Leachate Recirculation

by Kevin Fellin, Mike Cuccinello, and Becky Cheadle

Introduction to Leachate Recirculation

Methods of Leachate Recirculation

Advantages and Disadvantages of Leachate Recirculation

Alternative Methods of Leachate Management

Summary

References

Introduction to Leachate Recirculation

Leachate recirculation is one of many techniques used to manage leachate from landfills. Because of the characteristics of landfill leachate the main goal of leachate control is to prevent uncontrolled dispersion. Leachate should always be collected, treated or contained before it is released into the environment. During leachate recirculation, the leachate is returned to a lined landfill for reinfiltration into the municipal solid waste. This is considered a method of leachate control because as the leachate continues to flow through the landfill it is treated through biological processes, precipitation, and sorption. This process also benefits the landfill by increasing the moisture content which in turn increases the rate of biological degradation in the landfill, the biological stability of the landfill, and the rate of methane recovery from the landfill.

This table shows typical data on the composition of leachate from new and mature landfills. The values are expressed in mg/L.

Methods of Leachate Recirculation

There are several methods of leachate recirculation. These include:

Direct application to the waste during disposal-During this process the leachate is added to the incoming solid waste while it is being unloaded, deposited, and compacted. The problems with this method include odor problems, health risks due to exposure, exposure to landfill equipment and machinery, and off-site migration due to drift. This method also requires a leachate storage facility for periods such as high winds, rainfall, and landfill shutdowns when the leachate cannot be applied.

Spray Irrigation of landfill surface-Here leachate is applied to the landfill surface in the same method that irrigation water is applied to crops. This method is beneficial because it allows the leachate to be applied to a larger portion of the landfill, and because the leachate volume is reduced due to evaporation. However, the disadvantages associated with direct application are associated with this method as well.

Surface application-This is achieved through ponding or spreading the leachate. The ponds are generally formed in landfill areas that have been isolated with soil berms or within excavated sites in the solid waste. The disadvantages of these methods include an increase in the amount of required land area, and monitoring of the ponds to detect seepage, leaks, and breaks that would make it possible for leachate to escape directly or with stormwater runoff.

Subsurface application-This is achieved through placing either vertical recharge wells or horizontal drain fields within the solid waste. There is a large amount of excavation and construction required with this method, but the risk of atmospheric exposure is drastically reduced.

Advantages and Disadvantages of Leachate Recirculation

There are numerous advantages to treating leachate through recirculation, and the landfill productivity benefits as leachate is being treated.

Landfills that use leachate recirculation experience a decrease in the concentration of the leachate compared to landfills without recycle treatment. This reduces the amount of leachate treatment that is needed and therefore costs are also reduced.
The increased moisture content within the solid waste enhances the system conditions for improved biological decomposition of organic matter in the landfill.
The organic matter in the leachate , which requires treatment outside the landfill, receives further treatment each time it is recycled through the landfill. This reduces treatment costs of the landfill.
The reducing environment within the landfill removes inorganics in the leachate through precipitation and sorption.
Leachate recirculation stabilizes the biological system in the landfill and this reduces the environmental threats of the landfill, and reduces the amount of postclosure monitoring that is required. It also provides the opportunity for landfill mining and space reclamation.
Leachate recirculation increases the rate at which the waste decomposes and this inrease the rate of methane production. This makes methane recovery for energy much easier.
Leachate recirculation is a leachate management method that is relatively simple and inexpensive.

The disadvantages of leachate recirculation are:

Because landfills are heterogeneous the leachate may find discrete channels to travel through. This makes it difficult to insure that the leachate is reacting with all of the waste and is thoroughly treated.
The risk of environmental exposure when leachate is applied to the surface of a landfill.
The lack of information and education regarding the subject increases the chances that it will be misapplied.

Alternative Methods of Leachate Management

One of the most popular, which is the most common one in Virginia, is referred to as the "dry tomb" approach. This involves covering the waste with an impermeable layer and controlling the amount of moisture that enters the landfill. The purpose of this method is to control and reduce the moisture content in order to reduce the amount of leachate produced. However, this method eliminates the bioactivity of the landfill and since the solid waste will not degrade in these landfills, "dry tombs" are an environmental risk forever.

Another method of leachate management is to pump out the leachate from the bottom of the landfill, and store it in a large basin. From this basin, the leachate is often shipped to a municipal wastewater treatment facility where it can be effectively treated. Since the concentration of contamination of leachate is not as high as that of commercial wastewater, the leachate serves also as a dilutor and is consequently helpful.

Treatment lagoons can be a more specialized method of leachate management. Here, the treatment is pumped to a lagoon where it can be treated by the addition of chemicals. The type of chemicals used are completely specific to the characteristics of the leachate in question.. For example, if a leachate contains high concentrations of heavy metals, chemicals would be added to provoke flocculation and precipitation. Whereas if the leachate had high BOD (Biochemical Oxygen Demand) levels, some sort of aeration treatment technique may be more appropriate.

Summary

As you can see, leachate recirculation can be a solid alternative to the common methods of leachate management. It treats leachate, degrades the municipal solid waste, and helps stabilize the landfill at a faster rate than the conventional methods. As space for landfills in urban and suburban areas continues to decrease, we foresee the need for leachate recirculation becoming a more popular method.

In the Commonwealth of Virginia leachate recirculation is not permitted. With respect to landfill management regulations it has been the traditional goal to prevent the addition of any liquids to a landfill. The less liquids which enter a landfill means the less leachate leaving the landfill, this in turn means less problems with which to deal. The argument for leachate recirculation supports the idea for controlled degradation. In order for this occur you must have a dynamic process occurring within the landfill. The case with "dry tomb" landfills is that you will not get any degradation. As a result it is possible to excavate a 50 year old "dry tomb" landfill and still read the print on newspapers.

References

Earle, Miller, Townsend. Journal of Environmental Engineering; June, 1995. pp. 45-46

Pohland, Frederick G. Gas and Leachate from Landfills:Formation, Collection, and Treatment. USEPA, April, 1976.

Tchobanoglous, Theisen, Vigil. Integrated Solid Waste Management : Engineering Principles and Management Issues. New York, 1993.

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