June 2012, Vol. 24, No.6

Research Notes

Increasing the size and efficiency of microbial fuel cells

Microbial fuel cells (MFCs) are larger than ever. A research team at J. Craig Venter Institute (Rockville, Md.) has developed an MFC the size of a home washing machine that uses bacteria to clean municipal wastewater while generating electricity, according to an American Chemical Society (Washington, D.C.) news release.

The 379-L (100-gal) MFC, which is capable of turning 13% of the usable energy in wastewater into electricity, is an improvement over the group’s first MFC device, which held only 76 L (20 gal) of wastewater and recovered only about 2% of the usable energy, the news release says.

The team also swapped-out titanium components for a polyvinyl chloride frame and graphite electrodes to cut costs to $40/L ($150/gal), half the cost of the first MFC, the news release says. The team is working to reduce costs to $5/L ($20/gal) or less to be competitive with existing wastewater treatment technologies.

In these biological fuel cells, microbes emit electrons as they metabolize the organic matter in wastewater. As the electrons flow through a circuit, they produce electricity, the news release says.

These microbes even might be able to break down such pollutants as benzene and toluene, explained Orianna Bretschger, who presented a report on the improved technology at the 243rd National Meeting and Exposition of the American Chemical Society.

The MFC removes about 97% of the organic matter from wastewater. This degree of treatment does not achieve potable water standards — which would require 99.9% removal of organic material and more-complete disinfection, Bretschger explained at the meeting. But MFC might replace other existing steps in municipal wastewater treatment, she said.

The team, which received funding from the California State Public Interest Energy Research Energy Innovations Small Grant Program and the San Diego Foundation’s Blasker Science and Technology Award, reported that commercial versions of the device could be cheaper than conventional wastewater treatment. This could translate into availability of cleaner water in developing countries or more wastewater recycling in regions where water is scarce, the news release says.

Microbial fuel-cell technology keeps going and going …

Pennsylvania State University (Penn State; University Park) researchers continue to develop and improve the microbial reverse-electrodialysis cell (MRC) design.

In December, WE&T reported on the development of the MRC by environmental engineering professor Bruce Logan. The article, “Saltwater may unlock ‘inexhaustible’ source of hydrogen,” describes how the researchers combined microbial fuels and stacks of reverse-electrodialysis (RED) electrolysis cells to create the MRC, which produces hydrogen without adding auxiliary electricity.

The MRC produces enough electricity to hydrolyze water — that is, split it into hydrogen and oxygen. The microbial fuel cells produce electricity using exoelectrogenic bacteria; the RED stacks work by taking advantage of the ionic difference between fresh water and saltwater.

Now, Logan, along with graduate student Roland Cusick and post-doctoral fellow Younggy Kim, have switched salt sources to enable more electricity to be produced at more locations. Instead of saltwater from the sea, the researchers are using an ammonium bicarbonate salt solution, according to a Penn State press release.

Even though the researchers have shown that the MRCs can work with seawater, organic matter in the water fouls membranes without precleaning and treatment. Using seawater also restricts MRC operation to coastal areas, the news release says.

So, the researchers decided to use ammonium bicarbonate solution, which works similarly to seawater in the MRC and does not foul the membranes. The solution also is easily removed from the water at 43°C (110°F), because the ammonia and carbon dioxide that make up the salt in the solution boil out and can be recaptured and recombined with water for reuse, the news release says.

After testing the ammonium bicarbonate MRC, researchers found that the initial production of electricity was greater than that from an MRC using seawater. The tested MRC produced 5.6 W/m2, the news release says.

In addition, the MRCs can be configured to produce electricity from hydrogen without contributing to greenhouse gases, Logan said in the release.

The King Abdullah University of Science and Technology (Thuwal, Saudi Arabia) supported this work.



The submerged membrane electro-bioreactor discussed in the January 2012 article, “Charge it!: A ‘submerged membrane electro-bioreactor’ achieves high removal efficiencies,” is patented under United States Patent No. 8,147,700. The patent was filed Sept. 3, 2009 under application number 12/553,680.



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