Water treatment solutions firm VWS Envig is creating South Africa’s biggest desalination plant through the refurbishment of an existing desalination reverse osmosis (RO) plant for the Albany Coast Water Board (ACWB), in the Eastern Cape.

Once completed at the end of March, the plant, which is situated at Bushmans River Mouth, near Kenton-on-Sea, would have a throughput of 1 800 m³/d.

“The upgrade of the desalination plant is an important project, as it serves the Ndlambe Municipality, which in turn services a population of around 50 000 people,” VWS Envig project engineer Gareth Kearns commented.

The contract, which was awarded in August last year, required the supply of potable water to be maintained while the existing plant was being refurbished.

It also involved the supply of a new RO skid, the integration and improvement of existing plant equipment and the implementation of energy saving devices to improve efficiency and reduce operational costs.

“Since our initial involvement with ACWB, we have found the RO plant to be in a run down state of repair. The plant has been experiencing unacceptable amounts of downtime, as well as running at a recovery rate far below the plant’s operational specifications,” said Kearns.

He explained that the plant currently had three RO trains mounted on separate skids, which were in various states of operational functionality.

The existing RO1 and RO2 trains were now being combined and placed onto a single skid, to be called RO12, which would result in energy savings for ACWB.

Under the old configuration, the RO1 train used a 160-kW Grundfos pump, while the RO2 train used a 220-kW Grundfos pump.

The RO12 train, by comparison, incorporated the existing 160-kW pump, a new 15-kW booster pump and a new pressure exchanger to supply the RO train’s energy requirements.

“A pressure exchanger utilises the wastewater brine stream, which exits the system under high pressure to reintroduce energy into the RO process. Pressure exchangers are highly economical devices, which convert waste energy, in the form of high pressure, back into usable energy with a staggering 96,7% efficiency,” Kearns noted.

Further, a turbine-based energy recovery device had also been incorporated onto the new RO3 train.

“The turbine device, while not as efficient as a pressure exchanger, still manages to convert pressure back into energy at an impressive 56% efficiency,” he added.

The implementation of the energy recovery devices and the pressure exchanger would reduce the RO plant’s energy requirements by nearly 30%.

VWS Envig would, following the completion of the refurbishment, operate and maintain the facility for a 13-month period under an operations and maintenance contract.

In 2009, VWS Envig completed the refurbishment of another water treatment plant to deliver 750 m³/d of potable water to the Ndlambe municipality for distribution to the Cannon Rocks and Boknesstrand communities.