United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-122 Jan. 1984
Project Summary
Electroplating Plant Operating
Conditions Related to
Wastewater Sludge Leachability
A. Procko, E. Handel, and M. Moskowitz
The objective of this project was to
characterize the operating variables and
wastewater sludges from six
electroplating plants conducting a wide
variety of plating operations so that the
information developed would be
applicable on an industry-wide basis.
The results of the study in which
untreated wastewaters were collected
from each of six AES member plants,
chemically treated to provide solid
waste sludges are presented. The solids
were separated, and the effluents
analyzed for hazardous metals. All of
the sludges were subjected to the
ASTM "Method A" extraction
procedure and hazardous metals
analyses were conducted on the
leachate. During the study, the EPA
Extraction Procedure (EPA-EP) was
distributed nationally. As the EPA-EP
was one test of the hazardous
properties of electroplating sludges
under the Resource Conservation and
Recovery Act (RCRA), the EPA-
EP tests, rather than the ASTM Method
A extraction procedure, were replicated
for the six plants. All tests, chemical
treatment, pH, separation, sludges
generation, and extraction procedures
were replicated. An in-depth statistical
study was also performed of the analyt-
ical data for which sufficient
information was available.
This Project Summary was developed
by EPA's Industrial Environmental
Research Laboratory. Cincinnati, OH.
to announce key findings of the
research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Background
An earlier study,* from which the
current study developed, thoroughly
investigated the wastewaters and
attendant sludges from 12 electroplating
shops. To utilize the data generated from
the earlier study, six of the participating
plating shops were selected for this
current project. Selection was based on
the variety of metals utilized, the
wastewater treatment system, and the
leaching characteristics of the plants'
sludge. The presence of cadmium in the
plants' wastewater was highly desirable
as cadmium appears to be a problem with
regard to its leaching characteristics. The
facilities selected for this study showed
significant quantities of cadmium,
chromium, nickel, zinc, copper, and
aluminum present in their wastewater
and sludge. Two additional selection
factors included: 1) good cooperation
from plant management, and 2) the
plants' sludge had U.S. Environmental
Protection Agency - Extraction Procedures
(EPA-EP) extract levels above the haz-
ardous limits. This last factor was con-
sidered to demonstrate the benefits of the
current project, if indeed, the sludges
could be rendered nonhazardous by EPA's
definition.
Approach
The purpose of the overall test program
was to determine the effect of
wastewater treatment chemicals and the
pH on the leaching characteristics of
"Meredith, J. W., J. A. McCarthy, and A. Procko.
Electroplating Wastewater Sludge Characterization.
EPA-600/2-81-064, U.S. Environmental Protection
Agency, Cincinnati, Ohio, May 1981.
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sludges generated. The effect of the
treatment chemicals on the dewaterabil-
ity of the sludges by filtering and
centrifuging was also to be determined.
As a means to accomplish these goals, a
detailed test plan was prepared that
covered: (1) wastewater preparation; (2)
simulation of the plant treatment; (3)
screening tests; (4) dewatering tests; and
(5) analysis. Screening tests were to be
performed to determine the combination
of precipitation chemical and pH which
would produce a sludge with the best
leaching characteristics without
reducing effluent quality. Dewatering of
the sludge produced by each treatment
chemical followed, utilizing the pH value
at which each chemical performed best
during the screening tests.
Screening tests were conducted to
determine the relationship between
treatment chemical and pH on the treat-
ment system effluent and on the extract
from the sludges produced. The method
utilized to achieve these goals was to take
actual untreated electroplating waste-
waters and treat them with three
common neutralization chemicals: sodi-
um hydroxide (NaOH), soda ash (Na2CO3)
and lime (CaO). Tests were conducted
with each of these chemicals on the
untreated plant wastewater with pH's
adjusted to 8.5 and 10 (7, 8.5, and 10 for
Plant 7). The wastewater was treated in
a manner similar to the plants' treatment
system (except for the change in
chemicals and pH) so that the plants
could easily implement any recommend-
ed changes. Individual waste streams
were m ixed i n the proper proportions, and
kept agitated while pH was adjusted.
Appropriate retention times were used,
and after flocculation the mixture was
allowed to settle. The water layer
(overflow) was decanted and analyzed for
its metal content and the sludge layer
(underflow) was vacuum filtered. An
analysis of the filtrate for metals was
performed for comparison to the plant
effluent. The sludge cake was then sub-
jected to the American Society for Testing
and Materials Method "A", extraction
procedures (ASTM-A) and EPA-EP, the
extract of which was also analyzed for
metals (Figure 1).
