&EPA
United States
Environmental Protection
Aqency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA600/S-92/018 April 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for an Aluminum Extrusions Manufacturer
Gwen 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 waste but who lack
the expertise to do so. Waste Minimization Assessment Cen-
ters (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 the University of Tennessee performed an
assessment at a plant manufacturing aluminum extrusions —
over 36 million Ib/yr. Primary and scrap aluminum is melted
down, cast into logs, then heat treated. Next, the logs are
extruded into desired shapes. Extrusions are sheared, heat
treated, then either buffed, anodized (colorized), painted, or
shipped. The team's report, detailing findings and recommen-
dations, indicated that the majority of waste was generated in
the anodizing line but that the greatest savings could be ob-
tained by installing an electrostatic powder coating system to
eliminate spent toluene, air filters, plastic sheets, paint ash,
and evaporated solvents.
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 available from the authors.
Introduction
The amount of waste generated by industrial plants has be-
come an increasingly costly problem for manufacturers and an
additional stress on the environment. One solution to the
1 University City Science Center, Philadelphia, PA 19104
problem of 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 waste but who 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 manu-
facturing plants and also have the knowledge and skills needed
to minimize 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.
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 Opportu-
nity Assessment Manual (EPA/625/7-88/003, July 1988). The
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WMAC staff locates the sources of 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 produces aluminum extrusions for use by other
product manufacturers. The plant operates 6,240 hr/yr to
produce over 36 million Ib of aluminum extrusions.
Manufacturing Process
This plant forms aluminum extrusions from virgin and scrap
metal. Raw materials for this process include primary or virgin
aluminum ingots, scrap aluminum, and alloying metals such as
copper, zinc, and nickel. An abbreviated process flow diagram
is illustrated in Rgure 1.
Aluminum metal melted,
cast, and extruded
Evaporated
Solvents,
Dried Paint Waste
Figure 1. Abbreviated process flow diagram.
The following steps are involved in making the extrusions:
Rrst, the primary and scrap aluminum and alloying metals are
melted in natural gas-fired furnaces. Then the molten metal is
cast Into "logs" In the plant's water-quench hydraulic casting
system. The logs are heat-treated and extruded into the
desired cross-sectional shapes. Next the extrusions are sheared
and heat-treated again. The finished extrusions are then sent
to the buffing, anodizing, or painting areas of the plant for
further processing.
Buffing
In the buffing area, a total of 1.3 million Ib/yr of aluminum
extrusions are manually positioned on a table where they are
passed under a motor-driven cloth-pad buffing wheel several
times. A buffing compound is sprayed onto the pads prior to
buffing. Approximately 2% of the buffing compound powder is
blown onto the floor, swept up, and disposed of in municipal
waste. Spent buffing compound is blown and aluminum dust
and buffing pad fibers are vacuum aspirated into a large water-
filled separating tank. Sludge is chain-raked from the bottom
of the tank and shipped to the onsite landfill. Waste water from
the separating tank is directed to a skimming pit before being
discharged to a nearby river. No other treatment is performed.
Used buffing pads are also disposed of in the onsite landfill.
The polished extrusions are then sent to shipping.
Anodizing !
Aluminum extrusions which require ancjdizing for corrosion
control and coloring (14 million Ib/yr) are fjiung on an overhead
crane to facilitate dipping into a series of fanks. The first tank
contains an alkaline detergent wash heated to 140°F. A small
quantity of waste is dumped from this tank to a caustic waste
lagoon which is part of the plant's waste water treatment
system. The parts are then dipped in a Irinse tank (tank #2);
overflow from this tank is directed to thej rinse tank (tank #4)
that follows the etch tanks described beloW.
i
Approximately 98% of those parts are then processed in one of
two steam-heated etch tanks which contain sodium hydroxide
and caustic solution. In the etch tanks, small quantities of the
product surfaces are chemically removed in preparation for
further treatment. Waste water from the e^ch tanks is sent to a
reaction pit which is part of the waste water treatment system.
Gases emitted from the two etch tanks are directed through
duct work to a water spray fume scrubber. Waste water from
the fume scrubber is sent to the caustic waste lagoon.
After etching, the extrusions are rinsed in two tanks (tank #4
and tank #6). The first rinse tank (tank #4) is fed by overflow
water from tank #2 that follows the detergent wash tank and
recirculated water from tank #6. Waste! water is fed to the
caustic waste lagoon. i
The extrusions are then sent to an acid de-smut tank which
contains hydrogen peroxide and sulfuric acid. Waste water
from this tank is dumped once a year to an acid waste lagoon
which is part of the plant's waste wate|r treatment system.
Parts are then dipped in a rinse tank from which overflow water
is fed to the acid waste lagoon. |
!
