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Phenols in the Die Casting Wastestreams | |||||||||||||
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The principal law governing pollution in the nation's streams, lakes and estuaries is the Federal Water Pollution Control Act, commonly known as the Clean Water Act (CWA). Originally enacted in 1948, it was revised in 1972 by amendments that gave the Act is current shape. The legislation spelled out ambitious programs for water quality improvement that are still being implemented by industries and municipalities today. Congress made certain fine-tuning amendments in 1977, revised portions of the law in 1981, and enacted further amendments in 1987. The objective of the CWA is the restoration and maintenance of the "chemical, physical, and biological integrity of the Nation's waters." Two goals also were established in the 1972 legislation: zero discharge of pollutants by 1985 and, as an interim goals and where possible, water quality that is both "fishable and swimmable" by mid-1983. While those dates have passed, the goals remain, and efforts to attain the goals continue. The Clean Water Act consists of two parts, regulatory provisions that impose progressively more stringent requirements on industries and cities to abate pollution and meet the statutory goal of zero discharge or pollutant; and provisions that authorize federal financial assistance for municipal wastewater treatment construction. Both parts are supported by research activities, plus permit and enforcement provisions. The Act has been termed a "technology forcing statute" because of the rigorous demands placed on those who are regulated by it to achieve higher and higher levels of pollution abatement. According to the EPA, 86% of all cities met compliance deadline for existing sources by October 31, 1988. Under the CWA, both indirect and indirect wastewater discharges from aluminum and zinc die casting facilities are subject to regulation, and it is through the CWA that phenol comes into play. Specifically, the CWA attempts to control the amount of chemicals and toxins released into the environment. The standards set concentration and mass-based limits on the discharge of a given chemical by any one facility. Certain responsibilities are delegated to the States, and this Act, like other environmental laws, embodies a philosophy of Federal-State partnership in which the Federal government sets the agenda and standards for pollution abatement while States carry out day-to-day activities of implementation and enforcement. States may also develop more stringent standards using the EPA technology-based standards as a minimum baseline. States are responsible for establishing water quality standards, which consist of a designated use (recreation, water supply, industrial, or other), plus a numerical or narrative statement identifying the maximum concentrations of various pollutants that would not interfere with the designated use. These standards serve as the backup to federally set technology-based requirements, by indicating where additional pollution controls are needed to achieve the overall goals of the Act. Phenol is considered a pollutant under the CWA. Phenol, C6H5OH3, is a caustic, poisonous, acidic compound. When pure, phenol is a colorless or white solid, but typically is sold in a dilute solution and used as a disinfectant. It evaporates more slowly than water, and is also flammable. There are numerous sources of phenols within the die casting process. Primarily, phenols are found in the various oils used in the die casting process, such as phosphate ester-based hydraulic oil, die lube, way lube and die cast coolants. Phenols may also be found in the plant waste streams generated by mold release agents and machine wash-down, and secondary operations such as machining and deburring. Cast salts, degreasers, and heat transfer oils may also contain phenols as an impurity. See graphic on following page for aluminum process flow diagram. Graphic taken from, "Pollution Prevention Practices for the Die Casting Industry," published by NADCA, 1996. Interestingly, phenols are also found in everyday products. The following is a list of several products and the level of phenols found in each (ppb-parts per billion):
Although the EPA determined that phenol should be regulated in wastestreams, other federal agencies have not considered it a health risk, and therefore has not regulated it in everyday products. The EPA decided that waters should be limited to 0.3 milligrams phenol per liter of water (0.3 mg/L) to protect human health from the possible harmful effects of exposure to phenol through drinking water and/or eating contaminated water plants and animals. Below the 0.3 ppm acceptable level, no harm can be found to aquatic life. Exposure to phenol at the workplace may occur through breathing contaminated air or through skin contact with phenol when it is made and used. Laboratory animals that drank very large amounts of phenol in water had muscle tremors and loss of coordination, but there is no conclusive evidence showing that phenols present a health risk to humans. Interestingly, phenol can have positive effects on the body when used for medical reasons. The EPA developed national effluent guidelines for certain classes and categories of industries, including Metal Molding and Casting industries (40 CFR 464). The effluent limitation guidelines for each industrial category are based upon the degree of reduction of a pollutant that are achievable through the application of various levels of technology. Strict compliance with these effluent limitations represents one of the greatest environmental challenges faced by today's die caster. Historically, the effluent limitations for total phenols has been perhaps the single largest driver and limiting parameter for wastewater management and control at a given die casting facility. In addition to these technology-based standards, states developed standards to protect receiving waters, using EPA technology-based standards as a minimum. Applicable standards are incorporated into a facilities National Pollution Discharge Eliminate System (NPDES) permit. If a facility is discharging directly into a body of water, a NPDES permit must be obtained. The NPDES permit, which contains effluent limitations on what may be discharged by a source, is the Act's principal enforcement tool. If a facility discharges directly to a publicly owned treatment works (POTW), it must adhere to specified treatments. Die casters are subject to three types of restrictions for their wastewater discharge:
These restrictions are discussed below. Developed by EPA, national categorical standards limit discharges of specific pollutants on an industry-by-industry basis. Industrial categories, specifically the aluminum, zinc, copper, and ferrous casting industries, are subject to national categorical pretreatment standards for the metal molding and casting industry. The Magnesium Casting subcategory was excluded from regulation due to economic impacts. The aluminum and zinc subcategory industries and operations listed below are affected by the categorical standards.
