Evaluating the effects of agitation by shaking, stirring and air sparging on growth and accumulation of biochemical compounds in microalgae cells

Abstract

The economic feasibility of microalgae biomass production for biofuels is evaluated based on biomass concentration and productivity, and accumulation of pigments, lipid, carbohydrate, and protein. These parametric indicators are commonly promoted in microalgae cultures by manipulating the growth conditions, such as altering the growth nutrients, temperature, salinity, and mixing intensity. In view of this, the current study evaluated the potential of Dunaliella salina, Nannochloropsis oculata, Oocystis minuta, and Neochloris conjuncta to accumulate biomass, pigments, lipid, carbohydrate, and protein under different mechanical agitation conditions of the culture systems. The results show that the maximum biomass concentration (2423 mg/L) and productivity (544 mg/L/d) were observed in D. salina at a stirring speed of 1400 rpm and an aeration rate of 0.15 vvm. Also, the maximum total lipid content (23%) was recorded for N. oculata at a shaking speed of 200 rpm. The highest protein (49%) and carbohydrate (45%) contents were recorded for D salina and O. minuta at shaking speeds of 125 and 200 rpm, respectively. The higher proportions of protein and carbohydrate over lipid in all of the cultured microalgae species under the evaluated mechanical agitation conditions indicate that the microalgae species are better candidates for bioethanol production, and use as a protein source for animal feed, compared with biodiesel production.