Water Harvester
Summary
In 2017, some scientists from the University of California, Berkeley, demonstrated how a MOF ( Metal-organic Framework) can absorb water from dry air. They successfully tested their new prototype in the Arizona desert in 2018, which was able to harvest water from dry air and that too by using solar energy.
In 2019, in their latest version of the water harvester, the researchers claim that the water harvester can generate 1.3 liters of water per day by using 1 kg of the microporous aluminum-based metal-organic framework, MOF-303, considering that relative humidity is more than 32%.
The goal is to harvest sufficient water that can benefit many people.
Introduction:
At any given time, our atmosphere contains 13 sextillions (10^21) liters of water. This natural resource of water is recyclable and can be used to provide water in the dry regions of the world. Though the technique to harvest water from the air is tricky, it can be implemented anywhere with minimum wastage.
In a humid climate, the direct extraction of water is easy, but the main challenge arises in the arid conditions. This article explores the working of the latest version of water harvester implemented successfully.
How Does Water Harvesting Work:
In a humid climate, water is harvested either by using a fog harvester (or similar) or by condensation. But in climates where relative humidity (RH) is low, particularly lower than 40%, it is mandatory to bring down the air temperature below freezing point, making it impractical and energy-consuming.
To overcome this, water harvesting cycle is assisted with an absorbent, MOF-303.
The Water Harvesting Cycle (WHC) comprises of capture cycle and collecting cycle.
In the capture cycle, the desert air is captured with the saturation of MOF at night. During the day, the air inside is heated and humidified, resulting in the release of the captured air. Due to the property of convection, the hot and humid air is transported to the condenser that cools it below its dew point, which yields water. The collecting cycle is when the condensed water is released and collected.
Why MOF?
Metal-Organic Framework (MOF) is a super absorbent that easily absorbs and releases the water when heated. The first water-absorbing MOF which was MOF-801 was founded by Yaghi, who is a UC Berkeley professor of chemistry along with his UC Berkeley colleagues.
The new and upgraded MOF, that is MOF-303 is based on aluminum, while the MOF-801, that was used in the prototype of water harvester was based on zirconium. The new MOF has many advantages like more productivity, can hold 30% more water than MOF-801 and can adsorb and release the water faster.
The Water Harvester 2019 model:
This model can work in those regions where there are extreme water scarcity and no power source as it makes use of solar energy. The key material used in the framework is a powder called Metal-Organic Framework, MOF-303, spread across the framework that absorbs the water molecules.
The framework is kept for the absorption process during the night as the water content in the atmosphere is high. The MOF similarly adsorbs the water molecules as a sponge absorbs water and holds it. During the daytime, when the framework gets heated due to the sun, the material releases the water molecules that can be collected as liquid water. The harvester is powered by solar panels and batteries.
This harvester claims to pull 1.3 liters of water per kilogram of MOF per day considering low humidity. Even when the humidity is as low as 7%, this harvester can pull 0.2 liters of water per kg of MOF per day.
Future of this water Harvester:
Water Harvester Inc., is a startup of this project that aims to commercialize the water harvester. Their latest project which is under testing is in the size of a microwave oven that is capable of generating 7-10 liters of water per day.
Their more futuristic vision is to work on a larger version of this, of the size of a refrigerator, that can generate 200-250 liters of water per day.
Not stopping even at this they aim to build a village size harvester that can generate water for an entire village, up to 20,000 liters of water per day. The entire process of generating pure water will be green.