Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | NOVEMBER 2015 | 35 In the know Digging deeper: wastewater pumps Wastewater pump blockages: in numbers ● 2.2kW The most common small pump in the wastewater network ● £700 the annual cost of energy for a 2.2kW pump ● £350 The average cost of a call-out to clear a blockage at a small pumping station ● 75mm The minimum free passage speci- fi ed by most wastewater pump buyers is the S Tube, which is pitched at achieving both high free passage and competitive e ciency – but Ball admits that no pump can claim to be the "silver bullet" if the pumping station design is not correct. The way in which the pumps are controlled is also a big factor, he adds. "Particularly for bigger size pumps, where free passage is naturally bigger anyway, the main factors are e ciency and control of the pump," says Ball. "Control at that end-of-line station is very much about supporting the process at the treatment works and making sure you are not sending too much load and ow into the works. You need to make sure that you are not starting and stopping the pump a lot, you are getting the velocities and the start and stop levels right." Another consideration is the water company's ability to respond Grundfos's S Tube pump boasts one of the more innovative impeller designs to blockages: the largest „ nes received by utilities have tended to involve inadequate responses to problems. While the occasional pump failure could be viewed as unavoidable, a company that does not have the telemetry in place to show that a pump has failed, or allows its operators to ignore alarms, is asking for trouble. Investment in communications, people and training could therefore prove to be one of the best uses of money. It's unclear whether the Totex way of thinking which is being introduced to the industry in AMP6 will have a signi„ cant e‹ ect on pump speci„ cation decisions. However, approaches vary depending on who the buyer is. While a contractor on a capital investment project is likely to take factors around whole-life cost into account when buying a pump, an operator who needs a pump urgently will always just want something that works, says Grundfos's Ball. "I think no-one's really saying what good looks like in Totex," he says. "What is a good investment decision - should we invest in bigger pumping stations, di‹ erent controls and spend £10,000, or should we just keep changing that £2000 pump every year and spend another £2000 on unblocking it?" Awareness campaigns amongst the public, to reduce the number of inappropriate items being ushed into the sewers, could be considered a Totex-friendly approach, but it is certainly not yet one which has yielded quanti„ able results. Perhaps keeping wastewater pumps blockage-free will remain a perennial challenge, but it is one that the industry has every incentive to tackle. Free passage and effi ciency fi gures compared for four of the most popular pump impeller types (source: Hidrostal) For insights and show news visit utilityweeklive.co.uk INNOVATION CONTENT STREAM: For insights and show news visit utilityweeklive.co.uk DATA & ANALYTICS CONTENT STREAM: For insights and show news visit utilityweeklive.co.uk RESILIENCE CONTENT STREAM: For insights visit utilityweeklive.co.uk CONTENT For insights visit utilityweeklive.co.uk CONTENT For insights visit utilityweeklive.co.uk CUSTOMERS CONTENT

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