Microbial Fuel Cells Generate Electricity from Corn Stover
19 July 2006
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| Design of a microbial fuel cell (MFC). Click to enlarge. |
A team of Penn State researchers is exploring the use of microbial fuel cells (MFC) to convert corn stover directly into electricity following the pre-treatment of the biomass to release the sugars.
Previous work has shown that these fuel cells can generate electricity from glucose and from municipal wastewater and that these cells also can directly generate hydrogen gas.
People are looking at using cellulose to make ethanol. You can make ethanol from exploded corn stover, but once you have the sugars, you can make electricity directly.
—Bruce E. Logan, Penn State
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| MFC hydrogen production from carbohydrates. Click to enlarge. |
Corn stalks and leaves, amassing 250 million tons a year, make up a third of the total solid waste produced in the United States. Currently, 90% of corn stover is left unused in the field. Corn stover is about 70% cellulose or hemicellulose, complex carbohydrates that are locked in chains. Pre-treatment of the waste to release the sugars is the first step in fermentation processes for the production of cellulosic ethanol.
When anaerobic bacteria are placed in the oxygen-free anode chamber of an MFC, they attach to an electrode. Because they do not have oxygen, they must transfer the electrons that they obtain from consumption (oxidation) of their food somewhere else than to oxygen, and so they transfer them to the electrode. The two electrodes are at different potentials (about 0.5 V), creating a bio-battery (if the system is not refilled) or a fuel cell (if refilled).
The microbial fuel cells were inoculated with domestic wastewater and a nutrient medium containing glucose, the researchers report in the journal Energy and Fuels. Once established, the bacteria colonies were fed the sugary organic liquid obtained from steam exploding of corn stover.
The researchers, who include Logan, Yi Zuo, a Penn State graduate student in environmental engineering, and Pin-Ching Maness, a senior scientist with the National Renewable Energy Laboratory, report that “the conversion of organic matter to electricity, on the basis of biological oxygen demand removal, was relatively high with greater than 93% of the biological oxygen demand removed.”
In essence, there is no organic matter left to cause problems when disposing of the remaining liquid because there is nothing left to oxidize. The electrical production is about one watt for every square meter of surface area at about 0.5 volts. A typical light bulb uses 60 watts. To increase wattage, the surface area needs to increase. To increase voltage, fuel cells can be linked in series.
Producing electricity from steam-exploded corn stover adds to the energy diversity of our portfolio. Electricity can be used to pump water uphill for later use, directly run light, heat and equipment or electrolyze water to create hydrogen.
—Bruce Logan
The US Department of Agriculture and the National Science Foundation funded this research.
Resources:
“Electricity Production from Steam-Exploded Corn Stover Biomass”; Yi Zuo, Pin-Ching Maness, and Bruce E. Logan; Energy Fuels, 20 (4), 1716 -1721, 2006. 10.1021/ef060033l S0887-0624(06)00033-8
Bruce Logan: Microbial Fuel Cell Research
Does removing the corn stocks/stover deplete the soil. I mean for the last 50 to 100 years farmers have been tilling under 250 million tons of corn stocks/stover -- What happens when you stop doing that?? It just seems like all that waste material does something to enhance the soil.
Posted by: JJ | 19 July 2006 at 12:09 PM
But what's the energy conversion efficiency (theoretical or actual) and how does it compare to cellulosic ethanol production?
Posted by: JesseJenkins | 19 July 2006 at 12:15 PM
Yes removing all that corn stover, which otherwise is incorporated back into the soil, will have detrimental effects on the productivity of the soil over time. But our recent attitudes in this country are to live for today, and let someone else worry about tomorrow. This stover, or waste, adds humus to the soil, which also tempers the soil and helps it to hold moisture in. Without it, the soil will dry out, and be less inclined to accept fertilizer applications.
This stover also is used in low-till and no-till farming operations to cover and tie the soil surface, to keep the soil in place. In other words, to limit soil erosion problems due to wind, and or rain erosions. Does anyone remember the wind erosions in Oklahoma during the dust bowl era? With the wrong kinds of weather patterns and limited cover on our nations fields, we could see a repeat! Growing our fuel, especially if it totally strips the crop to bare earth, is total nonsense in my mind.
