Fate of Post-Harvest Fungicides and Microbial Dynamics in a Household Bokashi-Based Fermentation System: Implications for Urban Organic Waste Management

Urban household biowaste is shaped by recurring food categories, among which citrus peels represent a structured and seasonally patterned input. As these peels may carry postharvest fungicide residues, their movement through decentralized waste-treatment pathways represents a chemically meaningful component of the urban metabolism. This study examined how three widely used citrus fungicides—imazalil, pyrimethanil, and thiabendazole—behave within a household-scale sealed microaerobic fermentation system typical of common urban practices. The system displayed clear composition-driven concentration patterns: imazalil and pyrimethanil concentrations increased or remained elevated, whereas thiabendazole remained relatively stable in the solid phase while decreasing in the liquid phase. Physicochemical conditions (pH value, dry matter content) followed typical microaerobic fermentation behaviour, and microbial communities reflected acidity-driven and substrate-driven development rather than fungicide-driven suppression. Fungal colonies remained detectable despite the presence of residues, indicating that substrate composition and fermentation conditions played a more prominent role in shaping microbial responses than fungicide-associated effects. These findings position postharvest fungicides not as active inhibitors in household fermentation, but as citrus-associated residues moving through decentralized waste-to-soil pathways. The results provide new insights into how citrus-associated fungicide residues move through decentralized urban waste-treatment pathways and shape chemical and microbial flows relevant to urban soil systems and the safe use of Bokashi-based fermentation residues.