Moderate separation of household kitchen waste towards global optimization of municipal solid waste management

The sorting treatment of food waste is gradually considered as an available strategy to improve the sustainability of municipal solid waste (MSW) management, but the separation of household kitchen waste (HKW), the main component of food waste, is controversial because of its disperse sources and possible social cost. Social life cycle assessment is applied in this study to integrate environmental, economic, and social analyses, including the time investment of households, aiming to assess the influence of HKW separation comprehensively. The results show HKW separation at different separation rates improve the environmental performance of MSW treatment. When HKW separation rate increases by every 20 percentages, the net carbon emission reduces 5–7%, the acidic gas emission reduces by 3.1–3.5%, and the cumulative energy demand decreases by approximately 2.1–2.2%, owing to the higher heat value of incineration feedstock and more yield of energy products. HKW separation increases the energy consumption of waste collection and transportation system, but its contribution to the overall energy consumption is very limited. The whole MSW management system also has better economic performance along with more HKW separation and more energy output. In contrary, a huge amount of time cost of households increases the total social cost of MSW management, making HWK separation not an attractive option. From the point of view of residents, the external cost, including environmental cost and household time cost, should not exceed zero to ensure residents obtain some benefits from HKW separation, implying that HKW separation rate of 20% is acceptable. HKW water content and proportion in MSW are the two sensitive factors influencing the comprehensive performance of MSW management. Source HKW draining to water content 60% and source reduction by 30% can decrease the total social cost by 124–215% and 66–73%, respectively. The two effective measures are easy and convenient for residents to carry out with significant improvement of social sustainability of MSW management. Based on the effects on social cost, the priority of HKW management strategies should be given to source draining and then source reduction, followed by source separation from MSW at 20%.