Bubble Column Photobioreactor Research Articles

A novel bubble-driven internal mixer for improving productivities of algal biomass and biodiesel in a bubble-column photobioreactor under natural sunlight

The poor biomass titer and biodiesel productivity under natural sunlight are the major challenges for commercialization of algae-biodiesel. Apart from engineering the nutritional medium and CO2 input strategies, the photobioreactor (PBR) design needs high attention to increase light utilization efficiency. Hence, a novel bubble-driven internal mixer was designed for providing frequent light/dark fluctuation which can improve light utilization efficiency and installed in a bubble-column PBR (BC-PBR) to improve productivities of biomass and biodiesel from Chlorella sp. Without any extra energy requirement (via aeration), in 10 L scale BC-PBR with mixer under simulated sunlight, the productivities of biomass and biodiesel were increased by 13% and 62%, respectively, compared to without mixer. Under natural sunlight, the improvement of biomass productivity was 33% with mixer arrangement and final biomass of 8.6 g L−1 was achieved. Further to improve biodiesel productivity and quality under natural sunlight, the lipid induction was started right after the algae growth of 4.2 g L−1 (at the time of highest biomass productivity, 1.4 g L−1 day−1). Consequently, a very highest biodiesel productivity of 753 mg L−1 day−1 (induction-phase) was achieved. To the best of authors knowledge, this is the first study to report bubble-driven mixer in microalgae cultivation technology.

Evaluating the potential of carbohydrate-rich microalga Rhodosorus sp. SCSIO-45730 as a feedstock for biofuel and β-glucans using strategies of phosphate optimization and low-cost harvest

With the increase of global energy consumption, bioenergy from microalgae has been recognized as a potential alternative choice. A novel carbohydrate-rich microalgal strain, isolated from Xisha Islands (China), was identified as Rhodosorus sp. SCSIO-45730. To accumulate biomass for bioenergy production, strategies of phosphate optimization and chitosan flocculation were used to evaluate its potential for the production of biomass, total carbohydrates, and β-glucans. The biomass of this alga reached 12.3 ± 0.1 g L−1 in vertical bubble column photobioreactors at the phosphate concentration of 120 mg L−1, and the productivities of total carbohydrates and β-glucans maximized up to 242.6 ± 2.3 mg L−1 day−1 and 108.1 ± 4.0 mg L−1 day−1, respectively. Simultaneously, flocculation results demonstrated that the recovery rate of the biomass, total carbohydrates, and β-glucans were over 90% at a low chitosan concentration of 3 mg L−1. The flocs were easily collected and washed through a 300-mesh bolting cloth, presenting an ultralow harvest cost of 2.93 US$ per tonne of biomass. In summary, addition of suitable phosphate and flocculation with low chitosan concentration could be effective strategies to enhance the commercial potential of Rhodosorus sp. SCSIO–45730 as a feedstock for biofuel and β-glucans.

Enhancing Biomass and Lutein Production From Scenedesmus almeriensis: Effect of Carbon Dioxide Concentration and Culture Medium Reuse.

The main purpose of this study is to investigate the effects of operative parameters and bioprocess strategies on the photo-autotrophic cultivation of the microalgae Scenedesmus almeriensis for lutein production. S. almeriensis was cultivated in a vertical bubble column photobioreactor (VBC-PBR) in batch mode and the bioactive compounds were extracted by accelerated solvent extraction with ethanol at 67°C and 10 MPa. The cultivation with a volume fraction of CO2 in the range 0–3.0%v/v showed that the highest biomass and lutein concentrations – 3.7 g/L and 5.71 mg/g, respectively – were measured at the highest CO2 concentration and using fresh growth medium. Recycling the cultivation medium from harvested microalgae resulted in decreased biomass and lutein content. The nutrient chemical composition analysis showed the highest consumption rates for nitrogen and phosphorus, with values higher than 80%, while sulfate and chloride were less consumed.

