A matter of manganese 05 February 2019

Filtering out the naturally-occurring mineral from potable water in the North East is a new 37.3Mld pressure filtration plant

Anglian Water officially opened a £6 million water treatment plant in Hartlepool, County Durham, in December. The unusual above-ground plant filters out trace minerals found in pumped borehole water destined for the city’s drinking water supply. It is part of a £9 million package of water supply infrastructure investments made by the utility over the last five years.

Since the early days of the city’s history in the mid-nineteeth century, residents have drawn drinking water from wells. In the 1950s, when demand increased, supply moved away from the town centre to inland suburb Dalton Piercy, where a water treatment plant was built.

Before 2014, treatment consisted only of chlorination with plumbosolvency control to prevent the compound from dissolving lead pipes and seals. This relatively small-scale treatment process is credited to the high quality of the water, which is drawn from the local magnesian limestone aquifer.

But out of a desire to increase the resilience of the system, and the flexibility of the treatment process, Anglian Water embarked on an infrastructure programme, building first a UV (ultraviolet light) disinfection plant with storage bypass, and new pumping station. Next came another pumping station, to provide up to 82l/s of water to customers in the western suburb of Wynyard, and a new 5km (3.3 mile) pipeline to deliver it there.

The latest addition is the filtration plant, which was fully operational in April 2018. Its purpose is to remove turbidity from the borehole water, in particular due to the naturally-occurring manganese, to allow effective disinfection.

Strategic operations manager Kevin Ensell offers an overview of the entire filtration process, which is driven by the delivery pressure from the groundwater borehole pumps. With the pressure filters, the driving pressure is not broken through a traditional gravity filter, removing the requirement for additional interstage pumping.

In the filtration process, water from the off-site wellfield receives a pre-filtration dose of chlorine using hypochlorite. It then passes through the filters, then the UV disinfection plant, and then treated with chlorine and phosphoric acid for plumbosolvency, and then into storage. Although most supplies are gravity-fed direct to customers from there, high-lift pumps also supply Wynyard and off-site storage.

By using a pressure filter-based process, plant and equipment were able to all been installed above ground; that option helped reduce the footprint required, as available space on site was extremely limited. The construction method meant that most of the materials could be fabricated in modules offsite, delivered in packages, and then connected into assemblies on site.

Principal assets include steel pressure filter vessels with internal filtration media, steel washwater settlement tanks and chemical dosing equipment, as well as obligatory pumps, pipework and control equipment to feed them. Filter media is 16/30 sand (0.4-0.8mm grain diameter) with 5% manganese dioxide. The site has 10 filters working in parallel to achieve peak plant flow of 37.3Ml/d. The plant is the largest pressure filter plant installed by Anglian Water.

Although the investment has been made with an eye to the future, it isn’t stopping here. According to Ensell, Hartlepool Water’s five-year plan from 2020 will plan another £22 million of investments, including £1 million for increasing the resilience of the connection between the site and the storage tank in nearby Throston. Anglian Water says this will reduce the risk of supply interruptions to the northern part of Hartlepool.

Will Dalrymple

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