Factors that affect the permeability of commercial hollow-fibre membranes in a submerged anaerobic MBR (HF-SAnMBR) system

A demonstration plant with two commercial HF ultrafiltration membrane modules (PURON®, Koch Membrane Systems, PUR-PSH31) was operated with urban wastewater. The effect of the main operating variables on membrane performance at sub-critical and supra-critical filtration conditions was tested. The physical operating variables that affected membrane performance most were gas sparging intensity and back-flush (BF) frequency. Indeed, low gas sparging intensities (around 0.23 Nm3 h−1 m−2) and low BF frequencies (30-s back-flush for every 10 basic filtration–relaxation cycles) were enough to enable membranes to be operated sub-critically even when levels of mixed liquor total solids were high (up to 25 g L−1). On the other hand, significant gas sparging intensities and BF frequencies were required in order to maintain long-term operating at supra-critical filtration conditions. After operating for more than two years at sub-critical conditions (transmembrane flux between 9 and 13.3 LMH at gas sparging intensities of around 0.23 Nm3 h−1 m−2 and MLTS levels from around 10–30 g L−1) no significant irreversible/irrecoverable fouling problems were detected (membrane permeability remained above 100 LMH bar−1 and total filtration resistance remained below 1013 m−1), therefore no chemical cleaning was conducted. Membrane performance was similar to the aerobic HF membranes operated in full-scale MBR plants. [Display omitted] ► Membrane performance in SAnMBR treating urban wastewater was similar to aerobic MBRs. ► The main variables affecting K20 under sub/supra-critical conditions were tested. ► SGDm and BF are the physical variables that affect membrane performance most. ► No chemical cleaning was needed after two years operating sub-critically. ► K20 remained above 100 LMH bar−1 and RT below 1013 m−1.