Enzymatic recycling of bioplastics

The misuse of plastics has resulted in a global plastic pollution crisis that is threatening innumerable ecosystems. Bioplastics were developed in an effort to move away from fossil-based plastics and the industry has continued to grow in market share over the last decade. However, many bioplastics do not degrade as quickly as was envisioned, thus persisting in the environment long enough to cause harm. Furthermore, life cycle analysis on several bioplastics have indicated that better waste management strategies are required for the long-term sustainable use of bioplastics. Due to improper disposal practices, bioplastic materials end up in traditional plastic recycling streams, disrupting the recycling process and decreasing the value of recycled materials.

Certain microbial enzymes have been found to hydrolyse polyesters, including bioplastics, and have the added advantage of requiring moderate process parameters and delivering valuable monomers at the end of the hydrolysis reaction. This would allow for cradle-to-cradle recycling of bioplastics that could function as a stand-alone facility or to limit waste in polymer production and bioplastic manufacturing facilities. Using microbial enzymes for the hydrolysis of bioplastics can also be a versatile tool in organic waste management facilities, for the selective removal of bioplastics from recycling streams and/or as a product to enable home-composting of bioplastics.

We have genetically engineered microbial hosts to overproduce bioplastic hydrolysing enzymes. Recombinant microbes such as these could potentially produce a cocktail of enzymes from cheap plant biomass, thus making the process more economical. The enzyme solution is then collected and used in a hydrolysis reaction under optimised conditions to deliver monomers from various bioplastic materials. The produced monomers can be purified from the hydrolysis solution and used to repolymerise neat bioplastics or can be sold as fine chemicals.

·Polymer Industry

• Polymer production companies

 Waste management

• Organic waste treatment facilities
• Recycling companies

Home composting

This technology allows for the hydrolysis and recycling of bioplastic materials that are often discarded with municipal solid waste and pose a problem for plastic recyclers. This technology can derive value from bioplastic waste through clean, less-harmful methods using mild temperatures and buffer solutions together with an enzyme preparation. This has several advantages over chemical and other biological processing procedures, including the complete conversion to monomers within reasonable timeframes that would allow a circular recycling system for bioplastics.

Patent pending

• Mr. MW Myburgh
  • Co-tutelage PhD candidate, Dept. Microbiology, Stellenbosch University, South Africa, Dept. DAFNAE, University of Padova, Italy

• Prof. M Viljoen-Bloom
  • Associate professor, Dept. Microbiology, Stellenbosch University

• Prof. WH Van Zyl
  • Distinguished Professor, Dept. Microbiology, Stellenbosch University

Utilising recombinant Saccharomyces cerevisiae strains for the enzymatic hydrolysis of polylactic acid materials. Bioplastics were developed to answer the current threat on the environment. This method has advantages over the existing methods by reducing waste from bioprocessing of plastics. 

Funding is required for further optimisation and scale-up experiments.

Yes