Executive Summary
Acronyms
Industry Background
Environmental Issues and Regulations
Clean Technology Developments
Future Trends
References
TABLES
Table 1: Key Organizations in the U.S. Metal Fabrication Industry
Table 2: Process Materials Inputs and Outputs for Metal
Fabrication Processes
Table 3: Top 10 TRI Releases for 1993
Table 4: TRI Reductions Per Waste Stream
Table 5: Clean Technology Manufacturers
1. EXECUTIVE
SUMMARY
This report gives a brief overview of the state of the U.S. metal
fabrication industry, with an emphasis on efforts to incorporate pollution
prevention and clean technologies into metal-processing operations. This
report is not intended to be a thoroughly comprehensive industry guide or
study. Rather, it was written as guidance material for those who are seeking
general information about the U.S. metal fabrication industry and its use of
technologies and processes that reduce or prevent pollution.
This report concentrates on three areas of metal fabrication, with an
emphasis on the automobile industry. Metal fabrication encompasses three
distinct sectors: metal formation (casting, forging, and shaping), metal
preparation, and metal finishing (plating, painting, coating, and so on).
The latter two sectors are usually grouped as one because of the similar
nature of their operations.
Product demand from the automotive sector has continued to increase, and
automotive demand has outpaced U.S. production. The U.S. industry is one of
the largest producers and exporters in the world. Exports of metal products
are expected to continue to expand to developing countries in Asia and South
America. Canada still receives the largest amount of finished U.S. metal
components.
Key resources used by the industry include the following:
Water. Water is used extensively in metal preparation and finishing.
It is an active part in most metal immersion processes. In metal-forming
operations, the use of water is not as big a factor as in other metal
fabrication processes.
Protective Metals. The most common protective metals used by the
finishing industry include nickel, copper, zinc, and chromium. These metals
provide a chemistry that makes them less likely to form surface oxides;
these metals can also provide an attractive appearance. The automobile
industry has long used these metals in their component manufacturing.
Energy. Metal formation, particularly metal casting, is the most
energy-intensive process in metal fabrication. More than 60% of the energy
used by an iron foundry goes to molten metal operations. Significant amounts
of fossil fuels (e.g., coke and coal) are needed to keep the molten metal in
liquid form. Coal is readily available in the United States and is not
considered a limiting natural resource, but stack air emissions from fossil
fuel use have become a major pollution concern. The industry is just
beginning to utilize economical alternative fuels that create less
environmental pollution.
Raw Materials. There are a multitude of raw materials that go into the
metal fabrication process. Most of the more toxic and hazardous materials
are used in the surface preparation and finishing sectors, whereas metal
formation and casting use less toxic materials. Metals (e.g., steel, iron,
and aluminum), water, fossil fuels, aqueous cleaners, solvents, cooling
fluids, abrasives, and complexing metal bath agents are the major raw
materials used in metal fabrication.
Key environmental issues for the U.S. industry include the following:
Wastewater. Metal fabrication wastewaters are high in inorganic
materials and have a high chemical oxygen demand (COD). Like other
industrial operations, a majority of the companies have started to recycle
their wastewater within a plant. Cyanide and heavy metal waste streams from
metal preparation and finishing operations are the more difficult
wastewaters to treat. In the past, wastewater was combined and then treated,
but today most operations only combine waste streams when the combination
would be beneficial to the treatment process.
Air Emissions. Air emissions from metal preparation and finishing
operations represent one of the greatest areas of concern for pollution
prevention. For many years, air emissions were viewed as an unseen hazard,
because they were more difficult to quantify and regulate than solid and
liquid wastes. Attempts have been made to restrict the volatilization of
toxic chemicals from solvent and plating bath operations. Although both
fugitive and point air emissions have been reduced in the past 10 years,
fugitive emissions represent the greatest area of reduction.
Solid and Liquid Waste. For the metal-forming industry, the introduction
and subsequent disposal of machining and forming fluids is a source of
pollution once they outlive their usefulness. These cooling and cutting oils
are recycled and reused in the original process or left as a petroleum oil
lubricant (POL) waste stream.
Typically, solid waste streams (hazardous and nonhazardous) result from
excess metal material that is trimmed from manufactured metal products or is
a rejected metal component. In both cases, the scrap metal is almost always
recycled back into the metal formation process. Used foundry sand and
wastewater treatment processes generate most other solid
wastes for the industry.
The various federal environmental regulations and statutes that affect the
metal fabrication industry are the following:
- Federal Water Pollution Control Act or
the Clean Water Act (CWA)
- Clean Air Act (CAA)
- Resource Conservation and Recovery Act
(RCRA)
- Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA), commonly known as "Superfund"
- Pollution Prevention Act (PPA)
Clean technologies described in this
document include the following:
- Best Management Practices (BMPs)
include improving inventory control, preventing accidental spills,
segregating waste streams, and scheduling production runs that maximize
production and minimize waste.
- Recycling Metal-Working/Cutting
Fluids, Foundry Sand, and Lost Foam Casting reduces both the
amount of hazardous materials (HMs) procured and hazardous waste (HW)
generated for working fluids. Fluid life can be extended by 40% and
foundry sand can be used in construction fill applications.
- Alternatives to Solvent
Cleaning utilize ultrasonic cleaning or product substitution to
reduce and eliminate hazardous air emissions.
- Component Parts Washers
represent a contained system to reduce the amount and toxicity of
fugitive and point source air emissions.
- Water Use Reduction (Closed
Loop/Zero Emission Systems) reduces effluent from the
manufacturing process by either recycling or making waste material become
a useful raw material.
- Improved Sensors and Process
Control involve use of advanced techniques to control specific
portions of the manufacturing process to reduce wastes and increase
productivity.
- Mechanical Blast Media
use mechanical means to prepare and clean a metal surface for finishing.
- Electrodialysis Technology for
Bath Solutions efficiently maintain a low metal ion concentration
in the anodizing bath solution by transporting metal ions from the bath
solution through a selective membrane into a capture media using an
electrical current to induce flow.
- Hexavalent Chromium Plating
Substitution Options replace toxic chromium plating operations
with either physical plating or reduced toxicity plating operations.
- Electroless Plating Bath Life
Extension is used to extend the useful life of a plating bath
through addition of bath chemicals (reducing agents, complexing agents,
hypophosphite, and bath stabilizers).
- Ion Vapor Deposition
is fundamentally an evaporative coating process that gradually builds a
film on the metal surface to be coated.
- Electrolytic Recovery
Technology for Metal Cyanide Recycling uses an electrical current
to plate out the metals and oxidize the cyanides in the rinse waters.
The metal-forming industries have been
switching to continuous casting operations that allow the molten metal to be
formed directly into sheets to eliminate interim forming stages. Companies
are starting to utilize alternative fuels that create less pollution.
Mechanical surface preparation is expected to increase in use over
traditional chemical preparation. The more apparent trends concerning clean
technologies and pollution prevention (P2) are source reduction and process
recycling. Gradually, the industry is beginning to move from the more
hazardous heavy metals (e.g., chromium and cadmium) to less
hazardous metals such as nickel and zinc. Although improved HM/HW management
is one of the more difficult BMPs to implement quickly and efficiently, it
will continue to be a part of most companies' pollution prevention plans.
Ion Vapor Deposition (IVD) practices are expected to continue to replace
aqueous plating operations. Zero emissions and closed-loop systems are
expected to gain in importance as the industry tightens its "wastewater and
air emission" belts.
The U.S. metal fabrication industry will continue to face some of the most
stringent environmental regulations in the world. The development of new and
innovative pollution prevention technologies will be needed to ensure the
industry can achieve proposed and pending discharge limitations. Pollution
prevention and clean technologies will allow the industry to meet
environmental standards and still provide quality, cost-competitive
products.
