Quenching the Thirst for Potable Water Through Nanotechnology

After our last post discussing how experiments with carbon nanotubes (CNT’s) might greatly improve the effectiveness of reverse osmosis desalination now comes a new report from the Institute of Physics that shows researchers are getting closer to making this a reality. Already over a billion people do not have regular access to clean water and the problem will likely get worse as the demand for drinkable water is expected to grow dramatically in the near future. With natural sources increasingly scarce, this urgent need means there is an intense global interest in any potentially viable forms of water purification.

Right now the main issues preventing RO desalination on a large-scale basis are that the membranes used to perform seawater to freshwater separation do not remove salt ions with enough efficiency and they also require great amounts of energy (and therefore expense) in order to purify the water. Jason Reese, a Professor of Thermodynamics and Fluid Mechanics at the University of Strathclyde and also the author of this report, states, “The holy grail of reverse-osmosis desalination is combining high water-transport rates with efficient salt-ion rejection.” Incredibly, these little carbon nanotubes may be able to satisfy both of these requirements for widespread adoption.

Early tests and simulations have shown that CNT membranes could have water permeability that is 20 times greater than today’s materials. Additionally, carbon nanotubes can be chemically tailored to better reject salt ions, thus improving upon the desalination process in multiple key areas.

While it is still early, these features are promising enough that scientists such as Professor Reese feel it is a very real possibility that this application of nanotechnology could be used to curtail our growing water demand.

Read more about this report here.

ASTM Standards for SDI Testing

The good people at ASTM (American Society for Testing and Materials) have released their standard for determining the Silt Density Index of water. If you're interested in learning more about it, you can preview the document here. You can also look at our very own SDI test kits here.

Silver Nanoparticles to Reduce Membrane Biofouling

Scientists at Michigan State University and the PERMEANT Group describes how they are infusing membranes with nanotechnology in order to improve membrane performance, particularly in the field of water purification.  While the use of nanotechnology to expand membrane permeability, selectivity, and resistance has grown more frequent over the last 20 or so years, the new research by these groups is taking this approach in interesting directions.  For instance, on one project they have demonstrated that by adding silver nanoparticles into the polymer matrix of the membrane that the mixture is effective at reducing intrapore biofouling.  Experimentation also shows that this method could also be used to inhibit the biofilm growth on downstream membrane surfaces.  

Hopefully with every little improvement that these teams make will lead them a step closer to their goal of making the world’s supply of drinking water safer for all of us.  

   

You can read more about this research here.

Water Sterilization & Silver

From this recent article in NanoLetters, the American Chemical Society Journal, comes information about a new form of water sterilization out of Stanford University that takes advantages of the unique bacteria-killing properties of silver (the vampire and werewolf killing properties of silver have yet to be proven).  Basically, the proposed multiscale device would perform high speed electrical sterilization of water using a combination of silver nanowires, carbon nanotubes, and cotton.  The end result is that when operating at 100,000 L/(h m²) this device can inactivate greater than 98% of bacteria with only several seconds of total incubation time.

The author’s of this paper mention two interesting reasons for why silver is used in the device.  The first:        

Taking advantage of silver nanowires’ (AgNWs) and CNTs’ [Carbon Nanotube] unique ability to form complex multiscale coatings on cotton to produce an electrically conducting and high surface area device for the active, high-throughput inactivation of bacteria in water.

The other reason described for using silver in water sterilization:

Silver is chosen since it is a very well-known bactericidal agent, and recently a large amount of interest has been spurred by the discovery that silver nanoparticles work extremely well at killing bacteria and can be attached to various surfaces with chemical techniques.    

The outcome of the silver treatment in the author’s experiment provides further evidence of these properties:

The results clearly show that filters not treated with silver, including CNT-only cotton, showed a robust growth of bacteria, while the bacteria concentration in the solutions incubated with AgNW-treated material was reduced to the detection limit of the absorbance system used, at least a 2 to 3 order of magnitude reduction.

All in all, the findings in this paper are encouraging that implementation of this approach can kill microorganisms which cause biofouling in downstream filters.  The authors of the paper state, “Such technology could dramatically lower the cost of a wide array of filtration technologies for water as well as food, air, and pharmaceuticals, where the need to frequently replace filters is a large cost and difficult challenge.”

Their next step is to expand their experimentation to other microorganisms beyond the E. coli that was used for this study.  In their conclusion the authors note that, “Silver is known to be an extremely general agent so it can be expected that this device will also work over a wide array of organisms.” 

We’ll continue to monitor their progress and hope for the best!