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.     

Microalgae growth on concentrated human urine

In this study, for the first time, a microalga was grown on non-diluted human urine. The essential growth requirements for the species Chlorella sorokiniana were determined for different types of human urine (fresh, hydrolysed, male and female). Batch experimental results using microtiter plates showed that both fresh and synthetic urine supported rapid growth of this species, provided additional trace elements (Cu, Fe, Mn, and Zn) were added. When using hydrolysed urine instead of fresh urine, additional magnesium had to be added as it precipitates during hydrolysis of urea. C. sorokiniana was able to grow on non-diluted urine with a specific growth rate as high as 0.104 h^?1 under light-limited conditions (105 μmol photons m^?2 s^?1), and the growth was not inhibited by ammonium up to a concentration of 1,400 mg NH₄ ⁺-N L^?1. The highest growth rate on human urine was as high as 0.158 h^?1. Because it was demonstrated that concentrated urine is a rich and good nutrient source for the production of microalgae, its application for a large-scale economical and sustainable microalgae production for biochemicals, biofuels and biofertilizers becomes feasible.     

Optimization of CO2 concentration and light intensity for biodiesel production by Chlorella vulgaris FACHB-1072 under nitrogen deficiency with phosphorus luxury uptake

Microalgal biodiesel is an alternative bioenergy for the future. Nitrogen deprivation is usually used to increase lipid content in microalgae, however, it also lowers biomass production, resulting in not much increase of lipid productivity. Our previous study found that phosphorus played an important role in enhancing biodiesel productivity of C. vulgaris FACHB-1072 under nitrogen deficient condition. The aim of this study was to optimize two significant parameters of CO₂ concentration (0.03, 4, 6, 12 %) and light intensity (40, 120, 200 μmol photons m^-2 s^-1) with respect to biodiesel productivity and P uptake rate of C. vulgaris FACHB-1072. It was found that the optimized conditions were 4 % CO₂ concentration and 200 μmol photons m^-2 s^-1 light intensity. The maximum biodiesel productivity was 34.56 mg L^-1 day^-1; 2.7 times higher than the control (nutrient sufficient condition). Phosphorus was accumulated as polyphosphate and its maximum uptake rate was 2.08 mg L^-1 day^-1; twice that of the control. After optimization, the performances under nitrogen deficiency were significantly better compared with those under nitrogen sufficiency, which were rarely reported in literature. Our findings suggest a great potential to combine phosphorus removal from wastewater with biodiesel production via microalgae.     

Potential of diatom consortium developed by nutrient enrichment for biodiesel production and simultaneous nutrient removal from waste water

Because of the decreasing fossil fuel supply and increasing greenhouse gas (GHG) emissions, microalgae have been identified as a viable and sustainable feedstock for biofuel production. The major effect of the release of wastewater rich in organic compounds has led to the eutrophication of freshwater ecosystems. A combined approach of freshwater diatom cultivation with urban sewage water treatment is a promising solution for nutrient removal and biofuel production. In this study, urban wastewater from eutrophic Hussain Sagar Lake was used to cultivate a diatom algae consortium, and the effects of silica and trace metal enrichment on growth, nutrient removal, and lipid production were evaluated. The nano-silica-based micronutrient mixture Nualgi containing Si, Fe, and metal ions was used to optimize diatom growth. Respectively, N and P reductions of 95.1% and 88.9%, COD and BOD reductions of 91% and 51% with a biomass yield of 122.5 mg L^?1 day^?1 and lipid productivity of 37 mg L^?1 day^?1 were observed for cultures grown in waste water using Nualgi. Fatty acid profiles revealed 13 different fatty acids with slight differences in their percentage of dry cell weight (DCW) depending on enrichment level. These results demonstrate the potential of diatom algae grown in wastewater to produce feedstock for renewable biodiesel production. Enhanced carbon and excess nutrient utilization makes diatoms ideal candidates for co-processes such as CO₂ sequestration, biodiesel production, and wastewater phycoremediation.     

