Cultivation of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> with swine wastewater and potential for algal biodiesel production

In this study, an alga-based simultaneous process of treating swine wastewater (SWW) and producing biodiesel was explored. Chlorella vulgaris (UTEX-265) was employed as a model species, and a SWW-based medium was prepared by dilution with tap water. Chlorella vulgaris grew well in the SWW-based medium, and at optimum dilution ratios, it exceeded the conventional culture medium in terms of biomass concentration and productivity. In eightfold diluted SWW, which supported the maximum growth, biomass productivity was 0.247 g L^?1 day^?1, while the productivity was merely 0.165 g L^?1 day^?1 in standard tris-acetate-phosphorous (TAP) algal medium. In addition, fatty acid methyl ester (FAME) productivity was greater in the SWW-based medium (0.067 versus 0.058 g L^?1 day^?1). This enhanced productivity resulted in more than 95 % removal of both nitrogen and phosphorous. All these show that C. vulgaris cultivation is indeed possible in a nutrient-rich wastewater with appropriate dilution, and in so doing, the wastewater can effectively be treated.     

Carbon dioxide and poultry waste utilization for production of polyhydroxyalkanoate biopolymers by <Emphasis Type="Italic">Nostoc muscorum</Emphasis> Agardh: a sustainable approach

The new paradigm is to view wastes as resources for sustainable development. In this regard, the feasibility of poultry waste and CO₂ utilization for cultivation of a filamentous nitrogen-fixing cyanobacterium, Nostoc muscorum Agardh, was investigated for production polyhydroxyalkanoates, the biodegradable polymers. This cyanobacterium showed profound rise in biomass yield with up to 10 % CO₂ supply in airstream with an aeration rate of 0.1 vvm. Maximum biomass yield of 1.12 g L^?1 was recorded for 8 days incubation period, thus demonstrating a CO₂ biofixation rate of 0.263 g L^?1 day^?1 at 10 % (v/v) CO₂-enriched air. Poultry litter (PL) supplementation also had a positive impact on the biomass yield. The nutrient removal efficiency of N. muscorum was reflected in the significant reduction in nutrient load of PL over the experimental period. A maximum poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) [P(3HB-co-3HV)] copolymer yield of 774 mg L^?1 (65 % of dry cell wt.), the value almost 11-fold higher than the control, was recorded in 10 g L^?1 PL-supplemented cultures with 10 % CO₂ supply under the optimized condition, thus demonstrating that N. muscorum has good potential for CO₂ biomitigation and poultry waste remediation while simultaneously producing eco-friendly polymers.     

<Emphasis Type="Italic">Tetraselmis suecica</Emphasis> culture for CO<Subscript>2</Subscript> bioremediation of untreated flue gas from a coal-fired power station

The accumulation of atmospheric CO₂, primarily due to combustion of fossil fuels, has been implicated in potential global climate change. The high rate of CO₂ bioremediation by microalgae has emerged as a favourable method for reducing coal-fired power plant emissions. However, coal-fired power station flue gas contains other chemicals such as SO_x which can inhibit microalgal growth. In the current study, the effect of untreated flue gas as a source of inorganic carbon on the growth of Tetraselmis in a 1000 L industrial-scale split-cylinder internal-loop airlift photobioreactor was examined. The culture medium was recycled after each harvest. Tetraselmis suecica grew very well in this airlift photobioreactor during the 7-month experiment using recycled medium from an electroflocculation harvesting unit. Increased medium SO₄ ^2? concentration as high as 870 mg SO₄ ^2??L^?1 due to flue gas addition and media recycling had no negative effect on the overall growth and productivity of this alga. The potential organic biomass productivity and carbon sequestration using an industrial-scale airlift PBR at International Power Hazelwood, Gippsland, Victoria, Australia, are 178.9?±?30 mg L^?1 day^?1 and 89.15?±?20 mg?‘C’?L^?1 day^?1, respectively. This study clearly indicates the potential of growing Tetraselmis on untreated flue gas and using recycled medium for the purpose of biofuel and CO₂ bioremediation.     

