United States
                     Environmental Protection
                     Agency
      Risk Reduction Engineering
      Engineering Laboratory
      Cincinnati OH 45268
                     Research and Development
      EPA/600/S2-91/041  Sept. 1991
iSrEPA       Project Summary
                     Recovery  of Metals from  Sludges
                     and Wastewaters
                        This report presents information on
                     the state-of-the-art of metals recovery
                     technologies to assist in  Identifying
                     waste-management options for metal-
                     bearing sludges and wastewaters that
                     may be regulated under the Resource
                     Conservation and Recovery Act (RCRA).
                     Only a few of the technologies  ad-
                     dressed In this report (e.g., electrowin-
                     ning, high-temperature metals recovery
                     [HTMR]) are directly applicable to the
                     recovery of metals from wastes; other
                     technologies treat the wastes to a physi-
                     cal form that may be amenable to even-
                     tual metals recovery.
                        Wastewaters can be treated effec-
                     tively by several methods. Precipitation
                     processes have been widely used to
                     remove arsenic, cadmium, chromium
                     (+3), copper,  iron, manganese, nickel,
                     lead, and zinc from metal-bearing waste-
                     waters. For economic reasons, electro-
                     winning is a commercial technology that
                     has normally been restricted to the treat-
                     ment of wastewaters containing noble
                     metals such as gold and silver.
                        After appropriate pretreatment, slud-
                     ges can be effectively treated by HTMR
                     processes. These processes allow for
                     the direct recovery of metals from slud-
                     ges. The economic feasibility depends
                     on the amount of sludges treated and
                     the amount of metals contained In the
                     sludges.  Membrane separation  pro-
                     cesses such as microfiltratlon (MF) and
                     ultra filtration (UF) can be used in com-
                     bination with chemical treatment for the
                     physical separation of metal sludges.
                     Leaching may be used to extract cad-
                     mium, chromium, copper, lead, nickel,
and zinc directly from sludges by using
various process trains.
   This  Project Summary was devel-
oped by EPA's Risk Reduction Engi-
neering  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).

Introduction
   Section 3004 of the Resource Conser-
vation and Recovery Act (RCRA),  as
amended by the Hazardous and Solid
Waste Amendments of 1984, prohibits plac-
ing untreated RCRA-regulated hazardous
wastes in or on the land. Waste manage-
ment options are needed to help recyclers
comply with these  regulations. In the full
report, summarized here, we address the
following processes that are amenable for
recovery of metals from hazardous wastes:
chemical precipitation, electrolytic recov-
ery, HTMR, membrane separation, leach-
ing, ion exchange  and evaporation. For
each of these technologies, the following
parameters  are  summarized: (1) design
specifications of applicable processes, (2)
waste characteristics affecting  perfor-
mance, (3) pretreatment/posttreatment re-
quirements, (4) available performance data,
and (5) availability of the technology and
feasibility for treating various hazardous
waste categories.

Waste Chacterizatlon
   This report covers nine major metal-
waste-producing industries:
                                                                     Printed on Recycled Paper

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    (1) metal coatings; (2)  smelting and
 refining of nonferrous metals; (3) paint, ink,
 and associated products; (4)  petroleum
 refining; (5) iron and steel manufacturing;
 (6) photographic industry; (7) leather tan-
 ning; (8) wood preserving; and  (9) battery
 manufacturing. Waste streams  from each
 of these industries have unique character-
 istics; however, the wastes also contain
 common metals, such as aluminum (Al),
 arsenic (As), cadmium (Cd), chromium (Cr),
 copper (Cu), lead (Pb), nickel  (Ni), silver
 (Ag), and zinc (Zn).
    Table 1 presents the number of metal-
 waste generators (as of 1983) by Standard
 Industrial Classification (SIC) code for the
 major industry categories discussed in the
 report.
    Table 2 indicates the amount and num-
 ber of generators of metal-bearing wastes
 by D (wastes which are hazardous  be-
 cause they exhibit a particular  hazardous
 characteristic),  F (wastes from non-spe-
 cific sources), and K (wastes from specific
 sources) EPA hazardous waste codes. Until
 very recently, only about half of the indus-
 tries that generate metal-bearing wastes
 recovered the  metals from wastewaters
 and sludges.
    Table 3 presents brief descriptions of
 the hazardous wastes generated from the
 major industry categories included  in the
 report.
Metals Recovery Technologies

