The physical treatment method is the most direct and effective approach for dealing with leachate. Through methods such as physical adsorption, stripping, and membrane separation, harmful substances in the leachate can be removed.

Air Stripping Method: The air stripping method involves introducing a gas into the wastewater, allowing it to fully contact the liquid. This allows soluble ammonia nitrogen in the wastewater to transfer through the gas-liquid interface into the gas phase, thereby removing ammonia nitrogen. Air is commonly used as the carrier gas in this method. It has been applied in most municipal landfill sites, with an ammonia nitrogen removal efficiency of approximately 60%-80%, showing significant results.

Adsorption Method: The adsorption method primarily uses activated carbon as the adsorbent. Activated carbon has a large specific surface area and a porous structure. When leachate passes through it, organic compounds and heavy metals are adsorbed onto the internal surface of the activated carbon, thus achieving removal. Currently, activated carbon adsorption technology has been widely used in wastewater treatment. Research has shown that activated carbon can remove 75% of the total organic carbon (TOC), 85% of chemical oxygen demand (COD), and 95% of ammonia nitrogen (NH₃-N) in leachate.

Membrane Separation Method: The membrane separation method is a general term for the technique that uses special membranes to selectively allow certain components in a liquid to pass through. Polymer membranes can separate and concentrate specific substances in a solution. Membrane separation includes microfiltration, ultrafiltration, nanofiltration, and reverse osmosis. Currently, in leachate treatment, the more commonly used membrane separation methods are nanofiltration and reverse osmosis.

(1) Nanofiltration: Nanofiltration membranes are between ultrafiltration membranes and reverse osmosis membranes. The molecular weight cut-off (MWCO) of nanofiltration membranes ranges from 200 to 1000, and their pore size is about 1 nm. Nanofiltration is suitable for separating dissolved components of approximately 1 nm in size. In leachate treatment, nanofiltration is usually used as a pretreatment process, with the treated water meeting discharge standards. If there are specific requirements for the water quality, a reverse osmosis system is typically added afterward.

(2) Reverse Osmosis: Reverse osmosis was initially applied in seawater desalination projects and is now being used for the concentration of leachate in municipal landfills. This technology is highly effective in reducing COD, ammonia nitrogen (NH₃-N), and salinity in leachate.