Biosorption of Cr(VI) and Ni(II) onto Hydrilla verticillata dried biomass

In the present study Hydrilla verticillata dried biomass was modified by Fenton reagent and its technical feasibility for removal of Cr6+ and Ni2+ ions from wastewater were investigated. Fenton modification process was optimized by varying pH, biosorbent dose, contact time, and Fe2+/H2O2 ratio. For Fenton modification process the optimum values of pH, biosorbent dose, contact time, and Fe2+/H2O2 ratio were 4, 70 g L−1, 70 min and 0.04 w/w, respectively. The modified biosorbent was characterized by using SEM-EDX, FT-IR and Malvern particle size analyzer. SEM-EDX analysis revealed the enhancement in weight percent of Cr6+ (47.38%) and Ni2+ (41.26%) ions on the surface of Fenton modified dried biomass of Hydrilla verticillata (FMB) after biosorption. Maximum biosorption of Cr6+ and Ni2+ ions were observed to be 29.43 and 48.72 mg g−1 for raw biomass and 107.64 and 106.12 mg g−1 for Fenton modified biomass respectively. Experimental data were modeled using single and multi-component isotherm models. For single-metal component, the Freundlich isotherm model fits the data better than the Langmuir isotherm model. In case of binary-metal solution the experimental data show good agreement with multi-component Freundlich isotherm model. The enhancement in the overall biosorption capacity after the Fenton modification was observed which follows the sequence: Cr6+ > Ni2+. The biosorption process followed the pseudo-second order kinetics. The equilibrium data suggest the involvement of chemisorption mechanism. Positive values of enthalpy and negative values of Gibbs free energy obtained during thermodynamic study revealed that the biosorption process was endothermic and spontaneous in nature.