Desalination

titles_aquaculture oceans_4

Written for Coursera (MOOC) Class ‘Ocean Solutions‘ by University of Western Australia (June 2014)

Arguably, the greatest challenge facing humanity today is provision of fresh water.  Water is critical for all life on earth and humans consume an average of 1,385 m3/yr [1].  We are approaching the limit of natural fresh water availability required to match consumption [2].

PIC_Desalination Simple

The scope of this challenge is global.  According to UNESCO, more than 780 million people (10.8%) have no access to clean water, 2.5 billion (34.7%) have inadequate sanitation and around 7 million die annually from water related disease [3].

The reason for selecting this challenge is that with rising populations [4] and the prospect of significantly altered weather patterns due to global warming, provision of adequate fresh water supplies to areas of dense population and agricultural land is likely to intensify over the next few decades and beyond [5].

PIC_Desalination Global Capacity

One way to help alleviate water scarcity is by more efficient use of available water, recycling of grey water for sanitation, agriculture/horticulture, and industry [6].

The trend in the last century has been for increased global water consumption by a factor of ten [7].

  • China: 1.071 m3/yr
  • India: 1.089 m3/yr
  • USA: 2,842 m3/yr

Sources of freshwater are:

  • 74% Rainwater
  • 11% Ground/Surface Water
  • 15% Polluted Water

Agriculture is by far the largest consumer of fresh water [8].

Uses:

  • Agriculture 92%
  • Cereals 27%
  • Meat 22%
  • Milk Products 7%
  • Industry 4.4%
  • Domestic 3.6%.

The driest half of the earth is occupied by 85% of the human population [3].

An ocean-based initiative to this problem is Desalination, which converts salt water to fresh water, by a process of reverse osmosis.  Salt water is pressurised (250 – 1000 psi) and passed through a series of membranes, which strips out the impurities, including salt [9].  Desalination technology can be used to convert seawater, brackish water and waste water.

The reason and justification for making this decision is that desalination plants are already in use across the world, having been developed in the 1950s.  The technology has been particularly successful in arid regions which have the financial resources to construct plants, such as the Middle-East and the Western USA [10].

The cost of desalination plant is reducing with time, and the quantity of installations increasing.  Since the 1970s, global production doubles every decade, and costs have reduced by half every 15 years [11].

PIC_Desalination Process

Factors that impede desalination in delivering fresh water, a key resource for humanity include: Capital Cost, Energy Consumption and Public Perception of Water Quality.

As water becomes more scarce, the cost of plant will have to be met since few other options are available.  The cost is falling with time and with an expansion, economies of scale may make it more affordable.

Desalination is energy intensive, but since the worst drought affected areas are in the tropics, solar power can be harnessed [12].

Public perception is that desalinated water does not taste as good as natural fresh water.  However, ‘blind tests’ indicate that there is no real difference in water quality [13].  Desalinated water is often a healthier option, since the process also removes harmful bacteria [14].

References:

[1] ‘The water footprint of humanity’, Pratibha Joshi, March 6, 2012

[2] Ocean Solutions: Lecture Materials, 2.0 The Challenge 2.1.2 Water Security

[3] ‘United Nations: Water Cooperation’, Facts and Figures

[4] Ocean Solutions: Lecture Materials, 1.0 Problem Statement 1.1.1 Population Growth

[5] Ocean Solutions: Lecture Materials, 1.0 Problem Statement 1.1.2 Population Projections

[6] US Environmental Protection Agency, ‘Water Recycling and Reuse

[7] Ocean Solutions: Lecture Materials, 1.0 Problem Statement 1.2.4 Per Capita Water Use

[8] Ocean Solutions: Lecture Materials, 1.0 Problem Statement 1.5.9 Water Cycling

[9] Ocean Solutions: Lecture Materials, 5.0 Water  5.1.2 Process – Reverse Osmosis

[10] Ocean Solutions: Lecture Materials, 5.0 Water  5.1.4 Global Desalination Capacity

[11] Ocean Solutions: Lecture Materials, 5.0 Water  5.1.5 Desalination Production and Cost

[12] ‘Is solar-powered desalination answer to water independence for California?’, The Guardian, 28 January 2014

[13] Ocean Solutions: Lecture Materials, 5.0 Water  5.2.4 Perception Water Quality

[14] World Health Organisation, ‘Water Sanitation and Health’,

Advertisements

One thought on “Desalination

Comments are closed.