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Bubble formation at variously inclined submerged nozzles, fed with a continuous gas flow rate, is investigated. The average liquid velocity induced by bubble motion is determined, leading to a simple correlation for estimation of the liquid velocities induced by the repeated passage of bubbles. An effective model for the prediction of bubble sizes at their detachment from vertical nozzle orifices is presented which encompasses a bound expansion stage, followed by an accelerated expansion phase, and ends by an original bubble detachment criterion. The existence of a liquid-phase effective entrainment velocity, generated by the continuous passage of the bubble stream, is quantified and included in the model. Model predictions are found to correlate well with experimental and literature data. [ABSTRACT FROM AUTHOR]

The edible plant oils production is associated with the release of different types of by-products. The latter represent cheap and available substrates to produce valuable compounds, such as flavours and fragrances, biologically active compounds and bio-based polymers. Elizabethkingia meningoseptica Oleate hydratases (Em_OhyA) can selectively catalyze the conversion of unsaturated fatty acids, specifically oleic acid, into hydroxy fatty acids, which find different industrial applications. In this study, Design-of-experiment (DoE) strategy was used to screen and identify conditions for reaching high yields in the reaction carried out by Escherichia coli whole-cell carrying the recombinant enzyme Em_OhyA using Waste Cooking Oils (WCO)-derived free fatty acids (FFA) as substrate. The identified reaction conditions for high oleic acid conversion were also tested on untreated triglycerides-containing substrates, such as pomace oil, sunflower oil, olive oil and oil mill wastewater (OMW), combining the triglyceride hydrolysis by the lipase from Candida rugosa and the E. coli whole-cell containing Em_OhyA for the production of hydroxy fatty acids. When WCO, sunflower oil and OMW were used as substrate, the one-pot bioconversion led to an increase of oleic acid conversion compared to the standard reaction. This work highlights the efficiency of the DoE approach to screen and identify conditions for an enzymatic reaction for the production of industrially-relevant products. • Enzymatic production of hydroxy fatty acids for different application, such as flavors. • Screening of biocatalytic hydration of crude free fatty acids from waste cooking oils. • Design-of-experiment used to identify interactions between parameters. • Production of enzymatic cascade reactions. • Reproducibility of results on triglyceride-containing industrial feedstocks. [ABSTRACT FROM AUTHOR]

Microalgae have been reported to be excellent producers of bioactive molecules. Lutein is a pigment reported to have various beneficial effects for humans, and especially for eye well-being. In the current review, we summarize various methods that have been developed to optimize its extraction and bioactivities reported for human health. Several protective effects have been reported for lutein, including antioxidant, anticancer, anti-inflammatory, and cardioprotective activity. This review also reports attempts to increase lutein production by microalgae by changing culturing parameters or by using pilot-scale systems. Genetic engineering lutein production is also discussed. Considering the increasing aging of the worldwide population will create an increased need for lutein, a viable economic and eco-sustainable method to produce lutein is needed to face this market demand. [ABSTRACT FROM AUTHOR]