Enzymatic catalysis: An environmentally friendly method to enhance the transesterification of microalgal oil with fusel oil for production of fatty acid esters with potential application as biolubricants

This work aimed at the enzymatic synthesis of fatty acid esters with potential application as biolubricants from microalgae oil and fusel oil using Burkholderia cepacia lipase immobilized on Nb2O5. The lipid-bearing Dunaliella salina biomass was grown in bubble column photobioreactors, yielding 100 g of biomass and 20 g of oil containing high content of saturated (37.8%) and monounsaturated fatty acids (41.2%) and a low content of polyunsaturated fatty acids (20.9%). The reaction assays were carried out in 50 mL glass reactor containing 10 g of medium composed by microbial oil and fusel oil components (ethyl, butyl, or isoamyl alcohols) and fusel oil as acyl acceptors at a fixed molar ratio of 1:8 (oil to alcohol) using iso-octane as solvent. Batch runs were performed at 45 °C under constant magnetic stirring (150 rpm) for a maximum of 120 h. Macaw palm oil was used as a control under the same reaction conditions. The biocatalyst was found to be efficient in converting the microalgal oil fatty acids into their corresponding alkyl esters attained yields ranging from 70.8 to 89.0% at 120 h reaction, depending on size of the alcohol chain. The kinematic viscosities of the esters produced confirmed the high transesterification yields, considering the viscosity of microalgae oil decreased from 60.1 to a range of 8.9–11.3 m2 s−1 (40 °C) after the enzymatic modification.

Development of an Organic Culture Medium for Autotrophic Production of Chlorella vulgaris Biomass

Microalgal biomass has gained increasing attention in the last decade for various biotechnological applications, including human nutrition. Certified organic products are currently a growing niche market in which the food industry has shown great interest. In this context, this work aimed at developing a certified organic culture medium for the production of autotrophic Chlorella vulgaris biomass. A preliminary assay in 2 L bubble column photobioreactors was performed in order to screen different commercial organic substrates (OS) at a normalized concentration of N (2 mmol L−1). The highest growth performance was obtained using EcoMix4 and Bioscape which showed similar biomass concentrations compared to the synthetic culture medium (control). In order to meet the nutrient needs of Chlorella, both OS underwent elemental analyses to assess their nutrient composition. The laboratory findings allowed the development of a final organic culture medium using a proportion of Bioscape/EcoMix4 (1:1.2, m/m). This organic culture medium was later validated outdoors in 125 L flat panel and 10 m3 tubular flow through photobioreactors. The results obtained revealed that the developed organic medium led to similar microalgal growth performance and biochemical composition of produced biomass, as compared to the traditional synthetic medium. Overall, the formulated organic medium was effective for the autotrophic production of organic C. vulgaris biomass.

Improving light distribution and light/dark cycle of 900 L tangential spiral−flow column photobioreactors to promote CO2 fixation with Arthrospira sp. cells

The light distribution and light/dark cycle were improved in 900 L tangential spiral-flow column photobioreactors (TSCP) to promote CO2 fixation with Arthrospira sp. cells. Solar irradiation model was employed in CFD simulation to investigate light distribution and light/dark cycle in flow field composed of culture medium, CO2 bubbles and Arthrospira sp. cells under actual sunlight irradiation considering geolocation and time. An accurate way to divide light/dark zone based on saturate light intensity and light intensity field was adopted for the first time. When Arthrospira sp. cell concentration increased from 0.1 to 0.9 g/L, light/dark cycle frequency of cells firstly increased from 0.650 Hz to 0.868 Hz and then decreased to 0.117 Hz. Intracellular chlorophyll a content and carotenoids content of Arthrospira sp. cells in TSCP were 6% and 41% higher than those in conventional bubble column photobioreactor. This promoted cellular photosynthesis and stress resistance, which contributed to increase CO2 fixation rate of Arthrospira sp. cells by 59%. When CO2 aeration rate, CO2 volume concentration, and circulating pump power were 0.210 L/min, 15%, and 30 W, chlorophyll a content, helix pitch, and CO2 fixation rate of Arthrospira sp. cells all reached peak values of 8.769 mg/L, 78.26 μm and 0.358 g/L/d, respectively.