Chemical Precipitation
   Precipitation  of metal-laden wastewa-
ters involves adding chemicals to alter the
physical state of the  dissolved or  sus-
pended metals and  to facilitate their re-
moval  through sedimentation. These
precipitates may then  be processed fur-
ther for metals recovery. Chemicals used
to effect precipitation  include: caustic soda,
lime, ferrous and sodium sulfide, soda ash,
sodium borohydrkJe, and sodium phos-
phate. Some wastewater constituents, e.g.,
hexavalent chromium, cannot be effectively
precipitated without first chemically reduc-
ing the metal to a more favorable form for
precipitation. Reducing  agents typically
used  by industry include sulfur dioxide,
sodium bisulfite, sodium metabisulfite, and
ferrous sutlate. Coagulation chemicals may
be needed to enhance settling times of the
precipitated metal particles.  Examples of
coagulants currently  used by industry in-
clude lime, alum, and synthetic polyelec-
trotytes.
   Chemical precipitation is  commonly
used  to treat metal-bearing  wastewaters
from electroplating, pigment manufacture,
 Table 1.
Number of Major Metal-Waste Generators, by SIC Code, in 1983
SIC
Code No.
3471
2851
3479
3714
2819
3341
3400
9711
3721
3900
3356
2893
3312
3321
4911
2869
2821
3662
3679
3711
3545
SIC Description
Plating and surface finishing
Paints and allied products
Metal coating and allied products
Motor vehicle parts and accessories
Industrial inorganic chemicals
Metals, nonferrous, secondary
Fabricated metal products
National security
Motors and generators
Miscellaneous manufacturing industries
Metal, nonferrous, rolling, drawing
Printing ink
Blast furnaces, steel mills
Foundries, gray iron
Electric services
Industrial organic chemicals
Plastics material
Radio and TV communication equipment
Electronic components
Motor vehicle bodies
Machine tool accessories
No. of
Facilities
4,287
2,145
2,902
4,151
2,183
876
55,380
393
966
32,867
384
609
1,229
1,229
2,614
1,160
1,529
4,656
5,392
1,040
3,432
 Tablo 2.      Nationwide Metal-Waste-Generation Data by Waste Group

D Wastes
F Wastes
K Wastes
Waste
Volume,
10*gal/yr
3685
3920
219
Percent
of
Total
Metals
46.9
49.9
2.8
Number of
Generators
3860
2091
402
the photographic industry, leather tanning,
wood preserving, the electronics industry,
battery manufacture, and nonferrous metal
production. Approximately 75% of all elec-
troplating facilities use precipitation  in the
treatment of their wastewaters. The pro-
cess is several decades old, and chemical
feed reagents are being improved to yield
better metal removals from the aqueous
phase.
   Specific  waste characteristics that af-
fect the performance of chemical precipita-
tion systems include (1) the concentration
and type of metals, (2) the concentration of
total dissolved solids, (3) the concentration
of complexing agents, and (4) the concen-
tration of oil  and grease.
   Pretreatment  of wastewaters before
metals precipitation can involve segrega-
tion, removal of large solids, flow equaliza-
tion, cyanide  destruction  (if  applicable),
chrome  reduction, oil separation, neutral-
                              ization, and/or waste treatment of the indi-
                              vidual process streams.
                                 Sand filtration is a common  post-pre-
                              cipitation/sedimentation effluent treatment
                              technique. If concentrations in the effluent
                              do not meet discharge  standards, addi-
                              tional  metal treatment technologies (e.g.,
                              ion exchange,  reverse osmosis) may be
                              needed.

