United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/M-91/024 July 1991
&EPA ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Manufacturer of
Compressed Air Equipment Components
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 manu-
facturers 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
Minimization Opportunity Assessment Manual (EPA/625/7-
88/003, July 1988). The WMAC team at Colorado State Univer-
sity inspected a plant manufacturing zinc and aluminum alloy
filters, regulators, lubricators, fittings, and valves — compo-
nents for compressed air equipment. Each step of the manu-
facturing process creates waste: f abricating zinc and aluminum
diecast parts generates scrap metal and spent lubricants and
hydraulic fluid; milling, drilling, and tapping generate spent
cutting/cooling fluid and solvents and metal shavings; cleaning
machined parts and steel parts fashioned off-site generates
waste oil and 1,1,1,-trichloroethane; and surface coating of
metal parts generates effluents from chemical baths and alka-
line rinses, e.g., chromium, sulfate, and phosphate precipi-
tates. Other processes generate additional waste hydraulic
fluid, cutting/cooling fluid, and Freon.* Although the plant had
already changed several procedures to minimize its wastes,
the WMAC team's report, detailing findings and recommenda-
tions, identified several practices that might be changed to
effect greater waste reduction and savings. The recommenda-
tion resulting in the greatest reduction involves replacing chro-
mium-containing reagents with those that generate no hazard-
ous waste; the proposed coating process requires no rinsing
and would, therefore, not contaminate rinse waters.
This Research Brief was developed by the principal inves-
tigators and EPA's Risk Reduction Engineering Laboratory,
Cincinnati, OH, to announce key findings of an ongoing re-
search project that is fully documented in a separate report of
the same title available from the authors.
Introduction
The amount of hazardous waste generated by industrial
plants has become an increasingly costly problem for manufac-
turers and an additional stress on the environment. One solu-
tion 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 manu-
facturers who want to minimize their formation of hazardous
waste but lack the inhouse expertise to do so. Under agree-
ment with EPA's Risk Reduction Engineering Laboratory, the
Science Center has established three WMACs. This assess-
ment 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.
University City Science Center, Philadelphia, PA 19104
Mention of trade names or commercial products does not
constitute endorsement or recommendation for use.
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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 an-
nual 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 minimiza-
tion of the amount of waste generated by manufacturers, re-
duced waste treatment and disposal costs for participating
plants, valuable experience for graduate and undergraduate
students who participate in the program, and a cleaner environ-
ment without more regulations and higher costs for manufactur-
ers.
Methodology of Assessments
The waste minimization assessments require several site
visits to each client served. In general, the WMACs follow the
procedures outlined in the EPA Waste Minimization Opportunity
Assessment Manual (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 manufactures zinc and aluminum alloy filters,
regulators, lubricators, fittings, and valves. The plant is operated
over 7,000 hr/yr by its 400 employees to produce nearly 4 million
units annually.
Manufacturing Process
The manufacture of compressed air equipment compo-
nents begins with the fabrication of zinc and aluminum diecast
parts. Zinc and aluminum alloy ingots are melted in separate
furnaces and the molten metals are then transported to diecast -
ing machines. The diecasting machines force the liquid metals
into a mold-and-plunger assembly by hydraulic compression. A
water-based lubricant is sprayed on the molds, and an oil-based
lubricant is used for the plunger. Excess lubricants collect in a
sump and are mixed with other oil wastes for disposal. Small
amounts of solvent used to clean the diecasting machines are
also mixed with the oil wastes. An ethylene glycoI/water-based
hydraulic fluid provides the required hydraulic compression.
Extensive leakage in the hydraulic fluid reservoir requires that
fresh hydraulic fluid be added to maintain the proper fluid level.
Used fluid is mixed with the miscellaneous oil and solvent
wastes for disposal. Solid wastes in the diecasting area consist
of scrap and excess metal, which is remelted in the proper
furnace along with the raw metal ingots.
Diecast metal parts are transported to the machining area
to be milled, drilled, and tapped as required. Most of the
machining equipment uses a water-based cutting/cooling fluid.
