What Is Leachate? And How Is It Collected From The Bottom Of A Landfill?

Rainfall enters the landfill cell, and what isn't absorbed into the waste moves down to the basal filter. It passes through the pipe network, and rests in the sump. Pumps remove it from the sump, and may have to lift it 30 to 80 metres upward out of the top of the landfill. Make no mistake about how difficult this is. Even with modern pump technology to help, it is no easy feat to achieve this in the demanding conditions deep inside a landfill.

Leachate collection systems must be planned. The number, location, and size of the sumps are vital to an efficient operation of the landfill.

When designing sumps, the amount of leachate and liquid expected is the foremost concern. Areas in which rainfall is higher than average typically have larger sumps. This is called leachate management.

Leachate Management

A further criterion for leachate management sump planning is accounting for the pump capacity. The relationship of pump capacity and sump size is inversed. If the pump capacity is low, the volume of the sump should be larger than average. It is critical for the volume of the sump to be able to store the expected leachate between pumping cycles.

This relationship helps maintain a healthy operation. Sump pumps can function with preset phase times. If the flow is not predictable, a predetermined leachate height level can automatically switch the system on. Other conditions for sump planning are maintenance and pump drawdown.

Leachate Collection

Collection pipes typically convey the leachate by gravity to one or more sumps, depending upon the size of the area drained. Leachate collected in the sump is removed by pumping to a vehicle, to a holding facility for subsequent vehicle pickup, or to an on-site treatment facility.

Sump dimensions are governed by the amount of leachate to be stored, pump capacity, and minimum pump drawdown. The volume of the sump must be sufficient of hold the maximum amount of leachate anticipated between pump cycles, plus an additional volume equal to the minimum pump drawdown volume.

Sump size should also consider dimensional requirements for conducting maintenance and inspection activities. Sump pumps may operate with preset cycling times or, if leachate flow is less predictable, the pump may be automatically switched on when the leachate reaches a predetermined level.

Leachate Pipes

The leachate pipes should allow all the leachate to be pumped away, where it can be treated and the resultant slurry reintroduced either to the same landfill or sent to another. However, they can easily become clogged either by precipitation caused by chemical reactions due to the composition of the material that's in the landfill, or from a build-up of micro-organisms in the pipes, or due to the fact that unless designed correctly by experts the pipe walls may be crushed under the many thousands of tonnes of rubbish piled on top of them.

Summary

In the narrow environmental context leachate is therefore any liquid material that drains from land or stockpiled material and contains significantly elevated concentrations of undesirable organic and inorganic material derived from the material that it has passed through.


To prevent it building up inside landfills and escaping from the landfill liner, it has to be lifted out through  leachate collection system deep inside every modern landfill, using very robustly made pumps. This is an often costly challenge for pump manufacturers and landfill engineers alike, but the land around landfills and frequently also the drinking water supplies of the local people, depend upon this being done effectively both now, and for very many years into the future.

Find out more at the Leachate Website - www.leachate.co.uk.