&EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-81-142 Sept. 1981
Project Summary
Treatment of Metal Finishing
Wastes by Use of
Ferrous Sulfide
M. B. Yeligar, G. Bagenski, and R. M. Schlauch
The demonstration of a new patented
sulfide precipitation process
("Sulfex" ™ ), which removes heavy
metals from metal finishing waste-
waters, was performed to verify its
operational practicability and per-
formance quality. Operational data
was also gathered for an economic
evaluation of this process.
The study was performed at a
carburetor manufacturing plant in
Paris, Tennessee. Here, "Udylite"
processes are used,for chromate
conversion coatings on aluminum and
zinc carburetor castings before as-
sembly.
A newly installed sulfide precipita-
tion system removes chromium and
zinc from the plant's combined metal
finishing process wastewater. It also
removes suspended material such as
precipitated aluminum, iron, and
phosphates. Major steps in the system
are: equalization and neutralization of
untreated wastewater, precipitation
of metals and sedimentation of sus-
pended solids, polishing of settler
effluent with dual media filtration, and
final dewatering of settled sludge.
Results show all metals and sus-
pended solids were removed to levels
well below both the City of Paris
sewer system limitations and the
State of Tennessee guidelines for
indirect discharges to sewer systems.
A dewatered sludge was produced as
a firm, dry cake in a filter press without
the use of conditioning agents. No
hydrogen sulfide odor was detected
from the reaction process treated
effluent, or the solid waste produced.
Jar tests were demonstrated to be a
valuable tool for maintaining good
process control and economical op-
eration.
The chemical cost of sulfide precipi-
tation has been found to be directly
dependent upon the concentrations of
combined zinc and hexavalent chrom-
ium present during the sulfide reaction
process. Sulfide precipitation was
shown to be an economical as well as
effective treatment process for this
type of wastewater.
This report was submitted in ful-
fillment of Grant No. S-804648 by
Holley Carburetor Division of Colt
Industries under the sponsorship of
the U.S. Environmental Protection
Agency. This report covers the period
July 11, 1978 to August 11, 1978.
and work was completed as of August
25, 1978.
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory. Cincin-
nati, 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).
Introduction
In April 1974, a laboratory and pilot-
plant study of a new wastewater
treatment process, using sulfide pre-
cipitation, was sponsored by the Metal
Finisher's Foundation under Grant No.
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R802924-01 from the Environmental
Protection Agency. In July 1978,
another study was undertaken to
demonstrate effectiveness, operability,
and cost of this new process called
"Sulfex"™ as a full-scale installation at
Holley Carburetor Company in Paris,
Tennessee.
Laboratory and Pilot-
Plant Study
This work is described in the report
"Treatment of Metal Finishing Wastes
by Sulfide Precipitation" EPA-600/2-
77-049, February 1977.* The project
involved precipitating heavy metals
normally present in metal finishing
wastewaters by a novel process which
employs ferrous sulf ide addition as well
as by conventional treatment using
calcium hydroxide for comparison
purposes. A simulated metal finishing
wastewater containing common heavy
metals and chelating agents was used
in this laboratory and pilot-plant study.
Sulfide precipitation was demonstrated
to be a technically viable process that is
superior to conventional hydroxide
precipitation for removal of copper,
cadmium, nickel, chromium, and zinc
from the given influent.
Full-Scale Study
The present study was made during
the startup of a 7.9 mVhr (35 gpm)
wastewater treatment system at a
carburetor manufacturing plant. Here,
the production of carburetors produces
wastewater from chromate conversion
coating of zinc and aluminum castings
by a "Udylite" process. Combined
wastewaters from these metal finishing
operations contain heavy metal pollutant
concentrations in excess of local and
state limits set for direct discharge to
the city sewer system. Therefore, a safe,
reliable, and economic wastewater
treatment process was needed by the
manufacturer to meet the imposed
discharge requirements.
