Tryptophan-like fluorescence as a fingerprint of urban river water intrusion into storm drainage system

Abstract Inappropriate dry-weather misconnections into storm drainage system is a demanding environmental problem worldwide. Especially river water intrusion into storm drains may cause the overloading of storm pipes and unexpected serious dry-weather discharge. In this study, we evaluated the possibility of quantifying proportional source contribution in a storm drainage system with dry-weather misconnections from domestic sewage and river water inflow, using rapid and low-cost fluorescence spectroscopy methods. For this purpose, samples of both misconnection sources and outflows of storm drainage system were collected and analyzed in a downtown catchment of Shanghai, China. Results showed that fluorescent peak intensity of tryptophan-like T1 in domestic sewage (802±126 a.u.) was significantly higher than that in urban river water (57±12 a.u.), while fluorescent peak intensities of tryptophan-like T2 in urban river water (998±187 a.u.) was much higher than that in domestic sewage (241±72 a.u.) due to increased phytoplankton or algal activity in the polluted water. However, only Peak T2 passed the conservative behavior test in the incubation experiments, which could be used as a fingerprint for quantitatively identifying the misconnections of urban river water intrusion. We further developed a Bayesian fluorescence mass balance model (FMBM) to infer the percentage of dry-weather misconnections into the storm drainage system as a function of fluorescence intensities of Peak T2 in the samples of sources and outflows. It was found that the maximum posteriori probability estimate of the percentage of river water intrusion into the storm drains was up to 20.8% in this site, which was validated by the results of on-site investigation. Our findings implied that in-situ fluorescent sensors and Bayesian FMBM for the fingerprint fluorescence peak could be applied to fast track urban river water intrusion into storm drainage system from both qualitative and quantitative perspective with low costs.