Water and Effluent Treatment Magazine
Issue link: https://fhpublishing.uberflip.com/i/755145
10 WET NEWS DECEMBER 2016 ONSITE WatER tREatMEnt the tank roof was removed to enable the existing plant to be taken out by overhead crane and the new lamellas to be lifted into place Team effort saves time • How has innovation and collaboration knocked weeks off of timescales on Severn trent's Little Eaton WtW upgraded? projEcT SpEcS • Upgrade Little Eaton Water treatment Works • Remove legacy tube-type lamella plant and pipework, and clean the tanks • Install 16 Lamella Plate Pack Separators and four Zickert Reciprocating Sludge Scrapers S evern Trent Water's £2.4M upgrade to its Little Eaton Water Treatment Works (WTW) has been completed, helping to ensure high-quality drinking water provision for the Derbyshire area in a project that required technology and teamwork to overcome significant project challenges. An innovative approach and a close collaboration between Severn Trent, the design and build contractor MWH Treatment and Hydro International dramatically reduced project timescales by more than six weeks and achieved significant construction, equipment and operating cost savings. Located north-west of Derby, Little Eaton WTW treats raw water from the River Derwent to supply the strategic grid with between 70mld and 90mld. Improvements to the clarification stage at the works were needed to increase the design capacity to 120mld and replace life-expired plant that was presenting an increasing maintenance burden. At the same time, Severn Trent had to meet stringent Drinking Water Inspectorate (DWI) standards for cryptosporidium content in the treated water. In a contract worth £1M, Hydro International provided 16 specially modified Lamella Plate Pack Separators and four Zickert Reciprocating Sludge Scrapers to deliver the solids separation and removal required. Both the Lamella Plate Separators and Zickert Sludge Scrapers are suitable for use with drinking water – the lamellas have full regulation 31.4(a) approval, and the Zickert scrapers have regulation 31.4(b) approval via WRAS (Water Regulations Advisory Scheme) approved materials or dedicated BS6920 testing. "The project's first major challenge was to achieve the increased capacity within the plant's existing reinforced concrete tank structures," says Severn Trent programme engineer Stephen James. "The river turbidity at the inlet of the treatment works is usually under 5NTU, but it can go as high as 50NTU during heavy rainfall. With such a broad range of turbidity, lamellas were considered a favoured technology. However, other clarification technologies were also seriously considered. "We approached Hydro International and they came up with an innovative scheme to modify the Lamella plates to ensure increase separation capacity that could be incorporated within the same footprint." Footprint challenge Hydro developed new manufac- turing and production tech- niques to increase the length of the lamella plates to 3m, extend- ing the conventional design by half a metre, and thereby increasing the total projected settling surface area to 1,856m 2 . to accommodate the extra length and weight of the plates, Hydro made modifications to the lamella framework the longer lamella plates offer the advantage of a greater settling surface within the same footprint