Scenedesmus Almeriensis Research Articles

Effect of temperature on the oxygen production capacity and growth of scenedesmus almeriensis

The optimal temperature and irradiance to maximise oxygen production were 39.3 °C and 512.5 μmol photons·m−2·s−1, respectively. These values were obtained by photorespirometry, which is a quick method to measure the photosynthetic and respiration rates of microalgae at a laboratory scale. With these conditions, the global oxygen production rate of S. almeriensis was 246.23 mgoxygen·gbiomass−1·h−1. When the culture temperature was controlled at 39.3 °C for 1 h per day, the daily oxygen production capacity of S. almeriensis increased from 3129.5 mgoxygen·gbiomass−1 to 3778.5 mgoxygen·gbiomass−1. However, keeping the temperature at 39.3 °C for a longer time caused a damage to the photosynthetic apparatus. This was validated using laboratory-scale bubble columns. The damage was reversible when heating the cells for <2 h, but keeping the temperature of the culture at 39.3 °C for 3 h led to an irreversible damage and a 6 % decrease in the photosynthetic performance. Controlling the overheating of microalgal cultures is crucial to maximise growth. In addition, the duration of the exposure to high temperatures should also be included into growth and taken in consideration.

Coke formation and mineral accumulation on HZSM-5/Al2O3 catalysts during in-situ catalytic fast pyrolysis of microalgae over multiple regeneration cycles

Catalyst deactivation caused by coke formation and mineral accumulation occurs simultaneously and intensively during the catalytic pyrolysis of biomass. A comprehensive understanding of their distinction and interactions during the deactivation and regeneration process of shaped catalysts are essential for catalyst advancement and longevity in industrial application. In this study, we report the reversible and non-reversible catalyst deactivation caused by coke formation, mineral accumulation and the interactions thereof by a multi-technique characterization of a HZSM-5/Al2O3 catalyst (crushed extrudates; particle size 1–3 mm) in fast pyrolysis. A total of 5 cycles of catalyst reaction/regeneration were performed in a bench scale reactor (60 g/h feedstock feeding rate; pyrolysis temperature of 500°C) using both raw microalgae (Scenedesmus almeriensis, or SA) and citric acid treated microalgae (CA-SA). The measured properties of the fresh and used catalysts (SA-R5, 5th recycled and reacted catalyst mixed with SA) disclosed the anticorrelation of the metal contents (increased by a factor of 2.5 times) with surface area (-4.4 %) and Brønsted acid (-70.4 %). The presence of minerals in the feedstock might catalytically alter the pyrolysis chemistry, interfere with the shape selectivity and acidity of the catalysts, thus reduced the formation of coke. Additionally, metal species from the microalgae ash that ended up on the catalyst could promote coke combustion during the regeneration process. This work revealed the demineralization of the microalgae prior to fast pyrolysis minimized the rate of irreversible catalyst deactivation. Whereas, the trade-off between promoted coke formation after the ash removal of microalgae and accelerated minerals accumulation without microalgae demineralization should be evaluated.

Screening for alkaliphilic microalgae for carbon capture from ambient air and food production

SummaryThe production of alkaliphilic microalgae can contribute to address the challenging cost of using pure carbon dioxide in large reactors. At high pH values, carbon dioxide is rapidly scavenged and the supply rates of dissolved inorganic carbon from the atmosphere to alkaline media are high. The present study aimed to identify microalgal strains that can cope with high alkalinity and aeration rates. Eight strains were studied and the microalgae Chlorella vulgaris, Scenedesmus almeriensis and Nannochloropsis gaditana were the only ones that were able to grow under these conditions. Their biomass productivities using laboratory‐scale bubble columns with no pH control and high aeration flow were 0.20 ± 0.03, 0.24 ± 0.03 and 0.08 ± 0.01 g·L−1·day−1, respectively. The production of the two former was scaled up to pilot‐scale bubble columns. Overall, the amount of atmospheric carbon dioxide that was transformed into biomass was in the range of 10%–30%, depending on the strain used and the photobioreactor setup. The biomass was rich in proteins and β‐carotene, both valuable products, highlighting the potential production of food ingredients while capturing carbon dioxide from the atmosphere.

