United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/087 August 1995
vvEPA Project Summary
Chromate Recovery from
Chromating Rinsewater in the
Metal-Finishing Industry
Arun R. Gavaskar, Robert F. Olfenbuttel, and Eric H. Drescher
The recovery system evaluated in this
study combines various aspects of
vacuum evaporation and flash distilla-
tion. It provides a continuous supply of
good quality rinsewater to the
chromating line at the Quality Rolling
and Dehurring Co. (QRD). Recircula-
tion prevents nearly 450,000 gal of wa-
ter from going to waste every year.
Contaminants removed from the circu-
lating water include chromium, zinc,
and other dissolved solids. Contami-
nants are concentrated in a tiny waste
stream (one 55-gal drum) and disposed
of. Because QRD uses three different
chromate formulations on a single
chromating line, this concentrate could
not be reused. At plants that use a
single formulation, reuse should be
possible. Because wastewater (requir-
ing treatment) is not generated, the re-
covery system reduces operating costs.
At QRD, the return on investment was
sufficient for the initial capital outlay to
be recovered in approximately 4 yr.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Cincinnati, OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).
Introduction
The goal of the U.S. Environmental Pro-
tection Agency's (EPA) 33/50 Program is
to promote voluntary reductions in the re-
lease of hazardous chemicals by 33% by
the end of 1992 and by 50% by the end of
1995. One objective of the EPA 33/50
Program is to evaluate, in a typical work-
place environment, examples of prototype
or innovative commercial technologies that
have potential for pollution prevention.
Support for this program also was pro-
vided by the Connecticut Hazardous Waste
Management Service (CHWMS). The goal
of this study was to evaluate the techni-
cal, pollution prevention, and economic
issues involved in using a recovery sys-
tem to recover the rinsewater from the
chromating line in a metal finishing plant.
Chromium is a hazardous metal targeted
for early reduction under the EPA's 33/50
Program. The recovery unit tested was
manufactured and provided by Cellini Pu-
rification Systems, Inc.1 Similar units with
varying capabilities may be available from
other vendors.
The site for the testing was QRD Co., a
medium-size metal finishing plant, in
Thomaston, CT. QRD has operated the
chromating line with the recovery system
for about 1 yr. The recovery system con-
figuration at QRD is shown in Figure!
QRD uses three different chromate for-
mulations — blue, clear, and yellow — on
the chromating line. The chromating line
receives a variety of parts (from QRD's
customers) that first are zinc-plated and
then chromated.
Contamination accumulates mainly in
the Rinse 1 Tank, which functions as a
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use.
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From
Zn Electroplating
From Mechanical
Zn Plating
Still
Bottoms
Rinse 1 Rinse 2
"Ciear'A \Water
Chromate
Tank
Purge Water |
Recapture i
Sump \---*--'
Tank
Cooling \ 500 gal
Tower
Sample
Port
Water Recycle Line
Figure 1. Chromating rinsewater recovery system. (Sampling locations marked by an asterisk.)
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dragout rinse. This contaminated water is
processed through the recovery unit at an
average rate of 1 gal/min. The water is
first drawn into the recovery unit still. The
contents of the still are recirculated through
a steam heat exchanger and a spray
nozzle back into the column of the still.
The water is heated to 110°F before it
goes through the spray nozzle and is flash-
distilled under vacuum. In the column, the
down-flowing liquid returns to the bottom
of the still and the distillate vapor rises
upward and is later condensed by a wa-
ter-cooled condenser. The condensate is
stored in a small side tank, from which it
is returned periodically by level control to
the Rinse 2 Tank, which is the clean, final
rinse. The recovery system is fully auto-
mated and integrated into the chromating
line and requires very little operator atten-
tion.
The chromating line operates for 1 shift/
day, but the recovery unit remains on
24 hr/day so that the rinsewater gets ad-
ditional cleaning after the contaminant con-
tribution from the chromating line stops.
Approximately 50 gal/day of fresh tap wa-
ter is added into the Rinse 2 Tank to
make up for evaporative losses. Once ev-
ery 3 or 4 wk, the still bottoms are evacu-
ated into the sump tank. The sump tank
also stores the rinsate generated when
the chromate lines are purged before a
formulation switch. When the sump tank
is full, QRD plans to process its contents
through the recovery unit and concentrate
it down to around 55 gal. This 55 gal of
concentrate containing chromates can be
either reused or disposed of as hazard-
ous waste. QRD does not reuse it be-
cause it contains a mixture of three differ-
ent chromate formulations. Other plants
that use only a single formulation may be
able to reuse the concentrate.
