Study On Light Tranfer And Growth Kinetics Of Microalgae Photoautotrophic Cultivation

Microalgae are one increasingly important resource from which food, pharmaceuticals, finechemicals and engery can be obtained. Effective culture of microalgae has been one bottleneck for exploitation of this resource. Light intensity was the main factor affected the efficiency of the photosynthesis and the autophotophic cultivation of the microalgae, so study on light energy transfer and supply in autotrophic cultivation is an important aspect for maximizing the growth efficiency of microalgae.Synechococcus sp.PCC 7942, Synechocystis sp.PCC6803 and Chlorella Vulgaris were chosen as model microalgae to investigate the light attenuation in culture. A exponential model A( X ) = K_a^mX + CX exp( -εX) was proposed to estimate the light attenuation coefficient A( X ). The result shows that the value of K_a^m,C andεwere different by the variety of microalgae and showed obviously distinction in different culture conditions at the same kind algae, but the sum of K_a^m and C(K_a⁰ ) was constant, it may be an eigenvalue of the type microalgae. Study also found that the light attenuation coefficient of cyanobacteria is larger than that of chlorophyta.A mathematical model to estimate the surface light intensity of cylindrical photobioreactor was also proposed in this paper. This model was used to describe the surface light intensity of photobioreactor fixed on different numeral circular radiators. With the radiators increasing, the photobioreactor surface achieved a relatively uniform light density. When the numbers of radiator was eight, the surface light intensity of photobioreactor could close to be equal, which uniformity had achieved about 95%. Moreover, the light distribution of Synechocystis culture in 1.5L bioreactor was described when the incident light intensity was 4500 lx. Result shows that the light intensity was decreased by the growth of microalgal cell and the light zone was under 20% of the whole photobioreactor volume after 6 days. During this course, almost all the light energy was maintained the cell growth that resulted in the specific growth rate was only about 0.0045 h^-1.The characteristics of microalgae growth in different light intensities ranged from 400 lx to 6500 lx were explored in this paper. It was indicated that the specific growth rate and linear growth rate were increased with the elevation of incident light intensity under light saturation and achieved maximum 0.0115 g/ (L·h) and 0. 0495 h^-1 respectively when the incident light intensity was 4500 lx. But when the incident light intensity was in excess of 5000lx, the cell growth would be inhibited and the Y_max by Pirt's kinetic model was decreased with the increasment of incident light intensity, which the maximum Y_max was 0.0517 g/KJ at the incident light intensity of 400 lx. In parallel, the maximum yield based on light energy was 19.59% at 400 lx and 4.99% at 5600 lx, respectively.