DESCRIPTION

Project Description

The growing severity of plastic pollution and food waste has created an urgent need for efficient and sustainable resource recycling technologies. The generation of municipal solid waste continues to increase; for instance, in major cities worldwide, the total municipal waste reached approximately 201 million tons in 2016 and is projected to rise to around 340 million tons by 2050 (THE WORLD BANK). Among these wastes, plastics and starchy food residues constitute a substantial fraction, highlighting opportunities for resource recovery and reutilization.

Poly(ethylene terephthalate) (PET) is one of the most widely produced synthetic plastics, commonly used in beverage bottles, food packaging, and everyday consumer products. Global PET production is expected to reach 28.73 million tons in 2025 and 35.13 million tons by 2030. Nevertheless, PET recycling rates remain low—only about 20% in many developing countries—with the majority of PET waste being landfilled, incinerated, or released into the environment. Current recycling strategies mainly involve mechanical recycling (shredding followed by remelting) and thermal reprocessing. However, these approaches often lead to material degradation, limiting the generation of high-value products and preventing the establishment of a truly closed-loop system for PET resource recovery. To improve recycling efficiency, chemical and biological strategies have been explored: alkaline or acid hydrolysis can depolymerize PET into its monomers, but these methods typically require high temperatures and pressures, involve harsh reaction conditions, and consume considerable energy; catalytic pyrolysis can degrade PET within a short time frame, yet catalyst costs are high and controlling by-products remains challenging; enzymatic hydrolysis, for instance using PETase or TurboPETase, allows selective depolymerization under mild conditions with high catalytic efficiency, though industrial-scale applications are still constrained by enzyme stability and production costs.

Food waste is equally concerning. Approximately one-third of all edible food (around 1.3 billion tons per year) is lost or wasted across production, transportation, processing, and consumption stages, with starchy foods accounting for roughly 23%. Several valorization strategies have been proposed for these residues. Anaerobic fermentation can convert food waste into biogas, such as methane, and allows utilization of low-value residues; however, the process is time-consuming, product diversity is limited, and specialized digestate management facilities are required. Enzymatic hydrolysis can depolymerize starch and cellulose into fermentable sugars or functional oligosaccharides, offering high selectivity and environmental compatibility, but enzyme costs are significant and substrates often require pretreatment. Microbial fermentation can further transform waste into high-value chemicals, such as organic acids, sugar alcohols, or functional sugars, thereby enhancing economic value; yet, it typically necessitates metabolic pathway optimization and precise control of cultivation conditions, making the process complex. While each approach offers distinct advantages, achieving efficient, full-process utilization remains elusive. Therefore, there is an urgent need for new strategies that integrate waste biocatalysis into circular economy modes worldwide.

These observations not only reveal the scale of pollution and waste but also highlight the potential for waste-to-resource conversion. In recent years, advances in biocatalysis and enzyme engineering have enabled a range of functional enzymes to find applications in environmental remediation and functional material synthesis. For example, lipases have been employed for polyester degradation, xylanases and cellulases for lignocellulosic biomass conversion, and amylases and cyclodextrin glycosyltransferase (CGTase) for starch transformation into cyclodextrins and related functional oligosaccharides, providing a solid technical foundation for high-value utilization of waste streams. TurboPETase has emerged as the most efficient PET-degrading enzyme, catalyzing PET hydrolysis into terephthalic acid (TPA) under mild conditions with significantly enhanced thermal stability and catalytic performance compared to earlier PETase variants, making it a preferred tool for plastic biodegradation and sustainable recycling research. Meanwhile, CGTase converts starch into cyclodextrins, including α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), and γ-cyclodextrin (γ-CD), with β-CD as the predominant product. Owing to its exceptional host–guest complexation properties, β-CD has broad applications in food, pharmaceuticals, and functional materials, and its industrial-scale production provides a robust platform for valorizing starchy kitchen waste.

Based on these considerations, we propose the project “Enzymatic Upcycling of PET Waste and Starchy Food Waste”.

Proposed Approach

PETase/TurboPETase: Depolymerization of PET plastic → Terephthalic acid (TPA) → Conversion to PPA.

CGTase: Hydrolysis of starchy kitchen waste → Production of β-cyclodextrin (β-CD).

Self-Assembly: PPA and β-CD interact via host–guest complexation → Formation of PPA–CD supramolecular phosphorescent materials.

Project Highlights

Why SynBio: By leveraging enzymes as core tools, our project demonstrates how synthetic biology can address global challenges of pollution and resource waste.

Engineering Design: Through iterative “Design–Build–Test–Learn” cycles, we developed novel strategies for PETase and CGTase application, optimizing their catalytic performance and reaction conditions to ensure pathway efficiency and scalability of results.

Human Practices: Our investigations reveal strong societal demand for green recycling and high-value sustainable materials, motivating us to align project design with the UN Sustainable Development Goals (SDGs).

Global Impact: Beyond this project, our approach provides a transferrable framework for integrating biocatalysis into circular economy models worldwide.