A Future With Potable Water For All?


Image from kurzweilai.net

Two scientists out of MIT have theorized a better way to desalinize water—remove the salt ions from salt water—that could make the 97 percent of Earth’s water found in its oceans and seas potable to drink.

Earth can desalinify water through the natural process of evaporation and condensation, however this process takes time and often does not make it to the regions that need water most.  Being able to effectively, both in cost and in energy, control the desalination of salt water would be a giant landmark for humanity.

Currently only a small portion of Earth’s drinkable water is derived from the ocean.  This is largely due to the issues concerning existing desalinization processes.  The most widely used process now is called reverse osmosis and it calls upon the basic principles of osmosis: that is solvent molecules will freely move from an area of high concentration to a lower concentration.  Reverse osmosis puts salt water under high pressure (increasing its concentration).  The salt water then wants to move to an area with lower concentration, but to do so it has to pass through a selective membrane, which has pores big enough to allow water molecules through, yet small enough to kick off large ions such as salt.  It sounds great, but in truth the technology is not yet cost-effective or efficient enough to become incredibly widespread.

The two scientists, David Cohen-Tanugi and Jeffrey C. Grossman, have shown in simulations that a new membrane, nonporous graphene can filter salt from water 2-3 faster than reverse osmosis, and under low-pressure as well.  They predict that graphene’s superior water permeability could lead to future desalination techniques that are use less energy and can be smaller than current reverse osmosis contraptions.

There are drawbacks.  Graphene is a relatively new discovery—first isolated in 2004.  It’s a membrane is only a single atom layer and made up of sp2 bonded carbon atoms that are packed into a planar, honeycombed shaped pattern.  It has yet to be mass-produced because there is a lack of practical uses for it as of yet.  This means the cost of these new potential desalination techniques has yet to be hypothesized.  It also means that graphene has not yet been produced on a large-scale.  Also, the graphene has to have adequately measured pores that do not allow salt ions through.  The researchers have shown that hydrophilic hydroxyl functional groups attached to the membrane can increase the amount of water filtration (their hydrophilic, water-loving nature drives the water to the membrane) however, this has yet to be perfected as the graphene with these functional groups still allow some salt ions through.  Last, and I’m tedious on this, but it seems to me that the graphene membrane, much like reverse osmosis, not only removes the salt ions from the water but all other minerals as well…including the healthy ones.  This can be solved through of process of remineralization, a process the bottled water company Dasini uses, but that can only increase the cost of this technology.

Honestly, I shouldn’t even been christening this as technology yet.  It is still research in the dawn of its prime (and after further research and investigations, as well as bureaucratic interruptions who’s to say its prime is going to be all that glorious?).  It is promising, however.  From water there’s food, life, sustainability, and a brighter future.

O, and here’s the article published by the scientists.

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