Responses of a new isolated <Emphasis Type="Italic">Cyanobacterium aponinum</Emphasis> strain to temperature,pH, CO<Subscript>2</Subscript> and light quality

A new strain of cyanobacteria was isolated from seawater samples collected near Jimo hot springs, Qingdao, China, and was identified as Cyanobacterium aponinum by 16S rDNA analysis. This study examined the effects of temperature, pH, light quality and high CO₂ concentration on the growth of the cyanobacteria. Results showed that the strain exhibited a higher growth rate (about 168.4 mg L^?1 day^?1) at 35 °C than other temperatures (surviving at up to 50 °C) and a wide growth tolerance to acidic stress (pH 3.0 to 4.0) resulting from either H₂SO₄ or HNO₃. The four light qualities, ranked by greatest to least biomass effect, were as follows: LED white light (LW) > LED red light (LR) > fluorescent white light (FW) > LED blue light (LB), achieving a higher lighting effect at a LW light intensity (60 μmol photons m^?2 s^?1) lower than other light qualities, which implied less energy consumption therewith. This strain demonstrates excellent CO₂ tolerance at least 10% CO₂ with the highest productivity in biomass (about 337.8 mg L^?1 day^?1) measured at 1% CO₂ level. Results indicate that this strain is a promising candidate for use in biofixation of CO₂ from flue gases emitted by thermoelectric plants.     

The growth of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> as influenced by CO<Subscript>2</Subscript>, light,and flue gases

In order to achieve recognition as environmentally friendly production, flue gases should be used as a CO₂ source for growing the microalgae Chlorella sorokiniana when used for hydrogen production. Flue gases from a waste incinerator and from a silicomanganese smelter were used. Before testing the flue gases, the algae were grown in a laboratory at 0.04, 1.3, 5.9, and 11.0 % (v/v) pure CO₂ gas mixed with fresh air. After 5 days of growth, the dry biomass per liter algal culture reached its maximum at 6.1 % CO₂. A second experiment was conducted in the laboratory at 6.2 % CO₂ at photon flux densities (PFD) of 100, 230, and 320 μmol photons m^?2 s^?1. After 4 days of growth, increasing the PFD increased the biomass production by 67 and 108 % at the two highest PFD levels, as compared with the lowest PFD. A bioreactor system containing nine daylight-exposed tubes and nine artificial light-exposed tubes was installed on the roof of the waste incinerator. The effect of undiluted flue gas (10.7 % CO₂, 35.8 ppm NO _x , and 38.6 ppm SO₂), flue gas diluted with fresh air to give 4.2 % CO₂ concentration, and 5.0 % pure CO₂ gas was studied in daylight (21.4?±?9.6 mol photons m^?2 day^?1 PAR, day length 12.0 h) and at 135 μmol photons m^?2 s^?1 artificial light given 24 h day^?1 (11.7?±?0.0 mol photons m^?2 day^?1 PAR). After 4 days’ growth, the biomass production was the same in the two flue gas concentrations and the 5 % pure CO₂ gas control. The biomass production was also the same in daylight and artificial light, which meant that, in artificial light, the light use efficiency was about twice that of daylight. The starch concentration of the algae was unaffected by the light level and CO₂ concentration in the laboratory experiments (2.5–4.0 % of the dry weight). The flue gas concentration had no effect on starch concentration, while the starch concentration increased from about 1.5 % to about 6.0 % when the light source changed from artificial light to daylight. The flue gas from the silicomanganese smelter was characterized by a high CO₂ concentration (about 17 % v/v), low oxygen concentration (about 4 %), about 100 ppm NO _x , and 1 ppm SO₂. The biomass production using flue gas significantly increased as compared with about 5 % pure CO₂ gas, which was similar to the biomass produced at a CO₂ concentration of 10–20 % mixed with N₂. Thus, the enhanced biomass production seemed to be related to the low oxygen concentration rather than to the very high CO₂ concentration.     

Magnetophoretic harvesting of freshwater microalgae using polypyrrole/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocomposite and its reusability

A magnetophoretic harvesting agent, a polypyrrole/Fe₃O₄ magnetic nanocomposite, is proposed as a cost and energy efficient alternative to recover biomass of the microalgae Botryococcus braunii, Chlorella protothecoides, and Chlorella vulgaris from their culture media. The maximal recovery efficiency reached almost 99 % for B. braunii, 92.4 % for C. protothecoides, and 90.8 % for C. vulgaris. The maximum adsorption capacity (Q ₀) of the magnetic nanocomposite for B. braunii (63.49 mg dry biomass mg^?1 PPy/Fe₃O₄) was higher than that for C. protothecoides (43.91 mg dry biomass mg^?1 PPy/Fe₃O₄) and C. vulgaris (39.98 mg dry biomass mg^?1 PPy/Fe₃O₄). The highest harvesting efficiency for all the studied microalgae were at pH 10.0, and measurement of zeta-potential confirmed that the flocculation was induced by charge neutralization. This study showed that polypyrrole/Fe₃O₄ can be a promising flocculant due to its high efficacy, low dose requirements, short settling time, its integrity with cells, and with great potential for saving energy because of its recyclability.     

