SCOTLAND – 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, which is commonly used for bottles and containers, into adipic acid.

This process is said to reduce reliance on fossil resources. The study opens new opportunities for the packaging industry. Adipic acid is a crucial component in the production of various packaging materials and products.

By employing this microbial upcycling technique, manufacturers can decrease their reliance 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, enabling them to convert PET waste into Adipic acid.

Immobilizing the bacteria in alginate hydrogels increases 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.

The microbial upcycling process achieved a conversion rate of 79%, resulting in the production of 115 mg/L of adipic acid within a 24-hour period. This achievement not only demonstrates the viability of microbial biotechnology but also showcases a sustainable alternative to traditional methods that rely on petrochemicals.

“Adipic acid is an aliphatic 1,6-dicarboxylic acid and a versatile platform chemical that is widely utilized in 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 explain.

“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. Specifically, 1 kg of N2O is equivalent to 298 kg of CO2. As a result, the bioproduction of adipic acid from renewable feedstocks has been an active area of research.”

The researchers express their enthusiasm for the potential applications of their work in the packaging industry. They are currently exploring process intensification, scale-up, and the synthesis of other industrial chemicals using similar methods.

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

“Developing new sustainable bio-based methods to convert waste carbon into industrial small molecules is an elegant approach to establishing a circular chemicals economy,” write the researchers.

“Through a series of chemical and genetic optimizations, this study reports the first successful bioproduction of adipic acid, a versatile platform chemical. The adipic acid was produced directly from terephthalic acid, which was generated in situ from industrial PET waste and a post-consumer plastic bottle.”

“Future work from our lab will include process intensification, with a focus 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 chemically significant targets in the industry.”