Published on July 12th, 2012 | by James Ayre1
Improvements in Microbial Fuel Cells
July 12th, 2012 by James Ayre
Certain types of bacteria may be able help address two of the biggest environmental challenges of today. How do we effectively deal with the vast amounts of organic waste produced? And how can we switch to a less-polluting, renewable energy infrastructure in enough time to halt climate change?
Researchers César Torres and Sudeep Popat from Arizona State University’s Biodesign Institute think they have found a solution. There are specific types of bacteria that are very good at converting organic waste into useful energy.
Using an innovative technology known as a microbial fuel cell or MFC, the bacteria are applied to the conversion process.
Torres says, “the great advantage of the microbial fuel cell is the direct conversion of organic waste into electricity. “
The researchers think that, in the future, MFC’s could be linked to municipal waste streams, or agricultural and animal waste sources. They would provide a sustainable system for the treatment of waste, and at the same time, energy production.
Scaling up the technology will require some improvements in efficiency, though. “My particular focus is to understand at a fundamental level how anode respiring bacteria transfer electrons from their cells onto an electrode,” Popat says, “as well as to design new systems that are both economical and efficient.”
MFC’s are a unique kind of battery — they are part electrochemical cell, and part biological reactor. They usually contain two electrodes that are separated by an ion exchange membrane. Bacteria grow and spread on the anode side, forming a biofilm (a dense cell aggregate) that adheres to the MFC’s anode. The bacteria there then act as catalysts for the conversion of the organic substrate into CO2, protons, and electrons.
In a natural environment, many bacteria “use oxygen as a final electron acceptor to produce water, but in the oxygen-free environment of the MFC, specialized bacteria that send the electrons to an insoluble electron acceptor, namely the MFC’s anode, dominate.”
The bacteria are capable of then oxidizing organic pollutants, like the ones found in waste streams, and then transferring the electrons to the anode. The stolen electrons then move through an electrical circuit, that ends at the MFC’s cathode, creating electricity.
This study is the first comprehensive analysis of cathode limitations in MFC’s, and will help to further develop these systems, through continual refinement of operating conditions and materials.
“The main importance of our study is not to provide immediate answers, but to conduct a mechanistic study to determine how the cathode operates and identify the sources of inefficiency,” Torres explains. “Now we can begin to work on solutions.”