CHAPTER 27: Changes in Inorganic Nitrogen Ratio ([NH₄⁺-N]/[NO₃⁻-N]) During Ozonation of Drinking Water and Its Application for Micropollutant Removal Prediction

During the ozonation of drinking water, ozone and ^•OH react with organic matter including dissolved organic nitrogen. The extent of oxidation by these species varies depending on the water quality and conditions in which ozonation is performed. The contribution of these oxidants toward the overall oxidation process is commonly determined using the R_CT value, where exposures of ozone and ^•OH are quantified from the decay of both ozone and p-chlorobenzoic acid (an ^•OH probe compound). We have recently shown that changes in ozone and ^•OH exposures can be indirectly evaluated from the concentrations of NO₃⁻-N and NH₄⁺-N, and that R_CT values have a direct relationship with [NH₄⁺-N]/[NO₃⁻-N]. This present study aims to confirm the relationship using actual water samples taken from ozonation plants. For this purpose, inorganic nitrogen concentrations were determined from samples before and after ozonation. The actual inorganic nitrogen concentrations measured from the treatment plant were compared with the results obtained from laboratory batch experiments. It was observed that nitrate and ammonium levels in batch experiments increased after ozonation, and agreed well with the inorganic nitrogen concentrations obtained in actual treatment plant samples. Furthermore, the R_CT values calculated from the [NH₄⁺-N]/[NO₃⁻-N] were also used to predict the % removal of ibuprofen, carbamazepine, and atrazine. Experimental results were predicted well using the indirectly measured R_CT. These results demonstrate the potential of monitoring inorganic nitrogen species produced from dissolved organic nitrogen oxidation to evaluate the performance of an ozonation process.