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Leachate treatment

Introduction

A very wide range of treatment processes have been applied to leachate treatment with varying success. The processes which have been consistently successfully applied, for muncipal waste landfill leachate from controlled landfills, are biological processes designed by specialist leachate process designers.

In many countries standard national discharge consents limit the applicability of biological processes. In our view this is not a conscious decision made in favour of more expensive options, it is simply a result of consents which are designed for simplicity, and which adopt a requirement that all discharges must meet a high quality standard suitable for all cases.

Leachate treatment taking place in an aeration tank.

While this no doubt leads to simplified discharge consenting, and reduces the workload of government environmental regulators, the cost to industry will be unnecessarily high where watercourses provide substantial dilution which would, by site specific impact risk analysis, otherwise enable justification of a more relaxed consent.

For example, many national consents limit COD, and Salinity, both in arid areas and where little or no irrigation will be undertaken. Biological processes for the treatment of old landfill leachates are only partially effective in removing COD, and not at all effective in Salinity reduction, but in reality this is seldom likely to present a risk of impact on the receiving watercourse, (unless low flows are very low and provide little dilution). As a result other more highly technological processes have been used, in many countries. These include the use of the Reverse Osmosis process - sometimes as the sole treatment stage, but more often in combination with biological treatment.

It should be recognised from the start that such processes are inherently more expensive to run than biological processes (such as the SBR activated sludge extended aeration process), and depending on the destination of the concentrate produced may be very much less sustainable than biological treatment.

For example, if the concentrate is returned to the landfill, over many years the leachate emanating will actually become stronger, not weaker. In contrast, biological treatment is treatment in its fullest sense, and will remove most contaminants, by a natural conversion into far less harmful substances.

With more than 50 such biological treatment plants in use across the UK, and in many other countries, we firmly believe that biological leachate treatment in an SBR is the Best Available Technique (BAT) for most municipal landfill leachates.

The UK Environment Agency will continue for the foreseable future to apply a policy which, while ensuring compliance with minimum set Environmental Quality Standards for each watercourse, allows consideration of each discharge on the basis of a site specific impact risk assessment.

This provides the background to the next section - leachate treatment processes.

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