Hot Topic: Desalination & The Water Crisis

One of the least discussed topics associated with the climate emergency is the water crisis but it’s an issue that will affect every continent and most regions at some point in the future… even the UK, with its famously wet weather, is expected to see water shortages become problematic in the coming years. And, in fact, some cities – like Bristol – are already experiencing issues of this kind.

Figures from Unicef show that four billion people (which is nearly two-thirds of the global population) face severe water scarcity for at least one month every year, while more than two billion people live in places with inadequate water supplies.

And it’s expected that 50 per cent of the world’s population could be living in places threatened with water scarcity by as early as 2025. Furthermore, it has been predicted that, if current trends persist, global demand for water could outstrip supplies by 40 per cent come the year 2030… so the matter is an urgent one and the challenges need to be addressed now.

Part of the problem is that each region will face its own individual water stress and scarcity problems, either having too much of it (in the form of flooding) or too little (thanks to drought conditions).

These issues are being further exacerbated by climate change, water mismanagement, population growth, ageing infrastructure and more frequent extreme weather events.

But the good news is that there are all sorts of different solutions to the challenges being presented by the water crisis, everything from rainwater harvesting and wastewater recycling to conservation technologies, education, improving water management and desalination (desal).

This latter solution is one that has been garnering increasing amounts of attention across all quarters and, certainly, desalination is an effective way of increasing freshwater supplies, using membrane filtration, reverse osmosis and electrodialysis to remove excess salt and other minerals from seawater and brackish water.

Research published in the ScienceDirect journal analysing the global status of desalination shows that desal capacity has been growing around the world at a rate of approximately seven per cent per year since 2010 to the end of 2019.

A sharp increase in capacities in places that have previously not embraced this kind of technology has also been seen, including Africa and Europe.

But is desalination the best solution to the issues of water stress and scarcity, or could it cause more environmental concerns than it ultimately solves?

What’s the problem?

One of the biggest challenges we face when it comes to desal is the fact that it is an energy-intensive process and, as such, is an expensive way of addressing freshwater scarcity issues. There are also construction costs involved in building the plants in the first place, as well as maintenance costs and fossil fuel use to power them.

There are ways around these problems, however, such as the floating desalination plants being developed by UK firm Core Power. Traditional ship hulls are used to house desal facilities, which are powered by microreactors to provide desalinated water and electrical power.

These vessels would be capable of producing drinking water at a rate of between 60,000 and 450,000 cu m per day, which is at the same scale of land-based plants already in operation.

Renewable energy can also be used to help make desal more cost-effective and more efficient. Solar power seems to hold some of the answers, with a team from MIT and Shanghai Jiao Tong University in China developing a cost-effective solar desal device that could provide potable drinking water for as little as $4.

Of course, in this case, changes in weather can make it harder to store solar energy for large-scale plants and some parts of the world struggle to access direct sunlight.

Wind-powered desalination is another potential renewable solution that could help support the use of solar power and other technologies. The wind turbines of today are state of the art, modern and quick and easy to install – and pilot projects have already been underway to see whether they could be matched with desal technologies.

What about the brine?

It’s not just energy consumption and fossil fuel use that makes desal less attractive as an option. Desalination also creates highly concentrated brine as a waste product, which is typically disposed of by being dumped into the sea, which can have a big negative impact on marine ecosystems and marine life.

In 2019, a study carried out by the UN University Institute for Water, Environment and Health suggested that the world’s desal plants are pumping out a lot more of this brine than previously believed, with facilities producing 50 per cent more than expected.

Lead author of the study Edward Jones was quoted by the BBC as saying: “High salinity and reduced dissolved oxygen levels can have profound impacts on benthic organisms, which can translate into ecological effects observable throughout the food chain.”

However, steps are being taken to minimise the impact of brine on the natural environment, such as using reject brine for aquaculture or for cultivating spirulina and irrigating forage crops and shrubs.

And MIT has been developing new resources that could take this concentrated brine and turn it into chemicals to be used elsewhere, making desal processes more efficient and help protect marine environments.

For example, sodium hydroxide can be produced to pretreat seawater going into the desal plant, changing the acidity of the water and preventing fouling of the membranes used to filter seawater, which is a major cause for problems in typical reverse osmosis desalination plants.

The conclusion?

Desalination has an essential role to play in addressing the issues associated with water stress and scarcity but, as the industry grows, it will become increasingly important to find sustainable ways of operating these plants to protect the environment and ensure that freshwater supplies can be supplemented, without causing other problems elsewhere.

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