Comparison of microbial communities in the anaerobic digestion of Gracilaria under mesophilic and thermophilic conditions

Abstract

Mesophilic and thermophilic anaerobic digesters (MD and TD) utilizing Gracilaria and marine sediment as substrate and inoculum were compared with emphasis on the performance and composition changes of microbial community. The MD and TD produced methane yield with average of 222.6 ± 17.3 ml CH4/g VS and 246.1 ± 11 respectively. In the MD, volatile fatty acids (VFA) were efficiently removed with faster pH recovery from 6.6 to 7.5 but the VFAs concentration was doubled and followed by an intense pH drop to 6.4 with prolonged recovery in the TD. These VFA and pH profiles are suspected to affect the microbial compositions and the pyrosequencing of the digestion samples up to 35 days showed that the MD had a greater microbial diversity and changes of microbial community compared to the TD. Interestingly, an archaeal group distantly affiliated with the seventh methanogen order, Methanomassiliicoccales, dominated the MD while Methanobacteriales with Coprothermobarther, was favored in the TD. The data suggest that hydrogenotrophic methanogens and their syntrophs might play important roles for methane production in the MD and TD. The apparent bacterial successions with different possible functions integrated with methanogenesis in both MD and TD generated digester stability without compromising the methane production.uced methane yield with average of 222.6 ± 17.3 ml CH4/g VS and 246.1 ± 11 respectively. In the MD, volatile fatty acids (VFA) were efficiently removed with faster pH recovery from 6.6 to 7.5 but the VFAs concentration was doubled and followed by an intense pH drop to 6.4 with prolonged recovery in the TD. These VFA and pH profiles are suspected to affect the microbial compositions and the pyrosequencing of the digestion samples up to 35 days showed that the MD had a greater microbial diversity and changes of microbial community compared to the TD. Interestingly, an archaeal group distantly affiliated with the seventh methanogen order, Methanomassiliicoccales, dominated the MD while Methanobacteriales with Coprothermobarther, was favored in the TD. The data suggest that hydrogenotrophic methanogens and their syntrophs might play important roles for methane production in the MD and TD. The apparent bacterial successions with different possible functions integrated with methanogenesis in both MD and TD generated digester stability without compromising the methane production.