Water & Wastewater Treatment

18 | october 2014 | WWt | www.wwtonline.co.uk top: chris Hastings, opera- tions manager of GtM JV, at the site. below: the works were constructed in a way that met challenging carbon use targets set by Anglian Water Project focus: Water treatment duced under factory conditions, the panels have been carefully engineered to use less rebar and concrete than would be normal on a structure of this size. "This is the largest structure that we've done using this method. But we're discussing using it on a much bigger scale on another project for Anglian Water," says Hastings. The treatment works is expected to start supplying water to the local "The depth and the profile of the reservoir was optimised using computer fluid dynamics to reduce the risk of algal blooms developing. [The profile] is designed to ensure that the water mixes well, maximising dilution of contaminants," Bell explains. Focus on energy efficiency is apparent in every part of Hall. For example, water from the reservoir flows under gravity to the treatment plant, removing the need for pumps. And the filter screens at the intake from the River Trent are passive rather than mechanical. "[the screens] require minimal maintenance and very little energy to run them, apart from periodic air blasting," says Bell. Instead of specifying ductile pipes throughout the project, as would tra- ditionally be expected, the contractor has installed medium duty polyeth- ylene (MDPE) pipes in areas of low water pressure. "As MDPE has a smoother surface, it is more efficient for pumping," says Hastings. Even the most mundane elements, such as the foundations, have been rethought and reinvented to meet Anglian Water's stringent carbon targets. Instead of being supported on piles, the 19m x 30m structure rests on a base formed from locally-sourced secondary aggregates. "This was less than half the cost of piling and has zero embodied carbon, so it was a big win all round," says Hastings. He adds that the slab's design varies according to the weight it must bear. Under heavy tanks the slab is 600mm thick. Elsewhere, a depth of only 200m is required. Modular construction techniques have also been used to construct the 40m x 40m reservoir tank which holds the treated water before it is piped to consumers. Here, a series of 3m x 5m prefabricated reinforced panels, manufactured in Ireland by Carlow Precast, before being shipped to site, were jacked into place and stitched together with concrete pours. "It's a system not widely used in water retaining structures. I was sceptical about it to start with, but I'm now a convert," says Hastings. He adds that taking this modular approach saved a significant amount of time. Construction was completed in less than four months, in one of the wettest winters in living memory. The method also helps to ensure quality and efficient use of materials. Pro- population in September, easily beat- ing Ofwat's regulatory opening target of March 2015. "Ofwat have been to visit us several times. They are particularly interested in the process that has been developed here," says Hastings. "We've also had a lot of interest from other water companies, both in the UK and further afield. Helsinki Water is visiting us next week." For more info go to wwtonline.co.uk "We did a lot of investigation work to enable us to pick the site which had the right geological features" chris Hastings, operations manager, GtM JV • Perspectives chris Hastings, operations Manager, GtM JV "This is a mature joint venture and it works very well. Our goals and aspirations are aligned, and our good relationship with the client helps to speed up the decision making process." Dr Stewart bell, technical Manager, Imtech "Hall WTW has been a great team effort. Close collaboration has helped us find some solutions to some big challenges. On a personal level, Hall has been a great project." involved with because it is so different from conventional water treatment projects. It has been a fantastic learning opportunity."

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