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Anthropogenic Influences of Paved Runoff and Sanitary Sewage on the DOM Quality of Wet Weather Overflows: An EEM-PARAFAC Assessment Hao Chen, Zhenliang Liao, Xianyong Gu, Jiaqiang Xie, Huaizheng Li, and Jin Zhang Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 23 Dec 2016 Downloaded from http://pubs.acs.org on December 23, 2016
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Anthropogenic Influences of Paved Runoff and Sanitary Sewage on the DOM Quality of Wet Weather Overflows: An EEM-PARAFAC Assessment
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Hao Chen†‡, Zhen-liang Liao†‡*, Xian-yong Gu†, Jia-qiang Xie†,
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Huai-zheng Li†, and Jin Zhang§
1 2 3
†
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China
7 8 9
‡
UNEP-Tongji Institute of Environment for Sustainable Development, Tongji University, 1239 Siping Road, Shanghai 200092, China
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12 13
§
Institute of Urban Water Management, Technische Universität Dresden, 66 Berg Str., Dresden 01069, Germany *
Corresponding Author:
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Email:
[email protected].
16
Tel.: +86 (21)65981650; fax: +86 (21)65988292.
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ABSTRACT
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The quality of dissolved organic matter (DOM) in a wet weather overflow (WWF) can be
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broadly influenced by anthropogenic factors, such as non-point sources of paved runoff and point
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sources of sanitary sewage within the drainage networks. This study focused on the anthropogenic
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influences of the paved runoff and sanitary sewage on the DOM quality of WWF using
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Excitation-Emission Matrix - Parallel Factor Analysis (EEM-PARAFAC). Results show that: (1)
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EEM-PARAFAC fitted terrestrial humic-like, anthropogenic humic-like, tryptophan-like and
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tyrosine-like components can be regarded as indicators to identify the types of sewage overflows
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and the illicit connection status of drainage systems. (2) A short emission wavelength (em:
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302~313 nm) peak of the tyrosine-like component occurred in the reserved sanitary sewage, while
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a type of longer emission wavelength (em: 321~325 nm) peak came from the sump deposit. These
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tyrosine-like components were gradually evacuated in the initial phase of the overflow process,
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with the fading of their EEM signals. Fluorescence signal transformations of all the components
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confirmed the potential ability of EEM-PARAFAC to monitor the dynamic changes of the primary
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pollutant sources. (3) The input of the newly increased sanitary sewage had a dominant influence
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on the quality and yield of the WWF DOM.
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TOC/ABSTRACT ART
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INTRODUCTION
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Dissolved organic matter (DOM) is a ubiquitous constituent in aquatic
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environments. High loads of DOM carried by the urban wet weather overflow (WWF)
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cause serious pollution problems in receiving waters and give rise to the degradation
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of the aquatic ecological environment.1 Furthermore, DOM is considered to be a
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carrier of several toxic substances such as heavy metals2,3 and persistent organic
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pollutants (POPs).4,5 It is also regarded as an important precursor of disinfection
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by-products (DBPs).6,7 Hence, to minimize its adverse effect on the ecological
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environment, the study of the source influence and the component distribution of
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DOM in WWF is of great importance.
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Generally, the DOM characteristics are determined by the origins and the
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biogeochemical processes that occur along with their production and transport.8-10
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Since previous studies stated that anthropogenic sewer networks intensely changed
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the urban hydrology11-13 and further affected the biogeochemical transformations of
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the DOM,14-16 their original source could have a great influence on the DOM of WWF.
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Early investigations of urban DOM predominantly focused on their distributions in
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urban stormwater runoff from various landscape sources or the streams that were
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influenced by the stormwater runoff,17-19 but most of the studies paid less attention to
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the DOM of WWF. As terminal water bodies, urban streams also receive substantial
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amounts of WWF influents that are mainly composed of the point source discharge of
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sanitary sewage and the non-point source of paved runoff.20-22 Obviously, it is
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insufficient to study only the urban DOM influenced by the paved runoff. Thus,
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researchers such as McElmurry et al.10 suggested that it is important to stress the
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strong impacts from both of the paved surfaces and sewer sources. Considering that
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most of the freshwater DOM originating from terrestrial ecosystems,23 paved runoff
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and sanitary sewage bring highly bioavailable components24,25 that aggravate the
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ambiguous nature of DOM and pose more severe risks.22,26,27 However, the influences
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of the paved runoff and the sanitary sewage on the WWF DOM yields and
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characteristics are not well known, and this knowledge gap needs to be further filled.