From that rinse tank, the extrusions are Iconveyed to one of
three anodizing tanks. Anodizing is an Electrolytic oxidation
process in which an aluminum oxide layer is formed on the
etched surface of the extrusions. This aluminum oxide layer is
extremely porous and is useful in the coloring of the extrusions.
Sulfuric acid is added to each anodizing tank; fumes from
these tanks are ducted to a water spray fume scrubber which
removes carryover sulfuric acid. Scrubber! water is pumped to
the acid waste lagoon of the water treatment facility. After
anodizing, the parts are spray-rinsed in one of two spray-rinse
tanks and then water-rinsed in an ambient tank. Waste water
from these rinses is gravity-fed to the |acid waste lagoon.
Extrusions are then put into a holding tank where water is
added with a constant overflow to the acid waste lagoon.
From the holding tank, extrusions may be conveyed to one of
two coloring tanks or to rinse tank #19. Approximately 30% of
the product being conveyed through the anodizing line is im-
mersed in a coloring tank containing sulfurp acid and stannous
sulfate. In this tank, tin is absorbed into the pores of the
aluminum oxide coating and a dark brown-to-black product
color results according to customer specifications. Color tests
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are made at this point and the product may be immersed in this
solution several times to reach the desired color. Waste
solution from this tank is dumped once a month to the acid
waste lagoon. Next, the product is spray-rinsed and sequen-
tially dipped into two water rinse tanks (tank #19 and tank #20).
The first dip rinse receives overflow water from the second
rinse tank. Waste water from all three of the aforementioned
rinse steps is pumped to the acid waste lagoon. From rinsing,
the extrusions are conveyed to one of three color sealant tanks
which contain a nickel fluoride sealant. The product is then
passed through a final rinse stage before air-drying and ship-
ping.
The second coloring tank contains a Sandoz bronze solution
which also is absorbed into the pores of the product surface
but results in a bronze-colored product. Only about 1% of
product goes through this coloring process. Waste water from
the Sandoz bronze tank is dumped once a year to the acid
waste lagoon. From this coloring tank, parts are rinsed in a
water tank and then immersed in a nickel sealant tank. Parts
are then water-rinsed and air-dried before shipping. Waste
water from these rinse and sealant tanks is pumped to the acid
waste lagoon.
The remaining 69% of the product that is sent through the
anodizing line is sent directly to rinse tank #19, which
precedes the nickel fluoride sealant tanks mentioned in the
sulfuric acid-stannous sulfate coloring process. After rinsing in
tanks 19 and 20, these extrusions are sealed in the nickel
fluoride sealant tanks, rinsed, air-dried, and sent to shipping.
Painting
Approximately 21 million Ib/yr of the extrusions are painted
before shipping. Extrusions to be painted are manually hung
on an overhead conveyor system which transports them through
a series of spray booths for pretreatment and painting. The
first pretreat booth consists of a recirculated heated alkaline
cleaner spray which removes dirt and grease. Waste water
from this step is dumped to the chromium treatment tanks
which are part of the plant's waste water treatment system.
Next, parts are spray-rinsed and conveyed through a spray
chromic acid surface treatment booth which enhances paint
adhesion. Drag-out and evaporative losses are so excessive
that the chromic surface treatment collection tank is never
dumped. Waste hexavalent chromic acid is pumped to the
chromium treatment tanks. The chromic acid treatment of
extrusions is followed by two rinse stages which complete the
pretreatment steps in the paint line. Waste water from those
rinse tanks is also pumped to the chromic treatment tanks.
Next, extrusions are conveyed through a natural gas-fired dry-
off oven (250°F) before passing through two electrostatic,paint
booths. Over 180 different colors of paint are used, most of
which are polyester and acrylic with the remaining paint being'
fluorocarbon-based. To achieve the desired color, the plant
has six paint mixing stations. Acrylic and polyester paints are
thinned with a "150 solvent". Fluorocarbon paint is thinned
with both methyl isobutyl ketone (MIBK) and "DB" solvents.
Toluene is pumped through the lines for cleaning between
color changes. Air filters in the paint booths are changed
periodically; plastic sheeting is placed on the floor to collect
paint overspray. The plastic and filters are removed to a
landfill. Paint-contaminated toluene is collected in barrels and
hauled offsite as a hazardous waste. Toluene also evaporates
to the plant atmosphere. After painting, the extrusions are
conveyed through a gas-fired bake oven (350-480°F) for 10 to
12 min, manually removed from supporting conveyor hooks,
and transferred to shipping. Unsatisfactorily painted stock is
transported to the melt oven and used as scrap charge. Paint-
laden conveyor hooks are periodically put in a natural gas-fired
burn-off oven for paint removal by incineration; ash is hauled
away with air filters and plastic sheeting as a non-hazardous
waste.
Existing Waste Management Practices
• Toxic hexavalent chrome is transformed to non-toxic
chrome before offsite shipment.
