Drinking Water from Seawater

Sifting the salt from the water

It is predicted that by 2025 around 1.8 billion people across the world will be living in regions affected by water scarcity. Researchers at the University of Manchester have developed a new type of graphene-based membrane that could quickly filter salts from water, making seawater suitable for drinking water

By Patrick Truss

The discovery of a method of producing graphene in 2004 generated a great deal of interest in both the academic and commercial sectors. While the physical properties of the material were identified long ago, in particular its electrical and thermal conductivity, it was not until the early years of this century that researchers at the University of Manchester in the UK managed to isolate graphene.

Now that the material itself has been isolated, researchers across the globe are looking to exploit its properties and identify ways in which it can be applied in the real world. A 2-dimensional layer of graphite that is just an atom thick, graphene is the thinnest material on earth, yet at the same time also the most conductive, with remarkable strength.

This set off a renewed wave of interest in graphene, with researchers around the globe looking to harness the properties of the material and exploit its properties. Recent research from nanomaterials broker Fullerex shows that there are 142 graphene producers across 27 countries, with China alone holding around two-thirds of global production capacity.

A great deal of research is also focused on identifying practical applications for the material. Universities and businesses in the US and China are both thought to have filed large numbers of patents around the use of graphene-based technologies, while the UK lags behind, despite its key role in the initial development of the material.

The National Graphene Institute in Manchester is central to UK efforts to now capitalise on the wider potential of the material and translate research advances into commercial development. Home to more than 200 graphene researchers, from graduate students to Nobel laureates, the Institute also works in partnership with industry.

There are regular opportunities for researchers at the Institute to meet scientists in other disciplines and collaborate with industry, which is fundamental to sharing knowledge and identifying potential commercial applications. These extend across a diverse range of fields, including in energy, composite materials, and in water filtration.

The material itself is hydrophobic, yet researchers at Manchester found that membranes comprised of stacks of graphene oxide were impermeable to all gases and vapours, except water. Since this initial discovery, researchers have been working to improve graphene-based filters, aiming to enable precise and rapid filtering of salts and organic molecules from water.

Water scarcity

This holds particularly significant implications given wider concern about water scarcity, an issue which already affects a significant proportion of the global population. The UN estimates that around 1.2 billion people live in areas already affected by physical scarcity, a number which is set to rise

further over the coming years in line with the wider effects of climate change.

This may seem surprising given that around 70 percent of the earth’s surface is covered by water, yet the vast majority of it is saline water, with only a relatively small proportion drinkable freshwater. As the global population continues to grow and the global middle class expands, pressure on existing water resources intensifies.

It is estimated that over the past forty years the global population has doubled while water use has quadrupled, leading to intense pressure on water resources. The US Intelligence Community Assessment of Global Water Security found that, by 2030, humanity’s annual global water requirements will exceed current sustainable supplies by 40 percent.

The global economy is currently estimated to use around 2,600 cubic kilometres of water a year, and the gap between freshwater supply and demand is likely to widen further. While desalination plants have been established in many areas, conventional methods are typically quite expensive and energy-intensive to operate.

This is leading to a growing awareness of the need to both manage existing supplies more effectively and harness the power of technology to develop new technologies and methods that could help alleviate water scarcity concerns.

A team of researchers at the University of Manchester has now succeeded in developing a membrane capable of sieving common salts from water, raising the prospect of seawater being filtered to rapidly supply people with fresh water. The researchers used a chemical derivative called graphene oxide, which could be significantly cheaper to produce than singlelayer graphene.

These graphene-oxide membranes have already been shown to be able to filter out certain molecules, yet previously they were previously too large to sieve common salts. Now researchers are able to precisely control the pore size in a membrane, so that common salts can be sieved out and removed from salty water.

This brings the prospect of using membrane technology in water filtration a step closer. “Realisation of scalable membranes with uniform pore size down to atomic scale is a significant step forward and will open new possibilities for improving the efficiency of desalination technology,” says Professor Rahul Raveendran Nair, one of the leaders of the study.

“This is the first clear-cut experiment in this regime. We also demonstrate that there are realistic possibilities to scale up the desired approach and mass produce graphene-based membranes with required sieve sizes.”

The technique is limited to the laboratory at this stage, yet its potential is clear in terms of addressing water scarcity, while other companies are also exploring other options for improving water filtration. For example, one approach is coating polymer membranes with graphene oxide to improve the filtration process and speed up water transfer.

