A major problem associated with modern sanitary landfills is the disposal of leachate water. The leachate is generated when rainwater percolates through the landfill and absorbs chemical and biological compounds from decomposing materials in the landfill. New landfill regulations require installation of liners and collection systems for the leachate to prevent this water from entering the surrounding soil and groundwater. Disposal of the leachate becomes a major problem for the landfill owner because the leachate often requires some form of on site treatment to remove toxic metal and organic contaminants.
Landfill leachates are highly variable from site to site and over the life of the landfill. Flows change with the weather; increasing during rainy weather and decreasing during dry periods. Toxic heavy metal compounds are common to most landfills. In addition, many types of organic compounds may be produced. Leachate from young landfills is high in biodegradable organics. However, as the landfill ages, contents degrade and produce concentrations of complex organics which may not be readily biodegradable. Complex chemical/physical and biological treatment systems may be required.
Generally, the primary goal in treatment of landfill leachate is to remove metal compounds. This is done by chemical precipitation and clarification, followed by dewatering in a……press. Precoating and/or bodyfeeding with diatomaceous earth or perlite may be required depending upon the application and nature of the solids produced.
In addition to precoating and/or bodyfeeding, cake thicknesses of 25 mm or less may be required and should be considered during system design due to the potential difficulty in dewatering of the sludge. A precoat manifold should also be included to offer additional operational flexibility.
Solid Waste Landfills