Cryo-desalination – A nature inspired solution to obtain freshwater

New water innovations are needed to secure freshwater supply for human use, even in the Nordics that are typically perceived as water secure nations. Cryo-desalination, also known as freeze-melt desalination or freeze-thaw desalination, allows to obtain fresh water by freezing seawater. Is that even possible, how energy efficient is it and why is it not implemented yet?

In pursuit of new methods to obtain freshwater
Global availability of clean water is one of the Sustainable Development Goals set by the United Nations for 2030. The rise of global temperatures due to climate change is a major problem impacting every continent and threatening the ability to secure SDG 6. In many parts of the world the water footprint has already exceeded sustainable levels, whereas due to the global dimension of water consumption, many countries have significant impact on water consumption and pollution elsewhere. Looking into the future, it is important to think creatively about the types of innovations that will form tomorrow’s toolbox for securing not only water but also the health of ecosystems. Desalination is a very attractive nature inspired solution for obtaining fresh water from the seawater, which comprises 97% of the water in the world and yet has a marginal role in human water consumption. Traditional desalination processes (e.g. thermal evaporation, membrane processes) despite having improved performance over the years, they still lack sustainability and have systemic problems (e.g. linked to pollutants and membrane fouling).

The sustainability potential of cryo-desalination as opposed to traditional desalination is higher if we consider energy demand over the entire process.  As the melting of ice takes approximately 7 times less energy than boiling water, cryo-desalination has the potential to be more energy efficient.  In addition, since this approach does not rely on any filters in it can be fully sustainable form the perspective of new materials usage as well.

What is cryo-desalination?
Cryo-desalination, the separation of water and salt upon freezing, utilizes the natural tendency of water to push out salt upon freezing. In practice, one utilizes energy to cool water and form ice. As ice is forming it expels most of the salt, resulting to the so called brine, which is very highly concentrated saltwater. Then the ice and brine are separated followed by the warming up of the remaining ice in order to obtain the fresh water.

Most of the energy required for the freezing and melting of ice can be recovered by an external thermal bath and coupling to a process that has excess cold energy such as liquid natural gas. Thereby, this technology can be applied equally to both cold and warm climates. The ice-brine separation is the critical step that defines the amount of seawater that can be obtained. There is a difficulty here though since during freezing salt and water mix down to microscopic level forming small brine pockets inside the ice. Understanding the water-salt separation mechanism could therefore be an important part of creating better technological solutions for cryo-desalination.

A schematic describing the steps in cryo-desalination (also known as freeze-melt desalination). Most of the energy required of the cooling and heating can be recycled, whereas the ice-brine separation limits the amount of fresh water that can be obtained.








From water molecules to societal mainstreaming
There is no doubt that cryo-desalination is an expanding field of innovation with potential to address challenges of water insecurity. Nevertheless, few initiatives bridge this fundamental understanding of water with implications of the technology for market and societal mainstreaming.

Importantly, we find that a more broadly defined interdisciplinary approach could be beneficial for advancing cryo-desalination. It could for example combine basic research at the molecular level, with engineering and the social sciences, and thereby attempt to explore new connections across different fields of knowledge, with water as the common element.  How might a molecular study of water become combined with insights from a social study of key water players in a growing city such as Stockholm to deepen insights about its feasibility?

A combination of field observations and interviews with water experts, energy and water utility companies but also business actors could provide a better insight into whether decisions about future investments in different water innovation portfolios can include more radical solutions. We know that insights from basic research such as from theoretical physics are crucial for solving complex water questions at the molecular level, but how could we further couple these investigations with other important fields of study?

Creating a safe space for new partnerships
Entering the recent Skolar Award competition which took place in Finland has been an incentive to push ourselves to think outside the box.

As water researchers ourselves (from theoretical physics and the social sciences), we have entered what might at times feel like an uncomfortable partnership. Because of the distance, we sometimes feel between our own disciplines. Moving forward however, we are excited to explore how this new partnership around cryo-desalination could provide a platform for asking a different set of questions around water that joins insights from molecular and societal perspectives.

