MadSci Network: Environment & Ecology |
Leachate usually refers to the liquid that drains out the bottom of landfills, garbage dumps, or other waste disposal sites. A good, technical description is given at: http://www.owtinc.com/leachate_1.htm, the site of Organic Waste Systems, a company selling technology to deal with leachate.
Leachate forms as water percolates through solid waste. This water can come from rainwater falling on top of a landfill and seeping down into the waste or it can come from within the waste itself. As that water moves through the waste, it can dissolve metals, organic compounds, and other contaminants. If not contained or treated, the leachate can keep moving beyond the landfill, contaminating groundwater or streams and poluting the environment.
In modern landfills, layers of clay and plastic are used to keep the leachate from moving down into groundwater and a system of pipes is often put beneath the waste to allow lwacate to be collected and treated. Unfortunately, liners are not perfect, and they may degrade over time and develop leaks. In addition many older landfills do not have liners.
Leachate varies in compozition and appearance depending on what it is leaching out of, but at a suburban landfill I visited recently, it was a murky tan liquid that smelled like a garbage can that hadn't been cleaned in a really long time (peeuuuuw!) At this landfill, they treat the waste in their own sewage treatment plant, aerating it, using bacteria to break down the organic material, and adding lime and other chemicals to remove the metals. Their discharge is monitored and must meet the same standards as a sewage treatment plant before it can be allowed to flow into the nearby river.
The disposal of solid waste in a safe way, and the reduction of solid waste that needs to be disposed of are very important issues. You can learn more about solid wastes from the Environmental Protection Agency at http://www.epa.gov/epaoswer/osw/
Dave Smith
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