Rotork assisting Welsh Water in upgrade of Welsh water treatment works

The new plant at Cwellyn has been designed and built by Black & Veatch Ltd, one of Welsh Water’s Asset Management Alliance partners for water supply capital investment schemes. The new treatment regime is designed to clarify the water before it enters the existing works in order to deal with changing raw water conditions and consistently meet all water quality standards.

Rotork IQT direct drive quarter-turn intelligent electric actuators have been installed to operate butterfly valves controlling the flow of water throughout the new treatment plant. All the Rotork IQT actuators are Profibus DP-enabled and linked to an existing distributed control system (DCS) on five two-wire bus networks. The operation of the plant is supervised by a SCADA system designed by Oasis Engineering Ltd.

Water from Llyn Cwellyn, some two kilometres distant, gravitates to the new treatment plant at a rate of up to 850 m3/hour. The flow initially passes through inlet static mixers where coagulant is dosed to maximise the performance of the DAF (dissolved air flotation) process. The flow is divided into three identical DAF streams, which consist of one Flocculator followed by one DAF cell where particles in suspension are floated to the surface to form a sludge blanket.

The clarified water is then filtered through first stage RGF (rapid gravity filtration) before being pumped to the existing treatment works through UV disinfection to deactivate cryptosporidium. The Rotork IQT actuators, including some modulating units, control all valve operations including the inlet works flow control, automatic desludging of the DAF cells, automatic backwashing of the RGF plant and the plant treating the effluent created by the clarification and filtration processes.