ACRONYMS
BMP |
Best
Management Practice |
CAA |
Clean Air
Act |
CERCLA |
Comprehensive Environmental Response, Compensation, and Liability Act |
CERF |
Civil
Engineering Research Foundation |
CFC |
chlorofluorocarbon |
COD |
chemical
oxygen demand |
CWA |
Clean Water
Act |
DOD |
Department
of Defense |
EAF |
electric arc
furnace |
EPA |
United
States Environmental Protection Agency |
EPCRA |
Emergency
Planning Community Right-to-Know Act |
ERU |
electrolytic
recovery unit |
FIFO
|
first-in/first-out |
HAP |
hazardous
air pollutant |
HCFC |
hydrochlorofluorocarbon |
HM |
hazardous
material |
HVOF
|
High
Velocity Oxy-Fuel |
HW |
hazardous
waste |
IVD |
Ion Vapor
Deposition |
kg |
kilogram |
L |
liter |
MACT
|
Maximum
Achievable Control Technology |
NPDES |
National
Pollutant Discharge Elimination System |
ODS
|
ozone-depleting substance |
P2 |
pollution
prevention |
POL |
petroleum
oil lubricant |
POTW |
Publicly
owned treatment works |
PPA |
Pollution
Prevention Act |
RCRA |
Resource
Conservation and Recovery Act |
SBAA
|
sulfuric/boric acid anodizing |
TCLP |
Toxic
Characteristic Leaching Process |
TRI |
Toxic
Release Inventory |
VOC |
volatile
organic compound |
U.S. |
United
States |
US-AEP |
U.S.-Asia
Environmental Partnership |
USAID |
U.S. Agency
for International Development |
USD |
United
States dollars |
WWW |
World Wide
Web |
2. INDUSTRY
BACKGROUND
2.1 Description and History
The metal fabrication industry, most notably foundry operations, has existed
since the first Spanish and British colonies were established in North
America. Yet, it was not until the American Industrial Revolution in the
mid-1800s that the first modern large-scale metal fabrication industry took
root and grew both domestically and internationally. As the industry has
become more sophisticated, it has branched into more unique metal-finishing
operations.
The automobile industry is one of the largest consumers of fabricated and
finished metal products in the United States. The automobile industry relies
on metals to provide a safe and durable, building block material for
finished automobiles. The automobile industry recognized the need for
prefabricated and corrosion-resistant components for production line
manufacturing processes. The corrosive nature of the environment coupled
with consumer investment concerns created the need for protecting and
extending the life span of automobiles. Technology improvements in corrosion
protection have helped the metal-finishing sector to grow significantly
since the late 1800s. The states of the Ohio valley (most notably, Michigan,
Ohio, and Pennsylvania) were the first to develop large-scale, steel- and
iron-processing and finishing operations.
The steel and metal fabrication industry has seen many down cycles during
the past 200 years in the United States, but in the late 1970s and early
1980s the industry was at one of its lowest levels of productivity. Many
underlying reasons exist for the near collapse of the industry, and experts
differ on the exact cause. It is generally accepted that the industry failed
to (1) modernize, (2) capitalize on the growing international market of
post"World War II, and (3) keep executive and union workers" wages in check.
The industry also operates under some of the world's strictest environmental
laws and regulations.
Since its low point in the early 1980s, the industry has been regenerated by
modernization and reinvestment, as well as restructuring and controlling
overhead and other costs. The industry has returned to its competitive
spirit in both the domestic and international marketplace. The overall
industry is expected to continue to regain lost market share and prosper
into the next millennium.
2.2 Industry Demographics
This report concentrates on three areas of metal fabrication, with an
emphasis on the automobile industry. Metal fabrication encompasses three
distinct sectors: metal formation (e.g., casting, forging, and shaping),
metal preparation, and metal finishing (e.g., plating, painting, coating,
and so on). The latter two sectors are usually grouped together because of
the similar nature of their operations.
The metal fabrication industry has long been concentrated in the Ohio Valley
because of the area's rich iron ore and coal deposits and because the area
is located close to urban centers with good access to rail and water
transportation (i.e., the Ohio River and the Great Lakes). Gradually, the
metal fabrication industry, particularly the metal-finishing sector, has
branched out to different geographical regions of the United States. Today,
California has the largest concentration of companies that produce
metal-related products. This is attributed to the concentration of the
aerospace and defense industries in Southern California and the small shop
demographics of the industry (detailed below in sections 2.2.1, and 2.2.2).
For automotive products, Michigan, Ohio, and Pennsylvania still tend to have
the highest concentration of companies. Metal-processing companies tend to
prosper in areas that supply a skilled, but cost-effective labor force
(i.e., in urban areas), have a local source of inexpensive raw materials,
and support an adequate transportation infrastructure.
Table 1 provides a brief listing of some of the largest companies and
organizations associated with the U.S. industry. This list is not intended
to be exhaustive but rather provide a short overview of industry players,
which include metal-forming, metal preparation, and metal-finishing
companies; equipment and chemical suppliers; process design and consulting
engineers; professional trade associations; and research institutions. Small
companies tend to work directly with the supplier community to meet their
day-to-day needs for operation and maintenance of equipment. For large-scale
retrofits and redesigns, however, companies typically work with design and
consulting engineers, who in turn work directly with manufacturers to
specify the processes and equipment needed.
Product demand from the automotive sector has continued to increase, and
automotive demand has outpaced U.S. production. Exports of metal products
have also continued to expand to developing countries in Asia and South
America. Canada is still the largest export market for the United States.
Table 1: Key Organizations in the U.S. Metal
Fabrication Industry |
Organization |
Headquarters |
World Wide Web Address
if available |
METAL-FORMING COMPANIES |
Budd Co. |
Troy, MI |
www.buddcompany.com |
Douglas and
Lomason Co. |
Farmington
Hts., MI |
NA |
Hexcel Corp. |
Pleasanton,
CA |
www.hexcel.com |
JSJ Corp. |
Grand Haven,
MI |
NA |
Stolle Corp. |
Sidney, OH |
NA |
METAL
PREPARATION AND FINISHING COMPANIES |
Crown City
Plating |
El Monte, CA |
NA |
General
Motors |
Detroit, MI |
www.gm.com |
Metokote
Corp. |
Lima, OH |
NA |
Northern
Engraving Corp. |
Sparta, WI |
www.norcorp.com |
PreFinish
Metals |
Chicago, IL |
NA |
Winsdor
Plastics |
Evansville,
IN |
NA |
CHEMICAL
AND EQUIPMENT MANUFACTURERS |
Enthone Inc. |
New Haven,
CT |
enthone-omi.com |
Exxon
Chemical Co. |
Irving, TX |
www.exxon.com |
Hubbard Hall
Inc. |
Waterbury,
CT |
www.hubbardhall.com |
MacDermid
Inc. |
Waterbury,
CT |
macd.com |
Monsanto |
St. Louis,
MO |
www.monsanto.com |
Penetone
Corp. |
NA |
NA |
W. R. Grace
and Co. |
Lexington,
MA |
NA |
PROCESS
DESIGNERS AND CONSULTANTS |
ABB Lummus
Global Inc. |
Europe/Bloomfield, NJ |
www.abb.com |
Bechtel
Group Inc. |
San
Francisco, CA |
www.bechtel.com |
Brown and
Root |
Houston, TX |
www.b-r.com |
Fluor Daniel
Inc. |
Irvine, CA |
www.fluordaniel.com |
Jacobs
Engineering |
Pasadena, CA |
NA |
J. A. Jones |
Charlotte,
NC |
NA |
McDermott
International |
New Orleans,
LA |
www.mcdermott.com |
Sverdrup
Corp. |
Maryland
Heights, MO |
www.sverdrup.com |
PROFESSIONAL TRADE ASSOCIATIONS AND RESEARCH INSTITUTES |
American
Electroplaters and Surface Finishers Society |
Orlando, FL |
www.aesf.org |
American
Institute for Pollution Prevention |
Washington,
DC |
es.inel.gov/aipp |
National
Association of Automobile Manufacturers |
Chicago, IL |
NA |
Center for
Byproducts Utilization |
Milwaukee,
WI |
www.uwm.edu/dept/cbu/cbu.html |
Forging
Industry Association |
Cleveland,
OH |
www.forging.org |
Great Lakes
Regional P2 Roundtable |
Champaign,
IL |
www.hazard.uiuc.edu/wmrc/greatl |
American
Iron & Steel Institute |
NA |
www.steel.org |
National
Association of Metal Finishing |
Herndon, VA |
NA |
National
Metal Finishing Resource Center |
Washington,
DC |
www.iti.org/ee/eem |
Pacific NW
P2 Resource Center |
Seattle, WA
|
pprc.pnl.gov/pprc/p2tech/p2tech.html |
University
of Tennessee Center for Clean Products and Clean Technologies |
Knoxville,
TN |
www.ra.utk.edu/eerc/clean2.html |
2.2.1 Metal-Forming Sector
There are more than 3,100 metal-casting establishments in the United States,
which employ approximately 210,000 people, 170,000 of whom are production
workers. The metal-casting sector is fragmented and dominated by small
businesses. Thirty-eight percent of metal-casting establishments employ
fewer than 20 people; 63% employ fewer than 50 people; and 79% employ fewer
than 100 people. There are only 25 foundries that employ more than 1,000
people. These large foundries typically serve automotive and heavy equipment
markets.
