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- Supercritical carbon dioxide extraction of biological compounds from microalgaePublication . Nobre, B. P.; Gouveia, Luisa; Campenni, Luca; Marcelo, Filipa M.; Palavra, António F.; Mendes, Rui L.
- The production of pigments & hydrogen through a Spirogyra sp. biorefineryPublication . Pacheco, R.; Ferreira, Ana F.; Pinto, T.; Nobre, B. P.; Loureiro, David; Moura, Patrícia; Gouveia, Luisa; Silva, Carla M.This paper discusses the overall energy consumption and greenhouse gas emissions when extracting pigments and producing hydrogen from Spirogyra sp. microalga biomass. The energy evaluation from the biomass leftovers was also included in this work. The influence of the functional unit and different allocation criteria on the biorefinery assessments is also shown. The study consists of laboratory tests showing Spirogyra sp. growth, harvesting, drying, pigment extraction and fermentation by Clostridium butyricum. Electrocoagulation and solar drying were tested and compared to conventional centrifugation and electrical dewatering in terms of their energy consumption for harvesting and dewatering, respectively. To discuss the biorefinery viability, the pigments and biohydrogen (bioH2) retail costs are considered against operational costs according to electricity needs. The low yield of biochemical hydrogen and the high energy requirements for the pigment extraction were identified as main topics for further research. This research hopefully contributes to highlight the importance of energy and emission balances in order to decide on feasibility of the biorefinery.
- Nannochloropsis sp. biomass recovery by Electro-Coagulation for biodiesel and pigment productionPublication . Matos, Cristina T.; Santos, Marta; Nobre, B. P.; Gouveia, LuisaBiofuel production from microalgal biomass could be an alternative solution to conventional biofuels typically dependent on food and high land/water demanding crops. However, the economic and energetic viability of microalgal biofuels is limited by their harvesting processes. The finding of innovative, low cost and efficient harvesting method(s) is imperative. In this study, the Electro-Coagulation (EC) was studied as a process to harvest the marine Nannochloropsis sp. microalga. Several EC operational conditions were studied and the best EC recovery efficiency (>97%) was achieved using a current density of 8.3 mA cm2 for 10 min. The quality of the recovered microalgal biomass was evaluated in terms of total lipids, fatty acid and pigment profile where no significant differences were observed after EC treatment. The energy requirements of the harvesting process were estimated and the combination of EC and centrifugation processes proved to decrease significantly the energy demand when compared with the individual process.
- A biorefinery from Nannochloropsis sp. microalga – Extraction of oils and pigments. Production of biohydrogen from the leftover biomassPublication . Nobre, B. P.; Villalobos, Fidel; Barragan, Blanca E; Oliveira, Ana Cristina; Batista, Ana Paula; Marques, Paula; Mendes, Rui L.; Sovová, H.; Palavra, António F.; Gouveia, LuisaThe microalga Nannochloropsis sp. was used in this study, in a biorefinery context, as biomass feedstock for the production of fatty acids for biodiesel, biohydrogen and high added-value compounds. The microalgal biomass, which has a high lipid and pigment content (mainly carotenoids), was submitted to supercritical CO2 extraction. The temperature, pressure and solvent flow-rate were evaluated to check their effect on the extraction yield. The best operational conditions to extract 33 glipids/100 gdry biomass were found to be at 40 °C, 300 bar and a CO2 flow-rate of 0.62 g/min. The effect of adding a co-solvent (ethanol) was also studied. When supercritical CO2 doped with 20% (w/w) ethanol was used, it was possible to extract 45 glipids/100 gdry biomass of lipids and recover 70% of the pigments. Furthermore, the remaining biomass after extraction was effectively used as feedstock to produce biohydrogen through dark fermentation by Enterobacter aerogenes resulting in a hydrogen production yield of 60.6 mL/gdry biomass.
