desalination

Desalination on the Cheap for the Masses

- Adam Clare

ocean shore
Water water everywhere and plenty of drops to drink. Researchers from MIT have found a way to passively convert seawater into drinking water using a setup so simple it seems too good to be true. Their device basically uses heat from the sun rays and a siphon. The apparatus produces more water and rejects more salt than other passive setups, it can generate five litres of water if the device is one square meter in size. All of this with no external energy. They have even tested the device in open water – and it works! Imagine hundreds of these devices floating on the ocean bringing drinking water to cities.

The heart of the team’s new design is a single stage that resembles a thin box, topped with a dark material that efficiently absorbs the heat of the sun. Inside, the box is separated into a top and bottom section. Water can flow through the top half, where the ceiling is lined with an evaporator layer that uses the sun’s heat to warm up and evaporate any water in direct contact. The water vapor is then funneled to the bottom half of the box, where a condensing layer air-cools the vapor into salt-free, drinkable liquid. The researchers set the entire box at a tilt within a larger, empty vessel, then attached a tube from the top half of the box down through the bottom of the vessel, and floated the vessel in saltwater.

In this configuration, water can naturally push up through the tube and into the box, where the tilt of the box, combined with the thermal energy from the sun, induces the water to swirl as it flows through. The small eddies help to bring water in contact with the upper evaporating layer while keeping salt circulating, rather than settling and clogging.

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A More Robust Solar Desalination Solution

- Adam Clare

ocean shore

You should drink more water. We all should drink more water, however in some places water wells are drying up and water is getting harder to get. Fortunately for us, we have a lot of ocean to drink from. Costal cities have increasingly looking towards desalination as a solution to their water problems.

Producing clean drinking water from the sea is an energy-intensive process which makes it expensive to run. Researches in Australia recently found a way to combine solar power with a new material to filter salt out of water in an incredibly efficient way.

Wang and his colleagues explain in the study that a sustainable energy source, like sunlight, would be especially useful for communities that may not have access to a reliable electric grid necessary for other methods of desalination.
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“This study has successfully demonstrated that the photoresponsive [metal compounds] are a promising, energy-efficient, and sustainable adsorbent for desalination,” said Wang. “Our work provides an exciting new route for the design of functional materials for using solar energy to reduce the energy demand and improve the sustainability of water desalination.”

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Desalination Plants can Turn Their Waste into Solutions

- Adam Clare

Water

We all need water to live and we’re using our fresh water reserves faster than they can be replenished. South Africa knows this all too well, which is why there is an increased interest in desalination. Currently turning seawater into drinkable water is expensive and produces a lot of waste (like brine). Researchers around the world are looking to decrease the cost and waste of desalination systems so we can better manage our local water ecosystems. This month some research came out which proves desalination plants can convert byproducts of the process into on site useful chemicals.

The approach can be used to produce , among other products. Otherwise known as caustic soda, sodium hydroxide can be used to pretreat seawater going into the . This changes the acidity of the water, which helps to prevent fouling of the membranes used to filter out the salty water—a major cause of interruptions and failures in typical reverse osmosis desalination .

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“The desalination industry itself uses quite a lot of it,” Kumar says of sodium hydroxide. “They’re buying it, spending money on it. So if you can make it in situ at the plant, that could be a big advantage.” The amount needed in the plants themselves is far less than the total that could be produced from the brine, so there is also potential for it to be a saleable product.

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Don’t Give up on Desalination

- Adam Clare

desert and stars

How we manage local water sources drastically alters how we grow crops and get drinking water. Cape Town is currently experience a water crisis that was in the making for decades because of poor water use policies. Desalination plants can help coastal cities provide water to their populace by separating salt from seawater. Wired has a good article on how one company is improving desalination techniques for growing crops, which, they predict can help bring plant life to arid regions.

The structure’s double-layered fibreglass roof transmitted sunlight but captured heat, diverting it through ducts into a compartment at the building’s rear. There, the heat was used to distill freshwater out of seawater for irrigation. The rest was vaporised and sucked through the growing space by fans to cool and humidify the plants, reducing transpiration. Paton calculated that a square metre of crops adjacent to the greenhouse would have required eight litres of water per day to offset what they lost in transpiration. “But inside we were using closer to one litre per square metre per day, and we were growing a better crop.”
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Paton is also interested in the long term restorative benefits of his invention. Davies’ model predicted that the greenhouse’s cooling and humidifying effect would seep into the surrounding environment: “You can see there would be a plume of cool air coming off the greenhouse,” he says. And since the region hasn’t always been barren, Paton thinks greenhouses could return parts of it to the naturally vegetated state it was in before overgrazing and drought took hold. “I believe that when you get to, say, 20 years, you’d have enough vegetation to do the job of the greenhouses because they’re creating shade and shared humidity – changing the climate.” Because vegetation sequesters carbon, that also has broader ramifications for mitigating the effects of climate change.

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Using Seawater to Farm in the Desert

- Adam Clare

The future of farming in much of the world could look like something out of science fiction. Sundrop farms in Australia has a farm up and running that produces food using seawater pumped into a desert location where they use the power of the sun to power the entire process. Solar energy desalinates the water while purifying the environment (so no pesticides) of the greenhouse – the entire process is form renewable sources!

Seawater is piped 2 kilometres from the Spencer Gulf to Sundrop Farm – the 20-hectare site in the arid Port Augusta region. A solar-powered desalination plant removes the salt, creating enough fresh water to irrigate 180,000 tomato plants inside the greenhouse.

Scorching summer temperatures and dry conditions make the region unsuitable for conventional farming, but the greenhouse is lined with seawater-soaked cardboard to keep the plants cool enough to stay healthy. In winter, solar heating keeps the greenhouse warm.

There is no need for pesticides as seawater cleans and sterilises the air, and plants grow in coconut husks instead of soil.

The farm’s solar power is generated by 23,000 mirrors that reflect sunlight towards a 115-metre high receiver tower. On a sunny day, up to 39 megawatts of energy can be produced – enough to power the desalination plant and supply the greenhouse’s electricity needs.

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