Investigation of methane-rich gas production from the co-bioconversion of coal and anaerobic digestion sludge

Co-bioconversion of coal and anaerobic digestion sludge is a process that involves the simultaneous treatment of coal and sludge using microbial activity to produce methane-rich gas for energy harvest. This process has the potential to provide an innovative approach to managing these two waste materials while delivering valuable products such as biogas and biofertilizers. In this study, an experimental program is designed in three batch reactor clusters in which each batch is intended to test the biogas production with various media combinations. This study's primary goal is to understand the coal-sludge bioconversion pathway of subbituminous coal and lignite coal with different media combinations. In all batches, control reactors without coal loading were considered blank. For each batch, two sets of coal-loaded reactors with 4 g subbituminous and lignite coals were set up in duplicate with various combinations of deionized (DI) water, formation water and nutrient solution which were added to the reactors to evaluate their impacts on biogas production behaviors. The results show that co-bioconversion of coal and sludge lead to superior biogas production and methane-rich gas in lignite, subbituminous, and blank, respectively. Utilizing formation water and nutrients in the reactors reach maximum biogas production in a short period. However, the cumulative biogas production reaches maximum volume for a long duration when coal-sludge is mixed with DI water. The optimum nutrient needs to be designed based on the coal characteristic and the microbial community within the anaerobic digestion sludge to maximize methane-rich biogas production in the co-bioconversion of coal-sludge process.