español   français   english   português

dph participe la coredem
fr.coredem.info

rechercher
...
dialogues, propositions, histoires pour une citoyenneté mondiale

Environmental and economic challenges of water desalination

Mohamed Larbi BOUGUERRA

02 / 2008

First of all, I would like to thank warmly the organisers for their kind invitation.

It is well known that Jordan has a lot of experts and scientists in the field of water resources. I am eager to apologize of any shortcomings of this ten minutes talk as well as for my rusty English.

Nowadays, water supplies are under extreme swings. Storms, floods and other climatic events bring it in great abundance. Droughts and desertification create cripplings shortages and excruciating human hardships.

The mismatch of need and plenty reaches accross the globe from developed to developing nations.

In the USA for example, water levels have dropped dramatically at Hoover Dam, lake Mead and many other locations as booming population draws heavily on water supplies. Meanwhile, the great Ogallala aquifer as well as those of the Great Plains at large are being ransacked and depleted by an unsustenable irrigation without any regard for the future generations needs.

In China, 617 big cities are suffering from water shortages and because of the country hectic industrialisation, water pollution is very common and causes scores of health and environmental problems. Beijing have even recourse to irrigation water to quench its enormous thirst and the capital draws heavily on its underground aquifers.

In fact, water shortages affect nearly half a billion people worlwide and this figure will grow with an ever expanding human population even if, it must be stressed, that water consumption varies greatly from one country to another (compare for example in that regard USA and Mali, Burkina Faso or Bangladesh…)

The WHO estimates that about 1.2 billion people worlwide lack any access to clean drinking water and that 2 millions people- many of them children and elderly- die of hydric illnesses (bilharziosis, malaria, Chagas disease…) and diaorrhea because of contaminated drinking water.

The Middle East is prone to water challenges.

Water desalination is oftenly seen as a magic answer (stick) except, of course, for countries without sea shores (Mali, Niger…). Since 97% of earth water are sea water, desalination may be seen as a sensible solution to human thirst and since water quality, water scarcity and infrastructures challenges are growing around the globe.

But wresting fresh water from brakish water or seawater is a long standing technique, especially in oil – rich water starved countries and emirates where the cost of the energy intensive process is not an issue.

Historically, it started in this part of the world since in 1869, a water distillation unit was built in Aden in order to supply the British Navy. Today, this same technique requiring a lot of energy and greatly improved leads to half of the desalinated water produced in the world.

However, now, officials in Yemen are concerned about the dwindling water reserves supplying the capital city Sanaa. A fastly expanding population and increasing use of water for irrigation are rapidly drawing down the city’s water resserves. In fact, Yemeni officials are beginning to contemplate moving the tall walls historic city and its inhabitants to Red Sea coast where desalination could maintain water supplies.

Multiple effect evaporation was the technology of choice in seawater desalination from about 1880 till 1960. With the introduction of multiple flash evaporation in about 1960, multiple effect evaporation appeared to fade from view and seemed further forgotten with the advent of Reverse Osmosis (RO). However, with new refinements and a better understanding of the potential limits of the process, it has regained a modest but well-earned role in the production of freshwater from the sea.

RO came of age in the 1970 following the semipermeable membranes that could efficiently separate salts from water under pressure. Sometimes called hyperfiltration, RO is generally held to be the most complex of the membrane separation processes.

This technology is very popular in many areas in the Middle East, in the Caribbean and elsewhere where desalinated seawater is the main source of urban and municipal supplies.

But it’s also used in the US, Japan and Europe as well primarily to produce ultrapure water for many industries such as food or electronics.

A major drawback of membrane – based technology is cost.

Two factors contribute to making membrane technology expensive:

  • One is the amount of energy consumed by the pressure driven systems, particularly by high pressure RO;

  • The other is membrane fouling, a phenomena that has become a focus of much research. France is the leader in that research field.

RO membranes are cleaned chemically after months of duty. Over long periods of time, membrane units are replaced when they become fouled and their performances significantly diminish and deteriorate. That happen usually every 3 to 5 years.

