Articles & Case Studies

Sludge monitoring at Wessex

Posted: Tuesday 17th January 2012

Pulsar Process Measurement have supplied seven of their latest sludge blanket monitors, Sludge Finder 2, to Wessex Water for use at Christchurch STW. The acoustic technology replaced outmoded dipping probes which were unreliable and led to poor control of the system.

At Christchurch, the final settlement tanks are set up to run at an ideal sludge blanket level of 15 – 20% of tank depth, controlled by the use of RAS (Return Activated Sludge) valves. Before the Sludge Finder units were installed, the dipping probe measurement system previously in use had become unreliable, readings often including ‘spikes’ or ‘flatlines’ that would activate the RAS valves unnecessarily, using excess energy and making it more difficult to control the sludge blanket. The dipping probe system is mechanical, and the ageing system had become unreliable and prone to breakdown.

Pulsar are acknowledged experts in non-contacting ultrasonic technology, with thousands of installations all over the world. Sludge Finder makes use of Pulsar’s echo analysis expertise, allowing very accurate measurement of changes in sludge blanket. The self-cleaning ‘Viper’ transducer only needs to dip just below the surface of the liquid, signalling back to the Sludge Finder controller.

Wessex Water Scientists were delighted with the results they got from the Pulsar system. As Tony Towler, Area Scientist, put it: ‘The increased reliability of the reading means we can control the process more accurately, and that makes it easier for us to comply with the environmental consents.’

The improvement in control of the RAS valves has led to a 30% reduction in power consumption. The Sludge Finder signal is fed back to a local PLC adjustable by an HMI for control of RAS valves and also on to the data display system (Scope-x) which can be accessed remotely for monitoring and trending.




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