Wastewater generated by animal farms poses a significant environmental risk, as it can pollute soil and groundwater and can be hazardous to human health. However, animal farm wastewater also contains carbon and many other nutrients. What if we could extract the carbon and nutrients and then release treated water back into the environment?
That’s the future envisioned by Prathap Parameswaran, an associate professor at Kansas State University who researches how to use environmental biotechnology platforms for biological wastewater treatment and sustainable resource recovery.
“I envision a world where we can recover everything possible from wastewater or waste organics, from rural or urban communities,” Parameswaran said.
In 2019, he put together a team that would focus on making it more efficient to extract organic acids and other compounds from fermented wastewater. He reached out to Advanced Biofuels and Bioproducts Process Development Unit (ABPDU) staff scientist Ning Sun, whose research focuses on upgrading carbon from various waste streams into chemicals and fuels.
“I was very interested in her expertise in separations and extractions, as well as the valorization of waste carbon to useful products,” Parameswaran said. “I think ABPDU has done a terrific job in demonstrating that.”
The team, which also includes researchers at the University of Pittsburgh and the University of Kansas, received funding from the U.S. Department of Energy’s Advanced Manufacturing Office focused on decarbonizing water infrastructure.
The project utilized an anaerobic membrane bioreactor platform, a technology that is poised to be used in wastewater treatment in which anaerobic bacteria convert organic materials found in wastewater into new products. Specifically, the team focused on converting wastewater to biogas and organic acids, with efficient separation of organic acids from the wastewater being the focus of ABPDU’s contribution.
Sun, along with ABPDU postdoctoral researcher Ramkrishna Singh, focused on developing a process for separating and recovering volatile fatty acids (VFAs) from treated wastewater. VFAs are useful compounds widely used as raw materials in several industries, and as precursors to biofuels and bioplastics. They’re typically derived from petroleum, so producing them from wastewater is a more sustainable option.
ABPDU researchers were able to demonstrate a process that uses ion-exchange resins to adsorb VFAs. Their process successfully extracted over 70% of the VFAs present in the dilute fermentation broth. Plus, they were able to reuse the resins for 9 successive cycles without losing the VFA recovery efficiency.
The researchers then focused on a process that could extract VFAs from the dilute fermentation broth, using ionic liquids as an extraction solvent. Ionic liquids are powerful solvents/catalysts that are a greener alternative to traditional organic solvents, and they are able to achieve higher extraction efficiencies. Using ionic liquids also would allow for the VFAs to subsequently be converted into esters — organic compounds that are used in many industrial processes.
After testing several options, the researchers demonstrated high extraction efficiency through a specific hydrophobic ionic liquid. They also optimized the in-situ enzymatic esterification of VFAs in this ionic liquid, achieving up to 83% conversion.
“This is an integrated process for the extraction and esterification of VFAs using a single hydrophobic ionic liquid,” Sun said. “This project allows the team to explore both fundamental research, such as the molecular interaction between VFAs and solvents, and practical applications, i.e. science of scale-up.”
The teams are currently working on techno-economic and life-cycle analyses that will determine which of the processes they have researched are most efficient.
These results lay the groundwork for future collaborations on this topic with the ABPDU, said Parameswaran.
“I really admire the ABPDU’s facilities, equipment, and expertise,” he said. “It is really amazing that we can not only develop a novel lab-scale technology at ABPDU but also demonstrate and optimize its scale-up for real world applications.”
Parameswaran remains optimistic about the continued work on this project, which he hopes will bring us closer to the future for wastewater recovery that he envisions.
“The idea is that you get wastewater, you recover everything possible from it, primarily with anaerobic biotechnologies, and you’re still able to produce water for high quality reuse or discharge,” Parameswaran said. “We have demonstrated several aspects of this process. Now we just need to put it all together and continue to look at the economics and efficiency aspects. We have some promising results, but in order for it to be scaled up, we still need to work on improving fermentation and all subsequent extraction steps, which will continue beyond this project.”