Fermentation and Biogas Production of Alkaline Wasted Sludge Enhanced in a Bioelectrolysis-Assisted Anaerobic Digestion Reactor under Increasing Organic Loads

Abstract

Challenges are always proposed when pursuing more energy and resource recovery from waste activated sludge via the anaerobic digestion (AD) process. Recently, microbial electrolysis has been integrated with AD and has been proven to enhance sludge conversion and system stability. This study investigated the effect of organic load on fermentation and biogas production in a bioelectrolysis-assisted AD reactor. Four different organic loads of alkaline waste sludge from 6 g/L to 14 g/L were investigated for their effects on the methanogenesis rate, substrate metabolism, electrochemical performance, and contribution. The results showed that the integrated system had a stronger tolerance to organic loads than the traditional anaerobic system. When the sludge concentration reached 14 g/L, the methanogenic rate, total methane yield, and SS removal rate significantly increased, reaching 47.1 mL/d, 96.2 mL/gVSS, and 71.6%, which were 1.27, 2.08, and 1.28 times those of the control, respectively. A high organic load was beneficial to the overall methanogenic rate but prolonged the fermentation period. Under a low organic load, the energy efficiency of the system deteriorated because the power loss increased and the electrochemical contribution rate was less than 50%. This result suggests that the integrated system can work and improve the overall energy yield from a high organic load of wasted sludge digestion.