An Innovative Approach to Handle Shock Loading to Wastewater Treatment Process through Reusing Waste Activated Sludge

This paper reports findings of a pilot-scale study investigating the effectiveness and operational performance of reusing waste activated sludge (WAS) to handle shock loading to an activated sludge wastewater treatment process. The study consisted of both computer modeling and pilot testing. The computer modeling developed an operating plan that detailed rates of influent flow, return activated sludge (RAS) and WAS, as well as anticipated process response and the effluent quality. In this study, the influent flowrates were 13–24 gpm, the RAS flowrates were 20–24 gpm, and the discharged WAS flowrates were 0.28–0.56 gpm. The WAS was stored in a spare tank and was pumped into the aeration tank at 0.14 gpm when the shock loading occurred. Daily samples of the influent and the effluent were measured for COD, total nitrogen, TSS, NH₄⁺, and NO₃^–. Experimental results indicated that reusing WAS helped to stabilize the performance of the treatment process. For example, the rapid increase of influent loading didn't cause significant deterioration in COD of the effluent. Findings from this study suggest that blending WAS with the mixed liquor in the aeration tank can be an effective approach to handle shock loading of wastewater treatment process. Such an operational strategy can help to eliminate or defer the need of building a costly equalization tank and assist wastewater treatment plants to meet discharge criteria for protecting the quality of the receiving water.