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Aim: This study aims to determine how photosynthetic and antioxidant activities vary in vegetative and dormant cells of Haematococcus pluvialis subjected to stresses in conditions representative of industrial productions of microalgae under solar light., Methods and Results: The effects of short-term oxidative treatments were examined on photosynthetic and antioxidant activities of Haematococcus pluvialis vegetative and resting cells. The vegetative cells have 1.6 times higher levels of phenolic compounds, but 1.7 times less catalase, ascorbate peroxidase and superoxide dismutase activities than the astaxanthin-enriched resting cells. Mainly, a UVA dose of 4 J cm -2 induced increases in photosystem II electron transport rates (ETRmax) (+15%), phenolic compounds (+15%), astaxanthin (+48%), catalase (+45%) and superoxide dismutase (+30%) activities in vegetative cells., Conclusion: The UVA dose strongly stimulates the photosynthetic and antioxidant activities of vegetative cells, but only the accumulation of astaxanthin in resting cells., Significance and Impact of the Study: These preliminary results show that oxidative stresses at sub-lethal levels can stimulate the activities of microalgae. Further investigations are needed to estimate the real influence on metabolite productivities in industrial production conditions., (© 2022 Society for Applied Microbiology.)

Strain selection is one of the primary hurdles facing cost-effective microalgal biodiesel production. Indeed, the strain used affects both upstream and downstream biodiesel production processes. This study presents a screening procedure that considers the most significant criteria in microalgal biodiesel production including TAG production and wet extraction and recovery of TAGs. Fourteen freshwater and seawater strains were investigated. Large variation was observed between the strains in all the screening criteria. The overall screening procedure ultimately led to the identification of Parachlorella kessleri UTEX2229 and Nannochloropsis gaditana CCMP527 as the best freshwater and seawater strains, respectively. They featured the largest areal TAG productivity equal to 2.7×10(-3) and 2.3×10(-3)kgm(-2)d(-1), respectively. These two strains also displayed encouraging cell fragility in a high pressure bead milling process with 69% and 98% cell disruption at 1750bar making them remarkable strains for TAG extraction in wet environment., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Although the hydrothermal liquefaction is considered a promising technology for converting microalgae into liquid biofuels, there are still some disadvantages. This paper demonstrated that the bio-oil yield can be significantly improved by adding alcohols as co-solvents and carrying out the conversion at mild conditions (<250°C), but at the expense of a reduced bio-oil quality. By adding ethanol, the bio-oil yields obtained (up to ∼60%) were comparable to the yield obtained at severe operating conditions using only water as solvent (54±2% on average), but the quality of the bio-oil was lower. However, the main advantages of the process here described lie in the utilisation of wet microalgae (∼75% moisture) and alcohol concentrations which avoid both drying the microalgae and decreasing the amount of microalgae loaded in the reactor., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The aim of this work was to study the effect of the solvent N-methylmorpholine-N-oxide (NMMO) to pre-treat Nannochloropsis oculata before the anaerobic digestion process. The results indicated that the pre-treatment affects the characteristics of the cell wall, which consequently becomes more susceptible to the microorganisms attack during anaerobic digestion. The methane production was increased by 43% after the pre-treatment, from 238±6mLCH4/gVS until 339±4mLCH4/gVS. On the contrary, the methane production from Chlorella vulgaris decreased after the pre-treatment from 251±4mLCH4/gVS to 231±3mLCH4/gVS. The failure on the pre-treatment was attributed to the particular characteristics of the substrate in consequence of a previous drying step., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Nannochloropsis has emerged as a promising alga for biodiesel production. However, the genus consists of 6 species and hundreds of strains making strain selection a challenge. Furthermore, oil productivity is instrumental to economic viability of any algal strain for industrial production, which is dependent on growth rate and oil content. In most cases, these two parameters have been studied independently. Thus, the goal of this study is to provide a combined method for evaluating strain performance in specially designed photobioreactors together with an in-depth lipidomic analyses. The nine strains of Nannochloropsis tested showed considerable variations in productivity and lipidomics highlighting the importance of strain selection. Finally, Nannochloropsis gaditana CCMP527 and Nannochloropsis salina CCMP537 emerged as the two most promising strains, with an oil content of 37 and 27 dry wt% after 11-day nitrogen starvation, respectively, resulting in TAG productivity of 13×10(-3) and 18×10(-3) kg m(-3) d(-1), respectively., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Absolute concentrations of total macromolecules (triglycerides, proteins and carbohydrates) in microorganisms can be rapidly measured by FTIR spectroscopy, but caution is needed to avoid non-specific experimental bias. Here, we assess the limits within which this approach can be used on model solutions of macromolecules of interest. We used the Bruker HTSXT-FTIR system. Our results show that the solid deposits obtained after the sampling procedure present physical and chemical properties that influence the quality of the absolute concentration prediction models (univariate and multivariate). The accuracy of the models was degraded by a factor of 2 or 3 outside the recommended concentration interval of 0.5-35 µg spot(-1). Change occurred notably in the sample hydrogen bond network, which could, however, be controlled using an internal probe (pseudohalide anion). We also demonstrate that for aqueous solutions, accurate prediction of total carbohydrate quantities (in glucose equivalent) could not be made unless a constant amount of protein was added to the model solution (BSA). The results of the prediction model for more complex solutions, here with two components: glucose and BSA, were very encouraging, suggesting that this FTIR approach could be used as a rapid quantification method for mixtures of molecules of interest, provided the limits of use of the HTSXT-FTIR method are precisely known and respected. This last finding opens the way to direct quantification of total molecules of interest in more complex matrices.

