Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | AUGUST 2018 | 23 available at any one plant will depend on the raw water quality and how operators make use of the system; however, the project showed the value of the system both in optimising chemical use and reducing water quality risks, according to Sharp. "It allows us to operate within a really tight operational window, and make really small changes on a frequent basis, which we wouldn't be able to do if we were relying on more discrete sampling," she says. Following the successful collaboration, the Online Zetasizer WT is now a commercially available product from Malvern Panalytical with installations in place worldwide. "Developing new solutions in close collaboration with end-users and industry experts from Severn Trent has been highly bene† cial for both parties," Alon Vaisman, head of sensors & automation solutions at Malvern Panalytical, says. "It has enabled our teams to explore and better understand the application challenges in order to develop and validate appropriate methodologies. This valuable insight has resulted in a product that delivers proven value and has real potential to change the way the water treatment industry controls coagulation. Zetasizer WT is an automated platform that provides the accuracy and precision of our laboratory zeta potential analyzers in an on-line setting. This gives the water plant operator more con† dence to make dosing decisions and paves the path to a fully automated dosing process." Severn Trent is hosting an event for the water industry in Coventry on 4 October to share its learning from the Online Zetasizer project with professionals from other water companies. To register, visit https://tinyurl. com/y9d5vsuv or contact emma.sharp@ severntrent.co.uk • Zeta potential is a measure of the surface electrical charge of particles in a fl uid; in raw water, this is typically negative (-25 mV to -15 mV) meaning that particles repel one another rather than coagulating • Adding coagulants neutralises this negative charge, moving zeta potential towards zero and ultimately into the positive range. Optimised coagulation using charge neutralisation is typically seen at zeta potentials from -8 mV to +3 mV with particle re-stabilization occurring above +5 mV • Controlling coagulant dosing, either manually or automatically, involves choosing a desired set point for the zeta potential (typically in the region of -5mV to 0mV) and then choosing the right amount of coagulant to reach this fi gure • Continuously measuring the zeta potential of water following coagulant dosing is desirable because it can indicate whether more or less coagulant is required, enables a timely response to water quality changes and allows predictive, rather than reactive, control Š COAGULATION AND ZETA POTENTIAL "It allows us to operate within a really tight operational window, and make really small changes on a frequent basis, which we wouldn't be able to do if we were relying on more discrete sampling," she says. Following the successful collaboration, the Online Zetasizer WT is now a commercially available product from Malvern Panalytical with installations in place worldwide. close collaboration with end-users and industry experts from Severn Trent has been highly bene† cial for both parties," Alon Vaisman, head • Zeta potential is a measure of the surface electrical charge of particles in a fl uid; in raw water, this is typically negative (-25 mV to -15 mV) meaning that particles repel one another rather than coagulating • Adding coagulants neutralises this negative charge, moving zeta potential towards zero and ultimately into the positive range. Optimised coagulation using charge neutralisation is typically seen at zeta Š further development of a fully automated control system to optimise the dose will remove this reliance. The ability to trend data and to con† gure alarms and noti† cations means that operational sta‹ can concentrate on troubleshooting and preventing problems before they occur, while the ability to access the system remotely means that guidance can be sought from colleagues who are not on site at the time. "The Online Zetasizer really brings clarity to our coagulation and clari† cation processes: it means we are applying theory, and using data, to determine how we treat the water," Sharp says. "Where maybe in the past you might have relied on operator knowledge and experience, and on understanding all the di‹ erent scenarios, now we are improving on that with the online zetasizer by bringing in clear rules, guidelines and logic." As operational sta‹ gained con† dence in the online Zetasizer, it was clear that they were able to make signi† cant savings in the use of coagulants. For example, at Tittesworth WTW there was a 20 per cent reduction in coagulant use over a three-month period. The potential savings The Online Zetasizer WT is now on the market as a commercial product The Online Zetasizer won Severn Trent and Malvern Panalytical the Most Innovative Use of Existing Technology Award at the Water Industry Awards 2018