Water Desalination

Everyone knows that water is one of the most essential things that you need in order to survive.  What happens to your body if it does not have water?  Without water, your immune system would be disabled, which may cause severe illness.  Since water is a necessary substance that transports biological and pathogenic materials throughout your body, the lack of water would poison certain parts of your body.  Even spending a few hours outside in 80 degrees Fahrenheit without water could degrade your body due to its lack of cooling.  Water is a basic necessity of life.  Without it, living things would not survive.

There are many places throughout the world that lack a clean water supply.  For example, there was an extreme drought in California in July 14, 2009 that posed a tremendous issue for the wellbeing of its residents (University of California – Los Angeles, 2009).  Increasingly, our nation’s major reservoirs and groundwater basins are subpar in being able to supply clean drinking water.  We must face the facts that our increased population growth is causing a critical water shortage. Nevertheless, there is a solution, one of which is water desalination plants.

Desalination: Two Methods

Desalination is the general process of removing salt and other minerals from water so that we can drink it.  Salt is the primary byproduct of this process.  There are generally two processes that engineers have innovated in order to produce clean water:  distillation and membrane processes.

MSF Distillation

The commercial process of desalination primarily uses multi-stage flash evaporation, or MSF evaporation.  Plants that use this process are close to large bodies of water in order to obtain the necessary amount of water demanded by the consumer.  Throughout this process, saltwater is heated under pressure; however, this process does not allow for the water to evaporate or boil in its heaters (Deliyannis et al., 1978).  The warm water is flashed in a chamber, where there is a significant reduction in the quantity of pressure. The saltwater will be flashed multiple times, allowing for the formation of a liquid and a vapor state due to successively smaller changes in pressures being used in each flash drum.  Here, the clean vapor state can be separated from the saltwater using gravity, as the clean water vapor will rise and channel out of the system.  During this process, brine, or the liquid saltwater byproduct, is reintroduced to the beginning of the process.

Reverse Osmosis

The reverse osmosis system generally works under four processes: pretreatment, pressurization, separation, and stabilization.

1. The seawater is pretreated by removing suspended solids and by adjusting the pH.  The water is then biocompatible with the membranes and is suitable for use (Organization of American States, 2013).
2. The operating pressure is raised by a pump.
3. The primary separation allows the desalinated water to pass through the membrane, while the salts and other minerals are unable to do so due to their chemical and physical interactions with the membrane.  This desalinated water might not be completely pure.  As a result, it is reintroduced into the separation process until it meets the required purity.
4. The drinking water is distributed to the public after it is adjusted for its proper acidity and chemical state.  The water may undergo vapor-liquid equilibrium passing through the membrane and through its final product stream.  Consequently, it is condensed so it is viable for drinking.

Disadvantages of Desalination Plants

One of the primary disadvantages of using desalination plants is the tremendous quantity of energy that each plant must undergo on a daily basis.  It costs a lot of power and money in order to heat water.  Because of water’s high heat capacity, it is more resistant to the transfer of heat.  As a result, it takes more heat in order to put the water at the temperature at which it can be properly flashed.

Increasingly, it is difficult and costly to build the infrastructure required to desalinate water.  The pumps must be capable of compressing water in its saturated, liquid, and vapor phases.  Liquids cost an extreme amount of energy to compress, thus running up the energy costs of running the plant.

One of the primary environmental concerns of desalination is the production of greenhouse gas emissions.  Because massive amounts of energy are required for the process, nuclear power and fossil fuels have been the primary energy sources.

Increasingly, marine biologists have been concerned with the impact that these desalination plants have on the marine life.  Some of the fish, invertebrates, birds, and other smaller mammals have passed through the intake screens of the input streams of the plant (Nellen, 2011).

Moreover, the most significant environmental damage from the plant is the byproduct stream of saltwater that is not properly treated.  This causes thermal pollution and contamination to our local sea water as a result of the dumping of the brine back into the ocean (Nellen, 2011).

Should You Support Desalination?

Like most sustainable technological innovations, the benefits outweigh the risks.  Energy generation is moving towards a more green movement, as more renewable energy sources like solar and wind generated energy are being used rather than crude oil and coal.  Even though there are environmental drawbacks, desalination plants have been established worldwide in order to improve the economies and standard of living in poorer countries.  While we await the arrival of a sustainable and clean energy source that can be used on the global scale effectively, desalination plants are going to continue to provide the necessary amounts of water for places like the Middle East that could not survive without this technology.

References

Organization of American States. (2013). 2.1 Desalination by reverse osmosis. Organization of American States. Retrieved from http://www.oas.org/dsd/publications/Unit/oea59e/ch20.htm.

Deliyannis, E., & Deliyannis, A. (1978).  Water Desalination. Naturwissenschaften – The Science of Nature.  Retrieved from http://download.springer.com/static/pdf/296/art%253A10.1007%252FBF00702832.pdf?auth66=1362715242_9b9fadeccd018593abd6c9a359c56ce8&ext=.pdf.

University of California – Los Angeles. (2009, July 14).  Major breakthrough with water desalination system. ScienceDaily.  Retrieved from http://www.sciencedaily.com/releases/2009/07/090713144124.htm.

Nellen, A. (2011, July 28).  Desalination: A Viable Answer to Deal with Water Crises?  FutureDirections International.  Retrieved from http://www.futuredirections.org.au/publications/food-and-water-crises/166-desalination-a-viable-answer-to-deal-with-water-crises.html.