News & Events  arrow

Carbon recycling

 May 30, 2008


Carbon recycling

 May 30, 2008

Ohio University researchers have developed a patented ECO2Capture technology which enables industrial operations and power plants to recycle carbon emissions directly from flue gas by growing algae in a bioreactor. The algae, a valuable feedstock, can be harvested and used in pharmaceuticals, as a food additive, and as biofuel. This unique solution to the carbon problem is a result of the interdisciplinary research collaborations created through the Consortium for Energy, Economics, and the Environment (CE3).

Dr. David Bayless and Dr. Ben Stuart of the Ohio Coal Research Center began work on the bioreactor in order to reduce carbon emissions from coal fired power plants and industry. Instead of sequestering carbon as waste, they decided to recycle it and worked with phycologist Dr. Morgan Vis on using cyanobacteria, a photosynthetic algae. Stuart explained that carbon recycling is encouraging nature to take care of the carbon problem. Then engineering helps to "manipulate the laws of nature to
reach a desired outcome."

The bioreactor uses an updated version of an existing pollution-control technology—electrostatic
precipitation—which uses charged metal plates to collect particles from a gas stream. The metal plates are costly, take up a great amount of space, and are difficult to keep clean in order to maintain their effectiveness. Bayless solved these problems when he substituted the plates with a piece of fabric (wet membrane) that is kept wet by a steady flow of water from a stainless steel tube fixed
above it. Bayless and Vis took the concept further when they added algae to the wet membrane, thereby using photosynthesis to recycle carbon molecules released in the flue gas by burning coal. The algae-soaked membranes receive light from solar-powered fiber optics panels, allowing nature to take its course during daylight hours. At night, the algae could be fed carbon compounds (sugar) in
order to continue the carbon recycling process and generate valuable by-products.

Due to the extreme temperatures of flue gas produced by the burning of coal, the algae grown on the membrane are a special type that withstands temperatures up to 140 degrees Fahrenheit. The algae—cyanobacteria—were originally found in the steam vents at Yellowstone National Park. Not only can this type withstand high temperatures, it also grows in highly acidic environments and clings to surfaces, making it perfect for cultivation from the exhaust of power plants in the bioreactor.

The only problem remaining with the technology was what to do with all the algae produced by the process. The solution, to look at using the algae for biofuel, was sparked by a term paper written by one of Stuart's students. Stuart, also head of the Biofuels Research Lab, found that up to 20,000 gallons of oil could be extracted from one acre of algae each year—a dramatically higher figure than
conventional oil-seed crops such as soy, corn and palm.

The current pilot-scale bioreactor measures 6'x6'x10' with 15 m2 of membrane surface area. It is
estimated that this system could produce up to 3 pounds of dried algae per week using their current cyanobacteria strain and can recycle over 300 pounds of carbon dioxide each year. Although the technology is good on a small scale, the process still needs work to make it commercially viable, Stuart said.

The goal is to increase the size of bioreactors to that of a Wal-Mart store, which would produce as much as 2000 kilograms of dried algae a day, depending on the algae strain used. However, the cost of building bioreactors is quite expensive - a bioreactor the size of a Wal-Mart store would cost roughly $20 million. Stuart and Bayless are exploring options for reducing the cost by using greenhouses rather than closed boxes. Mirrors would be used to direct light to growing algae instead of the fiber optic panels currently in use. The value of the harvested algae can also make the system more financially viable. In addition to biofuels production, the harvested algae could be used commercially in a number of ways, including in pharmaceuticals, nutraceuticals, plastics production, and as a food additive.

One of the goals in making the process commercially viable is to achieve public acceptance of new energy sources. "We need people not only to think about new forms of energy," Stuart said, "but also to be willing to use them."

As part of the Russ College of Engineering and Technology, the Institute for Sustainable Energy and the Environment (ISEE), which includes the Ohio Coal Research Center and Biofuels Research Lab, works to provide innovative solutions to maintain the nation's fuel diversity and the production of
environmentally safe and reliable electric power. Part of this effort includes the creation of technologies that allow current power plants to conform to new carbon emissions standards, such as with the ECO2Capture bioreactor technology.

For more information related to this story, please visit the Ohio Coal Research Center website.