- New at-line flow cytometric protocols for determining carotenoidcontent and cell viability during Rhodosporidium toruloides NCYC 921batch growthPublication . Freitas, Claúdia; Nobre, B. P.; Gouveia, Luisa; Roseiro, J. Carlos; Reis, Alberto; Silva, Teresa Lopes daRhodosporidium toruloides NCYC 921 batch growth was monitored as a means to evaluate the yeastbiomass potential as a source for the production of carotenoids and other lipids.Carotenoid content, cell viability and size were assessed by multiparameter flow cytometry. Thesaponifiable lipid fraction was assayed by gas–liquid chromatography.The carotenoid production increased during the stationary phase, reaching 78 g/g while the total fattyacid content attained 32% (w/w) at the end of the fermentation. The fatty acid profile was suitable forbiodiesel purposes.As the yeast cells entered the stationary phase, the proportion of cells with depolarised mitochon-drial membrane and cells with permeabilised cytoplasmic membrane increased, attaining 65% and 14%,respectively. Nevertheless, a high proportion of cells (82%) showed esterase activity.These results demonstrated that flow cytometry can be a powerful at-line technique to monitor thetotal carotenoids and cell viability during the yeast growth, being useful for the yeast process optimisationat lab and pilot scales.
- Evaluation of the simultaneous production of lutein and lipids using a vertical alveolar panel bioreactor for three Chlorella speciesPublication . Araya, Blanca; Gouveia, Luisa; Nobre, B. P.; Reis, Alberto; Chamy, Rolando; Poirrier, PaolaThe concept of a biorefinery improves the economic efficiency of a biofuel production process from microalgae by recovering high value added compounds. Lutein is a carotenoid currently extracted from petals of Tagetes erecta with an established market in poultry and in human nutritional supplements. For the very first time, an extended study on the lipid and lutein production over three Chlorella species as well as cell disruption methods was performed. Chlorella vulgaris, Chlorella zofingiensis and Chlorella protothecoides were grown in an indoor vertical alveolar panel photobioreactor with continuous illumination, and two cell disruption methodswere assessed at a laboratory scale: glass bead vortexing and ball mill grinding. For C. vulgaris, C. zofingiensis and C. protothecoides the intracellular lutein content was measured as: 3.86, 4.38 and 3.59 mgg-1 respectively. Lipid contents vary slightly among microalgae with a value close to 9% w/w. Biomass and lutein productivities were found to be higher for C. vulgaris (0.131 gL-1 d-1, 0.51 mg L-1 d-1) and for C. zofingiensis (0.122 gL-1 d-1, 0.53 mg L-1 d-1) compared to C. protothecoides (0.103 gL-1 d-1, 0.37mg L-1 d-1). C. vulgaris 1803 and C. zofingiensis B 32 were found to be promising organisms for simultaneous production of lutein and lipids. Although all the microalgae under study belong to the same genus, a species-specific response was observed for each of the cell grinding methods tested.
- Dual-mode cultivation of Chlorella protothecoides applying inter-reactors gas transfer improves microalgae biodiesel productionPublication . Santos, Carla A.; Nobre, B. P.; Silva, Teresa Lopes da; Pinheiro, H. M.; Reis, AlbertoChlorella protothecoides, a lipid-producing microalga, was grown heterotrophically and autotrophicallyin separate reactors, the off-gases exiting the former being used to aerate the latter. Autotrophic biomass productivity with the two-reactor association, 0.0249 g L-1h-1, was 2.2-fold thevalue obtained in a control autotrophic culture, aerated with ambient air. Fatty acid productivity was1.7-fold the control value. C. protothecoides heterotrophic biomass productivity was 0.229 g L-1h-1. This biomass’ fatty acid con-tent was 34.5% (w/w) with a profile suitable for biodiesel production, according to European Standards.The carbon dioxide fixed by the autotrophic biomass was 45 mg CO2L-1h-1in the symbiotic arrange-ment, 2.1 times the control reactor value.The avoided CO2 atmospheric emission represented 30% of the CO2 produced in the heterotrophic stage, while the released O2 represented 49% of the oxygen demand in that stage.Thus, an increased efficiency in the glucose carbon source use and a higher environmental sustainability were achieved in microalgal biodiesel production using the proposed assembly.
