600
33,000
"Operating 5,000 h/yr. No interest on capital is included.
"None required.
"From Table 9.
dThe analysis beginning with this line is based on tax law as it existed at the time of the installation.
51
-------
Electrolytic Processes. The
electrolytic cell is the basic device
used in electroplating operations.
With the advent of innovations in
pollution control and interest in
material conservation, the
electrolytic cell has found other uses
in the plating shop:
« Recovery of metals from a plating
solution onto a conventional metal
cathode (electrowinning)
• Treatment of cyanide plating rinse
with simultaneous plating of
metals onto a cathode and
oxidation of cyanide at the anode
• Oxidation of cyanide contained in
waste process solutions
(electrolysis).
All electrolytic recovery/treatment
systems are predicated upon
principles well known to the
electroplater. First and foremost are
those devices based on an expanded
cathode surface area. Many
electroplaters have constructed their
own units by placing parallel rows of
closely spaced (1 to 3 in) anodes and
cathodes in a plating tank. The close
spacing shortens the path required
for metal ions to migrate before
meeting a cathodic surface, thus
increasing the rate at which they can
be removed from the rinses by
electrodeposition. Recirculation of
the rinse increases deposition rates
and improves deposit quality. A
modest heat buildup in the
recirculating waters, caused by the
passage of current through the dilute
solution will aid rinsing as well as
deposition quality.
New applications of this concept use
sponge-like cathodes fabricated
from carbon fibers and rigid
polymeric foams. While this type of
expanded cathode device may be
quite efficient, it does not lend itself
to direct reuse of the deposited
metal. In contrast to the flat cathode
units from which the
electrodeposited metal can be
physically stripped from the starter
cathode, the metal deposited on
foam cathodes is often sold to a
refiner or scrap dealer "as-is" and
the foam replaced. Alternatively,
chemical and/or reverse current
stripping of foam, carbon fiber, and
cylindrical cathode can be used to
recover the electrodeposited metal
for reuse in the plating bath.
Electrolytic recovery unit.
52
-------
Another method of eiectrodeposition
enhancement involves rapid
recirculation of the rinse or rapid
movement of the cathode areas. In
cylindrical or stacked-disk devices,
rotation of the cathodes by means of
a motor drive accelerates the
exchange of metal ions at the
cathode surface. Violently agitated
glass beads are also being used for
this purpose. Just as in conventional
electroplating, this "work agitation"
allows the application of higher
current densities while preserving
deposit integrity. Similarly, high-
speed pumped recirculation or
vertical-blade agitators in baffled
electrowinning tanks can accelerate
the deposition rates from dilute
rinses by improving the metal ion
availability at the cathode surface.
In addition to metal recovery
applications, electrolytic processes
are also useful for the destruction of
cyanides in aqueous solutions. This
process is particularly well-suited to
the treatment of strong solutions
(such as spent plating baths)
because their conductivity
maximizes the efficient use of
electrical current both to
electrodeposit metal and to oxidize
cyanide at the anode. While
conventional electroplating tanks
can be used for this purpose,
modifying the cells to provide more
anode and cathode areas will
expedite treatment (reaction times in
the range of from 1 to 3 d are not
uncommon). The addition of sodium
chloride has been reported to
accelerate this process, and heating
the solution to near-boiling has also
been reported helpful.
Standard electrowinning units are
available in packages with from 1 ft2
to 100 ft2 of cathode surface area.
Larger custom units are also
available. The packaged units
usually consist of a reactor tank,
copper bussing, cathodes, anodes,
recirculation pump, current
controller, and rectifier. The installed
cost for standard flat plate units as a
function of cathode surface area is
shown in Figure 35.
60
50
40
fe
o
o
O
30
03
20
10
I
I
I
J
20
80
100
40 60
CATHODE SURFACE AREA (ft2)
Note:
Includes reactor tank, copper buss bars, cathodes, anodes, recirculation pump,
rectifier and current control.
Figure 35. Investment Cost for Electrolytic Recovery Units
The capacity requirement depends
on the amount of metal to be
recovered. For example, at 10 g/l
copper and 140°F temperature, the
deposition rate is 0.06 Ib/h/ft2 at an
allowable current density of 25
amp/ft2. Drag-out recovery from a
plating bath at 90 g/l copper would
equal 88% if the recovery rinse were
maintained at 10 g/l. If the drag-out
rate is 1 Ib/h of copper, the required
cathode surface area would be (0.88
lb/h)/(0.06 Ib/h/ft2), or equal to 15 ft2.
