Enhanced water and energy recovery from anaerobic osmotic membrane bioreactors treating waste activated sludge based on the draw solution concentration and temperature regulation

Abstract

Anaerobic osmotic membrane bioreactors (AnOMBRs) have a great potential for water and energy recovery, but performance of AnOMBRs regulated by draw solution (DS) concentrations (0.5 M − 1.5 M) and temperatures (15 ℃ − 35 ℃) should be further enhanced. The results showed that the highest water production capacity of AnOMBR treating low-strength waste activated sludge was achieved under DS concentration of 0.75 M. When DS concentration exceeded this critical value, aggravated membrane fouling and cake-enhanced concentration polarization caused a negative contribution for net driving force maintenance of FO progress. More importantly, specific methanogenic activity of acetoclastic methanogens was suppressed under higher DS concentrations which further suggested that performance of AnOMBR was controlled by DS concentration to some extent. Under the critical DS concentration, removal of soluble chemical oxygen demand was above 90% during 60 days operation of AnOMBR. Dissolved methane in the bulk solution were not oversaturated at a ratio of 0.66, 0.48 and 0.17 and energy recovery of 2.0 kWh/m3, 3.1 kWh/m3 and 4.2 kWh/m3 was achieved at 15 ℃, 25 ℃ and 35 ℃, respectively. When AnOMBR was integrated with a microbial electrolysis cell (AnOMBR-MEC), CH4 component of AnOMBR-MEC was 97% and energy recovery reached at 5.1 kWh/m3 at 25 ℃ due to synergetic effect of electrochemical CO2 reduction by cathode and bio-conversion of produced formate. This work demonstrated that the optimal condition was DS concentration of 0.75 M under 25 ℃ for water (energy) recovery enhancement and biogas upgrading for AnOMBR-MEC simultaneously.