Foivos Perakis
Assistant Professor at Stockholm University.
Timos Kaprouzoglou
Researcher, Division of History, Science, Technology and Environment, KTH.
Research coordinator of the WaterCentre@KTH.

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Water is life. Water is circular. So life is … circular?

Every year around this time we do the accounts. What have we done in the past year? We look back to discern things that happened which distinguishes  this year from other years. We search for things that stand out as a deviation from routine. Maybe it has to do with modern Western view on life as a linear journey with a distinct beginning and a definitive end. Maybe in other cultures, where life and death are just stages in the perpetual cycle of generations, this obsession of progress is less marked.  In fact, most of our lives is about repetition anyway. But an end-of-year blog summing up things that have remained exactly the same will not be very interesting reading. So let me first give you the accounts. Then I’ll return to why life in the future might be more circular.

To communicate some of the cool KTH water research, we produced the exhibition ”Get Wet” for the KTH library which has thousands of visitors every day! Another new feature was the Water Expert Portal aimed at making it easier to find relevant water experts at KTH.

Speaking of experts. The visit of this year’s Stockholm Water Prize Laureates; Mark van Loosdrecht and Bruce Rittmann, was another highlight.  These superstar experts spent a whole morning at KTH talking with students and staff about their water research.

Mark van Loosdrecht and Bruce Rittmann, Stockholm Water Prize Laureates 2018 visiting KTH

In May, KTH signed a new partnership agreement with Värmdö Municipality. This partnership is already a very lively one, with project courses by master students, field trials of more sustainable desalination technology, and preparation of a new testbed for small-scale water supply.

Deshira Flankör, Mayor of Värmdö, and Muriel Beser Hugosson, Head of ABE school, at partnership dialogue in May

Our collaboration with IVL, SEI and City of Stockholm has also deepened in the course of the year. Through our collaboration initiatives, we have been able to catalyse several new research projects.

In the MISTRA InfraMaint programme, old networks for piped water and transport meets the digital age. How can sensors and artificial intelligence change the way we manage infrastructure? KTH contributes knowledge from structural engineering, environmental economics and industrial management, in close collaboration with the city of Stockholm. The programme runs for 4 + 4 years and comprises a broad range of actors, coordinated by RISE.

In a new Formas-funded project, a KTH team with competence in energy, water and innovation studies collaborate with ten private and public organisations to understand the system effects of on-property technology for water and heat recovery. A year ago I wrote a blog post about this phenomenon, and its fantastic that we now can learn more about it together with other actors.

We also congratulate our new colleague Dr Timos Karpouzoglou for managing to secure a grant from Formas to compare informal water provision systems in low-income areas of the metro regions of Nairobi and Delhi. These new projects, including a generous contribution from the city of Stockholm, means 25 fresh millions (kronor) to KTH. Not bad.

Finally. The year which passed showed us all with uncomfortable clarity that water is a finite resource. As I pondered in an earlier blog, maybe the summer of 2018 was, with extreme heat, fires, and water scarcity, a glimpse of our future.

In this not so distant future we will need new ways of managing water. The key will be to go from linear flows to circular. Every kid in elementary school knows the hydrological cycle. Yet, all our technical systems for water in human settlements have adopted a linear approach. In the linear approach, water is just a transport medium for carrying human waste. Cheap and easy. But it depends on nature’s moderation of the hydrological cycle, and a cycle turn-around fast enough for our ever-growing demand.

During 2018 we launched the ”Circular Water Challenge”. In the coming year, we will work with communities and students on eight islands in the Baltic Sea to look for solutions for water scarcity, where re-use of water will be at the centre stage. If you are interested in this project please contact Christian Pleijel at KTH Executive School.

Kick-off for Circular Water Challenge, at Artipelag on Värmdö, in Nov 2018

Moreover, we have begun building a wide coalition for circular water solutions. What started as an attempt to write a Vinnova application will hopefully grow into a national knowledge network for circular water technologies, including actors from municipalities and public agencies, private sector and academia. Curious? Drop us a line!

