## 6 Summary and Future Perspectives  
The acidogenic fermentation of waste streams has demonstrated significant potential as a pathway for the production of VFAs, which are essential intermediates for bioplastic synthesis. This approach aligns with circular economy principles, enabling waste valorization and fostering sustainable alternatives to petrochemical-based processes. However, transitioning from laboratory-scale studies to industrial applications remains a critical challenge, requiring holistic advancements in operational strategies, policy frameworks, and market integration. Key future directions include integrating acidogenic fermentation with complementary waste valorization technologies to enhance efficiency and product specificity. For instance, combining fermentation with anaerobic digestion or bioelectrochemical systems could optimize substrate utilization while enabling the co-production of energy or other value-added products. Research into microbial engineering and metabolic modeling is pivotal for achieving targeted VFA profiles tailored to specific industrial demands, such as bioplastics with desired mechanical and thermal properties. Currently, there is a growing body of research focusing on synthesizing PHAs from various organic waste streams, including industrial, agricultural, and urban organic wastes. However, improving the synthesis efficiency and yield of PHAs is challenging due to the complexity of substrate properties. Complex substrates can introduce inhibitors that negatively affect PHA accumulation. Therefore, it is necessary to investigate the impact of these complex substrate components on PHA accumulation based on different substrate types and to develop improved pretreatment methods, fermentation strategies, and synthesis processes to mitigate the negative effects of such inhibitors. Fermentation conditions such as pH, carbon-to-nitrogen ratio, OLR, and temperature are important factors influencing PHA production. Before large-scale production, optimizing these reaction conditions is essential to provide strong support for the standardization of synthesis. In terms of kinetics, establishing a comprehensive kinetic model based on chemical processes, enzyme processes, and biological processes--from pretreatment to fermentation--is necessary to provide reasonable assumptions and an accurate mathematical framework for the large-scale production of PHAs and the development of related systems. Moreover, research on the coupling process experimental platform of \"substrate fermentation-strain enrichment-PHA synthesis\" is needed, along with exploration of coupling process reactor design and parameter optimization, to realize the recycling of organic waste streams and the efficient, low-cost industrial synthesis of PHAs. Policy and market drivers will play a crucial role in the widespread adoption of these technologies. Increasing the awareness of environmental sustainability and the need to reduce reliance on fossil fuels are expected to accelerate regulatory support for bio-based production systems. Nonetheless, overcoming economic barriers, such as the high costs associated with pretreatment, fermentation, and downstream processing, will be essential. Advancements in low-cost feedstock utilization, particularly from heterogeneous waste streams, and scalable reactor designs are critical for improving economic feasibility. Despite these opportunities, challenges persist in scaling up acidogenic fermentation processes. The variability of waste stream compositions, along with the need for robust microbial consortia capable of adapting to fluctuating conditions, complicates process optimization. Innovations in real-time monitoring and predictive modeling can mitigate these issues by ensuring process stability and efficiency.