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Bournemouth and West Hampshire Water (BWHW) has commissioned a 25tph sand-processing system from Linatex for its Knapp Mill site in Christchurch.

Bournemouth and West Hampshire Water (BWHW) provides clean drinking water to around half a million people, from Poole to Beaulieu and Bournemouth to Salisbury, an area of more than 1000km2.

It supplies on average about 150 million litres of drinking water every day through nearly 3000km of water mains.

With a new pumping station to be installed at its Knapp Mill site in Christchurch, the organisation contacted Centristic of Newton Abbott to facilitate the re-siting of the existing Linatex sand filter-bed treatment plant.

A comprehensive review revealed that elements of the present Linatex sand plant were too small for the feed requirements.

Linatex was tasked to supply a new 25tph sand-processing system, with Centristic acting as main contractor on the plant build.

Maintenance of the sand filter beds at Knapp Mill is performed on a continuous cycle, with 30mm being skimmed off the beds approximately every four months.

To maintain effective operation, the filter beds must retain a minimum of 300mm of sand above the carbon, therefore after skimming the Knapp Mill team ensures that 100mm of clean sand is replaced on the filter bed.

This continual process is effectively a recycling operation, as new sand is only introduced approximately every ten years.

As it is essential that the sand quality is maintained in this operation, the skimmed sand requires scrubbing to release any impurities (silts, clays and weeds) before the Linatex sand plant effectively washes and dewaters the material.

The material, being essentially wet filter-bed sand (largest particle-size 5mm) is fed by wheel loader into a hopper that feeds onto a 15m-long inclined conveyor, which delivers the material into a trommel (sand scrubber barrel) with a 1.2m diameter and that is 3m long.

The trommel is lined with Linatex rubber and lifters.

Sand and water discharging from this barrel are then flumed down a Linatex-lined chute to the centre of a 2.1m-diameter Linatex feed-regulating sump, with any overflow from the sump gravitating to waste.

From the base of the sump a 100/100mm-bore Linatex-lined centrifugal pump draws the slurry and feeds via 100mm bore pipework to a Linatex-lined HK 100 extended sand separator, with the overflow from the separator returning to the vicinity of the feed sump for balancing the system or disposal to waste.

The Linatex HK 100 separator is constructed with mild steel and is Linatex-lined in all wear areas.

Fitted with extended feed box, discharge regulator and pressure flange assembly, the separator incorporates two pressure gauges to measure inlet pressure and vacuum, which are key to performance of the unit to maintain operational efficiency and maximise sand recovery.

The sand separator, which is mounted in a supporting tower, incorporates three discharge chutes providing approximately 2,000-tonne stockpile capacity.

With the need to retain as much fine material as possible (95 per cent above 50 micron) the Linatex extended separator ensures that the quality is achieved, proving to be a cost-effective method of providing clean sand to a high standard.

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