Binary-component anaerobic co-digestion: Synergies and microbial profiles

One of the key issues to create synergistic effect in anaerobic co-digestion (AcoD), is how to make the appropriate choice about co-substrate and determine the optimal mixing ratio. Adjusting organic component, namely carbohydrate (C), protein (P) and lipid (L), is expected to be a dependable strategy for obtaining synergistic effect in anaerobic co-digestion. In this study, the AcoD performances of organic components at different load levels were investigated in terms of methane yield, metabolic transformation, and microbial response. The synergistic interval at different loading levels showed considerable stability, and the significant synergy was achieved at C3P7 to C8P2 except for C6P4, C4L6 to C6L4, and P3L7 to P5L5 (based on mass ratio), respectively. Under high feeding load (4%VS), groups within synergistic interval could significantly reduce the toxic effects of intermediate metabolic inhibitors and improve methane production. However, AcoD of protein and lipid would induce antagonistic effects, and high proportion of protein was more serious. In the face of adversity, bacterial community diversity was weakened and the relative abundance of dominated phylum Firmicutes was strengthened. Furthermore, acetoclastic methanogenesis pathway was transformed to hydrogenotrophic pathway since hydrogenotrophic methanogens replaced acetoclastic methanogens as the dominant methanogenic archaea with the increase of syntrophic acetate oxidation bacteria. Suitable organic components proportion can effectively reduce inhibitor accumulation and maintain a well methanogens structure to ensure high methane production.