Changing from the linear to the circular will require not just a shift of knowledge and practices. It also requires a shift of attitude. We need to challenge our own ideas about what wastewater is and can be used for. Take the example of Pu:Rest, a beer produced in 2018 by our partner IVL and the Carnegie Breweries. A crisp nice lager made out of wastewater from the Hammarby Sjöstadsverk, the experimental treatment plant co-owned by KTH and IVL. Kudos to IVL and Carnegie for that!

Beer brewed on wastewater from Hammarby Sjöstadsverk

In the future perhaps ”recycled” beer will be the standard drink at our monthly WaterPubs. Quite naturally, circular water approaches will become more common as water becomes more scarce. Since water is life, maybe our lives will also be more circular.

Happy New Year!

David Nilsson


Director of the WaterCentre@KTH

Associate Professor in History of Science, Technology and Environment

KTH Royal Institute of Technology





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En reflektion runt Mål 6 och över gränsöverskridande kommunikation; vatten, sanitet och mänskliga rättigheter.

I fjol fick jag tillfället att medverka som samtalsledare på MRF – en filmfestival för mänskliga rättigheter. Filmen ”There will be water” kopplade till det 6:e globala hållbarhetsmåletSäkerställa tillgång och hållbar vatten- och sanitetsförvaltning för alla”.

Globalt sett har utvecklingen gått framåt och milleniemålet att halvera antalet utan tillgång till rent vatten uppnåddes i flera länder. Men ca 844 miljoner människor saknar ändå tillgång till rent dricksvatten, och många fler saknar tillgång till de enklaste former av sanitet (toaletter). Det mesta avloppsvatten släpps ut orenat i miljön (WHO & UNICEF, 2017). Utmaningen är stor för att åstadkomma adekvat skydd av både miljö och människors hälsa.

Kvinnor och flickor blir särskilt missgynnade vid avsaknad av rent vatten, sanitet och bristande hygien. Förlorad tid, sjukdomar, och attityder och tabun associerade med mens leder till förlorade skoldagar och slutligen lägre utbildning och förlorade arbetstillfällen.

Dessutom är vatten inte bara en grundläggande förutsättning för mänsklig hälsa och välbefinnande, utan också en förutsättning för jordbruk och energiförsörjning.

Filmen som jag och skoleleverna såg handlade om en forskares till synes enkla men ambitiösa mål att skapa vatten, energi och mat i öknen, genom ett system med solenergi för avsaltning och matodlingar. Ett storslaget ingenjörsprojekt där medverkande kämpade under hård tidspress.  Som lyckades… men sedan stötte på problem när finansiärerna drog sig ur. Fallgroparna är många, som eldsjälen i filmen fick erfara.

Utmaningarna inom vatten, sanitet, hygien, mat -och energiförsörjning är stora och komplexa. Även om man tycker sig ha den ultimata tekniska lösningen, kan det brista på grund av faktorer som kanske är svårare att påverka, t.ex. politik, samhällsstrukturer, finansiering, långsiktig hållbarhet, knyckfullt väder och förändrat klimat. Alltså både mänskliga, ekonomiska och miljömässiga faktorer, till synes utanför vår kontroll.

Att mötas och diskutera grundläggande frågor med nyfikna gymnasieungdomar är spännande och angeläget. I dessa dagar av ”fake news” och misstro mot fakta kanske det blir ännu viktigare att lämna de digitala forumen för att mötas i person. Dessutom får man raka och viktiga frågor, som kanske inte kan besvaras i en mening, men som vi alla gott kan fundera på, till exempel:

Om det är så lätt att rena vatten och det är sån vattenbrist i tex mellanöstern, och om man är orolig över konflikter med brist på vatten som orsak – varför renar man helt enkelt inte vattnet?!

”Är det inte lätt att bli frustrerad när inget görs?”

Vi har också här i Sverige anledning att fundera på hållbarhetsmålen, och mål 6 i ljuset av mänskliga rättigheter. Vi har människor som lever på samhällets marginaler som är särskilt utsatta och som bl.a. inte har regelbunden tillgång till vatten, sanitet och hygien (Davis & Ryan, 2017).

