Beetles & Stipagrostis sabulicola – Water harvesting in arid area

Fog represents a large untapped source of portable water, especially in the arid area. Numerous plants and animals in the arid area use their surfaces with special texture or constructions to harvest these valuable resource, which helps them survive the dry climate. Darkling beetles and the Stipagrostis sabulicola are the typical case of these animals and plants.

  • Climate in Marrakech, Morocco

The average annual relative humidity is 62.3% and average monthly relative humidity ranges from 48% in July to 87% in October.

humidity Marrakechmarrakech-julymarrakech-october

  • Darkling beetles

Darkling beetles (family Tenebrionidae) of the Namib Desert, located on the southwest coast of Africa, live in one of the driest habitats in the world. But some species of Darkling beetle can get the water they need from dew and ocean fog, using their very own body surfaces. Several researchers are studying the beetles, as well as synthetic surfaces inspired by the beetle’s body, to uncover the roles that structure, chemistry, and behavior play in capturing water from the air.

  • Surface pattern

Micro-sized grooves or bumps on the beetle’s hardened forewings can help condense and direct water toward the beetle’s awaiting mouth, while a combination of hydrophilic (water attracting) and hydrophobic (water repelling) areas on these structures may increase fog- and dew-harvesting efficiency. For certain species of Darkling beetle, the act of facing into the foggy wind and sticking its rear end up in the air (known as fog-basking behavior) is thought to be just as important as body surface structure for successfully harvesting water from the air.

According to the fog-chamber experiment of researchers, of those four species of beetle, only the O. unguicularis(A1), can apparently be observed to collect water from the humid air efficiently.

  • Temperature

Aside from the surface composition a key component to the beetles ability to capture water is its body temperature being colder than the air around it. Inspired by the fog-gathering technique of the Namib desert beetle, the Dew Bank Bottle is designed to harvest water from the air. Designed by Kitae Pak, the stainless steel, dome-shaped invention resembles the desert beetle’s body. The Dew Bank Bottle is meant to be placed outside in the evening, allowing the steel body to cool. In the morning, when the surrounding air begins to warm, water droplets condense on the cool surface of the bottle. The dewdrops collected are then channeled down ridges in the surface design to an enclosed circular holding chamber for drinking water. The designer, Kitae Pak, expects that this device could gather enough moisture for a full glass of water per use. Such a product could be particularly useful in arid environments where fresh drinking water is scarce, and has potential as a scaled-up version for greater water output.dew_bankdew_bank3dew_bank41

  • Stipagrostis sabulicola

Wetting properties are also involved in the interactions between plants and dew or fog. In many regions of the world, fog and dew represent regularly occurring phenomena, and the impact of these events on hydrology and ecology of the local vegetation is often substantial.stipagrotis

There is evidence that Stipagrostis sabulicola, a grass species endemic to the sand dunes of the Namib, depends to a large degree on fog collection. This species is able to extract substantial quantities of water from fog with collection rates of 4–5mm3mm22 of leaf surface and fog event as was shown by measurements in the field.

Leaf surface structures enable the endemic Namib desert grass Stipagrostis sabulicola to irrigate itself with fog water

A conspicuous feature of the leaves are—besides their acute tips and rigid character—the existence of distinct longitudinal ridges and grooves. The ridges have a diameter of about 100–150 mm and the grooves have a diameter of about 30–80 mm. The surface is rough and densely packed with silica bodies, amorphous silica within epidermal cells, and prickle hairs as is typical for many grasses. The oval prickle hairs are oriented with their longitudinal axis parallel to the longitudinal axis of the leaves and therefore, parallel to the grooves. The prickle hairs are positioned within the cuticle, the wax layer covering the leaf.

  • Fog-harvesting

People in Sidi Ifni, Morocco utilize the weather in the Boutmezguida mountain region as a means to provide fresh water to a rural community lacking this vital resource.They do this by installing Fog Collectors, which are thin screens covered by a layer of mesh, placed perpendicular to the wet winds so that they collect droplets of moisture from the fog.

  • New fog-harvesting mesh

Current systems tend to be fairly inefficient, condensing and capturing just 2% of the available water in a mild fog condition, but a new type of mesh developed by researchers at MIT and their colleagues in Chile, can boost water yields from airborne moisture by a factor of five or more.

“Detailed calculations and laboratory tests indicate that the best performance comes from a mesh made of stainless-steel filaments about three or four times the thickness of a human hair, and with a spacing of about twice that between fibers. In addition, the mesh is dip-coated, using a solution that decreases a characteristic called contact-angle hysteresis. This allows small droplets to more easily slide down into the collecting gutter as soon as they form, before the wind blows them off the surface and back into the fog stream.” – MITOptimal Design of Permeable Fiber Network Structures for Fog Harvesting

  • namibian biomimetic research center

NAMIB BIOMIMESIS RESEARCH TOWER (NABR) is a biomimetic research lab in the Namib Naukluft National Park with the purpose of studying indigenous plant and animal species which may act as role models for the creation of new ecological technologies. It consists of a research center, ecotourism hub, and a utility tower proposing a low-impact solution within the Namib Desert. Eco-tourism has recently become popular to thrill seekers looking to carve down the massive dunes on sand board. This coupled with a research center invested in new sustainable technology creates a micro-economy that can support the continued preservation of the land. NABR hopes to edify travelers on the biological phenomenons that dwell within one of the oldest most hostile environments on earth which has subsequently forced their evolution to take a very specific route. Environments like this yield the greatest amount of biomimetic potential, therefore it is in these places where man must look for sustainable solutions.pz9fxuyzu6plghe7

NABR was created with two such organisms in mind, those are: the fog basking beetle (genus Stenocara) and the Welwitschia plant (genus Welwitschiaceae).

The tower employs a similar strategy of the lower temperature than the surroundings but with inspiration from the Welwitschia plant which has a tap root that can extend up to 10 feet. The design here being that in order to cool the hydrophilic cells it would require cool water radiating through them. In order to achieve this the dripping water from the fog would be circulated deep into the earth where temperatures are cool then transferred up through the cells and back down again. The tubes situated higher on dune allow light to penetrate deep into the atrium space while also circulating hot air outward keeping the interior cool even when the temperature outside exceeds one hundred and twenty degrees Fahrenheit.

Thanks for watching!

  • Reference Links

  • Reference Readings

Efficient fog harvesting by Stipagrostis sabulicola (Namib dune bushman grass)


Optimal Design of Permeable Fiber Network Structures for Fog Harvesting


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