2,548 research outputs found

    A new photobioreactor for continuous microalgal production in hatcheries based on external-loop airlift and swirling flow

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    This study deals with the scale of a new photobioreactor for continuous microalgal production in hatcheries. The combination of the state-of-art with the constraints inherent to hatcheries has turned the design into a closed, artificially illuminated and external-loop airlift configuration based on a succession of elementary modules, each one being composed of two transparent vertical interconnected columns. The liquid circulation is ensured pneumatically (air injections) with respect to a swirling motion (tangential inlets). A single module of the whole photobioreactor was built-up to investigate how parameters, such as air sparger type, gas flow rate, tangential inlet, column radius and height can influence radiative transfer, hydrodynamics, mass transfer and biological performances. The volumetric productivities were predicted by modeling radiative transfer and growth of Isochrysis affinis galbana (clone Tahiti). The hydrodynamics of the liquid phase was modeled in terms of global flow behavior (circulation and mixing times, Péclet number) and of swirling motion decay along the column (Particle Image Velocimetry). The aeration performances were determined by overall volumetric mass transfer measurements. Continuous cultures of Isochrysis affinis galbana (clone Tahiti) were run in two geometrical configurations, generating either an axial or a swirling flow. Lastly, the definitive options of design are presented as well as a 120 Liter prototype, currently implemented in a French mollusk hatchery and commercialized

    Autotrophic and Heterotrophic Growth Conditions Modify Biomolecole Production in the Microalga Galdieria sulphuraria (Cyanidiophyceae, Rhodophyta)

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    Algae have multiple similarities with fungi, with both belonging to the Thallophyte, a polyphyletic group of non-mobile organisms grouped together on the basis of similar characteristics, but not sharing a common ancestor. The main difference between algae and fungi is noted in their metabolism. In fact, although algae have chlorophyll-bearing thalloids and are autotrophic organisms, fungi lack chlorophyll and are heterotrophic, not able to synthesize their own nutrients. However, our studies have shown that the extremophilic microalga Galderia sulphuraria (GS) can also grow very well in heterotrophic conditions like fungi. This study was carried out using several approaches such as scanning electron microscope (SEM), gas chromatography/mass spectrometry (GC/MS), and infrared spectrophotometry (ATR-FTIR). Results showed that the GS, strain ACUF 064, cultured in autotrophic (AGS) and heterotrophic (HGS) conditions, produced different biomolecules. In particular, when grown in HGS, the algae (i) was 30% larger, with an increase in carbon mass that was 20% greater than AGS; (ii) produced higher quantities of stearic acid, oleic acid, monounsaturated fatty acids (MUFAs), and ergosterol; (iii) produced lower quantities of fatty acid methyl esters (FAMEs) such as methyl palmytate, and methyl linoleate, saturated fatty acids (SFAs), and poyliunsaturated fatty acids (PUFAs). ATR-FTIR and principal component analysis (PCA) statistical analysis confirmed that the macromolecular content of HGS was significantly different from AGS. The ability to produce different macromolecules by changing the trophic conditions may represent an interesting strategy to induce microalgae to produce different biomolecules that can find applications in several fields such as food, feed, nutraceutical, or energy production

    Preparation, Proximate Composition and Culinary Properties of Yellow Alkaline Noodles from Wheat and Raw/Pregelatinized Gadung (Dioscorea Hispida Dennst) Composite Flours

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    The steady increase of wheat flour price and noodle consumptions has driven researchers to find substitutes for wheat flour in the noodle making process. In this work, yellow alkaline noodles were prepared from composite flours comprising wheat and raw/pregelatinized gadung (Dioscorea hispida Dennst) flours. The purpose of this work was to investigate the effect of composite flour compositions on the cooking properties (cooking yield, cooking loss and swelling index) of yellow alkaline noodle. In addition, the sensory test and nutrition content of the yellow alkaline noodle were also evaluated for further recommendation. The experimental results showed that a good quality yellow alkaline noodle can be prepared from composite flour containing 20% w/w raw gadung flour. The cooking yield, cooking loss and swelling index of this noodle were 10.32 g, 1.20 and 2.30, respectively. Another good quality yellow alkaline noodle can be made from composite flour containing 40% w/w pregelatinized gadung flour. This noodle had cooking yield 8.93 g, cooking loss 1.20, and swelling index of 1.88. The sensory evaluation suggested that although the color, aroma and firmness of the noodles were significantly different (p ≤ 0.05) from wheat flour noodle, but their flavor remained closely similar. The nutrition content of the noodles also satisfied the Indonesian National Standard for noodle. Therefore, it can be concluded that wheat and raw/pregelatinized gadung composite flours can be used to manufacture yellow alkaline noodle with good quality and suitable for functional food

