Optimizing waste leachate treatment for environmental and economic sustainability: Insights from a bottom-up study of over 300 cities

Municipal waste incineration in China reached 232 million tonnes in 2022, with increasing problems in treating waste leachate (WL). However, significant uncertainty exists in the emission performances, cost, and optimization strategies of city-level WL treatment. Herein, a bottom-up approach is utilized to investigate the WL status across over 300 cities and a life cycle thinking is employed to compare the environmental and economic effects of various WL and waste leachate concentrate (WLC) management options. Analysis reveals national production of WL has reached 57 million tonnes, with the top ten cities, including Guangzhou, Shanghai, and Chongqing, contributing 20.6 %. Biological coupled chemical treatment (BCT) demonstrates the best environmental performances in WL treatment technologies, while biologically coupled membrane treatment (BMT) offers the lowest economic expenses, and Mechanical Vapor Recompression (MVR) evaporation excels in treating WLC. In a business-as-usual scenario, the national carbon emissions, energy consumption, and economic costs of WL treatment are 24 million tonnes CO₂ eq, 264 million GJ, and RMB 19 billion, respectively. Under the WL and WLC technology optimization scenarios, estimations indicate a reduction in carbon emissions by 80.7 % (equivalent to 55.1 million trees) and 19.7 % (equivalent to 13.5 million trees), respectively. Viewed holistically, replacing BMT with BCT emerges as the optimal mitigation strategy, with the synergistic optimization of BMT and MVR evaporation systems following closely. In the formulation of the technology transition strategies, the urban economy, strategic positioning, and geographic location also should be considered apart from the technological aspects, to steadily achieve sustainable co-benefits across environmental and economic dimensions.