The Sludge Finder 2 monitors were specified by Wessex Water for use at the Christchurch STW. 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 return activated sludge (RAS) valves.
Before the Sludge Finder units were installed, the dipping probe measurement system 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.
Sludge Finder makes use of Pulsar’s echo analysis expertise, allowing accurate measurement of changes in sludge blanket. The self-cleaning Viper transducer needs only to dip just below the surface of the liquid, signalling back to the 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 resulted in a 30% reduction in power consumption.
