From kerbside waste to healthier soils

Black bin-bag waste may soon find a use, as new research explores converting it into compost that will then help enrich soils on which bio-fuels are grown.

If successful, the on-going trials could provide a way of dealing with mountains of unsorted municipal waste now going to landfill, while helping restore fertility to disused or derelict land and reduce the costs of producing bio-fuels at the same time.

The research project, ran by Envar composting centre in Cambridgeshire, is the first attempt at an in-depth study of the effects of compost made from mixed waste on soils and crops.

“In the last six or seven years, there has been strong concentration on source separation,” David Border, head of composting at Envar, told edie.

But even if recycling rates rise, giving increasing amounts of pure organic waste for composting, “there will always be circumstances under which source separation is not possible,” David Border said.

Under the £4.5m research project, funded by Waste Recycling Environmental Limited under the Landfill Tax scheme, mixed municipal waste from the Greater Manchester region is shredded, cleaned of the bigger, inorganic elements, mixed with organic garden and kitchen waste, and composted.

The final product is used to help energy crops or grass grow on restored land, such as former colliery sites. Current waste management licensing regulations do not allow compost made from non-source separated waste to be used in food production, ruling out agricultural use.

The first bio-fuels, including willow, miscanthus and reed canary grass, will be planted on soil enriched with the experimental compost this spring. Biologists and soil scientists will then conduct detailed research into the physical and bio-chemical properties of the soil.

“We will be looking at the effects the addition of the compost has on the soil and growing crops,” David Border said.

The four-year-long study will continue through to 2009, with two 1000 tonne batches of mixed-waste compost have already produced.

The compost will be used in the rehabilitation of limestone, grave and china clay spoil sites, as well as former collieries. Scientists will closely monitor plant growth and the soil properties over the four-year period.

The proportion of biodegradable municipal waste going to landfill has to reduce drastically if the UK is to meet EU Landfill Directive targets, which require a decrease to 75% from 1995 levels by 2010. Composting is one way of reaching these targets.

Biodegradable waste represents about 60% of the annual 29.1 million tonnes of municipal waste produced by Britain in 2003/4.

Although currently most UK compost is made using separated green waste, the Envar study could open the way to dealing with the simple fact that not everyone separates their rubbish.

By Goska Romanowicz

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