Effects On Lipid Accumulation Of Chlorella Vulgaris With Two-stage PH Control Method

Microalgae are a potential source of renewable energy, and they can convertcarbon dioxide into energy such as biofuel oil and gas. The lipid accumulation duringmicroalgae cultivation is very important for industrial production of biofuel. Manystudies showed that during the process of microalgae cultivation, the adjustment ofpH value could increase biomass accumulation, and a two-stage process, composed ofgrowth under nutrient-rich conditions followed by cultivation under nitrogenstarvation could increase lipid accumulation. This paper mainly studied the effect ofpH levels and pH adjustment methods on biomass and lipid accumulation ofChlorella vulgaris. In addition, our research team designed a novel concentric doubletubes using aeration through radial pores along the length direction of inner tube.Based on the preliminary experimental study on the concentric-tube photobioreactor,this paper also studied the optimization of intermittent aeration time and a preliminarystudy of carbon dioxide fixation by Chlorella vulgaris.Chlorella vulgaris were continuously cultured34days in light incubator, with250mL BG-11medium in500mL conical flasks. Result shows that in cases studiedin this paper, the biomass productivity of Chlorella vulgaris for pH10.0with pHcontrol was1.59g/L, which was highest, and that for17days was76.2%for34days.While the lipid content of Chlorella vulgaris for pH8.0with pH control was15.28%,which was highest. A two-stage process, composed of growth with pH control at10.0for17days followed by cultivation with pH control at8.0for17days, the totalbiomass productivity was1.50g/L, and the total lipid productivity was211.41mg/L.Compared with pH control at10.0, the total biomass productivity of microalgae withtwo-stage pH control decreased5.7%, but the total lipid productivity increased87.9%.Therefore, the two-stage pH control method can be helpful for increasing the lipidaccumulation of Chlorella vulgaris.Chlorella vulgaris were continuously cultured15days in the novel concentricdouble tubes with BG-11medium. Air was passed into the concentric-tubephotobioreactor at aeration flow rate10L/min for0.5h every time. This paper studiedthe effect of aeration interval time on cell concentration of Chlorella vulgaris. Resultsshowed that the cell concentration was7.75×106cells/mL at aeration interval0.5h. Compared to the cell concentration at aeration interval2h,1.5h,1h, the cellconcentration at aeration interval0.5h increased121.4%,35.96%,1.71%, respectively.Therefore, with the decrease of aeration interval time, the concentration of Chlorellavulgaris increased.Chlorella vulgaris were continuously cultured8days in the novel concentricdouble tubes with SE medium. Air contained10%CO2was passed into theconcentric-tube photobioreactor at aeration flow rate10L/min for0.5h every time.The aeration interval time was1h. Based on the dry weight of Chlorella vulgarisincreased during culture time and the carbon content of microalgae, we estimated thatthe CO2fixation rate was15.53mg/L/d.