Long-term operation of a pilot scale anaerobic membrane bioreactor (AnMBR) for the treatment of municipal wastewater under psychrophilic conditions

• Viability of AnMBR at psychrophilic conditions for treating municipal wastewater.
• Effluent with high quality (100–120 mg O2/L) at HRT of 7 h.
• The membrane permits the biodegradation of slowly biodegradable matter.
• SMY depends on the recirculation between the membrane module and the UASB reactor.
• Long-term reliability and operability of the AnMBR technology.

The performance of a pilot scale anaerobic membrane bioreactor (AnMBR), comprising an upflow anaerobic sludge blanket (UASB) reactor coupled to an external ultrafiltration membrane treating municipal wastewater at 18 ± 2 °C, was evaluated over three years of stable operation. The reactor was inoculated with a mesophilic inoculum without acclimation. The AnMBR supported a tCOD removal efficiency of 87 ± 1% at hydraulic retention time (HRT) of 7 h, operating at a volumetric loading rate (VLR) of between 2 and 2.5 kg tCOD/m3 d, reaching effluent tCOD concentrations of 100–120 mg/L and BOD5 concentrations of 35–50 mg O2/L. Specific methane yield varied from 0.18 to 0.23 Nm3 CH4/kg CODremoved depending on the recirculation between the membrane module and the UASB reactor. The permeate flow rate, using cycles of 15 s backwash, 7.5 min filtration, and continuous biogas sparging (40–60 m/h), ranged from 10 to 14 Lm2/h with trans-membrane pressure (TMP) values of 400–550 mbar.