Intensive Microalgal Cultivation and Tertiary Phosphorus Recovery from Wastewaters via the EcoRecover Process.

Mixed community microalgal wastewater treatment technologies have the potential to advance the limits of technology for biological nutrient recovery while producing a renewable carbon feedstock, but a deeper understanding of their performance is required for system optimization and control. In this study, we characterized the performance of a 568 m3·day-1 Clearas EcoRecover system for tertiary phosphorus removal (and recovery as biomass) at an operating water resource recovery facility (WRRF). The process consists of a (dark) mix tank, photobioreactors (PBRs), and a membrane tank with ultrafiltration membranes for the separation of hydraulic and solids residence times. Through continuous online monitoring, long-term on-site monitoring, and on-site batch experiments, we demonstrate (i) the importance of carbohydrate storage in PBRs to support phosphorus uptake under dark conditions in the mix tank and (ii) the potential for polyphosphate accumulation in the mixed algal communities. Over a 3-month winter period with limited outside influences (e.g., no major upstream process changes), the effluent total phosphorus (TP) concentration was 0.03 ± 0.03 mg-P·L-1 (0.01 ± 0.02 mg-P·L-1 orthophosphate). Core microbial community taxa included Chlorella spp., Scenedesmus spp., and Monoraphidium spp., and key indicators of stable performance included near-neutral pH, sufficient alkalinity, and a diel rhythm in dissolved oxygen.

High-throughput identification of novel heat tolerance genes via genome-wide pooled mutant screens in the model green alga Chlamydomonas reinhardtii.

Different high temperatures adversely affect crop and algal yields with various responses in photosynthetic cells. The list of genes required for thermotolerance remains elusive. Additionally, it is unclear how carbon source availability affects heat responses in plants and algae. We utilized the insertional, indexed, genome-saturating mutant library of the unicellular, eukaryotic green alga Chlamydomonas reinhardtii to perform genome-wide, quantitative, pooled screens under moderate (35°C) or acute (40°C) high temperatures with or without organic carbon sources. We identified heat-sensitive mutants based on quantitative growth rates and identified putative heat tolerance genes (HTGs). By triangulating HTGs with heat-induced transcripts or proteins in wildtype cultures and MapMan functional annotations, we presented a high/medium-confidence list of 933 Chlamydomonas genes with putative roles in heat tolerance. Triangulated HTGs include those with known thermotolerance roles and novel genes with little or no functional annotation. About 50% of these high-confidence HTGs in Chlamydomonas have orthologs in green lineage organisms, including crop species. Arabidopsis thaliana mutants deficient in the ortholog of a high-confidence Chlamydomonas HTG were also heat sensitive. This work expands our knowledge of heat responses in photosynthetic cells and provides engineering targets to improve thermotolerance in algae and crops.

Sustainable production of biofuels from the algae-derived biomass.

The worldwide fossil fuel reserves are rapidly and continually being depleted as a result of the rapid increase in global population and rising energy sector needs. Fossil fuels should not be used carelessly since they produce greenhouse gases, air pollution, and global warming, which leads to ecological imbalance and health risks. The study aims to discuss the alternative renewable energy source that is necessary to meet the needs of the global energy industry in the future. Both microalgae and macroalgae have great potential for several industrial applications. Algae-based biofuels can surmount the inadequacies presented by conventional fuels, thereby reducing the 'food versus fuel' debate. Cultivation of algae can be performed in all three systems; closed, open, and hybrid frameworks from which algal biomass is harvested, treated and converted into the desired biofuels. Among these, closed photobioreactors are considered the most efficient system for the cultivation of algae. Different types of closed systems can be employed for the cultivation of algae such as stirred tank photobioreactor, flat panel photobioreactor, vertical column photobioreactor, bubble column photobioreactor, and horizontal tubular photobioreactor. The type of cultivation system along with various factors, such as light, temperature, nutrients, carbon dioxide, and pH affect the yield of algal biomass and hence the biofuel production. Algae-based biofuels present numerous benefits in terms of economic growth. Developing a biofuel industry based on algal cultivation can provide us with a lot of socio-economic advantages contributing to a publicly maintainable result. This article outlines the third-generation biofuels, how they are cultivated in different systems, different influencing factors, and the technologies for the conversion of biomass. The benefits provided by these new generation biofuels are also discussed. The development of algae-based biofuel would not only change environmental pollution control but also benefit producers' economic and social advancement.

Mitigating membrane fouling in an internal loop airlift membrane photobioreactor containing Spirulina platensis: effects of riser cross-sectional area and hydrophilic baffles.

