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Mighty mussels offer smart answer

Hazard or asset?

Marine mussels have been used to filter water in a small salt water lake, part of a new development in the Ormeau Road area of Belfast.

Consultant Parkman claims its use of mussels instead of mechanical plant or chemicals is unprecedented in water engineering. The group hit on the idea of deploying these 'biological filters' after observing high levels of water clarity in Liverpool docks, achieved by naturally occurring mussels.

A single mussel can process between 45 litres and 70 litres of water a day. It feeds on vegetable and animal microorganisms that can cause visual 'pollution' in the form of reduced clarity, removing them from the excreted water stream.

En masse they can process large volumes.

For the Belfast scheme, the lake has been filled with salt water from the tidal River Lachan nearby. Large numbers of marine mussels artificially propagated on netting were imported from Scotland and are now colonising their new environment. Numbers will be controlled by annual harvesting.

Parkman is now looking for other locations to put the crustaceans to work. It is thought they could be effective in treating low level emissions of sewage into marine environments.

But, just as the consultant is congratulating itself on an innovative and environmentally sensitive engineering solution, Ireland is facing up to the menace of a prolific fresh water immigrant, the zebra mussel.

In the last decade zebra mussels have spread via international shipping from northern European waterways to the Great Lakes in the US. They have now multiplied to epidemic proportions, damaging marine ecosystems and fouling any and every surface. The 20mm long adults have been known to gather in densities of up to 700,000/m 2. Zebra mussels are particularly attracted to areas that are have strong water currents, colonising water intakes on boats, power plants and water treatment works. At best peak capacities are restricted and energy lost due to the increased friction caused by the mussels. At worst, zebra mussels can clog pipes solid. US industry is already counting the cost of zebra mussels in tens of millions of dollars. As yet, there is no strategy for preventing infestation.

Three years ago zebra mussels were first reported in Ireland's west coast waterways. The country is watching the mollusc's progress with unease. AM

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