Effect of supplementing commercially available and locally prepared carbon materials in anaerobic digestion : focusing on enhanced performance and potential mechanisms

Anaerobic digestion (AD) is a potential approach to treat organic wastes for energy and resource recovery. Adding various carbon materials in AD is being studied owing to its positive effects on the overall governing mechanisms. This study investigated the effect of adding seven different carbon materials in AD reactors in two sets of experiments. In the first set, five commercially available carbon materials were added to the batch assay, treating α-cellulose under anaerobic and oxygen-stressed conditions. The activated carbon amended reactor steadily provided methane yield even under oxygen-stressed conditions. In the second set, locally prepared hydrochar (HC) and pyrochar (PC) derived from biogas slurry were added to the anaerobic co-digestion of organic wastes. The reactor amended with HC, and its process water (PW) provided 478 mL/g·VSinput of biomethane yield while the PC-amended reactor achieved 411 mL/g·VSinput. This enhancement was attributed to functional groups in HC, volatile acids in PW, and PC’s pH buffering properties. Further, the grey relational analysis revealed that the HC and PW amendment is the best route for improved AD process efficiency. In short, from the two sets of experiments, these findings suggest that activated carbon, PC, and HC (with PW) have potential for improving AD efficiency. However, further research is needed to evaluate their long-term effectiveness and scalability.