Comparison and selection of leachate treatment processes
The treatment of leachate from urban landfills has always been a very difficult problem in landfill design, operation and management. Leachate is produced by the flow of liquid in the landfill under the action of gravity, and is mainly composed of precipitation and the internal moisture of the garbage itself. Since there are many factors that may affect the properties of the leachate during the flow of the liquid, including physical factors, chemical factors and biological factors, the properties of the leachate vary within a fairly large range. Generally speaking, its pH value is between 4 and 9, COD is in the range of 2000 to 62000 mg/L, BOD5 is from 60 to 45000 mg/L, and the concentration of heavy metals is basically the same as that of heavy metals in municipal sewage. If the leachate from the urban landfill is discharged directly into the environment without treatment, it will cause serious pollution to the environment. The composition of this leachate is complex and contains high concentrations of organic wastewater. For the purpose of protecting the environment, it is essential to treat the leachate.
The current status of leachate treatment technology
The main methods for treating landfill leachate are physical and chemical methods and biological methods. The physical and chemical methods mainly include activated carbon adsorption, chemical precipitation, density separation, chemical oxidation, chemical reduction, ion exchange, membrane dialysis, gas stripping and wet oxidation. When the COD is 2000-4000 mg/L, the COD removal rate of the physical and chemical method can reach 50%-87%. Compared with biological treatment, physical and chemical treatment is not affected by changes in water quality and water volume, and can obtain more stable effluent water quality. Especially for landfill leachate with a low BOD5/COD ratio (0.07-0.20) and difficult to treat by biological treatment, physical and chemical treatment can achieve good results. However, for the treatment of large amounts of landfill leachate, the cost of physical and chemical treatment methods is high and not very applicable. Therefore, we mainly use biological methods to treat landfill leachate.
The biological method is divided into aerobic biological treatment, anaerobic biological treatment and a combination of the two. Aerobic treatment includes activated sludge process, aerated oxidation pond, aerobic stabilization pond, biological rotating disk and trickling filter, etc. Anaerobic treatment can be carried out by various methods, including upflow sludge blanket, anaerobic immobilized bioreactor, hybrid reactor and anaerobic stabilization pond, etc.