Testing was conducted over one shift
(6 hr of continuous chromating line opera-
tion) and on the following morning before
the next day's shift. Samples were col-
lected periodically from the locations
shown by asterisks in Figure 1.
Product Quality Evaluation
Rinsewater quality was monitored
throughout the shift, and the results are
shown in Table 1. Water quality in Rinse
1 continues to deteriorate as the contribu-
tion from the dragout increases. Contami-
nation in the Rinse 2 Tank is maintained
at very low levels by the periodic influx of
clean processed water from the recovery
unit. As the Rinse 2 Tank gets full, some
water is transferred manually into Rinse 1
to simulate a countercurrent flow through
the rinses. Overnight processing, while the
chromating line is not operating, helps to
reduce contamination further, as observed
in the 8:00 a.m. sample collected the next
morning. Plants that operate the
chromating line three shifts per day will
not have the benefit of this additional over-
night processing, and contaminants may
accumulate to levels slightly higher than
those shown for Rinse 2 in Table 1, until
an equilibrium state is reached.
Processed water coming out of the re-
covery unit (before it reaches the Rinse 2
Tank) was also sampled and analyzed
(Table 2). A tap water sample was col-
lected and analyzed for comparison. The
recovery unit reduced contamination of
chromium and zinc in the processed wa-
ter to levels slightly above levels in the
fresh (tap) water supply. Because tap wa-
ter at QRD normally is high in dissolved
solids, the recovery unit was able to re-
duce the total dissolved solids (TDS) level
to below that in the tap water. Small
amounts of acidic components in the chro-
mate solution transfer over into the distil-
late as seen from the low pH of the
processed water. This, in turn, progres-
sively reduces the pH in the Rinse 2 Tank
(Table 1). The low pH is not a concern in
this operation.
Table 3 shows the characterization of
the still bottoms and the chromate solu-
tions. The contaminants that are removed
from the rinsewater can be noticed accu-
mulating in the still bottoms. From this
table, it can be seen that if the still bot-
toms materials is concentrated further, the
chromate concentrations would ultimately
reach those in the chromate tanks. If only
one formulation were being used, the final
concentrate could have been returned to
the chromate tanks. Zinc and dissolved
solids levels in the still bottoms are still
relatively low to be of concern during re-
use.
Pollution Prevention Evaluation
Without the recovery system, QRD
would maintain a continuous 5 gal/min
flow of fresh water to Rinse 2 (clean final
rinse). The overspray in Rinse 2 would be
collected and sprayed in Rinse 1 (dragout).
After Rinse 1, the water would be taken to
the on-site wastewater treatment plant.
For one 6-hr shift/day, 5 days/wk, 50 wk/
yr operation, 450,000 gal of wastewater
Table 1. Water Quality in Rinse Tanks
Sample No.
Rinse 1 Tank
W-R1-1
W-R1-2
W-R1-3
W-R1-4
W-R1-5
W-R1-6
Rinse 2 Tank
W-R2-1
W-R2-2
W-R2-3
W-R2-4
W-R2-5
W-R2-6
Time
9:30 a.m.
11:00 a.m.
12:30 p.m.
2:00 p.m.
3:30 p.m.
8:00 a.m.?
9:30 a.m.
11:00 a.m.
12:30 p.m.
2:00 p.m.
3:30 p.m.
8:00 a.m.?
Cr
mg/L
2.57
12.0
29.5
14.6
24.7
8.91
0.21
0.435
0.589
0.843
1.35
0.593
Zn
mg/L
4.5
23.5
61.0
32.5
53.2
26.1
0.4
1.15
1.50
3.28
3.97
2.42
TDS*
mg/L
48
162
372
273
374
196
42220
174
141
119
88
28
Cond.
nmhos/cm
60
200
475
340
450
312
190
180
160
130
55
pH
4.39
4.20
4.08
4.30
4.14
4.46
280 6.47
7.11
6.85
5.22
4.56
3.90
* Total dissolved solids.
Next day.
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Table 2. Processed Water Quality
Sample No.
W-PW-1
W-PW-2
W-PW-3
W-PW-4
W-PW-5
W-TW-lt
Time
9:30 a.m.
11:00 a.m.
12:30 p.m.
2:00 p.m.
3:30 p.m.
12:30 p.m.