Mechanisms of copper and zinc bioremoval by microalgae and bacteria grown in nutrient rich wastewaters

Swine farming produces large quantities of nutrient-rich wastewater, which often contains metals such as Cu and Zn, used as feed additives for pigs. These metals must be removed from the wastewater before discharge but their retention in the biomass can limit its subsequent utilization. Photobioreactors are a very promising alternative for swine wastewater treatment, as the consortium of microalgae and bacteria growing symbiotically in these reactors allows high nutrient and metal removal efficiency at moderate costs. This work studies the mechanisms of removal of Cu(II) and Zn(II) by the two types of microorganisms growing in these photobioreactors. A microalga commonly used in wastewater treatment (Scenedesmus almeriensis) and an activated sludge were kept in contact with synthetic wastewater containing 100 mg/L of Cu and Zn. After 72 h, Scenedesmus almeriensis removed 43% of Cu and 45% of Zn, while activated sludge removed 78% of Cu and 96% of Zn. Single and sequential extractions of the biomasses using different extracting reagents revealed that biosorption on protonable groups is the dominant removal mechanisms. Mild reagents solubilized 69% of Cu and 94% of Zn from the microalgae and 76% of Cu and 93% of Zn from the activated sludge. Low metal concentrations in the oxidizable and residual fractions evidenced minimal bioaccumulation inside the cells. FTIR and ESEM-EDX analysis confirmed biosorption by ion exchange and complexation as the main metal remediation mechanisms. The weak bonds of the biosorbed Cu and Zn ions are beneficial for the valorization of biomass and the obtaining of safe bioproducts.

Carbon nanotube production from algal biochar using microwave irradiation technology

In this study, we evaluated the transformation of algal-based biochar into carbon nanotubes by irradiation in a microwave oven at low energies (100–300 W). Three species of algae (Macrocystis pyrifera, Sarcothalia crispata, and Scenedesmus almeriensis) were selected and pyrolyzed to obtain biochar for carbon nanotubes (CNTs) growth in the presence of ferrocene as the catalyst. The CNTs obtained were characterized by dynamic light scattering, UVVIS spectroscopy, Raman spectroscopy, transmission electron microscopy, X-ray diffraction, and electrical conductivity. The results indicate that algal biochar can be used for CNT growth. The heterogeneous structure of algal biochar can initiate the graphitization process for the formation of CNTs. The characteristics of synthesized CNTs vary with the biochar source used as a precursor. Thus, both the degree of graphitization of the wall and the content of nanotubes were higher using biochar with higher carbon content (from microalga Scenedesmus almeriensis); otherwise, the hydrodynamic diameter and electrical conductivity were higher using biochar with upper mineral ash content (from microalga Macrocystis pyrifera). Furthermore, it was found that a low catalyst concentration was required to promote growth due to the reactivity of the mineral ash of the biochar, and it was demonstrated that microwave heating conditions, such as microwave power and temperature, lead to variations in the optical properties of CNTs, such as the band gap energy, CNTs content, and measurement of the size such as the hydrodynamic diameter.

Removal of veterinary antibiotics in swine manure wastewater using microalgae–bacteria consortia in a pilot scale photobioreactor

