Nitrate Adsorption Using Spent Coffee Ground: Kinetics, Isotherm, and Thermodynamic Studies

Excess amount of nitrate in water bodies can have harmful effects on humans and aquatic life. In this current study, the effectiveness of spent coffee grounds as adsorbents in nitrate adsorption from an aqueous solution was investigated. Spent coffee ground (SCG) was activated using hydrochloric acid (HCl) and used in the batch adsorption experiment. The removal performance was evaluated at different contact times ranging between 1 and 6 h. Removal efficiency was increased with the longest contact time of 6 h. Meanwhile, when nitrate concentration was increased from 100 to 500 mg/L, the removal efficiency was also increased from 39 to 78%. A temperature range of 298–328 K was applied in this study and the optimum operating temperature for nitrate adsorption was found to be at 308 K. Based on the experimental data, the Freundlich model showed R2 at 0.9802, which was the highest for the adsorption of nitrate using SCGs. In addition, the pseudo-first order kinetics model fitted the nitrate adsorption trend the best (R2 = 0.9652). The thermodynamic parameters obtained from this study described nitrate adsorption using SCG as endothermic in nature that required an external energy source for the interaction. This study has proven that spent coffee grounds activated by HCl have the potential of being an adsorbent for nitrate removal.