High biomass production and CO<Subscript>2</Subscript> fixation from biogas by <Emphasis Type="Italic">Chlorella</Emphasis> and <Emphasis Type="Italic">Scenedesmus</Emphasis> microalgae using tequila vinasses as culture medium

Tequila vinasses (TVs) generated during Tequila production are brown liquid residues rich in nutrients. The nutrient content of agro-industrial effluents represents an excellent resource to support low-cost biomass production of microalgae; nonetheless, it is crucial to select the suitable microalgal strain to attain the highest biomass production in each residue used. In this study, biomass production, CO₂ fixation from biogas, and cell compound accumulation by Chlorella vulgaris U162, Chlorella sp., Scenedesmus obliquus U169, and Scenedesmus sp. using biodigested and filtered TVs as culture medium were evaluated and compared with the conventional microalgal culture media, C30, BG-11, Bold 3N, and Bristol. The four microalgae evaluated attained the highest biomass production and CO₂ fixation rate cultured in both residues, accumulating mainly carbohydrates and proteins although the most appropriate microalga to be cultured in TVs was Chlorella sp., recording 2.30 g L^?1. Moreover, the nutrient ratio of filtered TVs was ideal to support biomass production while biodigested TVs need to be supplemented with nitrogen. Overall, these results demonstrated that tequila vinasses are an excellent resource to support high and quick biomass production of microalgae, which can be used to obtain biofuels as ethanol, biogas, and supplement food depicting an extra benefit during the appropriate disposal of this residue.     

Effect of high CO<Subscript>2</Subscript> concentrations on the growth and macromolecular composition of a heat- and high-light-tolerant microalga

A green microalga, Acutodesmus sp., a close relative of Acutodesmus deserticola, was isolated from the wastewater discharges of an oil refinery in India. This study examined the effects of light intensity, temperature, pH, and high-CO₂ treatments (up to 20 %) on the growth of the alga and investigated the effects of different CO₂ treatments on its macromolecular composition (protein, carbohydrate, and lipids). Under controlled laboratory conditions, the alga showed high growth rates over a wide range of light (up to 700 μmol photons m^?2 s^?1), temperature (up to 40 °C), and pH (5–10) conditions. In the stationary phase, the highest protein and carbohydrate content was found to be 71.52 and 40.72 % of dry weight at 5 and 15 % CO₂, respectively. After 5 days of cultivation, the maximum dry weight biomass attained in these cultures was 1.149, 1.99, 1.75, and 1.65 g L^?1 at 5, 10, 15, and 20 % CO₂, respectively, indicating that this strain has significant tolerance to CO₂. These results indicate that this strain is a promising candidate for use in biofixation of CO₂ from the flue gases emitted by industries, and it also has a strong potential as a feedstock for value-added substances.     

Effect of cement industry flue gas simulation on the physiology and photosynthetic performance of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis>

Cement plants account for significant emissions of CO₂ and other pollutants into the atmosphere. As a means for its mitigation, we tested the effect of a cement industry-based flue gas simulation (FGS — 18% CO₂, 9% O₂, 300 ppm NO₂, 140 ppm SO₂) on the green alga, Chlorella sorokiniana. Culture pH, cell density, cell viability and productivity, specific growth rates, photosynthetic performance, and biochemical composition were monitored. The treatments consisted of different FGS volumes (0.1, 0.3, 0.8, 1.5, 6, and 48 L day^?1) that were applied in a series of laboratory-scale semi-continuous batch cultures under controlled conditions. Controls were exposed to 18% CO₂ enriched air. Cell density showed that C. sorokiniana was able to grow in all treatments, but compared to the controls, low pH (~ 5.0) caused by 48 L FGS day^?1 led to 27% decrease in specific growth rate. Increasing FGS exposure decreased maximum and operational quantum yields obtained by pulse amplitude modulated fluorometry, while photochemical quenching remained constant (~ 0.93). The α and rETR _max parameters calculated from rapid light curves decreased with increasing FGS exposure. Total proteins and carbohydrates (per cell basis) increased after 6 and 48 L FGS day^?1, which can be advantageous for biotechnological applications, but cell productivity (cells L^?1 day^?1) decreased. Despite the effects in physiology, C. sorokiniana could withstand a pH range of 6.0–5.0 imposed by 48 L FGS day^?1. Overall, C. sorokiniana can be considered a robust species in flue gas bioremediation.     