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As the DOM has a complex assemblage of chemical structures, many analytical
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approaches provide only limited proxy information on the quality of DOM.10
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However, Excitation-Emission Matrix - Parallel Factor Analysis (EEM-PARAFAC) is
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a powerful tool to assess the natural DOM dynamics28-30 that can resolve the complex
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mixtures of EEM data sets into several typical components.31,32 Many published
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works had utilized the EEM-PARAFAC method to identify the sources of DOM in
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natural streams or lake ecosystems, such as terrestrial runoff, agricultural runoff,
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forest soil and aquatic production.33-37 In terms of the research matrix of municipal
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water supply, wastewater treatment and groundwater monitoring, this method had also
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been commonly applied.38-41 Furthermore, an increasing number of studies had
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characterized and traced the sources of DOM within urban stormwaters or streams
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using EEM-PARAFAC to explore the influences of urban landscapes, environmental
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factors and urbanization gradients on the urban waterbodies.10,42,43 More recently,
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EEM-PARAFAC had been successfully applied to DOM real-time monitoring of point page 5 / 42
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source contaminations, such as fecal matter in drinking water,44,45 which highlighted
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the capacity and prospect of this technique for online pollutant source identification.
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Therefore, the EEM-PARAFAC method has the potential ability to explain the
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anthropogenic influences of paved runoff and sanitary sewage on the quality of WWF
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DOM.
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Moreover, the relative maximal fluorescence intensity (Fmax) of the fitted
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EEM-PARAFAC components can be used as an indicator to identify the stormwater
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sources or catchment types by the use of a multivariate statistical analysis method,
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such as the principal components analysis (PCA). For example, Hosen et al.42
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conducted PCA on the Fmax rather than the common water quality indicators46 or
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complicated organic compounds47-50 to identify forested and urbanized sample types.
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Hence, by using the DOM source fingerprint with further data mining, it is possible to
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identify the types of drainage system sewage overflows and further identify the point
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source contaminations such as illicit connection discharges within the storm sewers.51
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Nevertheless, there have been few related studies focused on the DOM fluorescence
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characterization of sewer overflows, a fact that may be ascribed to the complexity of
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WWF pollutants.
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Consequently, this study investigated the changes of the WWF DOM
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characteristics and yields in response to the anthropogenic influences of paved runoff
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and sanitary sewage inputs. Samples of terrestrial runoff, paved runoff, sump deposit
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and dry weather flow (DWF) were collected for comparison with the possible sources
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of WWF DOM. DWF samples from pump station sumps were referred as the sanitary page 6 / 42
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sewages that involves the newly increased sewage and the reserved sanitary sewage.22
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It was further hypothesized that: (1) DOM components fitted by EEM-PARAFAC can
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assist the source apportionment of WWF and further identify the types of sewage
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overflow; (2) EEM-PARAFAC is a potential tool to monitor the dynamic changes of
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the primary pollutant sources within urban drainage systems; and (3) the newly
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increased sanitary sewage is a dominant source contributor that influences the
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characteristics and yields of WWF DOM.
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MATERIALS AND METHODS
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Study Sites and Sampling Campaigns
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Sampling campaigns were conducted in 7 residential urban catchments in
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southeastern China. The distributions of the various underlying surfaces are reported
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in SI Figure S1 and Table S1 for each catchment. WWF and DWF were primarily
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collected from 6 forced-pump stations located in densely populated catchments in
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Shanghai, namely, sites COM1 and COM2 (combined sewer systems) and sites SEP1
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to SEP4 (separated sewer systems). Another fraction of the WWF and DWF samples
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were collected from a gravity artesian overflow weir (COM3-OW) within a small
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combined system pump station (COM3) in Changzhou. Paved runoff samples were
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collected from a simplex short-haul rainwater pipe outlet (COM3-RWP) within the
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COM3 catchment that serves a road overpass composed of 92% impervious road
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surface and 8% green land. Terrestrial runoff samples were collected from a sealed
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green land within the COM3 catchment (COM3-green land) that has a surface area of
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15.4 m2 with a lawn cover of more than 98%.
