Modeling of biomass productivity in tubular photobioreactors for microalgal cultures: Effects of dilution rate, tube diameter, and solar irradiance (original) (raw)
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Biotechnology and Bioengineering, 1997
A mathematical model to estimate the solar irradiance profile and average light intensity inside a tubular photobioreactor under outdoor conditions is proposed, requiring only geographic, geometric, and solar position parameters. First, the length of the path into the culture traveled by any direct or disperse ray of light was calculated as the function of three variables: day of year, solar hour, and geographic latitude. Then, the phenomenon of light attenuation by biomass was studied considering Lambert-Beer's law (only considering absorption) and the monodimensional model of Cornet et al. (1900) (considering absorption and scattering phenomena). Due to the existence of differential wavelength absorption, none of the literature models are useful for explaining light attenuation by the biomass. Therefore, an empirical hyperbolic expression is proposed. The equations to calculate light path length were substituted in the proposed hyperbolic expression, reproducing light intensity data obtained in the center of the loop tubes. The proposed model was also likely to estimate the irradiance accurately at any point inside the culture. Calculation of the local intensity was thus extended to the full culture volume in order to obtain the average irradiance, showing how the higher biomass productivities in a Phaeodactylum tricornutum UTEX 640 outdoor chemostat culture could be maintained by delaying light limitation.
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.
Bioprocess and Biosystems Engineering, 2014
In this work, the production of Scenedesmus obliquus in a continuous flat-plate laboratory-scale photobioreactor (PBR) under alternated day-night cycles was tested both experimentally and theoretically. Variation of light intensity according to the four seasons of the year were simulated experimentally by a tunable LED lamp, and effects on microalgal growth and productivity were measured to evaluate the conversion efficiency of light energy into biomass during the different seasons. These results were used to validate a mathematical model for algae growth that can be applied to simulate a large-scale production unit, carried out in a flat-plate PBR of similar geometry. The cellular concentration in the PBR was calculated in both steady-state and transient conditions, and the value of the maintenance kinetic term was correlated to experimental profiles. The relevance of this parameter was finally outlined.
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.
Biotechnology Journal, 2011
Microalgae can be used to produce versatile high-value fuels, such as methane, biodiesel, ethanol, or hydrogen gas. One of the most important factors that influence the economics of microalgae cultivation is the primary production of biomass per unit area. This is determined by productivity rates during cultivation, which are influenced by the local climate conditions (solar irradiation, temperature). To compare locations in different climate regions for microalgae cultivation, a mathematical model for an idealized closed photobioreactor was developed. The applied growth kinetics were based on theoretical maximum photon-conversion efficiencies (for the conversion of solar energy to chemical energy in the form of biomass). Known or estimated temperature effects for different algal strains were incorporated. The model was used to calculate hourly average areal productivity rates as well as annual primary production values under local conditions at seven example locations. Here, hourly weather data (solar irradiance and air temperature) were taken into account. According to these model calculations, maximum annual yields were achieved in regions with high irradiation and temperature patterns in or near the optimum range of the specific algal strain (here, desert and equatorial humid climates). The developed model can be used as a tool to assess and compare individual locations for microalgae cultivation.
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.
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).
Cultivation of microalgae in a high irradiance area
2011
High annual microalgae productivities can only be achieved if solar light is efficiently used through the different seasons. During winter time the productivity is low because of the light and temperature conditions. The productivity and photosynthetic efficiency of Chlorella sorokiniana were assessed under the worst case-scenario during winter time in Huelva, south of Spain. The maximal light intensity (800 µmol m-2 s-1) and temperature (20 ºC) during winter was supplied to a 14 mm short light-path photobioreactor. Chemostat conditions were applied and the results were compared with a temperature controlled situation at 38 ºC (optimal growth temperature for C. sorokiniana). When temperature was optimal, the highest productivity was found at a dilution rate of 0.18 h-1 (P v = 0.28 g Kg-1 h-1) and the biomass yield on light energy was high (Y x,E = 1.2 g mol photons supplied-1). However, at suboptimal temperature the specific growth rate of C. sorokiniana was surprisingly low, not being able to support continuous operation at a dilution rate higher than 0.02 h-1. Therefore, also low productivity and biomass yield were found. At suboptimal temperature C. sorokiniana might experience the maximal winter intensity as excessive, yielding a very low photosynthetic efficiency. Temperature control and/or light dilution during winter time will clearly enhance the productivity. Chapter 3 Productivity of Chlorella sorokiniana in a short light-path (SLP) panel photobioreactor under high irradiance
Stratification of the Radiation Field inside a Photobioreactor during Microalgae Growth.
F o r P e e r R e v i e w ABSTRACT Light availability is a main issue in autotrophic growth of photosynthetic microorganisms. The changeofthe suspended cells concentration and that of their chlorophylls content during microalgal growth alters the optical properties of the aqueous suspension.This brings about changes in the properties of the radiation field inside the reactor. In this work,we have computed the evolution in time of the local flux density,as well asthat of the local volumetric rateof absorption of photons inside a photobioreactor by means of a Monte Carlo simulation algorithmpreviously developed.From this study we have computed two operational variables that areusefultoolsfor the analysis, performance comparison, optimization and scaling-up of photobioreactors: the average rate of photon absorption and the volumetric distribution function of photons absorption rates.Based on thesetwo variables it is possible to sistematically quantify
Biotechnology and Bioengineering, 1999
A model is developed for prediction of axial concentration profiles of dissolved oxygen and carbon dioxide in tubular photobioreactors used for culturing microalgae. Experimental data are used to verify the model for continuous outdoor culture of Porphyridium cruentum grown in a 200-L reactor with 100-m long tubular solar receiver. The culture was carried out at a dilution rate of 0.05 h −1 applied only during a 10-h daylight period. The quasi-steady state biomass concentration achieved was 3.0 g и L −1 , corresponding to a biomass productivity of 1.5 g и L −1 и d −1. The model could predict the dissolved oxygen level in both gas disengagement zone of the reactor and at the end of the loop, the exhaust gas composition, the amount of carbon dioxide injected, and the pH of the culture at each hour. In predicting the various parameters, the model took into account the length of the solar receiver tube, the rate of photosynthesis, the velocity of flow, the degree of mixing, and gas-liquid mass transfer. Because the model simulated the system behavior as a function of tube length and operational variables (superficial gas velocity in the riser, composition of carbon dioxide in the gas injected in the solar receiver and its injection rate), it could potentially be applied to rational design and scale-up of photobioreactors.