The National Water Resource Strategy, the official blueprint on which government has based its water management approach, has identified a number of regions that could be in significant water deficit by 2025 if measures are not implemented to prevent this. In some of these instances, desalination is seen as a possible solution, with the Department of Water Affairs (DWA) indicating that desalination plants could account for between 7% and 10% of the country’s overall urban water supply by 2030.
Water resource management specialist Anthony Turton tells Engineering News that the High Scenario of the National Water Resource Strategy states that the total national water deficit by 2025 is projected to be a massive 2 044- million cubic metres a year. Three water management areas, namely the Berg, in the Western Cape; the Mvoti to Mzimkulu water management area, in KwaZulu-Natal; and the Upper Vaal, will be particularly hard hit. The Upper Vaal, which sustains 25% of all South Africans and generates about 8% of the economic output of the entire African continent, is of particular concern.
DWA chief director of integrated water resource planning Solly Mabuda says that fresh water is a scarce resource and in many areas is reaching its limits, which implies that South Africa may well have to adopt desalination to enable reuse of available freshwater and to tap into seawater as a potential resource for coastal areas.
“Desalination technology is a well- developed, mature and reliable technology. However, the financial viability and operational efficiency are key success factors, which should not be underestimated,” Mabuda explained in response to emailed questions.
What is Desalination? How does desalination it work? Officially, desalination is a group of technologies that remove salt from water. It can be used to purify water for domestic use and is com- monly used in the industrial sector to treat water and wastewater.
International consulting company Frost & Sullivan South Africa programme manager David Winter says that it is becoming increasingly common in the domestic water market, especially in the Southern Cape, which is experiencing severe drought, with municipalities from Mossel Bay to East London looking at desalination as a viable option.
Global desalination body the International Desalination Association (IDA) director and past president Lisa Henthorne states, in her November 2009 state of desalination remarks, that the desalination market con- tinues to grow and, according to the DesalData IDA Worldwide Desalting Plant Inventory, there are 14 451 desalination plants with a combined capacity of 59,9-million cubic metres a day currently on line. This represents an increase of 12,3% over the previous year. In addition, a further 244 plants with a capacity of 9,1-million cubic metres a day are known to be under contract.
While the Middle East remains the largest market for desalination, IDA has seen a change in the geography of desalination since 2003. Large-scale programmes in Australia, Algeria and Spain have made these markets much more prominent.
Turton points out that Australia has taken a position that elevates desalination to the highest level of national priority. They have established a national centre of excellence to promote this vision and combined with the Western Australia Geothermal Centre of Excellence to form a new technology that desalinates water using low-grade energy sources. “This is being clever. South Africa needs to do the same. When the National Planning Commission is established, I intend to promote this idea with them, because I believe it will unlock massive potential in South Africa,” he says.
The most commonly employed desalination technology used in South Africa is reverse osmosis (RO), which occurs at high pressures. Henthorne states that RO accounts for nearly two-thirds of contracted global capacity. She attributed this to the increase in market share being driven by sharp acceleration in the growth of membrane markets in such countries as Spain, Algeria and Australia.
In the RO process, water from a pressurised saline solution flows through a water-permeable membrane and is separated from the dissolved salts. The permeate is encouraged to flow through the membrane by the pressure differential created between the pressurised feedwater and the product water, which is at near atmospheric pressure. The remaining feedwater continues through the pressurised side of the reactor as brine. A significant amount of energy is required for the initial pressurisation of the feedwater.
Consulting engineering firm SSI water sector head Francis Gibbons tells Engineering News that the main improvements in the technology have been in the membranes and recovery of energy, as there are some opportunities for energy recovery from filtered water at the downstream ends of desalination plants.
South African Institute of Civil Engineers water division chairperson Dr Chris Herold points out that thermal technologies can also be used, but these require large quantities of heat, which is expensive and generally less economical than RO. Thermal technologies account for about one-third of installed global capacity and are used in areas where energy is inexpensive and thermal plants can be run at low costs, such as in the Middle East region.
SOUTH AFRICAN DESALINATION VIABILITY
Turton says that he cannot see any choice but to consider desalination as a significant element of South Africa’s future national economic development strategy, as the country has reached the limit of what he calls the hydraulic mission phase of its development, which developed almost all of the country’s water resources.
He adds that the prospects for desalination in South Africa are excellent. All coastal cities have access to seawater and energy, making desalination viable – either that, or coastal regions will start to drink recycled sewage in 25 years. In Gauteng, the acid mine drainage (AMD) problem will provide a desalination solution that will be applied to the coastal areas. Turton says that, in short, the prospects are good.
