Transition of mesophilic anaerobic digesters to thermophilic conditions

Research Project, 2019 – 2020

Anaerobic digestion of sewage sludge and organic waste is an important process to minimize the waste mass and
produce energy-rich biogas. Increasing the temperature from mesophilic (35°C) to thermophilic (55°C) conditions is a
method to increase the biogas yield and kill pathogens. However, the microorganisms that carry out degradation of
organic matter are different in mesophilic and thermophilic conditions and the shift in microbial community that occurs
when the temperature is increased can lead to unstable operation or process failure. The best strategy for converting
mesophilic digesters to thermophilic conditions is unknown.
The goal of this study is to clarify how different conversion strategies affect the microbial communities in anaerobic
digesters. We will analyze samples collected during a pilot-scale experiment carried out at Rya wastewater treatment
plant in Gothenburg. Six reactors were operated in parallel, three were converted to thermophilic conditions and three
served as mesophilic controls. The measurements and samples collected during the experiment form a unique set of
data with high practical relevance because of the similarity to full-scale conditions. We will use high-throughput DNA
sequencing to examine changes in the microbial community during the temperature increase.