Nannochloropsis Gaditana Microalgae Research Articles

Hydrothermal liquefaction of Chlamydomonas nivalis and Nannochloropsis gaditana microalgae under different operating conditions over copper-exchanged zeolites

In this study, two different green microalgae, Chlamydomonas nivalis (C. nivalis) and Nannochloropsis gaditana (N. gaditana), were cultivated in open ponds and the harvested wet biomass was converted to bio-crude by hydrothermal liquefaction (HTL) with/without catalyst. Catalytic HTL experiments were performed by using copper-exchanged zeolites including Cu-MOR, Cu-ZSM-5, and Cu-SSZ13, synthesized by recently developed supercritical ion exchange method using scCO2. The composition of all bio-crudes was analyzed by elemental analysis and GC/MS. First, the effects of different operating conditions on the yields of the products and the bio-crude composition were determined for non-catalytic process. Temperature, duration, and water/algae biomass ratio in the feed were the process parameters investigated in the ranges of 250–350 ºC, 10–60 min, and 5–20 wt%, respectively. For C. nivalis, 300 ºC, 60 min, and water/algae ratio of 4 were the optimum conditions which led to maximum bio-crude yield of 18.8 wt%, while 300 ºC, 30 min, and water/algae ratio of 9 were the optimum ones for N. gaditana at which the maximum bio-crude yield of 34.0 wt% was observed. Bio-crude yield of N. gaditana was improved using Cu-MOR, while using catalysts for the case of C. nivalis resulted in more gasification with no positive effect on bio-crude yield. Moreover, elemental analysis showed that the fraction of nitrogen and oxygen in biocrude decreased in catalytic HTL runs, in line with the GC/MS results showing that the concentration of hydrocarbons and cyclic compounds increased in the presence of catalysts accompanied by a decrease in concentration of nitrogenous compounds.

Effect on Muscle Cellularity of Diet Supplementation with Nannochloropsis gaditana Microalgae in the Final Fattening Phase of Gilthead Seabream Culture up to Commercial Size

Previous studies have shown that Nannochloropsis gaditana can partially replace fishmeal in the diet of gilthead seabream, Sparus aurata. However, its effect on muscle growth is hardly known. This experiment was carried out with gilthead seabream adults that were fed with N. gaditana at two inclusion levels (2.5 or 5%) either raw (R2.5 and R5 groups) or cellulose-hydrolyzed (H2.5 and H5 groups) for 45 days in the final fattening phase. The body length and body weight were measured in all fish at the beginning and end of the experiment. Also, the white muscle transverse area (WM), size, number and fibrillar density of the white fibers were measured in 9 fish group−1. After 45 days, the body parameters and the WM did not show significant differences among the groups. However, muscle cellularity did show significant differences, such that the hypertrophy values were higher in the H2.5 and H5 than in the R2.5 and R5 groups. On the contrary, R2.5 and R5 showed the highest fibrillar density and hyperplasia values, which are often positively correlated with the fillet firmness and therefore could improve the final quality of the fish. No significant differences attributable to the inclusion levels of N. gaditana were observed.

Green extraction of microalgae components for incorporation in food and feed supplements

Microalgae have been long recognized as potential food and feed solution, since they are able to meet the population growth on demand for a more sustainable food and feed, especially with respect to protein production. In addition, bioactive components, such as eicosapentaenoic acid (EPA), with well-known antioxidant and anti-inflammatory properties, can be extracted and incorporated in food supplements. Microalgae cultivation and processing becomes even more sustainable if simultaneously coupled to green technologies for the environmental protection. One of the most promising techniques is the supercritical fluid extraction which allows to extract bioactive compounds without loss of their activity and free from extraction solvents. In this work, a pilot scale supercritical CO2 (ScCO2) extraction plant was exploited for performing the extraction of active components from microalgae biomass potentially usable in the food and the feed sectors. Nannochloropsis gaditana microalga was selected as natural producer of EPA. The extract obtained after ScCO2 tests was enriched of EPA and protein, therefore suitable for food applications. The exhausted biomass, having a high content of carbohydrates and total dietary fiber, might be proposed as feed suppl

