algae emissions reduction concept shows new promise

Well-informed readers of EL&P may recall that past studies by the U.S. Department of Energy and other organizations demonstrated that numerous species of algae can reduce carbon dioxide and nitrogen oxides from combustion emissions. However, despite excellent technical findings, past system designs were characterized by high costs which limited their economic viability.

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changing technology

Algae are single-cell plants which photosynthesize, or use sunlight to convert carbon into plant matter. Algae live nearly everywhere on earth: in polar seas, in geyser pools, and in stagnant and salt water. In nature, algae scavenge carbon dioxide from air and dissolved gases in the water in which they live.

In the GreenFuel Technologies beta system at the Massachusetts Institute of Technology (MIT), a slipstream from the MIT Cogeneration Plant is passed directly from a sampling port on the stack into a bank of triangle-shaped bioreactors containing algae in a salt water growth medium. Each bioreactor is self-contained; the gas enters at the bottom two vertices, and makes a single pass though the tubular bioreactor before exiting at the top vertex. The bioreactor dimensions-approximately 8 feet tall by 6 feet long by several inches wide-are determined by the amount of time required for the gas to dissolve in the growth medium as it rises through the vertical and hypotenuse legs. (The triangle design is patented by GreenFuel.)

Since August, the GreenFuel team has been growing algae on the Cogen gases, and harvesting algae ‘crops’ daily. Algae reduce NOx day and night, regardless of weather or lighting conditions. The process is essentially an effect of the surface configuration of the algae cell walls. Even dead algae can provide significant NOx reduction, up to 70 percent. The harvested algae can be used to generate renewable biofuel products, meaning an algae-based emissions reduction system could theoretically enable a power plant to meet emerging state regulations for both CO2 reduction and renewable power generation.

MIT director of utilities Peter Cooper is host to the beta test and responsible for the MIT Cogen plant, which provides 20MW electricity, heat, and chilled water to the MIT campus. Cooper and the plant staff were initially reluctant to bring an algae-based system to their plant-like many plants, they aim to eradicate algae from their cooling system-but they acknowledge that the technology has performed as promised.

Cooper said, “The system is even more effective than we expected. This new technology, which provides a significant reduction of carbon dioxide and NOx, is an important and very promising step toward addressing the difficult problem of global warming. We are proud to play a supporting role by hosting the first beta test here at Cogen.”

Independent testing firm CK Environmental, Inc. conducted a week-long evaluation of the GreenFuel beta system emission reduction performance. CK Environmental’s test report certifies that over the seven-day test period, the GreenFuel beta system simultaneously removed 85.9 percent NOx (±2.1 percent, regardless of weather or light conditions), and 82.3 percent CO2 (±12.5 percent) on sunny days, or 50.1 percent CO2 (±6.5 percent) on cloudy or rainy days. The testing methods conformed to EPA standards for measuring NOx and CO2 emissions. CK Environmental vice president Mike Cahill oversaw the project.

“This is one of the most promising and unique technologies to reach this stage of field demonstration in a very long time,” he said. “I have never seen anything like it in my career so far.”

GreenFuel project scientist Dr. Xiaoxi Wu also said the system’s early performance results have exceeded his initial expectations. “Previous systems using algae to mitigate both NOx and CO2 from flue gas emissions reported 5 percent CO2 and 70 percent NOx reductions. Our beta system has already surpassed those benchmarks, and we anticipate further performance gains from our ongoing optimization efforts.”

GreenFuel president Dr. Isaac Berzin admits, however, that the GreenFuel system isn’t a perfect fit for every plant. For one, the system requires unobstructed sunlight, which translates to surface area-in the case of even moderate size plants, the system would cover acres. But he says that a company survey indicates that about 70 percent of currently operating generating facilities have adequate land area available on their existing grounds. That’s not a bad start, given that there are no other technologies that offer inexpensive carbon dioxide mitigation at the source. Even though no one technology can offer the right answer for everyone, he acknowledges, “it’s always better to have more options.”

Boston-area locals and visitors who would like to get a more close-up view of the GreenFuel system can visit the Museum of Science, Boston, where two GreenFuel bioreactors are featured in an exhibit in the main hall. Those outside the Boston area can learn more at the company’s website, www.greenfuelonline.com.



The material in this press release comes from the originating research organization. Content may be edited for style and length. Want more? Sign up for our daily email.