A model for light distribution and average solar irradiance inside outdoor tubular photobioreactors for the microalgal mass culture (original) (raw)
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Biotechnology and Bioengineering, 1998
A macromodel is developed for estimating the year-long biomass productivity of outdoor cultures of microalga in tubular photobioreactors. The model evaluates the solar irradiance on the culture surface as a function of day of the year and the geographic location. In a second step, the geometry of the system is taken into account in estimating the average irradiance to which the cells are exposed. Finally, the growth rate is estimated as a function of irradiance, taking into account photoinhibition and photolimitation. The model interconnects solar irradiance (an environmental variable), tube diameter (a design variable), and dilution rate (an operating variable). Continuous cultures in two different tubular photobioreactors were analyzed using the macromodel. The biomass productivity ranged from 0.50 to 2.04 g L −1 d −1 , and from 1.08 to 2.76 g L −1 d −1 , for the larger and the smaller tube diameter photobioreactors, respectively. The quantum yield ranged from 1.1 to 2.2 g E −1 ; the higher the incident solar radiation, the lower the quantum yield. Simultaneous photolimitation and photoinhibition of outdoor cultures was observed. The model reproduced the experimental results with less than 20% error. If photoinhibition was neglected, and a growth model that considered only photolimitation was used to fit the data, the error increased to 45%, thus reflecting the inadequacy of previous outdoor growth models that disregard photoinhibition.
Journal of Biotechnology, 1996
From chemostat cultures of the marine microalga Isochrysis galbana (CCAP 927/ 15) simultaneous photolimitation and photoinhibition was observed. The extent of each phenomenon depends on the light gradient inside the culture and therefore on the incident irradiance. Variations in biomass concentration and average irradiance inside the culture with dilution rate at three incident irradiances, I,, were studied (from I, = 820 to 3270 PE mm2 s-'). At I, above 1630 PE mm2 s-' a photoinhibition effect was observed, although the specific growth rate remained a hyperbolic function of average irradiance regardless of incident h-radiance. To calculate average irradiance, a three-dimensional irradiance distribution model for cylindrical geometry is proposed, improving the estimation of the irradiance field inside culture with regard to other methods used up to now since the variations in illumination along the vertical axis are considered. Lastly, a new approach to model simultaneous photolimitation and photoinhibition is proposed by considering that specific growth rate is related to average irradiance and that parameters representing the cell adaptability to light are a function of the maximum irradiation at which cells are exposed, that is, the incident irradiance.
Evaluation of photosynthetic efficiency in microalgal cultures using averaged irradiance
Enzyme and Microbial Technology, 1997
The growth yield of the PUFA-producing marine microalga Isochrysis galbana grown in light-limited continuous operation was measured under a wide variety of conditions of incident irradiance (I0) and dilution rates (D). The experiments were conducted under laboratory conditions at 20°C with continuous light. D ranged from 0.0024–0.0410 h−1 at three values of I0 (820; 1,620; and 3,270 μE m−2 s−1) close to those found in outdoor cultures. A maximum efficiency of Ψmax = 0.616 g E−1 was obtained at I0 = 820 μE m−2 s−1 and D = 0.030 h−1, and the maximum capacity of the biomass to metabolize light was found to be 13.1 μE g−1 s−1. Above this value, a significant drop in system efficiency was observed. A new approach based on averaged irradiance is used to assess the photon flux absorbed by the biomass. The biomass productivity to be expected in an outdoor tubular photobioreactor growing I. galbana was predicted from efficiency data obtained in laboratory cultures and was found to be in agreement with the actual value.
Light irradiance and spectral distribution effects on microalgal bioreactors
Engineering in Life Sciences, 2014
The irradiance and light spectral distribution affect the growth and productivity of microalgal cultures. In extensive open pond cultures, the light control has limited options, mainly the culture depth. In photobioreactors, besides the culture depth, the light source, configuration of the reactor, light pathway, and flow rate can be used to control the characteristics of the light available to the cultures. The change of light conditions can also be used to modify the composition of the microalgal biomass produced to optimize the production of bioproducts of interest. Additionally, in mixed cultures, the species composition can be influenced by the light quantity and quality. Determining the effect of the light quantity and quality in photosynthetic cultures will help to develop strategies to optimize the production of biomass, lipids, pigments, proteins, and other compounds of interest in photosynthetic microorganisms. Information obtained from bench scale cultures can rarely be a...