Table 19 presents an analysis of an
electrolytic copper recovery system
in terms of installation and operating
costs, economic benefits, and return
on investment for the foregoing
example. The payback period for this
unit is estimated at 3.1 years. The
significant amount of copper
available for recovery makes the
investment in the unit justified. The
high surface area electrode systems
also come in modular units with
from one to four electrode modules
per unit. Total installed costs for
these units range from $49,000 for
one module to $90,000 for a four-
module unit.
53
-------
Table 19.
Economics of Electrolytic Copper Recovery System*5
Cost
INSTALLED COST, 330 ft2 unit ($):
Equipment:
Electrolytic unit including heater and
recirculation pump
Piping
Miscellaneous
Subtotal
Installation, labor and material:
Site preparation
Plumbing
Electrical
Miscellaneous
Subtotal
Total installed cost
ANNUAL COSTS ($/yr):
Operating:
Labor, 100 h/y rat $10/h
Supervisor
Maintenance
General plant overhead
Utilities, electricity ($0.08/kWhr)
Total annual operating cost
Fixed cost:
Depreciation, 10% of investment
Taxes and insurance, 1% of investment
Total annual fixed costs
Total annual cost of operation ($/yr)
ANNUAL SAVINGS ($/yr):c
Plating chemicals (1.0 Ib/h Cu or
2,5 Ib/h CuSO.,)
Water treatment chemicals
Sludge disposal cost
Water use (no saving)
Total annual savings
NET SAVINGS - annual savings -
(annual operating cost + annual fixed
costl(S.'yr)
NET SAVINGS AFTER TAXES, 48% tax rate,
10,800 X 0.52 ($/yr)d
AVERAGE ROI = (net savings after taxes/
total investment) x 100 (%)
CASH FLOW FROM INVESTMENT = net savings
after taxes + depreciation ($/yr)
PAYBACK PERIOD.= total investment/
cash flow (yr)
21,000
1,000
1,000
300
500
700
500
1,000
b
1,500
900
1,000
2,500
300
11,000
2,500
4,500
10,800
5,600
22
8,100
3.1
23,000
2,000
25,000
4,400
2,800
7,200
18,000
•Operating 5,000 h/yr. No interest on capital is included.
*None required.
cFrom Table 9.
''The analysis beginning with this line is based on tax law as it existed at the time of the installation.
54
-------
Bibliography
Brown and Caldwell. Lime Use in
Wastewater Treatment. NTIS No. Pb
248-181. Oct. 1975.
Brown, C. J., D. Davey, and P. J.
Simmons. "Nickel Salt Recovery by
Reciprocating Flow Ion Exchanger."
Paper read at 62nd Annual Technical
Conference of the American
Electroplating Society. June 1975.
"Current Prices of Chemicals and
Related Materials." Chemical
Marketing Reporter. Passim, Oct. 30,
1972; Feb. 20,1978; and Feb. 6,1984.
Cushnie, George C., et al. "An
Investigation of Technologies for
Hazardous Sludge Reduction and
AFLC Industrial Waste Treatment
Plants." Contract No. 086-35-81 -C-
0258, Air Force Engineering and
Services Center. Aug. 1983.
Eisenman, J. L. "Recovery of Nickel
from Plating Bath Rinse Waters by
Electrodialysis." Hanover MA,
Micropore Research Co. Undated.
Elicker, L N., and R. W. Lacy.
"Evaporative Recovery of Chromium
Plating Rinse Waters." EPA Grant
N.S. 803781. U.S. Environmental
Protection Agency. (Prepared by
Advance Plating Company, and
Corning Glass Works).
Hartley, H. "Evaporative Recovery in
Electroplating." The Pfaudler
Company, Division of Sybron
Corporation, Rochester, NY.
Undated.
Mace, G. R., and D. Casaburi. "Lime
vs. Caustic for Neutralizing Power."
Chemical Engineering Progress, 86-
90. Aug. 1977.
McNulty, K. J., P. R. Hoover, and R. L.
Goldsmith. "Evaluation of Advanced
Reverse Osmosis Membranes for the
Treatment of Electroplating Wastes."
Paper read at EPA/American
Electroplating Society Conference.
Jan. 17,1978.
Militello, Philip A. "Assessment of
Emerging Technologies for Metal
Finishing Pollution Control: Three
Case Studies." Contract No. 68-03-
2907-09, EPA Non-Ferrous Metals
and Minerals Branch, IERL,
Cincinnati, OH.
"Package Wastewater Treatment
Plans." Plant Engineering, 66-73.
Mar. 16,1978.
Stinson, Mary K. "Emerging
Technologies for Treatment of
Electroplating Wastewaters."
Presented by EPA at 71st Annual
Meeting of the American Institute for
Chemical Engineering. Nov. 15,1978.
55
-------
U.S. Environmental Protection
Agency. Advanced Treatment
Approaches for Metal Finishing
Wastewaters. Part 1. EPA 600/J-77-
056a. NTIS No. Pb 277-147. Oct.
