Simultaneous Effect of Temperature and Irradiance on Growth and Okadaic Acid Production from the Marine Dinoflagellate Prorocentrum belizeanum

Benthic marine dioflagellate microalgae belonging to the genus Prorocentrum are a major source of okadaic acid (OA), OA analogues and polyketides. However, dinoflagellates produce these valuable toxins and bioactives in tiny quantities, and they grow slowly compared to other commercially used microalgae. This hinders evaluation in possible large-scale applications. The careful selection of producer species is therefore crucial for success in a hypothetical scale-up of culture, as are appropriate environmental conditions for optimal growth. A clone of the marine toxic dinoflagellate P. belizeanum was studied in vitro to evaluate its capacities to grow and produce OA as an indicator of general polyketide toxin production under the simultaneous influence of temperature (T) and irradiance (I0). Three temperatures and four irradiance levels were tested (18, 25 and 28 °C; 20, 40, 80 and 120 µE·m−2·s−1), and the response variables measured were concentration of cells, maximum photochemical yield of photosystem II (PSII), pigments and OA. Experiments were conducted in T-flasks, since their parallelepipedal geometry proved ideal to ensure optically thin cultures, which are essential for reliable modeling of growth-irradiance curves. The net maximum specific growth rate (µm) was 0.204 day−1 at 25 °C and 40 µE·m−2·s−1. Photo-inhibition was observed at I0 > 40 μEm−2s−1, leading to culture death at 120 µE·m−2·s−1 and 28 °C. Cells at I0 ≥ 80 µE·m−2·s−1 were photoinhibited irrespective of the temperature assayed. A mechanistic model for µm-I0 curves and another empirical model for relating µm-T satisfactorily interpreted the growth kinetics obtained. ANOVA for responses of PSII maximum photochemical yield and pigment profile has demonstrated that P. belizeanum is extremely light sensitive. The pool of photoprotective pigments (diadinoxanthin and dinoxanthin) and peridinin was not able to regulate the excessive light-absorption at high I0-T. OA synthesis in cells was decoupled from optimal growth conditions, as OA overproduction was observed at high temperatures and when both temperature and irradiance were low. T-flask culture observations were consistent with preliminary assays outdoors

A model of chlorophyll fluorescence in microalgae integrating photoproduction, photoinhibition and photoregulation

This paper presents a mathematical model capable of quantitative prediction of the state of the photosynthetic apparatus of microalgae in terms of their open, closed and damaged reaction centers under variable light conditions. This model combines the processes of photoproduction and photoinhibition in the Han model with a novel mathematical representation of photoprotective mechanisms, including qE-quenching and qI-quenching. For calibration and validation purposes, the model can be used to simulate fluorescence fluxes, such as those measured in PAM fluorometry, as well as classical fluorescence indexes. A calibration is carried out for the microalga Nannochloropsis gaditana, whereby 9 out of the 13 model parameters are estimated with good statistical significance using the realized, minimal and maximal fluorescence fluxes measured from a typical PAM protocol. The model is further validated by considering a more challenging PAM protocol alternating periods of intense light and dark, showing a good ability to provide quantitative predictions of the fluorescence fluxes even though it was calibrated for a different and somewhat simpler PAM protocol. A promising application of the model is for the prediction of PI-response curves based on PAM fluorometry, together with the long-term prospect of combining it with hydrodynamic and light attenuation models for high-fidelity simulation and optimization of full-scale microalgae production systems

The effect of Time Scales in Photosynthesis on microalgae Productivity

International audienceMicroalgae are often seen as a potential biofuel producer. In order to predict achievable productivities in the so called raceway culturing system, the dy- namics of photosynthesis has to be taken into account. In particular, the dynami- cal effect of inhibition by an excess of light (photoinhibition) must be represented. We propose a model considering both photosynthesis and growth dynamics. This model involves three different time scales. We study the response of this model to uctuating light with different frequencies by slow/fast approximations. Therefore, we identify three different regimes for which a simplified expression for the model can be derived. These expressions give a hint on productivity improvement which can be expected by stimulating photosynthesis with a faster hydrodynamics