Sustainable cultivation of Nannochloropsis gaditana microalgae in outdoor raceways using flue gases for a complete 2-year cycle: a Circular Economy challenge

This research was undertaken in the framework of the Circular Economy. Its aim is to assess the technical feasibility and sustainability of a semi-industrial process for the outdoor cultivation of Nannochloropsis gaditana, using flue gases, on demand, from a coal-fired power generation plant. Within this main aim, three secondary objectives were defined: (i) to produce an accurate forecast of the annual average biomass production; (ii) to assess how the production rate and the biochemical composition of the biomass vary with the weather conditions over the course of a year; and (iii) to identify suitable markets for the biomass produced, in accordance with Spanish legislation. The study was carried out over 2 years, and an extra year was taken to analyze the results. The importance of this research is that it covers the lack of current knowledge, based on the available literature, regarding experimentation with microalgae culture outdoors, on a semi-industrial scale of 10,000 L, for a period of two full years. Our results show that, firstly, productivity changes from 0.025 ± 0.010 g (dry weight) L−1 day−1 (g d.wt L−1 day−1) to 0.160 ± 0.030 g d.wt L−1 day−1, as irradiation increases, and secondly, that the content of polyunsaturated fatty acids decreases, from 4.770 ± 0.770% dry weight (% d.wt) to 3.220 ± 0.535% d.wt, as irradiation increases. The maintenance of the culture during a complete cycle of 2 years, under the stated conditions, demonstrates the technical feasibility and sustainability of the process. In accordance with current Spanish regulations, the results of biochemical analysis of the harvested biomass confirm that it is suitable for use as animal feed.

Exploitation of Nannochloropsis gaditana biomass for biodiesel and pellet production

Abstract A comparison of different inorganic and organic flocculants at doses of 50, 100 and 200 mg/L was performed to achieve the maximum biomass harvesting of Nannochloropsis gaditana microalgae. The best results were reached by aluminium chloride with 90.9 ± 0.2% biomass recovered followed by copper sulphate with 70.8 ± 0.3% at the maximum doses used. If the behaviour is analysed after spending 24 h, all flocculants recovered more than 90% algal biomass. In the oil extraction process, a maximum of 29.25 ± 1.10% extracted oil was achieved by Soxhlet using methanol-chloroform 2:1 as solvent and applying previous disruption by microwave. 20.4% less oil was released when n-hexane was used. Ultrasound extraction assisted by microwave reached peak values of 22.60 ± 1.03%. Methyl esters of saturated fatty acids (C14:0, C16:0 and C18:0) were found as the major constituents, accounting for about 70% of the total content. Direct transesterification with previous incubation accomplished higher biodiesel conversions than without it. Finally, pellet manufacturing from algal wastes obtained after the transesterification reaction was studied. The results indicated that these pellet should be mixed with another type of biomass (e.g., miscanthus or eucalyptus) to be used as fuel in biomass boilers.

Robust Mesoporous CoMo/γ-Al2O3 Catalysts from Cyclodextrin-Based Supramolecular Assemblies for Hydrothermal Processing of Microalgae: Effect of the Preparation Method.

Hydrothermal liquefaction (HTL) is a promising technology for the production of biocrude oil from microalgae. Although this catalyst-free technology is efficient under high-temperature and high-pressure conditions, the biocrude yield and quality can be further improved by using heterogeneous catalysts. The design of robust catalysts that preserve their performance under hydrothermal conditions will be therefore very important in the development of biorefinery technologies. In this work, we describe two different synthetic routes (i.e., impregnation and cyclodextrin-assisted one-pot colloidal approach), for the preparation in aqueous phase of six high surface area CoMo/γ-Al2O3 catalysts. Catalytic tests performed on the HTL of Nannochloropsis gaditana microalga indicate that solids prepared by the one-pot colloidal approach show higher hydrothermal stability and enhanced biocrude yield with respect to the catalyst-free test. The positive effect of the substitution of the block copolymer Tetronic T90R4 for Pluronic F127 in the preparation procedure was evidenced by diffuse reflectance UV-visible spectroscopy, X-ray diffraction, N2-adsorption-desorption, and H2-temperature-programmed reduction measurements and confirmed by the higher quality of the obtained biocrude, which exhibited lower oxygen content and higher-energy recovery equal to 62.5% of the initial biomass.

