Common Chemical and Biological Treatment Processes for Landfill Leachate

Chemical precipitation process

This process adds soluble chemical reagents to the water, which react directly with dissolved pollutants to form insoluble solid precipitates; separating the solid and liquid phases then removes the pollutants. This method effectively removes 90% to 99% of heavy metals in the leachate while simultaneously reducing chemical oxygen demand (COD) by 20% to 40%.

Chemical oxidation process  

Chemical oxidation introduces strong oxidants such as chlorine gas, ozone, or hydrogen peroxide into the leachate to decompose and transform organic pollutants, thereby lowering the COD of the wastewater. The technology not only effectively decomposes refractory organics in the leachate but also significantly improves its biodegradability.

Biological treatment technology

As an environmentally friendly wastewater treatment approach, biological treatment technology has been widely studied at home and abroad and plays a key role in the complete leachate treatment train.

Aerobic biological technology

Under oxygen-rich conditions, aerobic microorganisms (including facultative ones) use pollutants in the wastewater as metabolic substrates and degrade them. The method runs stably, has high environmental compatibility, and produces no secondary pollution, making it a fairly ideal treatment approach. In leachate treatment, aerobic biological technology is currently applied mainly in the form of activated sludge processes and oxidation ponds. It offers fast reaction rates, low odor generation, and a small footprint.

Anaerobic biological technology

In environments without free oxygen, facultative and obligate anaerobic bacteria gradually decompose complex organics into methane and carbon dioxide, with the methane recoverable as an energy source. This method is widely used in landfill leachate treatment, commonly in the form of anaerobic biological filters, anaerobic contact processes, and upflow anaerobic sludge blanket (UASB) reactors.

• Anaerobic biological filter: This is a packed-media anaerobic biological reactor in which anaerobic biofilm grows attached to the surface of the internal packing. As wastewater passes submerged through the media, pollutants are removed through the combined action of biofilm adsorption, microbial metabolism, and media retention. The unit maintains a high microbial concentration, requires no separate sludge-water separation, and is simple in construction and easy to operate and manage. However, its piping is prone to clogging and biofilm mass-transfer efficiency is limited. In recent years, with the development of new materials technology, these problems are gradually being alleviated.

• Anaerobic contact process: This method adds anaerobic activated sludge to rapidly decompose the high-concentration organic leachate in the reactor, significantly shortening the reaction cycle and the residence time of the wastewater in the system. It is particularly suitable for organic leachate with high suspended solids content and shows good treatment performance.

• Upflow anaerobic sludge blanket (UASB): This anaerobic reaction technology was developed by the British scholar Professor Shiled in the 1970s. Through continuous improvement and research by later scholars, the UASB process has been successfully applied to landfill leachate treatment, showing significant treatment performance.

Anaerobic/anoxic-aerobic combined process

Anaerobic and aerobic treatment technologies each have a certain capacity to remove pollutants from leachate. The anaerobic process suits high-concentration organic wastewater but has a long hydraulic retention time and limited pollutant removal efficiency; the aerobic process achieves high organic removal but struggles to directly handle the high organic concentration of leachate, and involves high investment and operating costs. Therefore, in actual leachate treatment, anaerobic/anoxic and aerobic processes are often used in combination. Such combined processes take many forms, mainly including the A-O process, the A-A-O process, and anaerobic-aerobic fluidized bed technology.