Each of these subcategories contain pretreatment standards for both existing sources and new sources. The regulations impose strict limitations on wastewater discharged by aluminum and zinc die casters, including standards for copper, lead, zinc, total toxic organics (TTO), oil and grease, and total (4-AAP) phenols. Standards for aluminum and zinc die casters are production-based and expressed in terms of allowable pollutant mass discharge rate per unit of production (e.g., lbs. pollutant/1,000,000 lbs. of metal poured). To demonstrate compliance with the production-based standards, die casters are required to measure the flow of the regulated wastewater and determine the corresponding production rate. The compliance determination method is rather cumbersome, requiring several calculations each time a sample is taken. As an alternative to using these somewhat difficult production-based standards to demonstrate compliance, die casters may be able to incorporate equivalent concentration limits into your pretreatment discharge permit (See below).
Die casters must remember the critical importance of average production and flow data in the calculation of equivalent concentration limits. If there is considerable variation (greater than 20 percent is a rule of thumb) in production and flow data, the facility may be easily in compliance with equivalent concentration limits one month and "out" the next.
Compliance with an equivalent limit does not relieve the legal requirement to be in compliance with the production-based standards. A permit containing an equivalent limit does prevent from direct enforcement of the production-based standard. EPA supports the proper use of equivalent concentration limits and defers to the POTW's interpretation of how to apply them provided:
Remember that the standard for a given process (e.g., casting quench) applies to the wastewater leaving that process and not to the facility effluent. If wastewater is combined with other wastestreams, the combined wastestream formula must be used to calculate an alternate discharge limit (See below).
Prohibited discharge standards are nationally applicable general prohibitions against discharges that cause interference or pass through, as well as specific prohibitions against discharges that create hazards such as fire or explosion, corrosion, obstruction of wastewater flow, or extreme heat. The prohibited discharge standards apply to all industrial users of POTWs. Local limits are pollutant limits, developed by the individual POTWs, that implement the national categorical standards and prohibited discharge standards and supplement them as necessary to prevent interference and pass-through at the POTW facilities. More POTWs are imposing local restrictions on the discharge of wastewater from manufacturing facilities (including die casters) into the sanitary sewer system. Contact your local POTW for applicable wastewater regulations in your area. The pretreatment regulations require that industrial users notify the POTW of any discharge into the sewer system of any substance that is a hazardous waste under the Resource Conservation and Recovery Act (RCRA). The way to determine phenol levels in your wastestreams is through the use of the 4-AAP method. The commonly used 4-AAP testing procedure for wastewater, which is a spectrophotometric method, must be modified to eliminate potential oil and tar interferences while analyzing raw materials for phenol. This purification is accomplished by an alkaline extraction of oils and tars from the test sample prior to its analysis for phenols. 4-AAP has shown to have matrix interferences in laboratory samples. 4-AAP can be inaccurate due to false positive readings generated by oily industrial wastewater. Benzoquinone and Ethylene Glycol are suspected interferences with the 4-AAP procedure. An alternative testing method is the Gas Chromatography/Mass Spectroscopy (GCMS). Although more expensive, gas chromatographic methods may be used for a direct and more accurate determination of phenols in a test sample. These regulations impose strict limitations on wastewater discharged by metal molding and casting operations. Some companies are able to comply with these standards. Other die casters may not be aware that categorical standards apply, and may be in violation of them. EPA may issue a compliance order or bring a civil suit in U.S. district court against persons who violate the terms of the NPDES permit, or one issued under section 404. The penalty for such a violation is extensive fines, such as $25,000 per day, and eventual shutdown. If a facility is discharging directly to a publicly owned treatment works (POTW), it must adhere to specified treatment methods. Several methods are recommended in the CWA for ways for die casters to eliminate the level of phenols in their wastewater. One such option is pretreatment. Pretreatment systems often experience high operating and maintenance costs and/or compliance problems resulting from equipment malfunction and/or breakdown. The system may require a modification of the treatment capability. Consequently, if a process change occurs, producing different wastewater flows and characteristics from what the treatment facility was originally designed for, the treatment method may require a modification depending on the overall concentration and makeup of the wastestream. The selection of a wastewater treatment system involves the review of a number of key economic factors including capital costs, operation and maintenance costs, and financial resources. The volume of effluent and the concentration of phenols and other materials are among the factors that need to be considered. Three of the options available to die casters are ultrafiltration, ion exchange, and chemical treatment, all of which provide methods of contaminant removal and then a discharge of a cleaned effluent. A continual match between