To study the leaching characteristics of
the screening test sludges, a portion of
each sludge after filtering was washed in
a filter funnel with 200 ml of deionized
water and again vacuum filtered and the
sludge subjected to the ASTM-A and
EPA-EP. The washing water was also
analyzed for metals.
Combined
Untreated
Wastewater
CaO. NaOH.
or Na2CO3
pH Adjustment
Flocculant
Addition
Settling
Vacuum
Filter
Interstitial
Water
J_L
Filtrate
Wash
Figure 1, Test program and analytical plan.
Results
For Plant 2, at pH 10.0 more than 98
percent of the cadmium had been
removed by treatment. Chromium and
zinc were removed from the effluent with
a 99+ percent efficiency. At this pH, CaO
showed the lowest metal levels in the
effluent, although the difference is
slight and although the metals did not
resolubilize and leach out during the
ASTM-A procedure, the lower pH of the
EPA-EP caused Plant 2 to fail the EPA-EP
based on cadmium levels. Results of the
EPA-EP at pH 8.5 showed lower metal
levels, but failed to pass the EPA-EP test.
The chromium extract also failed the first
time, but passed during the replication
phase. Chromium levels in the effluent
and EPA-EP extract were not affected
very much by pH or chemical, except
when Na2C03 was used. With Na2C03,
chromium was an order of magnitude
higher in the EPA-EP extract.
A similar analysis for Plant 3 shows
cadmium and chromium removal
efficiencies of 91 and 68 percent, respec-
tively, at pH 8.5. At pH 10, cadmium and
chromium removal efficiencies were 93
percent and 56 percent. At either pH, the
plant's sludge failed the EPA-EP based on
cadmium. However, cadmium performed
very well during the ASTM-A procedure
by not resolubilizing and leaching out, as
chromium did. Chromium levels in the
plant effluent were more affected by pH
than by chemical, while cadmium was
affected by both. Results of the EPA-EP
testing showed 1000 times higher levels
of cadmium to be present than did results
of the ASTM-A. Chromium levels did not
vary with the two tests a nd appeared to be
independent of chemical, and only
slightly dependent on pH.
For Plant 4, at pH 10 chromium was
removed from the effluent with an 81-
percent efficiency, copper was removed
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with 84-percent efficiency, and nickel
was reduced by 85 percent. Although
CaO did not show a clear superiority with
the effluent samples, it was most clearly
the best overall performer for the EPA-EP
and ASTM-A testing. Plant 4 was one of
two plants that would have passed the
EPA-EP based on these screening tests
At a treatment pH of 10, metal levels in
the plant effluent and EPA-EP extracts
were always lower when using CaO.
Although the metals did not resolubilize
and leach out during the ASTM-A proce-
dure, the lower pH of the EPA-EP caused
considerably higher metals levels in the
extract. Metal levels were higher by two
orders of magnitude in some cases.
For Plant 6, at pH 8.5 chromium was
reduced by 99 percent and nickel by 97
percent in the plant effluent. Chrome in
the untreated wastewater was 21/2 times
higher than nickel, although this
difference was not evident in the plant
effluent. Results of the ASTM-A on the
plant sludges showed no significant
leaching for either chromium or nickel.
During the EPA-EP greater quantities of
metals were seen to leach in some cases
by as much as 100-fold. The plant's
sludge did not consistently pass the EPA-
EP. During the first series of tests, all
sludge samples passed. However, at pH
8.5 two samples failed during the repli-
cation, based on chromium. Best results
for the EPA-EP were obtained with treat-
ment at pH 10.
For Plant 7, at pH 8.5 more than 97
percent of the cadmium had been
removed by treatment. It is also evident
that the cadmium had not resolubilized
and leached out of the sludge during the
ASTM-A procedure. Copper was removed
from the effluent at approximately a 95-
percent efficiency. With the exception of
the lime test at pH 10, the copper found in
the ASTM-A extract did not resolubilize to
a large extent. The exception noted
leached at a concentration three to four
times higher than the copper
concentration in the untreated water.
Chromium, nickel, and zinc were present
in much higher quantities in the untreat-
ed wastewater than were cadmium and
copper. Chromium was removed from the
water at approximately a 98-percent
efficiency regardless of chemical or pH.
The quantity leached, as measured by the
ASTM-A extraction procedure, tended to
decrease as the pH of the treatment
increased. The removal of nickel from the
wastewater is very obviously dependent
on pH and only slightly dependent on
treatment, chemical with NaOH
performing somewhat more effectively
than CaO or Na2C03 as pH increased.
