Challenge

Bagnall was approached by Esh-Stantec to carry out part of the works required for a £4.9m refurbishment of Hexham Sewage Treatment Works. The investment by Northumbrian Water aims to ensure that the facility continues to deliver to the community and protect water quality in the River Tyne.

The project involved the decommissioning of two redundant filters and installation of two complete new 28m-diameter bio-filter structures and media including the supply and install of all components.

Solution

Bagnall commenced work on site in late September 2023, and the first task was to remove the existing distributor arms followed by removal of 2,200m³ of filter media from the redundant filters. The media was then processed through its purpose-built mobile wash plant to remove sewage waste from the media, making it suitable for disposal off-site under an appropriate EWC.

Once both filters were empty the filter walls were demolished and material pulverised; the resulting material was then sent off-site to ESH’s recycling facility at Tursdale. This process was carried out taking care not to damage the existing filter base as this was to be retained for the new structure to be built upon, subject to assessment by ESH’s engineers.

Next step was erection of the PCC filter walls and casting of the concrete ring beam to secure. When both filter structures were complete, Bagnall installed PCC filter tiles and the ventilation system to allow sufficient air circulation and drainage to support the necessary biological activity to enable the filter to operate efficiently. The final step was the installation of blast furnace slag filter media conforming to BS 1438:2004. Prior to installation, the BFS filter media was washed using Bagnall’s specially-designed plant to remove any fines and debris, ensuring a longer lifespan for the media (assuming correct maintenance is undertaken). The media was then placed into the beds taking care not to cause any further fines through movement, and finally levelled off taking care not to compact, which would reduce efficiency.

During the washing process of the old filter media for recycling, and of the new media prior to placing into the beds, the wash water was returned through Bagnall’s clarifier tanks supplied as part of the package, to settle out fines etc before returning the wash water to the head of works, to avoid overloading the PST’s with sediment.

Result

The contract was completed during the first week in December, well within programme and to the client’s satisfaction