Carbon footprints of centralized and decentralized food waste utilization pathways

Food waste is usually utilized in centralized treatment facilities and is sometimes treated in decentralized facilities; however, the latter has not been evaluated systematically regarding carbon emissions. This study surveyed fifty-nine centralized and decentralized food waste treatment projects in Shenzhen, and incineration, anaerobic digestion, composting, and emerging technologies such as insect bioconversion and organic acid production were applied. Their carbon footprints were analyzed based on real data covering collection and transport, energy and material consumption, secondary pollutant control, and impurity disposal. The results showed that centralized facilities had a lower overall carbon footprint, although carbon emissions from their collection and transportation were higher. Anaerobic digestion performed best with an average carbon emission of −136.63 kg CO2-eq/t, followed by black soldier fly larvae cultivation (−12.86 kg CO2-eq/t), incineration (−11.02 kg CO2-eq/t), and organic acid production (−6.86 kg CO2-eq/t). All decentralized facilities were operated with net carbon emissions because they consumed a large amount of electricity or thermal heat without the full use of organic matter in the food waste. An optimal route was recommended by combining centralized anaerobic digestion and decentralized squeezing dewatering with adequate oil recovery, and this can make the overall carbon emission decrease from −6.72 kg CO2-eq/t to −17.75 kg CO2-eq/t. These results can provide decision-makers with guidance on food waste management to support net zero and sustainable development goal 12 and 13.