Improving the stability and efficiency of anaerobic digestion of food waste using additives: A critical review

Anaerobic digestion is an effective technology to treat food waste, with methane production as renewable bioenergy. However, there are two key problems in the practical application, i.e., poor system stability and low reactor efficiency. In this paper, additives used in anaerobic digestion of food waste were systematically reviewed in view of system stability and reactor efficiency. Enzymes showed excellent property in food waste pre-hydrolysis stage with almost all macromolecular matters being rapidly resolved. Fungi fermentation process to produce hydrolytic enzymes, can be regarded as a promising and low-cost way to realize rate-limiting step elimination. It can be also concluded that adding neutralizers, buffer chemicals and some other materials are effective to maintain the pH level for practical application. Trace metals in food waste are not enough but needed for methanogens activation in long term and high loading rate operation. In addition, direct interspecies electron transfer could be much helpful for intermediate refractory organic acids degradation and methanogenesis promotion with additives of conductive materials, which is also discussed and should be studied further in anaerobic digestion of food waste. Based on literature review, a new concept is proposed for further study, suggesting that after being well liquefied with enzyme pre-hydrolysis, food waste could be co-digested with landfill leachate in a high-rate anaerobic reactor stably, resulting in a high bioenergy recovery efficiency.