Metal Finishing Guide Book

2013

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environmental controls WASTEWATER TREATMENT BY THOMAS J. WEBER WASTEWATER MANAGEMENT INC., CLEVELAND; WMI-INC.COM/HOMEPAGE.JHTML Today, some 15,000 companies in the United States perform electroplating and metal finishing operations. These firms discharge their spent process wastewaters either directly to rivers and streams, or indirectly to Publicly Owned Treatment Works (POTWs). Metal finishing, by far, comprises more individual wastewater discharges than any other industrial category. Typically, pollutants contained in metal finishing process waters are potentially hazardous, therefore, to comply with Clean Water Act requirements, the wastewaters must be treated, or contamination otherwise removed, before being discharged to waterways or POTWs. Regulations, in general, require oxidation of cyanides, reduction of hexavalent chromium, removal of heavy metals, and pH control. Understandably, for companies discharging wastewater directly to waterways (direct discharges), regulations promulgated through the years require attainment of the more stringent concentration-based limitations for toxic wastewater constituents necessary for protection of aquatic life. These stream standards were developed from Federal Water Quality Criteria and limit instream pollutant concentrations to levels that will not adversely affect drinking water quality and aquatic life. Since the mid 70s, state agencies have continued to drive direct discharge limitations downward to levels well below waterquality-based stream standards, using antidegration, antibacksliding, and existing effluent quality (EEQ) policies, and the number of direct dischargers has dropped precipitously. Implementation of biological-based criteria through biomonitoring and bioassay testing will continue to force direct discharging facility closures and relocation to POTWs. As the overwhelming majority of metal finishing companies are discharging to POTWs, wastewater treatment systems for these firms are installed for compliance with federal pretreatment standards, or local pretreatment limitations if more stringent than the federal regulations. Federal standards are technologybased, i.e., developed through historical sampling and testing of conventional wastewater treatment system discharges collected at select, best-operated facilities. The base level technology was called Best Practicable Control Technology Currently Available (BPCTCA), or simply BPT. The more stringent level was termed the Best Available Technology Economically Achievable (BATEA), and is usually referred to as BAT. The treatment technology of BAT differs mainly from the conventional physical-chemical treatment of BPT in that it includes subsequent polishing filtration, and normally addresses improved methods of plating bath recovery. The purpose and intent of federal and local pretreatment regulations are to prevent the introduction of pollutants into POTWs that will interfere with their operations; to prevent the introduction of pollutants, which will pass through the POTW and contaminate receiving waterways; to prevent pollutant concentrations that are incompatible with biological processes or otherwise inhibit the process; and to reduce the pollutant concentrations of POTW sludges. Since the pretreatment regulations became effective in 1984, the metal finish582

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