Seawater desalination a solution to reduce water shortage

By Peter Brabeck-Letmathe

19 February 2014 See comments (5)

DESALINATION has become an important tool for effective water management.

Desalination has become an important tool for effective water management. It can be seen as one solution to overcome rapid shortage in municipal water supply. But as I’ve stressed before, there is no single silver bullet to address the water issue overall. Desalination actually requires large amounts of energy and can be expensive.

In this blog post, I want to provide some insight and ideas on whether desalination can become a significant lever to combat water scarcity. It will not offer a complete answer but I do hope that the discussion generated here will provide a more comprehensive picture on this highly topical subject.

The impact of desalination is significant. In 2012, the installed global capacity for desalination totalled 27.3 cubic kilometres of generated fresh water annually. About 60% of desalination capacity treats seawater, and the rest treats other, less saline sources.

Today, capacity has increased from 17.4 cubic kilometres compared to five years earlier. This means it’s been growing at an average annual rate of 9.5%. Extrapolating with this growth rate, global capacity may reach about 140 cubic kilometres by 2030. Theoretically, the assumed increase between 2010-2030 may cover close to 5% of the estimated gap between fresh water withdrawals and sustainable supply.

But is 5% significant? Is it too high – or is there room to do more?

Price of desalination

Cost is a vital aspect to be considered. Today it has reduced to about USD 0.5-1 per cubic metre of fresh water. One cost-effective example is an installation in Singapore. In its first year of operation in 2013, the cost of desalinating water was as low as USD 0.45 per cubic metre.

But desalination cost depends on different factors. The most important is the type and stage of development in which technology is being used, and the cost of the amount of energy consumed in the process.

The table below shows the energy consumption and percentage of total installed capacity of the main types of seawater desalination:

Energy efficient reverse osmosis

Seawater reverse osmosis (SWRO) used in desalination is the most energy efficient process, and has the largest market share today – 63% of the total worldwide installed capacity. Over the past 20 years, technological progress has helped to reduce the energy requirements used in SWRO (pdf document):

The graph to the side from Yale University in 2012 suggests that such energy consumption is as low as 2 kWh (pdf document) per cubic metre. But this is still considerably higher than the 0.2 kWh per cubic metre, or even less, required for local fresh water supplies.

There is still potential for further gains in energy efficiency of desalination. In 2013, researchers from the Massachusetts Institute of Technology designed a new type of membrane composed of a one-carbon atom thick sheet of graphene. Until now, it’s only a computer model but it may pave the way for further improvements in desalination energy efficiency.

The theoretical minimum of energy required to remove 35 g/l of salt amounts to 0.8 kWh per cubic meter freshwater. This is the equivalent of the energy that would be generated when 'dissolving' the same amount of salt in water (law of conservation of energy). But getting to 0.8 kWh would need a perfect thermodynamic and mechanical system, which is not possible to build. Rather than trying to reach this limit, engineers are trying to get closer to it.

Bigger is better

Total cost also depends on the size of projects. As a rule of thumb, water produced in smaller plants – a few thousand cubic metres per day – would cost 3-5 times more than larger plants.

A new plant due to start operations early this year will be located in Ras Al Khair in Saudi Arabia. It will be the largest hybrid desalination plant in the world combining thermal and membrane technologies to serve about 3.5 million people in the city of Riyadh.

Part of the water debate

There seems to be opportunities in desalination, especially as seawater is available in nearly unlimited amounts. Desalination looks set to become more energy efficient, with a further reduction in costs, and high growth rates for new desalination capacity will continue.

But desalination is mainly a solution for communities based near a coast, as long-distance transfers of freshwater can be quite expensive.

More desalination not only comes with high investment and running costs but also has direct and indirect environmental impact from the different types of energy used.

From such insights, seawater desalination surely has its place in the global water debate. I welcome your thoughts, comments and ideas.

