Les algues font rêver les multinationales soucieuses de l’environnement et de leur image: Unilever et Richard Branson, le célèbre président de l’empire Virgin, viennent d’investir plusieurs millions de dollars dans une société californienne, Solazyme, qui développe des huiles et des carburants à base d’algues. Pas moins de 60 millions de dollars (47 millions d’euros) ont été apportés à Solazyme par différents investisseurs lors de sa dernière levée de fonds, selon le Wall Street Journal.
This paper describes the association of two bioreactors: one photoautotrophic and the other heterotrophic, connected by the gas phase and allowing an exchange of O(2) and CO(2) gases between them, benefiting from a symbiotic effect. The association of two bioreactors was proposed with the aim of improving the microalgae oil productivity for biodiesel production. The outlet gas flow from the autotrophic (O(2) enriched) bioreactor was used as the inlet gas flow for the heterotrophic bioreactor. In parallel, the outlet gas flow from another heterotrophic (CO(2) enriched) bioreactor was used as the inlet gas flow for the autotrophic bioreactor. Aside from using the air supplied from the auto- and hetero-trophic bioreactors as controls, one mixotrophic bioreactor was also studied and used as a model, for its claimed advantage of CO(2) and organic carbon being simultaneously assimilated. The microalga Chlorella protothecoides was chosen as a model due to its ability to grow under different nutritional modes (auto, hetero, and mixotrophic), and its ability to attain a high biomass productivity and lipid content, suitable for biodiesel production. The comparison between heterotrophic, autotrophic, and mixotrophic Chlorella protothecoides growth for lipid production revealed that heterotrophic growth achieved the highest biomass productivity and lipid content (>22%), and furthermore showed that these lipids had the most suitable fatty acid profile in order to produce high quality biodiesel. Both associations showed a higher biomass productivity (10-20%), when comparing the two separately operated bioreactors (controls) which occurred on the fourth day. A more remarkable result would have been seen if in actuality the two bioreactors had been inter-connected in a closed loop. The biomass productivity gain would have been 30% and the lipid productivity gain would have been 100%, as seen by comparing the productivities of the symbiotic assemblage with the sum of the two bioreactors operating separately (controls). These results show an advantage of the symbiotic bioreactors association towards a cost-effective microalgal biodiesel production.
Le ministre d'État de Développement économique Canada, l'honorable Denis Lebel, a profité de l'inauguration de l'usine de NutrOcéan inc. pour annoncer que l'entreprise a reçu une contribution remboursable de 175 542 $, consentie en vertu du programme Croissance des entreprises et des régions de Développement économique Canada.
À la faveur du premier choc pétrolier, en 1973, les États-Unis ont lancé une panoplie de projets de recherche en carburants alternatifs. L'un d'entre eux prévoyait la production de biocarburants à partir d'algues dans des bassins attenant à des usines de filtration d'eau, sur la base de travaux de pionniers californiens de l'utilisation des bactéries pour le traitement des eaux, William Oswald et Clarence Golueke.
Like any other living organisms, algae are plagued by diseases caused by fungi, protists, bacteria or viruses. As aquaculture continues to rise worldwide, pathogens of nori or biofuel sources are becoming a significant economic burden. Parasites are also increasingly being considered of equal importance with predators for ecosystem functioning. Altered disease patterns in disturbed environments are blamed for sudden extinctions, regime shifts, and spreading of alien species. Here we review the biodiversity and impact of pathogens and parasites of aquatic primary producers in freshwater and marine systems. We also cover recent advances on algal defence reactions, and discuss how emerging technologies can be used to reassess the profound, multi-faceted, and so far broadly-overlooked influence of algal diseases on ecosystem properties.
