AIR TOXICS EMISSIONS REDUCTION STRATEGIC PLAN FOR TWO LARGE WASTEWATER TREATMENT PLANT

The Orange County Sanitation District (OCSD) owns and operates two large wastewater treatment plants (WWTP) in Southern California providing services to 2.3 million residents and numerous businesses. Plant No. 1 treats approximately 3.9 m3/sec (90 million gallons per day – mgd) of wastewater and Plant No. 2 treats about 7.0 m3/sec (160 mgd). More than 80% of the total flow comes from the domestic sources, with the remaining flow originating from variety of industrial and commercial sources. In addition to the wastewater treatment processes, each plant operates a Central Power Generation System (CGS) and boilers to produce electrical power and heat for the plant operations. The CGS engines and boilers utilize as a fuel digester gas produced by the anaerobic digestion of wastewater solids at the facilities. The excess digester gas can be burned in flares. There are 19 emergency stand-by Diesel engines and two Diesel turbines at the plants operating mostly for maintenance and testing purposes. Both Plant 1 and Plant 2 have embarked on long-term capital improvement programs.Both plants are located in highly populated residential areas with the nearest houses within only 50 m distance from the plants' fenceline. Therefore, reduction of toxic and odorous emissions at plants' sites has been a high priority for OCSD. Determination of major sources of toxic emissions at the plants and evaluation and reduction of the cancer and non-cancer health risks to surrounding residents and businesses associated with these emissions represents one of the major air quality related goals of the OCSD. The strategic plan of reduction of the toxic emissions and health risks is currently being developed by OCSD staff and their consultants – Malcolm Pernie, Inc. from White Plains, New York (Malcolm Pernie, 2004).