Effect of alginate structure and microalgae immobilization method on orthophosphate removal from wastewater

Microalgae play an important role during the tertiary treatment of municipal wastewater. Cell immobilization techniques have been developed in order to improve the quality of the treated wastewater and avoid wash out of the biomass. Since cell immobilization method may affect the nutrient removal efficiency, ten strains of microalgae were immobilized in sodium alginate gel in different-diameter circular screens, and orthophosphate removal efficiency from municipal wastewater was studied. Results indicate that the alginate immobilization screen size and contact surface with wastewater affects the microalgae synthesis activity and thus orthophosphate removal efficiency. Increasing the contact surface by making smaller alginate screens will increase the cation exchange rate and reduce the orthophosphate concentration in the medium. Among all microalgae treatments, Scenedesmus rubescens MCCS 018, Chlamydomonas sp. MCCS 026, and Chroococcus dispersus MCCS 006 had the highest PO ₄ ^3- -P removal efficiency of 68.8%, 71.9%, and 72.3% within 12?days.     

Starvation enhances phosphorus removal from wastewater by the microalga Chlorella spp. co-immobilized with Azospirillum brasilense

In synthetic wastewater, growth and phosphorus absorption by two species of microalgae, Chlorella sorokiniana and Chlorella vulgaris, and in domestic wastewater by C. sorokiniana significantly enhanced after a starvation period of 3 days in saline solution, combined with co-immobilization with the microalgae growth-promoting bacterium (MGPB) Azospirillum brasilense Cd in alginate beads. Starvation of 5 days negatively affected the subsequent growth of C. vulgaris, but not of C. sorokiniana in fresh wastewater. Starvation of immobilized cultures of microalgae separately or microalgae with bacteria, followed by returning the immobilized cultures to the same wastewater did not enhance phosphorus absorption. However, a starvation period followed by subsequent submersion of the cultures in fresh wastewater allowed the continuation of phosphorus absorption. The best phosphorus removal treatment from a batch of synthetic or domestic wastewater was with tandem treatments of wastewater treatment with pre-starved, co-immobilized microalgae and replacement of this culture, after one cycle of phosphorus removal, with a new, similarly starved culture. This combination treatment with two cultures was capable of removing up to 72% of phosphorus from the wastewater. There was a direct correlation between the initial load of phosphorus in the domestic wastewater and the efficiency level of removal, being highest at higher phosphorus loads in co-immobilized cultures. This occurred for both immobilized and co-immobilized cultures. Further, the results showed that negative effects of starving the microalgae were mitigated by the application of the MGPB A. brasilense Cd. This is the first report of this capacity in Azospirillum sp. on a single-cell plant. This study showed that starvation periods, combined with co-immobilization with MGPB, have synergistic effects on absorption of phosphorus from wastewater and merits consideration in designing future biological treatments of wastewater.     

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.     

The air‐lift photobioreactors with flow patterning for high‐density cultures of microalgae and carbon dioxide removal

A photobioreactor containing microalgae is a highly efficient system for converting carbon dioxide (CO₂) into biomass. Using a microalgal photobioreactor as a CO₂ mitigation system is a practical approach to the problem of CO₂ emission from waste gas. In this study, a marine microalga, Chlorella sp. NCTU‐2, was applied to assess biomass production and CO₂ removal. Three types of photobioreactors were designed and used: (i) without inner column (i.e. a bubble column), (ii) with a centric‐tube column and (iii) with a porous centric‐tube column. The specific growth rates (μ) of the batch cultures in the bubble column, the centric‐tube and the porous centric‐tube photobioreactor were 0.180, 0.226 and 0.252 day^?1, respectively. The porous centric‐tube photobioreactor, operated in semicontinuous culture mode with 10% CO₂ aeration, was evaluated. The results show that the maximum biomass productivity was 0.61 g/L when one fourth of the culture broth was recovered every 2 days. The CO₂ removal efficiency was also determined by measuring the influent and effluent loads at different aeration rates and cell densities of Chlorella sp. NCTU‐2. The results show that the CO₂ removal efficiency was related to biomass concentration and aeration rate. The maximum CO₂ removal efficiency of the Chlorella sp. NCTU‐2 culture was 63% when the biomass was maintained at 5.15 g/L concentration and 0.125 vvm aeration (volume gas per volume broth per min; 10% CO₂ in the aeration gas) in the porous centric‐tube photobioreactor.     