Membrane photobioreactors (MPBRs) have gained significant attention due to their ability to support microalgae activities such as cultivation, harvesting, and production of beneficial products. Despite various efforts to mitigate membrane fouling, a fundamental issue in membrane processes, in these systems, a cost-effective and less energy-consuming method is still needed. This study examines the impact of the cross-sectional area of the riser and the baffle material on membrane fouling in an internal loop airlift MPBR. The use of hydrophilic polyester-polypropylene (PES-PP) baffles proves to be more effective than plexiglass baffles. Specifically, in configurations with d = 0.7 cm and d = 1.4 cm, RC/RT decreased by approximately 20% and 13%, respectively, compared to plexiglass baffles. As for the values of RP/RT at a distance of d = 0.7, nearly a 5% increase was observed, and at a distance of d = 1.4, an increase of approximately 11% was observed. This is due to the development of the cake layer on the matrix structure of the PES-PP baffles instead of the membrane itself. The most optimal outcomes were reached while working with PES-PP at a distance of 0.7 cm, as it prolonged the membrane fouling time to 46 h.

Sustainability and carbon neutrality trends for microalgae-based wastewater treatment: A review.

As the global economy develops and the population increases, greenhouse gas emissions and wastewater discharge have become inevitable global problems. Conventional wastewater treatment processes produce direct or indirect greenhouse gas, which can intensify global warming. Microalgae-based wastewater treatment technology can not only purify wastewater and use the nutrients in wastewater to produce microalgae biomass, but it can also absorb CO2 in the atmosphere or flue gas through photosynthesis, which demonstrates great potential as a sustainable and economical wastewater treatment technology. This review highlights the multifaceted roles of microalgae in different types of wastewater treatment processes in terms of the extent of their bioremediation function and microalgae biomass production. In addition, various newly developed microalgae cultivation systems, especially biofilm cultivation systems, were further characterized systematically. The performance of different microalgae cultivation systems was studied and summarized. Current research on the technical approaches for the modification of the CO2 capture by microalgae and the maximization of CO2 transfer and conversion efficiency were also reviewed. This review serves as a useful and informative reference for the application of wastewater treatment and CO2 capture by microalgae, aiming to provide a reference for the realization of carbon neutrality in wastewater treatment systems.

Mixotrophy in a Local Strain of Nannochloropsis granulata for Renewable High-Value Biomass Production on the West Coast of Sweden

A local strain of Nannochloropsis granulata (Ng) has been reported as the most productive microalgal strain in terms of both biomass yield and lipid content when cultivated in photobioreactors that simulate the light and temperature conditions during the summer on the west coast of Sweden. To further increase the biomass and the biotechnological potential of this strain in these conditions, mixotrophic growth (i.e., the simultaneous use of photosynthesis and respiration) with glycerol as an external carbon source was investigated in this study and compared with phototrophic growth that made use of air enriched with 1-2% CO2. The addition of either glycerol or CO2-enriched air stimulated the growth of Ng and theproduction of high-value long-chain polyunsaturated fatty acids (EPA) as well as the carotenoid canthaxanthin. Bioassays in human prostate cell lines indicated the highest antitumoral activity for Ng extracts and fractions from mixotrophic conditions. Metabolomics detected betaine lipids specifically in the bioactive fractions, suggesting their involvement in the observed antitumoral effect. Genes related to autophagy were found to be upregulated by the most bioactive fraction, suggesting a possible therapeutic target against prostate cancer progression. Taken together, our results suggest that the local Ng strain can be cultivated mixotrophically in summer conditions on the west coast of Sweden for the production of high-value biomass containing antiproliferative compounds, carotenoids, and EPA.

Antimicrobial and Antioxidant Potential of Scenedesmus obliquus Microalgae in the Context of Integral Biorefinery Concept.

