• Rawa Yousuf

Student thesis: Phd


Polyhydroxybutyrate (PHB) is a biodegradable, linear polyester that has potential as a promising alternative to petrochemical derived plastics as it possesses the same properties as several current and widely used synthetic, non-biodegradable petrochemical-based plastics. PHB is a natural polyester which is accumulated by many bacteria as an intracellular store of energy and carbon, under stress conditions; limited in one or more essential nutrient, with the carbon source in excess. Currently the PHB production cost is far greater than that of petroleum based plastics. Recent research, therefore, has focused on improving the cost- effective synthesis of PHB from different substrates and microorganisms. The improvement of fermentation processes and strains allowing for PHB to be produced from an inexpensive carbon source is required to compete with synthetic plastics and to mimic their desired properties. The goal of the work reported in this thesis is to assess the suitability of using waste date seed as a feedstock for PHB production under various stress conditions. Date seeds have The novelty of this study The results include fructose hydrolysis from date seeds and the development of a mass transfer model to describe the process, demonstrating that the high nutrient content of date seeds makes them a promising raw material for microbial growth and that a meaningful amount of PHB can be produced. Using fructose rich waste date seed derived medium, with an initial fructose concentration of 10.8 g/l, maximum dry cell weight and PHB concentrations of 6.3 g/l and 4.6 g/l, respectively, were obtained, giving a PHB content of 73%. An investigation into the suitability of using waste date seed oil extract as an alternative carbon source for PHB synthesis was also carried out. This date seed oil was used as the sole carbon source in a series of microbial fermentation experiments, and the results demonstrate that date seed oil is a feasible substrate for PHB production. A maximum dry cell weight (DCW) of 14.35 g/l was obtained, with a PHB content of 82%, using 20 g/l of date seed oil. Subsequently, the effect of using mixed-substrate (date seed hydrolysate media and date seed extracted oil) on PHB synthesis was investigated using various ratios of substrate feeding. A ratio of 1:1 fructose to oil produced the highest biomass and PHB concentrations of 15.22 g/l and 12.36 g/l, with PHB content 84.1%, respectively. Solid state fermentation using polyurethane foam (PUF) as inert solid support also proved to be a successful alternative for traditional SSF method for PHB production with ease. The maximum PHB production was 0.169±0.03 g/g PUF and biomass was 0.4±0.003 g/g PUF. This work results demonstrate that the use of a generic waste date seed medium as a feedstock for PHB synthesis is technically feasible. It is shown that waste date seed provides a novel approach to produce value added products, in this case biopolymer (PHB). The specific studies carried out lead to the wider outlook that a general feedstock derived from date palm by-product, seeds, has potential to be utilised to synthesise a wide range of products based on the microorganism used. More improvement of this process to develop the efficient production of nutrients as well as improve product yields and subsequently, integration of the process into a broader biorefining process would be an essential contribution in the improvement of the sustainable bio-products industries.  a high nutrient content, are available in large quantities and are relatively cheap. lies in the fact that waste date seed can be used as the feedstock for biopolymer production, based on the development of various techniques to make these nutrients bioavailable for the bacterium, Cupriavidus necator for PHB accumulation.
Date of Award1 Aug 2018
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorColin Webb (Supervisor) & James Winterburn (Supervisor)

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