Portable MBR technology extends leachate treatment options

Tony Robinson, Operations Manager of Wehrle Environmental, puts forward the case that new regulations and the mounting costs of landfill may prompt operators to take a fresh look at current practices. Wehrle has over 15 years of experience of working with European and Asian landfill companies. The company's plants have been installed on over 58 landfill sites throughout the world and treat over 10,000 m3/day of leachate. Wehrle designs and builds leachate treatment plants and also operates them on behalf of its customers.

It is becoming increasingly important to manage leachate levels within landfill sites. The implementation of new regulations means that landfill management practices, including the control of leachate levels, are becoming stricter. But there are also economic benefits to minimising leachate levels, namely improved landfill gas extraction. As energy prices rise, predicted to be at a rate greater than that of inflation, landfill gas will take on more importance and will be increasingly viewed as a valuable commodity.

The only environmentally sustainable way to minimise leachate levels is its removal from site. There are a number of options available for this but the most cost effective, with regards to operating costs, is onsite biological treatment. However, pursuing such a policy is fraught with financial risks. During an average 30-year life cycle for a landfill, leachate changes both in volume and strength depending on the operation of the site, and there is a risk that a treatment plant may either become too large or insufficient for the job. With this in mind, it may be difficult for landfill operators to justify large capital investment in order to reduce present leachate disposal costs.

West Oxfordshire-based Wehrle Environmental can mitigate these risks by providing portable leachate treatment plants that can adapt to changing requirements. The process is based on the membrane bioreactor process technology (MBR) and incorporates intense bio-oxidation with membrane filtration. Its compact design means that a plant, capable of treating up to 400 m3/day of leachate, can be transported from site to site, and be in operation within two to three weeks. These plants are modular in design and as such can be tailored to the changes in leachate volume and strength over the lifetime of a landfill. As they are available on a lease/rental basis there may be no need to invest large sums of capital.

MBR technology

MBR is a well-proven technology that has been used for landfill leachate treatment throughout Europe for over 15 years. MBR employs a similar biological process to that seen in the conventional sequenced batch reactors (SBR) treatment plants whereby bacteria suspended in solution (Mixed Liquor Suspended Solids or MLSS) aerobically digest organic compounds that contaminate the leachate. Ammonia is also removed by conversion to nitrate.

The key difference however, between MBR and SBR lies in the separation of the biomass from the treated effluent. Whereas an SBR would employ gravitational separation, MBR plants separate biomass using ultrafiltration membranes. This provides an excellent quality effluent, completely free of suspended solids, and improved removal of Red List substances. Using membrane separation also allows a much higher MLSS concentration to be maintained in an MBR bioreactor than would normally be seen in an SBR. This figure can be as high as a factor of ten which effectively means that the occupied space could be ten times smaller. This is the key to the portability of an MBR plant.

The portable MBR (pMBR) comprises two basic units. The first is a standardised 60m3 bioreactor. Should a larger volume be required then further tanks can be added in series. The second unit is a standard shipping container that contains the ultrafiltration plant, aeration equipment, control computers and other ancillary equipment such as dosing pumps, feed pumps and a laboratory. The complete plant can be transported by road from one site to another and be commissioned within two to three weeks. This extremely short start up time is facilitated by the transport of the biomass along with the pMBR plant.

The solids free effluent is ideally suited for tertiary treatment and if the removal of hard COD, colour or specific organic compounds, such as halogenated hydrocarbon is a necessity, then skid mounted activated carbon chambers and/or containerised nanofiltration/reverse osmosis units can be included. A pMBR plant installed on a landfill site in Coved Moréac, France, demonstrates such an application.

The standard pMBR package of a bioreactor and ultrafiltration container, is supplied with additional activated carbon and nanofiltration units and is capable of treating over 70m3/day of high strength leachate.
A package can be created to suit the current needs of each site and should these needs change, which they will, the package can be modified by either adding or removing unit processes.

Solution for newer landfills

This is particularly useful for operators of newer landfills where leachate volumes may be quite high. The knowledge that high volumes will diminish after capping the site may prevent investment in a large scale plant that may soon become redundant. During this time operators may needlessly bear a high disposal cost by tanking away leachate. A pMBR can help such landfill operators by providing a solution that can be working at the required capacity long into the future. Once leachate volumes drop, it is simply a matter of transporting the plant, or part of the plant, to a new site.

For example, a pMBR plant designed for high volumes of leachate now, could in the future be split into parts and re-deployed on two or more sites where leachate volumes are low. Each unit process is designed as a self-contained stand-alone system that can be integrated into other existing systems. This intelligent design means that as your leachate changes, so will your treatment capacity. This maximises the investment made in leachate treatment and ensures that invested capital works a lot harder for a lot longer.

The pMBR is an excellent short term solution for landfill operators who are unsure about their future requirements for controlling leachate in the face of a continual increase in regulatory requirements.

The benefits of the pMBR do not just stop at flexible and affordable leachate treatment. Once the need for treatment is gone, moving the pMBR to another landfill makes the whole process of site recovery and remediation a great deal simpler. This is of considerable benefit for landfill operators who have an obligation to maintain the aesthetics of a site once activities have wound down, as it removes the necessity to demolish and remove large structural elements normally associated with leachate treatment plants. With the pMBR it is now possible to meet the future needs of your landfill today.

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