Andreas Späth

Desalination: the answer to our water crisis?

2015-02-23 10:34

Andreas Wilson-Späth

Supplying South Africa’s growing population with clean, safe drinking water is a major challenge. Not only is the country’s water infrastructure in need of refurbishment in some places and entirely absent in many others, but access to sufficiently large quantities of potable water is increasingly becoming a problem.

This is not only a South African problem, of course. With population and industrial growth, poor watershed management, the widespread pollution and deterioration of rivers and other freshwater ecosystems, and with the impacts of climate change becoming more apparent every year, the world is facing a water crisis of potentially devastating proportions. By 2025, the UN estimates, some two-thirds of the planet’s population could be experiencing water stress conditions, especially those living in the dryer parts of the developing world.

You might have wondered why we haven’t used desalination of seawater to help us resolve our water supply problems. After all, much of South Africa is literally surrounded by oceans of the stuff. In addition, there is plenty of brackish groundwater in inland areas that could be converted into fresh water useable in agriculture, industry and for domestic use.

The basic technology is ancient. Humans have distilled salty water into potable water for centuries. So why not now?

Large-scale desalination plants are, in fact, increasingly being used worldwide. Thousands of them are in operation – the greatest number in the Middle East, from Saudi Arabia, the United Arab Emirates and Kuwait to Oman and Qatar. Most of Israel’s water already comes from such installations. The USA is home to about 300 of them and California, a state in the grip of the worst drought in history, is investing billions in the technology.

Several South African municipalities are considering desalination as part of their future water supply plans and government has suggested that in 15 years’ time as much as 10% of the country’s total urban water supply might be provided in this way.

The largest local desalination plant was opened in Mossel Bay in 2011 and mostly services PetroSA’s synthetic fuel operation there.

So what’s the problem? Although the technology has been improving steadily, there are several hitches. Most importantly it takes a lot of energy to convert salty water into fresh water.

In conventional high-pressure reverse osmosis systems, a large amount of electricity is needed to push saline water through a series of progressively finer membranes to remove salt and other chemicals. Using a more traditional distillation process, lots of electricity is used to heat water to its boiling point.

This massive energy requirement means that desalination plants tend to have large carbon footprints and contribute significantly to climate change – and thus to even worse water problems. Until now, large-scale desalination has only been a viable option for rich countries or those with plenty of fossil fuel to burn.

A secondary environmental problem results from the fact that for every litre of fresh water produced, about two litres of raw salty water needs to be processed, leaving behind significant quantities of toxic brine which can contain a variety of pollutants and represents a considerable threat to coastal ecosystem if it’s carelessly discarded into the ocean.

In a number of countries, including the Unites Arab Emirates, the USA and Australia, progress is being made in using renewable energy sources, principally the power of sunlight, to drive the desalination process. While this might be a low carbon alternative to conventional methods, the technology is still at an early stage of development and can’t be relied upon to solve our water problems at this point in time.

For now, the answer must lie in conserving existing freshwater sources. We can go a long way in countering the growing crisis by putting effort into water conservation strategies, using our precious freshwater more efficiently, with less waste, reusing water wherever possible, capturing stormwater that would otherwise just run into the sea and recycling used water whenever that is an option.

Ultimately, what’s required is a change in attitude from all of us. We need to change the way we look at water. We need to stop taking it for granted and treat it as a precious resource that needs to be treasured instead of wasted.

I’m part of a new non profit organisation called The Watershed Project. Our aim is to raise public awareness about water in all its aspects. Visit our website for more information, follow us on Twitter (@WatershedSA) and in March, join us for a festival of exciting water related activities from fun walks to outdoor film screenings (only in Cape Town for this year, but expanding to other parts of the country from 2016).

- Andreas is a freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath
 
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