Tapping into Nature: Wising up to water innovation
Designs that imitate cacti, beetles and termite combs can deliver water in the most unlikely places.
This is an excerpt from the Tapping into Nature report by Terrapin Bright Green.
Water, which is essential to life, is also essential to many industrial processes, systems and energy technologies. Its presence or absence affects the energy demands of buildings, the growth and processing of agricultural products, the corrosion or fouling of materials, and the health of human populations.
Increasingly, the use of water is threatened by limited access and availability of fresh water. Natural systems optimize the acquisition and use of water, gathering diffuse flows of water vapor and water from varied sources.
Almost 800 million people globally do not have access to potable water. Providing drinking water in an energy-efficient manner is both a necessity and a business opportunity. All organisms leverage the natural phenomenon of osmosis — the movement of water across a membrane from one concentration to another — to their advantage. Plants and animals rely on this passive transfer to extract pure water from salt, brackish and contaminated water sources.
Mimicking osmosis may lead to scalable technologies for producing clean drinking water that can be deployed globally. Aquaporin A/S uses osmosis in its low-energy water filtration and desalination technology. The use of osmotic pressure to spin turbines — osmotic power — is also under development as a renewable energy source.
Moisture — at high and low levels — poses a challenge to building environmental control systems and can degrade materials over time. Plants, however, maintain high humidity levels in the interior air spaces of their leaves through simple, responsive ventilation using openings on the bottom side of leaves.
Also, termites impede humidity fluctuations by means of absorbent fungal structures. A research team collaborating with Terrapin is investigating ways to mimic this and other strategies in a passive humidity damping device for application in buildings.
Much of the water that humans use is in a liquid state, but several ingenious organisms harvest water vapor. A cactus native to Mexico uses its spines to collect water droplets from fog; the Namib Desert beetle uses its black bumpy shell to condense water vapor; and some bryophytes (mosses, liverworts and hornworts) readily absorb moisture from the air.
Taking cues from nature, researchers at MIT and Pontifical Catholic University of Chile have tapped this resource. Their fog harvesting mesh technology can capture 10 percent of the water vapor contained in fog, offering a market-ready solution for semi-arid regions such as Chile, where capturing only 4 percent of the water content in fog would meet the water needs of the nation’s northern regions.
Aquaporin Inside, commercialized by Aquaporin A/S, uses biological water transportation to filter wastewater, saltwater and contaminated fresh water. All organisms have specialized water transport channels in their cells, called aquaporins, that selectively move water across membranes while preventing other molecules from passing through. Aquaporin A/S has embedded functioning aquaporins into water membrane technology to harness this water filtration capability.
The technique — a form of forward osmosis — reduces energy costs of water filtration by 80 percent compared to reverse osmosis filtration methods, which require high pressures. In addition to manufacturing filters for current filtration equipment, the company has formed strategic partnerships to commercialize new applications in the Chinese and Singaporean markets.
Seawater greenhouse systems emulate the water harvesting strategy used by the Namib Desert beetle, which leverages the abundant solar resource, diurnal temperature differentials and prevailing warm winds to condense humidity into fresh water. These systems distill seawater to grow crops year-round in arid climates where horticulture is otherwise cost prohibitive. The technology uses cool seawater, solar thermal systems and warm, ambient air to evaporate and then condense water vapor into considerable volumes of fresh water. The Sahara Forest Project’s Qatar pilot plant deployed this system to grow high-value food crops using 50 percent less water than comparable operations.
Seawater Greenhouse Ltd. and Australia-based Sundrop Farms have commercialized this technology and claim that reduced operating and fixed costs and the ability to use non-productive, inexpensive land results in up to 35 percent greater returns on invested capital than conventional modern greenhouses.
In collaboration with Terrapin, researchers are developing a humidity damping device to passively dehumidify buildings in humid climates. The device is based on the fungal combs found in Macrotermes termite colonies, which help maintain the interior humidity level of the termite mound despite outside humidity fluctuations. These fungal combs — constructed by the termites as a food source — absorb water vapor from air in high relative humidity (RH) conditions and release it during times of low RH, passively regulating interior RH.
To create this device, the team is experimenting with materials that mimic the absorption properties and the complex shape of the comb. Unlike current technologies such as enthalpy or desiccant wheels, the device would greatly reduce the amount of energy currently used in HVAC systems to maintain industry-standard RH levels and low RH levels in moisture-sensitive industrial processes.