Industrial Applications of Hydrothermal Carbonization Products from Olive Residues: Progress and Perspectives (Post-2018 Evidence)

Abstract

Hydrothermal carbonization (HTC) of olive mill residues and pruning wastes has gained momentum as a sustainable conversion route for biomass. Recent studies highlight application-ready advances in energy products, particularly hydrochars that meet industrial fuel standards, alongside emerging catalytic uses. This review synthesizes post-2018 evidence, focusing on industrial applications of hydrochars, process water, and co-products. Combustion/co firing and pelletization of olive pomace hydrochars are most industrially ready. Presence of continuous flow pilot processing with weeks long stability and downstream pellet conformance, coupled with ash chemistry benefits and combustion relevant metrics at lab scale, collectively indicate the closest pathway to industrial uptake. More precisely, hydrochars from pruning/trimmings are pre commercial, technically mature at lab scale with with HHV up to 29.6 MJ/kg at higher severities (220-280° C; 3-9 h). O/C-H/C ratios approach lignite, with increased ignition temperature and activation energy, indicating more stable, coal like fuels. Catalytic remediation with Fe-loaded hydrochars shows also promising environmental applications. However, process water and gas valorization, as well as agricultural uses, remain underexplored. This article discusses the application landscape, operating conditions, and industrial implications of olive-derived HTC products.