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Last Updated: Saturday, 17 November 2018 18:03

“If we could ever competitively, at a cheap rate, get freshwater from saltwater, that would really dwarf any other scientific accomplishments.” John F. Kennedy

Various desalination technologies have been since developed. Numerous large scale plants have started decades ago. Respectable achievements are seen in many places in the world; but many questions remain, such as, but not limited to: Are these efforts enough? Is the throughput/watt sufficient to guarantee sustainability? Are the employed technologies well adapted to the user conditions. Are employed technologies economically sound, and affordable by users? Are they competitive with other technologies and with existing fresh water sources? Are they energy independent, or at least weakly constrained by the type of energy source?  Are the desalination solutions durable? What are the impact of current techniques on the environment?

The ultimate solutions for "fresh water to everyone on the planet" and that answer all the above questions at once are nothing but: Solar Desalination, Decentralized Desalination, Offshore Wind Desalination, Water Conservation, and Water Re-use. 

Decentralized Solar Desalination is not only convenient but also affordable for many developing countries, whereby  small desalination units can be purchased or made by individuals and families and utilized to produce fresh water for their drinking and for watering plants for modest food production. Small villages can employ mid-size solar desalination units. Both have optimal scales for solving the water problem in large regions of semi-arid and arid countries. In addition, they are the least costly, while the most environmental friendly, both during fabrication and operation. Larger solar desalination units with radiation concentration technologies are suitable for producing water for large farming and for feeding villages.

 

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One of my favorite research experiences as a group leader was solar desalination. Although it was short, I value it because of the technology usefulness, the wide open prospects associated with it, and its broader impacts. I was not a desalination expert, as I was initially rather skeptical about the technology. My skepticism was essentially for two main reasons. The first was the need for large amount of energy to separate salt from water, the second was the then high-tech aspect of the desalination, which, to me at that time, was a non-starter for countries that needed desalination the most. For instance, the then popular reverse osmosis and electrodialysis necessitated expensive and sophisticated membranes, which were then not available on the market, except for some special use. However, I fell in love with the idea of using solar energy to desalinate brackish water, for countless reasons. 

One of these reasons was not at all science related, but rather administrative, and exposure to a dynamic desalination research team that was collaborating with Commissariat a l'Energie Atomique (CEA) at Cadarache, France, in my former department. I was then appointed head of a research department, namely the Physics and Renewable Energy Dept., which performed research and development on renewable energy technologies for the government of Tunisia. The responsibility was great, but I had to approach it from my own specialty and from my own view point. The more important reasons for supporting Solar Water Desalination was its usefulness, the multi-disciplinary aspect of the research field, the fascinating physics and electrochemistry issues underlying the mechanisms of phase separation in liquid solutions, and on top of these, the utilization of solar energy. A lot of science is needed to i) understand phase separation, which could be either by thermal distillation, or through ionic transport and segregation of ions using polymer membranes or active porous media, and ii) subsequently develop efficient technologies.

The solar energy could be utilized in various ways, depending on the used method and the employed physics principles underlying the method. During my tenure, I have contributed in the scientific debate on solar desalination and worked with the team on several topics. One of the outcomes was the production of appropriate desalination technologies, which were analyzed by the research group through designing and building prototypes and evaluating their performances and their energetics. The technologies had to be low cost, and intended to serve the water needs by families, aggregates of families in small villages, aggregate of villages, and a small town. Each scale had an appropriate technology and an expedient scaling.

All in all, what we have been researching and promoting was alternative low cost desalination technologies. The alternative feature was in relation to what used to be complex and high tech methods and the associated hardware. Our technology choice was purposely (at the level of fresh water production) non-industrial oriented and was targeting small user groups and cluster of groups.

I will be writing more about this fascinating technology. Comments from readers are welcome.

A. Karoui