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Small Groundwater Site Requires Metals Removal System
West of Scotland Water (WoSW) awarded a contract, under competitive tender, for its first ultrafiltration plant to PCI-Water. The treatment works, being built for Carradale, near Cambeltown, Kintyre, was designed by PCI-Water, using hydranautics vertically mounted ultrafiltration membranes. This is the first installation in the United Kingdom using a hydranautics-based UltraBar system.
Located on croft land, the water treatment plant operated for 18 hours per day, treating 270m3 daily and serving a population of 750—1,000 in the Carradale area. Currently under commissioning test, the plant manufacture and installation was completed within 32 weeks. The contract covers the project’s full mechanical and electrical requirements, installation of four borehole pumps and a rising main at the site, typical of many new small groundwater sites, which need borehole pumping to supply the works.
Metals are present in the raw water supply as a result of the local geology. Drinking water must comply with regulated limits above which the incidence of metals present is not acceptable. Where levels are too high, they must be reduced to the regulated limits, achieved on this site by a novel metals removal stage at the head of the works. The PCI-Water design uses duty and standby contact tanks containing calcium carbonate. Dosing the raw water with sodium hypochlorite removes the unwanted soluble metals, through oxidation. This precipitates and the insoluble metals in the water adhere to the high pH surfaces of the calcium carbonate media. The resultant fouling is cleared using a backwash facility.
Conventional metals removal systems operate using pressure filters with catalytic media. These are more expensive to install and operate. However, the PCI-Water system, which uses sodium hypochlorite as the chlorination media for oxidation, consequently provides extra residual chlorine for disinfection in the water supply thus removing a process stage and reducing opex costs. The ultrafiltration unit also is run on chlorinated water, which helps reduce membrane fouling and hence cleaning requirements.
"We are pleased to have the opportunity to provide and install our first ultrafiltration plant for WoSW," commented Mike Hughes, sales manager of PCI-water. "Our approach to disinfection, metals removal and process control shows that we can compete well in the small ultrafiltration plant market."