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The flexible solution

Waste management in the UK continues to undergo rapid change as councils come to terms with the challenges of meeting increasingly stringent targets for recycling and reducing their dependence on landfill. Environmental consultant AEA has worked with West Sussex County Council for much of the past decade, helping it to modernise and deliver sustainable, affordable and high-quality waste management and services that can cope with its municipal solid waste (MSW) arisings during the next 25 years.

The heart of its household waste recycling contract is the materials recycling facility (MRF) at Ford, which opened in May 2009. It recovers paper, cardboard, metals and glass for recycling from commingled recyclables delivered to the site by the district councils in West Sussex. AEA is currently helping the council to procure facilities and services to treat and dispose of the residual MSW that will be essential for meeting landfill diversion targets.

“Many local authorities are now progressing solutions based on MBT, which is well established elsewhere in Europe and is increasingly seen as a deliverable and flexible solution for residual waste management in the UK”

The solution is based on mechanical-biological treatment (MBT) with anaerobic digestion (AD) of organic wastes (phase 1), and producing a refusederived fuel (RDF) that can be used as an industrial fuel or to produce heat and electricity at an on-site advanced thermal treatment plant that may be developed under phase 2 of the contract. Phase 1 of the residual waste disposal contract is expected to be awarded this summer while Phase 2 is expected to be triggered later in 2010 if no suitable markets for RDF are identified.

Local councils such as West Sussex have made much progress in working towards their EU Landfill Directive targets through the implementation of source-segregated dry recyclable schemes and green waste and food waste composting projects. But these alone will not deliver the challenging targets set for 2020, when only 35% of biodegradable municipal waste will be allowed to landfill compared with the 1995 reference year. Attention is now moving increasingly towards options for treating and recovering value from the residual waste stream. The traditional solution has been incineration, which reduces the waste to an inert residue and produces heat and/or electricity that can replace conventional fuels.

But despite these advantages, and compliance with strict environmental controls, mass-burn incineration remains unpopular with the public and some politicians. A number of incineration-based projects have faced protracted delays in planning, such as in Cornwall, sometimes leading to cancellation. As a result, many local authorities are now progressing solutions based on MBT, which is well established elsewhere in Europe and is increasingly seen as a deliverable and flexible solution for residual waste management in the UK.

Ten English waste disposal authorities, including West Sussex, are currently in the process of developing MBT facilities for their residual waste treatment, which are expected to come on-stream within the next five years, representing about two million tonnes a
year of treatment capacity. The public perception is that MBT is perhaps a more welcome neighbour than an incinerator, offering a flexible solution to residual waste management.

Outputs from an MBT plant will vary with design and waste input, but they tend to produce a similar range of outputs. An RDF fraction, enriched in high calorific value components such as paper, cardboard and plastics, can be used as a direct replacement for fossil fuel if suitable markets are found, or can be processed in dedicated thermal treatment plants that can be considerably smaller than an equivalent mass-burn facility. The organic materials are combined to form an organic-rich fraction that can feed a biological treatment facility.

The residue from the biological treatment plant is de-watered to produce a solid cake, the so-called compost-like output (CLO). This is usually sent to landfill, mainly for use as daily cover, but of course attracting landfill tax and contributing towards methane formations as it continues to decompose in the landfill. This is why MBT is sometimes cited as only a partial solution to residual waste management. Some MBT facilities are able to dry the de-watered cake using reject heat from the biogas engines and
produce a biomass-rich solid that has application as an industrial fuel. But what else could be done with it?

Under current regulations, CLO continues to be regulated as waste and can only be used in agriculture under the terms of a specific waste permit. This contrasts with the position on compost and digestate produced from source-segregated food and/or garden wastes. These materials, provided they meet the relevant quality criteria, are no longer classed as wastes and may be used without further involvement of the waste regulatory regime. So while some CLO could be approved for specific application in agriculture, this would be very much on a case-by-case basis and is unlikely to open up on a large scale.

But things will change if separate collections of food and garden wastes become widespread. This could lead to greater quantities of high-quality compost becoming available for agricultural use. But wouldn’t this starve MBT plants of their feedstock? Not necessarily. Provided the biological treatment plant is designed on a modular basis, source-segregated organics could be processed separately from residual organics, giving rise to high- and low-quality output streams. This would allow a smooth
transition in MBT processing capability, in step with a shift from bulk to separate collection of organics.

The technology options that can provide the flexibility of processing capability and outputs to suit market trends are going to come to the fore. MBT will be a significant player for the foreseeable future in treating residual wastes in West Sussex and much of the rest of the UK.

Dr Keith Brown and Dr Andy Godley are specialist
consultants in AEA’s waste management and resource
efficiency group; Phillip Russell is head of wastes
management at West Sussex County Council; and Dr
Adam Read is practice lead for AEA’s resource

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