Bio-based succinic acid has been explored as a renewable building-block for a host of chemicals and polymers, but its production process remains costly due largely to the complicated purification process that generates a large waste stream. Now, researchers at the University of Illinois Urbana-Champaign (www.illinois.edu) led by bioengineer Huimin Zhao have piloted a process for streamlining the purification process and eliminating the waste stream generated in the current process. The approach could reduce the cost of producing bio-succinic acid significantly, placing it at a cost that is competitive with conventional chemical synthesis of succinic acid.
Previous attempts to make bio-based succinic acid have been expensive because the production organisms carrying out the fermentation cannot tolerate low-pH environments. “In existing bio-succinic acid production processes, the organisms can’t survive the acidic conditions generated as the succinic acid is produced, so researchers have to add a base to keep the pH neutral,” explains Zhao, “The addition of base generates a calcium sulfate (gypsum) side product that complicates the downstream purification and leaves the process with a large waste stream to address.”
Zhao’s team started with a naturally occurring strain of yeast that is tolerant of low pH, and then genetically engineered its metabolic pathways so that it produces more than ten times the levels of succinic acid compared to the original yeast. “With acid-tolerating yeast in the fermentation process, you no longer have to add base, so you eliminate several purification steps and eliminate the need to handle calcium sulfate solutions,” Zhao says (diagram).
After a years-long process to develop genetic engineering tools for use in this organism, Zhao’s group was able to coax the yeast into producing succinic acid from a range of sugars, including glucose, sucrose and xylose, at concentrations of more than 100 g/L. After laboratory studies, the team recently piloted the process in 100-L and 300-L fermentation bioreactors.
“This bio-succinic acid production process was also the subject of a technoeconomic assessment that we conducted, which showed the process is economically competitive with chemically synthesized succinic acid,” Zhao says. The researchers are now looking for commercial partners to license the technology.
“This project is an important development for the industry because the methods could apply to other chemicals used in everyday products, and it further highlights how bioindustrial manufacturing can unlock a new future where everyday plastics, chemicals, materials, clothing and more are safely manufactured in the U.S. using biology,” said Melanie Tomczak, head of programs and chief technology officer at BioMADE (Twin Cities, Minn.; www.biomade.org), an organization supporting bio-industrial manufacturing innovation. BioMADE provided funding for the project.