Effects Of Light And PH Adjustment On Cell Density Of Microalgae Chlorella Vulgaris

Improving the cell density on large-scale microalgae cultivation is one of thekeys to reduce the cost of microalgae biodiesel. Many studies showed that during theprocess of microalgae cultivation, the adjustment of pH and light intensity couldincrease cell density. This paper mainly studied the effects of light intensities, pH andpH adjustment method on the growth of Chlorella vulgaris (FACHB-1227) in lightincubator. Besides, based on the conceptual structure of the tangent double tubesdesigned by our research group, the tubes were re-designed and processed formicroalgae cultivation and the period of light/dark cycle was preliminarily analyzed.Chlorella vulgaris were cultured20days in light incubator, with250mL BG-11medium in500mL conical flasks. The light intensities were set at3960,7920and11920lux; values of pH were7,8,9and10respectively; and pH adjustment methodsincluded: without pH control, which refers to only adjusting the initial value of pH atthe beginning of microalgae cultivation, and with pH control refers to adjusting dailythe value of pH to some certain values during the process of microalgae cultivation.Results show that:(1)Under our experimental conditions, in terms of light intensity,we found that the with initial pH adjustment, the cell density under the light intensityof3960lux is highest in various pH levels; and the highest cell density was14.622×106cells/mL, obtained without pH control at7.0. With pH control, the cell densityunder7920lux is more higher than other levels in various pH levels; and the celldensity with pH control at10.0is29.7%higher than that under11920lux.(2) In termsof pH, under three light intensities, the pH with initial pH adjustment increased withthe increase of time, and fluctuates between10.0and11lately, in which the highgrowth rate was obtained. With pH control, under the same level of light intensity, thecell density with pH at10is highest, which indicates the light intensity will not affectthe optimal pH value. And the pH fluctuates between10and10.5with pH control at10, which is the suitable range for Chlorella vulgaris cultivation.(3) In terms of pHadjustment methods, under the light intensity of7920lux, the cell density with pHcontrol at10.0is56.7%higher than that with initial pH at10.0, which indicates thepH control which keeps the pH in the optimal scope is best for cell multiplication; while the cell density with initial pH at7.0is34.7%than that with pH control at7.0,which indicates the pH with the initial adjustment quickly fluctuates to10.0and isbetter than the method with pH control at values far away from the optimum pH.Based on the conceptual structure of the tangent double tubes, the tubes wereprocessed for Chlorella vulgaris cultivation. The tubes were drived by are at anaeration rate of10L/min and Chlorella vulgaris were cultured in BG-11mediumunder the light intensity of3960lux. Results show that after10days cultivation, thecell density is2.7×106cells/mL. The dissolved oxygen in the tangent double tubesfluctuates between7.0and7.3mg/L, and the pH rises from7.5±0.1to9.0. And theperiod of light/dark cycle in the tangent double tubes is longer, which can beimproved by larger aeration rate.