Over the past years, the substitution of the classical biochemical quantification techniques by Fourier transform infrared (FTIR) spectroscopy has been widely studied on microalgae because of its tremendous application potential for bioprocess monitoring. In the present work, mandatory aspects that have never been approached by FTIR end-users working onto fresh biomass were assessed. We demonstrated first that fresh cells' FTIR spectra main characteristics could be severely and unspecifically altered when the properties of the sampled biomass were not monitored. Microscopy indicated that important cell reorganization could occur when diminishing the cells density of the sample. Molecular probing approach suggested that such a modification could provoke an alteration of the hydrogen-bonding network of the sample. The sample heterogeneity was found to impact also the shape and intensity of the recorded FTIR bands, participating then to a matrix effect uncharacterized until now. In the second part of our study, we selected FTIR spectra not influenced by this matrix effect and the corresponding accurate calibration data obtained by the whole cell analytical procedure to elaborate an optimized total lipid quantification PLS-R model. Results demonstrated that our strategy could provide a small volume sampling (1 mL of fresh culture), rapid (within minutes), robust (physiological condition independent), and accurate (as accurate as the reference method could be) FTIR absolute quantification method to determine the fresh microalgae intracellular total lipid content. To validate our unbiased FTIR approach, a photobioprocess monitoring pipeline was developed and allowed assessing the effect of light attenuation on total lipid production by the marine microalga Nannochloropsis oculata.

Lipids production of the marine microalga species Nannochloropsis oculata was deeply investigated by studying under continuous light the effects of different nitrogen starvation strategies in photobioreactors of various thicknesses. Operating parameters like incident photons flux density (PFD), initial nitrogen (progressive starvation strategy) or biomass concentrations (sudden starvation strategy) were examined, with a detailed analysis of their effects on the quality and production kinetics of total (TL) and triglycerides (TG). In addition to the already known effect of nitrogen starvation to trigger reserve lipids accumulation (mainly TG), it was demonstrated the relevance of the light received per cell affecting TG content and productivities, as well as fatty acids (FA) profiles. With appropriate optimization, N. oculata was confirmed as an interesting candidate for biodiesel application, with high FA accumulation (up to around 50%DW with 43%DW in TG-FA), high productivity (maximum 3.6×10(-3)kg(TG-FA)m(-2)d(-1)) and a TG-FA profile close to palm oil., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In the context of hydrogen production by the green alga Chlamydomonas reinhardtii, the control of light attenuation conditions is used to set-up anoxia under illuminated and autotrophic conditions, without affecting photosynthetic capacities of cells (as with sulphur deprivation or PSII inhibitors like DCMU). This paper presents a full description of the protocol where the incident photons flux density (PFD) is adapted during cultivation in order to obtain a sufficiently low illuminated fraction γ under 0.25 leading to anoxic hydrogen producing conditions during several days. The protocol is validated in a torus-shape photobioreactor (PBR) revealing after few days of anoxic conditions a peak of hydrogen production (1.44 ml H2/h/l of culture; [0.8-1.0] ml H2/h/g of dry weight biomass) concomitant with a decrease of biomass concentration, protein content and maximal photosynthetic yield. Effect of over-accumulating starch, as being known to increase hydrogen production by the PSII-independent pathway, is also investigated., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

