vvEPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/60Q/S-92/021 May 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Manufacturer of
Sheet Metal Cabinets and Precision Metal Parts
Gweh P. Looby and F. William Kirsch*
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
who lack the expertise to do so. Waste Minimization Assess-
ment Centers (WMACs) were established at selected universi-
ties, and procedures were adapted from the EPA Waste Mini-
mization Opportunity Assessment Manual (EPA/625/7-88/003,
July 1988). The WMAC team at Colorado State, University
performed an assessment for a plant that manufactures sheet
metal cabinets and precision metal parts. To make the cabi-
nets, sheet metal is cut to size, bent, welded, and polished.
The metal parts are then surface treated and painted. The
machined parts are produced from bar stock which is cut,
drilled, milled, and ground as needed. The team's report, de-
tailing findings and recommendations, indicated that the most
waste was generated by the chromate conversion and iron
phosphate coating processes that prepare the parts for paint-
ing. The plant could achieve the greatest cost savings by
replacing solvent-based painting with powder-based painting.
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cincin-
nati, OH, to announce key findings of an ongoing research
project that is fully documented in a separate report of the
same title, which is available from the authors.
Introduction
The amount of hazardous waste generated by industrial plants
has become an increasingly costly problem for manufacturers
*Universfty City Science Center, Philadelphia, PA 19104.
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
who lack the in-house expertise to do so. Under agreement
with EPA's Risk Reduction Engineering Laboratory, the Sci-
ence Center has established three WMACs. This assessment
was done by engineering faculty and students at Colorado
State University's (Fort Collins) 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 in-house expertise in waste minimiza-
tion.
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.
Methodology of Assessments
The waste minimization assessments require several site visits
to each client served. In general, the WMACs follow the proce-
' oĢ6 Printed on Recycled Paper
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durss outlined in the EPA Waste Minimization Opportunity
Assessment Afam/a/(EPA/825/7-88/003, 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
This plant manufactures sheet metal cabinets and precision
metal parts. Approximately 1.15 million parts are produced
annually by 140 employees who operate the plant 2,210 hr/yr.
Manufacturing Process
Sheet Metal Parts
Sheets of aluminum and steel are cut to the proper size and
shape. Holes are punched into the metal that is then bent as
needed. Some pieces are welded together. Rough edges and
surfaces are polished with power sanders and buffers. Metal
scrap is shipped to a scrap metal dealer for recycling. Spent
cutting fluid and waste hydraulic oil are combined and shipped
offsite for recycle or incineration.
Before painting, metal parts are surface treated to improve
paint bonding and provide corrosion protection. Aluminum parts
receive a chromate conversion coating while steel parts re-
ceive an iron phosphate coating.
Aluminum parts are first dipped in a caustic cleaning solution
that is followed by a continuous-flow tap-water rinse. A third
tank contains a desmut solution and is followed by another
continuous-flow tap-wafer rinse tank. A fifth tank contains the
chromic acid-based chromate conversion solution. A sixth tank
is a continuous-flow tap-water rinse and a final tank is a heated
dead rinse of tap water. The caustic cleaner, desmut, and first
rinse tanks are dumped monthly; the chromic acid tank is
dumped every three to four years; and the remaining solutions
are dumped every five months. In addition, sludge accumu-
lates in the caustic cleaner tank and is disposed of monthly.
In iron phosphate coating of steel parts, the first stage involves
a caustic cleaning tank followed by a continuous-flow tap-water
rinse. A third tank contains the iron phosphating solution and is
followed by another continuous-flow tap-water rinse. A final
tank contains a deoxidizing solution. All of these baths are
dumped and replenished on a monthly basis. Combined waste-
waters from the iron phosphate and chromate conversion lines
drain to an overflow tank and are then drained to the sewer as
Industrial wastewater. Typically, pretreatment before discharge
is not required because the wastewater meets discharge limits
set by the publicly owned treatment works (POTW). Sludge
accumulates in the caustic cleaner and iron phosphate tanks
and is disposed of monthly.
Solvent-based paint is applied to metal parts in dry paint
booths. Waste paint that is generated when the paint mixture
becomes too thick to be used is shipped to a hazardous waste
treatment, storage, and disposal facility (TSDF). Spent paint
thinner is also shipped offsite. Painted parts are dried and
cured in ovens. The plant uses powder-based paint coatings
on a small portion of parts. The type of paint used is dictated
by customer requirements.
