EPA-625/5-79-016
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Technology Transfer
f/EPA
Environmental Pollution
Control Alternatives:
Economics of'*' ^
Wastewater Treatmltit
Alternatives fqythe f
Electroplating tliidus:
*&
U.o. environmental Protection Agency
Region 5, Library (PL-12J)
n West Jackson Boulevark 12th Floor
Chicago, !L 60604-3590
-------
Technology Transfer EPA 625/5-79-016
Environmental Pollution
Control Alternatives:
Economics of
Wastewater Treatment
Alternatives for the
Electroplating Industry
June 1979
U.S. Environmental Protection Agency
Region 5, Library (PL-12JJ
77 West Jackson Boulevard. 12th
Chicago, IL 60604-3590
Technical content of this report was provided by the
Industrial Environmental Research Laboratory
Cincinnati OH 45268
-------
Concentrated dump tank and modular cyanide oxidation and
neutralization/flocculation units
-------
Contents 1 • Overview 1
2. Costs of Conventional Wastewater Treatment Systems 3
Introduction 3
Capital Cost 4
Operating Costs 11
Determining the Total Annual Cost of Wastewater Treatment 15
3. Alternatives to Conventional Wastewater Treatment 19
Introduction 19
Electrochemical Chromium Reduction 19
Selection of Neutralization/Precipitation Chemicals 22
Sulfide Precipitation 25
Integrated Wastewater Treatment 28
4. Reducing the Costs of Wastewater Treatment 31
General 31
Housekeeping Practices 31
Minimizing Water Use 32
Reducing Drag-Out Loss 35
Using Spent Baths as Treatment Reagents 41
Example of Cost/Benefits Analysis 42
5. Recovery Processes 47
Introduction 47
Evaporation 48
Reverse Osmosis 51
Ion Exchange 55
Electrodialysis 57
6. EPA's Research and Development Programs 63
General 63
Donnan Dialysis 63
Electrolytic Techniques 63
Insoluble Starch Xanthate 64
Immiscible Organic Solvents 65
Centralized Waste Treatment 65
Bibliography 66
Appendix A. Drag-Out Recovery Cost Reduction Worksheet 67
III
-------
Pretreatment, neutralization, and flocculation tanks with clarifier/thickener
-------
1. Overview
The Water Pollution Control Act
Amendments (Public Law92-500), en-
acted in 1 972, required a base level of
removal for pollutants being discharged
by industry to waterways or public
treatment systems. The Clean Water
Act of 1977 (Public Law 95-217)
granted the Environmental Protection
Agency (EPA) additional regulatory
powers to set effluent standards and to
prohibit the presence of specified toxic
chemicals in wastewater discharged
to waterways or to publicly owned
treatment works (POTW). Industrial
pollutants that are discharged to
POTW's and thereby reduce plant ef-
ficiency or contaminate plant sludge
will be regulated. The EPA is iden-
tifying the toxic materials to be covered
by the regulations. The Resource Con-
servation and Recovery Act of 1976
(Public Law 94-580) will regulate the
disposal of industrial sludges contain-
ing toxic materials.
Costs of meeting the pollution control
requirements of these Federal laws,
combined with the rising costs of
energy, raw materials, and chemicals,
can greatly affect operating costs in
the electroplating industry. The raw
materials typically found in electro-
plating waste water as well as the costs
of those materials and of wastewater
treatment chemicals, utilities, and
sewer fees are shown in Table 1.
Common electroplating chemicals,
such as cyanide, chromium, nickel,
cadmium, and zinc, already are classi-
fied as toxic substances. Moreover,
the costs of these chemicals and of
utilities have risen from 50 to 150 per-
cent since 1 972. The changes in prices
and regulations dictate that the eco-
nomics and technologies for water
pollution control be reevaluated and
that methods for improving raw ma-
terial yields be analyzed. In some
cases, m-plant changes, proper selec-
tion of pollution control or recovery
technologies, and reduction in waste-
water flow rates can improve operating
costs while reducing or eliminating
discharge of toxic pollutants.
This report addresses the economics
forthe foregoing techniques as a guide
for minimizing the costs of meeting
water pollution control requirements
Initially, operating and investment
costs are presented for conventional
wastewater treatment systems em-
ployed by the electroplating industry
These systems are then compared
with alternative treatment technologies
that may offer cost savings. Finally,
modifications capable of reducing raw
material use and pollution control
costs are described.
-------
Table 1.
Raw Material, Pollutant Control Chemicals, and Utilities Used by the
Electroplating Industry
Mem
Nickel sulfate
'
..£,-., ,~v5,^,4>i.r,^ -&'t<\
-
'
^ *i t..>*«,&&, UEjgStf *.{!%?
. € i 3^4.^5 "s J , ,* 1-
*" •>. « ,A?Hsf*/» . ^A< « .-^i-s.^-
^
-------
2. Costs of Conventional
Wastewater Treatment
Systems
Introduction
Treatment of metal finishing wastes by
neutralization followed by gravity set-
tling for separation of suspended
solids—with additional treatment steps
for hexavalent chromium and cyanide—
has become so widely used in the
metal finishing industry that it is
usually referred to as "conventional"
treatment. Figure lisa schematic of a
conventional treatment facility for
electroplating wastes containing
chromium and cyanides in addition to
other heavy metals, acids, and alkalis.
The purpose of this section is to pro-
vide guidance to the plater in estimat-
ing the cost of installing and operating
these systems in an electroplating
facility. Predicting the performance of
any treatment system requires labora-
tory testing to simulate its operation
on the intended feed material. Based
on the test results, the ability of the
system to bring a discharge into com-
pliance with the environmental control
regulation can be ascertained.
Excellent advice on conducting the m-
plant evaluation leading to the final
sizing of waste treatment equipment is
available in several publications listed
in the bibliography. Detailed guidance
in minimizing the cost of wastewater
treatment techniques is given in
Section 4. One major precaution stands
out so strongly as a factor in improper
selection of equipment, however, that
it deserves a brief discussion before
the cost of treatment equipment is
estimated.
Pollutant loading on a waste treatment
system is often subject to wide varia-
tion. Table 2 lists the variations in
wastewater characteristics found by
EPA in its survey of the electroplating
industry. The table shows variations
between plants as well as within each
plant. It is essential that the variations
be understood and that the waste
treatment system be sized to handle
variations that cannot be eliminated.
In this section, the capital and operat-
ing costs of the treatment system are
discussed under five categories:
• Chromium reduction
• Cyanide oxidation
• Neutralization/precipitation
• Clarification
• Sludge handling
These units can be combined into a
configuration that matches the need
and capital of the individual electro-
plater. Flow rate is a major factor in
determining equipment cost, and pol-
lutant loading and flow rate are both
significant in determining the operating
cost of the system. This section con-
cludes with an example to illustrate
how total costs can be estimated for a
specific facility.
-------
Figure 1.
Electroplating Industry Conventional Wastewater Treatment
Table 2.
Composition of Raw Waste Streams from Common Metals Plating
Capital Cost
General. The unit processes shown in
Figure 1 are used extensively in the
electroplating industry, and as a result
their design has become somewhat
standard. Standardization and the
high cost of site preparation and con-
struction have led to the development
of skid-mounted package systems,
complete with all hardware and auxil-
iaries. The installation costs for
package systems usually will range
between 1 0 and 30 percent of the pur-
chase price of the equipment as com-
pared with 70 and 150 percent for
component systems.
The costs presented in the following
sections assume all components of
the individual systems must be pur-
chased. Reduced costs can be realized
by using existing pumps, tanks, and
instrumentation. Higher installation
-------
costs, however, can result from site-
specific costs for wastewater collec-
tion systems, new building space,
structural modifications, or relocation
of existing equipment.
Chromium Reduction Units. Chromium
complexes are usually present in elec-
troplating wastewater as tnvalent
chromium (Cr+3) or as hexavalent
chromium (Cr+6). Although most heavy
metals are precipitated readily as in-
soluble hydroxides by pH adjustment
in the neutralizes hexavalent chromium
first must be reduced to trivalent
chromium. Reduction usually is done
by reaction with gaseous sulfur
dioxide (S02) or a solution of sodium
bisulfite (NaHSO3). The net reaction
using sulfur dioxide is:
3S0
2H2CrO4
3H20
Cr2(S04)3
Because the reaction proceeds rapidly
at low pH, an acid is added to control
the chromic acid wastewater pH be-
tween 2 and 3. Gaseous sulfur dioxide
is metered continuously into the
reaction tank to satisfy the reduction
demand based on the concentration of
hexavalent chromium.
The installation and package unit costs
for continuous and batch chromium
reduction systems are shown in Figure
2. The continuous system costs are for
units using sulfur dioxide as the reduc-
ing agent, as shown in Figure 1. The
cost includes storage and feed sys-
tems for the treatment reagents. The
batch system cost is for a system with
two reaction tanks, each sized to hold
4 hours of wastewater flow and
equipped with high level alarms, port-
able pH and oxidation reduction po-
tential (ORP) probes, a portable mixer,
and storage tanks and feed pumps to
add sodium metabisulfite and sulfunc
acid to the reaction tanks.
For very small flows, simpler and less
costly batch systems are feasible.
Figure 2 includes the costs for hard-
ware, piping, instrumentation, and
utility connections. The graph shows
that the initial cost of batch chromium
reduction systems is more attractive
for wastewater flow rates below 20
gal/min (76 l/min). The smallest con-
tinuous units are rated to process up to
30 gal/min (11 3 l/min) wastewater.
Cyanide Oxidation Units. Dilute cya-
nide rinse streams resulting from plat-
ing operations and cyanide dips also
must be treated separately to oxidize
the highly toxic cyanide, first to less
toxic cyanate, then to harmless bicar-
bonates and nitrogen. The oxidation
reagent is usually chlorine, which
can be introduced into the system by
adding chlorine gas (CI2) or sodium
hypochlorite (NaOCI). Using chlorine,
the typical reaction in the first stage is:
NaCN + 2NaOH + CI2 — »
NaCNO + 2NaCI+H20
and in the second stage,
2NaCNO + 5NaOH + 3CI
6NaCI + C02
+ NaHC0
N2
2H2O
When sodium hypochlorite is used,
the typical reaction in the first stage is:
NaCN + NaOCI — »• NaCNO + NaCI
and in the second stage,
2NaCNO + SNaOCI + H20 -»
SIMaCI + N2 + 2NaHC03
Continuous systems (Figure 1) use two
series-connected reaction tanks. In
the first stage, the pH is adjusted
30
o
o
o
20
C/3
O
(J
10
Minimum size
unit
w^^^^ Continuous systems , • • • *
• *
Batch systems8
• *
20 40
FLOW RATE (gal/mm)
60
80
Legend:
^^™ total installed investment
• • • hardware cost
'Installed cost is twice hardware cost; sys-
tem consists of two 4-hour reaction tanks and
necessary auxiliaries.
bSystem pictured in Figure 1, hardware cost for
package system equals 80% of installed cost.
Note.—Cost basis, July 1 978.
SOURCE: Equipment vendor.
Figure 2.
Investment Cost for Chromium Reduction Units
-------
Small modular treatment system for 10-gal/min design flowrate
between 9 and 1 1 using an alkali such
as caustic or lime. The pH in the
second reaction chamber is controlled
at approximately 8.5. Chlorine is added
continuously to both stages. Because
the demand for chlorine in the second
stage is proportional to demand in the
first stage, the chlorine is fed to both
stages from the same feeder at a set
ratio based on demand in the first
stage. Demand in the first stage is
determined by measuring ORP. The
reaction time needed is approximately
25 to 30 minutes in each stage.
Figure 3 presents the installed cost
curves for continuous and manual batch
systems. The continuous system cost
is forthe unit shown in Figure 1, which
uses chlorine gas as the oxidizing
agent. The cost includes storage and
feed systems for the treatment rea-
gents. The batch system cost is for a
system with two 4-hour reaction tanks
and the required auxiliaries associated
with oxidizing the cyanide with sodium
hypochlonte and caustic.
Again, for very small flows, simpler and
less costly batch systems are feasible.
At wastewater flow rates below 20
gal/min (76 I/mm) batch systems
should be considered. At higher flow
rates, the labor cost savings make the
total cost to operate a continuous
system (depreciation plus operating
cost) less than the total cost to operate
a batch system.
Neutralization/Precipitation Techniques.
The mixed acid/alkali waste streams
from the various metal cleaning and
plating operations are combined in the
neutralizer with the effluent from the
chromium reduction and cyanide
oxidation steps. Because the heavy
metals are soluble at low pH (acidic)
conditions in the wastewater, the pH
is adjusted to a range of 7.5 to 9.5.
In this pH range, the minimum solu-
bility of a mixture of metals is reached
and the metals precipitate as hydrox-
ides.
-------
r?v v^w&:/ vr-* f^ ?
Figure 3.
Investment Cost for Cyanide Oxidation Units
Many types of neutralization systems
can be designed with various degrees
of automation and controls, depending
on the volumetric flow rates and the
variability of the flow rates or pH
entering the neutralizer. Because a
change of 1 pH unit represents a
tenfold change in hydrogen ion con-
centration (Table 3), it will be difficult
to maintain the pH in the narrow range
where maximum removal of pollut-
ants is realized if the neutralizer feed
is subject to wide variations.
Table 3.
Ion Concentration vs. pH for Water Solutions
pH
1
2
3 .....
4 ...
5 . ...
6
8
9
10
11
12 . .
13
Free hydrogen ion
(acid) concentration
(gram-ions/hter)
0 1
0 01
0001
0 0001
0 00001
0 000001
0 0000001
000000001
0.000000001
0.0000000001
0.00000000001
0.000000000001
0.0000000000001
Free hydroxyl ion
(base) concentration
(gram-ions/liter)
0 0000000000001
0 000000000001
0 00000000001
0 0000000001
0 000000001
0 00000001
00000001
0 000001
0.00001
0.0001
0.001
0.01
0.1
-------
Single-stage, continuous neutralizers—
where all the alkali such as lime,
Ca(OH)2, or caustic soda, NaOH, is
fed into a single reaction vessel—are
usually suitable for electroplating
applications. If, however, the waste-
water is subject to rapid changes in
flow rates or pH, a multistage neu-
tralizer 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 waste-
water are made in the remaining reac-
tion vessels to promote precipitation
and to enhance the settling charac-
teristics of the metal hydroxides. To
maintain adequate pH control, the re-
tention time for typical neutralization
systems is 10 to 30 minutes. A sys-
tem using lime usually requires more
retention time, as the time required
for completely dissolving the lime
retards the response of the system to
the reagent addition.
Figure 4 shows the installed cost
for a continuous neutralization sys-
tem (see Figure 1) typically used in the
electroplating industry. This system
is single stage with pH-controlled
addition of the treatment chemicals;
caustic soda is used as the alkali and
sulfunc acid is used as the acid.
