A hybrid approach breaks down both bio-based and conventional plastic waste and converts it into useful bioproducts.
The Science: Polylactic acid (PLA) is an environmentally friendly bio-based plastic. PLA is compostable, but because it looks so similar to conventional plastic, it often ends up in recycling facilities. There, it’s mixed together with conventional plastic, challenging the existing recycling process of conventional plastic. To avoid this tricky separation issue, researchers developed a process that breaks down mixed plastic waste in the same vessel. Using microbes, they can then convert this waste into useful bioproducts.
The Impact: A scaled-up version of this process would ensure that both bio-based and conventional plastic could be recycled together. Both consumers and recycling facilities would not need to separate the two. This process also provides a way to turn this plastic waste into new materials. They found that 95% of the plastic mixture could be converted into their corresponding monomers which could be further utilized by microbes to produce bioproducts such as polyhydroxyalkanoate (PHA), a biodegradable plastic substitute. Because this is all done in the same vessel, there is no need for expensive, time-consuming separation steps. The researchers found that once this process is optimized, it could reduce the cost of PHAs by 62%, and reduce their carbon footprint by 29%.
Summary: The researchers developed a hybrid upcycling approach that first utilized ionic liquid to chemically depolymerize the plastic mixture into monomers in water. Because the ionic liquid they tested is biocompatible, they were able to then test biological conversion of the depolymerized plastics without intermediate separation steps. An engineered strain of Pseudomonas putida used the depolymerized plastic mixture as its sole carbon source. Using this one-pot process reduced both the production cost and carbon footprint of PHA. Their research shows that plastic waste could be used as an inexpensive feedstock for biomanufacturing sustainable fuels and products. They also found that this process could be cost competitive and have a low carbon footprint. Further research and optimization would improve the process’s economic viability.
Publication: Dou, C., Choudhary, H., Wang, Z., et al. A hybrid chemical-biological approach can upcycle mixed plastic waste with reduced cost and carbon footprint. One Earth (2023). [DOI: 10.1016/j.oneear.2023.10.015]
Written by Emily Nelson