Posted by Callum Vallance-Poole, on September 24, 2024.
The National Trust for Scotland’s Threave Garden and Estate in Dumfries and Galloway recently upgraded its sewage treatment system with the help of GRAF UK. The new installation is designed to protect the water environment and reduce the carbon footprint of this iconic site.
After more than twenty years, the existing sewage system at Threave Garden needed replacement. Moir Environmental, a sustainable drainage design specialist and long-time collaborator with the National Trust for Scotland, was tasked with designing a modern solution. With extensive experience working with GRAF UK, Moir Environmental selected their 250-person SBR (Sequence Batch Reactor) system, featuring a large primary settlement tank and two smaller SBR tanks.
The new OneAdvanced system from GRAF UK is one of Moir Environmental’s largest projects. The system directs wastewater to a pumping station and then to a new vertical-flow sand-media reed bed. This setup ensures the final effluent is of exceptional quality, clear, and has minimal environmental impact.
Stewart Moir, Managing Director of Moir Environmental, highlighted several advantages of the GRAF UK system:
- Reduced tankering costs and fewer tanker movements, resulting in a smaller CO2 footprint.
- Simple design with no internal electrical or mechanical components, making future repairs easier and cheaper.
- Capacity to handle varying visitor loads effectively, thanks to the SBR process.
The installation serves the Terrace Café and visitors centre uphill and the Stables Café and toilets downhill, requiring a pumping station to transport sewage. The sewage treatment SBR tanks use fine bubble diffusers and air lift pumps to manage sewage and effluent efficiently.
Initially scheduled for March 2020, the COVID lockdown delayed the project and began over a year later. RH Irving Construction, chosen through a tender process, managed the installation despite challenges such as rocky ground and reusing cleaned gravel from former reed beds. Their team, equipped with heavy machinery, completed the excavation and installation within two months.
John Birkett, Director at RH Irving, praised the GRAF UK sewage treatment system for its reliability and the support from their local representative, Lisa Rossi. Despite its complexities, he noted that the project was successfully completed with timely delivery and installation of the tanks.
Stewart Moir added that the client was delighted and made plans to enhance the project area with wildflower sowing.
Dr Samuel Gallacher, NTS Operations Manager, emphasised the project’s importance in providing critical infrastructure to support the growing visitor numbers at Threave. As a conservation charity, the National Trust for Scotland aims to operate sustainably, and this project exemplifies their commitment.