According to FAO estimates, by 2025 nearly 2 billion people may not have enough drinking water to satisfy their daily needs. One of the possible solutions to this problem is desalination, namely treating seawater to make it drinkable. However, removing salt from seawater requires 10 to 1000 times more energy than traditional methods of freshwater supply, namely pumping water from rivers or wells.
Motivated by this problem, a team of engineers from the Department of Energy of Politecnico di Torino has devised a new prototype to desalinate seawater in a sustainable and low-cost way, using solar energy more efficiently. Compared to previous solutions, the developed technology is in fact able to double the amount of water produced at given solar energy, and it may be subject to further efficiency improvement in the near future. The group of young researchers who recently published these results in the journal Nature Sustainability is composed of Eliodoro Chiavazzo, Matteo Morciano, Francesca Viglino, Matteo Fasano and Pietro Asinari (Multi-Scale Modeling Lab).
The working principle of the proposed technology is very simple: “Inspired by plants, which transport water from roots to leaves by capillarity and transpiration, our floating device is able to collect seawater using a low-cost porous material, thus avoiding the use of expensive and cumbersome pumps. The collected seawater is then heated up by solar energy, which sustains the separation of salt from the evaporating water. This process can be facilitated by membranes inserted between contaminated and drinking water to avoid their mixing, similarly to some plants able to survive in marine environments (for example the mangroves),” explain Matteo Fasano and Matteo Morciano.
While conventional ‘active’ desalination technologies need costly mechanical or electrical components (such as pumps and/or control systems) and require specialized technicians for installation and maintenance, the desalination approach proposed by the team at Politecnico di Torino is based on spontaneous processes occurring without the aid of ancillary machinery and can, therefore, be referred to as ‘passive’ technology. All this makes the device inherently inexpensive and simple to install and repair. The latter features are particularly attractive in coastal regions that are suffering from a chronic shortage of drinking water and are not yet reached by centralized infrastructures and investments.
Up to now, a well-known disadvantage of ‘passive’ technologies for desalination has been the low energy efficiency as compared to ‘active’ ones. Researchers at Politecnico di Torino have faced this obstacle with creativity: “While previous studies focused on how to maximize the solar energy absorption, we have shifted the attention to a more efficient management of the absorbed solar thermal energy. In this way, we have been able to reach record values of productivity up to 20 litres per day of drinking water per square meter exposed to the Sun. The reason behind the performance increase is the ‘recycling’ of solar heat in several cascade evaporation processes, in line with the philosophy of ‘doing more, with less’. Technologies based on this process are typically called ‘multi-effect’, and here we provide the first evidence that this strategy can be very effective for ‘passive’ desalination technologies as well.”
After developing the prototype for more than two years and testing it directly in the Ligurian sea (Varazze, Italy), the Politecnico’s engineers claim that this technology could have an impact in isolated coastal locations with little drinking water but abundant solar energy, especially in developing countries. Furthermore, the technology is particularly suitable for providing safe and low-cost drinking water in emergency conditions, for example in areas hit by floods or tsunamis and left isolated for days or weeks from electricity grid and aqueduct. A further application envisioned for this technology are floating gardens for food production, an interesting option especially in overpopulated areas. The researchers, who continue to work on this issue within the Clean Water Center at Politecnico di Torino, are now looking for possible industrial partners to make the prototype more durable, scalable and versatile. For example, engineered versions of the device could be employed in coastal areas where over-exploitation of groundwater causes the intrusion of saline water into freshwater aquifers (a particularly serious problem in some areas of Southern Italy), or could treat waters polluted by industrial or mining plants.
Materials provided by Politecnico di Torino. Note: Content may be edited for style and length.
Eliodoro Chiavazzo, Matteo Morciano, Francesca Viglino, Matteo Fasano, Pietro Asinari. Passive solar high-yield seawater desalination by modular and low-cost distillation. Nature Sustainability, 2018; 1 (12): 763 DOI: 10.1038/s41893-018-0186-x
Cite This Page:
Politecnico di Torino. “Seawater turns into freshwater through solar energy: A new low-cost technology.” ScienceDaily. ScienceDaily, 7 January 2019.
Matter & Energy
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Recycling In Colorado Just Got Harder Thanks To New Restrictions From China – (A Better Title Would Be “Wishcylcing”)
As a state, Colorado hasn’t been the greatest recycler. New restrictions imposed by China on contamination levels, mixed paper and plastics aren’t making things any easier.
China used to be the leading re-manufacturer of recyclable material, and took in over half of America’s recycling. These new restrictions are not something the industry can easily rebound from. West Coast states that heavily rely on exporting their recyclables to China have even resorted to landfilling their materials. Colorado isn’t at that level yet, but the ripples of China’s decision are being felt around the state.
