Determination of the Growth Curve of Chlorella sp. under Optimum Conditions in Automated Growth Chambers for Biofuel Production

Abstract

Microalgae have a great potential for producing biofuels because of their capacity to accumulate high content of lipids. Chlorella sp. is the mostly applied microalgae sp. for biofuel production at the industrial level. The current study aimed to determine the optimum conditions for mass culture Chlorella sp. and to generate a growth curve to determine growth patterns over time. The samples were collected from Chlorella pure cultures available in the laboratory. Chlorella colonies were identified morphologically. Liquid cultures were prepared in BG 11 medium, The effects of four different temperatures (20°C, 25°C, 30°C, and 35°C), two light intensities (6000 lux and 2000 lux.) under aerated and non-aerated conditions on the growth of Chlorella cultures in 250 mL flasks (n=3) were studied using a custom-designed automated growth chamber using Arduino technology. The culture growth was monitored by determining the cell density (cells/ml) and light absorbance (750 nm) at 0, 96, 192, 288, and 384 hours after inoculation. and After 16 days, cells were harvested (6000 rpm, 5 min, room temperature) and the dry biomass (g/ml) was measured after oven drying at 70 °C. Optimal conditions for the efficient mass culture of Chlorella sp. were found as 30 °C temperature, 6000 lux light intensity with aeration conditions. Under those optimum growth conditions, 6L photo-bioreactors were designed. Absorbance and cell density (cells/ml) of Chlorella sp. were monitored with time to develop the growth curve of Chlorella sp. The growth of isolated Chlorella sp. was characterized by an exponential phase from 8.86 to 45.41 hr after inoculation with a specific growth rate of 0.06 hr-1 and a doubling time of 11.46 hr. The Chlorella growth rate was 0.027 hr-1 without optimum conditions, and the doubling time (Tg) was 25.6 hr.