Optimization of the outdoor raceway cultivation to improve microalgae biomass production in Parachlorella kessleri wild type and starch-deficiency mutants

Abstract

This research focuses on the optimization of microalgal biomass production in outdoor raceway cultivation. Microalgae pose many advantages over higher plants in biofuel production such as higher photosynthetic efficiency, higher biomass productivity, and higher growth rate. To achieve high outdoor algal productivity, algal culture should be provided with appropriate light intensity. Excessive light intensity causes photoinhibition, whereas low light levels become a growth-limiting factor. Cultivation depth is a key factor for outdoor raceway cultivation. Maximum biomass was achieved at 0.163 g/l at 10 cm depth. Light shading alleviated photoinhibition, resulting in a higher growth rate than the control culture with no light shading. An increase in shading levels at low cell density led to higher photosynthetic efficiency (Fv/Fm). To examine whether the outdoor cultivation conditions were more critical for microalgae species with low tolerance to high light stress, an experiment was conducted in the lab-scale raceway ponds using Parachlorella kessleri wild type and two starch-deficient mutants (ST05 and ST01). Final biomass obtained from the experiment showed the highest biomass productivity in the wild-type strain, followed by the ST05 and ST01 mutant strains, respectively.