Comparison of Different Start-up Strategies for Thermophilic Anaerobic Digestion: Process Stability and Microbial Community Structure Shifts

The aim of this study was to compare between step-wise and one-step increase in temperature from mesophilic (35°C) to thermophilic (55°C) for better start-up of thermophilic anaerobic digestion (AD) from a mesophilic digester. The stability of the reactors as well as shifts in microbial community structures were investigated. Stable thermophilic AD (biogas yield of more than 500mL/L/d) was achieved within 10 days from a mesophilic digester treating food waste by adopting the one-step start-up strategy. On the other hand, biogas yield of thermophilic AD with the step-wise start-up strategy dropped to less than 200mL/L/d after the temperature was raised beyond 50°C. After the increase of temperature, thermophilic methanogenic community was established, which was characterised by the colonisation of Thermotogae, Methanosarcina, Methanomassiliicoccaceae and Methanoculleus. Results from this study demonstrated that the one-step start-up strategy could allow the rapid establishment of the thermophilic anaerobic microbial community.