Advanced anaerobic digestion by co-immobilization of anaerobic microbes and conductive particles in hydrogel for enhanced methane production performance

Recent research has increasingly focused on the enhancement of anaerobic digestion (AD) through direct interspecies electron transfer (DIET) facilitated by conductive particles (CP). Although this approach can significantly accelerate the AD process, the contact efficiency between CPs and AD microbes is relatively low due to the flow of water in a dispersed condition, leading to possible DIET inefficiency. In this study, a unique approach involving the “co-immobilization” of anaerobic microbes and multi-walled carbon nanotubes (MWCNTs) as CP into a hydrogel matrix was developed to improve the AD process. The advantages of this method include improved contact efficiency between microbes and CPs for enhanced DIET, and increased CP retention within the reactor, thereby omitting the need to compensate for CP washout. The methane production rate for the co-immobilized hydrogel was 2.5-fold and 1.9-fold faster than that of the control (dispersed sludge) and conventional DIET (dispersed sludge with MWCNT addition), respectively. Microbial analysis indicated the enrichment of functional microbes such as Anaerolineacea, Sedimentibacteraceae, Rhodocyclaceae, and Methanothrichaceae, which could be involved in the DIET under co-immobilized conditions. These results demonstrate the potential of the proposed method for realizing an advanced continuous AD process through improved DIET.