Valorizing the waste bottom ash for improving anaerobic digestion performances towards a “Win-Win” strategy between biomass power generation and biomethane production

Abstract Anaerobic digestion of food waste is operationally challenged by rapid over-acidification. Bottom ash, a largely abandoned solid waste from biomass power generation, was supplemented in the anaerobic digestion of 2 typical food wastes of kitchen waste and fruit/vegetable waste for an attempt on this challenge. Results indicated no methane was recorded in anaerobic digestion of only food waste, indicating a complete failure by over-acidification. When bottom ash was involved, the digestion performances were significantly improved with the cumulative methane of 431.63 mL/g and 428.59 mL based on 1.0 gram total solid of kitchen waste and fruit/vegetable waste. It was found that the digestate pH was stabilized to approximately 7.5 during the digestion of these food wastes because of the excellent buffering capacity of bottom ash to the derived volatile fatty acids, indicating a main contributor to the improvement. 47.9%-71.8% promotion on digestate conductivity and the obviously enriched Methanosarcina abundance also were observed, suggesting the intensified direct interspecific electron transfer; this also had a contribution to the improved digestion. Technically, it can be proposed as a novel solution to valorization of bottom ash via facilitating the efficient anaerobic digestion of food wastes, by which a “Win-Win” strategy for these 2 bioenergy industries can be achieved to make them more sustainable.