South Africa’s biggest seawater desalination plant has opened in the seaside town of Mossel Bay in the Western Cape. This facility will ensure the economic hub achieves greater water security and economic growth going into the future.

The plant, which has a capacity of 15 million megalitres per day, started operating in September, but currently puts out only five million megalitres of water, as the area has had excellent rains, and dams supplying the town are full.

The five million megalitres are used entirely by the synthetic petroleum plant of the Petroleum, Oil and Gas Corporation of South Africa (PetroSA) – the town’s biggest employer and its biggest user of water. It consumes almost as much water daily as the municipality itself.

“The development of a desalination plant was always envisaged for the near future, but after the town was faced with a severe drought, the project was escalated,” confirms Harry Hill, spokesperson for the municipality.

Water resource strategy

South Africa’s Department of Water Affairs foresees that by 2030, up to 10% of the country’s urban water supply could come from water desalination plants. The National Water Resource Strategy (NWRS) is the blueprint on which the government bases its future water management approach.

The most recent version of the NWRS was drafted in 2004 and paints an alarming picture of water availability in years ahead, with a worst-case scenario showing a national deficit of 2 044 million cubic metres of water a year by 2025.

Currently, South Africa has a few desalination plants: the plant in nearby Knysna is the second biggest, but pumps a mere 1.5 megalitres a day. There are others at Bitou Municipality, Sedgefield on the Garden Route and Boknes in the Eastern Cape.

“Seawater desalination technology is widely used across the world, and it makes good common sense for a water-scarce country like South Africa to begin to do the same,” said Hill.

Suitable for human consumption

The process of desalination is increasingly being used as a way to provide fresh water for human use in regions such as the Middle East, the Mediterranean and Australia, where potable water from other sources is limited.

Despite all its benefits, desalination does not offer a “silver bullet” solution to the world’s growing water problems.

Besides using very expensive equipment, the process utilises a considerable amount of electricity and is not without environmental consequences.

Both the intake and discharge processes of the water may affect water quality and marine life. Aquatic species have a tolerance for natural salinity, an aspect that may be affected by the highly concentrated seawater pumped back into the ocean.

And while the intake structure is designed to maintain a flow of less than 0.15 metres per second – the minimum escape velocity for aquatic species – there is still a risk that plants, fish eggs and fish larvae around the intake areas may die.

The process uses chemicals which, untreated, can be harmful to the environment.

Green Drop certification

The most widely held belief is that desalination should be used in conjunction with other water-saving mechanisms such as waste-water reclamation. This treated water is suitable for industrial use.

Mossel Bay Municipality achieved Green Drop status in 2011 for two of its water treatment plants.

The Municipal Green Drop Certification Programme was introduced in 2008 as an incentive-based regulation of waste-water quality and waste-water management systems in South Africa.

A total of 821 waste-water systems were assessed by the Department of Water Affairs in 2011, with only 40 systems achieving the coveted Green Drop status. The Western Cape fared the best, scoring 83% – the highest average percentage. KwaZulu-Natal scored 82%, and Gauteng 79%. The Northern Cape finished last with 23%.

Municipalities were assessed in 11 categories namely: process control; maintenance and management skills; waste-water quality monitoring programmes; credibility of waste-water sampling; the submission of waste-water results; waste-water quality compliance; reaction management to waste-water failures; storm water and water demand management; bylaws; capacity of the waste-water treatment plants; and waste-water asset
management.

Emily van Rijswijck

MediaClubSouthAfrica