    Effect of pH Change on the Microalgae-Based Biogas Upgrading Process

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    An alternative way to remove CO2 from biogas is the use of photosynthetic microorganisms, such as microalgae. This can be achieved by the operation of an open photobioreactor, connected with a mass transfer column, such as a counterflow column. This technology provides up-graded biogas with high quality. The microalgal uptake of CO2 from the biogas in counterflow columns generates pH changes in microalgae culture. To clarify the potential effect of these dynamic pH conditions in the culture, the effect of pH change on the photosynthetic activity and PSII quantum yield was studied for microalgae Chlorella sorokiniana. Thus, assays were carried out, where the pH drop reported in the counterflow columns was replicated in batch microalgae culture through HCl addition and CO2 injection, moving the culture pH from 7.0 to 5.0 and from 7.0 to 5.8, respectively. Moreover, the effect of light/darkness on photosynthetic activity was tested when the pH decreased. The results obtained in this research showed that the photosynthetic activity decreased for the light conditions when the pH was shifted by HCl addition and CO2 injection. Despite this, the value of the PSII quantum yield remained at 0.6–0.7, which means that the microalgae culture did not suffer a negative effect on the photosynthetic system of cells because a high value of PSII efficiency remained. In the same way, the results indicated that when the pH change was corrected, the photosynthetic activity recovered. Moreover, the apparent affinity constant for dissolved inorganic carbon (KDIC) was 0.9 µM at pH 5 and 112.0 µM at pH 7, which suggests that the preferred carbon source for C.sorokniana is CO2. Finally, all the results obtained indicated that the pH drop in the counter-flow column for biogas upgrading did not cause permanent damage to the photosynthetic system, and the decrease in the photosynthetic activity as a result of the pH drop can be recovered when the pH is corrected.This research was funded by FONDECYT-ANID CHILE, grant number 1120488, CRHIAM Centre (CONICYT/FONDAP) grant number 15130015, and VRIEA-PUCV grant number 039.315/2022

    Design and Bench-Scale Hydrodynamic Testing of Thin-Layer Wavy Photobioreactors

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    In a thin-volume photobioreactor where a concentrated suspension of microalgae is circulated throughout the established spatial irradiance gradient, microalgal cells experience a time-variable irradiance. Deploying this feature is the most convenient way of obtaining the so-called flashing light effect, improving biomass production in high irradiance. This work investigates the light flashing features of sloping wavy photobioreactors, a recently proposed type, by introducing and validating a computational fluid dynamics (CFD) model. Two characteristic flow zones (straight top-to-bottom stream and local recirculation stream), both effective toward light flashing, have been found and characterized: a recirculation-induced frequency of 3.7 Hz and straight flow-induced frequency of 5.6 Hz were estimated. If the channel slope is increased, the recirculation area becomes less stable while the recirculation frequency is nearly constant with flow rate. The validated CFD model is a mighty tool that could be reliably used to further increase the flashing frequency by optimizing the design, dimensions, installation, and operational parameters of the sloping wavy photobioreactor

    Development of an Efficient Photobioreactor for CO2 Mitigation and Microalgae Biomass Production: Simulation and Optimisation

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    Recently microalgae cultivation has been intensively investigated as a sustainable and eco-friendly approach for CO2 mitigation. Among the effective parameters, the light availability considered as one of the most outstanding limiting factors and an obstacle due to complexity. Light intensity, light period and light distribution inside the culture, as well as their influence on the performance of the photobioreactor in terms of biomass growth, CO2 biofixation and CO2 utilisation efficiency were investigated in this study