Kinetic characterization and modeling of a microalgae consortium isolated from landfill leachate under a high CO2 concentration in a bubble column photobioreactor

Abstract Background The determination of kinetic parameters and the development of mathematical models are of great interest to predict the growth of microalgae, the consumption of substrate and the design of photobioreactors focused on CO2 capture. However, most of the models in the literature have been developed for CO2 concentrations below 10%. Results A nonaxenic microalgal consortium was isolated from landfill leachate in order to study its kinetic behavior using a dynamic model. The model considered the CO2 mass transfer from the gas phase to the liquid phase and the effect of light intensity, assimilated nitrogen concentration, ammonium concentration and nitrate concentration. The proposed mathematical model was adjusted with 13 kinetic parameters and validated with a good fit obtained between experimental and simulated data. Conclusions Good results were obtained, demonstrating the robustness of the proposed model. The assumption in the model of DIC inhibition in the ammonium and nitrate uptakes was correct, so this aspect should be considered when evaluating the kinetics with microalgae with high inlet CO2 concentrations. How to cite: Saldarriaga L F, Almenglo F, Ramirez M, et al. Kinetic characterization and modeling of a microalgae consortium isolated from landfill leachate under a high CO2 concentration in a bubble column photobioreactor. Electron J Biotechnol 2020;44. https://doi.org/10.1016/j.ejbt.2020.01.006 .

Synergistic effects between autotrophy and heterotrophy in optimization of mixotrophic cultivation of Chlorella sorokiniana in bubble-column photobioreactors

Mixotrophic cultivation of microalgae enables inorganic carbon capture through photosynthesis along with simultaneous organic carbon uptake. Extremophilic microalga Chlorella sorokiniana, capable of tolerating high CO2 levels, was cultivated mixotrophically in 1 L bubble-column photobioreactors. This study shows how the biomass yield increases as the algal CO2 uptake process shifts from being driven by Carbon Concentrating Mechanism (CCM) to being driven by direct diffusion, as the CO2 concentration increases from very low (0%) and low (atmospheric: 0.04%) to high (1%, 2%, 3%, 5%). The biomass yield and productivity increase from 1.05 g/L and 0.33 g/L/day, respectively, at atmospheric CO2 to 1.85 g/L and 0.48 g/L/day, respectively, at 3% CO2, with a corresponding doubling of the lipid yield. Using acetic acid as the organic carbon source allows it to directly enter the metabolic pathways at the acetyl-CoA junction and enhance fatty acid synthesis, while enhanced reactor illumination (below photo-inhibition) synergizes the phototrophic and photo-heterotrophic pathways. These three reactor scale parameters, namely, organic (acetic acid) and inorganic (CO2) carbon loading and illumination, are co-optimized to activate the synergies between the metabolic pathways for autotrophy and heterotrophy in mixotrophic algal growth, which, in turn, significantly enhances the biomass and the macromolecular yields at the cellular scale. This multiscale synergy leads to a four-fold increase in the biomass yield (from 0.7 to 2.79 g/L), a five-fold increase in biomass productivity (from 0.124 to 0.593 g/L/day), and a six-fold increase in the total lipid yield (from 0.12 to 0.75 g/L), while eliminating night-time biomass losses. Such an approach of co-optimising reactor-scale parameters to synergize the autotrophic and the heterotrophic metabolic pathways can be implemented in mass cultivation of microalgae, resulting in faster carbon sequestration and higher yields of biomass, lipids and other value-added co-products.

