Landfill leachate is a highly concentrated wastewater formed from the moisture content in waste, rainwater, and snowmelt that enters the landfill site and other water sources. After passing through waste and cover layers, it becomes a complex mixture containing high concentrations of organic matter, heavy metal salts, suspended solids, and ammonia.
Landfill leachate not only pollutes soil and surface water but also contaminates groundwater. Although there are numerous studies on the removal of CODCT (chemical oxygen demand) from landfill leachate, the treatment methods generally involve biological processes, which have been found to be less effective and relatively expensive.
Technology Selection: Evaporation and Concentration Process
The evaporation and concentration process utilizes a steam compression system that relies on the heating principle of compressors and a specially designed heat transfer fluid. This technology generates steam from the wastewater solution within a closed container, which is then compressed by a steam compressor to produce a gas with a temperature between 85°C and 101°C. This heated gas can be reused as a regenerative heat source for continuous evaporation and heat transfer of the wastewater solution.
In this process, the gas also cools down rapidly and eventually becomes reusable condensate water (which can be purified to produce drinking water, softened water, or pure water, depending on the customer’s needs).
Based on principles of physics, an equal amount of heat energy is absorbed when a substance transitions from liquid to gas and released when it transitions from gas to liquid. This type of heat energy is known as “latent heat.” The system includes components such as a vapor-liquid separator, a liquid film latent heat main heat exchanger, a liquid film sensible heat auxiliary heat exchanger, circulation pumps, vacuum pumps, liquid transfer pumps, centrifugal (roots-type) steam compressors, water drainage devices, electrical control systems, and self-control systems.
Methods for Treating Landfill Leachate
1. Physical-Chemical Methods
This includes activated carbon adsorption, chemical precipitation, density separation, chemical oxidation, chemical reduction, ion exchange, membrane permeation, air stripping, and wet oxidation. When COD levels are between 2000 and 4000 mg/L, these methods can achieve a COD removal rate of 50% to 87%.
Compared to biological treatments, physical-chemical treatments are less affected by changes in water quality and quantity and provide more stable effluent quality. They are particularly effective for landfill leachate with a low BOD5/COD ratio (0.07 to 0.20), which is challenging to treat biologically. However, physical-chemical methods have higher treatment costs and are not suitable for large volumes of landfill leachate, so biological methods are primarily used.
2. Biological Methods
This method is divided into aerobic, anaerobic, and combined treatments.
- Aerobic treatments: include activated sludge processes, aeration oxidation ponds, aerobic stabilization ponds, rotating biological contactors, and trickling filters.
- Anaerobic treatments: include upflow sludge blanket reactors, anaerobic fixed-film reactors, hybrid reactors, and anaerobic stabilization ponds.