Since the 21st century, with increasing urbanization and improvements in residents' living standards, people have become more concerned about environmental quality. At the same time, however, the amount of waste generated by residents is increasing. In 2014, the total municipal solid waste (MSW) collected and transported in Chinese cities reached 179 million tons, growing at an annual rate of 8-10%. The phenomenon of "cities besieged by waste" has sounded an alarm bell for Chinese cities.

Approximately 80% of municipal waste in China is treated by sanitary landfilling. In landfills, waste, under the influence of its own moisture, incoming precipitation (rain, snow), and other water sources, percolates through the waste layer and soil cover, forming a highly concentrated wastewater known as landfill leachate. Furthermore, with the rising popularity of waste incineration technology in recent years, waste requires temporary storage before incineration. During this period, a significant amount of leachate is also generated. However, as this period is short-lived, the leachate produced has good biodegradability.

Main Sources of Landfill Leachate:

1.Atmospheric Precipitation: During rainy or snowy weather, a large amount of rainwater infiltrates the leachate, increasing its volume.

2.Inflow of External Surface Water.

3.Groundwater Infiltration: Especially in landfills that lack impermeable lining systems. If the water level within the landfill is low, groundwater can easily seep in.

4.Moisture Inherent in the Waste Itself: Primarily moisture originally present in the waste when it is generated, plus rainwater incorporated during transportation due to weather conditions, and wastewater produced during the natural fermentation of the waste.

5.Water Produced by Anaerobic Microbial Decomposition of Waste after Sanitary Landfilling: Under anaerobic conditions, numerous microorganisms decompose the organic components of the complex waste mixture, generating wastewater.