Degradation coefficients for pollutants in water are important parameters that are significantly influenced by environmental conditions. In controlled experiments, the processes and trends of ammonia nitrogen (NH3-N) degradation in raw waters were studied under different flow conditions using a laboratory annular flume. Analysis of the observed change in NH3-N concentration with time under various flow conditions allowed calculation of a degradation efficiency (concentration change amount/initial concentration) which for NH3-N increased as the flow velocity increased. According to a first-order kinetic equation to fit the experimental data, the range of variation of the degradation coefficient of NH3-N at different flowrates was between 0.047 per day (0.01 m/s) and 0.203 per day (0.30 m/s). Dimensional analysis was used to analyze the relationship between the degradation coefficient and flow velocity (v), water depth (H), Froude number (Fr), and Reynolds number (Re), which was verified through field data collected in the Chishui River.
Keywords: Ammonia nitrogen; Degradation coefficient; Field monitoring; Hydrodynamic conditions.