Effect of seed sludge source and start-up strategy on the performance and microbial communities of thermophilic anaerobic digestion of food waste

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 degrees C. A great increase in absolute abundance of bacteria but reduced archaea for step-wise temperature increase reactors likely resulted in the oversupply 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. (C) 2020 Elsevier Ltd. All rights reserved.