Energy Use Impacts of Flow Conveyance Alternatives for Membrane Bioreactor (MBR) Facilities

Flow conveyance through membrane bioreactor (MBR) facilities requires a combination of pumping and gravity flow elements. Conveyance of mixed liquor suspended solids (MLSS) between the reactors and membrane tanks (MTs) includes the options of pump forward/gravity return activated sludge (RAS) vs. gravity forward/pumped RAS return. Membrane permeate is typically drawn through the membranes and pumped to disinfection using permeate pumps, however, if the downstream water surface elevation is significantly lower than the MT water surface elevation, gravity (siphon) can be used to draw permeate through the membranes. This paper explores these flow conveyance options and compares the associated energy costs through case studies of the Cox Creek WRF and Brush Creek WPCF.