Posted by: Mark A | 19 July 2006 at 01:08 PM
Couldn't find how many kwh/kg of stover. It may be more efficient to just burn the stover in a powerplant boiler.
Posted by: tom deplume | 19 July 2006 at 01:11 PM
well, I believe that most of the cellulose and hemicellulose in stover left on the field is being degraded by the bacteria anyhow and transformed in CO2, water and heat ( did you notice than in the winter if you dig in a stack of stover you see vapors coming out and that the middle of the stack is warm?)...
what is indeed very slowly degraded is the lignin ( more abundantly found in wood) and that contributes mostly to humus formation, but that is not used in the process they discovered. I bet there would result some residues from the "steam-exploded cord stover" and that can be recicled back to the fields.
there is also still poor use of the cow and hog dejections as a fertilizer and use of that can also be both a source of energy ( there is a significant amount of metane that results in the proces that is now wasted in the atmosfere) and of natural fertilizer.
Posted by: marius | 19 July 2006 at 04:54 PM
We looked at this in a Renewable Energy group and found that 50% of the stover can be used and 50% plowed under would still be fine. Right now too much is plowed under which can be harmful over time.
Posted by: sjc | 19 July 2006 at 08:09 PM
Microbial Fuel Cells to get electricity seems like an expensive, round-about way of extracting energy.
Why not just burn it in a boiler, then spread the ash back into the field?
Posted by: Dursun | 21 July 2006 at 01:33 PM
Two Lies a Truth Don't Make.
Ethanol is not a renewable substitute for oil, not even close to be a solution. Ethanol is grown with huge amounts of energy + fertilizers + pesticides all made from ... what else ? oil + natural gas by 'farmers' who don't give a hoot about the land, you, me, themselves or the planet, devastate the watershed, polute air, water, soil, food, poison children, men, women alike with vast amounts of carcinogens and mutagens, are sold slaves of the genetically modified and pesticide corporations, use fertilizer, chemicals, herbicides, pesticides, diesel transportation, diesel tractors, and guess where all that comes from ? oil...yes ?
If in doubt, read the published research papers in peer reviewed scientific journals by Prof. Patzek, UC Berkeley, and Prof. Pimentel, Cornell U. The energy balance of ethanol is at least negative 6:1, ie, pay for six gallons of gas, drive one, could be worse, plus all the above, not the positive 1:1.2 or 1:1.3 without any consequences claimed by the 'industry' peddlers.
Have a great day.
Posted by: no more wars | 22 July 2006 at 05:19 PM
I have seen no proof of a 6 to 1 negative energy balance for ethanol. The general concensus seems to be around a 1.2 to 1 positive energy balance for corn ethanol, a 4 to 1 positive energy balance for sugar cane ethanol and up to an 8 to 1 positive energy balance for cellulose ethanol.
Posted by: sjc | 22 July 2006 at 07:24 PM
No more wars:
Relax, man. Have a good meal, couple of drinks, and start smiling. It will be OK.
Posted by: Andrey | 23 July 2006 at 03:41 AM
Marius:
You're right the material is being bio-degraded into organic humus, nitrates, etc by aerobic bacteria... however anaerobic bacteria deeper under the earth may be using a different process & have different by products, that is why 'sjc' may be right .. too much may increase undesirable amounts of other compounds. For spreading the ash, too high phospates isn't too healthy for good humus either ?
But these "microbe fuel cells" are certainly a refreshing twist I can imagine some sci-fi movie taking *that* further ahaha ;-)
Posted by: Fishlipps | 08 August 2006 at 10:57 AM
We need some really good soil science study on the effects of using corn stover, and not returning it. We cannot go on preformed opinions and prejudices. My hunch is that there is a good solution available. Something that would allow us to use a good portion of the corn stover for energy, while adding material from other sources.
Would welcome more ideas on this.
Ron Wagner
Central Illinois corn country.
Posted by: Ronald Wagner | 27 June 2007 at 12:06 PM