Landfill leachate is a black or yellowish brown odorous liquid that is the product of gravity flow in a landfill, mainly from precipitation and internal water content of the waste itself. It includes various refractory organics (such as various aromatic compounds and humus), inorganic salts (such as ammonium, carbonate and sulfate) and metal ions (such as chromium, lead and copper). The composition of landfill leachate is extremely complex, with many types of pollutants, high concentration, difficult to degrade components, poor biochemical treatment, high treatment difficulty, and direct emission hazard.

Municipal landfill leachate is a high-concentration organic wastewater with complex composition. If it is discharged into the environment without treatment, it will cause serious environmental pollution. It is essential to treat leachate for the purpose of protecting the environment.