Problemática de la determinación de especies nitrogenadas(nitrógeno total y amoniacal) en aguas residuales

Nitrogen is a significant indicator in environmental studies, due to its importance in treatment processes, quality control of waters and control of wastewater discharge to the environment. The Kjeldahl method is the most widely used for determining total nitrogen. There are different nitrogen species in wastewater: organic and ammonia nitrogen, nitrites, nitrates, among others. The National Standard of Wastewater Discharge (NC: #2012) mandates the determination of total nitrogen (Ntotal) by the Kjeldahl method. Selective electrodes (SE) have allowed the determination of ammonia nitrogen (Namm) with limits of quantification (LOQ) below the Kjeldahl method. This paper, evaluates the problems of determination of Ntotal and Namm in wastewater, taking into account the maximal permissible averages limits (MPAL) of the NC 27:2012 and the LOQ of the analytical methods studied.For the experiments, reference materials and swine wastewater were used. Under laboratory conditions, the LOQ of Kjeldahl nitrogen was higher (10 mg/L) the one established in the standard method (5 mg/L), which matches with the MPAL for the Cuban standard of discharge. Therefore, the laboratory has had to implement multiple standard additions, just to achieve reliable results at concentrations below its LOQ. Furthermore, it was proven that Kjeldahl and SE methods showed no significant differences in determining Namm, for concentrations at or above 10 mg/L, but for those one below the lab LOQ in the Kjeldahl method.