Desalination an alternative solution to SA’s water supply challenges
Water is an essential resource in the production of goods and services, including food, electricity and most manufactured products. In order to support financially sustainable economic activities, it is therefore essential to ensure that water supply is reliable and predictable.
Given the current drought that is gripping most parts of the country, there has never been a more opportune time for us to look at alternative water supply solutions at our disposal - with desalination being one such solution.
While water conservation awareness and the reduction of consumption are but some of the ways to help curb the effects of the drought, they are far off from offering a complete solution to the country’s water scarcity.
Coastal towns like Mosselbay and Sedgefield in the Western Cape have tapped into desalination as a solution for their water challenges, both using seawater reverse osmosis plants to supplement water provision during drought conditions.
In the Eastern Cape, we have the Albany Coast seawater reverse osmosis (RO) plant located at Bushman’s River Mouth in the Ndlambe Local Municipality, which is owned and operated by Amatola Water. The Albany Coast RO plant is the first desalination plant in South Africa, having been commissioned in 1997.
Reverse Osmosis is the most common form of desalination, and involves forcing water through cartridges that contain thin-film composite polyamide membranes, which trap salt and other impurities but allow the fresh water through.
According to a study done by Keith Turner from Royal Haskoning DHV and published by the Water Research Commission in 2016, as a water scarce region, Ndlambe has limited access to freshwater dams and rivers.
“The scarcity is also increased by the geological conditions imposed by the Bokkeveld shale which limit the use of boreholes because of its imperviousness (limits to the passage of water into the ground) and the releasing of salts into groundwater.”
The Albany Coast plant abstracts raw water from beach wells (Diaz Cross well field) which supplements the plant’s supply; produces potable water through the process of reverse osmosis (RO); and supplies treated desalinated water to the Bushmans River reservoir and Kenton-on-Sea settlements, serving the communities of Bushman’s River, Harmony Park, Marselle, Kenton and Kenton Eco Estate.
Due to the deteriorating quality of the water sourced from the Diaz Aquifer, the only alternative and available water resource for the area is seawater.
The Albany Coast water supply system, including the RO plant and nearby well fields, has a capacity of approximately 1.8 Mℓ/day RO and 1.2 Mℓ/day from the dune wells.
Like the Mosselbay and Sedgefield plants, the Albany Coast RO plant also utilises high pressure reverse osmosis where the Electric Conductivity (EC) is >20 000mS/m of which seawater is ±55 000 mS/m).
Even with its numerous positives for water security, the cost of desalinated water remains a bone of contention for many. One reason is the huge amount of energy required to push water through the membranes. The key challenge to running a desalination plant is the cost of production, especially during winter months when electricity tariffs tend to be on a high. With higher than anticipated electricity and maintenance costs, desalination remains about twice as expensive as treating rainwater or wastewater.
Some environmentalists have long opposed desalination due to the high energy the process demands, and other environmental considerations such as the impact of drawing large quantities of seawater from the ocean.
However, with the effects of climate change, such a decreasing rainfall resulting to lower dams levels and the prevalence of drought, a growing number of countries are looking to desalination for water security.
A case in point is Australia, which launched a massive desalination plant build programme when the worst drought broke in the country between 1997 and 2009.
In Perth, Western Australia, the general sentiment towards desalination is very positive, wherein the desalination plants are fully utilised and supply nearly half of Perth’s water requirement, with the view that these plants were key investments in building water resilience.
In the words of Western Australian Water Minister, Bill Marmion: “Nothing is more important to Western Australians than the security of our water supply.
As we experience an increasingly dry climate, evidenced by dwindling inflow to our dams, we must re-think the way we source water.” In line with this thinking, Water Corporation has embarked on an 10- year plan to drought-proof Perth by 2022 so that sufficient water supplies are maintained, whatever the weather, (Water Research Commission: The Water Wheel, June 2015).
The Australian example offers a preview of where much of the world is headed, should the dry conditions prevail. As the pressure on South Africa’s water resources continues to rise as a result of the prevailing drought and increasing demand, it remains to be seen whether these will encourage a positive shift towards desalination as an alternative solution to the country’s water challenges.