Optimization of cultivation conditions for Microcystis aeruginosa for biodiesel production using response surface methodology

BackgroundBiodiesel is expected to play a key role in the development of a sustainable, economical, and environmentally safe source of energy. The third generation of biodiesel is derived from microalgae and cyanobacteria that have sufficient amount of oil. The optimization of biomass and oil content in biodiesel production based on algal cultivation relies upon several factors. The present experimental work aims at optimizing some of the cultivation conditions to obtain maximum oil and biomass yield and create a prediction model that describe the effect of the initial inoculum concentration, and irradiance on the biomass yield and oil concentration were designed using Design Expert 6.0.8.ResultsThe results revealed that the optimum surface-to-volume ratio for the airlift bubble column photobioreactor was 0.9, and the most applicable model for describing Microcystis aeruginosa growth was the hyperbolic tangent model with a model constant value of 1.294 mg·L− 1·d− 1/μmol·m− 2·s− 1. The optimum cultivation conditions were 81 μmol·m− 2·s− 1 irradiance and 67 mg·L− 1 initial inoculum concentration, and these conditions achieved a biomass yield of 163 mg·L− 1·d− 1 and an oil concentration of 143 mg·L− 1.ConclusionsThis work focused on the cultivation of microalgae in closed systems. Cyanobacteria as M. aeruginosa has high lipid content, and high lipid productivity makes it suitable as a lipid feed stock for biodiesel production. The response surface method was the most suitable route to study the simultaneous influence of irradiance and initial inoculum concentration through statistical methods as well as to establish a model for predicting the biomass yield and oil concentration of M. aeruginosa.

Trimethylamine abatement in algal-bacterial photobioreactors.

Trimethylamine (TMA) is an odorous volatile organic compound emitted by industries. Algal-based biotechnologies have been proven as a feasible alternative for wastewater treatment, although their application to abate polluted air emissions is still scarce. This work comparatively assessed the removal of TMA in a conventional bacterial bubble column bioreactor (BC) and a novel algal-bacterial bubble column photobioreactor (PBC). The PBC exhibited a superior TMA abatement performance compared to the conventional BC. In this sense, the BC reached a removal efficiency (RE) and an elimination capacity (EC) of 78% and 12.1g TMA m-3h-1, respectively, while the PBC achieved a RE of 97% and a EC of 16.0g TMA m-3·h-1 at an empty bed residence time (EBRT) of 2min and a TMA concentration ~500mgm-3. The outstanding performance of the PBC allowed to reduce the operating EBRT to 1.5 and 1min while maintaining high REs of 98 and 94% and ECs of 21.2 and 28.1gm-3·h-1, respectively. Moreover, the PBC improved the quality of the gas and liquid effluents discharged, showing a net CO2 consumption and decreasing by ~ 30% the total nitrogen concentration in the liquid effluent via biomass assimilation. A high specialization of the bacterial community was observed in the PBC, Mumia and Aquamicrobium sp. being the most abundant genus within the main phyla identified. GraphicalAbstract.

CO2 capturing by chlorella vulgaris in a bubble column photo-bioreactor; Effect of bubble size on CO2 removal and growth rate

In this study, a modified gas feeding bubble column photo-bioreactor was utilized for microalgae cultivation and CO2 capturing. By applying response surface methodology, the optimum values of temperature, pH, light intensity, aeration rate, light-dark cycle and time were determined as 25 ° C, 8, 2700 lx, 0.5 LPM and 16−8 h, respectively. Two air spargers (with different aperture size) were used to study the effect of the bubble size on the CO2 removal and microalgae growth rate. Besides, the inlet air was humidified to avoid the evaporation from the photo-bioreactor. For the smaller bubbles and 7% CO2 concentration, the maximum values for the CO2 fixation rate, productivity and concentration of microalgae were determined to be 633.73 mg L−1d−1, 337 mg L−1d−1 and 4244 mg L−1, respectively. CO2 utilization efficiency was 35% for the smaller bubbles, showing a 15% increase over that for the larger bubbles.

