Biosorption of copper, cobalt and nickel by marine green alga Ulva reticulata in a packed column

Abstract

Biosorption of copper, cobalt and nickel by marine green alga Ulva reticulata were investigated in a packed bed up-flow column. The experiments were conducted to study the effect of important design parameters such as bed height and flow rate. At a bed height of 25 cm, the metal-uptake capacity of U. reticulata for copper, cobalt and nickel was found to be 56.3 ± 0.24, 46.1 ± 0.07 and 46.5 ± 0.08 mg g −1, respectively. The Bed Depth Service Time (BDST) model was used to analyze the experimental data. The computed sorption capacity per unit bed volume ( N 0) was 2580, 2245 and 1911 mg l −1 for copper, cobalt and nickel, respectively. The rate constant ( K a ) was recorded as 0.063, 0.081 and 0.275 l mg −1 h −1 for copper, cobalt and nickel, respectively. In flow rate experiments, the results confirmed that the metal uptake capacity and the metal removal efficiency of U. reticulata decreased with increasing flow rate. The Thomas model was used to fit the column biosorption data at different flow rates and model constants were evaluated. The column regeneration studies were carried out for three sorption–desorption cycles. The elutant used for the regeneration of the biosorbent was 0.1 M CaCl 2 at pH 3 adjusted using HCl. For all the metal ions, a decreased breakthrough time and an increased exhaustion time were observed as the regeneration cycles progressed, which also resulted in a broadened mass transfer zone. The pH variations during both sorption and desorption process have been reported.