Master of Science in Civil Engineering (MSCE)
Civil and Environmental Engineering
Stormwater runoff is one of the most common sources of non-point source water pollution to lakes, rivers and estuaries. Nitrate-nitrogen in stormwater runoff is an important limiting factor to the eutrophication phenomenon. While most pollutants and nutrients, including nitrate-nitrogen, in stormwater are discharged into receiving waters during the first-flush period, no existing Best Management Practices (BMPs) are specifically designed to capture and treat the first-flush portion of urban stormwater runoff. In addition, nitrate-nitrogen removal rates of most existing BMPs are relatively low. This thesis presents results from both laboratory experiments and numerical modeling of nitrate-nitrogen removal in a designed first-flush reactor. A new numerical tool, called VART-DN model, for simulation of denitrification process in the designed first-flush reactor was developed using the Variable Residence Time (VART) model. The new model is capable of simulating various processes and mechanisms responsible for denitrification in the first-flush reactor, including (1) dispersion and transport, (2) mass exchange, (3) oxygen variation, (4) bacterial growth, and (5) nitrate-nitrogen consumption. The VART-DN model is intended to investigate the influence of oxygen, biomass, dissolved carbon, and temperature on denitrification process. The data used in the development of the VART-DN model were from laboratory experiments conducted using both highway stormwater and secondary wastewater. Based on sensitivity analysis results of model parameters, the dispersion coefficient, maximum nitrate utilization rate in mobile phase, biomass concentration, oxygen inhibition constant, biomass inhibition constant, temperature and temperature coefficient for denitrification have significant influence on the denitrification process, with percent change in root mean square error (RMSE) being 16.9%, 15.8%, -13.1%, -11.5%, 14.5%, -9.2% and -29.7%, respectively, when values of the parameters increase by 10%. The average removal rate of nitrate-nitrogen in natural stormwater was 92.05%. The average influent and effluent concentrations in the column experiment with wastewater were 1.189 mg/L and 0.260 mg/L, respectively, with a removal rate of 78.1% for nitrate-nitrogen. The VART-DN model results for the denitrification process of natural stormwater showed good agreements with observed data; the simulation error was lower than 9.0%. The RMSE for simulating denitrification process of wastewater was 0.8157, demonstrating the efficacy of the VART-DN model.
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Sun, Shaowei, "Modeling of first-flush reactor for stormwater treatment" (2011). LSU Master's Theses. 3241.