Marburg, Universiẗat, Diss., 1999.

Proefschrift - Rijksuniversiteit te Utrecht. / Bibliography: p. 51-55.

Zugl.: Marburg, Universiẗat, Diss., 1999.

Algae are a prolific source of biochemicals with economic importance, including nutraceuticals, biofuels, animal feed, etc. The general aim of this study was to establish how the hydrodynamic conditions generated within specific types or designs of photobioreactors determine their respective algae growth. The specific objectives of this study were: (1) To determine and compare key hydrodynamic parameters in the Air Accordion photobioreactor and the conventional bubble column, including Residence Time, Vessel Dispersion Number, Bodenstein Number, Mixing Time and oxygen liquid mass transfer coefficient (kla); and, (2) To test how differences in the hydrodynamic conditions would result in significant difference in growths of the green alga Scenedesmus obliquuus between the photobioreactors. The results of the study showed that: (1) The Residence Time of 566 s for the Air Accordion significantly exceeded by 28% that of 444 s for the bubble column, signifying greater liquid mixing in the Air Accordion; (2) The Vessel Dispersion Number for the Air Accordion of 0.168 significantly exceeded that for the bubble column of 0.166, indicating greater degree of mixing in the Air Accordion than in the bubble column; (3) The Mixing Time in both the Air Accordion and the bubble column declined as the air flow rate increased, indicating that the tracer ions in both photobioreactors mixed more quickly. For each of the flow rates tested, however, the mixing time for the bubble column significantly exceeded that for the Air Accordion, indicating that liquid mixing in the Air Accordion occured significantly quicker than in the bubble column. At 1.0 LPM, the bubble column's Mixing Time of 10 s exceeded by 25% that of the Air Accordion of 8 s; (4) The oxygen liquid mass transfer coefficients in both photobioreactors increased as the air flow rate increased, indicating that the transfer of oxygen from the air bubbles into the liquid within the photobioreactors gained efficiency. For each of the air flow rates tested, however, the oxygen liquid mass transfer coefficient for the Air Accordion significantly exceeded that for the bubble column, indicating a significantly more efficient oxygenation of the liquid in the Air Accordion occurring than in the bubble column. At 1.0 LPM, the Air Accordion's oxygen liquid mass transfer coefficient of 0.00138 s⁻¹ exceeded by 48% that of the bubble column of 0.000931 s⁻¹; and (5) The growth of Scenedesmus obliquus in the Air Accordion significantly exceeded that in the bubble column for both 0.1 LPM and 1.0 LPM. The final algae density of 0.25 g DW/L in the Air Accordion significantly exceeded by 31% that of 0.18 g DW/L in the bubble column at 0.1 LPM. Similarly, the final algae density of 0.37 g DW/L in the Air Accordion significantly exceeded by 19% that of 0.31 g DW/L in the bubble column at 1.0 LPM. Thus, the growth of Scenedesmus obliquus in the Air Accordion photobioreactor -- with significanlty more favorable hydrodynamic characteristics in terms of Residence Time, Vessel Dispersion Number, Mixing Time and oxygen liquid mass transfer coefficient -- significantly exceeded algae growth in the bubble column of the same volume and under the same environmetal conditons.

