Optimization of aeration for biodiesel production by <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis> grown in municipal wastewater

Despite the significant breakthroughs in research on microalgae as a feedstock for biodiesel, its production cost is still much higher than that of fossil diesel. One possible solution to overcome this problem is to optimize algal growth and lipid production in wastewater. The present study examines the optimization of pretreatment of municipal wastewater and aeration conditions in order to enhance the lipid productivity of Scenedesmus obliquus. Results showed that no significant differences were recorded in lipid productivity of S. obliquus grown in primary settled or sterilized municipal wastewater; however, ultrasound pretreatment of wastewater significantly decreased the lipid production. Whereas, aeration rates of 0.2 vvm significantly increased lipid content by 51 %, with respect to the non-aerated culture, which resulted in maximum lipid productivity (32.5 mg L^?1 day^?1). Furthermore, aeration enrichment by 2 % CO₂ resulted in increase of lipid productivity by 46 % over the CO₂ non-enriched aerated culture. Fatty acid profile showed that optimized aeration significantly enhanced monounsaturated fatty acid production, composed mainly of C18:1, by 1.8 times over the non-aerated S. obliquus culture with insignificant changes in polyunsaturated fatty acid proportion; suggesting better biodiesel characteristics for the optimized culture.     

Optimization of biomass and fatty acid productivity of Scenedesmus obliquus as a promising microalga for biodiesel production

Nowadays, microalgae are discussed as a promising feedstock for biodiesel production. The present study examines the possibility of enhancement of fatty acid productivity of Scenedesmus obliquus by modifications of the culture medium composition. The effect of different concentrations of sodium bicarbonate, salinity, potassium nitrate, glycerol and sugarcane molasses on the enhancement of biomass and esterified fatty acids production was studied. NaHCO₃ caused an increase in the biomass productivity at low concentrations (0.5 g L^?1), while negatively affected fatty acid productivity at all tested concentrations. Increase of salinity enhanced both biomass and fatty acid productivity. The optimum NaCl concentration and sea water ratio were 0.94 g L^?1 and 25 % which resulted in 56 and 39 % increase in fatty acid productivity, respectively. Nitrogen deficiency showed increase in fatty acid content by 54 % over control but fatty acid productivity was decreased as a result of growth inhibition. Nitrogen-free cultures and cultures treated with ?50 % concentrations of KNO₃ showed 96 and 42 % decrease in EFA productivity, respectively, as compared with the control. Addition of 0.05 and 0.1 M of glycerol increased the biomass productivity by 6 and 5 %, respectively but showed no significant effect on fatty acid productivity as a result of decrease in fatty acid content. Finally, usage of sugarcane molasses stimulated both biomass and fatty acid content. The increase in fatty acid productivity was 32, 65 and 73 % above the control level at 1, 3 and 5 g L^?1 of sugarcane molasses, respectively.     

Lipid productivity and fatty acid composition-guided selection of Chlorella strains isolated from Malaysia for biodiesel production

The need to develop biomass-based domestic production of high-energy liquid fuels (biodiesel) for transportation can potentially be addressed by exploring microalgae with high lipid content. Selecting the strains with adequate oil yield and quality is of fundamental importance for a cost-efficient biofuel feedstock production based on microalgae. This work evaluated 29 strains of Chlorella isolated from Malaysia as feedstock for biodiesel based on volumetric lipid productivity and fatty acid profiles. Phylogenetic studies based on 18S rRNA gene revealed that majority of the strains belong to true Chlorella followed by Parachlorella. The strains were similarly separated into two groups based on fatty acid composition. Of the 18 true Chlorella strains, Chlorella UMACC187 had the highest palmitic acid (C16:0) content (71.3?±?4.2 % total fatty acids, TFA) followed by UMACC84 (70.1?±?0.7 %TFA), UMACC283 (63.8?±?0.7 %TFA), and UMACC001 (60.3?±?4.0 %TFA). Lipid productivity of the strains at exponential phase ranged from 34.53 to 230.38 mg L^?1 day^?1, with Chlorella UMACC050 attaining the highest lipid productivity. This study demonstrated that Chlorella UMACC050 is a promising candidate for biodiesel feedstock production.     

