Comparison of anaerobic co-digestion of vacuum toilet blackwater and kitchen waste under mesophilic and thermophilic conditions: Reactor performance, microbial response and metabolic pathway.

ABSTRACT

Co-digestion of kitchen waste (KW) and black water (BW) can be considered as an attractive method to efficiently achieve the clean energy from waste. To find the optimal operation parameters for the co-digestion, the effects of different temperatures (35 and 55 °C) and BWKW ratios on the reactor performances, microbial communities and metabolic pathways were studied. The results showed that the optimum BWKW ratio was 13.6 and 14.5 for mesophilic and thermophilic optimal reactors, with methane production of 449.04 mL/g VS and 411.90 mL/g VS, respectively. Microbial communities showed significant differences between the reactors under different temperatures. For bacteria, increasing BWKW ratio significantly promoted Defluviitoga enrichment (1.1%-9.5%) under thermophilic condition. For Archaea, the increase in BWKW ratio promoted the enrichment of Methanosaeta (8.6%-56.4%) in the mesophilic reactor and Methanothermobacter (62.0%-89.2%) in the thermophilic reactor. The analysis of the key enzymes showed that, acetoclastic methanogenic pathway performed as the dominant under mesophilic condition, with high abundance of Acetate-CoA ligase (EC6.2.1.1) and Pyruvate synthase (EC1.2.7.1). Hydrogenotrophic methanogenic pathway was the main pathway in the thermophilic reactors, with high abundance of Formylmethanofuran dehydrogenase (EC1.2.99.5).