Estudo da qualidade da água dos rios umbelúzi e incomáti para fins de consumo doméstico e irrigação

Abstract

In this work, water quality was determined for the purposes of domestic consumption and irrigation. The parameters studied in determining water quality were as follows: pH, TDS, EC, turbidity, NO 3-, NO 2- and NH 4+ (measured at the sampling site); CO 32-, HCO 3-, Cl - and COD (determined by volumetry); SO 42- (by gravimetry); Na and K by flame photometry (FC); Ca, Mg, Cu, Fe and Zn by atomic absorption spectrophotometry with flame atomization (FAAS). The samples were taken at three points on the Umbelúzi rivers (in the district of Boane), and Incomáti (two points in the district of Manhiça and one point in the district of Marracuene). The accuracy control for the determination of metals by the FC and FAAS methods was carried out using the reference material LGC6019 from the River Thames (England), having calculated the relative error (Er) and the percentage of recovery (% R). In the FC method, The accuracy in determining Na and K was very good with Er 2.47% and 2.51% and% R 97.6% and 97.5% respectively. Regarding the FAAS method, the accuracy in determining Ca, Cu, Fe and Zn varied from very good to good, with Er as 0.28%, 2.59%, 6.27% and 2.85% and% R of 100%, 97.4%, 93.7% and 97.2% respectively, with the exception of Mg with Er of 11.9% and% R of 88.1%. The experimental value was compared with the known value and there was only a significant difference for Fe. For the interpretation of the results on water quality for domestic consumption and irrigation purposes, the concentration limits established by the NM and FAO standards were used as a reference; it was also compared with the limits of the NAS, NP, NE, WHO and CONAMA standards. According to these standards, it can be said that the samples of water from the analyzed rivers are of good quality for the purposes of domestic consumption although with Fe and turbidity values ​​of the water of the Incomáti river above the concentration limits established by the standards above referred to. The water of the Umbelúzi and Incomáti rivers is also of good quality for irrigation in contrast, according to the levels of CO 32- and K, it is not considered good quality water for irrigation. For the turbidity, COD and NO 2- parameters, water quality was not interpreted for irrigation purposes as no data were found in the standards consulted.