Microbes Turn Hazardous Waste Into Valuable Products

The Science

To make fuels and other products from plants, manufacturers must treat the plant fibers to break apart sugars and other parts of the plant cell wall. The leftover liquid from the process (called liquor) has hazardous compounds. Companies must process the liquor to remove the hazardous components before they can safely throw it away. Researchers have explored reusing spent liquor or extracting the organic compounds for use as fuels or industrial chemicals. In this study, researchers examined spent liquor from a pretreatment process that used ammonia dissolved in water. In this liquor, they identified phenolic compounds, a group of ring-shaped aromatic molecules. These compounds can be made into valuable chemicals. The team evaluated how different metals used in the pretreatment process affected how phenolic compounds formed. Finally, the scientists tested using microbes to convert the phenolics into chemicals for plastics, adhesives, and medicines.

The Impact

Bioenergy crops include grasses, fast-growing trees, and crop residues. They are a potential source of home-grown fuels and industrial chemicals that can be grown on land not suitable for food crops. To make these biofuels cost effective, biorefineries must extract value from all parts of the plant. Being able to make high-value chemicals from a waste product can make producing biofuels more economically viable.

Summary

Researchers used multiple techniques (chromatographic fractionation, nuclear magnetic resonance, and liquid-chromatography mass spectrometry) to characterize the phenolic content of spent liquors. These liquors were from aqueous ammonia pretreatment of poplar wood using five metal additives. The scientists evaluated the potential to use an engineered strain of the bacterium Novosphingobium aromaticivorans to convert the phenolics into 2-pyrone-4,6-dicarboxylic acid (PDC). PDC is a building block of nylon and other plastics..

The main phenolics identified were phenol, p-hydroxybenzamide (pHBAm), and p-hydroxybenzoic acid (pHBA). pHBAm and pHBA were produced from the ester-linked p-hydroxybenzoates in poplar wood. Phenol was produced from pHBA via decarboxylation. Compared to the control, metal additives reduced the phenolic recovery and phenol yield. Biotransformation of pHBAm to PDC was shown to be possible in the presence of pHBA. However, it was not possible when pHBAm was the sole phenolic substrate. The phenol present was not transformed to PDC and didn't inhibit PDC production. This is the first report on making PDC from phenolic amide using N. aromaticivorans.

Contact

Steven KarlenGreat Lakes Bioenergy Research [email protected]

Funding

This material is based upon work supported by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, Biological and Environmental Research Program.

Publications

Zhou, S., et al., Biotransformation of phenolics in spent liquor from aqueous ammonia pretreatment. ChemSusChem, n/a, 2500881. [DOI:10.1002/cssc.202500881]