Pilot-scale production of lutein using Chlorella vulgaris

Lutein is a carotenoid pigment which has applications in the food and nutraceutical sectors, both for its use as a colourant and for its applications as a nutraceutical. Microalgae are a promising source of lutein, however to meet market demand there is a need to develop technologies which can used for large-scale production. The effect of process conditions at a 5L scale were quantified, it was found that at low light intensities (160μmol photons m−2 s−1) the measured specific lutein concentration was 7.4±2.1mg g−1 which was greater than the concentration of 3.1±1.1mg g−1 obtained at higher (440μmol photons m−2 s−1) light intensities. Supplementation of the medium with nitrate led to significant increases in the maximum specific lutein concentration (10.4±5.5mg g−1) compared to medium without nitrate addition (4.3±2.9mg g−1). These conclusions were used to scale-up the process using 50L bubble column photo-bioreactors, it was found that the productivity was maximised (1.6mgL−1 day−1) using an air flow-rate of 1 vvm and 24h lighting. Finally, it was found that the process could be operated on a semi-continuous basis for 32 days, achieving high lutein concentrations (15–20mgL−1) with the performance of the system being consistent for this duration. Results from this work have clear application in the development of large-scale systems for the microalgal production of lutein.

Bubble column photobioreactor for Chlorella pyrenoidosa cultivation and validating gas hold up and volumetric mass transfer coefficient

ABSTRACT The cultivation of microalgae in bubble column photobioreactors is essential to improve the biomass productivity for biofuel production. This work comprises the design and fabrication of bubble column photobioreactor of 20 L culture volume for the cultivation of Chlorella pyrenoidosa. The theoretically parameters such as gas hold up and volumetric mass transfer coefficient was predicted. The bubble column photobioreactor of 20 L culture volume was fabricated. The C. pyrenoidosa was cultivated in bubble column photobioreactor and the actual gas hold up and volumetric mass transfer coefficient was measured and with predicted values. The results showed similar trend of variation of experimental theoretically predicted gas hold up and volumetric mass transfer coefficient at different gas velocities. The comparison of biomass concentration and lipid content of C. pyrenoidosa cultivated in bubble column photobioreactor showed 1.18 ± 0.02 g/ L and 19.04 ± 0.03% dwt, respectively, at the end of the cultivation period as compared with conical flask and glass tank cultivation.

High-yield cultivation of Botryococcus braunii for biomass and hydrocarbons

Botryococcus braunii is one of the most promising energy microalgae with a high content of hydrocarbons. Photoautotrophic cultivation is essential while the productivity is lowered by the long period of preparation for seeds. Therefore, a new strategy of photoautotrophic culture with heterotrophic seeds was proposed. The pH-auxostat fed-batch heterotrophic cultivation was developed, by which the biomass reached 37.02 g L−1 at 28 day in the 5 L fermenter. The effects of inoculum with heterotrophic seeds into photoautotrophic cultivation were verified. By this strategy, the final content and productivity of hydrocarbon was 35.9% and 128.3 mg L−1 d−1 respectively in 1 L bubble column photo-bioreactors indoors, the highest ever reported. Furthermore, the heterotrophic seeds were successfully applied to photoautotrophic cultivation in 3 L flat panel photo-bioreactors and 120 L open circle ponds outdoors, in which the final content and productivity of hydrocarbon were 27.85% and 35.06 mg L−1 d−1, indicating an efficient and feasible approach for producing biofuel from B. braunii.

Effective valorization of microalgal biomass for the production of nutritional fish-feed supplements

