Model‐supported phototrophic growth studies with Scenedesmus obtusiusculus in a flat‐plate photobioreactor

Abstract

Light-dependent growth of microalgae can vary remarkably depending on the cultivation system and microalgal strain. Cell size and the pigmentation of each strain, as well as reactor geometry have a great impact on absorption and scattering behavior within a photobioreactor. In this study, the light-dependent, cell-specific growth kinetics of a novel green algae isolate, Scenedesmus obtusiusculus, was studied in a LED-illuminated flat-plate photobioreactor on a lab-scale (1.8 L, 0.09 m ). First, pH-controlled batch processes were performed with S. obtusiusculus at different constant incident photon flux densities. The best performance was achieved by illuminating S. obtusiusculus with 1400 μmol photons m s at the surface of the flat-plate photobioreactor, resulting in the highest biomass concentration (4.95 ± 0.16 g L within 3.5 d) and the highest specific growth rate (0.22 h ). The experimental data were used to identify the kinetic parameters of different growth models considering light inhibition for S. obtusiusculus. Light attenuation within the flat-plate photobioreactor was considered by varying light transfer models. Based on the identified kinetic growth model of S. obtusiusculus, an optimum growth rate of 0.22 h was estimated at a mean integral photon flux density of 1072 μmol photons m s with the Beer-Lambert law and 1590 μmol photons m s with Schuster's light transfer model in the flat-plate photobioreactor. LED illumination was, thus, increased to keep the identified optimum mean integral photon flux density constant in the batch process assuming Schuster's light transfer model. Compared to the same constant incident photon flux density (1590 μmol photons m s ), biomass concentration was up to 24% higher using the lighting profile until a dry cell mass concentration of 14.4 ± 1.4 g L was reached. Afterward, the biomass concentration remained constant, whereas cell growth continued in the batch process with constant incident photon flux density. Finally, biomass concentration was 15.5 ± 1.5 g L and, thus, 7% higher compared to the corresponding batch process with lighting profile. Biotechnol. Bioeng. 2017;114: 308-320. © 2016 Wiley Periodicals, Inc.

Modelling growth and CO2 fixation by Scenedesmus vacuolatus in continuous culture

“…The bibliography regarding to light flux intensity used for Scendesmus cultivations is quite extended and diverse, varying from 60 to 3900µE m -2 s -1[41,45]. Similar to our results, Scenedesmus species did not show photo-inhibition despite of the high light flux intensities.Overall, these results indicate that the optimal growth conditions and thus CO 2 assimilation for S. vacuolatus are as follows:Modelling growth is an interesting tool for the design and operation of an efficient process for CO 2 removal based on phototrophic microorganisms.…”

Light attenuation in photobioreactors and algal pigmentation under different growth conditions – Model identification and complexity assessment

“…Our results ( Fig. 2c and 2d [21] or the PLM approach is needed to accurately predict light attenuation in reactors with narrow diameter, e.g. flat-plate PBR.…”

“…Light attenuation in the PBR is affected by the absorption capacity of photosynthetic pigments, the shading effect by cells and light scattering caused by reactor wall and cells [10]. The Lambert-Beer expression accounts for the light absorption in the reactor by the biomass concentration [21] or by the combination of biomass and pigments concentration [22], but does not account for scattering.…”

“…Schuster's law can be used in cases where the light scattering is considered [21]. When the pigment concentration impact on light distribution is considered, it is necessary to include pigments concentration in the biological model as a state-variable.…”

“…Type 1 consists of biokinetic models that employ incident or average light intensity, i.e., algal cells are assumed to be exposed to the same light intensity through the entire reactor volume and have the same photosynthetic rate, thus neglecting the effect of photoacclimation and light attenuation (see, e.g., [25]). Type II models account for light distribution in the culture by applying, e.g., the Lambert-Beer expression (e.g., [21,26]) to predict the light intensity at a given reactor depth. Finally, type III models account for culture history in terms of light exposure as cells move around in the system (e.g., [27]).…”