United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/144 September 1993
Project Summary
Evaluation of Ultrafiltration to
Recover Aqueous Iron
Phosphating/Degreasing Bath
Gary D. Miller, Timothy C. Lindsey, Alisa G. Ocker, and Michelle C. Miller
Pollution prevention efforts studied in
the report summarized here targeted the
hazardous waste generated from a 5000-
gal iron phosphating/degreasing bath used
by a metal fabricator to clean and precon-
dition steel parts for painting. When oil
buildup in the bath began to sacrifice prod-
uct quality and the discharge levels of oil
and grease in the rinse water edged closer
to the maximum allowable limit, all 5000
gal were dumped and replaced. Periodic
dumping, about three times each year,
resulted in at least 15,000 gal/yr of hazard-
ous waste. Several waste minimization al-
ternatives were considered, and ultrafiltra-
tion was selected as the most promising
technology to recover and reuse the bath
and to reduce the total amount of hazard-
ous waste generated.
This project was carried out in four
stages: (1) initial assessment of the prob-
lem and evaluation of alternatives, (2)
bench-scale screening of Ultrafiltration
membrane candidates, (3) pilot-scale study
at the Illinois Hazardous Waste Research
and Information Center (HWRIC), and (4)
full-scale implementation and testing
onsite at the company's facility. Full-scale
testing integrated the new waste reduc-
tion scheme into the facility's production
process by applying Ultrafiltration directly
to the 5000-gal iron phosphating/
degreasing bath. Ultrafiltration success-
fully removed oil contamination from the
bath and returned clean process solution
back to the original 5000-gal tank. Ultrafil-
tration concentrated the hazardous com-
ponent down to 10 gal of oily waste and
reduced hazardous waste generation
99.8%. Permeate flux rates were high
enough to compete with the constant in-
put of oil from the production line, and
concentrations of oil in the bath were main-
tained at acceptable operating levels. The
estimated payback period associated with
implementing Ultrafiltration was only 6.9
mo.
This Project Summary was developed
by EPA's Risk Reduction Engineering
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 order-
ing information at back).
Introduction
The objective of the U.S. Environmental
Protection Agency (EPA) and the Illinois
HWRIC was to evaluate potential technolo-
gies and operational modifications that could
reduce the amount of hazardous waste gen-
erated at a metal fabrication facility. The goal
of this project was to find an environmentally
responsible means to extend the life a 5000-
gal iron phosphating/degreasing bath and
thereby reduce hazardous waste generation.
The relative feasibility of Ultrafiltration as well
as its capability to reduce waste generation
were assessed on an engineering and eco-
nomic basis. Results of this project were used
to justify installing a permanent Ultrafiltration
system and operating practices that would
improve product quality.
Industrial Participant
R.B. White, Inc., of Bloomington, IL, oper-
ates a sheet metal fabrication facility that
manufactures painted steel shelving units.
Cold-rolled steel arrives at the plant from the
steel mill coated with mill oils to protect the
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bare metal from corroding or staining during
storage and fabrication operations. During fab-
rication, coolants and lubricants are also ap-
plied to the metal working surface. Before
being painted, the metal surfaces are cleaned
to remove the mill oils and metal working
fluids and then preconditioned to bond well
with the paint coating. Fabricated parts are
cleaned and phosphated in a 5000-gal heated,
aqueous immersion tank and rinsed with a
fresh water spray. The company previously
operated separate degreasing and
phosphating tanks using trichbroethylene in
the degreasing tank and in 1985, switched to
a single-stage aqueous iron phosphating/
degreasing system to improve worker safety
and reduce the generation of organic solvent
emissions and hazardous waste. Although
the switch eliminated the risks and liabilities
associated with organic solvents, it introduced
a new waste disposal problem.
Problem Description
Simultaneous degreasing and phosphating
in the same bath formed an oil-water emul-
sion. With extended use, the buildup of oil in
the bath reduced cleaning and phosphating
efficiency, and product quality was compro-
mised. Additionally, dragout of oil from the
bath into the rinse water eventually pushed
oil and grease levels in the discharge over
the allowable limit. In the past, oil skimmers
were used to control oil slicks on the surface
and prolong the life of the bath, but the skim-
mers were only partially effective. When oil in
the bath began to sacrifice product quality
and the discharge levels edged closer to the
maximum allowable limit, the bath had to be
replaced. Depending on production rates, the
bath typically lasted 3 to 4 mo. Replacing the
bath required a full day of lost production time
to take the process off-line, make arrange-
ments with a waste transporter to drain and
dispose of the entire contents, and recharge
the tank with 5000 gal of fresh water and raw
materials. The spent bath was classified as
RCRA hazardous waste because it failed
Toxicrty Characteristic Leaching Procedure
(TCLP) tests for xylene. Since land disposal
of liquid wastes is prohibited, the bath, sludge,
and skimmed oil were incinerated in a ce-
ment kiln. Disposal costs including transpor-
tation and incineration ran about $1/gal which
came to $5000/bath, or about $15,000/yr in
addition to the costs associated with lost pro-
duction time and replacement of water and
raw materials.
