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.