Un biocarburant fabriqué à partir de la pollution industrielle ? L’idée n’est pas nouvelle, mais le procédé complexe, essentiellement à cause du monoxyde d’azote. Ce gaz inhibe le développement des microalgues consommatrices de dioxyde de carbone, et donc bonnes candidates pour le processus. La microalgue Heterosigma akashiwo semble pourtant se distinguer du lot.
Microalgae are small in size with negatively charged surface. They are usually stable in suspension culture and hard to flocculate. The present work emphasizes on the synthesis of cationic guar gum (CGG) by the introduction of quaternary amine groups onto the backbone of guar gum (GG) from N-3-Chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC). The optimal dosage of the synthesized cationic guar gum is used to flocculate two different green algae viz. Chlorella sp. CB4 and Chlamydomonas sp. CRP7.
This study investigated the removal of nitrogen and phosphorus from the effluent of a submerged anaerobic membrane bioreactor (SAnMBR) by means of a lab-scale photobioreactor in which algae biomass was cultured in a semi-continuous mode for a period of 42 days. Solids retention time was 2 days and a stable pH value in the system was maintained by adding CO2. Nitrogen and phosphorus concentrations in the SAnMBR effluent fluctuated according to the operating performance of the bioreactor and the properties of its actual wastewater load. Despite these variations, the anaerobic effluent proved to be a suitable growth medium for microalgae (mean biomass productivity was 234 mg·l-1·d-1), achieving a nutrient removal efficiency of 67.2% for ammonium (NH4+-N) and 97.8% for phosphate (PO4-3- P). When conditions were optimum, excellent water quality with very low ammonium and phosphate concentrations was obtained.
Harvesting of secreted fuel precursors is an alternative approach to sustainable biofuel production from algae, and relies on selective separation of growth media from algal suspensions. Membrane fouling and species fractionation for selected ultrafiltration (UF) and microfiltration (MF) membranes were investigated for this purpose. Suspensions were filtered using total recycle, flux-stepping protocols to measure fouling rates and subsequent fouling reversibility. Severe fouling was observed at high flux values for 50 kg/mol UF and 0.22 μm MF membranes, with much of the fouling irreversible. In contrast, a 5 μm MF membrane showed essentially no increase in resistance, even though the whole algal cells were rejected to form a cake on the membrane surface. Analysis of the permeate from the 5 μm MF filtration indicated the presence of “protein-like”, “humic-like”, and high-molecular-mass polymeric materials, as well as submicron particles. However, model solutions of dissolved organic material showed very low fouling compared to the as-grown algal suspensions. Instead, submicron particles present in the algal suspensions and in the 5 μm MF permeate are thought to be the primary foulants by forming high-resistance cakes on the UF and 0.22 μm MF membranes and also by plugging the pores of 0.22 μm MF membranes. Thus, the flux decline and lack of “easy“ reversibility for our algal suspensions, filtered on specific membranes, appears to be primarily associated with deposition of smaller colloidal species within the membrane and/or near its surface, rather than with macromolecules or a cake of whole algal cells. Furthermore, membrane characteristics similar to those of the 5 MF μm membrane employed may offer a unique strategy for separation of these undesirable particulate materials from healthy cultures of algae with large-enough size.
Microalgae are photosynthetic microorganisms living in marine or freshwater environment. In this study, samples of Chlorella spp. and Nannochloropsis from two different origins were analysed to settle a preliminary characterization of these microorganisms as intermediate energy carriers and their properties compared to a conventional lignocellulosic feedstock (pine chips). Both microalgae samples were characterized in terms of elemental composition (CHONS and P) and thermogravimetric behavior. This was investigated through non-isothermal thermogravimetric analysis in nitrogen atmosphere at heating rate of 15 °C min−1 and temperature up to 800 °C. Solid residues produced at 300 °C and 800 °C from TGA were also analysed to determine the ultimate composition of chars. Activation energy, reaction order and pre-exponential factor were calculated for the single step conversion mechanism of 1 g of Chlorella spp. and compared to literature data on Chlorella protothecoides and Spirulina platensis. Calculated kinetic parameters, given as intervals of several determinations, resulted to be: pre-exponential factor (A) 1.47–1.62E6 min−1, activation energy (E) 7.13–7.92E4 J mol−1, reaction order (n) 1.69–2.41. 1.2 kg of Chlorella spp. was then processed in a newly designed batch pyrolysis pilot reactor, capable of converting up to 1.5 kg h−1 of material, and pyrolysis liquid collected, analysed and compared with a sample of fast pyrolysis from pine chips. This preliminary investigation aimed at carrying out a first characterization of algae oil and optimise the operational aspects of the reactor, tested with the first time with this unconventional feedstock. The algae pyrolysis oil exhibited superior properties as intermediate energy carrier compared to pyrolysis oil from fast pyrolysis of pine chips, in particular higher HHV and carbon content and lower oxygen and water content. These data can potentially be used in the design and modelling of thermochemical conversion processes of microalgae.
