Final tests for Scots’ potable water

Equipment from Ondeo Degrémont is currently undergoing its final testing at a potable water treatment works for Scottish Water. The works lie in the upper Clyde Valley near Glasgow in the west of Scotland.

For many years, water treatment had been by chemical dosing, but now to meet the highest EU standards, Ondeo has supplied, installed and commissioned a complete range of treatment plant, including Aquazur filters and a Densadeg washwater thickening unit.

Raw water comes from two impounding reservoirs and is blended for treatment. Colour values at a maximum of 40 Hazen and turbidity of nearly 5 FTU, Iron (up to 222 microg/l), aluminium and manganese(132 microg/l max) are also a concern.

Among other requirements, Ondeo Degrémont’s task was to guarantee that colour would be reduced to 5.0 Hazen, turbidity to 1.0 FTU, aluminium and iron to 50 microg/l, manganese to more than 20 microg/l.

‘The big advantage of Aquazur T filters is that they are packaged steel units which can be brought on site and set up with no more than a concrete slab foundation as a base,’ said Nick de Tisi of Ondeo Degrémont’s design department.

The filters can be sized to suit the required throughput and are designed to provide the most efficient dispersion of water over the filter medium. Backwash systems use a combination of air scour and water to clean the medium with the minimum of disturbance.

Following automatic dosing with lime slurry and aluminium sulphate coagulant, first stage treatment at the plant is via a 2-stage flocculation plant. Each stage is designed for a holding time of at least 5 minutes, with polyelectrolyte flocculant aid add in in the first tank. From here it passes to the first array of Ondeo Degrémont Aquazur filters.

Second stage filtration uses three Ondeo Degrémont Aquazur T rapid gravity sand filters, each 17.6m². At 18m³/m² per hour, the process here is much faster than in the Aquazur Vs. It is primarily designed to remove the oxidised manganese, but also deals with any remaining suspended solids, but like the Aquazur V units, they also have a backwashing facility.

Backwashing water passes to a single Densadeg lamella settlement plant of two chambers – one for flocculation followed by settlement in the other. Thickened sludge is dewatered to produce a cake with dry solids of at least 17%.

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