IS DESALINATION THE ANSWER?

By 2050 the World Health Organisation predicts that four billion people, almost two thirds of the world’s current population, will face severe fresh water shortages.1  The demand for water has increased due to a number of factors including population growth, climate change and an increase in demand from industry and agriculture.

Global water consumption is doubling every 20 years and the World Water Organisation estimates that by 2025 the demand for water will exceed supply by 56%.2

Less than 1% of the Earth’s water is fresh and available for drinking and because of the rise in demand, conservation organisations and governments are looking at a number of techniques to improve water management including the desalination of sea water.

Desalination involves separating sea water from the salt to create fresh water and there are two main techniques, distillation and membrane filtration. New techniques have been developed with modern technology, such as reverse osmosis and electrodialysis which use filters and an electronic current. Although the basic process of desalination has been around for thousands of years it has never been used on a large scale and there are a number of concerns about widespread use. There are currently more than 12,000 desalination plants in 120 countries but these only produce less than 1% of the fresh water consumed globally.3

Before the water is desalinated it must first be pre-treated to remove any harmful material and pathogens and this process uses a number of chemicals. Desalination plants are often located near an ocean, so the untreated water doesn’t have far to travel, but this also offers a simple solution for disposing of the waste product. Disposal methods of the concentrate include dumping it back in the ocean, injecting it into deep underground wells, storing it above ground in evaporation ponds and zero-liquid discharge procedures that produce a solid waste product.4

Unfortunately the process of desalination can harm the environment in a number of different ways. Disposing of the concentrate back into the ocean can disrupt the ecosystem and harm aquatic organisms. Pumping large quantities of sea water requires a large amount of energy and if fossil fuels are used this will increase greenhouse gas emissions. There are also cost issues related to desalination as it is generally two to four times as expensive as treating fresh water.5 In some arid and desert locations desalination is the only choice for producing fresh water, but due to the cost it isn’t an option for poor regions.

In the last ten years advances in desalination technology have led to a reduction in the energy needed but the cost and environmental issues prevent it from being used more widely. However, there are a number of benefits to using desalination together with other techniques. The increase in demand for water, together with a number of potential drought events, means some areas cannot rely on a single source of water. Desalination can help relieve stress on surface and groundwater supplies and it can be used to clean naturally occurring brackish groundwater.6 As there is less salt to remove in brackish water the energy required to desalinate is less, which reduces the cost.

Another cost saving measure is to locate desalination plants together with thermoelectric power plants that use seawater to cool their generators. The power plant would preheat seawater that could then be desalinated at a lower cost, since less energy would be needed.

With the growing demand for clean water, new techniques for treating various sources of water and improved water management will become more important. Desalination may not be the ultimate solution but modern technology is focused on making it even more cost-effective and less harmful to the environment. By carefully selecting sites for desalination projects it may be used as part of the solution to better manage our water supply.

References

  1. http://www.who.int/topics/water/en/
  2. http://www.theworldwater.org/water_facts.php
  3. Aaron Lada, Ph.D. | Article (Eco Hearth)
  4. Aaron Lada, Ph.D. | Article (Eco Hearth)
  5. www.athirstyplanet.com