Olivia Basile
Disclaimer—This paper partially fulfills a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering. This paper is a student, not a professional, paper. This paper is based on publicly available information and may not provide complete analyses of all relevant data. If this paper is used for any purpose other than these authors’ partial fulfillment of a writing requirement for first year (freshman) engineering students at the University of Pittsburgh Swanson School of Engineering, the user does so at his or her own risk.
REVERSE OSMOSIS DESALINATION
Olivia Basile ()
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Olivia Basile
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Olivia Basile
Reverse Osmosis Desalination: A Potential Solution
The water crisis is the #1 global risk to society on a planet that is 70% water [1]. In other words, it’s a problem that shouldn’t be a problem. The issue lies in the types of water on the planet. Due to the amount of salt in seawater, it is unable to be consumed as is [2]. One of the ways salt is removed from saltwater is reverse-osmosis desalination. This involves pushing saltwater through small filters that catch the salt and leave freshwater behind. This would be a perfect solution if not for the high cost and potential damage to the environment. Experts are split, with some saying it isn’t a viable solution because of the damage to the environment, the astronomical cost, and the high amount of energy needed to run desalination plants. Proponents say the advantages outweigh the disadvantages. They believe that if more companies and governments invest in RO Desalination, the cost would go down. They also say that the environmental impact can be decreased with an increased investment in the technology [3].
RO Desalination is currently being used around the world with successful results. Israel’s reverse-osmosis desalination plant in the city of Sorek is the largest plant in the world. Israel, a country known for its water shortages, now has a surplus, which is mainly attributed to its investment in desalination plants [4]. Given the severity of water shortages worldwide and the minor disadvantages, I believe that reverse-osmosis desalination could be a major solution to the water crisis.
What is Desalinationand Why is it Important?
Desalination is one of many methods that can help solve the water crisis, but it has the potential to make the biggest impact. Only 1% of the world’s water is usable freshwater. If the Earth itself is 70% water, that leaves a lot left over, in fact it leaves more than we could ever need. The issue with this water is that it’s salt water, and thus unable to be used by the world’s population for most things (drinking, cooking, agriculture, etc.). Desalination solves that issue, and on a wide scale it would essentially solve the water crisis.
One of the main problems with desalination is how expensive it is. Desalination of saltwater requires large plants to be built and a separate structure to retrieve water from the ocean. The plants require large amounts of energy to power them. Ideally, they could run on renewable energy, but that is another added cost and without a huge investment in desalination, the plants would be too expensive to run long-term [3].
Different Methods
The preferred method by many chemical engineers is the ElectrodialysisMembrane Process. This is like reverse osmosis in that it takes water directly from the ocean and separates the salt by a filter, but the main difference is that they are removing salt ions from water, not vice versa. The removal process involves moving cations and anions through a charged membrane using a voltage gradient. Moving the lower concentration species (salt) is easier to do because there is less of it, but there are two problems with this method. The electrode-membrane instruments are not easily assembled packaged, since they require a plate and frame setup. They are also very expensive to make. Although the process is simpler than most, these two problems are responsible for its limited use [5]
Another process is Membrane Distillation, which filters out the water using microporous and hydrophobic membranes, which allow the water to pass through as vapor. This involves using thermal energy, which is not environmentally friendly. In theory, it could be modified to use solar power, but that would make the process even more expensive than it already is [5].
Why Reverse-Osmosis Desalination?
Reverse Osmosis Desalination is currently the most popular method of desalination. It starts with the intake of water from the ocean. This is usually done in a structure adjacent to the plant. The water is then taken to the plant and pre-treated with chemicals and filtered using reverse osmosis membranes. These membranes are molded into thin films that sit atop a porous support layer. The films are wrapped in spirals and packaged into modules, thus known as “spiral wound modules.
The next step is Energy Recovery. Only half of the water filtered is ready for use. The other half still has low to moderate levels of salt and cannot be used. It is normally referred to as brine water. The water that can be used is then post-treated. This normally involves adjusting the pH to a safe number (ideally 7), removing any Boron and adding Calcium. This water is then ready to be used, while the brine water is discharged and will be treated again.
