From waste to wealth: Production, properties, and emerging applications of agro-industrial biochar through the lens of TRL and trends

Agro-industrial waste represents one of the largest biomass waste streams worldwide. Its conventional management through open burning or landfill disposal causes environmental problems, including greenhouse gas (GHG) emissions, soil degradation, and odor pollution. Sustainable valorization of these residues into value-added resources is therefore essential within a circular-economy framework. Among the available options, biochar production has gained significant attention because of its versatility, environmental potential, and compatibility with diverse residual feedstocks . This review examines the main thermochemical routes for carbon-material production, including slow, fast, and flash pyrolysis, hydrothermal carbonization, microwave-assisted pyrolysis, and torrefaction, and evaluates how feedstock composition and operating conditions determine product properties, process performance, and industrial feasibility. Biochar applications are critically evaluated using an evidence-based technological maturity framework, with TRL 7–8 assigned to soil amendment, TRL 5–6 to wastewater treatment, TRL 4–5 to biochar-assisted composting, TRL 3–4 to CO 2 adsorption, and TRL 2–3 to biochar-assisted anaerobic digestion, where current evidence supports improved process stability and methane production but direct odor characterization remains limited . Overall, the review identifies biochar as a versatile platform for waste valorization, pollution control, soil improvement, and resource recovery. Its practical deployment depends on matching feedstock characteristics, production route, and material properties to the intended application, while also accounting for process economics and technological maturity. The analysis therefore highlights the main technical, economic, standardization, safety, regulatory, and validation barriers that must be addressed to translate laboratory and pilot-scale evidence into reliable industrial implementation.