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In 2013, Boyan Slat began to question the large volumes of plastic accumulating in our oceans and why no one was doing anything to clean it up. At 16 years old, he began research into potential solutions to effectively recover and remove it

Stabilised Graphene Membranes Could Bring Waves of Change for Desalination

As the Western Cape experiences its most severe drought in recent history and with the latest dam levels effectively at 11.2%, Cape Town has less than 95 days of potable water left. Its time to think of alternative water sources.

A recent breakthrough by a team of researchers at the University of Manchester has got everyone talking about graphene and its potential to affordably filter water. The scientists developed graphene-oxide membranes capable of sieving commons salts and other organic materials from water making it safe to drink.

graphene-membranes-filtration-seawater-desalination

Atom level filtration by graphene membranes

Think about the stuff in your pencil (graphite), but on an atomic level, graphene is simply one atomic layer of pure graphite. Graphene-oxide membranes can be produced cost effectively in a lab and previous research has already demonstrated that they can filter out nano-particles and even large salts. However, when immersed in water during large-scale testing the graphene-oxide membranes would become swollen and filtration would effectively cease. The Manchester-based research team found that by placing epoxy resin walls on either side of the membrane prevented this expansion. As a result, the pore size of the membranes can now be precisely controlled to filter out the salt ions in seawater.

Let’s put this in perspective, the Earth’s surface is composed of about 71% water, of which 96.5% can be found in its oceans and is therefore not potable (in its current state). The bulk of the remaining 3.5% of the Earth’s water is trapped in glaciers and aquafers (groundwater). That leaves less than 0.5% of the Earth’s freshwater to be shared amongst an ever-growing population of over 7.5 billion people. According to a recent UN Report, 14% of the world’s population will encounter water scarcity by 2025. With that said, seawater desalination just seems logically doesn’t it?

Two desalination techniques are currently in use: multi-stage flash distillation, which flash heats a portion of the water into steam through a series of heat exchanges; and reverse osmosis (RO), which uses a high-pressure pump to push sea water through semipermeable membranes to remove ions and other particles from drinking water. Improving current desalination methods is a necessity, as they are energy intensive and have adverse environmental effects.

This technology could potentially transform the water filtration industry by radically reducing the operational costs of large scale desalination plants, thereby opening untapped markets in developing nations. Smaller scale plants would also become more economically viable and could be rolled out on mass.

Eskom is set to build a desalination plant at Koeberg in order to reduce its dependency on the municipal water supply. According to Velaphi Ntuli, Koeberg Power Station Manager, the entire Koeberg nature reserve uses approximately 1300kl per day of which 357kl is consumed in the power generation process. The City of Cape Town is also considering desalination as one of its solutions to address its water security issues.

Although this development is still its early stages, this approach of stabilising the graphene membrane structure appears to be promising and initial results are encouraging. Graphene membranes will mostly likely be used to optimise or replace current RO membrane technology. Applications also exist in oil/water separation as well as in wastewater treatment.

Author: Linden Smith – Energy Engineer

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