Achieving low-carbon municipal wastewater treatment by anaerobic membrane bioreactor at seasonal temperatures: A pilot scale investigation on reducing sludge yield and greenhouse gas emissions

Abstract

Anaerobic membrane bioreactors (AnMBRs) are efficient wastewater treatment technologies characterized by energy savings and reduced sludge production. However, research on sludge production and greenhouse gas (GHG) emissions from AnMBRs treating municipal wastewater (MWW) at seasonal temperatures is lacking. To fill this gap, the current study investigated the above issues in a pilot-scale AnMBR plant treating real MWW at 15–25 °C. The results show that the AnMBR achieved good chemical oxygen demand (COD) removal of 85–90% and methane and sludge yields of 0.205–0.244 NL/g-COD and 0.137–0.445 kg-MLVSS/kg-COD, respectively. The excess sludge was carbon-rich, with no risk of heavy metals, and thus suitable for further anaerobic treatment and easily disposable. GHG emissions of the AnMBR process were assessed in a simulated full-scale AnMBR plant in temperate climate regions, including both wastewater treatment (mainstream line) and sludge treatment (sidestream line). The assessment showed that the GHG emissions of the full-scale AnMBR plant were 0.341 kg-CO2eq/m3-MWW under non-energy recovery, and the mainstream line and sidestream line emitted approximately 61.1% and 38.9% of the total GHG, respectively. Owing to the significant energy recovery from the methane, the GHG emissions of the full-scale AnMBR plant were reduced to 0.142 kg-CO2eq/m3-MWW. The results of this study demonstrate that AnMBR is a promising MWW treatment process in temperate climate regions.