Cr
mg/L
0.235
0.348
0.437
0.445
0.482
0.079
Zn
mg/L
0.338
0.592
0.793
0.796
0.870
0.291
TDS*
mg/L
30
32
42
31
9
250
Cond.
^mhos/cm
55
60
80
80
80
400
pH
3.88
3.76
3.63
3.68
3.71
6.39
* Total dissolved solids.
Field blank consisting of tap water supply at QRD.
Table 3. Characterization of Distillation Still Bottoms and Chromate Tanks
Sample No.
Still Bottoms
C-SB-1
C-SB-2
C-SB-3
C-SB-4
Chromate Tanks
Blue
Yellow
Clear
Time
9:30 a.m.
12:30 p.m.
3:30 p.m.
8:00 a.m.?
2:00 p.m.
2:00 p.m.
2:00 p.m.
Cr
mg/L
162
168
216
224
1,254
1,471
3,860
Zn
mg/L
258
277
385
420
1,739
15
0.743
TDS*
mg/L
2,280
2,240
3,170
3,610
16,740
3,590
25,110
Cond.
^mhos/cm
2,700
2,500
3,200
4,000
12,000
15,000
28,000
pH
3.52
3.59
3.80
3.95
2.57
1.55
2.87
Next day.
Total dissolved solids.
(requiring treatment) would be generated
annually. Not only would QRD have to
accommodate this new influx of wastewa-
ter; the sludge generated in their treat-
ment plant would have to be handled and
disposed of as hazardous waste because
of the presence of chromium. By using
the recovery system, QRD not only saves
nearly 450,000 gal of water, but also pre-
vents the creation of a large, new, haz-
ardous waste stream. Instead, it generates
only about four drums of still bottoms con-
centrate that has to be disposed of. This
waste concentrate can be avoided through
reuse by plants that use only one formula-
tion. QRD adds approximately 50 gal of
fresh water to the Rinse 2 Tank daily to
make up for evaporative losses in the
system.
Economic Evaluation
Table 4 lists the major costs of operat-
ing with and without the recovery system.
The recovery unit provides a savings in
annual operating costs of $23,082. QRD's
recovery unit cost $78,000 with an addi-
tional $9,000 cost for installation and aux-
iliary equipment (such as cooling tower,
piping, etc.). A payback period of 4 yrwas
estimated at QRD for the investment.
Conclusions
The recovery system at QRD prevents
the generation of large volumes of waste-
water and hazardous sludge that other-
wise would result from the chromating
operation. Further pollution prevention
would be possible at plants that use only
one formulation, through potential reuse
of the chromium contained in the still bot-
toms concentrate. Rinsewater quality is
maintained at acceptable levels through-
out the shift without adding large volumes
of fresh water. By eliminating wastewater
treatment costs, considerable savings are
realized at QRD that result in a reason-
able payback period.
This system has potential for use in
many applications that generate waste-
water. One concern is the relatively high
energy (steam) consumption of the recov-
ery unit. Future versions of this system
are focusing on reducing this energy re-
quirement.
The full report was submitted in fulfill-
ment of Contract No. 68-CO-0003, Work
Assignment No. 3-36, by Battelle under
the sponsorship of the U.S. Environmen-
tal Protection Agency.
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Table 4. Major Operation Costs Comparison
Item
Annual Amount
Without Recovery System
Water (rinse)
Wastewater treatment
450,000 gal
450,000 gal
With Recovery System
Water (rinse, makeup)
Water (cooling, makeup)
Waste disposal
Energy
- electricity
- steam
Maintenance
Labor
12,500 gal
12,500 gal
55 gal
60,950 kW hr
3,000,000 Ib
100hr
Unit Cost, $
Annual Cost, $
4.65/1,000 gal
88.00/1,000 gal
TOTAL
4.65/1,000 gal
4.65/1,000 gal
350.00/55 gal
0.068/kW hr
0.004/lb
8.00/hr
TOTAL
2,093
39,600
41,693
58
58
350
4,145
12,000
1,200
800
18,611
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Arun R. Gavaskar, Robert F. Olfenbuttel, and Eric H. Drescher are with
Battelle, Columbus, OH 43201.
Lisa Brown is the EPA Project Officer (see below).
The complete report, entitled "Chromate Recovery from Chromating
Rinsewaterin the Metal-Finishing Industry,"(OrderNo. PB95-243044;
Cost: $17.50, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
National Risk Management Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection Agency
National Risk Management Research Laboratory (G-72)
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-95/087
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