Experimental investigation of the combined effect of light and temperature on microalgae growth in milli-photobioreactors

openMicroalgae represent one of the most potential sustainable alternatives for producing energy and environmentally benign products. However, costs of production are still limitative for many applications and photobioreactors play important roles in these processes. The aim of this thesis is to develop a suitable model for large-scale cultivation for finding the best condition of light and temperature to optimize the productivity in a microalgal artificially illuminate system. For this purpose, several experiments with the microalga Acutodesmus obliquus 276-7 were conducted in a small-scale photobioreactor of 45 ml.Microalgae represent one of the most potential sustainable alternatives for producing energy and environmentally benign products. However, costs of production are still limitative for many applications and photobioreactors play important roles in these processes. The aim of this thesis is to develop a suitable model for large-scale cultivation for finding the best condition of light and temperature to optimize the productivity in a microalgal artificially illuminate system. For this purpose, several experiments with the microalga Acutodesmus obliquus 276-7 were conducted in a small-scale photobioreactor of 45 ml

A CFD-VOF based model to address intensive photobioreactor design

The design and optimization of photobioreactors for intensive microalgal cultures are key issues to increase process performance. A model to assess the photosynthetic performance of tubular, bubble column and flat photobioreactors is presented. The model has coupled microalgal light distribution, photosynthesis kinetics and gas-liquid hydrodynamics. A lumped kinetic parameter model of photosynthetic unit (PSU) has been adopted for photosynthetic reactions. The dynamics of a microalgal cell has been described according to the gas-liquid flow of a bubble column. The flow field induced by liquid turbulence and bubbles uprising throughout the photobioreactor have been simulated with ANSYS-FLUENT. A representative domain of the flat photobioreactor has been selected by adopting proper periodic boundary conditions. Turbulence dispersion fields have been assessed by numerical simulations for several bubble size. A random-walk model developed in MATLAB has been adopted to microalgal cells to assess the irradiance experienced by the PSU-cell in the photobioreactors. The photobioreactor performances - expressed in terms of global photosynthesis rate – have been assessed. Irradiance level and biomass concentration have been changed in the range of operating conditions typically adopted for known processes

Experimental study of substrate limitation and light acclimation in cultures of the microalgae Scenedesmus obliquus—Parameter identification and model predictive control

In this study, the parameters of a dynamic model of cultures of the microalgae Scenedesmus obliquus are estimated from datasets collected in batch photobioreactors operated with various initial conditions and light illumination conditions. Measurements of biomass, nitrogen quota, bulk substrate concentration, as well as chlorophyll concentration are achieved, which allow the determination of parameters with satisfactory confidence intervals and model cross-validation against independent data. The dynamic model is then used as a predictor in a nonlinear model predictive control strategy where the dilution rate and the incident light intensity are simultaneously manipulated in order to optimize the cumulated algal biomass production.Fil: Gorrini, Federico Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages"; ArgentinaFil: Lara, Jesús Miguel Zamudio. Université de Mons; Bélgica. Universidad de Guanajuato; MéxicoFil: Biagiola, Silvina Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages"; ArgentinaFil: Figueroa, Jose Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages". Universidad Nacional del Sur. Departamento de Ingeniería Eléctrica y de Computadoras. Instituto de Investigaciones en Ingeniería Eléctrica "Alfredo Desages"; ArgentinaFil: Escoto, Héctor Hernández. Universidad de Guanajuato; MéxicoFil: Hantson, Anne Lise. Université de Mons; BélgicaFil: Wouwer, Alain Vande. Université de Mons; Bélgic

A Model-Based investigation on the effect of Light on Microalgae Growth: Focusing on Photoproduction, Photoregulation and Photoinhibition

