In-vessel composting moves centre-stage

Many local authorities are looking at in-vessel composting of black bag waste to help meet EU landfill diversion targets and, if they can get away with it, the targets to recycle and compost household waste in England. However, the composting sector fears that composting of mixed waste could stymie collections of segregated organic waste, and that dirty compost could find its way onto farms.

Several factors are driving the composting of municipal waste higher up local authorities' agendas. As well as needing to comply with the landfill Directive - under which landfilling of biodegradable municipal waste must be reduced to 35% of 1995 arisings by 2020 - English councils have been set statutory recycling/composting targets for 2003/04 and 2005/06. In addition, some councils, responding to public sentiment, are seeking alternatives to mass-burn incineration (ENDS Report 319, pp 14-15 ).

Until now, most composting has relied on low-cost windrow systems in the open air. The technique is likely to continue to be used for green waste, but not for other biodegradable materials such as kitchen waste - which councils will need to recover.

Composting of kitchen waste, currently prohibited in response to the foot and mouth and BSE crises, is likely to be permitted under a forthcoming EU Regulation on animal by-products - but only in "in-vessel" plants meeting specified operational standards. The Regulation is expected to come into force next year (ENDS Report 318, pp 13-14 ).

In-vessel plants offer advantages over open-air systems in terms of reduced local impacts from dust and bioaerosols. In August, the Environment Agency announced a presumption against new composting plants within 250 metres of a workplace or home unless bioaerosol emissions can be demonstrated to be sufficiently low (see p 36 ).

However, large in-vessel plants for municipal waste remain rare in the UK. Anglian Water operates a Gicom tunnel in Ipswich which composts sewage sludge and municipal waste, while Biffa composts household organic waste in a plant on the Isle of Wight supplied by Wright Environmental (ENDS Report 292, pp 12-13 ).

Another two Wright plants were brought on stream last year by Aberdeenshire County Council, at Banff and Mintlaw. The plants, which consume 20,000 tonnes and 32,000 tonnes of black bag waste per year, respectively, produce stabilised "biowaste". This is used for landfill restoration and daily cover.

According to waste disposal manager Jack Clark, the council has had visits from other local authorities almost monthly. Environmental body Scottish Agricultural Council is hoping to develop a standard contract for in-vessel composting.

Aberdeenshire admits that its operations are "questionable" under recent animal by-products legislation - which makes it clear that composting is not a permitted disposal route for catering waste, including food from households. A study to assess the risk to animal health from the composting and landspreading of such materials is under way.

The Scottish Environment Protection Agency (SEPA) is discussing with Aberdeenshire whether the material, which is defined as waste, is fit for landfill restoration. Permission has been given for trials at licensed landfills. But it is up to trading standards authorities to enforce the animal by-products order - something they may be reluctant to do given that EU legislation may soon legalise such activities.

According to SEPA, almost every Scottish council is looking at in-vessel composting of mixed waste as a way of complying with the landfill Directive without incineration.

Argyll and Bute, whose project with waste firm Shanks has just received funding from the Scottish Executive's strategic waste fund, is planning three facilities, each taking 20,000 tonnes of mixed waste annually. The plants would use a new technology developed by Cambridge Recycling Services and output, at least initially, would be material for land restoration. Planning permission has already been granted for sites at Lochgilphead and Dunoon.

A project involving Midlothian Council and its existing disposal contractor, Waste Recycling Group (WRG), is looking at the agitated bay system supplied by Italian company Sorain Cecchini. Planning permission has been granted for a facility near Penicuik handling either 100,000 tonnes or 200,000 tonnes of mixed waste per year. Again the material would be used for land restoration or daily cover, with the hope being that longer-term a marketable product would emerge.

United Waste Services, which has a private finance initiative (PFI) contract with South Gloucestershire, is looking for a local site to build an in-vessel plant taking 20,000 tonnes of waste per year to produce land restoration material. The contract also includes plans for kerbside collection of green waste within 2-3 years and "hopefully" fruit and vegetable waste.

Leicester City Council, which is about to select preferred bidders for a 25-year PFI contract, told ENDS that most waste firms have so far recommended in-vessel composting based on forced air tunnels, similar to the Wright and Gicom systems. Another option on offer is anaerobic digestion, although this is complicated by the need to find a use for the methane it generates.

Most, if not all, major waste companies are including in-vessel composting in tenders for municipal waste disposal contracts. But the problem is cost. "We're looking at some of the big fully mechanised systems, such as the Wendelin units made by B├╝hler," said one company. "But windrows are appropriate for green waste because in-vessel, at £30-40 per tonne, is too expensive."

Another firm has looked at three or four processes, including one that is "a compromise between open windrow and a closed system" which would keep costs down to £20/tonne for a plant processing 5,000-6,000 tonnes. "The problem," it says, "is that there is very little regulation of windrow composting and therefore it's much cheaper."

"Councils are saying they want to buy time to avoid incinerators by maximising recycling and composting in the hope that alternative technologies will appear, but the animal by-products order has temporarily put a spanner in the works."

"There will inevitably be a move towards in-vessel, whether it's for mixed or segregated waste," said another waste company manager. "Councils can only meet their recycling/composting targets if they use in-vessel, bearing in mind the 250 metre limit and the EU animal by-products Regulation."

As well as securing planning permission for an in-vessel plant in Midlothian, WRG has applied for permission for a facility near Stanton in Suffolk which would include in-vessel composting of 100,000 tonnes of mixed and separated municipal waste. The plant, which would use technology "well proven" in the mushroom compost market, would partly serve an existing recycling contract with Waveney District Council.

Some waste businesses are concerned that the development of in-vessel systems for segregated waste may be stifled because of concerns about the quality of composts made from mixed waste and whether it might find its way into agriculture.

They also fear that if mixed waste composting takes off it will prevent councils from developing separate collection of organic waste. But, the companies argue, producing land restoration material from mixed waste could be the only way some councils, such as those in deprived areas, will be able to divert enough biodegradable waste to meet their targets under the landfill Directive.

Controversially, some English authorities also intend to count material used to restore brownfield sites or old landfills towards their statutory recycling and composting targets. One in the south-east told ENDS: "I'm going to include land restoration in ours until someone says I can't."

Guidance for the statutory recycling and composting standards set for English authorities under the Best Value regime defines composting as the production of a material suitable for use as a soil improver or growing medium.

However, including land restoration material will not be an option if the Agency decides that it is "bio-stabilised waste" rather than a product. The Agency has recently begun looking at how to define such materials, while the European Commission is planning a Directive on the biological treatment of biodegradable waste which would include standards for different classes of "compost" and stabilised biowaste (ENDS Report 314, pp 51-52 ).

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