Innovative Techniques for Harvesting Freshwater from the Air
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Chapter 1: Understanding Freshwater Scarcity
Freshwater is a vital resource for human survival, with the average person able to survive only a few days without it. The issue of freshwater scarcity is becoming increasingly urgent, not only in arid regions but globally, due to climate change. While I have previously discussed methods for converting saltwater into freshwater and reusing wastewater, what options do we have when we are far from oceans or when recycling is insufficient?
One promising solution is atmospheric water harvesting. The air around us contains moisture in the form of tiny droplets or vapor, amounting to about 50,000 km³ of water—equivalent to around 200 Olympic-sized swimming pools. This represents approximately 10% of the Earth's freshwater supply. By harvesting this atmospheric water, we can eliminate the need for long-distance water transport and improve water access in rural communities.
This process can be achieved through two primary techniques: condensing and trapping.
Section 1.1: Condensing Atmospheric Water
The first method for extracting water from the atmosphere involves cooling air to a point where it becomes saturated with water vapor, leading to condensation. Once the water condenses, it can be collected for drinking purposes.
This technique is particularly effective in high-humidity environments where dew naturally forms, such as at dawn. However, artificially cooling air for condensation requires significant energy. Here’s a practical example of a condensation-based harvester used in Ethiopia:
Section 1.2: Trapping Water Vapor
The second method for atmospheric water harvesting relies on trapping water through absorption or adsorption.
- Absorption refers to water being drawn into another material, while adsorption involves water molecules adhering to the surface of a material.
Water harvesters that utilize absorption typically employ materials with a strong affinity for water, such as certain gels and salts. One such material is zeolite, which consists of a network of silica (silicon dioxide) and alumina (aluminum oxide). Despite their complex names, silica and alumina are common substances found in everyday items like sand and glass. The porous structure of zeolite allows it to capture and retain water molecules. For a deeper understanding of this absorption method, check out the following video:
Water harvesters that function through adsorption use materials that can chemically bond with water. Silica gel is a commonly used example, often found in small packets labeled "do not eat." This gel contains hydroxyl groups that can bond with water molecules, increasing water retention. To retrieve the captured water, hot air is blown over the silica gel, causing the water to evaporate, which can then be collected through condensation.
Chapter 2: Practical Steps to Reduce Water Usage
While harvesting water from the atmosphere is a viable solution, we can also take proactive measures to reduce our own water consumption:
- Opt for washing at the sink instead of taking a shower.
- Choose showers over baths.
- Save bathwater for flushing toilets.
- Collect water that runs while the shower heats up.
- Turn off the tap while soaping hands or brushing teeth.
- Reuse towels and clothing to minimize laundry loads.
- Avoid fully opening the tap during showers.
What additional strategies can you think of to conserve water? Feel free to share your suggestions in the comments section to inspire others!
Credit
This article is based on:
Zhou, X., Lu, H., Zhao, F., & Yu, G. (2020). Atmospheric water harvesting: a review of material and structural designs. ACS Materials Letters, 2(7), 671–684.