Linking the characteristics of leachate resulting from the transition to circular MSW management with strategies for biological leachate treatment

Growing environmental awareness has driven significant changes in municipal solid waste (MSW) management, with a strong emphasis on increasing recycling rates and minimizing biodegradable waste landfilling, particularly in developed countries. Methods such as aerobic stabilization of the organic fraction of MSW (OFMSW) and diversion of organics via composting of selectively collected biowaste are being prioritized over landfilling. These shifts in waste management practices have altered the physico-chemical characteristics of leachate generated from different masses of MSW, for example, leachate from landfilled untreated MSW, aerobically stabilized OFMSW, or composted biowaste. Consequently, managing the resulting leachate has become an increasingly important issue. Limited information is available on the composition and treatment of leachate produced via processes like aerobic OFMSW stabilization, often inconsistently referred to as composting and composting of biowaste, which is expected to dominate future waste management. To address these issues, the present review provides consistent terminology, describes currently available information, and proposes a new leachate classification system based on its physico-chemical properties, categorizing it as low-, moderate-, and high-strength leachate, rather than on landfill age, as was previously used. It also emphasizes the need to tailor treatment strategies according to the leachate's specific characteristics and biodegradability. This review synthesizes findings from current studies on biological leachate treatment, evaluating various technologies' effectiveness and factors influencing the removal of organics, nutrients, and other contaminants. The insights offered in this article will support future research and technological development of leachate management in alignment with circular economy principles.