Bad wine makes for good energy

Scientists in the United States and India are using microbes to turn the sugar and vinegar resulting from improper fermentation into electricity and hydrogen.

The technology could provide a new and cost effective way to clean wastewater from wineries and get some value out of a bad bottle of wine.

"There is nothing special about the bacteria," says Bruce Logan, a scientist at Penn State University who recently installed a microbial electrolysis cell at a winery in Napa Valley, California. "We just give them a good environment to grow in."

A good home and plenty of food, that is. It takes a lot of water to grow, harvest, process and ferment the sugar in grapes into the alcohol Americans love to consume by the bottle.

All that wastewater, loaded with unfermented sugar, improperly fermented vinegar, biomass and other contaminants, has to be cleaned, and cleaning wastewater is expensive.

According to Logan's estimates, about 1.5% of all the electricity in the US goes into wastewater treatment. Up to 5% of all the country's electricity goes into our nation's water management systems.

The winery in the study doesn't have specific statistics on how much they pay to treat their wastewater, but it is expensive.

To offset the cost of treatment, its owners installed a 1000-litre, refrigerator-sized microbial electrolysis cell to help treat some of the wastewater. Until this point, Logan's microbial fuel and electrolysis cells have been smaller than a teakettle.

Splitting off hydrogen

Two steps are required to treat the water flowing into the unit. First, one group of bacteria turns unused sugar and unwanted vinegar from improper fermentation into electricity. It's a small amount, but not enough to reach the 1.2 volts necessary to split water; therefore, a little extra electricity from the normal power grid is needed.

Another group of bacteria uses that electricity to split water molecules into oxygen and hydrogen, which escape into the atmosphere.

At least, that's the idea. "We are producing more methane than we wanted," says Logan, who is trying to correct the problem.

The scientists could collect the hydrogen for a fuel cell or burn the methane for heat, says Logan, but for now they let it escape into the atmosphere.

The microbial electrolysis cell only treats 0.1% of all the winery's wastewater, most of which flows into a traditional treatment lagoon.

The project isn't meant to save the winery a significant amount of money, just to prove the technology is feasible. Logan estimates it will take three to five years before a commercially viable microbial electrolysis cell is available.

While Logan uses a microbial electrolysis cell to split water, a group of scientists from India recently developed a microbial fuel cell that uses wine to produce energy.

"Sugars like glucose, alcohols and effluents containing sugars or alcohols can be used (to produce electricity)," says Professor Sheela Berchmans of the Central Electrochemical Research Institute in India, who recently co-authored a paper in the journal Environmental Science and Technology.