Methane Production from the Anaerobic Co-Digestion of Lignocellulosic Materials and Paper Plant Sludge Cakes

Anaerobic co-digestion was evaluated for lignocellulosic materials and paper plant sludge cakes (PSL). The methane production, crystallinity, residual cellulose, and next-generation sequencing (NGS) were analyzed and compared. It was found that microcrystalline cellulose (MCC) had the highest accumulated methane production among the different materials in the anaerobic digestion system. The residual content and crystallinity of cellulose both decreased to a much larger extent, and the accumulated methane production was higher than that of the anaerobic digestion system with the added anaerobic sludge cake. NGS showed that the domain bacteria in the anaerobic digestion system with the added anaerobic sludge cake were Methanosaeta, which can convert organic sugars into methane. This substantially reduced the number of bacteria that can degrade cellulose. As the ability to degrade cellulose decreased, the residual cellulose content and crystallinity of cellulose became higher than those of the anaerobic digestion system without adding anaerobic sludge cake.