Scenedesmus almeriensis microalgae–bacteria consortia were evaluated for the removal of a mixture of tetracycline (TET), ciprofloxacin (CIP), and sulfadiazine (SDZ) from the real liquid fraction of pig slurry in a pilot scale photobioreactor. After 15 days of operation, the reactor was spiked with a mixture of 100μg/L of each antibiotic. The experiment ran for 20 additional days. From the liquid phase, antibiotic removal were 77 ± 5 %, 90 ± 14 %, and 60 ± 27 % for TET, CIP, and SDZ, respectively. The antibiotics found in the solid phase were 979 ± 382 ng/g for TET and 192 ± 69 ng/g for SDZ; CIP was not detected in the biomass. The parameters analyzed before and after antibiotic addition showed that the antibiotics did not have a negative effect on the reactor biomass. The removal efficiencies of the analyzed parameters were 64.6 ± 0.6 % for TOC, 56.9 ± 0.6 % for IC, 63.9 ± 0.6 % for TN, 88.6 ± 0.9 % for N-NH4+, 64.9 ± 0.6 % for N-NO3−, and 30.1 ± 0.3 % for P-PO43−. This study demonstrated the good performance of microalgae-based technology for swine manure wastewater treatment, not only in terms of organic matter and nutrient removal, but also regarding the removal of antibiotics. The mass balance analysis of the entire process is presented. Additionally, the present study is a validation of previous laboratory scale batch studies operating in a quasi-continuous mode on veterinary antibiotics (VA) removal efficiencies and kinetics.

Extraction of phytostimulant molecules from Scenedesmus almeriensis using different extractor systems

There is an increasing demand for bio-based fertilizers and phytostimulants. Microalgae biomass contains a number of compounds that have positive effects on plant growth (for instance, phenolic compounds). Other valuable substances are simultaneously produced in the biomass, enabling a biorefinery approach to be applied. Downstream processing optimization for sustainable economic biostimulant production must involve the use of microalgal wet paste instead of dry biomass. The present study investigated the effect of different parameters, such as the solvent, temperature, and time, on the extraction of biostimulant molecules from Scenedesmus almeriensis microalgal biomass. The extraction process optimization was determined by calculating the germination index in the watercress seed bioassays. Since phenols and other bioactives are extracted together, and purification should be avoided, biological methods are preferred for assessing biostimulation. Water was compared to organic solvents of lower polarity such as acetone, ethanol (96%), and an ethanol:hexane:water (76:18:6 v/v/v) mixture. Different solvent extraction ratios (0.5–8 mL solvent g−1 of dry biomass), temperatures (25–50 ºC), and extraction times (0.5–6 h) were tested, after which the best combination was selected for each solvent. The optimal conditions were obtained with organic green solvents (acetone or ethanol), which resulted in a Germination Index above 120% (at least 20% above the distilled water control). Consequently, from a biorefinery perspective, this process was considered to be the most suitable for microalgal biomass exploitation.Graphical

Dietary Effects of a Short-Term Administration of Microalgae Blend on Growth Performance, Tissue Fatty Acids, and Predominant Intestinal Microbiota in Sparus aurata.

Given the potential of microalgae as new aquafeed ingredients, this study focuses on using a blend of microalgae, Tisochrysis lutea, Nannochloropsis gaditana, and Scenedesmus almeriensis, as a dietary ingredient for feeding Sparus aurata juveniles. The growth performance, carcass composition, tissue fatty acid profile, and intestinal microbiota were evaluated after a 30 day-feeding period. A microalgae-free diet was used as control, and three experimental diets were formulated containing 5%, 15%, and 25% of the microalgae blend (MB-5%, MB-15%, and MB-25%, respectively). After 7, 15, and 30 days of feeding experimental diets, biological samples were taken. Growth performance and nutrient utilization were not significantly modified at the end of the experiment. Microalgae inclusion tended to decrease body lipids and affected the fatty acid profile, especially MB-25 diet increased DHA levels. Diet MB-25 promoted appropriate microbial diversity, favoring the presence of probiotic bacteria, such as Lactobacillus, and significantly influencing the fatty acid composition and lipid metabolism in fish. In conclusion, using a short pulse of dietary administration of 25% microalgal blend in S. aurata modulates the intestinal microbiota and lipid composition while maintaining growth performance.