Kinetic analysis of the combustion process of Nannochloropsis gaditana microalgae based on thermogravimetric studies

Combustion and co-combustion of biomass are recognized as possible ways to apply renewable energy sources. The application of Nannochloropsis gaditana as a feedstock in thermal processes needs some fundamental research. This study presents the determination of thermochemical properties and kinetic parameters of the thermo-oxidation of Nannochloropsis gaditana using thermogravimetric data with combined evolved gas analysis via FTIR spectroscopy. Three stages of thermo-oxidative degradation were noted: moisture removal, decomposition of intrinsic lipids, carbohydrates and proteins, and oxidation of the formed remaining char. The main gaseous products generated during combustion were water, light hydrocarbons, oxygenated compounds, CO and CO2. However, above 730K, all intermediates were oxidized to CO and CO2.The parameters for the evaluation of fuel combustibility were determined and compared to those of other biomass sources. Ash-related issues were analyzed and discussed.Isoconversional and “data fitting” methods were used to determinate kinetic parameters. The isoconversional method proves that there is more than a single reaction mechanism of combustion due to the variability of activation energy values. Therefore, this method is not good for determining kinetic parameters of the thermo-oxidative process. The “data fitting” model could be interpreted in two ways: considering consecutive n-order (Fn) or first order (F1) reactions and considering consecutive first order reactions (F1F1) for two fractions of microalgae (first, carbohydrates and proteins; second, lipids). The devolatilization stage of the combustion process occurs with a definitively lower activation energy than the oxidation stage. The F1F1 reaction model could simulate the weight loss a little better than the Fn and F1. Correlation coefficients were all greater than 0.999, which can prove that the kinetic models were correctly found.

CO2 gasification process performance for energetic valorization of microalgae

In this study, CO2 gasification process of a marine biomass (Nannochloropsis gaditana microalgae char) has been evaluated. The experiments have been carried out according to a central composite design (CCD), by using a high-pressure thermogravimetric analyzer (HP-TGA). The effect of temperature, total pressure and gasifying agent volume concentration on the CO2 gasification process was studied. Within the CCD studied range, the process performance, expressed as reactivity and gasification rate at 50% conversion, was positively influenced by the increase of temperature and pressure, while CO2 concentration effect was negligible. Empirical models describing the gasification performance as a function of temperature and pressure are presented and discussed. The proposed models allow a more realistic approach of the microalgae gasification process, in comparison with other models where the catalytic effect is often neglected. This study reveals useful process aspects for the development and implementation of microalgae CO2 gasification at industrial scale.

Supercritical water gasification of microalgae and their constituents in a continuous reactor

The supercritical water gasification of Nannochloropsis gaditana microalgae has been studied in term of process development at 24MPa and 663°C. Gasification has been investigated using a 200cm3 down flow reactor working continuously. The effect of microalgae slurry concentration, with or without alkali catalysts, was studied. Moreover, the role played by different constituents of microalgae on gasification was investigated. Particularly, gasification of amino acids, carbohydrates and model mixtures among them was studied. Nannochloropsis gaditana was successfully gasified up to 97.4wt% as gasification efficiency and 86.0wt% as carbon efficiency. The product gas is mainly composed of hydrogen (52.0%), methane (17.9%) and CO2 (23.0%). Gasification of pure amino acids, which are the main components of microalgae, showed a very different resistance to gasification depending on the molecular structure of the molecules. Among the amino acid that have been studied in this work, gasification resistance is in the order glycine>leucine>glutamic acid, whereas CH4 concentration increases in order leucine>glutamic acid>glycine due to the number of methyl groups that are present in the molecules. From this work it can be concluded that gasification of microalgae is feasible in a continuous mode and that, depending on their molecular structure, amino acids offer a different resistance to gasification. These results can be of help in evaluating the feasibility of gasification of defatted microalgae after extraction of the oil.