This method, although one of the best, does have its drawbacks. For the cost of the desalination, the amount of brine water is both concerning and wasteful. A modification that is currently being implemented is improving the filters so that there is less brine water. Another problem is the amount of energy it takes to complete desalination. While its reputation of being a big energy consumer is an exaggeration, it does use more energy than treating fresh water from a reservoir would. Using renewable energy and lowering the amount of energy needed is another useful modification [5].
A lesser but still relevant problem is the damage to marine life. Water is currently retrieved near the surface, which can harm and kill small marine life. Efforts are being made to make sure there is minimal harm done; desalination plants in California are working with the California Coastkeepers Alliance on different ways to preserve marine life. They are currently developing different techniques to intake water at deeper levels of the ocean where marine life isn’t as prevalent [3]. Even with its negative aspects, reverse osmosis remains the most popular method of desalination. It’s relatively straightforward and can be implemented easily with a lower cost compared to other forms of desalination. If countries can afford it, the cost is worth the gain.
An Amazing Impact
Israel has felt this gain. Since investing in reverse osmosis desalination in 2005, the country has gone from dehydrated to having a surplus of water. Israel in 2007 was facing the depths of their worst drought in the past 9 centuries. They made the decision to create a desalination plant in the city of Ashkelon in 2005, and noting the massive amount of freshwater it provided (166 million cubic yards), they soon had two more. Their most recent plant in Sorek provides an additional 196 million cubic yards.
As seen in the middle east, water affects more than just health. Syria, Iran, and Jordan, among others, face many problems that can be attributed to water shortages. Drought and agricultural collapse have caused overcrowding, crime, and unemployment to rise in those countries. Israel could avoid this, which has allowed them to start thinking about sharing all their extra water as an act of diplomacy. They have also been planning to build a larger desalination plant and share the water between Israelis, Jordanians, and Palestinians, which would also create peace amongst tensions between these powers [4].
Goals within Engineering
Reverse Osmosis Desalination was made feasible by chemical engineer Sidney Leob when he created a functional reverse osmosis membrane from cellulose acetate polymers [6]. I doubt he realized, in 1959, the amazing impact his work would have decades later. His invention has saved numerous lives and created a booming field in engineering.
I can see myself working with desalination in the future, which is nice, since the inventor was a chemical engineer himself. As I talked about in my last paper, I want to make the world a better place through my future career as a Chemical Engineer [7]. It is important to me that I use the knowledge I gain to make a difference in the lives of others. I think it’s a goal that all engineers share, even if they don’t realize it. Engineers create systems and technology for the world to use, and the most meaningful of these will have a positive impact on those who use them.
Reverse Osmosis Desalination is the Answer
Desalination is the answer that the world needs to solve the water crisis. The earth has an enormous amount of saltwater, more than enough for everyone on this planet. Extracting the salt through a cost-effective method like reverse osmosis desalination can provide a surplus of freshwater at a reduced cost. It is still expensive, it still uses a great deal of energy, and it still has an environmental impact. But there are ways to reduce the negative effects, and the advantages span farther than just basic needs. Reverse Osmosis Desalination has the potential to bring a country to its feet and bring the world together.
Sources
[1] “Facts about Water & Sanitation.” Water.org. Accessed 10.29.2016.
[2] “Provide Access to Clean Water.” National Academy of Engineering. 3.30.2016. Accessed 10.30.2016.
[3] M. Werth “Is Desalination the Answer to Water Shortages?”Global Citizen. 9.1.2016. Accessed 10.30.2016.
[4] R. Jacobsen. “Israel Proves the Desalination Era is Here”Scientific American. 7.29.2016. Accessed 10.30.2016.
[5] “Getting the Salt Out.” The Chemical Engineer. 7.1.2013. Accessed 10.30.2016
[6] “First Demonstration of Reverse Osmosis” UCLA Engineering. 2016. Accessed 10.30.2016.
[7] Olivia. Basile. “The Swanson School and Me.” 9.8.2016. p.1
Acknowledgements
I would like to thank Tim Maddocks for grading my papers. I would also like to thank Maya Zaatari for reviewing this essay with me. I would like to thank Julia Lynch for supporting my idea to write about reverse osmosis desalination
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Olivia Basile
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