Clarification. Metal hydroxides and
other insoluble pollutants are removed
from the wastewater by gravity set-
tling. The solids removal efficiency
depends on the settling rate of
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 economical design of the
clanfier 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, flocculating
agents—such as polymers, alum, or
ferrous sulfate—are added in a
mixing chamber before the f locculator.
In the flocculator, the wastewater is
agitated gently to allow the solids to
30
CO
Ul
10
tptal installed investment
Minimum size
unit
• ••*
*»**
•*«'
1 ••
20
40
60
80
WO
stalled cflst
Figure 4
Installed Cost for Continuous Single-Stage Neutralization/Precipitation System
coagulate. The wastewater then enters
the clanfier, where the solids settle
out. The solids in the underflow can
be discharged to a holding tank for
thickening, or they can be discharged
directly to sludge disposal. The opti-
mum dosages of flocculating agents,
the size and costs for flocculation
and clarification hardware, and
the associated solids removal efficien-
cies can be estimated only by laboratory
testing.
Figure 5 shows hardware and total
installed costs for flocculation and
clarification systems typically em-
ployed m the electroplating industry.
These costs are presented as a
function of volumetric flow rate, but
they will depend also on the solids
settling rates and the level of solids
allowed in the effluent.
Sludge Handling. The solids from
clanfiers are typically discharged to
sludge holding tanks at solids concen-
trations of 0.5 to 3 percent; overflow
from the tank is recycled to the
clarifier. Usually metal hydroxide
solids will concentrate to approxi-
mately 3- to 5-percent solids in these
tanks if given adequate retention
time. The tanks also provide adequate
storage time and volume for the sludge
before shipment to a disposal site.
Figure 6 shows the investment for
tanks used for sludge storage 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 dry-
ness the device will achieve, can only
be determined by bench-scale testing
with the intended feed material.
-------
Figure 5.
Installed Cost for Flocculation/Clarification System
Figure 6.
Installed Cost for Sludge Storage/Thickening Tank
-------
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 an as-
sumed feed and cake solids concen-
tration and a press cycle time of
4 hours.
The costs shown in Figure 7 do not
include costs of installation or of the
auxiliary equipment associated with
the press, because these costs are
both variable and site specific. Items
that will contribute to the total cost
of the installation include:
• High pressure feed pump(s)
• Sludge feed storage
• Filtrate return to clanfier
• Cake solids handling and discharge
Recessed plate filter for sludge dewatering
600
% 45°
a>
UJ
2>
D
O
> 300
uj
<
ir
UJ
H
[I 150
A
J
, /
- s -
s
/
r
ff
-/'
jif
/f"
,C'?"
A ,,)«**"
^^
/'*'*""
I I I I
1,720 Legend'
A = manual plate shift, manual closure
B = automatic plate shifter, hydraulic ram
1,290
.0
^C
cu
s
UJ
860 §
li Cake volume based on 1Vi" thick sludge cakes.
§ bFeed volume capacity based on: feed solids =
Q 2%; cake solids = 20%; cycle time of 4 hours
uj and filter press on-stream factor = 70%.
430 °Pnce includes carbon steel frame, polypro-
pylene plates and filter cloths, no installation
costs.
Note. — Cost basis, July 1978.
f\ SOURCE: Eouioment vfmdnr.
0 10 20 30 40 50
UNIT PRICE ($1,000)°
Figure 7.
Unit Prices for Recessed Plate Filter Presses
10
-------
Operating Costs
Basis. Although the investment costs
for conventional wastewater treat-
ment systems depend principally on
wastewater flow rate, the operating
costs will depend on the following
factors:
• Utility costs (primarily electricity
to operate pumps and agitators)
• Overhead and depreciation
• Sludge disposal costs and
municipal sewer charges (sludge
disposal cost dependent on con-
tract hauling distances and
disposal requirements, municipal
sewer fees based on volumetric
discharge)
• Chemicals (costs based on
pollutant loading and types of
treatment chemicals)
• Operating and maintenance labor
The chemical and sludge disposal
costs offer the best opportunity for
cost savings because labor and
utility requirements are usually fixed,
based on the design and operational
procedures. Table 4 shows the basis
for estimating economics used in
this report.
Sludge Disposal and Municipal
Charges. Installation of wastewater
treatment systems will result in the
discharge of two streams: overflow
from the clanfier and sludge from the
clanfier or thickener/holding tank
The costs associated with these
discharges will be site specific for
each plant, and will depend on the
availability of local disposal sites to re-
ceive the sludge and on municipal
sewer costs. All these costs probably
will escalate as the regulations are
implemented.
Typical charges for sewer fees for a
major city were presented in Table 1.
Figure 8 shows the effects of waste-
water flow rates on sewer fees, based
on a sewer fee of $0.60/1,000 gal.
Table 4.
Basis for Economic Evaluations
Annual operating costs:
„
If*^ •***•!** "*%*** * * ^ {< ,
winrtc /*/vM "" .. > **^. t j>^^
AjMAs *•%! '•i*'
„ „ Tt* !
"6- jp r"^ m i » I
„ ,^,,,,^1 ,rt
Figure 8.
Annual Sewer Fee as a Function of Clarifier Overflow Rate
11
-------
Figure 9.
Annual Cost for Disposal of Industrial Sludge
Assuming the sludge will be hauled
to a licensed chemical landfill, the
costs will depend on the volume
of sludge, the distance hauled, and
the sludge composition. In most areas,
the costs of sludge disposal are cur-
rently in the range of $0.05/gal to
$0.20/gal, but there are cases
where disposal costs run as high as
$0.50/gal. Figure 9 shows the annual
costs for disposal of each 100 pounds
(45 kg) of solids over a range of
sludge concentrations and disposal
costs. If 100 pounds (45 kg) of solids
are present in the sludge at a con-
centration of 6 percent, the annual
cost for disposal is $6,000 at a
disposal cost of $0.10/gal (point A on
Figure 9).
The disposal cost savings achievable
by thickening also can be estimated
by using Figure 9 to calculate the
difference between the disposal costs
at the present concentration and the
projected final concentration after
thickening. For example, a plant now
disposes of 200 Ib/d (90.7 kg/d) of
dry solids as a sludge with a concen-
tration of 1 percent solids. At $0.10/
gal of sludge, the disposal cost would
be $72,000 per year ($36,000 X
200/100 pounds dry solids). A test on
the performance of a thickening tank
predicted a further thickening to
2 percent solids. Atthis concentration,
the sludge disposal costs would
decrease to $36,000 ($18,000 X
200/100 pounds dry solids). The dis-
posal cost savings for thickening the
sludge from 1 percent to 2 percent
would be $36,000 ($72,000 -
$36,000).
Further dewatering of metal hydroxide
sludges by mechanical dewatering
equipment can reach solids concen-
trations in the range of 1 5 to 50
percent. Figure 10 shows the total
installed investment that could be
justified for additional dewatering
equipment to concentrate a sludge
containing 2 percent solids to higher
solids concentrations. The cost reduc-
tion 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 de-
watering devices could be significant.
These additional costs would result
in a lower ROI.
12
-------
Figure 10.
Investment Justified for Sludge Thickening Equipment
Because the volume of sludge does
not change radically at concentrations
above 10 percent, there is a de-
crease in economic incentive to invest
m additional dewatermg equip-
ment to provide concentrations above
this level, as is indicated by the de-
creasing slope of the curve in Figure
10. For this particular case, the plant
would not generate significant addi-
tional savings by selecting a system
that concentrated the solids beyond 8
to 1 2 percent.
To illustrate the disposal cost savings
that can be realized by mechanical
dewatering of a dilute sludge, assume
that the same plant was able to con-
centrate the thickener tank bottoms
from 2 to 20 percent solids with
a filter press. The annual disposal cost
would be reduced from $36,000 to
$3,200 (Figure 9, $1,600 X 200/100).
The capital investment justified to
achieve this saving, using the basis
developed in Figure 10, is $54,000
($27,000 X 200/100). Figure 7
defines 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:
200 Ib solids 0.02 Ib solids
d Ib
gal sludge _ 1,200 gal sludge
8.34 Ib/gal ~ d
d _ 150 gal sludge
8h h
From Figure 7, the minimum size com-
mercial unit could dewater this feed
rate and would cost $11,500. Assuming
the total installed cost of the system
is twice the press cost, or $23,000,
the ROI would be well m excess of
the 40 percent used as a basis for
Figure 10.
Chemical Costs. The concentration of
pollutants, the volumetric flow rate
of the waste stream, and the types of
chemicals chosen for wastewater
treatment will affect the chemical
costs. The demand for treatment
chemicals will be proportional to the
volumetric flow of the wastewater
if the composition of the wastewater
is constant. 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. All these factors affect
the operating costs and must be
considered by the plant.
13
-------
Common treatment reagents used in
the electroplating industry are S02
for chromium reduction, chlorine
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 the
conventional wastewater treatment
systems shown in Figure 11. This
figure enables the userto calculate the
consumption of treatment chemicals
(consumption factor) and the
associated cost (cost factor), based
on the mass flow of each pollutant
and the volumetric flow rate of the
wastewater being treated. 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 defines the cost for disposal of
each pound of metal precipitated,
assuming the resulting sludge is dis-
posed of at 4 percent solids concen-
tration at a cost of $0.10/gal.
Cyanide waste
(gal/mm, Ib CN
Ib metal")
Heavy metal waste
(gal/mm, Ib metal3)
Chromium waste
(gal/mm, Ib Cr+6
,0 Ib NaOH/1,000 gal |$0.06/f ,000 pM
8 Ib NsQH/lb CW
0,2 Ib SO,/} ,000 gal
0.2 H> H,SO,/1,Q00 gal I $0.025/1.000 ga(
t.5«aN8GH/1tOQOgs!
Precipitation (NaOH)
2.3 Ib NaOH/lb Cr I $0.18/fb Cr
2.0 Ib NaOH/lb metal I $G.16/tb metal
Flocculation (polyelectrolyte)
0.1 Ib/1,000gal I $Q,10/t,OOOgal
Wastewater
discharge
Sludge storage
thickening
7.frlbNaOCl/teCN I 5300/lbCN
Solid waste
disposal
3 tt> NaHSOJIb Cr*8
$0.447lb Cr
$0.045/1,000 gal
2 Ib H-SIX/lb Cr+e
0.3 tt» Na HSO3/1,000 gal
0,2tbH2SO4/1,OQOgat
Consumption
ftctor
Figure 11.
Consumption and Cost Factors for Wastewater Treatment Chemicals
14
-------
Precipitation (NaOH)
ft»
-------
Figure 13.
Electroplating Wastewater Treatment Flow Chart: Example System
16
-------
Table 5.
Chemical and Sludge Disposal Cost: Example System8
Treatment step
Treatment chemicals
Sludge disposal
Waste streams
Rates
(Ib/h)
Cost
rates
($/h)
Dry solids
generated
(Ib/h)
Disposal
cost
($/h)
Total
annual costs
($1
Chromium reduction 30 gal/min = 1,800 gal/h 1.86 S02 0.18
0.75 Ib/h Cr+6 0.36 H2S04
0.15 Ib/h Cr+3
Cyanide oxidation 20 gal/mm = 1,200 gal/h 5.6 CI2 0.93
0.80 Ib/h CN~ 6.4 NaOH
0.60 Ib/h 2n+2
Neutralization:
Chrome effluent 1,800 gal/h 2.7 NaOH 0.22
Cyanide effluent 1,200 gal/h (b) (b)
Acid/alkali waste 60 gal/mm = 3,600 gal/h 3.6 NaOH 0.29
Precipitation 0.90 Ib/h Cr+3 2.1 NaOH 0.17 1.80
0.60 Ib/h Zn+2 1.2 NaOH 0.10 0.91
3.01 Ib/h Fe+2 6.0 NaOH 0.48 4.83
2.41 Ib/h Ni+2 4.8 NaOH 0.38 3.80
1.51 Ib/h Cu+2 3.0 NaOH 0.24 2.30
Subtotal, precipitation 17.1 NaOH 1.37 13.64
Flocculation 110 gal/mm = 6,600 gal/h 0.66 polyelectrolyte 0.66
Total 1.8 S02
0 36 H2S04
5.6 CI2 365 13.64°
29.8 NaOH
0.66 polyelectrolyte
Chemicals
Sludge disposal
053
0.28
1.44
1 10
0.68
4.03
4.03
17,500
19,300
"System shown in Figure 13.
bpH adjustment not required.
°Sludge volume at 4% solids = 40 gal/h.
17
-------
Table 6.
Investment Cost: Example System3
Component ,„
Chromiumreduotionunit(continuoussystemr8tedat30g8l/min,fronTFi8ure,2|,.,.. „ 23,000
Cyanideoxidation«nit(eontinuoussystemratadat2Qfat/min,frorttFigure3)..... 40,000
Neutralizer (single-sttge continuous system ratatl at I^Ogat/minjffornpigore 4^.,;«. ? ,28*000
Flocculation/clarification unit (continuous system rated at 110 gaf/mirt, fro,m
FigureS) ..:.., .......,,..;.., '26,000
Polymer feed tank, mixer, and feed pump,..»....., , ,,., 3,000
Sludge storage tank (5,000-gal tank to provide studge storage «<»lu«ne, f rorn Figut* ,
6) ,......,,, ;;• •- i3,o6o
Total equipment and installation cost , „; ". 133,000
Contingency (10% of total equipment and installation cost)..,,,.,,..,,.',.,,;. .T3,
-------
3. Alternatives to
Conventional Wastewater
Treatment
Introduction
In many cases, proper consideration
of the options available for design or
operation of the conventional
wastewater treatment system can
lead to chemical, sludge-handling,
and investment cost savings. There
are some alternatives to consider
before selecting a wastewater treat-
ment system. These alternatives
can also provide a cost reduction in an
existing system. They are:
• Electrochemical chromium reduc-
tion
• Selection of neutralization/
precipitation chemicals
• Sulfide precipitation
• Integrated treatment for waste
streams requiring individual treat-
ment
Electrochemical Chromium
Reduction
Electrochemical reduction units
(Figure 14) are being marketed to
compete with chromium reduction
systems that use chemical reducing
compounds. The process uses con-
sumable iron electrodes and an electri-
cal current to generate ferrous ions
that react with hexavalent chromium
to produce trivalent chromium as
follows:
3Fe+2 + Cr04~2 + 4H20 -*
3Fe+3 + Cr+3 + 80 H~
The reaction occurs rapidly and requires
minimum retention time. Hexavalent
chromium in the effluent can be
reduced to less than 0.05 ppm. Be-
cause hydroxide ions are generated,
the pH of the stream usually increases
from 0.5 to 1 pH unit. If the pH of
the chromium wastewater is maintained
between 6 and 9, the ferric and
trivalent chromium ions will precipi-
tate as hydroxides, and the effluent
can be fed directly to the clanfier,
bypassing the neutralizes At lower pH
values, the chromium wastewater is
fed to the neutralizer. Because
ferrous ions are introduced into the
wastewater, some additional solids
will be generated.