Other processes call on ion exchange and membrane technology microfiltration or nanofiltration or ultrafiltration.

Desalination now costs 50 cents of US dollar per cubic meter but that depends on scale, on electricity requirements or another power source and distribution. It is clear that doesn’t fit the rural poor of the world where water crisis is mainly and painfully felt. Moreover, it is clear that desalination is not able to supply water to agriculture.

Anyway, according to the Texas Water Development Board, the cost per cubic meter of water treated by distillation is between 95 cents and $ 1.04 while the cost via RO is 82 cents.

Every desalination unit needs usually an energy producing unit. The latter generates of course a great amount of GHG which are going to have an impact – actually a negative impact – on the climate and on the water cycle. Or, in most instances, desalination is made to counteract the water cycle and climatic change vagaries. One is caught here in a vicious cycle.

Then one has to face the brine issue. A desalination unit generates a lot of brine which is made of various salts, heavy metals, organic compounds… If you throw it back to the sea, you are going to put a great chemical imbalance on the seawater physical and chemical constitution and hence biodiversity will experience dire consequences. In some places, brine is injected in the underground but there are concerns about that operation because it is believed to ease or to catalyse earthquakes. It is for that reason that some desalination utilities were temporary closed in California.

For some analysts, water desalination may appear as a technological fix to the water needs of our modern societies or, sometimes, as a political trick as in the case of the Israeli- Palestinian conflict.

Natural resources such as water are of course limited and finite. Desalination is deceiving. It’s a fool paradise rubbing that fact. Illimited abundance in any field or realm is a hoax.

Rather, one must take into account of all the techniques aiming at a wise water use, to conserving of the resource and processes intented to save water. One must manage water in order to eliminate leakages which amount up to 20-30% on average worlwide (NAFW not accounted for water).

According to recent studies, it appears that conservation measures may meet the new water needs for a cost which is 10 to 25% of incurred expenses of water desalination.

In that regard, water efficiency must be improved. Leakages and wastings must be eliminated. According to the Washington based Worldwatch Institute, we can avoid thus desalination and its negative effects on the environment and the atmosphere.

Finally one must point to the fact that desalinated water quality must be carefully monitored for bromate, a suspected carcinogen. According to international regulations, bromate levels may not exceed 10 ppb on average over a year in a reservoir.

* Author’s addition: On Sunday 25th February 2008, President Bouteflika and Jeff Garwood, chief executive of GE Cy opened in Hamma, near Algiers, one of the largest seawater desalination plants in the world. It is built and operate for 25 years by GE. It costs 250 millions $.

It can handle up to 53 millions gallons of seawater a day according to ENS. It will provide water to two millions people in Algiers. It uses GE’s proprietary RO membranes.

Mots-clés

salinité de l’eau, accès à l’eau, qualité de l’eau, mer, innovation technologique

Notes

Author’s lecture during the roundtable on « Natural resources and security » during the seminar on « Natural resources » organized on the 18th of January 2008 by the French Embassy in Amman and the Institut Français du Proche-Orient.

Source

Collection of Chemical & Engineering News, American Chemical Society, Washington, D.C .

Worldwatch Institute annual report «State of the World 2004», Washington, D.C. (translated in French by M.L. Bouguerra « La consommation assassine. Comment le mode de vie des uns ruine celui des autres. Pistes pour une consommation responsable », Editions Charles-Léopold Mayer, Paris, 2005)

M .L. Bouguerra in «Manière de voir. Le Monde Diplomatique» N° 81, Juin-Juillet 2005, p. 41-44.

M.L. Bouguerra, «Water under threat», Zed Books, London, 2006

«L’eau. Attention fragile», Dossier in Pour la Science (Scientific American), Paris, Janvier-Mars 2008.

FPH (Fondation Charles Léopold Mayer pour le Progrès de l’Homme) - 38 rue Saint-Sabin, 75011 Paris, FRANCE - Tél. 33 (0)1 43 14 75 75 - Fax 33 (0)1 43 14 75 99 - France - www.fph.ch - paris (@) fph.fr

contact plan du site mentions légales