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

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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

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Concentrated dump tank and modular cyanide oxidation and
neutralization/flocculation  units

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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

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Pretreatment, neutralization, and flocculation tanks with  clarifier/thickener

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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.

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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.^-
          ^

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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.

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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

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 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

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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.

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                                                                          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

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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.

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Figure 5.
Installed Cost for Flocculation/Clarification System
Figure 6.
Installed Cost for Sludge Storage/Thickening Tank

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                                                                           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

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 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

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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

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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

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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

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                                       Precipitation (NaOH)
                                      ft» 
-------
                                   Figure 13.
                                   Electroplating Wastewater Treatment Flow Chart: Example System
16

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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

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                                           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

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                                                                                                    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

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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

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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

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                                                                                  $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

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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

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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

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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

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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

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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

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       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
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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

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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

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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

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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

-------
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

-------
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.
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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
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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














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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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