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ODOR CONTROL STUDY • Other relatively minor and transient odor sources exist at the Central WWTF . Reasonable efforts should be taken to eliminate emissions from these sources . 3 . 0 Odor Control Alternatives Several different odor control alternatives were considered for the major sources of odorous emissions . Descriptions and evaluations of the alternatives are provided below. In considering these odor control alternatives , those related to the WWTF are presented in a separate subsection from those related to the RSF . This is because the County is currently considering alternative sludge management options that could potentially cause the existing RSF to cease operation . 3 . 't Wastewater Treatment FacTty - Anoxic Tank Several alternative improvements were considered for reducing odorous emissions from the Anoxic Tank. These alternatives are discussed below. 3 . 1 . 1 Biological Oxidation Since there are no primary clarifiers at the Central WWTF , raw wastewater exits the Headworks and proceeds directly to the Anoxic Tank. The wastewater is pumped over long distances and is therefore likely to be partially septic . It typically contains high concentrations of dissolved sulfides , such as 1-12S . Return activated sludge is added to the raw wastewater in the Anoxic Tank . In many Wastewater Treatment Facilities , anoxic tanks also receive internal recycle from the activated sludge process . There is currently no internal recirculation system utilized at the Central WWTF . The presence of such a system would likely improve biological oxidation of the incoming wastewater and reduce the amount of 1-12S that is released from the Anoxic Tank. Following the sampling program , PBSU recommended that the County install an internal recirculation system to improve biological oxidation of the influent wastewater. Our estimate , absent any site-specific data , is that approximately 50 % of the 1-12S emissions from the Anoxic Tank could be eliminated by the addition of the internal recycle . The construction and engineering costs for the internal recycle system is estimated to be $ 70 , 000 . The operating cost for the internal recycle is estimated at $2 , 000 per year. The reduction of sulfide emissions after the return activated sludge system was restored provides evidence that a "fresher" sludge can significantly reduce sulfide emissions . 3 . 1 .2 Cover and Control with New Scrubber An alternative approach or additional step to reduce emissions from the Anoxic Tank would include the installation of aluminum or fiberglass covers over the Anoxic Tank, collect the air under the covers , and scrub the odorous air with a packed tower scrubber. Based on preliminary calculations , approximately 2 , 500 cfm would be drawn 6 15 Indian River County, Central Wastewater Treatment Facility PBS& #071230, February 2003