Optimization of microalgae oil extraction under ultrasound and microwave irradiation

AbstractBACKGROUNDMicroalgae are one of the most promising biofuel sources that the world has to offer; nevertheless the conversion process is hampered by technical and economic problems that are mainly related to de‐watering and extraction. The efficiency of the process can be dramatically improved by means of non‐conventional techniques such as ultrasound (US) and microwaves (MW). Scaling‐up feasibility is strictly linked to reactor efficiency, energy consumption, environmental impact and overall cost. In the present work, the optimization of lipid extraction from Nannochloropsis gaditana microalga is investigated.RESULTSA series of selected solvent mixtures and procedures have been tested and compared. Conventional extraction procedures with chloroform/methanol mixtures and fast US‐ and MW‐assisted extractions with methanol gave comparable fatty acid (FA) w/w% from dried microalgae. The highest extraction yield and lowest energy consumption was found to occur under MW irradiation, especially at high temperatures and under pressure.CONCLUSIONThis study highlights the advantages of US‐ and MW‐assisted lipid extraction from microalgae, both in terms of efficiency and operational costs. © 2013 Society of Chemical Industry

Characterization of different heat transfer fluids and degradation study by using a pilot plant device operating at real conditions

A pilot plant was designed to evaluate the degradation of (heat transfer fluids) HTF for their application in (concentrating solar power) plants CSP. Firstly, the characterization of six HTFs was carried out: two ionic liquids ([BMIM][BF4] and [EMIM][BF4]), two molten salts (Hitec XL and solar salt), a commercial HTF (Mobiltherm 605) and an oil extracted from Nannochloropsis gaditana microalgae (NG oil). Mobiltherm 605 was selected for tuning the pilot plant due to its similarity to HTFs used in CSP, low cost and easy acquisition. The operating conditions were set according to thermogravimetric analysis. Thus, three isothermal experiments were carried out at 140, 160 ant 180 °C for 15 days. Mobiltherm 605 viscosity increased with time indicating that polymerization of hydrocarbon chains took place. Two mathematical models were developed to assess the HTF behaviour in the pilot plant. A mathematical model for the estimation of the most representative parameters (viscosity, heat capacity and overall heat transfer coefficient) of HTF performance was proposed. Furthermore, an activation/deactivation model was proposed to predict the variation of the estimated parameters with time. This model was validated with experimental viscosity measurements (average error of about 3%). Finally, the statistical significance of the model was proved.

Pyrolysis, combustion and gasification characteristics of Nannochloropsis gaditana microalgae

Pyrolysis, combustion and gasification characteristics of Nannochloropsis gaditana microalgae (NG microalgae) were investigated by thermogravimetric analysis (TGA). NG microalgae pyrolysis and combustion could be divided into three main stages: dehydration, proteins and polysaccharides degradation and char decomposition. The effects of the initial sample mass, particle size and gas flow on the pyrolysis and combustion processes were studied. In addition, gasification operation conditions such as temperature, initial sample mass, particle size, sweep gas flow and steam concentration, were experimentally evaluated.The evolved gases were analyzed online using mass spectroscopy (MS). In pyrolysis and combustion processes, most of the gas products were generated at the second degradation step. N-compounds evolution was associated with the degradation of proteins. Furthermore, SO2 release from combustion could be related to sulphated polysaccharides decomposition. The main products detected during gasification were CO2, CO, H2, indicating that oxidation reactions, water gas and water gas shift reactions, were predominant.

Thermogravimetric–mass spectrometric analysis of lignocellulosic and marine biomass pyrolysis

The pyrolysis characteristics of three lignocellulosic biomasses (fir wood, eucalyptus and pine bark) and a marine biomass (Nannochloropsis gaditana microalgae) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA–MS). Thermal degradation of lignocellulosic biomass was divided into four zones, corresponding to the decomposition of their main components (cellulose, hemicellulose and lignin) and a first step associated to water removal. Differences in volatile matter and cellulose content of lignocellulosic species resulted in different degradation rates. Microalgae pyrolysis occurred in three stages due to the main components of them (proteins), which are greatly different from lignocellulosic biomass. Heating rate effect was also studied. The main gaseous products formed were CO2, light hydrocarbons and H2O. H2 was detected at high temperatures, being associated to secondary reactions (char self-gasification). Pyrolysis kinetics were studied using a multiple-step model. The proposed model successfully predicted the pyrolytic behaviour of these samples resulting to be statistically meaningful.