Comprehensive assessment of biochar derived from thermochemical processing of food waste digestate: Properties, preparation factors, and applications

Abstract

Food waste digestate (FWD), a by-product of anaerobic digestion (AD), urgently needs to be properly and effectively disposed of. As a viable solution for FWD disposal and utilization, the preparation, formation mechanisms, influencing factors, and diverse applications of biochar (pyrochar and hydrochar) were reviewed. Specifically, the formation of pyrochar relies on precise control of surface area, porosity, and morphology, with optimal preparation conditions including a temperature range of 500–600 ℃, a low heating rate, and a water content below 30 %. In contrast, the properties of hydrochar are primarily influenced by temperature, residence time, and S/L, with ideal conditions being 150–250 ℃, a residence time of approximately 30 minutes, and an S/L between 1:5 and 1:10. For the applications, pyrochar is mainly used as an adsorbent, catalyst, soil amendment, additive in AD, compost and electrode materials due to its exceptional specific surface (SSA) area and porosity, and remarkable water retention capacity. Conversely, hydrochar, characterized by its high HHV and low ash content, finds use as a solid fuel. This study offers valuable insights and strategic guidance for the sustainable management of FWD.