Clean water shortage affects every continent, with almost one-fifth of the world’s population living in areas where water is in short supply (United Nations). And renewable freshwater resources are projected to dwindle further, according to the Intergovernmental Panel on Climate Change (AR5 Chapter 3).
One group of researchers looked to the Stenocara, or Namib desert beetle, for a solution. The beetle’s built-in water collection system allows it to survive in one of the driest climates on Earth. Its morning routine includes standing atop a sand ridge and facing the wind at an angle, head down and bottom up. Here, its bumpy wing case has hydrophilic (water-attracting) peaks that draw water droplets from the morning fog. The droplets get larger until they eventually fall into the hydrophobic (water-repelling) valleys and trickle into the beetle’s mouth.
Although not the first scientists to take a lesson from the desert beetle, the team experimented with different structures and chemical processes as described in a June 14 article in ACS Applied Materials & Interfaces. The researchers created multi-walled carbon structures called nanotube forests (NTFs) and coated the ends to attract or repel water to mimic the beetle’s water-harvesting system.
The carbon nanotubes used in their technique are strong and can be easily treated with polymers to increase their water collection and retention capabilities (see our Carbohydrates module for an explanation of polymers). A hydrophilic polymer is applied to one side of the NTF, allowing the structure to capture water from atmosphere – even when there is very little humidity. The other side is superhydrophobic, so it holds in the water and prevents the structure from collapsing.
Initial tests of the NTF water-collection apparatus were encouraging. The first test, performed in low humidity, yielded a 27.4% increase in water over 11 hours. In a test of water retention, the polymer-treated NTF lost only about 8% of its water weight through evaporation after 6 hours, as opposed to 60% of water lost from an open vessel during the same period. The device requires no external energy source, and the research team believes it has the potential to benefit regions where water is scarce, provided that NTFs could be manufactured at a lower cost and scaled for greater capacity.
In The parched planet: Water on tap, Quirin Schiermeier gives an overview of water-capturing methods used around the globe (Nature, 510, June 19, 2014).
Read about traditional techniques for fog harvesting in the Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean (Organization of American States / United Nations Environment Programme).
Ozden, S., Ge, L., Narayanan, T. N., Hart, A. H. C., Yang, H., Sridhar, S., Vajtai, R., & Ajayan, P. M. (2014). Anisotropically Functionalized Carbon Nanotube Array Based Hygroscopic Scaffolds. ACS Applied Materials & Interfaces (Just Accepted Manuscript), June 4, 2014. Web.
Written by Bonnie Denmark
Bonnie Denmark holds an MA in linguistics and teacher certification in English, ESL, and Spanish. She has devoted her professional life to educational and accessibility issues as a computational linguist, multimedia curriculum developer, educator, and writer. She has also worked nationally and internationally as a language instructor, educational technology consultant, and teacher trainer. Bonnie joined the Visionlearning team as a literacy specialist in 2011, assisting the project by developing comprehension aids for science modules and creating other STEM learning materials.