Desert Life-Inspired Solutions to Harness Clean Water from Air

Although humans can manage in the roughest shelters and can make a meal from the most humble of ingredients, they cannot survive without clean water. Moreover, in places where there is water scarcity—for instance, the deserts across the globe—high-cost and cumbersome feats of engineering and irrigation are required to provide water to people.

Scientists at The Ohio State University have come up with two new studies that offer a possible solution. The studies draw inspiration from nature.

We thought: ‘How can we gather water from the ambient air around us? And so, we looked to the things in nature that already do that: the cactus, the beetle, desert grasses.

Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of Mechanical Engineering, The Ohio State University.

The outcomes of the studies have been reported in the Philosophical Transactions of the Royal Society journal on December 24^th, 2018. The papers were co-authored with Ohio State PhD student Dev Gurera and with Ohio State engineering researcher Dong Song.

The focus of Bhushan’s study is on discovering nature-inspired solutions to societal problems. In this study, his research group turned toward the desert to find life that survives in spite of very less access to water.

Water condensed from nighttime fog is collected by the cactus, desert grasses, and beetle. Droplets from the air are gathered and filtered to roots or reservoirs, enabling adequate hydration to survive.

Drops of water get collected on water-repellant, wax-free bumps on the back of a beetle and then slide toward the beetle’s mouth on the flat surface between the bumps. Water gets collected at the tips of desert grasses, where the water is then channeled toward their root systems through channels in each blade. Water is collected by cactus on its barbed tips before it guides droplets down conical spines to the base of the plant.

Bhushan and his colleagues examined each of these living things and identified that a similar, but larger, system can be built to enable humans to collect water from nighttime fog or condensation.

They started investigating the means through which different surfaces might collect water, and the surfaces that are the most efficient. They used 3D printers to built surfaces with barbs and bumps, and subsequently created foggy, enclosed environments with the help of a commercial humidifier to find out the system that collected the most water.

It was observed that conical shapes collected more water compared to cylindrical shapes—“which made sense, given what we know about the cactus,” stated Bhushan. He said that this is due to a physics phenomenon known as the Laplace pressure gradient. Water gets collected at the tip of the cone, and subsequently flows down the slope of the cone to the bottom, where there is a reservoir.

When compared to ungrooved surfaces, grooved surfaces moved water more rapidly—“which seems obvious in retrospect, because of what we know about grass,” stated Bhushan. In the experiments performed by the researchers, grooved surfaces collected nearly twice as much water as ungrooved surfaces.

Moreover, the materials the cones were made out of also played a role. The highest amount of water was collected by hydrophilic surfaces—those that permitted water to bead up rather than absorbing it.

The beetle’s surface material is heterogeneous, with hydrophilic spots surrounded by hydrophobic regions, which allows water to flow more easily to the beetle’s mouth.

Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of Mechanical Engineering, The Ohio State University.

The researchers also experimented with a structure that had multiple cones and observed that more amount of water gathered when water droplets could coalesce between cones that were 1 or 2 mm apart. Bhushan told that the group is continuing the experiments.

So far, the study has been performed on a laboratory-only level; however, Bhushan believed the study would be scaled up with structures in the desert with the ability to collect water from fog or condensation. According to him, that water could supplement water from wells public or systems, either on a community-wide basis or on a house-by-house basis.

The precedent for the concept is something like this: In regions across the globe, including the Atacama Desert in Chile, water from fog is captured by large nets and collected in reservoirs for farmers and others to use. Bhushan presumes that such nets may not be the most effective way to harness water from the air.

Water supply is a critically important issue, especially for people of the most arid parts of the world. By using bio-inspired technologies, we can help address the challenge of providing clean water to people around the globe, in as efficient a way as possible.

Bharat Bhushan, Ohio Eminent Scholar and Howard D. Winbigler Professor of Mechanical Engineering, The Ohio State University.