Researchers at Ithaca, N.Y.-based Cornell University are developing a method to make biorefineries more profitable through a modified form of anaerobic digestion that will produce carboxylates instead of methane. Carboxylates are a precursor to the alkanes found in fuels, and can be processed to produce drop-in biofuels, such as renewable gasoline and diesel.

According to Lars Angenent, an associate professor of biological and environmental engineering, work to develop the carboxylate platform has been ongoing for approximately three years. Angenent and his team recently published results of a project that studied the microbial communities of several anaerobic digester systems. “These [microbial communities] are what we call an undefined mixed culture,” he said. “There are thousands of species that work together in a food web” to ultimately produce methane. “We were interested in learning what types of microbes were in those systems, what they were doing, how they work together, and how the system can be improved,” he explained.

To complete the study, Angenent and his team collected samples of microbial communities from nine anaerobic digester systems owned and operated by Anheuser-Busch InBev. Samples were collected from each system once a month over a period of 12 months, resulting in 112 samples. According to Angenent, there have been important technological advances in gene sequencing in recent years. These advances allowed the Cornell team to generate 400,000 sequences of a particular gene from the microbes to characterize them. “It’s kind of like a fingerprint of the community,” Angenent said.

“We found about 5,000 different species of microbes in these reactors,” he continued. “They were all working together to treat waste and eventually make methane.” Through a great deal of statistical analysis, the team was able to determine that each of the nine anaerobic digestion systems has its own unique community structure, which didn’t change much over time.

In addition to the gene sequencing data and community samples gathered by Angenent and his team, the researchers were also given access to a wide range of data collected by Anheuser-Busch InBev. “These breweries are very professional,” Angenent said. “They take data off those reactors all the time. They almost have an army of operators that run these systems and measure whatever there is to be measured, so there is a lot of data.” This includes data related to pH and temperature. Ultimately, the research team was able to access approximately 20,000 data points gathered by Anheuser-Busch InBev related to environmental and functional data. Then, with all this data, the team was able to link function and community structure.

The primary goal of Angenent and his team is to use the undefined mixed cultures found in these anaerobic digestion systems to produce carboxylates rather than methane. Once fully developed, the technology would allow biorefineries to convert their waste products into high-value drop-in biofuels. While Angenent said that methane production can make sense for some companies that use the resulting methane onsite to produce heat and power, for most other entities, methane production is not economically feasible. The ability to produce biobased liquid fuels from waste, however, could provide biorefineries with an important source of additional revenue.

According to Angenent, his team is working to manipulate the undefined microbial communities found in anaerobic digesters by adjusting the pH of the environment. A pH at 5.5 has been shown to mitigate methane production by the communities.

Initial funding for the project was provided through a USDA grant. The team is now in the process of applying for additional funding to move the research to the next phase. While there are several types of carboxylates, Angenent and his team are focused on producing C6 and C8 carboxylates. If the project continues to be successful, Angenent estimates pilot-scale evaluations could begin in three or four years.