Global water summit

Many of these technologies and new methods were discussed at the 2017 Global Water Summit, which was held recently in Madrid. The summit is held annually, providing an opportunity for representatives from municipalities, water companies and

The ultimate goal is to create a filtration device that will produce potable water from seawater or wastewater with minimal energy input

industry to network, collaborate, and work together to address the key challenges around water scarcity.

This is not limited to looking just at new technologies around water recovery, important although that is, but also considering the general business climate and access to finance. Water is of course essential to life, yet there is wide variety in the business models used across the world, and in many countries private companies play a central role.

The summit brought together leaders in technology and finance to explore the possibilities around using technology to improve provision of clean water, and helping to remove obstacles to development. With the UN estimating that around 1.6 billion people face economic water shortage, there is a clear need for innovative solutions.

This shortage is partly due to the process of desertification, as fertile land is lost, yet it is thought that overall there is enough freshwater on the planet overall to meet demand. However, this water is distributed unevenly, and certain areas of the globe are already experiencing water scarcity, in particular in sub-saharan Africa.

Many different ideas have been put forward to alleviate the problem, including more efficient water management in the agricultural sector, and improved irrigation technologies. In some countries, water scarcity is not caused by lack of physical access to water, but rather insufficient investment in the infrastructure required to meet demand.

The economic circumstances in the countries that make up the Gulf Cooperation Council (GCC) are very different. While the region is relatively affluent, it does not enjoy abundant water resources, and the local climate makes it challenging to manage existing resources effectively, leading the GCC states to invest heavily in desalination plants.

The Middle East as a whole is home to around 70 percent of the world’s desalination plants, demonstrating their wider importance, yet the economics are becoming more challenging. In desalination, concentrated wastewater is pumped back into the sea, causing the surrounding waters to become ever saltier and the process to become more expensive.

This is likely to have long-term consequences, believe some observers. “In time, it’s going to become impossible to use desalination in a way that makes economic sense,” said Gökçe Günel, an anthropologist at the University of Arizona. “The water will become so saline that it will be too expensive to desalinate.”

Water scarcity is also a prominent issue in other areas of the world, including China, with a recent Greenpeace report shedding new light on the scale of the problem. More than 85 percent of surface water in Shanghai was found to be unsafe to drink, while the figure rose to 95 percent for the port city of Tianjin.

Whatever the underlying causes of water scarcity, or the surrounding social and economic circumstances, water filtration could represent a highly attractive and financially viable option to addressing the issue, potentially providing an effective, efficient and rapid way of enhancing the supply of clean water.

Water separation

The research from the University of Manchester holds rich potential in these terms, potentially providing an economic means of filtering out salts from seawater and providing a more sustainable supply of clean water to areas in need. There’s a world of difference between the laboratory and a large-scale commercial operation however, so there are many hurdles still to negotiate.

Some steps have been made in this direction, with the University of Manchester working together on a collaborative research programme with the Masdar Institute for Science and Technology, based in Abu Dhabi. The programme will receive funding of $500,000 from the UK (1.5 million AED), spread across projects looking at various engineering applications, including water desalination.

This is key to the wider commercialisation of graphene. “Graphene has huge potential for applications in a large range of sectors, and we are delighted to be collaborating with the Masdar Institute for Science and Technology on these important areas of research,” said James Baker, Graphene Business Director at the University of Manchester.

“Our partnership with Masdar Institute is crucial to the commercialisation of graphene and we look forward to seeing ground-breaking research develop into exciting applications with potential industrial partners as a result of this activity.”

The Masdar Institute is also involved in the development of the Graphene Engineering Info Centre (GEIC), a £60 million facility which is set to open in 2018. Masdar will contribute approximately half of the cost of the facility, with funding also from various UK-based sources, testament to the level of interest in the material.

A number of other initiatives have also been established across the world, exploring a wide variety of potential applications of the material, yet water filtration will continue to attract a lot of interest as policy-makers grapple with the problem of water scarcity. Graphene membranes could aid millions of people, now researchers aim to improve them further.

“The selective separation of water molecules from ions by physical restriction of interlayer spacing opens the door to the synthesis of inexpensive membranes for desalination,” wrote Ram Devanathan of the Pacific Northwest National Laboratory. “The ultimate goal is to create a filtration device that will produce potable water from seawater or wastewater with minimal energy input.”

www.manchester.ac.uk