The knowledge of oxygen evolution characteristics, which is a symbol of photosynthetic activity, under various light conditions is important for photobioreactor design and operation. In this study, we constructed a device to investigate oxygen evolution characteristics of Spirulina platensis under two different light regimes: 1) continuous illumination of various light intensities (14-6 500 micromol/(m2 x s)); 2) medium frequency L/D cycles of four different light intensities (69, 505, 1 330, 4 265 micromol/(m2s)). Light limited region, intermediate region, light saturated region and light inhibited region of light intensity were recognized according to their relationship with oxygen evolution rate (OER) under continuous illumination. Investigation of S. platensis under L/D cycles showed whether photosynthetic efficiency could be increased with increasing L/D frequency largely depended on the light intensity applied. The higher the light intensity, the larger the photosynthetic enhancement could be expected with the increase of L/D frequency. The largest light integration effect was found under L/D cycles of high light intensity (4 265 micromol/(m2 x s)) and medium light fraction (k = 0.6), while light integration effect was totally absent under low light fractions (k < 0.2). We also discussed their implications to the practical aspects of microalgae cultivation.
Light ; Oxygen ; metabolism ; Photobioreactors ; Photosynthesis ; physiology ; Spirulina ; metabolism

Flashing light effect on microalgae could significantly improve the light efficiency and biomass productivity of microalgae. In this paper, the baffles were introduced into the traditional flat plate photobioreactor so as to enhance the flashing light effect of microalgae. Making Chlorella sp. as the model microalgae, the effect of light intensity and inlet velocity on the biomass concentration of Chlorella sp. and light efficiency were evaluated. The results showed that, when the inlet velocity was 0.16 m/s, with the increase of light intensity, the cell dry weight of Chlorella sp. increased and light efficiency decreased. With increasing the inlet velocity, the cell dry weight of Chlorella sp. and light efficiency both increased under the condition of 500 μmol/(m2 x s) light intensity. The cell dry weight of Chlorella sp. cultivated in the novel flat plate photobioreactor was 39.23% higher than that of the traditional one, which showed that the flashing light effect of microalgae could be improved in the flat plate photobioreactor with inclined baffles built-in.
Biomass ; Chlorella ; growth & development ; Culture Techniques ; instrumentation ; Light ; Microalgae ; growth & development ; Photobioreactors

Photoautotrophic cultivation with heterotrophic cells as seeds (heterotrophic cells/photoautotrophic cultivation) is an effective way for the development of microalgal biofuel, but its development potential from the point of process optimization has not been investigated in literatures. To evaluate this, the optimizations of medium and culture conditions for Chlorella ellipsoidea were studied. In the heterotrophic stage, the biomass concentration reached 11.04 g/L with the optimized medium in flask, which were 28.0% higher than that with the original medium, and the biomass concentration reached 73.89 g/L in 5-L fermenter. In the photoautotrophic stage, the culture medium and conditions were studied in a 2-L column photobioreactor. The maximum biomass concentration, lipid content and lipid productivity reached 1.62 g/L, 36.34% and 6.1 mg/(L·h) under the optimal photoautotrophic conditions. The lipids were mainly composed of C16-C18 fatty acids, which were raw material suitable for biodiesel. After optimization, heterotrophic cells/photoautotrophic cultivation can significantly improve the capacity of biofuel production by Chlorella ellipsoidea, this method is also expected to be an efficient way for the cultivation of other microalgae that can grow heterotrophically.
Biofuels ; Biomass ; Cell Culture Techniques ; Chlorella ; metabolism ; Culture Media ; Fatty Acids ; biosynthesis ; Heterotrophic Processes ; Lipids ; biosynthesis ; Photobioreactors

Municipal wastewater is usually problematic for the environment. The process of oleaginous microalgal culture requires large amounts of nutrients and water. Therefore, we studied the feasibility of oleaginous microalgal culture of Scenedesmus dimorphus in bubbled column photobioreactor with municipal wastewater added with different nutrients. S. dimorphus could adapt municipal nutrient-rich wastewater by adding some nutrients as nitrogen, phosphorus, ferric ammonium citrate and trace elements, and the amounts of such nutrients have significant effects on cell growth, biomass yield and lipid accumulation. At optimum compositions of wastewater medium, the algal cell concentration could reach 8.0 g/L, higher than that of 5.0 g/L in standard BG11. Furthermore, S. dimorphus had strong capacity to absorb inorganic nitrogen and phosphorus from its culture water. There was almost no total nitrogen and phosphorus residues in culture medium after three or four days culturing when the adding mounts of nitrate and phosphate in wastewater medium were no more than 185.2 mg/L and 16.1 mg/L respectively under the experimental conditions. As a conclusion, it was feasible to cultivate oleaginous microalgae with municipal nutrient-rich wastewater, not only producing feedstock for algal biodiesel, but also removing inorganic nitrogen and phosphorus from wastewater.
Biofuels ; Cities ; Culture Techniques ; methods ; Lipids ; biosynthesis ; Microalgae ; metabolism ; Photobioreactors ; Scenedesmus ; growth & development ; metabolism ; Waste Disposal, Fluid ; methods ; Waste Products

A system coupling ethanol fermentation with microalgae culture was developed, in which CO2 produced during ethanol fermentation was used as carbon source for the growth of Tetraselmis subcordiformis, a microalgae accumulating starch intracellularly. The biomass concentration about 2.0 g DCW/L was achieved within the photobioreactor for the batch culture of 7 days, and intracellular starch accumulation was about 45%. Furthermore, ultrasonic pretreatment and enzymatic hydrolysis were applied to the microalgae biomass, and 71.1% of the intracellular starch was converted into glucose that was fermented sequentially to ethanol by Saccharomyces cerevisiae with an ethanol yield of 87.6% of the theoretical value, indicating that the microalgae biomass could be an alternative feedstock for ethanol production to save grain consumption, and in the meantime mitigate the CO2 emission.
Batch Cell Culture Techniques ; Carbon Dioxide ; metabolism ; pharmacology ; Cells, Cultured ; Ethanol ; metabolism ; Fermentation ; Microalgae ; drug effects ; growth & development ; metabolism ; Photobioreactors ; Saccharomyces cerevisiae ; metabolism ; Starch ; metabolism

Wastewater resources, CO2 emission reduction and microalgae biodiesel are considered as current frontier fields of energy and environmental researches. In this paper, we reviewed the progress in system of microalgae culture for biodiesel production by wastewater and stack gas. Multiple factors including microalgal species, nutrition, culture methods and photobioreactor, which were crucial to the cultivation of microalgae for biodiesel production, were discussed in detail. A valuable culture system of microalgae for biodiesel production or other high value products combined with the treatment of wastewater by microalgae was put forward through the optimizations of algal species and culture technology. The culture system coupled with the treatment of wastewater, the reduction of CO2 emission with the cultivation of microalgae for biodiesel production will reduce the production cost of microalgal biofuel production and the treatment cost of wastewater simultaneously. Therefore, it would be a promising technology with important environmental value, social value and economic value to combine the treatment of wastewater with the cultivation of microalgae for biodiesel production.
Biodegradation, Environmental ; Biofuels ; Biotechnology ; methods ; Carbon Dioxide ; metabolism ; Cell Culture Techniques ; methods ; Cells, Cultured ; Microalgae ; growth & development ; metabolism ; Photobioreactors ; microbiology ; Waste Disposal, Fluid ; methods ; Waste Water ; microbiology