Maintenance requirements include
replacing electrodes biweekly and
washing the electrode surfaces for 10
to 1 5 minutes daily with a dilute acid
solution to remove any surface fouling
that would reduce the electro-
chemical efficiency of the unit.
19
-------
Wastewater
discharge
y~X Sludge
N
-------
Figure 16 compares the chemical
and operating costs for electrochem-
ical reduction systems and for
chromium reduction using sulfur
dioxide for each 1,000 gallons
(3,780 liters) of wastewater being
treated. These costs do not include the
charge to dispose of the solids
generated. The electrochemical re-
duction process has a treatment cost
advantage until the concentration
of hexavalent chromium exceeds 25
ppm. The costs of the electrochemical
reduction system to treat each 10 ppm
of Cr"1"6 contained in 1,000 gallons
(3,780 liters) of wastewater are based
on $0.07 for replacement electrodes
and $0.02 for electricity (using an
electricity cost of $0.045/kWh).
The major disadvantage of the electro-
chemical reduction system is that it
results in an increased quantity of
sludge; the additional sludge results
from the precipitated iron hydroxide
(Figure 17). Based on the sludge
disposal cost model presented in
Figure 1 2, the chemical reduction sys-
tem has a combined treatment and
sludge disposal cost advantage over
the electrochemical system when
the influent Cr+6 concentrations
exceed 5 ppm.
0.40
a:
L1J
a.
0.20
O
u
LLJ
0.10
Reduction with S02C
Electrochemical reductionb
20 40 60
Cr+6 CONCENTRATION (ppm)
80
Excludes pumping and sludge disposal costs.
bBased on $0.07 for replacement electrodes and $0.02 for electricity for each 10 ppm treated.
°From Figure 11.
Figure 16.
Treatment Cost Comparison of Electrochemical and Chemical Chromium
Reduction Units
For example, the cost to treat 1,000
gallons (3,780 liters) of wastewater
containing 10 ppm of Cr+6 is $0.09
using an electrochemical reduction
system (Figure 1 6). The treatment
cost for a chemical reduction
system would be in the range of
$0.18/1,000 gal. Based on data pre-
sented in Figure 1 7, the chemical
treatment will generate only 0.5 gallon
(1.9 liter) of sludge at 4 percent
solids per 1,000 gallons (3,780 liters)
of wastewater treated, and the sludge
disposal cost is $0.05. The elec-
trochemical unit would generate 2
gallons (7.6 liters) of sludge at the
same concentration for a disposal
cost of $0.20/1,000 gal of waste-
water being treated. The cost for dis-
posal of the additional sludge would
amount to $0.15/1,000 gal of water
containing 10 ppm Cr+6 treated. The
total cost (treatment plus waste dis-
posal) would amount to $0.23/1,000
gal for chemical reduction, com-
pared with $0.28/1,000 gal for the
electrochemical system.
21
-------
Figure 17.
Sludge Generation Factors: Electrochemical vs. Chemical Chrome Reduction
Selection of Neutralization/
Precipitation Chemicals
The selection of neutralization
chemicals usually is based on con-
venience and cost factors. It must
be remembered that the choice of
neutralization reagent will affect the
volume of sludge generated, the costs
of sludge disposal, and the invest-
ment cost for storage and handling for
each chemical. Because neutralization
chemicals can affect the perform-
ance of existing neutralizes and gravity
settling equipment, laboratory tests
must be run in cooperation with
vendors before changing chemicals.
If a new system is being installed, the
cost and performance analysis should
be made during the design phase
of the project.
Sodium hydroxide (caustic soda), lime,
and soda ash are used as neutraliza-
tion/precipitation agents (Table 8).
Although lime and soda ash are much
cheaper than caustic, their use requires
more expensive feed systems.
Lime is only slightly soluble in water.
Soda ash is more soluble, but dis-
solves very slowly. Both usually are
purchased in dry form and handled as
slurries; this practice increases the
capital costs for the associated neu-
tralization feed systems. Because
caustic is purchased as a liquid, the
feed system is simpler and lower in
cost. The plant, therefore, must
evaluate the cost benefits of paying
higher costs for neutralization
chemicals or of adding capital for
storage and handling facilities for
lime or soda ash. Because soda ash is
more expensive than lime, the plant
usually will select between lime and
caustic. These reagents therefore will
be compared and discussed.
22
-------
Table 8.
Cost Comparison of Common Alkaline Reagents
Lime has a solubility in water of
approximately 1 percent. It must be
fed as a slurry, and, because of its
low solubility, a 10 to 25 percent ex-
cess is required for complete neutral-
ization. The hydrated lime feed system
would be identical to the quicklime
(CaO) system, except that the slaking
equipment would not be required.
The additional investment in
slaking equipment (approximately
$10,000 to $15,000) is typically
justified if quicklime use requirements
exceed 3 tons (2.7 Mg) per day. The
additional capital investment required
for a hydrated lime feed system over
that required for a caustic feed system
varies considerably, but the investment
should be considered if requirements
exceed 0.5 tons (0.45 Mg) per day
of hydrated lime. Heavy metal pre-
cipitates resulting from lime neutrali-
zation will have superior settling and
dewatering characteristics compared
with those resulting from precipita-
tion using caustic soda. The lime
sludge will have a granular nature,
primarily because of the presence of
the calcium solids; caustic soda use
will result in a fluffy, gelatinous floe.
Consequently, lime treatment can
improve the performance of clarifica-
tion chambers and sludge dewatering
equipment, thereby reducing the
required size of these units.
As shown in Figure 1 8, lime waste-
water treatment produces a greater
quantity of dry solids than does
Ate
Figure 18.
Solids Generation Using Lime or Caustic for Neutralization
caustic neutralization. The additional
solids result from unreacted calcium
hydroxide, insoluble compounds
contained in the lime feed, and cal-
cium byproducts of the treatment
reactions, which precipitate because
of their low solubility. Insoluble by-
products usually precipitate only when
high lime doses are required for
treatment; treatment of wastewater
with a pH greater than 2 should not
result in calcium byproduct precipi-
tation.
23
-------
$0.045/Ib Cr
$0.040/lb metal
Process step (treatment reagent
Figure 19.
Consumption and Cost Factors Using Lime for Wastewater Treatment
The lime requirements and chemical
and sludge disposal costs can be
estimated by using Figure 19, which
is similar to the models developed
in Figures 11 and 1 2 for caustic
neutralization. Because sludge solids
concentrations differ for lime and
caustic, settling tests must be run
to compare accurately the total costs
of the two reagents. Using the waste-
water flow rates and pollutant loading
shown in Figure 1 3, the chemical cost
for neutralization and precipita-
tion using lime would be $2,400 per
year, as compared with $9,000 per
year for caustic. If the sludge is dis-
posed at 4 percent solids and $0.10/
gal in both cases, the disposal cost
using lime will be $23,400 per
year compared with $19,300 for
caustic.
24
-------
Filter plate and dewatered sludge cake
Sulfide Precipitation
Recently, with the more stringent
control of the dissolved metal
content of the wastewater effluent,
the use of reagents to precipitate
metals as sulfides has increased.
Sulfide precipitation is capable of
reducing the solubility of heavy metals
to much lower concentration levels.
Table 9 compares the solubilities of
metal sulfides with the corresponding
hydroxides. The sulfide process
has other advantages, which include
the following:
• The need for separate hexavalent
chromium reduction is eliminated.
The sulfide will reduce the Cr+6
to its trivalent state; as Cr"1"3, under
proper pH conditions, it will pre-
cipitate as the hydroxide.
Table 9.
Solubility of Metals when Precipitated at pH 8.0 as Hydroxides and Sulfides
•T@fl»l«ty
ken.,.
Nickel.
1*2X«5a
Cadmium
Tin,
T"
.
wx^-
•"10.79
42.65
+5.92
—3.34
; ?' +8.64
Copper.
Silver
*PoSi«v« magnitude (+J intfieat^s ti?wsr
SOUBCfe Aa»e«'s Handtook of Chemist^ J »«h *&, «s^ York !<¥,
25
-------
Figure 20.
Sulfide Waste Treatment
• Sulfide precipitation, unlike
hydroxide precipitation, is relatively
insensitive to the presence of
most chelating agents and
eliminates the need to treat these
wastes separately.
• Sulfide precipitation performs well
on many complexed heavy metals.
In practice, sulfide precipitation is ac-
complished by one of two processes.
In thessoluble sulfide process, a
probe that measures the concentra-
tion of sulfide ions is used to control
the addition of soluble sulfides, such
as sodium sulfide or sodium hydro-
sulfide. In the insoluble sulfide
process, an excess of ferrous sulfide
is added to the wastewater. The iron
will give up its sulfide and precipitate
any metal that has a lower solubility
than the ferrous sulfide (Table 9).
Under alkaline conditions, the iron will
then precipitate as the hydroxide.
In practice, the sulfide process is
used mainly as a polishing system after
hydroxide precipitation to further
reduce the solubility of the dissolved
metals in the wastewater effluent.
Figure 20 shows two approaches to
using sulfide precipitation to augment
an existing hydroxide neutralization
system.
The first approach (Case 1) requires
a minimum investment to achieve the
treatment benefits of sulfide precipita-
tion. It only requires the installa-
tion of a chemical feed system to add
26
-------
Polymer addition tank with treatment system in background
the insoluble sulfide to the mixing
zone of the clarifier or flocculator.
This approach will require enough
iron sulfide both to precipitate the
remaining dissolved metals and to
convert the precipitated metal hydrox-
ides to metal sulfides. Consequently,
iron sulfide consumption is high,
and a large volume of metal sulfide
and iron hydroxide sludge results.
The second approach (Case 2) requires
a second clarifier to remove the pre-
cipitated metal hydroxides before
sulfide precipitation. For large or mod-
erate flows, the savings in treatment
chemicals and disposal costs may
justify this approach.
The costs of sulfide precipitation
presented in Figure 20 for treatment
chemicals and sludge disposal should
not be considered additional treat-
ment costs. For both cases, if sulfide
treatment were not used to reduce
the hexavalent chromium and to
precipitate the dissolved cadmium,
the wastewater containing these
compounds would have to be treated
separately before the neutralizes
The least expensive treatment
system can be determined by compar-
ing the capital and operating costs
for each approach. To determine the
costs for a sulfide polishing system,
use the cost presented in Figure 5 for
installing a mixerclarifier; the costs for
the feed systems to introduce the
polymer and the insoluble sulfide are
in the range of $2,200 to $4,000 each.
Sulfide precipitation is a relatively
new approach for removal of heavy
metals from the waste streams.
The long-term stability of the sulfide
sludge has not been determined, nor
have the precautions for its safe
disposal been defined.
27
-------
Warkpiece
Rinse water
I cyanide I
I plating I
I bath I
~J^^^^i^*""iAa^^^^'
Solid waste
disposal
Figure 21.
Integrated Treatment for Chromium and Cyanide Plating Rinse Water
Integrated Wastewater
Treatment
For the pollutants that require special
treatment before neutralization—for
example, chromium reduction and
cyanide oxidation—it is possible to
achieve operating costs and
investment savings by incorporating
the waste treatment step as part of
the plating operation. In systems
using this approach, the drag-out on
the workpiece is treated in a rinse
tank containing the treatment
chemicals Consequently, the drag-out
is not diluted with rinse water before
treatment. When the contaminated
rinse water can be treated in a com-
mon neutralization/precipitation and
gravity settling process, the use of
multiple integrated systems may
require additional capital, although
the operating cost savings may still
favor the integrated treatment
approach.
An integrated wastewater treatment
system for both chromium and cyanide
drag-out is shown in Figure 21.
The treatment tanks prohibit pollut-
ants from entering the rinse tanks.
The chemical reactions and treat-
ment chemicals are identical to the
conventional approaches (see Figure
1). No controls are required, how-
ever, because the workpiece is dipped
directly into a rinse tank contain-
ing a concentrated solution of treat-
ment chemicals. The workpiece is then
rinsed with fresh water to cleanse
the surface of any treatment chemicals
or treated pollutants. The over-
flow from the water rinse tank is dis-
charged to the neutralizer. The overflow
from the treatment rinse tanks enters
a treatment reservoir where makeup
chemicals are added and the sus-
pended solids settle out of solution.
The installed costs of integrated
treatment systems are typically site
specific. The hardware requirements
shown in Figure 21 would include
Chemical rinse tank
Chemical treatment reservoir
Treatment solution recirculation
pump and piping
Sludge draw-off pump and piping
Treatment chemical storage tank
and feed system
As an alternative to conventional
treatment systems, the integrated
system approach can offer a signifi-
cant investment cost savings. The
installed cost for an integrated
28
-------
system can be estimated using the
data in Figures 22 and 23 for pumps
and in Figure 24 for tanks. Assuming
no extraordinary installation costs
(such as new building space or re-
location of existing equipment) are
involved, each of the integrated
systems pictured in Figure 21 should
cost between $10,000 and $12,000.
Often a plant will connect several
waste treatment rinses of the same
type to one common treatment
reservoir. The costs for integrated
treatment systems compare favorably
with the investment cost required for
conventional chromium reduction
and cyanide oxidation systems
presented in Figures 2 and 3.
10
8 4
o 4
« 3
H
t/1
O
I
I
I
I
103
3 5 104 23 5 105
CAPACITY FACTOR (gal/mm X psi)b
'Price includes ductile iron pump, motor foundation.
bFor pumps operating at 3,500 r/mm.
SOURCE: Chemical Engineering, Oct. 10, 1977.
Figure 22.
Hardware Cost: Centrifugal Pumps
Figure 23.
Hardware Cost: Positive Displacement Pumps
29
-------
Figure 24.
Hardware Cost: Tanks
The chemical use for a typical inte-
grated treatment system can be
determined from the composition of
the plating bath and the volume
of drag-out. The total treatment chem-
ical cost should be approximately
the same as that incurred in the con-
ventional treatment systems. There
will be some savings of acid and alkali
required to adjust the rinse water pH
in the conventional treatment systems
These savings should not be a sig-
nificant factor, however, because
the wastewater flow rates of these
streams are usually low.
Other advantages of the integrated
treatment approach include the
following.
• The sludge generated is segregated
in individual treatment reser-
voirs. Mixing of sludges does
not occur and recovery or disposal
of hazardous sludges in smaller
volumes is possible. Currently,
nickel is being recovered
from an integrated treatment sludge
by a plating chemical supplier,
who in turn gives the sludge
generator a purchase credit for the
nickel value. This practice
should become more widespread
and should be applied to other
plating materials in the future.
• The sludge formed m integrated
treatment systems usually settles
to a higher solids concentra-
tion because of its precipitation
m the concentrated chemical solu-
tion. This effect will decrease
the volume of sludge and reduce
disposal costs.
30
-------
4. Reducing the Costs of
Wastewater Treatment
General
The operating and investment costs
for wastewater treatment systems
were shown to depend directly on the
quantity of pollutants and on the
volumetric flow rate of the wastewater.
In-plant modifications to the plating
baths and rinse systems can reduce
wastewater flow rates and pollutant
loading, and thereby can improve raw
material yields and reduce pollution
control costs. The methods described
in this section are usually cost-effective
alternatives to end-of-pipe waste-
water treatment.
