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

Abstract

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.