Barr Environmental Explains the Background to the Garlaff Leachate Treatment Plant Project

The following is based upon an article about the latest Enviros designed and commissioned Leachate Treatment Plant, published in the July 2009 Edition of the Community Newsletter published by Barr:

Rain falling on the waste in a landfill is held within the plastic lining the waste sits on, which is intended to stop the rainfall entering the soil and rock beneath.

As site operator Barr Environmental needs to pump it out of the waste and treat it as per their SEPA waste permit. Till last year the leachate from the waste at Garlaff was treated in an open lagoon system close to the site entrance. While this plant still worked it was built many years back and wasn't able to treat the leachate to the highest standards now feasible. This old plant has been substituted by a state of the art treatment system beside Cell two of the rubbish heap.

The new plant is one of the most recent systems in the United Kingdom and was designed by leading leachate professionals Enviros. The consultants have designed over one hundred plants around the globe to treat this kind of waste water and have advised the UK govt and in particular the DEFRA government department in the Best Available Techniques (BAT) available for this kind of leachate treatment.

The plant is entirely automated and computer controlled and can nicely treat all of the leachate the landfill site produces every day. The system was built by Barr Surfacing & Civil Engineering and largely invisible from outside of the site as four fifth's of the plant is built below ground, rather like a below ground multi-storey car park.

The leachate is pumped from the rubbish heap from a series of wells in the waste to an large holding tank in the plant. There were some concerns about odour from this tank. So, all the tanks have been sealed at the top to stop any smells entering the air round the site before the leachate starts to be dealt with.

The main treatment tank is aerated and the leachate treated using the natural microbes in the sludge in the tank in the same way a sewage plant works. These microbes are specifically evolved to treat the ammonium rich liquid to provide a clean liquid that is fit for discharge to the brook.

The plant has been engineered to the most recent standards with a high efficiency energy rating that's achieved by insulating the tank with earth around it and transferring the heat from the aerators into the treatment liquid. Keeping up the leachate temperature through the winter at about 25 degrees C creates the ideal conditions for fast decrease in the pollutants within the aeration tank.

Still working with nature the final part of the treatment process uses natural reedbeds on site to shine and take away the last traces of solids and nitrogen.

The reedbeds have proven to be a helpful habitat as well to wildlife. They will quickly become home to many insects and the tiny birds that eat them.

Barr have been so happy with this new leachate plant that they have just built its twin at their other landfill site, at Auchencarroch in West Dunbartonshire, Scotland. Together these plants are the biggest and most modern leachate plants to ever be built in Scotland and controlled by one company.

The plants will operate for no less than the next 30-40 years till the leachate has been fully treated on the site and no longer is required to be removed.

Environment Agency UK Issues Guidance on Environmental Permitting for "Orphan" Leachate Treatment Plants

Earlier this month (July 2009) the EA's Modernising Waste Regulation Panel issued a Regulatory Position Statement about Environmental Permits for Waste Treatment Plants.

This has updated a previous pair of statements on this subject which we found hard to interpret, and which were issued a least a year ago.

Under the original EU Directive based PPC Regs. and UK permitting rules it appeared that in due course all leachate treatment plants greater than 50 tonnes per day (50 cubic metres per day) capacity would have to be officially issued with a permit by the Agency. This would be the case even if the plant had been in existence for many years and was clearly complying with its watercourse (or sewer) discharge consent and not causing any environmental problems at all.

From the start this seemed absurd, and an enormous cost and bureaucratic burden on the operators of these plants, without anyone really being clear what benefit would result.

As time progressed and the Environment Agency concentrated on prioritising the most important treatment processes and all new landfills, we all wondered when they would catch up with this and start contacting the operators of these so called "orphan" sites.

Now, finally it seems that most if not all leachate treatment plant owners and operators that do not already have an Environmental Permit, or have been required to submit for one, for their leachate treatment plant can relax about this.

The position statement says:

The Environment Agency’s position:

We will not pursue an environmental permit application for an IPPC directive waste treatment activity where all the following conditions are met:

• the treatment plant is subject to a consent issued under the Water Industry Act or the Water Resources Act;

• the plant only treats waste/waste water produced on-site and does not import it from other sites;

• management of the activity ensures that the risk of pollution incidents from the site, including nuisance, remains low;

• relevant operational records are kept for a period of four years and made available to Environment Agency officers when requested.

However, if you do own or operate a leachate treatment plant on what would usually be a closed landfill, you should not rely on this posting alone, and you really should visit the EA's web site and read it for yourself at the WTP Orphan page/pdf.

However, here is a thought to end this post. How many closed landfill leachate treatment plant operators have a full 4 years of data properly archived and ready for inspection, if requested. I wonder!?

WRG Arpley Landfill Passes 1/2 Million Tonnes of Leachate Treated

From the WRG Newsletter

During early 2008, WRG’s Arpley leachate treatment plant passed a total of 500,000m3 of leachate treated. Since it was commissioned in October 2001, the plant has been treating very strong leachates which routinely contain greater than 2000mg/l of ammoniacal-N, to standards which allow safe discharge of effluent into the River Mersey.