Winter and Herold agree, telling Engineering News that desalination is certainly a viable option in South Africa, although it accounts for less than 1% of the country’s drinking water. Plants have already been installed and upgraded in the Cape coastal regions of the country. Herold adds that in some dry coastal regions, remote from fresh water resources, desalination is less expensive than building a dam, but KwaZulu-Natal still has options for recycling effluent that is currently lost to the sea and tapping into existing water resources, making desalination not yet an economical or viable option for the area.
“There are areas where desalination has to be carried out and it is becoming increasingly looked at as a way to filter effluents and reclaim polluted resources,” says Herold.
The DWA has, over the last four years, carried out reconciliation strategy studies for the major systems and metropolitan areas in the country to ensure that water will be available into the future. Mabuda says that most of these studies list seawater desalination as one of the strong options for implementation in the near future. The primary strategy in all of these areas is, however, the efficient use of existing resources. Desalination is going to be very expensive and the country cannot afford to use any of its resources wastefully.
“Desalination can make marginal water resources accessible and usable. Further, it complements existing water-use systems to maximise the use of local water resources.”
He adds that the viability of desalination is site specific and a critical prerequisite for successful implementation of desalination works. Specific considerations include high energy costs, specialist operating skills and diligent management of pre- and posttreatment requirements to protect the RO membranes. The extracted brine must be disposed of carefully and in an environ- mentally responsible manner.
THE POTENTIAL BENEFITS
Winter says that one of the greatest advantages of desalination is that there is an unlimited supply of water along the coast. Frost & Sullivan environmental technologies research analyst Kudzanayi Bangure adds that, besides the benefits of recycling water, the salt by-product from the desalination process can also be used.
“Desalination is an alternative to using other water resources. Seawater can be used, as opposed to depleting the country’s natural water resources.”
Gibbons says that natural resources have a certain limit and, although dams can be built and boreholes used, these are finite resources. SSI is looking at combining resources by using existing surface resources, such as boreholes and introducing desalination as a further resource.
Mabuda suggests that the desalination of seawater is not nearly as vulnerable to the effects of climate change as the surface resource could be.
However, not everyone views desalination in a positive light. Nature conservation foundation the World Wide Fund (WWF) for Nature views seawater desalination as having a limited place in South Africa’s water supply chain. Its integrated catchment management programme manager, Dr Mao Amis, says that desalination must be considered on a case-by-case basis in line with other integrated approaches to water management supply and demand.
“There is the need to protect natural assets, such as wetlands and rivers. The WWF does not think desalination is the optimum way to tackle water demand challenges. The country must rather manage water demand appropriately and use it efficiently before it resorts to desalination,” says Amis.
He points out that there are potential catastrophic effects of desalination on the environment and, although the WWF has to consider cases where there are no alternatives, it will have to determine the potential effect on the environment before it can give any support for any desalination endeavours.
Turton explains that desalination needs a large amount of energy and feedstock and produces perfectly clean water and brine. The downside, therefore, is twofold: the carbon emissions generated in the energy phase and the brine.
“The ocean is an ecosystem – it is not just a body of water that is not living. By extracting water directly from the ocean, plants are disrupting the functioning of the system. There is also effluent that must go back into the ocean, which may cause a brine build-up,” says Amis.
He says that, if desalination plants are built, the design must minimise any environmental effects. Environmental considerations of the sea, which is a fully functional ecosystem, should be key to any desalination plants.
There are also alternatives to desalination. Amis points out that South Africa’s infrastructure is failing and the country is not tackling the water demand challenges that it needs to and doesn’t have the infrastructure to effectively deliver water from storage facilities to end- users.
He says that South Africa must reduce water demand and ensure that infrastructure is upgraded.
Further, Amis points out that desalination is energy intensive and South Africa has committed itself to helping combat climate change. By developing strategies that will potentially increase global warming, the country will most likely backtrack on its commitment to cut down carbon dioxide emissions.
An environmental concern is the disposal of leftover brine but, if the disposal is managed correctly and released in the correct way into the environment, Winter believes the effects will be negligible. Herold agrees that the environmental effects of disposing of the brine in the ocean are negligible, as it is a huge reservoir of water that covers two-thirds of the earth’s surface.
In the coastal zone, there may be beach obstruction works and these must be managed carefully, but Gibbons points out that this can be managed and monitored, as is the case with discharging the concentrated brine back into the sea.
Mabuda states that the direct environmental risks of desalination in coastal areas are minimal and it is possible to place the abstraction and brine disposal pipelines and points on the coast in such a way that the impacts will be fully acceptable.
The potentially more serious effects arise from the fact that desalination is still energy intensive, but the membrane technology, as well as energy recovery systems in the desalination plants, has made huge reductions in the energy required for desalination, and further improvements are ongoing.
There are solutions to these environmental effects. Turton points out that, in a coastal setting, brine is not a problem and, maybe, wind energy can be used to reduce the carbon footprint. Inland, the feedstock would be AMD, which means that concentrated brine would result. Ion exchange technology can be used to clean up that brine by separating it into specific chemical elements for onward sale.