Housekeeping Practices
Implementing a successful house-
keeping program as a rule requires
little or no capital investment. As
shown in Figure 25, the raw material
and wastewater treatment savings can
be significant, especially when loss of
concentrated solutions of plating
chemicals is prevented. Although
substantial savings can be achieved by
a housekeeping program, they can
be easily lost unless routine surveil-
lance procedures are implemented.
Major corrective actions would
include:
• Repair leaks around processing
equipment (tanks, valves, pump
seals, transfer lines, heating coils,
etc.). Losses of 2 gal/h (7.6 l/h)
can occur easily through leaking
pump seals alone.
• Install antisiphon devices, equipped
with self-closing valves, on inlet
water lines where warranted.
• Inspect tanks and tank liners
periodically to avoid failures that
might severely overload the waste
treatment system.
• Inspect plating racks frequently
for loose insulation that would
cause excessive drag-out of plat-
ing solutions.
• Ensure that cyanide solutions do
not mix with compounds (iron,
nickel) that would form difficult-
to-treat wastes.
• Use dry cleanup, where possible,
instead of routine flooding with
water.
• Install drip trays and splash guards
where required.
For example, Figure 25 shows that
correcting an average loss of 1 gal/h
(3.8 l/h) from cyanide and chromium
tanks (curves 1 and 5, total $15,000
loss) and 2 gal/h (7.6 l/h) from caustic
soda storage (curve 4, total $5,000)
would reduce the operating costs by
$20,000 per year.
31
-------
Legend:
A » chromic acid plating solution 34% H2CrO.
B » 93% H2S04
C * acid copper plating solution: CuS04,
10 oz/gal; H2S04, 25 oz/gal
D » 50% NaOH (replacement cost only)
E a zinc cyanide solution: zinc (as metal),
30 oz/gal; NaCN, 6 oz/gal; NaOH, 12
oz/gat
Not*.—Basis: Operating 4,800 h/yr. Costs from
Table 1 and Figures 12 and 13.
LEAKAGE RATE (gal/h)
Figure 25.
Annual Cost of Chemical Leakage into Waste Treatment System
Minimizing Water Use
General. Major savings in treatment
chemicals, sewerfees, and investment
costs for wastewater treatment are
achievable by conserving water.
The major demand for water (as much
as 90 percent) is in the rinse tanks
that follow the different plating
process steps. Consequently, the
greatest potential for reducing waste-
water flow rates ;s in these tanks.
EPA has not determined whether to
regulate pollution discharges based
on an allowable quantity of pollutant
per some production related parameter,
or on pollutant concentration in
the waste stream. If the former,
minimizing the volume of water dis-
charged will be a necessary step to
comply with these regulations. Further-
more, if a plant is able to reduce
its process water discharge to below
10,000 gal/d (37,850 l/d), it probably
will be classified as a "small plater"
and be regulated by different pretreat-
ment standards. (This size criterion
only applies to plants discharging
to a publicly owned treatment works.)
Reducing Rinse Water Rates. Rinsing
is used to dilute the concentration
of contaminants adhering to the
surface of a workpiece to an accept-
able level before the workpiece passes
on to the next step in the plating
operation. The amount of water re-
quired to dilute the rinse solution
depends on the quantity of chemical
drag-in from the upstream rinse or
plating tank, the allowable concentra-
tion of chemicals in the rinse water,
and the contacting efficiency between
the workpiece and the water.
32
-------
Figure 26.
Rinse Water Rates Required and Effluent Concentration for Counterflow Rinse Systems
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
after a processing bath to reduce
the required rinse rate drastically
• Subjecting the workpiece to a
spray rinse as it emerges from the
process tankto reduce the quantity
of chemicals adhering to the
workpiece and thereby the
quantity of water needed for dilu-
tion
• Using conductivity cells to
control water addition to rinse
tanks and avoid excessive dilution
of the rinse water
• Installing flow regulators on rinse
water feed lines to control the
addition rate at the minimum
amount required
• Reusing contaminated rinse
water where feasible
If multiple rinse tanks are installed
after the process bath where the rinse
flows in a direction counter to that
of the parts movement (Figure 26),
the quantity of chemicals entering the
final rinse will be significantly re-
duced compared with that entering
a single-tank rinse system. The amount
of rinse water required for dilution
will be reduced by the same degree;
the volume can be predicted for each
rinse step by the use of a model that
assumes complete rinsing of the
workpiece. The ratio, r, of rinse water
volume to drag-out volume is approxi-
mated by
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 will not be achieved unless
there is sufficient residence time and
agitation in the rinse tank.
The volume of rinse water required
as a function of initial concentration in
the plating bath, required concentra-
tion in the final rinse tank, and num-
ber of rinse tanks are shown in Figure
27. For example, a typical Watts-type
nickel plating solution contains
270,000 mg/l of total dissolved
solids, and the final rinse must con-
tain no more than 37 mg/l of dissolved
solids. The ratio of Cp/Cn is 7,300,
and approximately 7,300 gallons
(27,630 liters) of rinse water are re-
quired for each gallon of process solu-
tion drag-in with a single-tank rinse
system. By installing a two-stage
rinse system, water requirements are
reduced to 86 gallons (326 liters)
of water per gallon of process solution
33
-------
100,000 i—
10,000
1,000
(J
&
u
100
10
n = 4
n = 1
10
100 1,000
RINSE RATIOb
10,000
aC = concentration in final rinse; C = con-
n p
centration in process bath, n = number of rinse
tanks.
bRinse ratio = gal rinse water/gal drag-out.
Note.—This graph shows rinse ratios for coun-
tercurrent rinse systems. For series rinse
systems, multiply the rinse ratio for a counter-
current arrangement with the same number
of tanks by the number of tanks, e.g , two-stage
countercurrent rinse with C /C = 104 has a
rinse ratio of 100 gal/gal But, with the two-
stage series the required rinse ratio is
100 X 2 = 200 (gal rinse water/gal drag-out).
100,000
Figure 27.
Estimating Rinse Ratios Based on Drag-Out and Final Rinse Concentration for Multiple-Tank Rinse Systems
drag-in. The same degree of dilution
is obtained in the final rinse, and
the rinse water consumption is re-
duced by 99 percent. The mass
flow of pollutants exiting the rinse
system remains constant.
If this bath had a drag-out rate of 0.5
gal/h (1.9 l/h), the single rinse tank
would require 3,650 gal/h (1 3,820 l/h)
of rinse water (0.5 X 7,300). A three-
stage countercurrent rinse arrange-
ment would reduce water consumption
from 3,650 gal/h (13,820 l/h) to
10 gal/h (38 l/h) (0.5 X 20). The re-
sulting cost benefits would include
reducing water use and sewer fees
by $4/h (based on $1.10/1,000 gal
combined water use and sewer fees)
and reducing the size of the required
waste treatment systems, which
are designed on the basis of volumet-
ric flowrate.
The investment cost to add two addi-
tional rinse tanks is highly site
specific; for manual plating opera-
tions the major factor affecting
cost would be the availability of space
in the process area. For automatic
plating machines, the cost of modify-
ing the unit to add additional stations
may be as high as $20,000 per
station. Costs for the rinse tanks are
given in Figure 24 for rubber-lined
steel open top tanks with appropriate
weir plates and nozzles. The cost,
excluding installation, is in the range
of $1,000 to $1,500, depending on
cross-sectional area required for the
workpiece.
A series rinse arrangement also can 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 by r= n
(C /Cn)1/n. If the rate given in Figure 27
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 sig-
nificantly higher for series rinsing.
A conductivity probe is another
effective water-saving device to use
m rinsing systems. Except on highly
automated plating machines, the fre-
quency of rinse dips generally vanes
considerably. Because the fresh rinse
water usually is fed continuously,
there are periods of excess dilution
and, consequently, of excess water
being used. A conductivity cell
measures the level of dissolved solids
34
-------
in the rinse water and, when the
level reaches a preset minimum, it
shuts a valve interrupting the fresh
water feed. When the concentration
of dissolved solids builds up to the
maximum allowable level, it opens the
valve. Thousands of these units are
used throughout industry because
they are so reasonable m price. A
complete set, including a probe, con-
troller, and automatic 1-inch (2.5-cm)
valve can be purchased and installed
for $200 to $1,000.
A further water conservation step
employs flow regulators as a means
of controlling the fresh water feed
within a narrow range despite varia-
tions in line pressure. These devices
also eliminate the need to reset the
flow each time the valve is closed.
They also have been designed to
act as syphon breakers and aerators
(by the ventun effect) and are pro-
vided in a wide range of flow settings.
The units cost approximately $20 to
$30.
Water Reuse. Reusing water is
another method of reducing water
use. In critical or final rinsing opera-
tions, the level of contaminants re-
maining on the workpiece must be
extremely low; for some intermed-
iate rinse steps, however, the level
of contaminants can be higher.
Water consumption can be reduced by
reusing the contaminated overflow from
the critical rinse in a rinse for which
water specifications are less critical.
Water also may be reused where the
contaminants in rinse water after
a processing step do not detract from
the rinse water quality at another
rinsing station. For example, the over-
flow from the rinse after an acid dip
may be reused as the feed to rinse
after an alkaline dip. Choosing the
optimum configuration requires ana-
lyzing the particular rinse water
needs. Interconnections between
rinsing systems might make operations
more complicated, but the cost
advantage they represent justifies the
extra attention they require.
Table 10.
Economic Penalty for Losses of Plating Chemicals
Cost ($/lb)
Chemical
Replacement Treatment8 Disposal6 Total
Using Clj for cyanide oxida-
tion
Using NaOCI for cyanide oxida-
tion
Chromic acid as H2Cr04'
Using S02 for chromium reduc-
tion
Using NaHS03 for chromium
reduction
Copper cyanide as Cu(CN)2:
Using CI2 for cyanide oxidation . . .
Using NaOCI for cyanide oxida-
tion
Copper sulfate as CuS04
1.41
1.41
0.78
0.78
1 95
1.95
0.56
072
1.53
0.48
0.69
0.72
1.53
0.28
025
0.25
0.32
0.32
0.25
0.25
0.17
2.38
3 19
1.58
1.79
292
3.73
1.01
aBased on treatment model presented in Figure 1 2 at a concentration of 100 mg/l in wastewater.
bBased on Figure 13.
Reducing Drag-Out Loss
General. As a workpiece emerges
from a plating bath, it carries over
a volume of plating solution into the
rinse system. This carryover, known as
drag-out, is usually the major source
of pollutants in an electroplater's
waste stream. Table 10 shows the
economic penalty suffered for each
pound of assorted plating chemicals
lost to the waste stream. The cost of
replacing the raw materials and
treating and disposing of the waste is
high; consequently, the cost effective-
ness of modifications to minimize
drag-out is very attractive.
Generally, one of two approaches can
be used: reduction of drag-out before
rinsing or recycling rinse water to
the plating bath. Various percentages
of recovery are achievable depending
on the number of rinse tanks in the
rinsing system, the concentration
of pollutants permissable in the
final rinse tank, and the volume of
rinse waterthat can be recycled to the
plating tanks. To assess the potential
economy of drag-out recovery,
the quantity of plating solution lost
to the rinse system must be deter-
mined. A first approximation of this
quantity can be derived by multiply-
ing the quantity of plating chemicals
added to the bath by an assumed loss
factor. Typically for chrome plating
operations, about 0.9 pound (0.4 kg)
of chrome is lost as drag-out per
pound added to the plating tank. The
loss factors for other plating baths
are between 50 and 90 percent.
If the chemical loss represents a signifi-
cant cost (Table 10), a more precise
determination may be required
to substantiate the benefits of invest-
ing in drag-out recovery modifications.
The following five steps constitute
the recommended analytical tech-
nique:
1. Fill the rinse station after the
process bath with a known volume
of water.
2. Using normal production proce-
dures, plate and rinse a represen-
tative production unit.
3. Stir the rinse tank and collect a
sample of rinse water.
4. Plate and rinse several additional
production units and collect
another sample of rinse water.
5. Repeat Step 4.
35
-------
The rinse water samples then must be
sent to a laboratory to determine the
concentration of plating chemicals in
the rinse. Multiplying the volume of
rinse solution by the concentration
of chemical will determine the quantity
of chemical drag-in per production
unit. The volume of drag-out per hour
can be determined if the production
rate and the chemical concentration
of the plating solution are known.
Drag-Out Recovery from Rinse Tanks.
The drag-out lost from the plating bath
can be reduced significantly by
usually low-cost recycle modifica-
tions after rinsing modifications are
completed. As a rule these modifica-
tions are applicable to baths that
have a considerable amount of surface
evaporation. The rinse water con-
taining dragged-out plating chemicals
can be returned to the plating bath
from the rinse tanks to make up for
water lost by surface evaporation.
Low temperature baths have minimum
surface evaporation and their tem-
perature cannot be increased without
degrading heat sensitive additives.
Recently, new additives, which are
not as readily heat degraded, have
been developed for many of these
plating baths. These additives might
make operation of the plating bath
possible at higher temperatures, facili-
tating drag-out recovery by recycle
techniques. Usually, the value of the
recovered chemicals is much greater
than the increased energy cost
associated with operating the bath
at a higher temperature.
Figure 28.
Surface Evaporation Rate from Aerated Plating Baths
The evaporation rate determines the
total volume of rinse water that can
be recycled to the plating tanks. The
quantity of the plating chemicals
in the recycled rinse water represents
the savings of plating chemicals pre-
viously lost to the pollution con-
trol system. If the required rinse water
rate can be matched to the evapora-
tion rate, no rinse water is discharged
to waste treatment and the plating
bath is operated as a closed-loop
system.
The rate of surface evaporation for
plating tanks with air agitation is
shown in Figure 28; the rate for those
without air agitation (surface evapora-
tion only) is shown in Figure 29. If
the use of air agitation significantly
increases the evaporation rate, it also
will significantly increase the heat loss
from a plating tank and the energy
cost to keep the bath at its operating
temperature. Figure 30 presents
the heat input required to compen-
sate for heat loss resulting from the
use of air agitation. The heat loss
caused by surface evaporation in a
plating bath without air agitation can
be calculated from: Heat load (Btu/h) =
surface evaporation (gal/h) X 8,300
(Btu/gal).
36
-------
For example, two plating tanks, each
with a 30-ft2 (2.8-m2) surface area,
are operated at 1 50° F (66° C). One
uses 100 stdft3/min (2.8 normal
m3/min) air agitation, and the second
operates without air agitation. The
surface evaporation rates would be 9.8
gal/h (37.1 l/h) and 4.2 gal/h (15.9
l/h), respectively. The heat inputs re-
quired would be 107,500 and 34,860
Btu/h (31,505 W and 10,216 W),
respectively. Using indirect steam
heating to compensate for the heat
loss would cost $0.32/h for the air
agitated bath compared to $0.10/h for
the bath without air agitation, based
on an energy cost of $3/106 Btu.