                              Electrolytic Recovery
                                 Electrolytic processes are used exten-
                              sively  to  recover  metals from  industrial
                              wastewaters. The electrolytic cell is  the
                              basic device used in electrolytic recovery
                              operations. The cell consists  of an anode
                              and a cathode immersed in an electrolyte.
                              When  current is applied, dissolved metals
                              in the  electrolyte are reduced and depos-
                              ited on the cathode. Because the metal(s)
                              removed from solution can  be reused, the
                              technology, termed "electrowinning," is con-

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Table 3. Metal-Bearing Hazardous Wastes From Major Industry Categories
EPA Hazardous Listed
Waste No. Hazardous Waste Description Constituent(s)
F006









F007

F008


F009


F019




K002


K003

K004

K005

K006

Wastewater treatment sludges from electro-
plating operations except the following:
(1) sulfuric acid anodizing of aluminum;
(2) tin plating on carbon steel; (3) zinc
plating (segregated basis) on carbon steel;
(4) aluminum or zinc-aluminum plating on
carbon steel; (5) cleaning/stripping asso-
ciated with tin, zinc, and aluminum plating
on carbon steel; and (6) chemical etching and
milling of aluminum.
Spent cyanide plating bath solutions from
electroplating operations.
Plating sludges from the bottom of plating
baths from electroplating operations where
cyanides are used in the process.
Spent stripping and cleaning bath solutions
from electroplating operations where cya-
nides are used in the process.
Wastewater treatment sludges from the chemi-
cal conversion coating of aluminum.



Wastewater treatment sludge from the pro-
duction of chrome yellow and orange pigments.

Wastewater treatment sludge from the pro-
duction ofmolybdate orange pigments.
Wastewater treatment sludge from the pro-
duction of zinc yellow pigments.
Wastewater treatment sludge from the pro-
duction of chrome green pigments.
Wastewater treatment sludge from the pro-
duction of chrome oxide green pigments
Cadmium, hexa-
valent chromium,
nickel, cyanide
(complexed)






Cyanide/salts

Cyanide/salts


Cyanide/salts


Cadmium,
hexavalent
chromium,
cyanide
(complexed)
Hexavalent
chromium,
lead
Hexavalent
chromium, lead
Hexavalent
chromium
Hexavalent
chromium, lead
Hexavalent
chromium
K007




K008

K048

K049

K050

K051

K052

K060

K061


K062


K064
(anhydrous and hydrated).
Wastewater treatment sludge from the pro-
duction of iron blue pigments.
Oven residue from the production of chrome
oxide green pigments.
Dissolved air flotation (DAF) float from the
petroleum refining industry.
Slop oil emulsion solids from the petroleum
refining industry.
Heat exchanger bundle-cleaning sludge from
the petroleum refining industry.
API separator sludge from the petroleum
refining industry.
Tank bottoms (leaded) from the petroleum
refining industry.
Ammonia still lime sludge from coking
operations.
Emission control dust/sludge from the primary
production of steel in electric furnaces.

Spent pickle liquor generated by steel-
finishing operations of facilities
within the iron and steel industry.
Acid plant blowdown slurry/sludge resulting
from the thickening of blowdown slurry from
primary copper production.
Cyanide
(complex),
hexavalent
chromium
Hexavalent
chromium
Hexavalent
chromium, lead
Hexavalent
chromium, lead
Hexavalent
chromium
Hexavalent
chromium, lead
Lead

Arsenic

Hexavalent
chromium,
lead, cadmium
Hexavalent
chromium, lead

Lead, cadmium
                                                                    (continued on p.4)
sidered a recovery process. If a membrane
is used between the cathode and the an-
ode for the  selective transport of some
ions, the process is called electrodialysis.
Electrowinning is most effective for recov-
ery of  noble  metals such as gold  and sil-
ver. These  metals have  high electrode
potentials and are easily reduced  and de-
posited on the  cathode.  Metals such as
cadmium, copper, chromium, lead, tin, and
zinc can be removed, but a greater amount
of current is required. Electrowinning  is
very effective for plating solutions used in
printed circuit boards; these contain che-
lated metals  that are difficult to remove by
other means.
    Electrowinning of metals is a  particu-
larly attractive process  because  it com-
pletely eliminates the  generation of  a
metal-bearing sludge. Its applicability, how-
ever, is limited to waste streams contain-
ing metals in solution such as cadmium,
copper, chromium, gold, lead, silver, tin, or
zinc. For dilute solutions, electrowinning
can be difficult because of the low mass-
transfer rates; however, mass transfer rates
can be  enhanced  both by agitating the
solution and by increasing the  effective
surface area of the cathode.
   The principal area of application of elec-
trodialysis  is the recovery of  metals from
electroplating bath rinse waters.
    In many  cases, the wastewater must
be filtered before it  is fed through the elec-
trolytic reactor. Adjustment of  pH is a nec-
essary pretreatment measure  because the
waste pH affects metal  speciation.
    Metal recoveries of  up to 98% from
plating  rinse waters  have been  demon-
strated with the use of high-surface area
(HSA)  electrodes.
   Several vendors are currently manu-
facturing electrodialysis systems for treat-
ment of wastes from gold, chromium, silver,
and zinc cyanide plating operations and
from nickel plating  operations. Other suc-
cessful electrodialysis applications include
recovery of metals from tin  and trivalent
chromium baths and the recovery  of chro-
mic acid and  sulfuric acid from spent brass
etchants. Electrowinning and  electrodialy-
sis systems  have both  been  used exten-
sively in industrial applications.