The supercritical water gasification (SCWG) of glucose as a model compound for H 2 production is studied in term of process development at 25 MPa and 650 °C. Gasification has been investigated using a laboratory scale continuous plant comprising a continuous down flow reactor with a volume of 200 cm 3 , a heat recovery section and pre-heat of the biomass to simulate more closely an industrial design. Feed streams (pure water and glucose solution) are introduced at the top of the vessel and products are extracted from the bottom. The reactor is equipped with various inlet points that allow to modify the inlet position of reacting streams in order to study the effect of stream mixing on reaction performance. Moreover, in order to obtain a description of the fluid flow inside the reactor, computational fluid dynamics (CFD) simulations were carried out. The simulations were conducted by the ANSYS CFX 15 code which uses a finite volume method. Simulation allowed not only to understand the complex fluid dynamics that describes the system, but also to optimize the reactor configuration in order to attain good process performance. Experimental results coupled with CFD analysis, allowed to find that the reactor has the top section that behaves like a mixed reactor and the bottom section that behaves like a plug flow reactor. The two jet streams (water and glucose solution) entering the reactor cause back mixing in the top-side of the reactor, so contributing to rapid initiation of reaction and down-flow of species through the chamber. Using the best reactor configuration in term of mixing and temperature distribution allowed to maximize the gasification efficiency and H 2 yield up to 72% and 74% by mole, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyphenols extracted prior to heterogenous catalytic treatment. • Heterogeneous catalytic conversion of biomass sugars into furans. • NbOPO 4 has highest catalytic activity due to its acidic nature. • Catalytic treatment of olive mill wastewater yields 5-hydroxymethylfurfural. • Catalytic treatment of olive industry waste solid fractions yields furfural. The production of furans from the valorization of olive mill biomass waste streams including olive mill wastewater (OMW), olive virgin pomace (OVP), dry pelletized pomace (DPP), and olive dry leaves (DL) was investigated using acidic Nb 2 O 5 , NbOPO 4 and TiO 2 -PO 4 heterogeneous catalysts. Batch reactions were performed in an autoclave at 210 °C in the presence of the suspended catalysts and the yield of furfural and 5-hydroxymethylfurfural (5-HMF) was determined. The valorization of OMW was found more effective in the presence of NbOPO 4 as a result of its high acidity nature. The amount and strength of the acid sites of NbOPO 4 were much higher than the other catalysts. The highest yield of hexoses sugars in OMW to 5-HMF was 44 %, while furfural was a minor product. The 5-HMF yield further increased to 91 % after pre-extraction of the polyphenolic species from the OMW. Recycling tests of NbOPO 4 catalyst, the most performant one, indicated the very good stability of this material. As result of the highest xylose content in the olive mill solids fractions (olive pomace, dry pellet pomace and dry leaves), furfural's yields of 100 %, 57 % and 31 %, respectively, were observed, while 5-HMF in contrast to OMW was a minor product. This work demonstrates the feasibility of using acidic catalysts for the valorization of olive mill waste streams targeting the desired furan product. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyphenols extracted prior to heterogenous catalytic treatment. • Heterogeneous catalytic conversion of biomass sugars into furans. • NbOPO 4 has highest catalytic activity due to its acidic nature. • Catalytic treatment of olive mill wastewater yields 5-hydroxymethylfurfural. • Catalytic treatment of olive industry waste solid fractions yields furfural. The production of furans from the valorization of olive mill biomass waste streams including olive mill wastewater (OMW), olive virgin pomace (OVP), dry pelletized pomace (DPP), and olive dry leaves (DL) was investigated using acidic Nb 2 O 5 , NbOPO 4 and TiO 2 -PO 4 heterogeneous catalysts. Batch reactions were performed in an autoclave at 210 °C in the presence of the suspended catalysts and the yield of furfural and 5-hydroxymethylfurfural (5-HMF) was determined. The valorization of OMW was found more effective in the presence of NbOPO 4 as a result of its high acidity nature. The amount and strength of the acid sites of NbOPO 4 were much higher than the other catalysts. The highest yield of hexoses sugars in OMW to 5-HMF was 44 %, while furfural was a minor product. The 5-HMF yield further increased to 91 % after pre-extraction of the polyphenolic species from the OMW. Recycling tests of NbOPO 4 catalyst, the most performant one, indicated the very good stability of this material. As result of the highest xylose content in the olive mill solids fractions (olive pomace, dry pellet pomace and dry leaves), furfural's yields of 100 %, 57 % and 31 %, respectively, were observed, while 5-HMF in contrast to OMW was a minor product. This work demonstrates the feasibility of using acidic catalysts for the valorization of olive mill waste streams targeting the desired furan product. [ABSTRACT FROM AUTHOR]