A centrifuge removes metal contaminants so that the fluid may
be reused. Solids and sludge that remain are mixed with oil and
solvent wastes for disposal. Some of the machining equipment
uses an oil-based lubricant; no liquid wastes are generated from
these machines because the oil is recycled. Occasionally,
lubricant is added to compensate for lubricant that remains on
the metal parts. Small amounts of solvent used to clean the
machines are mixed with the oil wastes. Oil-contaminated metal
shavings from the machining area are sold to an outside firm for
reuse.
After machining, parts are washed with an alkaline solution
containing borax to remove remaining cutting oil and are deburred
before application of protective coatings. Oil is collected by a
skimmer in the alkaline washer and mixed with the water-based
lubricant from the machining area. Effluent from the washer is
combined with other aqueous wastes that flow to an on-site
wastewater treatment unit.
Steel parts that have been manufactured at an off-site
facility are cleaned in a small vapor degreasing unit with 1,1,1-
trichloroethane. Waste solvent and still bottoms from the vapor
degreaser are drummed and disposed of as hazardous waste.
Surface coatings are applied to all metal parts. Chromate
conversion, phosphate, or anodized coatings are applied by
immersing the parts in a series of chemical baths and rinses. The
chromate conversion coating line is automated, and the phos-
phate and anodized coating lines are operated manually. The
actual treatment process varies for each metal coated. Effluents
from the coating lines and alkaline washer are combined and
treated inthewastewatertreatmentfacility. Sodium metabisulfite
is added to reduce hexavalent chromium to trivalent chromium.
Sodium hydroxide is then added to raise the pH from about 2.75
to 8.5 and to form insoluble metal hydroxides. Adding calcium
chloride removes sulfate and phosphate ions as insoluble
calcium compounds. Precipitates are flocculated with a polymer
and allowed to settle to form a metal hydroxide sludge, which is
periodically pumped to a filter press for dewatering and shipped
to a hazardous waste disposal facility. The supernatant's con-
taminant level is below the pretreatment specifications of the
local Publicly Owned Treatment Works (POTW), so it is dis-
charged to the sewer system.
Powder coating is applied to some of the metal parts, which
are then cured in a furnace. No hazardous waste is generated
in the powder coating process.
Plastic injection molding machines, which use an oil-based
hydraulic fluid, produce the plastic components of the com-
pressed air equipment. The hydraulic fluid is filtered periodically
and reused. Contaminated fluid is mixed with other oil and
solvent wastes for disposal.
Hazardous wastes are also generated in processes not
directly related to manufacturing. The tooling area, where molds
and equipment are maintained, contains equipment that em-
ploys the same water-based cutting/coolant fluid used for ma-
chining. This fluid is also reused after processing with the
centrifuge. The clean room generates about 10 gal/mo of waste
Freon from cleaning components to be used for medical and
other special applications; the waste is sent off-site for disposal.
Small amounts of solvent-based paints are used for machinery,
and any waste is sent off-site for disposal.
Existing Waste Management Practices
Before the WMAC's assessment, the plant had already
taken the following steps to minimize and manage its generation
of hazardous wastes:
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Using a centrifuge to remove metal chips and fine
particles from the water-based coolant/cutting
fluid used in the machining area. The clean fluid is
then collected and reused.
Eliminating on-site treatment of steel parts in the
near future; this will reduce or eliminate the need
for solvent degreasing and also the need to dispose
of contaminated 1,1, 1-trichloroethane.
Using an alkaline wash to remove oil from metal
parts before surface treatment. This alkaline
wash replaced more traditional cleaners, such as
halogenated organic compounds.
Using a filter press to reduce the water content of
the hazardous metal hydroxide sludge before
shipment off-site for disposal.
Using powder coatings on metal parts. Replacing
solvent-based paints with powder coating
eliminated solvent-based paint wastes and
reduced the emission of volatile organic
compounds.
Collecting metallic wastes from the diecasting
process and remelting them in the appropriate
furnace. Oil-contaminated metal chips from the
machining area are collected and sold to a metal
recycle r.
Minimizing the use of solvent-based paints for
general painting. Solvent-based paints are only
used on machinery and other items not suited for
water-based paints.
Waste Minimization Opportunities
Table 1 summarizes the principal sources of waste, the
amounts generated, and the associated management costs.