Application of sodium erythorbate to promote the growth of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>

Sodium erythorbate (NaE) is a common antioxidant in food processing. In this study, the abilities of NaE to reduce photosynthetic oxygen accumulation in culture medium and improve microalgal growth were evaluated using the green microalga Chlorella vulgaris and glucose as a reference. NaE (from 2.0 to 16.0 g L^?1) led to a lower accumulation of dissolved oxygen (DO) in a concentration-dependent manner. A significant negative correlation (p < 0.05) between the optical density (OD₆₈₀) and DO level suggested that algal growth was promoted by NaE through depleting oxygen in the medium. After 12 days of cultivation, maximum OD₆₈₀ and biomass were obtained with a NaE dosage of 8.0 g L^?1 (respectively, 3.99 and 6.26 times greater than in the control without NaE). Compared with this dosage group which maintained an appropriate low DO level (2 to 6 mg L^?1), higher dosage groups showed relatively little growth promotion due to an insufficiency of DO (<2 mg L^?1). When glucose was added into mixotrophic systems for C. vulgaris, to the same total carbon amount as NaE, DO fell rapidly to less than 2 mg L^?1 owing to its greater consumption (43.9%) compared to that of NaE (16.7%). Furthermore, in the NaE treatment, the pigment contents, cell density, and algal biomass were, respectively, 4.17 to 4.44 times, 2.67 times, and 1.21 times greater than in the glucose treatment. These findings indicate that algal autotrophic growth could be enhanced effectively by NaE through the moderate control of DO.     

Process Engineering for High-Cell-Density Cultivation of Lipid Rich Microalgal Biomass of <Emphasis Type="Italic">Chlorella</Emphasis> sp. FC2 IITG

In the present study, process engineering strategy was applied to achieve lipid-rich biomass with high density of Chlorella sp. FC2 IITG under photoautotrophic condition. The strategy involved medium optimization, intermittent feeding of limiting nutrients, dynamic change in light intensity, and decoupling growth and lipid induction phases. Medium optimization was performed using combinations of artificial neural network or response surface methodology with genetic algorithm (ANN-GA and RSM-GA). Further, a fed-batch operation was employed to achieve high cell density with intermittent feeding of nitrate and phosphate along with stepwise increase in light intensity. Finally, mutually exclusive biomass and lipid production phases were decoupled into two-stage cultivation process: biomass generation in first stage under nutrient sufficient condition followed by lipid enrichment through nitrogen starvation. The key findings were as follows: (i) ANN-GA resulted in an increase in biomass titer of 157 % (0.95 g L^?1) in shake flask and 42.8 % (1.0 g L^?1) in bioreactor against unoptimized medium at light intensity of 20 μE m^?2 s^?1; (ii) further optimization of light intensity in bioreactor gave significantly improved biomass titer of 5.6 g L^?1 at light intensity of 250 μE m^?2 s^?1; (iii) high cell density of 13.5 g L^?1 with biomass productivity of 675 mg L^?1 day^?1 was achieved with dynamic increase in light intensity and intermittent feeding of limiting nutrients; (iv) finally, two-phase cultivation resulted in biomass titer of 17.7 g L^?1 and total lipid productivity of 313 mg L^?1 day^?1 which was highest among Chlorella sp. under photoautotrophic condition.     

