Water quality modeling in the Paraibuna River in Juiz de Fora/MG: diagnosis and prognosis

To support the implementation of instruments of the National Water Resources Policy, as well as the new legal framework for basic sanitation, the environmental assessment of water courses becomes important to guide the planning, monitoring and management of a watershed. Thus, this research aims to contribute to the creation of information structures about the Paraibuna River and its water basin in the central and more urbanized region of Juiz de Fora/MG. The QUAL2K model was used considering two different hydrological periods. The study considered water quality data for the following variables: dissolved oxygen, biochemical oxygen demand, temperature, electrical conductivity and pH. The flow rates in the Paraibuna River and its tributaries were quantified using an Acoustic Doppler Current Profile (ADCP) and a hydrometric windmill. With the calibrated model, future water quality scenarios were simulated for the moment when the new sewage treatment plants are operating at maximum capacity, in accordance with the Juiz de Fora’s Municipal Plan for Basic Sanitation Service. The results show that the Paraibuna River, in the central section of Juiz de Fora, provided data with reduced water quality, mainly in the dry season, leading us to conclude that the flow had a direct influence on the water quality. As for the simulated scenarios, we reached the conclusion that the best result obtained for the sewage treatment of the Paraibuna River will be achieved when the treatment conditions of scenario 3 are applied. This scenario includes the Wastewater Treatment Plants of União Indústria, Santa Luzia, and the renovation of the Wastewater Treatment Plant of Barbosa Laje, with an expected reduction of 90% of the polluting load in the streams covered by the present work, and a reduction of 50% of the organic load upstream of the section under study.