Chemical Processes:

Precipitation

This process involves adding soluble chemical reagents to water, causing them to react with dissolved pollutants to form insoluble solid precipitates. These precipitates are then separated from the liquid phase to remove pollutants. This method can effectively remove 90% to 99% of heavy metals from leachate and simultaneously reduce chemical oxygen demand (COD) by 20% to 40%.

Oxidation

The oxidation method introduces strong oxidizing agents such as chlorine, ozone, or hydrogen peroxide into leachate, breaking down organic pollutants and thus reducing the COD of the wastewater. This technology can not only effectively decompose recalcitrant organic matter in leachate but also significantly improve its biodegradability. 

Biochemical Processes:

As an environmentally friendly wastewater treatment method, biochemical treatment technology is widely researched both domestically and internationally and plays a key role in the complete leachate treatment process.

Aerobic

Under oxygen-rich conditions, aerobic microorganisms (including facultative microorganisms) can use pollutants in wastewater as metabolic substrates for degradation. This method is stable, environmentally compatible, and does not produce secondary pollution, making it an ideal treatment method. Currently, in leachate treatment, aerobic technology is mainly applied in activated sludge systems and oxidation ponds. The technology offers advantages such as fast reaction rates, minimal odor production, and small land footprint. 

Anaerobic

In the absence of free oxygen, facultative and obligate anaerobic bacteria can gradually break down complex organic matter into methane and carbon dioxide, with methane being recoverable as an energy source. This treatment method is widely used in landfill leachate treatment, commonly applied in anaerobic biofilters, anaerobic contact processes, and upflow anaerobic sludge blanket (UASB) reactors. 

Anaerobic Biofilter: This anaerobic biochemical reactor uses a filled medium, on which anaerobic biofilms grow. When wastewater passes through the filter material, pollutants are removed through the combined actions of biofilm adsorption, microbial metabolism, and material interception. This system maintains a high microbial concentration without the need for separate sludge-water separation, making it simple and easy to operate. However, its pipes can become clogged, and the mass transfer efficiency of the biofilm is limited. Recent advances in new material technologies are gradually addressing these issues. 

Anaerobic Contact: This method involves adding anaerobic active sludge to rapidly decompose high-concentration organic leachate in the reactor, significantly shortening the reaction period and reducing the residence time of the wastewater in the system. This process is especially 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 Professor Shiled in the 1970s. After continuous improvements and research by subsequent scholars, the UASB process has been successfully applied in leachate treatment and has shown significant treatment effects.

Anaerobic – Aerobic Combined

Both anaerobic and aerobic treatment technologies have certain removal capabilities for pollutants in leachate. The anaerobic process is suitable for high-concentration organic wastewater but has a longer hydraulic retention time and limited pollutant removal efficiency. The aerobic process achieves a high organic removal rate but struggles to directly address the high-concentration organic matter in leachate and comes with high investment and operational costs. Therefore, in practical leachate treatment, anaerobic and aerobic processes are often combined. These combined processes come in various forms, including A-O process, A-A-O process, and anaerobic-aerobic fluidized bed technology.