High-Temperature Metals Recovery
(HTMR)
   Several types of HTMR processes are
currently available or under development
for the  recovery of metals from sludges
generated either directly by industrial pro-
cesses or from the treatment of industrial
wastewaters. These HTMR processes may
involve plasma-based or high-temperature
fluid-wall reactor systems (which use elec-

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Table 3.   (Continued)
EPA Hazardous
Waste No.
    Hazardous Waste Description
(continued on p.4)

   Listed
Constituents)
K065


K066


K069



K086




K090

K100
D004
D006
D007
D008
D009
D011
Surface impoundment solids contained in and
dredged from surface impoundments at primary
lead smelting facilities.
Sludge from treatment of process wastewater
and/or acid plant btowdown from primary zinc
production.
Emission control dust/sludge from secondary
lead smelting.
Solvent washes and sludges, caustic washes,
and sludges from cleaning tubs and equipment
used in the formulation of ink from pigments,
driers, soaps, and stabilizers containing
chromium and lead.
Emission control dust or sludge firom ferro
chromium silicon production.
Waste leaching solution from add leaching
of emission control dust/sludge from
secondary lead smelting.
Characteristic waste based on concentrations.
Characteristic waste based on concentrations.
Characteristic waste based on concentrations.
Characteristic waste based on concentrations.
Characteristic waste based on concentrations.
Characteristic waste based on concentrations.
Lead, cadmium
Lead, cadmium
Hexavalent
chromium,
lead,
cadmium
Lead,
hexavalent
chromium
Chromium

Hexavalent
chromium, lead,
cadmium
Arsenic
Cadmium
Chromium
Lead
Mercury
Silver
trterty as the energy source) or coal/natu-
ral- gas-based technologies.
   HTMR processes are applicable only
for the processing of sludges, not for waste-
waters.  One significant advantage of the
HTMR processes is that  other toxic con-
stituents in the wastes, such as complexed
cyanides/organics, would also be destroyed
at the high temperatures (>1100°C) pre-
vailing in the furnaces.
   Important waste characteristics affect-
ing the  performance of HTMR processes
include: (1) concentrations of undesirable
volatile  metals, (2) boiling  points of the
metal constituents, and (3)  thermal con-
ductivity of the  waste. Pretreatment  re-
quirements for HTMR processes vary with
the type of process. This  may include op-
erations such as drying of feed sludges or
pelletizing with special additives. The crude
metallic oxides produced in certain HTMR
processes must be further treated for sepa-
ration and recovery of metals. Gases from
the high temperature furnaces must  be
treated before atmospheric release.
   The  INMETCO Plant in  Ellwood City,
PA (which utilizes a rotary hearth/electric
furnace) and the Horsehead  Waelz Kiln in
Palmerton, PA, have  processed hazard-
ous wastes (sludges) under an Interim Per-
mit status. The INMETCO Plant has
processed the following waste codes: F006,
                          K061, K062, D006, D007, and D008. The
                          Horsehead Waelz kiln has processed F006,
                          F019, K061, D006, and D008.
                             Horsehead has two  operating Waelz
                          plants in the  United  States—one  at
                          Palmerton, PA,  and one at Calumet City,
                          IL. The Palmerton plant has three Waelz
                          kilns with a total capacity of 270,000 tons/
                          y r; the Calumet plant has one kiln with a
                          capacity of 80,000 tons/yr. The INMETCO
                          plant is capable of treating 50,000 tons of
                          wastes per year. Both of the Horsehead
                          Waelz plants as well as the INMETCO
                          plant are operated primarily  to treat steel-
                          making electric  arc furnace dust (K061);
                          however, as  previously  mentioned, they
                          are capable of  treating  other sludges.  A
                          third Horsehead Waelz plant with a capac-
                          ity  of 60,000  tons/yr  is  planned  for
                          Rockwood, TN.

