Carbon-based conductive materials facilitated anaerobic co-digestion of agro waste under thermophilic conditions

Abstract

Management of agro-waste is a major challenge globally due to inefficient disposal techniques, which concominantly leads pollution and loss of renewable bioenergy. Anaerobic digestion of agro-waste is one of the ways to tackle this problem but hindered by the recalcitrant nature of agro-waste. This study investigated the effect of granular activated carbon (GAC) and granular biochar (GBC) addition to enhance the thermophilic anaerobic co-digestion of wheat husk and sewage sludge. The conductive materials (particle size: 2-5 mm) were added separately at five different concentrations: 10, 20, 30, 40, 50 g/L_inoculum. The findings revealed that samples amended with GAC and GBC at 20 g/L dosage had the highest biogas yield of 263 and 273 mL/gVS_added, respectively, corresponding to 22 and 27% higher yield than the control. Additionally, a shorter lag phase was observed in both cases compared to the Control. However, the GBC amended samples showed relatively stable biogas production compared to GAC and consistent results regarding pH, alkalinity, total volatile fatty acids, and soluble chemical oxygen demand. The preliminary techno-economic analysis indicates that addition of GAC or GBC may not be feasible and require other innovative engineered solutions for the addition of conductive materials. This study confirms that GAC and GBC amendments enhance the biogas productivity and process stability in anaerobic digestion of recalcitrant agro-waste under the high-temperature regime and calls for further research in this direction.

Keywords: Anaerobic co-digestion; Carbon-based conductive materials; Direct interspecies electron transfer (DIET); Lignocellulosic waste; Sewage sludge; Wheat husk.