Multifactorial comparison of photobioreactor geometries in parallel microalgae cultivations (original) (raw)
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Biotechnology and Bioengineering, 2013
Temperature-tolerant Chlorella sorokiniana was cultivated in a 51-L column photobioreactor with a 1.1 m 2 illuminated area. The reactor was operated outdoors under tropical meteorological conditions (Singapore) without controlling temperature and the culture was mixed at a power input of 7.5 W/m 3 by sparging CO 2 -enriched air at 1.2 L/min (gas hold-up of 0.02). Biomass productivity averaged 10 AE 2.2 g/m 2 illuminated area -day over six batch studies, yielding an average photosynthetic efficiency (PE) of 4.8 AE 0.5% of the total solar radiation (P ¼ 0.05, N ¼ 6). This demonstrates that temperature-tolerant microalgae can be cultivated at high PE under a mixing input sevenfold to ninefold lower than current operational guidelines (50-70 W/m 3 ) and without the need for temperature control (the culture broth temperature reached 418C during operation). In this study, the PE value was determined based on the amount of solar radiation actually reaching the algae and this amount was estimated using a mathematical model fed with onsite solar irradiance data. This determination was found to be particularly sensitive to the value of the atmospheric diffusion coefficient, which generated a significant uncertainty in the PE calculation. The use of the mathematical model, however, confirmed that the vertical reactor geometry supported efficient photosynthesis by reducing the duration and intensity of photoinhibition events. The model also revealed that all three components of direct, diffuse, and reflected solar radiation were quantitatively important for the vertical column photobioreactor, accounting for 14%, 65%, and 21% of the total solar radiation reaching the culture, respectively. The accurate prediction of the discrete components of solar radiation reaching the algae as a function of climatic, geographic, and design parameters is therefore crucial to optimize the individual reactor geometry and the layout/spacing between the individual reactors in a reactor farm.
Horizontal or vertical photobioreactors? How to improve microalgae photosynthetic efficiency
Bioresource Technology, 2011
The productivity of a vertical outdoor photobioreactor was quantitatively assessed and compared to a horizontal reactor. Daily light cycles in southern Spain were simulated and applied to grow the microalgae Chlorella sorokiniana in a flat panel photobioreactor. The maximal irradiance around noon differs from 400 lmol photons m À2 s À1 in the vertical position to 1800 lmol photons m À2 s À1 in the horizontal position. The highest volumetric productivity was achieved in the simulated horizontal position, 4 g kg culture À1 d À1. The highest photosynthetic efficiency was found for the vertical simulation, 1.3 g of biomass produced per mol of PAR photons supplied, which compares favorably to the horizontal position (0.85 g mol À1) and to the theoretical maximal yield (1.8 g mol À1). These results prove that productivity per unit of ground area could be greatly enhanced by placing the photobioreactors vertically.
Biotechnology and Bioengineering, 2009
Maximal productivity of a 14 mm light-path panel photobioreactor under high irradiance was determined. Under continuous illumination of 2100 µmol photons m-2 s-1 with red LEDs (light emitting diodes) the effect of dilution rate on photobioreactor productivity was studied. The light intensity used in this work is similar to the maximal irradiance on a horizontal surface at latitudes lower than 37º. Chlorella sorokiniana, a fast-growing green microalga, was used as a reference strain in this study. The dilution rate was varied from 0.06 h-1 to 0.26 h-1. The maximal productivity was reached at a dilution rate of 0.24 h-1 , with a value of 7.7 g of dry weight m-2 h-1 (m 2 of illuminated photobioreactor surface) and a volumetric productivity of 0.5 g of dry weight L-1 h-1. At this dilution rate the biomass concentration inside the reactor was 2.1 g L-1 and the photosynthetic efficiency was 1.0 g dry weight per mol photons. This biomass yield on light energy is high but still lower than the theoretical maximal yield of 1.8 g mol photons-1 which must be related to photosaturation and thermal dissipation of absorbed light energy.
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.
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).
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.
Food technology and biotechnology, 2019
The cultivation of Chlorella sp., the most abundant microalga in the Persian Gulf, took place in a novel pyramid photobioreactor (PBR), a modified version of plate PBR, consisting of four completely separate equal-volume chambers. In this study we used two light sources incident in each chamber: light-emitting diode (LED) at various wavelengths (red, white and blue) of 108 µmol/(m2·s) photosynthetic photon flux density as internal lighting, and the same photon flux density for external white lighting. PBR served to study the effects of light sources on chlorophyll a production, maximum specific growth rate (µmax), biomass productivity rate (rp) and photon performance. The results showed that the highest chlorophyll a production was obtained under red LED illumination. The highest values for rp, µmax and photon performance were obtained under white light.
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
Maximum Photosynthetic Yield of Green Microalgae in Photobioreactors
Marine Biotechnology, 2010
The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m−2 s−1). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3–37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons−1 and a maintenance requirement of 0.0133 and 0.0068 mol photons g−1 h−1 were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenanc...