October 2013, Vol. 25, No.10

Waterline

Small-scale desalination process shows promise

Energy-intensive desalination processes may be a thing of the past. A new method developed by chemists from The University of Texas (Austin) and the University of Marburg (Germany) requires such a small amount of energy that it can run on a store-bought battery, according to a news release from The University of Texas.  

The electrochemically mediated seawater desalination process eliminates the need for a membrane and separates salt from water at a microscale. This makes the process less complex and less energy-intensive than other conventional techniques, the news release says.  

The process takes place inside a plastic chip that contains a microchannel with two branches. For desalination, 3.0 volts are applied to the plastic chip filled with seawater. At the junction of the channel, an embedded electrode neutralizes some of the chloride ions in seawater to create an ion-depletion zone that increases the local electric field compared to the rest of the channel. This change in the electric field redirects salt into one branch and allows desalinated water to pass through the other branch, the news release says.  

Currently the microchannels are about the size of a human hair and produce about 40 nL/min of desalinized water. One challenge is scaling up the process, but the researchers are confident that this can be achieved too, the news release says. 

With the system, the research team has achieved 25% desalination. While drinking water requires 59% desalination, the researchers believe the system can achieve this, the news release says. 

The patent-pending process, which is in commercial development by Okeanos Technologies (Union, Ky.), has been described in the journal, Angewandte Chemie. 

 

 Accurate water quality readings require identification of E. coli strains 

Conventional water quality tests that measure the overall levels of Escherichia coli may not be as accurate as originally thought, according to a study from University at Buffalo (N.Y.) and Mercyhurst University (Erie, Pa.). With the assistance of the Shiga toxin, E. coli may fend off aquatic predators and survive longer in waterways, according to a University at Buffalo news release.   

The study, published in the Applied and Environmental Microbiology journal, suggests that measuring overall E. coli in waterways may be a poor way to find out if water poses a danger to swimmers.  

Strains of E. coli that produce the Shiga toxin are harmful to humans. And these strains also persist longer in water than other strains because the toxin helps E. coli resist predation by bacterial grazers, explained Gerald Koudelka, University at Buffalo professor of biological sciences who led the study.  

Researchers placed several different strains of E. coli into the water samples from Presque Isle State Park and Mill Creek Stream in northern Pennsylvania to test how Shiga affects its survival. Water contained protists that feed on E. coli. The toxin producers fared better against grazing protists than the toxin-free E. coli strains, with less reduction in numbers and persisting longer in water, the news release says. 

Conventional water quality testing could inaccurately predict the safety of waterways. Because waterways with low levels of Shiga-producing E. coli still can harm human health, showing safe levels of E. coli may underestimate the danger. And conversely, waterways with high levels of non-Shiga-producing E. coli may be closed but actually be safe for recreation, the news release says. 

“You could have high E. coli populations in a lake, but absolutely no [Shiga-producing E. coli],” Koudelka said in the news release. “This is the economic part of it: It’s a problem because you might have a beach that’s closed for days even though it’s safe.” 

 

Water infrastructure financing explained in new report    

The facts behind financing drinking water infrastructure are revealed in a new report released by American Rivers (Washington, D.C.). The report, “Drinking Water Infrastructure: Who Pays and How,” covers the sources for and risks accompanying financing water infrastructure, information on rate structure, and conservation efforts and analysis.  

The report includes current information designed to help those advocating for clean water and infrastructure projects understand how water utilities finance new projects, according to an American Rivers news release.  

“This guide is an essential resource for advocates working in their communities to ensure that water is provided equitably and sustainably, for present and future generations,” said Sharlene Leurig, senior manager with the Ceres Water Program (Boston), in the release. 

Read the report at www.americanrivers.org/advocateguide . 

  

Mussels equipped with backpacks retrieve water-quality data  

Anton Kruger has a special place in his heart for a filter-feeder, the freshwater mussel. Kruger, a University of Iowa (Des Moines) IIHR—Hydroscience & Engineering associate research engineer and associate professor of electrical and computer engineering, has been named Donald E. Bently Faculty Fellow in Engineering. This recognizes his commitment to students and research. One of these ongoing research projects involves using river mussels as water-quality sensors, according to a university blog.  

Kruger is leading a water-quality research project where each mussel is equipped with a “backpack” of electronic sensors to regularly and remotely transmit data, the blog says. This will create a network of sensor-collecting data about the nitrogen cycle in waterways. The wireless backpack — designed by university electrical engineering student, Hannah Taylor — contains a small radio and sensors that measure nitrogen in water.  

“They actually filter the amount of water that a major city, like Minneapolis, consumes on a daily basis,” Kruger said in the blog. “I am captivated with the idea of getting a backpack on a mussel.” 

The mussel chosen for the project is the larger, pocketbook mussel species, so the backpack does not restrict the mussel’s movement and behavior. Currently the backpack-wearing mussels are in a laboratory microhabitat that pumps in fresh river water and has lights that create artificial day and night cycles. The researchers plan to release these mussels back into the Iowa River to collect data, the blog says. 

Kruger’s team is working to make the sensors inexpensive so they could be disposable and to develop batteries with a longer lifespan for the backpacks. They hope to gather data from 5 years or more, the blog says.