Significant drag-out recovery can
be achieved for each plating tank by
using a multistage rinse system and
returning the concentrated rmse
water to the bath to compensate for
the evaporation losses. If the required
rinse water rate were equal to the
evaporation rate, the entire volume
of rinse water could be returned to
the plating bath. For this case, the
reduction of drag-out loss as compared
to an operation with no recycle is
given by the following formula:
Percent recovery of drag-out
/ C \
= h __!: JX100%
where:
Cp= concentrations in plating bath
Cn = concentrations in final rinse tank
The only loss is drag-out from the last
rinse tank, which has a dilute con-
centration of plating chemicals.
Figure 29.
Surface Evaporation Rate from Plating Baths with No Aeration
When a low final rinse concentration
is required, excessive drag-out occurs,
or surface evaporation is minimal,
a closed-loop, countercurrent rinse-
and-recycle system probably will
be impractical because of the large
number of rinse stages required.
By operating the final rinse in a
multiple-tank system as a free rinse
and using the upstream tanks as a
countercurrent rinse-and-recycle sys-
tem, significant drag-out recovery still
can be realized while rinsing quality
37
-------
500 —
.E
~5
m
Q
<
O
O
u
_ 0.03
0.003
100
AIR SPARGE RATE (stdft3/min)
1,000
Notes.—Supply air at 75° F, 75% relative humidity. Plating solution is 95% mole fraction
H20.
Fuel cost to supply heat load based on energy supply at $3/106 Btu.
T = plating bath temperature.
Figure 30.
Heat Load Resulting from Aeration of Plating Baths
is maintained. Figure 31 depicts such
a system, and Figure 32 defines the
percent recovery of drag-out as a
function of recycle ratio, which is the
volume of recycled rinse divided by the
volume of drag-out. The recycle
rinse rate in the recovery rinse tanks
is equal to the evaporation rate. The
data presented in Figure 27 can be
used to determine the required water
rates for the final rinse once the
concentration in the recovery rinse
is known.
As an example, a nickel plating opera-
tion has these operating characteristics:
a drag-out rate of 0.5 gal/h (1.9 l/h),
a surface evaporation rate of 5 gal/h
(19 l/h), and a final rinse concentra-
tion of 40 mg/l. Therefore, the recycle
ratio could be set at 10. From Figure
29, a one-stage recovery rinse and re-
cycle system would reclaim 91 percent
of the drag-out (point A). At this re-
covery rate, the concentration ratio is
0.09. 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 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 sys-
tem. The rinse water required in the
final rinse tank, calculated by using
Figure 27, is 304 gal/h (1,150 l/h).
The curves in Figure 32 were plotted
assuming that water is added contin-
uously to make up for surface evapora-
tion losses. This practice may not be
feasible and the water usually will
be added in increments, resulting in
cyclical movement along the curves
presented in Figure 32. The longerthe
time interval between additions, the
greater the variation m the recovery
of the drag-out realized. Particularly at
low recycle rates, where the recovery
potential is very sensitive to changes
m the recycle ratio, minimizing the
time between additions will sig-
nificantly increase the amount of drag-
out recovered. A level control device
will approach the potential of con-
tinuous water addition and is
recommended if the recycle ratio is
in the range of 3 or less. These con-
trol loops cost between $500 and
$1,200.
Deiomzed water is specified for any
rinse stream that is recirculated to
the plating bath to avoid the progres-
sive buildup of contaminants in the
bath.
Reducing Drag-Out from Plating
Tanks. Two effective methods of re-
ducing the concentration or volume
of plating solution lost from the plating
tanks are spray rinses and air knives.
Spray rinses are ideal for reducing
drag-out from the plating tank on
automated lines. As the workpiece is
withdrawn mechanically from the plat-
ing solution, a spray of water
automatically washes the part,
draining as much as 75 percent of the
chemicals back into the plate tank.
Again, the volume of spray rinse
cannot exceed the volume of surface
evaporation from the plate tank. Spray
rinsing is best suited for flat parts,
but will reduce drag-out effectively
on any part plated.
38
-------
Deionized water
Parts
movement
Automatic
valve
JUnse #«er
Recovery rinse
i
Free
rinse
To waste
Drag-out (gtf/b}
Now,—Ce » ceneenttitfw»« plating battw C,« concwitwtton Jn finat stage of recovery, Cn *= concentration in fsnat rinse,
LC, LT = fevet uotttfol Wf anrf tisnsmftter.
Figure 31.
Rinse-and-Recycle Drag-Out Recovery
Figure 32.
Percent Drag-Out Recovery with Rinse-and-Recycle System
The savings are calculated m terms
of the concentration change in the
drag-out. For example, if the concen-
tration of the drag-out were 100,000
mg/l and a spray rinse reduced the
concentration to 50,000 mg/l, the
chemical losses would be reduced by
50 percent.
An air knife can be used to reduce
drag-out in much the same way as
a spray rinse, particularly when the
surface evaporation rate in the plating
bath is low. The savings in operating
costs are equal to the percent reduc-
tion in volume of drag-out adhering
to the workplace. The concentration
of the dragged-out solution remains
the same.
An air knife also can be used to
improve the drag-out recovery of
the rinse and recycle system (shown
in Figure 31), which is character-
ized by a low recycle ratio. Installing
an air knife (as shown in Figure 33)
reduces the volume of drag-out from
the plating bath from 1 to 0.5 gal/h
(3.8 to 1.9 l/h). Also, the recycle
rinse ratio of the recovery rmse is
increased from 2 to 3, which increases
recovery from 84 percent to 92 per-
cent (Case B).
39
-------
Surface evaporation
**«*$ $>•
Dt83-o«t
ft«fft/t»
tSjWt*
i)raf-out
1 gal/h
Drag-out
tflat/h
Install air knife ring install two air knife rings
Figure 33.
Impact of Air Knife on Drag-Out Recovery and Rinse Water Use
40
-------
Further recovery of drag-out can be
achieved by installing an air knife in
the upstream rinse tank. The reduction
in drag-in would increase the amount
of recycle returned to the plating
bath from the rinse system by an equal
amount. Consequently, recovery
potential would be increased (Figure
33, Case C).
Impact on Drag-Out Losses of Mini-
mizing Bath Concentrations. In
operations where a metal finish is
applied to a surface by immersion
of that surface in a chemical solution,
the quantity of the chemicals removed
from the bath is a function of the
concentration in the solution and the
quantity of solution carried over the
edge of the bath by the emerging piece
of work.
Traditionally, the midpoint within a
range of operating concentrations is
chosen for plating solutions. This
practice derives from sound reasoning,
as long as the incremental cost of
the additional chemicals lost is less
than the cost of more rigorous control
procedures. Consider a standard
nickel plating solution that has the
concentration limits shown in
Table 11.
A typical small plating shop that oper-
ated at an average of 1 2 h/d, 250 d/yr,
and processed 600 ft2/h (56 m2/h)
would lose 2,700 gal/yr (10,220 l/yr)
of process solution attributed to
drag-out, based on drag-out rate of 1.5
gal/1,000 ft2 (61 1/1,000 m2). Modify-
ing the operating conditions to the
minimum values indicated above
would save this shop 390 pounds
(1 77 kg) of nickel sulfate and 1 50
pounds (68 kg) of nickel chloride an-
nually. The money saved in replace-
ment chemicals, treatment costs, and
sludge disposal (as shown in Table 10)
would amount to $700 per year.
The same type of assessment could be
applied to any metal finishing oper-
ation.
Table 11.
Standard Nickel Solution Concentration Limits
Nietort suHn»:
ton's
"f^ '-A*"
Using Spent Baths as Treatment
Reagents
Often the processing solutions used
in alkaline or acid cleaning steps of the
electroplating process can be used
as pH adjustment reagents in the
waste treatment system. These baths
are either dumped when the con-
taminant level exceeds some accept-
able concentration or bled off to
waste treatment and replaced with
fresh reagents to maintain the concen-
tration of contaminants below that
level. In either case, the solution
could be transferred to a holding
tank instead, and could be used to
treat the wastewater.
Spent caustic soda solutions can be
used for pH adjustment in the neu-
tralization/precipitation step. Spent
sulphuric and hydrochloric acid
solutions also can be used here, but
because waste streams are usually
acidic, the quantity used would be
minimal.
Waste acid solutions (HCI, H2S04)
can be used for pH adjustment in the
chrome reduction process (Figure 34).
A minor added benefit in this case
would be a decrease in the demand
for reducing agent caused by the
presence in the acid of any Fe+2 iron,
which will reduce Cr+6.
Acid feed pump with neutralizer in background
41
-------
Spent hydrochloric
acid storage
Sodium bisulfite
storage
Wastewater, 30 gal/mm at
30 ppm Cr+e
pH = 4
Chrome reduction vessel
Item
Amount
Chemical savings by using spent HCI (Ib/h):
H2S04 (replaced by HCI) at 93% 9.2
Na2S205 (replaced by Fe+2 reduction) 0 04
NaOH (not needed to neutralize spent HCI) 7 5
Value of chemicals saved, at 3,600 h/yr ($/yr)
H2S04
NaHSO3
NaOH
708
19
2,204
Figure 34.
Chemical Savings Resulting from Use of Spent HCI in Chrome Reduction Treatment
Further reduction in reducing agent
demand could be achieved by dis-
solving scrap iron in the spent acid,
thus raising the concentration of the
Fe+2. For each pound of sodium
bisulphite reducing agent replaced with
iron, however, an additional 1.7
pounds (0.77 kg) of iron hydroxide
sludge will be generated. At a dis-
posal cost of $0.10/gal, it will
probably cost more to dispose of the
additional solid waste than will be
saved by reducing chemical con-
sumption.
If additives are used to improve the
properties of these spent solutions for
their original function, the impact
of the additives on the waste treat-
ment process should be considered
before they are used as treatment
reagents.
Example of Cost/Benefits Analysis
Cost-Saving Examples. The potential
savings in water and chemicals can
be predicted using the data developed
in this section. The example that
follows illustrates application of these
modifications to a typical nickel-
chromium-plating operation. The
worksheet provided in Appendix A
can be used to develop a similar anal-
ysis for most plating shops
The shop plates approximately 600
ft2/h (56 m2/h) in its nickel-chromium
operation, operating an average of
10 h/d, 300 d/yr. Figure 35 shows the
processing sequence and water use
rates for the operation. The original
processing sequence used two-stage
countercurrent rinse systems after
the nickel and chromium plate tanks.
As shown in Figure 36, m-plant
modifications were made at six loca-
tions (Stations 2 and 4 through 8)
to reduce raw material losses and
waste treatment costs.
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 effi-
ciency. This reduction was accomplished
by installing a ventun-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. Combined,
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
$2,000; this total consisted of:
• Pump and foundation, $1,300
• Flow regulators, piping, valves,
and electrical connections, $300
• Labor, $400
42
-------
Alkaline
clean
o
Figure 35.
Nickel-Chrome Plate Sequence and Waste Flow Rates
Nickel Plate and Rinse (Stations 5
and 6): The nickel plating bath oper-
ates at 1 50° F (66° C) and has the
following chemical composition:
• NiSCy6H20 = 45 oz/gal (337
g/l); NiS04 = 1.65 Ib/gal (0.2 kg/I)
• NiCI2-6H20 = 10 oz/gal (75
g/l); NiCI2 = 0.34 Ib/gal (0.04 kg/I)
• H3B03 = 6 oz/gal (45 g/l), or
0.38 Ib/gal (0.045 kg/I)
• Specific gravity = 1.25
The plate tank has a surface area of
30 ft2 (2.8 m2) and drag-out is de-
termined by testing to equal 1.5 gal/
1,000 ft2 (61 1/1,000 m2) of work
plated, or at 600 ft2/h (56 m2/h) plated,
0.9 gal/h (3.4 l/h) drag-out. The tank is
aerated at a rate of 60 stdft3/mm (1.7
normal m3/min). From Figure 28, the
evaporative rate in the plating tank will
be 5.85 gal/h (22.14 l/h).
The plant decided to reduce drag-out
losses by employing a rmse-and-
recycle system similartothat in Figure
31. By use of the existing two-stage,
countercurrent rinse as a single-stage
recovery rinse and a single-stage
final rinse, drag-out losses can be
reduced by 85 percent—from Figure
29 based on a recovery rinse ratio of
(5.85 gal/h)/(0.9 gal/h) = 6.5. If an
additional rinse tank were installed,
and a two-stage recovery rinse were
operated before the single-stage final
rinse, the recovery system would re-
claim 98 percent of the current
drag-out losses. An evaluation of
whethertoaddan additional rinse tank
was performed. Table 12 summarizes
the results. Case 1 represents the
current operating practice. Case 2
represents a rinse and recycle system
using the two existing rinse tanks.
Case 3 represents adding an additional
rinse tank and operating a two-stage
recovery rinse.
The additional $3,000 investment
for a third rinse tank further reduced
operating costs by $2,545 per year
(Case 3). Because of this excellent
return on investment, Case 3 was
chosen.
43
-------
Alkaline
clean
o
Figure 36.
Nickel-Chrome Plate Sequence with Wastewater Flow Rates Revised
Chrome Plate 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 at
600 ft2/h (56 m2/h) plated, 0.9 gal/h
(3.4 l/h) drag-out. This tank is also
aerated at a rate of 60 stdft3/mm
(1.7 m3/mm). The plating solution
contains 50 oz/gal (375 g/l), or 3.1 25
Ib/gal (0.375 kg/I), chromic acid
(H2Cr04), has a specific gravity of 1.25,
and is maintained at 120° F (49° C).
From Figure 28 surface evaporation
rate is 2.4 gal/h (9.1 l/h).
A rinse-and-recycle system, as shown
in Figure 31, would operate at a
rinse ratio of (2.4 gal/h)/(0.9 gal/h) =
2.66. If an additional rinse tank were
installed and a two-stage recovery
rinse were operated, 90 percent of the
drag-out would be recycled (Figure
32). A one-stage recovery rinse
could recover 72 percent of the cur-
rent losses. The plant decided to add
a third rinse tank and an 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 13
summarizes the results. Case 1 repre-
sents the current operating practice.
Case 2 represents the case with
a two-stage final rinse. Case 3 is the
option using a two-stage recovery
rinse.
The two investment options (Cases 2
and 3) require equal capital and
reduce operating costs by almost equal
amounts; however, Case 3 would
result in a tenfold increase in waste-
water flow to the chromium reduc-
tion waste treatment system: 81 gal/h
vs. 730 gal/h (307 l/h vs. 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 consid-
ered, Case 2 represented the most
attractive option and these modifica-
tions were incorporated into the
plating sequence.
44
-------
Table 12.
Nickel Plate Cost Reduction Evaluation of Rinsing Options
Table 13.
Chrome Plate Cost Reduction Evaluation of Rinsing Options
Item
Cost of modifications
Water use cost (at $1 10/1 000 gal) . . .
