Stover powering

researchers are using microbes to make electricity directly from corn stover, the dried stalks and leaves left after the harvest, skipping the intermediate stage of manufacturing ethanol.

The process, developed by Bruce E. Logan, a professor of environmental engineering at Penn State, uses a microbial fuel cell to convert organic material into electricity. Previous work has shown that these fuel cells can generate electricity from glucose and from municipal wastewater and that these cells also generate hydrogen gas.

Corn stover is about 70 percent cellulose or hemicellulose; complex carbohydrates that are locked in chains. A steam explosion process releases the organic sugars and other compounds in the corn waste and these compounds can be fed to microbial fuel cells.

The microbial fuel cells contain two electrodes and anaerobic bacteria that consume the sugars and other organic material and release electrons. These electrons travel to the anode and flow in a wire to the cathode, producing electrical current. The water in the fuel cell donates positive hydrogen atoms that combine with the electrons and oxygen to form water.

The microbial fuel cells were inoculated with domestic wastewater and a nutrient medium containing glucose. Once established, the bacteria colonies were fed the sugary organic liquid obtained from steam exploding of corn stover.

The researchers found that the conversion of organic matter to electricity gave a relatively high 93 per cent rate of biological oxygen demand removal. This means there is little organic matter left to cause problems when disposing of the remaining liquid because there is nothing left to oxidise. The process converts all the available energy to electricity.

The electrical production from the cells is about 1W for every square metre of surface area at about 0.5V. A typical light bulb uses 60W. To increase wattage, the surface area needs to be increased. To increase voltage, fuel cells can be linked in series.