Process Background
Iron phosphating/degreasing processes are
widely used in the manufacture of metal prod-
ucts to clean and precondition ferrous sur-
faces. Many metal fabricators and others that
paint or coat steel choose iron phosphating/
degreasing processes because they effec-
tively clean metal parts, provide an excellent
surface for paint adhesion, and protect against
under-paint corrosion. The goals and mecha-
nisms associated with the degreasing and
phosphating process are discussed bebw.
The goal of degreasing is to remove mill
oils, metal working fluids, and any other shop
soils from the steel surface and prepare it for
finishing. Degreasing was accomplished us-
ing nonbnic surfactants in a heated (140°F),
air-agitated bath. The surfactants surrounded
the oil and dirt particles and formed a stable
emulsbn that cleaned the parts and pre-
vented the oil and dirt from redepositing on
the metal surface.
Phosphating is a common type of pre-
paint coating process used to simultaneously
provide corrosion resistance and enhance
paint adhesion to a metal surface. Phosphate
salts chemically bond to the metal surface to
produce an amorphous conversbn coating.
The phosphate conversbn coating is non-
conductive so it protects the metal surface
from electrochemical oxidation that leads to
rust and corrosbn. The matrix of the phos-
phate coating forms capillaries that increase
the surface area and provide a mechanical
interlocking structure on which the paint can
adhere.
The 5000-gal bath was charged with Dura-
Gard Soke and Tart liquid acid (supplied by
DuBois Chemicals),* which contained non-
ionic surfactants, phosphate salts, phosphorb
acid, and accelerators to promote phosphate
precipitation. The concentratbn of Dura-Gard
Soke and the pH in the bath were checked
daily with a simple titration kit and litmus
paper to ensure that concentrations were
maintained between 1.5 and 2.0 oz Dura-
Gard/gal and at a pH of 3.5.
Waste Reduction in the Metal
Fabricated Products Industry
The EPA's campaign for waste reduction
is bringing change to industries through the
1984 Hazardous and Solid Waste Amend-
ments (HSWA) to RCRA, the Toxics Release
Inventory (TRI), the 1990 Pollution Preven-
tion Act (PPA), and the more recent 33/50
Program. The HSWA require industries to set
up waste minimization programs and to pro-
duce certified manifests demonstrating their
waste reduction efforts. The TRI is a comput-
erized data base that tracks the routine and
accidental release of approximately 300 toxic
chemicals reported by U.S. manufacturers.
The 1990 PPA brought about stricter TRI
industrial report requirements that include pro-
viding information on pollution prevention ef-
forts. The 33/50 Program is EPA's voluntary
"Mention of trade names or commercial products does
not constitute endorsement or recommendation for
use
pollution preventbn initiative to reduce the
Natbn's releases of 17 TRI chemicals 33%
by the end of 1992 and 50% by the end of
1995. Backed by federal legislatbn and eco-
nomic incentives, EPA's pollutbn preventbn
campaign has targeted several operatbns
associated with the metal fabricated products
industry. Finding environmentally responsible
solutions to the industry's waste disposal prob-
lems has focused on source reductbn (in-
cluding process modifications and raw mate-
rials substitution) and recycling.
The EPA recommends various strategies
for pollution prevention in the metal fabricated
products industries. Until now, waste reduc-
tion in surface preparation operations has
focused on conserving or finding alternatives
to organic solvent cleaners. For years, the
metal finishing industry has relied on organic
solvents for cleaning metal parts. Trichbroet-
hylene, methylene chloride, perchloroethyl-
ene, and 1,1,1-trichloroethane account for a
majority of the chbrinated solvents used by
industry. Recently, however, environmental
concerns for health and disposal conse-
quences have increased. Chbrinated solvents
were not only targeted by the TRI and 33/50
Program, but solvent wastes were among the
first to be banned from land disposal by the
1984 HSWA. More recently, 1,1,1-
trichloroethane has been linked to ozone
depletion in the upper atmosphere and will no
longer be manufactured in the U.S. after 1995.