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A total number of 231 samples of WWF, paved runoff and terrestrial runoff, were
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collected from 16 rainfall events that occurred between May and June 2015 using
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automatic samplers (Teledyne ISCO, Portable Sampler 6712, USA). With a 15 min
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interval, the continuous collection of samples was started at the beginning of the
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overflow (stormwater pump launch) or runoff process, and stopped at the end. The
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rain conditions are provided in SI Table S2. A total of 112 DWF samples were page 8 / 42
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continuously collected at 3 h intervals over 48 h under the baseflow conditions. The
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baseflow condition was defined as any dry weather period of more than 48 h after a
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rainfall event.42 Sump deposits from 6 pump stations in Shanghai were sampled under
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the baseflow conditions. Samples were collected in 1 L acid-washed HDPE bottles
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and stored overnight at 4 °C prior to further lab analysis. All the analyses were
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finished within one week.
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The leachates of the sump deposits were the liquid supernatants after 30 min of
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mechanical agitation at 300 rpm. A 2 mg/L humic acid (≥90% purity, Aladdin
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Biochemical Technology Co., Ltd, peat source, CAS No. 1415-93-6) solution was
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prepared with ultrapure water (Millipore).
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EEM-PARAFAC Analysis of the DOM
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EEM data were acquired using a Horiba Fluoromax-4 spectrofluorometer under
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the constant temperature of 20± 2 °C. The excitation wavelengths of the EEM were
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incrementally increased in 5 nm steps from 250 to 450 nm; for each excitation
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wavelength, the emission wavelengths were detected in 2 nm steps from 300 to 550
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nm.42 All samples for EEM determination were diluted 5 times with ultrapure water
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and filtered through 0.45 µm PVDF filters (Durapore, Millipore). The dissolved
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organic carbon (DOC) and ultraviolet absorbance (UV254) of these preprocessed
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samples were in the ranges of 0.9~4.8 mgC/L and 0.011~0.056 cm-1, respectively,
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which met the requirement of UV254 (< 0.05 cm-1) for minimizing the inner-filter
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effect.53 Positive linear correlations existed between the DOC and EEM peaks when page 9 / 42
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the DOC was diluted to be below 5 mgC/L (SI Figure S2). This confirmed that the
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inner-filter effect was limited to induce the deviation of the linear correlations when
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the DOC was in the range of 0.9~4.8 mgC/L. Such positive linear correlations also
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guaranteed the comparability of each sample EEM result. The preprocessed samples
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were adjusted to pH 2± 0.2 and 10 mM ionic strength using a KCl solution of 0.1 M
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strength,52,53 aiming to inhibit the fluorescence signal disturbance from aquatic metal
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ions (pH selection shown in SI Figure S3).53 Specifically, < 100 µL of buffer was
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added to each 10 mL preprocessed sample solution. Each EEM sample was scanned
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in triplicate to investigate the reproducibility of the PARAFAC analysis. The inner
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filter correction was performed using a controlled dilution approach with a 2.0 ×
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dilution factor for the diluted sample of which UV254 was still greater than 0.05
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cm-1.53-55 Ultrapure water EEM was subtracted from each sample EEM. Delaunay
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triangulation interpolation algorithm was used for handling the first and second order
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Rayleigh scatter regions before PARAFAC.56,57 This interpolation algorithm was
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applied to address the high signals of the scatter regions in the EEM of samples that
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had low concentrations of DOM, as suggested by previous studies.57,58 The samples
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which had been diluted and adjusted also presented the characteristics that the scatter
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signal orders of magnitude were obviously higher than those of the DOM signals (SI
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Figure S4). The PARAFAC modeling approach (computed by the DOM-Fluor
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Toolbox, www.models.kvl.dk/source) has been described in detail elsewhere.59-62
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Repeated convergence of the model was examined based on the iteration of the
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minimum squares principle. Non-negativity constrains and initialization method of page 10 / 42
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direct trilinear decomposition were applied in the PARAFAC modeling.