This work presents the rational development up to its final characterization and validation of an intensified solar photobioreactor (PBR) for microalgal production, AlgoFilm©. Our aim was to achieve very high volumetric performance for phototrophic conditions, in the range of that found in fermentation processes. The overall design procedure was underpinned by robust engineering rules derived from knowledge models developed for PBR in-depth modeling. This approach was used to pinpoint the main engineering parameters governing PBR kinetic performance. It introduces generic principles of PBR performance enhancement for the setting-up of culture systems combining high volumetric and areal productivities. These principles were then applied to the design of a solar culture system, integrating the attendant constraints. The result was the AlgoFilm© PBR, based on the falling-film principle, which enables very thin culture depth (around 1.5–2 mm) and provides a high specific illuminated surface area (around 500 m 2 ·m − 3 , corresponding to 2.1 L/m 2 illuminated surface). A complete experimental characterization was then conducted to (i) determine operating conditions for the setting of optimal parameters governing AlgoFilm© PBR performance, such as depth of the falling film, and (ii) ensure that no limitation other than light occurred, a mandatory condition to control the system and ensure high biomass productivities. AlgoFilm© PBR performance was characterized by Chlorella vulgaris culture. Batch, continuous and semi-continuous cultures were run, and typical irradiation conditions of a year's operation in Nantes (France) were applied using a LED panel to simulate constant, and then fully-controlled day/night cycles. Our results demonstrate the high performance of the AlgoFilm© PBR, with volumetric productivities very close to those expected from the prior theoretical design. The best measured productivity was 5.7 kg·m − 3 ·day − 1 (7.07 kg·m − 3 ·day − 1 in constant light). This value was significantly higher than those reported in the literature, and similar to those generally found for microalgal production in heterotrophic processes. [ABSTRACT FROM AUTHOR]

Modeling was performed to investigate solar production of the microalga Chlamydomonas reinhardtii in photobioreactors (PBRs). Maximal biomass productivity achievable on Earth was calculated (ideal reactor concept). Effect of PBR location and of given operating conditions was simulated. An ideal productivity (upper limit) in the range of 60 t x ha − 1 year − 1 was obtained for a fixed horizontal PBR. For a facility sited in France (Nantes), a maximal biomass productivity of around 37 t x ha − 1 year − 1 was predicted. The comparison against the cyanobacterium Arthrospira platensis highlighted the marked influence of non-ideal light attenuation conditions in the culture volume when growing microalgae. Not only light transmission but also dark volumes were found to negatively impact biomass productivity. Consequently, as biomass growth rate is unable to compensate for rapid changes in sunlight intensity, it proved impossible to maintain optimal light conversion throughout time in outdoor solar conditions. The outcome was a significant decrease in expected productivities, in contrast to cyanobacteria where appropriate optimization resulted in actual productivities approaching the maximal achievable productivities. For microalgae, productivity optimization promoted low light attenuation to safeguard against the marked negative influence of dark volume on microalgae growth. If combined with high PFD, this could impair PBR stability in solar use. [ABSTRACT FROM AUTHOR]

A generic model for the simulation of solar rectangular photobioreactors (PBR) is presented. It combines the determination of the time-varying solar radiation intercepted by the process with the theoretical framework necessary for PBR simulation, namely modeling of the radiant light energy transport inside the culture volume, and its local coupling to photosynthetic growth. Here, the model is applied to illustrate the full dependency of PBR behavior on solar illumination regimes, which results in a complex, transient response. Effects of day-night cycles, culture harvesting, and the interdependency of physical (light) and biological (growth) kinetics are discussed. It is shown that PBR productivity is the result not only of light intercepted on the illuminated surface but also of light attenuation conditions inside the bulk culture as influenced by incident angle and beam/diffuse distribution of solar radiation. Results are presented for a location in France for 2 months representative of summer and winter. © 2010 American Institute of Chemical Engineers AIChE J, 2011 [ABSTRACT FROM AUTHOR]

