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Leachate Treatment

Introduction

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

Specialist leachate treatment process designers are essential to ensure a high success rate in the provision of leachate treatment plants. Non-specialist leachate design consultants have a poor track record in leachate treatment although they may undertake such work when requested.

"Non-specialist leachate design consultants have a poor track record in leachate treatment"

For a successful leachate treatment project it has been repeatedly been shown that successful projects require a team of leachate specialists to combine all the necessary skills to implement the highly complex and integrated modern plants demanded by discharge consents and the many other regulatory constraints.

National Discharge Standards versus Site Specific Risk Assessment 

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.  

Biological aeration viewed from the air.

 Image: Aerial view of 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, and where irrigation use is significant. The environmental benefit in removing salinity for example, from the leachate discharge may provide a negligable benefit when the available dilution is considered in most main rivers.

The dilution effect for a watercourse with a reasonable summer minimum flow, may be so great for a comparatively low 200 cubic metre constant leachate discharge per day, into the thousands flowing past each hour, to be undetectable downstream. Such a flow is a mere trickle, and is diluted within say 100mm from the discharging pipe end. But, the cost increase of the more complex plant to treat to the higher standard may be 20% to 30% on initial investment, and up to 50% on running costs.

Biological Treatment Compared with Reverse Osmosis

The biological processes for the treatment of mature landfill leachates may be 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 a negative impact on the receiving watercourse, (unless low flows are very low and provide little dilution).

As a result other more highly technological processes in addition to, or instead of, biological treatment are being 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.

In most landfills, if the concentrate is returned to the landfill, over many years the leachate discharged to the treatment plant will actually become stronger, not weaker over time, as the returned contaminants recirculate. 

By contrast, biological treatment is treatment in its fullest sense, and will remove most contaminants, by a natural conversion into far less harmful substances, and mostly carbon dioxide and water.

Biological treatment is a natural process using organisms naturally available within the environment.

IPPTS Associates Consulting for example, is a specialist designer of biological leachate treatment plants, and has with more than 80 such biological treatment plants in use across the UK, and in many other countries. They firmly believe that biological leachate treatment in an SBR is the Best Available Technique (BAT) for most municipal landfill leachates, and also most industrial and commercial landfill leachates.

The UK Environment Agency applies the principal of BAT (Best Available Technique) to leachate treatment, in accordance with its responsibilities for Envrionmental Cosnets (under "PPC" - the Pollution Prevention & Control Regs.), and will expect the site owner/operator to show that the process proposed for leachate treatment at each location is a BAT technique appropriate to that site.

The UK Environment Agencies 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. The BAT philosophy avoids the unecessary and even inappropriate technological solutions which can result from inflexible national water quality standards.

What matters to the wildlife and ecological health of any watercourse is whether the discharge (of a very small proportionate volume compared with the total flow) will create an impact.

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

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