Electrochemical process separates valuable industrial chemicals from animal waste

A collaboration between chemical engineers and animal scientists has created a system for recovering valuable industrial chemicals from animal waste, representing a major step towards circularity and environmental sustainability.

Researchers at the University of Illinois Urbana-Champaign have developed a nanofiltration system for separating volatile fatty acids (VFAs) – organic molecules that are critical in fine chemical production across many sectors – from cattle manure fermented in bioreactors. Thanks to the incorporation of selective ion-exchange membranes into an electrochemical separation system, the system is 80% more energy efficient than previous standard electrochemical processes.

“It’s incredible that we’re able to obtain industrial chemicals like VFAs from something like manure,” said Xiao Su, a professor of chemical and biomolecular engineering at Illinois. “Through our work, we believe that we are closer to circularity, where the waste is reprocessed into valuable resources, making chemical production more efficient and sustainable as a whole.”

The research was led by Wangsuk Oh, a postdoctoral research associate in Su’s research group. It was published in the journal Advanced Functional Materials, and the article was featured on the inside front cover of the February 5, 2025, issue.

VFAs – such as acetate, butyrate and propionate – are chemical building blocks used in a wide range of products, including cosmetics, food additives, pharmaceuticals and plastics. Their production often involves carbon-intensive processing of petrochemical feedstocks, but a more energy-efficient alternative has recently emerged: microbial anaerobic digestion, in which microorganisms break down biowaste. The main barrier to its widespread implementation is the lack of an efficient method for extracting VFAs from the chemically complex broths that result.

The Illinois researchers turned to redox-mediated electrodialysis, an electrochemical separation technique that has been extensively investigated by Su’s research group. Like standard electrodialysis, it uses an electrical field to capture charged chemical species. However, redox-mediated electrodialysis uses “redox” molecules – capable of altering their electrical structures on demand – to decrease energy consumption. When combined with selective membranes, it can differentiate among VFAs based on chemical structure.

“Electrodialysis is a very common separation technique used mostly in water desalination,” Su said. “The problem is that ion-exchange membranes normally used in electrodialysis are not designed to distinguish between valuable VFAs used in chemical production. Through our work, we have designed new membranes with specific properties that can identify and discriminate between particular chemical species such as VFAs of different sizes.”

To demonstrate the technique, Su’s chemical and biomolecular engineering research group collaborated with animal sciences professor Roderick Ian Mackie. The team fermented a broth of cattle manure and then used a redox-mediated electrodialysis nanofiltration system to recover lower-weight VFAs from the longer-chain VFAs and other chemicals in the mixture.

“This is an innovative approach to utilizing waste material from concentrated animal production facilities, which contribute to environmental pollution, and converting it into valuable industrial chemicals,” Mackie said.

Since the separation method uses electrical means to separate molecules instead of chemical means, it is significantly more efficient and generates far less chemical waste than conventional separation processes. Moreover, Su believes that this technology can readily be adapted to industrial settings.

“The next phase of this work is figuring out how to implement our technology in a full process,” he said. “That involves carrying out more detailed materials design and development to make the membranes even more selective than they already are. If we can do that, then we can decrease the overall cost and energy expenditure for the process even further.”

Nayeong Kim and Hyewon Kim also contributed to this work.

The researchers’ article, “Controlling Bicontinuous Polyelectrolyte Complexation for Membrane Selectivity: Redox-Mediated Electrochemical Separation of Volatile Fatty Acids,” is available online. DOI: 10.1002/adfm.202410511

Support was provided by the Energy & Biosciences Institute through the EBI-Shell program.

Roderick Ian Mackie is a professor of microbiology in the Department of Animal Sciences in the College of Agricultural, Consumer and Environmental Sciences (ACES) at Illinois. He also holds an appointment in the Department of Nutritional Sciences in ACES at Illinois. He is a member of the Carle R. Woese Institute for Genomic Biology at Illinois.

Xiao Su is an associate professor of chemical and biomolecular engineering in the Department of Chemical and Biomolecular Engineering in the College of Liberal Arts & Sciences (LAS). Su is also affiliated with civil and environmental engineering in The Grainger College of Engineering, chemistry in LAS and the Beckman Institute for Advanced Science and Technology at Illinois.