Water Online

September 2015

Water Online the Magazine gives Water & Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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prone to fouling are clearly desirable. While sewage levels are monitored quite widely using non-contact methods, non-contact velocity measurement is also now available using products such as the Raven-Eye and the LaserFlow. Both user Doppler methods — the former based on radar and the latter on lasers. These afford the opportunity to better understand what is going on in a sewer and distinguish, for example, level increases due to blockages and genu- ine high-flow storm events, both of which might lead to flooding but require different responses. The Future In-Sewer In-sewer flow measurement can also help manage loads going into treatment processes. WRc, an independent public limited company that provides water/wastewater research and consultancy, has recently been investigating the opportunity for smarter auto-desludging of primary settlement tanks. Desludging may be initiated by in-sewer meters warning of an incoming high load, thus creating headroom to deal with the first foul flush from a storm event and avoiding excess solids being carried through into second-stage treatment. The Manning Formula (or derivatives) has long been used to estimate flow-rate based solely on a single level reading, though some of its assumptions and limitations mean that it is usually only an estimate at best. However, at the International Flow Measurement Conference held this July at Warwick University in Coventry, England, Laurent Solliec of Nivus presented an improved method using two-level sensors. This new approach can overcome some of the difficulties with traditional slope-area methods, such as coping with backwater. Tests in a sewer in Germany have been promising. Two-level sensors could provide a relatively easy-to-install and low-cost method for sewer flow monitoring. The non-contact area-velocity meters are causing considerable interest for use on treatment works inflows and outflows, particularly now that independent testing by WRc under the Environment Agency's Monitoring Certification Scheme (MCERTS) has shown such approaches as being capable of producing data of the quality required by the regulator. LaserFlow and Raven-Eye are opening up the market for such devices, but, like all innovations, their work raises new questions. One key aspect that is being debated is the in situ calibration and verification of these devices. Under MCERTS, users are required to have ongoing confidence in the operation of their effluent flow meters, including measurement validation. Systems are also subjected to an external inspection and in situ verification every five years by an MCERTS inspector. There are a number of methods for doing this at the moment, but recent papers have identified new and potentially more convenient methods. Tamari, et al. 1 report promising results from handheld radar, and Lüthi, et al. 2 have developed an app for a mobile phone that captures the movement of the liquid surface using the device's camera and analyses to give a measurement of flow. Emerging, there are a large number of innovations for wastewater flow measurement driven by the need for better management of wastewater flows for environmental protection and the opportunities to develop new charging methods. It is often difficult to get new technologies accepted by a conservative water industry. There are encouraging signs that the U.K. water companies are becoming much more interested in implementing innovative solutions. Independent test schemes such as MCERTS and the European Environmental Technology Verification pilot project play a significant role in establishing the capabilities of new developments, though there is still work needed to develop methods for field verification. n References 1. S. Tamari, F. Garcia, J. Arciniega-Ambrocio, A. Porter, Testing a Handheld Radar to Measure Water Velocity at the Surface of Channels. Houille Blanche (3) p. 30-36, 2014. 2. B. Lüthi, T. Phillippe, S. Peña-Haro. Mobile Device App for Small Open Channel Flow Measurement. Proceedings. 7th International Congress on Environmental Monitoring and Software: Bold Visions for Environmental Monitoring, iEMS 2014 p. 283-287. 32 wateronline.com n Water Innovations FLOWMEASUREMENT Andy Godley is a senior consultant for Flow Measurement and Metering at WRc plc. Godley has been involved with flow for more than 25 years, working across both the clean and wastewater sides of the industry for users, suppliers, and regulators. He sits on a number of British, European, and international standards committees on flow topics. About The Author Measurement Points In The Wastewater Network

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