Articles & Case Studies

Flygt pumps keep United Utilities’WarringtonNorth Sewage Treatment Works flowing

Posted: Friday 7th November 2008

Serving a population equivalent of more than 310,000, United Utilities’ Warrington North Sewage Treatment Works is known for its innovative solutions including the handling of primary sludge.

The primary sludge from the sedimentation tanks is drawn off at between 4 and 6% total dry solids; this high level of solids is achieved by the incorporation of picket fence thickeners within the primary desludging tanks. The primary sludge is held in two storage tanks where imported sludge of a similar thickness is introduced from smaller treatment works in the area. From the holding tanks, the sludge needs to be pumped to two sludge screen strain presses to extract the high level of rag; this is prior to digestion. As the site was continually let down by the failure of its existing screw impeller primary sludge transfer pumps, United Utilities called onITTWater & Wastewater, the global market leader in water and wastewater treatment technology, who suggested the trusted ability of the Flygt N-Pump as a solution.

As the pumps are located in a 7m deep pump chamber adjacent to the sludge holding tanks which is prone to flooding, IP 68 pumps were required to ensure continued trouble free operation. With the original pumps requring daily unblocking it was imperative that the site owners were provided with a solution they could rely upon.

As the pumps have to deliver a flow rate of not greater than 25ls-1 against a variable head, dependent upon the sludge level within the sludge holding tanks and the sludge thickness, two Flygt NT3153 dry well submersible pumps were selected following initial visits and assessments by theITTWater & Wastewater team.

ITTWater & Wastewater’s Flyps selection program sludge module was used for the selection of these pumps as it de-rates pump curves according to sludge thickness and applies the coefficients within TR185 for calculating losses through pipes and fittings.

As part ofITTWater & Wastewater’s commitment to providing the correct solution, it offered the Flygt pumps on a two month trial. The installation was undertaken by a contractor appointed by United Utilities and the pumps set to work in June 2007. Since installation there has been really positive feedback from the operations staff especially as the site is particularly ‘raggy’.

As the team at United Utilities has found, one of the major benefits of using the Flygt N-impeller when pumping sludge is the reduced incidence of blockage. On theWarringtonNorth site the United Utilities’ operations team is saving approximately 32 man hours a week purely in labour. As there are no digester disruptions, cost savings also come from the now undisrupted process.

Tony Price, Market Manager – Sludge & Wastewater forITTWater & Wastewater, comments on the success of the Flygt N-Pump: “The Flygt N-Pump is capable of handling municipal sludge of up to 8% total dry solids and is therefore suitable for around 75% of treatment works pumping applications. Armed with this knowledge, water companies should consider the cost savings of using a Flygt N-Pump compared to a positive displacement pump.”

Chris Connor, Process Controller for United Utilities comments on the improved efficiency and cost savings since the installation of the Flygt N-Pumps: “We are really impressed with the reduction in blockages and resulting increase in efficiency and decrease in costs which the Flygt N-Pump has brought to our Warrington North site. TheITTWater & Wastewater team have been invaluable in providing a solution to deal with our individual site needs including the heavy sludge and high rag content at the works.”

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