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ODOR CONTROL STUDY <br /> The existing scrubbing system requires that the operators manually change hypochlorite <br /> dose to maintain a set-point ORP . For automatic control , solenoid valves or flow control <br /> valves can be added to the feed pipes or new sodium hypochlorite feed pumps could be <br /> used instead of the existing hypochlorite generation system . A gas phase chlorine <br /> monitor in the last scrubber would help keep adequate hypochlorite in the scrubber <br /> sump . The addition of hypochlorite could then be controlled automatically via the ORP <br /> and/or gas phase chlorine sensors . <br /> If all of these improvements were made , the overall scrubber removal efficiency would <br /> be expected to improve to at least 90 % efficiency and perhaps greater than 95 % . The <br /> construction and engineering costs for these improvements are estimated to be <br /> approximately $ 170 , 000 . If a new hypochlorite storage and feed system is needed , the <br /> estimated costs would increase to $300 , 000 . Operating costs for 24 hour per day, 7 <br /> days per week operation are conservatively estimated at $ 100 , 000 to $ 140 , 000 per <br /> year, mostly for chemicals and power. These estimated operating costs are <br /> approximately $ 50 , 000 to $90 , 000 more than existing operating costs because of the <br /> additional run time and chemical usage . The construction costs for these improvements <br /> include approximately $ 50 , 000 for adding a permanent drain for the mechanical <br /> thickener, opening the existing dampers , and pulling more air through the Sludge <br /> Storage Tanks . This should increase the negative pressure within the tanks and reduce <br /> fugitive emissions . <br /> Alternatively, the existing RSF blower could be operated at nearly full speed for 8 hours <br /> per day, 5 days per week during sludge dewatering and operated at half speed when <br /> sludge is not being dewatered . This would require retrofitting the existing blower with a <br /> VFD . When sludge is not being dewatered , the existing blower could be -lowered to <br /> approximately half speed and a new automated damper on the exhaust duct from the <br /> Dewatering Building could be partially closed so that much of the air would be drawn <br /> from the headspace of the Sludge Storage Tanks . The amount of air drawn from the <br /> Dewatering Building would be about half the amount drawn during sludge dewatering <br /> operations . A second smaller blower could also be used in addition to retrofitting the <br /> existing blower with a VFD . This would provide more redundancy for the odor control <br /> system . The construction and engineering costs for these improvements are estimated <br /> to be approximately $ 320 , 000 . Operating costs for this mode of operation are <br /> conservatively estimated at $ 80 , 000 to $ 95 , 000 per year, which is about $ 30 , 000 to <br /> $45 , 000 more than current operating costs . Table 6 provides a comparison of estimated <br /> costs for alternative improvements to reduce emissions from the RSF . <br /> 3 . 2 .2 Sludge and Septage Storage Tanks <br /> Instead of using the existing large RSF scrubber to treat emissions from the Sludge and <br /> Septage Storage tanks , a smaller odor control device could be used to treat these <br /> emissions . A 4 , 000 cfm modular two-stage scrubber could be constructed and operated <br /> 24 hours per day, 7 days per week . A modular or custom biofilter could also be used to <br /> `' 20 Indian River County, Central Wastewater Treatment Facility <br /> PBS&J #071230, February 2003 <br />