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6 DEVELOPMENT AND EVALUATION OF ALTERNATIVES <br /> <br />Summary of Odor Control ~ernat~ves Comparison <br />MWM¢ Facilities Plar~, Eugene-Springfield <br /> <br /> Capital Cost Non~[~,~onetary <br /> Alternative (millions of dollars) Rating~ <br /> <br />1 -Conventional OpemSpace Organic Media Biofilter $3.75 17 <br />2 -Conventional Open-Space Soil Media Biofitter $4.14 21 <br />3 - Bioscrubbers (Biotdckling Tower) $4.55 24 <br /> <br />Notes: <br />~ Non-monetary score is out of a possible maximum score of 30 points. <br /> <br />MWMC views odor control as an extremely important issue. One of MWMC's highest <br />priorities is to maintaLn their status as environmental stewards in the commurdty by <br />providing facilities that are neighborhood friendly. Bioscrubber and biofilter technologies <br />produced a nearly equivalent result in the evaluation. Considerations such as site space, <br />more advanced technolog/es, and higher atmospheric dispersion make bioscrubber <br />technology more favorable over biofilter technology. It is recommended that bioscrubbers <br />be incorporated into the overall odor control design for future use and to replace the <br />existing biofilter operations. The biofilters will be phased out over the next 20 years of <br />facility operation so that they achieve their original intended design life. <br /> <br />6.2.6 Tertiary Filtration <br />Unchanged dry weather mass lirrdts wilt drive effluent TSS and CBOD concentrations down <br />below the current effluent concentration limits of 10 mg/L. As effluent concentrations are <br />driven down over time it will become exceedingly more difficult to achieve the requRed <br />effluent limits unless tertiary filtration is added. Figure 6.2.6-1 show how the effluent TSS <br />concentration limits are reduced over time as the maximum month flows increase over the <br />planning period. Operations must provide an effluent quality that is sufficiently below the <br />effluent TSS requirements so that any process upsets may be absorbed by the system <br />without resulting in perrrfit violaticrns. Figure 6.2.6-1 shows the desired operating <br />performance to meet this requ/rement. Process upsets can occur in the secondary biological <br />treatment process dudmg periods of operational transition and can result irt poor settling <br />suspended solids for periods sufficiently long to adversely impact the monthly effluent <br />CBOD and TSS concentrations. It is well established that process upsets may occur during <br />periods of significant wastewater temperature changes, or during periods when the process <br />ks transitioning from winter operations (where no nitrification is required), to summer <br />operations (where nitrification/s required). <br /> <br />Effluent filtration can provide an effective defense against these types of situations. <br />Filtration also provides the added benefit of operational flexabil~ty, consistent performance <br />reliability, and provides the opportunity to develop reuse ptogram_s. For those reasons <br />previously outlined, it is recommended that 30 mgd of partial secondar~f effluent filtration <br />be implemented over the planning period. The pre-filtered flow would be removed from the <br />secondary effluent flow stream, pumped up to filtration for treatment, and then re-blended <br />with secondary effluent prior to disinfection. Filtration will provide performance reliability <br /> <br /> O_REVI 1 DOC 6.19 <br /> <br /> <br />