    Engineering the sequestration of carbon dioxide using microalgae

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    With greenhouse gas emissions (of which CO2 is the major component) being a major environmental concern, mitigation of those emissions is becoming increasingly imperative. The ability to use a fast growing, photosynthetic organism like microalgae that can survive primarily on nutrients such as sunlight and air (with increased CO2 levels) makes it a desirable agent for CO2 sequestration. The primary goal of this project is the engineering of the sequestration of CO2 using the cultivation of the microalgae species Chlorella vulgaris. Secondary goals of the project are the exploration and development of valuable by-products of the cultivation and the determination of whether utilizing microalgae to capture CO2 could be integrated economically into an industrial facility. The batch growth kinetics of the photosynthetic algal species C. vulgaris were investigated using a well-mixed stirred bioreactor. The growth rate was found to increase as the dissolved CO2 increased to 150 mg/L (10% CO2 by volume in the gas), but fell dramatically at higher concentrations. Increasing the radiant flux also increased growth rate. With a radiant flux of 32.3 mW falling directly on the 500 mL culture media, the growth rate reached up to 3.6 mg of cells/L-h. Both pH variation (5.5 - 7.0) and mass transfer rate of CO2 (KLa between 6 h-1 and 17 h-1) had little effect on growth rate. The operation of continuously stirred tank bioreactors (CSTBs) at minimum cost is a major concern for operators. In this work, a CSTB design strategy is presented where impeller stirring speed and aeration rate are optimized to meet the oxygen demand of growing cells, simultaneously minimizing the capital and operating cost. The effect of microbial species, ions in the culture medium, impeller style, as well as changing CSTB size and biomass input density on the optimum operating conditions, is examined. A study of the effects of various parameters on the CSTB design is shown. Using the kinetic data collected in the batch growth study, a novel external loop airlift photobioreactor (ELAPB) was designed and tested. A model was developed for C. vulgaris growth in the ELAPB that incorporated growth behaviour, light attenuation, mass transfer, and fluid dynamics. The model predicts biomass accumulation, light penetration, and transient CO2 concentrations, and compares predictions to experimental data for radiant fluxes of 0.075 – 1.15 W/m2 and 0 – 20% CO2 enrichment of feed air, with a 10% average error. The effect of radiant flux and CO2 concentration is presented with discussion of radial and vertical profiles along the column. For a fed-batch culture at a biomass density of 170 mg/L, the penetration of the radiant flux was found to decrease by 50% within the first 1 cm, and 75% at 2 cm. Theoretical optimum growth conditions are determined to be 0.30 W/m2 and 6% CO2 enrichment of inlet feed air. The algal culture was observed to be a workable electron acceptor in a cathodic half cell. A net potential difference of 70 mV was achieved between the growing C. vulgaris culture acting as a cathode and a 0.02 M potassium ferrocyanide anodic half cell. Surge current and power levels of 1.0 µA/mg of cell dry weight and 2.7 mW/m2 of cathode surface area were measured between these two half cells. The recently developed photosynthetic cathode was also coupled to a fermentative anode to produce a completely microbial fuel cell. Loading effects and the effect of changing culture conditions on fuel cell operation are reported. The maximum power output measured was 0.95 mW/ m2 at 90 V and 5000 ohms. A significant increase in this output is achieved with the addition of supplemental glucose to the anodic half cell and the enrichment of the feed air bubbled into the cathodic half cell with 10% CO2. Two economic feasibility studies were performed on the integration of ELAPBs into an industrial facility. These integration studies operated the ELAPBs continuously as biocathodes in coupled microbial fuel cells (MFCs) that capture CO2 from an existing 130 million L/yr bioethanol plant, while generating electrical power and yielding oil for biodiesel to provide operational revenue to offset costs. The anodes for the coupled MFCs are the existing yeast batch fermentors, and the CO2 to be sequestered comes from the existing bioethanol production. Two different design schemes were evaluated, in both cases the maximum profit was achieved with the maximum number of tall columns operated in parallel. The first design evaluated a batch bioethanol facility with off-site oil processing, and the economic feasibility is demonstrated by the positive Net Present Worth achieved over the 20 year life of the plant, at a 10% rate of return on investment. The second design, for a continuous bioethanol operation, processes both oil and algae biomass on-site, but the economics of this second process are only positive (Internal Rate of Return 9.93%.) if the government provides financial assistance in the form of generous carbon credits (a speculative $100 per tonne of CO2 not yet attained) and a 25% capital equipment grant