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.     

Euglena sp. as a suitable source of lipids for potential use as biofuel and sustainable wastewater treatment

Prolific algal growth in sewage ponds with high organic loads in the tropical regions can provide cost-effective and efficient wastewater treatment and biofuel production. This work examines the ability of Euglena sp. growing in wastewater ponds for biofuel production and treatment of wastewater. The algae were isolated from the sewage treatment plants and were tested for their nutrient removal capability. Compared to other algae, Euglena sp. showed faster growth rates with high biomass density at elevated concentrations of ammonium nitrogen (NH₄-N) and organic carbon (C). Profuse growth of these species was observed in untreated wastewaters with a mean specific growth rate (μ) of 0.28 day^?1 and biomass productivities of 132 mg ?L^?1? day^?1. The algae cultured within a short period of 8 days resulted in the 98 % removal of NH₄-N, 93 % of total nitrogen 85 % of ortho-phosphate, 66 % of total phosphate and 92 % total organic carbon. Euglenoids achieved a maximum lipid content of 24.6 % (w/w) with a biomass density of 1.24 g ?L^?1 (dry wt.). Fourier transform infrared spectra showed clear transitions in biochemical compositions with increased lipid/protein ratio at the end of the culture. Gas chromatography and mass spectrometry indicated the presence of high contents of palmitic, linolenic and linoleic acids (46, 23 and 22 %, respectively), adding to the biodiesel quality. Good lipid content (comprised quality fatty acids), efficient nutrient uptake and profuse biomass productivity make the Euglena sp. as a viable source for biofuel production in wastewaters.     

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.     

Carbon dioxide utilisation of Dunaliella tertiolecta for carbon bio-mitigation in a semicontinuous photobioreactor

Bio-fixation of carbon dioxide (CO₂) by microalgae has been recognised as an attractive approach to offset anthropogenic emissions. Biological carbon mitigation is the process whereby autotrophic organisms, such as microalgae, convert CO₂ into organic carbon and O₂ through photosynthesis; this process through respiration produces biomass. In this study Dunaliella tertiolecta was cultivated in a semicontinuous culture to investigate the carbon mitigation rate of the system. The algae were produced in 1.2-L Roux bottles with a working volume of 1 L while semicontinuous production commenced on day 4 of cultivation when the carbon mitigation rate was found to be at a maximum for D. tertiolecta. The reduction in CO₂ between input and output gases was monitored to predict carbon fixation rates while biomass production and microalgal carbon content are used to calculate the actual carbon mitigation potential of D. tertiolecta. A renewal rate of 45 % of flask volume was utilised to maintain the culture in exponential growth with an average daily productivity of 0.07 g L^?1 day^?1. The results showed that 0.74 g L^?1 of biomass could be achieved after 7 days of semicontinuous production while a total carbon mitigation of 0.37 g L^?1 was achieved. This represented an increase of 0.18 g L^?1 in carbon mitigation rate compared to batch production of D. tertiolecta over the same cultivation period.     

