Development of a non-linear growth model for predicting temporal evolution of Scenedesmus obliquus with varying irradiance.

In the present study, the effect of irradiance on growth performance of Scenedesmus obliquus was investigated, and various non-linear growth models were evaluated to predict its temporal evolution. This microalga was cultured in a LED-illuminated flat-panel gas-lift photobioreactor operated in batch mode at varying irradiance ranging from 50 to 200 µmol/m/s keeping all the other physico-chemical parameters constant. When growth data in terms of optical density were fitted in sigmoidal growth models, three non-linear models, namely, Richards model, Gompertz model, and logistic model, were found to be the best fit. Comparing these models based on statistical information, the logistic model could more appropriately and precisely describe algal growth under varying light intensity. Finally, the parameters of the logistic model were determined using regression analysis and were incorporated in the logistic equation to investigate the kinetic characteristics of S. obliquus. The optimum light intensity (I) for growth was found to be 150 µmol/m/s, at which a maximum specific growth rate (µ) of 0.35/day was obtained. The model developed was validated experimentally and could successfully explain the photo-inhibition phenomenon occurring at light intensity above 150 µmol/m/s.