Nannochloropsis gaditana is a promising microalga for biotechnology. One of the strategies to stimulate its full potential in metabolite production is exposure to flashing lights. Here, we report how N. gaditana adapts to different flashing light regimes (5, 50, and 500 Hz) by changing its cellular physiology and the relative expression of genes related to critical cellular functions. We analyzed the differential mRNA abundance of genes related to photosynthesis, nitrogen assimilation and biosynthesis of chlorophyll, carotenoids, lipids, fatty acids and starch. Analysis of photosynthetic efficiency and high mRNA abundance of photoprotection genes supported the inference that excess excitation energy provided by light absorbance during photosynthesis was produced under low frequency flashing lights and was dissipated by photopigments via the xanthophyll-cycle. Increased relative expression levels of genes related to the synthesis of carotenoids and chlorophyll confirmed the accumulation of photopigments previously observed at low frequency flashing lights. Higher differential mRNA abundance of genes related to the triacylglycerol biosynthesis were observed at lower frequency flashing lights, possibly triggered by a poor nitrogen assimilation caused by low mRNA abundance of a nitrate reductase gene. This study advances a new understanding of algal physiology and metabolism leading to improved cellular performance and metabolite production. • Differential mRNA abundance was analyzed on N. gaditana exposed to flashing light (FL). • Excess energy dissipation via xanthophyll cycle was triggered at low frequencies FL. • High mRNA abundance of photopigment genes was promoted at low frequencies FL. • High mRNA abundance of Kennedy pathway genes observed at low frequencies FL. • Nitrate reductase transcripts showed low abundance at low frequencies FL causing nitrogen stress. [ABSTRACT FROM AUTHOR]

[Display omitted] • Use of Volume of Fluid (VOF) method to model free surface dynamics in UUSTs. • Comprehensive assessment of suitable turbulence models for unbaffled stirred tank analysis. • Study of effects of impeller speed on vortex shape and aeration at different viscosities. • Prediction of Power Number (Np) and vortex shape in non-aerated and aerated conditions. • Prediction of cavities near the impeller blades in super-critical regime. The transition between non-aerated and aerated regimes in uncovered unbaffled stirred tanks (UUSTs) was investigated using computational fluid dynamics (CFD). The Volume of Fluid (VOF) method was employed to model the free surface dynamics under various operational conditions. The simulations were able to predict the peculiar experimentally observed behavior of UUSTs and revealed that at velocities below a critical threshold (N_ < _N crit) , the system remains non-aerated, while exceeding this threshold (N_ ≥ _N crit) induces bubble ingestion, leading to significant changes in power consumption and flow patterns. The CFD simulations accurately predicted the behaviour of the Power Number (Np) as well as the vortex shape inside the tank both in subcritical and supercritical regimes and showed good agreement with original experimental data and correlations from the literature. Additionally, the modeling of the aerated regime successfully predicted the vortex shape, the bubble dispersion within the tank, and the cavities formed behind the blades. [ABSTRACT FROM AUTHOR]

• CFD simulations were performed in baffled and unbaffled stirred vessels. • Early to fully turbulent conditions were simulated in both systems. • k- ω SST , k- ε and the SSG Reynolds stress models were adopted and compared. • The three models were found to predict fairly well Np and N Q in baffled vessels. • k- ω SST is a good option at low Re in unbaffled stirred vessels. Laboratory scale unbaffled tanks provided with a top cover and a baffled tank both stirred by a Rushton turbine were simulated by carrying out RANS simulations. Three different turbulence models were adopted (k- ω SST , k- ε and the SSG Reynolds stress model) to predict the flow field and the relevant performance parameters (power and pumping numbers) of the tank operated from early to fully turbulent conditions. CFD results were compared with literature experimental data and DNS simulation results to validate and properly compare the models. In the range of Reynolds numbers investigated, results showed that, for the unbaffled tank, the SSG model based on Reynolds stresses is a better choice at larger Re, while the k- ω SST model better reproduces the experiments at lower values. Conversely, no significant differences between the predictions of the three models were found in the baffled vessel. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nb 2 O 5 -based catalysts were prepared and tested for Chlorella sp. algae valorization. • The study was carried out using a variety of Nb 2 O 5 catalysts and reaction conditions. • The best Nb 2 O 5 catalysts exhibited a larger number of Brønsted acid sites. Despite the interest in niobia-based catalysts and the importance of biomass valorisation, studies on these catalysts typically utilize model substrates like simple sugars. In this study, a series of niobium oxide-based catalysts was prepared for the application in aqueous phase catalytic conversion of sugars extracted from Chlorella sp. microalga into value-added furans. The solid catalysts were firstly characterized by various techniques including X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Raman and X-ray photoelectron (XPS) spectroscopy as well as low-temperature N 2 physisorption. Moreover, the acidity of the catalysts was assessed by using the temperature-programmed NH 3 desorption (NH 3 -TPD), by titration of water suspended catalyst with NaOH solution, and by P-bearing molecular probes loaded catalysts through 31P and 1H solid-state nuclear magnetic resonance (NMR) techniques. Herein, we focused on the catalytic transformation of Chlorella sp. and glucose solution as model molecule into furans. The best Nb 2 O 5 catalysts for valorizing Chlorella sp. into furans exhibited a larger number of Brønsted acid sites, achieving conversion yields to 5-HMF and furfural of ca. 20–22 % with respect to the extracted sugars from algae. The results showed a discernible dependence of the conversion yields to 5-HMF and furfural on catalyst acidity, specific surface area, and the presence of the Brønsted acid sites. Conversely, when using the glucose solution as substrate is concerning, the highest yield to 5-HMF was reached by using a catalyst that showed also the presence of Lewis acid sites. A systematic investigation of the structure–activity relationships in niobium oxide application for aqueous phase dehydration using real biomass substrates to obtain furanic derivatives has not been documented thus far. Therefore, the current research is significant as it demonstrates the feasibility of transforming the carbohydrate content in microalgal biomass into furans by identifying the best catalyst to use. [ABSTRACT FROM AUTHOR]

