WET News

TECHKNOW • Two 13.6m x 6m Zickert scrapers are installed at the bottom of each tank • The Zickert design was modified to ensure the hydraulic rams were positioned vertically above the water level • Water is gravity fed through the lamellas to separate out the solids NEED TO KNOW 1 The Lamella Plate Separators and Zickert Sludge Scrapers are suitable for use with drinking wate 2 The river turbidity at the inlet of the treatment works can go as high as 50NTU during heavy rainfall 3 Using a conventional lamella design would have meant extending the existing tanks THE VERDICT "The project was completed on time and within budget overcoming some significant difficulties" Stephen James, Severn Trent Water Paul Barter, principal process engineer for Hydro Interna- tional, says: "The longer plates offer the advantage of a greater settling surface within the same footprint. A longer plate-to- width ratio also improves the clarification performance because there is more laminar flow between the plates, mean- ing smaller particles are able to settle. "Extending lamella plates to 3m is very unusual indeed, and a first for the UK. As part of the project we secured Regulation 31 approval for the design, which is a significant advance on the only other installation in the world that we're aware of, which was in the US more than 15 years ago." Without the new design, to achieve the additional 30mld output with a conventional lamella design would have meant extending the existing tanks. With consequent civil engineering costs and time implications that would have DECEMBER 2016 WET NEWS 11 Malvern, Worcs WR14 1JJ, UK Tel: +44 (0) 1684 891 371 info@pulsar-pm.com www.pulsar-pm.com SLUDGE INTERFACE DETECTION Sludge Finder 2 reliably measures primary, secondary and tertiary interface levels in treatment and process applications. l Remote monitoring – no need for site visit l Gives tank profile, status and blanket level in up to two tanks simultaneously l Self cleaning and maintenance free l 4-20mA with optional radio modem and RS485 been very difficult to accommo- date within the project deadlines. Stephen James adds: "Extending the tanks would have been challenging and we also looked at incorporating other clarification methods in the footprint such as a micro- sand process. Neither option was feasible on a cost-benefit basis; operating costs would also have been significantly higher than a lamella plate setup." Completing the works within the required timescales to meet DWI consent deadlines was a critical target. The MWH team worked with Hydro's team, con- quering the first challenge by removing the legacy tube-type lamella plant and pipework then cleaning the tanks of residual sludge. Timescales Kelvin Smith, project manager for MWH, says: "To achieve the project timescales, we came up with a solution to remove the roof from the existing tank structure. Although this entailed some risk of weather-related delays, it enabled us to remove the existing plant by overhead crane and then build the lamellas onsite in sight of the crane pad, before li™ing them into place. "With good collaboration, the solution knocked ten weeks off the programme, reducing the initial timescales by more than half. "Hydro International were very helpful in supporting this plan by making the required modifications to the lamella and Zickert designs to enable a quick and smooth installation. Their team also attended onsite to optimise the clarification process to ensure successful commissioning." Assembly of lamella plate packs entails sliding each plate into a framework. At Little Eaton, the uniquely long plates made it even more cost-effective to deliver the lamella packs 'flat packed', saving on transportation costs, and assemble them onsite. To accommodate the extra length and weight of the plates, Hydro also made modifications to the lamella framework including fabricating a guiding V-notch frame in the bottom beam to reduce the sliding force. This made it quicker and easier to assemble the plates smoothly onsite. The Hydro team also modified the Zickert Sludge Scraper design for potable water application, ensuring the hydraulic rams were positioned vertically above the water level to avoid any risk of contamination, using a pivot joint to transfer the motion smoothly to the horizontal scrapers on the tank bottom. Further design modifications were made to enable an additional walkway to be constructed between each tank allowing better access for clean down and maintenance. At Little Eaton, the raw inlet water is dosed with ferric sulphate and polyacrylamide for flocculation and coagulation of suspended solids. The water is then gravity fed through the lamellas to separate out the solids. Two 13.6m x 6m Zickert scrapers are installed at the bottom of each tank to provide transportation and collection of the settled sludge. The sludge is transferred to the outlet with minimal disturbance thanks to the reciprocating action of Zickert, then pumped to a sludge thickener for onward treatment and disposal. Meanwhile, the clarified water is passed through rapid gravity filters, granular activated carbon, then through a contact tank for chlorination before being held in service reservoirs before distribution to the grid. Close teamwork and collaboration between Severn Trent, MWH and the Hydro project and site services teams resulted in successful outcome from a challenging set of circumstances. The solution optimised the clarification process within the existing footprint, with a best value operating cost outcome. The modified lamella and Zickert equipment also offered a low maintenance, totex-friendly solution. Installation and com- missioning of both tanks was completed well within project timeframes. The project met regulatory deadlines three months ahead of time with the first tank gaining "plant in use" status on December 22, 2015. Stephen James concludes: "Hydro International were very happy to engage with us, listen to our ideas and support the development of the design and construction solution. "The project was completed on time and within budget overcoming some significant difficulties. Good teamwork and dedication between MWH, Hydro International and ourselves was critical to the project outcome." The lamellas were built onsite The tanks were cleaned of residual sludged Design modifications were made during the project Each plate is slid into a framework

• Cover