Small-scale photobioreactors (PBRs) in the inoculum stage were designed with internal (red or green) and external white LED light as an initial step of a larger-scale installation aimed at fulfilling the integral biorefinery concept for maximum utilization of microalgal biomass in a multifunctional laboratory. The specific growth rate of Scenedesmus obliquus (Turpin) Kützing biomass for given cultural conditions was analyzed by using MAPLE software. For the determination of total polyphenols, flavonoids, chlorophyll "a" and "b", carotenoids and lipids, UHPLC-HRMS, ISO-20776/1, ISO-10993-5 and CUPRAC tests were carried out. Under red light growing, a higher content of polyphenols was found, while the green light favoured the flavonoid accumulation in the biomass. Chlorophylls, carotenoids and lipids were in the same order of magnitude in both samples. The dichloromethane extracts obtained from the biomass of each PBR synergistically potentiated at low concentrations (0.01-0.05 mg/mL) the antibacterial activity of penicillin, fluoroquinolones or oregano essential oil against the selected food-borne pathogens (Staphylococcus aureus, Escherichia coli and Salmonella typhimurium) without showing any in vitro cytotoxicity. Both extracts exhibited good cupric ion-reducing antioxidant capacity at concentrations above 0.042-0.08 mg/mL. The UHPLC-HRMS analysis revealed that both extracts contained long chain fatty acids and carotenoids thus explaining their antibacterial and antioxidant potential. The applied engineering approach showed a great potential to modify microalgae metabolism for the synthesis of target compounds by S. obliquus with capacity for the development of health-promoting nutraceuticals for poultry farming.

Transcriptomic analyses of cacao flavonoids produced in photobioreactors.

BACKGROUND: Theobroma cacao is a major source of flavonoids such as catechins and their monomers proanthocyanidins (PAs), widely studied for their potential benefits in cardiovascular diseases. Light has been shown to promote plant secondary metabolite production in vitro. In this study, cacao cells cultured in 7.5 L stirred tank photobioreactors (STPs) were exposed to a change of white to blue LED lights for 28 days (d). RESULTS: Transcriptomic analyses were performed in three time points comparing changing expression patterns, after cell exposure to white light (d0-VS-d14), after a shift from white to blue light (d14-VS-d15), and after an extended period of blue light for the following 15 days (d15-VS-d28). Under white light, there was enrichment in metabolic pathways associated with cell growth (carbon, glycolysis, and amino acid biosynthesis) accompanied by a significant increase in the PAs content. In the shift to blue light, further increase in PAs content was observed concomitantly with the significant expression of TWO-COMPONENT RESPONSE REGULATOR genes involved in the early stress responses via circadian clock and hormone pathways. Under blue light exposure, we observed a depletion of PAs content associated with ROS-mediated stress pathways. CONCLUSIONS: Light effects on large-scale cell cultures in photobioreactors are complex and pleiotropic; however, we have been able to identify key regulatory players upstream cacao flavonoid biosynthesis in STPs, including TWO-COMPONENT SYSTEM and ROS-signaling genes. The crosstalk between flavonoid biosynthesis and regulatory networks led to understand the dynamics of flavonoid production and degradation in response to light-driven ROS signals. This can be used to optimize the time, and the yield of in vitro targeted metabolites in large-scale culture systems.

Nanoscale characteristics of conditioning film development on photobioreactor materials: influence on the initial adhesion and biofilm formation by a cyanobacterium.

Adsorption of conditioning films on a solid surface is the first step in the development of biofilms. With the goal of understanding the preliminary adhesion mechanisms of cyanobacteria on photobioreactor (PBR) materials to prevent biofouling, the physical changes occurring on PBR materials were investigated during the initial adhesion and biofilm formation by Anabaena sp. PCC 7120, a cyanobacterium that is genetically modified to produce linalool. Atomic force microscopy (AFM) revealed that the conditioning film deposition was in the form of spike-like structures on all the materials except PVC. The average heights (in the range 9 - 16 nm) of the conditioning films deposited on glass, PMMA, PC and HDPE were 11 to 20 times higher than on PVC at 96 h. The time dependent change in thickness of conditioning films correlated well with Anabaena cell attachment to the PBR materials. The rapid and significant colonization of Anabaena on glass within 48 h was consistent with the increase in thickness of the conditioning film within this time period. Lack of the conditioning film spike structures and no change in thickness of the conditioning films with time on the PVC together with comparatively delayed cell attachment and conditioning-film protein deposition on this material, indicated that the nanoscale spike structures on the other PBR materials may be accelerating the cell attachment process but are not a prerequisite for cell attachment. These results suggest that PVC should be explored further as an antifouling material for photobioreactors. The thickness of the conditioning films on glass measured by a scratch and scan method was in good agreement with the thickness values measured by an adhesive tape method, indicating that both these methods can be used for fast and reliable AFM thickness determination of bacterial conditioning films.

Biomass and pigment production for Arthrospira platensis via semi-continuous cultivation in photobioreactors: Temperature effects.