As restrictbns increased the cradle-to-grave
liability for solvent waste generators, the metal
finishing industry began to turn to other op-
tions for cleaning operations. Aqueous clean-
ers, emulsion cleaners, mechanical and ther-
mal methods, and abrasive cleaners emerged
as alternatives to organb solvents. These
optbns help reduce emissions of volatile or-
ganb compounds (VOCs) and lessen worker
exposure. The switch to aqueous cleaners
can also reduce the annual reporting required
under SARA Title III, Section 313, Toxic
Chemical Release Reporting: Community
Right-To-Know.
Aqueous cleaners have already replaced
solvent degreasers in many industrial surface
preparation operations. The water-based
cleaners effectively remove protective oils,
cutting oils, hydraulic fluids, silbone oils, wa-
ter soluble coolants, shop dirts, finger prints,
and other soils. Special additives also make
the aqueous cleaners versatile coating solu-
tbns. Making the switch has even made it
possible to eliminate some separate
degreasing and coating processes as well as
reduce waste generation. Aqueous cleaners
are finding success in many industrial surface
preparation operatbns including airplane com-
ponents, printed circuit boards, advanced com-
posites, fasteners, and automotive parts.
The tank life of the aqueous cleaners is
limited by the buildup of the dirts and oils in
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the bath. Cleaning effectiveness begins to
deteriorate, and the performance of other
chemicals in the bath is inhibited. Although
the aqueous degreasers do not carry all the
risks and liabilities associated with the dis-
posal of waste organic solvent cleaners, peri-
odic replacement of the bath creates a differ-
ent waste disposal problem.
Current disposal options for spent aqueous
cleaning solutions include tankering, incinera-
tion, or discharge. The rising costs associ-
ated with these disposal and pollution control
options are the main incentives to extend the
life of the aqueous cleaner baths. Rather than
wasting valuable raw materials, the aqueous
cleaners have the potential to be recycled
again and again. Depending on the physical
characteristics of the bath solution, the life of
the bath can be extended by skimming con-
taminants off the top, settling heavier frac-
tions to the bottom, or filtering out suspended
species.
Ultrafiltration
Conventional filtration techniques rely on
depth or screen filters to remove oil and dirt
from a process solution, but conventional fil-
ter media clog easily. They require frequent
backflushing or disposal, which result in addi-
tional wastes. Membrane filtration is a more
advanced technique that takes advantage of
thin-film membranes and turbulent flow pat-
terns to deliver a more consistent flow rate
and a higher quality filtrate than conventional
filtration. Ultrafiltration is one class of mem-
brane filtration that uses membranes with
pore diameters ranging from 10'9 to 1Q-6 m.
The Ultrafiltration process works by produc-
ing two separate streams: concentrate and
permeate. The permeate stream contains
only the components in the feed solution
small enough to pass through the membrane
pores (water, solubilized species). The con-
centrate stream contains everything else that
is rejected by the membrane (emulsified oil
and dirt).
The recent development of more durable
membranes, such as PVDF, has expanded
the application of Ultrafiltration beyond its ori-
gins in the food industry to successfully handle
industrial process solutions with extreme pHs,
high temperatures, and high oil concentra-
tions. Because of its unique capabilities to
concentrate oily wastewater and produce a
clear filtrate, Ultrafiltration has emerged as a
promising technology for extending the life of
aqueous cleaner baths. Ultrafiltration of oil-
water emulsions is a more straightforward
method for removing and concentrating oil
than are other physical, chemical, or thermal
means. Ultrafiltration does not require a stock-
pile of chemicals and does not produce a
chemical sludge that requires special treat-
ment or disposal. Instead, Ultrafiltration pro-
duces a water phase that requires no further
treatment and a concentrated phase only a
fraction of the original volume that can sus-
tain combustion or be disposed of efficiently.
Ultrafiltration requires no heat input, low en-
ergy, and little operator attention.
One of the greatest limitations of Ultrafiltra-
tion membranes is their tendency to foul.
Fouling is detected as the decrease in per-
meate flux over time, where the flux is de-
fined as the volumetric flow rate of permeate
per cross-sectional area per time. Fouling is
mainly due to the accumulation of particles
on the membrane surface and/or within the
pores of the membrane itself. In industrial
applications where Ultrafiltration could be used
to filter aqueous cleaning baths, fouling will
typically be due to oils, suspended solids,
free surfactants, and metal precipitates. When
a membrane shows signs of fouling, the flux
can largely be restored by cleaning the mem-
brane, but a portion of the flux may be unre-
coverable because of irreversible fouling.
