Response of semi-continuous anaerobic digestion of food waste to progressively increasing temperature: Methanogen community, correlation analysis, and energy balance

Digestion temperature affects the activity of methanogens and thus the methanogenic process in the anaerobic digestion of food waste. Therefore, controlling the digestion temperature for optimal activity of methanogens and renewable energy production is key to achieving sustainable applications of anaerobic digestion. This study investigated the responses of semi-continuous reactors and methanogens to progressively increasing temperature (39–50 °C). The activity of methanogens was analyzed by high-throughput sequencing, and the correlation between methanogens and environmental factors (average biogas yield, digestion temperature, volatile fatty acid concentration, etc) was explored by redundancy analysis, Pearson analysis and Mantel test analysis. Results showed that the highest average biogas yield and methane concentration (14.5–43.2 % and 0.4–5.2 % points higher than others, respectively) were obtained at 47.5 °C. However, energy balance analysis showed that increasing the temperature to 47.5 °C reduced energy balance by 65.3 %, mesophilic condition (39 °C) exhibited a higher energy recovery efficiency. Increasing digestion temperature decreased microbial activity and resulted in a structural transformation from hydrogenotrophic to acetoclastic methanogens, which was closely related to the substrate composition of AD. Correlation analysis showed that acetoclastic methanogens were significantly positively correlated with temperature, soluble chemical oxygen demand, and acetate concentration, and negatively correlated with average biogas yield and methane concentration, whereas hydrogenotrophic methanogens were the opposite. This result provides a theoretical basis for the industrial application of anaerobic digestion towards more energy-efficient and sustainable development.