Experimental design and response surface modeling for optimization of humic substances removal by activated carbon: A kinetic and isotherm study

The presence of humic acid (HA) in water treatment processes is very harmful and the cause of undesirable color, taste, and smell. Drinking water containing high concentrations of humic substances can be the cause of many health problems. Therefore, the removal of these compounds from water resources is a very important topic. In this research, response surface methodology (RSM) has been used to optimize the effect of main operational variables responsible for higher HA removal by activated carbon (AC). A three-level Box–Behnken factorial design (BBD) was used to optimize initial concentration of HA, time, pH, and AC dose for humic substances removal. The characterization of AC was carried out using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) analysis. A coefficient of determination (R2) value of 0.98, model F-value of 82.32 and its low P-value (F < 0.0001), and low value of coefficient of variation (9.94%) indicated the fitness of the response surface quadratic model during the present study. At initial optimum concentration (5.25 mg HA/L), pH (5.85), contact time (36.01 minutes), and dose (1.38 g AC/L), the model predicted 1.90 mg HA/L. Equilibrium adsorption of HA onto AC had best fitness with the Freundlich isotherm and pseudo-second-order kinetic model.