Optimization of alginate bead size immobilized with Chlorella vulgaris and Chlamydomonas reinhardtii for nutrient removal.

Photo-bioreactor experiments using three different size beads (2.0, 3.5, and 5.0 mm) immobilized with two different types of microalgae namely Chlorella vulgaris and Chlamydomonas reinhardtii were conducted to evaluate the nutrient removal efficiency. The highest nutrient removal was obtained at gel bead pore size of 3.5 mm for both species of C. vulgaris and Ch. reinhardtii. 95% removal of T-N and complete reduction of T-P were achieved within 3 stages of treatment in photo-bioreactors containing 20% algal bead volume fraction. Moreover, the results observed by confocal laser scanning microscopy (CLSM) using SYTOX red dye and SYTOX green dye in alginate beads indicated that the effective depth of C. vulgaris and Ch. reinhardtii was about 3.6 mm and 3.0 mm, respectively. This optimized cell immobilization technology would accelerate the nutrient uptake rate of microalgae for improving efficiency of wastewater treatment systems.