B&E hears about a remediation concept aimed to put an end to landfill.

IT’S CALLED Cluster and it is an initiative developed to establish a systematic and more sustainable approach to dealing with types of sites that contain insufficient volumes of contaminated soil to justify setting up and using on-site decontamination technologies. Or the sites are too small to house the associated equipment.

Such constraints have traditionally led to decontamination by landfill disposal - ‘dig and dump’ - but, by collaborating with other similar sites, a Cluster approach is said to offer a viable alternative with additional benefits.

The benefits
Cluster is claimed to be an excellent vehicle to deliver the aims of the Landfill Directive, diverting waste away from landfill disposal in full compliance with relevant waste regulation.

The concept encourages a joint and voluntary approach to the remediation of land affected by contamination in order to achieve the government’s suitable for use objective – i.e. bringing land back into beneficial use in an economically-sustainable manner as outlined in the National Brownfield Strategy.

The overarching principle of Cluster is to provide a realistic alternative to landfill and reduce the need for imported fill on-sites. And Cluster sites are a local and temporary activity, not a permanent waste treatment facility.

These factors have been instrumental in achieving planning permission and wasterelated approvals for the first pilot Cluster, which began being assembled in Sheffield in 2006 and which is soon due to report its results.

The Cluster concept and pilot project has been developed and supported by CL:AIRE, English Partnerships, the Environment Agency, Grantscape, the National Grid, Sheffield City Council, the Soil and Groundwater Technology Association and VHE Construction.

Call for future sites
Cluster is now looking for potential groups of sites in a nationwide roll-out, to which the expertise and experience of interested organisations and the Cluster partners can be applied.

This roll-out is an opportunity for both public and private sector organisations alike as it has the potential to bring forward sites for development, deliver substantial cost savings of decontaminating such sites and underpin the adoption of more sustainable remediation practices.

The Cluster team say they would be grateful if interested organisations could consider whether this approach might be valuable to them. All sites and partners from across the UK will be welcomed and assessed for suitability as part of a new Cluster, in the strictest of confidence.

International interest
As part of a current German research project, a team comprising Detlef Grimski, from the German Federal Environment Agency, and Michael Konig from HPC-AG, visited the UK Cluster pilot site to explore opportunities for the inclusion of several sites into a single and coherent remediation strategy.

The basic objectives of the German project are similar to the Cluster objectives in terms of incorporating several sites into one strategy to make sites quickly available for reclamation and subsequent reuse, using optimum clean-up technologies that would otherwise not be costefficient for only one site due to the small amounts of material to be treated, and providing an overarching efficiency for brownfield redevelopment of an area affected by contamination.

Grimski said: “It was very useful. We got a lot of information that must now be evaluated with respect to the situation in Germany. We received confirmation that obvious problems in terms of contracting and legal risks can be overcome by proper project preparation.

“Although the Cluster pilot project in Sheffield has been designed to be very simple, its results seem to be promising for further and larger Clusters in the UK.”

Ready for action
Norwest Holst is currently looking to develop its jet pump system to put together an English hub station, which is designed and manufactured for English soil. “At the moment everyone is brining all the equipment in from Holland,” says Mike Turland, general manager for Norwest Holst Environmental, “which appears to be good but is not used to dealing with our clay type soils.”

Norwest Holst Environmental is working on the development of a soil washing process specifically designed to suit variable UK soils and which achieves total recycling of all materials, including where possible the residual filter cake

Norwest, which owns and continues to invest in jet pump technology, is seeking to use that technology to develop a soil washing process that will work effectively on those finer soils. It is partnering with a number of companies, including aggregates cleaning company CDE and chemical company Goldcrest.

Turland explains that, using jet pump technology, material below 12mm is vigorously washed, reducing the level of contamination by driving it into the wash water and further concentrating it into the finer element of the soil below 300 micron.

This material below 300 micron is then moved by jet pump to the tertiary scrubber where, under high pressure and with the addition of a scrubbing media, the contamination is further reduced and driven again into the water.

The fine material coming from the scrubbing stage leaves the process as slurry, which is unsuitable for use. To rectify this, the material is thickened using flocculants (Goldcrest) and processed by either plate or belt, dependant on the material type and final contamination level.

The water is sent through an oil/water separator and oils are recovered and sent for recycling. This makes the technique most suitable for hydrocarbon contamination but experiments are also underway with metals.

The sludge is pressed and dried and work is currently underway, with CDE, to define the right press; moisture levels of 27% (which technically describes a solid) have so far been achieved.

Norwest is also in early discussion with glass-production companies about mixing in the residual sludge with glass to produce blocks that can be sold to the construction industry.

Norwest Holst has carried out around 20 trials so far and is working to produce a detailed report of its data.

Soil washing, like many other decontamination systems, can and are used on sites under their mobile treatment licence. Norwest Holst believes this may be one route for the clean up of sites but on a smaller scale could form part of a treatment plant. To this end Norwest Holst is actively looking for partners to develop this approach and establish a number of treatment centres/hub sites.