Clean water breakthrough: A new way to recover almost 100 percent of the water from highly concentrated salt solutions

Hot brines used in traditional membrane distillation systems are highly corrosive, making the heat exchangers and other system elements expensive, and limiting water recovery (a). To improve this, UCR researchers developed a self-heating carbon nanotube-based membrane that only heats brine at the membrane surface (b), where the porous carbon nanotube layer acts as a Joule heater (c).

UCR research expands efforts to provide clean water for the world’s growing population

Engineers at the University of California, Riverside have developed a new way to recover almost 100 percent of the water from highly concentrated salt solutions. The system will alleviate water shortages in arid regions and reduce concerns surrounding high salinity brine disposal, such as hydraulic fracturing waste.

The research, which involves the development of a carbon nanotube-based heating element that will vastly improve the recovery of fresh water during membrane distillation processes, was published today in the journal Nature Nanotechnology. David Jassby, an assistant professor of chemical and environmental engineering in UCR’s Bourns College of Engineering, led the project.

While reverse osmosis is the most common method of removing salt from seawater, wastewater, and brackish water, it is not capable of treating highly concentrated salt solutions. Such solutions, called brines, are generated in massive amounts during reverse osmosis (as waste products) and hydraulic fracturing (as produced water), and must be disposed of properly to avoid environmental damage. In the case of hydraulic fracturing, produced water is often disposed of underground in injection wells, but some studies suggest this practice may result in an increase in local earthquakes.

One way to treat brine is membrane distillation, a thermal desalination technology in which heat drives water vapor across a membrane, allowing further water recovery while the salt stays behind. However, hot brines are highly corrosive, making the heat exchangers and other system elements expensive in traditional membrane distillation systems. Furthermore, because the process relies on the heat capacity of water, single pass recoveries are quite low (less than 10 percent), leading to complicated heat management requirements.

To improve on this, the researchers developed a self-heating carbon nanotube-based membrane that only heats the brine at the membrane surface. The new system reduced the heat needed in the process and increased the yield of recovered water to close to 100 percent.“In an ideal scenario, thermal desalination would allow the recovery of all the water from brine, leaving behind a tiny amount of a solid, crystalline salt that could be used or disposed of,” Jassby said. “Unfortunately, current membrane distillation processes rely on a constant feed of hot brine over the membrane, which limits water recovery across the membrane to about 6 percent.”

In addition to the significantly improved desalination performance, the team also investigated how the application of alternating currents to the membrane heating element could prevent degradation of the carbon nanotubes in the saline environment. Specifically, a threshold frequency was identified where electrochemical oxidation of the nanotubes was prevented, allowing the nanotube films to be operated for significant lengths of time with no reduction in performance. The insights provided by this work will allow carbon nanotube-based heating elements to be used in other applications where electrochemical stability of the nanotubes is a concern.

Learn more: Squeezing Every Drop of Fresh Water from Waste Brine



The Latest on: Thermal desalination

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VIDEO – Damian Palin: Mining minerals from seawater


The world needs clean water

The world needs clean water, and more and more, we’re pulling it from the oceans, desalinating it, and drinking it. But what to do with the salty brine left behind? In this intriguing short talk, TED Fellow Damian Palin proposes an idea: Mine it for other minerals we need, with the help of some collaborative metal-munching bacteria.

Damian Palin is developing a way to use bacteria to biologically “mine” minerals from water — specifically, out of the brine left over from the desalinization process.

Read more . . .

via TED

The Latest Streaming News: Mining minerals from seawater updated minute-by-minute



Oil field brine proposed to treat Hungary’s red sludge spill

The bauxite residue container pond spill near Kolontar, Hungary

It might sound like fighting fire with fire, but geologist Chen Zhu proposes the application of another industrial waste to the Hungarian bauxite residue spill, with the aim of reducing toxicity via a technique called carbon sequestration.

While he says it wouldn’t render the residue completely harmless, it would at least minimize the environmental damage.

Bauxite residue is created as a by-product of the aluminum industry, and since there is currently no regulation or imposed company responsibility to neutralize the waste, the corrosive material is often left in container ponds. It is estimated that worldwide there are in excess of 200 million tonnes (220.46 million US tons) of “red sludge” in ponds like this.

When the pond near Kolontar, Hungary burst on October 4th, it released between 598 and 697 million liters (158-184 million US gallons) of toxic waste – between 79-92 percent of the entire gulf spill that dominated the press this summer. Thirteen people have been killed, 150 injured and several communities destroyed and potentially abandoned. The immediate and long-term damage to the ecosystem is untold, covering an area of 40 square kilometers (15.4 square miles). The devastation spread as the spill reached the Danube, Europe’s second-longest river, having already killed all the fish in the Marcal river.

It is ironic, then, that this could be addressed by the addition of another industrial waste – oil field brine – the by-product of oil and gas production. This approach has been proposed by Indiana University Bloomington geologist Chen Zhu, who submitted a U.S. Department of Energy patent application in 2007 describing the technique.

“Carbon sequestration” is the process by which carbon is removed and stored. In this case, the brine provides the medium in which the carbon dioxide can dissolve. Once dissolved, CO2 reacts with water to create carbonic acid which will reduce pH (currently between 11 and 13) and cause the precipitation of salts that would otherwise react with living matter.

It’s important to realize, however, that this is both expensive and certainly not a cure-all solution. “By reducing the pH and causing the precipitation of problematic salts, what we’re left with is not something that’s non-toxic, but less toxic than what we started with,” says Zhu.

Read more . . .

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