October 2010, Vol. 22, No.10

Research Notes

Harnessing bacteria to generate energy

Research in reconfiguring microbial electrochemical cells (MXCs) to carry out electrolysis could help enhance the efficiency of clean energy production. Prathap Parameswaran and colleagues in the Biodesign Institute at Arizona State University (Tempe) used a microbial electrolysis cell (MEC) to form hydrogen gas, according to an article by Biodesign Institute science writer Richard Harth.

MXCs use bacterial respiration to liberate electrons and generate an electrical current. Bacteria, grown in the positive (anode) chamber, can use waste materials as food to grow while transferring electrons onto the electrode to generate this electricity, as shown by another research team, led by Bruce Rittmann, director of Biodesign’s Center for Environmental Biotechnology.

In the current study, researchers reconfigured MXCs into an MEC so that electrons produced at the anode join positively charge protons in the negative (cathode) chamber to form hydrogen gas. The reactions in the MEC anode are similar to what happens in a microbial fuel cell to generate electricity, Parameswaran said, according to the article.

The study shows that the level of electron flow from the anode to the cathode can be improved by selecting for additional bacteria known as homo-acetogens in the anode chamber. Researchers identified homo-acetogens using both chemical and genomic methods. Homo-acetogens produce acetate, which is a favorable electron donor for the anode bacteria. Under favorable conditions, anode bacteria that formed a relationship, or syntrophy, with homo-acetogens were found to convert hydrogen into a current more efficiently, the article says.

Researchers also reduced the negative effect of other hydrogen-consuming microbes, which remove some of the available electrons from the system and reduce the current, the article says. In the study, researchers added the chemical 2-bromoethane sulfonic acid to inhibit methanogens, one type of hydrogen-consuming microbe.

This and future research could help commercialize systems that treat wastewater and generate energy, the article notes. The researchers also plan to explore ways to sustain syntrophic relationships between homo-acetogens and anode bacteria in the absence of chemical inhibitors, the article says.

Read more in Harth’s article, “Microbe power as a green means to hydrogen fuel production,” at www.biodesign.asu.edu/news/microbe-power-as-a-green-means-to-hydrogen-fuel-production.


Membrane filters oil from water

A Purdue University (West Lafayette, Ind.) researcher has created a new type of membrane that separates oil from water. Jeffrey Youngblood, an assistant professor of materials engineering at Purdue, has created technology that enables a membrane to allow water but not oil to pass, according to a Purdue news release.

With a higher flow rate than conventional filters that separate oil from water, the new membrane filter results in 98% separation, according to Youngblood. Researchers have tested the materials with solutions containing oil suspended in water, similar to concentrations existing in oil spills and other environmental cleanup circumstances.

To create these membranes, researchers covalently attach perfluorinated end-capped polyethylene glycol (PEG) surfactants to fritted glass membranes, the release says. Fritted glass is finely porous glass through which gas or liquid may pass.

In the 2007 report “Self-cleaning and anti-fog surfaces via stimuli-responsive polymer brushes,” Youngblood found that surfaces with PEG layers were stimuli-responsive. External stimuli led to changes in the surfaces’ inherent properties, allowing the surfaces to act as chemical gates.

“It is possible to control the selectivity of a membrane by taking advantage of differences in polymer-solute interactions,” according to the article “Amphiphile grafted membranes for the separation of oil-in-water dispersions,” published in 2009 in the Journal of Colloid and Interface Science.

The study found that oil suspended in water coalesced at the membrane surface with a small contact area on the membrane, compared to water. The water spread out along the membrane surface, filtering through. Only small amounts of oil were found in permeate from the treated membrane filter. Untreated filters, however, were found to allow between 90% and 98% of the oil to pass through, the article says.

Another unique characteristic of the membrane is that those tested were in the microfiltration pore range of 10 to 174 µm, which is larger than would be expected and increases the speed of filtration. Typical organic separation filters are in the nanofiltration pore range, the article says.

Youngblood’s membrane filter relies on chemical selectivity to optimize the amount of water that can pass through and avoid the common problem of pore clogging from particulates, the article says.

The study resulted in the desired goal: Create a filtration system capable of separating oil from water without a marked decrease in permeability. This technology, licensed through the Purdue Research Foundation’s Office of Technology Commercialization, could be used to help with environmental cleanups, water purification, and industrial filtration, the news release says. Youngblood also is working to develop a coating using the technology that could prevent windshields from fogging up or accumulating oily deposits, the release says.  

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