Removal of ammonium through adsorptive coagulation- flocculation process in drinking water treatment

Abstract

The nitrogen compounds such as ammonia (NH3) and ammonium (NH4 + ) are the most common pollutants in surface water, groundwater and wastewater. The increasing amount of NH4 + in the source of water supply emitted from agricultural activities, sewage and industries has caused problems to the existing drinking water treatment system to remove it to meet the required drinking water standards. The adsorption removal of NH4 + using natural zeolites and thus the adsorptive coagulation/flocculation process (ACF) was studied aiming for application in drinking water treatment process. The natural zeolites (i.e. NZ01, NZ02, and NZ03) were characterized using scanning electron microscope (SEM), X-ray diffractometer (XRD), nitrogen adsorption-desorption (NAD) analyzer, Fourier transform infrared spectrophotometer (FTIR), X-ray fluorescence (XRF) spectrophotometer. The cation exchange capacity (CEC) of natural zeolites was also determined. The NH4 + removal experiments were conducted in batch adsorption and adsorptive coagulation/flocculation (ACF) methods carried out at various experimental conditions. It was found that all natural zeolites used were of Clinoptilolite and Heundlite types. Natural zeolite (NZ01) had the highest (64.42 cmol/kg) cation exchange capacity (CEC) compared to NZ02 and NZ03 which both had 62.18 cmol/kg and 59.97 cmol/kg respectively. The time taken for NH4 + adsorption performance to reach equilibrium was detected in 12 hours contact time with adsorption capacity of 2.5mg/g observed at NH4 + concentration of 20 mg/l and pH 7. The high NH4 + removal was observed at pH 8 with 2.76 mg/g adsorption capacity. The NH4 + adsorption capacity increased with increasing the initial NH4 + concentration from 1 mg/l to 200 mg/l. Adsorption data followed the Langmuir isotherm at 34.48mg/g maximum adsorption capacity and it shows that the surface of NZ01 is homogeneous. The adsorption process obeys pseudo-second order kinetic models. The thermodynamic properties (?G, ?S, and ?H) were also studied at different temperatures (30, 40, 50, 70°C). The negative value of ?H for NH4 + adsorption confirmed the process is exothermic in nature. The adsorptive coagulation-flocculation (ACF) results revealed that the NH4 + removal increased with adsorbent dosage, ranging from 0.2 to 2.0 mg/ml at 5 hours contact time. The percentage removal of NH4 + in ACF for the effect of initial NH4 + concentrations (i.e. 1 mg/l, 20 mg/l, 50 mg/l and 100 mg/l) showed the increasing value up to 20% efficiency compared to adsorption. The NH4 + adsorption isotherm data for ACF followed the Temkin isotherm model and the kinetic adsorption data was observed to obey a pseudo-second order. All these results demonstrate that the natural zeolites can be potentially used for the removal of NH4 + in drinking water treatment process.