Metal Finishing Industry
To varying degrees, all metal finishing processes tend to have pollution problems and to generate hazardous and solid wastes. Unlike other manufacturing operations, the vast majority of chemicals that platers use end up as waste. Of particular concern are those processes that use highly toxic or carcinogenic ingredients that are difficult to destroy or stabilize. Some of these processes are:
The metal finishing process often produces undesirable byproducts or wastes including air emissions, wastewater, and hazardous and solid wastes. These wastes predominately result from organic halogenated solvents, ketones, aromatic hydrocarbons, and acids used during the surface preparation stage of the process and from metals (primarily present in the form of dissolved salts in the plating baths) used during the surface treatment stage. Cyanide, used in many plating baths, is also a pollutant of concern. This chapter provides an overview of wastes generated from the various processes found in a metal finishing facility. Table 2 provides a summary of these pollutants and their sources.
The rinsing process is the primary source of waste generated in metal finishing operations. Rinsing removes plating solutions or cleaners from the workpiece. Rinsewaters often contain low concentrations of process chemicals carried by the workpiece into the rinse (also known as dragout).
Sources of wastewater that are typically treated on site include:
Wastewater that is typically regulated but not treated includes:
To meet air emission regulations, vapors and mists, which are emitted from process baths, are controlled by exhaust systems equipped with mist collection and scrubbing systems. This treatment process generally produces a metal hydroxide sludge that must be managed as a hazardous material. Once treated, wastewaters are discharged to a sewer authority or to a body of water (EPA 1995b).
Metal finishers periodically discharge process baths when they lose their effectiveness because of chemical depletion or contamination. Accidental discharges of these chemicals also can occur (e.g., when a tank is overfilled). These concentrated wastes are either treated on site or hauled to an off-site treatment or recovery facility. In general, the sources of hazardous and solid wastes at a plating shop include:
Spills, if they occur, can contribute significantly to the volume of waste. Samples of plating chemicals, which are provided by vendors but not intended for manufacturing use, also can contribute to the amount of waste that a metal finisher generates. Outdated chemicals are another example of wastes that platers and others typically do not attribute to the production process. These samples and obsolete or expired materials often accumulate and can violate waste storage requirements. These wastes eventually must be returned to the supplier or disposed of appropriately (EPA 1995b).
There are several air emission sources at a metal finishing facility. Those of greatest environmental concern are chrome plating and anodizing processes that use hexavalent chromium and solvents from vapor degreasing. Chromium emissions frequently are controlled by wet scrubbers. The discharge of these systems is sent to wastewater treatment and combined with other wastewaters for processing.
Solvents evaporate substantially during degreasing operations. Contaminated liquid solvents are recovered either by distillation (on site or off site) or sent for disposal (incineration). Most shops do not have controls for organics. However, some larger plants use carbon adsorption units to remove hydrocarbons (EPA 1995b).
Metal finishing results in a variety of hazardous compounds that are released to the land, air, and water. As a result, facilities are required to comply with numerous regulations. Regulations for metal finishers are promulgated at the federal, state, and local level. The requirements are complex and can vary, not only from state to state, but also from municipality to municipality.
The metal finishing industry has made extensive progress in improving operations in recent years as environmental regulations regarding discharges have become more stringent. However, in the future, platers will need to meet new standards that require further reductions in the amount and types of wastes that they discharge. Increased costs for materials and discharges will continue to cut profit margins and force businesses to search for new ways to reduce these costs.
The metal finishing industry is regulated under numerous federal, state, and local environmental statutes. Three major federal laws regulate releases and transfers from the metal finishing industry: the Clean Air Act as amended in 1990 (CAAA), the Clean Water Act (CWA), and the
Resource Conservation and Recovery Act (RCRA). Also, the emissions reporting requirements under EPA's Toxics Release Inventory (TRI) cover many of the chemicals used in metal finishing. Table 3 presents an overview of the federal regulations affecting the metal finishing industry.
Environmental assistance providers should consult with state and local regulatory authorities to identify specific requirements that might be more stringent than those promulgated under federal law. A myriad of state and local laws pertain to metal finishers, and helping them to understand all of these regulations can be an important aspect of providing assistance. This manual does not provide specific information on state and local regulations because of the lack of consistency across state and local programs.
