THEORY OF FATE AND TRANSPORT OF SELENIUM COMPOUNDS THROUGH AN ACTIVATED SLUDGE WASTEWATER TREATMENT FACILITY

摘要

The County Sanitation Districts of Los Angeles County (Districts) own and operate thernJoint Outfall System which consists of seven interconnected wastewater treatmentrnfacilities and 10,500 miles of sewers within the greater Los Angeles CountyrnMetropolitan Area in Southern California. The largest of these facilities located inrnCarson California treats on average of 330 million gallons per day of combinedrnindustrial and domestic sewage. The Districts?Carson facility utilizes a pure oxygenrnactivated sludge secondary treatment process and along with biosolid dischargesrnfrom upstream wastewater treatment plants, generates approximately 330 tons per dayrnof high quality biosolids.rnIn 1993, the EPA revised the regulations dealing with biosolids (EPA 503,rnTable 3) and in particular set a limit for total selenium in biosolids of 36 mg/kgrndry. Subsequent tests of Districts biosolids showed levels of total seleniumrnapproaching the proposed limit of 36 mg/kg. The Association of MetropolitanrnSewerage Agencies (AMSA) challenged EPA抯 proposed selenium biosolids limits onrnlack of technical merit. An interim limit was placed back at the historic levels of 100