For many people “greenhouse gas” or “carbon sequestration” conjure images of belching smokestacks and spewing tailpipes -- and some vague notion of technology to capture the sooty emissions.

Kim Ogden

Verdant ponds are not in the picture.

But the ability of simple algae to remove carbon from the atmosphere and produce cleaner energy and food took center stage in a presentation on February 29 by Kimberly Ogden. The University of Arizona professor of chemical and environmental engineering spoke to a packed Centennial Hall audience as part of the 2016 UA Science Lecture Series.

In “Carbon Sequestration: Can We Afford It?” Ogden gave an upbeat and easy-to-understand overview of various technologies for sequestering, or capturing, atmospheric carbon dioxide -- the major greenhouse gas contributing to global warming. She noted the scientific and economic challenges in reducing atmospheric carbon and the strides engineers are making on numerous fronts.

“There is no silver bullet for carbon sequestration,” Ogden said, advocating instead for a “suite of solutions” to address climate change for different industries and regions.

Ogden described carbon sequestration techniques at electricity plants, which contribute approximately 30 percent of the human-caused atmospheric carbon dioxide. These methods include scrubber systems that separate carbon from water vapor before flue gas escapes from smokestacks.

Several power companies are evaluating the feasibility of sequestering carbon dioxide in this way and storing the captured, concentrated gas by pumping it 6,000 feet underground into porous rock. The geology of the storage site is key, because the porous rock has to have layers of nonporous or shale-like rock above the storage area to prevent the gas from returning to the atmosphere. This technology for carbon capture and storage has been safely used for decades for enhanced oil recovery, she said.

On the transportation side, with automobiles, diesel engines and airplanes contributing nearly another third of the carbon dioxide that is emitted into the skies, engineers are evaluating devices such as automobile tailpipe filters that capture and store carbon dioxide before it gets released into the air.

All of these technologies are promising but expensive, Ogden stressed.

For example, utilities could pass on the cost of sequestration to customers, which according to some estimates could increase bills by as much as 30 percent, she said.

“Power Plants” on a Different Scale

Ogden summarized the benefits and costs of renewable energy sources like solar, solar thermal, wind, hydro, nuclear and photovoltaics. But she devoted most of the talk to the potential of microalgae, single-celled, nonplant organisms ubiquitous in freshwater and marine environments, for reducing atmospheric carbon dioxide and producing fuels that are cleaner than fossil fuels, particularly coal, oil and natural gas.

She was the engineering lead for a multimillion-dollar, multi-university research project -- funded by the U.S. Department of Energy’s National Alliance for Advanced Biofuels and Bioproducts and several companies -- to develop microalgae as a practical, affordable source of clean energy. Currently she is the principal investigator for a Regional Algal Feedstock Testbed project. Her research team grow and conduct experiments on microalgae in ponds and aboveground photoreactors at a UA agricultural experiment station located near campus.

Because photosynthesis and solar-powered pumps drive the system, operating costs are next to nil, she said.

Together with the UA’s professor of agricultural and biosystems engineering Murat Kacira, Fei Jia, a doctoral student in biosystems engineering, and research associate professor of chemical engineering Greg Ogden, she has developed sensor technology that continuously monitors the algae’s capture of carbon dioxide and -- for the first time -- continuously monitors algal growth. That’s bigger than it might sound.

“We still know relatively little about the genetics, biology and biochemistry of microalgae,” she said. “By collecting this data, and comparing it with data from similar algal farms in Texas, New Mexico and the Pacific Northwest run by other participating universities, we are getting a much better understanding of algae -- and developing it as a technology for carbon sequestration.”

The collaborators are in the process of patenting the sensor technology with the help of Tech Launch Arizona, the office of the UA that commercializes inventions stemming from University research.

Biofuels from algae became a hot research area when U.S. gas prices skyrocketed in the late 1970s. Interest in the subject has fluctuated over the years, she said, but interest and innovation have picked up in recent years.

If algal biofuel were available at gas stations, customers would not be rushing to fill their tanks -- yet.

“The good news and the bad news is that when we started our project in 2009-2010, researchers were calculating the cost of algal fuel at about $250 a gallon,” Ogden said. “Through better harvesting and reactor designs, and better understanding of algae biology, engineers and scientists have been able to drive down the cost from $250 a gallon to $7 to $10 a gallon. That’s still a problem; last week you could buy a gallon of gas near the Tucson airport for a buck twenty-one.”

“But think about it: That’s an order of magnitude less expensive than when we started. This really shows how large teams working together are cutting the costs of technology and making the array of solutions to climate change more possible.”

Ogden’s lecture can be viewed on Arizona Public Media’s website.