The effect of backwash frequency (15, 30 and 60 min) and influent flux (3.75, 7.50 and 11.25 L/h/m(2)) on fouling amelioration in an innovative external side-stream dead-end microfiltration anaerobic membrane bioreactor (AnMBR) for the treatment of domestic wastewater at 25 degrees C was investigated. During 6 months of reactor operation, a constant COD removal of 88% and an accumulation of 350 mg TSS/L/d inert matter in the reactor were observed. Experiments with different backwash frequency and fluxes showed that the increase in transmembrane pressure with time (fouling rate) follows in a two-step manner: a slow linear rise at the beginning, followed by a sudden increase in transmembrane pressure. Based on the fouling rates during the slow linear phase, the best backwash frequency for energy savings and fouling amelioration was determined to be in between 30-60 min. Moreover, the effect of particulate matter load on fouling rate was determined.