Off-site aeration project completed at Thames Water's Dorking STW
Engineering services company FLI Water recently completed an innovative off-site solution for Thames Water at Dorking Sewage Treatment Works which enabled the company to replace its activated sludge plant (ASP) aeration without having to drain the entire system, saving it in excess of £400,000.
The existing ASP had a diffuser-based system that had been installed in the 1990s and required replacement. However, the challenge was that although the ASP comprised of four lanes, the lanes were all linked, acting as one tank, meaning that individual lanes could not be isolated and upgraded. Therefore a large temporary treatment system would be required while the complete ASP was drained and replaced.
However, by utilising off-site build with a lift-out aeration system, principal contractor FLI Water was able to design and build a system that enabled the grids to be fitted while the tanks remained on-line. The design included 12 separate aeration lift-out grids which were tied into the existing air blower arrangement.
Duncan Wildgoose, Business Development Director at FLI Water said: “Our solution was efficient and effective, and cost in the region of £235,000 to complete. This represents a huge saving for Thames Water as with the initial scope of works the temporary treatment alone would have cost over £300,000. In addition, as much of the project was carried out off-site we reduced our health and safety risks too.”
The project offered a number of additional challenges including low hanging power lines, which limited the lift of the cranes and inhibited access. In addition, as part of the installation was in live tanks, the project required the use of floating pontoons. FLI Water worked closely with the crane operators, UKPN and the Thames Water Operations team to ensure that all these challenges were safely and successfully overcome.
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