waste stream flow rates and the process chemical injection and/or membrane/filter change must be maintained in order to ensure continuous discharge within limits. All three waste-fluid treatment systems require high capital expenditures and high operating costs. In addition, they require constant, skilled personnel for monitoring, which imposes an additional workload on the operations without any compensating benefits other than a potential reduction in disposal costs. Another available option is chemical destruction, in which chemical oxidation is used to destroy phenols. It is able to treat concentrated batches of wastewater which is high in phenols and low in other organics. Levels less the 0.1 ppm of phenol are able to be obtained. An effective method for source control of phenols would be to check each individual raw material used in die casting for phenols, and use or substitute with materials that have little or no phenols. Another effective method of reducing or eliminating phenols in wastewater is to segregate the various waste streams at the point of generation by collecting the materials in catch pans and handling them separately. For example, die lube spray can be collected in a metal pan installed below the die, screened to remove debris, filtered to remove fine particulate matter, treated for bacteria contamination, and recycled for reuse in the plant. Plunger lubricants and other drippings may also be collected in pans and recycled off-site as used oil. Several die casters have contacted the EPA expressing concern over the requirements relating to phenols. A reason why the regulation is unfair to die casters is that it groups die casters into a "one size fits all" category. In other words, die casters were put into the same category as steel and iron foundries, even though these industries do not use common raw materials, chemicals or processes to manufacture castings. During the comment period for the regulation, the Small Business Administration contracted the JACA Corporation to evaluate the impacts, both economical and environmental, or the proposed regulation. Their analysis, made in 1984, found several inconsistencies with the regulation. They pointed out in their report that there were inconsistencies and flaws in the EPA's reasoning for including some of the subcategories in the regulation. The findings of the JACA Corporation stated that the subcategories "should be excluded from the regulation because the total toxic wastewater loadings are not significant." One proposed subcategory was later excluded. More interesting, however, was the statement that many processes and pollutant categories could be excluded from the guidelines based on the fact that either the amount of pollutants involved are not toxic, therefore do not require a national regulation, or the amounts that would be reduced are insignificant. An industry recently further challenged the EPA's regulation of phenol. In order to have phenols removed from its industrial category, the Organic Chemicals and Synthetic Fibers (OCSF) category sued the EPA. Using the EPA's own data, the OCSF was able to win their case, having the court ordering the EPA to amend the regulations. Some die casters believe that the 4-AAP method, which was developed over 20 years ago, is an outdated test. This testing method, which is mandated for use by the regulation, has a tendency to be inaccurate due to false positive readings, as previously stated. The EPA has failed to consider that the die casting wastewater contains large quantities of other dissolved organics which react with the permanganate. An alternative intent of the use of the 4-AAP method for phenol analysis is to monitor a wide range of non-conventional pollutants including phenolic compounds, rather than a specific set of chlorphenols and phenol, as described in the GCMS procedure. There is a growing group of die casters that have gone beyond environmental compliance and are leading the way in environmental matters. One die casting facility decided to treat 100% of its own wastes. The company had previously taken steps to reduce waste, such as new holding and breakdown furnaces, and reducing the die lubricant concentration in the lubrication system. Treating their own wastewater significantly reduced their transportation and disposal costs. The die caster utilizes a continuous-treatment system. The resulting effluent, containing water and phenol, is pumped through a three-stage carbon filtration bed. The phenols are absorbed into the activated carbon, which produces a clean effluent. This treatment system for wastewater meets the industry's standards for wastewater.Another die caster had a waste treatment system custom designed. The system is a chemical precipitation system with flocculent additions and polymerization for efficient coagulation of solids, and pH adjustment. The resulting sludge is pumped to a filter press where is it squeezed and dried. Following the treatment, the clean process water is pumped back into operations. The system not only had environmental benefits to the company, but also allowed for a more efficient and cost effective use of labor, a reduction in the cost of water treatment chemicals, and a reduction in discharge testing costs. The EPA, through the CWA, regulates the wastestreams, including phenol levels, of die casters. Many die casters are not aware of the specific level of allowable phenol and those that are aware, have questioned the limits. Although the EPA has attempted to make recommendations for phenol elimination, some methods are not always feasible. Die casters are finding methods to control phenol, however, many of these processes are not cost-effective. For phenol-specific questions, contact your EPA region. They are listed below:
Prepared for the North American Die Casting
Association under a grant from the
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