Pilot Scale Demonstration of Cross-Flow Ceramic Membrane Microfiltration for Treatment of Combined and Sanitary Sewer Overflows

A pilot scale investigation was undertaken at the Allegheny County Sanitary Authority (ALCOSAN) for approximately 12 months to evaluate the feasibility of using cross-flow microfiltration for the treatment of primary sewage effluent simulating combined and sanitary sewer overflows. Ceramic membranes of various pores sizes (0.05-1.4  (mu)m) were tested to understand the impact of cross-flow velocity, transmembrane pressure, and feed suspended solids on permeate water quality and permeate flux rate. A 0.2  (mu)m membrane operated with a 1.8  m/s cross-flow velocity, a transmembrane pressure below 2.1 bar and a backpulse frequency of 60 s showed the best performance among the conditions evaluated in this study. The 0.2  (mu)m membrane consistently met water quality objectives for fecal coliforms, E Coli, enterococci, BOD5, and suspended solids independent of the feed concentration, suggesting that direct discharge to surface water may be feasible. Feed suspended solids concentration and temperature influenced membrane permeate flux. Membrane cleaning with alkaline sodium hypochlorite solution is recommended as the first step followed by nitric acid cleaning if needed.