2.2.2 Metal Preparation and Finishing Sector
There are approximately 5,600 metal-finishing establishments in the United
States, which employ approximately 110,000 people. As with metal-casting
operations, the small demographics hold true for the noncasting sectors of
metal fabrication (i.e., metal finishers and other operations). Typically,
the market operates with a small number of employees and only a few large
companies that provide sizable shipments of finished material to the
automotive industry. Most of these larger companies are specialized (or
considered captive) and provide specific components to the automotive
industry. Approximately 48% of the metal-finishing establishments employ
fewer than 10 people; 90% employ fewer than 50 people; and only 3% employ
more than 100 people.
2.3 Use of Natural Resources
Water
Water is used extensively in metal preparation and finishing. For surface
preparation, water is most commonly used to clean and remove contaminants
from metal surfaces. Water is the principal "carrier solvent" used to
complete the etching effect for surface preparation. Processes such as metal
pickling use water baths with special agents to remove metal oxides and/or
pretreat the metallic surface for a finishing product. Similarly,
metal-finishing operations use water for complete product immersion. Water
baths are used to provide a media to transfer a finish from the aqueous
environment to a metal's surface. Water is used less extensively in
metal-forming operations. Pure water is used mostly as a cooling agent and
rarely comes in contact with the casting metal materials.
Protective Metals
Metal finishing's main goal is to protect a virgin metal surface (e.g.,
iron, steel, and aluminum) with either a less corrosive metal or another
protective covering. The most common protective metals used by the finishing
industry include nickel, copper, zinc, chromium, silver, and gold. These
metals provide a chemistry that makes them less likely to form surface
oxides; the metals can also provide an attractive appearance, as is the case
with chromium. The automobile industry has long used these metals in their
component manufacturing. Environmental concerns for using them are discussed
below in section 2.4.
Energy
Metal formation, particularly metal casting, is the most
energy-intensive process in metal fabrication. More than 60% of the energy
used by an iron foundry goes to molten metal operations. Significant amounts
of fossil fuels (e.g., coke and coal) are needed to keep the molten metal in
liquid form. Coal is readily available in the United States and is not
considered a limiting natural resource, but stack air emissions from fossil
fuel use have become a major pollution concern. The industry is just
beginning to utilize economical alternative fuels that create less
environmental pollution (i.e., low coke cupola and coal conversion using
gasification).
Raw Materials
A multitude of raw materials go into the metal fabrication process. Most of
the more toxic and hazardous materials are used in the surface preparation
and finishing sectors, whereas metal formation and casting use less toxic
materials. Metals (e.g., steel, iron, and aluminum), water, fossil fuels,
aqueous cleaners, solvents, cooling fluids, abrasives, and metal bath
complexing agents are the major raw materials used in metal fabrication.
The metal-forming process uses foundry sands, binding agents, cutting oils,
degreasing solvents, cleaners (including water), and metals. Typically,
"feedstock" molten metal is poured into a cast or die and formed into the
desired configuration and then prepared for finishing. Defective cast
products are recycled back as feedstock. The foundry sands and binding
agents are used in the actual casting operations whereas cutting oils and
cooling agents are used in metal-forming and -shaping processes. The
inherent stresses and strains placed on metal-shaping
operations creates the need for cooling and working fluids. Degreasers and
cleaners are used in the intermediate steps to prepare the metal part for
either more shaping operations or for metal preparation and finishing.
Metal preparation is the first step in the metal protection process.
Preparation and finishing go hand-in-hand; without proper preparation, the
finishing process would fail and not last nearly as long. The automotive
industry has set high standards because it is in their best interest,
legally and economically, to provide long-lasting quality products to its
consumers. Metal cleaning and preparation is accomplished by using one or
more of four types of media: (1) solvents, (2) aqueous cleaners, (3) water,
and (4) abrasives. In the past, the U.S. industry relied exclusively on
chemical means to achieve surface preparation. Chemical surface preparation
involves using either solvents or aqueous cleaners. Although solvents are a
preferred cleaner because they evaporate quickly and leave little to no
residue on the metallic object, solvent preparation has been declining due
to increased restrictions on using ozone-depleting substances (ODSs).
Driven by increased treatment and disposal costs, the
industry has moved to mechanical preparation processes. Abrasive blast media
are the primary mechanisms used to prepare a metallic surface mechanically.
Other means include grinding or using a wire brush to scar the surface of a
metal component (see section 4.7).
Through improved industry operations, metallic components' life spans have
been increased in both the automobile industry and other manufacturing
sectors. Methods such as cathodic protection and hot tempering have been
used in the past but not quite understood until the 1950s. Electroplating,
anodizing, and painting are the more common protection techniques used by
the U.S. metal-finishing industry.
2.4 Waste Streams of Concern
Metal fabrication produces waste streams for all three media: land, air, and
water. The typical process material inputs and outputs for the industry are
highlighted in Table 2. Environmental concerns ranging from the
formation of acid rain to soil and groundwater contamination have been
attributed to the metal fabrication industry. Human health effects are
closely studied and workers' exposure risks are well documented for the
industry. Metal formation processes tend to produce air emissions and solid
wastes, whereas metal surface and finishing operations produce all three
types of waste. Wastewater volume is much higher for surface and finishing
operations than for metal formation processes.
Stack air emissions from fossil fuels, foundry waste sands, and
waste-binding agents are not listed in Table 2, but they represent
large waste streams for metal formation processes. As mentioned earlier,
fossil fuels are burned to obtain the high temperatures needed to heat the
metal ore into molten metal. Foundry sand and binding agents assist in
providing a uniform cast material.
Some of the larger "calculated" Toxic Release Inventory (TRI) releases for
the metal fabrication industry are shown in Table 3. The Department
of Defense (DOD) and other federal facilities are not included in these
totals, although they are required to report these data from 1993 onward.
The industry has addressed the pollution issue in the typical pattern that
most American industries have followed in the past: by starting with
end-of-pipe treatment modifications and then slowly analyzing the entire
manufacturing process to isolate critical pollution generation points. At
these pollution points, owners have realized the ultimate goal and benefits
of implementing pollution prevention and clean technologies. Today, the most
advanced breakthroughs in pollution prevention implement the multimedia
approach of decreasing the air, liquid, and solid waste streams. Chapter 4
below will detail the currently accepted practices used in the metal
fabrication industry.
Wastewater. Metal fabrication wastewaters have high concentrations of
inorganics and have a high chemical oxygen demand (COD). The various waste
streams are outlined in Table 2. Water is the primary solvent used in
cleaning and finishing metal surfaces. Like other industrial operations, a
majority of the companies have started to recycle their wastewater within a
plant. Through filtering and removing contaminants (e.g., metal
precipitation), the life span of these wastewaters can be extended and the
overall water consumption can decrease.
Cyanide and/or heavy metal waste streams from metal preparation and
finishing operations are the more difficult wastewaters to treat. Both
require monitoring of pH levels to remove and destroy the maximum amount of
contaminants (e.g., cyanide oxidation). In the past, wastewater from various
operations was combined and then treated, but today most operations combine
waste streams only when the combination would either benefit or not inhibit
any contaminant removal kinetics.
Air Emissions. Air emissions from metal preparation and finishing
operations represent one of the most recent concern areas for pollution
prevention. For many years, air emissions were viewed as an unseen hazard
because they were more difficult to quantify and regulate than solid and
liquid wastes. Elevated temperatures created during the manufacturing
process and high volatile organic compound (VOC) levels in solvents and
cleaners are the primary reasons that in the metal fabrication process these
hazardous materials volatilize. Table 4 shows the metal fabrication
industry's reductions in TRI reportable chemical releases from 1988 to 1993.
Air emission quantities represent the largest waste stream.
The primary waste streams for cleaning solvents are air emissions and
contaminant debris (e.g., rags soaked with solvents and excess cutting
fluids). Compared to solvent preparation, aqueous cleaning operations are
less hazardous and create fewer air emissions (see section 4.3).
