Microbial community adaptability to altered temperature conditions influences prospect for optimization in anaerobic digestion. Microbial community adaptability to altered temperature conditions

The operating temperature strongly affects biogas yield, process stability and prospect for process optimization. Yet, many questions remains how to predict and manage disturbances related to temperature changes and how this influences on microbial communities. A long-term anaerobic digestion experiment was conducted to determine temperature-related questions raised by operative full-scale biogas plants and to evaluate optimization potentials and links to microbial community structure and responses. Four digesters fed household and slaughterhouse waste were operated in sets of two, at 37°C or 52°C, followed by a gradual increase or decrease in temperature in one digester in each set. Stability and flexibility of the digesters were then assessed by step-wise increases in organic loading rate (OLR) from 3 to 7 g VS/L/day, concurrently with decreased hydraulic retention time from 33-40 days to 14-17 days. Microbial dynamics were monitored by Illumina sequencing and quantitative PCR. The digester altered from thermophilic to mesophilic conditions failed at 6 g VS/L/day, whereas the digesters with constant temperature and the mesophilic-to-thermophilic digester remained stable at all OLR investigated. The microbial community structures developed in in the processes after transition in temperature resembled the taxonomic profiles in the digesters that constantly had operated at the corresponding temperature. However, both biological and chemical parameters indicated that lagging in resilience of the acetate and propionate-degrading populations inherited from the community initially shaped by thermophilic temperature conditions caused the thermophilic-to-mesophilic digester less resistant to stress and counteracted process optimization.