Effects of light and pH on cell density of Chlorella vulgaris

Abstract

Improving the cell density of microalgae cultivation is one of the keys to reduce the cost of microalgae biodiesel. Many studies showed that the adjustment of pH and light intensity could increase cell density. The effects of light intensities, pH and pH adjustments on the growth of Chlorella vulgaris were studied in light incubator. The light intensities were set at 3960, 7920 and 119201ux; values of pH were 7, 8, 9 and 10 respectively; and pH adjustment methods included without and with pH control. Results show that: (1) In terms of light intensity, without pH control, the cell density under 39601ux is highest. With pH control, the cell density under 79201ux is higher than other levels. (2) In terms of pH, under the same light intensity, the cell density with pH control at 10 is highest, which indicates the light intensity will not affect the optimal pH value. And the pH fluctuates between 10 and 10.5 with pH control at 10, which is the most suitable range of pH for Chlorella vulgaris cultivation. (3) For pH adjustment methods, under 79201ux, the cell density with pH control at 10.0 is 56.7% higher than that with initial pH at 10.0, while the cell density with initial pH at 7.0 is 34.7% than that with pH control at 7.0, which indicates the method with pH control at values of the optimum pH makes better growth of microalgae.