Author(s)

K. Mohammed, Z. S. Ahammad, P. J. Sallis & C. R. Mota

Abstract

This paper evaluates the effect of variation in red light-emitting diodes (LEDs) irradiance on the growth rate and biomass productivity of a mixed culture of microalgae grown on synthetic municipal wastewater, with and without CO2 addition. Red LEDs were used to illuminate microalgal culture from the centre of 21-L stirred-tank photobioreactors made of transparent Plexiglas, each reactor having a working volume of 16 L. The reactors were operated in batch mode with pH control, and under continuous illumination for 30 days at ambient temperature. Mixing was achieved through the use of overhead mechanical stirrers operated at 100±1 and 60±1 revolution per minute, before and after the addition of CO2, respectively. Three average values of irradiance of 429.9, 582.7 and 730 .8 μmol.s-1.m-2 were used to illuminate the reactors, with a control reactor operated in the dark. CO2 addition resulted in about two-fold increase in biomass productivity in all the experimental reactors. The bioreactor with medium irradiance yielded the highest biomass productivity and maximum specific growth rate of 0.034 g.L-1.d-1 and 0.109 d-1, respectively. The findings in this study show that both microalgal growth rate and biomass productivity are not always directly proportional to irradiance, despite the influence of process and operational parameters. Furthermore, a medium amount of irradiance resulted in optimum growth and productivity of the mixed microalgal culture. Keywords: microalgae, biomass productivity, growth rate, optimum irradiance, red light emitting diode, synthetic municipal wastewater.

Keywords

microalgae, biomass productivity, growth rate, optimum irradiance, red light emitting diode, synthetic municipal wastewater