Favorable reaction: Turning sun-loving bacteria into renewable energy

Far from home
Biyela arrived in the U.S. in 2005, travelling from her native South Africa, where she had been a lecturer in microbiology at the University of Zululand, having received her B.Sc Decree with majors in microbiology, biochemistry and zoology, followed by  B. Sc. (Hons) and master’s degrees in microbiology. She is the recipient of the highly prestigious Fulbright-Amy Biehl Award, which has helped fund her doctoral research at ASU.

“To me, being a Fulbrighter, means being a cultural ambassador for South Africa while in the U.S.,” she says, adding, “It’s not every day that one gets mentioned as a top student in the country!” Biyela dates her fascination with science to childhood, pointing to an early passion for medical research.

Later, as a microbiologist, Biyela began to focus on water quality and public health issues. “One of the coolest things about environmental engineering,” she says  “is that it is so multidisciplinary. Although I have a microbiology background, I’m now able to incorporate engineering principles into my research.”

In addition to attracting Fulbright scholars like Biyela from around the world, in 2009, ASU was the second highest public research university in the nation for winning Fulbright grants, with 18 ASU students studying in 16 different countries.

“One of the things that I love about working for Dr. Rittmann, is the caliber of people that he attracts,” Biyela says, adding, “it’s very gratifying to work on real world problems—issues in science that directly affect people.”

Reserves of fossil fuels—a cornerstone of industrialized society—are being depleted and most atmospheric scientists today agree that their continued use puts our air quality as well as the stability of the earth’s climate, in peril. Finding viable alternatives to burning oil, natural gas and coal is not just desirable, it is essential.

At Arizona State University’s Biodesign Institute, several research teams are exploring solutions to the current energy impasse. Microorganisms known as cyanobacteria—earthly residents for some 3.5 billion years, are being harnessed in innovative ways, with the hope of providing a sizeable portion of tomorrow’s clean energy.

Precious Biyela, a Ph.D. candidate in the Department of Civil and Environmental Engineering at the Ira A. Fulton Schools of Engineering, specializes in the use of  microbial populations to improve water quality in drinking water distribution systems. For a recent class project however, Biyela applied her microbiology and engineering expertise to help refine a device that could be used for harvesting microbial components suitable for alternative fuels like biodiesel, green diesel, green gasoline and green jet fuel.

Biyela works in the laboratory of Dr. Bruce Rittmann—Regents’ Professor and director of Biodesign’s Center for Environmental Biotechnology. As part of Rittmann’s fall graduate seminar, “Advanced Environmental Biotechnology,” Biyela led her colleagues Chou-An Chiu, Fariya Sherif and Youneng Tang, in an investigation of a newly designed photobiorereactor—a sort of incubator for growing large amounts of photosynthetic organisms to produce biodiesel.

Microscopic factories

During the Archaean and Proterozoic eras between 3.8 billion and 544 million years ago, innumerable cyanobacteria first helped to generate the oxygen-rich atmosphere we now depend on for life. Cyanobacteria comprise a range of mostly unicellular microbes that hold great potential not only for increasing our available energy, but also for decreasing environmental pollutants in wastewater. “These microorganisms provide us with a double benefit,” Rittmann explains, “they help us deal with environmental problems and produce energy at the same time.” Such photosynthesizers are the power source at the core of a new type of energy station. In order to prosper and proliferate, cyanobacteria require only sunlight, water and carbon dioxide , (which they absorb from the atmosphere, and sequester).

Photobioreactors that cultivate photosynthetic microbial cells, including algae and cyanobacteria, require light to be supplied to drive cellular energy and growth. Optimizing the amount of light these microbes receive is the tricky part. In open pond settings, sunlight is only able to penetrate the algal or bacterial layer about an inch or so, limiting efficiency and yield.

