A systematic review on the potential of agro-industrial waste for pyrolysis: feedstocks properties and their impact on biochar and pyrolysis gas composition
Hamad Gohar, Giovanni Beggio, Marco Schiavon, Maria Cristina Lavagnolo
Abstract
Massive agro-industrial waste is generated yearly due to tree pruning, food processing, and crop residues. Pyrolysis can convert agro-industrial waste into valuable products such as biochar, bio-oil, and pyrolysis gas. However, there is a lack of systematic reviews that comprehensively evaluate the potential of various agro-industrial wastes for pyrolysis to produce energy and biochar. In this study, the Scopus database was used to gather literature. The statistical analysis was performed on a defined set of agro-industrial wastes (tree pruning, nutshells, crop residues, and pomace waste) to identify significant differences in properties and suitability for pyrolysis. In general, the investigated feedstocks were characterised by high higher heating value (16–21 MJ/kg), which followed the trend: pomace > pruning > nutshells > crop residues. The higher heating value (HHV) of the resulting pyrolysis gas was in the range of 5–16 MJ/Nm 3 , which shows its potential for sustainable energy production. Correlation analysis revealed that elevated temperatures support pyrolysis gas production and the HHV of pyrolysis gas due to increased H 2 and C n H m concentrations. Pruning and nutshell biochar properties, such as surface area, showed their potential for pollutant adsorption. The high cation exchange capacity and nutrient contents depicted pomace and crop-residue biochar suitability for soil amendment. The preferred feedstocks for a pyrolysis plant aiming to produce good-quality biochar and pyrolysis gas are pruning > nutshells > pomace > crop residue. This literature review provides insights on a solution for agri-food sector operators and farmers to valorise agro-industrial waste locally to produce energy and biochar.