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 the UK leachate treatment has over the last 30 or more years, mostly required just biological nitrification treatment, in sequencing batch reactor type leachate treatment plants.
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 as national standards, and which adopt a requirement that all discharges must meet a high quality standard suitable for all cases.
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 could be providing substantial dilution which would, by site specific impact risk analysis, under a different licensing regime, enable justification of a more relaxed consent to the UK model.
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 of such “national Standard” consents leachate treatment plants overeas from the UK, have on several occasions been built to provide the further process stage after nitrification which is known as denitrification.
Other more highly (non-biological) 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 from an RO Plant, over many years the leachate emanating will actually become stronger, not weaker.
In contrast, biological treatment is treatment in its fullest sense. It converts the contaminants into other chemicals with a far lower contaminating potential, and will remove those contaminants from the waste.
“Leachate treatment by biological nitrification is the most common and most successful”
There are more than 70 nitrification type biological treatment plants in use across the UK, and there are more in many other countries.
At IPPTS Associates we firmly believe that biological leachate treatment in an SBR remains the Best Available Technique (BAT) for many 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 into which treated leachate will pass, allows consideration of each discharge on the basis of a site specific impact risk assessment.