Colocasia esculenta stem as novel biosorbent for potentially toxic metals removal from aqueous system

Biosorption is an ingenious technique that uses biological materials to acquire trace metal ions from wastewater. In the present study, the ability of Colocasia esculenta stem biomass was explored for the biosorption of toxic trace metals. The maximum removal was observed for arsenate (As⁵⁺) with 58.63%, followed by chromium (Cr⁶⁺) with 56.56%, and cadmium (Cd²⁺) with 41.2%. However, for copper (Cu²⁺), nickel (Ni²⁺), and zinc (Zn²⁺), low adsorption was observed. Batch sorption tests revealed that adsorbent dosage of 0.5g, 0.5g, and 0.3g; time of 10 h, 4 h, and 10 h; room temperature range of 25-30°C; pH range of 7.0-4.5; and initial concentration of 30 μg/L, 20 mg/L, and 30 mg/L were the optimum conditions for the removal of As⁵⁺, Cr⁶⁺, and Cd²⁺, respectively. Scanning electron microscope and energy-dispersive X-ray spectroscopy (SEM-EDX) analysis of Colocasia esculenta stem biomass before and after adsorption revealed that the trace metals successfully get adsorbed on the surface of the biosorbent. The equilibrium data fitted well with the adsorption isotherm model of Langmuir (for As⁵⁺, Cr⁶⁺, and Cd²⁺), Dubinin-Radushkevich (for As⁵⁺ and Cr⁶⁺), and Flory-Huggins (for Cd²⁺), and the kinetic data of As⁵⁺, Cr⁶⁺, and Cd²⁺ biosorption were best described by pseudo-second-order kinetic model. Thermodynamic studies revealed that the adsorption process for all concerned trace metals acts in a spontaneous manner and is endothermic in nature. Thus, the use of Colocasia esculenta stem biomass proved to be an efficient and economical alternative for the treatment of effluents contaminated with these trace metals.