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ODOR CONTROL STUDY 3 . 1 . 5 Recommended Improvements Since emissions from the Anoxic Tanks are significant and require aggressive controls , the following improvements are recommended to achieve maximum odor control , • Construct and operate an activated sludge internal recycle system to allow improved biological oxidation of odorous compounds in the Anoxic Tank . • Construct aluminum or fiberglass covers over the Anoxic Tank and collect odorous air from the headspace under the covers . • Construct and operate a modular biofilter for controlling the odorous emissions from the Anoxic Tank . The biofilter has the second lowest capital cost and lowest operating cost of any of the options . • The construction and engineering costs for the above improvements are estimated to be approximately $ 520 , 000 . The annual operating costs for these improvements are estimated to be approximately $ 12 , 000 . 3 .2 Regional Sludge Facility The mass odor emissions inventory revealed that two of the top three odor sources are found at the RSF . Alternative improvements to these facilities are discussed and evaluated below. 3 . 2 . 1 Existing Odor Scrubber Improvements were recently made to the odor collection system within the belt filter press area of the Dewatering Building . As indicated above , these improvements should improve the collection of odors emanating from the belt filter presses and reduce fugitive emissions from this facility. However, if the scrubber is not performing well , odorous gas will still be emitted to the atmosphere . Air from the Sludge and Septic Storage Tanks and the belt filter press dewatering room is scrubbed with an existing scrubber system that consists of two 12-ft diameter packed tower scrubbers . This scrubber system was originally intended to be operated as a two- stage unit. However, the system is currently operated with only one stage operating at a time . The other stage provides system redundancy. Either stage can be operated with caustic soda addition . According to the operators , sufficient caustic soda is added to maintain the scrubber sump pH at a set point of approximately 12 . The County also has the ability to add hypochlorite solution to each of the scrubbers . However, hypochlorite or chlorine solution has not been used for some time . Sludge processing facilities typically emit both H2S and organic sulfides . Organic sulfides are poorly removed with caustic soda scrubbers . An oxidant, such as chlorine or sodium hypochlorite , is required for good removal of organic sulfides . Hypochlorite �°� 18 Indian River County, Central Wastewater Treatment Facility PBSU #071230, February 2003