Chemo-biological upcycling system for converting polystyrene waste into biodegradable γ-polyglutamic acid biopolymers

Background

Polystyrene (PS) is a ubiquitous plastic used extensively in packaging, food service items, and consumer products due to its low cost and versatile properties. However, its widespread use has led to significant environmental concerns, as PS is highly resistant to natural degradation and accumulates in landfills and ecosystems. The persistence of PS waste, coupled with the global increase in plastic consumption, has intensified the need for innovative solutions that can mitigate plastic pollution while recovering value from discarded materials. Addressing the environmental impact of PS is particularly urgent, as traditional waste management strategies are often inadequate for this durable polymer, leading to long-term ecological harm and resource inefficiency.

Current approaches to managing polystyrene waste, such as mechanical recycling, pyrolysis, and chemical dissolution, face substantial limitations. Mechanical recycling is hindered by contamination, degradation of polymer quality, and limited market demand for recycled PS. Pyrolysis and other chemical methods are typically energy-intensive, require high temperatures, and often yield low-value products or fuels rather than useful materials. Additionally, these methods may generate hazardous byproducts and are not always economically viable at scale. Enzymatic or purely biological degradation of PS has shown limited success due to the polymer’s recalcitrance and the slow rates of microbial breakdown. As a result, there is a critical need for sustainable, scalable, and economically attractive technologies that can efficiently convert PS waste into valuable, biodegradable products, thereby supporting circular economy goals and reducing environmental burdens.

Technology

This technology provides a sustainable solution for upcycling polystyrene (PS) waste into γ-polyglutamic acid (γ-PGA), a valuable biodegradable biopolymer, by integrating chemical and biological processes. The method begins with the photooxidative degradation of PS: waste polystyrene is dissolved in acetone and exposed to visible light in the presence of a ferric chloride (FeCl3) photocatalyst and molecular oxygen. This process cleaves the PS polymer backbone, converting it primarily into benzoic acid. After removing acetone to prevent toxicity, the resulting degradation mixture is introduced to an engineered strain of Corynebacterium glutamicum. This microorganism, modified with the capABC gene cluster from Bacillus licheniformis, metabolizes benzoic acid via the β-ketoadipate pathway and synthesizes γ-PGA, which is then purified using standard bioprocessing techniques. The system is compatible with post-consumer PS products and leverages standard laboratory and industrial equipment.

What differentiates this technology is its seamless integration of chemical depolymerization and microbial bioconversion, enabling the direct transformation of persistent plastic waste into a high-value, biodegradable product. Unlike traditional PS recycling methods—which are often energy-intensive, inefficient, or yield low-value outputs—this approach produces γ-PGA, a polymer with significant applications in food, cosmetics, pharmaceuticals, and water treatment. The process is robust, requiring minimal purification of intermediates and tolerating most byproducts, and it avoids reliance on sugar-based fermentation substrates, reducing competition with food resources. By utilizing engineered microbes specifically tailored for efficient γ-PGA production and optimizing the photooxidative step for high benzoic acid yields, the technology offers a scalable, economically viable pathway for circular plastic waste management, supporting both environmental sustainability and industrial adoption.

Benefits

• Converts non-biodegradable polystyrene waste into biodegradable γ-polyglutamic acid (γ-PGA), reducing plastic pollution.
• Integrates photooxidative degradation with microbial bioconversion for efficient upcycling of post-consumer polystyrene products.
• Uses engineered Corynebacterium glutamicum to metabolize benzoic acid derived from polystyrene into valuable biopolymer.
• Operates with standard bioprocessing equipment and is compatible with industrial-scale applications.
• Avoids reliance on sugar-based fermentation substrates, supporting sustainable and circular bioeconomy principles.
• Produces γ-PGA, a biopolymer with diverse applications in food, cosmetics, pharmaceuticals, and water treatment.
• Requires minimal purification of degradation mixtures, enhancing process simplicity and cost-effectiveness.
• Demonstrates robustness to byproducts and toxicity, ensuring reliable microbial growth and product yield.

Applications

• Polystyrene packaging waste recycling
• Biodegradable food packaging production
• Cosmetic ingredient manufacturing
• Pharmaceutical excipient synthesis
• Water treatment biopolymer supply

Additional info

This chemo-biological method upcycles polystyrene via integrated photooxidative degradation and microbial bioconversion. Visible light and a ferric chloride catalyst first oxidatively cleave the polymer into benzoic acid. An engineered *Corynebacterium glutamicum* strain, expressing the *capABC* gene cluster, then metabolizes this intermediate through the β-ketoadipate pathway. This process successfully synthesizes and secretes γ-polyglutamic acid, a high-value biodegradable biopolymer, providing a sustainable alternative to traditional plastic recycling.