Case 1
(present
2-stage
rinse)
o
.... $1 3,300/yr
81 gal/h
. . . $270
$13 570
Case 2
(proposed 1 -stage
recovery nnse,
2-stage final rinse)
Level control rinse feed, conduc-
tivity controller, repiping, addi-
tional nnse tank
$5,500
72%
$3,720/yr
43 gal/h
$140
$4410
$9 160
Case 3
(proposed 2-stage
recovery rinse,
1 -stage final rinse)
Level control rinse feed, conductiv-
ity controller, repiping, additional
rinse tank
$5,500
90%
$1,330/yr
730 gal/h
$2,410
$4 290
$9,280
aSee Table 10.
bFrom Figure 27, Cn = 37 mg/l.
°Depreciation at 10-year straight line.
45
-------
Summary of Savings. The total cost
of the modifications described was
$12,500. The cost assumes that the
plate baths already have purification
systems that would control any
contaminant buildup resulting from
recycling the drag-out back to the
baths. The benefits from the modifica-
tions include:
• The cost to operate the nickel
plating bath is reduced by $5,100
per year.
• The cost to operate the chrome
plating bath is reduced by $9,300
per year.
The baseline flow to waste
treatment is reduced from 910
gal/h to 330 gal/h (3,445 to
1,250 l/h) (Figure 29). The plater
is now ensured of having a dis-
charge rate of less than 10,000
gal/d (37,854 l/d), putting
the plater in an industry category
with different treatment regulations
in the proposed pretreatment
standards.
• Because the waste treatment
process reduces the solubility
of pollutants to an equilibrium
level, the quantity of pollutants dis-
charged in the wastewater effluent
is reduced to the same degree
as the volume of effluent.
46
-------
5. Recovery Processes
Introduction
The high cost of replacing and treating
plating chemicals lost to the waste
stream has resulted in the application
of various separation processes to
reclaim these materials for reuse.
These processes all operate on the
same basic principle; they concentrate
the dragged-out plating solution
contained in the rinse water to the
degree that the solution can be
returned to the plating bath.
Recovery processes include evapora-
tion, reverse osmosis, ion exchange,
and, most recently, electrodialysis.
Their use can result m an essentially
closed system around a plating bath;
no plating chemicals are consumed
other than those plated on the ware,
and no rinse water is sent to waste
treatment. Except in the case of purge
streams from the recovery unit, under
very favorable conditions a recovery
system (Figure 37a) can achieve zero
effluent discharge.
Using a recovery unit requires reducing
the volume of rinse water to a quantity
that can be processed economically.
The use of a multistage counterflow
rinse system is therefore recom-
mended. A bath purification system is
needed to eliminate the buildup of
contaminants in the closed-loop
system resulting from return of the
drag-out to the process bath. The drag-
out formerly acted as a bleed stream
and served to control the buildup of
contaminants. The type of purification
system required depends on the type of
plating chemicals being recovered.
One objection to recovery systems is
that the quality of the rinse operation
may be compromised. Rinsing quality
can be ensured by segregating the final
rinse from the recovery process (Figure
37b), but this approach results in a
rinse water flow to waste treatment.
Figure 37.
Recovery Systems: (a) Closed Loop; (b) Open Loop
47
-------
The chemical recovery potential for a
recovery system is shown as a function
of rinse ratio in Figure 38. The curve is
the same as that developed for the
recovery potential of a two-stage rmse-
and-recycle system in Figure 32. The
major difference is that now the
recovery rinse ratio is determined by
the processing capability of the
recovery unit, not the surface
evaporation rate of the plating bath.
Recovery processes should be
considered for those baths for which
rinse-and-recycle modifications are
not applicable. If a plater can reclaim
90 percent of his drag-out losses by
low-cost modifications to the plate
line, as realized by the nickel system
described in Section 4, then it would
not be economical to install a recovery
system.
In cases where the rinse waters
following a plating operation require a
separate waste treatment system
(chromium and cyanide are examples),
closing the loop around the plating
operation with a recovery system can
avert the need for the treatment
system. The capital savings resulting
from eliminating the treatment
hardware will make the investment in
recovery units more attractive.
This section will examine the operating
parameters, costfactors, and reliability
of the different recovery systems used
in the electroplating industry. This
information will enable the electro-
plater, after an assessment of specific
loss factors, to determine the economy
that could be realized by installing
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 currently several
hundred units are being operated to
reclaim plating solutions from rinse
streams.
Figure 38.
Recovery Potential for a Two-Stage Counterflow Rinse
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 steam is recycled for use as
rinse water in the rinse tanks. The boil-
off rate, or evaporator duty, is set to
maintain the water balance of the
plating bath. The evaporation usually is
performed under a vacuum to prevent
any thermal degradation of additives in
the plating solution and to reduce the
amount of energy consumed by the
process.
Figure 39 diagrams a closed-loop
evaporative recovery system used on a
chromium plating bath with a three-
stage, countercurrent rinse system. No
losses in plating chemicals occur. Only
the chromium plated on the wares
must be added to the plating tank.
Water consumption is reduced to the
water lost to surface evaporation. A
cation exchange column is required to
prevent the buildup of metallic
impurities—mainly dissolved metals
from the work processed and excess
trivalent chromium—in the closed-
loop system.
48
-------
Figure 39.
Chromic Acid Evaporative Recovery Unit
Total installed investment, operating
costs, and economics for installing a
20-gal/h (76 l/h) evaporator (as shown
in Figure 39) are given in Table 14. The
before tax annual savings for this
system is approximately $1,800. The
cost for steam and fixed charges are
the major costs of operation,
approximately 55 percent of the total
costs. The annual savings resulting
from recovery of plating chemicals and
wastewater treatment cost reduction
comes to $14,880.
The steam costs and investment for
evaporators depend on the evapora-
tive duty, which for plating rinse
recovery systems is equal to the
required rinse water flow rate (Figure
40). To minimize rinse rates, such
methods as countercurrent rinse
systems are usually cost effective. A
50-percent steam saving can be
achieved with double-effect
evaporators; however, the capital
costs are much higher and operation is
more complicated. As a rule, at
evaporation rates below 1 50 gal/h,
(568 l/h), additional investment for
double-effect evaporators is not
justified.
Because of the high initial investment,
the savings and economics for
evaporative recovery depend to a great
extent on the concentration of the rinse
water being evaporated and the
volume of drag-out. For example, if the
20-gal/h (76-l/h) evaporator (Table 1 4)
were fed a stream with 50 percent
more plating chemicals, the annual
savings for treatment and recovery
would increase by 50 percent to
approximately $22,300 (14,880 X
1.5). The net savings would increase to
$9,100, and the payback period would
reduce to 4.3 years.
49
-------
Table 14.
Economics of Evaporator System for Chromic Acid Recovery, Operating 5,000 h/yr
3***¥tf"""r
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t )* n"£ l i* s*
50
-------
100 i-
5 75
8 50
25
I
I
I
25 50 75 100 125
EVAPORATIVE CAPACITY (gal/h)
Legend:
highly corrosive duty, borosilicate glass
mm body and tubes
mm mm highly corrosive duty, fiberglass-
reinforced plastic body with tantalum
tubes
' corrosive duty, fiberglass-reinforced
plastic body titanium tubes
• •• mild service, carbon steel body with
stainless steel tubes
"Includes vacuum evaporator, product and
rinse water feed tanks, condensate and
product return pumps, rinse filter, all piping,
electrical and installation costs.
Note.—Based on $3/106 Btu, the steam cost
will equal $3.50/h per 100 gal/h of water
I evaporated.
150
Figure 40.
Installed Costs and Energy Costs for Evaporative Recovery Systems
If the concentration of the plating
chemicals shown in Table 14 were to
remain constant, but the volume of
drag-out were to double, a 40-gal/h
(151 -l/h) evaporator would be
required. As Figure 40 shows, the
installed cost would be approximately
$45,000. Because the installed cost
increased by only $9,000, the net
annual savings would be $10,300,
which yields a payback period of 4.6
years after taxes.
Reverse Osmosis
Reverse osmosis (RO) (Figure 41) is a
pressure drive membrane separation
process. The feed is separated under
pressure—400 to 800 Ib/m2 gauge—
into a purified "permeate" stream and
a concentrate stream by selective
passage of water through the micro-
scopic pores of the semipermeable
membrane. Commercial RO units have
been successful in concentrating
and recycling rinse streams in metal
plating operations for a number of
years. The main area of application
is the concentration of rinse waters
from acid nickel plating baths.
The major limitation of commercial RO
systems is the inability to maintain
membrane performance. Fouling and
gradual deterioration of membranes
can reduce the processing capacity of
the unit and require frequent
membrane replacements. Currently
feed solutions must be in a pH range
between 2.5 and 11 to ensure
reasonable life for commercially
available membranes.
Moreover, these membranes are not
suitable for treating solutions having a
high oxidation potential. RO units have
limited capability for high concen-
tration of dilute feed solutions. Table
15 lists typical maximum concentra-
tions reached in commercial appli-
cations. Because of these con-
centration limits, additional
concentration by a small evaporator
may be required for ambient tem-
perature baths where there is minimum
surface evaporation. Therefore, acid
nickel plating baths, which have
considerable surface evaporation, are
the primary area of application for RO.
Furthermore, the membrane does not
completely reject certain species, such
as non-ionized organic wetting agents.
This limitation necessitates more
frequent bath analysis to maintain the
desired chemical makeup of the
plating bath.
51
-------
Figure 41.
Reverse Osmosis for Nickel Plating Drag-Out Recovery
Table 15.
Reverse Osmosis Operating Parameters
Feed solution
Nf1-2 . .
Cu+2 ....
Cd+2
Cr04~2lal ... .
CN~'al . .
Zn+2
Maximum
concentration F
of concentrate
(%)
10-20
10-20
10-20
10-12
4-12
10-20
(b)
Rejection
(%)
98-99
98-99
96-98
90-98
90-95
98-99
(")
"Performance depends greatly on pH of solution.
bThese compounds are concentrated in permeate stream because of selective passage through
membrane.
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 constituents 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-CD
Percent rejection = X 100
Cf
where
Cf = concentration in feed stream
Cp = concentration in permeate stream
Figure 42 presents the cost of RO units
as a function of membrane surface
area. Determination of the flux rates for
a specific application, and thus the
membrane surface area necessary,
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 41 for a nickel
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.
52
-------
Figure 42.
Reverse Osmosis System: Unit Cost vs. Membrane Surface Cost
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 concen-
trate volume by 50 percent (increasing
the permeate/feed ratio from 0.95 to
0.975) will decrease the flux rate by 25
percent. For example, if the RO
system shown in Figure 41 were 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 31 7 to 422 ft2 (29.5 to
39.2 m2).
The RO system shown in Figure 41 is
used to recycle the chemical drag-out
in an acid nickel plating operation. The
system uses a 50-/xm 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 cost of the system, itemized
in Table 16, comes to $19,500.
Theoretically, the system would re-
cover 99 percent of the plating chem-
icals lost to the rinse system. Table
16 also presents the operating cost
reduction that would be achieved
if the unit operated 90 percent of the
time. The system has a payback period
of 4.3 years.
53
-------
Table 16.
Economics of Reverse Osmosis System for Nickel Salt Recovery, Operating 5,000 h/yr
Item Cost
Installed cftst $30rft2 m»it{$)t .-.-•."• - '".'.•• '
..
BO -Kwiful* tnoludirig 6Q»/tii» fitter, pump, arid 9 membrartf.rtiotMes "at&j> fl2 per modulo ,,,.....,,,..,, .......... 1 5,000
Activated earf»f» lifter. ',',-,',-. ..... ........... ......'. .J-. — ..",','.,.,,..,•.-.,. ........... „• ................... 2,000
Piping ,-,,.• ,...::,„.......»......, ..... ,.,,..,,;...-: ____ .„..,..",,",...., ..... .,..,_.,...., ................ 500
Miscellaneous ..... ..... ____ ,',.,,-, ............... , ______ ..• ..... .,; ---- ____ ,,, ...... ., ....... . ............ 500
Subtotal ____ ...., ....... ... ..... . ....... . ..... . ..... ;...,:.;......,-,,,.;.-,,/., ..... ..,,; ................... 18,000
matetiafc "••,", . . . - ~ • •
.--;.. fl.-,, :,...".,. .;,....,..., ......... , . ,,..r + .. ';,'...';.,•.;,."»;;.',.......„... ....... . ............ 200
.Plumbing,-., . „, .„.;.; . .-. .,'. .-,_„.,-, ,.,.,,.-.,.,.,,......., ..... /«,,;,. ..... ..... ;;....'., .................... 300
' ',.-.;;.,,,,,,,...;.',-.- ..... ",,.,,..,.,,,, , 1. '..„.,.,,. ,,„; ;,.•, ', ',, :,.',_ ____ '.,".,,;,., .................. 500
,:. ...;«,.-'- •'•,•*>•'• '• ..... ____ "> ____ • ---- • ••". ;,f.-i '.'.,'•;._:'..•.--.... .,-," ......... -. ................. 500
., -. ;.,'-. -: . . ../.„.. '.-. .,..,., _____ ..... - ..... ...,,,. ,-.,I'.\ ,',.". : , „'.-.". ... ,;.•.', ..... .,: .................. 1,500
,e« *-. .'. .•.'...-..".,,.;..' ---- .. ---- . ......... „'•„ ..,-.;; »;, '. .','', .'....;.../ ........ : ..... . ............. 19,500
:,-. .', ... ;_:•. . .;<. . ,.;. .-.". .-,.:,.. :.. .v,;". ',-:•. ,-.,....,,., ....... - ................... 700
».- ..... -." ...... ,• .......... ,...'..,.'," .......... -..,.: ...... -. ................ (a)
.» 4 .....;....'....;.....,:.. ....... •. .......... ' .............................. 1 .1 70
.,;.,...".. ....... " ............... .'. , ........ .,/....'...', ..... . ................ 660
b, (& X «32Q)/imodulei X 0.6 yfS . , . . . . ...... - ...................................... 960
. , ., .". ................ '.;.,......,/;,..• ..................................... 500
Utilities,, et«e|rieityl0.048/lsV^f»> , . . ............. , ..... . ____ :,,.,'.,: ......... . ---- . , . . . ................... 510
totaJ.operatfng'cost- . , .;". .v, .".'."'. .»...,.-..• ..... « ......... , — ..»..,...,,..., .............. : ................ 4.500
AnnwaHwstl costs '( ., . .
Oefsmci«tion," 10% of Investment;, ,.:.",-,;;..,, ........ ,..,,-,.', ........ ; .".,-.. ..... - ....... , ....................... 1 ,950
T«3«ss'"9n«l'l4si*8r»ce» 196; ®f M^w^mtnt; ,-, . . i ............... ,". ..... .•.,,,.,,..',..... ^ ,..' ............. . ............ 200
•/Tot«t:fixe«l-«ast*, ''.•.,., J, '.;.,;,_,,;,;.',;...'..., ....... ...-.,. ...... . .......................................... 2,150
-,, . . '.-.\ ,.-,,,_,,.., ---- '....., ........ -, .......... ', ......... .' ...... .... .................. 6.650
5,6*0
1.590
2,520
1.810
11, 560
!^ ..... , — -. ..; .................. 4,910
W;««^-«^tfc^^;^ ,.,.,;.,,,>,....' ....... ' ........... 2,550
' '- ' '
1 3
4-500
54
-------
Figure 43.
