Boosting methane production and raw waste activated sludge treatment in a microbial electrolysis cell-anaerobic digestion (MEC-AD) system: The effect of organic loading rate

Abstract

This study deals with the effect of different organic loading rates (OLRs) on the organic load removal and the productivity of methane, in a microbial electrolysis cell-anaerobic digestion (MEC-AD) system treating raw waste activated sludge (WAS). For comparison, two identical reactors, a control (AD) and a MEC-AD reactor were constructed. Both reactors operated for 131 days, during which different Organic Loading Rates (OLRs) were examined; 1.1, 1.7 and 2.9 g_COD/(L*d). The results showed that the MEC-AD reactor performed better, relative to the AD reactor, at high OLRs. Specifically, the additional total particulate carbon and Kjeldahl nitrogen removal reached 12% and 13%, respectively, at an OLR of 1.7 g_COD/(L*d), while they reached 19% and 13%, respectively, at an OLR of 2.9 g_COD/(L*d). Moreover, the biogas production and the methane content increased by 30% and 6%, respectively, at an OLR of 1.7 g_COD/(L*d) and by 32% and 5%, respectively, at an OLR of 2.9 g_COD/(L*d). The electrochemical measurements indicated that the power output increased from 5 to 30 mW/m² when the OLR increased from 1.1 to 2.9 g_COD/(L*d). Overall, the results showed that the MEC-AD accelerated and enhanced the WAS treatment, boosting methane productivity.

Keywords: Applied potential; Bio-electrochemical systems; Methanogenesis; Microbial electrolysis cell-assisted anaerobic digestion; Organic loading rate; Waste activated sludge.