OCU Group

Harpenden WwTW

Purestream LS15 lamella settlement tanks at Harpenden WwTW

Purestream Process Solutions – an OCU Group company, delivered a temporary wastewater treatment solution at Harpenden Wastewater Treatment Works to enable the replacement of permanent process assets while maintaining continuous treatment performance. Designed for an initial operational period of 12 months, with the flexibility to remain in service for up to four years if required, the temporary plant supports Thames Water’s long-term investment programme, enabling future growth and enhanced treatment standards while helping to maintain resilient wastewater services for the customers and communities served by the network.

The installation represents one of the UK’s largest temporary wastewater treatment systems of its kind, providing full primary settlement, biological treatment and secondary clarification. The project demonstrates OCU’s capability to design, integrate and deliver complex temporary process solutions in support of major infrastructure programmes.

Developing an integrated temporary treatment solution

Delivering temporary treatment within a live operational wastewater treatment works required a solution capable of maintaining full effluent consent standards while integrating with existing upstream and downstream processes.

Working in partnership with Kier Infrastructure and Thames Water, OCU’s Purestream team developed a temporary treatment system that balanced process performance with the practical constraints of a live operational site. The plant layout was carefully designed to maximise the available footprint while maintaining safe access for both operational and construction activities throughout the upgrade programme.

Hydraulic compatibility with the existing treatment process was a key consideration, ensuring the temporary system could operate reliably alongside ongoing construction without compromising treatment performance.

Process design & installation

OCU teams delivered the complete mechanical, electrical and process installation, integrating the temporary treatment system with the existing site infrastructure.

The solution consisted of eight LS15 lamella settlement tanks providing primary solids separation, together with four Moving Bed Biological Reactors (MBBRs) configured across four treatment streams to provide the required biological treatment capacity.

Purestream LS15 lamella settlement tanks

The temporary treatment system was designed to treat a guaranteed flow of 60 litres per second, while maintaining full effluent consent compliance. During commissioning, the plant successfully processed incoming flows of approximately 78 litres per second, demonstrating both the robustness of the process design and the operational flexibility of the temporary solution.

Maintaining operational performance

Maintaining uninterrupted wastewater treatment throughout the replacement of permanent assets was fundamental to the success of the project. Through detailed planning, collaborative working and phased installation, the team successfully integrated the temporary plant into the live treatment process while maintaining continuous operational performance.

The temporary treatment system was delivered within the client’s programme and budget, enabling permanent assets to be taken offline without interrupting treatment or affecting compliance. This provided Thames Water with the operational resilience needed to progress the wider upgrade while maintaining essential services for customers.

Supporting long-term infrastructure investment

As investment across the UK’s wastewater network continues to accelerate, temporary treatment solutions are becoming an increasingly important enabler of infrastructure renewal.

Projects such as Harpenden demonstrate how integrated process engineering, mechanical and electrical installation, and collaborative delivery can maintain environmental compliance while allowing critical assets to be modernised.

Harpenden highlights OCU’s ability to combine process engineering, mechanical and electrical installation, and collaborative project delivery to develop practical solutions for complex operational environments.

By delivering reliable temporary treatment systems that maintain performance throughout construction, OCU’s Purestream team continues to support clients in upgrading essential wastewater infrastructure, protecting the environment, maintaining services for the communities they serve and preparing networks for future demand.

For More Information, contact us at https://www.ocugroup.com