Researchers have devised a method to dismantle the blend of traditional and bio-based plastics typically arriving at recycling centers.
A graphic showcasing the scientists' streamlined one-pot process. Image Credit: Bianca Susara/Berkeley Lab
Bio-based plastics like polylactic acid (PLA) were created to address the plastic waste issue. However, they often complicate waste management. These materials closely resemble conventional petroleum-based plastics in appearance and texture. Consequently, well-intentioned consumers frequently place them in recycling streams instead of composters, where they decompose as intended.
When added to recyclable plastics, these products are shredded and melted together, reducing the mixture's quality and complicating the production of functional items from recycled plastic resin. Currently, the only recourse is attempting to segregate the different plastics at recycling facilities. Despite utilizing advanced automated sorting tools, some bio-based plastics still infiltrate the segregated streams.
Currently, the sole option is to try segregating these diverse plastics at recycling centers. Nevertheless, despite employing advanced automated sorting systems, certain bio-based plastics persist in contaminating the segregated streams.
Researchers from Lawrence Berkeley National Laboratory (Berkeley Lab) and the Joint BioEnergy Institute (JBEI) are partnering with X—the moonshot incubator under Alphabet, Google's parent company. Their aim is not just to bypass the challenging separation process but also to enhance the final product's environmental impact.
The team has developed a straightforward "one-pot" technique that disintegrates blends of petroleum-based and bio-based plastics by using naturally sourced salt solutions combined with specific microbes.
Within a single container, these salts serve as catalysts, breaking down the materials from polymers—large structures comprising linked repeating molecules—into individual molecules known as monomers.
Subsequently, the microbes ferment these monomers to produce a novel form of biodegradable polymer, ready to be fashioned into new commodity products. This process is detailed in One Earth.
It’s sort of ironic because the purpose of using bio-based plastics is to be more sustainable, but it’s causing problems. Our project is trying to get around the separation issue and make it so you don’t have to worry about whether you mix your recycling bin. You can put all the plastic in one bucket.
Chang Dou, Study First Author and Senior Scientific Engineering Associate, Advanced Biofuels and Bioproducts Process Development Unit, Lawrence Berkeley National Laboratory
Dou was recently named as one of the American Institute of Chemical Engineer’s 35 Under 35.
Beyond simplifying recycling, the team's methodology could facilitate the bio-based production of various valuable goods using the bacteria currently metabolizing plastic monomers. Envision a scenario where biofuels or even pharmaceuticals are created from plastic waste—an abundance of approximately 8.3 billion tons lying in landfills.
There is an open discussion on whether we can use waste plastics as a carbon source for biomanufacturing. It is a very advanced idea. But we proved that using waste plastics, we can feed microbes. With more genetic engineering tools, microbes might be able to grow on multiple types of plastics at the same time. We foresee the potential to continue this study where we can replace the sugars, traditional carbon sources for microbes, with the processed hard-to-recycle mixed plastics that can be converted to valuable products through fermentation.
Zilong Wang, Postdoctoral Researcher, Joint BioEnergy Institute
The next phase for the Berkeley Lab scientists involves experimenting with various organic salt catalysts to discover one that effectively disintegrates polymers while being reusable across multiple batches to reduce expenses. Additionally, they are modeling the process's functionality at the larger scales seen in real-world recycling facilities.
Their recent paper showcased the viability of their approach through laboratory bench-scale experiments involving mixtures of polyethylene terephthalate (PET)—the prevalent petroleum-based plastic utilized in items such as water bottles and spun into polyester fibers—and PLA, the predominant bio-based plastic.
Their approach involved utilizing an amino acid-based salt catalyst, initially developed by collaborators at JBEI, alongside a strain of Pseudomonas putida that had been engineered by scientists at Oak Ridge National Laboratory. This combined strategy effectively disintegrated 95% of the PET/PLA mixture, transforming the molecules into a form of polyhydroxyalkanoate (PHA) polymer.
PHAs represent a novel category of biodegradable plastic alternatives engineered to efficiently decompose across various natural environments, differing from conventional petroleum-based plastics.
Hemant Choudhary, a member of the team, highlighted that while their chemical recycling process is presently validated solely for PET plastics contaminated with biodegradable PLA, it would offer advantages for the diverse array of plastic streams typically encountered in real recycling facilities.
“It can be completely integrated with existing plastic sources,” noted Choudhary, a Sandia National Laboratories staff scientist working at JBEI. As he explained, the majority of commercial products are not comprised of solely one type of plastic but rather a mix of several different kinds. For instance, a fleece jacket is crafted using PET-based polyesters in conjunction with polyolefins or polyamides.
“We can throw it in our one-pot process and easily process the polyester component from that mixture and convert it into a bioplastic. These monomers are soluble in water, but the leftover parts, the polyolefins or polyamides, are not.” Choudhary mentioned that the residual components can be readily eliminated through straightforward filtration. Subsequently, these components can be directed toward a conventional mechanical recycling process wherein the material is shredded and melted.
“Chemical recycling has been a hot topic, but it’s difficult to make it happen at the commercial scale because all the separation steps are so expensive. But by using a biocompatible catalyst in water, the microbes can directly convert the depolymerized plastics without extra separation steps. These results are very exciting, although we acknowledge that a number of improvements are still needed to realize the economic viability of the developed process,” stated Ning Sun, a Staff Scientist at the ABPDU, Lead Author, and Principal Investigator of this project.
Co-authors Nawa R. Baral and Corinne Scown, proficient in technoeconomic analysis at JBEI and Berkeley Lab's Biosciences Area, showcased that once fine-tuned with a reusable salt solution, the procedure had the potential to slash the cost of PHAs by 62% and curtail the carbon footprint by 29%. These figures were in comparison to the current commercial production methods of PHAs.
JBEI is a Department of Energy (DOE) Bioenergy Research Center managed by Berkeley Lab. The ABPDU is a collaboration facility supported by the DOE BioEnergy Technologies Office.
Journal Reference
Dou, C., et al. (2023). A hybrid chemical-biological approach can upcycle mixed plastic waste with reduced cost and carbon footprint. One Earth. doi.org/10.1016/j.oneear.2023.10.015.