Distribution of PCDD/Fs in a food waste anaerobic digestion process with biogas utilization

Food waste(FW)is a major component of municipal solid waste(MSW)in developing countries such as China.Anaerobic digestion(AD)is a widely-applied FW biological treatment method following MSW classification.With FW diversion from conventional incineration plants,the environmental risk caused by trace toxic pollutants,such as polychlorinated dibenzo-p-dioxins and dibenzofurans(PCDD/Fs),should be reevaluated.This study investigated a full-scale FW-AD plant in Shenzhen,China,and addressed two important underexplored issues:the distribution patterns of PCDD/Fs during the FW-AD process and PCDD/F emission characteristics of the biogas utilization exhaust gas.Mass balance demonstrated a negative balance of 2.48μg I-TEQ/t of raw FW(RFW),thus indicating that AD produced moderate PCDD/F emissions.The detailed findings were as follows:1)PCDD/F toxic equivalents(TEQs)in pure FW(RFW without impurities)were lower than in RFW,indicating that MSW source separation is crucial for decreasing the PCDD/F input into the AD system;2)PCDD/F contents(6.20–8.27 pg I-TEQ/g dry weight)in solid digestate were near the screening value of development land in China’s national standard(GB36600-2018),thus indicating that the potential environmental risk from the land application of solid digestate should be considered;and 3)PCDD/F TEQs(0.001–0.022 ng I-TEQ/Nm^(3))in biogas utilization exhaust gas were roughly equivalent to those produced by MSW incinerators in Shenzhen.This study indicated that compared with co-incineration with other waste,FW-AD will reduce PCDD/F emissions(air)from MSW incineration plants by 12.5%–21.3%at the national level under an FW separation scenario.