Numerical Simulation Of Light Transmission And Kinetics In Photobioreactors For Microalgae Cultivation

In the contemporary age of global warming induced by the greenhouse gas which is almost composed of CO₂, researches on CO₂ capture and storage and a clean, renewable energy are becoming the frontiers. Among all the new and sustainable fuel technologies, the biofuel turns into more promising and potential since it is one of the environmental-friendly energy, which sequestrates CO₂ generating the beneficial biomass. Currently, the green algae and cyanobacteria, are regarded as one of the most promising platform for biofuel production, as they have an ability to efficiently capture CO₂, while producing biomass, which can later be converted into various types of bioproducts such as biodiesel, human and animal nutritional supplements, cosmetics and medications.Enclosed devices called photobioreactors?PBRs? are widely utilised to cultivate high biomass of microalgae, meanwhile avoiding the contamination from external environments. In this study, the simulation work is aim to solve the issue of light transmission, combining with the specific growth rate and uptake rate, to gain the microalgae growth and uptake kinetics in the flat plate PBR, the tubular PBR, the cylindrical PBR and the central vessel-helical tubular PBR. The main studies and conclusions are as follows:?1? For the cell concentration and light path effects on the Chlorella pyrenodiosa growth and uptake kinetics in the PBR, the Chlorella pyrenodiosa kinetics under 30 ?mol m^-2 s^-1 are in the photo limitation region, and when the Chlorella pyrenodiosa is under 70 ?mol m^-2 s^-1, its kinetics start entering into the photo-inhibition region. Besides, within the incident light intensities increasing to 200 ?mol m^-2 s^-1, its kinetics near the incident light intensity direction decreases but still larger than that far from the incident light intensity direction, however, the specific growth rate opposite to the incident light direction is still in the photo-limitation region.?2? For the Chlorella pyrenodiosa kinetics in the flat plate PBR, it is in the photo limitation region under the incident light intensities of 27.6 ?mol m^-2 s^-1, and when the Chlorella pyrenodiosa is under 55.2 ?mol m^-2 s^-1, its kinetics close to the incident light intensity begins to be lower, which represents that its kinetics starts entering into the photo-inhibition region. Continually, under the increasing incident light intensity of 90 ?mol m^-2 s^-1, its kinetics near the incident light intensity direction decreases but still larger than that far from the incident light intensity direction, however, the specific growth rate opposite to the incident light direction is still in the photo-limitation region. For the Chlorella pyrenodiosa kinetics in the tubular PBR, it is in the photo limitation region under the incident light intensities of 27.6 ?mol m^-2 s^-1, and when the Chlorella pyrenodiosa is under 58 ?mol m^-2 s^-1, its kinetics close to the incident light intensity begins to be lower, which represents that its kinetics starts entering into the photo-inhibition region. Continually, under the increasing incident light intensity of 90 ?mol m^-2 s^-1, its kinetics near the incident light intensity direction decreases but still larger than that far from the incident light intensity direction, however, the specific growth rate opposite to the incident light direction is still in the photo-limitation region. For the Chlorella pyrenodiosa kinetics in the cylindrical PBR, it is in the photo limitation region under the incident light intensities of 27.6 ?mol m^-2 s^-1, and when the Chlorella pyrenodiosa is under 50 ?mol m^-2 s^-1, its kinetics close to the incident light intensity begins to be lower, which represents that its kinetics starts entering into the photo-inhibition region. Continually, under the increasing incident light intensity of 70 ?mol m^-2 s^-1, its kinetics near the incident light intensity direction decreases but still larger than that far from the incident light intensity direction, however, the specific growth rate opposite to the incident light direction is still in the photo-limitation region.?3? To investigate the light/dark cycle frequency of microalgae which is significant for efficiency of microalgal-CO₂ fixation, three-dimensional numerical simulations are conducted on hydrodynamics and light distribution of microalgae fluid in a curved tubular photobioreactor under steady laminar flow. The frequencies of the streamlines locating close to the wall are larger than that of the streamlines locating at the center of the curved tubular photobioreactor. The frequency of light/dark cycle of a specific streamline increases and the optimal incident light irradiance decreases with increasing fluid speed.?4? For the cyanobacterium Cyanothece sp. ATCC 51142 kinetics in the helcail tubular PBR, its in the photo limitation region under the incident light intensities of 1000 ?mol m^-2 s^-1, and when the cyanobacterium Cyanothece sp. ATCC 51142 is under 2100 ?mol m^-2 s^-1, its kinetics close to the incident light intensity begins to be lower, which represents that its kinetics starts entering into the photo-inhibition region. Besides, within the incident light intensities increasing to 2380, 2500 and 3000 ?mol m^-2 s^-1, the photo-inhibition effect on the cyanobacterium Cyanothece sp. ATCC 51142 kinetics keeps increasing. For the cyanobacterium Cyanothece sp. ATCC 51142 kinetics in the central vessel PBR, its in the photo limitation region under the incident light intensities of 1000 ?mol m^-2 s^-1, and when the cyanobacterium Cyanothece sp. ATCC 51142 is under 2000 ?mol m^-2 s^-1, its kinetics close to the incident light intensity begins to be lower, which represents that its kinetics starts entering into the photo-inhibition region. Besides, within the incident light intensities increasing to 2100, 2300 and 3000 ?mol m^-2 s^-1, the photo-inhibition effect on the cyanobacterium Cyanothece sp. ATCC 51142 kinetics keeps increasing.?5? For the varation of cyanobacterium Cyanothece sp. ATCC 51142 specific growth rate with time and light path in the PBR, the cyanobacterium Cyanothece sp. ATCC 51142 specific growth rate decreases and specific uptake rate increases with time and light path increasing. Besides, with the incident light intensity increasing, its specific growth rate decreases rapidly, and its specific uptake rate increases rapidly. In addition, its maximum specific growth rate and maximum specific uptake rate increase gradually.