Adding value

Phytostabilisation is a remediation technique whereby contaminants are immobilised in the soil through absorption by roots or precipitation within the root zones of plants, preventing contaminant migration via wind or water erosion, or leaching

When Dinnington Colliery in South Yorkshire was closed over 10 years ago, a derelict, contaminated wasteland was left behind. Yorkshire Forward, which owns the site, now plans to regenerate the land using phytostabilisation in a project funded by English Partnerships and led by Future Energy Solutions.

Altered soil conditions

In this case, the highly acidic coal shale will be treated with an ameliorant – an application of organic material such as treated sewage or green waste compost. This alters the soil factors that influence contaminant mobility – such as acidity, alkalinity and low oxygen levels – and creates a more conducive environment for plant growth.

Fast-growing willow and poplar trees will be planted at high density. These species can withstand the harsh conditions of the land, and with vigorous growth rates of around 1-2m a year, will swiftly transform the appearance of the site.

Due to changes in the chemistry of the contaminants – they become insoluble and/or immobilised in the soil – they accumulate in the plant tissues and in the soil around the roots. This usually reduces their toxicity.

After three years, the coppice can be harvested and chipped for burning to produce a local and renewable source of energy. Different sections of the woodland can be cut back each year, to maintain a varied habitat for wildlife.

Following successful trials at Dinnington and Kiverton Collieries, planting will go ahead from spring 2004. The wood will be used to fuel boilers for local consumers – redirecting existing heating budgets into the local economy.

The plan is for a cluster of at least 10 medium-sized boilers, supplied by a local wood company, to join the scheme to make it viable.

Traditionally, the cost of wood-fired boilers has been a barrier to take-up but under this scheme they will be supplied free – remaining the property of the wood heat company – with capital costs being covered by the contract for heat supply.

The price of the heat is competitive with other sources and has other benefits such as reducing fossil fuel use consumption.

Benefits of the scheme

Phytostabilisation can be used where brownfield land has no commercial worth, and would otherwise not become a target for remediation. Also, it costs about half the price of conventional remediation techniques.

As a low-cost approach it makes good commercial sense, using organic wastes that are in plentiful supply, avoiding landfill tax and potentially creating an income for the site.

Russell Dixon, who is project managing the work for English Partnerships, explains why phytostabilisation was chosen for the site: “The National Coalfields Programme is regenerating a lot of land for park use,” he says.
“However, when parkland is handed over to the local authority, it creates a management liability and a cost for the authority. At Dinnington, we hope to make an income from the green space at the same time as regenerating the area.”

Future Energy Solutions’ Julian Wilczek, adds: “Phytostabilisation is a low-cost route to brownfield site restoration that offers a number of benefits. The technique restores the land quickly. The trees can be harvested for use as a source of energy.

“By linking phytostabilisation to the creation of local markets for wood fuel, additional economic, social and environmental benefits flow.”