1977.
Advanced Treatment
Approaches for Metal Finishing
Wastewaters. Part 2. EPA600/J-77-
056b. NTIS No. Pb 277-148. Nov.
1977.
. Control Technology for the
. Chemical Treatment of
Plating Waste for Removal of Heavy
Metals. EPA R2-73-044. NTIS No. Pb
227-363. (Prepared by Beaton and
Corbin Manufacturing Company).
May 1973.
Control and Treatment
Technology for the Metal Finishing
Industry: Ion Exchange. EPA 625/8-
81-007. (Prepared by Centec
Corporation). June 1981.
Metal Finishing Industry:
Evaporators. EPA 625/8-79-002.
(Prepared by Centec Corporation).
June 1979.
Controlling Pollution from
the Manufacturing and Coating of
Metal Products: Water Pollution
Control. EPA 625/3-73-009. (Prepared
by Centec Corporation). May 1977.
. Development Document
for Existing Source Pretreatment
Standards in the Electroplating Point
Source Category. EPA 440/1-78/085.
Aug. 1979.
Ozone Treatment of
Cyanide-Bearing Plating Waste. EPA
600/2-77-104. NTIS No. Pb 271-015.
(Prepared by Sealectro Corporation).
PBl Reverse Osmosis
Membrane for Chromium Plating
Rinse Water. EPA 600/2-78-040. NTIS
No. Pb 280-944. (Prepared by
American Electroplaters' Society).
Mar. 1978.
Removal of Chromium
from Plating Rinse Water Using
Activated Carbon. EPA 600/2-75-055.
NTIS No. Pb 243-370. (Prepared by
Battelle Memorial Laboratories).
June 1975.
Removal of Heavy Metals
from Industrial Wastewater Using
Insoluble Starch Xanthate. EPA
600/2-78-085. NTIS No. Pb 283-792.
(Prepared by U.S. Department of
Agriculture, Agricultural Research
Service). May 1978.
"Standards Applicable to
Owners and Operators of Hazardous
Waste Treatment, Storage, and
Disposal Facilities."FederalRegister
45(98): 33154-33258. May 19, 1980.
• Treatment of Metal
Finishing Wastes by Sulfide
Precipitation. EPA 600/2-77-049.
NTIS No. Pb 267-284. (Prepared by
Metal Finishers' Foundation). Feb.
1977.
U.S. Environmental Protection
Agency and American Electroplaters'
Society, Inc. (cosponsors).-Annua/
Conference on Advanced Pollution
Control for the Metal Finishing
Industry (1st), held at Lake Buena
Vista, Florida on January 17-19,
1978. EPA 600/8-78-010. NTIS No. Pb
282-443. May 1978.
Proceedings of a
Conference on Advanced Pollution
Control for the Metal Finishing
Industry (2nd), held at Kissimmee,
Florida on February 5-7, 1979. EPA
600/8-79-014. NTIS No. Pb 297-453.
June 1979.
56
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Appendix A.
Drag-Out Recovery
Cost Reduction
Worksheet
This worksheet is intended to lead
the user through the analysis
required to determine the potential
cost reduction achievable by
recovering plating solution drag-out.
Figure A-1 illustrates the procedure;
Figure A-2 is a blank worksheet. The
annual operating cost (C.14)
represents only the cost of raw
material losses, bath heating,
pollution control, and waste disposal
for a plating line. A comparison of
the operating cost associated with
several different investment options
will indicate the relative economy of
the different options.
Other items to consider in a
complete cost comparison include
the labor and investment associated
with the modifications. Table 6 of
this report shows a precedure for
determining the total annual cost of
a waste treatment system. The same
procedure can be used to determine
total annual cost for drag-out
recovery options.
57
-------
Figure A-1.
Worksheet Completion Procedure
A, Plant conditions 10 be measured
1. Drag-out rate (gal/h)
2. Plating tank temperature (CF)
3. Plating tank air agitation rate (stdfWmin)
4, Plating tank surface area (ft2)
5. Number of rinse tanks
6. Dissolved solids concentration in plating tank (mg/l)
7. Dissolved solids concentration in final rinse (mg/l)
8. Plating solution composition
Mi 504 =
NiCl2 =
Boric acid =
B. Cost factors for each plant
1. Plating solution value (S/gal)
Bori
NiS04 (1.66 Ib/gal X $1.74/lb)a =
NiCl2 (0.34 Ib/gal X $1.76/lb)a =
c acid (1.40 Ib/gal X $0.30/lb)b =
Total =
2. Water use and sewer changes
3., Energy cost for plating tank heaters
4. Annual operating hours
1.5 gal/h
150°F
0
36 ft2
4
260,000 mg/l
50 mg/l
1.66 Ib/gal
0.34 Ib/yal
0.40 Ib/gal
$2.89
$0.60
$0.42/gal
$3.91/ gal
$1.80/1000 gal
$6.00/106 Btu
3,600
58
-------
Figure A-1.
