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Pollution Prevention and Control Technologies for Plating Operations
Section 1 - Overview of Project Results
1.2 Overview of Users Survey Results
1.2.5 Wastewater Treatment/Sludge Management
The Federal electroplating and metal finishing pretreatment wastewater standards were developed by EPA by identifying commonly used treatment practices, and determining their effectiveness by collecting effluent data from well-operated systems. Conventional treatment (a series of unit processes used extensively by industry that have provided reliable treatment for many electroplating operations) was selected by EPA as the standard system. Therefore, for most plating shops, use of conventional treatment will provide sufficient pollutant removal to meet discharge standards. There are two major exceptions to this rule. First, many plating shops are regulated by local discharge standards that are more stringent than the Federal standards and conventional treatment may be insufficient to meet these limitations. Second, the treatment systems selected by EPA for establishing the Federal standards were those systems that EPA determined to be "properly operating facilities." For example, EPA omitted facilities that: (1) did not have well operated treatment processes; (2) had complexing agents (e.g., non-segregated wastes from electroless plating); and (3) had dilution from non-plating wastewaters. As a result, some plating facilities may not meet the properly operated facility criteria used by EPA and may have difficulty meeting Federal standards using conventional treatment.
In cases where conventional treatment is insufficient to meet discharge limitations for a given facility, there are three basic choices for attaining compliance: (1) correct or upgrade the existing processes; (2) make internal changes (e.g., improve rinsing, add recovery, segregation of waste streams) to "normalize" the wastewater, (3) use conventional treatment plus additional treatment (i.e., polishing), and (4) use alternative treatment reagents and/or processes. Information on each of these methods is covered in this text.
Pretreatment standards for the electroplating industry were first established in 1974, but it was not until promulgation of 40 CFR 413 on September 7, 1979 that Electroplating Categorical Pretreatment Standards became a reality. Several years later, EPA promulgated the Metal Finishing Categorical Standards (40 CFR 433). Prior to the existence of Federal standards, plating shops were regulated locally (if at all), presumably with wide variation in effluent limitations and levels of enforcement. Most plating shops did not have treatment systems for cyanide destruction and metals removal. Approximately 12 percent of the surveyed plating shops that were in business in 1975 (excludes zero discharge shops) indicated that their initial treatment system was installed by that year. Exhibit 1-16 presents a breakdown of the data in five year increments. These data indicate that by 1985, after the compliance dates for Federal regulations, 70 percent of the surveyed plating shops had installed their initial treatment system (excludes zero discharge shops).
Most plating shops installed conventional treatment to meet Federal regulations. Although it is difficult to assess exactly the respondents' data concerning end-of-pipe technology, it appears that an early trend occurred during the late 1970's and early 1980's when a significant percentage of shops attempted to utilize advanced technology in place of conventional treatment. These early efforts generally resulted in failure and the shops later resorted to conventional systems. One prominent example of this trend is the implementation of high surface area electrowinning as an end-of-pipe technology. Between 1979 and 1983, approximately 4 percent of the shops (excludes zero discharge shops) in existence installed this technology at an average cost of $66,360.
Only one of these systems is currently operating and that unit was extensively modified by its user. Early failures such as these appear to have had a negative impact on advanced technology. No single technology has since emerged as a significant replacement for conventional treatment. In fact, changes in end-of-pipe methods have tended toward simpler technologies. This conclusion is supported by the fact that the most significant technology change with respect to end-of-pipe treatment since 1975 is the use of sludge dehydration equipment (i.e., sludge dryers) to reduce the volume of sludge shipped off-site (29 percent of the respondents have installed this relatively simple technology with approximately 80% purchased between 1988 and 1993). Approximately 10% of all the shops surveyed presently rely on non-conventional treatment methods (includes zero discharge shops). The most popular non-conventional end-of-pipe treatment methods (ion exchange, evaporation, and membrane technology) are addressed in Section 6.
It should be noted that the majority of respondents to the Users Survey were job shops. More frequent use of advanced end-of-pipe technology may exist in other industry segments such as captive aerospace facilities.
Approximately 8% of the shops surveyed have attained zero discharge (24 shops). These shops are generally smaller and less diverse than the shops with discharges. The maximum, average and median number of employees at the zero discharge shops is 30, 16 and 15, respectively (for all shops responding to the survey, the employee figures are: maximum = 3,000, average = 67 and median = 35). Of the zero discharge shops, 58% are primarily hard chrome platers. The hard chrome process is one of the easiest to operate as a close-loop because of the high ratio of evaporation to drag-out (i.e., permits use of spray rinsing over the bath, drag-out recovery rinsing, etc.). The remaining zero discharge shops operate various metal finishing processes, including: cadmium, nickel and zinc plating; conversion coating; and aluminum finishing. Details of their metal finishing processes and pollution prevention and control technologies are contained in the NCMS database and summarized in this text.
One of the most frequent concerns of platers is the availability and cost of disposal for treatment process residuals (mainly F006 sludge). Of the respondents that generate F006 sludge, the average and median generation rates are 158,272 lbs/yr and 50,000 lbs/yr, respectively (excludes shops with zero generation rates and PS 273 which generates a large volume of dilute sludge). These shops spend an average of $0.52/lb for sludge disposal (includes, where applicable: transportation, stabilization, disposal or recycle, and taxes) (median cost is $0.25/lb). The unit costs for sludge disposal vary widely, depending mostly on the annual quantity of sludge generated. For example, shops that generate less than 10,000 lbs/yr pay an average rate of $1.58/lb, while shops generating more than 1 million pounds per year pay an average of $0.05/lb.
Discussions of sludge generation rates and costs are presented in Sections 6 and 7. Section 6 provides data from each respondent covering sludge generation rates, the location of their disposal site, the distance that sludges are hauled, the solids concentration of the sludge, and the disposal charges. Many platers (33% of the respondents) are using off-site metals recyclers as an alternative to land disposal of their treatment residuals and spent process solutions. Section 7 identifies the recycling companies used by the respondents, presents an overview of their recovery processes (provided by the recycling companies themselves), presents criteria for determining the applicability of off-site recycling, and compares the costs of recycling to land disposal.