Seawater to Freshwater using Graphene Filters

By Mary Mahon

Water makes up 70% of the Earth’s surface, so it is easy for us to assume that water scarcity doesn’t exist or is a concern. However, freshwater makes up only 3% of this, with only 40% of freshwater being accessible. Much of this 3% of water is trapped in glaciers or underground aquifers.

Additionally, the effects of climate change and droughts have been an added stress to areas that rely on the surrounding freshwater. Access to freshwater has been increasingly difficult, leading to a higher demand for change. Many areas throughout Canada lack access to clean and safe water, particularly in rural regions. Canada has the largest coastline in the world, providing an opportunity to utilize the desalination process.

What is desalination?

Desalination is the process of dissolving and removing mineral salts and impurities, including transferring seawater to freshwater. Traditionally, this process was used in submarines to desalinate seawater and convert it into freshwater for the crew onboard, ensuring they had safe and clean water during long trips. The process of desalination was not used on an industrial scale for larger populations for centuries until the Industrial Revolution. Starting in Australia, many countries have now adopted desalination plants for use in producing safe and clean drinking water, as well as for agricultural purposes. A 2019 study found that there are 16,000 desalination plants across 177 countries.

Desalination Processes

Distillation

Distillation consists of boiling seawater and collecting and condensing the steam to gather freshwater. This method is not the most effective on a larger scale, as it can be time and energy-consuming.

Reverse Osmosis

Reverse Osmosis is the most commonly used method of desalination as it uses minimal energy to produce freshwater. The seawater is taken and treated to eliminate impurities. The seawater is forced through a semipermeable membrane under pressure, allowing water to pass through but not salt, thereby producing freshwater. Due to the potential presence of bacteria on the membrane, the water must be treated again for human consumption.

Nanofiltration

Nanofiltration is a method similar to reverse osmosis, but it uses a nanotube membrane for processing. The process of nanofiltration allows for high levels of water within a smaller space and uses less energy than reverse osmosis.

Graphene Filters

As the need for clean and safe water grows, technologies and processes need to adapt to become more accessible and improve sustainability. Introduced in 2004, graphene is made from a very thin single layer of carbon atoms. The layer is so thin that it is nearly translucent. The seawater passes through graphene filters with nanometer-sized pores, allowing for water to pass through while blocking salt and pollutants.

Advantages of Graphene Filters

Graphene filters have emerged as a prominent area of research in recent years and continue to be explored for use in industrial-scale desalination.

Many advantages have already been proven, including:

Carbon is one of the most abundant elements, making graphene filters accessible and economically friendly on an industrial scale and allowing the opportunity to be accessible to a wider range of the population.
Graphene filters are made of a durable material. The nano membrane graphene filters provide clean and fully filtered water, as the nano membrane does not allow organic materials to pass through. The clean process leaves less room for bacteria of organic matter to build up, which makes the process shorter as less filtration is needed throughout.
Graphene membranes allow for water to pass through up to 100 times faster than other methods because of the atomic thinness and smooth channels. As a result, the energy input is significantly reduced.
Graphene filters are made of a durable material that is robust and has less chance of degradation by chlorine and biofouling, which results in increasing the lifespan and reducing the number of times replacement is required.

A water energy plant in Toronto has swapped from the traditional reverse osmosis method to graphene filters, producing 1,000 gallons of water using one-third of the energy used through the reverse osmosis method. Thus, providing an energy-efficient and economically viable option.

Limitations of Graphene Filters

While there are numerous advantages to the implementation of graphene filters in the desalination process, this does not come without limitations, including:

While the process itself is economically efficient, the production of defect-free graphene with equal-sized nanopores is costly.
Additionally, achieving equal and precisely sized pore sizes is challenging and adds an extra layer of complexity to the manufacturing process.
The costly production of graphene is not feasible for many communities, defeating the purpose of creating a fully economically sustainable method of producing safe and clean for everyone.

While the desalination processes have come a long way in research, much research is still required to allow for industrial-sized use to ensure the quality of the water and production process is up to the same standard as smaller-scale lab results.

Further research would be required to understand the long-term impacts of graphene at a large scale. While graphene is the most effective in eliminating salt and pollutants, the buildup and residue over long-term use have not been fully understood. Additionally, the environmental impact of graphene is minimal, but the impact of by-products has yet to be fully researched.

Conclusion

These limitations can be overcome with further research and testing on a larger scale. Research is necessary into graphene filters and reverse osmosis, running in parallel, all the way through to producing clean water, to provide a comparative result. Further research into the full picture of long-term environmental impact from the production of the filter and process should be carried out to fully understand not only the environmental impact but also the associated costs. While the potential of significant costs associated with graphene filters is unaffordable to many communities, providing desalination through graphene filters could be useful for these areas during emergencies or crisis scenarios.

Overall, graphene filters offer multiple benefits in providing safe and clean water to populations that have limited access or no access at all. While traditional methods of desalination, like distillation, reverse osmosis, and nanofiltration, have been established, graphene filters provide an insight into a future of accessible, safe potable water for millions of people who lack it today.

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