Investigation of Effects of Nutrients and External Parameters on Kinetic Growth of Outdoor Microalgal Cultivation

Abstract

Microalgal productivity under changing conditions of light intensity and temperature is a crucial parameter for evaluating profitability and sustainability of an outdoor cultivation in cylindrical photobioreactors. The control of the principal outdoor variables, even for the more accurate systems, is subject to a wide number of factors that might influence the measures taken, thus falsifying their correlation with the microalgal growth. In this work two principal external variables (Temperature and Light) have been monitored and controlled, studying their variability for the reactors in a pilot plant having 10 column photobioreactors, by means of statistical analyses. Preliminary data obtained indicated how the position of the reactors in the pilot plant didn’t affect light exposition, that was instead influenced by sampling position along reactors, time and data of the measurement. Temperature was significantly variable between outside and inside of the reactors, but the used control system successfully avoided excessive internal temperature increments.
Collection of growth data (cell count and biomass dry weight) for two different species: Scenedesmus obliquus and Graesiella emersonii at different initial NaNO₃ concentrations showed an increment in both maximum cell concentration and time to reach stationary phase when initial NaNO₃ concentration was increased. These tests permitted to obtain the best concentration of NaNO₃ at each inoculum: 0.35 g/L. However, these data were collected in different periods of the year. Further statistical analyses will be conducted to find also the principal input factors influencing microalgal growth parameters in order to develop an empiric and working model.