Table 2: Process Materials Inputs and Outputs for
Metal Fabrication Processes |
Process |
Material
Input |
Air
Emission |
Process
Wastewater |
Solid
Waste |
Metal
Shaping |
Metal
Cutting and/or Forming |
Cutting
oils, degreasing and cleaning solvents, acids, alkalis, and heavy metals |
Solvent
wastes (e.g., 1,1,1-trichloroethane, acetone, xylene, toluene, etc.) |
Waste oils
(e.g., ethylene glycol) and acid (e.g., hydrochloric sulfuric, nitric),
alkaline, and solvent wastes |
Metal chips
(e.g., scrap steel and aluminum), metal-bearing cutting fluid sludge,
and solvent still-bottom wastes |
Surface Preparation |
Solvent
Degreasing and Emulsion, Alkaline, and Acid Cleaning |
Solvents,
emulsifying agents, alkalis, and acids |
Solvents
(associated with solvent degreasing and emulsion cleaning only) |
Solvent,
alkaline, and acid wastes |
Ignitable
waste, solvent wastes, and still bottoms |
Suface Finishing |
Anodizing |
Acids |
Metal
ion�bearing mists and acid mists |
Acid Wastes |
Spent
solutions, wastewater treatment sludges, and base metals |
Chemical
Conversion Coating |
Metals and
acids |
Metal
ion�bearing mists and acid mists |
Metal salts,
acid, and base wastes |
Spent
solutions, wastewater treatment sludges, and base metals |
Electroplating |
Acid/alkaline solutions, heavy metal bearing solutions, and cyanide
bearing solutions |
Metal
ion�bearing mists and acid mists |
Acid/alkaline cyanide, and metal wastes |
Metal and
reactive wastes |
Plating |
Metals
(e.g., salts) complexing agents, and solutions |
Metal
ion�bearing mists |
Cyanide and
metal wastes |
Cyanide and
metal wastes |
Painting |
Solvents and
paints |
Solvents |
Solvent
wastes |
Still
bottoms, sludges, paint solvents, and metals |
Other
Metal-Finishing Techniques (including Polishing, Hot Dip, Coating, and
Etching) |
Metals and
acids |
Metal fumes
and acid fumes |
Metal and
acid wastes |
Polishing
sludges, hot dip tank dross, and etching sludges |
Resources:
EPA, Profile of the Fabricated Metal Products Industry,
EPA/310/R-95/007, September 1995. |
Table 3: Top 10 TRI Releases for 1993 (Releases
reported in pounds/year) |
Chemical
Name |
Number of Facilities
Reporting Chemical |
Total Releases
|
Average Releases per
Facility |
Glycol
Ethers |
269 |
18,271,419 |
67,923 |
N-Butyl
Alcohol |
215 |
10,582,558 |
49,221 |
Xylene
(Mixed Isomers) |
336 |
8,968,845 |
26,693 |
Methyl Ethyl
Ketone |
254 |
6,717,615 |
26,447 |
Trichloroethylene |
185 |
5,320,702 |
28,761 |
1,1,1
Trichloroethane |
189 |
4,774,195 |
25,260 |
Toluene |
205 |
4,692,281 |
22,889 |
Dichloromethane |
57 |
2,157,730 |
37,855 |
Methyl
Isobutyl Ketone |
114 |
1,658,287 |
14,546 |
Acetone |
61 |
1,498,389 |
25,564 |
Reference:
EPA, Profile of the Fabricated Metal Products Industry,
EPA/310/R-95/007, September 1995. |
|
Table 4: TRI Reductions Per Waste Stream
(pounds/year) |
Releases |
1988 |
1993 |
Percent Reduction |
Total Air
Emissions |
131,296,641 |
90,380,667 |
31.2 |
Surface
Water Discharges |
1,516,905 |
101,928 |
93.3 |
Underground
Injection |
386,120 |
1,490 |
99.6 |
Releases to
Land |
4,202,919 |
660,072 |
84.4 |
Transfers to
POTWs |
17,149,495 |
3,809,715 |
77.7 |
Transfers to
Disposal |
43,529,628 |
19,736,496 |
54.7 |
Transfers to
Treatment |
34,313,199 |
18,561,504 |
45.9 |
Reference:
EPA, Profile of the Fabricated Metal Products Industry,
EPA/310/R-95/007, September 1995. |
Attempts have been made to restrict the volatilization of toxic
chemicals. Although both fugitive and point source air emissions have been
reduced in the last 10 years, fugitive emissions represent the greatest area
of reduction. Point source emissions are treated by utilizing equipment
(e.g., air scrubbers) that removes the contaminants of concern. Fugitive
emissions are contaminants that escape during the manufacturing process and
are not easily collected. Simple low-tech options and process modifications
are employed to decrease emissions that elude treatment.
Solid and Liquid Waste. Table 2 outlines some of the most common solid
and liquid wastes generated by the industry. Some of the liquid waste
streams shown are not combined with general wastewater. These waste streams
are usually concentrated and can easily be regenerated into their original
product. For the metal-forming industry, the introduction and subsequent
disposal of cooling and forming fluids is a source of pollution once these
fluids outlive their usefulness. Over time, these virgin oils and liquids
break down and/or pick up contaminants from the production process. These
cooling and cutting oils are recycled and reused in the original process or
left as a POL waste stream.
Typically, solid waste streams (hazardous and nonhazardous) result from
excess metal that is trimmed from manufactured metal products or is a
rejected metal component. In both cases, scrap metal is almost always
recycled back into the metal formation process. Used foundry sands and
wastewater treatment processes generate most other solid wastes (e.g.,
sludges).
3. ENVIRONMENTAL
ISSUES
Various federal environmental regulations and statutes have changed the way
the metal fabrication industry conducts business. The following is a listing
of the primary acts that dictate how the industry handles its materials and
waste.
- Federal Water Pollution Control Act, or the Clean Water Act (CWA)
- Clean Air Act (CAA)
- Resource Conservation and Recovery Act (RCRA)
- Comprehensive Environmental Response, Compensation, and Liability Act
(CERCLA), commonly known as "Superfund"
- Pollution Prevention Act (PPA)
The CWA's increasingly stringent regulations for discharging wastewater
are the primary regulatory drivers for the metal fabrication industry. RCRA
regulations contained in Subtitle C (Hazardous Waste) and Subtitle D (Solid
Waste) handle the industry's disposal issues and have helped level the
playing field among air, land, and water. Prior to RCRA, the CWA and CAA
disproportionally shifted hazardous waste (HW) streams to landfills.
Companies that discharge to a receiving water are required to have a
National Pollutant Discharge Elimination System (NPDES) permit as mandated
in the CWA. Complying with an NPDES permit has proved difficult for the
predominately small, metal fabrication facilities (e.g., fewer than 50
employees). Only the largest companies look to obtain their own NPDES
permit; most facilities only pretreat their wastewater and then discharge to
a publicly owned treatment works (POTW).
Superfund's Emergency Planning Community Right-to-Know Act (EPCRA) has had a
major impact on the hazardous material handling and waste generation
practices of the metal fabrication industry. EPCRA requires that each
manufacturer give a detailed account of the hazardous material inventory
located at an individual facility. EPCRA also requires most metal
fabrication facilities to plan and detail possible pollution prevention
opportunities on a yearly basis.
The CAA was one of the pioneer regulatory acts, but its complexity is just
beginning to be a compliance issue. The U.S. Environmental Protection Agency
(EPA) has recently proposed some of the toughest regulations for air quality
in the United States. One of the main targets of the new air standards is on
"particulate matter."
Air emissions and the phasing out of ODSs, such as chlorofluorocarbons
(CFCs) and hydrochloro-fluorocarbons (HCFCs), have greatly affected the type
of cleaners and solvents used in metal fabrication. Part of the reason for
the increased emphasis on air emissions stems from Superfund's EPCRA
compliance reporting. TRI reporting has helped to quantify the amounts of
toxic materials being released as air emissions.
Environmental regulations pose a large burden on small metal-finishing
establishments and have caused many companies to close rather than comply
with complex environmental regulations.
During the 1990s, pollution prevention and clean technologies have come to
the forefront of attempts to reduce and control the environmental effects
created by metal fabrication facilities. The policy set forth in the PPA of
1990 outlines a systematic approach for efficiently reducing pollution. The
following is a passage from the PPA:
. . . pollution should be prevented or reduced at the source
whenever feasible; pollution that cannot be prevented should be recycled
in an environmentally safe manner, whenever feasible; pollution that
cannot be prevented or recycled should be treated in an environmentally
safe manner whenever feasible; and disposal or other release into the
environmental should be employed only as a last resort and should be
conducted in an environmentally safe manner.
Typically, most federal and state regulations and statutes are met with
resistance from private industry. Conversely, the PPA's pollution prevention
principles and the subsequent development of clean technologies have been
viewed as ways of providing cost savings and sometimes even improving
product quality, while simultaneously improving public relations for
companies and industries that aggressively pursue their implementation.
Pollution prevention has proved an effective means of reducing compliance
and treatment costs for the metal fabrication industry.
Pollution prevention and clean technologies are meant to focus on a
multimedia (i.e., air, water, and land) approach to reducing waste, and all
three media sources are a concern for the metal fabrication industry.
EPA is looking for several ways to promote voluntary pollution prevention.
The PPA lacks the regulatory powers needed to force companies to implement
pollution prevention practices into their production processes.
Environmental agencies are exploring ways to write more flexible permits to
allow companies to make process changes without having to resubmit a lengthy
permit modification. These agencies are encouraging pollution prevention by
doing such things as reducing the cost of a permit, or extending the
compliance schedules for companies that are proactive in pollution
prevention practices.
4.
