Direct membrane filtration (DMF) for recovery of organic matter in municipal wastewater using small amounts of chemicals and energy

The recovery and utilization of organic matter in municipal wastewater are essential for the establishment of a sustainable society, such that these factors have drawn significant recent attention. The upconcentration of organic matter via direct membrane filtration (DMF), followed by anaerobic digestion, is advantageous over the treatment of the entire wastewater by an anaerobic process, such as an anaerobic membrane bioreactor (AnMBR). However, the occurrence of severe membrane fouling in the DMF is a problem. In this study, DMF was carried out at an existing wastewater treatment plant to attempt long-term operation. A combination of vibration of membrane modules, short-term aeration, and chemically enhanced backwash (CEB), with multiple chemicals (i.e., the alternative use of citric acid and NaClO), was found to be effective for the mitigation of membrane fouling in DMF. Furthermore, switching the feed from influents to effluents in the primary sedimentation basin significantly mitigated membrane fouling. In this study, in which microfiltration membrane, with a nominal pore size of 0.1 mm, was used, similar to 75% of the organic matter in raw wastewater was recovered, with the volumetric concentration of wastewater by 50- or 150-fold. Organic matter recovered by DMF had significantly higher potentials for biogas production than the excess sludge generated from the same wastewater treatment plant. An analysis of the energy balance (i.e., the energy used for DMF and recovered by DMF) suggests that the proposed DMF can produce a net-positive amount of electricity of similar to 0.3 kWh from 1 m(3) of raw wastewater with a typical strength (chemical oxygen demand of 500 mg/L). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study conducted DMF at an existing wastewater treatment plant and found that methods such as vibration, aeration, and chemically enhanced backwash can effectively mitigate membrane fouling in DMF and improve organic matter recovery efficiency. Organic matter recovered by DMF has higher potential for biogas production compared to excess sludge generated by wastewater treatment plants.