Water Desalination Reference2009-32

Water Desalination ReporTTechnologynew Nanotube makes media splash

Researchers at Australian National University (ANU) in Canberra, Australia have published a paper that describes promising results using boron nitride nanotubes to desalt seawater. The work, done on computers using molecular dynamic simulations, shows that boron nitride nanotubes (BNT) embedded in a silicon nitride membrane have superior desalination properties over conventional polymeric membranes and carbon nanotubes (CNT).

Tom Pankratz, Editor, P.O. Box 75064, Houston, Texas 77234-5064 USATelephone: +1-281-857-6571, www.waterdesalreport.com, email: tp@globalwaterintel.com© 2009 Media Analytics. Published in cooperation with Global Water Intelligence.

31 August 2009Volume 45, Number 32

The international weekly for desalination and advanced water treatment since 1965

The first, an academic involved in new membrane technologies, said, “Interesting. Elegant. However, it seems unlikely that 100 percent salt rejection could hold up over time, and fouling limitations could impact short-term performance stability at a high flux. Surface modifications resulting from acid, base and chlorinated flushes could pose challenges for both CNT and BNT materials.”

WDR also asked Mark Shannon, director of the WaterCAMPWS at the University of Illinois. Dr Shannon said that he likes the overall idea of BNTs because the high dipole between boron and nitrogen means that the interior pore should be more selective, but he also wonders if surrounding the BNT with silicon nitride might change the electronic structure.

“The molecules at the entrance and termination of the nanotubes are absolutely vital and can dramatically change the screening potential, so much that it can switch which ion passes. The ANU modeling was done without termination of the BNT ends, so it will be interesting to see the effects of attaching different functional groups,” he said, noting that it will also be very difficult to make the BNT’s active layer long and thin enough without introducing extrinsic processing defects such as pinholes. “Going to larger diameter and longer BNTs will help, but it comes at the expense of selectivity. It is hard to have it both ways.”

FloridaStimulus package helps fund RO project

Two of four contracts, valued at almost $3.25 million, have been awarded as the City of Oldsmar moves forward with an RO project slated to receive $3 million under the American Recovery and Reinvestment Act (ARRA). The funding includes a ‘buy American’ provision and is part of the federal economic stimulus package. Florida also attached a provision that the money be committed by the first of October so that it would have an immediate impact on the local economy.

According to Lisa Rhea, Oldsmar’s utilities administrator, the project was broken down into four separate contracts: the production wells, which were awarded to Advanced Drilling for approximately $750,000, an RO equipment supply contract awarded to Harn R/O Systems for $2.49 million, the concentrate injection well, which will be awarded in early September, and the general construction contract, which is to be bid in December and awarded by mid-February.

But before utilities plan to retrofit existing RO elements with their nanotube counterparts, they should note that the performance predictions are based solely on computer simulations. These simulations may prove accurate, but they are impossible to confirm without experimental validation; then comes the daunting task of figuring out how to make the BNTs at a competitive price.

The researchers themselves are much more reasonable and cautious. Tamsyn Hilder, a postdoctoral fellow in ANU’s Research School of Biology, told WDR that while the results of the proof-of-principle computational studies are promising, there is much experimental research ahead. “We need to explore, for example, how the system we designed can be fabricated effectively and test if the engineered nano-material does indeed prevent charged particles from entering the pore,” she said.

WDR asked two other membrane scientists not affiliated with the project for their thoughts on the study results – and the science supporting it – based on a paper published in the July issue of the journal Small. Both were impressed.

Enthusiastic university press releases, and the stories they generated, claim that BNTs can operate at a flux more than four times higher than conventional membranes while achieving 100 percent salt rejection at concentrations twice that of seawater, all at operating pressures comparable to existing RO processes. Media responses are reminiscent of the wildly optimistic mid-2006 announcement of the desalting possibilities of CNT, and they are fueling buoyant news stories in the international press, predicting that BNTs “are set to transform desalination.”Water Molecules