Optimization of flow rate, initial metal ion concentration and biomass density for maximum removal of Cu2+ by immobilized Microcystis

Abstract

The potential of alginate-immobilized Microcystis packed in a column for maximum removal of Cu2+ at different flow rates, biomass, and initial metal ion concentration was assessed in a continuous flow system. Although Cu2+ removal did occur at all the flow rates tested, it was maximum (54%) at 0.75-ml min-1 flow rate, 30 μg ml-1 initial metal ion concentration and 0.016 g biomass. Cu2+ removal was influenced by inlet metal ion concentration and biomass density. An increase in the biomass concentration from 0.016 to 0.128 g resulted in an apparent increase in percentage removal but the Cu2+ adsorbed per unit dry wt. declined. When the flow rate (0.75 ml min-1) and biomass density (0.064 g) were kept constant and the inlet metal ion concentration was varied from 10 to 150 μg ml-1, a 68% removal of Cu2+ was obtained at 50 μg ml-1 initial concentration in a time duration of 15 min. The metal-laden columns were efficiently desorbed and regenerated following elution with double distilled water (DDW) (pH 2) (89%). This was followed by 1 mM EDTA > 1 mM NTA > 0.1 mM EDTA > 1 mM HCl > 1 mM HNO3 > 5 mM CaCl2 > DDW (pH 7.0) > 1 mM NaHCO3 > 1 mM CaCl2. Of the total (2.83 mg) adsorbed Cu2+, 1.89 mg (67%) was desorbed by DDW (pH 2) within the first 20 min of elution time. Thereafter the desorption rate slowed down and only 22% (0.632 mg) desorption was obtained in the last 20 min. In contrast to water pH 2, the desorption of Cu2+ by 1 mM EDTA was very slow, the maximum being 8% after 40 min of elution.