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Breath of fresh air blows through bioremediation

VHE CONSTRUCTION is using innovative aeration processes to speed up biodegradation of contaminants on brownfield sites in Portsmouth and Edinburgh.

At a former gasworks in Portsmouth, Finnishmanufactured allu buckets are being used to remediate the site for client Lattice Property Holdings and consultant WSP Environmental.

The buckets, fitted to hydraulic excavators, have rotary blades which shred and grade the material, enabling the removal of oversize particles.

After the soil has been heaped into windrows, the excavator moves along scooping up material, turning and shredding it before reforming the windrow.

This process homogenises and aerates the material, two of the key requirements for successful bioremediation.

Over 12 months, three buckets will treat up to 30,000m 3of fill contaminated with hydrocarbons.

At another former gasworks in Edinburgh, the firm is working on a project involving portable aeration equipment to speed up biodegradation of hydrocarbons contaminating silty and gravelly sand.

Again the client is Lattice Property Holdings with consulting engineer White Young Green Environmental.

Here the bioremediation process makes use of a custom-built air-lance allied with accurate monitoring of conditions within biopiles. The portable aeration equipment injects air into the areas of the biopiles that require additional oxygenation. About 6,500m 3of diesel-contaminated material is being treated.

Bioremediation techniques are designed to create the best conditions for bacterial decomposition of carbon chains. On gasworks sites these normally constitute organic, fuel-based contaminants such as coal tars and other carcinogenic hydrocarbons such as benzene and naphthalene.

The rate of biodegradation can be greatly increased by adding nutrients and enzymes, and by controlling moisture, oxygen, pH and temperature levels.

The approaches used at both sites offered many advantages. There was no need to transport large amounts of waste material off site, reducing the need for clean imported material and lowering the costs of landfill disposal.

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