Bio-electrochemically assisting low-temperature anaerobic digestion of low-organic strength wastewater

Abstract

This study provides a new approach by using bio-electrochemical systems (BES) to improve the performance of anaerobic digestion (AD) for treating low-organic strength wastewater and recovering energy in the form of CH4. The BES had a relatively higher capability for temperature shock. At an applied voltage of 0.4 V, the BES significantly enhanced both the chemical oxygen demand (COD) removal and CH4 yield efficiency compared with those of the control at operational temperatures of 20, 12, and 8 °C. Energy balance evaluation indicated that the net energy obtained from the BES was higher than the energy recovered from the control, suggesting that operation of BES was economically available. Analysis of microbial physiological characteristics elucidated that electrochemical effects stimulated the production of extracellular polymeric substances, suggesting a faster metabolic activity of biomass in the BES. 16S rRNA sequencing showed that genera of H2-utilizing methanogens, Methanobacterium, Methanoregula, and Methanospirillum, dominated the consortia at low temperatures. On the surfaces of cathodes, considerable enrichments of H2-producing bacteria, Acetobacteroides and Anaerolinea were observed, implying the formation of H2-mediated syntrophic communities in the BES. The combined results suggest that operation of BES for low-temperature AD of low-organic strength wastewater will be an attractively potential technology.