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ODOR CONTROL STUDY the plenum and supply ducts occupy a larger area . The supply ducts are typically constructed from 6 to 8-inch drainage pipe and the plenum consists of hardwood chips . A 50 : 50 mix of hardwood chips and compost could be used for the biofilter media . Drip tubes could be used to provide moisture inside the biofilter. A small moisturizinTp sray chamber is often provided to assure the process gas. is at 100 % humidity at all imes . The advantages and disadvantages of a custom biofilter is as follows : Advantages • Lowest capital costs • Low operations and maintenance costs • Good H2S and VOC control Disadvantages • Possible poor removal of organic sulfur • Periodic reconstruction of biofilter (2-5 year intervals) • Large land area required • Most difficult to construct • Higher engineering and operating costs Because custom biofilters require considerable maintenance and periodic reconstruction , modular biofilters are preferred . It is conservatively estimated that this alternative could reduce sulfide emissions from the Anoxic Tank by approximately 90 % . The construction and engineering costs for a modular biofilter are estimated to be approximately $450 , 000. The operating costs are estimated to be $ 10 , 000 per year, mostly for power. 3 . 1 .4 Cover and Control with RSF Scrubber This alternative is the same as the two alternatives above , except the existing RSF Scrubber would be used in lieu of a new 2-stage scrubber or biofilter. Blowers and a long duct from the Anoxic Tank to the RSF scrubber would be needed . Because there are no primary clarifiers at the Central WWTF, the existing RSF scrubber would have to be modified for National Fire Protection Association (NFPA) , Standard 820 . The existing blowers and controls would need to be modified with explosion-proof motors and intrinsically safe controls . Check valves would also be needed on ducts from the Dewatering Building and Sludge Storage Tanks so that the air from the Anoxic Tank would not be blown into these structures . The existing RSF scrubber would be operated 24 hours per day. The construction and engineering costs for this alternative is estimated to be approximately $ 350 , 000 . The operating costs are estimated at $ 80 , 000 for chemical and power required to operate the scrubber at current conditions for 24 hours per day. J 17 Indian River County, Central Wastewater Treatment Facility PBSU #071230, February 2003