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R ODOR CONTROL STUDY M • 1 ,4-dichlorobenzene : STEL — N . A . PEL — 75 ppmv The OSHA exposure limits are much , much higher than the concentrations measured at the site . Although no extensive health analysis was performed , 1 , 44chlorobenzene is used in common household products to which people are frequently exposed , and the measured concentrations do not appear to provide concern for adverse health effects for operators or anyone else . 8 . 0 Conclusions and Recommendations Odor and sulfur emission inventories and evaluations performed in this study show that the existing Regional Sludge Facility ( RSF ) Scrubbers , Anoxic Tank , and Sludge and Septage Storage Tanks are , in order, the major sources of odorous emissions from the Central WWTF . H2S and organic sulfides are the major odorants emitted from these sources. Emission data show that the existing RSF scrubbers are not adequately removing H2S and organic sulfides . Evaluations also show that improvements to the RSF scrubbers will provide the most odorant removal . Although recent efforts to eliminate sludge dewatering filtrate and Aerobic Digester emissions have reduced total plant emissions by an estimated 25 to 33 % , air dispersion models shows that additional improvements are needed to further reduce emissions from the major sources . Air dispersion modeling also indicates that 90 % reduction of emissions from the major sources should help make the Central WWTF a "community- friendly facility". Several alternative improvements were evaluated for each of the major sources . Based on the advantages , disadvantages , effectiveness , and estimated costs associated with these alternatives , the following improvements ( in order of importance ) are recommended for the Central WWTF and the RSF . 8 . 1 RSF Scrubber Improvements • Install automatic chlorine solution addition facilities to both scrubbers and operate the existing scrubbers in series , as a two-stage system . • Install oxidation -reduction potential (ORP ) controls on both scrubbers . The ORP monitors will control the addition of chlorine solution . Add a gas phase chlorine monitor to the last scrubber to ensure adequate chlorine addition in the last stage . • Operate the first scrubber with mostly caustic soda . Operate the second scrubber with mostly chlorine solution . Engineering start- up , testing , and training services should be used to help determine appropriate operating conditions . i� 29 Indian River County, Central Wastewater Treatment Facility 111 PBSW #071230, February 2003