We looked at desalination, particularly using solar power, not long ago. (Renewable Thursday: Desalination) Almost all of it uses energy-intensive distillation or reverse osmosis. It turns out that there is a lot of research going on to find more energy-efficient methods of desalination, not only for seawater, but for far more salty "hypersaline" brines resulting from various industrial and oil well drilling processes.
For example:
Each of these new technologies promises greatly reduced cost for desalination. I draw no conclusions about which of these will be commercialized, and which will win out in the variety of locations and applications out in the real world.
But I have no doubt that one will.
TSSE
Radical Desalination Approach May Disrupt the Water Industry
Columbia Engineering researchers design new desalination method for hypersaline brines that is low-cost, efficient, and effective; could address the growing water challenges across the globe.
Hypersaline brines—water that contains high concentrations of dissolved salts and whose saline levels are higher than ocean water—are a growing environmental concern around the world. Very challenging and costly to treat, they result from water produced during oil and gas production, inland desalination concentrate, landfill leachate (a major problem for municipal solid waste landfills), flue gas desulfurization in fossil-fuel power plants, and effluent from industrial processes.
If hypersaline brines are improperly managed, they can pollute both surface and groundwater resources. But if there were a simple, inexpensive way to desalinate the brines, vast quantities of water would be available for all kinds of uses, from agriculture to industrial applications, and possibly even for human consumption.
A Columbia Engineering team led by Ngai Yin Yip, assistant professor of earth and environmental engineering, reports today that they have developed a radically different desalination approach—“temperature swing solvent extraction (TSSE)”—for hypersaline brines. The study, published online in Environmental Science & Technology Letters, demonstrates that TSSE can desalinate very high-salinity brines, up to seven times the concentration of seawater. This is a good deal more than reverse osmosis, the gold-standard for seawater desalination, and can handle approximately twice the seawater salt concentrations.
Filter Paper Coated with Carbon Nanotubes
Hydrophilic disc uses solar power to separate salt from water
Current approaches to water desalination are tremendously expensive and energy-intensive, so the search is very much on for new technologies that can get the job done more efficiently. Scientists in Melbourne have put forward one rather promising solution, developing a new kind of system that heats up and purifies water using only the power of the Sun.
The device was developed by scientists at Australia's Monash University, who say that water treatment accounts for around three percent of the world's energy supply. Like other researchers around the globe, they have turned to sunlight to try and lighten the load, this time directing it toward what is known as a solar steam generator.
In simple terms, these devices concentrate sunlight onto a body of water, heating it up and causing it to evaporate. The resulting steam can then be used to drive turbines that produce electricity in concentrated solar power plants, perhaps sterilize medical equipment cheaply for the developing world, or simply to separate salt from water.
But one problem with the lattermost application is that the salt tends to gather on the surface of the material, which makes it difficult to produce pure water. The Monash University researchers worked around this problem with an intricately designed solar steam generator that prevents the salt from spoiling the broth.
It consists of a disc crafted from super-hydrophilic filter paper, a material that attracts water, which is coated with a layer of carbon nanotubes that convert sunlight into heat. Water is fed into the center of the disc via a simple cotton thread, where the heat turns it into steam that builds up on the disc while pushing the salt to the edge.
In this way, the device removes almost 100 percent of salt from the water, a level that leader of the team Professor Xiwang Zhang assures us is "high enough for practical applications." The salts that accumulate at the edges, meanwhile, can also be harvested for use.
Zhang and his team tested out the device using salty water from a bay in South Australia, and found that it absorbed 94 percent of the light across the solar spectrum. It worked whether wet or dry, with light exposure heating up the device from 25 to 50° C (77 to 122° F) when dry and from 17.5 to 30° C (63.5 to 86° F) when wet, within just one minute.
"This device can produce six to eight liters (1.6 to 2.1 gal) of clean water per square meter (of surface area) per day," Zhang tells New Atlas. "We are working to further improve the water production rate."
Nanowood Filters
This “nanowood” could revolutionize desalinization
Scientists think a new filter made from wood could make it easier to make clean drinking water from the ocean.
"We are trying to develop a new type of membrane material that is nature-based,” says Z. Jason Ren, an engineering professor at Princeton University and one of the coauthors of a new paper in Science Advances about that material, which is made from wood. It’s designed for use in a process called membrane distillation, which heats up saltwater and uses pressure to force the water vapor through a membrane, leaving the salt behind and creating pure water. The membranes are usually made from a type of plastic. Using “nanowood” membranes instead can both improve the energy efficiency of the process and avoid the environmental problems of plastic.
Cavitation
Scientists create device that cuts desalination costs by 90%
The new method suggested by the Russian scientists does not require high energy consumption.
It uses cavitation, the formation of voids within a fluid. In the case of salt water, the voids fill with pure water vapor, forming bubbles which can be extracted from the bulk fluid.
Graphene-Based Membranes
Jun 18, 2019 - The biggest problem keeping desalination from becoming an even more widespread source of water is its costs, both environmental and financial. Thermal distillation and reverse osmosis require huge amounts of energy (the former more than the latter), and are still expensive relative to other sources of fresh water.
The most common desalination methods are thermal distillation and reverse osmosis. In thermal distillation, water is heated until the pure vapor separates from the salt and other components. In reverse osmosis, high amounts of pressure push water through a filter to separate it from salt.
According to the International Desalination Association, there are 20,516 desalination plants across 150 different countries, providing water to 300 million people.
At just one atom thick, graphene—a material made of carbon atoms arranged in a hexagonal lattice—has been widely hyped its strength and conductivity, but thus far it’s proved difficult to scale its manufacture. Graphene holds promise for water filtration, but the technology is far from ready for use in large-scale desalination.
It’s slowly getting closer, though. Last week an international research team from the US, China, and Japan published a paper in Science detailing their work to reinforce graphene membranes for filtration purposes.
The research team created a graphene-nanomesh/single-walled carbon nanotube hybrid membrane. The nanotubes act as a microscopic framework to support the graphene and increase its structural integrity. The result was a centimeter-sized mesh with a honeycomb appearance, and when tested as a membrane in a filtration system it rejected 85-97 percent of the salt from saltwater.
A graphene roll-out
Scalable manufacturing process spools out strips of graphene for use in ultrathin membranes.
Other
“We do believe that brine is not just for discharge,” said Nikolay Voutchkov, a technical adviser to the Saline Water Conversion Corp., a government corporation that is the largest producer of desalinated water in the world, responsible for three-fourths of Saudi Arabia’s production. “That’s what we do with it today. But it is actually a very valuable source of minerals.”
Process developed at MIT could turn concentrated brine into useful chemicals, making desalination more efficient.
Moving Forward on Desalination - Berkeley Lab News Center
Jul 31, 2019 - A Q&A with scientist Jeff Urban, who explains forward osmosis and how Berkeley Lab is pushing the frontiers of this emerging technology.
Scientists at Berkeley Lab have been exploring different approaches for efficiently separating out salt and other contaminants to generate water that’s fit for drinking or other uses, such as agricultural irrigation. For example, they’re looking at charge-based brackish water desalination, nanoconfinement of water, better membranes, and
other advanced water treatment techniques.
Seawater turns into freshwater through solar energy: A new low-cost technology
Engineers have developed an innovative, low-cost technology to turn seawater into drinking water.
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).
New system recovers fresh water from power plants
Technology captures water evaporating from cooling towers; prototype to be installed on MIT’s Central Utility Plant.
That's not desalination, of course. But it is notable for not requiring energy to heat the water, which is already hot enough to produce lots of water vapor.