Long-term assessment of the nutrient recovery capacity and biomass productivity of Scenedesmus almeriensis in raceway reactors using unprocessed urban wastewater

The present work aims to assess the treatment of unprocessed urban wastewater using the microalga Scenedesmus almeriensis. Two 12 m3 raceway reactors, one supplemented by wastewater and the second by chemical fertilizer, operating outdoors in a semi-continuous mode, were used for eight months. Results suggested that S. almeriensis can be produced in wastewater without affecting the photosynthetic apparatus reaching a productivity of 13 g·m−2·day−1 on average in both the systems. Furthermore, the nutrient content in terms of nitrogen, phosphorous and chemical oxygen demand of the wastewater was reduced under the European limitations during most of the period, with an average removal rate of 2.2, 0.2 and 3.0 g·m−2·day−1 respectively. Therefore, raceways demonstrated a high potential for microalgal production and successful biotreatment, proving robust and reliable. Finally, the effect of environmental conditions on biomass productivity of the clean system was evaluated in a model with high accuracy (R2 = 0.9, p = 0.0002).

Design and Testing of a Disposable Flow Cuvette for Continuous Electroporation of a Bioreactor’s Initial Algae Cultivation

Electroporation is a technique applied both in biomedical and biotechnological fields which uses a high-voltage electric current to temporarily destabilize the plasma membrane of living cells, permitting the introduction of small molecules as well as nucleic acids into the cytosol. Besides viral and chemical transfections, this method is a common way to manipulate living cells. However, the majority of electroporation machines available on the market can only work using batch-based cuvettes treating only a few micrograms of cells. To transform cells in the order of several grams in the quickest possible way, it is necessary to use a continuous-flow method. In this work, we present the design, electric and fluid dynamics simulations, construction and testing of a flow cuvette that can adapt to standard electroporator systems. The flow cuvette connected with a peristaltic pump was able to successfully electroporate 20 mL of medium containing microalgae cells in less than 5 min. Microalgae Scenedesmus almeriensis cells were transfected with a fluorescent siRNA oligo as well as magnetically transformed by introducing magnetic nanoparticles in their cytoplasm. The flow cuvette presented here offers a valid tool for the high-throughput transformation/transfection/transfer of both prokaryotic and eukaryotic organisms, especially suitable for bioreactor cultivation and other industrial biotechnological contexts.

Rheology of microalgae concentrates and its influence on the power consumption of enzymatic hydrolysis processing

The optimization of downstream processing is a critical step in any microalgae-related process. The microalgal biomass is separated from the initial diluted cultures to form a concentrated slurry, the properties of which greatly influence the design and performance of further processing steps, such as enzymatic hydrolysis. In this work, the rheological behaviour of two microalgal concentrates produced both in freshwater (Scenedesmus almeriensis) and seawater (Nannochloropsis gaditana) were studied. Measurements were performed on the entire range of biomass concentrations, from 0.5 g/L to 264 g/L. Non-Newtonian behaviour was observed whatever the water type and biomass concentration used, especially at high biomass concentrations above 10 g/L. The rheological data were adjusted to the Power Law model, and the consistency and flow behaviour indexes were correlated with the biomass concentration. The results show that the freshwater and seawater biomasses exhibited different behaviours, with freshwater slurries being more viscous than seawater ones. The high viscosity of freshwater slurries requires increased energy consumption for mixing, with an estimated cost increase of 60% when using them under the non-Newtonian conditions considered. These findings highlight the considerable effect of algal biomass rheology on the mixing power required during microalgal biomass processing.

Comparative life cycle assessment of conventional and novel microalgae production systems and environmental impact mitigation in urban-industrial symbiosis

