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Graphene-Based Sieve Turns Seawater Into Drinking Water (bbc.com)
An anonymous reader quotes a report from BBC: A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes. It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide. Isolated and characterized by a University of Manchester-led team in 2004, graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications. But it has been difficult to produce large quantities of single-layer graphene using existing methods, such as chemical vapor deposition (CVD). Current production routes are also quite costly. On the other hand, said Dr Nair, "graphene oxide can be produced by simple oxidation in the lab." Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn't be used to filter out common salts, which require even smaller sieves. Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules. Now, Dr Nair and colleagues demonstrated that placing walls made of epoxy resin (a substance used in coatings and glues) on either side of the graphene oxide membrane was sufficient to stop the expansion.
1. What throughput / flowrate can you achieve, per unit of area?
2. How do you clear clogging?
"The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating."
This is classic enviro bullshit. You just claimed that if we suck in some seawater, separate the water from the minerals, and then return the minerals to the ocean again, that they magically turn toxic against the same species that have been spending their lives in it? Human desalination cannot change the amount of water or salt in the environment. "Excess salt" does not exist.
In fact, because salt has value in commerce, a lot of desalination salt will be retained on land for use in industrial processes. So large-scale desalination could technically be used to decrease the amount of salt in the ocean - though the amounts of salt and water we are talking about are so small compared to what is in the oceans that we could never detect the change in any foreseeable future.
Los Angeles consumed about 17,957,000,000 in August of 2013
A gallon of sear water contains 4.5 oz of salt
So if LA used exclusively desalinized water, they would have 10,100,812,500 lbs of salt on their hands (17,957,000,000*4.5/8)
This is about 126,260,156 cubic feet.
Your average Panamax cargo ship has about 3.6 million cubic feet of space.
This is about 35 ships worth of salt.
There are about 16,900 bulk carrier ships operating in the world.
When Fascism comes to America, it will call itself Anti-Fascism, and tell you to give up your guns.
This entire thread has been idiotic, because everybody's missing the most important factor:
The desalinized water doesn't leave the system; it gets used and returned.
People drink the water, piss it back out, and flush it down the drain. The drain goes to the sewer. The sewer goes to the wastewater treatment plant. So re-salinize the wastewater after treating it and you can dump it back into the ocean at the same salinity you started with! (Give or take losses from outdoor watering and gains from precipitation falling into combined sewers, anyway. The net difference could be significant, but we shouldn't dismiss the idea out-of-hand by assuming so.) So just build the two treatment plants next to each other and pipe the salt across from the desalinizer to the resalinizer.
Or better yet, just build one plant capable of treating any water (seawater or wastewater) to a drinkable standard, and make the damn thing a closed loop!
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