Dissertação para obtenção do Grau de Doutor em
Engenharia Química e BioquímicaBiomass can be converted into biofuels by two different ways: thermochemical or biochemical.
Both processes produce waste streams that can be valorised in order to increase the
sustainability of the biofuels production process. Recent research on polyhydroxyalkanoates(PHA) production has focused on developing cost-effective processes using low cost substrates combined with mixed microbial cultures (MMC). The intent of this thesis was to study and
characterise MMC able to produce PHA using the by-products resulting from the biofuels
production.
Bio-oil resulting from the fast-pyrolysis of chicken beds was used as substrate to select cultures under feast/famine conditions with a good PHA storage response. Several operational conditions were investigated and optimized. A copolymer composed by hydroxybutyrate and hydroxyvalerate monomers (70%:30%) was obtained. The impact of the bio-oil matrix on PHA production was also investigated suggesting that some compound may inhibit or interfere with the ability of the enriched culture to accumulate PHA. For further maximization of polymer accumulation two strategies for bio-oil upgrade were performed, anaerobic fermentation and vacuum distillation. The increased of volatile fatty acids on the fermented bio-oil led to an increase on the production yield compared to the ones obtain with pure bio-oil (0.63 and 0.31Cmmol HA/Cmmol S, respectively).
In another system, MMC selected with crude glycerol from biodiesel production as feedstock had the ability to simultaneously store PHA and glycogen. Although the methanol fraction present in the crude was also consumed, glycerol was the only carbon source that contributed for the biopolymers production. During PHA accumulating assay a content of 47% cell dry weight was achieved.
The dynamics of the microbial community of both PHA production systems was assessed by
denaturing gradient gel electrophoresis, fluorescent in situ hybridization and sequencing. Both systems had a high microbial diversity with a predominance of Betaproteobacteria class and Amaricoccus genus in the bio-oil and crude glycerol system, respectivel
