Avaliação da qualidade da água por meio de índices numéricos: um estudo de caso do córrego Brejo Alegre em Araguari (MG)

Abstract

This study aimed to evaluate the water quality of the Brejo Alegre Stream, in the city of Araguari, Minas Gerais, through the analysis of chemical, physical and microbiological parameters required in legislation, applying a water quality index (WQI). The water samples were collected in 02 distinct points, chosen for having the direct contribution of domestic sewage, effluents from hospitals, refrigerators, tanneries, Charqueadas, bovine and equine bone processing industry, refrigerators, and other business initiatives. The collection period occurred from May 2021 to April 2022 and the analyzes were carried out at the Sanitation Laboratory of the Faculty of Civil Engineering of the Federal University of Uberlândia, at the physical-chemical Laboratory in industrial and domestic liquid effluents of the National Service of Industrial Learning Fábio de Araújo Mota de Uberlândia and the Laboratory of environmental analysis of Bioética Ambiental. The parameters investigated were: pH, dissolved oxygen, total phosphorus, turbidity, biochemical oxygen demand (BOD), thermotolerant coliforms, total nitrogen, total solids, temperature, electrical conductivity, chemical oxygen demand (COD), total cadmium, total lead, total zinc, dissolved copper, chlorophyll-a, cyanobacteria density, oils and greases, surfactants, total sulfide, and total chloride. The results indicated that the Brejo Alegre stream has poor water quality due to sewage and industrial effluents discharge without treatment. The parameters total phosphorus, BOD, thermotolerant coliforms, nitrogen, and heavy metals lead and zinc, exceeded the limits established by CONAMA Resolution 357/2005, for freshwater class 02, at some moment during the sampling period. The water quality index remained between 22 and 49, characterizing the level of very poor to poor quality, according to the Minas Gerais State Water Resources Institute classification. The main parameters that contributed to these results were BOD, phosphorus, and thermotolerant coliforms. Therefore, the results serve as a basis to verify that the Brejo Alegre stream goes through a process of degradation of the quality of its waters and can also alert public agencies about the possible problems and risks to public health.