Comprehensive valorization of oil-rich food waste through coupling transesterification with pyrolysis

Abstract

Recent shifts in food consumption trends toward fried foods have increased the generation of oil-rich food waste. Although biological processes show promise for the food waste valorization, the presence of oil components limits microbial activity. This study proposes a thermochemical approach for valorizing oil-rich fried debris, a by-product of deep-frying, by coupling transesterification with pyrolysis. Characterization of fried-debris-extracted oil (FDO) revealed high impurity levels, free fatty acids and aldehydes. This necessitates transesterification method with more tolerance to these impurities than the conventional acid-treated process. A thermally-induced transesterification demonstrated the impurity tolerance, representing biodiesel yield exceeding 95 wt% regardless of the mixing ratio of aldehyde-to-refined olive oil. When applying to FDO, this process yielded a consistent biodiesel output (41.1 wt%), representing a 1.43-fold increase compared with the conventional transesterification. As a strategy for the comprehensive valorization of fried debris, de-fatted fried debris (DFD) remaining after oil extraction was further pyrolyzed. To impart a sustainability to the pyrolysis system, CO₂ was employed as a reactive agent. CO₂ showed a reactivity of converting DFD-derived volatiles into syngas, particularly CO, while producing biochar. The CO₂ reactivity was accelerated when conducting catalytic pyrolysis over Ni catalyst, resulting in 71.43 wt% syngas and 18.47 wt% biochar. To evaluate the environmental benefits of this process, the CO₂ mitigation potential of biodiesel, syngas, and biochar was estimated, representing an annual reduction of 14.24 × 10⁸ kg CO₂ in South Korea.