Recycling crawfish shell waste as co-digestion substrates to promote methane recovery and the underlying mechanisms

The efficient disposal of municipal organic wastes in low-carbon strategies is urgent but faces critical challenges. Anaerobic digestion is effective to recover high-valued resources (i.e., methane) from organic wastes; however, conventional mono-anaerobic digestion is restrained by limited organics content and imbalanced nutrient composition. This work proposed crawfish shell wastes and waste activated sludge co-digestion for effective biogas production. Results demonstrated an increase of 249.5 % methane yield in co-digestion systems compared to waste activated sludge mono-digestion. The crawfish shell wastes introduced considerable organics, which enhanced the microbial utilization of proteinaceous substrates, and prompted solubilization, hydrolysis, acidification, and methanogenesis steps. The microbial consortia were reshaped with the enrichment of hydrolytic-acidogenic bacteria (i.e., Proteiniclasticum ruminis and Acetoanaerobium sticklandii) and functional methanogens (i.e., Metanobacterium sp. and Metanopirillum sp.). Also, the methanogenic metabolic networks were stimulated, especially hydrogenotrophic methanogenesis, which was mainly attributed to the favorable conditions (including organics, pH, ORP, and trace elements) induced by crawfish shell wastes.