With the enactment of the Clean Air Act Amendments, air emissions have become a greater concern for metal finishers. Any metal finishing operation with processes that could emit Hazardous Air Pollutants (HAPs) or volatile organic compounds (VOCs), as defined in the CAAA, could be required to obtain an operating permit and/or comply with other regulatory requirements for those processes. Regulations covering the use of halogenated solvents, a common material in most metal finishing operations, will directly affect most companies. Facilities that have processes which emit airborne metals, particularly chromium, are also going to be subject to increasing requirements (Haveman 1995).
The Clean Air Act Amendments of 1990 established a list of 189 hazardous air pollutants. Of the 56 SIC 3471 substances reported in the TRI database for 1990, 33 are included on the list of HAPs. Under the CAAA, Congress required EPA to identify major and area source categories associated with the emissions of one or more listed HAPs. To date, EPA has identified 174 categories. Congress also required EPA to promulgate emissions standards for listed source categories within 10 years of the enactment of the CAAA (November 15, 2000). These standards are called the National Emission Standards for Hazardous Air Pollutants (NESHAPs).
The standards will require regulated metal finishers to apply Maximum Achievable Control Technology (MACT) to all new sources of HAPs, while existing sources could be in compliance using less strict control measures. The MACT determination processes is quite complicated. Put simply, it is the lowest emission rate or highest level of control demonstrated on average by the top performing companies (top 12 percent) in the source category. MACT determination is subject to negotiation among industry, environmental groups, and EPA (Haveman 1995). State environmental agencies will determine exactly which businesses are subject to the permit requirement as part of their State Implementation Plans (SIPs).
Currently, EPA is finalizing three NESHAPs (Chromium Electroplating, Solvent Degreasing, and Steel Pickling) that will directly affect the metal finishing industry (EPA 1995a). A summary of these three NESHAPs follows.
These standards limit the air emissions of chromium compounds in an effort to protect public health. The promulgated regulation will be a MACT performance standard that will set limits on chromium and chromium compounds emissions based upon concentrations (e.g., mg of chromium/m3 of air).
The chromium electroplating process emits a chromic acid mist in the form of hexavalent chromium (Cr+6) and small amounts of trivalent chromium (Cr+3). Human health studies suggest that acute, intermediate, and chronic exposure to hexavalent chromium results in various adverse effects. EPA has developed a NESHAP for chromium emissions for hard and decorative chromium electroplating and chromium anodizing tanks. There is not one standard emission limit. The proposed emission standards differ according to the sources (e.g., old sources of chromium emissions will have different standards than new ones). EPA argues that these proposed performance standards allow facilities a degree of flexibility because they recognize a difference in facilities and allow facilities to choose any technology that meets the emission standards established by the MACT (EPA 1995a).
EPA also has promulgated a NESHAP for the halogenated solvent degreasing/cleaning source category that will directly affect the metal finishing industry. EPA has designed this standard to reduce halogenated solvent emissions based on MACT. The standard will apply to new and existing organic halogenated solvent cleaners (degreasers) that use any of the HAPs listed in the CAAA. Specifically, EPA is targeting vapor degreasers that use the following HAPs: methylene chloride, perchloroethylene, trichloroethylene, 1,1,1-trichloroethane, carbon tetrachloride, and chloroform (EPA 1995a).
This NESHAP sets two standards. Facilities can meet these standards in a variety of ways. The MACT-based equipment and work practice compliance standard requires a facility to use a designated type of pollution prevention technology along with proper operating procedures. Existing operations that use a performance-based standard can continue to do so if they can achieve the same level of control as the equipment and work practice compliance standard (EPA 1995a).
EPA has identified steel pickling processes that use hydrochloric acid (HCL) and HCL regeneration processes as potentially significant sources of HCL and chlorine emissions. Hydrochloric acid and chlorine are among the pollutants listed as HAPs in Section 112 of the CAAA. EPA has drafted a presumptive MACT standard for these processes, which is currently under review. This standard is slated for promulgation by November 15, 1997, however, it might be delayed (EPA 1995a).