Dessutom har de tre senaste åren varit ovanligt torra, vilket ledde till vattenbrist på stora håll i Sverige, särskilt vid öar och kustområden. För enskilda brunnsägare, som kanske saknar kunskap och kapacitet att hantera vattenbrist och överhuvudtaget kontrollera eller åtgärda vattnets kvalitet, kan detta vara en stor utmaning, och något det svenska samhället kommer behöva planera för och hantera. I dagsläget saknas t.ex. en helhetlig kunskap baserad på systematiskt insamlade data om vattenkvaliteten hos hushåll med enskilda brunnar (SCB, 2017). Nyligen kom också betänkandet från den statliga utredningen ”Vägar till hållbara vattentjänster” som tittar just på småskaliga VA-lösningar. Utan tvekan kommer små och enskilda anläggningar bli en viktig fråga i Sverige framöver.

Det finns trots allt anledning att leva hoppfullt, att lära och att sträva mot förändring och förbättring. Utvecklingen har globalt sett gått framåt, och långt fler människor har tillgång till grundläggande rättigheter än vid millennieskiftet. Men kanske behöver vi tänka om, vara lyhörda och samarbeta med andra aktörer än de från vår egen bakgrund, ämnesområde, kultur och gärna över generationsgränser för att förverkliga den värld vi vill ha. VI har så oerhört mycket att vinna genom att mötas och lära av varandra.

Ett exempel av utbyte omkring vatten, sanitet, hygien och nutrition hittar ni här: WASHnut, vilket också porträtterats som del av UR skola, riktat mot gymnasieungdomar och förstagångsväljare.


Helfrid Schulte Herbrüggen
Vattenexpert på Ecoloop AB, affilierad forskare vid KTH

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Summer of ’18: a hot wormhole

Photo: Rymdstyrelsen/Copernicus Sentinel data 2017′ and 2018′ for Sentinel data/Google.

This was a summer to remember! Swedes are normally not spoilt with sunshine and we know how to complain about too much rain and too many mosquitoes. But this year most of us got more than we bargained for. July was extraordinarily hot and dry, it shows on satellite images. Major Tom agrees from his spaceship; Sweden has turned dry and brown.

The weather is always unpredictable, some may say, and next year we could find ourselves back in umbrella and long-john mode. This may be true in the short run. But this summer has shown us a glimpse, and a very hands-on experience, of the future. Climatologists, scientists and well-known weathermen like Pär Holmgren left no trace of a doubt: the stable ‘heat dome’ over Sweden (värmekupol) was linked to the ongoing process of global warming.

Very recently, researchers linked to the Stockholm Resilience Centre warned about the jittery behaviour of our climate. Some rather complex interactions between the atmosphere, the land masses and our oceans may create “tipping elements” in the planet’s temperature. We may therefore – the researchers suggest – be heading for a faster warming than earlier predicted; towards a permanent ”hot house” of 4-5 degrees above the pre-industrial mean temperature. As a matter of coincidence, this was exactly the temperature rise recorded in Sweden during the month of July, compared to the long-term average.

Mean temperature in July 2018, compared to long-term average. Source: SMHI,


What we have seen this summer is most likely a first serving of what is to come. Thanks to this extreme summer, we can also start to grasp the consequences of a warmer world also in Sweden. And I’m not thinking about how to chill our bag-in-box-rosé on the beach.

Wild fires have spread across Sweden, at a scale never witnessed before. Tens of thousands of hectares of forest land have gone up in smoke, with inhabitants of entire villages having to flee. Our “arctic wildfires” made headlines all over the world. This said, ours were nothing compared to the massive wildfires still raging in California or the fires in Greece that left almost a hundred people dead.

The Swedish agriculture has taken a huge blow; with crops devastated in large parts of the country and livestock being sent to slaughter as the feed supply dries up. Swedish agriculture is largely rain fed with rather small acreage under irrigation. So when there is no rain, there is no crop. Farmers with irrigation installations have in some places been barred from using them due to water scarcity.

