Solar desalination: a solution to a growing global problem?

Solar desalination: a solution to a growing global problem?

Water is a molecule with extraordinary physical and chemical properties that essentially makes life on earth possible. It is capable of transporting nutrients or hormones through waterways or through our blood and allows cellular machinery to function. Due to its physical properties, it also helps protect aquatic life in even very cold weather, thanks to the formation of protective ice on the surface. Water is so essential to life that science has shown that it is the presence of liquid water, which determines whether a planet can support life in a solar system.

The Earth possesses lots of water, most of which is predominantly concentrated in its oceans. But the capabilities of water solvents mean that throughout geological history, these waters gradually concentrated salts and minerals, which resulted in the fact that today this water is saltwater. Unlike marine species, the majority of life on the continents cannot absorb salt water, it instead needs fresh water. On land, this fresh water is supplied through the water cycle, which passes through the stages of evaporation and precipitation. When a fraction of the water evaporates from the ocean, it discards the minerals it contained and becomes fresh water in gaseous form. It accumulates in this form to form clouds; which the winds carry up to dry land. The precipitation of clouds in the form of rain or snow then distributes fresh water on land masses.

Fresh water: an essential, rare and precious resource for mankind.

On Earth, 97.5% of the water is thus found in the form of salt water in the oceans, the remaining 2.5% is found in the form of fresh water on the continents. Fresh water is rare on earth, but even more so if one looks at its distribution. In fact, 68.9% of the available freshwater on Earth is found trapped in glaciers and permanent snow, while 30.8% is found in soil moisture, permafrost and wetlands. This leaves only 0.3% of the remaining fresh water found in the lakes and rivers of the world, and it is only this tiny fraction of the Earth's fresh water that is available for human consumption (Palenzuela et al, 2015).

Furthermore, we know that fresh water is not distributed evenly on Earth. Some regions have abundant rainfall, while others are barren. Significant hydric stress is found particularly in the Middle East and the Gulf countries in the Mediterranean basin, in some US regions, in northern China, southern India, Chile, as well as in Australia and South Africa.

Heading towards a natural freshwater shortage

Hydric stress in the world has increased in the last century; we continue to increase our consumption, while freshwater sources are increasingly being degraded by pollution. Experts predict that by 2030, 47% of the world population will live in a region experiencing hydric stress. In regards to the global freshwater consumption, in the year 2000, humans consumed 30% of all fresh water on our planet (4200 km3). It was three times more than the global freshwater consumption in the 50s. Our consumption is increasing so much that we expect that in 2030 we will consume 70% of the available fresh water on Earth. This increase is notably due to the global population increase and a modern lifestyle that requires more water, particularly for industrial needs.

Hydric stress is therefore increasing with the increase of the world's population, but also with the degradation or overuse of freshwater resources, industry and human populations discarding a lot of wastewater.Global warming is also to blame for this problem, since the dramatic melting of the glaciers and perpetual snow also causes a depletion of the freshwater resources available, as is the case for many rivers that are sourced by glaciers such as is the case in Tibet (Woldai, 2016). Global warming also alters and disrupts the natural cycle of water precipitation causing exceptional drought cycles in some regions of the world, and resulting in extreme weather phenomena such as El Niño.

Since 2002, the UN has been warning the international community of this increasingly critical problem which is becoming a planetary issue. Limited access to fresh water is one of the most limiting factors in what is attractive to economic growth, social progress, as well as food and energy security. Access to clean water is one of the fundamental rights of human beings.

Desalination: the solution to the global water crisis?

Because 70% of the world's population lives near the ocean, the most abundant source of water on Earth, desalination naturally emerged as the solution to the problem of access to clean water for some countries (and Palenzuela al, 2015). Saudi Arabia began to use desalination techniques for seawater in 1930. Today it is the first desalinating freshwater producer in the world with over 7 million m3 produced per day. The majority of freshwater consumed there has been desalinated, as is the case for most countries in the Persian Gulf. In the production of global freshwater by desalinization, Saudi Arabia is followed by the United Arab Emirates, the United States and Spain. But desalination is not a miracle solution and does present certain problems as these techniques do require a lot of energy and some countries simply do not have cheap energy resources such as oil to develop this industry.

Furthermore, due to the use of fossil fuels to produce fresh water, greenhouse gas emissions from this new industry have become a very problematic issue, emphasizing global warming. Not to mention salt residue management and other pollutants generated by this industry and the potential environmental degradation if they're not properly managed.

Renewable energy based desalination as a sustainable solution

Renewable energy such as solar concentration, photovoltaic and wind power are increasingly being considered to carry out desalination for intermediate or local scales of production in countries with limited conventional energy resources, or for producers wanting to reduce their environmental footprint.

Desalination by solar concentration seems to be particularly well positioned, because the sun is often very abundant in the areas of the world suffering from significant hydric stress. In addition, solar concentration is technically a simpler solution than that of other technologies; it requires less maintenance and offers many technical possibilities. In some cases, solar desalination could be integrated with electricity producing and autonomous power units, in geographically isolated communities and with multiple needs. Concentration technologies also allow mixing several techniques of desalination while developing useful tools for management of salt rejection.

Finally, the desalination techniques can also be applied to wastewater treatment; solar desalination would lessen the deterioration and restore our global water resources. Increasingly stringent environmental standards are causing more and more Western industrial customers to turn to such technologies in order to limit wastewater discharges. In this context, desalination by solar concentration offers several interesting technical options from both an economic and ecological point of view, as we will see in the next article: The market for solar desalination and the different technical solutions available.

References:


- Palenzuela et al, Concentrating Solar Power, springer. 2015

- Woldai, Multi-flash desalination, CRC Press, 2016