It is clear that extracting petroleum from the environment
and burning it for power is warming the planet on a global level.
This fact and others has driven the search for alternative
sources of energy.
It is clear that extracting petroleum from the environment
and burning it for power is warming the planet on a global level.
This fact and others has driven the search for alternative
sources of energy.
The big names here, in the long term and on a large scale, seem to be wind, solar and hydrogen-based power. A more specialized future source of energy may be from bacteria.
A common theme here is to utilize the electrons generated by bacteria over the course of catabolism (breaking down large molecules into smaller ones) to power an electrical circuit. This constitutes a bacterial fuel cell.
One can envision bacteria that break down toxins in wastewater, and pump the resultant energy produced into an electrical device. A major technical hurdle for achieving optimal fuel cell performance is finding bacteria of superior electrochemical activity.
Paul de Figueiredo, Arum Han, and coworkers at Texan A&M University have pursued research in this direction. They have developed rapid screening technology that has found bacteria which are twice as efficient energy producers as a reference bacteria strain, a step towards improving the prospects of bacterial fuel cells for energy production.
Initial device performance.
The scientists grew biofilms (dense clusters of bacteria) on the gold anode (electron input segment) of their bacterial fuel cell. Close physical contact and tight bacterial packing enhances the probability of efficient utilization of the electrons produced by the bacteria.
Under optimized conditions, they found that their control strain of bacteria, from the Shewanella class of bacteria (one often utilized for investigations of bacterial power generation), generated a little over three times the current density as a blank sample (no bacteria) after 100 minutes. Current density was reduced to roughly twice that of the blank after 15 hours.
Biofilms prepared on different days and separately fabricated fuel cells exhibited similar performance. The results are therefore reproducible and useful as baseline measurements of bacterial performance.
Finding superior bacteria.
The scientists pre-screened approximately 12,000 bacteria (from soil and water) for use in their bacterial fuel cell, with the goal of finding a strain that was more effective than their control strain. This pre-screening involves growing the bacteria under conditions in which discoloration of the growth medium is observed for bacteria that are electrochemically active.
Twenty-six possible candidates were found in this manner. Ten of them were either from the gamma-proteobacteria or Bacillus classes of bacteria.
One bacterial isolate was more successful than the others, and is thought to be from the Shewanella class of bacteria, the same class as the control bacteria. It generated more than twice the current density as the control bacterial strain.
Future utility.
These scientists' bacterial fuel cells can be used in at least ten separate experiments before they degrade, require 380 times less solution volume than typical designs, and the device components can be easily changed for performance optimization experiments. Additionally, numerous variables (such as choice of anode, bacteria, and culture medium) and many experiments (conceivably over a thousand) can be compared simultaneously.
These are all very useful features for rapidly fishing out useful bacteria from a large population. They will also facilitate studies aimed at uncovering the genetic and physiological basis of power generation by the successful bacteria that are found.
Bacterial fuel cells clearly aren't yet a match for other alternative sources of energy, and I suspect they never will be. However, one can realistically envision harvesting them for the energy they do produce over the course of performing other more useful functions, such as wastewater treatment.
for more information:
Hou, H., Li, L., Cho, Y., de Figueiredo, P., & Han, A. (2009). Microfabricated Microbial Fuel Cell Arrays Reveal Electrochemically Active Microbes PLoS ONE, 4 (8) DOI: 10.1371/journal.pone.0006570