Machined Parts
Bar stock is cut, drilled, milled, and ground as needed. Fin-
ished parts are assembled (if required) and shipped to custom-
ers. Metal scrap is shipped to a scrap metal dealer for recycle.
Spent cutting fluid and waste hydraulic oil are combined with
similar waste from the manufacture of sheet metal parts and
shipped offsite for recycle or incineration.
Existing Waste Management Practices
This plant has taken the following steps to manage and mini-
mize its wastes:
Scrap metal is segregated onsite and sold to a recycler.
All reagent tanks in the phosphating and chromating lines
are located in a large pit with a central drain to contain
spills.
Drain boards are used between surface treatment tanks to
reduce drag-out.
Reagent solutions in the surface treatment lines are agi-
tated with air to increase the effectiveness of the reagents.
Dry paint booths are used for painting to avoid generating
aqueous paint-laden wastes that are generated in wet
paint booths.
A small powder coating unit is used for painting some
products in order to avoid using solvent-based paints.
Tank dumps are coordinated to achieve neutralization so
that the sewered effluent meets POTW requirements.
Waste Minimization Opportunities
The type of waste currently generated by the plant, the waste
management method used, the quantity of the waste, and the
annual management costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC team recommended for the plant. The present practice,
the recommended action, and the waste reduction and associ-
ated savings are also given in Table 2. The quantities of
hazardous waste currently generated by the plant and possible
waste reduction depend on the production level of the plant. All
values should be considered In that context.
ft should be noted that, in most cases, the economic savings of
the minimization opportunities result from the need for less raw
material and from reduced present and future costs associated
with hazardous waste treatment and disposal. Other savings
not quantifiable by this study include a wide variety of possible
future costs related to changing emissions standards, liability,
and employee health. It should also be noted that the savings
given for each opportunity reflect the savings achievable when
implementing each waste minimization opportunity indepen-
dently and do not reflect duplication of savings that would
result when the opportunities are implemented in a package.
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Additional Recommendations
In addition to the opportunities recommended and analyzed by
the WMAC team, several additional measures were consid-
ered. These measures were not analyzed completely because
of insufficient data, implementation difficulty, or a projected
lengthy payback. Since one or more of these approaches to
waste reduction may, however, increase in attractiveness with
changing conditions in the plant, they were brought to the
plant's attention for future consideration.
Install filtration units for the iron phosphating and caustic
cleaner solutions to increase solution lifetime.
Use deionized water to make-up and maintain the caustic
cleaner and iron phosphating solutions, thereby reducing
sludge formation.
Substitute nonchromate conversion coating for the chro-
mate conversion coating currently used on aluminum parts.
Increase drainage times over the tanks in the iron
phosphating and chromate conversion lines in order to
reduce drag-out.
Segregate waste oil from the spent cutting fluid and re-
cycle ft.
Improve segregation of scrap metal before recycling.
Implement a preventive maintenance program for the ma-
chine shop to reduce the quantities of spent cutting fluid
and waste oil.
This research brief summarizes a part of the work done under
Cooperative Agreement No. CR-814903 by the University City
Science Center under the sponsorship of the U.S. Environmen-
tal Protection Agency. The EPA Project Officer was Emma Lou
George.
