An Approach for Interpreting the Fingerprints of Urban Sewer Flows Using Fluorescence Spectroscopy : Insights into the Low Influent Concentration of a Wastewater Treatment Plant

Low degradability of wastewater treatment plant (WWTP) influents negatively affects its ability to effectively degrade pollutants through wastewater treatment processes. Proactive assessment of urban sewer performance is highly valued in the selection of targeted countermeasures for this occurrence. In this study, a fluorescence spectrum interpretation approach was developed to probe the low biodegradability of WWTP influent by introducing parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) of excitation-emission matrix spectroscopy. Statistical analysis was also used to further interpret the PARAFAC- and FRI-derived data. The urban sewer catchment served by a WWTP in Wuhan City, China, was taken as the study site, to demonstrate the cost-effectiveness of this approach. The results show that electronics manufacturing industrial wastewater and groundwater entries into the urban sewer significantly decrease the fluorescence peak intensities, especially for protein-like substances, including tryptophan-like T and tyrosine-like B1 and B2, which results in the low biodegradability of the WWTP influents. The potential conversion of high freshness T into low freshness B2 within the sewer may also contribute to this unfavorable scenario. The ratio of peak T to peak B2 and the ratio of the FRI fraction of region I to that of region II can be used together to determine the predominance of industrial wastewater and groundwater. T/B2 < 1.3 indicates the entry of industrial wastewater or groundwater into urban sewers, and further I/II > 0.5 screens the entry of industrial wastewater. Accordingly, the low biodegradability of the WWTP influents in our study site is dominated by the inflow of industrial wastewater rather than groundwater infiltration into the urban sewers. Therefore, actions should be focused on the surveillance of industrial wastewater rather than widespread sewer inspection and repairs. In this way, this methodology is cost-effective in aiding targeted countermeasures to improve the urban sewer system performance