This study describes the response of Arthrospira platensis to a variety of temperature conditions as reflected in variations of photosynthetic parameters, pigmentation, and biomass productivity in indoor photobioreactor (PBR) cultivations. These experiments are designed to better understand the impact of temperature, seasonal variations, and acclimation effects on outdoor biomass production. The irradiance level and temperature range (20-39°C) are chosen to enable modeling of semi-continuous operation of large-scale outdoor PBR deployments. Overall, the cultivations are quite stable with some pigment-related instabilities after prolonged high-temperature exposure. Changes in productivity with temperature, as reflected in measured photosynthetic parameters, are immediate and mainly attributable to the temperature dependence of the photosaturation parameter, a secondary factor being variation in pigment content on a longer time scale corresponding to turnover of the culture population. Though pigment changes are not accompanied by significant changes in productivity, prolonged exposure at 35°C and above yields a clear degradation in performance. Productivities in a semi-continuous operation are quantitatively reproduced with a productivity model incorporating photosynthetic parameters measured herein. This study confirms the importance of temperature for biomass and pigment production in Arthrospira cultivations and provides a basis for risk assessments related to temperature mitigation for large-scale outdoor cultivations.

Effects of pH, temperature and salinity on P3HB synthesis culturing the marine Rhodovulum sulfidophilum DSM-1374.

Rhodovulum sulfidophilum DSM-1374 is a potential producer of polyester when growing in phototrophic conditions. The present study investigated on a polyester product (P3HB) by culturing Rhodovulum sulfidophilum DSM-1374 in two different photobioreactors (PBR-1 and PBR-2) both with 4-L working volumes. PBR-1 is equipped with an internal rotor having 4 paddles to mix the bacterial culture while PBR-2 has an internal coil-shaped rotor. After selecting PBR-1, which best performed in the preliminary experiment, the effect of different stressing growth conditions as pH (7.0, 8.0, and 9.0), temperature (25, 30, and 35 °C), and medium salinity (1.5, 2.5, 3.5, and 4.5%) were tested. When the pH of the culture was set to 8.0, the capability of the bacterium to synthetize the polyester increased significantly reaching a concentration of 412 mg (P3HB)/L; the increase of the pH at 9.0 caused a reduction of the P3HB concentration in the culture. The medium salinity of 4.5% was the best stress-growth condition to reach the highest concentration of polyester in the culture (820 ± 50 mg (P3HB)/L) with a P3HB mass fraction in the dry biomass of 33 ± 1.5%. Stresses caused by culture temperature are another potential parameter that could increase the synthesis of P3HB.

Bioremediation of emerging micropollutants in irrigation water. The alternative of microalgae-based treatments.

The present study evaluated the efficiency of a semi-closed horizontal tubular photobioreactor (PBR) at demonstrative scale to remove a total of 35 target compounds, including benzotriazoles, benzophenones, antibiotics and different pharmaceuticals present in irrigation water in a peri-urban rural area. This water run through an open channel and was a mixture of reclaimed wastewater from a nearby wastewater treatment plant (WWTP) and run-off from the different agricultural fields in the area. Most of the compounds studied are usually not fully eliminated during conventional wastewater treatment, which justifies the need to investigate alternative treatment strategies. A total of 21 of these compounds were detected in the irrigation water. Benzotriazoles were only partially removed after the microalgae treatment, with elimination rates similar to those of conventional WWTPs. The UV filter benzophenone-3 (BP3) showed variable removals, ranging from no elimination to 51%, whereas 4-methylbenzilidenecamphor (4MBC) was completely eliminated. Regarding pharmaceuticals, average removals were higher, in the range of 60-100%, with the exception of the antibiotics sulfamethoxazole (46%) and sulfapyridine, which was not removed. Despite the low biomass productivity of the PBR, parameters such as the size of the reactors, the specific mixed cultures developed and the high temperatures and pH in the closed system may account for the overall good results, The efficiency and sustainability of these systems make them a solid, feasible treatment choice.

Technological mapping and trends in photobioreactors for the production of microalgae.

Photobioreactors (PBRs) are equipment of central importance for the massive cultivation of microalgae, providing controlled conditions for high cell productivity. There are a few popular PBR designs, with contrasting advantages and limitations, such as poor light distribution, mass transfer, or hydrodynamic behavior. Due to the environmental concerns in recent decades and the discovery of new, useful microalgal metabolites, the interest in finding alternatives to solve technological bottlenecks of PBRs has intensified. In this process, new geometries, materials, and modes of light supply were developed, generating a significant scientific and technological output, reported in papers and patents. We present a technological landscape analysis of photobioreactor design, focusing on improvements of the classical geometries and trends in industrial photobioreactors. The analysis of 412 patent documents showed a surge in innovation filing since 2005 and a reduction in the number of new documents along the last decade. The recent efforts in design improvement, the leading countries, institutes and companies that innovate, and the trends in PBR technology are presented and discussed.

Phycoremediation of paddy-soaked wastewater by indigenous microalgae in open and closed culture system.

Phycoremediation; biotransformation of nutrients and or pollutants by microalgae, supports sustainable wastewater treatment, coupled with biomass production, resulting in enhanced cost savings, waste minimization, and energy conservation. A major challenge in this technique involves cultivation system to be adopted, mode of treatment and harvesting methods. Three different algal cultivation systems; polybags (PB), photobioreactors (PBR) and race way ponds (RWP) were employed for culturing an indigenous microalga, Scenedesmus obliquus in rice mill paddy-soaked wastewater (PSW). The maximum biomass productivity (BP) of 340 ±â€¯2 mg/L/d was observed in PBR with an ammonical nitrogen (NH3-N) removal (RN) of 96.12 ±â€¯0.21% and the phosphates (PO4-P) removal (RP) of 97.58 ±â€¯0.18%. Highest lipids (L)∼12% (% biomass), protein (P)∼40% and carbohydrates (C)∼20%) were gained in PBR culture system, followed by RWP and PB.

Progress on the development of floating photobioreactor for microalgae cultivation and its application potential.

Microalgae present great potential to replace land crops for the efficient production of large volumes of biomass for food, feed, fuels, and chemicals, as well as to treat wastewater and capture carbon. However, the commercialization of these technologies for bulk commodities requires a great reduction in the current microalgal biomass production cost. The bioreactor is the core of bioprocess engineering and is the premise for the commercial application of certain types of biotechnology. The challenges of phototrophic cultivation are completely different from those of heterotrophic processes because the efficiency of phototrophic cultivation is limited by the energy density of the input sunlight and the inorganic carbon supply. Thus, the development of microalgae cultivation technologies with low manufacturing and operating costs is key to addressing this problem, and floating photobioreactors (PBRs) are a promising solution. PBRs are deployed on the water surface without any land requirements, and wave energy provides free mixing energy. Additionally, the surrounding water can be used to control the culture temperature and to supply nutrients for microalgae growth. In this mini-review, the development of floating PBRs and their recent progress are presented. The effect of the carbon supply approach on the mixing and scaling-up of floating PBRs are critically discussed. The limitations and challenges in commercial applications of floating PBRs are analysed, and the need for future research is proposed. Finally, it is noted that microalgae farming on the ocean is a promising solution for human society to address the challenge of land space exhaustion due to the global population boom.

Utilization of centrate for the outdoor production of marine microalgae at the pilot-scale in raceway photobioreactors.

In this study, the outdoor production of marine microalgae in raceway photobioreactors was investigated, modifying the centrate percentage in the culture medium (20, 30, 40 and 50%) and using two different dilution rates (0.2 day-1 and 0.3 day-1). The data obtained showed that microalgae are capable of producing biomass in addition to recovering the nutrients contained in the centrate. The best results for biomass productivity and light efficiency were obtained when the centrate was set at 20% with a dilution rate of 0.3 day-1. The biomass productivity was 32.42 g m-2·day-1 while the photosynthetic efficiency was 0.74 gbiomass·E-1 (3.66%). Regarding the nutrients, nitrogen (the majority being in the form of ammonium [NH4+]) and phosphorus were only fixed into biomass when optimal conditions were set; if this was not the case, they were lost to stripping or precipitation. The maximal nutrient removal capacities under the optimal conditions were 28.72 mgN·l-1·day-1 and 3.99 mgP·l-1·day-1. Population changes were determined by the dilution rate set whilst the centrate percentage had little effect. Four strains were present in the culture, Nannochloropsis g. being the main one. Biochemical changes did not vary greatly between the conditions set for the culture, with a composition rich in proteins and carbohydrates being observed. One can conclude that to produce marine microalgal biomass for a range of potential commodities such as feed, biofertilizers and biofuels, it is possible to use centrate from anaerobic digestion as the sole nutrient source, as a way of reducing costs.

Lipids rich in ω-3 polyunsaturated fatty acids from microalgae.