The groundwater levels in small reservoirs have been low or very low throughout Sweden which has not only created problems for the agriculture, but also for municipal drinking water supply. This year, over 100 municipalities introduced irrigation bans or other measures to save on the drinking water supplies. Even Stockholm, drawing water from the huge basin of Lake Mälaren, noted capacity problems as people were filling up their swimming pools and watering lawns in the early summer months.  On the national level, the agency Livsmedelsverket has issued recommendations for water saving, and the drought has been a real test for national crisis coordination. As if this was not enough, the national food agency warned that the warm weather can increase the risk for cyanobacteria, adding water quality risks to the shortage of supply.

All these “new “ water-related problems of 2018 almost made me forget the “old” climate challenges. We still have to deal with increased flood events due to heavy rainstorms, and with the sea level rise.

All doom and gloom? At least we can give the Swedish Environmental Protection agency right. In a 2016 report, the agency predicted that climate change will pose serious challenges to our current conventional water infrastructure.

In some ways, we should be thankful for this summer. It was a wormhole in the time warp; an exclusive pre-screening of a not very distant future. It is also a necessary wake-up call. We need to get serious about reducing our greenhouse gas emissions. For water management, the summer of ’18 tells us that “business as usual” will not be an option. On the whole, water will become more rare, unpredictable and expensive, and our infrastructure will have to follow new design principles. Designs that are more resilient and less wasteful. Designs that promote the principles of reduce and re-use; designs that don’t presuppose that we mix our precious water with human faeces. Designs for a warm, but also sustainable, future society.

Fold up your sleeves. Welcome back to work!


David Nilsson

Director, WaterCentre@KTH

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Can Water Die?

Report on PhD mid-Seminar on Algae Blooms and the Baltic Sea.

Based on my current research on algae blooms, the Water Centre has kindly invited me to post a blog on my mid-seminar which took place on April 16th at the Division of History of Science, Technology, and Environment.

Algae blooms have been present in the Baltic Sea for a long time, but they have not always been a regular feature in the broader cultural and social imaginations that exist in and around the Baltic Sea Catchment Basin. That people in Sweden know and care about algae blooms today partially stems from the foundation of HELCOM (an intergovernmental organization tasked with protecting the Baltic Sea) in 1974 and the large algae blooms of 1988. Of course, earlier algae blooms have also been important, including blooms from around the 1920s or 30s that caused an illness reportedly known as Haff-sjukan.

To a certain extent, therefore, my research attempts to contextualize or historicize this interest in algae blooms, but it also seeks to understand how people experience, relate to, communicate about, and value algae blooms and their causes and effects. Some research I’ve done up to this point explores how monitoring algae blooms came into being, how monitoring takes place, and in what ways monitoring efforts communicate contamination and disgust. Also, an article that I’ve recently published, “Are Dead Zones Dead?: Environmental Collapse in Popular Media about Eutrophication in Sea-based Systems,” tells a story about how different understandings of algae blooms in the Baltic Sea contribute to alternate ways of conceptualizing the health of the Baltic Sea, in this case, whether as collapsing or collapsed.

It was a pleasure to share some of this work I’ve been doing with colleagues and other scholars for my mid-seminar. Invited discussant, Heather Anne Swanson from Aarhus University detailed her thoughts on my work with algae blooms and my ongoing efforts. She gave me some really good advice along with others in attendance. I learned a lot from everyone who was involved and would be happy if any readers of this blog would like to contribute or share their experiences related to algae blooms with me as well. For example, I’ve had a difficult time finding out detailed information on Haff-sjukan. But, of course, I’d be just as interested in your latest sailing adventure or your own research that relates to eutrophication, algae, or de-oxygenated marine environments (sometimes known as bottendöd or “dead zone”). Please email me if you’d like:

Besides addressing the questions and comments given to me at the seminar, I hope to research differences in the cultural values given to algae and algae blooms and how nutrients become pollution among other issues.

Scholars at KTH research waters and what happens in them in all sorts of ways. I am happy to be part of this diverse group and hope that my research will shed further light on the social and cultural relationships that people develop with algae blooms in the Baltic Sea.

Jesse D. Peterson
PhD Candidate



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