Science News
from research organizations

Waste to watts: Improving microbial fuel cells

July 10, 2012
Arizona State University
Some of the planet's tiniest inhabitants may help address two of society's biggest environmental challenges: How to deal with the vast quantities of organic waste produced and where to find clean, renewable energy. Anode respiring bacteria generate useful energy in a device known as a microbial fuel cell.

Credit: Image courtesy of Arizona State University

Some of the planet's tiniest inhabitants may help address two of society's biggest environmental challenges: how to deal with the vast quantities of organic waste produced and where to find clean, renewable energy.

According to César Torres and Sudeep Popat, researchers at Arizona State University's Biodesign Institute, certain kinds of bacteria are adept at converting waste into useful energy. These microorganisms are presently being applied to the task, through an innovative technology known as a microbial fuel cell or MFC.

As Torres explains, "the great advantage of the microbial fuel cell is the direct conversion of organic waste into electricity. " In the future, MFC's may be linked to municipal waste streams or sources of agricultural and animal waste, providing a sustainable system for waste treatment and energy production.

To scale up the technology however, improvements in efficiency will be required. "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."

The group was able to demonstrate that significant loss in MFC efficiency was due to reactions occurring at the fuel cell's cathode. By modifying materials used in the cathode, as well as adjusting pH levels, they were able to improve cathode performance.

The group's research results appeared recently in the journal ChemSusChem in a special issue devoted to MFC technology.

Torres and Popat work in Biodesign's Swette Center for Environmental Biotechnology, directed by ASU Regents' professor Bruce Rittmann -- a co-author of the current study. Environmental biotechnology is a rapidly developing discipline in which disparate fields including microbiology, bioinformatics, chemistry, genomics, materials science, and engineering join together to harness biological entities -- including bacteria -- for the purpose of helping society.


An MFC is a unique kind of battery -- part electrochemical cell, part biological reactor. Typically, it contains two electrodes, separated by an ion exchange membrane. On the anode side, bacteria grow and proliferate, forming a dense cell aggregate known as a biofilm that adheres to the MFC's anode. In the course of their microbial metabolism, the bacteria act as catalysts for converting the organic substrate into CO2, protons, and electrons.


The anode-respiring bacteria are able to oxidize organic pollutants, such as those found in waste streams, and transfer the electrons to the anode. The scavenged electrons then flow through an electrical circuit, terminating at the MFC's cathode, thus generating electricity. Ions are transported through the fuel cell's ion membrane, to maintain electroneutrality, although the membrane is often excluded.


"We found that the cathodes were limiting the power densities we can produce in these MFCs," Popat says. "This is very surprising because, in chemical fuel cells, the same catalyst allows much greater power densities."

A key to the disparity lies in the fact that MFC's, unlike chemical fuel cells, must operate at neutral pH in the anode chamber to ensure optimum growth and activity of the microorganisms catalyzing the reactions. At the cathode, OH- ions cause a local increase in pH, due to a limiting rate of their transport. Further, every unit of pH increase at the cathode results in a loss of 59 millivolts of energy -- the authors found that the local cathode pH could easily reach >12, representing a substantial loss.



The study represents the first comprehensive analysis of cathode limitations in MFC's and will further the development of these systems through refinement of materials and operating conditions. "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."

Story Source:


Journal Reference:

  1. Sudeep C. Popat, Dongwon Ki, Bruce E. Rittmann, César I. Torres. Importance of OH− Transport from Cathodes in Microbial Fuel Cells. ChemSusChem, 2012; 5 (6): 1071 DOI: 10.1002/cssc.201100777

Cite This Page:

Arizona State University. "Waste to watts: Improving microbial fuel cells." ScienceDaily. ScienceDaily, 10 July 2012. <>.
Arizona State University. (2012, July 10). Waste to watts: Improving microbial fuel cells. ScienceDaily. Retrieved July 30, 2015 from
Arizona State University. "Waste to watts: Improving microbial fuel cells." ScienceDaily. (accessed July 30, 2015).

Share This Page: