ADSORÇÃO DE NITROGÊNIO AMONIACAL E NITRATO EM ZEÓLITA NATURAL E MODIFICADA

Abstract

The presence of high ammonia load in sources of water supply has been recurring due to the several anthropogenic sources of this compound. Among the main related impacts are eutrophication and the toxicity of the aquatic environment, as well as negative public health aspects associated with nitrate coming from ammonium oxidation. This study evaluated the removal of ammoniacal nitrogen (N-NH4+) and nitrate (N-NO3-) from adsorption in zeolites. The adsorption performance of N-NH4+ and N-NO3- was compared between three samples of zeolites, Natural zeolite, NaCl modified zeolite (Na-clinoptilolite) and Modified Surfactant Zeolite (MSZ). The Box-Behnken experimental design and Response Surface Methodology were used to analyze the influence of parametres: initial concentration, zeolite mass and pH. As well as to obtain optimum treatment conditions. From the experimental design, batch wise tests were performed to remove N-NH4+, N-NO3- and N-NH4+ and N-NO3- simultaneously, for each of the three zeolite samples. For the three zeolites analyzed, lower initial concentrations of nitrogen compounds and higher zeolite mass provided the highest removal efficiencies. Under the experimental conditions used, pH had no significant effect on adsorption. The zeolite Na-clinoptilolite and the MSZ presented higher performance in the removal of N-NH4+ and N-NO3-, respectively, compared to Natural zeolite. As for simultaneous adsorption, the presence of N-NH4+ and N-NO3- in the same solution did not change the performance in the removal of this compounds. The Box-Behnken experimental design can be used to develop mathematical models to predict the adsorption of N-NH4+ and N-NO3- by zeolites. With the optimal treatment conditions found, 24 hours experiments were performed to analyze the influence of contact time on adsorption. In the adsorption of N-NH4+ by the zeolite Na-clinoptilolite, 2 hours were necessary to achieve equilibrium, however, for the removal of N-NO3-, 6 hours were required using the MSZ. Fixed-bed filter experiments were performed to evalueted the influence of the initial concentration on the removal of N-NH4+ and N-NO3-. With the Natural zeolite, removal of N-NH4+ reached 97% for all concentrations tested. The maximum removal of N-NO3- with the ZSM was 50%, for the lowest concentration tested.