We live in times of aridity and global warming. All the possibilities to increase the amount of drinkable water must be considered and desalination, in my humble opinion, deserves our best attention. As for the subject we want to treat here, desalination is the procedure of extracting minerals from saline water (seas, oceans…) in order to obtain water suitable for human consumption or irrigation. (There also is, e.g., soil desalination, but it is a definitely different issue).
Desalination is particularly relevant in countries such as Australia but many others could take advantage from this procedure; Italy too is these days suffering for aridity and insufficiency of drinkable water, and this is one of the reasons for I am so interested in. Also consider that, given the increasing level of the oceans and of the seas, desalination could be an effective idea to partially change a problem in an opportunity.
According to “Desalination industry enjoys growth spurt as scarcity starts to bite” (globalwaterintel.com), the UN expects that 14% of the world’s population will encounter water scarcity by 2025. According to the International Desalination Association, in June 2015, 18,426 desalination plants operated worldwide, producing 86.8 million cubic meters per day, providing water for 300 million people. This number increased from 78.4 million cubic meters in 2013, a 10.71% increase in 2 years. The single largest desalination project is Ras Al-Khair in Saudi Arabia, which produced 1,025,000 cubic meters per day in 2014, although this plant is expected to be surpassed by a plant in California Kuwait produces a higher proportion of its water than any other country, totaling 100% of its water use.
Desalination can be done in several methods:
- Vacuum distillation: boiling the water to leave impurities behind;
- Multi-stage distillation: water is evaporated and separated from sea water through a series of flash evaporations.
- Multiple- effect distillation: incoming water is sprayed onto vertically or, more commonly, horizontally oriented pipes which are then heated to generate steam, and the steam is used to heat the next batch of incoming sea water.
- Vapor- compression distillation: using a mechanical compressor or a jet stream, the vapor present above the liquid is compressed and used to provide the heat needed for the evaporation of the rest of the sea water.
- RO, Reverse osmosis, the most used: the RO membrane processes use semipermeable membranes and applied pressure (on the membrane feed side) to preferentially induce water permeation through the membrane while rejecting salts. Reverse osmosis plant membrane systems typically use less energy than thermal desalination processes. Currently, the cost of seawater desalination is higher than traditional water sources, but it is expected that costs will continue to decrease with technology improvements that include, but are not limited to, reduction in plants footprint, improvements to plant operation and optimization, more effective feed pretreatment, and lower cost energy sources. Unfortunately, this procedure is highly environmental risky, since contaminated water is rejected into the ocean without treatment, and sensitive marine habitats could be irreversibly crushed.
- Freezing: partially freezing the seawater and removing the ice to then clean and melt back down into now clean water.
- Solar evaporation: as well as it normally happens in water cycle, the sun heats the sea water and the water vapor is condensed onto a cool surface.
- Electro-dialysis reversal: electric potential moves the salts through a membrane.
There also are other experimental procedure, not to be exhaustively quoted in this post.
Some methods of desalination, particularly in combination with evaporation ponds, solar stills, and condensation trap (solar desalination), do not discharge brine. A new approach that works like a solar still, but on the scale of industrial evaporation ponds is the integrated biotectural system. It can be considered “full desalination” because it converts the entire amount of saltwater intake into distilled water. The advantages of this system are the feasibility for inland operation, no air pollution, no temperature increase and the production of sea salt for industrial and other uses. As of 2015, 50% of the world’s sea salt production relies on fossil energy sources.
Of course, before considering desalination, the most cost-effective ways remain to increase water conservation and efficiency. In Italy, a large part of water is wasted because of the law level of the infrastructure system.
Sources:
- “Biggest ocean desalination plant in California nears completion”. The Economic Times;
- Laurene Veale (August 19, 2015, MIT TECHNOLOGY NEWS);
- Khawaji, Akili D.; Kutubkhanah, Ibrahim K.; Wie, Jong-Mihn (March 2008). “Advances in seawater desalination technologies”. Desalination. pp. 47–69. ) ;
- Al-Shammiri, M.; Safar, M. (November 1999). “Multi-effect distillation plants: state of the art”. Desalination. pp. 45–59;
- Fritzmann, C; Lowenberg, J; Wintgens, T; Melin, T (2007). “State-of-the-art of reverse osmosis desalination”. Desalination. 216: 1–76;
- Thiel, Gregory P. (2015-06-01). “Salty solutions”. Physics Today. 68 (6): 66–67.
- Van der Bruggen, Bart; Vandecasteele, Carlo (June 2002). “Distillation vs. membrane filtration: overview of process evolutions in seawater desalination”. Desalination. pp. 207–21;
- Jollibee, Merci. “Best Reverse Osmosis System”. Reviews 2015 Ultimate Guide.
- Gleick, Peter H., Dana Haasz, Christine Henges-Jeck, Veena Srinivasan, Gary Wolff, Katherine Kao Cushing, and Amardip Mann. (November 2003.) “Waste not, want not: The potential for urban water conservation in California.” (Website). Pacific Institute. Retrieved September 20, 2007.
- Cooley, Heather, Peter H. Gleick, and Gary Wolff. (June 2006.) Pacific Institute. Retrieved September 20, 2007.
- Gleick, Peter H., Heather Cooley, David Groves. (September 2005.) “California water 2030: An efficient future.” Pacific Institute. Retrieved September 20, 2007.
- Sun Belt Inc. Legal Documents. Sunbeltwater.com. Retrieved May 29, 2011.
- Giorgio Micale, Andrea Cipollina, Lucio Rizzuti, Seawater Desalination: Conventional and Renewable Energy Processes, Springer, 2009.