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4.2 Filter Cake from Metal Finishine Pretreatment Facility Site 2010 quantity (lb) SLAC 12,507 Input Materials: Non -hazardous wastewater from metal plating operations, spent cleaning and plating baths (Category A Hazardous Waste) including: stment, Filter Cake , coagulation, from MFPF on, filtration, (CWC 181) ryingarge q of Off-site waterdisposal TW FIGURE I11.4.2. RINSE WATER TREATMENT PROCESS AND WASTE GENERATION FLOW DIAGRAM Hazardous Waste and Process Description The major generator of this waste stream at SLAC is the MFO Group in the MFD, which performs plating of carbon steel, stainless steel, copper and aluminum parts. The various baths clean parts and plate them with metal such as nickel, copper, tin, rhodium, indium, silver and gold. Non -hazardous rinse water is generated by using tap or de -ionized water to rinse residual plating solutions from parts being plated. The non -hazardous rinse water and spent plating baths (Category A wastes — acids and alkaline with metals but not cyanide baths) are treated at the MFPF, which allows SLAC to meet the sanitary sewer discharge requirements to the local POTW authorized under the Clean Water Act. The quantity of the filter cake will in part fluctuate from year to year based on the quantities of Category A wastes - alkaline cleaners (CWC 121) and spent acids (CWC 792) treated. Since these baths are more concentrated than the rinse water, these waste streams can generate a higher quantity of filter cake and thus raise the ratio of the pounds of filter cake to gallons of rinse water treated. Other variations in this ratio are not easily accounted for-, however, overall there is a trend toward decreasing this ratio that is discussed later in this section. The treatment process includes pH adjustment, precipitation, coagulation, solid separation, filtration and drying processes to remove metals and adjust the pH of the water before discharge. As a result of the process, a filter cake is generated, which is subsequently sent off-site for disposal to a permitted treatment, storage and disposal facility. Because the filter cake from Category A aqueous hazardous waste treatment and from non -hazardous rinse water treatment are not segregated, some double -counting of filter cake occurs. Since an integrated approach is being considered to reduce rinse water usage and to eliminate cyanide baths and rinse waters, the double -counting is not considered an issue for SLAC. SLAC is trying to achieve source reduction in filter cake by reducing its non -hazardous rinse water usage. Hazardous Waste Management Approaches Two noteworthy practices have been implemented by MFO that have helped reduce filter cake and chemical usage in the MFPF: One major source reduction measure that has been implemented since 2006 was the electrochemical generation of ferric hydroxide, which is used as a coagulant/flocculating agent used in the sedimentation of metal precipitates. The electrochemical system provides better control of ferric hydroxide in the treatment process. An improved ferric chloride metering system acts as a backup for the electrochemical system. The electrochemical process provides tighter control of the iron hydroxide than ferric chloride injection. This in tum reduces the volume and weight of the sludge that is generated during the removal of metals in the sedimentation process. 2. A second source reduction measure was eliminating the use of hexavalent chromium in cleaning and plating operations in the 2006 -to -2007 time period and using alternative technologies that provide the benefits of hexavalent chromium without any of the drawbacks. The elimination of hexavalent chromium provided several side - benefits that are not easy to quantify, but definitely contributed to the following achievements : a. Eliminated the need to treat hexavalent chromium rinse waters in the MFPF, thus helping to eliminate the tank that was used to convert hexavalent chromium to trivalent chromium. b. Reduced the generation of heavy metal sludge and treatment chemical usage associated with the treatment of hexavalent chromium in the MFPF. c. Eliminated the potential for worker exposure from hexavalent chromium in the metal finishing and MFPF work areas. The opportunities to further reduce filter cake are limited. Changing the composition of the sludge to make it lighter may result in more metals passing through to the POTW. The purity of rinse water used by MFO is high in order to retain a high degree of quality that is needed for parts that can be in service in ultra-bigh vacuum environments used by SLAC to operate the two-mile accelerator, as well as to conduct various experiments demanding high purity materials under ultra-high vacuum conditions. Rinse water is necessary to meet the stringent cleaning and plating specifications required at SLAC. MFO strives to reduce quantities of rinse water usage in its operations where feasible. The MFPF is a conventional pH adjustment -flocculation -sedimentation September 1, 2011 SB14 Plan 28 September 1, 2011 SB14 Plan 29