Fixed-Bed Ion Exchanger System for Chromic Acid Recovery
Ion Exchange
In ion exchange, a chemical solution is
passed through a bed of resin, which
selectively removes either the posi-
tively charged cations (e.g., Cu+2, Fe+2)
or the negatively charged anions
(e.g., CrO^2, CN~) from the solution.
This removal is accomplished by the
exchange of an ionb from the sur-
face 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, the
economics of which are inversely
proportional to the chemical concen-
tration, ion exchange is ideally suited
for dilute solutions. The treated water
is of high purity.
A major drawback of ion exchange is
that the resin must be regenerated
after it has exhausted its exchange ca-
pacity. This problem complicates the
operation of the system considerably
and results in small volumes of wash
solution, which adds to the waste
treatment loading.
Figure 43 is a fixed-bed ion exchange
system used to recover chromic acid
from rinse waters. Initially, water
would pass in series through a cation
column and two anion columns. The
cation column is 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 sites, it is
taken off stream and regenerated with
a caustic solution. This column is then
returned to service as the down-
stream anion column.
bAn ion is a charged molecule; it is a cation if its
charge is positive, an anion if its charge is
negative.
55
-------
The product of the anion column
regeneration is sodium chromate and
any excess caustic used; it would be
passed directly to a second cation
column where the sodium ions would
be exchanged for hydrogen ions,
yielding chromic acid and water. This
solution can be returned to the plating
bath. Both cation columns are
regenerated with an acid solution
when saturated. The spent
regeneration solutions must be treated
in the neutralizer for pH adjustment
and precipitation of dissolved heavy
metals.
Two approaches have been used
to simplify the operation of ion ex-
change systems: the continuous ion
exchange column and the reciprocating
flow ion exchanger.
The continuous ion exchange column
(Figure 44) is a closed loop of
connected vessels providing
simultaneous ion exchange,
regeneration, back wash, and rinse
cycles in separate sections. This
design eliminates the need for multiple
columns and regeneration labor. It also
uses regeneration chemicals more
efficiently. The unit's automation,
however, makes its capital cost higher
than fixed-bed units and feasible only
for large volume treatment systems.
The reciprocating flow ion exchanger
(Figure 45) was especially developed
for purifying the bleed stream of a
large-volume solution, such as the
rinse overflow from an electroplater's
rinse tank. This unit operates on the
principle that for the short period of
time the unit goes off stream for
regeneration, the buildup of
contaminants in the rinse system is
negligible. Capital costs are
significantly lower for units of this
design than for fixed-bed units.
Moreover, because the units are
automated, they require only minimum
operator attention.
ffltt&t ry I i
-------
Electrodialysis
Electrodialysis (Figure 46) concen-
trates or separates ionic species
contained in a water solution. The
process is well established for purify-
ing brackish water, and recently has
been demonstrated for recovery of
metal salts from plating rinse. Compact
units suitable for this application have
been recovering metal values
successfully from rinse streams for
approximately 3 years. In addition, a
recent EPA demonstration project
confirmed the applicability of
electrodialysis for recovery of plating
solutions.
In electrodialysis, a water solution is
passed through alternately placed
cation permeable and anion permeable
membranes. An electrical potential is
applied across the membrane to
provide the motive force for the ion
migration. Essentially, these ion
selective membranes are thin sheets of
ion exchange resin reinforced by a
synthetic fiber backing.
Figure 45.
Reciprocating Flow Ion Exchanger Operating Cycle
57
-------
Table 17.
Economics of Reciprocating Flow Ion Exchange System for Chromic Acid Recovery, Operating 5,000 h/yr
Item
Cost
Installed cost ($):
Reciprocating flow ion exchanger, including cartridge fitter and three ten exchanger beds ............. . ........ ; . . 28,500
Pining ,.,....! .......... , ..... -, ,, ---- ' ............................. . ..... . ............................ 500
Miscellaneous ......... , ... . . ......... . ................... , ..... ,,,',,.,,.,... ... ...... , .............. SOO
S«t««ta». . . , ........... .,,.,,., ........................... , ......... ..... ,,.,,., ........................ 23,500
r»fl*fli|teriafc , " , ...•-
8^^,:A .".,,,, .,',,, '..',,., ,,,.;. . .', ................ .....,....,, ........ „,.„,,,,,,, ............ , . ;
•"•'"* ,»./."»".'. , '..i'.'.'/i';., .;....»-,..' ............. ,.,.,,,,.,-.-,..,., ^,, .\ ,.,..,.,.. .............. " •
e«e«fcat. I,-.,,...'.;.,..,,,, .-;• ........................ ,,,,.,.,.; ............. , ..... , ......... ..,.,,.,. MO
Miscellaneous . , , . , 4 , , , , . „'.-, ,,.,.,,. ...... , ........ . , .......... , , ....... ........ ...... ... ....... , ...... . 500
Subtotal ...... -, ........ .;,'..'!....,... ..... .... ........................... ..... ......... ... .............. 1-jQO '
Tota! irwWtecl cost .,,.....»,...;.,..,,,. ................. ; ................. , .', ..................... . , , . , 31 ,000
Annuaf operating eost ($/w|:
W»«, 100 h/yr at $7 .00/fc,,, ..,,,,.,,.,,,,.,,.,, ...... , .............. . .......... ............ ............... TOO
Su$»eJV»sio«. . : ---- ......,, ....... . _____ ,,,,,.,, .............. . ..... ........................ ......... ........ ' f j
Maintenance -------- ..... , ...... ,.;, ---- .,;,.., ..................... .-.,. ..... ,.,.,,,. ............ . ......... t,880
General plant overhead ____ . ,,. ____ ;,, ____ ...,., ......... ', ........... ,.,'. ..... , ............................. 800
Raw matewsls; ,'~- ...,.-.,','-'•.-
RepJ»«en»«nt'r«it»> ,..,.,.,..,.....,...',,,'.,. ............... .....,,,.,.,..,.,,.. ........ ...,,- ........... SOO
Raaentrtioft chewioate: ',.,;•"• •
NtOH ..... ,,'...-.',;..'.„' ____ . , , . , ............ ... ____ , , , , .......... ;'.»,., .'[ . .', ..................... ' 880
H2S04 .......... ' ........ .- ...... . .............. -. , ................ , ....... . J, .......... ............ 870
Utilities, compressed air ..... ..... ,.,,..., ......... ...... ...... , ....... . ......... -..,..'.............. ..... ... 200
Total operating cost ........ ... ...... , ................... ........ ........... ,..-.....,., ........ ............ 8,4tO
Annual fixed costs $8/yrj;
Depreciation, 10% ef investmf nt . , . , ...,.,,. y.- ............. , ...... , ........ ....,.:,. ,e,«». ',-;'. t, .. . ,. ............ . . 3,100
Taxas a«el iwswaftce, 1% of investteffrt ,..".,.'..•......... ...... ." ....... .,.,,-,.... ,:~.\'f., « ^,. ........... .......... . . • 310
Total fixed cost ____ , .............. . .-. ......................... , ....... i'. . . ,: . . '; ; ,-, ; , , ............... , ---- 3,410
Total cost of oj>w»t»on ... ....... ..,..,.,... ........ , . ,, ..... , . ....... ........... i .• ... M ,,..., ......... . ..... 8,82<3 ',
Annual savings {S/yrJs* '"..'. .'.',-•
Plating chemiealf* 2- Ibflt HjCri^. .,..,...,....,. ............ .... .......... ..... ;,..,.;,.. ... ................. 7,£?0
WatwttestfnwitchWRicalis. ...,...,-. ..-,,;,. . i. ,.....,.....,. .. ........... .,,.,...;.;.,,"..... ................ 4.S20
Sfutlfe dispos&t* .,.,-...,....'.;.'.;..'';,..,... ....... , ............. . ....... , ........ ,.;„„'/,.'.....,, .............. 2,880
Water use, 18 s?W* « $t.10/i,flpO 0al ............. . ......................... ...... ... , , ..................... 100
Total annuaJ savings .,".;.... ..... ........... .......... . .. , ...... , ........ ,..,;.-..•:;.,- ....... . . . . .......... 14.320
Net savings * annttJit sa«fc»g« — {9jp«fflt»Ra east •*• ftK8d cost) f$/yr| ............................ . ............. . ......... 5,500
Net sawinfts «ft* taxis, *8*t«i r««i (f/y4 ------- " ................... , ---- , ................ ;,..", .............. . ..... 2,860
Average RQ1* f««t |s»»b»|(s aft»* tgxes/ietff S»vest«n*nt} X 100 PS) ..... , ____ . ..... , ............ ..... .................. 9-2
Cash flow from investment * net savings after taics* •*• depreciation ($/y4 • . ................ . ..... . ............. • ....... 5.860
Payback, per»««t * tottJ iwest«»ntfciisS Ifow ^ .................. . ........... ,. ........ ,,..;.. ..... ... ............ 5.2
*Mort« required.
bFrom Tabte 10, based on a WM operating fa6t«>f.
58
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Figure 46.
Electrodialysis Unit Flow Schematic
The flow is directed through the
membrane in two hydraulic circuits—
one ion depleted, the other ion
concentrated. The flow rate through
each circuit can be set to achieve the
high level of concentration required for
returning the plating chemicals to the
plating bath. The degree of purifi-
cation achieved in the diluting circuit is
set by the electrical potential passed
across the membrane. The ability to
pass the charge is proportional to the
concentration of ionic species in the
dilution stream. Because ion migration
is proportional to electrical potential,
the optimum system is a trade-off.
The recent EPA demonstration project
tested the applicability of an
electrodialysis unit to recover nickel
from rinse waters for reuse in the
plating bath. Operation of the system
diagramed in Figure 47 began in
September 1975 and continued until
June of 1976, with no significant
operating problems. Table 18 itemizes
the cost of the demonstration unit and
the operating advantages attributable
to the unit.
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. Their cost is
approximately $25,000.
59
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Clarifier/thickener with sludge holding tank
Figure 47.
Electrodialysis Unit for Nickel Plating Drag-Out Recovery
60
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Table 18.
Economics of Electrodialysis System for Nickel Plating Solution Recovery, Operating 5,000 h/yr
item
Cost
Installed cost ($):
Equipment: „
Electrodiatysis unit, complete with cartridge filter strainer afttf electrode rinse system ..,.., ,,,,.,%., Y.. 1.',,,, ,\ t§,,000
Piping , , , ....",„,.,...,".,_,.«,,...,..,,.,., .».,.,..,, , ~§SO
Miscellaneous , ,.,....,, ^~".,,,. tf»«, , »,...,,,.,",,.;......,. * 800
Subtotal , ,,..,...,,...,..,,,»,» ., ..,,.,. ^,.,1
Installation, labor and materia.1: ' • • „ ' " •
Site preparation , ,„..,,.,,.,,..,,,,',., ..,.,,.,..,,»,,.,...,,. i,. 200
Plumbing , , , ,,..»,, ,,,»,»...4,.»,,..Jj,.-/,»
Electrical..., ,..,,.....,.,,.....,.,.,,,.,.,,,.....,, > ....,,,. ,..S • 800
Miscellaneous ..., , .,,.., ,*,....... .,...,,...,,..,,,»,,,.,,,"",,„,,,,,,"
Subtotal.. , ,,,v ,.,.•.,. ,,..,.,,,..,„,,,,.,,?,„,, , :^J
Total installed cost , ..„.,„,.,<» »,", ,.,.,..«.*."^, ,."';, ,
Annual operating cost ($/yr): - .' v
Labor, 100 h/yr at $7, OQ/h., .',,.',.»..'.'.'.'..".'. .'.V^', '.V'.,""^". ^'.1«,,,.'.......".'.,. .^V»,"«'^^ ,17.^,', '.~L-' '
Supervisor ....,..,..,,...,,...*,,,.._,,......»,» ,"., >„»•...,»,,,',,...,.,..,",,.».,,.,...,. {^
Maintenance — ..,..,...,.....,,....,.;„,»».,..,.,j^>,..... .,,.,. »,, ....,4 .,i.S-r. „, V t^O -
General plant overhead.,..,,,..,,...."...., .»'..,„., ,JT,-»., ,^,.,.'....,,,, ^. »'...,,-.,,,.»*.»,I,- .,,, > ?§Q
Raw materials...-.,.. ,,.,.,.,.... ...... lt....«,.,,..-,.»,.,,,.,«,w.,,......,,,..„„,.„.-.,,.«».,,,!»%".j "*"-
Filter cartridge's .....'. —,..,..,...,........«...,. ,,£, ,..,.,<%., ,.,,..,.».,..,,.. f.,,../,,, •' 780
Replacement membranes ,.,.».,>, ,\^i,. ,',•.....'..,.,.... .»,'„,,...-.,, nf.,.. ,s»,.', ,. ®6lO
UtHWes, electricity J0.046/kVWi) ,..-..,..„..„.., v ,1 „,„,«..., ,,..,..,,.,..,,., ^ ^,%', .,, . 2M
Total operating cost..... r.,.,.,.» „., ,...», .,...,>.,,,. t.,,,» »,..,,,.,.,,.,.,,,_,,x„,_. t.,".., ^, ' 4,350
Annual fixed costs ($/yrJ:
Depreciation, 10% of investment..,.,>...,,,.,.,...., ,^.,.,..,,.,, ,. «...,..........»,,(.- - 2,?SO
Taxes and insurance, 1% of investment ...,,...,....,.,.. -:....... ..,..,, s.,«..,,.,, 280
Total fixed costs ,.,..,....,.,,, .«....» .,., ,.....,,, ,,.,,,...».,, ~" 3,030
Total cost of operation » ., ,, , , ;„ • 7^80
Annual savings ($/yr):b
Plating chemicals, 3.8 Ib/h WS04 ,.,,, . ..,.,...,,.. , I3.2SO
Water treatment chemicals... ,„.,..., ,..,..,,., ...»,.,< • „ 4,880
Sludge disposal cost....,..,. ,, ,,, , ...,,.,,,.,,, t,,,..,... 2,960
Water use (no saving) ,.» ,..,.,.,. ,..,,.,„, ...».,.,,«,,...,.j...',«-. ^ »~
Total annual savings °. .,.,,,,..... , ,.,,..,.....,, + ,,...,,. 21,090
Net savings «* annual ^aytegs — (operating cost + 8x*d cost) <$/y>) ,.....,.,,.. ,.,...'. , , *„ ° 13,710
Net savings after taxes, 48% tax «te <$/yf) . ,4J,.,..,,,..,..».,..,..».... ..- ,... ,t........ >,.,,,«, ?,130
Average ROI =» (net savings after taxes/total investment) X tOO |%>, .•.,.-.,..*.. , >, ...<,.....,.>' 28
Cash flow from investmfnt * net savings after tmss •*• tteprewatteft ($/yr) ...,.,,.... ^.,,.,,,. , i ,...„, ' 9,880
Payback period« total investnwnt/ca^hflow(yr)....t, .,.,<,.,,..,.,.,.,;...»..« .*.,.,,.,,,,,.,,,,.,,,»«,.:»,* ' 2.8
"None required. -*
"From Table 10, based on a WW operating fsoaw.
