Tryptophan-like fluorescence as a fingerprint of dry-weather misconnections into storm drainage system

Hailong Yin,Zuxin Xu,Yue Wang,Yang Yang,Jingshui Huang

doi:10.1186/s12302-020-00336-3

Abstract

BackgroundInappropriate dry-weather misconnections into storm drainage system are a demanding environmental problem worldwide, which leads to unexpected dry-weather discharge into surface waters. It often costs a large amount of manpower and resources to identify the source of misconnections and estimate its contributions. 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.ResultsResults 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 (732 ± 304 a.u.) was much higher than that in domestic sewage (261 ± 64 a.u.) due to increased algal activity in the local river and upstream inflow chemistry. 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. 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 outflow. 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.ConclusionOur findings implied that in situ fluorescent sensors and Bayesian FMBM for the fingerprint fluorescence peak could be applied to fast track inappropriate dry-weather misconnections into storm drainage system qualitatively and quantitatively with low costs.

Highlights

Inappropriate dry-weather misconnections into storm drainage system are a demanding environmental problem worldwide, which leads to unexpected dry-weather discharge into surface waters
The excitation–emission matrix (EEM) from samples collected from the domestic raw sewage and urban river water have been evaluated and show 3 peaks (T1, T2, B1) with the strongest fluorescence intensities (Fig. 2)
The first fluorescence intensity peak is at excitation wavelength (Ex)/emission wavelength (Em) of 275/350 nm, which corresponds to tryptophan-like peak T1 components

Summary

Introduction

Inappropriate dry-weather misconnections into storm drainage system are a demanding environmental problem worldwide, which leads to unexpected dry-weather discharge into surface waters It often costs a large amount of manpower and resources to identify the source of misconnections and estimate its contributions. 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. Current use of above chemical or biological markers is still less automated for higher throughputs especially in a catchment-scale assessment

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Conclusion