New role of radical-induced polymerization: Base/self-heating synergistically activate persulfate to boost food waste humification

Abstract

Radical-induced polymerization in persulfate (PS)-based advanced oxidation process (AOP) is attracting attention in water decontamination. Herein, we revealed its new role in rapid recycling of perishable food wastes using KOH activated PS. A glucose (Glu) solution of 250 g C/L was applied to mimic the carbohydrate-rich raw material with 50–60% moisture in conventional composting, wherein boosted humification occurred after addition of solid KOH/PS. Intense heat release (from 25 to 79.4 °C), mainly generated from KOH dissolving and exothermic radical chain polymerization, was observed within 2 min. Solid KOH addition contributed to synergistic PS activation by base and self-heating, realizing complete PS decomposition and fulvic like acid (FLA, 210.8 g C/L) formation within 10 min. Extracted FLA promoted cucumber seed germination and fresh weight of chickweeds by 40.0% and 128.3%, respectively. Identified •OH and SO4•- played primary roles in FLA formation through aromatization, carboxylation, and polymerization, wherein several key reactive intermediates such as 5-hydroxymethylfurfural and aromatic radicals (i.e. 1,2,4-benzenetriol radical) were formed. Moreover, the humification process simultaneously produced K2SO4 (i.e. the end product of PS decomposition) which could be used as a typical K/S fertilizer. Scaling-up humification of waste cooked rice and fertilization results further supported the potential of solid KOH/PS in efficiently converting food wastes into FLA and K+-rich compound fertilizer.