A review of the biological treatment of leachate: Available technologies and future requirements for the circular economy implementation

Leachate, which refers to dark-colored toxic wastewater generated from landfills, has become an issue of envi-ronmental concern, posing a threat to soil, surface water, and groundwater quality, thereby negatively affecting humans' health. Therefore, it is necessary to select the most appropriate leachate treatment methods considering its complex properties. Among several treatment processes available for this purpose, the biological treatment process is notably effective at removing pollutants and also relatively affordable to operate. Its application to leachate treatment has received much attention in recent years. This study summarizes the leachate character-istics and the methods of leachate treatment with a focus on biological approaches, either aerobic or anaerobic. In addition, this paper concisely discusses the effectiveness and the factors influencing the performance of each treatment technology in case of organics, nutrients, and other pollutants removal. The findings of this paper are expected to provide a deeper insight into the future research and development of leachate treatment, especially the biological treatments concerning the circular economy.