Table 2 briefly describes current plant practices, the recom-
mended waste minimization opportunities, and savings and cost
data.
Additional Recommendations
The WMAC also investigated several other opportunities
for waste minimization that require relatively lengthy paybacks
or are considered to be beyond the scope of this program. These
measures are:
Implementing a preventative maintenance
program for the diecasting machinery to reduce
the frequency and cost of unscheduled repairs.
Establishing a program to segregate oil wastes to
allow recycling of waste oils.
Using a water/glycol fluid instead of a petroleum-
based fluid as the hydraulic fluid in the plastic
injection molders. The water/glycol fluid would
reduce waste generation because of its longer
lifetime.
Installing a solvent recovery unit to remove
contaminants from the 1,1,1-trichloroethane used
in the vapor degreasing unit.
Using deionized water in the reagent baths in the
chromate conversion coating line.
Removing waste oil from the alkaline wash water.
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. Environ-
mental Protection Agency. The EPA Project Officer was Brian A.
Westfall.
The EPA contact, Emma L. George, can be reached at:
Pollution Prevention Research Branch
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
Table 1. Summary of Current Waste Generation
Waste Stream Source of Waste
Combined wastes including water-based die
lubricant, oil-based plunger lubricant,
water- soluble cutting coolant, water/glycol
hydraulic fluid, and equipment cleaning
solvents.
Combined wastes including petroleum-based
cutting coolant, water-soluble cutting coolant,
water/glycol hydraulic fluid, and equipment
cleaning solvents.
Combined wastes including petroleum-based
and water-based cutting coolants and
equipment cleaning solvents.
1,1,1-trichloroethane and still bottoms.
Rinse water laden with heavy metals and
reagents used in chromate conversion coating,
phosphating, and anodizing.
Chromium hydroxide and other metal hydroxide
solids.
Annual Quantity
Generated (gal)
Annual Waste
Management Cost
Die casting 9,660
Plastic molding 1,780
Machining of die cast parts 18,060
Vapor degreaser unit 350
Treatment of rinse water from
the coating operation and the
alkaline washer 2,930,000
Treatment of rinse water from
the coating operation and the
alkaline washer 5,700
$5,300
980
9,920
1,750
4,900
10,400
•&U.S. GOVERNMENT PRINTING OFFICE: 1991 - 548-028/40025
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Table 1. Continued.
Waste Stream
Waste Freon.
Waste solvent-based paint and thinner.
Source of Waste Annual Quantity
Generated (gal)
Cleaning of parts used in
special applications 100
Painting of plant equipment 400
Annual Waste
Management Cost
130
2,560
Table 2. Summary of Recommended Waste Minimization Opportunities
Present Practice Proposed Action
Reagents used to create a conversion
coating on aluminum parts contain
chromium and therefore generate
hazardous waste. These reagents
contaminate rinse water and
contribute to the amount of hazardous
solid waste that is generated.
Oil wastes from the die casting,
injection molding, and machining
areas are combined and form a
multiphase fluid that is sent to a
disposal facility.
Drainage time over reagent baths in
the chromate conversion coating line
is 5 sec.
Replace the chromium-containing
reagents with reagents that generate
no hazardous waste. The proposed
coating process does not require
rinsing after coating and therefore
will not contaminate rinse waters.
Use magnesium chloride as a de-
emulsifying agent to break the oil-
water emulsion. The oil waste can be
collected in a tank and sent to an
oil recyder. The aqueous phase can be
treated at the plant's wastewater
treatment facility.
Increase the drainage time to 10 sec
to allow more reagent to drain back
into the bath. Waste reduction will
result from extended lifetimes for the
baths.
Waste Reduction and
Associated Savings
Solid waste reduction = 1280 gal/yr
Liquid waste reduction = 659,300 gal/yr
Cost savings = $5,480/yr
Implementation cost = $0
Payback is immediate.
Waste reduction = 16,230 gal/yr
Cost savings = $6,820/yr
Implementation cost = $2,500
Payback = 0.4 yr
Waste reduction = 17 gal/yr
Cost savings = $210/yr
Implementation cost = $ 0
Payback is immediate.
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/M-91/024
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