Enhancing Bioenergy Production through Novel Interaction of Microbes with Granular Activated Carbon-admixed Cement Mortar

Against the backdrop of realizing water-energy nexus and Net Zero transition, the anaerobic digestion treatment of sewage sludge fo biomethane has gained importance. During this bioprocess, microbes break down complex sludge organics to release carbon and electrons, a portion of which are converted into biomethane. However, the reaction kinetics of methane formation are limited by the diffusion of electron carriers (i.e., hydrogen and acetate). There is mounting evidence demonstrating that the addition of conductive materials, such as granular activated carbon (GAC), can promote microbial attachment and direct interspecies electron transfer (DIET), overcoming chemical diffusion limits. The occurrence of DIET in wastewater treatment has been known to significantly promote methane production. However, the addition of loose GAC materials to anaerobic digesters are impractical at full-scale operation due to material washout, incurring high cost and increased waste volume. Given that anaerobic digesters are constructed from concrete material, the immobilization of GAC within the concrete structure could present a feasible approach to realize the benefits of DIET. This paper explores the potential of using GAC-admixed cement mortar to stimulate and promote DIET in wastewater treatment applications to enhance methane production. Our results show that the granular activated carbon-admixed cement mortar was able to boost methane production from sludge by 26.8% at a GAC proportion of 5% to 33.5% boost at 20%, surpassing the classical limits of methane production. But, this comes at the cost of the cement mortar’s reduced compressive strength by 6% to 19.5% as GAC proportion increases from 5% to 20%. Overall, this study provides initial evidence to demonstrate the feasibility of promoting DIET-induced methane production through functionalizing the anaerobic digester’s concrete material. Future studies focusing on GAC-amended concrete and enhancing concrete’s compressive strength will be needed. If proven successful, DIET at full-scale anaerobic digester will be made possible without significant complexity or additional cost of supplemental chemcicals. This presents a new way forward for the sewage treatment industry to achieve greater water-energy nexus and Net Zero targets.