&EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/M-91/015 Jul. 1991
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Metal Parts Coating Plant
F. William Kirsch and Gwen P. Looby*
Abstract
The U.S. Environmental Protection Agency (EPA) has funded
a pilot project to assist small- and medium-size manufacturers
who want to minimize their generation of hazardous waste but
lack the expertise to do so. Waste Minimization Assessment
Centers (WMACs) were established at selected universities
and procedures were adapted from the EPA Waste Minimiza-
tion Opportunity Assessment Manua/(EPA/625/7-88/003, July
1988). The WMAC team at the University of Tennessee per-
formed an assessment at a plant where automotive parts are
coated with epoxy, vinyl, or polyester powders; with liquid
plastisol; or with paint. After the WMAC team analyzed five
process lines (for applying coatings) and the reworking opera-
tion (where unacceptably finished parts are stripped), a report
was prepared detailing their findings and recommendations.
They found three ways to reduce the evaporation of methylethyl
ketone (MEK), the largest source of waste on the process lines:
reduce the open surface area of the MEK container, cool the
MEK, or meter the MEK. They also found ways to reduce
wastes from the rework process by installing controls, repairing
defective drive components, or using alternative methods to
remove defective coatings.
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cin-
cinnati, OH, to announce key findings of an ongoing research
project that is fully documented in a separate report of the same
title available from the authors.
'University City Science Center, Philadelphia, PA 19104.
Introduction
The amount of hazardous waste generated by industrial plants
has become an increasingly costly problem for manufacturers
and an additional stress on the environment. One solution to the
problem of hazardous waste is to reduce or eliminate the waste
at its source.
University City Science Center (Philadelphia, PA) has begun a
pilot project to assist small- and medium-size manufacturers
who want to minimize their formation of hazardous waste but
lack the inhouse expertise to do so. Under agreement with
EPA's Risk Reduction Engineering Laboratory, the Science
Center has established three WMACs. This assessment was
done by engineering faculty and students at the University of
Tennessee's (Knoxville) WMAC. The assessment teams have
considerable direct experience with process operations in
manufacturing plants and also have the knowledge and skills
needed to minimize hazardous waste generation.
The waste minimization assessments are done for small- and
medium-size manufacturers at no out- of-pocket cost to the
client. To qualify for the assessment, each client must fall within
Standard Industrial Classification Code 20-39, have gross
annual sales not exceeding $50 million, employ no more than
500 persons, and lack inhouse expertise in waste minimization.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers, reduced
waste treatment and disposal costs for participating plants,
valuable experience for graduate and undergraduate students
who participate in the program, and a cleaner environment
without more regulations and higher costs for manufacturers.
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Methodology of Assessments
The waste minimization assessments require several site visits
to each client served. In general, the WMACs follow the proce-
dures outlined in the EPA Waste Minimization Opportunity
Assessment Manua/(EPA/625/7-88/003, July 1988). The WMAC
staff locates the sources of hazardous waste in the plant and
identifies the current disposal or treatment methods and their
associated costs. They then identify and analyze a variety of
ways to reduce or eliminate the waste. Specific measures to
achieve that goal are recommended and the essential support-
ing technological and economic information is developed. Fi-
nally, a confidential report that details the WMAC's findings and
recommendations (including cost savings, implementation costs,
and payback times) is prepared for each client.
Plant Background
The plant coats metal automotive parts with epoxy, vinyl, or
polyester powders; liquid plastisol (a vinyl plastic in a liquid
carrier); or paint. Each year, the plant produces approximately
52 million parts ranging in size from 1/4 to 1 Ib.
Coating Operations
The following basic steps are employed to coat the metal parts:
surface cleaning and/or priming the metal parts,
heating metal parts for improved coating in a natural
gas or electric oven at 350° F to 900° F,
applying the desired coating,
• curing the coated part in a natural gas, electric, or infra-
red oven, and
water- or air-cooling the finished parts.
The following distinct process lines were analyzed by the WMAC
team, with each line using a different method for applying the
coating:
a line for the dipping of parts in a f luidized bed of water
containing epoxy, nylon, or vinyl powders;
two lines for dipping parts in plastisol, one of which
includes a step for applying a priming coat;
a line in which plastisol is mechanically applied to
specific areas of small metal parts;
two lines for the spraying of parts with a polyester or
epoxy powder; and
a line for the electrostatic painting of parts.
Rework Operations
Unsatisfactory coating of the parts can result from inadequate
control of the level of the coating material in the troughs;
adhesion problems related to improper curing oven tempera-
tures; variations in the speed of the parts conveyors; environ-
mental dust; or inadequate coating thickness resulting from
mechanical breakdowns. The plant uses three different rework
operations to reclaim unacceptable finished parts.
Epoxy, nylon, or vinyl coatings applied in the f luidized
bed line and the coatings apptied to 75% of the parts in
the electrostatic paint line are removed by incinerating
the parts in a natural gas oven at 1150° F. (The rework
operation used for the electrostatically painted parts is
determined by the type of paint used.)
Plastisol coatings are removed by overnight immer-
sion in MEK.
The coatings of 25% of the parts rejected after the
electrostatic painting and all of the parts rejected after
the polyester powder spray lines are removed with a
commercial acid stripping solution.
The reclaimed metal parts are sent back to the appropriate
process line after reworking.
