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Keeping maintenance and disruption to a minimum was a priority when it came to replacing an outdated sewage treatment plant in the picturesque Yorkshire village of Letwell. The existing works in the historic village near Rotherham, which has a population of just 107, was a trickling filter which had come to the end of its life.
The utility for the region, Severn Trent Water (STW), required a plant that would treat effluent to a high standard. The environmental consent a minimum of 60mg/l suspended solids and 40mg/l biochemical oxygen demand.
Initially a rotating batch contactor (RBC) was considered, but the need for extensive excavation and concreting to install an RBC meant the idea was dropped. Contractor NMC Nomenca was determined to meet the client’s requirement that onsite civils work was kept to a minimum.
Instead NMC Nomenca opted for a High Performance Aerated Filter (HiPAF) plant.
Usually the packaged HiPAF (SAF biozone) midi, which can service a population up to 250 people, is manufactured from glass-reinforced plastic and fitted below the ground. On this occasion the plant did not need to receive gravity flows so there was no need for a below-ground solution, allowing installation and maintenance to be more straightforward.
The contractor requested an equivalent HiPAF plant in steel for above-surface installation. The tank was finished with a green coating to ensure its presence was weather protected and as discreet as possible for the rural setting. A fitted staircase was included to allow for easy top-level sampling and maintenance.
A large walk-in kiosk housing duty/standby blowers, blower manifold, framework supplier’s control panel, telemetry, solonoids and lighting was also built.
In order to keep the time spent onsite to a minimum, the plant was manufactured off-site at a purpose-built facility in Hampshire.
Technical Director Andrew Baird said: “We pride ourselves in manufacturing package treatment plants designed to meet our clients’ needs. It was important for Severn Trent Water and the people of Letwell to have a treatment works which could be installed with the least possible disruption and built in harmony with the natural environment.”
Like all HiPAF plants, the custom model has no interior moving parts and is designed so sludge can be safely and quickly removed. The duty/stand-by blowers selected by the client will increase energy efficiency and make it more economical to run. The HiPAF plant has a minimum life expectancy of 25 years.
Mr Baird said: “UK water utilities are now being asked to consider combined operational and capital investment. The new onsite treatment works at Letwell is a great example of how investing in a custom-built plant can improve whole-life cost by factoring in the cost of full installation, maintenance and servicing from the outset.”
John Tidy, Project Manager for NMCNomenca said: “To ensure swift installation it was important that onsite mechanical and electrical work was kept to a minimum. The bespoke design and factory-build meant that onsite installation of the HiPAF Midi only took two days.
“The use of steel and a green coating made above-ground installation possible, meeting the expectations of the client and minimising disruption for the villagers.”