*data from Desware; **data from IDA

  1. IQBAL NARAIN @ Nestle India Ltd.

    22 Feb 2014 - 13:19 (GMT)

    The problem faced globally is perhaps not so much of water-availability but of not having adequate water where it is needed the most. Furthermore, household water usage accounts for less that 8%of total water usage worldwide, though again there could be major regional variations. Most of the water would be consumed for industry, infra-structure, irrigation and sanitation. India perhaps provide a good example of the kind of challenge faced in bridging the gap between demand and supply of water. Here is a country with almost 17% of world population and only 4% of its water availability----that too largely inequitably distributed. It is one of the faster growing economies urbanizing and industrializing at a relatively rapid pace. Yet it lacks resources to set up large capacities to tap sea water for which it has a 7500 Km coastline. It has therefore so far depended heavily on its rivers, ground water resources, diversion technologies and more recently on desalination plants mainly for coastal cities in Tamilnadu, Andhra and Gujarat states. Unlike the Middle East, India has progressed on this front only through relatively smaller, decentralized capacities using both thermal and membrane technologies. If the pace is to really pick up, there is need to (a) have a coordinated approach in the nature of a national water grid, (b) develop newer technologies that consume less energy and offer cheaper options namely, nano-osmosis and solar-power and (c) creating better awareness of processes like re-cycling. It is in these areas and not so much in conventional processes that countries with better technologies could be the early riders in markets with exciting potential.

  2. Peter Brabeck-Letmathe @ Nestlé

    28 Feb 2014 - 10:14 (GMT)

    Dear Iqbal Narain, thanks for this interesting information on India. Some time ago on this blog I reported back from a water discussion in Delhi:–-WEF-Water-Summit-at-India.aspx . My conclusion of what I heard: water scarcity in India is set to be one of the world’s most acute issues over the coming decades. And the main issue to be addressed, one that can not be solved with desalination, is water for agriculture. About 90% of all freshwater withdrawals in India for human use goes to farms. Enough water, and better water use efficiency are matters of survival of the rural population and also matters of food supply security for all India and beyond. Siddharth Chatterjee wrote a guest post on my blog about this: Regards, Peter Brabeck.

  3. Mayank Trivedi @ Nestle

    19 Mar 2014 - 10:30 (GMT)

    As the water rises above our collective noses on this tsunami waiting to hit our shores leaving large sections of humanity high and dry, nations and governments may not have an option other than to turn to desalination.

    Hence, desalination may not be a matter of choice but an absolute social and political imperative which can and will be justified juxtaposed with the tragedy of a potentially thirsty human race. And, those who could and should have been responsible and able to prevent the issue in the first place (politicians, governments) will be the first ones to champion the new solution, regardless of the costs involved and insensitive to the collateral environmental damage.

    And, when there is a need there will be a business opportunity – both, private enterprise and tied aid from rich to poor nations. As the desalination business acquires scale, the costs will be driven down for sure. The same can’t surely be said of the environment consequences. Issues of energy emissions and ecological imbalance (where does all the salt go ?) are unlikely to create any waves and, even if they do, there will be adequate justification available.

    Desalination may be the inevitable future of water availability and if it is so, then the best thing to do will be for society to hope and support the efforts which make it less costly and more environmentally conscious.

  4. Shiney - Writer @ Wininfo

    13 Jul 2016 - 11:49 (GMT)

    Despite the supposed disadvantages associated with it, desalination is inevitable. We are depleting groundwater with unimaginable madness and the oceans contain 96% of the total water on earth. That makes it easy to understand what our future water source is going to be. Reverse Osmosis makes it realistic. The energy and marine life consideration will eventually be taken care of. As you can see the latest hardware components are becoming more and more energy and cost-efficient. Perfect example here:

  5. Peter Brabeck-Letmathe - Chairman @ Nestle

    02 Sep 2016 - 08:09 (GMT)

    Dear Shiney, many thanks for the comment.

    Indeed, desalination is inevitable. I also took a look at the site you referred to, but did not find an indication of cost and energy efficiency of desalination there.

    Where do we stand today (e.g., USD total cost as well as oil equivalents per cubic metre of freshwater generated) and where do you think we will be in 10 and 20 years from now concerning efficiency.

    And ultimately, is there an absolute limit in energy efficiency we will never be able to overcome?

    Regards, Peter

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