CLEAN TECHNOLOGY DEVELOPMENTS
The following listing of clean technologies focus on air and hazardous waste
for the metal fabrication industry. Most of the technologies listed are
geared to metal-cleaning and -finishing operations; they do not focus on
waste treatment options but rather on source reduction and recycling
opportunities. Table 5 lists some manufacturers for clean
technologies. It is intended to be used as a point of reference, rather than
a comprehensive list.
This section will detail the following pollution prevention and clean
technologies:
- Best Management Practices (BMPs)
- Recycling Metal-Working/-Cutting Fluids, Foundry Sand, and Lost Foam
Casting
- Alternatives to Solvent Cleaning
- Component Parts Washers
- Water Use Reduction (Closed Loop/Zero Emission Systems)
- Improved Sensors and Process Control
- Mechanical Blast Media
- Electrodialysis Technology for Bath Solutions
- Hexavalent Chromium Plating Substitution Options
- Electroless Plating Bath Life Extension
- Ion Vapor Deposition
- Electrolytic Recovery Technology for Metal Cyanide Recycling
Although not discussed in depth in this report, some of the pollution
prevention initiatives for the metal-forming industry are outlined below.
Pollution prevention opportunities include reducing coke-making emissions,
electric arc furnace (EAF) dust, and spent acids used in finishing
operations. Substituting coal for coke in blast furnace operations has
significant potential to reduce pollution in steelmaking. Also, using coal
gasification is expected to be a more viable option in coming years.
Recycling tar decanter sludge, a coke byproduct, by injecting it into ovens
improves the coke yield and effectiveness. New recycling processes are being
explored to reduce the cost of recycling EAF dust. Recovering and recycling
hydrochloric acid from spent acids has substantial benefits in reducing
material and treatment costs.
The amount of raw materials and hazardous waste generated by the metal
fabrication industry is staggering. The following is an example of
one operation's material needs and waste generation.
To paint a car it takes approximately 7,940 liters (L) of water,
23.3 L of chemical materials, and 400 kilograms (kg) of coal. . . . The
painting of one car produces 6 kg of VOC, 9 kg of sulfur dioxide, 13 kg of
nitrogen oxides, 1.5 kg of carbon dioxide, 1.4 to 6.3 kg of hazardous air
pollutants (HAPs), 7,250 L of wastewater, 2.8 kg of solid waste, and 5.3
kg of hazardous waste. (Source: "Improved management of automotive
painting operations," Automotive Engineering, February 1996)
Some of the metal fabrication and automobile pollution problems have been
attributed to automobile design engineers, who in the past rarely considered
the downstream environmental impacts when selecting a process material.
Through use of clean technologies and pollution prevention equipment, the
industry continues to decrease the total amount of hazardous waste it
releases into the environment each year.
Clean technologies as used in this report are defined as
"manufacturing processes or product technologies that reduce pollution or
waste, energy use, or material use in comparison to the technologies that
they replace."
Table 5: Clean Technology Manufacturers |
Company |
Headquarters |
World
Wide Web Address, if Available |
Cuitting Fluid Recyclers |
Cincinnati
Milacron |
Cincinnati,
OH |
www.industry.net/milacron |
Fluid
Recycling Services Inc. |
Santa Anna,
CA |
NA |
Solvent Substitution |
Blackstone
Ultrasonics |
Jamestown,
NY |
www.blackstone-ultra.com |
Branson
Ultrasonics |
Danbury CT |
www.industry.net/branson.ultrasonics |
Fredrick
Gumm Chemical Company, Inc. |
Kearny, NJ |
NA |
Inland
Technology |
Tacoma, WA |
www.inlandtech.com |
Safety Kleen |
|
www.safety-kleen.com |
Parts Washers |
Inland
Technology |
Tacoma, WA |
www.inlandtech.com |
Concurrent
Technologies Corp. |
Johnstown,
PA |
www.ctc.org |
Better
Engineering Manufacturing |
Baltimore,
MD |
www.betterengineering.com |
The Mart
Corporation |
Maryland
Heights, MO |
NA |
Sensors and Process Control |
Lehigh
University |
Lehigh, PA |
www.lehigh.edu |
Case Western
Reserve University |
Cleveland,
OH |
www.cwru.edu |
Mechical Blast Media Equipment |
Burr King
Manufacturing Co. |
Warsaw, MO |
www.norelco.com/burrking |
National
Detroit Co. |
Rockford, IL |
NA |
Electrodialysis |
Ionsep Corp. |
Rockland, DE |
NA |
Technic Inc. |
Pawtucket,
RI |
www.technic.com |
US Filter |
Palm Desert,
CA |
www.usfilter.com |
Hex-Chrome Substitution |
TAFA Inc. |
Concord, NH |
NA |
Noramax
Technologies Inc. |
Atlanta, GA |
NA |
Faraday
Technology Inc. |
Dayton, OH |
NA |
Electroless Plating Extension |
Electroless
Technologies Corp. |
Los Angeles,
CA |
NA |
McGean-Rohco,
Inc. |
Cleveland,
OH |
NA |
Ion Vapor Deposition |
Vacuum
Plating Technology Corp. |
San Jose, CA
|
NA |
Multi Arc
Inc. |
Rockaway, NJ |
www.geartechnology.com/copage/multi |
Electrolytic Recovery |
BEWT
Recovery Technologies Inc. |
Whittier, CA |
NA |
ELTECH
International |
Fairport
Harbor, OH |
NA |
4.1 Best Management Practices (BMPs)
Description. Best Management Practices (BMPs) represent the quickest
ways to reduce pollution cheaply and usually without purchasing additional
equipment. These good operating practices include improving inventory
control, preventing accidental spills, segregating waste streams, and
scheduling production runs that maximize production and minimize waste. BMPs
also include improving teamwork between coworkers and training people on
response to environmental workplace hazards.
A unique BMP for decreasing hazardous waste generation has been to improve
hazardous materials (HM) management. Some effective management steps for HM
management are to:
- Centralize the storage of HM
- Restrict HM access by individual workers
- Streamline the amount of unique materials inventoried
- Purchase minimal HM quantities.
By restricting workers' access to hazardous materials, there is less
chance of stockpiling or misusing products or products passing their
expiration dates without use. A worker can only exchange empty hazardous
material containers for new material on a one-for-one basis, and HM
inventory follows the first-in/first-out (FIFO) management principle.
Efforts are made to reduce the number of different hazardous materials being
purchased and stocked. An example is reducing the number of cutting fluid
products used for the same metal-forming process. Quick and accurate
inventorying can be achieved by centralizing HM storage to assure that only
usable quantities of hazardous materials are stored at any one time.
Segregation of HW and non-HW streams prevents an entire waste stream from
becoming hazardous and reduces the volume of waste requiring treatment or
disposal. Maintaining separate waste streams can enhance a company's ability
to reuse or recycle waste materials. Waste treatment practices for the metal
fabrication industry involve changing the pH of a wastewater to make it
easier to remove contaminants. Sometimes different waste streams are mixed
to help change the pH of a wastewater, but if the total amount of hazardous
waste is increased and the new wastewater interacts, it may become unsafe
for workers. Special attention should be given whenever mixing waste
streams.
Scheduling production runs to maximize production and minimize waste is a
basic principle that can easily be applied to metal fabrication. An example
of smart scheduling would be performing operations using light paints first,
leaving darker paint operations for the end of a production run. Typically,
switching to the darker paints later in the cycle will decrease the amount
of clean outs needed over the entire run. Efficient scheduling includes
performing material quality control before a finishing process is started.
For example, removing rejected metal components before applying a finish
reduces the number of wasteful product operations and maintains a longer
life for the finishing material.
A trained work force is often an overlooked part of a company's pollution
prevention plan. Training not only helps avert or limit accidents, it also
empowers workers and makes them feel more valued by their company. Many
companies have developed training and documents for Spill Response Control
and Countermeasures Plans for their facilities and practice events to
simulate how workers can respond in an emergency.
Benefits. BMPs save in three ways: by decreasing (1) procurement
costs, (2) hazardous waste disposal costs, and (3) compliance costs. BMPs
cost little to implement, but savings can be realized by tracking the annual
expired shelf life of HM, total volume of spilled HM, total HM used, and the
like.
Status of Use in the United States. Both private industry and federal
government facilities actively implement BMPs. In particular, the DOD
community aggressively implements these procedures because they are cost
effective and relatively easy to incorporate into existing operations. The
U.S. Navy has estimated that after the initial set-up phase of HM inventory
control, most installations will have an immediate reduction in procurement
costs and materials that have passed their expiration dates. In short, these
types of inventory management systems end up saving money.
