Hydraulic assessment of waste stabilization ponds : Comparison of computational fluid dynamics simulations against tracer data
The overall performance of a wastewater treatment plant is in addition to the effectiveness of the biokinetic processes controlled by the flow dynamics. A wide used technique to characterize the water flow dynamics is the use of tracers. At full-scale tracer experiments in wastewater treatment plants provide insufficient information to completely grasp the flow dynamics. Additionally results are often biased by uncontrolled external factors. As alternative, computational fluid dynamic (CFD) models for performance analysis of existing and the design of new wastewater treatment plants have been increasingly used over the last decade. The paper presents the results of a tracer experiment against the output of a CFD model with application to a 7 ha large maturation pond. The tracer study was conducted with the fluorescence dye Rhodamine WT using the stimulus response technique. The three dimensional CFD model was built considering a variable density distribution of spatial grids based on the specific characteristics of the system. For the unsteady flow simulations the turbulence model k- was adopted. Residence time distribution (RTD) generated by both approaches were compared and showed fairly good agreement. The velocity and turbulence profiles of the CFD model were compared with experimental data confirming, although the high computational demand, the robustness of the used CFD model.
Determination of Pollution Loads in Spillways of the Combined Sewage Network of the City of Cuenca, Ecuador
Combined sewer overflow (CSO) is one of the main causes of contamination in receiving bodies during the rainy period. The objective of this research was to evaluate the behavior of three combined sewage discharges into the Tomebamba River in the city of Cuenca, Ecuador. For this, the registration of 18 CSO events was carried out. The following water quality parameters were analyzed from the field survey (March 2017 to May 2018): conductivity, turbidity, BOD5, COD, fecal and total coliforms, nitrates, nitrites, ammoniacal nitrogen, dissolved orthophosphate and total phosphorus. The results show that CSOs contribute to the deterioration of the water quality of the Tomebamba River during the rainy season. The analysis of the dynamics of the pollutants determined that the maximum conductivity values occur at the beginning of the discharge, and the maximum turbidity is located near the peak discharge flow. The relationship between rain and the characteristics of the CSO was also analyzed through a canonical correlation analysis and partial least squares regression, obtaining a prediction model of pollutants based on the precipitation parameters. These results can be used for the implementation of integrated ecological models that enable a complete analysis of the city’s sanitation systems, their impact on the receiving bodies and their restoration.
Evaluation of the wastewater stabilization pond at the METU treatment plant
As a case for the improvement of efficiency of the wastewater stabilization pond, Middle East Technical University (METU) treatment plant's operation was investigated. The measured hydraulic detention time was half of the theoretical value indicating short circuiting. Also, the BOD removal efficiency was very low. The substrate removal rate constant, k, was determined for first and second order reactions with different methods by using dye test and BOD analysis results. A new pond inlet configuration was proposed as a method of improving the hydraulic efficiency