Water & Wastewater Treatment

Project focus: Pumps and pumping systems was the minimum impact that it would have on the environment of Mont St Michel. Design and operating requirements that KSB had to consider were the non-emission of odours and gases, variable flow demands on the pumps, potential storm conditions, discharging wastewater and effluent over a long distance, space and access constraints, absence of water storage, high performance, energy efficiency, low environmental impact and easy maintenance. "The design that we proposed involved the installation of four pumps in a 3 + 1 arrangement, with frequency inverters for speed control," reports Stéphane Quertain, Product Manager Pumping Station KSB France. "The Amarex KRT is a dedicated wastewater pump and is more than capable of handling the type of solids-laden fluids that are discharged from toilets, kitchens and other facilities used both by residents and tourists. In addition there was the safe removal of rainwater to be considered. The design of the impeller and pump housing ensure a free flow of solids-laden liquid directly to the treatment works without the need for a holding tank ahead of the pumps." A significant factor in the selection of KSB's Amarex KRT pump for the project is that it is IP68 rated for operation when fully submerged in water. The ability to comply with this requirement was a stipulation of the contract because during periods of exceptionally high tides, seawater could enter the pumping station. Each pump uses high efficiency IE3 motors and can provide flows of up to 540m³ at pressures of 10 bar. The ability to deliver on-demand pumping is of major importance for the Mont St Michel pump station as it removes the need for liquid storage and screening facilities, thereby reducing the foot print area. A further benefit of this arrangement is that odours and gases are contained in the effluent pipes and never linger in the pump station. This eliminates any unpleasantness for visitors and residents, and removes the need for maintenance personnel to work with dirty water. Variable pump speed Because of the variations in flow throughout the day and year due to visitor numbers, it makes economical sense to vary pump speeds to meet demand. Flow monitors positioned in the inflow pipes measure the incoming flow, and when a set level is reached the frequency flow controller activates the required number of pumps and the speed at which they need to run. By equipping all four pumps with frequency flow control, the pump speed of each pump is matched to the incoming flow so power consumption is optimised and greatly reduced. Savings of up to 30% can be attained over an equivalent fixed speed drive. Each pump has its own dedicated control panel with an easy to operate, touch-sensitive screen contained in robust, water-resistance cabinets. The purpose-designed so™ware program enables operators to switch the operation of all four pumps, record and interrogate historical events, monitor pump performance and provide external communications. The communications package offers double protection for service continuity and flexibility of use between peak and off-peak hours. During peak hours, electronic control ensures that pumps run in accordance with fluctuating flow rates and discharge effluent and wastewater in the same proportion. Construction of the subterranean pumping station 20 | MAY 2015 | WWT | www.wwtonline.co.uk • Innovations ● Specially designed subterranean chamber reduces visual impact of pumping station ● Impeller and pump housing design allow free flow of solids- laden liquid ● On-demand pumps react to flow rate and ensure energy efficiency ● Effluent had to be removed from the site in a safe, effective and environmentally acceptable manner ● Discreet pumping station required to preserve character of UNESCO heritage site ● System needs to cope with variable flows caused by tourist numbers across the year • Drivers The design of the Amarex KRT impeller and pump housing ensure a free flow of solids-laden liquid

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