Articles & Case Studies

Cross filter assists recycling at Wessex Water STW

Posted: Tuesday 18th March 2008

A Cross automatic backwashing water filter has been installed at the Wessex Water Bridport Sewage Treatment Works to enable final effluent to be used as a virtually free-of-charge alternative to expensive clean water for the screen washing operations on the site’s drum thickeners.

Drum thickeners demand a constant supply of clean water to maintain efficient operation by keeping the drain holes in the rotating drums free from the build-up of debris. The water is sprayed under pressure through nozzles, which themselves will become blocked if the water is not of a good, clean quality. By filtering out any solids with a size in excess of 200 microns, the Cross filter therefore ensures that final effluent can be safely used for this application without the risk of interruption to normal operations.

With a flow capacity of up to18 litres/second, the compact Cross Phoenix filter installed at Bridport has the potential to make dramatic savings in terms of reduced clean water consumption. There are no additional running costs since the pump which supplies the water to the thickeners creates enough pressure in the system to backwash the filter. The Phoenix is designed to backwash without interrupting the forward flow of filtered water and using only minimal quantities of backwash water. Backwashing is triggered by an adjustable pressure differential switch, with a set time lapse back-up.

Central to Cross filtration technology is an ingeniously designed “zero-gravity” stainless steel coil with raised nodes on the surface which define a precise filter rating. Selectable in seven ratings between 12 and 400 microns, the coil is designed to open slightly and evenly along its total length when the flow across it is reversed during backwashing, ensuring that the build-up of particles is completely washed away. Cross filter systems are tailored to suit any size of duty by simply adding enough “zero-gravity” coils to meet the required flow capacity. In the case of the Phoenix, six coils are fitted in a specially designed housing that creates a cyclonic flow path for the water passing through, helping to keep suspended solids away from the surface of the coils and therefore extending the length of time before a backwash is required.

Tel: +44 1225 837000
Fax: +44 1225 834115

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