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MWMC FACILITIES PLAN <br /> <br />Disadvantages: <br />· There are few pasteurization treatment systems operating in the U.S. Pre-pasteurization. <br /> systems have been installed in Perris, CA; Franklin Township, PA; and Carmel, IA; and <br /> one is under construction in Alexandria, VA. <br /> <br />· Fouling tendencies in sludge-sludge heat exchangers <br /> <br />· Production of odorous air <br /> <br />· Does not provide additional VSS destruction or volume reduction <br /> <br />· If heat is not recovered, then energy requirements are high <br /> <br />The major components associated with pre-pasteurization include sludge/sludge heat <br />exchangers for pre-heating undigested sludge and for recovering heated digested sludge, <br />hot water heat exchangers for primary sludge heating, pasteurization tank(s) (three small <br />tanks are commonly used to maintain a batch process: fill, hold, and draw pasteurization <br />cycles), mesophilic digester, and recycle and transfer pump. <br /> <br />Site-specific issues associated with the implementation of pre-pasteurization at the WPCF <br />are as follows: <br /> <br />· New pasteurization tank(s) would be needed prior to sludge entering the digester(s). <br /> The tank(s) would need volume for 30 minutes of theoretical SRT. This detention time is <br /> equivalent to 6000 gallons of storage (based on 2025 WWMM flows), or 1500 gallons per <br /> mesophilic digester. Typical pasteurization processes use three pasteurization tanks (fill, <br /> hold, and draw cycles). <br /> <br />· New hot water heat exchangers will most likely be needed. Undigested sludge must be <br /> heated to 70°C (160°F) prior to entering the pasteurization tank(s). Further evaluation of <br /> the heat exchangers is needed. <br /> <br />· New boilers may be needed to supply the necessary hot water to the existing heat <br /> exchangers. Further evaluation of the boilers is needed to determine if they can supply <br /> enough hot water to increase undigested sludge to pasteurization temperatures. <br /> <br />· New sludge/sludge heat exchangers are needed. These will serve as pre-heat treatment <br /> to the hot water heat exchangers and in recovering heat from the heated sludge after the <br /> pasteurization process. <br /> <br />· A fourth mesophilic digester, similar in size to the existing three units, would be <br /> installed. <br /> <br />· The existing digestion system would remain unchanged. Mesophilic digestion would <br /> sti[l occur. <br /> <br />· New instrumentation and controls (I&C) would be needed for the pasteurization tanks <br /> and heat exchangers. Longer-term, new I&C would be needed with the construction of <br /> the third digester. If the pasteurization process were immediately implemented, it could <br /> be fully automated. Plant staff would be able to monitor and operate the process in one <br /> shift per day. With future facility modifications, the process would remain automated. <br /> <br />6-36 MWMC_6.0_REV11.DOC <br /> <br /> <br />