Client: Southern Water
Services: Complex delivery
JV partners: MWH Treatment
A major upgrade of Southern Water’s Horsham New Wastewater Treatment Works (WTW) in West Sussex is being undertaken by CMDP, a joint venture between Costain and MWH Treatment.
As one of Southern Water’s Delivery Partners for its AMP6 and AMP7 Capital Investment programmes, CMDP is delivering a range of schemes to maintain and improve Southern Water’s water supply and waste water treatment works, including Horsham New WTW.
The £31 million project, which will improve the site’s treatment processes and capacity, commenced in September 2022 and is expected to be finished in Spring 2025. Once complete, it will boost the quality of the final effluent returning to the River Arun, thanks to a range of new hi-tech machinery, control and monitoring systems, as well as the replacement and refurbishment of existing equipment.
The capital scheme at Southern Water’s Horsham New WTW will deliver an upgrade to the treatment facilities at the site to cater for the significant growth forecast within the Horsham catchment and surrounding areas over the next ten years, together with an improvement in the Total Phosphate final effluent emission standard, tightening from 1 mg/l to 0.25mg/L. These improvements to the site’s treatment processes have been designed for a 2035 population equivalent of 93,345, representing a 15% increase since 2020.
The project also encompasses an element of capital maintenance to be delivered by 31 March 2025:
- Replacement of two existing band screens with two new fine screens, located within the existing inlet chamber and configured as duty/assist. Each screen is rated at 1,700 l/s. Provide duty/standby screenings handling equipment (SHE) and a common launder channel.
- Provide a new centrifugal pump with a duty of 640 l/s to assist the two existing storm screw pumps.
- Replace the two new screw pumps within the existing Works, each pump rated at 640 l/s. Replace the two diesel engines and gearboxes with electric motors.
The project
As the project moves towards completion, a number of significant successes have already been achieved, including the following.
Replacement inlet screens
The replacement of the existing 40 year old inlet screens was always going to be a significant milestone for the project and a very challenging operation.
Before the new screens could be installed, which are needed to remove a vast amount of solid matter from the treatment process, the existing inlet channels were widened in places using a wire saw to provide additional room for the inclined toe of the new screens. The existing screens were electronically isolated and disconnected, along with an existing spiral conveyor, before being mechanically disconnected and removed.
This complex activity required specialist support from supply chain partners John F Hunt, FSD and R&B Engineering, to ensure a safe and successful operation.
Deep Bed Sand Filter Extension
As part of the project scope for water quality, the tertiary treatment process has been enhanced by extending the existing deep bed sand filter. This has involved the construction of three extra cells, to complement the four cells already in situ.
Moving Bed Biofilm Reactors (MBBR)
The addition of a new Moving Bed Biofilm Reactor (MBBR) nitrification process stage to the treatment process is a key element of the project, with installation of two new reactors undertaken by Veolia Water Technologies. As part of the scope for the project’s Growth driver, this introduces fixed film controllable biological treatment to the Works’ capabilities.
Alkalinity Dosing
The scope for the project’s Quality driver includes an enhancement to the Works’ alkalinity dosing capability, with a new 80m3 bulk storage facility comprising of two 40m3 tanks in a common bund and two-point dosing facility at the carbonaceous filter’s distribution chamber and the humus tanks effluent chamber. This element of the project was led by MEICA specialist Bridges Ltd.
The Works’ existing dosing capability will remain in operation until the upgrade goes ‘live’, at which point it will be decommissioned.
Key benefits
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At a ceremony held in London, CMDP Construction Manager Garry Burgess was presented with a Bronze Considerate Constructors Scheme (CCS) National Site Award to recognise the efforts of the Horsham New team in terms of creating value in the local community and being respectful to the public, the workforce and the environment.
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A ‘self-delivery’ approach to construction was adopted, which resulted in significant cost savings, through a reduction in the amount of non-productive time spent on site by the supply chain.
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Landscaping and habitat enhancements on-site ensured an overall 9% gain in biodiversity within the boundaries of the Works.
The numbers
£2.4m
spent with local businesses
65
weeks of apprenticeships spent on the project
>150
hours spent volunteering locally
Contact
Gerard Shore
Sector director
[email protected]