Articles & Case Studies


Posted: Wednesday 8th July 2009

MEETING growing demands for potable water in the Scottish Highlands poses an additional challenge for water engineers, because the water is frequently extracted from the local watercourse, with consequent wide variation in initial quality. By installing a Hydro DynaSand® filter and Johnson Lamella Separator package on Deeside, Scottish Water Solutions have been able to provide high quality mains water from a compact and cost-effective treatment plant.

The new treatment plant is being established at Ballater to meet the needs of a growing population - designed to a maximum 12,000 population equivalent, around 1.8 megalitres a day. The raw water is being extracted from the River Gairns, a tributary of the Dee, which as a rain-fed spate river, is subject to wide variations in quality and flow.

“The River Gairns typically carries a lot of peaty colour as well as a high turbidity, especially when in spate, and Cryptosporidium,” comments Fayed Khan, project engineer for Scottish Water Solutions. “The quality required for potable water must be consistently good, no matter what the input, which is why we sought a high performance solution.”

“After evaluating several technologies, including membrane filters we selected Hydro’s DynaSand® and Lamella Separator package, because it combined proven performance with cost-effectiveness and a small footprint which suited the chosen treatment plant site.”

The process was designed by Hydro for Scottish Water Solutions and consists of treatment of the incoming water through flocculation tanks and mixers with alum flocculant and H2SO4 to correct the pH. The water is then fed to the three DynaSand® DS5000 filters. Here two Hydro Johnson Lamella separators are used to treat the washwater from the filters, and return it to the inlet flow, while the clean treated water is discharged to storage units.

Two Lamella units were specified by Scottish Water to act as duty and standby, thus enabling regular maintenance without interruption to the treatment.

Technical Notes on Hydro Lamella separation

Proven over many years in Europe, lamella separation has remained a slightly specialised solution in the UK, but its combination of compact dimensions and simplicity with low maintenance and power requirements is prompting a review of its benefits. Very versatile, applications include potable water clarification, primary settlement of screened sewage, secondary settlement of biologically treated sewage, backwash water recovery from treatment such as sand filter and industrial effluent clarification.

The primary advantage is that it offers operators high performance clarification of water in around one fifth to one tenth of the space occupied by an equivalent settling tank. With a flow rate of 180 m3/hr, a separator with a footprint of 2.9 by 4.4 m contains 120 m2 of settling area.

Tel: 0800 269371

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