Abstract: It is well-known that the response of photosynthetic microorganisms in photobioreactor (PBR) is greatly influenced by the geometry of the process, and its cultivation parameters. The design of an adapted PBR requires understanding of the coupling between the biological response and the environmental conditions applied. Cells culture under well-defined conditions are thus of primary interest. A particular lab-scale PBR has been developed for this purpose. It is based on a torus shape, that enables light to be highly controlled while providing a very efficient mixing, especially along the light gradient in the culture, that it is known to be a key-parameter in PBR running. A complete characterization of hydrodynamic conditions is presented, using computational fluids dynamics (CFD). After validation by comparison with experimental measurements, a parametric study is conducted to characterize important hydrodynamics features with respect to PBR application (light access, circulation velocity, global shear-stress), and then to investigate a possible optimization of the process via modification of the impeller used for culture mixing. The final part of the study is devoted to a detailed investigation of mixing performance of the torus PBR, by numerically predicting dispersion of a passive tracer in various configurations. The high degree of mixing observed shows the great potential of such innovative geometry in the field of photosynthetic microorganisms cultivation, especially for the design of a lab-scale process to conduct experiments under well-controlled conditions (light and flow) for modeling purpose. [Copyright &y& Elsevier]

Vertical flat-panel photobioreactors for microalgae culture can be integrated into building facades. On top of providing the large solar illuminated surfaces needed for microalgae production, this original combination opens various optimization opportunities, such as the possibility to create mutual benefits for both systems with appropriate and efficient integration. For example, microalgal photosynthesis can be used to fix the CO 2 contained in flue gas emitted from the building (in a factory set-up) or to significantly reduce energy consumption for thermal regulation of both photobioreactors and building. Here we report the results of a theoretical modelling-based investigation designed to define how the specific building integration conditions affect photobioreactor operation. Expected biomass production and light attenuation conditions encountered in the culture volume were determined for the green microalgae Chlorella vulgaris for a location based in Nantes (France). Results were compared to figures from the more conventional systems such as horizontal or ideally-inclined microalgal culture systems. We conclude with an energetic analysis that underlines the relevance of optimizing thermal exchanges between microalgal culture and building. [ABSTRACT FROM AUTHOR]

Abstract: With the objective of addressing issues related to the temperature control of a solar closed photobioreactor (PBR), a laboratory set-up representative of an intensified closed flat panel PBR was designed. Only its thermal behaviour was considered, with no cultivation of microalgae. It was characterized indoors under controlled artificial irradiation and outdoors under solar irradiation on sunny days in summer. A simplified thermal model to predict the temperature time course was developed and validated by comparison with experimental results. The thermal model was then used as a simulation tool to investigate relevant parameters influencing thermal behaviour, such as the optical properties of the illuminated surface and the surrounding wind speed. A heat balance was applied for different cases to determine the energy consumption during one year of operation with temperature regulated in a range suitable for microalgae growth. [Copyright &y& Elsevier]

Abstract: We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the “light-limited” regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25–37% of DW), while the highest TAG content was found in C. vulgaris (11–14% of DW). These two species showed similar TAG productivities. [ABSTRACT FROM AUTHOR]

Abstract: The fresh water microalga Neochloris oleoabundans was investigated for its ability to accumulate lipids and especially triacylglycerols (TAG). A systematic study was conducted, from the determination of the growth medium to its characterization in an airlift photobioreactor. Without nutrient limitation, a maximal biomass areal productivity of 16.5gm−2 day−1 was found. Effects of nitrogen starvation to induce lipids accumulation was next investigated. Due to initial N. oleoabundans total lipids high content (23% of dry weight), highest productivity was obtained without mineral limitation with a maximal total lipids productivity of 3.8gm−2 day−1. Regarding TAG, an almost similar productivity was found whatever the protocol was: continuous production without mineral limitation (0.5gm−2 day−1) or batch production with either sudden or progressive nitrogen deprivation (0.7gm−2 day−1). The decrease in growth rate reduces the benefit of the important lipids and TAG accumulation as obtained in nitrogen starvation (37% and 18% of dry weight, respectively). [Copyright &y& Elsevier]

Abstract: In the aim of β-carotene biocompatible extraction, toxicity of various pure solvents belonging to different homologous series has been investigated for Dunaliella salina. The results showed that solvents having log P oct >5 or having a molecular weight over 150g/mol can be considered biocompatible for this microalga. The membrane critical solvent concentration for each series of solvents has been calculated applying Osborne''s model, showing that the aliphatic chlorinated hydrocarbon is the most toxic family studied. Mixtures of a biocompatible solvent (decane) with a toxic solvent (CH2Cl2, MEK, MTBE) have been studied. The β-carotene extraction ability of CH2Cl2-decane mixture was found six times more efficient than with pure decane. It has been demonstrated that the extraction ability of solvent depends on its affinity with the product extracted and on its concentration incorporated in the cellular membrane. [Copyright &y& Elsevier]