Desalination has no known negative impacts on the environment. True or False?

The correct answer is False. Desalination is the process by which dissolved salts are removed from the water. It is used to treat seawater and groundwater, and it is done to make the water usable. Our bodies are not adapted to drinking salt water and we would not survive drinking this water unless the salt is removed first.

Some parts of the world are in dire need of drinkable water, which has led to the development of various methods of removing salt from water. Desalination is expensive and uses a lot of energy, which is why it is only done where absolutely needed. Depending on the method used it can also have a negative impact on the environment.

By Spazio Infinito [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Desalination is done commercially mainly using distillation and reverse osmosis. These two methods do need to use energy in order to work. In fact, these processes use a lot of energy which can mean more fossil fuels being burnt to provide this energy.

This adds to the greenhouse gases and air pollution problem, which further exacerbates global warming. In addition, the plant may generate a lot of brine waste that is released, which can be a problem especially if pipes happen to leak.

Even when there are screens on the pipes that are pumping water out of the ocean, a number of organisms are killed because they are small enough to pass through the screen and end up in the system. Another problem is the very high salt concentrations right at the outlet pipes where the waste is pumped out.

The process of desalination

There are a number of ways that water can be desalinated. In all cases, the aim is to separate the water and solutes. Commercially today the main methods in use are reverse osmosis and multi-stage flash distillation. The latter method relies on making steam in flashes.

The reverse osmosis process instead works to move water against its natural tendency to move towards where there is a high concentration of solutes. Instead, it is forced through a membrane which separates the solutes from the water.

The process also needs energy because it is against the natural concentration gradient of water but it does not need as much energy as distillation where water has to be heated so that it will change phase and become steam.

The impact of desalination

A certain number of animals are directly killed by the process where pipes extract water directly from the ocean. There are screens on the pipes to stop most organisms from being pulled in with the water, however, small fish fry, fish eggs, and other small organisms are so small that they are still taken in and killed by the process.

The other problem is the effluent that is discharged after the water has been extracted. The waste product contains highly concentrated brine and chemicals used in the desalination process.

The salt content of brine is usually about double that of natural seawater. This substance is pumped back into the ocean often where it settles on the ocean floor. Ecologists are concerned over the impact this has on ocean life on these sediments. Brine raises the salinity of water by 70%.

The impact is seen in areas of the Arabian Gulf where numerous desalination plants are in operation. In 1996 alone, 14 million cubic millimeters of brine per day was being pumped into the Arabian Gulf.

Another concern is if the pipe develops a leak and accidentally discharges this substance before it reaches the ocean. This would then contaminate soils and vegetation and may eventually find its way into groundwater aquifers, contaminating freshwater.

Organisms are adapted to a narrow range of salinities. Changes in salt concentration near where the effluent is discharged are very likely to cause organisms to die.

How animals osmoregulate

Animals have to regulate the amounts of salts and waters in their cells. This process of osmoregulation is necessary for survival. Aquatic organisms are adapted to the conditions in their environment.

Animals in freshwater have the problem of there being too little salt in their surroundings so they actively take in salt to avoid losing too much water to their surroundings. These animals are known as osmoregulators.

Animals in marine environments have the opposite problem with their surroundings being too salty. This means that they tend to lose water from their cells to the surroundings by osmosis. To compensate for this they often drink seawater.

Many species of fish live in a narrow range of conditions and can only survive in either freshwater or in saltwater. This means that any change to the salinity of their habitat is likely to kill them. When organisms are eliminated from a habitat it can have consequences for the entire food web.

Global warming

Another ramification of desalination plants is that they need a lot of energy. In many cases, this energy is supplied by the burning of fossil fuels. This causes the release of greenhouse gases such as carbon dioxide, nitrous oxides and methane into the atmosphere. These gases trap heat and accelerate global warming.

The global warming then has adverse consequences such as impacting the distribution of plants and animals, impacting life cycles of species and entire food webs.

It is also likely to cause a rise in sea level which can lead to flooding of low-lying areas around the world. This then poses a threat to people living in such regions.

Advantages of desalination

There are advantages of desalination, for instance, the oceans are a vast source of water that is unlikely to run out. Freshwater systems are far more limited in terms of water availability compared with the oceans.

Cities would not even be possible in desert areas if it were not for the ability to desalinate ocean water. Therefore it has allowed colonization of large areas of formerly inhospitable land.

It also means that people have not had to worry about running out of water or having to ration water. Desalinating water is also often less expensive than having to transport large quantities of water from other places.

Using such desalting systems also means that what freshwater is present can be conserved and not overused and depleted. This means that it is a more reliable source of water for people in regions of the world where rainfall is unpredictable.

References

  1. Editors of Encyclopedia Britannica (2018). Excretion. Retrieved from Encyclopedia Britannica.
  2. Editors of Encyclopedia Britannica (2018). Desalination. Retrieved from Encyclopedia Britannica.
  3. S Lattemann, T Höpner (2008). Environmental impact and impact assessment of seawater desalination. Desalination.
  4. JJ Sadhwani, JM Veza, C Santana (2005). Case studies on environmental impact of seawater desalination. Desalination.
  5. AD Khawaji, IK Kutubkhanah, JM Wie (2008). Advances in seawater desalination technologies. Desalination.

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