Cape Town’s emergency desalination plant online

Cape Town’s emergency desalination plant online

The desalination plant at the V&A Waterfront feeds 2.0 megalitres of fresh water a day into Cape Town’s water infrastructure network.

Multi-disciplinary engineering consultancy, WSP, played a crucial role in the fast-tracked development of the City of Cape Town V&A desalination plant, which will feed 2.0 megalitres of fresh water into the city’s network a day.

This desalination plant at the V&A Waterfront forms part of a series of emergency water supply projects the City of Cape Town is implementing to supplement critically low water resource levels in the district. Quality Filtration Systems (QFS), along with Osmoflo, were awarded the work as the main contractor – to build, own and operate the plant, as well as to decommission the plant at the end of the contract term. WSP tendered as sub-consultants to QFS, providing design engineering and site supervision services.

Marthinus Retief, Principal Associate: Coastal, at WSP Maritime Africa, says: “Given the severity of the water crisis in the region, this had to be a rapid execution, top priority project for all parties involved.

“The project was awarded to QFS in January 2018, and WSP immediately started working on the designs, drawings and specifications for the plant’s ancillary components. Practical completion of these components was reached within two months and the plant is now finalising overall commissioning.

“We provided concept to detailed designs, as well as construction drawings and specifications for the desalination plant’s ancillary works. As this project was fast-tracked, significant focus was placed on where we could save time without compromising quality of design or constructability. We also designed the ancillary works in such a way that production can be upgraded by up to 50% if required,” says Retief.

The three main components that make up the ancillary works include the marine intake pipeline and seawater pumping system, the brine discharge system and the injection system to convey the fresh water to the localised water infrastructure network. WSP provided the marine, civil and mechanical design of these components. The desalination process is owned and operated by QFS, along with Osmoflo.

“The seawater abstraction system is close to the entrance to the V&A basins, but designed for optimised water quality and rapid construction. The desalination process separates the salts from the seawater and produces brine, which is then discharged back into the sea – and the fresh water is fed into the City of Cape Town’s infrastructure networks. Care was taken to discharge the brine in an environmentally acceptable manner,” says Retief.

WSP also provided project management services, as well as site supervision for quality assurance and quick decision-making on site during construction.

“There was always a member of our team on site, working closely with QFS and Southern Oceaneering (the contractor) to ensure that everything was done according to the design and for quality control purposes. This also enabled the project team collectively to collaborate better and ensure that any queries from site could be addressed and decisions executed rapidly.”

Rethinking the norm

WSP designed the brine discharge system to operate under gravity, rather than a pumping system as envisaged within the tender document. By changing the hydraulics WSP was able to optimise this process, which saved the client capital and operational costs on the project.

Together with Southern Oceaneering, WSP designed a geotextile bag weighting system to provide stability for the marine intake pipeline. This enabled the contractor to more easily install the pipeline onto the existing revetment slope and down to the required depth on the seabed. The bags were filled with concrete after installation to provide the required stability against wave action. Being an alternative solution to conventional pre-cast concrete weight collars, it saved time on construction, while reducing risk during pipeline installation. WSP worked closely with the contractor to ensure that the solution was constructible and optimised.

Herman Smit, Managing Director, Quality Filtration Systems (QFS) says: “To ensure the project deadline could be met, we leveraged on the world class expertise of our team of coastal and civil engineers to find solutions that were workable from a design perspective and quick to implement from a construction perspective.