Optimization of an External Nanofiltration Anaerobic Membrane Bioreactor Treating a High-Strength Starch-Based Wastewater

Membrane and reactor performance for an anaerobic membrane bioreactor (AnMBR) treating a high-strength starch-based wastewater [average chemical oxygen demand (COD) of 84.8 +/- 8.9g/L] was examined under six varied cleaning protocols to find optimal operating conditions. The AnMBR was composed of a 1,000-L anaerobic continuous stirred tank reactor (CSTR) integrated with an external, tubular nanofiltration membrane module operated in cross-flow mode. The polyvinylidene fluoride-based membrane module had a nominal pore size of 30 nm, a total membrane area of 0.42m2, and a cross-flow velocity of 2.5m/s. The different cleaning protocols were provided by varying the membrane's permeate backwash duration, frequency, and flow rate and by incorporating chemically enhanced backwash cycles with the use of a mixed 250-ppm sodium hydroxide and 250-ppm hypochlorite solution. Reactor performance did not appear to be cleaning protocol dependent; however, a decline in reactor-specific methanogenic activity (SMA) was noticed over the duration of the study. A single, longer-duration chemically enhanced backwash offered the highest improvement in membrane performance over all other cleaning protocols.