## 1 Introduction  
Polyhydroxyalkanoates (PHA) are natural polyesters of hydroxyalkanoate (HA) building blocks that are produced and accumulated intracellularly by numerous bacteria as an energy reserve material in the presence of excess carbon source and/or under limited nutritional conditions [1; 2; 3; 4; 5]. PHAs are biodegradable bioplastics and have mechanical properties similar to those of conventional thermoplastics, such as polyethylene (PE) and polypropylene (PP), and are alternates for petroleum-derived polymers [1; 6; 7]. Poly-3-hydroxybutyrate (PHB) was the first known PHA and as a consequence the most extensively studied PHA [6; 7]. Some inherent limitations of PHB including high brittleness and low thermal stability have hampered its commercialization [7; 8; 9; 10]. Adding plasticizers, and low molecular weight additives is an effective way to improve the flexibility and processing window of PHB [10]. Plasticizers penetrate into the polymer network to reduce deformation tension, elastic modulus, and viscosity of a polymer to increase polymer chain flexibility, resistance to fracture, and dielectric constant [10].  
Improving the flexibility of PHB can be achieved by the introduction of HA comonomers, such as 3-hydroxyvalerate (3 HV), to form the copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV). Compared to PHB, PHBV is less crystalline and as a result is more flexible with improved impact resistance and toughness which makes PHBV suitable for applications such as flexible packaging [6; 10]. The performance of PHBV highly depends on its 3 HV content. Higher 3 HV content reduces the polymer's crystallinity, increases its flexibility, and results in a more easily biodegradable polymer [8; 10]. An increase in the 3 HV content of the PHBV from 0 to 50% can also significantly reduce its melting point (\(T_{m}\)) [7].  
Current commercial production of PHBV uses pure bacterial culture and/or genetically modified strains in a sterile environment. Furthermore, commercial production uses refined carbon substrates such as glucose and fatty acids which also increase production costs [3; 8; 11]. Recently, PHBV production processes using mixed microbial cultures (MMCs) have attracted more attention due to having a simplified operations and using non-sterile conditions allowing for a potentially sustainable and closed-cycle process for polymer synthesis [6; 11]. Using a renewable waste carbon substrate and MMCs for PHBV biosynthesis can reduce the production expenses [3; 12; 13; 14]. Depending on the type of renewable waste carbon used as substrate, the type of bacteria and the applied production parameters the production expenses can be reduced by greater than 50% [3; 12; 13; 14; 15]. The carbon feed substrate can influence the structure and properties of PHBV [6; 16]. PHBV can be synthesized using fatty acids with even (e.g., acetate and butyrate) and odd (e.g., propionate and valerate) numbered carbon chains [6]. The even numbered fatty acids will produce 3-hydroxy butyrate (3 HB) while the odd numbered fatty acids will produce 3 HV. Therefore, the 3 HV to 3 HB ratio in PHBV will be dependent on the carbon feedstock [10]. Studies have focused PHBV production parameters and optimizing the extraction and recovery yield in small scale (\(\leq\)3 g) [17; 18; 19; 20; 21] or characterizing the properties of PHBV [22; 23; 24]. However, there is a gap in comprehensive studies examining PHBV biosynthesis using MMC and various feed compositions, extraction of PHBV, and polymer properties at the pilot scale.  
This study aims were to (i) produce PHBV with different 3 HV contents using MMC that are fed with fermented dairy manure liquor over a several month operating period [6], (ii) determine PHBV chemical composition, (iii) determine their mechanical properties, and (iv) determine their thermal and rheological properties. These results show how PHBV properties will vary in a pilot plant over a 3-month operation.