Leachate Treatment for Landfills
Rain falling on the top of the landfill is the main contributor to the generation of leachate, and is by far the largest contributor for modern sanitary landfills which do not accept liquid waste. In old unlined and un-engineered landfills, some leachate is produced from groundwater entering the waste. Some, additional leachate volume is produced during waste decomposition, and some additional surface water will sometimes run onto waste from its surroundings.
Most landfills are designed to minimize the amount of leachate they create during their lifetimes. However, there are good scientific reasons to suggest that it would be better to flush all landfills out and to do this, would produce more leachate, faster. Landfills where the latter philosophy is adopted, are called, “bio-reactor” landfills. In Europe, bio-reactor landfills are effectively prohibited by EU directives, leading them to be called “dry tombs” by some, due to their rapid capping, and minimized leachate production.
Leachate is formed when water passes through the waste in the landfill cell. The precipitation can be from rain, melted snow or the waste itself. As the liquid moves through the landfill many organic and inorganic compounds, like heavy metals, are transported in the leachate. This moves to the base of the landfill cell and collects.
The amount of leachate produced is directly linked to the amount of precipitation around the landfill. The amount of liquid waste in the landfill also affects the quantity of leachate produced. A large landfill site will produce greater amount of leachate than a smaller site.
Modern landfills are often designed to prevent liquid from leaching out and entering the environment; however, if not properly managed, the leachate is at risk for mixing with groundwater near the site, which can have dire effects.
The liquid may be virtually harmless for old and dilute landfills, or dangerously toxic, depending upon what is in the landfill and the amount of flushing and decomposition which has already taken place, but it typically has high concentrations of nitrogen, iron, organic carbon, chloride and phenols (if oily wastes have been disposed). Other chemicals, including pesticides, solvents and heavy metals, may also be present. As the leachate emerges from a landfill site, it is black or yellow when fresh, with a strong acidic smell. When the leachate is older or methanogenic it will be whisky colored with a more typical landfill odor. In the past, this soup was allowed to slowly leak into the nearby environment, eventually mixing with the groundwater system and could cause wells and boreholes to become contaminated and no longer drinkable.
In modern landfills perforated pipes placed throughout the landfill collect leachate. The leachate then drains into a pipe and afterward into a leachate collection pond. The pipes and containers that transport or hold leachate must be made of special materials that prevent leakage and hold up to the acidity of the liquid. The collection pond or lagoon is tested for acceptable levels of chemicals like magnesium, organic chemicals, sulfate and iron. After the water is tested, it is treated like any other sewage and discarded on-site or off-site. Sometimes it is circulated again and then treated afterward.
All landfills produce some leachate. Whether the leachate contaminates groundwater depends on how the landfill is built, as well as on characteristics of the site.
Groundwater is the water source for wells and springs, and commonly supplies drinking water to over half of the people in most countries, and possibly over 90 percent of the residents in rural areas. Geological formations which yield significant amounts of groundwater are called aquifers. The top of the groundwater layer is called the water table.
Silage Leachate Treatment
Silage leachate is an issue for all farmers who have silage. Silage leachate can come from all forms of silage storage: bunkers, upright silos, bags, and piles. Handling leachate can be simple or complex depending on the scope of your operation.
Silage leachate is an organic liquid that is formed when water, or in some cases pressure from the structure, comes in contact with silage and runs off. Leachate can be formed as a part of silage storage, especially if the corn or alfalfa is harvested too wet. Water comes in contact with the silage because it is part of the silage. The other source of leachate is rain water coming in contact with silage and carrying nutrients with it. This leachate has a high biological oxygen demand, BOD. If silage leachate is allowed to reach surface water, oxygen in the water will be consumed so quickly that anything living in the water, including fish, could immediately be in peril. It is estimated that one gallon of silage leachate can lower the oxygen content of 10,000 gallons of river water to such an extent that there is a chance for fish kill. Leachate also can cause algal blooms that will further deplete the oxygen levels of surface water and it can also produce high levels of ammonia which will also cause fish kill.
Landfill leachate quality has proven to be highly variable in relation to location within the landfill and the age of the facility. Thus, the term “typical leachate” must be used with caution and in the context of a given type and age of landfill. In addition, the chemical characteristics of any leachate sample, regardless of its source, may not be representative of the total volume of leachate.
Leachate treatment is becoming more challenging and typically is one of the largest operating costs for landfill owners. Sewage works, or publicly owned treatment works (POTWs), face more stringent discharge standards today than ever before, which are resulting in increased limitations being placed on accepting leachate from landfills, with some sewage works facilities no longer accepting leachate at all. Thus, landfill owners must seek new and more efficient means to cost-effectively treat leachate by either making it acceptable to POTWs or by pre-treating it on-site.
Leachate information pages you may find interesting on other websites:
Related terms: Landfill Leachate Treatment Methods, Leachate Treatment Costs, Leachate Treatment Process, What Is Leachate From Landfills, Treating Landfill Leachate, Leachate Disposal, Leachate Pictures, Leachate Pond