This paper investigated the effect of cell rupturing methods on the drying characteristics and the lipid compositions of a green algae consortium grown in an open raceway pond. The ruptured microalgae samples obtained from French press, Autoclave & Sonication methods were used for conducting thin layer drying experiment at four drying temperatures (30, 50, 70 and 90 °C). The rate of moisture removal at each drying condition was recorded until no change in moisture loss. A typical drying curve for a microalgae consortium indicated that the rate of drying was limited by diffusion. Among three drying models (Newton, Page and Henderson & Pabis) used to fit the drying data, Page model fitted well on the experimental drying data with a coefficient of determination (R2) of 0.99. Solvent extraction of French press ruptured cells produced the highest total lipid yield with no significant change in lipid compositions.
Microalgae are a potential resource for biodiesel production. A green alga, Chlorella sp., was isolated from Arctic sea ice, which was named ArM0029B. These algae displayed faster growth at a wide temperature range of 4°C to 32°C compared to Chlorella vulgaris. ArM0029B also accumulated high levels of total fatty acids under nitrogen starvation conditions, reaching 39% of dry cell weight, with the proportion of oleic acid (18:1) and linoleic acid (18:2) reaching 54% of total fatty acids. Taken together, these results indicate that the newly identified Chlorella species, ArM0029B, is a promising candidate for biodiesel production.
Microalgae have garnered interest for the production of valuable molecules ranging from therapeutic proteins to biofuels. However, microalgae also are associated with the considerable problem of phytoplankton bloom. In this study, we demonstrated algal growth using Isochrysis galbana as a model can be controlled photobiologically. Long dark period (24-h light: 24-h dark) unlike common photoperiod resulted in biomass loss and slower growth rates, but were unlikely to cause fatal damage. Algal cell growth can be significantly recovered with the onset of light. Also, it was confirmed that blue light-emitting diode (LED) illumination was able to effectively support cell growth of I. galbana as the sole light source. The blue LED intensity with 200% (580 l×, 18.52 μmol m−2 s−1) based on 8000 l× (98.4 μmol m−2 s−1) fluorescent lamp provided the best support for growth of I. galbana. We verified excessive light intensities lead to inhibition of algal growth, whereas low light intensities also did not promote algal growth. Further, I. galbana cell growth can be controlled using blue LED with extremely high LED intensities. These results may provide means to control algal population for either goal of growth or inhibition through proper use of such illumination.
The pyrolysis of algal (Laminaria digitata, Fucus serratus and mix macroalge species from Black sea) and lignocellulosic (safflower oil cake and grape seed) biomasses was studied at 500 °C in a fluidized bed reactor. The yields of pyrolysis products (char, liquid and gas) were quantified. Pyrolysis condensates were produced in two separate phases; aqueous phase and oil. The yield and composition of products from seaweed pyrolysis were compared with those obtained from terrestrial biomass. Chemical compositions of pyrolysis products relevant to fuel applications were determined. In addition, oils and aqueous phases were analyzed by GC-MS and HPLC. The oil yields from seaweeds varied between 11 and 17%, whereas yields from lignocellulosic biomasses were in the range of 23 - 40%. The oils from lignocellulosic biomasses showed a higher heating value (30.04-31.25 MJ kg−1) than that of oil from seaweeds. The aqueous phase yields from lignocellulosic biomasses and seaweeds were about 19-21% and 17-26%, respectively. The pyrolysis gases with a yield of about 17-37% were composed of mostly of carbon oxides. The yields of char were in the range 29 - 36% for seaweeds and 23-26% for lignocellulosic biomass. Due to the higher content of ash (41-52%), the char obtained from seaweeds had a lower heating value than those from grape seed and safflower oil cake
A highly efficient microalgae cultivation process was developed for carbon dioxide capture using nutrients from treated sewage. A submerged-membrane filtration system was installed in a photobioreactor to achieve high nutrient loading and to maintain a high concentration and production of microalgae. Chlorella vulgaris, Botryococcus braunii and Spirulina platensis were continuously cultivated with simulated treated sewage and 1%-CO2 gas. The optimum hydraulic retention time (HRT) and solids retention time (SRT) were explored to achieve the maximum CO2 capture rate, nutrient removal rate and microalgae biomass productivity. The carbon dioxide capture rate and volumetric microalgae productivity were high when the reactor was operated under 1-day (HRT) and 18-days (SRT) conditions. The independent control of HRT and SRT is effective for efficient microalgae cultivation and carbon dioxide capture using treated sewage.