Biomass and Lipid Production of Dinoflagellates and Raphidophytes in Indoor and Outdoor Photobioreactors

The principal fatty acids from the lipid profiles of two autochthonous dinoflagellates (Alexandrium minutum and Karlodinium veneficum) and one raphidophyte (Heterosigma akashiwo) maintained in bubble column photobioreactors under outdoor culture conditions are described for the first time. The biomass production, lipid content and lipid productivity of these three species were determined and the results compared to those obtained when the strains were cultured indoors. Under the latter condition, the biotic values did not significantly differ among species, whereas under outdoor conditions, differences in both duplication time and fatty acids content were observed. Specifically, A. minutum had higher biomass productivity (0.35 g·L^?1 day^?1), lipid productivity (80.7 mg lipid·L^?1 day^?1) and lipid concentration (252 mg lipid·L^?1) at harvest time (stationary phase) in outdoor conditions. In all three strains, the growth rate and physiological response to the light and temperature fluctuations of outdoor conditions greatly impacted the production parameters. Nonetheless, the species could be successfully grown in an outdoor photobioreactor and were of sufficient robustness to enable the establishment of long-term cultures yielding consistent biomass and lipid production.     

Triacylglycerol content,productivity and fatty acid profile in Scenedesmus acutus PVUW12

A detailed lipid characterization of Scenedesmus acutus PVUW12, with emphasis on the evaluation of triacylglycerols (TAGs) as a biodiesel feedstock, is presented. When algal cells were grown in nitrogen-free medium (N stress), a lipid increase was detected that was mainly due to TAG accumulation. In situ fluorescence measurements allowed the kinetics and extent of neutral lipid accumulation to be followed. Under N stress, the productivity of total lipids and TAGs increased significantly (80.99 and 63.74 mg L^?1 day^?1, respectively) compared with controls (29.51 and 16.23 mg L^?1 day^?1, respectively). Monounsaturated fatty acids were the major fraction and increased further (49.74 %) in stressed cells, with oleic acid as the most abundant compound (46.97 %). The polyunsaturated fatty acid composition of this algal oil appears to meet the European Standard EN 14214. These results indicate that S. acutus oil meets the requirements for its use as a biodiesel feedstock. Since this strain was also proposed for wastewater bioremediation, this opens up the possibility of its use in an integrated system combined with biofuel production.     

Lipid productivity and fatty acid composition in Chlorella and Scenepdesmus strains grown in nitrogen-stressed conditions

Thirty Chlorella and 30 Scenedesmus strains grown in nitrogen-stressed conditions (70 mg L^?1 N) were analyzed for biomass accumulation, lipid productivity, protein, and fatty acid (FA) composition. Scenedesmus strains produced more biomass (4.02?±?0.73 g L^?1) after 14 days in culture compared to Chlorella strains (2.57?±?0.12 g L^?1). Protein content decreased and lipid content increased from days 8 to 14 with an increase in triacylglycerol (TAG) accumulation in most strains. By day 14, Scenedesmus strains generally had higher lipid productivity (53.5?±?3.7 mg lipid L^?1 day^?1) than Chlorella strains (35.1?±?2.8 mg lipid L^?1 day^?1) with the lipids consisting mainly of C16–18 TAGs. Scenedesmus strains generally had a more suitable FA profile with higher amounts of saturated fatty acids and monounsaturated fatty acids (MUFAs) and a smaller polyunsaturated fatty acid (PUFA) component. Chlorella strains had a larger PUFA component and smaller MUFA component. The general trend in the FA composition of Chlorella strains was oleic > palmitic > α-linolenic = linoleic > eicosenoic > heptadecenoic > stearic acid. For Scenedesmus strains, the general trend was oleic > palmitic > linoleic > α-linolenic > stearic > eicosenoic > palmitoleic > heptadecenoic acid. The most promising strains with the highest lipid productivity and most suitable FA profiles were Scenedesmus sp. MACC 401, Scenedesmus soli MACC 721, and Scenedesmus ecornis MACC 714. Although Chlorella sp. MACC 519 had lower lipid productivity, the FA profile was good with a lower PUFA component compared to the other Chlorella strains analyzed and a low linolenic acid concentration.     