Abstract Falling supply and rising demand of conventional feed ingredients leads to soaring fishmeal prices, which necessitates the need for alternate feed sources. This study aims to evaluate the performance of dried dietary Chlorella sp. on the survival and growth of the freshwater juvenile- Common Carp (Cyprinus carpio var. Koi) in a 60-day feeding trials. Microalgae was cultivated in bubble column photobioreactors with ambient air and flue gas and found to be very promising as carbon-dioxide mitigation agent. The microalgal biomass was included at dosage of 15% (w/w) to formulate two iso-nitrogenous (358 g protein kg−1 diet) and iso-caloric (19.23 MJkg−1) diets as a replacement of fishmeal. The algae derived diets contained essential macronutrients for the nutrition and survival of carp fishes. Performance evaluation of formulated diets vis-a-vis control feed (CF) showed significant improvement in weight gain (up to 55%), lower feed conversion ratio (2.17) and protein efficiency ratio (3.3). Cost estimates showed a marked reduction (26.10%) in cost of formulated feeds compared to conventional commercial feed that can significantly affect the profit margin of fish farmers. Further, histo-architectural changes in the intestinal sections of fishes confirmed the suitability of algal-based diets. This study highlights an interesting innovative strategy of producing cleaner microalgal biomass after waste carbon dioxide capture for the formulation of alternative nutritional feed supplement and paves a way for algal farmers to culture microalgae as unconventional feed source for the aquaculture industry. Lastly, the outcomes of this study are first of its kind in fish feed research and technology development.

Quorum-sensing mediated signals: A promising multi-functional modulators for separately enhancing algal yield and power generation in microbial fuel cell

Quorum-sensing molecules (QSMs) extracted from anaerobic sludge can help to enhance the overall productivity of algal culture, thus diminishing the per unit production cost of algae based-biofuel. In this investigation, QSMs extracted from anaerobic bacterial sludge of microbial fuel cell (MFC) was used to enhance the overall productivity of Chlorella sorokiniana cultivated in a separate bubble column photobioreactor. With the dosage of QSMs, algal biomass productivity and lipid content were increased by 2.25 times and 1.28 times, respectively. Further, lipid extracted biomass of quorum-sensing induced algae (LEB-QSA) was applied in anodic chamber of MFC to function as substrate and mediator, which enhanced the coulombic efficiency of this MFC by 74% as compared to the control MFC operated without LEB-QSA. Thus, this exploration demonstrated successful improvement in the macromolecular properties of algal culture dosed with QSMs and improved performance of MFC with the application of LEB-QSA as mediator and substrate.

Assessment of stress conditions for carotenoids accumulation in Chlamydomonas reinhardtii as added-value algal products

BackgroundMicroalgae, the third-generation source of biofuel have invaluable bio-refineries such as carotenoids. The accumulation of carotenoids in the algal cell is based on several parameters during algal growth. Some of these parameters are irradiance and cultivation periods which figures the photoperiod during algal growth. In this work, 0.6 g/L Chlamydomonas reinhardtii, green algae strain, was cultivated using the BG-11 medium in bubble column photobioreactor illuminated by white cool fluorescent 24 h per day, irradiance range 40.5–149 μmol.m−2.s−1, and cultivation period range 10–20 days. The carotenoids were extracted using two solvents, petroleum ether, and ethyl acetate in ratio 7:3. The carotenoids fractions were quantified using HPLC and the design expert program 8.6 was used to optimize the irradiance and cultivation period in order to gain maximum carotenoids accumulation in C. reinhardtii using response surface method.ResultsThe results revealed that the optimum conditions of C. reinhardtii cultivation are illuminating the culture 24 h a day for 10 days with irradiance 149 μmol.m−2.s−1 producing 0.85 mg/g astaxanthin, 0.87 mg/g lutein, and 0.64 mg/g β-carotene, as a maximum value of accumulating carotenoids in 2.15 g/L biomass yield.ConclusionsHigh irradiance and cultivation period are two essential parameters for accumulating carotenoids in algae. Response surface method is an affordable method to optimize these parameters simultaneously via predicting a model describe the relation and analyze the results statistically. The experimental verification of results proved the model’s validity. The prospective research is going to study the effect of more parameters on carotenoids accumulation in algae.