Water Treatment
The assessment team also anatyzed the plant's water treatment
facility. Waste water streams from the process lines are fed into
three major collection pits; from there, the waste water feeds into
a large tank. The pH of the water is adjusted as necessary and
the fluid is pumped to a large sludge tank where solid sludge
settles out. Plant personnel have not determined the nature of
the sludge; however, a substantial amount of sludge has not yet
accumulated on-site. The water that is separated from the
sludge goes to a municipal sewer.
Waste Minimization Opportunities
The type of waste currently generated by the plant, the source
of the waste, the quantity of the waste, and the annual treatment
and disposal costs are given in Table 1.
Table 2 shows the various opportunities for waste minimization
that the WMAC team identified for the facility. The type and
source of the waste, the minimization opportunity, the possible
waste reduction and associated savings, and the implementa-
tion cost along with the payback time are described in the table.
As shown in Table 2, two sources of waste are the focus of the
waste minimization opportunities analyzed and recommended
by the WMAC. The first is the evaporation of MEK used as a
primer thinner in the plastisol dipping and mechanical applica-
tion lines. Three possible methods for reducing the amount of
evaporation are described in the table. The other source of the
waste is the rework operation. The generation of waste by the
rework processes can be reduced either by reducing the number
of parts that require reworking (through installation of controls or
repair of defective drive components) or by using an alternative
method to remove the defective coatings.
The quantities of hazardous waste currently generated by the
plant and possible waste reduction depend upon the production
level of the plant. All values stated should be considered in that
context.
Issues for Further Consideration
In addition to the recommended waste minimization opportuni-
ties, the WMAC team indicated that plant personnel should
continue to investigate the possible availability of a new, less
hazardous stripper/thinner to replace MEK and that each waste
water stream should be analyzed to determine its composition.
The current method for handling the waste water in the plant is
inefficient and imprecise.
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Table 1. Summary of Current Waste Generation.
Waste Generated
MEK (used as a primer thinner)
MEK
Plastisol sludge (contains
plastisol & MEK)
Spet acid stripping solution
Stripped paint residue & residual
spent stripper
Paint residue in paint tank
Spent, contaminated primer
Ash
Source of Waste
Evaporation from plastisol dipping and
mechanical application lines
Evaporation from plastisol rework line
Plastisol rework line
Acid stripping rework line
Acid stripping rework line
Electrostatic painting line
Plastisol lines
Incineration oven in rework line
Annual Quantity
Generated
8,400 gal
3,900 gal
600 gal
2, 100 gal
250 to
4,800 gal
680 gal
1,200 to4
Annual Waste
Management Cost
$0'
O1
O2
10,410
O3
20,020
3,560
1,260
1 Currently there are no costs for monitoring or controlling MEK emissions from evaporation; however, the MEK that evaporates must be
replaced.
2 Plastisol sludge is disposed of in municipal waste.
3 The material is accumulating on-site. There are no current costs for waste management.
4 Of the total 1,200 Ib/yr of ash produced, 700 Ib/yr resulting from the electorstatic painting rework is considered hazardous. The remaining
ash is disposed of in municipal waste.
Table 2. Summary of Recommended Waste Minimization Opportunities.
Annual Waste Reduction
Waste Generated
Evaporation of MEK from
plastisol dipping and
mechanical application
lines
Minimization Opportunity
Reduce open surface area
of primer/MEK container.
Cool MEK to reduce its
partial pressure.
Meter MEK concentration
Quantity
3, 160 gal
840 gal
1 ,400 gal
Percent
37.6
10.0
16.7
Net Annual
Savings
$11,240'
3.0001
4,980'
Implementation Payback
Cost Years
$3,000
2.900
12,400
0.3
1.0
2.5
Spent acid stripper from
the rework line
Stripped paint residue
and residual stripper
from rework line
Ash from the incineration
oven
MEK used in rework
line
Plastisol sludge
Spent acid stripper from
rework line
automatically to reduce
peak evaporation rate.
Install interlocking controls 1,510 gal
on the conveyor's speed and
paint volume flows in the
electrostatic painting and 180lb
powder spray lines
Replace defective drive
system components in
electrostatic paint line.
469 Ib
Install a cryogenic- 3,900 gal
mechanical stripping system
to remove coatings of rework
parts. 600 gal
2,100 gal
72.1
72.1
67.0
100.0
100.0
100.0
22.4302
134.0403
2.5304
13.8801
O4
42.780s
24,600
0.2
3,400 1.3
150.000 2.6
1 Cost savings because less MEK needed.
2 Includes $14,810/yr because less stripper is needed.
3 The material is accumulating on-site. There are no current costs for waste management. The cost savings are because less coating material
needed.
4 Includes $1,900/yr because less paint needed.
5 Includes $32,370/yr attributed to purchase of stripper.
6 U.S. GOVERNMENT PRINTING OFFICE: 1991 - S4»-0«t/40036
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This Research Brief summarizes a part of the work done under The EPA contact, Emma L. George, can be reached at:
Cooperative Agreement No. CR-814903 by the University City
Science Center under the sponsorship of the U.S. Environmen- Pollution Prevention Research Branch
tal Protection Agency. The EPA Project Officer was Brian A. Risk Reduction Engineering Laboratory
Westfall. U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States Center for Environmental Research BULK RATE
Environmental Protection Information POSTAGE & FEES PAID
Agency Cincinnati OH 45268 EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/M-91/015
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