WATER QUALITY MODELLING OF TANNERY EFFLUENTS (CR, SULFUR, CL) UPPER BOGOTA RIVER BASIN (COLOMBIA)

摘要

In this research the extension of a dynamic water quality model in order to simulate the impact caused by tannery effluents with high contents of sulphides, chlorides and chromium is presented. The model subroutines, designed and implemented in MATLAB/SIMULINK in this work, were coupled to a dynamic water quality model applied within the project framework "Dynamic water quality modeling of the Bogota river", UNAL-EAAB. The implemented Chromium (Cr) subroutine describes the behavior of the heavy metal transport and chemical reaction in the water column. Also the speciation of Cr~3 and Cr~6 and the fractions of dissolved and particulate Cr are determined in order to compute water-sediment interactions under anoxic and anaerobic conditions depending on the oxidation state of Cr. The sulphides model can represent the behavior of H_2S (Sulphides), Sulphates and Sulphites based on a speciation and chemical equilibrium model depending on the pH. As a study case application, the results along a 20 km stretch of the Bogota River - Colombia between the municipalities of Villapinzon and Choconta are presented and analyzed. Within this reach the river temporal water quality dynamics caused by spatial and temporal variations of non-treated tannery effluents is very high. The dynamic model is calibrated in the studied reach using field data and laboratory analyses of water samples taken during two measurement campaigns carried out under different hydrological conditions. Additionally, model verification is performed with an independent data series. With the proposed model satisfactory values of the Nash determination coefficient were obtained during calibration and verification phases in the range of R~2 0.74 to 0.97. Finally, the calibrated model is used as part of a decision support tool, simulating the impact on the river water quality of different treatment scenarios for the tannery effluents.