• Low frequency flashing light limits species-specific growth. • Microalgae respond similarly to high frequency flashing light and continuous light. • Flashing light used in a two-stage cultivation system improves pigment productivity. • Microalgae under low frequency flashing light show low- and high-light responses. • Protein, PUFA or pigment contents increased under low frequency flashing light. As the periodic emission of light pulses by light emitting diodes (LEDs) is known to stimulate growth or induce high value biocompounds in microalgae, this flashing light regime was tested on growth and biochemical composition of the microalgae Nannochloropsis gaditana , Koliella antarctica and Tetraselmis chui. At low flashing light frequencies (e.g., 5 and 50 Hz, Duty cycle = 0.05), a strain-dependent growth inhibition and an accumulation of protein, polyunsaturated fatty acids, chlorophyll or carotenoids (lutein, β-carotene, violaxanthin and neoxanthin) was observed. In addition, a 4-day application of low-frequency flashing light to concentrated cultures increased productivities of eicosapentaenoic acid (EPA) and specific carotenoids up to three-fold compared to continuous or high frequency flashing light (500 Hz, Duty cycle = 0.05). Therefore, applying low-frequency flashing light as finishing step in industrial production can increase protein, polyunsaturated fatty acids or pigment contents in biomass, leading to high-value algal products. [ABSTRACT FROM AUTHOR]

Highlights • Experimental k L a data in unbaffled vessels stirred by PBTs are presented. • Comparison with RT performance is provided. • Influence of scale-up on mass transfer performance is investigated. • Down-pumping and up-pumping operations are compared and discussed. Abstract Unbaffled stirred tanks are increasingly recognized as a viable alternative to common baffled tanks for a range of applications such as biochemical, food or pharmaceutical processes where the presence of baffles is undesirable for some reason. In this work, the mass transfer performance of unbaffled stirred tanks with pitched blade turbine, operating either in up-pumping or down-pumping mode, was investigated. The influence of impeller size and liquid viscosity were also investigated. The mass transfer intensity was measured by means of the Simplified Dynamic Pressure. Method The measurements concerned both coalescent and non-coalescent (viscous) batches. Results confirm that increasing apparatus size has a slightly positive effect on gas-liquid mass transfer coefficient. It was also found that when the PBT is operating in the up-pumping mode the formation of surface oscillations, which lead to undesired instabilities of the whole apparatus, is conveniently minimized. In the super-critical regime, the unbaffled tanks provide a performance comparable with that of the standard (baffled) bioreactors at the same power dissipation, which makes them a viable alternative for general fermentation operations and other gas–liquid reactions. [ABSTRACT FROM AUTHOR]

