• John Lienhard and Ronan McGovern

    John Lienhard and Ronan McGovern

    Photo: Tony Pulsone

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Study shows forward osmosis desalination not energy efficient

The two-step process is better suited for other applications


Press Contact

Alissa Mallinson
Email: alissam@mit.edu
Phone: 617-258-7511
Department of Mechanical Engineering

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 seawater, 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 reverse osmosis.


Topics: Mechanical engineering, Desalination, Water, Research

Comments

The point is not the absolute energy consumption, but the cost of the energy consumed and ultimately the cost to produce desalinated sea-water ....the analysis has a fatal flaw in that this aspect was not considered. Stay tuned for a real world trial to prove this...

How does forward osmosis affect the amount of pretreatment and membrane fouling? If this pretreatment requirement is less than than required for RO, then that energy would have to be accounted for.

Can you tell me the exact amount of energy required for both the processes?

Have you some data for this

Process should not be energy consuming with forward osmosis, absence of negative cation will allow dilution. Major consumption of charged particles,advanced cell particle treatment,subdivided miniaturization of permeable zone.Law of Inertia draws substance into micro particle substrate allowing attachment to supersaturated ionized particles.Initial solution, high molecular value,impregnation of Gold Salt& electric or solar powered spin force energy conservation,entails a constant monitoring process of speed & regularity of interval rotations 45rmp, repeated by rocking motions at 75rmp reversals. Cellular renewal of membrane not to exceed 4,421 ppm. at .001cm.
Hope this will be of some use to your organization.

Thanks Laurie Farell for an attempted explanation (that I do not understand)
Access to the paper would be helpful, but as usual all I can get is the abstract.
Can you post the paper here?
http://pubs.acs.org/doi/full/1...

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