Biofuels derived from microalgae may represent a key source for alternative energy vectors. Moreover, microalgae exhibit a great potential for sustainable production of a wide range of commodities and value-added products, including cosmetics, pharmaceuticals and nutraceuticals, which makes them suitable for biorefinery applications. Their high productivity and their ability to accumulate large amounts of lipids, along with their independence from arable land, put them in a competitive position with respect to traditional oil crops. However, the economical and energetic sustainability of large scale microalgae cultivation for biodiesel production are still debated. The most optimistic previsions are in fact based on gross estimates of productivity, derived by extrapolation of laboratory-scale data. Therefore, the development of reliable mathematical models that are capable of quantitative predictions of the behaviour of large-scale outdoor microalgae culture is of paramount importance. Such models prove especially useful in identifying which parameters have the largest impact on productivity, thereby providing a means for enhancing the growth conditions through design and operational changes. Moreover, accurate forecasts of microalgal growth in the outdoor conditions can lead to a better understanding of the real potential of microalgae-based biofuels. This Thesis aims of investigating the complex effect of light in the photosynthetic apparatus activity, and its effect on microalgae growth. The work presented in this Thesis follows two general lines. The first contribution has been to propose a general approach for model development. The proposed methodology guides the modelling effort in order to assure both an accurate representation of the calibration data, but most importantly also the identifiability of the model. The identifiability of a model, i.e. the possibility to estimate in accurate and reliable way its parametric set, is in fact, a necessary property for the model to be confidently used in process scale-up and optimization. The proposed methodology has been successfully applied to growth and fluorescence data of the sea water alga Nannochloropsis Salina. A second contribution is concerned with Pulsed Amplitude Modulation (PAM) fluorometry. A dynamic model of chlorophyll fluorescence has been developed. The model integrates photoproduction, photoregulation and photoinhibition processes in a semi-mechanistic way. The model has been calibrated against fluorescence data of a sample of the microalga Nannochloropsis gaditana. The proposed fluorescence model is capable of quantitative prediction of the state of the photosynthetic apparatus of microalgae in terms of their open, closed and damaged reaction centres under variable light conditions. Two promising application of the fluorescence model have also been analysed: (i) the model has been used for the prediction of photosynthesis rate versus irradiance (PI)-response curves based on PAM fluorometry; and (ii) a model based experiment design (MBDoE) approach has been followed to define new information rich PAM protocols to further validate and refine the model structure

A study of the growth and hydrogen production of Cyanothece sp. ATCC 51142

Hydrogen (H2) has long been promoted as an ideal fuel, as it permits a completely clean combustion and has great potential to provide clean power needed for transport and electricity generation. The unicellular, nitrogen-fixing cyanobacterium Cyanothece sp. ATCC 51142 is a promising strain with a remarkable capability of producing large quantities of H2. Under anaerobic condition, the cyanobacterium carries out the biological fixation of atmospheric nitrogen (N2) into ammonia (NH3), concurrently producing H2 as by-product. The aim of this thesis was to improve our understanding of the growth and H2 production of Cyanothece sp. ATCC 51142 in order to develop a continuous and practical cyanobacterial H2 production process. In order to achieve effective H2 production, it is prerequisite to grow dense and healthy Cyanothece 51142 cultures. Favourable cyanobacterial growth conditions included a continuous illumination at 207 - 320 μmol m-2 s-1, temperature of 35 °C and nitrogen-replete (addition of nitrate salts) condition. The critical temperature, which induces photoinhibition upon the cyanobacterium, was found at 40 °C. In the case of H2 production, favourable conditions included a continuous illumination at low light intensities of 46 – 92 μmol m-2 s-1, temperature of 30 °C, nitrogen-fixing (sole presence of atmospheric N2) and photoheterotrophic (sole presence of organic glycerol substrate) growth condition. In order to effectively handle incompatible requirements between the cyanobacterial growth and its sequential H2 production, a novel two-stage chemostat photobioreactor (PBR) system was designed and developed, with an aim to improve H2 production yield as well as extend its production duration. The system has been operated non-stop for consecutive 31 days without any losses in its performance and subsequently demonstrated a remarkable improvement in H2 production, with more than 6.4 times higher yield than that of a single-stage batch system. With the continuous mode of operation, a continuous collection of produced biomass from the PBR is also permitted (more than 7.3 times improvement in biomass yield than that of a single-stage batch system). At an industrial scale, this biomass could undergo further downstream processing to generate a multistreamline of high valued by-products such as e.g. vitamins, pharmaceuticals and human nutrition, which can subsequently contribute to a significant improvement in an economic viability of biohydrogen process.Open Acces

New mechanistic model to simulate microalgae growth

The prospect of treating wastewater and at the same time producing microalgae biomass is receiving increasing attention. Mechanistic models for microalgae growth in wastewater are currently being developed for new systems design as well as to improve the understanding of the involved biokinetic processes. However, mathematical models able to describe the complexity of microalgal cultures are still not a common practice. The aim of the present study is to present and calibrate a new mechanistic model built in COMSOL Multiphysics™ platform for the description of microalgae growth. Carbon-limited algal growth, transfer of gases to the atmosphere; and photorespiration, photosynthesis kinetics and photoinhibition are included. The model considers the growth of microalgae as a function of light intensity and temperature, as well as availability of nitrogen and other nutrients. The model was calibrated using experimental data from a case study based on the cultivation of microalgae species in synthetic culture medium. The model was able to reproduce experimental data. Simulation results show the potential of the model to predict microalgae growth and production, nutrient uptake, and the influence of temperature, light intensity and pH on biokinetic processes of microalgae.Peer ReviewedPostprint (author's final draft