The versatility of microalgae biomass as candidates for various products and bioremediation needs motivates interests towards design and implementation of novel microalgae bioreactors. Conventional open-reactors are reliant on large quantities of sunlight and space while yields are constrained by outdoor environment conditions. Conversely, closed-reactor systems like bubble columns reduces these constrains on microalgae growth while occupying far less space at the expense of high energy demands, notably from lighting systems. A novel patented closed reactor design has recently been proposed that improves the bubble column concept with an efficient and effective lighting system. The present study uses Life Cycle Assessment approach to compare the environmental performance of conventional reactors and the proposed internally luminated novel closed reactor design, expressing impacts per kg biostimulant for the Scenedesmus almeriensis harvest from such units. All performance data was collected from a pilot facility in Almeria, Spain. Urban-industrial symbiosis scenarios are also portrayed in the study using wastewater and incinerator flue gas. Results show that under synthetic nutrient and carbon inputs in Spanish pilot operations, the cumulative energy demand for the novel photobioreactors is similar to conventional vertically-stacked horizon bioreactors but are substantially more demanding than conventional open reactors. However, when leveraging renewable energy sources and the photosynthesis process to consume wastestreams in urban-industrial symbiosis scenarios, the novel photobioreactor was able to achieve up to 80 % improvements in several impact categories e.g. eutrophication and climate change. Impact mitigation credits per kg dwt biomass across all energy scenarios in symbiosis amount to ≈1.8 kg CO2eq and ≈0.09 kg PO4 eq. This highlights that such closed and internally illuminated photobioreactors can be competitive with conventional reactors, and have potential to harness photosynthesis to reduce environmental burdens in an urban-industrial symbiosis setting. Possible economies of scale and the associated potential gains in efficiencies are further discussed.

Pilot-scale annual production of Scenedesmus almeriensis using diluted pig slurry as the nutrient source: Reduction of water losses in thin-layer cascade reactors

The microalga Scenedesmus almeriensis was produced using diluted pig slurry as the sole nutrient source during one year using a 30 m2 thin-layer cascade photobioreactor located outdoors. Evaporation contributes significantly to the water requirements of microalgae production; approximately 1000 L of water are required to produce 1 kg of microalgal biomass. The aim of this study was to assess the potential of plastic covers to avoid or minimise water evaporation in open photobioreactors. The N–NH4+ concentrations at the inlets ranged from 40 to 100 mg L−1, depending on the experimental run. These values could not be increased because of the dark colour and turbidity of the pig slurry. The biomass productivity of the system was 17.6, 18.8, 23.4, and 17.3 g m−2·day−1 in winter, spring, summer, and autumn, respectively. Covering the reactors led to a decrease in biomass productivity that ranged from 8.5 to 16.9% depending on the season. However, water evaporation was reduced by 24.9–42.0% depending on the season. In summer, covering the reactors reduced the amount of water evaporated from 6.3 to 3.6 L m−2·day−1. In a theoretical 1 ha production facility, this would represent 2700 L of water saved per day. Overall, the processing of pig slurry using microalgae is challenging because of their variable nutrient concentration, colour and turbidity. Covering the reactors with inexpensive commercial plastics could significantly reduce the water requirements of the system.

Color of extra virgin olive oils enriched with carotenoids from microalgae: influence of ultraviolet exposure and heating

A carotenoid-rich extract containing 2.5 mg/mL of lutein and 3.3 mg/mL of β-carotene from the microalga Scenedesmus almeriensis was added to ten extra virgin olive oils from four Spanish cultivars with differing degrees of ripeness, obtaining carotenoid enriched oils with lutein and β-carotene concentrations of 0.082 and 0.11 mg/mL, respectively. Extra virgin olive oils enriched with carotenoids from microalgae were studied by analyzing the effect on color of three different treatments: ultraviolet exposure, microwave heating and immersion bath heating. The methodology was designed to simulate, in controlled laboratory conditions, the effects of household treatments. Spectrophotometric color measurements were then performed to monitor color changes in the enriched and non-enriched extra virgin olive oil samples. Enriched oils are much more chromatic, darker and redder than natural oils. After 55 days UV irradiation, 40 min microwave heating, and 72 hours thermostatic heating, the average color differences for natural/enriched extra virgin olive oils were 98/117, 15/9 and 57/28 CIELAB units, respectively. In general, increasing temperature and ultraviolet exposure produced higher CIELAB color differences in the non-enriched samples. The addition of microalga extracts to extra virgin olive oils was found to induce some color stability and may constitute a future way of increasing the daily intake of beneficial bioactive compounds such as carotenoids.

A seasonal simulation approach for culture depth influence on the temperature for different characterized microalgae strains.