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Five components of DOM were retained and validated using the core consistency
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diagnostic (score> 90%) and visual inspection (SI Table S3).63 Acidic conditions
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showed a very limited influence on the core consistency diagnostic score compared to
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the neutral pH condition (SI Figure S3d). Split-half analysis was used to validate the
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identified components.64 The source fingerprints of each component are described in
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SI Table S4.42 Briefly, component c1 (ex/em= 250, 325 nm/ 438 nm) is a humic-like
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component of terrestrial origin which is absent from wastewater.25,32 Component c2
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(ex/em= 250, 380 nm/ 510 nm) is a ubiquitous and recalcitrant (terrestrial) humic-like
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and fulvic-like component.25,65 Component c3 (ex/em= 250, 280, 300, 325 nm/ 388
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nm) is an anthropogenic and microbial originated humic-like and fulvic-like
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component.25,28,66 Component c4 (ex/em= 280 nm/ 350 nm) is a recently produced
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tryptophan-like component.32,67 Component c5 (ex/em= 280 nm/ 315, 325 nm) is a
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tyrosine-like component.68,69 The component distribution was calculated based on the
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Fmax (Raman units) of each identified component.66
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Using the distribution proportions of the 5 fitted EEM-PARAFAC components,
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PCAs were conducted on a standard humic acid solution, terrestrial runoff, paved
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runoff, DWF and WWF samples to identify the types of sewage overflows. In
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addition, another PCA was conducted using 5 common water quality indicators as a
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group to compare the advantage of the 5 fitted EEM-PARAFAC components. The 5
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common water quality indicators were total suspended solids (TSS, mg/L), chemical
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(NH3-N, mg/L) and total phosphorus (TP, mg/L). Their detection methods are
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described in SI.
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DOM Indicators and Molecular Feature Determination
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The DOC concentration, aromaticity (SUVA254), molecular weight (MW) and
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polydispersity (ρ) are generally utilized as indicators of the DOM yield and
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bioavailability.70-72 Samples were pre-filtered and adjusted to pH 6.7± 0.2 and 10 mM
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ionic strength. The DOC concentration was determined using a Shimadzu V-CPN
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total organic carbon analyzer. SUVA254, which positively correlates to the DOM
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aromaticity, was calculated by dividing the UV254 value by the DOC
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concentration.73,74 UV254 was collected using the ultraviolet spectrum (UV-2550,
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Shimadzu) with 1 cm quartz cuvettes and further corrected for the Fe3+ concentration
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using a previously defined relationship: A254‑corrected= A254‑measured - 0.0687×[Fe3+].75
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The Fe3+ concentration was determined using inductively coupled plasma-optical
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emission spectrometry (ICP-Agilent720ES).
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In addition, the DOM MW and ρ were determined using a gel-filtration
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chromatograph (GFC, LC-10ADVP, Shimadzu). A differential refraction detector was
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coupled with the GFC. (Mobile phase: ultrapure water; flow rate: 0.5 mL/min;
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analysis time: 25 min; column temperature: 40 °C; chromatographic column type:
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TSK gel G4000PWXL; and standard substance: polyethylene oxide/glycol EasiVials,
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4 mL). The MWs discussed here are not the actual values since there are no available
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standards with chemical properties comparable to the organic substances in WWF.76,77 page 12 / 42
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The MW values referenced throughout the text are the weighted averaged MW values.
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Data Analysis
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OriginPro (version 9.0, OriginLab) and SPSS (version 20, IBM) were used for
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the repeated-measure analysis of variance (ANOVA), analysis of covariance
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(ANCOVA), and linear regressions. An alpha-level of 0.05 was used to determine the
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significance. Data were not included in the statistical analyses if they met the outlier
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criterion using Dixon’s Q-test at the 95% confidence level.78 The underlying surface
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characteristics of each sampling catchment were determined using ArcGIS (version
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10.1, ESRI). The EEM data preprocessing, PARAFAC modeling and exported
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contour maps were computed in MATLAB (version R2012a, MathWorks) and
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OriginPro. The PCA results were generated using SPSS.
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RESULTS AND DISCUSSION
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Component Distribution and Possible Sources of WWF DOM
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The distributions of the five DOM components of terrestrial runoff, paved runoff,
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DWF and WWF samples were obtained using the EEM-PARAFAC (Figure 1).
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Compared to the characteristics and original source information described in the
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methods section (and in SI Table S4), the first hypothesis that the DOM analyzed by
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EEM-PARAFAC can assist the source apportionment of WWF has been supported.