Full-Scale Testing
Results from the bench- and pilot-scale
studies were used to develop a full-scale,
modified-batch test conducted onsite at the
facility. Figure 1 shows how the full-scale test
applied Ultrafiltration directly to the 5000-gal
iron phosphating/degreasing bath. The objec-
tive was to directly measure the effect of
Ultrafiltration on the process solution under
actual plant conditions. The full-scale test took
into account the constant input of oil from the
production line and the daily addition of bath
chemicals. Additionally, the full-scale test also
helped identify problems with the Ultrafiltration
equipment and anticipate changes that should
be made on a permanent unit.
The full-scale in-plant testing featured an
Ultrafiltration system provided by Koch Mem-
brane Systems (Model UF-4) equipped with
four 1-in tubular PVDF membranes (100,000
Concentrate
Pump
ffrr
Men brane
Permeate to bath
Figure 1. Modified-batch scheme Ultrafiltration.
MWCO, 4.4 sq ft total area). Data obtained
from the full-scale modified-batch test was
used to determine whether Ultrafiltration would
be a viable option for waste reduction at the
plant. Technical, operational, and economic
aspects associated with the Ultrafiltration equip-
ment were examined to evaluate the feasibil-
ity of this technology to improve the company's
metal fabrication operation.
When field testing began, the iron
phosphating/degreasing bath had not been
replaced in over 3 mo. The aqueous solution
was murky with dirt and oil, and large patches
of free oil floated on the surface. The changes
that took place over the next 11 days of
Ultrafiltration testing produced a dramatic ef-
fect. Surface oil slicks disappeared and were
replaced by a clean, light foam. The bath
solution was visibly clearer, and plant person-
nel testified that it looked like a freshly re-
charged bath. Results of total organic carbon
(TOC) analyses for the full-scale testing
showed the change in oil and surfactant con-
centrations during the test (Figure 2).
Economic Analysis
The costs and benefits associated with
installing an Ultrafiltration system were ana-
lyzed to determine the economic feasibility of
this technology. Based on the estimated ex-
penditures and savings, the payback period
associated with this technology, was only 6.9
mo. The net present value and interest rate of
return indices were $152,143 and 178%, re-
spectively. Therefore, investment in an ultra-
filtration system represented a very attractive
economic alternative.
Conclusions
The overall evaluation of this pollution pre-
vention project was based on Ultrafiltration
performance, product quality, and econom-
ics. Results indicated that the concentration
of oil in the iron phosphating/degreasing bath
was substantially reduced and maintained at
acceptable operating levels. Virtually all of the
unused phosphating agents were conserved
although a portion of the unused surfactants
was not. Permeate rates exhibited excellent
performance during the acidic (pH=3.5), high
temperature (140°F) operation and were high
enough to process the constant input of oil
from the production line. The entire 5000-gal
bath was processed in 180 Ultrafiltration oper-
ating hours. Coating weight, rust creepage,
and paint adhesion tests conducted by DuBois
Research Laboratory and plant personnel on
samples of steel parts indicated that product
quality achieved during the full-scale study
was good for the plant's application. The
payback period for implementing the Ultrafil-
tration system was 6.9 mo. By using Ultrafil-
tration, the company will reduce its hazard-
ous waste generation by at least 15,000 gal/
yr, a 99.8% reduction.
£l).S. GOVERNMENT PRINTING OFFICE: 1993 - 7«NMm/moS9
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300
,
200 -1
O
roo
Increased surfactant
due to increased
Dura-Gard additions
'Surfactant
Oil
0 100 200
Operating Time (hours)
Figure 2. Oil and surfactant in bath vs time.
This project has successfully demonstrated
the ability of membrane filtration to reduce
hazardous waste generation and recover valu-
able raw materials in a metal fabrication op-
eration. This application introduces another
innovative waste reduction technique to the
metal fabricated products industry that could
benefit the many plants nationwide that use
aqueous cleaner systems like the iron
phosphating/degreasing process at the R.B.
White company. The ultrafiltration system
implemented in this project saves money,
maintains good product quality, and reduces
waste generation.
G.D. Miller, T.C. Lindsey, A.G. Ocker, and M.C. Miller are with the Illinois
Hazardous Waste Research and Information Center (HWRIC), Champaign,
IL 61820.
Paul Randall is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Ultrafiltration to Recover Aqueous
Iron Phosphating/Degreasing Bath," (OrderNo. PB93-221 638/AS; Cost:
$19.50, 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/144
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