The present work addresses energy consumption in raceway ponds (RWPs). This kind of systems are today the most utilized industrial plant for outdoor algae cultivation. The problem has been addressed combining theoretical correlations and experimental data. Head losses for conventional raceway ponds were evaluated, and the results were compared with data available in literature. Computational fluid dynamics was used to support the theoretical analysis. This study suggested possible improvements to the traditional RWP design: an Innovative Raceway Pond (IRP II) was therefore designed, built and operated in parallel with a reference pilot RWP in a test site. Several modifications to traditional RWP design were implemented in the IRP II: the paddle wheel was substituted by a propeller, the water head was reduced and baffle boards were installed in the curves. To validate the new design, head losses and therefore energy consumption in the different systems were evaluated, during cultivation experiments, with two microalgae strains. The theoretical and experimental study allowed a validated calculation, which showed the importance of concentrated head losses towards distributed ones. The analysis highlighted how these losses weight at different pond scales, suggesting possible improvements of the RWP energy performance – as achieved in the IRP II – through revised design for optimized mixing.
The 6th Dubrovnik Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES Conference), attended by 418 scientists from 55 countries representing six continents. It was held in 2011 and dedicated to the improvement and dissemination of knowledge on methods, policies and technologies for increasing the sustainability of development, taking into account its economic, environmental and social pillars, as well as methods for assessing and measuring sustainability of development, regarding energy, transport, water and environment systems and their many combinations.
Microalgae are attracting renewed interest from both the scientific and public communities owing to their potential applications as sustainable feed stocks for the production of biofuels and high value compounds, and environmental remediation. Recent advances in molecular and biochemical analyses of microalgae point toward interesting differences in lipid metabolism between algal species and in comparison to plants. These differences range from distinct acyl groups present in algal lipids, to a possible more direct role of plastids in the assembly of TAGs with consequences for the overall subcellular organization of glycerolipid metabolism. Thus, studying lipid metabolism in microalgae points to new possible avenues of genetic engineering of lipid metabolism in this organism group, and may also inform studies of lipid metabolism in plants.
In this study, the effects of enzymatic hydrolysis on lipid extraction from microalga (Chlorella vulgaris) were investigated prior to biodiesel production. The initial fatty acids content of C. vulgaris was 87.6 mg/g cell. The microalgal cell walls were hydrolyzed by cellulases and then their lipid fractions were extracted using various organic solvents such as hexane, methanol, and chloroform. Optimal pH and temperature for the enzymatic hydrolysis were pH 4.8 and 50 °C, respectively, and the maximal hydrolysis yield was 85.3%, which was achieved after 72 h. After the enzymatic hydrolysis, the lipid extraction yield by the organic solvents was improved compared to when there was no enzymatic hydrolysis process, by 1.29–1.73-fold depending on the solvents used. The total fatty acid methyl ester (FAME) productivity through the enzymatic hydrolysis was higher than when there was no enzymatic hydrolysis, by 1.10–1.69-fold depending on the solvents used. When lipid was extracted from the C. vulgaris after the enzymatic hydrolysis in chloroform-methanol solution, FAME productivity was 59.4 mg FAME/g cell.
Volatile fatty acids (VFAs) were produced from the marine macroalgae, Laminaria japonica, Pachymeniopsis elliptica, and Enteromorpha crinite by anaerobic fermentation using a microbial community derived from a municipal wastewater treatment plant. Methanogen inhibitor (iodoform), pH control, substrate concentration, and alkaline and thermal pretreatments affected VFA productivity. Acetic, propionic, and butyric acids were the main products. A maximum VFA concentration of 15.2 g/L was obtained from 50 g/L of L. japonica in 3 days at 35°C and pH 6.5-7.0. Pretreatment with 0.5 N NaOH improved VFA productivity by 56% compared to control. The result shows the applicability of marine macroalgae as biomass feedstock for the production of VFAs which can be converted to mixed alcohol fuels.