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Terrestrial runoff (site COM3-green land surface runoff) contained the same
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components (c1 and c2) as the standard humic acid solution, namely, a predominance
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of terrestrial source humic-like and fulvic-like organic matters.25,32,65,67,79
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Paved runoff input contained a number of anthropogenic humic-like substances
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(c3). As the site COM3-RWP serves a road overpass with paved runoff influents from
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the impervious road surfaces and green land, the DOM in both groups of samples
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from site COM3-RWP contained more than 50% of the c3 + c4 ratios, of which, the
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anthropogenic humic-like substances indicated by c3 made up the largest
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portion.17,25,28,66 The recently produced protein-like components indicated by c4
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accounted for a smaller percentage (approximately 15%), and the natural humic-like
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components (c1 + c2) accounted for only 45%. This result corroborates the previous
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findings that an increase of the impervious surface area is associated with a decreased
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amount of natural humic-like DOM and enriched amount of anthropogenic fulvic-like
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and protein-like DOM.17,42 Actually, as sanitary sewage normally has a low page 14 / 42
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concentration of humic-like substances,80 this finding implies that the anthropogenic
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humic-like substances (c3) in the WWF samples primarily originated from the paved
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runoff.
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DWF, including newly increased and reserved sanitary sewages, carried
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tryptophan-like (c4) and tyrosine-like (c5) components. In the DWF samples from the
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catchments of Shanghai, components c4 + c5 represented approximately 55~75%
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percent of the total, and c1 + c2 always accounted for less than 30%. Component c4
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generally indicates the less degraded and ‘‘fresher’’ proteins, while c5 suggests the
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degraded or ‘‘older’’ proteins.68,81,82 Simultaneously, since the DWF samples were
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collected under baseflow conditions without agitated deposits (no stormwater pump
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launching), the c4 and c5 components might indicate the newly increased and
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reserved sanitary sewage contained in the DWF samples, respectively. This inference
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was further confirmed by the obvious degradation of the c4 component and the
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preservation of the c5 component in freshly collected sanitary sewage having a long
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holding time in the laboratory (SI Figure S5). Furthermore, the compositions of DWF
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DOM from the four separated sewer systems were similar to those from the two
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combined sewer systems, suggesting that there were distinct illicit connections within
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the four separated sewer system networks. However, the degrees of the illicit
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connections seem to be different among these systems, especially the SEP4 system.
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Component distributions of WWF DOM were found as different combinations of
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terrestrial runoff, paved runoff and DWF, which revealed that the sources were clearly
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different. Although the condition parameters of the six rainfall events in sites SEP1 to page 15 / 42
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SEP3 were greatly different (SI Table S2), their WWF DOM component distributions
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were relatively consistent, implying that a similar illicit connection status existed
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among these three drainage networks. The c5 component did not present in the six
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batches of WWF samples, indicating that there was no reserved sanitary sewage.22 All
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of the WWF DOM from the two rainfall events at site SEP4 contained large ratios of
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c4 and c5 components, and such ratios were comparable or even higher than them in
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both the dry and wet weather effluents of the combined sewer system COM2,
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demonstrating that more severe illicit connections remained in the drainage networks
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of site SEP4. The compositions and original sources of WWF DOM from the two
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rainfall events at site COM1 were different. At the 1st rainfall event, c5 components
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composed approximately 40% of the DOM, suggesting that the reserved sanitary
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sewage was the predominant pollutant source. The c3 components were more
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prevalent in the DOM compositions of the 2nd WWF, which was similar to those from
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sites SEP1 to SEP3, thus indicating that paved runoff was their main source.
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Identification of the Types of WWF by PCA
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A PCA was further conducted on the EEM-PARAFAC component (c1 to c5)
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results, as shown in Figure 2. The Fmax percentages of the fitted DOM components,
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rather than the common water quality indicators (SI Figure S6), can efficaciously
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identify the paved runoff-like and sanitary sewage-like types of the sewage overflows
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from drainage systems and notably differentiate the influence of paved runoff and
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sanitary sewage in the WWF samples. page 16 / 42
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To ensure the sufficient influence of the extracted principal component (PC), its
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eigenvalue was required to be greater than 1. Hence, only the first two PCs could be
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retained according to the loading panels in SI Table S5 for the PCA of Figure 2, as
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well as SI Figure S6. In Figure 2, the first component (PC1) accounted for 48.1% of
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the total variance and the second component (PC2) accounted for 27.1% of the total
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variance. Both together explained 75.2% of the total variance of the dataset. Variables
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of c1 and c2 (humic-like substances) primarily contributed to PC1 according to their
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square cosines (SI Table S5), while variable c4 could also be better represented by PC1
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and appeared to be negatively correlated. Variable c3 (anthropogenic humic-like
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substances) continued to have a high loading on PC2, yet variable c5 was also better
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represented by PC2 and appeared to be negatively correlated.
