Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | ocTober 2014 | 17 An overhead view of the works. Treat- ment processes used include GAc roughing filters, submerged mem- branes and UV disinfection Project focus: Water treatment required to run the plant, can be attributed to the joint venture's close working relationship with Anglian Water. Anglian set tough targets of reduc- ing embodied carbon within the facil- ity by 50% and operational carbon by 20% against a benchmark measure. By the latest project calculations, embodied carbon has been reduced by 63% and GTM JV believes that the facility is on track to meet its opera- tional carbon targets. Other goals included sending zero toxic waste to landfill. Hastings says that the targets required "a huge mindset change" and had a strong influence on the design and the location of many of the features of the new facility. Hall WTW consists of three main sites linked by several kilometres of pipes: a pumping station by the Trent, a raw water reservoir and treatment plant. The fastest and cheapest option would have been to place the treat- ment plant next to the existing plant in Newton-on-Trent. But because the surrounding land is vulnerable to flooding, Anglian Water has taken the more resilient option of locating the new facility almost at the top of a hill, where the flooding risk is around one in 1,000 years. The pumping station by the Trent is similarly protected, set back on a steep embankment roughly 60m from the river. Water flows through an in- take tunnel into a 12m wet well sha", from where it is pumped through 800mm diameter pipes up into the reservoir. Unusually in this age of concrete, the reservoir is a clay-lined earthwork structure. Its location has been carefully selected. "We did a lot of investigation work to enable us to pick the site which had the right geological features," says Hastings. The site, separated from the treatment works by a road, consisted of ground that did not need to be extensively treated, avoiding the need to import or export material. "It wasn't the easiest ground to work with, but it was the most suitable in the area," says Hastings. "Being able to cut and fill using on- site material saved a lot of vehicle movements." Excavators were linked to GPS systems to ensure that the profile was cut with precision. This was important because the reservoir, which has up to ten days of storage, is considered to be an integral part of the water treatment process. • Innovation "Our multi barrier treat- ment solution deviates significantly from more conventional surface water treatment flow sheets. We believe this combination of processes and technologies is a UK - if not world – first," says Imtech's Dr Stewart Bell. Processes include: submerged membranes; ultraviolet peroxide oxida- tion and granular activated carbon (GAC) polishing filters. Ultraviolet disinfec- tion is replacing the more usual super chlorination process. GAC roughing filters are being used, unusually, to remove sludge from the water in the early phase of treatment. The water is then allowed to settle in two large clay lagoons behind the plant. Bell explains that, be- cause this front-end phase of the process is virtually chemical free, 98 per cent of the water can be recycled back to the raw water reservoir, fitting in with Anglian Water's 'Love Every Drop' campaign to save as much water as possible. More conventionally, GAC adsorbers are also used to polish the water later in the treatment process. Most of the treatment processes at Hall are low energy, with the excep- tion of advanced oxidation which employs hydrogen peroxide dosing in conjunc- tion with UV irradiation. This has been introduced because it is capable of removing metaldehyde. "The fact that advanced oxidation avoids the forma- tion of bromate was also an important factor in its selection," says Bell. Unprecedented levels of rainfall during the construction of Hall WTW saw metaldehyde levels in the water spike from a concretration of 0.35 ug/l to a peak in winter of 2012 of over 2 ug/l. "Our studies highlighted potential problems of metaldehyde entering the water supply in adverse weather conditions," says Bell. As a result, treatment capacity was increased with the addition of a fourth UV/ peroxide reactor stream to the design. Space has been le inside the plant to increase capacity for other parts of the process, such as an extra submerged membrane, should it be needed. "This multi barrier pro- cess has produced some very encouraging results," Bell says. Water flows into the new reservoir at Hall

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