Bioproduction of polyhydroxyalkanoates from olive oil mill effluents
authors Francisca A. e Silva
supervisors Mauro Majone, Luísa Serafim
thesis type MSc in Biotechnology
nationality International
author keywords Polyhydroxyalkanoates, Mixed Microbial Culture, Storage, Sequencing Batch Reactor,
abstract The aim of this research was the development of a low-cost multi-stage process for the production of biodegradable polymers, polyhydroxyalkanoates (PHAs), by using mixed microbial cultures (MMCs) and olive oil mill effluents (OMEs) as feedstock. Prefermented OMEs were used, in which about 60% of the soluble chemical oxygen demand (COD) had been transformed into volatile fatty acids (VFAs) that are more direct substrates for PHA storage. This VFA-rich stream was fed to a successive stage performed in a lab scale sequencing batch reactor (SBR), 1 L working volume. The aim of this stage was to select and enrich MMCs in microorganisms with high and stable storage ability through the establishment of “feast and famine” regime. Two different organic loading rates (OLRs) – 2.34 and 4.74 g L-1 d-1 (referred to the soluble COD) – were assayed in the SBR by diluting the fermented OMEs (soluble COD = 23.7 ± 1.1 g L-1) with mineral medium. The storage response of the microbial culture selected at the higher investigated OLR was analyzed in a following stage, aimed at maximizing the intracellular PHA content in the biomass by successive pulse feeding of no diluted OME (whose nitrogen content is very low). The produced polymer was a poly β-hydroxybutyrate-hydroxyvalerate [P(HB-HV)] with an HV content between 10 and 15 % (w/w). Finally, the attention has been paid at developing the further PHA recovery stage which consisted in a solid-liquid separation followed by chemical digestion using sodium hypochlorite. In conclusion, this study pinpoints the great potential of the proposed process to convert organic wastes, such as OMEs, into valuable products.
year published 2012