The utilisation of microalgal biomass as feedstock for bioethanol production has been very promising owing to the large amounts of carbohydrates embedded in the physiology of the microalgal cell. This is coupled with the potential of microalgae to achieve targets required for high growth rate bioethanol production, climate change mitigation and economic growth. The high content of complex carbohydrates entrapped in the cell wall of the microalgae makes it essential to incorporate a pre-treatment stage to release and convert these complex carbohydrates into simple sugars prior to the fermentation process. Hence, this study explores the influence of acid exposure as a microalgal pre-treatment strategy for bioethanol production. Different parameters were investigated: acid concentration, temperature, microalgae loading and pre-treatment time. A central composite design technique was employed to optimize the acid pre-treatment conditions. Results showed that the highest bioethanol concentration obtained was 7.20 g/L and this was achieved when the pre-treatment step was performed with 15 g/L of microalgae at 140 °C using 1% (v/v) of sulphuric acid for 30 min. In terms of ethanol yield, not, vert, similar52 wt% (g ethanol/g microalgae) maximum was obtained using 10 g/L of microalgae and 3% (v/v) of sulphuric acid under 160 °C for 15 min. The statistical analysis revealed amongst the parameters investigated that temperature is the most critical factor during acid pre-treatment of microalgae for bioethanol production.
Two conventional chemical coagulants (FeCl3 and Fe2(SO4)3) and five commercial polymeric flocculants (Drewfloc 447, Flocudex CS/5000, Flocusol CM/78, Chemifloc CV/300 and Chitosan) were comparatively evaluated for their ability to remove algal-bacterial biomass from the effluent of a photosynthetically oxygenated piggery wastewater biodegradation process. Chlorella sorokiniana, Scenedesmus obliquus, Chlorococcum sp. and a wild type Chlorella, in symbiosis with a bacterial consortium, were used as model algal-bacterial consortia. While the highest biomass removals (66-98 %) for the ferric salts were achieved at concentrations of 150-250 mg L-1, dosages of 25-50 mg L-1 were required for the polymer flocculants to support comparable removal efficiencies. Process efficiency declined when the polymer flocculant was overdosed. Biomass concentration did not show a significant impact on flocculation within the concentration range tested. The high flocculant requirements herein recorded might be due to the competition of colloidal organic for the flocculants and the stationary phase conditions of biomass.
The present work deals with the evaluation of hydrodynamic effects on the ultrafiltration of microalgae suspensions for harvesting or metabolite production by coupling photobioreactors with membrane separation processes. Two ultrafiltration systems were compared: the first was a cross flow ultrafiltration unit equipped with a flat sheet membrane and the second was a dynamic filtration module, consisting of a disk rotating close to a stationary membrane in order to reduce fouling. Cylindrotheca fusiformis and Skeletonema costatum microalgal suspensions have been ultrafiltered at 1 bar with a 40,000 Da polyacrilonitrile (PAN) membrane with a shear rate equal to 16,000 s−1. First results have shown that the dynamic filtration module yielded permeate flux almost twice higher than the cross flow filtration system both at constant concentration and in concentration mode for the two microalgae species. Further work will be required to better evaluate the potential of the dynamic module, its maximum concentration, treatment capacity, investment cost, energy consumption and impact of shear on microorganisms
The potential of microalgae as feedstock for methane production is evaluated from a process technical and economic point of view. Production of mixed culture algae in raceway ponds on non-agricultural sites, such as landfills, was identified as a preferred approach. The potential of straightforward bio-methanation, which includes pre-concentration of microalgae and utilization of a high rate anaerobic reactor was examined based on the premises of achievable up-concentration from 0.2 – 0.6 kg dry matter (DM) m-3 to 20 - 60 kg DM m-3 and an effective bio-methanation of the concentrate at a loading rate of 20 kg DM m-3 d-1. The costs of biomass available for bio-methanation under such conditions were calculated to be in the range of € 86 - € 124 ton-1 DM. The levelised cost of energy by means of the process line “algae biomass – biogas – total energy module” would be in the order of € 0.170 – 0.087 kWh-1, taking into account a carbon credit of about € 30 ton-1 CO2(eq).
