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Universidade do Minho (2012)

Biotechnological valorization of olive mill wastewaters

Gonçalves, Cristiana

Titre : Biotechnological valorization of olive mill wastewaters

Auteur : Gonçalves, Cristiana

Université de soutenance : Universidade do Minho

Grade : Tese de doutoramento em Química e Engenharia Biológica (2012)

Mediterranean countries are known to have favorable conditions for olive oil production. The three-phase extraction technology demands the addition of hot water to the process, and olive oil, olive cake and olive mill wastewater (OMW) are produced. An approach for using this waste as a renewable resource is of greater interest. Accordingly, the present investigation aims the OMW valorization, by producing high-value compounds (lipase and methane) while degrading this waste. Thus, the research work presented in this thesis essentially describes a study about an integrated process, where the effluents are firstly submitted to a lipase producing aerobic fermentation, followed by an anaerobic degradation process, to produce methane. This work is of great interest, since Portugal is one of the world leading producers of olive oil, with crescent production values from campaign to campaign, in the last years. This work was started with a study about the major problem attributed to the olive mill wastewaters (OMW), the phenolic compounds toxicity. These experiments showed that the nonconventional yeasts Y. lipolytica, C. rugosa and C. cylindracea are able to grow in different phenolic compounds, usually found in OMW. This was later confirmed in bioreactor batch experiments with OMW-based media, where the studied yeasts, not only were capable of achieving similar cell growth, to glucose synthetic media, but also to highly consume the existing and analyzed phenolic compounds. The experiments on batch fermentations, with OMW-based media, were then performed in Erlenmeyer baffled flasks, in order to study the effect of ammonium, cell and surfactant addition as well as to investigate the use of different yeast strains ; Candida rugosa (PYCC 3238 and CBS 2275), Candida cylindracea CBS 7869 and Yarrowia lipolytica (CBS 2073, W29 ATCC 20460 and IMUFRJ 50682) ; and different non-diluted OMW. C. cylindracea was the best strain concerning the effluent degradation. After preliminary tests, a study of optimal batch and fed-batch conditions was performed in bioreactor, using Candida rugosa CBS 2275, Candida cylindracea CBS 7869 and Yarrowia lipolytica W29 ATCC 20460. It was confirmed that C. cylindracea CBS 7869 was the best lipase-producing yeast (6 U mL-1). However, using a fed-batch strategy, with cell pre-growth directly on the bioreactor, C. rugosa CBS 2275 was the strain that obtained the best values of lipase (17 U mL-1) ; achieving at the same time, a significant effluent degradation (64 % of COD, 27% of phenolics and 77% of total lipids). Anaerobic biodegradability tests showed that the aerobic treatment had a positive effect on the anaerobic degradation of the OMW. Best results were achieved for the initial concentration of 5 g COD-treated OMW L-1, where 78% of the COD added was recovered as methane. Furthermore, when the COD degradation in the aerobic step was higher, even better results were possible to achieve, with a faster conversion of COD to methane. The obtained results demonstrates that the olive mill wastewaters (OMW) are becoming a competitive and valuable growth medium in fermentation processes and also the potential application of non-conventional lipolytic yeasts for OMW valorization, for biomass and enzymes production. This treatment was successful to detoxify the effluent, having a very positive effect in the anaerobic digestion. The utilization of this valorization process will possibly have a positive impact on the environmental problem of OMW management.


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