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The majority of the generalized data points were grouped into 3 distinct clusters
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as shown in Figure 2b. In cluster A, COM3-green land runoff and humic acid solution
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arose as the terrestrial runoff, which contained only 2 types of humic components in
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EEM-PARAFAC (c1 and c2). However, it showed that cluster A correlated not only
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with PC1, but also to a less extend with PC2. The dissimilarity analyzed between
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cluster A and the other clusters justified its unique composition. In cluster B, WWF
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sample points were regularly distributed with relatively similar loadings on both PC1
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and PC2, which explains why the cluster B data points possessed greater positive
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relationships with the variables of c1, c2 and c3. Simultaneously, paved runoff from
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site COM3-RWP also appeared in this cluster. These findings reveal that the WWF
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samples in cluster B had a distinct type of paved runoff characteristics. The cluster C page 17 / 42
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samples possessed a completely different pollution status and pollutant source
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compared to those from cluster B. The data points in cluster C presented significantly
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negative correlations with both PC1 and PC2. Nevertheless, they showed positive
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correlations with variables c4 and c5. DWF samples from the sites COM2 and SEP1
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to SEP3 and WWF samples from the sites COM1-Rf1, COM2 and SEP4, were
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distributed within this cluster, confirming that these WWF samples were a type of
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sanitary sewage-like overflow.
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Therefore, it can be concluded that separated sewer systems with fewer illicit
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connections discharged a type of paved runoff-like overflow; while the combined
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sewer systems, as well as the separated sewer systems with a severe number of illicit
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connections, discharged a type of sanitary sewage-like overflow. In addition, as the
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derived indicators of pollutant composition, the EEM-PARAFAC components are not
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easily disturbed by some uncertain factors, such as their numerical concentration.83
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Hence, those results were more reliable.
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By contrast, the data points of the PCA based on the 5 common water quality
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indicators: TSS, NH3-N, CODCr, TP and TN, presented distinctly different loadings on
328
both PC1 (CODCr and TP) and PC2 (TSS, TN and NH3-N) (SI Figure S6b). There
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were no clearly formed clusters that were related to the characteristics of the WWF
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samples. Hence it remains difficult to identify the types of overflow samples using
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these 5 common water quality indicators.
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A commercial humic acid solution was added into the PCA of Figure 2. However,
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was found in the comparison of the loadings of variables and sample data points (SI
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Figure S6c and S6d, SI Table S5). Given that the terrestrial runoff sample added in
336
both PCAs (Figure 2 vs SI Figure S6c and S6d) containing the same EEM-PARAFAC
337
components as the humic acid solution (Figure 1), such similar results were
338
predictable.
339
Dynamic EEM-PARAFAC Monitoring of Overflow Process
340
EEM analyses of the continuously collected WWF DOM with PARAFAC
341
processing verified the feasibility of using EEM-PARAFAC for monitoring the
342
dynamic changes of the primary pollutant sources within an urban drainage system,
343
such as the runoff, sewage and deposit (Figure 3). This conclusion supports
344
hypothesis 2. Particularly, the obvious “first flush” phenomena of the fluorescence
345
intensity and the Fmax ratio of EEM-PARAFAC fitted c4 component to c3 component
346
were found in WWF batches. A gradually fading of the c5 component signals in the
347
initial phase of the WWF demonstrated an evacuation process of the reserved sanitary
348
sewage (Figure 3 and SI Figure S8). Meanwhile, the agitated sump deposit may also
349
release the c5 component, which presented a longer emission wavelength
350
tyrosine-like peak than that of the reserved sanitary sewage (Figure 4).
