Removal of ammonium from groundwater using NaOH-treated activated carbon derived from corncob wastes: Batch and column experiments

High ammonium concentration in groundwater represents a major public health concern in Hanoi, Vietnam. In this study, mesoporous activated carbon was prepared from corncob using H₃PO₄ through a one-stage chemical activation process. Corncob activated carbon (CCAC) was subsequently treated with NaOH to enhance its cation exchange capacity. The results showed that this NaOH-modified corncob activated carbon (M-CCAC) exhibited a large specific surface area (1097 m²/g) and high total pore and mesopore volumes (0.804 cm³/g and 0.589 cm³/g, respectively). The batch experiments indicated that the NH₄⁺-N removal was strongly dependent on the coexisting cations and pH of the solution, while in the kinetic experiments adsorption equilibrium was quickly reached within 60 min. The activation energy was calculated to be 49.7 kJ/mol. The maximum Langmuir adsorption capacity of M-CCAC exhibited the following order: 17.03 mg/g at 20 °C > 15.4 mg/g at 35 °C > 11.99 mg/g at 50 °C. The NH₄⁺ adsorption process was spontaneous (–ΔG°) and exothermic (–ΔH°), and it increased the randomness (+ΔS°) in the system. The column experiments were conducted using real underground water to analyze the effects of different flow rates (1–3 mL/min), influent concentrations (10–40 mg/L), and bed heights (8.07–23.9 cm) on the adsorption capacity. The maximum adsorption capacity (8.69 mg/g) was achieved at a flow rate of 2 mL/min, an initial concentration of 40 mg/L, and a column height of 15.8 cm. Ion exchange was found to be the principal mechanism that controls ammonium adsorption, while pore-filling and electrostatic attraction played minor roles in the process. This study proved that M-CCAC is an effective adsorbent to remove ammonium from real groundwater.