Urban garbage is a major problem in urban environmental management. Landfill leachate from refuse transfer stations, incinerators, or landfills is produced by a variety of compounds, as well as contaminated and decaying materials. It contains extremely high concentrations of biochemical oxygen demand, chemical oxygen demand, nitrogen-containing compounds, phosphorus-containing compounds, organic halides, sulfides, and inorganic salts. Not only does it smell bad, but many of them are carcinogens. If it is discharged to the surface, it will pollute the environment, dissolve into the ground, and pollute water sources, which will be extremely harmful to the urban environment and human health. In addition, the longer the landfill time, the higher the leachate concentration and the greater the harm. In recent years, people have paid more and more attention to the disposal of domestic garbage.
Landfill leachate is a kind of high-concentration organic wastewater, its composition is complex, and water quality and quantity vary greatly. The sources of landfill leachate mainly include direct precipitation, surface runoff, surface irrigation, groundwater, water from the garbage itself, water in the covering material, and water produced by the biochemical reaction of the garbage. The main factors affecting the composition of landfill leachate are: garbage composition, site climatic conditions, site hydrogeological rainfall conditions, landfill conditions, and landfill time. This determines that the quality and quantity of landfill leachate vary widely and the change law is complex. The content of CODcr, BOD5 and ammonia nitrogen is high. With the extension of landfill time, the organic nitrogen in the refuse is converted to inorganic nitrogen, and the ammonia nitrogen concentration increases. Due to the dissolution of CO2 produced by the waste degradation, the landfill leachate is slightly acidic. This acidic environment exacerbates the dissolution of water-insoluble carbonates, metals and metal oxides in garbage. Therefore, the leachate contains a relatively high concentration of metal ions.
Refractory landfill leachate also shows its variability. First of all, production varies with the season, and the rainy season is significantly larger than the dry season. The second is the seasonal change in the composition and concentration of pollutants. In dry and cold seasons, the composition and concentration of pollutants in landfill leachate in the plains are relatively low. Third, the composition and concentration of pollutants change with the life of the landfill. The physical, chemical, and biological characteristics of each part of the landfill layer and their activities are different. The “young” landfill leachate (used for less than 5 years) has a lower pH, higher biochemical oxygen demand, chemical oxygen demand, VFA, metal ion concentration, and higher biochemical oxygen demand / chemical oxygen demand. The “lean” landfill (used for more than 10 years) has a near-neutral pH, with low biochemical oxygen demand, chemical oxygen demand, VFA concentration, and low biochemical oxygen demand / chemical oxygen demand concentration. Low, but higher ammonia nitrogen concentration. Therefore, when selecting a landfill leachate treatment process, it must adapt to the changing characteristics of landfill leachate. Because the landfill leachate has complex changes, only stable operation can be better treated.
Due to the high concentration of organic pollutants in the landfill leachate, the toxic and harmful heavy metals have the characteristics of biological inhibition, large load changes, and complex pollutant components, the biodegradability of the waste liquid is poor. If the traditional wastewater treatment technology is adopted, the new discharge requirements cannot be met. However, some of the latest technologies in the world have met the emission requirements, but the investment is huge and the operating costs are high. Some treatment technologies can meet emission requirements in theory, but have not been verified by actual engineering, and the risks are high.