Removal of nitrate ion from aqueous solution using palmyrah nut shell activated carbon: factorial optimization and equilibrium studies

Nitrate, a prevalent contaminant in drinking water due to its high solubility, poses health risks when consumed excessively. This study employed citric acid-activated carbon (CAC) derived from palmyrah to remove nitrate from drinking water. The physicochemical properties of non-activated carbon (NAC) and CAC were analyzed using SEM and FT-IR to identify microstructure and functional groups. Batch adsorption experiments with a full factorial design evaluated nitrate adsorption onto CAC, considering dosage, contact time, and solution pH. The activation treatment significantly enhanced adsorption efficacy compared to NAC. Optimal conditions were obtained statistically at pH 2, 60 min, and 1.5 g/L of adsorbent. These conditions were applied in groundwater from agricultural areas in Jaffna, Sri Lanka and significantly confirmed the removal efficiency of nitrate which was found to be 92% at pH 2 and adsorbent dosage of 6 g/L. The Freundlich isotherm model was best fit compared to Langmuir, Temkin and Dubinin-Radushkevich isothermal models. Accordingly, the most fitted kinetic model was pseudo-second-order and thermodynamic study revealed that the adsorption process was spontaneous and exothermic for nitrate removal. Overall, citric acid-modified palmyrah nutshell-derived activated carbon is an effective adsorbent for nitrate removal.