Evaluation of Potential Energy Savings through Aeration Reduction in Aeration Tanks at the Stickney WRP
Abstract:Nearly half of the total electricity usage at a secondary wastewater treatment plant is in the activated sludge process. The majority of the electricity usage is for aerating the mixed liquor to provide dissolved oxygen (DO) for treatment. The amount of aeration in the aeration tanks of the Stickney Water Reclamation Plant is even more than for a typical treatment plant because the aeration tanks are used to raise the DO to a target of 8 mg/L at the end of the aeration tanks to meet the NPDES permit requirement for DO of 6.0 mg/L or greater in the final effluent. A field sampling study was conducted to measure the DO concentrations at key locations in the process to assess the efficacy of using the aeration tank to meet effluent DO requirements. The date collected in the study indicated that DO loss due to endogenous respiration in the final settling tanks was consistently roughly 2.7 mg/L regardless of the DO concentrations entering the tanks. DO concentrations increased because of turbulence caused by flow over the weir aeration and in the effluent channel; the amount of DO increase through the final settling tanks was 1.75 mg/L in the Phase I study and 1.95 mg/L in the Phase II study; the DO increase appeared to be inversely related to the DO concentration in the middle of the final settling tanks. For the sake of energy savings, the optimal DO set point at the end of aeration tanks is slightly above 7 mg/L, if aeration tanks are the only means for raising DO. However, more significant energy savings may be achieved by maximizing the weir aeration in the final settling tanks, utilizing more efficient ways of raising DO in the final effluent channel and lowering DO set point at the end of aeration tanks.
Document Type: Research Article
Publication date: 2011-01-01
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