Desalination Using Engineered Osmosis  

Technology Review has an article on a new, energy efficient desalination technique called 'engineered osmosis" - A Low-Energy Water Purifier. The mechanism sounds similar to the schemes that aim to draw energy from bodies of water where salt and fesh water come into contact that I mentioned in my desalination post last year.

Access to clean water is severely limited in many parts of the world, and while desalination plants can separate freshwater from sea and brackish water, they typically require large amounts of electricity or heat to do so. This has prevented desalination from being economically viable in many poorer cities and countries.

A Yale University spinoff called Oasys is driving one effort to change all this. Professor Menachem Elimelech and graduate students Robert McGinnis and Jeffrey McCutcheon have developed a novel desalination device that reduces the energy needed to purify water to one-tenth of that required by conventional systems.

In many parts of the world, freshwater supplies are strained due to population growth and increasing agricultural, industrial, commercial, and domestic demand. Goldman Sachs estimates that global water consumption is doubling every 20 years, and in 2008, the total worldwide water market was worth $522 billion, according to the analyst firm Lux Research.

The most common approach to desalination is currently reverse osmosis, and the market for this technology is expected to grow at a rate of 10 percent per year. Reverse osmosis involves forcing a solution through a semipermeable membrane using hydraulic pressure or thermal evaporation. The energy required to do this has spawned new thinking and innovation on lower-energy purification technologies. "The primary driver behind this technology is to get at the heart of the problem of energy cost," says Aaron Mandell, CEO of Oasys.

The company is using what it calls engineered osmosis. Unlike conventional desalination systems, the Oasys system establishes an osmotic pressure gradient instead of using pressure or heat to force water through a purifying membrane. The approach exploits the fact that water naturally flows from a dilute region to one that's more concentrated when the two solutions are separated by a semipermeable material, thereby saving the energy normally needed to drive the process. ...

Oasys says that the first market it will focus on will be wastewater reuse. The second will be reprocessing wastewater produced by the oil and gas industries. Instead of having to pay to haul this water away, companies would treat it on-site using the Oasys system.