Knapp Mill WTW

RSE is delivering a major modular upgrade at Knapp Mill Water Treatment Works (WTW) in Christchurch, helping Bournemouth Water and South West Water enhance drinking water quality, capacity and resilience for customers across the region.

The project forms a key part of Bournemouth Water’s wider £200 million investment programme and will provide cleaner, better-tasting and more reliable drinking water to the population across Christchurch, Ringwood, New Milton, Lymington and Beaulieu.

At the heart of the upgrade is RSE’s innovative m-CTU® solution, integrating advanced ceramic membrane technology with offsite modular construction to deliver significant programme, safety and sustainability benefits. A major advantage of the modular approach is scalability. m-CTU® units can be installed as demand increases, allowing treatment capacity to expand without the need for extensive redevelopment of the site. This flexibility ensures that the facility can adapt efficiently to future water demand.

As one of Bournemouth Water’s key treatment facilities, Knapp Mill WTW required a major £85 million upgrade to modernise its water treatment processes while minimising disruption to the surrounding community and maintaining programme certainty. The project was designed to increase treatment capacity and operational resilience, enhance water quality and sustainability performance, reduce construction activities on site, and improve both programme certainty and safety outcomes. In addition, the upgraded infrastructure needed to be future-proofed to serve customers reliably for decades to come. The scheme also demanded the efficient coordination of a complex logistics programme involving multiple stakeholders, authorities and subcontractors, alongside the rapid deployment and installation of more than 70 modular treatment units.

Knapp Mill WTW is the second Design for Manufacture and Assembly (DfMA) ceramic membrane treatment plant delivered by RSE for South West Water and Bournemouth Water, building on the success of the 84 MLD Alderney WTE in Bournemouth. Developed as a like-for-like upgrade, the project capitalised on a proven design philosophy and established delivery model, enabling greater efficiency, reduced risk and accelerated programme delivery.

A key feature of the Knapp Mill WTW project is the deployment of the same standardised ceramic membrane treatment plant successfully delivered at Alderney WTW. Rather than simply reusing individual standard products, Knapp Mill WTW demonstrates the scalability of RSE’s fully standardised treatment solution at a significantly larger capacity, highlighting the benefits of repeatable design, manufacture, assembly, and testing processes. By leveraging a proven plant design, the project has benefited from reduced engineering risk, greater programme certainty, and enhanced quality through the replication of a proven solution.

The facility incorporates RSE’s modular m-CTU® technology, integrating a ceramic membrane system with a suite of advanced treatment processes. Including high-velocity backwash systems for effective membrane cleaning, Cleaning in Place (CIP) facilities to support operational reliability, and to ensure safe and efficient process management. The result is a resilient, sustainable treatment solution designed to meet Bournemouth Water’s long-term operational needs.

Developed through focused research and development and supported by clients seeking innovative, cost-effective, and sustainable solutions, RSE’s m-CTU® system addresses specific challenges within the water sector. By integrating cutting-edge ceramic membrane technology into a modular format, the m-CTU® provides a more efficient and effective alternative to conventional water treatment systems.

The design incorporates ceramic membrane filtration and complementary wrap-around solutions to enhance bacterial barrier performance and organics removal, delivering high-quality water while shaping the future of water treatment in the UK. Ceramic membranes are a transformative technology, offering durability, reduced energy consumption, and long-term operational benefits.

To maximise quality and minimise onsite activity, all process modules were manufactured, assembled and fully tested at RSE’s facilities in Muir of Ord before being transported to site for installation.

Building on the experience gained at Alderney WTW, the project team utilised established engineering, manufacturing and installation methodologies to streamline delivery and improve certainty across all phases of the programme. The shared design platform significantly reduced development requirements, allowing resources to be focused on efficient execution and project optimisation.

Over 70 modular Transportable Treatment Units (TTU®s) were produced, assembled and tested within RSE’s controlled factory environment before being transported to site during an intensive delivery programme. This manufacturing-led approach achieves delivery at approximately twice the speed of conventional construction methods while providing improved quality assurance and reduced on-site risk.

Following the project successes at Alderney WTW, RSE delivered the Knapp Mill WTW plant at an increased pace and efficiency, despite working with a different Tier 1 contractor for the same end client, South West Water. This achievement demonstrates both the flexibility of RSE’s delivery model and its ability to consistently replicate successful outcomes across varying project environments and stakeholder teams. The project further validates the effectiveness of RSE’s standardised modular approach, enabling accelerated delivery while maintaining high standards of quality, safety, and performance.

The success of the modular delivery required meticulous planning and collaboration between RSE, Bournemouth Water, the principal contractor and key supply chain partners including GF Job and Stoddart Crane Hire.

A 4D delivery and construction simulation accompanied by a comprehensive logistics programme was developed to provide complete visibility of every modular unit through transportation and installation. This ensured all stakeholders, site teams and relevant authorities had assurance regarding the location and status of each unit at every stage of delivery.

