Abstract
We investigated changes in dissolved organic carbon (DOC) and the abundance of fluorescent dissolved organic matter (FDOM) components in a river before and after the occurrence of primary treatment discharge from a sewage treatment plants with a separate sewage system. We tested DOC, the score value (SP) of the protein-like component (Comp. 3) of the FDOM, the sum of score values (ST) for microbial humic-like component (Comp. 1), terrestrial humic-like component (Comp. 2) and Comp. 3 of the FDOM, and FDOM (SP, ST)/DOC as indicators detecting the change in river water quality due to the inclusion of untreated sewage discharge from the sewage treatment plant during rainy events. Then, we evaluated the suitability of the five indicators by comparing their absolute values and their change rates with ratios of estimated primary treatment discharge to river flow. The suitability of the indicators was judged based on binary classification, that is confusion matrix with accuracy, and F-value. As the results, it was found that the absolute value of FDOM (ST) was most effective in detecting of the occurrence of primary treatment discharge at the downstream point of the receiving river because of the largest accuracy and F-values.