                          Membrane Separation
                             The commercially available membrane
                          processes for removal of metals  from  in-
                          dustrial wastewaters are  microfiltration, ul-
                          trafiltration, reverse  osmosis,  and
                          electrodialysis. Microfiltration (MF) and ul-
                          trafiltration (UF) are used in combination
                          with chemical treatment for the  physical
                          separation of metal sludges. Reverse os-
                          mosis (RO)  and electrodialysis (ED)  are
                          used to  recover plating  compounds from
rinse water and to enable reuse of rinse
waters.
   MF and UF membranes cannot be ap-
plied directly to recover metals present as
dissolved solids in wastewaters. UF, how-
ever,  can  be  used as  a pretreatment
method for RO units to avoid fouling of the
RO membranes.
   When applied to  heavy metal wastes
with appropriate  pretreatment chemistry,
the metal content of the effluent can be
extremely low. Each application requires
treatability studies to integrate the chemi-
cal pretreatment and the MFAJF mem-
brane system.
   If oil  and  grease are present,  addi-
tional pretreatment of the waste stream
will be required. Well-run precipitation/
UF and  MF systems can achieve metal
removals greater than  99%. Over 150
full-scale industrial systems,  ranging  in
size up  to 400 gal/min, have been  in-
stalled in the electroplating,  printed cir-
cuit board   manufacturing,  battery
manufacturing, and photographic process-
ing industries.
   RO systems consist of several  mod-
ules connected in series, or parallel, or a
combination of both. The application of RO
to the treatment of metal-containing wastes
is limited by  the pH range in which the
membrane can operate. Cellulose acetate
membranes cannot  be  used on  waste
streams  where the pH is much above  7.
The amide or polysutfone membranes, how-
ever, have a pH range of 1 to 12. Collodial
matter, low-solubility salts, and dissolved
organics can seriously inhibit the effective-
ness of RO. Pretreatment steps such as
pH adjustment, carbon adsorption, chemi-
cal precipitation, or filtration are therefore
recommended to ensure extended service
life of  RO systems. Systems are being
used  commercially to  recover brass,
hexavalent chromium, copper, nickel, and
zinc from metal-finishing solutions.

Leaching
   Leaching is a process in which a solid
material  is contacted with a liquid solvent
for selectively dissolving some components
of the solid into the liquid phase. Leaching
can sometimes be used to extract various
metals from sludges. The goals of this
process are: (1) to dissolve the metals in a
liquid phase to produce a solution that can
be reused directly in a process or from
which the metal can be recovered by other
techniques, such as electrowinning; and
(2) to produce a secondary sludge that is
nonhazardous or from  which additional
metals can be reclaimed by  other pro-
cesses. Several leaching agents can po-
tentially be used, including sulfuric acid,

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 ferric sutfate, ammonia or ammonium car-
 bonate, hydrochloric acid, sulfur dioxide,
 ferric chloride, nitric acid, or a caustic solu-
 tion. Selection of a suitable solvent and
 unit process depends on the chemical state
 and physical environment of the metals.
    Sludges that contain  only  one metal
 often can be sent directly to a refiner for
 reclamation; however, in some operations
 (e.g., electroplating), all metals are precipi-
 tated from solution in the same wastewa-
 ter treatment plant, usually as hydroxides.
 A process train with numerous  unit opera-
 tions, therefore, is  necessary to separate
 each metal. Complete recovery of the met-
 als typically includes electrowinning of the
 leachate.
    At the Recontek waste recycling facility
 in Newman, IL, zinc-bearing  solutions are
 leached with  alkaline  solutions, whereas
 non-zinc sludges are  treated with  acidic
 solutions. Zinc-bearing sludges are  di-
 gested at approximately 80*C whh sodium
 hydroxide for a sufficient period of time,
 cooled,  and filtered. The  filtrate is pro-
 cessed in a zinc cementation tank to pre-
 cipitate metals more electronegative than
 zinc (e.g., lead, cadmium) and then pumped
 to a zinc electrowinning system. The non-
 zinc sludge waste from the digester (pri-
 marily copper and nickel) is digested with
 suffuric acid and filtered to produce a resi-
 due containing precious metals  (e.g., gold,
 silver). The filtrate is then sent to the cop-
 per electrowinning  system for  production
 of copper cathodes.

