Anaerobic treatment of raw domestic wastewater in a UASB-digester at 10 °C and microbial community dynamics

Abstract

Direct anaerobic treatment of domestic wastewater is becoming attractive as it can change a wastewater treatment plant from energy consuming to energy producing. A pilot scale UASB-digester was studied to treat domestic wastewater at temperatures of 10–20 °C and an HRT of 6 h. The results show a stable chemical oxygen demand (COD) removal efficiency of 60 ± 4.6% during the operation at 12.5–20 °C. COD removal efficiency decreased to 51.5 ± 5.5% at 10 °C as a result of insufficient methanogenic capacity caused by low temperature and increased influent COD load (from 2.0 g/(L·d) to 3.0 g/(L·d)). Suspended COD removal was 76.0 ± 9.1% at 10–20 °C. Soluble COD removal fluctuated due to variation of the influent COD concentration, but the effluent COD concentration remained 90 ± 23 mg/L at temperatures between 12.5 and 20 °C. The methane production was 39.7 ± 4.4% of the influent COD, which was 80% of influent biological methane potential. The specific methanogenic activity of the UASB sludge and the digester sludge was 0.26 ± 0.03 and 0.29 ± 0.03 g CH4 COD/(g VSS d), respectively. The methanogenic community analysis revealed an overall dominance of the acetoclastic Methanosaetaceae and the hydrogenotrophic Methanomicrobiales during the operation between 10–20 °C. The results of the UASB-digester treating domestic wastewater at 10–20 °C as reported in this paper provide support for application of anaerobic domestic wastewater treatment in moderate climate zones.