The interest in the process industry on unbaffled stirred tanks has greatly expanded in the last years because they may bring about significant advantages in a number of applications, including biochemical, food and pharmaceutical processes where the presence of baffles is undesirable for several reasons. Despite their application potential, unbaffled vessels still lack fundamental information, due to the fact that only recently their capabilities have started being dug out. The lack of information on scale up effects is possibly the main reason hindering practical applications. In this work the influence of vessel size and liquid viscosity on the mass transfer performance in unbaffled stirred vessels, is investigated. As regards the first issue (scale-up) quite surprisingly results show that comparable mass transfer coefficients may be obtained in larger vessels, for a given power input per unit volume, with typical k L a values up to 2 × 10 −3 s −1 in ungassed conditions and of 2 × 10 −2 s −1 in gassed conditions. This is opposite to expectations based on the fact that the exchange surface in subcritical conditions only grows with D 2 while volume grows with D 3 . Notably, the same result is obtained at an increased liquid viscosity (a feature often exhibited by biological cultivation broths) and confirms that unbaffled stirred tanks should be regarded as a strong candidate for industrial applications. Finally, also at the larger scale, in the super-critical regime unbaffled tanks are found to provide a performance comparable with that of standard (baffled & sparged) stirred tanks, hence resulting in a viable alternative to baffled tanks for all gas–liquid processes and bio-processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Valorisation of recalcitrant Chlorella biomass in 5-HMF was performed in two steps. • The conversion of hexoses was optimised in the presence of niobium-based catalysts. • Process optimisation occurred through DoE and reactive extraction. • An overall yield to 5-HMF of 29% on total sugars was obtained. The valorisation of recalcitrant Chlorella sp. microalgal biomass by the extraction of the sugar content and its conversion into 5-hydroxymethyl furfural (5-HMF) has been carried out in two-steps. In the first step, a pre-treatment of the biomass was optimized to obtain, by sonication and hydrothermal treatments also in the presence of acetic acid and SiO 2 pellets, the maximum release of carbohydrate and their hydrolysis to monosaccharides. The second step, carried out under hydrothermal conditions, was devoted to the heterogeneous catalytic isomerisation/dehydration of the monosaccharides (essentially glucose and fructose) released from algae in the first reaction step to yield 5-HMF in presence of two commercial samples of niobium-based catalysts that were characterized with several techniques like specific surface area and superficial acidity measurements, SEM, HRTEM, EDX, FTIR and Raman. Other important features of the two catalysts are largely present in the literature due to the fact that they are commercial materials. The isomerisation/dehydration reactions of the monosaccharides proceed through a tandem pathway involving the Lewis and Brønsted acid sites provided by the surface of the acidic solids giving rise to the isomerization of glucose to fructose, followed by dehydration of fructose to 5-HMF. The optimisation of the reaction conditions was carried out in the presence of Nb 2 O 5 by using a Design of Experiment (DoE) approach. The optimised parameters were identified as temperature 210 °C and 4.45 h of reaction time, providing a yield to 5-HMF of about 18% on the total sugars contained in the algae. A further optimisation has been achieved in the presence of NbOPO 4 instead of Nb 2 O 5, which still led to 21% yield to 5-HMF on the total sugars. Moreover, using an H 2 O/MIBK system, a reactive extraction was performed, obtaining the very good value of yield to 5-HMF of 29% on total sugars. In this way, a multi-approach process optimisation was performed, in line with the principles of process intensification, with the aim of improving the energy-efficiency of the entire process. [ABSTRACT FROM AUTHOR]

The supercritical water gasification of Nannochloropsis gaditana microalgae has been studied in term of process development at 24 MPa and 663 °C. Gasification has been investigated using a 200 cm 3 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 97.4 wt% as gasification efficiency and 86.0 wt% as carbon efficiency. The product gas is mainly composed of hydrogen (52.0%), methane (17.9%) and CO 2 (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 CH 4 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. [ABSTRACT FROM AUTHOR]

Three-phase processes in which particle suspension has to be achieved in conjunction with gas dispersion are traditionally carried out in sparged, baffled stirred tanks. The operation of such tanks can suffer, however, from particles tending to block the sparger holes. A viable alternative might be provided by uncovered unbaffled stirred tanks (UUSTs), where gas self-injection can occur when the free-surface vortex reaches the impeller blades and gas bubbles begin to be ingested by the liquid. In this work, the particle suspension and liquid aeration performances in three-phase UUSTs were experimentally investigated and compared with relevant literature correlations concerning baffled systems. The results show that, at least at the investigated scale, UUSTs are more efficient for suspending particles than relevant baffled systems. Impeller clearance scarcely affects power requirements. Finally, a down-pumping PBT with D/T = 1/3 was found to be the best choice for attaining complete suspension under self-aeration conditions. [ABSTRACT FROM AUTHOR]