Chapter 1 - Leachate Generation and Characteristics

Abstract

Leachate is a by-product derived from municipal solid wastes due to their physical, chemical, and biological changes and will be formed in landfills, incineration plants, composting plants, and transfer stations, with high strength and toxicity. Leachate usually contains various toxic organic pollutants, heavy metals, ammonia nitrogen compounds, and other components, which are much more complex than domestic sewage. The composition of leachate is related to some factors, including properties of waste, location, seasons, landfill time and structures, retention time in holding cell at incineration plants, operation modes of transfer stations, etc. Among the leachate sources, landfill leachate is of the most concern. The incineration leachate will be reused for fly ash solidification and stabilization processes after treatment, using membrane bioreactors and reverse osmosis system and the concentrated liquid is injected into the furnace. The quantity and quality heavily depends on the waste components and rain for leachate in landfills, which can be predicted using several models. It may contain heavy metals, such as Cd, Cr, Cu, Pb, Ni, Zn and Hg, and toxic organic matters, which distribute among different particles with various sizes. Anionic ions, such as Cl−, Br−, F−, NO3−, HCO3−, and SO42− are also present as salts in leachate and in the concentrated liquid from reverse osmosis process. Micronuclei induced by municipal landfill leachate in mouse bone marrow cells in vivo may be used to describe the biotoxicity of leachate. The mouse may be damaged when it is fed the leachate, even at low concentration such as 5mg/L COD. Roughly, the leachate quantity should be less than 20%–30% of the wastes to be placed daily in landfill, which can be predicted using suitable models. The quantity of leachate may considerably increase when the lining system is destroyed and the underground water will enter into the waste mass. Careful management for landfill is very important for the reduction of leachate quantity. The most common treatment methods for leachate are biological and physicochemical techniques, which possess the differential removal capacities for various pollutants. The effluents must meet the discharge standards or recycle within incineration plants without any discharge into the environment.