- Lipid and carotenoid production by a Rhodosporidium toruloides and Tetradesmus obliquus mixed culture using primary brewery wastewater supplemented with sugarcane molasses and ureaPublication . Dias, Carla; Nobre, B. P.; Santos, J. A. L.; Reis, Alberto; Silva, Teresa Lopes daABSTRACT: In this study, Rhodosporidium toruloides and Tetradesmus obliquus were used for lipid and carotenoid production in mixed cultures using primary brewery wastewater (PBWW) as a culture medium, supplemented with sugarcane molasses (SCM) as a carbon source and urea as a nitrogen source. To improve biomass, lipid, and carotenoid production by R. toruloides and T obliquus mixed cultures, initial SCM concentrations ranging from 10 to 280 g L-1 were tested. The medium that allowed higher lipid content (26.2% w/w dry cell weight (DCW)) and higher carotenoid productivity (10.47 mu g L-1 h(-1)) was the PBWW medium supplemented with 100 g L-1 of SCM and 2 g L-1 of urea, which was further used in the fed-batch mixed cultivation performed in a 7-L bioreactor. A maximum biomass concentration of 58.6 g L-1 and maximum lipid content of 31.2% w/w DCW were obtained in the fed-batch cultivation. PBWW supplemented with SCM was successfully used as a low-cost medium to produce lipids and carotenoids in a R. toruloides and T obliquus mixed culture, with higher productivities than in pure cultures, which can significantly reduce the cost of the biofuels obtained.
- Microalgae biomass harvesting by electrocoagulationPublication . Matos, Cristina T.; Santos, Marta; Nobre, B. P.; Gouveia, LuisaThe use microalgae biomass for the production of biofuels has received great attention in the last decades. Microalgae biofuels could be important alternative to conventional biofuels since microalgae could be produced at high rates without the need of neither arable land, potable water or competition with food. However, the high energy intensive harvesting processes are limiting the commercial production of microalgae biofuels. In this study, Electro-Coagulation (EC) was used for harvesting the freshwater microalga Chlorella vulgaris and the marine microalga Nannochloropsis sp. The results show that EC could be an alternative to the conventional harvesting processes since it is efficient and produces good quality biomass with low energy requirements.
- Use of flow Cytometry as a quick way to select low cost carbon sources for biodiesel and carotenoid production by the red yeast Rhodosporidium toruloides NCYC 921Publication . Freitas, Claúdia; Parreira, Teresa M.; Nobre, B. P.; Gouveia, Luisa; Reis, Alberto; Roseiro, J. Carlos; Silva, Teresa Lopes daSome yeasts like Rhodosporidium toruloides are oleaginous and can be used for biodiesel production. In addition, some strains are able to produce valuable carotenoid pigments which are of great commercial interest, contributing significantly to reduce the biodiesel production costs. Carotenoid extraction and quantification are time consuming, generate high amounts of waste and require the use of considerable amounts of biomass. Flow Cytometry (FC) can monitor carotenoids accumulation in yeasts, at line, and with a high statistical resolution, during growth. Moreover, during the cultivation it is important to assess cell physiological states, since injured or dead cells decrease the bioprocess yield. If this information is obtained near real time, it is possible to change the process control strategy in order to achieve the maximum lipid and carotenoid productivities. To obtain a more sustainable biodiesel production, it is also important to use low cost substrates, such as industrial by-products. In the present work, different low cost substrates were used as carbon sources [glycerol as a biodiesel byproduct, sugarcane molasses and carob pulp (syrup) as a cheap by-product of the food industry in the European south countries] to produce lipids and carotenoids by the yeast R. toruloides NCYC 921, and a comparison was made. Flow cytometry was used to monitor carotenoid content and cell viability (enzymatic activity, membrane potential and membrane integrity) during all the yeast cultivations.