61
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Effluent pH adjustment system for 200-gal/min design flowrate
62
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6. EPA's Research and
Development Programs
General
Programs to develop pollution control
technologies that can reduce the
operating and sludge disposal costs for
treating metal finishing wastewater are
being conducted by the Metals and
Inorganic Chemicals Branch of EPA's
Industrial Environmental Research
Laboratory in Cincinnati, Ohio, in
cooperation with industry, vendors,
and industrial associations. This
section will cover briefly some of these
programs.
Donnan Dialysis
Donnan dialysis is a membrane
separation process similar to reverse
osmosis or electrodialysis (discussed
in Section 5). The driving force used in
Donnan dialysis is a result of con-
centration differences across the
membrane as opposed to a pressure or
electrical potential differential. The
wastewater solution containing metal
ions (e.g., nickel) passes through the
inside of small diameter tubes
fabricated from a cation exchange
resin. A regenerant solution (e.g.,
dilute sulfuric acid) that will dissolve
the metal ion is passed overthe outside
of the tubes countercurrent to the
waste stream flow. The metal ions
migrate through the membrane and
concentrate in the acid solution. Tests
have shown that the metal ion con-
centration in the regenerant solution
can be increased to over 10 times the
original concentration in the waste
stream. Donnan dialysis can achieve
metal concentration of 1 ppm in the
treated water. The regenerant solution
can be returned directly to the plating
bath.
The advantage of Donnan dialysis over
reverse osmosis and electrodialysis is
lower energy use. A major disadvan-
tage of the system is that the regen-
erant solution will slightly acidify
the wastewater, and a useforthis water
must be found if neutralization and
discharge of the stream are to be
avoided.
Commercial application of Donnan
dialysis to metal recovery or
wastewater polishing has been
impeded by the lack of a stable ion
exchange membrane. A new resin
developed by Du Pont may provide a
cation exchange membrane of
exceptional chemical resistance and
good mechanical properties. A full-
scale prototype unit employing this
membrane is currently being tested for
nickel recovery from rinse waters under
an EPA grant.
Electrolytic Techniques
Electrolytic techniques can be used to
plate out dissolved metals, oxidize
cyanide, or reduce chromium from
wastewaters. Electrical power needed
to supply the current is the major
operating cost, and no chemical
treatment is required. The major
problem is that dilute solutions of
electrolytes have a high degree of
electrical resistance; consequently,
treatment of dilute waste streams
becomes prohibitive because of high
electricity costs. Recent investiga-
tions have, therefore, centered on
development of an electrolytic method
that could treat dilute solutions and
overcome the high electrical
resistance of the cell.
Two of the demonstration projects for
electrolytic processes nearmg
commercialization are discussed in the
paragraphs that follow.
New England Plating. EPA has
cooperated with New England Plating
to demonstrate an electrolytic system
that employs semiconductive beds of
carbon particles to reduce electrical
resistance. The full-scale plant
designed by Joseph Schockorfor New
England Plating achieves reduction of
chromium and oxidation of cyanide in
separate cells. Preliminary economics
indicate a cost advantage in this
system compared with costs for
chemical treatment for chromium
concentrations of approximately 1 50
ppm. Subsequent chemical treatment
of the cyanides was required to reach
effluent discharge limits.
63
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HSA Electrochemical Reactor on Electroless Nickel
Varland Metal Services. EPA, in
cooperation with the Metal Finishing
Foundation, is conducting a full-scale
demonstration of a carbon fiber
electrochemical system that is capable
of removal and recovery of heavy
metals with simultaneous cyanide
oxidation. The system—developed by
H.S.A. Reactors, Limited—has been
proven successful in recent pilot plant
tests. No sludge will result from the
process, and concentrated salts can be
recycled to the plating baths.
Insoluble Starch Xanthate
Insoluble starch xanthate (ISX) is a new
process developed by the U.S.
Department of Agriculture and
demonstrated in cooperation with
EPA. It removes heavy metals from the
wastewater to a fraction of 1 ppm. ISX
is made from commercial crosslinked
starch by reacting it with sodium
hydroxide and carbon disulfide.
Magnesium sulfate is also added to
give the product desired stability and
to improve the sludge settling rate. ISX
acts as an ion exchange material,
removing the heavy metal ions from the
wastewater and replacing them with
sodium and magnesium.
The treatment process generates a
significant amount of sludge (10
pounds of ISX are required to remove 1
pound of copper). The sludge settles
rapidly, however, and dewaters to 30
to 90 percent solids content when
filtered or centrifuged. The resulting
sludge is quite stable, and no leachate
problems are anticipated.
64
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The process is now in use at Clarostat,
a plating shop, to remove heavy metals
from the wastewater before discharge.
Metals can be recovered from ISX
sludge, but the process requires either
chemical treatment or incineration.
Currently, only gold is recovered from
ISX sludge.
Immiscible Organic Solvents
The use of immiscible organic solvents
for extraction of heavy metals from
waste effluents is gaining industrial
importance, particularly outside the
United States. In Sweden, four solvent
extraction processes have been
developed, and at least two are applied
in large treatment plants for recovery of
metals from industrial waste.
A prototype of a patented solvent-
based process for metal recovery was
demonstrated by EPA on a chrome
plating line. The system uses a two-
stage solvent spray rinse followed by a
single aqueous immersion rinse. The
metal value is extracted from the
solvent and returned to the plating
bath, and the solvent is recycled
continuously. The system has resulted
in significant savings in operating,
chemical, and watercosts. At this time,
the system is still in the pilot stage of
development.
Centralized Waste Treatment
The concept of centralized treatment is
one in which industrial metal finishers
in a regional area share the costs of
operation and construction of a waste
treatment plant to handle metal
finishing wastewater. Cost sharing is
based on volume, concentration, and
types of pollutants.
The major advantage of centralized
waste treatment is that the investment
required for a single large facility is
much less than that associated with
installing a treatment plant at each
company. Other advantages include
the ability to store and use selected
wastes as treatment reagents, waste
segregation that would facilitate
feasible resource recovery, ancf lower
sludge disposal and operating costs.
EPA recently evaluated a centralized
waste treatment plant in Western
Germany, and has initiated an
evaluation of the economic potentials
and applicability of this concept in the
United States.
65
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Bibliography
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.
"Current Prices of Chemicals and
Related Materials." Chemical
Marketing Reporter, passim, Feb. 20,
1978.
Eisenman, J. L. "Recovery of Nickel
from Plating Bath Rinse Waters by
Electrodialysis." Hanover MA, Micro-
Pore Research Co., undated.
Elicker, L. N., and R. W. Lacy.
Evaporative Recovery of Chromium
Plating Rinse Waters. Prepared by
Advance Plating Company, Cleveland
OH, and Corning Glass Works, Corning
NY, EPA Grant N.S. 803781. U.S.
Environmental Protection Agency, in
press.
Hartley, H. "Evaporative Recovery in
Electroplating." The Pfaudler
Company, Division of Sybron
Corporation, Rochester, NY, undated.
Brown and Caldwell, Lime Use in
Wastewater Treatment. NTIS Pub. No.
PB 248-1 81, Oct. 1975.
Mace, G. R., and D. Casabun. "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.
"Package Wastewater Treatment
Plants." Plant Engineering, 66-73,
Mar. 16, 1978.
Robinson, A. K. "Sulfide vs. Hydroxide
Precipitation of Heavy Metals from
Wastewater." Paper read at
EPA/American Electroplating Society
Conference, Jan. 17, 1978.
Spatz, D. Dean. Reclaiming Valuable
Metal Wastes. Minneapolis MN,
Osmosis Inc., undated.
Stinson, Mary K. Emerging
Technologies for Treatment of
Electroplating Wastewaters, Pre-
sented by EPA at 71 st Annual Meeting
of the American Institute for Chemical
Engineering, Nov. 15, 1978.
U.S. Environmental Protection
Agency. Development Document for
Proposed Existing Source Pretreat-
ment Standards for the Electroplating
Point Source Category. EPA 440/1 -
78/085, Feb. 1978.
. "Development Document for
Effluent Limitations Guidelines and
Standards of Performance for
Machinery and Mechanical Products
Manufacturing Point Source Category.
June 1975. (Draft)
. In Process Pollution
Abatement, Upgrading Metal
Finishing Facilities to Reduce
Pollution. EPA 625-3-73-002, July
1973.
. Waste Treatment, Upgrading
Metal Finishing Facilities to Reduce
Pollution. EPA 625/3-73-002, July
1973.
S. K. Williams Company, Wastewater
Treatment and Rinse in a Metal
Finishing Job Shop. NTIS Pub. No. PB-
234476, July 1974.
66
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Appendix A. Drag-Out
Recovery Cost Reduction
Worksheet
The worksheet is intended to lead the
user through the analysis required to
determine the potential cost reduction
achievable by recovery of plating
solution drag-out.
Table A-1 illustrates the procedure,
and Table A-2 is the worksheet with
blanks unfilled.
In the tables 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. Comparing the operating
cost associated with 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 modifi-
cations. Table 5 of this report shows a
cost analysis 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.
67
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Table A-1.
Worksheet Completion Procedure
A Plant conditions to be measured
1 Drag-out rate (gal/h)
2 Plating tank temperature (°F)
3 Plating tank air agitation rate (stdft3/mm)
4. Plating tank surface area (ft )
5 Number of rinse tanks
6 Dissolved solids concentration
7. Dissolved solids concentration
8. Plating solution composition
in plating tank (mg/l)
in final rinse (mg/l)
NiSO4 =
NiCl2 =
Bone acid =
1 5 gal/h
150° F
0
36ft2
4
260,000 mg/l
50 mg/l
1 66 Ib/gal
0 34 Ib/gal
0 40 Ib/gal
B Cost factors for each plant
1 Plating solution value ($/gal)
NiSO4 (1 66 Ib/gal X $1 21/lb)a =
NiCl2 (0 34 Ib/gal x $1 57/lb)a =
Bone acid (1 40 Ib/gal X $0 176/lb)b =
Total =
2 Water use and sewer changes
3 Energy cost for plating tank heaters
4 Annual operating hours
$2 01 /gal
$0 53/gal
$0 07/gal
$2 61 /gal
$1 10/1, 000 gal
$300/106Btu
3,600
68
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Table A-1.
Worksheet Completion Procedure—Concluded
C. Operating cost estimation for rinse and recycle system (Figure 31)
1 Surface evaporation rate (gal/h)c
(0 1 4 gal/h- ft2) X 36 ft2
2 Recycle rinse ratio (surface evaporation rate/drag-out rate) or (C 1/A 1)
3 Number of countercurrent rinse tanks in recovery rinse
4 Percent recovery of drag-out (from Figure 32)
5. Concentration of drag-out from recovery rinse (mg/l) Cr = 0 06 C (from Figure 32)
6 Number of countercurrent rinse tanks in final rinse
Cr 15,600
C, 50
8. Rinse ratio in final rinse (from Figure 27)
9 Rinse water requirements in final rinse; gal/h (rinse ratio
10 Drag-out chemical losses ($/h) (drag-out rate) X (plating
X (100 - percent recovery/100) or (A 1 X B.1) X [100
1 1. Rinse water use cost ($/h) (water use rate X cost factor)
X drag-out rate) or (C.8 X A.1)
solution value)
-(C 4/1 00)]
or (C.9 X 82)
1 2 Bath heating load due to surface evaporation, Btu/h, (5 04 gal/h) X (8,300 Btu/gal)d
13 Heating load cost ($/h) (C.12 X B 3)
14 Annual operating cost ($/yr) (C.10 + C. 11 + C 1 3) X B.4
504
336
2
94
15,600
2
312
18
27
$0 23/h
$0 035/h
4 1,800 Btu/h
$0 125/h
$l,404/yr
aFrom Table 10.
bFrom Table 1.
cFrom Figure 29 For aerated baths use Figure 28
dFrom page 36 For aerated baths use Figure 30
69
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Table A-2.
Cost Reduction Worksheet
A. Plant conditions to be measured
1 Drag-out rate (gal/h)
2. Plating tank temperature (°F)
3 Plating tank air agitation rate (stdft3/mm)
4 Plating tank surface area (ft2)
5 Number of rinse tanks
6 Dissolved sohds concentration in plating tank (mg/l)
7 Dissolved solids concentration in final rinse (mg/l)
8. Plating solution composition
B. Cost factors for each plant
1. Plating solution value ($/gal)
2 Water use and sewer changes
3 Energy cost for plating tank heaters
4 Annual operating hours
70
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Table A-2.
Cost Reduction Worksheet—Concluded
C Operating cost estimation for rinse and recycle system (Figure
1 Surface evaporation rate (gal/h)
2 Recycle rinse ratio (surface evaporation rate/drag-out rate]
31)
or (C.1 /A.1)
3. Number of countercurrent rinse tanks in recovery rinse
4 Percent recovery of drag-out (from Figure 32)
5 Concentration of drag-out from recovery rinse (mg/l)
(from Figure 32)
6. Number of countercurrent rinse tanks in final rinse
cr
7. Dilution ratio m final rinse — or (C.5/A.7)
Cf
8. Rinse ratio m final rinse (from Figure 27)
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 ($/h) (drag-out rate) X (plating solution value)
X (100 - percent recovery/100) or (A.1 X B 1) X [100 - (C.4/100))
1 1. Rinse water use cost ($/h) (water use rate X cost factor) or (C 9 X B 2)
12 Bath heating load due to surface evaporation (Btu/h)
1 3. Heating load cost ($/h) (C. 1 2 X B 3)
1 4. Annual operating cost ($/yr) (C.1 0 + C.1 1 + C 1 3) X B.4
71
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U.S. Environmental Protection Agency
legion 5, Library (5PL-16)
Dearborn Street, Room 1670
IL 60604
This report has been reviewed by the
Industrial Environmental Research
Laboratory, U.S. Environmental
Protection Agency, Cincinnati OH, and
approved for publication. Approval
does not signify that the contents
necessarily reflect the views and
policies of the U.S. Environmental
Protection Agency, nor does mention
of trade names or commercial products
constitute endorsement or recom-
mendation for use.
This economic control alternatives
report was prepared for the Industrial
Environmental Research Laboratory's
Metals and Inorganic Chemicals
Branch in Cincinnati OH. The Centec
Corporation, Fort Lauderdale FL,
prepared the report. The EPA Project
Officer is Mr. Ben Smith.
EPA wishes to thank Aqualogic® Inc.,
Bethany CT, for providing photographs
for the report.
72
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