mass transfer coefficient of ammonia in the air stripping process for municipal wastewater: an experimental study

This study evaluated the effects of different operating conditions and the air-to-water ratio (g/l) on the kinetics and the mass transfer coefficient of ammonia (k_l) in the air stripping method for removing ammonium ions (nh_4+) from wastewater with low concentrations in municipal wastewater treatment plants (wwtps). the impact of operating conditions including the temperature, initial ammonium ion concentration, ph, and air-to-water ratio (g/l) of <2000:1 (60:1, 70:1, and 80:1) on k_l in the air stripping method was investigated using artificial wastewater at laboratory scale. the nh_4+ concentrations in the wastewater samples were determined with the nesslerization method (the standard method for the examination of water and wastewater). according to the results, the minimum (0.0528 h^-1) and maximum (0.64825 h^-1) of k_l were obtained within 1 to 4 h in the operating status that included an initial ammonium ion concentration of 33.63-52.81 mg/l, a temperature of 34 -45.7 °c, a ph of 9.48-12.2, and an air-to-water ratio of 60:1-80:1. a comparison of the results of three regression models showed that the air-to-water ratio was the most effective factor on k_l. furthermore, in model 3 (multivariate linear regression model/comparing four parameters), the effects of the air-to-water ratio, ph, and temperature increased, leading to the acceleration and conversion of ammonium ions (nh_4+) to a gaseous form (nh_3). also, the initial nh_4+ concentration and ph in model 4 (multivariate linear regression model by subgroup) at a low (60:1) and high (80:1) g/l ratio were the most influential factors on k_l, respectively. the results of this study revealed that the air-to-water ratio (60:1, 70:1, and 80:1) could be used successfully for the elimination of ammonium ions from municipal wwtps, leading to lower energy costs for the required aeration in the air stripping method.