03 Nov 2023 — A team of researchers from the UK has successfully demonstrated a novel method for converting plastic waste into valuable industrial chemicals. The scientists employed microbial upcycling, a process that harnesses the power of microorganisms to transform waste plastics into valuable chemicals. They used the approach to upcycle PET plastic, commonly used for bottles and containers, into adipic acid. 

This process is said to reduce the reliance on fossil resources. The study opens new doors for the packaging industry. Adipic acid is a crucial component in producing various packaging materials and products. By utilizing this microbial upcycling method, manufacturers can reduce their dependence on raw petrochemicals and contribute to a more sustainable, circular economy.

The researchers genetically engineered Escherichia coli (E. coli) bacteria to perform the conversion. They optimized the expression of specific genes and enzyme activity within the microorganisms, allowing them to transform PET waste into adipic acid.

Immobilizing the bacteria in alginate hydrogels increased the efficiency of the process, making it more stable and effective. Additionally, the researchers integrated hydrogen gas generated by other engineered E. coli bacteria with a biocompatible palladium catalyst to synthesize adipic acid from metabolic cis,cis-muconic acid.

Their study is published in ACS Central Science. 

Bio-upcycling of PET plastic waste into the prolific platform petrochemical and nylon precursor adipic acid in the bacterium E. coli (Image credit: ACS Cent. Sci. 2023).A “bioproduction first” 
The microbial upcycling process achieved a 79% conversion rate, with 115 mg/L of adipic acid produced in 24 hours. This achievement not only demonstrates the viability of microbial biotechnology but also showcases a sustainable alternative to the traditional methods that rely on petrochemicals.

“Adipic acid is an aliphatic 1,6-dicarboxylic acid and prolific platform chemical that is used throughout the materials, pharmaceuticals, fragrances and cosmetics industries. It is currently manufactured on a 2.6 M ton per year scale from petrochemically derived benzene via the nitric acid-catalyzed oxidation of cyclohexanol and cyclohexanone,” the scientists detail.

“The process is highly energy intensive and releases a mol/mol equivalent of nitrous oxide into the atmosphere. These emissions have been shown to significantly contribute to global greenhouse gas levels; 1 kg of N2O equates to 298 kg CO2 equivalents. As a result, the bioproduction of adipic acid from renewable feedstocks has been an active area of research.”

The researchers say they are excited about the potential applications of their work in the packaging industry and are now looking into process intensification, scale-up and the synthesis of other industrial chemicals through similar methods.

The research publication brings optimism that a more environmentally sustainable future for packaging and other industries is within reach, due to the ingenuity of microbial biotechnology.

“Developing new sustainable bio-based methods to valorize waste carbon into industrial small molecules is an elegant approach to creating a circular chemicals economy. Through a series of chemical and genetic optimizations, this study reports the first bioproduction of the prolific platform chemical adipic acid directly from terephthalic acid generated in situ from industrial PET waste and a post-consumer plastic bottle,” write the researchers.

“Future work from our lab will include process intensification focused on cofactor recycling and parameters such as terephthalate import, BcER engineering, scale-up and extension of this pathway to encompass the microbial synthesis of other chemical targets of industrial significance.”

Edited by Radhika Sikaria

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