Effects of Process Variables in Semi-continuous Cultivation of Chlorella Minutissima on the Biomass Composition

Abstract

The biomass composition of Chlorella minutissima 26a was evaluated in different conditions for the microalgae cultured in landfill leachate in airlift photobioreactor operated in semi-continuous mode. The effects of the following factors in cells composition were evaluated: landfill leachate concentration (LC), CO2 percentual flow added in the gas stream (GP), aeration flow in the reactor (AF) and feed flowrate (FR). A Taguchi L9 orthogonal arrangement was used to evaluate the effects of those four factors on the following response variables: Biomass Productivity (BP), Lipid Productivity (LP), Carbohydrate Productivity (CP) and Proteins Productivity (PP). Results showed that the microalgae had high selectivity to produce proteins, reaching a maximum content of 69,60% in the following conditions: LC: 10%, GP: null, AF: 0,30 vvm and FR: 0.9 µmax vvm. The highest contents of lipid and carbohydrate were 17.4% (LC: 15%, GP: null, AF: 0,45 vvm and FR: 0.7 µmax vvm) and 11.6% (LC: 10%, GP: 15%, AF: 0,15 vvm and FR: 0.7 µmax vvm.), respectively, both values achieved at the two experiment with the highest values of specific growth rate (0.44 d-1 and 0.47 d-1, respectively). Statistical analysis showed LC was the most influential factor in the cell chemical composition, being significant (p<0,1) in the productivity of lipids, proteins and carbohydrates, with high values observed using between 5 and 10% of LC in the medium. GP did not show significance for any response studied, while the variables AF and FR showed significance in the productivity of proteins.