As water shortages threaten to destabilize many of the world’s driest regions, including California, researchers have developed an innovative new type of greenhouse that can provide fresh water and grow food. Engineers from Murdoch University believe that a 1,615 square foot Bubble Greenhouse “could produce around eight cubic metres of freshwater and up to 30 kilograms of crops each day.” The sealed design of the greenhouse will also protect crops from insects and disease, and the researchers say the technology should be easy to implement.
The bubble greenhouse uses existing desalination technology, where the ability to produce freshwater from saltwater is possible through evaporation and condensation. The greenhouse also produces a cooler, wetter environment in which plants can flourish. The new approach places the evaporation and condensation processes outside the greenhouse. Inside the greenhouse, two water-filled ‘bubble columns’, stream thousands of tiny bubbles creating a large surface for water to evaporate or condense. Seawater has an inability to let small bubbles join together to form big bubbles, so a large surface area is maintained.
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Mario Schmack, an author of the paper in the journal Desalination, said unlike the seawater greenhouse that operates at the ambient temperature, the Bubble Greenhouse’s “separated evaporators/condensers allow the use of higher temperatures.” More water can then be held in the hotter air stream, he said. This process, Schmack adds, makes the desalination process easier and prevents salt from building up in the chamber — eliminating the need for constant maintenance.
Emily Tow, a mechanical engineer at the Massachusetts Institute of Technology, who was not involved in the study, told Scidev, “The desalination system employs bubble columns, which are more compact and inexpensive than conventional humidifiers/dehumidifiers because of the large area for phase change and high heat transfer coefficients.” But she also warns that the estimated cost of $10 for every 1,000 kilograms of water produced means the idea may not be practical for growing staples. Solar-powered reverse osmosis might “be more efficient.”
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This process would be very similar to the distillation process. However, distillation does not provide water as pure as people believe. As anything with a lower boiling point that water, remains in the water. If this type of greenhouse uses fertilizers, this water will still need to be run through a water filter to make the water very clean and suitable for drinking.