351
The fluorophore intensity of DOM has a typical temporal variability that mainly
352
depends on its related component concentrations or yields.63,80 In particular, the DOC
353
concentration showed a directly proportionality to the fluorophore intensity when the
354
DOM content was at a low level (SI Figure S2). However, the shift of fluorophore page 19 / 42
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wavelength indicates a minor transformation of its molecular structure.84,85 All these
356
are the theoretical basis of dynamic EEM-PARAFAC monitoring.
357
Among all the WWF batches, the c5 components occurred only in COM1-Rf1,
358
COM2-Rf1, COM-Rf2, SEP4-Rf1 and SEP-Rf2 (Figure 1). Hence the monitoring of
359
these five batches demonstrated more completely the dynamic changes of the DOM
360
discharging from various pollutant sources (Figure 3). COM1-Rf1, COM2-Rf1,
361
COM2-Rf2 and SEP4-Rf1 showed obvious “first flush” phenomena in their
362
fluorescence. In particular, considerably strong protein-like peaks (both c4 and c5)
363
suggested that the high DOC concentrations of sanitary sewage were discharged
364
during the initial phase of the overflow process. The dynamic transformation of the
365
Fmax ratio of the EEM-PARAFAC fitted c4 component (newly increased sanitary
366
sewage) to c3 component (paved runoff) also showed clear “first flush” effects (SI
367
Figure S7). The overflow process of SEP4-Rf2 was different from those of the other
368
sites, which had no “first flush” effect. This may suggest that the sanitary sewage
369
influent was an uninterrupted process.
370
A fluorescence fading phenomenon of the tyrosine-like peak (c5) occurred as
371
well with the “first flush” effect in the initial phase of the overflow process (Figure 3),
372
while the tryptophan-like peak (c4) presented throughout the entire overflow period.
373
This phenomenon explains the evacuation process of the reserved sanitary sewage
374
during the initial phase of overflow, which also confirms the use of the c4 and c5
375
components as reasonable and convincing indicators for newly increased and reserved
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sanitary sewages, respectively. As the c5 component did not appear in the WWF page 20 / 42
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batches from sites SEP1 to SEP3 (Figure 1), it may be involved in the dry weather
378
outfall operation of these municipal pumping stations in the separated sewer systems
379
that existed with illicit connection problems.86 The protein-like organics (in sanitary
380
sewage) in these pump sumps were difficult to continuously accumulate and degrade.
381
Thus, it is hard to be transformed into degraded ‘‘older’’ proteins under the frequent
382
dry weather outfall conditions.68
383
However, the tyrosine-like components that presented in the initial phase also
384
revealed a significant qualitative change. Their EEM peaks appeared at both of the
385
short (em: 302~313 nm) and long (em: 321~325 nm) emission wavelength positions,
386
which can be found in the elaborated spectrum (SI Figure S8). Tyrosine-like peaks in
387
COM2-Rf1 and COM2-Rf2 WWF samples were found at long emission wavelengths,
388
while those from the SEP4-Rf1 and SEP-Rf2 WWF samples were found at shorter
389
emission wavelengths. Both short and long emission wavelength tyrosine-like peaks
390
repeatedly occurred in the overflow process of COM1-Rf1. In fact, all of the
391
tyrosine-like peaks in the DWF samples from sites COM1, COM2 and SEP1 to SEP4
392
were found to occur in the short emission wavelength range of 302~313 nm according
393
to the EEM-PARAFAC results shown in Figure 4, and all of the tyrosine-like peaks of
394
the sump deposit leachate samples occurred in the long emission wavelength range of
395
321~325 nm. A possible explanation might be that the tyrosine-like proteins that
396
originated from the sanitary sewage could be further degraded when they came into
397
contact with biofilms on deposits during minor hydraulic disturbance conditions in
398
dry weather.87 Heterotrophic microorganisms preferentially consume carbohydrates page 21 / 42
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and peptides and release aromatic structures.71 It leads to the tyrosine-like structures
400
having a higher aromaticity, and a red shift of emission wavelength in the EEM
401
plots.10,69,71,88 In addition, the hydraulic disturbance during the overflow process was
402
generally hard to resolve in the dissolved organic components, such as extracellular
403
polymeric substances released from the interior of microorganisms.89,90 This result
404
suggests the longer emission wavelength of the c5 component might be the most
405
degraded tyrosine-like protein that indirectly originated from sanitary sewage.
