Water availability has already become a major concern area for humankind. Some UN studies already estimate that some 1 billion people worldwide do not have access to adequate drinking water. Water borne diseases already account for over 50% of preventable human ailments in the poorer regions of the world.Even in the more advanced regions of the world, municipal water supply is no longer considered safe enough to drink. This has spawned a $ 50 billion packaged drinking water industry.
The atmospheric air always has water vapor present in it. This is part of the Hydrologic cycle, where water evaporates from the seas and other water bodies, the vapor is carried by air into the upper atmosphere where it forms clouds which then condense into water as rain or snow. The total water vapor in the atmosphere is so large that it can meet all of human water needs.
Scientists and engineers are attempting to find means to extract water from the air without waiting for the natural rain cycle. The two basic processes to extract water from air are cooling condensation and wet desiccation. Cooling condensation is the familiar sight we see of water droplets forming on the outside of a bottle or glass of any cold liquid. The air in the atmosphere is cooled below its dew point by contact with the bottle or glass,causing the water vapor in the air to condense. Desiccant cooling is illustrated by the fact of common salt in a salt shaker becoming damp by absorbing water vapor from the air.Many commercial air-to-water devices have now become available. Some alternative approaches are also being attempted. An air-to-water industry appears to be developing
1. Using natural stone structures for condensation
Examples of condensation cooling exist even from early human civilization. In some parts of Europe and the Middle East, there are 10 meter tall beehive-like stone structures dating from the 19th century, called air walls. The stones cool rapidly in the night. When moist air comes in contact with these stones, the condensation yields water that is collected in troughs inside the structure and used for drinking and washing.In France, these structures were also used in some vineyards.
2. Using water nets for condensation
This is the modern adaptation of the ancient stone walls for water harvesting. At a village named Cabajane in sub-Saharan Africa, a team from the South African Agricultural University helped the villagers string up plastic nets across a mountain pass. The clouds and fog through the pass, condensed water on the nets, which ran down through plastic pipes to be collected in a tank. Several hundred liters of potable water became available to the village from this simple device , where they earlier had to walk over 2 km to the nearest stream. This experiment is now being replicated in other villages in sub-Saharan Africa and also in Chile and in some places in Nepal.
3. Foldable structure for water harvesting
Two Israeli architects, Joseph Cory and Eyak Malka have designed this foldable triangular structure, named WatAir, that is said to imitate the leaves of a tree to condense atmospheric water vapor and collect it into a tank. The structure folds into a a package of 1 meter maximum dimension and 3.5 kg weight, that the designers claim can be erected anywhere, to harvest atmospheric water.
4. Max Whisson’s Gust Water Trap
Dr Max Whisson of Perth, Australia has come up with a wind turbine design that produces water by condensation, instead of electricity. The wind turbine has vertical blades and is mounted on a swivel with a wind vane tail, so that it can turn to face the direction of the wind. When the turbine turns, the wind gets forced into the hollow tower. The air passes over a refrigerant compressor driven by the wind turbine and condenses into water, that flows into tanks at the base of the tower. A company named Water UN Limited has been formed to commercially apply this technology.
5. Windmill to make water from air
The company Dutch Rainmakers of Netherlands has installed a windmill Surinam to produce water instead of electricity. In their design, the air is forced through a heat pump, where the water vapor condenses. This heat pump replaces the refrigerant compressor. The wind mill is said to produce 5000-7000 liters a day, a real boon in a place where the groundwater is brackish.
6. Refrigerant based condensation
The modern condensation cooling devices, generally use a refrigeration coil to provide the cooling. Many manufacturers worldwide have come up with condensation cooling machines that work on the following principle.Inlet air is filtered to remove dust and suspended particles using fabric filters. This air is passed over coils containing cold refrigerant gases. The condensate water is collected in a stainless steel tank and exposed to ultraviolet light for about 30 minutes to remove bacteria and then filtered through an active carbon filter. The typical cost for a model that produces 20-25 liters a day is about $ 1500 and these machines consume about 500 watts of electricity. These condensation machines are styled like the conventional water coolers installed in offices and public places, and are intended to be used in such locations.
One of the largest companies in this field appears to be Air Water Corporation of Miami Beach, Florida which makes a range of machines from the 25 liter per day single office type capacity to larger 2500 liter per day trailer mounted machines complete with their own diesel power generator that can be installed at a construction site or even in a village as they have done in Jalmudi in India. Air Water Corporation says that its products are sold in 21 countries through local affiliates.
Another company that has targeted the home user with this technology is Element Four Technologies Inc.,of British Columbia, Canada which has launched an attractively packaged product they have named the WaterMill. The home model is dsigned to produce 11 liters of water per day enough to meet the drinking needs of a small family. The air intake and condensation is planned to be mounted outside the home and the potable water tank inside the home ( like a split air-conditioning unit). An upgraded model for 20 liters per day in planned. However, there are many companies with product variants for this market.
7. DRIPS for growing crops with water from air
Two high school students from San Francisco, with mentoring by professors from the University of California, Berkeley, have proposed this system for water harvesting from air. DRIPS stands for Deep Root Irrigation Precipitation System and is made of a 1 foot diameter, or larger, plastic or aluminum conical surface mounted on a hollow tube that is buried 1.5 feet into the ground. The plastic or aluminum surface cools in the night and in contact with air, causes water droplets to condense. This water, by capillary action aided by small ribs on the cone, drains into the ground. The depth of 1.5 feet prevents this water from evaporating back into the atmosphere and helps nourish the roots of plants. This method of water harvesting has been demonstrated to grow potatoes.
8. Fraunhofer Institute’s brine tower
The Fraunhofer Institute of Interfacial Engineering and Biotechnology (ICB) in collaboration with the company Logos Innovationen is working on this concept of a tall tower like structure down which hygroscopic brine solution runs down. This brine in contact with air absorbs moisture and runs into a tank at the base of the tower which has a slight vacuum. The tank is heated with solar collectors that causes the brine solution to boil. The vacuum in the tank lowers the boiling point of the brine solution.The water absorbed from the air evaporates and is led out through a tube filled with water. This water column maintains the vacuum in the tank without the need for a vacuum pump. The brine is recovered and pumped up again to flow down the tower.
9.Liquid desiccant for water harvesting from process air
Sciperio Inc., an Orlando, Florida based technology is working on using liquid Lithium Chloride as the desiccant to remove water from air. Their finding is that this is more energy efficient than using refrigerant based water harvesting technology and have proposed using this for water extraction from air in process plants for industrial use, rather than for drinking.
10. Use of solar energy for regenerating the desiccant
One variant of the use of wet desiccation by the company A2WH of Atlanta, Georgia which uses a proprietary desiccant for water vapor absorption. This desiccant is heated by solar energy to expel the absorbed water. The unit, installed outdoors, also has photo voltaic panels to generate the electricity needed for operating the units pumps and valves. A2WH says it has models both for the individual home and for irrigation of farms.