Hybrid Biological and Chemical Process for Upcycling Mixed Plastics

A streamlined one-pot process

A process diagram for a chemical-biological approach for upcycling mixed plastic waste.

A hybrid chemical and biological approach for upcycling mixed plastics waste. The one-pot process uses an amino-acid-based salt catalyst to breakdown mixtures of petroleum-based and bio-based plastics into monomers. The monomers are then fermented by bacteria into polyhydroxyalkanoate polymers, a new class of biodegradable plastic substitutes which can be used to produce new bioproducts.
[This article was published in One Earth, Vol 6(11), C. Dou et al., "A Hybrid Chemical-Biological Approach Can Upcycle Mixed Plastic Waste with Reduced Cost and Carbon Footprint," pp. 1576-90, Copyright Elsevier (2023).]

The Science

Bio-based plastics such as polylactic acid (PLA) were invented to help solve the plastic waste crisis, but they often end up making waste management more challenging. Because these materials look and feel so similar to conventional, petroleum-based plastics, many products end up not in composters, where they break down as designed, but instead get added to the recycling stream by well-intentioned consumers. There, the products get shredded and melted down with the recyclable plastics, bringing down the quality of the mixture and making it harder to manufacture functional products out of recycled plastic resin. The only solution, currently, is to try to separate the different plastics at recycling facilities. Yet even with the most high-end, automated sorting tools, some bio-based plastics end up contaminating the sorted streams.

Scientists at Lawrence Berkeley National Laboratory and the Joint BioEnergy Institute (JBEI) collaborated with X—the moonshot incubator led by Alphabet, Google’s parent company—to develop a process that skips the problematic separation step and also produces an environmentally friendly final product.

The team has invented a “one-pot” process to break down mixtures of petroleum-based and bio-based plastics using naturally derived salt solutions paired with specialized microbes. In a single vat, the salts act as a catalyst to break the materials down from polymers to monomers. Microbes then ferment the monomers into a new type of biodegradable polymer that can be used to produce commodity products.

In addition to streamlining recycling, the approach could enable bio-based manufacturing of other valuable products using the same bacteria that ferment the plastic monomers. The team envisions potential applications ranging from biofuels to even medicines produced from the approximately 8.3 billion tons of plastic waste currently in landfills. And with more genetic engineering tools, microbes might be able to grow on multiple types of plastics simultaneously.

Other future avenues of investigation include experimenting with other organic salt catalysts—to find one that is both highly effective at breaking polymers down and can be reused in multiple batches to lower costs—and modeling how the process would work at large-scale real-world recycling facilities. 

The Impact

The biology-driven mixed plastic upcycling process requires no specialized equipment and yields molecules of a biodegradable plastic alternative that can be converted into new commodity products. Initial tests indicate that the process could be successfully applied to real-world mixed plastic streams.

Although the chemical recycling process is currently only proven for polyethylene terephthalate (PET) plastics contaminated with biodegradable PLA, it could be used with the diverse plastic streams encountered in real recycling facilities. Most commercial products are composed of mixed plastics. For example, a fleece jacket is made with PET-based polyesters alongside polyolefins or polyamides. The polyester component can be converted into bioplastics that are soluble in water while the insoluble polyolefins or polyamides can be easily filtered out sent for traditional mechanical recycling.

The team also demonstrated that once optimized with a reusable salt solution, the process could reduce the cost and carbon footprint of polyhydroxyalkanoates (PHAs) by 62% and 29%, respectively, compared with current commercial PHA production.


The research team demonstrated the potential of their one-pot approach in laboratory bench-scale experiments with mixtures of PET—the most common petroleum-based plastic, used in things like water bottles and spun into polyester fibers—and PLA, the most common bio-based plastic.

They used an amino-acid-based salt catalyst previously developed by colleagues at JBEI and a strain of Pseudomonas putida engineered by scientists at Oak Ridge National Laboratory. This combination successfully broke down 95% of the PET/PLA mixture and converted the molecules into a type of PHA polymer. PHAs are a new class of biodegradable plastic substitutes designed to efficiently break down in a variety of natural environments, unlike petroleum-based plastics.

Principal Investigator

Hemant Choudhary
Joint BioEnergy Institute
[email protected]

Related Links

BER Program Manager

Shing Kwok

U.S. Department of Energy, Biological and Environmental Research (SC-33)
Biological Systems Science Division
[email protected]


Funding support comes from X The Moonshot Factory; the Advanced Biofuels and Bioproducts Process Demonstration Unit at Lawrence Berkeley National Laboratory; the Bioenergy Technologies Office within the DOE Office of Energy Efficiency and Renewable Energy; the Joint BioEnergy Institute supported by the DOE Office of Science, Biological and Environmental Research program under contract DE-AC02-05CH11231; and Sandia National Laboratories under contract DE-NA0003525.


Dou, C., et al. 2023. “A Hybrid Chemical-Biological Approach Can Upcycle Mixed Plastic Waste with Reduced Cost and Carbon Footprint,” One Earth 6(11), 1576-90. DOI:10.1016/j.oneear.2023.10.015.