Dual purpose system that treats anaerobic effluents from pig waste and produce Neochloris oleoabundans as lipid rich biomass

Dual purpose systems that treat wastewater and produce lipid rich microalgae biomass have been indicated as an option with great potential for production of biodiesel at a competitive cost. The aim of the present work was to develop a dual purpose system for the treatment of the anaerobic effluents from pig waste utilizing Neochloris oleoabundans and to evaluate its growth, lipid content and lipid profile of the harvested biomass and the removal of nutrients from the media. Cultures of N. oleoabundans were established in 4 L flat plate photobioreactors using diluted effluents from two different types of anaerobic filters, one packed with ceramic material (D1) and another one packed with volcanic gravel (D2). Maximum biomass concentration in D1 was 0.63 g L⁻¹ which was significantly higher than the one found in D2 (0.55 g L⁻¹). Cultures were very efficient at nutrient removal: 98% for NNH₄⁺ and 98% for PO₄³⁻. Regarding total lipid content, diluted eflluents from D2 promoted a biomass containing 27.4% (dry weight) and D1 a biomass containing 22.4% (dry weight). Maximum lipid productivity was also higher in D2 compared to D1 (6.27 ± 0.62 mg L⁻¹ d⁻¹ vs. 5.12 ± 0.12 mg L⁻¹ d⁻¹). Concerning the FAMEs profile in diluted effluents, the most abundant one was C18:1, followed by C18:2 and C16:0. The profile in D2 contained less C18:3 (linolenic acid) than the one in D1 (4.37% vs. 5.55%). In conclusion, this is the first report demonstrating that cultures of N. oleoabundans treating anaerobic effluents from pig waste are very efficient at nutrient removal and a biomass rich in lipids can be recovered. The maximum total lipid content and the most convenient FAMEs profile were obtained using effluents from a digester packed with volcanic gravel.     

Cultivation of a new microalga,Micractinium reisseri,in municipal wastewater for nutrient removal,biomass, lipid,and fatty acid production

Coupling of advanced wastewater treatment with microalgae cultivation for low-cost lipid production was demonstrated in this study. The microalgal species Micractinium reisseri and Scenedesmus obliquus were isolated from municipal wastewater mixed with agricultural drainage. M. reisseri was selected based on the growth rate and cultivated in municipal wastewater (influent, secondary and tertiary effluents) which varied in nutrient concentration. M. reisseri showed an optimal specific growth rate (μ_opt) of 1.15, 1.04, and 1.01 1/day for the influent and the secondary and tertiary effluents, respectively. Secondary effluent supported the highest phosphorus removal (94%) and saturated fatty acid content (40%). The highest lipid content (40%), unsaturated fatty acid content, including monounsaturated and polyunsaturated fatty acids (66%), and nitrogen removal (80%) were observed for tertiary effluent. Fatty acids accumulating in the microalgal biomass (M. reisseri) were mainly composed of palmitic acid, oleic acid, linoleic acid, and a-linolenic acid. Cultivation of M. reisseri using municipal wastewater served a dual function of nutrient removal and biofuel feedstock generation.     

Evaluation of microalgal consortia for treatment of primary treated sewage effluent and biomass production

The present investigation was aimed towards analyzing the potential of consortia of native filamentous microalgal strains (MC2), native unicellular microalgal strains (MC3), and selected microalgae from germplasm (MC1) in terms of nutrient removal, water quality improvement, and biomass production using primary treated sewage water. Highest NO₃-N (90 %) and PO₄-P (97.8 %) removal was obtained with MC2-inoculated sewage water. Highest decrease in total dissolved solids to 806 from 1,120 mg L^?1 and highest increase in dissolved oxygen of 9.0 from 0.4 mg L^?1 were obtained using MC2-inoculated sewage water on the sixth day. The biomass production was also highest in MC2 (1.07 g L^?1) followed by MC1 and MC3 (0.90 and 0.94 g L^?1, respectively) on the sixth day. The consortium of filamentous strains from native environment not only proved promising in nutrient removal efficiency but also led to enhanced biomass. The present study highlighted the utility of such a consortium for sewage wastewater treatment and the promise of sewage water as a growth medium for biomass production.     

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.     