Removal rates were approximately 90
percent at pH 8.5. Nickel levels in the
sludge leachate were affected by both pH
and treatment chemical. At a treatment
pH of 10 both the CaO and NaOH
generated sludges leached very high
levels of nickel while the Na2CO3 sludge
leached less by a factor of 10. Zinc
removal from the wastewate.r
approached 98 percent with little
difference between chemicals and with
minimal pH effects. Sludge leaching test
results varied with respect to treatment
chemicals.
During the screening tests for Plant 7,
the EPA-EP was not performed. Instead, a
series of leaching tests were performed
on larger batch samples prepared at the
pH value which gave best results with
each treatment chemical during the
screening tests. In the leaching tests, as
with the screening tests for this plant,
none of the metals seemed to resolubilize
and leach out of the sludge during the
ASTM-A procedure. Metal levels in the
EPA-EP were generally higher than the
ASTM results.
In order to derive a measure of the
statistical significance of these Plant 7
large batch test results, the ASTM
procedure was applied to washed sludge
precipitated by each of the three
chemicals a total of three times. This
replication provided the ability to
calculate the experimental variation due
to chance alone. The test for statistical
significance is based on the ratio of the
variation in leachate concentration (for
each metal) from one treatment chemical
to another to the variation due to chance
(the F-statistic). Any observed
dependence on treatment chemical is
significant if this ratio is large enough.
A one-way analysis of variance was
performed based on the results. There
were significant results at the 99-percent
level. The dependence of nickel concen-
tration in the leachate on the treatment
chemical was signf icant at the 95-percent
level.
Results for Plant 8 at pH 8.5 indicate
that chromium was removed by 96
percent, copper by 97 percent, and nickel
by 96 percent from the untreated
wastewater. The plant effluent results
were best when using CaO. The use of
NazCOs always gave higher metal con-
centrations in the effluent by at least
tenfold over the CaO results. The ASTM-
A procedure did not cause the metals to
resolubilize and leach out as did the EPA-
EP. The sludge from this plant failed the
EPA-EP on the basis of chromium.
Although the sludge would still have
failed the EPA-EP, less chromium leach-
ing occurred when treatment was with
Na2C03. If nickel were to be considered a
hazardous material under RCRA, the use
of Na2CO3 for treatment would need to be
more thoroughly investigated as it works
better for some metals than for others.
It should be remembered that direct
comparisons between the EPA and the
ASTM-A extraction procedures are not
possible due to the differences in the
amount of dilution water used in the
respective tests. In the tests done during
this part of the study, the EPA-EP extracts
had a much higher water-to-solids ratio
than the ASTM-A tests.
The analytical results of plant effluent
and sludge filtrate show that the sludge's
interstitial water (filtrate) had metal
levels lower than the effluent. The
kinetics of the precipitation reaction, are
initially rapid, but very slow to reach
equilibrium - the point at which
precipitation essentially stops. The
interstitial waters are in direct contact
with the sludge particles for a longertime
than the effluent waters and therefore
have more opportunities to take
advantage of nucleation sites for
precipitation. The net result is a lower
level of metals in the interstitial water.
This theory is reinforced by the observa-
tion that the filtrate from the washed
sludges had metal levels lower than the
filtrate from unwashed sludge. It is
assumed that equilibrium had not yet
been reached.
An unexpected observation was that
for most cases cadmium and zinc levels in
the EPA-EP extract were higher with the
washed sludges than with the unwashed
sludges. Chromium and nickel levels
were generally lower in the EPA-EP
extract of the washed sludge than in the
unwashed sludges. It has been assumed
that washing with deionized water would
flush out the high metal levels expected
to be found in the interstitial water.
Similar mixed results were obtained for
washed and unwashed sludges during
the ASTM-A extraction where pH was not
maintained. This seemed to indicate that
this phenomenon was not pH related. It
was apparent that washing sludges had
no benefit from a teachability standpoint,
and may actually have caused higher
leaching if the sludge contained
cadmium.
Certain observations appeared for one
plant but could not be broadly applied to
others in this study. An example of this
comes from Plant 7. In every case except
the unwashed cadmium sample, the
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sludges generated by Na2C03 had higher
metal levels in the EPA-EP extract than
did those produced by CaO or NaOH. This
effect was especially notable for chrom-
ium and zinc. These and other observa-
tions, as mentioned above, could not be
applied to other plants in the study.
The effect of treatment chemical on the
solids content of the sludges showed that
calcium oxide, in general, resulted in
treated wastewater streams with a higher
total solids (TS) content while NaOH
resulted in the lowest TS. For CaO and
Na2C03, the TS also tended to increase
directly with pH, while TS was basically
unaffected by pH for NaOH. Three
treatment pH's were studied for Plant 7.
