We could be a step closer to industrial food production in floating ocean biodomes: a team of Australian researchers have built a completely self-sustaining system that uses only seawater, solar energy, and soil to grow crops of broccoli, lettuce, and pak choi. 

The novel invention departs from previous floating farm designs by building a two-tier structure that harvests freshwater from saltwater and provides it to the crops hovering above. The water that this new system generates is so fresh that it’s safe enough to harvest even for humans to drink, the researchers found.

The critical feature at the core of their design is a process called interfacial solar evaporation. Simply, this relies on a seawater-absorbent material being heated by solar radiation, which traps the salt in the material while the fresh water is released as steam. 

In the researchers’ prototype, they built a special chamber at the base which would float on the ocean’s surface, putting the absorbent material in contact with the sea. As the saturated material is heated, the steam is released from its tall vertical spires, so shaped to increase the surface area for water to evaporate from. 

Then, up the sides of this floating chamber, the walls are lined with strips of highly absorbent bamboo paper—which the researchers call ‘belts’. As these become saturated by the condensing water, they transport it up to a second enclosed plant chamber that’s positioned above. These belts also run across the base of the higher chamber, from where they release the liquid directly into its soil. 

Once the researchers had built this prototype and run some successful initial tests, they scaled it up in a large saltwater pool. In this pretend-ocean, they floated six mini-farms, each one planted with either broccoli, lettuce, or pak choi seeds. For 20 days they monitored the growing conditions.

After just three days in this system, they noticed that the broccoli seeds had begun to sprout. After two weeks the plants had grown to 4cm high, with no signs of uncompromised growth in the unusual circumstances. The lettuce and the pak choi fared well, too, In fact, across the experimental farms, seeds of all types showed germination rates of over 80%. And when compared to different farm designs—variously containing either no water belts or no evaporators to test the validity of the design package as a whole—the researchers’ prototype was the only one that successfully grew seeds. 

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