Scenedesmus obliquus is a freshwater microalga which has high lipid content and biomass productivity. It is regarded as a promising species for production of biodiesel and other valuable organic compounds. Given the high cost of using potable water and commercial fertilizers, the use of municipal wastewater as algal growth medium is attractive in view of its constituent organic carbon and inorganic nutrients, including nitrogen and phosphorus. Investigating the mixotrophic cultivation of S. obliquus in an imitation municipal wastewater, the results of this study showed that: (1) The unmodified imitation wastewater by itself as expected yielded poor S. obliquus growth owing to its pH significantly decreasing to 3.5 as caused by the presence of Ammonium Chloride in the wastewater, inhibiting cell growth; (2) Adding either Acetic Acid or Sodium Acetate to the wastewater medium maintained its pH at 6.5 to 7.0, and its algae biomass on day 6 increased significantly by 212% and 194%, respectively; (3) Adding either Acetic Acid or Sodium Acetate to the wastewater medium maintained its pH at 6.5 to 7.0, and its algae biomass during exponential phase (day 4) significantly exceeded that in the MF control by 220.6% and 165.8%, respectively, while its algae biomass during saturation (day 6) significantly exceeded that in the MF control by 60.8% and 51.5%, respectively; and (4) Addition of NaNO₃ to the wastewater to match the level of N in the MF medium improved the algae biomass by 10%. This study developed ways for how the successful mixotrophic cultivation of S. obliquus in municipal wastewater could be achieved.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2017-05-30T13:27:50Z No. of bitstreams: 1 texto completo.pdf: 796270 bytes, checksum: 7fff46a9d3a52c63d7b42f821ece99fa (MD5) / Made available in DSpace on 2017-05-30T13:27:50Z (GMT). No. of bitstreams: 1 texto completo.pdf: 796270 bytes, checksum: 7fff46a9d3a52c63d7b42f821ece99fa (MD5) Previous issue date: 2014-10-20 / A busca pela redução no custo de produção de biodiesel a partir de microalgas é um fator essencial para viabilizar a utilização desta fonte de energia na matriz energética mundial. Diante desta questão, verificou-se a possibilidade da utilização do gás ozônio na recuperação dos nutrientes assimilados pela microalga Scenedesmus obliquus BR003, durante seu cultivo em meio BG11 e posterior reuso em cultivo subsequente. O espectro de absorbância no visível da microalga durante a ozonização revelou que, a partir de 34 minutos de tratamento não ocorrem variações significativas nos valores de absorbância. Os picos de absorção encontrados foram de 436, 470 e 680 nm, que representam a clorofila a (436 e 680 nm) e os carotenóides (470 nm). Para os resultados de massa seca durante o processo de ozonização, o tempo de estabilização dos valores foi similar, durando cerca de 35 minutos. Após análise do perfil eletroforético em gel de poliacrilamida, foi possível identificar a oxidação das proteínas ao longo da ozonização. Para os nutrientes, os teores disponibilizados de amônio, nitrato e fosfato, após 50 minutos de ozonização, foram de 1,1, 5,7 e 1,2 mg L -1 , respectivamente, evidenciando a possibilidade de recuperação dos nutrientes presentes nas células de microalgas. O cultivo realizado somente com o extrato decorrente da ozonização de microalgas, obteve biomassa final de 0,64 g L -1 , resultado semelhante ao cultivo em meio BG11 suplementado com o mesmo extrato (0,66 g L -1 ) e três vezes superior ao meio BG11 sem suplementação (0,21 g L -1 ). De forma geral, os tratamentos em que o nitrogênio presente no meio BG11 não foi aplicado apresentaram maiores teores de lipídios. Outro indicador de estresse por falta de nitrogênio foram os teores de clorofila a, clorofila b e carotenoides totais, em que, os tratamentos com baixo teores de nitrogênio apresentaram menores concentrações destes pigmentos. O custo estimado de ozonização das microalgas para se obter um litro de lipídios ficou em R$ 5,75, contudo com o aumento da escala e melhorias na produtividade de lipídios este custo caiu para R$ 2,33. Ressalta-se que, o aumento da eficiência do processo de ozonização pode permitir a redução do custo destes valores. Os resultados obtidos neste trabalho indicam a possibilidade da utilização do gás ozônio, no processo de reaproveitamento de nutrientes a partir do cultivo da microalga Scenedesmus obliquus. / The need of reducing the cost of microalgae-based biodiesel production is a crucial factor to turn its adoption feasible in the world energy matrix. Faced with this issue, an experiment was set up to investigate the potential use of ozone gas on recovering nutrients assimilated by the microalgae Scenedesmus obliquus BR003 during its subsequent cultivation in BG11 medium. After 34 min of ozonization, analyzes of absorbance in the visible spectrum of the microalgae revealed that no significant variation in absorbance values was observed. Absorption peaks were found at 436, 470 and 680 nm, which represents chlorophyll a (436 and 680 nm), and carotenoids (470 nm). Moreover, assessment of dry mass weights during the ozonization process showed similar values for stabilization period of approximately 35 minutes. The polyacrylamide gel electrophoresis showed the oxidation in proteins bands along the process of ozonation. For nutrients, the levels of available ammonium, nitrate and phosphate, after 50 minutes of ozonization, were 1.1, 5.7 and 1.2 mg L -1 , respectively; therefore, indicating that nutrients present in the microalgae cells can be potentially recovered. The cultivation carried out solely with the extract obtained after microalgae ozonization resulted in 0.64 g L -1 of final biomass. Similar results were found when BG11 culture medium supplemented with the same extract were used (0.66 g L -1 ); however, values were three-fold higher when BG11 medium without supplementation was adopted (0.21 g L -1 ). Generally, the treatments with no nitrogen supplementation showed higher levels of lipids. Furthermore, other indicators of nitrogen deficiency such as low levels of chlorophyll a, chlorophyll b and carotenoids were noticed. Accordingly, the treatment with low levels of nitrogen showed lower concentrations of these pigments. The estimated cost to produce one liter of lipids via microalgae ozonization was R$ 5.75, even though this cost decreased to R$ 2.33 per liter when large production scales and improvement of lipids yield was adopted. Consequently, increasing the efficiency of the ozonization process might enable further reduction of the costs previously calculated. The results obtained in this study, indicate the possibility of the use of ozone gas in the process of nutrient recycling, from the cultivation of microalgae Scenedesmus obliquus.