Formation of extracellular β-chitin nanofibers during batch cultivation of marine diatom Cyclotella sp. at silicon limitation

Diatoms are unicellular algae that make nanostructured biosilica shells called frustules possessing ordered pore arrays. Dissolved silicon (Si) in the form of Si (OH)4 is the required substrate for cell wall biosynthesis and cell division. The extracellular formation of β-chitin nanofibers by the centric diatom Cyclotella sp. was followed during batch cultivation of the cell suspension within a bubble-column photobioreactor at a low initial Si concentration (0.25 mM) leading to 1–2 cell divisions, and high Si concentration (1.7 mM) leading to 4–5 cell divisions. Fibers were excreted from 20 specialized pores (fultoportulae) lining the rim of each frustule valve face. In Si-limited batch cultivation, 80% of the fibers formed during the last cell division after dissolved Si was depleted from the medium. Within 24 h after the final cell division, fibers were nominally 56 nm diameter and 60 μm length, with 85% of the fibers between 20 and 80 μm, and one fiber per fultoportula was formed. After the final cell number density was maintained for 72 h, a second fiber per fultoportula was formed, presumably after breakage or scission of the first fiber from the cell. X-ray diffraction (XRD) analysis confirmed that isolated fibers were composed of pure β-chitin. The unprecedented length and purity of the β-chitin nanofibers suggest future advanced material applications.

Bench-Scale Cultivation of Microalgae Scenedesmus almeriensis for CO2 Capture and Lutein Production

In this study, Scenedesmus almeriensis as green microalga was cultivated on bench-scale for carbon dioxide (CO2) capture and lutein production. The autotrophic cultivation of S. almeriensis was carried out by using a vertical bubble column photo-bioreactor (VBC-PBR) with a continuous flow of a gaseous mixture of oxygen (O2), nitrogen (N2), and CO2, the latter in content of 0.0–3.0 %v/v. The liquid phase was batch. S. almeriensis growth was optimized. In addition, lutein extraction was carried out by using accelerated solvent extraction with ethanol as Generally Recognized as Safe (GRAS) solvent at 67 °C and 10 MPa. Upon optimization of CO2 concentration, the maximum biomass productivity, equal to 129.24 mg·L−1·d−1, was achieved during the cultivation by using a content of CO2 equal to 3.0 %v/v and it allowed to obtain a lutein content of 8.54 mg·g−1, which was 5.6-fold higher in comparison to the analogous process carried out without CO2 addition. The ion chemical analysis in the growth medium showed that by gradually increasing CO2 content, the nutrient consumption during the growth phase also increased. This study may be of potential interest for lutein extraction at industrial scale, since it is focused on pigment production from a natural source with a concomitantly CO2 capture.

An integrated approach towards agricultural wastewater remediation with fatty acid production by two cyanobacteria in bubble column photobioreactors

Cyanobacteria are capable of rapidly sequestering CO2 into lipid-enriched biomass while utilizing dissolved inorganic nutrients in wastewater. Semi-batch 30-d cultures of Anabaena sphaerica and A. variabilis were simultaneously monitored for biomass and lipid productivities, CO2 sequestration rates and dissolved macronutrient (N, P) utilization rates under varying photoperiods (8, 10, 12, 14, 16 and 18 h) and CO2 concentrations (control (air), 2% and 5%) in media supplemented with 15% (v/v) agricultural run-off water in bubble column photobioreactors. Effect of enhanced CO2 supply was significantly beneficial for all parameters. Longer or shorter photoperiods from the originally acclimated 14 h led to diminished and enhanced parameters respectively, but these changes were staggered due to inherent adaptibilities. The long-chain fatty acid (LCFA) profiles of A. sphaerica and A. variabilis were respectively dominated by saturated fatty acids (SFA) and polyunsaturated fatty acids (PUFA). Eight LCFAs were common between the two species while the SFA myristic acid was found in A. sphaerica and the ω-6 PUFA cis-8,11,14-eicosatrienoic acid was found in A. variabilis. It was concluded that A. sphaerica and A. variabilis showed potential in biodiesel and nutraceutical production, respectively. However, culture conditions including photoperiod and CO2 supply were found to affect the LCFA profiles slightly.