Biomass and lipid enhancement in Ankistrodesmus sp. cultured with reused and minimal nutrients media

Microalgae are a promising feedstock for biofuel production. Lipid content in microalgae could be enhanced under nutrient depletion. This work investigated the effect of the nutrient on lipid accumulation in Ankistrodesmus sp. culture. Batch cultures were carried out using fresh BG11 medium, and after the harvest, the medium was reused for the next culture; this method was repeated two times. The maximum lipid productivity of 29.75 mg L^?1 day^?1 was obtained from the culture with the second reuse medium. In continuous cultures, Ankistrodesmus sp. was cultured in both fresh and modified BG11 mediums. The modified BG11 medium was adjusted to resemble the content of the first reuse medium. As a comparison between batch and continuous cultures, it was proven that the productivity in the continuous culture was better than in the batch, where the achievable maximum biomass and lipid were 188.30 and 38.32 mg L^?1 day^?1. The maximum lipid content of 34.22% was obtained from the continuous culture at a dilution rate of 0.08 day^?1, whereas the maximum saturated and unsaturated fatty acid productivities of 79.96 and 104.54 mg L^?1 day^?1 were obtained at a dilution rate of 0.16 day^?1.     

Interspecific biodiversity enhances biomass and lipid productivity of microalgae as biofuel feedstock

Large improvements in biomass and lipid production are required to make massive scale algal biodiesel production an economic reality. The application of the biodiversity strategy to enhance algal biomass as biofuel feedstock is little. The algal diversity was manipulated in this study to investigate the effects of a combination of biodiversity complementarity and a new medium consisting of seawater and agricultural fertilizer on lipid productivity. The algae diverse community includes two strains of Dunaliella salina (Dunaliella salina 19/30 and 19/18) and three species of Nannochloropsis (Nannochloropsis oculata, Nannochloropsis salina, and Nannochloropsis gaditana). The results showed that the most diverse community (5 species) produced an average of sixfold more biomass in the new medium than did the standard f/2 culture medium. The most diverse polyculture had the highest growth rate (1.01 day^?1), biomass (1.2 g L^?1), and lipid productivity (0.31 g L^?1 day^?1). The assessment of algal polycultures relative to monocultures is particularly interesting and novel for this biofuel field, and the observations that these polycultures resulted in significant lipid productivity improvements are very useful addition to the biofuel research. The possible mechanism (resource diversity) to explain the synergy in mixed cultures warrants further investigation.     

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.     

Productivity and biochemical composition of <Emphasis Type="Italic">Tetradesmus obliquus</Emphasis> and <Emphasis Type="Italic">Phaeodactylum tricornutum</Emphasis>: effects of different cultivation approaches

The present work evaluated biomass productivity, carbon dioxide fixation rate, and biochemical composition of two microalgal species, Phaeodactylum tricornutum (Bacillariophyta) and Tetradesmus obliquus (Chlorophyta), cultivated indoors in high-technology photobioreactors (HT-PBR) and outdoors both in pilot ponds and low-technology photobioreactors in a greenhouse in southern Italy. Microalgae were grown in standard media, under nitrogen starvation, and in two liquid digestates obtained from anaerobic digestion of agro-zootechnical and vegetable biomass. P. tricornutum, cultivated in semi-continuous mode in indoor HT-PBRs with standard medium, showed a biomass productivity of 21.0?±?2.3 g m^?2 d^?1. Applying nitrogen starvation, the lipid productivity increased from 2.3 up to 4.5?±?0.5 g m^?2 d^?1, with a 24 % decrease of biomass productivity. For T. obliquus, a biomass productivity of 9.1?±?0.9 g m^?2 d^?1 in indoor HT-PBR was obtained using standard medium. Applying liquid digestates as fertilizers in open ponds, T. obliquus gave a biomass productivity (10.8?±?2.0 g m^?2 d^?1) not statistically different from complete medium such as P. tricornutum (6.5?±?2.2 g m^?2 d^?1). The biochemical data showed that the fatty acid composition of the microalgal biomass was affected by the different cultivation conditions for both microalgae. In conclusion, it was found that the microalgal productivity in standard medium was about doubled in HT-PBR compared to open ponds for P. tricornutum and was about 20 % higher for T. obliquus.     