Worksheet Completion Procedure—Concluded
C. Operating cost estimation for rinse and recycle system (Figure 21)
1. Surface evaporation rate (gal/h)c
(0.14gal/h-ft2)x36ft2
2. Recycle rinse ratio (surface evaporation rate/drag-out rate) or(C.1/A.1)
3. Number of countercurrent rinse tanks in recovery rinse
4. Percent recovery of drag-out (from Figure 22)
5. Concentration of drag-out from recovery rinse (mg/l) Cr = 0.06 C (from Figure 22)
6. Number of countercurrent rinse tanks in final rinse
^ | _ cr 15,600
C, 50
8. Rinse ratio in final rinse (from Figure 17)
9. Rinse water requirements in final rinse; gal/h (rinse ratio X drag-out rate) or (C.8 X A.1)
10. Drag-out chemical losses ($/h) (drag-out rate) X (plating solution value)
X (100 - percent recovery/100) or (A.1 X B.I) X (100 - (C.4/100)]
T 1 . Rinse water use cost ($/h) (water use rate X cost factor) or (C.9 X B.2)
1 2. Bath heating load due to surface evaporation, Btu/h; (5.04 gal/h) X (8,300 Btu/gal)d
13. Heating load cost ($/h) (C.12 X B.3)
14. Annual operating cost ($/yr) (C.10 + C.1 1 + C.1 3) X B.4
5.04
3.36
2
94
15,600
2
312
18
27
$0.34/h
$0.049/h
41,800 Btu/h
$0.25/h
$2,300/yr
'From Table 9,
""From Table 1.
GFrom Figure 19. For aerated baths use Figure 18.
dFrom page 33. For aerated baths use Figure 20.
59
-------
Figure A-2.
Cost Reduction Worksheet
A Plant conditions to be measured
1, Drag-out rate (gal/h)
2, Plating tank temperature (°F)
3, Plating tank air agitation rate (stdfi3/min)
4, Plating tank surface area (ft
5, Number of rinse tanks
6. Dissolved solids concentration tn plating tank (mg/l)
7. Dissolved solids concentration in final rinse (mg/l)
8. Plating solution composition
B, Cost factors for each plant
1. Plating solution value ($/gal)
2. Water use and sewer changes
3. Energy cost for plating tank heaters
4, Annual operating hours
60
-------
Figure A-2.
Cost Reduction Worksheet—Conclude'd
C. Operating cost estimation for rinse and recycle system (Figure 21)
1 Surfarp evaporation rate (gal/h)
2. Recycle rinse ratio (surface evaporation rate/drag-out rate) or (C.1/A.1)
3. Number of countercurrent rinse tanks in recovery rinse
4. Percent recovery of drag-out (from Figure 22)
5, Concentration of drag-out from recovery rinse (mg/l)
(from Figure 22)
6. Number of countercurrent rinse tanks in final rinse
cr
7. Dilution ratio in final rinse — or (C.5/A.7)
Cf
8. Rinse ratio in final rinse (from Figure 17)
9. Rinse water requirements in final rinse; [gal'/h (rinse ratio X drag-out rate) or (C.8 X A.1)]
10. Drag-out chemical losses ($/h) (drag-out rate) X (plating
X (100 - percent recovery/100) or (A.1 X B.I) X [100
1 1 , Rinse water use cost (S/h) (water use rate X cost factor)
12. Bath heating load due to surface evaporation (Btu/h)
solution value)
-(C.4/100)]
or (C.9 X B.2)
13. Heating load cost ($/h) (C.12 X B.3)
14. Annual operating cost ($/yr) (C.10 -1- C.11 + C.13) X B,4
61
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This report was prepared by CENTEC Corp., Reston, VA and JACA Corp.,
Fort Washington, PA. Regulatory content was reviewed by EPA's Office of
General Counsel and the Office of Water Enforcement and Permits. EPA would
like to thank the American Electroplaters' Society, Inc. for technical review.
Photos courtesy of Rainbow Research, Stuart, FL; Hydro-Fax Division of
Amchem Products, Ambler, PA; Baldwin Hardware Inc., Reading, PA;
SPS Technologies, Jenkintown, PA; Zerpol, Hatfield, PA.
This document has been reviewed in accordance with U.S. Environmental
Protection Agency policy and approved for publication. Mention of
trade names or commercial products does not constitute endorsement or
recommendation for use.
62
U.S. GOVERNMENT PRINTING OFFICE: 1986 — 661-960
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