Light-emitting diodes (LEDs) with various light wavelengths (red, yellow, green, blue and white) and various levels of light intensity (750, 1500 and 3000 μmol m−2 s−1) are applied to study the effects of light sources on chlorophyll a (Chl) and phycocyanin (Phy) production of Spirulina platensis. Logistic rate equations are used to depict the kinetic behavior of algal growth and pigments formation under various light sources and intensities. According to the regression results, a red LED is the best for algae growth. On the other hand, yellow light gives the best specific Chl production rate with a light intensity of 750 or 1500 μmol m−2 s−1, and blue light yields the best specific pigments (for Chl and Phy) production rates at 3000 μmol m−2 s−1. From the model fitting results, it is found that, at a higher light intensity, a higher specific Chl production rate accompanied by a higher S. platensis biomass is obtained. However, as for Phy production, a higher biomass results in a lower specific Phy production rate. The only exception is the use of blue light, which shows a positive effect on both Chl and Phy production rates under a higher light intensity.
Photosynthetic mitigation of CO2 with microalgae is promising from many aspects, thereby becoming a popular research topic. In this study, seven out of twenty-two indigenous Scenedesmus obliquus isolates obtained from southern Taiwan were selected for detailed study on their CO2 fixation ability. Among them, two strains, namely, S. obliquus CNW-N and AS-6-1, displayed high cell growth rate and CO2 removal ability when they were grown on 20% CO2. The two strains show a high specific growth rate of 1.019 and 1.065 d−1, respectively, along with a high biomass concentration (2.63 and 1.90 g L−1, respectively). The biomass productivity of S. obliquus CNW-N and AS-6-1 was 201.4 and 150.7 mg L−1d−1, respectively and the CO2 consumption rate could reach 390.2 and 290.2 mg L−1 d−1, respectively, which are higher than that reported by most relevant studies.
The dual objective of sustainable aquaculture, i.e. to produce food while sustaining natural resources is achieved only when production systems with a minimum ecological impact are used. Recirculating Aquaculture Systems (RAS) provides opportunities to reduce water usage and to improve waste management and nutrient recycling. RAS makes intensive fish production compatible with environmental sustainability. This review aims to summarize the most recent developments within RAS that have contributed to the environmental sustainability of the European aquaculture sector. The review first shows the ongoing expansion of RAS production by species and country in Europe. Life cycle analysis showed that feed, fish production and waste and energy are the principal components explaining the ecological impact of RAS. Ongoing developments in RAS show two trends focusing on: (1) technical improvements within the recirculation loop and (2) recycling of nutrients through integrated farming. Both trends contributed to improvements in the environmental sustainability of RAS. Developments within the recirculation loop that are reviewed are the introduction of denitrification reactors, sludge thickening technologies and the use of ozone. New approached towards integrated systems include the incorporation of wetlands and algal controlled systems in RAS. Finally, the review identifies the key research priorities that will contribute to the future reduction of the ecological impact of RAS. Possible future breakthroughs in the fields of waste production and removal might further enhance the sustainabilty of fish production in RAS.
Production of biofuel from algae is dependent on the microalgal biomass production rate and lipid content. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a key role. In this research, the marine microalgae Dunaliella tertiolecta was used as a model organism and a profile of its nutritional requirements was determined. Inorganic phosphate (PO43-) and trace elements: cobalt (Co2+), iron (Fe3+), molybdenum (Mo2+) and manganese (Mn2+) were identified as required for algae optimum growth. Inorganic nitrogen in the form of nitrate (NO3-) instead of ammonium (NH4+) was required for maximal biomass production. Lipids accumulated under nitrogen starvation growth condition and this was time-dependent. Results of this research can be applied to maximize production of microalgal lipids in optimally designed photobioreactors
A rigorous chemical engineering mass balance/unit operations approach is applied here to bio-diesel from algae mass culture.
An equivalent of 50,000,000 gallons per year (0.006002 m3/s) of petroleum-based Number 2 fuel oil (U.S., diesel for compression-ignition engines, about 0.1% of annual U.S. consumption) from oleaginous algae is the target. Methyl algaeate and ethyl algaeate diesel can according to this analysis conceptually be produced largely in a technologically sustainable way albeit at a lower available diesel yield. About 11 sq. miles of algae ponds would be needed with optimistic assumptions of 50 g biomass yield per day and m2 pond area. CO2 to foster algae growth should be supplied from a sustainable source such as a biomass-based ethanol production. Reliance on fossil-based CO2 from power plants or fertilizer production renders algae diesel non-sustainable in the long term.