4.2 Recycling Metal-Working/-Cutting Fluids,
Foundry Sand, and Lost Foam Casting
Description. Generation of waste metal-working fluids can be minimized
by extending the useful life of the fluids. Useful life is a function of
various factors, including the type of metal-working operation, type/quality
of fluid used, housekeeping practices, bacterial and other contamination,
and water quality (see section 2.4 above). Off-the-shelf systems are
available for on-site batch recycling of metal-working fluids. These systems
clean the fluids by removing solids, bacteria, and oil contaminants. Water
or fluid concentrate may be added to the reclaimed fluid to adjust the fluid
concentration to the desired level. Capital costs for a fluid collection
device and recycling equipment vary depending on unit size. An alternative
to the purchase, operation, and maintenance of recycling equipment is to use
an off-site recycling service. The economics of recycling metal-working
fluids improves as a metal-forming operation decreases the number of
different metal-working fluids used in the manufacturing process.
As noted in section 2.4, foundry sand is subject to contamination by binding
agents and metal debris from casting operations. Recycling of foundry sand
involves material encapsulation. The foundry sand must past EPA's Toxic
Characteristic Leaching Process (TCLP) analysis to be recycled into
construction activities. Earth fill material and highway construction fill
are the two primary means of recycling.
Another new technology being implemented is called lost foam casting. The
process operates by creating a polystyrene foam copy of the part to be cast
and packing it with foundry sand. The polystyrene cast is vaporized when the
molten metal is poured into the foam copy and the cast metal part is left.
Benefits. Recycling metal-working fluids will reduce both the amount
of hazardous material procured and hazardous waste generated. Fluid life can
be extended by 40%, and the extended service life will reduce labor and
machine downtime (clean out) costs. Recycling also improves fluid and
machine tool cleanliness, which can lead to reduced operation and
maintenance costs. Recycling of foundry sands provides the generator with
hazardous waste disposal cost savings.
Lost foam casting produces less foundry sand waste and results in cast parts
that require much less machining to achieve tolerances, therefore, reducing
metal turnings and machining fluids.
Status of Use in the United States. Almost all metal formation
companies are starting to implement either on-site or off-site metal fluid
recyclers. This technology is well tested and easily implemented and is
expected to continue being used throughout the industry. Foundry sand
testing procedures vary from state to state but are expected to be
increasingly scrutinized as states look to limit the amount of solid waste
disposal in landfills. Lost foam casting is being used at the Saturn
Corporation and is expected to be used at other General Motors foundries.
4.3 Alternatives to Solvent Cleaning
Description. Conventional solvent substitutions simply involve utilizing
a more environmentally friendly cleaner in lieu of a hazardous material. The
Defense Logistics Agency produces an annual catalog that lists acceptable
substitutes for specific hazardous aqueous cleaners, degreasers, lubricants,
and other products used in critical military applications.
Ultrasonic cleaning is a process enhancement used in immersion cleaning to
improve the cleaning efficiency of most liquids, including neutral,
alkaline, acidic aqueous solutions, and semiaqueous solutions. It is a
viable alternative to traditional solvent-based cleaning operations such as
vapor degreasing. Ultrasonic cleaning can be used to clean from gross to
precision levels and effectively removes particles, machining chips, grease,
oils, and other contaminants. Ultrasonic cleaning is usually employed in a
multistage process of ultrasonic wash, rinse, and dry.
An ultrasonic cleaning system consists of transducers, a generator, a tank,
and a liquid medium. The transducers convert the energy supplied by the
generator to sonic energy vibrations. These vibrations are transmitted
through the tank and produce cavitation bubbles in the liquid medium in the
tank. The formation and collapse of these bubbles create a scrubbing action
that is effective at removing contaminants. The energy provided by the
ultrasonics raises the temperature of the liquid; thermostats and cooling
coils are required to control the operating temperature.
A second alternative is conventional solvent substitutions, which
simply involve utilizing a more environmentally friendly cleaner in lieu of
a hazardous material. The Defense Logistics Agency produces an annual
catalog that lists acceptable substitutes for specific hazardous aqueous
cleaners, degreasers, lubricants, and other products used in critical
military applications.
Benefits. Ultrasonic cleaning can achieve high levels of cleanliness
for metal surfaces and is capable of removing extremely small particles.
Ultrasonic cleaning can remove debris from parts with complex geometries
more quickly than immersion dipping processes that utilize the same cleaning
solution. Advantages to ultrasonic cleaning and other solvent substitutions
are decreased air emissions (ODSs and other toxic air hazards) and decreased
hazardous waste generation. Also, because these cleaners are less hazardous,
worker safety is improved and the need for compliance reporting is reduced.
Status of Use in the United States. Solvent substitution has long
been an accepted practice in the United States and most metal fabrication
companies are implementing changes when feasible. Companies have been slower
to use ultrasonic systems because they are new to the industry and have just
become affordable. Ultrasonic systems vary in size from 5 to 35 gallons of
capacity and, as a result, are not used in larger metal component
applications. Custom systems are expected to make ultrasonic cleaning
available to a wider number of industrial cleaning applications.
4.4 Component Parts Washers
Description. Aqueous jet parts washers use a combination of water and
detergent as a cleaning solution, whereas nonaqueous washers utilize
low-hazard cleaning solutions. These parts washers make up a cleaning
cabinet with spray nozzles that apply high pressure streams of water at the
metal components to be cleaned. The cleaning process will remove
contaminants, oil, and grease. Aqueous part washers are frequently compared
to household dishwashing machines.
The detergent solution used in these systems is typically biodegradable, and
the solution may be discharged into the local POTW if it meets discharge
limitations. Nonaqueous washers use solvents similar to mineral spirits to
clean component parts in a contained vessel. Most of the washers have a
purifying/recycling system that allow the detergent or solvent solution to
be recycled and reused. These purifying/recycling systems skim oil from the
solution and remove sludge waste that settles to the bottom of the washer.
These closed-loop systems enable the user to reuse the cleaning solutions
several times before requiring fresh solution. Many systems, particularly
those that are solvent based, are employed through a service contract with
an outside contractor. The washer units come in a variety of sizes from 75-
to 400-gallon capacities.
Benefits. Aqueous parts washers replace hazardous solvents with
biodegradable detergents and minimize the disposal of hazardous waste. Spent
water or detergent solutions may be discharged to the local POTW.
Solvent-based parts washers capture and reuse evaporated cleaning fluid,
which in turn decreases the amount of cleaner needed. This saves on material
and disposal costs for spent solvent. The enclosed cleaning process
eliminates and lessens workers' exposure to hazardous substances. Both
aqueous and nonaqueous part washers reduce the amount and toxicity of
fugitive and point source air emissions (e.g., ODSs).
Status of Use in the United States. The use of parts washers has
increased since 1,1,1-trichloroethane vapor degreasing and other ODS
cleaning technologies have been curtailed. Parts washers are used in all
types of industries in the United States, and many support companies have
been created as a result. The unit cost for these washers has decreased as
they become more commonplace in today's metal-cleaning and preparation
operations. The current technology and practice has been to make these parts
washers as closed-loop and low maintenance as possible.
4.5 Water Use Reduction (Closed-Loop/Zero Emission
Systems)
Description. An increasingly viable option for companies is the "zero
discharge" system. The decision point for this option is when it is more
expensive to discharge a company's wastewater than to treat it and recycle
it back into the plant. A large capital expenditure and a customized
treatment solution are required to handle this option. Furthermore, the
uniqueness of various metal fabrication operations makes it difficult, if
not impossible, to find off-the-shelf treatment designs to fit a user's
needs.
A more plausible approach is that of achieving a "zero emissions" strategy
that relies on a network of companies that utilize waste streams from other
companies as their raw material. It should be noted that the term "zero
emissions" is an ideal. This strategy is a more economically efficient
system than a "closed loop" because the waste products do not have to be
fully treated. Although facilities are moving toward decreased volumes of
effluent, material mass balances still dictate that process residuals such
as sludges will require management and possibly off-site disposal.
Benefits. Both zero discharge and zero emission systems improve
effluent water quality and have fewer negative impact on the environment.
Status of Use in the United States. A zero discharge or emission
facility is a lofty goal. Through regulation and other restrictions, the
U.S. metal fabrication industry is expected to invest more time, money, and
effort in reducing effluent levels and contamination to the lowest
economically feasible levels. Improved communication among companies will
help foster the principle of "one company's waste is another's raw
material."
4.6 Improved Sensors and Process Control
Description. Automation has always been a part of the metal
fabrication industry due to concerns about worker safety and exposure.
Improvements in technology and reductions in costs have made analytical
sensors, PC interfaces, and closed-loop control systems more attractive.
These types of automated products allow the user to improve efficiency,
control raw material inputs, and limit the amount of wastes generated.
Sensors can be used to control process temperature, humidity, pH, flow
rates, and contamination levels.
