Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance

Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L?1 day?1, while solids retention time (SRT) varied from 20–90 days. This achieved at constant flux, by adjusting transmembrane pressure (TMP) in the range 1.8–9.8 kPa. Membrane fouling assessed based required TMP, mixed liquors characterised using capillary suction time, frozen image centrifugation quantification of extracellular polymeric substances (EPS). SRT had significant effect these parameters: least an 30 highest 60 days, some reduction as this extended to 90 Operation < showed no further benefits. Although operation short optimal performance it led lower specific methane productivity, higher biomass yields effluent COD. Short may also have accelerated loss essential trace elements, leading reduced under conditions. A COD-based mass balance conducted, including both dissolved effluent.