The effect of light conditions on the growth of green algae Chlorella vulgaris and cyanobacteria Gloeothece membranacea was investigated by filtering different wavelengths of visible light and comparing against a model daylight source as a control. Luminescent acrylic sheets containing violet, green, orange or red dyes illuminated by a solar simulator produced the desired wavelengths of light for this study. From the experimental results the highest specific growth rate for C.vulgaris was achieved using the orange range whereas violet light promoted the growth of G.membranacea. Red light exhibited the least efficiency in conversion of light energy into biomass in both strains of microalgae. Photosynthetic pigment formation was examined and maximum chlorophyll-a production in C.vulgaris was obtained by red light illumination. Green light yielded the best chlorophyll-a production in G.membranacea. The proposed illumination strategy offers improved microalgae growth without resorting to artificial light sources, reducing energy use and costs of cultivation.
The efficiency of treating citric acid effluent by green algae Chlorella was investigated. With the highest growth rate, Chlorella vulgaris C9-JN2010 that could efficiently remove nutrients in the citric acid effluent was selected for scale-up batch experiments under the optimal conditions, where its maximum biomass was 1.04 g·l-1 and removal efficiencies of nutrients (nitrogen, phosphorus, total organic carbon, chemical oxygen demand and biochemical oxygen demand) were above 90.0%. Algal lipid and protein contents were around 340.0 and 500.0 mg·g-1 of the harvested biomass, respectively. Proportions of polyunsaturated fatty acids in the lipids and eight kinds of essential amino acids in algal protein were 74.0% and 40.0%, respectively. Three major fatty acids were hexadecanoic acid, eicosapentaenoic acid and docosadienoic acid. This specific effluent treatment process could be proposed as a dual-beneficial approach, which converts nutrients in the high strength citric acid effluent into profitable byproducts and reduces the contaminations.
Major challenges of the modern world: energy security, oil price, resources depletion and climate change, have prompted significant advances in research and development of biomass-derived energy and fuels. Algal biofuels are seen as one of the most promising solutions of global energy crisis and climate change for the years to come. Major advantages of algae are potentially high yield and no competition with food crops for arable land and fresh water resource. This review summarises recent advances in algal biofuel production and focuses on synthesis of transportation fuel rather than characterising algal feedstocks or their well-documented potential as bioenergy resource. The available literature covering production of bioethanol, biodiesel and other potential liquid fuels are evaluated. Overall finding from this study suggests that to date the most effective methods of producing biofuels from algal feedstocks are: fermentation of microalgae to bioethanol and production of biodiesel via in situ transesterification of microalgal biomass. The real breakthrough however is expected from metabolic engineering of photosynthetic organisms to produce and secrete biofuels that promises significant simplification of down-stream processing.
This review discusses anaerobic production of methane, hydrogen, ethanol, butanol and electricity from microalgal biomass. The amenability of microalgal biomass to these bioenergy conversion processes is compared with other aquatic and terrestrial biomass sources. The highest energy yields (kJ g-1 dry wt. microalgal biomass) reported in the literature are 14.8 as ethanol, 14.4 as methane, 6.6 as butanol and 1.2 as hydrogen. The highest power density reported from microalgal biomass in microbial fuel cells has been 980 mW m-2. Sequential production of different energy carriers increases attainable energy yields, but also increases investment and maintenance costs. Microalgal biomass is a promising feedstock for anaerobic energy conversion processes, especially for methanogenic digestion and ethanol fermentation. The reviewed studies have mainly been based on laboratory scale experiments and thus scale-up of anaerobic utilization of microalgal biomass for production of energy carriers is now timely and required for cost-effectiveness comparisons.
This study evaluated growth and lipid productivity of Nannochloropsis salina in bubble columns sparged with ambient air. Experiments were conducted in batch mode at gas-to-culture volume ratios of 0.08–0.28 min−1, under constant light input. The net energy from the process, considering the energy equivalence of the lipid produced and the energy input for sparging, is proposed as the basis to optimize the sparging rate. Based on this energetic measure, the optimal gas-to-culture volume was found to be 0.18 min−1. Under this optimal condition, the specific growth rate was 0.224 d−1; the gravimetric lipid content was 59.7%; and the carbon dioxide utilization efficiency was 57%. Considering the temporal profiles of biomass growth and pH, it is concluded that sparging with ambient air could limit biomass growth due to limited carbon availability, supporting the case for sparging with carbon dioxide-enriched air.