Nanoparticles boost water treatment

Super-hydrophilic nanoparticles dispersed in a conventional polyamide reverse osmosis (RO) membrane allow dramatically better water permeability than possible with conventional membranes while maintaining comparable salt rejection, according to researchers at the University of California – Los Angeles (UCLA). The particles provide a preferential flow path for the water, while also enhancing the membrane’s resistance to organic and bacterial adhesion, explains Eric Hoek, an assistant professor in the civil and environmental engineering department, who heads the research team.

The thin polymer film itself can’t be changed much without sacrificing its stability and salt rejection, he explains. So, the key to better performance is uniformly incorporating the nanoparticles within the membrane. They attract the water and provide a more regular pore structure than the film, leading to higher throughput, Hoek notes. The result is a membrane that requires significantly less energy consumption for a given flux. Sometimes, the reduction can amount to as much as 50%, he adds.

Hoek hasn’t identified any tradeoffs or limitations with the use of the nanoparticle membranes, as yet. While the nanoparticles are expensive, only small amounts are required. So, the impact on membrane cost is almost insignificant, he claims.

The UCLA researchers are developing technology to synthesize the specialized nanoparticles and to integrate them in the RO film. A whole family of tailored nanoparticles is possible, Hoek notes, adding that biocidal particles already can be generated. Existing commercial membrane-product lines should require only modest modifications to be able to produce the membranes, he says.

NanoH2O LLC, Santa Monica, Calif., holds exclusive rights to commercialize the technology. Field trials of conventional-size spiral-wound nanoparticle RO membranes should begin in 2008, says Jeff Green, the company’s CEO. If the trials go as hoped, the firm may commercially launch membranes early in 2009.

The commercial membranes will be drop-in replacements. They will boast a dramatic increase in permeability, Green says — NanoH2O is targeting twice the throughput. Despite the higher flux, the membranes’ fouling resistance will allow the service period to match that of conventional units, he adds. A single version of nanoparticle will initially be offered. Later, a biocidal particle may be introduced, once its long-term performance is assessed, says Green, and then perhaps particles tailored to specific applications.

The membranes should cost 1% to 5% more than conventional units, reckons Green. However, they will provide significant savings in operating and capital costs, he says.

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