Study shows forward osmosis desalination not energy efficient

Jul 24, 2014 by Alissa Mallinson

In a recent study published in the Journal of Membrane Science, MIT professor John Lienhard and postdoc Ronan McGovern, both of the Department of Mechanical Engineering, reported that, contrary to popular support, forward osmosis desalination of seawater is significantly less energy efficient, compared to reverse osmosis.

In forward osmosis, water is drawn from the seawater into a concentrated salt solution, known as a draw solution. Then, a second step is required to regenerate the concentrated draw solution and produce purified water. With reverse osmosis, the seawater is directly desalinated by being pressurized and driven through a membrane that only allows water to pass through.

McGovern performed an energetic comparison of reverse osmosis and forward osmosis to identify their respective energy consumptions. The problem, he says, is that even if the second step of draw regeneration—in which the concentrated salt solution is dewatered, producing fresh water—can achieve the same level of efficiency as the reverse osmosis process, the actual energy consumption of forward osmosis will consistently surpass that of reverse osmosis. This is because the salt solution that results from the first step of forward osmosis is necessarily more highly concentrated than standard , meaning it always requires a higher level of energy for regeneration.

According to McGovern, forward osmosis is better suited to alternate applications, such as the production of hydration drinks. In such applications, only the first step of the forward osmosis process is required—where a concentrated sugar syrup is diluted to a desirable level—placing forward osmosis at an advantage to .

Explore further: Research makes desalination cheaper and greener

More information: Ronan K. McGovern, John H. Lienhard V, "On the potential of forward osmosis to energetically outperform reverse osmosis desalination," Journal of Membrane Science, Volume 469, 1 November 2014, Pages 245-250, ISSN 0376-7388. DOI: 10.1016/j.memsci.2014.05.061.

add to favorites email to friend print save as pdf

Related Stories

From seawater to freshwater with a nanotechnology filter

Jun 01, 2011

In this month's Physics World, Jason Reese, Weir Professor of Thermodynamics and Fluid Mechanics at the University of Strathclyde, describes the role that carbon nanotubes (CNTs) could play in the desalination of wat ...

Energy-efficient water purification

Jan 14, 2009

Water and energy are two resources on which modern society depends. As demands for these increase, researchers look to alternative technologies that promise both sustainability and reduced environmental impact. Engineered ...

Osmosis: Everything you know about it is (probably) wrong

Apr 01, 2013

Osmosis – the flow of a solvent across a semipermeable membrane from a region of lower to higher solute concentration – is a well-developed concept in physics and biophysics. The problem is that, even though the concept ...

Britain unveils desalination plant for London reservoirs

Apr 25, 2011

(PhysOrg.com) -- Britain has brought online a new desalination plant near London capable of providing the city with 150 million gallons (568 million litres) of water per day, should the need arise. At a cost ...

Recommended for you

Toyota, Grenoble set stage for test in ride-sharing

Sep 14, 2014

Toyota is testing ride-sharing. As simple as that may sound, the experiment indicates an innovative model for the future of urban transportation. The Grenoble metro area could turn out to be the trial stage ...

Sparks fly as Di Grassi wins first electric race

Sep 14, 2014

A spectacular crash at the last corner that ended leader Nicolas Prost's race and sent ex-F1 driver Nick Heidfeld flying into the fencing gave Brazil's Lucas di Grassi victory in the first ever Formula E ...

First electric car race to zoom off on Saturday

Sep 12, 2014

Formula E will be a laboratory for new technology, according to motor sport great Alain Prost, while Bruno Senna said drivers will face a "lottery" when electric car racing kicks off in Beijing Saturday.

User comments : 0