Kidney-like membrane boosts desalination

A polymer membrane that mimics how biological membranes work promises to provide at least 10 times greater fluxes than reverse osmosis membranes now used for water desalination, claim researchers at the University of Illinois, Champaign, Ill. The key is the incorporation of the water-channel protein Aquaporin Z into the polymer.

“We took a close look at how kidneys so efficiently transport water through a membrane with aquaporins and then we found a way to duplicate that in a synthetic system,” notes Manish Kumar, a graduate research assistant at the school. The polymer gives chemical and mechanical stability while the aquaporin provides high selectivity and high permeability for water, he explains.

The researchers use a triblock copolymer, with a hydrophilic top and bottom and a thicker hydrophobic middle, that slowly self assembles in an aqueous solution to form hollow spheres called vesicles. While the vesicles are developing, the Aquaporin Z, solubilized in detergent, is added; the protein is attracted to the hydrophobic middle, inserting itself and thus forming a channel for water transport.

The next step in the development of the technology is to make flat membranes, says Kumar, who adds that within a year or two such membranes, likely around 5 in. by 5 in., should be produced for trials with both forward and reverse osmosis. If all goes well, commercial membranes might be available in less than 10 years, he hopes. They undoubtedly will cost more than conventional membranes but will be much less energy intensive to operate, he says.

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