• An onsite waste water treatment facility controls sus-
pended and dissolved species concentrations in efflu-
ent water.
• A water-spray fume scrubber is utilized in the anodiz-
ing area for air quality control.
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 man-
agement costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC team recommended for the plant. The type of waste,
the minimization opportunity, the possible waste reduction and
associated savings, and the implementation cost along with the
payback time are given in the table. The quantities of 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.
It 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 waste treatment and disposal. Other savings not quantifi-
able 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.
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.
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Ttbla 1. Summary of Currant Waste Generation
Wests Generated
Butting compound sludge
Used buffing pads
Spent toluene
Evaporated toluene
Used air fitters, used plastic
shoaling, and paint ash
Evaporated paint solvents
Trivalant chromic sludge
Waste water sludge
Waste water
Source of Waste
Water-filled separating tank in the buffing line.
Sludge is disposed in the on-site landfill.
Cloth-pad buffing wheels in the buffing line.
Used pads are disposed in the on-site landfill.
Cleaning of paint lines between color changes.
Spent toluene is hauled off-site as a hazardous waste.
Cleaning of paint lines.
Electrostatic paint booths. Used air filters,
used plastic sheeting, and ash which results
from the removal of paint from conveyor hooks
in the burn-off oven are combined and hauled
away as non-hazardous waste.
Bake oven in the paint line.
Clarifior following the chromium treatment tanks
in the waste water treatment system.
Chromic sludge is disposed in the on-site landfill.
Clariffer fed by the acid and caustic waste lagoons and
the reaction pit in the waste water treatment system.
Sludge is disposed in the on-site landfill.
Waste water treatment system.
is discharged to a nearby river.
After treatment, water
Quantity Generated A
26,000 Ib
7,271 pads
1,430 gal
13,130 gal
50,000 Ib
6,973 gal
240,000 Ib
1, 800,000 Ib
47,160,000 gal
anagement Cost
$ 4,770
5,430
19,660
0'
7,990
O1
14,230
46,910
&
'Currently the plant reports no waste management cost associated with solvent evaporation.
*Currentty the plant reports no waste management cost associated with water discharge.
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Table 2. Summary of Recommended Waste Minimization Opportunities
Waste Generated Minimization Opportunity
Annual Waste Reduction Net Implementation Payback
Quantity Per Cent Annual Savings Cost Years
Spent toluene
Evaporated toluene
Used air filters, used plastic sheets,
and paint ash
Evaporated paint solvents
Waste water sludge
Buffing compound sludge
Spent toluene
Waste water sludge
Waste water
6,973 gal 100
Replace the solvent-based painting 1,430 gal 100
system with an electrostatic powder 13,130 gal 100
painting system. The proposed system 50,000 Ib 100
will eliminate the need for paint solvents
and spray gun and paint line cleaning.
In addition, the powder coating will
provide for more even coating of the
product surfaces and easy collection
and reuse of overspray powder.
Reduce drag-out from the tanks in the 3,600 Ib 0.2
anodizing line. An array of rinse spray
nozzles should be installed above the
detergent, etch, acid de-smut, anodizing,
stannous sulfate, nickel fluoride seal,
"Sandoz" bronze, and "Sandoz" seal tanks
to spray water onto each parts rack as it
is raised from the tank. Drag-out boards
should be installed on all tanks in the line
and the drain time of parts over the tanks
should be increased.
Install an automatic metering system 5,200 Ib 20
to minimize the amount of buffing
compound used.
Recover spent toluene using a distillation 1,144 gal 80
unit. The recovered toluene can be used
for cleaning the paint lines.
Recover and recycle caustic and acid 3,600 Ib 0.2
solutions in the rinse tanks of the 40,000,000 gal 85
anodizing process line. Install dedicated
reverse osmosis (RO) solution recovery
systems on the rinse tanks following the
etch, acid de-smut, and "Sandoz" bronze
tanks. An electrodialysis unit in series with
the etch rinse tank RO system Will be required
to remove aluminum hydroxide before reuse.
Waste water collection tanks with RO units
should be installed beneath the spray rinses
that precede the anodizing and stannous
sulfate tanks. In addition, the flow rates of
water through the rinse tanks should be
lowered to 5 gpm; air agitation units should
be installed in the tanks to increase rinsing
effectiveness and to compensate for the
lower flow rates. Savings will result from
recovery of raw materials lost in the rinsing
operations and reduced water purchases.
$1,084,440' $147,580 0.1
52,900s
28,910 0.5
6,590* 25,960 3,9
17,030s 37,060 2.2
105,480s 419,160 4.0
'Includes raw material cost savings attributed to the lower cost of powder coatings.
includes raw material cost savings.
•U.S. Government Printing Office: 1992 — 648-080/60076
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United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
B(JLK RATE
POSTAGE & FEES PAID
j EPA
PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/S-92/018
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