The metal finishing operations used
at the plant involved degreasing,
deburring, deoxidizing, acid etching,
and chromate bath treatment to give
carburetor castings corrosion resistant
coatings. In the process, various mater-
ials including zinc, hexavalent chrom-
ium, aluminum, ortho- and polyphos-
phates, silicates, organic surfactants
and chelants, as well as chelated
metals, are released into the plant's
wastewater discharge.
Since manufacturing specifications
vary, all castings do not undergo treat-
ment by each of these finishing opera-
tions. Furthermore, the production
schedule is quite variable. As a result,
the composition of the wastewater
fluctuates periodically on hourly, daily
and weekly bases.
This type of metal finishing operation
is generally used for providing corrosion
resistant coatings on surfaces of a wide
variety of metal parts, components and
appliances. Consequently, these
wastewater characteristics are typical
of many industrial manufacturing
discharges that have to be treated to
meet present and future discharge
standards.
The laboratory and pilot-plant study
had demonstrated the effectiveness of
sulfide precipitation on a synthetically
prepared metal finishing wastewater.
The full-scale system study at the plant
is useful in further proving that the
process is practical under actual manu-
facturing conditions. For example, Table
1 summarizes the overall effectiveness
of the process in removal of pollutants.
Figure 1 shows the total chemical
operating cost, on a per shift basis.
Other variables and economics are
described individually on per shift and
per year basis. Therefore, this study
shows how practical, controllable, and
economical it is to operate the process
under the fluctuating contaminant,
loadings that are characteristic of many
metal finishing wastewaters.
Conclusions
Effectiveness
The effectiveness of the sulfide
precipitation process has demonstrated
that heavy metals can be removed from
metal finishing wastewaters to very low
levels. The effluent quality produced by
this wastewater treatment process (as
monitored by direct flame atomic
absorption and diphenyl carbazide
colorimetric methods for metal analyses)
reveals that the process achieves metal
values close to or less than are routinely
detected by the accepted analytical
methods (i.e. Cr and Fe detected at 0.05
mg/l, Cu and Zn detected at 0.01 mg/l).
Economics
The chemical cost of the sulfide
precipitation process is directly depen-
dent upon the influent metal loading of
various heavy metals. At the carburetor
plant, influent zinc and hexavalent
chromium are the metal concentrations
that dictate the dosage of ferrous sulfide
that is required. Here, the chemical cost
of sulfide precipitation is competitive
with the cost of conventional bisulfite j
and hydroxide treatment for removal of'
average concentrations of zinc and
hexavalent chromium in the untreated
wastewater (i.e. about 34 mg/l Zn and
34 mg/l Cr*6).
When hexavalent chromium is pres-
ent in combination with other heavy
metals, as it is at this plant, there can be
a savings in equipment cost with sulfide
precipitation since the metals can be
removed simultaneously in one step
But, as the concentration of zinc (01
other heavy metals increases), the
chemical cost of direct treatment b>
sulfide precipitation becomes increas
Table 1. Average Wastewater Compositions During "Sulfex"™ Study
Metal
Zn
Fe
Cu
Cr
Cr*
TSS
Untreated*
influent
(mg/l)
39.5
0.52
<0.01
32.3
25.6
46.5
Treated*
effluent
(mg/l)
<0.07t
0.10
<0.01
<0.04
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$30
$25
~ $20
I
I $15
8
1 $70
$5,
I I V I I I
Total Chemical Cost vs. Shift Numbers
04 8 12 16 20 24
Shift Number
Figure 1. Total chemical cost as a function of time.
28 32 , 36 40
ingly more than by hydroxide precipita-
tion. At Holley, the chemical cost for
sulfide precipitation treatment is justified
since conventional treatment cannot
effectively meet the city sewer limita-
tions (i.e. 0.1 mg/l zinc maximum).
