A leachate treatment system is a necessary provision for all sanitary landfills that produce leachate, with the exception of those which opt to tanker all their leachate off-site to a suitably equipped water treatment works. Only a very small proportion landfills are located in arid locations sufficiently dry not to produce leachate and therefore not to need a leachate treatment system.
Leachate treatment systems use various technologies including: biological extended aeration SBR plants, nitrification/denitrification leachate treatement plants, activated carbon, constructed wetlands, anchemical treatment to address site-specific leachate characteristics and site conditions. The selection of a treatment approach is dependent on many variables, including site location, leachate quality and quantity, availability of utilities, discharge limitations, and environmental regulations. Because of variability in leachate quality, treatment approaches must be evaluated on a case by case basis.
Leachate characteristics must be defined first before selecting a leachate treatment system and these are determined by the site, design, solid waste, mode of operation at the landfill, as well as the age of the landfill itself. Young landfills (less than 4 years old) tend to have a lower pH as well as higher levels of COD, BOD and heavy metals. high ammonia concentrations and salinity can also be a factor no matter the age of the landfill.
Wastewater generated by the runoff of leachate from municipal and hazardous waste landfills can have a negative environmental impact if not controlled and treated correctly.
No two leachates are the same, because each landfill has its own constituents, the liquid that passes through the solid waste takes on its own unique properties. Leachate quality also changes over time, so a treatment system must be sized according to individual parameters and should be flexible enough to treat a varied influent stream.
The quality of the leachate stream is an important management issue. Leachate is categorized by water chemistry, heavy metals and volatile and semi-volatile compounds.
The management of leachate produced by a landfill is a major engineering challenge. To design and operate an efficient leachate treatment system, which is essential to minimize potential impact on the environment, several key factors must be considered. The characteristics of the landfill waste, the local climate, the hydrogeological conditions, the operational procedures and the landfill’s age all impact the quantity and quality of the leachate.
The proper characterization of leachate, backed by treatability studies, is essential to select a reliable system. Leachates are typically characterized by extreme values of parameters such as pH, ammonia nitrogen (NH3-N), alkalinity, dissolved metals, and oxygen demand.
The leachate collection system for old closed landfills often consisted of subsurface pipes which collected and transferred the leachate from the landfill to a leachate treatment system consisting of a wetland network constructed on the edge of the landfill or on the restored surface.
The size and number of sections of the wetland network for unlined and old leachate treatment systems was determined by evaluating both the contaminants to be treated for, and the size of, the flows entering into the system. When designing the wetland network, expected flow into the system along with sufficient reserve capacity is needed to contain accumulated precipitation from previous rainfall events, as well as sediment and sludge accumulation.
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