Removal of nitrate from synthetic aqueous solution and groundwater in a continuous pilot system using chemical activated carbon derived from walnut shell

Excessive nitrate in the water impose a danger to human health and contribute to eutrophication. The present continuous fixed bed pilot study was carried out using granular activated carbon made from walnut shell for removal of nitrate from aqueous solution and natural groundwater. The carbon was characterized using SEM, FTIR and BET. The BET specific surface area and average pore size before nitrate adsorption were 1434.6 m²g⁻¹ and 2.08 nm, respectively, and after were 633.28 m²g⁻¹ and 2.04 nm, respectively. Optimum removal of nitrate was achieved at a contact time of 2 min, pH of 6.5 and a nitrate concentration of 200 mg/l. The hydraulic loading rate was calculated to be 10 m³/h.m² and the maximum adsorption capacity using the Langmuir adsorption isotherm model (R² = 0.99) was 10 mg NO₃/g. These experiments were also carried out using groundwater and the removal of nitrate decreased from 68% to 60% because of competition with other cations and anions.