# Urban Biorefinery Demonstration: Production of Polyhydroxyalkanoates from a Municipal Solid Waste
## 1 Introduction
Furthermore, achieving a balance between high PHA productivity and microbial growth remains complex. Excessive substrate availability may lead to biomass proliferation rather than polymer accumulation. Finally, downstream processing, particularly PHA extraction and purification, remains a bottleneck, as conventional solvent-based methods are costly and present environmental concerns [45]. Overcoming these outlined challenges requires fine-tuning operational strategies, and developing cost-effective and scalable recovery techniques to make PHA production viable for its industrialization. [PERSON] et al. [46] successfully converted crude glycerol into VFAs for PHA production. They achieved 76 g scl-PHA/100 g TSS in a 1.7 L sequential batch reactor (SBR) under feast/famine (F/F) conditions, with a PHB:PHY ratio of 84:16. Similarly, [PERSON] et al. [47] used glycerol in a 1.5 L SBR, applying 24 h cycles with three 50 mM carbon source pulses per cycle, obtaining a biomass with 59 wt.% scl-PHA. [PERSON] et al. [48] studied the production of scl-PHAs using paper mill wastewater at laboratory scale with a 24 h cycle length, reaching a maximum PHA content of 48 wt.%. Few studies have reported PHA production beyond the pilot scale. The RES URBIS H2020 project [25, 26, 27] investigated PHA production from OFMSW at a pilot scale, using a 380 L anaerobic reactor to produce VFAs, followed by a 100 L SBR for activated sludge cultivation over 8.5 months. The process maintained a 1-day HRT, a cycle length of 6-12 h, and controlled temperature above 24 \({}^{\circ}\)C in colder months. The pH was not regulated, and the C:N:P ratio was 100:7:1. Accumulation occurred using a fed-batch strategy, achieving up to 0.4 g scl-PHA/g TSS with a PHV content between 22-40 wt.%. PHA extraction is also challenging for industry nowadays due to solvent cost, solvent selectivity, environmental concerns of the solvent, or degradation of the polymer during extraction. Since bacterial PHAs are more costly than fossil-based plastics, cost-effective recovery methods are crucial [45]. Factors such as biopolymer type, purity, PHA properties, cost, and environmental impact must be considered [49, 50]. PHA extraction typically follows two main approaches: biomass dissolution using oxidants or solvent-based extraction, with a growing emphasis on eco-friendly alternatives such as dimethyl carbonate (DMC) [51, 52, 53]. The efficiency and feasibility of these methods are highly dependent on process scale, as solvent costs, selectivity, and polymer stability become more critical at larger scales. This study contributes to process sedation by exploring a sustainable DMC-based extraction method, advancing environmentally friendly and industrially viable PHA recovery. Bio-based scl-PHA obtained after extraction with DMC showed better mechanical properties due to higher plastic deformation capability than that obtained from the same biomass using chloroform and dichloromethane [54]. [PERSON] et al. [55] extracted PHA at lab scale and employed DMC and a combination of DMC and sodium hypochlorite as solvents for 1 h and 90 \({}^{\circ}\)C. The experiment resulted in a PHA recovery of 49 \(\pm\) 2 wt.% with a purity above 94%. [PERSON] et al. [52] also reported in another study a recovery yield of 88 \(\pm\) 6% at the same temperature but increasing the contact time of up to 4 h. On the other hand and to the best of our knowledge, studies have not been reported on DMC-base or not PHA solvent extraction processes at demo or pilot scale. This is because of the harmful and flammable characteristics of the most used solvents that can create hazards for the environment and the operators [28]. Therefore, PHA extraction technology requires further maturity. Another study was found that employs supercritical fluid extraction but this methodology requires high investment in equipment and high energy consumption [56].