LAUSR

Abstract The objective of this study was to determine the effect of seed sludge on the start-up of thermophilic anaerobic digestion (AD) and to compare two methods of converting mesophilic to thermophilic consortium. Seed sludge source played an important role in the start-up while one-step temperature increase was the preferred start-up strategy. Biogas yields, pH and VFA levels of step-wise temperature increase reactors were initially comparable to that of the mesophilic control. However, they showed signs of instability and failure after temperature exceeded 50 °C. A great increase in absolute abundance of bacteria but reduced archaea for step-wise temperature increase reactors likely resulted in the over-supply of AD intermediates which were not consumed in time by methanogens, causing reactor souring. An initial drop in biogas and significant VFA accumulation were observed by one-step temperature increase reactors. However, owing to the successful acclimatization of thermophilic bacteria – Thermotogae, Thermoanaerobacterales, and Thermoanaerobacterium, as well as Methanosarcina, the one-step temperature increase reactor recovered from VFA accumulation and poor biogas yield within 10 days. By adopting the one-step temperature increase strategy and a suitable seed sludge, microbial consortia for thermophilic AD was established effectively, which aided the start-up of thermophilic AD of food waste.