# Microbial and Enzymatic Biodegradation of Plastic Waste for a Circular Economy
## 1 Introduction
Increasingly, researchers are exploring the possibility of biotechnological approaches to plastic degradation involving the use of microbes or enzyme preparations. Considerable research has focused on the biodegradation of synthetic plastics [28; 29; 30]. Ideally, biodegradable plastics are those which can be completely decomposed from complex polymeric structures into simpler chemicals and biomass when exposed to natural environmental conditions and microbial enzymatic action [22; 23] (see Table 2). Concurrently, newly synthesised biodegradable plastics are an active research area. However, it is important to note that not all bioplastics are inherently biodegradable under typical en  
Figure 2: A schematic overview of the different approaches to plastic waste management, including conventional and sustainable approaches. vironmental conditions; many require specific conditions such as industrial composting to facilitate effective degradation [31]. It is also worth noting that many biodegradable plastics can persist for long periods in landfills due to a lack of bioplastic-degrading organisms. Although plastic biodegradation is considered a green, safe, and low-energy input process, it is worth noting that these benefits have primarily been proven on laboratory scales [32; 33]. The scalability and effectiveness of this process on an industrial scale has not yet been fully demonstrated. The concept of a circular economy is based on reducing waste, reusing materials, and recycling products to create a closed-loop system that minimises environmental impact. In this context, biodegradable plastics are crucial as they can be easily degraded and integrated back into the environment compared with synthetic plastics [34]. However, significant research is required to fully achieve a closed loop of minimised plastic use, coupled with re- or up-cycling, as positive steps towards a circular economy. Key biological strategies to achieve this goal are synthesising biodegradable bioplastics, bio-driven degradation and recycling of plastics, and upcycling of plastics for waste into valuable products. In the next section, the focus is on the methods of bio-driven degradation of plastics and bio-based plastic valorisation as a waste-to-resource approach, contributing to the goal of a sustainable circular economy. By enhancing waste management practices, improving the microbial and enzymatic degradation, and developing new biodegradable plastics, plastic pollution can be reduced and its reuse promoted, thereby supporting the principles of a circular economy. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Types** & **Structure** & **Biodegradation** & **Biodegradation** & **Uses** & **References** \\  & & **in Soil** & **in Aqueous** & **Environment** & & \\ \hline Poly butylene succinate (PBS) & & 85\% after & 150 days & 2\% after 117 days & Packaging material and coating films & [35; 36] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Common types of biodegradable plastic and their structures and their uses. Figure 3: Production of biodegradable plastics in 2023 (based on data derived from [22; 23; 24]), where PHA is polyhydroxyalkanoate, PLA is polylactic acid, PBS is polybutylene succinate, and PBAT is polybutylene adipate terephthalate.