With CaO and NaOH the suspended
solids (SS) reached a maximum at pH 8.5
and then dropped off as the pH was
increased to 10. SS increased with pH for
Na2C03.
Conclusions
The conclusions drawn as a result of
tests conducted and observations made
are valid only to the plants that were
sampled; however, it is likely that the
results will be generically useful to many
electroplating shops with similar waste-
water characteristics.
Considerable lack of agreement was
found between the analytical results for
replicate samples prepared by the same
technique. This scattering effect gives a
surprisingly high background or random
variation. This is especially true in
samples containing chromium (+6).
Against such a background, only rather
large changes in sludge teachability could
be said to correlate to given treatment
parameters with statistical significance.
In spite of this masking effect, some
correlations appeared to be significant,
and the following conclusions can be
drawn from the results:
• In the screening tests, the ability of
wastewater treatment variables to
influence extract quality by variation
of treatment parameters was
apparently plant specific. The ability
to influence extract quality appears
to vary among metals under
consideration.
• Optimum flocculant and flocculant
concentration were determined for
each plant's wastewater. A simple
jar test was developed to enable
plant operators to do their own
evaluations.
• The treatment chemical and pH
affected the solids content of the
wastewater sludges. The higher
solids sludge was produced by CaO
at pH 10. Less solids were produced
by NaOH and Na2C03 and were the
same at pH 8.5 and 10.
• The teachability of metals was lower
when performed by the ASTM-A
extraction procedure than by the
EPA-EP. The pH that produced the
least leaching was different for each
plant. The parameters (pH, treatment
chemical, or interaction)that showed
a statistical significance for a plant
can only be said to be significant for
that particular plant. No generalities
could be found to apply to sludge
teachability.
• The interstitial of free water
associated with the sludges had
lower metal levels than the effluent
waters.
• The precipitation chemical had little
effect on sludge dewatering by centri-
fuge and vacuum filtration. The fresh
sludges that dewatered fastest dur-
ing vacuum filtration all were at pH
8.5. In most cases, fresh sludge
dewatered faster than aged sludge
though not exclusively. Each plant's
sludge behaved differently.
• No quick acceptance test related to
the EPA-EP was found that could be
broadly applied to all plants. Each
individual plant may be able to
develop a quick acceptance test that
applies to its own sjudge. However,
potential for development of a quick-
acceptance test for segregated
landfills (ASTM-A) was discovered.
During the sampling portion of the
study, it was observed that many waste
treatment areas within the electroplating
shops were not being operated as well as
the equipment would allow. Control
instrumentation in some shops was not
being properly maintained and therefore
could not treat the wastewater properly.
In other shops, important indicators were
missing so that the effectiveness of
treatment was never known.
Recommendations
The following recommendations are
based on observations made during the
testing and engineering evaluations of
the data.
• Additional data should be obtained
and necessary analysis performed in
order to derive a quick acceptance m
test for operators of segregated "
nonhazardous waste landfills, based
on the significant correlations
between filtrate and ASTM-A extract
results found in the present study.
• The testing procedures and their
evaluations should be incorporated
into a "Standard Electroplaters
Wastewater Evaluation Procedures,"
which can be of general interest and
value to individual plant operators
who wish to make their own in-plant
studies.
• To determine the validity and
magnitude of some of the more
positive conclusions, such as the use
of CaO or NaOH, selection of pH, the
use of selected flocculants, etc., it is
recommended that these variables
be studied at one electroplating
plant. The study would involve
operating the plant under existing
conditions, and then operating for a
week at steady state with one or
more selected changes. The testing
of plant effluents and wastwater
sludges would be analyzed and the
data evaluated in the same manner
as described in this report.
• The data for each plant participating
in the study was given to plant
management with a request for
comments, suggestions and
criticism. No replies were received.
Perhaps the American Electroplaters'
Society might be of assistance in
obtaining feedback, even if it is of
general nature.
• A study to determine the "in-practice"
variability of the EPA-EP and the
ASTM-A should be undertaken. This
request has come from many others
using the two procedures, and the
data from this report also indicates
the need for such a study.
0
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A. Procko. E. Handel, and M. Moskowitz are with CENTEC Corporation, Reston,
WV22090.
Thomas J. Powers is the EPA Project Officer (see below).
The complete report, entitled "Electroplating Plant Operating Conditions Related
to Waste water Sludge teachability," (Order No. PB 84-120 781; Cost: $19.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V'A 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
Illi A
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
*
AGENCY
it 60604
U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/843
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