Circular economy approach to valorizing horticultural waste via thermochemical process

Abstract

Horticultural waste (HORW), a representative form of agricultural biomass, holds promise as a carbon-rich feedstock for the production of value-added materials. This study aimed to maximize carbon utilization from HORW into syngas and carbon-based biosolid through thermochemical conversion, contributing to a circular economy. To improve syngas production, CO₂ was introduced during the pyrolysis. In conventional pyrolysis, additional CO production was observed, attributed to a homogenous reaction between CO₂ and VOCs derived from HORW. To further promote this reaction, an in-line pyrolysis setup was applied, which facilitated thermal cracking of VOCs and led to a 1.7-fold increase in syngas yield compared to the conventional pyrolysis, but did not significantly enhance CO₂ reactivity. In contrast, the presence of Ni-based catalyst effectively activated the CO₂-induced homogenous reaction, resulting in a 3.4-fold higher syngas yield than conventional pyrolysis. Moreover, CO₂-assisted pyrolysis modified the physicochemical properties of the biosolid, yielded a biosolid with enhanced specific surface area and cation exchange capacity compared to the inert condition. These enhancements contributed to superior soil amendment potential. Overall, the use of CO₂ in the thermochemical conversion of HORW could be a promising pathway for valorizing waste, aligned with circular economic principles.