Abstract

Laboratory experiments were performed to study nitrogen and phosphorus uptake by the unicellular green microalga Chlorella vulgaris immobilized in calcium alginate beads. Different cell stockings in beads, different bead sizes and different algal bead concentrations in wastewaters were tested. Significant higher nutrients reductions were found in bioreactors containing algal beads than the blank alginate beads (without algae). The bioreactor containing algal beads (4 mm diameter) with 1.5 x 10⁶ cells bead^-1 (cell stocking) at concentration of 10.66 beads ml^-1 wastewater (1:3 bead: wastewater, v/v) achieved complete removal of NH₄⁺-N and about 95% reduction in phosphate removal within the experimental period (48 h). Algal uptake and adsorption on alginate gels were the major processes involved in the removal of N and phosphate from wastewater. Increasing cell stocking in beads did not cause any improvement in the efficiency of treatment, but caused some leakage problems. Also, increasing the beads concentrations in wastewater caused reductions in light penetration and enhanced self-shading effects and the beads settled at the bottom of the reactor.

Key words: Algae, cell stocking, bead concentration, ammonia, phosphate, removal, and wastewater.