Growing interest in biofuel production from non-fossil fuel sources has resulted in several studies exploring different raw material sources as feedstock, including many algae species, for large-scale production of biofuel. Algae are promising feedstock due to advantages such as its short growth cycle, high biomass production, and lipid content. However, there are still challenges to overcome in order to use algae for commercial biofuel production. One of these challenges is the requirement for a large quantity of water and nutrients needed for growing large quantities of the algae. This work explores a potential solution to this challenge by studying the possibility of using industrial wastewater to grow algae for biofuel production. However, many industrial wastewaters, including effluents from semiconductor processing plants, are known to contain heavy metals that are toxic to humans and the environment. In this work, the effects of four of such metals ions, As(V), As(III), Ga(III), and In(III) on Chlorella sorokiniana and Scenedesmus obliquus strains were studied. In particular, the heavy metal toxicity on the strains, effects on its growth rate, biomass yield, lipid content and fatty acid methyl esters (FAME) were studied. Also, the effect of controlling pH on growth rate, biomass yield, lipid content, and FAME was studied for Chlorella sorokiniana in the presence of Ga(III). The results of the study confirmed the toxicity of these metals on both strains. However, Ga(III) and In(III) had the highest effect, while As(V) showed the least toxicity to the strains, with Chlorella sorokiniana withstanding concentrations of As(V) as high as 140mg/L. The heavy metals were slightly more toxic to Scenedesmus obliquus compared to Chlorella sorokiniana. In addition, the heavy metals reduced the growth rate of both strains. High percent changes in growth rate (more than 50%) were seen in cultures containing Ga(III) and In(III). Furthermore, concentration measurements with Inductively Coupled Plasma Optical Emission Spectrometer (ICP) before, during, and at the end of the growth period, showed that Scenedesmus obliquus adsorbed higher amounts of the heavy metals compared to Chlorella sorokiniana. Microalgae biosorption of heavy metals limits its end use, hence making Scenedesmus obliquus a less favorable option for this study, but may be a better choice for wastewater treatment applications. The effects of the four metals on the lipid content and FAME profile of Chlorella sorokiniana were studied. The result showed an increase in Chlorella sorokiniana lipid content in the presence of In(III), but a decrease in the presence of As(V) and As(III). The heavy metals had effects on the strain’s FAME compositions. The fatty acid composition included C16:0, C16:1, C16:2, C16:3, C18:0, C18:1, ω-6, C18:2, ω-6, and C18:3, ω-3 accounting for more than 97% of the total FAME composition. Furthermore, controlling the pH of the culture in the presence of Ga(III) at 6.5 led to higher adsorption of the heavy metal, increase in lipid content, but no significant change in FAME composition.

This study evaluated the effect of several heavy metals that are present in flue gases on the algae, focusing on the growth and accumulation of lipids in the algae that can be converted to biodiesel. Concentrations for the heavy metals were calculated based on literature and assumptions. Metals were tested individually first at the highest concentrations that might be present (reference concentrations). The metals and their reference concentrations were: arsenic at 1.56 mg/L, cadmium at 0.3 mg/L, chromium at 2.6 mg/L, cobalt at 0.32 mg/L, copper at 2.62 mg/L, lead at 1.09 mg/L, nickel at 5.08 mg/L, mercury at 0.2 mg/L, selenium at 0.2 mg/L, and zinc at 8.8 mg/L. At these concentrations, most of the metals had a negative effect on the growth and lipid content of the algae. All of the metals were then tested at lower concentrations. At 1/20 the reference concentrations, the metals enhanced growth as well as lipid accumulation in the algae. At higher concentrations there was a negative effect.