In effort to control smog, the CAAA required EPA to develop standards on the following substances:
The standard of interest to metal finishers is ozone. Ground level ozone results from the reaction of VOCs with nitrogen oxides. Many of the substances used in solvent cleaning and degreasing, as well as stripping, are VOCs. The extent to which a small source of VOCs will be regulated depends upon the air quality in the region in which the source is located. Basically, if a source is located in an "attainment" area (in compliance with the National Ambient Air Quality Standards (NAAQS)), it will be required to obtain a permit if its potential to emit is greater than 100 tons of VOCs per year. Special provisions for attainment areas have been made for sources located in the Northeast and Mid-Atlantic states. Facilities located in an attainment area will be subject to a permit if they have the potential to emit 50 tons of VOCs per year (Haveman 1995).
For those facilities located in non-attainment areas, the regulatory thresholds are much lower. How much lower depends on the degree of non-compliance with the NAAQs in that region. EPA classifies non-attainment areas into five types: marginal, moderate, serious, severe, and extreme. As air problems increase, the likelihood that a small source of VOCs will be required to obtain a permit will increase.
The Clean Water Act regulates the amount of chemicals/toxics released via direct and indirect wastewater/effluent discharges. EPA has promulgated effluent guidelines and standards for different industries under the CWA provisions. These standards usually set concentration-based limits for the discharge of a given chemical. EPA defines two types of discharges: direct and indirect. Both types have different requirements.
A facility that is discharging directly into a body of water is regulated under the National Pollution Discharge Elimination System (NPDES) and must apply for a NPDES permit. The permit specifies what type of pollutants can be discharged and includes a schedule for compliance, reporting, and monitoring. The NPDES regulation limits the amount of metals, cyanides, and total toxic organics that a facility can discharge. These limitations remain the same whether the facility is discharging to a body of water or to a treatment facility (Haveman 1995).
Most metal finishing facilities discharge their wastewater to publicly owned treatment works (POTWs). These indirect dischargers must adhere to specified pretreatment standards because the POTWs are designed to deal mainly with domestic sewage, not industrial discharges. Often, specific state or local water regulations require more stringent treatment or pretreatment requirements than those in the federal effluent guidelines because of local water quality issues (Haveman 1995). All facilities discharging to a POTW are governed by the General Pretreatment Standards. These standards state that discharges must have a pH greater than 5.0 and cannot:
In addition, two CWA regulations affect the metal finishing industry: the Effluent Guidelines and Standards for Metal Finishing (40 CFR Part 433) and the Effluent Guidelines and Standards for Electroplating (40 CFR Part 413) (Haveman 1995). Companies regulated by the electroplating standards before the metal finishing standards were promulgated become subject to the more stringent metal finishing standards when they make modifications to their facility's operating functions (e.g., facility equipment and process modifications). If these companies make no such modifications, they remain subject to the electroplating standards only. All new facilities are subject to the metal finishing standard.
The Effluent Guidelines and Standards for Metal Finishing are applicable to wastewater generated by any of the following processes:
If a facility performs any of the processes listed above, it is subject to this standard. In addition, discharges from 40 additional processes including cleaning, polishing, shearing, hot dip coating, and solvent degreasing could be subject to this standard.
The metal finishing and electroplating standards include daily maximum and monthly maximum average concentration limitations. The standards, which are based on milligrams per square meter of operation, determine the amount of wastewater pollutants from various operations that can be discharged (EPA 1995b).
The Effluent Guidelines and Standards for Electroplating cover wastewater discharges from electroplating and related metal finishing operations. This standard was developed prior to the metal finishing standard and has less stringent requirements than the metal finishing standard. Facilities that are currently regulated by the electroplating standard can become subject to the more stringent metal finishing standard if they make modifications to their facility's operations. EPA has made some exceptions to this rule, for example printed circuit board manufacturers (primarily to minimize the economic impact of regulation on these relatively small firms). EPA defines independent printed circuit board manufacturers as facilities that manufacture printed circuit boards primarily for sale to other companies. Also excluded from the metal finishing standard are facilities that perform metallic platemaking and gravure cylinder preparation within printing and publishing facilities.