To date, various enclosed designs have been explored, including plastic sleeves or bags to hold the microorganisms or aquarium-like rectangular tanks. Biomass may be harvested from the reactor at intervals or continuously. In the case of cyanobacteria, such biomass doubles in volume roughly every 24 hours. Photosynthetic bacteria contain a lipid or fatty component, which may be extracted as a pure vegetable oil and further processed into biodiesel or other fuel.

Class action

Rittmann’s graduate course featured detailed sections on microbial ecology, biotechnology and renewable energy sources. Biyela and her team chose as their semester project a newly designed photobioreactor, evaluating its efficiency compared with traditional designs and modifying various features in the course of their study. The design itself was provided by local Phoenix entrepreneur, Stafford “Doc” Williamson, CEO of DaoChi Energy of Arizona, a company devoted to clean energy solutions. Williamson hoped the class’s research data could be used to improve the design and help entice state and private investors.

Jason DiBari, a spokesman for Williamson’s company, describes some of the highlights of the new design. “We’re trying to create a hybrid system, offering all the protection of a lab, which keeps out the invasive species, while retaining the low cost of an exterior system, like an open pond.” DaoChi’s semi-enclosed photobioreactor is able to eliminate evaporation and stabilize the growth environment. “It was interesting to do the patent search and realize that no one had figured this out,” he says, adding that existing systems are energy and labor intensive, requiring sophisticated apparatuses and artificial light.

As Biyela notes, photosynthetic organisms like algae and cyanobacteria share several advantages over higher plants, making them ideally suited for clean energy production. These include very modest space requirements, low generation times, and high productivity. Further, they produce roughly 100 times the energy per unit volume of other forms of biomass, including corn, switchgrass, forest products, or other terrestrial crops, without displacing arable land for food cultivation. Healthy photosynthetic bacteria require only a nutrient medium, carbon dioxide and sunlight to prosper, offering flexibility in terms of cultivation site.

While photosynthetic algae typically produce the highest lipid content under conditions of stress, cyanobacteria yield high lipid content under optimal growth conditions—an advantage when trying to maintain a healthy colony. “Cyanobacteria are prokaryotes, a simpler life form compared with eukaryotic organisms,” Biyela adds, emphasizing that such prokaryotes are easier to manipulate through genetic engineering techniques.

Modeling sessions

Biyela’s team spent the bulk of the semester carrying out detailed modeling of the photobioreactor design, which improves the surface area to volume ratio so that the entire volume of the photobioreactor can act as the effective volume for bacterial cultivation. One of the numerous modifications the team came up with was the idea of adding convex mirrors to the design, maximizing sunlight penetration for the culture.

Photosynthetic active radiation data for Phoenix, Arizona on summer and winter solstices as well as spring and autumn equinoxes were used for the detailed quantitative modeling. Their study concluded that the innovations designed to enhance the surface area to volume ratio significantly improved the performance of the photobioreactor, producing an overall increase of biomass production throughout the year and reducing seasonal variability in biomass production.

The improved photobioreactor design provides a low cost and low-tech solution to the cultivation of energy-producing bacteria, using inexpensive construction materials available at retail outlets like Wal Mart and Ikea. New studies underway by DaoChi will evaluate the potential to scale up the process in order to produce a commercially viable system. Ultimately, photobioreactors could make use of waste streams, allowing the microorganisms to purify contaminated water before the bacterial feedstock is harvested and converted into fuel. The DaoChi Energy team were impressed with the professionalism of the class report and the recommendations for improvement. As DiBari notes, “Biodesign was the lynchpin that allowed us to gain traction for this project.”

Hands-on research, like that carried out at the Biodesign Institute, provides students like Biyela with a competitive edge. Theoretical insights and computer modeling are combined with physical testing and experimentation, providing a dynamic environment for learning. “We share resources and share knowledge—it’s one of the things I love about the environment Dr. Rittmann has created,” Biyela says.  She also stresses the gratification derived from attacking scientific challenges aimed at societal betterment. “In this setting, we are pushed, not only in an academic sense. Investors are also calling on us to produce something of the highest quality.”