Irradiance and temperature are among the most important variables that affect microalgae growth, being both difficult to control in outdoor raceway reactors utilized for large-scale production of microalgae biomass. They are mainly a function of the location of the reactors, thus, producing certain strains of microalgae in inappropriate places conduces to the failure of the systems. To be able to determine important parameters of any microalgae strains on the performance of the culture, such as the influence of irradiance and temperature, is a powerful tool in decision-making processes. In addition, whatever the strain and location, operation strategies must be defined for each specific case, such as the imposed dilution rate and culture depth, both influencing the light availability and temperature of the culture as major variables determining the biomass productivity. In this paper, a simulation-based methodology is proposed to establish the influence of season and culture depth on the 1-year age irradiance and temperature of the culture, and thus on the biomass productivity of different microalgae strains. Up to five of the most frequently produced strains, such as Spirulina platensis, Chlorella vulgaris, Nannochloropsis gaditana, Isochrysis galbana, and Scenedesmus almeriensis have been considered. The challenge is to develop an easy-to-manage decision-making tool for the optimal design and operation of large-scale microalgae facilities. Especially, dates for microalgae production and culture depth at which the reactors must be operated will be provided, being valid for any microalgae strain. The proposed methodology will largely contribute to the risk of investment in this field, then to enlarge the relevance of the microalgae production industry.

Hydrolyzed microalgae from biorefinery as a potential functional ingredient in Siberian sturgeon (A. baerii Brandt) aquafeed

The development of sustainable and functional feed represents an opportunity and a need for the aquaculture industry, supporting beneficial physiological effects on fish that go beyond traditional feed formulations. This study aims to evaluate the potential application of microalgae, produced through a sustainable process, as a functional ingredient in practical diets for Siberian sturgeon (Acipenser baerii) fingerlings. For this purpose, the effects of the dietary administration of two different microalgae, Nannochlopsis gaditana and Scenedesmus almeriensis, cultivated on conventional synthetic medium (SM) or diluted pig manure (PM) and included in diets as crude or hydrolyzed biomasses, were tested.Growth performance and oxidative status of the fish were evaluated and compared in relation to the different diets. Biochemical characterization revealed a higher protein and lipid content both in N. gaditana and S. almeriensis which were grown on PM. Anyway, regardless of the growth medium used, N. gaditana presented higher protein and lipid content than S. almeriensis. Microbiological analysis shows no evidence of pathogen contamination (absence of Salmonella spp.; E. coli < 100 cfu/g), neither in microalgae produced on SM nor in those produced on PM. Growth performance, nutrient utilization and muscle composition in fish fed microalgae-supplemented diets were similar to those of the control group, showing they fulfilled the fish nutrient requirements for assuring sturgeon fingerlings growth and fillet nutritional quality. However, sturgeon fed-diets containing hydrolyzed N. gaditana biomass, grown on PM, reached greater average final weight then the other fish groups, included the control group. These results suggest the potential application of microalgae obtained by biorefinery as a protein and lipid source in practical diets for Siberian sturgeon (A. baerii). In particular, N. gaditana was revealed to be a potential functional ingredient in aquafeed, usable to improve the sustainability of microalgae production and of the aquaculture sector, through a circular bioeconomy approach.

Long-Term Assessment of the Nutrient Recovery Capacity and Biomass Productivity of Scenedesmus Almeriensis in Raceway Reactors Using Unprocessed Urban Wastewater

Long-Term Assessment of the Nutrient Recovery Capacity and Biomass Productivity of Scenedesmus Almeriensis in Raceway Reactors Using Unprocessed Urban Wastewater

Optimisation of Scenedesmus almeriensis production using pig slurry as the sole nutrient source