Energetic evaluation of an internally illuminated photobioreactor for algal cultivation

An annular internally illuminated photobioreatcor (IIPBR) configuration based on the airlift/bubble column principles was developed and validated at an 18 l prototype scale using Scenedemus sp. and Nannochloropsis salina in batch and semi-continuous modes, at constant light supply and constant gas-to-culture volume ratio, but at varying CO₂-to-air ratios. Highest biomass production was recorded at CO₂-to-air ratio of 4% with Scenedesmus sp. and at 1% with Nannochloropsis salina. The energetic performance of this IIPBR was quantified in terms of biomass productivity per unit energy input, P/E (g W^?1 day^?1), considering energy input for illumination and for pneumatic mixing and circulation. Under optimal conditions, the IIPBR evaluated in this study achieved P/E of 1.42 g W^?1 day^?1 for Scenedesmus sp. and P/E of 0.34 g W^?1 day^?1 for Nannochloropsis salina. These P/E values are better than those estimated for airlift and bubble column photobioreactor configurations reported in the literature.     

Improvement of biomass and fatty acid productivity in ocean cultivation of <Emphasis Type="Italic">Tetraselmis</Emphasis> sp. using hypersaline medium

In this study, hypersaline media were used for ocean cultivation of the marine microalga Tetraselmis sp. KCTC12432BP for enhanced biomass and fatty acid (FA) productivity. Hypersaline media (55, 80, and 105 PSU) were prepared without sterilization by addition of NaCl to seawater obtained from Incheon, Korea. The highest biomass productivity was obtained at 55 PSU (0.16 g L^?1 day^?1) followed by 80 PSU (0.15 g L^?1 day^?1). Although the specific growth rate of Tetraselmis decreased at salinities higher than 55 PSU, prevention of contamination led to higher biomass productivity at 80 PSU than at 30 PSU (0.03 g L^?1 day^?1). FA content of algal biomass increased as salinity increased to 80 PSU, above which it declined, and FA productivity was highest at 80 PSU. Ocean cultivation of Tetraselmis was performed using 50-L tubular module photobioreactors and 2.5-kL square basic ponds, closed- and open-type ocean culture systems, respectively. Culturing microalgae in hypersaline medium (80 PSU) improved biomass productivities by 89 and 152% in closed and open cultures, respectively, compared with cultures with regular salinity. FA productivity was greatly improved by 369% in the closed cultures. The efficacy of salinity shift and N-deficiency to enhance FA productivity was also investigated. Lowering salinity to 30 PSU with N-starvation following cultivation at 80 PSU improved FA productivity by 19% in comparison with single-stage culture without N-deficiency at 30 PSU. The results show that salinity manipulation could be an effective strategy to improve biomass and FA productivity in ocean cultivation of Tetraselmis sp.     

Impact of elevated CO<Subscript>2</Subscript> in <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> rooted stem cuttings inoculated with <Emphasis Type="Italic">Frankia</Emphasis>

Impact of different levels of elevated CO ₂ on the activity of Frankia (Nitrogen-fixing actinomycete) in Casuarina equisetifolia rooted stem cuttings has been studied to understand the relationship between C. equisetifolia, Frankia and CO₂. The stem cuttings of C. equietifolia were collected and treated with 2000 ppm of Indole Butyric Acid (IBA) for rooting. Thus vegetative propagated rooted stem cuttings of C. equisetifolia were inoculated with Frankia and placed in the Open top chambers (OTC) with elevated CO₂ facilities. These planting stocks were maintained in the OTC for 12 months under different levels of elevated CO₂ (ambient control, 600 ppm, 900 ppm). After 12 months, the nodule numbers, bio mass, growth, and photosynthesis of C. equisetifolia rooted stem cuttings inoculated with Frankia were improved under 600 ppm of CO₂. The rooted stem cuttings of C. equisetifolia inoculated with Frankia showed a higher number of nodules under 900 ppm of CO₂ and cuttings without Frankia inoculation exhibited poor growth. Tissue Nitrogen (N) content was also higher under 900 ppm of CO₂ than ambient control and 600 ppm levels. The photosynthetic rate was higher (17.8 μ mol CO₂ m^?2 s^?1) in 900 ppm of CO₂ than in 600 ppm (13.2 μ mol CO₂ m^?2 s^?1) and ambient control (8.3 μ mol CO₂ m^?2 s^?1). This study showed that Frankia can improve growth, N fixation and photosynthesis of C. equietifolia rooted stem cuttings under extreme elevated CO₂ level conditions (900 ppm).     

