Review on biochar for enhancing biogas production from anaerobic digestion of food waste

Abstract

Food waste is the major waste fraction in municipal solid waste and is indeed a significant issue in society, with substantial economic, environmental, and social impacts. Various technologies exist to manage food waste, including animal feeding, anaerobic digestion, composting, incineration, and landfilling. Among these technologies, anaerobic digestion is the most recognized, efficient, and sustainable method. It can produce biogas and nutrient-rich fertilizer simultaneously. Because of the high organic load of food waste and the presence of mass nutrients, it is a suitable substrate for the anaerobic digestion process. However, the anaerobic digestion process faces challenges such as process instability, slow rate of biogas generation, and sudden failure of biogas generation due to susceptibility to inhibitors. All these challenges have affected its efficiency. Biochar has been identified as a promising alternative to address most of the drawbacks in the anaerobic digestion process and enhance methane production. Biochar is a carbon-rich material produced through thermochemical conversion processes. Because of its specific properties, such as its high specific surface area, porous structure, adsorption capacity, buffering capacity, and a higher number of functional groups, it has the potential to enhance biogas production in anaerobic digestion processes. Biochar exhibits pH buffering properties, enhances the enrichment of functional microbes, alleviates the effects of inhibitors, and accelerates the process of direct interspecies electron transfer. This paper reviews the effectiveness of biochar as an additive in the anaerobic digestion process of food waste. It further examines the properties of biochar, the factors influencing these properties, and the mechanisms through which biochar enhances the AD process.