Effects of different nitrogen concentrations on growth and chemical composition of a freshwater microalga Scenedesmus obliqnus

An experiment was carried out to evaluate the effects of different nitrogen concentrations on growth and chemical composition of a freshwater microalga Scenedesmus obliqnus. In this study，the culture solutions were designated with seven nitrogen concentrations，which were 0.247 mg/L，2.47 mg/L，24.7 mg/L，123.5 mg/L，247 mg/L，370.5 mg/L and 740 mg/L，respectively. The results showed that different initial nitrogen concentrations had significant effects on the growth and the nitrogen and phosphorus contents of S. obliqnus（ P<0.05）. The growth rate of algae increased with the nitrogen concentrations of nutrients increasing，peaking at the 247mg/L of nitrogen concentration and decreasing thereafter. Therefore，the nitrogen concentration of 247 mg/L is the saturation concentration for the growth of S. obliqnus. When the nitrogen concentration was 0.247～24.7 mg/L，the N content of unit algae volume（ mg/L） increased with the increase of nitrogen concentration of nutrients，but as the nitrogen concentration continued to increase，the N content of algae had no significant difference. With the increase of nitrogen concentration of nutrients，the P content of unit algae volume（ mg/L） increased and then decreased，the P content of cell（ mg/cell） declined sharply. Therefore，the high nitrogen concentration in surrounding environment would inhibit the production of algal phosphorus composition.