Nearly 97 per cent of all water on Earth is found in our oceans. The remainder is freshwater – 3 per cent for all of humanity's needs.
As the climate continues to change Earth’s freshwater, supply continues to diminish. This poses a threat to life on Earth. With two-thirds of the Earth's freshwater locked up in glaciers and ice caps, it is no wonder that access to clean drinking water has become one of the planet's most prevalent problems.
Matt Margeson, a Ph.D. student at Dalhousie University, is seeking to combat this problem from the ground up through research. Working in the research group of Professor Mita Dasog, Matt is looking into new technology to sustainably desalinate seawater.
The Ocean Frontier Institute is funding this work.
The challenge of desalination
The desalination of saltwater via evaporation is not a new idea – it is how the water is recycled within the natural world. Researchers have been attempting to utilize this technology for human consumption.
The base technology of the desalination devices being developed in the Dasog lab is plasmonic nanomaterials, which can absorb or scatter light very strongly.
“Plasmonic materials have existed since the 4th century, maybe even earlier”, says Mita. “People have been making [these materials] unknowingly, they are in the Roman culture artifacts and the stained glass made in the medieval period… all of those beautiful colours come because of the plasmonic materials”.
These materials have astounding photothermal properties which means they are able to absorb light and transform that energy into heat with very high efficiency. This localized heat can then be used to evaporate and thus desalinate water.
Plasmonic materials are typically made up of precious metals, like gold and silver, which are expensive and less abundant. Refractory materials such as nitrides and carbides are mostly used for their physical properties. They are incredibly hard and corrosion resistant, making them useful for hardware or medical tools. They also have high melting points for use in nuclear fuel generation and aerospace application. However, they have been proposed as an alternative plasmonic material, but little experimentation has been done to confirm their feasibility.
About the floating desalination unit
The desalination unit floats atop the ocean surface. The most recent model is designed to withstand ocean conditions, having just been tested in the Halifax harbour.
The device consists of 3 main parts:
- Foam
- Plasmonic carbide nanoparticles
- A transparent plastic cover
A thin layer of the nanomaterial sits on top of foam – designed to prevent the nanomaterials from losing heat to the cold waters below. Seawater is brought up to this thin film via wicks, where the solar-heated plasmonic materials evaporate the water and leave behind the salts. The water vapour then floats up to the transparent cover where water droplets are formed and collected in a separate bag.
“The evaporation area [of our device] is about one-third of a meter squared, and with that, we can generate about 1.2 litres of [fresh]water just in an afternoon out on the [ocean]” says Matt.
One goal of the project, as Matt explains, was to make the evaporation device, including the plasmonic components, from locally available materials. The Dasog lab has been able to use biomass, food, and tire waste to make carbide nanoparticles. “[Our goal is to] come up with a recipe that people can use to make a high-performing material wherever they are with whatever carbon-based waste they have”, says Mita.
The recipe model of the device benefits the environment as well; It greatly reduces the carbon footprint by eliminating the emissions associated with the transport of its materials.
The challenge, of course, is maintaining the performance and efficiency of the device despite the variability of the available materials.
Future plans
Prior to Matt’s research, the fundamental materials of this device had not yet been explored experimentally. There is the possibility to use the heat produced by the plasmonic materials to generate electricity by incorporating a thermoelectric material. This aspect of the device could allow for remote sensing and monitoring, making the floating unit a very integrated system.
There is a surge of effort trying to find ways to sustainably make water amidst the diminishing natural freshwater sources. The device's simplistic design allows for it to be used in a wide range of areas, creating access to this technology without the need for major infrastructure.
“It's exciting on our part to contribute to one of the areas where this [device] could be employed completely off-grid… a fully passive water generation device where the only energy source that you need is the sun”, says Matt.
As of right now, the floating unit is an individual module with the possibility to tether units together. It is predominantly for individual or smaller community use. Further testing is needed to ensure its longevity and scalability.
