Investigating and modelling the effect of light intensity on Rhodopseudomonas palustris growth

Photosynthetic bacteria can be useful biotechnological tools – they produce a variety of valuable products, including high purity hydrogen, and can simultaneously treat recalcitrant wastewaters. However, while photobioreactors have been designed and modelled for photosynthetic algae and cyanobacteria, there has been less work on understanding the effect of light in photosynthetic bacterial fermentations. In order to design photobioreactors, and processes using these organisms, robust models of light penetration, utilisation and conversion are needed. This article uses experimental data from a tubular photobioreactor designed to focus in on light intensity effects, to model the effect of light intensity on the growth of Rhodopseudomonas palustris, a model photosynthetic bacterium. The work demonstrates that growth is controlled by light intensity, and that this organism does experience photoinhibition above 600 W/m2, which has implications for outdoor applications. Further, the work presents a model for light penetration in circular photobioreactors, which tends to be the most common geometry. The work extends the modelling tools for these organisms, and will allow for better photobioreactor design, and the integration of modelling tools in designing processes which use photosynthetic bacteria.

PHOTOBIOREACTOR FOR MICROALGAE-BASED WASTEWATER TREATMENT

Purpose and Objectives of the Work. This scientific article is devoted to creation of an advanced photobioreactor design for wastewater treatment from biogenic compounds. Research Methods are based on a systematic analysis of theoretical research, synthesis, anology and comparison. Research Results. As a result, the improved photobioreactor design was proposed, in which the application of new elements and connections reduces the required area for its placement, immobilization of microalgae in the working area and, as a result, reducing the working area, the ability to quickly replace the sleeves of the working area, covered with sediment inside, and, as a result, reduce labor costs and downtime of the photobioreactor. Discussion. The problem is solved by the fact that the photobioreactor is made in the form of a transparent flowing rectangular open-topped tank, inside of which are vertically attached to the bottom of the tank by quick-release fasteners transparent flowing flexible hoses, to which at the bottom by means of non-return valves are connected pipelines for wastewater and microalgae supply and tubes for carbon dioxide supply and are connected by means of shut-off valves pipelines for drainage of a mixture of microalgae with residual wastewater, and in the upper hermetic part, where there are valves for drainage of accumulated gases , while the pipeline for the purified wastewater discharge is connected to a guide tray purified wastewater supply inside of a flowing rectangular open-topped tank, and at the outlet of the pipeline for drainage of a mixture of microalgae with residual wastewater is a microalgae separator to separate return and excess biomass. Conclusion. The proposed construction of photobioreactor can have good perspectives to be use in communal services for sewage water purification from biogenic compounds.

Impact of salinity on the kinetics of CO2 fixation by Spirulina platensis cultivated in semi-continuous photobioreactors

In this research, the physiological response of the microalgae Spirulina platensis to salinity stress (1 and 100 g L-1 ) was investigated. Spirulina platensis and Spirulina platensis (adapted to high salt concentration) were operated at laboratory scale in a semi-continuous photobioreactors. The responses examined were within 0.5 to 10% CO2 concentration, temperatures from 10 to 40 oC, light intensities from 60 to 200 μmol m-2 s -1 and presented better results in terms of all kinetic parameters. The highest rate of CO2 biofixation for Spirulina platensis was 25.1 gCO2 m-3 h -1 , and the maximum specific growth (μmax) achieved was 0.44 d-1 - 0.67 d-1 at 2.5% CO2, 150 µmol m-2 s -1 at 25 oC. Corresponding determined values of Spirulina platensis adapted were 18.2 gCO2 m-3 h -1 , 0.31 d-1 - 0.58 d-1 at 2.5% CO2, 60 µmol s-1 m-2 and 28 oC. However, both microalgae exhibited experimental limiting growth factors, CO2 10%, 40 oC and 200 µmol m-2 s -1 , conditions under which photosynthetic CO2 biofixation may be inhibited and photoinhibition of photosynthesis may be enhanced by salinity. The efficiency of 2.5% CO2 removal by Spirulina platensis achieved 99%, whereas Spirulina platensis adapted to 96%, respectively. The kinetic parameters estimated for Spirulina platensis can be used to improve photobioreactor design for reducing of atmospheric carbon dioxide.

A review on photobioreactor design and modelling for microalgae production

A microorganism culture process is a complex system in which physical operating parameters and biological responses strongly interact. Mathematical formulation and modelling of the different phenomena involved in the process...

Continuous Microalgal Cultivation for Antioxidants Production

Microalgae, including cyanobacteria, represent a valuable source of natural compounds that have remarkable bioactive properties. Each microalga species produces a mixture of antioxidants with different amounts of each compound. Three aspects are important in the production of bioactive compounds: the microalga species, the medium composition including light supplied and the photobioreactor design, and operation characteristics. In this study, the antioxidant content and productivity performance of four microalgae were assessed in batch and continuous cultures. Biomass productivity by the four microalgae was substantially enhanced under continuous cultivation by 5.9 to 6.3 times in comparison with batch cultures. The energetic yield, under the experimental conditions studied, ranged from 0.03 to 0.041 g biomass kJ−1. Phenols, terpenoids, and alkaloids were produced by Spirulinaplatensis, Isochrysisgalbana, and Tetraselmissuecica, whereas tocopherols and carotenoids were produced by the four microalgae, except for phycocyanin and allophycocyanin, which were only produced by S. platensis and Porphyridiumcruentum. The findings demonstrate that the continuous cultivation of microalgae in photobioreactors is a convenient method of efficiently producing antioxidants.

Helical tubular photobioreactor design using computational fluid dynamics

In this paper we present the design problem of helical tubular PhotoBioReactors (PBR) based on energy consumption minimization, using the radius of curvature for the cultivation of microalgae. Computational Fluid Dynamics (CFD) is used to design a configuration of the helical pipeline with minimum energy consumption. We determined how flow direction changes affect energy consumption. Additionally, it was found that the radius of curvature affects the pressure drop in the PBR’s pipe, so a cost function has been developed to solve an optimization problem seeking to obtain the optimum radius of curvature and a helical tubular PBR design with low pumping rates.