Hydraulic Modeling of Mixing in Wastewater Dechlorination Basin

Flow and mixing in a wastewater dechlorination basin are investigated by tracing dye concentrations in a 1:12 scale sectional model and in a fullscale installation. The injection of an SO2 solution that neutralizes residual chlorine is simulated by dye. Time series measurements of dye concentrations are obtained in the model and in the full‐scale basin. Mean dye concentrations and standard deviations of concentration fluctuations measured throughout the model and the full‐scale basin compare favorably. Both show incomplete mixing of SO2 solution and residual chlorine. The model is then used to develop a substantially improved basin design by relocation of SO2 injection and addition of a columnar wall to redistribute the flow and create small‐scale turbulence. The modifications can be implemented without interruption of wastewater treatment. The performance of the improved design is again validated in the full‐scale operation. The study shows that existing problems of mixing and flow processes can be explored and corrected efficiently and effectively using a scale model. It is recommended that this method be used for the study of novel designs before construction.