Water Purification with a Nanostructured Membrane

A new composite-membrane distillation process capable of removing salt, toxic elements and microorganisms from water is being offered commercially for the first time this month

The process, known as NanoClear, was developed by Dais Analytic Corp. (Odessa, Fla.; www.daisanalytic.com) for industrial wastewater treatment and desalination. The process is said to offer significant advantages in fouling resistance and eventually cost savings over reverse osmosis at similar flowrates.

The NanoClear process (diagram) leverages the unusual properties of Dais’ patented Aqualyte membrane, which has been used commercially in HVAC (heating, ventilation and air conditioning) applications for over a decade. “Our nanostructured Aqualyte membrane is able to remove a wide range of contaminants to parts-per-billion levels, and is highly resistant to fouling,” says Dais chief technology officer Brian Johnson.

The 25–30-micron-thick membrane is made from a block copolymer with regions of polystyrene and rubber. A polar functional group is added to the styrene to make those regions hydrophilic, while the rubber regions remain hydrophobic. As the polymer solidifies, it develops inherent structure at the nanometer scale: hydrophilic channels form that allow water molecules to selectively pass through the membrane, while contaminants are retained. The channels are not open pores, Johnson says, but rather solid regions of hydrophilic plastic that interact with water molecules via hydrogen bonding to enhance their permeation between the polymer molecules.

Nanoclear operates via a pervaporation process, in which heated wastewater is circulated on one side of the membrane, and water molecules are drawn through the membrane by a vacuum on the other side. The membrane allows significant surface area density while eliminating defects in the film of source liquid that lead to scaling in conventional evaporators.

Dais now operates two pilot-scale facilities using the NanoClear process and is working with partners to retrofit the system into existing facilities.

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