Pig slurry was used as the sole nutrient source to produce biomass of the microalga Scenedesmus almeriensis using laboratory-scale bubble column photobioreactors. No differences in terms of biomass productivity were observed between fresh and digested pig slurry. The optimum dilution of the slurry to enable the processing of the largest amount of pig slurry per litre was 5%, which led to a biomass productivity rate of 0.68 g·L−1·day−1, comparable to that of the standard growth medium formulated using pure chemicals (0.70 g·L−1·day−1). The inlet N-NH4+ concentration was approximately 180 mg·L−1, with inhibitory effects being observed at concentrations higher than 200 mg·L−1. The N-NH4+, N-NO3−, P-PO43−, and chemical oxygen demand removal rates were 34.1, 0.5, 2.1, and 519.3 mg·L−1·day−1. The observed turbidity of the media did not affect microalgal growth at the studied dilutions. Ozonation effectively reduced the chemical oxygen demand concentration of the media, but no effect on microalgal growth was observed. Overall, pig slurry was an effective nutrient source for the production of S. almeriensis, and this strain was shown to be robust with a N-NH4+ tolerance up to 200 mg·L−1 and the potential use in the bioremediation of agro-industrial wastes.

Effects of demineralization on the composition of microalgae pyrolysis volatiles in py-GC–MS

This study compared the volatiles distribution in analytical scale pyrolysis (py-GC–MS) of Nannochloropsis gaditana (marine microalgae) and Scenedesmus almeriensis (freshwater microalgae) and their demineralized counterparts. The role of inorganic elements and their removal via ultrasonic treatment, water washing and (in)organic acid leaching were elucidated. Principal component analysis (PCA) and grey relational analysis were applied to analyze the pyrolysis volatiles distribution and demonstrate the influence of inorganic elements in pyrolysis, respectively. Demineralization affects (breaks down) the chemical structure of carbohydrates, followed by (to a lesser extent) proteins and lipids. Acid leaching promoted hydrolysis and suppressed the catalytic effect associated to inorganic elements in subsequent pyrolysis, compared to ultrasonic treatment and water washing. Elements like K and Na had a larger catalytic influence on microalgae pyrolysis than Ca and Mg. The composition and pyrolytic formation mechanism of major product groups at 500 °C were studied, including anhydrosugars, phenolics, furans, carboxylic acids, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, N-heterocyclic compounds, nitriles and amides. The results indicate that demineralization shows positive effects on fast pyrolysis of microalgae: (1) by disrupting the cell wall and releasing the lipids and cellular contents. Based on the py-GC–MS peak area normalized to sample mass, the relative contribution of hydrocarbons in the pyrolysis vapors increased from 25.5 % (NG: Nannochloropsis gaditana) to 32.1 % (NG-HCl: Nannochloropsis gaditana, HCl treated), and from 16.1 % (SA: Scenedesmus almeriensis) to 22.4 % (SA-HCl: Scenedesmus almeriensis, HCl treated); (2) by decreasing the relative yields in O-containing compounds resulting from the suppressed catalytic effects of alkali and alkaline earth metals (53.3 % (NG) to 37.1 % (NG-HCl), 57.5 % (SA) to 47.8 % (SA-HCl)) that would otherwise have been present in non-demineralized microalgae feedstock. The effects of demineralization on the denitrogenation of pyrolysis vapors were not that obvious. Suggestions for potential full scale applications have been proposed.

A Polyphasic Characterisation of Tetradesmus almeriensis sp. nov. (Chlorophyta: Scenedesmaceae)

The microalga Tetradesmus almeriensis, previously known as Scenedesmus almeriensis, has been isolated and cultivated as a highly productive, fast-growing strain known as a natural source of different products of commercial interest, including bioactive compounds such as lutein. This strain produces up to 40 g·m−2·day−1 of lutein under optimal conditions and is highly recommendable for outdoor production in temperate and warm climates, showing maximal performance at temperatures up to 35 °C with no photo-inhibition taking place with irradiances greater than 1000 μE·m−2·s−1. Morphological and molecular data allow its assignment to the Chlorophycean genus Tetradesmus. The new species can be distinguished from similar Tetradesmus taxa due to its unique combination of features that are seen under light microscopy. We present herein a robust and comprehensive phylogenetic analysis of T. almeriensis, together with several additional Scenedesmaceae species, using a combination of maximum likelihood and Bayesian approaches. Our results confirm T. almeriensis as a distinct species consistently clustering with other Scenedesmaceae.