Beneficial role of biochar addition on the anaerobic digestion of food waste: A systematic and critical review of the operational parameters and mechanisms

The generation of huge amounts of food waste due to the increasing population is a serious global issue. The inadequate management of food waste and lack of proper handling approaches have created adverse negative impacts on the environment and the society. The use of traditional disposal (i.e. landfilling) and treatment (i.e. incineration and composting) methods are not considered to be efficient for managing food waste. Thus, anaerobic digestion (AD) has proven to be promising and cost-effective, as an alternative technology, for digesting and converting food waste into renewable energy and useful chemicals. However, mono-digestion of food waste suffers from process inhibition and instability which limit its efficiency. Adding biochar that has high buffering capacity and ensures optimum nutrient balance was shown to enhance biogas/methane production yields. This review reports on the physicochemical characteristics of food waste, the existing problems of food waste treatment in AD as well as the role of biochar amendments on the optimization of critical process parameters and its action mechanisms in AD, which could be a promising means of improving the AD performance. Also, this review provides insights regarding the selection of the desired/appropriate biochar characteristics, i.e. depending on the source of the feedstock and the pyrolysis temperature, and its role in enhancing biogas production and preventing the problem of process instability in the AD system. Finally, this review paper highlights the economic and environmental challenges as well as the future perspectives concerning the application of biochar amendments in AD.