 Ion Exchange
   Ion exchange is a  treatment technol-
 ogy  applicable to (1) metals in wastewa-
 ters where the metals are present as soluble
 ionic  species  (e.g., Cr3 and CnV); (2)
 nonmetallic anions  such as  halides, sul-
 fates, nitrates,  and cyanides; and (3) wa-
 ter-soluble,  ionic  organic  compounds
 including (a) acids  such as carboxylics,
 sulfonics, and some phenols, at  a pH suffi-
 ciently alkaline to yield ionic species, (b)
 amines,  when the solution acidity is suffi-
 ciently acid to form the corresponding acid
 salt,  and (c) quaternary amines and aklyl-
 sulfates.
   Ion exchange is  a reversible chemical
 reaction  in which an ion from solution is
 substituted for a similarly charged ion at-
tached to an immobile solid particle. The
 use of this  process is  practical only on
wastewaters and sludge leachates. In con-
ventional ion exchange, metal  ions from
dilute wastewater solutions are exchanged
for ions electrostatically held on the sur-
face  of  the exchange  medium.  Ion ex-
change systems have proven to be effective
in the removal of barium, cadmium, chro-
 mium  (VI), copper, lead, mercury, nickel,
 selenium, silver, uranium, and zinc.

 Evaporation
    Evaporation is a simplified recovery sys-
 tem for the separation of substances based
 on volatility differences. Although the tech-
 nology is established, recent advancements
 have made mechanical evaporation a more
 viable cost-efficient method  for metals re-
 covery. The four basic types of evapora-
 tors used in the electroplating industry today
 are rising-film, flash, submerged-tube, and
 atmospheric.

 Conclusions
   Only a few  of the technologies ad-
 dressed in this report (e.g., electrowinning,
 HTMR) are directly applicable to recover-
 ing metals from wastes; other technologies
 treat the  wastes to a  physical form that
 may be amenable to eventual metals re-
 covery.
   Commercial waste  recycling facilities
 render services that are important if metals
 are to  be recovered as opposed to being
 treated and disposed. Technologies used
 at the metals recovery facilities include
 chemical  precipitation, leaching,  electro-
 winning, and evaporation.
   Current information on metals recovery
 technologies  show that combinations  of
 technologies may often be required to re-
 cover metals from wastewaters and slud-
 ges. Additional  studies are needed  to
 determine the  specific combinations  of
 methods that will most  effectively recover
 metals from different types of wastes.
   The full report was  submitted in fulfill-
 ment of  EPA  Contract No. 68-03-3413,
Work Assignment 2-63, by IT Corporation,
Cincinnati, OH (formerly PEI Associates,
 Inc.), under the  sponsorship of the U.S.
Environmental Protection Agency.
                                                                          6l).S. GOVERNMENT PRINTING OFFICE: 1991 - S4H-OU/40080

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This Project Summary was prepared by the staff of IT Corporation, Cincinnati, OH
  45246.
Ronald J. Turner is the EPA Work Assignment Manager (see below).
The complete report, entitled "Recovery of Metals from Sludges and Wastewaters,"
  (Order No. PB91-220384/AS; Cost: $23.00, 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 Work Assignment Manager can be contacted at:
        Risk Reduction Engineering Laboratory
        U.S. Environmental Protection Agency
        Cincinnati, OH 45268
 United States
 Environmental Protection
 Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
      BULK RATE
POSTAGE & FEES PAID
 EPA PERMIT NO. G-35
 Official Business
 Penalty for Private Use $300
 EPA/600/S2-91/041

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