Sensor technology has advanced to the point that computers can now be used
for assessing conditions that in the past only human workers could access.
Artificial intelligence was the phrase coined in the 1980s to describe the
capabilities of these new pieces of equipment. Sensors are now capable of
characterizing physical and chemical properties of processing materials.
Benefits. Use of automation further reduces the chance of human error
in manufacturing processes. Automation improves speed and accuracy in
measuring process variables and also reduces labor costs. Through the use of
automation, workers are now able to dedicate their time to other more
pressing production issues. Automated equipment makes real-time data
available to plant personnel without interrupting the production run.
Status of Use in the United States. Since the mid-1980s, facilities
have continued to modernize and make these sensor technologies a larger part
of metal manufacturing. A new wave of cost-effective automated products are
becoming available for all aspects of metal fabrication. Sensors and process
controls have made great inroads in pretreatment technologies for metal
fabrication wastewaters.
4.7 Mechanical Blast Media
Description. Mechanical cleaning and preparation of almost any metallic
surface is possible if it is sturdy enough to withstand the friction and
force produced by the mechanical work of cleaning operations such as
sanding, grinding, polishing, brushing, and scraping. Mechanical operations
remove surface imperfections and prepare metal components for future coating
or plating operations. These technologies are not meant to be used on
precision or delicate parts. Mechanical cleaning processes are viable
alternatives to traditional solvent-based, metal-cleaning and preparation
operations. They reduce waste production and eliminate potential safety
problems with the handling and usage of toxic, ODS-type, and often flammable
solvents. Mechanical blast media vary from the use of plastic media to
baking soda and solid carbon dioxide pellets.
Benefits. Mechanical preparation significantly reduces the amount and
cost of handling hazardous waste compared to chemical preparation. The
elimination of solvents provides cost savings in terms of procurement.
Mechanical preparation reduces worker exposure to toxic solvents, hazardous
waste, and hazardous air emissions.
Status of Use in the United States. High capital costs and a large
facility space requirement have slowed the use of mechanical cleaning and
preparation processes, but the tightening of air emission standards is
expected to make this a more cost-effective option. Cleaning operations for
precision parts or removal of viscous compounds are expected to continue to
use chemical methods, but these operations are expected to use solvents that
are more environmentally friendly. The percentage of companies that use
mechanical processes is expected to rise steadily.
4.8 Electrodialysis Technology for Bath Solutions
Description. Electrodialysis is a process that efficiently maintains a
low metal ion concentration in the anodizing bath solution by transporting
metal ions from the bath solution through a selective membrane into a
capture media using an electrical current to induce flow. When anodizing
aluminum, for example, the bath solution must be changed out and disposed of
when the aluminum concentration reaches 80-100 grams/liter. The spent
solution contains high levels of sulfuric acid and aluminum, requiring
neutralization and metal removal prior to disposal to a POTW.
Electrodialysis does not affect the anodizing process but is simply a
process that can indefinitely extend the useful life of the bath solution by
maintaining a low concentration of metal ions. The capture media, catholyte,
captures the metal ions and forms a concentrated sludge. The sludge must be
removed from the unit and the catholyte changed out on a regular basis to
ensure effective metal removal from the anodizing bath solution. The
recovered sludge is a hazardous waste containing high concentrations of
metal that can be reclaimed.
Benefits. Electrodialysis reduces hazardous waste volume and
associated disposal costs associated with anodizing baths. First, heavy
metals can be reclaimed and reused. Second, electrodialysis can extend the
useful life of the anodizing bath solution; as a result, a company can lower
its annual costs for chemical makeup and bath replacement. Third,
controlling the metal ion concentration in the anodizing bath solution
improves the production quality of manufactured parts.
Status of Use in the United States. Due to the moderately high
capital cost for this equipment, most companies have been slow to accept
this technology. Locating companies that will recover and reclaim metals
from the sludge has proved difficult at times, but an organization called
the Center for Byproduct Utilization (see Table 1) helps to link
companies for this purpose. As disposal costs increase, electrodialysis will
prove more economically beneficial.
4.9 Hexavalent Chromium Plating Substitution Options
Description. Hexavalent chromium is an extremely toxic substance that
proves difficult to treat and remove from industrial waste streams. Recent
industrial practices have been directed at removing or decreasing the use of
hexavalent chromium.
High Velocity Oxy-Fuel (HVOF) thermal spray technology is a dry process that
produces a dense metallic coating whose desired physical properties are
equal to or surpass those of hard chrome plating with hexavalent chromium.
HVOF thermal spray uses a fuel/oxygen mixture (i.e., propylene, hydrogen,
and kerosene) in a combustion chamber. This combustion process melts a metal
powder that is continually fed into a gun using a carrier gas (argon) and
propels it at high speeds (3,000-4,000 feet/second) toward the surface of
the part to be coated. The high speed of the spray produces a coating on
impact that can be used as an alternative to chromium plating. The metal
powder is available in many compositions, including nickel, chrome carbide,
and tungsten carbide. Uniform coating thickness of up to 0.250 inches can be
achieved.
Other substitution options for hexavalent chromium plating are the use of
trivalent chromium plating or the use of the sulfuric/boric acid anodizing
(SBAA) process. Only minor process changes are needed for trivalent chromium
plating, and waste trivalent chromium is much easier to precipitate from
wastewater. The SBAA process is a direct replacement for the chromic acid
anodizing process used on aluminum production pieces. The SBAA process
consists of a sulfuric/boric acid anodizing bath and a chromate sealer bath.
The SBAA process contains a small amount of chromium in a separate sealer
bath in which the parts are dipped after the SBAA process. The rinse waters
still contain metals and acids that must be pretreated prior to being
released to a POTW, but the overall level of chromium needing treatment is
much less than in conventional finishing operations.
Benefits. The HVOF process gives performance properties similar to
chrome plating, which include wear resistance, corrosion resistance, low
oxide content, low stress, low porosity, and high bonding strength to the
base metal. The only waste stream produced by HVOF is from overspray. The
current technique to limit overspray is to install a water curtain filter
system or a particulate air filter. Because the overspray contains only the
pure metal or alloy, it is feasible to recycle or reclaim it as a raw
material. By using HVOF, annual costs will decrease, along with air
emissions, hazardous waste generation, and associated disposal costs.
Trivalent chromium is less viscous and toxic compared to hexavalent
chromium. The lower viscosity decreases the amount of drag out from a
plating bath and lessens the frequency of countercurrent flow operations.
SBAA offers a significant reduction in the treatment of chromic acid, as
well as a reduction in toxic air emissions from the chromium plating. SBAA
operating costs are similar to existing chromium plating operations.
Status of Use in the United States. The estimated payback period for
using HVOF is 2-4 years, depending on the size of operations. HVOF is
steadily gaining acceptance, whereas substitution of trivalent chromium has
been slow because the level of plating quality is lower than using
hexavalent chromium. Automobile manufacturers continue to demand the high
quality, high-gloss finish that hexavalent chromium delivers. Reductions in
allowed chromium levels to U.S. waters are expected to make all three clean
technologies (HVOF, SBAA, and trivalent chromium) more prevalent
alternatives in metal-finishing operations in the next 5-10 years.
4.10 Electroless Plating Bath Life Extension
Description. Electroless plating consists of a chemical process in
which a reaction occurs to reduce charged metal ions to a neutral solid
state; the ions (primarily nickel ions) then deposit onto another metallic
part. The current practice is to change out the plating bath solution as it
becomes contaminated with byproducts of the chemical reactions that
interfere with the plating process and dispose of it as hazardous waste.
Typical electroless plating waste streams include orthophosphite, sulfate,
plating metal ions, and sodium ions. The electroless plating bath life
extension technology accomplishes this by performing two functions: (1) it
removes the chemical byproducts formed during the plating process and (2) it
maintains the overall chemical balance of the electroless plating bath
(metal ion concentration, pH, and phosphite) through the addition of bath
chemicals (reducing agents, complexing agents, hypophosphite, and bath
stabilizers).
Benefits. Utilizing the electroless plating bath life extension
technology to augment current electroless plating operations can increase
the life of the plating bath up to tenfold and reduce the volume of
hazardous waste generated by up to 90% along with the associated disposal
costs. Production quality is improved due to the stability of plating bath
parameters and quick removal of bath impurities that can cause poor plating
quality. Also, there is a reduction in the need to replate poorly plated
materials.
Status of Use in the United States. Electroless plating extension
technology involves no major capital costs and only requires purchasing
additional bath chemicals. The metal-finishing industry is always looking
for new ways to reduce the amount of wastewater produced in a plating
process. Electroless plating extension is gaining acceptance and similar
bath extension technologies are making inroads within the industry. Another
trend seen in the finishing sector is replacement of more hazardous cadmium
and chromium operations with zinc and nickel chemistries, respectively.
