Metal Removal from Wastewater Using Sludge from a Natural Stabilization Pond as Biosorbent

The present work was focused on evaluating the potential use of a sludge produced in a municipal natural facultative pond as biosorbent to remove metal ions (Pb 2+ , Cd 2+ , Ni 2+ , and Cr 6+ ) from aqueous solutions. The influences of different initial conditions of pH, metal concentration, mass biosorbent, and contact time were studied to find the optimum conditions for the biosorption process. The sludge has different functional groups such as hydroxyl, carboxyl, and amide groups that could play major roles in the adsorption of metallic ions according to the FTIR results. Kinetic experimental data fitted very well the pseudo-second-order equation ( R 2 = 0.995 − 1), which implied that chemisorption is the rate-controlling step of adsorption process. The equilibrium isotherms were evaluated in terms of maximum adsorption capacity and adsorption affinity by the application of Langmuir and Freundlich equations. Despite experimental data fitted well to both adsorption isotherm models, the Langmuir one was the best-fitted to characterize equilibrium adsorption ( R 2 = 0.992–0.999) evidencing monolayer adsorption. The maximum uptake capacities calculated from Langmuir isotherm were 19.88, 11.49, and 7.70 mg/g for Pb, Cd, and Ni at pH 6, respectively, and 3.55 mg/g for Cr at pH 2. The goal of this research was to achieve a double positive environmental impact by promoting the use of a solid residue of high availability and low extraction cost to clean a liquid residue, which can then be reused or discharged healthily into the environment. Graphical Abstract