The new Knapp Mill WTW includes a 67 MLD ozonated ceramic membrane treatment plant, designed with future resilience in mind through the provision for additional membrane streams as demand increases. Upstream of the membrane process, slow sand filtered water is collected and transferred via a new interstage pumping station to flow balance tanks, providing consistent hydraulic conditions for treatment. A side stream from the combined flow balance tank outlet is directed to the ozone generation system before being reintroduced to the main process flow through a static mixer, optimising membrane performance and water quality.

At the heart of the treatment process is RSE’s CeraMac® ceramic membrane plant, where each membrane vessel is equipped with a dedicated feed pump and backwash vessel. Shared utility systems provide air, backwash fill water, and cleaning-in-place (CIP) functionality, ensuring efficient operation and maintenance. Permeate from the membrane plant is collected within a common header and dosed with sodium bisulphite to neutralise any residual ozone before a portion is used to supply the backwash and CIP systems. The remaining treated water then passes downstream to granular activated carbon (GAC) filtration, providing a further treatment barrier before progressing through the final stages of the water treatment process.

The Knapp Mill WTW upgrade benchmarks modular delivery in the water industry. It demonstrates how innovative thinking and modern construction methods can tackle challenges facing water networks, while also laying the foundation for more sustainable future infrastructure. It demonstrates what can be achieved in partnership with innovative clients who are committed to providing high levels of engagement and collaboration.

The project upgrade exemplifies the benefits of embracing innovation and a modular, factory-built approach. Integrating advanced treatment processes into standardised units allowed the project to deliver significant gains in efficiency, quality, and sustainability. The delivery of Knapp Mill WTW also created opportunities to further refine processes and introduce additional innovations. These improvements informed best practices across both facilities, enhancing consistency, operational performance and long-term value for the client. Through close collaboration and continuous improvement, the project not only met its objectives but also strengthened the standardisation of ceramic membrane treatment infrastructure across Bournemouth Water’s network.

By adopting a modular delivery model, RSE significantly improved safety performance while reducing the environmental impact associated with traditional construction activities. The m-CTU® solution delivered substantial benefits throughout the project lifecycle, including up to a 20% reduction in design and installation costs, carbon savings of more than 30% through the use of low-carbon and recycled materials, and construction programme reductions of up to 50% when compared with conventionally delivered membrane treatment plants. The offsite manufacturing approach also minimised disruption to site operations and the surrounding community while enhancing quality control through factory-based assembly and testing.

The modular “Lego® block” philosophy further supports long-term flexibility, enabling additional treatment capacity to be incorporated efficiently as future demand increases. This scalable approach provides Bournemouth Water with a resilient solution capable of adapting to changing operational requirements over time.

Alongside the treatment process upgrades, a number of site enhancement works were undertaken to improve the surrounding environment and deliver lasting benefits for the local community. These included the construction of a landscaped earth mound to reduce noise levels and enhance the visual appearance of the site, the installation of new tree planting and green infrastructure to support biodiversity, and the creation of a new pedestrian crossing linking the Mill Road green space with the Avon Valley Footpath.

Once operational, the upgraded facility will strengthen water supply resilience across the region and deliver enhanced drinking water quality for Bournemouth Water customers. Combined with the environmental and community improvements delivered as part of the project, Knapp Mill WTW has been developed to provide sustainable benefits for both the local area and future generations of customers for decades to come.

 

Following construction contract award in May 2024, RSE commenced early procurement activities and the off-site fabrication of standard products in June 2024. Off-site assembly and testing began in January 2025 and was successfully completed by June 2025, with all modular units fully assembled, tested, and ready for shipment. The first modular unit was delivered to site in July 2025, followed by the final unit in August 2025, demonstrating the efficiency of the modular delivery model. The project commenced energisation and commissioning from October 2025, pending the provision of power by the Client and Tier 1 contractor in accordance with the overall project programme.

RSE has remained on programme throughout delivery, with the rapid execution of its scope enabling a phased installation approach that reduced disruption to both the operational site and the surrounding community, while minimising the duration and intensity of on-site activities. The Knapp Mill WTW upgrade demonstrates the advantages of combining advanced ceramic membrane technology with standardised modular delivery.

By replicating the successful Alderney WTW model, RSE has achieved significant programme savings, accelerated delivery and reduced project risk while continuing to drive innovation across both facilities. The project highlights how Design for Manufacture and Assembly (DfMA) principles can transform infrastructure delivery, providing clients with greater certainty, improved sustainability performance and faster access to critical water treatment capacity.

As the project progresses towards energisation and commissioning, Knapp Mill is set to become another landmark example of how modular water treatment solutions are shaping the future of the UK water sector.

To find out more about how our modular approach speeds up delivery, reduces embodied carbon and supports the secure and sustainable growth of water infrastructure, click on the button below and please fill in the form. We’ll get back to you shortly.