In all cases, however, the relative
economics can be evaluated before-
hand by the average heavy metal
concentrations present in the waste-
water. In some cases, it may be more
economical to remove the bulk of the
heavy metals by hydroxide precipitation,
and apply sulfide precipitation as a
polishing step when stringent criteria
must be met.
Most of the basic equipment used for
the sulfide precipitation process is the
same as would be required for a
conventional wastewater treatment
process. Therefore, major capital costs
as well as operating costs are estimated
to be commensurate for both of these
treatment processes.
Operation
The operation of the wastewater
treatment system at the carburetor
plant is basically simple. Good control is
maintained because the system is
designed to handle sudden changes in
wastewater flow and composition.
An equalization tank is an essential
part of the system for dampening
fluctuations in wastewater flow and
metal concentrations into the reactor-
settler unit. The concentrated waste
sump receives spent metal finishing
baths and slowly feeds them into the
equalization tank. This sump is essential
to minimize variations that could com-
plicate the operation and downgrade the
effectiveness of the waste treatment
process.
Since it is possible that some residual
suspended solids carryover can occur
periodically from the settler, the dual-
media filter is necessary to ensure
removal of suspended metals from the
effluent before discharge to the city
sewer system.
Without further use of coagulants or
conditioners, a filter press will provide
excellent dewatering of the settler
sludge. A dry sludge cake is produced
that releases easily from the press and
is ready for disposal.
Control
The pH control of the neutralization
process is accomplished in the equal-
ization tank. This type of system is
satisfactory for maintaining an appro-
priate pH for effective metal precipitation
in the reactor-settler unit. High con-
centrations of hexavalent chromium in
the wastewater can cause moderate pH
increases in the reactor-settler effluent.
Controlling the pH at 8.0 in the neutral-
ization step is an effective way of
compensating for this pH increase.
Periodic visual jar tests performed on
the reactor-settler influent are a satis-
factory means of monitoring and con-
trolling optimal ferrous sulfide and
polyelectrolyte dosages. These visual
tests, for determining chemical dosage
requirements, eliminate the need for
laboratory analysis of influent heavy
metals.
Operating Personnel
The need for wastewater treatment
system operators must be determined
on the basis of each plant. Due to
frequent variation in the mode of the
metal finishing operations at the
demonstration plant, a full-time operator
is required on each shift to monitor the
wastewater treatment system. How-
ever, in installations where manufac-
turing processes are not as variable on a
daily and weekly basis, a full-time
operator may not be required on each
shift.
Recommendations
The sulfide precipitation process has
demonstrated that more complete metal
removal can be obtained and acceptable
effluent quality achieved, as opposed to
conventional hydroxide treatment of
metal finishing wastewaters. But the
cost of precipitating most heavy metals
(except hexavalent chromium) is higher
by sulfide methods tha n by the hydroxide
methods on a per unit weight of metal
removed basis.
Present day technology reveals that
hydroxide precipitation removes high
percentages of zinc and other metals
from metal finishing wastewaters.
However, this removal method can still
allow unacceptably high residuals of
heavy metals in the treated effluent for
discharge.
Therefore, in cases of very high metal
loadings, a combination of the two
methods in series shpuld prove to be an
economically attractive way of achieving
superior quality effluents. Sulfide
precipitation, is thus precipitation, as a
polishing step following conventional
hydroxide recommended when either
heavy metal loadings on new systems
are high enough to warrant the addi-
tional equipment or a conventional
treatment system already exisits.
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M. B. Yeligar. G. Bagenski. andR. M. Schlauch are with the Permutit Company,
Inc., Monmouth Junction, NJ 08852.
Mary K. Stinson is the EPA Project Officer (see below).
The complete report, entitled "Treatment of Metal Finishing Wastes by Use of
Ferrous Sulfide," (Order No. PB 81-233 579; Cost: $9.50, subject to change)
will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 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
U S. GOVERNMENT PRINTING OFFICE, 1981 — 757-012/7358
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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