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.