Abstract:
This research studied the use of water treatment sludge to produce pellet adsorbents to adsorb fluoride and nitrate in water. The experiment was carried out by batch adsorption to investigate the effects of the improvement of the adsorbents by heat, acid and alkali, respectively. Then, the physical and chemical characteristics of the adsorbents were analyzed. In addition, absorption kinetics and adsorption isothermal of fluoride and nitrate in water were tested at different conditions. Moreover, the influence of other ions on adsorption and leaching test of the water treatment sludge were investigated. The results showed that the adsorbents prepared from the sludge except alkaline treated adsorbents were capable of adsorbing fluoride and nitrate. The thermal and acid activation adsorbents were found to have the higher porosity and specific surface area. All adsorption experiments were compatible with second order kinetics and reached the equilibrium within 4 hours. Fluoride adsorption with thermal-activated water sludge adsorbents was fitted with Langmuir and Freundlich isotherms. However, nitrate adsorption of acid-activated adsorbents corresponds to the Langmuir isotherm. At thermal activation 500 degree Celsius and 0.1 molar of acid, the adsorbent was found to have the best efficiency for fluoride and nitrate adsorption and the adsorption capacity was 9.17 mg/g and 5.77 mg/g, respectively. Furthermore, the presence of carbonate, bicarbonate and sulfate ions resulted in lower fluoride adsorption. Carbonate bicarbonate, chloride and sulfate ions contributed to lower nitrate adsorption onto the adsorbents. However, the positive charge ions i.e., sodium and calcium did not affect the absorption of fluoride and nitrate. In terms of leaching test, the results showed that the leachable water was under the standard of drinking water in accordance with the standards of the Department of Health.