A mathematical model of the microalgal growth under various light regimes is required for the optimization of design parameters and operating conditions in a photobioreactor. As its modelling framework, bilinear system with single input is chosen in this paper. The earlier theoretical results on bilinear systems are adapted and applied to the special class of the so-called intermittent controls which are characterized by rapid switching of light and dark cycles. Based on such approach, the following important result is obtained in the present paper: as the light/dark cycle frequency is going to infinity, the value of resulting production rate in the microalgal culture goes to a certain limit value, which depends on average irradiance in the culture only. As a case study, the so-called three-state model of photosynthetic factory, being a simple four-parameter model, is analyzed. The present paper shows various numerical simulations for the model parameters previously published and analyzed experimentally in the biotechnological literature. These simulation results are in a very good qualitative compliance with the well-known flashing light experiments, thereby confirming viability of the approach presented here.
An indoor sun simulator was used to provide elevated UV-B radiation (280-315 nm) in combination with realistic ratios to PAR (400-700 nm) and UV-A radiation (315-400 nm) in order to test the physiological response of a soil- and snow microalga during a three-day stress scenario, which may occasionally occur in their respective arctic and alpine habitats.
Chlamydomonas nivalis and Tetracystis sp. are initial colonizers of harsh habitats like summer snow fields and bare arctic soils. The two species were chosen because of their role as primary successors in places where life is generally limited by extreme climatic and nutritional conditions.
The influence of the increased UV-B irradiation (1.43 W m-2; control: 0.52 W m-2) on photosynthesis and pigment composition was measured. Both species survived this incubation without any morphological signs of damage, but oxygen production was reduced by 20-56%. Under control conditions, the amount of chlorophylls (Chls) and carotenoids (Cars) per dry mass increased after three days due to optimal light conditions. After the same period, the treated samples of the soil alga Tetracystis sp. showed a smaller increase in Chls and primary Cars than the control. However, the production of extraplastidal, secondary Cars was induced. On the contrary, the snow alga C. nivalis already had high amounts of secondary Cars before the experiment, and after exposure, all pigment classes increased more compared to control conditions. The results show that these microalgae can tolerate short episodes of enhanced UV-B radiation. Photosynthesis may be temporally impaired, but the cells respond by the production of secondary Cars, which can shield their chloroplasts against excessive irradiation or quench reactive oxygen species. and D. Remias, A. Albert, C. Lütz.