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24 wateronline.com n Water Innovations in an overall decrease in the need for aeration, which in turn equates to lower energy costs. Also, as a result of the extended sludge age and hydraulic retention time, the microorganisms actually use their own protoplasm as food. They do this through a process known as endogenous respiration, when a living organism uses its own cellular mass instead of outside organic matter for energy. This results in less sludge per pound of carbonaceous oxidation. This brings down overall sludge production, resulting in reduced disposal, chemical, and electrical costs for biosolids. Operating at higher sludge ages, however, is not without its disadvantages. The older microorganisms are less resilient than younger microorganisms. The system is therefore more prone to quantity and quality disturbances from changes in flow. In addition, older sludges are also more granular in shape, which increases the amount of time it takes to settle the sludge. The older sludges challenge the clarifier systems. To combat these issues, MAWSA adds ferric chloride to assist in settling in the clarifiers, which not only assists in settling the sludge but it also helps to remove phosphorus. Like any wastewater treatment system and process, operating the oxidation ditches at an old sludge age has it disadvantages and advantages. MAWSA has determined that for its system, the advantages outweigh the disadvantages. The high sludge age ensures maximum usage of the new facilities, which in turn led to ENR-level nutrient removal results. The average monthly effluent concentrations from August 2014 through July 2015 were 2.04 mg/L for total nitrogen and 0.25 mg/L for total phosphorus (as seen in MAWSA's WWTP Effluent Quality Data table, on page 23). By working together, the staff at MAWSA and the engineers at RETTEW have been able to blend the upgrades and process improvements to produce an excellent water quality effluent that exceeds the PADEP's limits and MAWSA's goals. This results in a positive outcome for the receiving stream in southeastern Pennsylvania, which is connected through a network of waterways to tributaries of the Chesapeake Bay. MAWSA's emphasis on operational quality is benefiting end users via reduced costs as well as the environment, by contributing to improvements to the Chesapeake Bay. n NUTRIENTREMOVAL Michele Braas, PE, specializes in wastewater system and drinking water distribution system design. She has coordinated design of wastewater treatment facilities, including BNR evaluations, sanitary sewer systems, and sewage pumping stations. Her experience also includes the writing of permit applications, grant applications, and contract documents, and the performance of construction administration. About The Author Wastewater enters oxidation ditches at MAWSA.