Mabuda says that, in Australia, the full energy requirements of the desalination plants are offset by the building of wind farms and this will have to be the direction that South Africa follows.
IT DOESN'T COME CHEAP
Another downside to desalination is the high cost of the process. Herold says that it is an expensive exercise, especially if supplied to inland areas, as it will have to be transported and pumped across great distances, increasing the cost.
Winter adds that changing technologies are making the expense of desalination more competitive.
Gibbons agrees that it is an expensive approach, but it becomes an option when surface water is no longer available, such as in coastal regions. He says that SSI is looking at ways to counteract the large amount of power needed for pumping, such as building wind power farms along the coast to provide the power for the desalination process.
However, Henthorne reports that the global desalination industry has been successful in lowering operating costs, but the variability is largely a function of the local cost of power.
Amis says that if the country focuses on desalination, it has the potential to take capital away from exploring cheaper means of increasing our water supply. He points out that the country already has challenges with State-owned power utility Eskom concerning energy and desalination plants will exacerbate South Africa’s power challenges.
Further, Amis points out that desalination involves significant investment, which will result in corporate involvement in any endeavours. Access to water is a basic human right and he worries that, if the responsibility of water supply falls to the private sector with little regulation, prices may be dictated by corporates and ordinary people will not be able to afford this basic need.
“Desalination will need proper guidance and regulation. In general, this can be accommodated within the existing structures and processes of the DWA, which are being extended to manage the accelerated growth,” says Mabuda.
The DWA is currently developing an implementation strategy, which addresses regulation, as well as the planning and governance requirements for successful implementation. The pricing of water and affordability for institutions will require specific attention.
PROJECTS IN PLAY
Currently, there are a number of desalination plant projects under way in South Africa. SSI is involved in three in the Southern Cape, including a seawater desalination plant for Sedgefield that was commissioned in December. The containerised, or mobile, plant was installed together with an upgraded membrane bioreactor wastewater treatment plant, enabling indirect reuse, and new boreholes to augment existing ground- and surface water supplies.
George, Plettenberg Bay and Knysna have now adopted similar schemes for a percentage of their water demand to be provided from alternative water sources.
SSI has also been awarded a 20-Mℓ a day plant for Knysna, which will be located alongside the wastewater treatment plant and abstract water from a borehole next to the lagoon. The brine from the desalination process will be mixed with the wastewater effluent and returned to the lagoon. Gibbons says that this is quite a suitable solution as it dilutes the brine and effluent and does not lower the salinity of the lagoon.
In addition, a low-pressure RO project in Mossel Bay is currently in the process of being awarded to the contractor. The plant will provide potable water to national oil company PetroSA for its refining process. A reuse scheme has been accepted to provide PetroSA with polished final effluent, freeing up valuable fresh water supplies for the town.
Water treatment firm VWS Envig also announced, in January, that it is refurbishing an existing desalination plant for the Albany Coast Water Board, in the Eastern Cape. The plant, which is situated at Bushmans River Mouth, will have a throughput of 1 800 m3/d and be completed at the end of March to serve the Ndlambe municipality.
FUTURE OF DESALINATION
Winter says that desalination will certainly become more common in the future, especially in coastal regions, such as the Southern Cape and other regions that are prone to drought. He says that municipalities will have to weigh up the cost benefit of building dams against building desalination pants, but as plants have a quicker ramp-up time, there is definitely a future for desalination in South Africa.
Gibbons says that there are areas in South Africa that will not be able to avoid using desalination plants, as these areas, especially in the Cape region, are running out of surface water. He says that there have been investigations into desalination plants for KwaZulu-Natal, but this will only be necessary much further in the future.
Amis accepts that, in cases where there is a critical water situation and desalination is the only solution, there is nothing else that can be done, as people need fresh water. He says that desalination has a role, but it is a very limited one for water supply.
He says that desalination plants do not necessarily tackle water supply challenges, as everything is interlinked; hence, there is no easy solution to the water crisis. The resources we have must be managed more efficiently before desalination is considered.
Henthorne states that the demand for water continues to increase and factors such as population and economic growth, pollution of existing water resources, and climate change continue to drive the need for new, reliable sources of water. Desalination is one of the answers, and it continues to be an increasingly important part of global water solutions.
Mabuda says that the DWA has adopted desalination as a key element of water resource management and is establishing the necessary protocol, standards and guidelines to establish and further the use of desalination in the sector.
Turton feels strongly that South Africa needs to transition from the hydraulic mission, which includes dams and pipelines, to the Soft Path, which includes desalination, alternative energy and a range of other exciting technologies, including hydrogen cracking. He says that the National Planning Commission should consider these technologies and South Africa can make it happen as a nation.
“As a nation, we are flying blind if we do not include desalination in our overall national strategy,” he concludes.