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 2.48 µg 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/Nm3) 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. [graphic not available: see fulltext]