Operations similar to electroplating that are specifically exempted from coverage under the electroplating standards include:
Congress is considering reauthorization of the CWA that could change the standards affecting metal finishing operations. In addition to possible congressional changes to the CWA, EPA also is reviewing the Effluent Guidelines and Standards for Electroplaters and Metal Finishers, which were promulgated in the 1970s and amended in the 1980s.
EPA also is developing effluent guidelines and standards for a related industry, the metal products and machinery industry. Phase 1 of these regulations was due in May 1996. These regulations would have set new effluent limits for some metal finishers. However, as a result of comments received, EPA is considering combining Phases 1 and 2 of these regulations and promulgating them in 2 years. Although this standard contains only cleaning and finishing operations as captive processes, it is likely that EPA might integrate the new regulatory options for metal finishing processes into this guideline. Under this scenario, electroplaters and metal finishers would most likely reference appropriate sections of the Products and Machining Industry Guideline to determine their effluent limits. What is not clear is how this guideline will affect job shop operations, which are not considered part of this industry. If job shops are not included, different requirements could be developed for them.
The Resource Conservation and Recovery Act (RCRA) of 1976 addresses solid (Subtitle D) and hazardous (Subtitle C) waste management activities. Regulations promulgated under
Subtitle C establish a "cradle to grave" system that governs these wastes from point of generation to disposal. A material is classified under RCRA as a hazardous waste if the material meets the definition of solid waste and exhibits one of the characteristics of a hazardous waste (i.e., corrosiveness, flammability, toxicity, or reactivity, designated with the code "D") or if it is specifically listed by EPA as a hazardous waste (designated with the code "F"). Metal finishers generate a variety of hazardous wastes during the plating process. Within RCRA subtitle C, EPA includes hazardous waste from non-specific sources in a series of "F" listings. Table 4 presents the F-listed wastes that might be relevant to the electroplating industry.
The universe of RCRA listed wastes is constantly changing. In some states, the list of specific wastes might be different because they have added to EPA's list of hazardous chemicals.
A waste can exhibit one or more of the RCRA Subtitle C characteristics but not be listed as a specific waste. Waste generated in electroplating operations that are not specifically listed but might exhibit a RCRA characteristic include:
To determine what a plater must do to comply with RCRA requirements, the facility first must determine its generator status. Generator status is based upon the amount of waste generated on a monthly basis. The following criteria determine the quantity of waste that is regulated by RCRA:
In general, there are three classes of generators. Although individual states might have different names for them, EPA classifies them as:
Each state has varying degrees of regulation for the three generator classes. At a minimum, however, EPA requires each class to comply with the requirements listed in Table 5.
Metal finishers must publicly report many of the chemicals they use in plating under the federal Toxic Release Inventory (TRI) reporting requirement. Facilities report information on a TRI data form (Form R) for each toxic chemical that is used over the threshold amount. Basic information that is reported in a Form R includes:
The releases and transfers reported on a Form R include:
A facility must fill out Form R if it:
The manufacturing and processing thresholds have dropped over the reporting years from 75,000 pounds in 1987 to 25,000 pounds in 1989. For a chemical "otherwise used," the threshold amount is 10,000 pounds. The following list presents the top 22 chemicals in the TRI database for metal finishing (SIC 3471) from 1987 through 1990 (the list ranks the chemicals in order of decreasing release quantities with national TRI rankings presented in parentheses):
Technical assistance providers can use TRI data to develop an aggregate picture of the releases and transfers from the metal finishing industry.
EPA. 1995a. Profile of the Fabricated Metal Products Industry. Washington, DC: Office of Enforcement and Compliance Assurance.
EPA. 1995b. Metal Plating Waste Minimization. Arlington, VA: Waste Management Office, Office of Solid Waste.
EPA. 1994. Sustainable Industry: Promoting Strategic Environmental Protection in the Industrial Sector: Phase I Report Metal Finishing Industry. Washington, DC: Office of Policy, Planning and Evaluation.
Haveman, Mark. 1995. Profile of the Metal Finishing Industry. Minneapolis, MN: Waste Reduction Institute for Training and Applications Research.