Leachate is the liquid that is produced when water percolates through any permeable material. Silage leachate is a form of leachate that is a serious environmental problem, however, when people refer to leachate, they are usually referring to contaminated water that is produced by seeping water through waste.
Leachate occurs when water seeps down through a landfill and in doing so picks up dissolved materials from decomposing waste. Depending on the characteristics of the landfill and the waste it contains, the leachate can range from being relatively innocuous to extremely toxic.
Landfills with low-permeability daily coverage, in high-rainfall, humid climates with steep slopes (less than 20 to 1) are particularly susceptible. Leachate seepage is also possible if operators use recirculation to return concentrates from, for example, RO systems, and we know that seepage is particularly persistent when systems are inadvertently placed on well-compacted old haul roads.
Landfill leachate can also be defined as liquids that seep out of a landfill and enter the environment. This liquid can exist in the landfill as it is deposited or it can be created after rainwater mixes with chemical waste in a landfill.
The quality of landfill leachate varies based on many factors, including the type of waste, depth of waste, time, climate, and landfill operations.
Designed to contain our trash and prevent it from contaminating our soil and drinking water, the modern landfill has become a highly technical and complex structure. Contrary to what many may think, a landfill is not just a pile of rubbish. Because these landfills are designed not to allow leachate to escape and contaminate the surrounding soil, landfills hold leachate for a long time before it can flow down through the waste and be removed from the bottom. This means that the modern landfill produces some of the strongest and most polluted leachate ever produced anywhere.
The treatment of these polluted waters is a complex task due to its nature. A typical leachate is highly contaminated with ammonia, organic contaminants, halogenated hydrocarbons, and some heavy metals (although this can be exaggerated in well-controlled modern landfill leachate). Additionally, leachate commonly contains high concentrations of inorganic salts.
Treatment ponds and leachate ponds are one method of managing leachate, but they are generally ineffective for all but the freshest, weakest landfill leachate.
In dry climates and arid areas, removing the organic content of highly contaminated drainage (such as landfill leachate) is not enough. This is because the introduction of salts and other inorganic contaminants from leachate into the natural water cycle, even at minute concentrations, can lead to bioaccumulation (an increased potential for environmental contamination) in the resulting ecosystems that receive the discharge. of the treated leachate. .
Furthermore, although the biodegradability of organic compounds in leachate decreases over time, complex organic compounds, such as humic substances and manufactured chemicals, remain in solution.
Biological treatment is the most favorable procedure to use for leachate treatment, and biological treatment should also be used in those cases where chemical/physical treatment is also required. Biological treatment of leachate is a relatively low cost process in which organic compounds are degraded mainly to carbon dioxide, water and biomass.
All those substances that are removed by biological degradation pretreatment no longer have to be treated by the much more expensive chemical/physical procedures available.
As landfills age, treatment of the leachate they produce will focus primarily on ammonia nitrification. Biological denitrification can be achieved later when an external organic substrate is added to the leachate.
It is important to emphasize that wastewater treatment plant design criteria cannot be used for these polluted waters. For the design and operation of biological leachate treatment plants, specific points must be respected and it is essential to have an expert in the leachate treatment process. For many, adopting the advice of wastewater treatment experts for leachate treatment has resulted in inadequate process designs and a waste of money, time and effort.