Biomass,Lipid and Fatty Acid Production in Large-Scale Cultures of the Marine Macroalga Derbesia tenuissima (Chlorophyta)

Biomass productivity was quantified for the marine macroalga Derbesia tenuissima cultivated outdoors at seven stocking densities from 0.25 to 8 g L^?1 for 5 weeks. Total lipids and fatty acid quantity and quality was measured from samples that were freeze-dried, dried by oven (75 °C), food dehydrator (60 °C), or outdoor in the sun (40 °C) or shade (38 °C). Stocking densities of 0.25 to 2 g L^?1 yielded the highest biomass productivities (>20 g dry weight m^?2 day^?1) with no effect on total lipid quantity (11 %), or fatty acid quantity (5.3 %) or quality at any density tested. However, there was an interactive effect of stocking density and drying technique, with a decrease of up to 40 % in polyunsaturated fatty acids in sun-dried compared to freeze-dried biomass. Notably, while fatty acid and biomass productivity may be inseparable in macroalgae, cultivation conditions have a significant carryover effect in the post-harvest delivery of high-quality bio-oils.     

Evaluation of indigenous microalgal isolate Chlorella sp. FC2 IITG as a cell factory for biodiesel production and scale up in outdoor conditions

The present study reports evaluation of an indigenous microalgal isolate Chlorella sp. FC2 IITG as a potential candidate for biodiesel production. Characterization of the strain was performed under photoautotrophic, heterotrophic, and mixotrophic cultivation conditions. Further, an open-pond cultivation of the strain under outdoor conditions was demonstrated to evaluate growth performance and lipid productivity under fluctuating environmental parameters and in the presence of potential contaminants. The key findings were: (1) the difference in cultivation conditions resulted in significant variation in the biomass productivity (73–114 mg l^?1 day^?1) and total lipid productivity (35.02–50.42 mg l^?1 day^?1) of the strain; (2) nitrate and phosphate starvation were found to be the triggers for lipid accumulation in the cell mass; (3) open-pond cultivation of the strain under outdoor conditions resulted in biomass productivity of 44 mg l^?1 day^?1 and total lipid productivity of 10.7 mg l^?1 day^?1; (4) a maximum detectable bacterial contamination of 7 % of the total number of cells was recorded in an open-pond system; and (5) fatty acid profiling revealed abundance of palmitic acid (C16:0), oleic acid (C18:1) and linoleic acid (C18:2), which are considered to be the key elements for suitable quality biodiesel.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

Mixotrophic and photoautotrophic cultivation of 14 microalgae isolates from Saskatchewan, Canada: potential applications for wastewater remediation for biofuel production

