Direct membrane filtration of municipal wastewater: Effects on biogas production, anaerobic biodegradability and settling properties of the up-concentrated stream

Direct membrane filtration (DMF), which can increase the amount of organic matter derived to anaerobic digestion, has emerged as a feasible option for implementing the principles of the Circular Economy in Wastewater Treatment Plants (WWTP). In this work, the effect of DMF on the anaerobic digestion performance and the sedimentation properties of the up-concentrated stream, for which a DMF pilot plant and a laboratory scale mesophilic anaerobic digester were operated for a period of two years, were evaluated. Since the DMF can be placed either after the pretreatment or after the primary settler, the pilot plant was fed with both raw and settled wastewater during the experimental period. The primary sludge and the up-concentrated stream were thickened and fed to the anaerobic digester. The results showed that including an ultrafiltration module in the WWTP increases biogas production of anaerobic digestion, whatever its location. The findings showed an increase of 28–52 % in the amount of organic matter that reached anaerobic digestion that led to an increase of 45–74 % in daily biogas production. A 0.663 kWh· kgCOD_rem⁻¹ / 0.256 kWh·m⁻³_inf energy recovery related to anaerobic digestion has been found when including the DMF after the pretreatment. Better settling properties were obtained when the DMF was placed after the pretreatment, while there was no improvement when PACl was added as a coagulant.