Hybrid process produces biofuels and chemicals

Eric Debner

In the near future, Iowa farmers may have access to a reliable source of additional revenue growing in their fields. Fibrous, woody biomass, such as leftover corn stover from harvest and waterway switchgrass, can be sold and converted into biofuels and chemicals.

A research team led by Laura Jarboe, an ISU assistant professor of chemical and biological engineering, is currently developing an economically viable hybrid process which will produce biofuels and chemicals from fibrous biomass.

“We call it hybrid [because] we’re using the thermochemical approach to make substrates from biomass and then the biochemical approach (microbes) to make those fuels and chemicals,” Jarboe said. “Our overall goal is to be able to make fuels and chemicals from biomass in a manner that is economically competitive with petroleum-based processes.”

Biomass is biological material from living or recently living organisms containing rich amounts of carbon and energy from the sun, said Robert Brown, director of ISU-based Bioeconomy Institute and Anson Marston distinguished professor of engineering.

Researchers look for a substrate which can be fed to the microorganism. A substrate is basically food obtained from biomass, which can be fed to microbes to produce biofuels and chemicals.

Brown said this hybrid process uses both a thermal step, which applies heat to a biomass feedstock called pyrolysis, and a biological process, which applies microbial fermentation using bacteria and microalgae to produce biofuels and chemicals.

Jarboe said the hybrid process research team is working toward developing economically efficient methods for extracting the bacteria’s dinner from fibrous biomass. Unfortunately, these microbes are picky eaters.

“Fibrous biomass is built up of sugar molecules that are chained together,” Brown said. “Our goal is to break those [fibrous biomass] into molecules that microorganisms can use.”

Corn stover and switchgrass cannot simply be dumped into a fermentation tank with the hope that the bacteria will consume it; in order to drive the production of fuels and chemicals, the the chosen material must be in a form readily accessible to the microorganisms.

The research team is searching for different methods to efficiently process the biomass into a simpler form, such as glucose.

“We want to take biomass, such as sugarcane bagasse, corn stover or leftover wood, and convert it into a form which the microbes can eat,” Jarboe said.

Using the hybrid processing to produce biofuels and chemicals is more economically viable than the enzyme-based process, Jarboe said.

Both the enzymes and the large tank required for the process are expensive, but there is a trade-off: cost for cleanliness. Pyrolytic sugars contain contaminant compounds which prove detrimental to the health of the bacteria. These cheap sugars are “dirty” and cost more money to clean into substrates, which no longer harm the microbes.

“It’s like having poison in your food,” Jarboe said. “We are trying to make [Escherichia coli] less sensitive to the contaminants in the [pyrolytic sugars]. Right now, we can’t do that because the contaminant compounds in those pyrolytic sugars [would kill the bacteria].”

Zhanyou Chi, a postdoc research associate for Iowa State’s Center for Sustainable Environmental Technologies, said there are many different treatment approaches, which researchers use to remove the contaminants from the sugar.

“There’s a separation process to remove the toxins from the sugar,” Chi said. “We’re looking at four different approaches right now.”

The evolution of these microbes in and of itself is not the end product, Jarboe said; the real output is finding which mutations occurred during the evolution process.

“This is still an immature technology,” Jarboe said. “That’s why we need to do this research on how to modify the ‘bugs’ so they can eat those [pyrolytic] sugars.”