The Town Branch Wastewater Treatment Plant (TBWWTP) is a 30 million gallons per day (mgd)(113,500 m3/d) single stage activated sludge nitrification plant in Lexington, Kentucky. The Lexington Fayette Urban County Government (LFUCG) had received odor complaints from residential
neighborhoods surrounding the plant for years and had installed several systems to control the odors from individual processes, but off-site, odor complaints persisted. The LFUCG decided to conduct an odor study of the entire plant, meet with the neighbors, identify and rank the major odors
sources, identify the best and most cost effective means of controlling these odors and develop preliminary engineering plans. A thorough investigation of numerous odor control technologies was conducted, including several site visits to inspect operating systems, and it was concluded that
the most reliable and cost effective method of controlling emissions from the primary clarifier influent channels, primary effluent weirs and primary effluent channels was to cover the structures, capture the air and treat it in existing aeration basins using activated sludge diffusion. In
addition to the primary clarifier influent and effluent channels and weirs, the other major uncontrolled odor source at the site was the exhaust from the belt filter press (BFP) room. In this situation, oxygen ionization, along with other technologies, was investigated, and eventually
selected, as the best method of not only reducing odor emissions but also improving the working environment inside the BFP room. Oxygen ionization is a relatively new technology in the United States market but is very common in Europe. Several oxygen ionization system installations were inspected
on a trip to Switzerland and the technology proved to be sound, therefore it was selected for use in the BFP room. The LFUCG approved of the innovative approaches outlined in the odor study, and authorized design of the recommended improvements. The design was completed in May 2000, and construction
of the project was completed in August 2001. The activated sludge diffusion process typically has inlet hydrogen sulfide (H2S) concentrations from the primary clarifier influent and effluent channels of 20 parts per million (ppm) and outlet H2S concentrations of less
than 0.01 ppm for an H2S removal efficiency of greater than 99%. The oxygen ionization system has dramatically improved the working environment inside the BFP room and H2S concentrations are now typically less than 1 ppm. H2S and odor removal efficiency
testing has been inconclusive thus far but the operating staff is pleased with the improvements to the working atmosphere in the BFP room.
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