Experimental study of the anaerobic urban wastewater treatment in a submerged hollow-fibre membrane bioreactor at pilot scale

► Biological and separation process performance has been evaluated at 33 °C, 70 days SRT, and variable HRT. ► Almost 90% of COD removal was achieved with low effluent volatile fatty acid concentrations (<20 mg L−1). ► The observed methane yield was quite low due to the low influent COD/SO4-S ratio and SRB and MA competition. ► No irreversible fouling problems were detected, even for high total solid concentrations. ► A flux of 10 LMH and MLTS above 22 g L−1 (sub-critical conditions) led to a low TMP (<0.1 bar).