Biopolymers production by " Halomonas boliviensis " in an integrated biorefinery

Abstract

The main aim of this Thesis is to develop processes that allow the integrated production of biopolymers into biorefineries, using feedstocks from first and second generation as raw materials. Climate change, the decrease of the fossil fuel resources and the rapid increase of the world population trigger the development of new processes based on the utilization of renewable raw materials for the replacement of the processes based on the petrochemical synthesis. Moreover, the generation of plastics residues is turning into an important environmental problem due to the recalcitrant feature of the plastics derived from petrol. Biopolymers, biodegradable and/or biobased plastic-like materials, are an environmentally sustainable alternative to the use of petroleum-based plastics. Among the several types of biopolymers, polyhydroxyalkanoates (PHA) stand out. PHA is a type of thermopolyester, biobased and biodegradable, produced by certain microorganisms as a storage material. Nevertheless, despite the benefits presented by the biopolymers, the industrial production of PHA is threatened by production costs higher than that of the petroleum-based plastics. The reduction of the PHA production costs depends on the development and application of new fermentation strategies, downstreams processes, the microorganism and carbon source used for its production. The halophilic bacterium Halomonas boliviensis was used in this Thesis as PHA producer organism due to its capacity to accumulate PHA in high amounts. Firstly, experiments were carried out in order to determine the basic nutritional requirements for growth and PHA accumulation with this microorganism. Besides, an analytical methodology based on flow cytometry was developed for a faster quantification of the PHA content. Then, two different substrates from first generation feedstocks, cereal and sugarcane juice, were evaluated as carbon source for PHA production by H. boliviensis. A novel process configuration was implemented and evaluated, based on the strategy of simultaneous saccharification and fermentation, for the PHA production from cereal mash. Finally, the utilization of volatile fatty acids, derived from residual streams, was evaluated as carbon source. This allowed to upgrade the biorefinery concept. To sum up, the results of this Thesis provide different routes for the formulation of processes that allow the integration of the biopolymers production into a biorefinery and, particularly, information about the general PHA accumulation capacity of H. boliviensis and its specific performance growing on complex carbon sources.