US research challenges value of forward osmosis in seawater desalination
Researchers in the US have claimed that forward osmosis desalination of seawater is significantly less energy efficient than reverse osmosisProfessor John Lienhard and co-worker Ronan McGovern of the Massachusetts Institute of Technology have reported that even if the level of purity of water generated from forward osmosis could be match that of the reverse osmosis the second stage of the forward process intrinsically requires more energy.
In forward osmosis, water is drawn from the seawater into a concentrated salt solution, known as a draw solution. In a second step the concentrated draw solution is treated to produce purified water. The salt solution that results from the first step is more highly concentrated than standard seawater so it must need a higher level of energy for regeneration the MIT team concluded.
According to McGovern, forward osmosis is better suited to applications where only the first step of the forward osmosis process is required -- such as where a concentrated sugar syrup is diluted to a desirable level. In such applications the forward process has the advantage over reverse osmosis.
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