Characterization of microbial evolution in high-solids methanogenic co-digestion of canned coffee processing wastewater and waste activated sludge by an anaerobic membrane bioreactor

The effects of the microbial community and dynamics on the efficiency of a methanogenic co-digestion system that treats canned coffee processing wastewater and waste activated sludge by means of an anaerobic membrane bioreactor, were investigated and analyzed. The co-digestion system had a chemical oxygen demand (COD) removal efficiency ≥90%, and a COD to methane ratio ≥85%. Phyla Synergistetes, Firmicutes, Proteobacteria and Ca. OP9 were dominant bacteria throughout the investigation, and the main contributors to the hydrolysis and fermentation processes. The degradation paths and functional microbes indicated that genera Caldicoprobacter and Clostridium were the main contributors in the hydrolysis process, while genus Anaerobaculum dominated the acidogenesis and acetogenesis at the most efficient hydraulic retention time (HRT) of 10 d (HRT10). The dominant methanogenesis varied from genus Methanosarcina (71.1%, HRT10) to Methanothermobacter (56.4%, HRT3), indicating a transition from acetic methanogenesis to hydrogen-dependent methanogenesis. Furthermore, a microbial analysis indicated that Acinetobacter was the main contributor to caffeine degradation in this system. This also appears to be the first time that Acinetobacter is reported to be capable of degrading caffeine in the anaerobic condition.