Wooden filtration membrane promises efficient and more sustainable water desalination

Wooden filtration membrane promises efficient and more sustainable water desalination
Published: 6 August 2019 - 9:59 a.m.
By: Baset Asaba

Water desalination technologies play a vital role in converting saltwater into freshwater in parts of the world where access to the latter is lacking, but there is plenty of room for improvement. One opportunity for this lies in the materials used for water filtration systems, with scientists putting forward a wood-based alternative to the plastic-based membranes currently in use, with early experiments indicating a heightened performance to boot.

Current approaches to water desalination are very expensive and require huge amounts of energy. Not helping on the environmental side of things is that the membranes used to filter the water are predominantly made from polymers, which require fossil fuels to produce and are tricky to recycle.

In developing their new wood-based membrane, scientists from Princeton University together with colleagues from the University of Maryland and the University of Colorado Boulder drew inspiration from the natural water circulation systems of a tree. More specifically, a tree's thermal stability and the way its pores allow for water and nutrient transport during growth offered the scientists a useful new blueprint.

"The hierarchical pore structure of the tree and the natural insulation property inspired the idea of using wood material for water evaporation," Z. Jason Ren, a professor in environmental engineering at Princeton University, tells New Atlas.

We have seen wood used as water filtration systems in the past, with a number of experimental systems showing promise as ways of eliminating bacteria. In preparing the material for the removal of salt, the team behind the latest study started with American Basswood and treated it to remove the hemicellulose, strands that hold cellulose in place, along with lignin, which gives wood its brown texture and rigid form. The material was then treated with silane to make it hydrophobic and sliced into wafer-thin sheets.

"The membrane is about 500 microns thick, which is currently thicker than commercial polymer membranes at around 180 microns," Ren explains.

The team calls the resulting material "nanowood," and says that it boasts some impressive water filtering capabilities. They tested these out by suspending it over a source of water vapor. As the water is heated and moves into a gas phase, the molecules become just small enough to squeeze through the tiny channels within the treated wood, allowing salt-free water to accumulate on the top side.

They compared its effectiveness to that of a conventional membrane, with respect to how much water vapour could pass through the surface per hour. The scientists say that it outperformed the currently-used membrane by 20 percent, owing to its very high porosity and excellent insulation, which works to avoid heat loss.

Ren tells us that the team continues testing out different wood materials in a bid to optimize performance of the membrane, while its latest research was published in the journal Science Advances.

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