Utilization of gaseous emissions from a methanol plant for cultivation of <Emphasis Type="Italic">Acutodesmus obliquus</Emphasis>

This study aimed to culture the green alga Acutodesmus obliquus utilizing the gaseous emissions containing a high concentration of CO₂ (99.13 %) from a methanol plant and study the tolerance of microalgae. The effect of CO₂ concentration, aeration rate, inoculum concentration, intermittent sparging, and nitrogen sources on the growth of A. obliquus was examined. Acutodesmus obliquus also was cultivated in a 500-L pilot outdoor tubular photobioreactor (OTP) to advance the laboratory scale system to outdoor scale-up applications. The results showed that A. obliquus could tolerate high CO₂ concentrations of 50 %, and a maximum biomass of 0.935 g L^?1 (dry weight) was achieved at 20 % CO₂. An aeration rate of 500 mL min^?1, inoculum concentration (optical density at 680 nm [OD₆₈₀]?=?0.3), and intermittent sparging of 10 min per 2 h enhanced growth to the optimum and influenced culture pH and photosynthesis. Urea as a nitrogen source was shown to be more beneficial to cell growth. A urea concentration of 0.3 g L^?1 and an N/P ratio of 15 led to maximum biomass accumulation thus enhancing the gaseous emission utilization efficiency. In conclusion, this work demonstrated that gaseous emissions containing high concentration of CO₂ from a methanol plant could be directly introduced into A. obliquus cultures and that A. obliquus was suitable well for large-scale outdoor cultivation in a tubular photobiorecator.     

High-performance recombinant protein production with <Emphasis Type="Italic">Escherichia coli</Emphasis> in continuously operated cascades of stirred-tank reactors

The microbial expression of intracellular, recombinant proteins in continuous bioprocesses suffers from low product concentrations. Hence, a process for the intracellular production of photoactivatable mCherry with Escherichia coli in a continuously operated cascade of two stirred-tank reactors was established to separate biomass formation (first reactor) and protein expression (second reactor) spatially. Cascades of miniaturized stirred-tank reactors were implemented, which enable the 24-fold parallel characterization of cascade processes and the direct scale-up of results to the liter scale. With PAmCherry concentrations of 1.15 g L^?1 cascades of stirred-tank reactors improved the process performance significantly compared to production processes in chemostats. In addition, an optimized fed-batch process was outperformed regarding space–time yield (149 mg L^?1 h^?1). This study implicates continuous cascade processes to be a promising alternative to fed-batch processes for microbial protein production and demonstrates that miniaturized stirred-tank reactors can reduce the timeline and costs for cascade process characterization.     

Biomass productivity of two <Emphasis Type="Italic">Scenedesmus</Emphasis> strains cultivated semi-continuously in outdoor raceway ponds and flat-panel photobioreactors

Semi-continuous algal cultivation was completed in outdoor flat-panel photobioreactors (panels) and open raceway ponds (raceways) from February 17 to May 7, 2015 for side-by-side comparison of areal productivities at the Arizona Center for Algae Technology and Innovation in Mesa, AZ, USA. Experiments used two strains of Scenedesmus acutus (strains LB 0414 and LB 0424) to assess productivity, areal density, nutrient removal, and harvest volume across cultivation systems and algal strains. Panels showed an average biomass productivity of 19.0?±?0.6 g m^?2 day^?1 compared to 6.62?±?2.3 g m^?2 day^?1 for raceways. Photosynthetic efficiency ranged between 1.32 and 2.24 % for panels and between 0.30 and 0.68 % for raceways. Panels showed an average nitrogen consumption rate of 38.4?±?8.6 mg N L^?1 day^?1. Cultivation in raceways showed a consumption rate of 3.8?±?2.5 and 7.1?±?4.2 mg N L^?1 day^?1 for February/March and April/May, respectively, due to increase in biomass productivity. Excess nutrients were required to prevent a decrease in productivity. Daily biomass harvest volumes between 18 and 36 % from panels did not affect culture productivity, but density decreased with increased harvest volume. High cultivation temperatures above 30 °C caused strain LB 0414 to lyse and crash. Strain LB 0424 did not show any difference in biomass productivity when peak temperatures reached 34, 38, or 42 °C, but showed decreased productivity when the peak temperature during cultivation was 30 °C. Using algal strains with different temperature tolerances can generate increased annual biomass productivity.     

