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

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.

Effect of Superficial Gas Velocity on Continuous Hydrogen Production by Anabaena sp. in an Internal-loop Airlift Bioreactor

Global warming and rising air pollution which has been caused by using too much fossil fuel has led to look for a new clean source, sustainable and eco-friendly of energy like H2, which can be produced by cyanobacteria and microalgae. In this study, Anabaena sp. was used in a continuous operation to achieve biohydrogen production. To this end, an airlift photobioreactor (20 L) was considered. The effects of the gas holdup, liquid circulation velocity, and the amount of dissolved oxygen on hydrogen production were investigated. Gas holdup, liquid circulation velocity, and KLa (mass transfer coefficient) showed an upward trend by increasing the velocity of the inlet gas. Maximum biomass concentration of and maximal H2 production were observed 1.2 g L-1 d-1 and 371 mL h-1 PBR-1, respectively under light intensity of 3500 lux/m2 applying a light-dark cycle in 7 days, at Ad/Ar of 1.25 and 0.185 and 0.542 cm/s. pH, temperature (30+2 °C), light intensity, and inlet gas flow to the bioreactor (containing 98% air and 2% carbon dioxide) were remained steady. Using the airlift photobioreactor with a good mass transfer and light availability to cyanobacteria growth can be a cost-effective and environmentally technology for biological H2 production.