Bio-valorization of crude glycerol through polyhydroxyalkanoates production

Due to the prospective partial replacement of fossil fuels by biodiesel, its production has continuously grown in the last decade. The increase in global biodiesel production demands the development of sustainable applications of its main by-product, crude glycerol. In this thesis the feasibility of producing polyhydroxyalkanoates (PHA) by a mixed microbial community using crude glycerol as feedstock was investigated. Several incubation conditions were studied in order to maximize PHA production. The microbial population selected under aerobic dynamic feeding conditions had the ability to consume both major carbon fractions present in the crude, glycerol and methanol. Two biopolymers were stored, poly-3-hydroxybutyrate (PHB) and glucose biopolymer (GB), apparently using glycerol as the only carbon source for their production. The microbial enrichment obtained was able to accumulate up to 47% PHB of cell dry weight with a productivity of 0.24 g HA/L d. The overall PHA yield on total substrate consumed (0.32 g COD HB/g COD crude glycerol) was in the middle range of those reported in literature (0.08–0.58 g COD PHA/g COD real waste). The increase of temperature from 23ºC to 30ºC favored the culture fraction that accumulates glucose biopolymer with a maximum accumulation value of 25% of cell dry weight, which is an interesting value but not the main goal of this thesis. The fact that crude glycerol can be used to produce PHA without any pre-treatment step, makes the overall production process economically more competitive, reducing polymer final cost. This was the first study that demonstrates the valorization of the glycerol fraction present in the crude glycerol into PHA using an aerobic mixed microbial consortium.