4.11 Ion Vapor Deposition
Description. Ion Vapor Deposition (IVD) comprises a group of
surface-coating technologies used for decorative-coating, tool-coating, and
other metal-coating applications. It is fundamentally an evaporative coating
process that gradually builds a film on the metal surface to be coated.
Benefits. IVD is a desirable alternative to electroplating and some
painting applications. IVD can be applied using a wide variety of materials
to coat an equally diverse number of substrates. IVD coating processes are
even compatible with some plastics, either as coatings or as substrates. The
application of IVD surface-coating technologies at large-scale, high volume
operations will result in reduction of hazardous waste generated compared to
electroplating and other metal-finishing processes that use large quantities
of toxic and hazardous material. Up to 90% of all water use in
electroplating goes to rinsing operations, and IVD virtually eliminates all
rinse water.
Status of Use in the United States. Many companies are replacing aqueous
plating operations with IVD, most notably electroplating processes such as
cadmium plating. One limitation of IVD is that coatings do not work well
where lubrication is required; they are also not a good choice for fastener
parts. Also, IVD has limited success in applications that involve coating
annular-shaped objects. The IVD process requires detailed attention to
operate. Apart from these limitations and similar to other clean
technologies listed in this report, IVD processes are expected to grow in
their uses in metal-finishing applications.
4.12 Electrolytic Recovery Technology for Metal
Cyanide Recycling
Description. Wastewater generated from the rinsing of metal
cyanide-plated parts contains metals (primarily cadmium, copper, and silver)
and cyanide-containing compounds (cyanides). These waste streams require
pretreatment to reduce toxic loadings prior to discharge to a POTW.
Typically, the treatment requires the use of hazardous chemicals, including
acids, alkalis, and chlorine-containing chemicals. Electrolytic recovery
technology uses an electrical current to plate out the metals and oxidize
the cyanides in the rinse waters. The metal is recovered from the
electrolytic recovery unit (ERU) as a foil that can be returned to the
cyanide plating bath as an anode source. The ERU is plumbed to a stagnant
rinse tank in a closed-loop fashion. The cyanides are partially oxidized to
cyanates in the ERU, which can remove more than 90% of the metal ions used
in the rinse waste stream and oxidize up to 50% of the cyanides.
Benefits. The benefits of electrolytic recovery for metal cyanide
recycling include cost savings and reduction of hazardous waste. Cost
savings result from a reduction in the use of treatment chemicals for
cyanides and heavy metals; the reuse of heavy metals, which reduces the
costs for anodes or chemicals; and a reduction in the volume of
metal-containing hazardous sludge. This technology is applicable to other
plating baths, such as nickel, zinc, and lead.
Because the ERU is run in a batch mode, few process changes are required.
ERU is a pretreatment operation that has a relatively short payback period,
estimated at two years for operations that generate more than 300,000
gallons of metal silver-cyanide rinse wastewater.
Status of Use in the United States. Electrolytic recovery is only
feasible for highly concentrated metal wastewaters. The efficiency of the
operation decreases as the concentration of metal ions decreases. Typically,
it is used to recover and recycle more valuable metals (e.g., silver and
gold) and has not been widely used in the metal-finishing industry.
5. FUTURE TRENDS
Regulations and Standards
The U.S. metal fabrication industry will continue to prosper in the
foreseeable future. Industry standards and business practices will continue
to be driven by both government intervention and economical reality. The
strengthening of the CWA and CAA and concerns about RCRA's solid waste
disposal issues will continue to drive the industry closer to "sustainable
development."
EPA, through new guidelines, will propose further limitations in wastewater
effluents from metal fabrication operations. As mentioned earlier in the
report, EPA has proposed standards on Maximum Achievable Control Technology
(MACT)?based performance standards that set limits on air emissions based on
concentration values. EPA has targeted vapor degreasers that use the
following HAPs: methylene chloride, perchloroethylene, trichloroethylene,
1,1,1-trichloroethane, carbon tetrachloride, and chloroform. MACT standards
have been proposed for various metal fabrication operations.
International standards developed by the Geneva-based International
Organization of Standardization, called ISO, represent an attempt to provide
a global environmental management system. ISO 14000 was designed to help
organizations manage and evaluate the environmental aspects of their
operations without being prescriptive. The International Organization of
Standardization intends to provide companies with a framework to comply with
both domestic and foreign environmental regulations. ISO 14000 contains
sections calling for implementation of pollution prevention programs; many
U.S. companies are evaluating the pros and cons of becoming fully certified
in ISO 14000. Furthermore, EPA is talking about easing reporting
requirements for U.S. companies that earn ISO 14000 certification.
Industry Trends
There are several ongoing trends and research and development activities
apparent within the metal fabrication community in the areas of pollution
prevention and clean technology implementation.
The metal-forming industries have been switching to continuous casting
operations that allow molten metal to be formed directly into sheets to
eliminate interim forming stages. As mentioned earlier in this report,
companies are starting to utilize alternative fuels that create less
pollution. Mechanical surface preparation is expected to increase in use
over traditional chemical preparation. The more apparent trends concerning
clean technologies and pollution prevention are source reduction and process
recycling. The phasing out of Class 1 and Class 2 ODSs has pushed the
industry to find alternative solvent and cleaning operations. Gradually, the
industry is beginning to move from the more hazardous heavy metals (e.g.,
chromium and cadmium) to lesser metals such as nickel and zinc.
Although improved HM/HW management is one of the more difficult BMPs to
implement quickly and efficiently, it will continue to be a part of most
companies' pollution prevention plans. Ion Vapor Deposition (IVD) practices
are expected to continue to replace aqueous plating operations. Zero
emissions and closed-loop systems are expected to gain in importance as the
industry tightens its "wastewater and air emission" belts.
Mechanical versus Chemical Preparation
Companies will increasingly consider using mechanical methods for surface
preparation. Mechanical processes can be used to perform many of the same
functions as chemical processes. The costs and benefits of using mechanical
versus chemical processes will be further quantified to aid in decision
making.
Water Conservation and Wastewater Reduction
Water use will continue to be the principal target for pollution prevention
source reduction practices in the metal fabrication industry. Water
used in plating and finishing, facility cleanup, or other noningredient uses
will be reduced, which in turn will reduce the wastewater volume from metal
fabrication facilities. Wastewater treatment will continue to be the
pollution prevention treatment focus for metal fabrication companies.
The industry will continue to implement advanced innovative techniques to
lessen the environmental impact of metal fabrication discharge wastewaters.
In summary, the U.S. metal fabrication industry will continue to face some
of the most stringent environmental regulations in the world. The
development of new and innovative pollution prevention technologies will be
needed to ensure that the industry can achieve proposed and pending
discharge limitations. Pollution prevention and clean technologies will be a
means to let the industry meet environmental standards and still provide
quality, cost-competitive products.
REFERENCES
Chalfant, Robert V. "The new emphasis on pollution prevention," New
Steel, v12, n3, p82, March 1996.
Gedlinske, Brian. "Aqueous parts washing and pollutant loadings," Pollution
Prevention Review, v7, n2, p47, Spring 1997.
Hanson, David. "EPA to shift focus from pollutants to industries," Chemical
& Engineering News, v72, n30, p9, July 25, 1994.
Katzel, Jeanine. "Managing nonhazardous solid wastes," Plant Engineering,
v48, n11, p42, September 1994.
Mason, Keith D. Richard J. Dauksys, Terry A. Cullum. "Improved management of
automotive painting operations," Automotive Engineering, v104, n2, p79,
February 1996.
Sheridan, John H. "Pollution solutions," Industry Week, v243, n7, p32, April
4, 1994.
Zuckerman, Amy. "Don't rush into ISO 14000," Machine Design, v68, n1, p38,
January 11, 1996.
Other Readings:
Joint Service Pollution Prevention Opportunity Handbook, Naval Facilities
Engineering Service Center, June 1997.
Profile of the Fabricated Metal Products Industry, EPA Office of Compliance
Sector Notebook, EPA/310-R-95-007, September 1995.
Guides to Pollution Prevention: Municipal Pretreatment Programs, EPA Office
of Research and Development, EPA/625/R-93/006, October 1993.
Guides to Pollution Prevention: The Fabricated Metal Products Industry, EPA
Office of Research and Development, EPA/625/7-90/006, July 1990.
Environmental Products Catalog, 2nd edition, Defense Logistics Agency,
December 1995.
Pollution Equipment News, 1997 Buyer's Guide.
Chemical Engineering Magazine, McGraw Hill.
Hazardous and Industrial Wastes, Proceedings of the Twenty-Fifth
Mid-Atlantic Industrial Waste Conference, July 9-13, 1993.
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