How biowaste valorization can contribute to decarbonization

Biowaste valorization is increasingly promoted as a strategy for climate-change mitigation, yet converting waste into useful products does not inherently guarantee decarbonization. This review critically examines how biowaste can function as a renewable carbon resource and identifies the conditions under which its valorization delivers genuine life-cycle greenhouse-gas benefits. Biowaste streams are first classified according to physicochemical characteristics that govern pathway selection, followed by evaluation of biological, biochemical, thermochemical, chemical, and integrated biorefinery routes. Particular attention is given to five mechanisms through which valorization can contribute to decarbonization: avoidance of conventional waste-management emissions, displacement of fossil energy, displacement of fossil-derived chemicals and materials, carbon retention and durable removal, and decarbonization of the conversion process itself. The carbon value of resulting products is further assessed according to their function and residence time, distinguishing rapidly cycled fuels from chemicals, long-lived materials, stable carbon products, and geological storage of biogenic CO2. Methodological challenges in quantifying climate benefits are critically evaluated, with emphasis on system boundaries, functional units, allocation, substitution, counterfactual waste-management scenarios, temporal carbon accounting, and geographic energy mixes. Environmental burden shifting, economic viability, technological maturity, and scale-up constraints are also considered. Based on this synthesis, harmonized metrics and a feedstock-specific decision framework are proposed for selecting valorization pathways according to carbon performance, product function, economics, technological readiness, and spatial context. The review concludes that future biorefineries should evolve from biomass-conversion facilities toward integrated carbon-management systems that optimize fossil displacement, carbon utilization and permanence, environmental performance, and economic viability simultaneously.