Effect of phosphorus-limited nutrients on growth and glucose production from microalgae

The application of microalgae has been increasing lately especially in several industries like pharmaceutical, biotechnology and automotive. In biofuel industry, bioethanol produced from microalgae are recognized as a clean, renewable and non-toxic energy source that can provide energy security and ecological sustainability. However, commercialization of bioethanol from microalgae is still slow and among the reasons are due to the low carbohydrate content in the cells and low biomass productivity. In this research, the suitable macronutrient dosage of nitrogen (N) and phosphorus (P) in culturing microalgae to maximise biomass productivity and carbohydrate content as reflected by its glucose content was investigated. The chosen microalgae, Scenedesmus obliquus was cultivated at temperature of 20°C with light intensity of 1200 lux, light and dark (L/D) cycle of 16 hrs/8hrs. Nitrogen to phosphorus ratio in the range of 0.125:1 - 28:1 was applied in cultivation. Dry cell weight and glucose yield was measured to observe the effect of phosphorus limitation in nutrients dosage on the growth and carbohydrate production of Scenedesmus obliquus. The growth of Scenedesmus obliquus took approximately 14 days to reach stationary phase. The effect of nutrient dosage on biomass concentration is found to be more apparent compares to glucose yield. The maximum biomass concentration and glucose yield obtained were 5.07 mg/mL and 67.7 % respectively from molar N:P ratio of 12:1 after 15 days of cultivation. The optimum N:P ratio for biomass productivity and glucose yield is under phosphorus-limited condition of 12:1. A higher biomass concentration and glucose yield is indeed desirable as this will directly bring a positive impact on the bioethanol production in the subsequent fermentation step. Biomass concentration increases as molar N:P ratio increases up to molar N:P ratio of 12 and then biomass concentration started to decrease.