Effect of immobilized microalgal bead concentrations on wastewater nutrient removal

A unicellular green microalga, Chlorella vulgaris, entrapped in calcium alg inate as algal beads were employed to remove nutrients (N and P from simula ted settled domestic wastewater. A significantly higher nutrient reduction was found in bioreactors containing algal beads (at concentrations ranging from 4 to 20 beads ml(-1) wastewater) than the blank alginate beads (withou t algae). A complete removal of NH4+-N and around 95% reduction of PO43--P was achieved within 24 h of treatment in bioreactors having the optimal alg al bead concentration (12 beads ml(-1), equivalent to 1:3 algal beads:waste water, v/v). The NH4+-N removal was significantly lower at low (around 4 be ads ml(-1)) and high (>15 beads ml(-1)) algal bead concentrations. On the o ther hand, the effect of bead concentration on phosphate removal was less o bvious, and bead concentrations ranging from 8 to 20 beads ml(-1) showed co mparable percentages of phosphate reduction. Algal uptake and adsorption on alginate gels were found to be the major processes involved in the removal of N and phosphate in the present study. In addition, NH4+-N could be lost via ammonia volatilization while PO43--P was removed by chemical precipita tion, as alkaline pH was recorded in the immobilized microalgal treatment s ystem. (C) 1999 Elsevier Science Ltd. All rights reserved.