Dioxin formation during biogas utilization from anaerobic digestion of food waste: Potential role of non-methane volatile organic compounds

While chlorinated volatile organic compounds (VOCs) are often considered dioxin precursors, the formation pathways of dioxins during biogas combustion from food waste anaerobic digestion plants remain poorly understood. This study investigated the generation and emission characteristics of VOCs and dioxins in the exhaust gas from a steam generator (SG) and a combined heat and power (CHP) unit. Exhaust gas analysis revealed that total VOC concentrations were significantly higher in the SG exhaust gas (2735.10 ± 1007.82 μg/m3) than in the CHP exhaust gas (1096.88 ± 196.26 μg/m3), reflecting different combustion efficiencies. Notably, common precursors like chlorobenzenes and chlorophenols were not detected. Statistical analysis revealed a strong correlation between non-chlorinated VOCs and Cl1−8DD/Fs congeners in both systems. The only detected chlorinated VOC, dichloromethane, did not cluster with any Cl1−8DD/Fs congeners. Our findings indicate a functional separation: non-chlorinated VOCs may provide the carbon skeleton for dioxin formation, while chlorinated compounds primarily act as chlorine donors in the chlorination process. This study provides a new hypothesis on the role of VOCs in dioxin formation from biogas combustion and underscores that effective control requires optimizing combustion, pretreating biogas to remove chlorine sources, and installing advanced flue gas control devices.