Removal of nitrate from groundwater by eggshell biowaste

This study concerns nitrate ion removal, which is one of the most dangerous issues of water contamination in the Gaza Strip. Eggshell biowaste was used as a denitrification biosorbent for water and groundwater. The results showed that the highest removal of nitrate was at pH 6.0–7.5, eggshell particle size in the range 90–710 μm, drying temperature at 45 °C, incubation temperature of adsorbent/adsorbate mixture at 37 °C and contact time of 24 hours. At the optimum conditions, the maximum amount of nitrate removed was 8.25 mg/g eggshell, when 1,500 mg/L of NO3− was applied. It was found that the eggshell biosorbent could be recovered and reused for removing the nitrate with removal capacity of 0.79–0.92 mg/g eggshell (79–92%) in the case of washed samples while the removal capacity was 0.79–0.92 mg/g eggshell (89–93%) in the case of unwashed samples when 100 mg/L of NO3− was applied. Results using the eggshell column method showed a nitrate removal efficiency of 90% at a flow rate ≤2 mL/min of the eluents. The biosorbent was applied to remove nitrates in real groundwater samples from different locations in the Gaza Strip and the efficiency of nitrate removal was in the range (77.4–93%).