Alpine Waste & Recycling is responsible for collecting the recyclables for the entire city of Denver. Brent Hildebrand, Alpine’s vice president of recycling, said they were shipping about 40 percent of their materials to foreign markets — the bulk going to China. So the new restrictions presented some challenges for Alpine.
“We had to add some more labor to the system to help sort better and get some of the contaminants out of the stream,” Hildebrand said. “But then on top of that we had to slow down the system so the people could see the materials a little easier.”
The new limit on recycling contaminants set by China is no more than 0.5 percent.
Since January, Alpine has increased its workforce by 15 percent to keep up with the 0.5 percent contamination limit. Hildebrand said they’re still sending as much recycling as they can to China, but they’ve had to find new buyers in other countries to supplement.
Brent Hildebrand, Vice President of Recycling for Alpine Waste and Recycling, June 19, 2018.
Xandra McMahon/CPR News
China is cracking down partly because American material recovery facilities have gotten a little lax about how much contamination goes into the recycling, said Wolf Kray with the Colorado Department of Public Health and Environment. For example, anytime a stray red Solo cup ended up in a bale of mixed paper, the materials were contaminated.
“Because the markets have been so high and there’s been such a demand from China,” Kray said. “We haven’t done the best job necessarily as far as limiting the waste that’s gone into the recycling stream.”
And that “we” includes not just the processing facilities but also anyone who might not be recycling in the most diligent way. Colorado has a problem with what the industry likes to call “wishcycling.” Since there’s no set standard, Kray said it can be tricky to know what each program does and does not accept. “It varies even in the metro area,” he said.
Things We Shouldn’t Be Tossing In Our Purple Bins… But Probably Are*
Crinkly Plastic Cups (Red Solo Cups)
Food Take Out Containers
Plastic Film Wrap (Saran Wrap)
Scrap Metal (Broken Utensils, Old Cookie Sheets)
Plastic Grocery Bags
*Recyclables vary by collector statewide. Be sure to check with your local operator for acceptable items.
“There’s a lot of wishful recycling that goes on where people assume that if it’s got the recycling arrows on it that means it’s automatically a recyclable material and that’s certainly not the case,” Kray pointed out.
Even if the recognizable arrows are there, it doesn’t mean a facility can process or re-sell it. Some things recyclers get are not as questionable. At the Boulder County Recycling Center, conservation manager Darla Arians pointed out every time a shocking object came down the conveyor belt where workers were sorting.
“You can see that huge piece of metal he just pulled out!” she exclaimed. “That would destroy our OCC screen — our cardboard screen — which is the first piece of equipment that the material hits. If that had gone past him, the facility would have to shut down.”
Another way Alpine and other haulers across the state are handling these changes? They’re shipping material to Boulder County. Boulder has become a popular spot thanks to a new plastic sorting machine and the facility’s reliance on American buyers. They’ve been able to save more money than other recyclers around the state, putting Boulder in a position where they can help other haulers.
“Our inbound tonnage has gone up around 1,500 to 2,000 tons per month from other MRFs and haulers in the region because our gate fees are lower here than they are elsewhere,” she said.
In a millisecond, Boulder’s plastic sorting machine is able to tell the difference between a milk jug and a shampoo bottle using infrared detection. It then uses its 100-horse power air jet to shoot the material into the right container. The machine sorts more efficiently than any person, and Arians said a few are considering “this type of equipment, and with the new restrictions from China, they pretty much have to in order to keep up.”
Boulder County’s Conservation Manager Darla Arians inside the county’s recycling center, June 22, 2018.
Xandra McMahon/CPR News
Ninety-eight percent of Boulder’s material goes to American buyers for remanufacturing. Even with Boulder taking other counties’ materials, many are still scrambling to find new markets for a lot of it.
“You have essentially this big buildup of all the recyclables that are still getting collected and stored at recycling centers that need to go somewhere,” CDPHE’s Wolf Kray said. “So, because there’s more generation, essentially it’s devaluing the prices so that’s tough for the recyclers who aren’t making as much money on the actual end products when they sell them.”
Market values for recycled paper, plastics, aluminum, etc. have plummeted since restrictions went into place. That affects all recyclers, even ones like Boulder County that export very little because they sell most of their material stateside.
“If we get to the point where we’re getting a zero dollar or we were gonna be charged for a particular type of material, then we will hold on to it for 30 days and see what sort of pricing we can get in the next month,” Arians said.
For Kray, the solution lies in developing and bolstering domestic markets for recyclables. To that end, CDPHE offers grants to organizations to help develop recycling infrastructure in the state. In 2017, the program handed out 22 grants that went as high as $400,000. An Iowa company called Rewall that buys waste and turns it into building material is expanding to Colorado with the help of the grant program.
Another solution Kray mentioned has to do with the three R’s everyone learned in elementary school — reduce, reuse and recycle. Kray said there should be more emphasis on the first two and less reliance on the third.
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