Table 1. Summary of Current Waste Generation
Waste Generated
Waste Management Method
Annual Quantity
Generated (gal)
Annual Waste
Management Cost ($)
Machining '
Scrap metal
Cutting fluid/hydraulic oil
Chromate Conversion Coating
Spent caustic cleaner
Caustic cleaner sludge
Caustic cleaner rinse water
Spent desmut solution
Desmut rinse water
Spent chromating solution
Chromating rinse water
Heated dead rinse
Iron Phosphate Coating
Spent caustic cleaner
Caustic cleaner sludge
Caustic cleaner rinse water
Spent iron phosphate solution
Iron phosphate sludge
Phosphating rinse water
Spent deoxidizer solution
Painting
Waste paint and paint sludge
Spent paint thinner
Shipped to scrap dealer for recycle
Off site recycle or incineration
Sewered as industrial wastewater
Conventional disposal in landfill
Sewered as industrial wastewater
Sewered as industrial wastewater
Sewered as industrial wastewater
Sewered as industrial wastewater
Sewered as industrial wastewater
Sewered as industrial wastewater
Sewered as industrial wastewater
Conventional disposal in landfill
Sewered as industrial wastewater
Sewered as industrial wastewater
Conventional disposal in landfill
Sewered as industrial wastewater
Sewered as industrial wastewater
Offsite recycle or incineration
Offsite recycle or incineration
N/A
1,320
14,400
60
359,160
14,400
345,260
300
345,260
2,880
33,600
60
378,360
33,600
60
378,360
33,600
1,430
1,320
N/A
5,780
20
0
660
20
640
0
640
0
60
0
700
60
0
1,160
60
61,370
11,330
A U.S. GOVERNMENT PRINTING OFFICE: 199Z - 648-080/40265
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Summary of Waste Minimization Opportunities Recommended
Present Practice Proposed Action
Savings
Solvent-based paints are used to
coat tho majority of this plant's
products. Wasta paint, paint
sktdgo, and spent thinner are
disposed of off site.
A solvent recovery unit In tfte plant
currently Is not operational because
of o/7 and water leaks.
Cutting fluid currently is used
until It becomes malodorous or until
Us viscosity and lubricity are
unacceptable. Average fluid
Sfoiimo is about three months.
Rinso water rates set by operators
exceed flow rates required by the
rinses in the chromate conversion
and phosphating lines.
Replace solvent-based painting
with powder-based painting for a
portion of the plant's products.
Cost savings will result from reduced
disposal costs and reduced raw
material costs. Installation of a
batch spray booth for powder
coating will be required.
Replace solvent-based painting
with water-based painting fora
portion of the plant's products (a
separate portion from previous WMO).
Cost savings will result from
reduced disposal costs and reduced
raw material costs. Requires the
purchase of new paint application
equipment and may require increased
curing times.
Overhaul the solvent recovery unit to
permit reuse of spent paint thinner.
Cost savings will result from reduced
disposal costs and reduced purchases
of thinner.
Institute a program to recycle the
cutting fluid onsite. Fluid should be
filtered periodically to remove metal
chips and particulate matter, thereby
extending the life of the cutting fluid.
In addition, the spent cutting fluid can
be treated with acid to reduce the
volume of wastes that must be shipped
offsite. The addition of acid will cause
a phase separation; the aqueous
phase can be neutralized and sewered
and the organic phase should be
disposed of offsite.
Install a flow reducer and flow meter
in the water supply line upstream of
the rinses in the chromate conversion
' andiron phosphating lines, thus reduc-
ing the quantity of water purchased
and sewered.
Waste reduction = 72 gal/yr
(waste paint and paint sludge) + 66 gal/yr (spent thinner)
Waste management cost savings = $740/yr
Net raw material cost savings = $14,230/yr
Total cost savings = $14,970/yr
Implementation cost = $20,600
Simple payback = 1.4 yr
Waste reduction = 72 gal/yr
(waste paint and paint sludge) + 66 gal/yr (spent thinner)
Waste management cost savings = $740/yr
New raw material cost savings = $10,930/yr
Total cost savings = $11,670/yr
Implementation cost = $2,500
Simple payback = 0.2 yr
Waste reduction = 660 gal/yr
Waste management cost savings = $3,890/yr
Raw material cost savings = $1,780/yr
Operating cost of recovery unit = $430/yr
Net cost savings = $5,240/yr
Implementation cost = $2,500
Simple payback = 2.1 yr
Waste reduction = 425 gal/yr
Waste management cost savings = $2,920/yr
Raw material cost savings = $570/yr
Operating cost of filtration unit = $370/yr
Total cost savings = $3,120/yr
Implementation cost = $7,050
Simple payback = 2.3 yr
Waste reduction = 331,500 gal/yr
Waste management cost savings = $100/yr
Raw material cost savings = $510/yr
Total cost savings - $610/yr
Implementation cost = $100
Simple payback = 0.2 yr
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
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Penalty for Private Use $300
EPA/600/S-92/001
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