    Design and development of a packedbed scrubber for upgradation of biogas using a closed-loop process: An economical and environmental approach

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    Biogas can be produced from any biomass source and is renewable fuel. The main drawbacks in the composition of biogas are the presence of carbon dioxide (CO2) and hydrogen sulphide (H2S) which affect the storage devices. The removal of CO2 and H2S is of great interest today. Different methods for removal of both the elements were suggested by many researchers. The present work aims to remove the CO2 and H2S using combined effects of water scrubbing and algae. For this purpose a packed bed scrubber was designed using Solid Works and fabricated in our department. The present experimental investigation shows that upto 73% methane in biogas is obtainable with the mixing ratio of SCK: CD (25: 75), in which carbon dioxide is about 17% and hydrogen sulphide is 0.23%. By using a packed bed scrubber, the biogas was purified and after purification the methane percentage increased by approximately 27% and the CO2 decreased by 77%. And H2S decreased by about 94%

    Investigate the influence of the hydrodynamics on the photobioreactor performance: Effect of configuration and gas distributor

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    Study the effect of gas sparger on gas holdup, and bubble dynamics such as bubble passage frequency, chord length distribution, and interfacial area in an air-water system in a bubble column PBR. Study the influence of gas sparger on hydrodynamics of PBR using real system. Study the impact of gas sparger for nutrients removal using wastewater as a medium. Lastly, study the synergistic effect and optimization of most influential parameters on CO2 fixation and nutrients removal

    Experimental and model-based analysis for optimizing Chromochloris zofingiensis growth from laboratory to plant scale

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    This thesis is focused on verifying large-scale feasibility of a hybrid chemical and biological process for CO2-fixation, combining carbon dioxide absorption by means of a carbonate-based solvent with microalgal sequestration, where CO2 is fed to the culture in bicarbonates form. A rigorous simulation is carried out using Aspen Plus process simulator to solve material and energy balances, and to check whether this process can be scaled-up at industrial level. The steam methane reforming plant data are taken as the starting point to set up the process simulation. The plant layout includes a first section where the carbon dioxide in the steam methane reforming tail gas is chemically absorbed by using a sodium carbonate aqueous solution. The liquid from the bottom of the column is then fed to the photobioreactor, microalgae are separated from water, which is recycled to the absorption column, after a suitable make up. The model kinetic parameters are obtained from experimental growth data of Arthrospira Platensis species measured in laboratory continuous cultivation systems, and takes into account the effect of temperature and light. Simulation results are used to calculate the volume of the photobioreactor and the irradiated area required, as a function of light intensity. Photosynthetic efficiency and electrical energy consumption are also evaluated. Eventually, a reactor design proposal is suggested, and costs related to energy supply to microalgae culture are presented.This thesis is focused on verifying large-scale feasibility of a hybrid chemical and biological process for CO2-fixation, combining carbon dioxide absorption by means of a carbonate-based solvent with microalgal sequestration, where CO2 is fed to the culture in bicarbonates form. A rigorous simulation is carried out using Aspen Plus process simulator to solve material and energy balances, and to check whether this process can be scaled-up at industrial level. The steam methane reforming plant data are taken as the starting point to set up the process simulation. The plant layout includes a first section where the carbon dioxide in the steam methane reforming tail gas is chemically absorbed by using a sodium carbonate aqueous solution. The liquid from the bottom of the column is then fed to the photobioreactor, microalgae are separated from water, which is recycled to the absorption column, after a suitable make up. The model kinetic parameters are obtained from experimental growth data of Arthrospira Platensis species measured in laboratory continuous cultivation systems, and takes into account the effect of temperature and light. Simulation results are used to calculate the volume of the photobioreactor and the irradiated area required, as a function of light intensity. Photosynthetic efficiency and electrical energy consumption are also evaluated. Eventually, a reactor design proposal is suggested, and costs related to energy supply to microalgae culture are presented
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