Northern regions are generally viewed as unsuitable for microalgal biofuel production due to unfavorable climate and solar insolation levels. However, these conditions can potentially be mitigated by coupling microalgal cultivation to industrial processes such as wastewater treatment. In this study, we have examined the biomass and lipid productivity characteristics of 14 microalgae isolates (Chlorophyta) from the Canadian province of Saskatchewan. Under both photoautotrophic and mixotrophic cultivation, a distinct linear trend was observed between biomass and lipid productivities in the 14 SK isolates. The most productive strain under cultivation in TAP media was Scenedesmus sp.-AMDD which displayed rates of biomass and fatty acid productivities of 80 and 30.7?mg?L^?1?day^?1, respectively. The most productive strain in B3NV media was Chlamydomonas debaryana-AMLs1b which displayed rates of biomass and fatty acid productivities of 51.7 and 5.9?mg?L^?1?day^?1, respectively. In 11 of the isolates tested, secondary municipal wastewater (MCWW) supported rates of biomass productivity between 21 and 33?mg?L^?1?day^?1 with Scenedesmus sp.-AMDD being the most productive. Three strains, Chlamydomonas debaryana-AMB1, Chlorella sorokiniana-RBD8 and Micractinium sp.-RB1b, showed large increases in biomass productivity when cultivated mixotrophically in MCWW supplemented with glycerol. High relative oleic acid content was detected in 10 of the 14 isolates when grown mixotrophically in media supplemented with acetate. There was no detectable effect on the fatty acid profiles in cells cultivated mixotrophically in glycerol-supplemented MCWW. These data indicate that biomass and lipid productivities are boosted by mixotrophic cultivation. Exploiting this response in municipal wastewater is a promising strategy for the production of environmentally sustainable biofuels.     

Statistical evaluation and modeling of cheap substrate-based cultivation medium of Chlorella vulgaris to enhance microalgae lipid as new potential feedstock for biolubricant

Chlorella vulgaris (C. vulgaris) microalga was investigated as a new potential feedstock for the production of biodegradable lubricant. In order to enhance microalgae lipid for biolubricant production, mixotrophic growth of C. vulgaris was optimized using statistical analysis of Plackett–Burman (P-B) and response surface methodology (RSM). A cheap substrate-based medium of molasses and corn steep liquor (CSL) was used instead of expensive mineral salts to reduce the total cost of microalgae production. The effects of molasses and CSL concentration (cheap substrates) and light intensity on the growth of microalgae and their lipid content were analyzed and modeled. Designed models by RSM showed good compatibility with a 95% confidence level when compared to the cultivation system. According to the models, optimal cultivation conditions were obtained with biomass productivity of 0.123 g L^?1 day^?1 and lipid dry weight of 0.64 g L^?1 as 35% of dry weight of C. vulgaris. The extracted microalgae lipid presented useful fatty acid for biolubricant production with viscosities of 42.00 cSt at 40°C and 8.500 cSt at 100°C, viscosity index of 185, flash point of 185°C, and pour point of ?6°C. These properties showed that microalgae lipid could be used as potential feedstock for biolubricant production.     

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.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Inorganic carbon and pH effect on growth and lipid productivity of Tetraselmis suecica and Chlorella sp (Chlorophyta) grown outdoors in bag photobioreactors

There has been considerable interest in cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. However, almost all mass cultures of algae are carbon-limited. Therefore, to reach a high biomass and oil productivities, the ideal selected microalgae will most likely need a source of inorganic carbon. Here, growth and lipid productivities of Tetraselmis suecica CS-187 and Chlorella sp were tested under various ranges of pH and different sources of inorganic carbon (untreated flue gas from coal-fired power plant, pure industrial CO₂, pH-adjusted using HCl and sodium bicarbonate). Biomass and lipid productivities were highest at pH 7.5 (320?±?29.9 mg biomass L^?1 day^?1and 92?±?13.1 mg lipid L^?1 day^?1) and pH 7 (407?±?5.5 mg biomass L^?1 day^?1 and 99?±?17.2 mg lipid L^?1 day^?1) for T. suecica CS-187 and Chlorella sp, respectively. In general, biomass and lipid productivities were pH 7.5?>?pH 7?>?pH 8?>?pH 6.5 and pH 7?>?pH 7.5?=?pH 8?>?pH 6.5?>?pH 6?>?pH 5.5 for T. suecica CS-187 and Chlorella sp, respectively. The effect of various inorganic carbon on growth and productivities of T. suecica (regulated at pH?=?7.5) and Chlorella sp (regulated at pH?=?7) grown in bag photobioreactors was also examined outdoor at the International Power Hazelwood, Gippsland, Victoria, Australia. The highest biomass and lipid productivities of T. suecica (51.45?±?2.67 mg biomass L^?1 day^?1 and 14.8?±?2.46 mg lipid L^?1 day^?1) and Chlorella sp (60.00?±?2.4 mg biomass L^?1 day^?1 and 13.70?±?1.35 mg lipid L^?1 day^?1) were achieved when grown using CO₂ as inorganic carbon source. No significant differences were found between CO₂ and flue gas biomass and lipid productivities. While grown using CO₂ and flue gas, biomass productivities were 10, 13 and 18 %, and 7, 14 and 19 % higher than NaHCO₃, HCl and unregulated pH for T. suecica and Chlorella sp, respectively. Addition of inorganic carbon increased specific growth rate and lipid content but reduced biomass yield and cell weight of T. suecica. Addition of inorganic carbon increased yield but did not change specific growth rate, cell weight or content of the cell weight of Chlorella sp. Both strains showed significantly higher maximum quantum yield (F_v/F_m) when grown under optimum pH.     

