Orange County Sanitation District (OCSD) operates two large wastewater treatment plants (WWTP) in Southern California providing services to more than 2.2 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). Both plants are located in highly populated residential areas. Therefore, reduction of toxic and odorous emissions at both plants' sites has been a high priority for OCSD. Since 1981 when the first
odor control program was initiated, OCSD has implemented many projects to reduce odors in the treatment plants and collection systems. These include covering the preliminary and primary wastewater treatment processes, collecting and scrubbing the foul air, addition of chemicals to influent
trunklines, which help oxidize odor causing compounds, and installation of mechanical contrivances to reduce wastewater turbulence and therefore emissions of toxic and odorous compounds. As a result, the number of odor complaints received from the residents decreased from 125 to four or five
per year for each of the plants over the last ten years. Emissions of toxic compounds decreased by approximately 20% since 1991. Nevertheless, a complete elimination of odor related complaints and further reduction of health risk to surrounding residents and businesses remains one of
the OCSD's most important air quality related goals. The presented paper contains results of comparative study of emissions of odorous compounds from OCSD WWTPs and their health effects. Different wastewater, solids handling and combustion processes were considered. The results of
source testing, modeling and engineering calculations were used in determination of emissions. The related information from other WWTPs was also utilized.
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