Monitoring and calibration of quality model of Passo Fundo river

Abstract

Passo Fundo is considered a reference in the interior of Rio Grande do Sul, because it is one of the largest cities present in the northern region of the state. The growing population demand has been responsible for the excessive generation of effluent and consequent increasing of pollutant load, a fact that ends up aggravating the water quality of the rivers that through the city, being the Rio Passo Fundo the main one. This study monitored the water

quality in a section of river Passo Fundo, located in the influence zone from urban area in Passo Fundo city, RS, and performed calibration of data monitored through QUAL2K quality model. The monitoring occurred in a period of 117 days, starting in January 2011, and it was performed sampling in five selected points with monthly intervals. The analyzed parameters were flow, pH, dissolved oxygen (DO) and biochemical oxygen demand (BOD5). The results for pH are according to CONAMA Resolution No. 357/2005 and 430/11 for Class 2, corresponding classification of the river studied. The other parameters DO and BOD5 showed disagreement with the legislation in some samples, for class 2. The average spatial variation showed significant load from effluent, mainly in the first point of analysis (11,07 mg/L), decreasing downstream, with concentration of 6,70 mg/L. The flow increasing is the predominant cause for the decreased of this pollutant load due to dilution. The model QUAL2K allowed to obtain kinetic and degradation coefficients of river Passo Fundo, as well as pollutant loads quantification, Therefore, it showed how a tool to water resources management, since it was able to observe that the depuration is low and, for the most part, due to increased flow.