HYTECH WATER LTD

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Landfill Leachate Treatment

The Scope of the Problem

Leachate strength can vary significantly from site to site, as well as with the seasons and the age of the site itself. Ideally before treatment is considered it is important to establish the range of flows and leachate strengths which will need to be treated.

Once the leachate quality and quantity data has been collected, a comparison with the discharge consent enables the treatment requirement to be identified.

Potential Solutions

Tankerage to the nearest STW

For small daily flows this may be the cheapest solution.

Discharge direct to sewer via pipeline

If the STW is close by and the leachate is acceptable to the treating authority, for small daily flows direct discharge may be the most cost effective option.

Partial treatment

The addition of chemicals such as hydrogen peroxide (to reduce BOD) may be sufficient for discharge to a STW, but the charges levied by the local works may be prohibitive.

Full treatment

The traditional way of treating landfill leachate involves using an activated sludge (similarly to a STW) in an aerobic process (aerated) – usually in a Sequencing Batch Reactor.

The basic process eliminates BOD and all ammonium. It usually gets COD down by around 50%, dependent on the biologically treatable content of the leachate.

The effluent from the standard plant will contain up to 150 mg/litres of suspended solids.

Increasingly, the discharge authority (EA or Water Authority) is demanding low nitrates (which requires the plant to include a denitrification stage) and very low suspended solids ( 30 mg/litre) which may necessitate a DAF plant or backwash filter – dependent on the nature of the solids to be removed.

It is possible that — if the effluent from the SBR is only marginally over the consent limit — that a Reed Bed to act as a final polishing stage may be sufficient for compliance.

Preliminaries

Once the scope of the leachate treatment problem has been identified, it is normally necessary for a Purchaser to present an outline design for the proposed plant to the Planning Authorities and the Environment Agency, as well as the senior management of the company. Accurate capital and running costs for the plant are also required.

Hytech Water — with their extensive experience as specialists in the treatment of landfill leachate and their contacts within the industry — are well equipped to provide such outline data quickly and at low cost early in the planning stage.

The Detail Design of the Treatment Plant

Currently — in 2006 — we would consider only the Activated Sludge based process for the routine long term treatment of strong leachates. However, Membrane Bioreactors are being used successfully for sewage treatment. Their possible use for leachate treatment is under active investigation . . . . but leachate treatment practices are very different from those required to treat sewage.

In designing the SBR, the quality and quantity of the leachate will dictate the size of the treatment tank.

The size of the aeration system will also be fixed by an analysis of the leachate. However, the way in which the treatment tank is aerated is dependent upon the particular system design. Traditionally, Venturi aerators have been used as a reliable but inefficient source of aeration and mixing. Modern plants can incorporate the more efficient fine bubble aerator systems (as used in STWs) along with a dedicated, very efficient, mixer.

The quality of the leachate will also determine the amount of alkali that will need to be dosed into the treatment tank on a regular basis. The dosing plant itself and the associated chemical storage facility would be incorporated into the plant design.

The requirement for an upstream balance tank for the raw leachate and a downstream balance tank for the treated leachate will be determined by the location and particular requirements of the site.

Finally the overall layout of the completed treatment plant, tailored to suit the size and shape of the available space, would be provided.

All designs would be fully discussed with the Purchaser, his plant operators, and his Health & Safety Officer before the final design was cleared for construction.

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