Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | FEBRUARY 2015 | 17 Hippokrates Pappas, director at Metri- ca. "They were interested in in having a real-time monitoring network, with alarms for unusually low or high flow that would help them react quickly to any problems that develop. Another important aspect is that although they do have a separate network for waste- water and surface run-off water, they wanted a clearer idea of the proportion of run-off water that actually ends up in the sewers." Detectronic's flow and velocity meters were identified as suitable for the job. EYDAP's preference was for the monitors not to be in contact with the sewage flow, to eliminate the need for frequent cleaning; this require- ment meant that Detectronic's MSFM Lite, a non-contact monitoring system consisting of an ultrasonic sensor and a GSM/GPRS data logger, was chosen. Installation solution However, their installation presented a number of unique challenges. To en- sure the best and most useful readings, the sensors had to be installed in the main section of the pipes, away from intersections and access chambers. But EYDAP did not want contractors to access these points from within the sewer, for both health and safety reasons and for ease of maintenance aŒerwards. The solution was to dig down to the required locations and drill into the top of the pipes; the sensors could then be inserted in such a way that they can be brought in and out through a shaŒ, Pappas explains. "The engineered solution means we are a suitable distance from the tur- bulent flows and therefore measuring laminar flow patterns. AŒer excavating and digging down to the sewer pipe, the engineers drill into the crown of the pipe using a 200mm core-drill. They then insert a vertical shaŒ and feed the sensor, which is fixed on a special bracket." The sensor, and the accuracy of its readings, is protected from contact with the sewage even in flood condi- tions because of the unique mount- ing arrangement of the sensor, he continues. "The ultrasonic sensor is fitted in- side an IP68 barrel-type housing that, if the water level reaches the sensor, will retract via buoyancy to protect the electronics." Meanwhile, the data logging unit is permanently installed at ground level in a compartment beneath a manhole. Special antennae with the ability to withstand more than two tonnes • Perspectives Dave Walker, Detectronic: "This was a challenging project but the results so far look very accurate and consistent. The relation- ship with Metrica has worked very well – they have skilful engineers and when it came to under- standing the application and the solutions, we have found that we speak the same language." Hippokrates Pappas, Metrica: "Detectronic were able to support us with ideas and brainstorming solutions and their experience was very valuable. This was a real example of teamwork- ing, not just having the right instrumentation but having the right people and the right expertise to integrate it all together." Above: Following excavation, a 200mm core drill was used to drill a hole in the crown of each sewage pipe Below le : The data logger was inserted in a compart- ment at street level: Bottom right: The unusual bonnet-shaped design of some of the sewers meant that the calculations to work out the flow rate were unusu- ally complicated • Innovations ● To overcome the chal- lenge of not being able to enter the sewers to install the monitors, an excavation method was developed, drilling into the crown of each pipe and installing a sha for maintenance access ● The sensor was fitted in barrel housing that would re- tract with buoyancy if the wa- ter level reaches the sensor, protecting the electronics ● Unusual egg-shaped and bonnet-shaped pipes meant extra calculations needed to be built into so ware to effectively calculate flow

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