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Untreated tannery discharges to rivers are still a common practice in developing countries causing severe pollution. In this paper the development and application of a dynamic water quality model to simulate the impact caused by tannery effluents with high contents of sulphides, chlorides and chromium is presented. The proposed model subroutines, designed and implemented in MATLAB/SIMULINK in this work, were coupled to an existing efficient aggregated dynamic river transport and water quality model of conventional determinands. A Chromium (Cr) transport and fate modeling subroutine was implemented to determine the speciation of Cr3 and Cr6 and the dissolved and particulate fractions in order to correctly represent sediment water interactions. A chemical equilibrium sulphide subroutine is proposed to represent the behavior of H2S, Sulfur and Sulfites based on a speciation model depending on pH. As a study case, the proposed model is applied to a 20 km reach of the Bogotá River - Colombia at Villapinzón – Chocontá. Within this reach water quality river dynamics and river pollution caused by spatial and temporal variations of untreated tannery effluents is very high. The dynamic model was calibrated using intensive field data and laboratory analyses of water samples taken under two different hydrological conditions. Additionally, model verification was performed with an independent data series under medium flows. With the proposed model, satisfactory values of the Nash determination coefficient R2 were obtained during calibration and verification phases in the range of 0.74 to 0.97 considering all conventional and toxic water quality determinands. Finally, the calibrated model is used as part of a decision support tool, simulating the impact of different tannery effluents treatment scenarios. The results demonstrate that in the studied reach biological secondary treatment is urgently necessary in order to achieve target water quality standards.


Session R25, Eco-Hydraulic Modeling: Water Quality Aspects



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