When WRG took over Arpley Landfill in the spring of 1999, leachate was not under control. Although heads of leachate on the liner were limited to a maximum depth of 1 metre, levels were typically 7 or 8 metres, and well out of compliance. A key part of site remediation was investment of more than £1 million in a dedicated pneumatic leachate collection system, to automatically manage leachate levels in nearly 100 boreholes. From the start of 2001 leachates then began to be tankered off-site for treatment, at rates of up to 10,000m3 per month.

This allowed detailed pilot-scale treatability trials to be carried out by Enviros, to enable an optimum treatment scheme to be developed, which would represent the largest load of contaminants to be treated at any landfill site in the UK. WRG were no stranger to leachate treatment. In 1994, working with Enviros, a large leachate treatment plant had previously been designed and commissioned at Buckden Landfill near to Huntingdon, where a discharge consent into the sensitive River Great Ouse demands that rainbow trout shall be unharmed after 96 hours exposure to the final effluent. That plant continues to perform well, nearly 15 years later.

The treatment process adopted at Arpley (Plate 1) includes aerobic biological treatment of up to 450m3 of leachate each day, in three identical large Sequencing Batch Reactors. The SBR process has been pioneered for leachate treatment by Enviros, and shown to provide very stable and robust treatment of the very high ammonia and COD values which characterise leachates from large landfills. Effluent from the SBRs then passes through a Dissolved Air Flotation (DAF) process, which removes any remaining suspended solids. The treated leachate receives final “polishing” by passage through the root zone of extensive engineered reed beds, before being discharged safely into the River Mersey which flows beside the site.

WRG and Enviros worked closely with the Environment Agency to plan and implement the leachate treatment solution, and by 2004 leachate levels had been brought back into compliance with the site licence in every monitoring borehole. The plant remains a key part of controlled landfilling at Arpley, and continues to treat leachates at typical rates of 8,000 to 9,000 cubic metres per month.

Operation of all functions of the plant is completely automated. A programmable logic controller (PLC) provides maximum reliability, and the plant operator interfaces with this using a PC. Many dozens of failsafe systems, alarms, and telemetry links provide enormous security of operation. Experiences at Arpley have also formed the basis for many other large leachate treatment plants around the world. For example, Taman Beringin is a very large landfill located close to the centre of the city of Kuala Lumpur, in Malaysia. Remediation of the site has included a new leachate treatment plant (see Plate 2). It achieves very high effluent quality standards, which allow discharge of treated leachate to be made into a nearby watercourse.

As environmental standards at landfill sites are raised around the world, the ability to treat leachates reliably, and to high standards, remains critical, and WRG and Enviros are presently designing several new plants that will be commissioned during 2009.

Enviros is a UK-based full-service environmental consultancy, with an international reputation in wastes management. In the specialised field of landfill leachate management, the company has unique expertise, having worked on every continent except Antarctica, and has designed and commissioned more than 80 full-scale
leachate treatment plants throughout the World.

Can Landfill Leachate be Treated by Anaerobic Digestion?

Every now and again the question of whether landfill leachate can be effectively treated by Anaerobic Digestion is raised.

My reply is yes, and in fact, it has already happened in the landfill before you usually see most leachate. After an initial aerobic (acetogenic) stage, modern landfills in effect become anaerobic digesters themselves. Once this has occurred the leachate produced has already been subjected to a form of anaerobic digestion, so there is little additional treatment which an AD Plant can provide to these mature leachates once leachate is removed from the landfill.

In a modern Municipal Solid Waste (MSW) landfill. as it is filled, each cell or area within it, will within 6 months to one year, or, at the most eighteen months, not only become airless, but methanogenic (methane producing). Once this happens, the decomposition process taking place in the landfill is broadly similar to, but slower than, that which occurs in an anaerobic digester.

So, modern lined and well regulated landfills these days do, almost without exception, produce a mature methanogenic leachate.

As a result the use of Anaerobic Digestion to treat landfill leachate is not normally a good choice and the use of the Anaerobic Digestion process to treat landfill leachate is not very effective. This can be readily deduced just by thinking about the processes which leachate undergoes within a landfill. The big problem with using AD on a mature leachate would be the lack of significant reduction of ammoniacal nitrogen in the discharge, and ammoniacal nitrogen is one of the most important contaminants to remove, for reduced toxity to water life.

However, the opposite does work. Now think of using aerobic reactors to treat Anaerobic Digestion concentrates, if these concentrates cannot for any reason be disposed as a fertiliser product and thus have to be treated as a waste material.

So, leachate treatment plant aerobic biological reactors can be used very effectively to treat AD liquid digestate, if that "product" ends up proving to be unsaleable locally. Indeed, on site aerobic digestate treatment might be essential in these circumstances if no sewage treatment works was available to accept tanker loads of liquid from an AD Plant.