This paper revisits the recent developments in biofuel markets and their economic, social and environmental impacts. Several countries have introduced mandates and targets for biofuel expansion. Production, international trade and investment have increased sharply in the last few years. However, some analysts linked biofuels to the 2007–2008 global food crisis. Existing studies diverge on the magnitude of the projected long-term impacts of biofuels on food prices and supply, with studies that model only the agricultural sector showing higher impacts and studies that model the entire economy showing relatively lower impacts. In terms of climate change mitigation, biofuels reduces GHG emissions only if GHG emissions related to land-use change are avoided. When biofuel production entails conversion of forest to cropland, net reduction of GHG would not be realized for many years. Existing literature does not favor the diversion of food for large-scale biofuels production, but the regulated expansion of biofuels in countries with surplus lands and a strong biofuel industry cannot be ruled out. Developments in non-food based or cellulosic (or second generation) biofuels may offer some hope, yet they still compete with food supply through land use and are currently constrained by a number of technical and economic barriers.
Chlorella variabilis NC64A, a unicellular photosynthetic green alga (Trebouxiophyceae), is an intracellular photobiont of Paramecium bursaria and a model system for studying virus/algal interactions. We sequenced its 46-Mb nuclear genome, revealing an expansion of protein families that could have participated in adaptation to symbiosis. NC64A exhibits variations in GC content across its genome that correlate with global expression level, average intron size, and codon usage bias. Although Chlorella species have been assumed to be asexual and nonmotile, the NC64A genome encodes all the known meiosis-specific proteins and a subset of proteins found in flagella. We hypothesize that Chlorella might have retained a flagella-derived structure that could be involved in sexual reproduction. Furthermore, a survey of phytohormone pathways in chlorophyte algae identified algal orthologs of Arabidopsis thaliana genes involved in hormone biosynthesis and signaling, suggesting that these functions were established prior to the evolution of land plants. We show that the ability of Chlorella to produce chitinous cell walls likely resulted from the capture of metabolic genes by horizontal gene transfer from algal viruses, prokaryotes, or fungi. Analysis of the NC64A genome substantially advances our understanding of the green lineage evolution, including the genomic interplay with viruses and symbiosis between eukaryotes.
Un an après la visite express du premier ministre François Fillon sur les plages du département, les Côtes-d'Armor gardent l'œil sur leurs rivages et constatent qu'après trois années de fortes marées, le phénomène des algues vertes connaît une sensible réduction en 2010.
Photosynthetic hydrogen production Suleyman I. Allakhverdiev, Velmurugan Thavasi, Vladimir D. Kreslavski, Sergey K. Zharmukhamedov, Vyacheslav V. Klimov, Seeram Ramakrishn, Dmitry A. Los, Mamoru Mimuro, Hiroshi Nishihara and Robert Carpentier
Among various technologies for hydrogen production, the use of oxygenic natural photosynthesis has a great potential as can use clean and cheap sources—water and solar energy. In oxygenic photosynthetic microorganisms electrons and protons produced from water and redirected by the photosynthetic electron-transport chain via ferredoxin to the hydrogen-producing enzymes hydrogenase or nitrogenase. By these enzymes, e- and H+ recombine and form molecular hydrogen. Hydrogenase activity can be very high but is extremely sensitive to the photosynthetically evolved O2 that leads to reduced and unstable H2 production. However, presently, several approaches are developed to improve the energetic efficiency to generate H2. This review examines the main available pathways to improve the photosynthetic H2 production.
We determined the influence of a Pt/C catalyst, high-pressure H2, and pH on the upgrading of a crude algal bio-oil in supercritical water (SCW). The SCW treatment led to a product oil with a higher heating value (not, vert, similar42 MJ/kg) and lower acid number than the crude bio-oil. The product oil was also lower in O and N and essentially free of sulfur. Including the Pt/C catalyst in the reactor led to a freely flowing liquid product oil with a high abundance of hydrocarbons. Overall, many of the properties of the upgraded oil obtained from catalytic treatment in SCW are similar to those of hydrocarbon fuels derived from fossil fuel resources. Thus, this work shows that the crude bio-oil from hydrothermal liquefaction of a microalga can be effectively upgraded in supercritical water in the presence of a Pt/C catalyst.