Increased applied voltage in the presence of GAC enhances microbial activity and methane production during anaerobic digestion of food waste†
Suspended conductive materials and bioelectrochemical systems (BES) have independently been shown to improve methane production by enhancing anaerobic digestion (AD). Little is known, however, about their potential combined effect in AD systems. This study investigates a BES–AD system with and without granular activated carbon (GAC) supplementation under applied voltage ranges of 1.25 V and higher. Results indicated that the BES–AD system with GAC could achieve robust methane production (>300 mL CH4 per g COD) from food waste at up to 2.75 V, whereas the BES–AD system alone did not. Microbial analysis revealed that improved performance of the BES–AD system with GAC coincided with higher relative activity of exoelectrogenic bacteria (Geobacter) on anodic biofilms. This advantageous application of GAC also resulted in Methanospirillum emerging as a dominant contributor to methanogenic relative activity in cathodic and GAC biofilms. These observations suggest that suspended GAC can serve to enhance the already beneficial coupling of BES with AD.