Stressholme STW is on the outskirts of Darlington, Durham and serves a PE of 100,000. A recent major refurbishment of the plant included the retrofit installation of an automated storm tank flushing system into the six existing concrete storm tanks, assigned to CSO Technik.
The scope of work included the design, manufacture and supply as well as the offloading, contract lift, installation, testing and commissioning of 12 tipping buckets and associated wash water supply pipework, actuated valves, traced heating and thermal insulation.
The tank dimensions were the following: six tanks, each 47m long x 13.5m wide x 3m deep with a 1% fall. Each tank was divided into two separate lanes of 6.5m width by a 400mm high x 600mm wide dwarf concrete dividing wall.
Description of the plant: 12 1,300l/m tipping buckets in 304 stainless steel were installed into the six tanks. The buckets were mounted on brackets attached to the side and intermediate dividing walls of the tanks. The filling system is via stainless-steel pipework, trace heated and lagged, which provides final effluent. The actuated valve opens on a signal from an ultrasonic sensor mounted within the tanks. When the bucket is full it automatically swings on its bearings as the tipping point is reached. As the bucket tips a proximity switch closes the actuated valve. The bucket automatically returns to its balance point and is set for the next storm event.
Deliveries commenced in January 2009. Installation of the buckets were carried out in three phases so that only one set of storm tanks were out of action in at any one time. The final phase of the project was completed in September 2010.
Key project partners were Northumbrian Water (client), Entec UK (consulting engineers) and Carrillion (main contractor).