In microalgae based biofuel technology, the light is one of the important factors for the proper growth of microalgae cells as microalgae is a photosyn-thetic microorganism. For a large scale outdoor culture the irradiance of sunlight and associated temperature is also need to consider. In this study aims to present computational model of microalgae growth taking effect of solar irra-diance and corresponding temperature in a tubular photo bioreactor for an outdoor culture system. We consider the transient behavior of temperature inside the photo bioreactor for a microalgae culture. The optimum range of temperature for outdoor cultivation of microalgae is about 22˚C-27˚C and out of this range the microalgae cell growth inhibits. Many correlations have already been established to investigate the algal productivity based on the dynamic conditions of temperature in case of full scale outdoor cultivation. However, none of them are validated yet numerically considering the model as a function of weather conditions, operational behavior and design criteria. A tubular photobioreactor (PBR) with length 20.5 m and radius 0.05 m has taken account as a simulation model. The PBR is horizontally placed as temperature variations can be observed with greater accuracy. As the solar irra-diance varies at any geographic latitude for a year and so thus temperature, equations and parameters are established relating the irradiance with the temperature to simulate the effect. We observed some significant effects of temperature on the growth of microalgae. Moreover, for the maximum growth of the cells we should control the surrounding temperature.
Biotechnology progress, 2016
We present an in-depth investigation of how various illumination conditions influence microalgal growth in photobioreactors (PBR). Effects of both the light emission spectrum (white and red) and the light incident angle (0° and 60°) on the PBR surface were investigated. The experiments were conducted in two fully controlled lab-scale PBRs, a torus PBR and a thin flat-panel PBR for high cell density culture. The results obtained in the torus PBR were used to build the kinetic growth model of Chlorella vulgaris taken as a model species. The PBR model was then applied to the thin flat-panel PBR, which was run with various illumination conditions. Its detailed representation of local rate of photon absorption under various conditions (spectral calculation of light attenuation, incident angle influence) enabled the model to take into account all the tested conditions with no further adjustment. This allowed a detailed investigation of the coupling between radiation field and photosynthet...
Biotechnology and Bioengineering, 2005
The light attenuation in a photobioreactor is determined using a fully predictive model. The optical properties were first calculated, using a data bank of the literature, from only the knowledge of pigments content, shape, and size distributions of cultivated cells which are a function of the physiology of the current species. The radiative properties of the biological turbid medium were then deduced using the exact Lorenz-Mie theory. This method is experimentally validated using a large-size integrating sphere photometer. The radiative properties are then used in a rectangular, one-dimensional two-flux model to predict radiant light attenuation in a photobioreactor, considering a quasi-collimated field of irradiance. Combination of this radiative model with the predictive determination of optical properties is finally validated by in situ measurement of attenuation profiles in a torus photobioreactor cultivating the microalgae Chlamydomonas reinhardtii, after a complete and proper characterization of the incident light flux provided by the experimental setup .
Applied and Environmental Microbiology, 1996
This article describes a novel method for the measurement of light absorption by cultures of phototrophic microorganisms. The rate of light absorption is calculated as the difference between the rate of light output from a culture containing cells and the rate of light output from a culture containing only growth medium. The specific rate of light uptake is calculated by dividing the rate of light absorption by the total biomass present in the culture. Application of the method to several case studies shows that light output from a culture varies widely depending on the absorption and scattering characteristics of the suspension.
Journal of Applied Phycology, 2000
An account is given of the setting up and use of a novel type of closed tubular photobioreactor at the Academic and University Centre in Nove Hrady, Czech Republic. This Љpenthouse-roofЉ photobioreactor was based on solar concentrators (linear Fresnel lenses) mounted in a climate-controlled greenhouse on top of the laboratory complex combining features of indoor and outdoor cultivation units. The dual-purpose system was designed for algal biomass production in temperate climate zone under well-controlled cultivation conditions and with surplus solar energy being used for heating service water. The system was used to study the strategy of microalgal acclimation to supra-high solar irradiance, with values as much as 3.5 times the ambient value, making the approach unique. The cultivation system proved to be fully functional with sufficient mixing and cooling, efficient oxygen stripping and light tracking. Experimental results (measurement of the maximum photochemical yield of PSII and non-photochemical quenching) showed that the cyanobacterium Spirulina (= Arthrospira) platensis cultivated under sufficient turbulence and biomass density was able to acclimate to irradiance values as high as 7 mmol photon m −2 s −1 . The optimal biomass concentration of Spirulina cultures in September ranged between 1.2 to 2.2 g L −1 , which resulted in a net productivity of about 0.5 g L −1 d −1 corresponding to a biomass yield of 32.5 g m −2 d −1 (based on the minimum illuminated surface area of the photobioreactor).