Regulation of carbon metabolic fluxes in response to CO<Subscript>2</Subscript> supplementation in phototrophic <Emphasis Type="Italic">Chlorella vulgaris</Emphasis>: a cytomic and biochemical study

As one of the promising species of microalgae for biofuel production, Chlorella vulgaris CS-42 was cultivated phototrophically in two cylindrical photobioreactors with aeration of 5 % (v/v) CO₂ or air for 13 days to evaluate the effects of CO₂ supplementation on biomass, CO₂ fixation performance, and biochemical content. Significant increases of specific growth rate and total carbon content in biomass resulting in a higher CO₂ fixation rate were found with 5 % CO₂. The maximum biomass concentration, carbohydrate and fatty acid contents with 5 % CO₂ were significantly higher than those with air, while carbohydrate biosynthesis was most affected as compared to other biochemical components. Cytomic analysis revealed a rapid accumulation of neutral lipid in the late growth phase with more lipid bodies visualized by confocal laser scanning microscopy (CLSM), when nitrate consumption was accelerated with CO₂ supplementation. Gas chromatography mass spectrometry (GC-MS) analysis indicated that 5 % CO₂ favored the formation of C18:2, which led to a decrease in the degree of lipid unsaturation (DLU). These results proved that CO₂ supplementation was one of the most efficient methods to significantly prompt the growth of microalgae and increase the C/N ratio in the medium, which in turn regulated the carbon metabolic flux to enhance neutral lipid and fatty acid production in C. vulgaris.     

Photosynthetic CO<Subscript>2</Subscript> uptake in seedlings of two tropical tree species exposed to oscillating elevated concentrations of CO<Subscript>2</Subscript>

Do short-term fluctuations in CO₂ concentrations at elevated CO₂ levels affect net CO₂ uptake rates of plants? When exposed to 600 μl CO₂ l^?1, net CO₂ uptake rates in shoots or leaves of seedlings of two tropical C₃ tree species, teak (Tectona grandis L. f.) and barrigon [Pseudobombax septenatum (Jacq.) Dug.], increased by 28 and 52% respectively. In the presence of oscillations with half-cycles of 20 s, amplitude of ca. 170 μl CO₂ l^?1 and mean of 600 μl CO₂ l^?1, the stimulation in net CO₂ uptake by the two species was reduced to 19 and 36%, respectively, i.e. the CO₂ stimulation in photosynthesis associated with a change in exposure from 370 to 600 μl CO₂ l^?1 was reduced by a third in both species. Similar reductions in CO₂-stimulated net CO₂ uptake were observed in T. grandis exposed to 40-s oscillations. Rates of CO₂ efflux in the dark by whole shoots of T. grandis decreased by 4.8% upon exposure of plants grown at 370 μl CO₂ l^?1 to 600 μl CO₂ l^?1. The potential implications of the observations on CO₂ oscillations and dark respiration are discussed in the context of free-air CO₂ enrichment (FACE) systems in which short-term fluctuations of CO₂ concentration are a common feature.     

Bicarbonate-based carbon capture and algal production system on ocean with floating inflatable-membrane photobioreactor

This study aims to develop a low-cost microalgae culture system which uses a simple closed vessel as photobioreactor to save manufacturing cost, waves for mixing to save energy cost, and high concentration of bicarbonate for carbon supply to avoid the high cost of CO₂-bubbling pipeline construction on the ocean as well as to control pH by buffering the effect of bicarbonate/carbonate. To test this idea, the alkalihalophilic cyanobacterium Euhalothece sp. was cultured with 1.0 M NaHCO₃ in small-scale floating photobioreactors (PBRs) on 10-cm-high artificial waves at first. The final biomass concentration was up to 0.91 and 1.47 g L^?1 for indoor and outdoor cultures, respectively. However, the recorded dissolved oxygen (DO) was occasionally over-saturated (> 500% of air saturation), indicating mass transfer problem. k _L a in these PBRs with different culture depth was measured then, and the results showed great variation, from 0.13 to 4.87 h^?1. At the scale of 1.0 m², this floating PBR was made with low-cost membrane and inflatable design. It was placed on the ocean surface and mixed with natural waves. Biomass concentration of 1.63 g L^?1 and productivity of 8.27 g m^?2 day^?1 were obtained in this culture. With these results, the feasibility of a low-cost microalgae culture system was proven, which could systematically reduce the cost of photobioreactor manufacturing, operating, and maintenance.