United Utilities adds PAC dosing system

Rochdale, UK - As part of its AMP4 capital investment programme, United Utilities has installed a powdered activated carbon (PAC) dosing system for the new Cowm water treatment plant at its Watergrove Water Treatment Works, at Wardle near Rochdale. The reason that the PAC is added to the water is to neutralise a naturally occurring material known as Geosmin - an organic compound produced by microbes and algae which gives untreated water an undesirable earthy taste.

The dosing system comprises a Spiroflow bulk bag discharger, with integral lifting hoist on a runway beam for the easy loading of bags of PAC into the discharger, and a flexible screw conveyor to transfer PAC from the discharger up to a volumetric metering feeder with buffer hopper above, from here it is transferred to a second buffer hopper. The latter unit maintains a constant head of material above a ‘Transvac’ venturi ejector.

PAC is then drawn under vacuum from the second buffer hopper and metered proportionately into a by-pass water stream to form a slurry that then re-enters, and is mixed, with the main water flow into the water treatment works and subsequently the distribution system that serves homes and businesses in the Rochdale area.

Transvac, which specialises in ejector technology, supplied the skid-mounted components that introduce the solids into the water stream. The second buffer hopper that feeds PAC into the ejector incorporates ‘high’ and ‘low’ level probes which, along with the flow sensors in the by-pass pipe-work, make up the highly reliable monitoring system developed by Transvac to shut-down the dosing system and to trigger an alarm in the event of a foreign body causing a disturbance to the balance of the treatment process.