Despite microalgae recently receiving enormous attention as a potential source of biodiesel, their use is still not feasible as an alternative to fossil fuels. Recently, interest in microalgae has focused on the production of bioactive compounds such as polyunsaturated fatty acids (PUFA), which provide microalgae a high added value. Several considerations need to be assessed for optimizing PUFA production from microalgae. Firstly, a microalgae species that produces high PUFA concentrations should be selected, such as Nannochloropsis gaditana, Isochrysis galbana, Phaeodactylum tricornutum, and Crypthecodinium cohnii, with marine species gaining more attention than do freshwater species. Closed cultivation processes, e.g., photobioreactors, are the most appropriate since temperature, pH, and nutrients can be controlled. An airlift column with LEDs or optical fibers to distribute photons into the culture media can be used at small scale to produce inoculum, while tubular and flat panels are used at commercial scale. Depending on the microalgae, a temperature range from 15 to 28 °C and a pH from 7 to 8 can be employed. Relevant conditions for PUFA production are medium light irradiances (50-300 µmol photons m(-2) s(-1)), air enriched with (0-1 % (v/v) CO2, as well as nitrogen and phosphorous limitation. For research purposes, the most appropriate medium for PUFA production is Bold's Basal, whereas mixotrophic cultivation using sucrose or glucose as the carbon source has been reported for industrial processes. For cell harvesting, the use of tangential flow membrane filtration or disk stack centrifugation is advisable at commercial scale. Current researches on PUFA extraction have focused on the use of organic solvents assisted with ultrasound or microwaves, supercritical fluids, and electroporation or are enzyme assisted. Commercial-scale extraction involves mainly physical methods such as bead mills and expeller presses. All these factors should be taken into account when choosing a PUFA production system, as discussed in this review.

Wastewater treatment using microalgae: how realistic a contribution might it be to significant urban wastewater treatment?

Microalgae have been proposed as an option for wastewater treatment since the 1960s, but still, this technology has not been expanded to an industrial scale. In this paper, the major factors limiting the performance of these systems are analysed. The composition of the wastewater is highly relevant, and especially the presence of pollutants such as heavy metals and emerging compounds. Biological and engineering aspects are also critical and have to be improved to at least approximate the performance of conventional systems, not just in terms of capacity and efficiency but also in terms of robustness. Finally, the harvesting of the biomass and its processing into valuable products pose a challenge; yet at the same time, an opportunity exists to increase economic profitability. Land requirement is a major bottleneck that can be ameliorated by improving the system's photosynthetic efficiency. Land requirement has a significant impact on the economic balance, but the profits from the biomass produced can enhance these systems' reliability, especially in small cities.

Effect of daytime CO2 supplement on productivity and biochemical composition of Scenedesmus armatus under outdoor cultivation.

The cultivation of Scenedesmus armatus was carried out under outdoor Thailand climate conditions. The highest actual growth rate occurred at around 9:00 a.m. to 3:00 p.m., with a wide pH range of 6.4 to 11. The supply of CO2 had slight influence on growth characteristics but did exert some observable effects on nutritional accumulations. Adding CO2 from 2 to 15% by volume in the aeration (0.2 vvm) caused an increase in lipid and protein from 19.8 to 25.6 and 37.8 to 48.2% w/w, respectively, whereas carbohydrate decreased from 42.5 to 26.2% w/w. Scenedesmus armatus cultivated with 2% CO2-enriched air provided the highest the average of the average biomass productivity of 91.25 mg L(-1) d(-1), which corresponded to a CO2 fixation of 165 mg CO2 L(-1) d(-1) with the average lipid, protein, and carbohydrate productivities of 22.24, 38.34, and 30.67 mg L(-1) d(-1).

Effects of outdoor cultures on the growth and lipid production of Phaeodactylum tricornutum using closed photobioreactors.

One of the principal challenges for large scale production of microalgae is the high costs of biomass production. Aiming for minimize this problem, microalgal biodiesel production should focus on outdoors cultures, using available solar light and allowing lower energy cost process. Testing species that proved to be common and easy to culture may be a good approach in this process. The present work reports indoor-outdoor cultures of Phaeodactylum tricornutum using different bioreactors types, using cell growth, biochemical composition, and the profiles of the fatty acids produced as the parameters to test the optimization processes. The results show that the use of outdoor cultures is a good choice to obtain P. tricornutum biomass with a good potential for biodiesel production. The microalgae produced reached better growth efficiency, major lipid content and showed an increment in the percentage of saturated fatty acids (required on the biodiesel production) respect indoor cultures. These results are important to show the relevance of using outdoor cultures as a way to improve the efficiency and the energetic balance of the biodiesel production with P. tricornutum algae.