Characterization of cell growth and starch production in the marine green microalga Tetraselmis subcordiformis under extracellular phosphorus-deprived and sequentially phosphorus-replete conditions

Microalgal starch is a potential feedstock for biofuel production. Nutrient stress is widely used to stimulate starch accumulation in microalgae. Cell growth and starch accumulation in the marine green microalga Tetraselmis subcordiformis were evaluated under extracellular phosphorus deprivation with initial cell densities (ICD) of 1.5, 3.0, 6.0, and 9.0?×?10⁶ cells mL^?1. The intracellular stored phosphorus supported cell growth when extracellular phosphorus was absent. The maximum starch content of 44.1 % was achieved in the lowest ICD culture, while the maximum biomass productivity of 0.71 g L^?1 day^?1, starch concentration of 1.6 g L^?1, and starch productivity of 0.30 g L^?1 day^?1 were all obtained in the culture with the ICD of 3.0?×?10⁶ cells mL^?1. Appropriate ICD could be used to regulate the intracellular phosphorus concentration and maintain adequate photosynthetic activity to achieve the highest starch productivity, along with biomass and starch concentration. The recovery of phosphorus-deprived T. subcordiformis in medium containing 0.5, 1.0, or 6.0 mM KH₂PO₄ was also tested. Cell growth and starch accumulation ability could be recovered completely. A phosphorus pool in T. subcordiformis was shown to manipulate its metabolic activity under different environmental phosphorus availability. Though lower starch productivity and starch content were achieved under phosphorus deprivation compared with nitrogen- or sulfur-deprived conditions, the higher biomass and starch concentration make T. subcordiformis a good candidate for biomass and starch production under extracellular phosphorus deprivation.     

Effects of different nitrogen, phosphorus, and iron concentrations and salinity on lipid production in newly isolated strain of the tropical green microalga, Scenedesmus dimorphus KMITL

The fatty acid composition, the effect of different concentrations of nitrogen (16.5-344 mg ?L^?1), phosphorus (9–45 mg? L^?1), iron (9–45 mg? L^?1) and salinity levels (0–20 psu) on lipid production in the green microalga Scenedesmus dimorphus KMITL, a new strain isolated from a tropical country, Thailand, were studied. The alga was isolated from a freshwater fish pond, and cultured in Chlorella medium by varying one parameter at a time. The main fatty acid composition of this strain was C16–C18 (97.52 %) fatty acids. A high lipid content was observed in conditions of 16.5 mg? L^?1-N, or 22 mg ?L^?1-P, or 45 mg ?L^?1-Fe, or 5 psu salinity, which accumulated lipids to 20.3?±?0.4, 19.4?±?0.2, 24.7?±?0.5, and 14.3?±?0.2 % of algal biomass, respectively. Increasing lipid content and lipid productivity was noted when the alga was cultured under high iron concentration and high salinity, as well as under reduced phosphorus conditions, whereas nitrogen limitation only resulted in an increased lipid content.