Treatment of Spent Filter Backwash Wastewater Using Dissolved Air Flotation Process
Spent Filter Backwash Water (SWW) is a major recycle stream that accounts for 10% (about 30 mgd) of the average flow at Blue Plains Advanced Wastewater Treatment Plant (AWTP) and a similar proportion of nitrification and denitrification treatment process capacity (DCWASA Focus, November 2004). The peak SWW flow and load result from increased filter washing during high flow events. The combined flows of SWW recycle plus raw influent especially during high flow (washout) events ultimately cause disruptions in process performance throughout the plant. Treatment of SWW by folded flow dissolved air flotation was explored to reduce the hydraulic load at the head of the plant and to ultimately eliminate this recycle flow stream from the treatment process. A bench-scale Dissolved Air Flotation (DAF) tester followed by a pilot-scale DAF unit was used to conduct the study. The bench scale unit was used to determine the reduction of suspended solids from SWW and the pilot scale unit was used to estimate the maximum hydraulic loading rate at which total suspended solids of 10 mg/l or less can be achieved.