Design of an airlift loop bioreactor and pilot scales studies with fluidic oscillator induced microbubbles for growth of a microalgae Dunaliella salina

Abstract

This study was conducted to test the feasibility of growing microalgae on steel plant exhaust gas, generated from the combustion of offgases from steel processing, which has a high CO 2 content. Two field trials of batch algal biomass growth, mediated by microbubble transfer processes in an airlift loop bioreactor showed only steady growth of biomass with 100% survival rate. The gas analysis of CO 2 uptake in the 2200 L bioreactor showed a specific uptake rate of 0.1 g/L/h, an average 14% of the CO 2 available in the exhaust gas with a 23% composition of CO 2. This uptake led to a steady production of chlorophyll and total lipid constituency in the bioreactor, and an accelerating exponential growth rate of biomass, with a top doubling time of 1.8 days. The gas analysis also showed anti-correlation of CO 2 uptake and O 2 production, which along with the apparent stripping of the O 2 to the equilibrium level by the microbubbles, strongly suggests that the bioreactor is not mass transfer limited, nor O 2 inhibited. Removing O 2 inhibition results in high growth rates and high density of biomass.