Optimization of entrapment efficiency and evaluation of nutrient removal (N and P) of Synechococcus elongatus in novel core-shell capsules

Removal of nitrogen and phosphorous by immobilized microalgae is an advantageous approach for wastewater treatment. Although immobilized microalgae cells remain viable to remove nutrients for several weeks, early leakage of cells because of deterioration of the capsules prevents further use of the immobilized microalgae. This study aimed at increasing the entrapment efficiency of Synechococcus elongatus by core-shell capsules of alginate (as the core) and 2-hydroxyethyl methacrylate (HEMA)-poly(ethylene glycol) methyl ether methacrylate (PEGMA) (as the shell). Cyanobacteria cells were immobilized into: 2 % alginate-1 % CaCl2, 2 % alginate-2 % CaCl2 and 4 % alginate-2 % CaCl2, and submerged into HEMA-PEGMA solution for: 1, 5, or 10 min. A liquid and transparent (93 % transparency) HEMA-PEGMA solution was obtained and used to form a shell over the alginate matrix. Capsules with a shell formed after 10 min of contact with HEMA-PEGMA increased four times (22 days) the cell entrapment efficiency relative to uncoated capsules, independently of alginate or CaCl2, while keeping cells metabolically active and able to remove nutrients.