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Author
Agüera del Baño, David
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Abstract
Polyhydroxybutyrate (PHB) is a biobased and biodegradable polymer that represents an excellent alternative to petrochemical plastics. This bioplastic is stored intracellularly by some bacteria as a response to physiological stress. One of the major drawbacks for the widespread PHB applications in the market are the higher production costs compared with conventional plastics. The use of industrial waste materials as fermentation substrate is expected to reduce the overall PHB production cost and make it economically competitive.
This master’s thesis has been conducted within the scope of the NewPack project, which aims to produce sustainable and biodegradable plastic packaging materials starting from agro-food wastes. This conversion process consists of three steps: biomass pre-treatment, fermentation and downstream processing. The scope of this thesis is the optimization and upscaling of the two initial process steps. Potato peel waste was studied as a possible feedstock due to its extensive availability.
The potato peel pre-treatment processing method was optimized at laboratory scale and led to a glucose syrup with purity levels of 94 % (g glucose/ g DM). This process was scaled up to produce a 2020 kg sugar solution with glucose and lactic acid concentrations of 316 g/L and 88 g/L, respectively. Different nanofiltration membranes were assessed to separate lactate and glucose at laboratory scale and the best result was a 94 % glucose recovery and a 41 % lactic acid removal. Since the pre-treatment is still under development, all the P. sacchari 17165 fed-batch cultivations were performed with raffinate glucose. A pulsed feeding system was utilized and phosphate was limited to enhance PHB accumulation. The highest productivity in 10 L fermentations was 1.07 g PHB/L·h, with a maximum polymer accumulation of 63 % (g PHB/g cell). These results were improved in the 1500 L fermentation, which exhibited a volumetric productivity of 1.23 g PHB/L·h and a PHB cell content of 74 % (g PHB/g cell). Finally, a lactic acid concentration around 3 g/L was demonstrated to affect negatively the bacterial growth and the PHB accumulated inside the cells.
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