Influence of culture density, pH, organic acids and divalent cations on the removal of nutrients and metals by immobilized Anabaena doliolum and Chlorella vulgaris.

The potential of alginate-immobilized Anabaena doliolum and Chlorella vulgaris was assessed for removal of nutrients (NO inf3 (sup-) and NH inf4 (sup+) ) and metals (Cr2O inf7 (sup2-) and Ni(2+)) at different biomass concentrations (0.05, 0.1, 0.25, 0.49 and 1.22 g dry wt l(-1)) and pH values (4 to 10). Though uptake of all these substances was higher in concentrated algal beads (0.25, 0.49 and 1.22 g dry wt l(-1)), their rate of uptake was significantly (P<0.001) lower than that of low (0.05 g dry wt l(-1)) cell density beads. For A. doliolum, there was no significant difference in uptake rates for beads having densities of 0.05 and 0.1 g dry wt l(-1). Chlorella vulgaris, however, showed maximum efficiency at 0.1 g dry wt l(-1). Uptake of both the nutrients and the metals was maximal at pH 7 followed by pH 8, 6, 9, 10, 5 and 4. Of the different substances (organic acids and divalent cations) used, humic acid was most efficient in decreasing metal uptake. Mg(2+) was, however, more efficient than Ca(2+) in decreasing Ni(2+) uptake. Immobilized algae with a cell density of 0.1 g dry wt l(-1) were the most efficient for nutrient and metal removal at pH 6 to 8.