Production of microalgae from olive mill wastewater

With olive mill wastewater (alpechin) used as a nutrient medium, the influence of the aeration level and the composition of the culture medium were analysed in relation to the concentration of alpechin and KNO₃ added in a batch culture of the microalgae Chlorella pyrenoidosa and Scenedesmus obliquus. The pH and temperature of the culture were previously fixed at 6.5 and 30°C. As kinetic parameters, the maximum specific growth rate (μ_m) and the biomass productivity (P_max) were determined. The biomass composition obtained was evaluated for chlorophyll and crude protein content as well as fatty-acid composition corresponding to the lipid fraction. To achieve a balanced biomass composition in terms of proteins and lipids, the most suitable conditions included an alpechin concentration of 10%, without the addition of nitrates and with an aeration level of 1 v/v min. Under these conditions, the μ_m values reached with both microalgae were around 0.03h⁻¹.     

Carbon dioxide biofixation by Chlorella vulgaris at different CO2 concentrations and light intensities

In order to develop an effective CO₂ mitigation process using microalgae for potential industrial application, the growth and physiological activity of Chlorella vulgaris in photobioreactor cultures were studied. C. vulgaris was grown at two CO₂ concentrations (2 and 13% of CO₂ v/v) and at three incident light intensities (50, 120 and 180 μmol m^?2 s^?1) for 9 days. The measured specific growth rate was similar under all conditions tested but an increase in light intensity and CO₂ concentration affected the biomass and cell concentrations. Although carbon limitation was observed at 2% CO₂, similar cellular composition was measured in both conditions. Light limitation induced a net change in the growth behavior of C. vulgaris. Nitrogen limitation seemed to decrease the nitrogen quota of the cells and rise the intracellular carbon:nitrogen ratio. Exopolysaccharide production per cell appeared to be affected by light intensity. In order to avoid underestimation of the CO₂ biofixation rate of the microalgae, exopolysaccharide production was taken into account. The maximum CO₂ removal rate (0.98 g CO₂ L^?1 d^?1) and the highest biomass concentration (4.14 g DW L^?1) were determined at 13% (v/v) CO₂ and 180 μmol m^?2 s^?1. Our results show that C. vulgaris has a real potential for industrial CO₂ remediation.     

Optimisation of biomass and lipid production by adjusting the interspecific competition mode of Dunaliella salina and Nannochloropsis gaditana in mixed culture

The high cost of algal cultivation has been a barrier associated with the commercialisation of algal biodiesel. Therefore, this study aimed to enhance lipid production by optimising the nutrient supply to benefit the coexistence of Dunaliella salina and Nannochloropsis gaditana. The effects on biomass and lipid production of using different proportions of D. salina and N. gaditana, urea and NaHCO₃ were optimised by response surface method with a 17-run Box–Behnken design. The optimal conditions for the algal growth are 58 % of D. salina in the mixture at OD₆₈₀, 150 μL day^?1 urea (0.0044 g day^?1) and no addition of NaHCO₃. The biomass concentration and lipid production reached 1.00 and 0.383 g L^?1, respectively, which are exceeded by the amount before optimisation, indicating the efficiency of the model obtained by response surface method.     

Growth characteristics of Botryococcus braunii 765 under high CO2 concentration in photobioreactor

To understand the potential of cultivating Botryococcus braunii with flue gas (normally containing high CO₂) for biofuel production, growth characteristics of B. braunii 765 with 2-20% CO₂ aeration were investigated. The results showed that the strain could grow well without any obvious inhibition under all tested CO₂ concentrations with an aeration rate of 0.2 vvm, even without any culture pH adjustment (ranged from 6.0 to 8.0). The maximum biomass among all conditions was 2.31 g L⁻¹ on 25th day at 20% CO₂. Hydrocarbon content and algal colony size increased with the increase of CO₂ concentration. A negative correlation between algal biomass and culture total phosphorus was observed (from −0.828 to −0.911, P < 0.01). Additionally, 2% sodium hypochlorite solution was used for photobioreactor sterilization to cultivate B. braunii.