Journal of Environmental Management 290 (2021) 112537 0301-4797/© 2021 Elsevier Ltd. All rights reserved. Research article Benefcial role of biochar addition on the anaerobic digestion of food waste: A systematic and critical review of the operational parameters and mechanisms Teklit Gebregiorgis Ambaye a, b, c, ** , Eldon R. Rene b, * , Abdul-Sattar Nizami d , Capucine Dupont b , Mentore Vaccari a , Eric D. van Hullebusch e a Department of Civil, Environmental, Architectural Engineering and Mathematics, University of Brescia, Via Branze 43, 25123, Brescia, Italy b Department of Water Supply, Sanitation and Environmental Engineering, IHE Delft Institute for Water Education, Westvest 7, P.O. Box 3015, 2601 DA, Delft, the Netherlands c College of Natural and Computational Sciences, Department of Chemistry, Mekelle University, P.O. Box 231, Mekelle, Ethiopia d Sustainable Development Study Centre, Government College University, Lahore, 54000, Pakistan e Universit´ e de Paris, Institut de Physique Du Globe de Paris, CNRS, UMR 7154, F-75238, Paris, France A R T I C L E INFO Keywords: Biochar Food waste Anaerobic digestion Biogas yield Process parameters ABSTRACT 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. landflling) and treatment (i.e. incineration and composting) methods are not considered to be effcient 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 effciency. 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 pa- rameters 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 pro- duction 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. 1. Introduction Worldwide, the generation of a huge volume of food waste due to the increasing population and economic growth is adding pressure on the existing waste treatment facilities and waste management system (collection, pre-treatment, and landfll). Besides this, inadequate man- agement and lack of proper handling of especially food waste create serious adverse impacts that may be detrimental to the environment and human health due to toxic liquid leachate pollution and greenhouse gas emissions (Ariunbaatar et al., 2018; Stenmarck et al., 2016). The global food waste (FW) volume is estimated to be equivalents to 1.6 Gigatons of the primary product, while the total wastage for the edible part of the food is equivalent to 1.3 Gigatons. This amount can be weighed against the total agricultural production (for food and non-food uses), which is about 6 Gigatons (food wastage footprint impacts on natural resources reports. This is a great challenge to the government’s goal of reducing FW by 20% and the UN’s goal to cut global FW generation to ~50% by the year 2030 (Ariunbaatar et al., 2018; Stenmarck et al., 2016; * Corresponding author. ** Corresponding author. Department of Water Supply, Sanitation and Environmental Engineering, IHE Delft Institute for Water Education, Westvest 7, P.O. Box 3015, 2601 DA, Delft, the Netherlands. E-mail addresses: t.ambaye@unibs.it (T.G. Ambaye), e.raj@un-ihe.org (E.R. Rene). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: http://www.elsevier.com/locate/jenvman https://doi.org/10.1016/j.jenvman.2021.112537 Received 24 December 2020; Received in revised form 14 March 2021; Accepted 31 March 2021