Harvesting fog could quench world's thirst

Inspired by a desert beetle an ex-IIT Mumbai student has created a material that can absorb pure water from fog.  He hopes the tech will help millions of poor people with no access to running water

In the arid Namib Desert on the west coast of Africa, one type of beetle has found a distinctive way of surviving.  When the morning fog rolls in the Stenocara gracilipes species, also known as the Namib Beetle, collects water droplets on its bumpy back, then lets the moisture roll down into its mouth, allowing it to drink in an area devoid of flowing water.

What nature has developed, Shreerang Chhatre wants to refine to help the world’s poor. Chhatre is an engineers and aspiring entrepreneur at Massachusetts Institute of Technology who works on fog harvesting, the deployment of devices that like the beetle, attract water droplets and corral the runoff. This way, poor villagers could collect clean water near their homes, instead of spending hours carrying water from distant wells or streams.

Access to water is a pressing global issue:  the World Health Organisation and UNICEF estimate that nearly 900 million people worldwide live without safe drinking water.  The burden of finding and transporting that water falls heavily on women and children. As a middle class persion, I think it’s terrible that the poor have to spend hours a day walking just to obtain a basic necessity.  Chhatre says. A fog-harvesting device consists of a fence like mesh panel which attracts droplets, connected to receptacles into which water drips.

Interest in fog harvesting dates to the 1990s and increased when new research on Stenocara gracilipes made a splash in 2001.  A few technologists saw potential in the concept for people.  One Canadian charitable organization, FogQuest has tested  projects in Chile and Guatemala. Chhatre’s training as a chemical engineer has focused on the wettability of materials, their tendency to either absorb or repel liquids (think of a duck’s feathers, which repel water). One basic principle of a good fog-harvesting device is that it must have a combination of surfaces that attract and repel water.  For instance, the shell of Stenocara gracilipes has bumps that attract water and troughs that repel it, this way, drops collects on the bumps, then run off through the troughs without being absorbed, so that the water reaches the beetle’s mouth.


                                                   

To build fog-harvesting devices that work on a human scale, Chhatre syas, “The idea is to use the design principles we developed and extend them to this problem.” To build larger fog harvesters, researchers generally use mesh, rather than a solid surface like a beetle’s shell, because a completely impermeable object creates wind currents that will drag water droplets away from it.  In this sense, the beetle’s physiology is an inspiration for human fog harvesting, not a template. “We tried to replicate what the beetle has but found this kind of open permeable surface is better.”  Chhatre says.

The beetle only needs to drink a few micro-litres of water.  We want to capture as large a quantity as possible. In some field tests, fog harvesters have captured one litre of water per one square meter of mesh, per day.  Chhatre and his colleagues are conducting laboratory tests to improve the water collection ability of existing meshes.