Leachate treatment is very necessary to reduce environmental effects. When choosing the type of treatment process, various aspects should be considered. Various factors such as rainfall, weather and seasonal changes, type, composition and density of disposed waste affect the quality and concentration of waste leachate. Considering the complexity and variety of leachate, biological or physico-chemical processes alone do not have a significant effect in order to achieve standard values for its discharge. Membrane bioreactors process followed by membrane separation process (nanofiltration and reverse osmosis) can be a complete process in leachate treatment. This technology is widely used in China, European countries and tropical countries such as Brazil, where the cost of its treatment is generally lower than the costs of its disposal in domestic sewage collection systems.
Various technologies are available for leachate treatment, the following methods can be mentioned:
· Biological processes (activated sludge, aerobic and anaerobic stabilization ponds and biological filters)
Physical-chemical processes (coagulation/flocculation, adsorption, chemical precipitation, separation, chemical oxidation, ion exchange and electrochemical)
Membrane filtration (microfiltration/ultrafiltration, nanofiltration and reverse osmosis)
Advanced oxidation processes (Fenton and ozonation)
· Natural systems (wetlands)
Considering the characteristics of waste leachate, it should be considered that the best treatment process cannot be selected only based on the content of BOD, COD and nitrogen compounds. It is very important that in addition to removing the mentioned parameters and complying with the discharge rules, the treatment process can remove other compounds such as chlorides, rare metals and toxic compounds. Leachate treatment should not only focus on compliance and water reuse, but also on resource recovery. Leachate treatment by anaerobic biological methods allows the conversion of organic matter into biogas. This source can be used to supply the energy needed for the wastewater treatment plant. In addition, the use of mineral salts in leachate to produce biofuels (biolipids and carbohydrates) by microalgae is also promising due to concerns related to global warming.