406
Consequently, in the two batches of WWF from site COM2 may originate from the
407
reserved sanitary sewage, and the two WWF batches from site SEP4 were more likely
408
to be directly released from the sump deposit. However, the tyrosine-like components
409
found in COM-Rf1 may be from the both sources.
410
Dominant Influence of Newly Increased Sanitary Sewage
411
The c3 component from paved runoff and the c4 component from newly
412
increased sanitary sewage were resulted from the anthropogenic influences and were
413
also ubiquitous components of the WWF DOM. Both components presented a certain
414
extent of influence on the DOM quality indicators, such as MW, ρ and aromaticity
415
(SUVA254). Particularly the c4 component, which indicates the newly increased
416
sanitary sewage, had a dominant influence on the WWF DOM quality and yields
417
(Figure 5).
418
MW and ρ were positively correlated with the percent of c4 components at r2=
419
0.63 and 0.66 (Figure 5a and 5b), respectively. It demonstrates that tryptophan-like page 22 / 42
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fresh proteins from newly increased sanitary sewage were an important influencing
421
factor of the WWF DOM molecular weight and polydispersity. Conversely, there was
422
only a weak negative relationship (r2= 0.49) between the c3 component percentage
423
and the WWF DOM MW (Figure 5e). Similarly, c3 had no obvious regular impact on
424
the molecular polydispersity (SI Figure S9g). As the paved runoff DOM from
425
COM3-RWP consisted of more humic- and fulvic-like components (Figure 1), this
426
runoff was determined to have the lowest molecular weight, and polydispersity and
427
the highest aromaticity (SI Table S6 and Figure 5h), which was consistent with the
428
results of previous studies.10,77,91,92 Simultaneously, no notable correlation (r2= 0.5)
429
was found between SUVA254 and MW as reported by the other studies (Figure 5i).73,74
430
In addition, since the biomolecule-like proteins or polypeptides always have higher
431
molecular weight values,77,91 the point source of sanitary sewage from the various
432
urban underlying surfaces could distinctly increase the molecular weight of the WWF
433
DOM. Hence, the WWF DOM from sites in Shanghai had a higher molecular weight
434
and polydispersity (SI Table S6).
435
Furthermore, the variations of WWF DOM MW and ρ values were not found to
436
be impacted by the ratios of catchment impervious cover (SI Figure S9c and S9d) or
437
the percent of c3 and c4 components (SI Figure S9a and S9b). However, the WWF
438
samples from COM1, COM2, SEP1 to SEP4, and COM3-OW presented a negative
439
correlation between DOM aromaticity and impervious cover ratio (r2= 0.67, Figure
440
5h), which is consistent with the previous conclusions.42 In addition, increasing the c4
441
component would also enhance the WWF DOC and CODCr concentrations (r2= 0.58 page 23 / 42
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Page 24 of 42
and 0.78, Figure 5d and 5g).
443
On the other hand, SUVA254 presented a descending relationship (r2=0.64) with
444
the percent of the c4 component (Figure 5c). Theoretically, it should be positively
445
correlated to the c3 component, but it was not (SI Figure S9e). The result implies that
446
the c4 component (newly sanitary sewage) may control the holistic quality of the
447
WWF DOM to a greater degree. Similarly, we found that the NH3-N concentration
448
(primarily indicating sanitary sewage) had a strong negative linear relationship
449
(r2=0.92) with the percent of the c3 component (Figure 5f), but not the c4 component
450
(newly increased sanitary sewage, SI Figure S9f). The possible causes of this finding
451
need to be further evaluated.
452
Implications
453
Applying
EEM-PARAFAC
can
directly
distinguish
the
complicated
454
anthropogenic influences of the non-point source of paved runoff and the point source
455
of sanitary sewage on the WWF DOM from the drainage systems in highly urbanized
456
catchments. The presented results support our hypotheses and achieves critical
457
observations as follows. (1) The fitted c3 and c4 components could indicate the paved
458
runoff and newly increased sanitary sewage, respectively. A short emission
459
wavelength (em: 302~313 nm) of the c5 component conspicuously exists in the
460
reserved sanitary sewage, and a type of longer emission wavelength (em: 321~325 nm)
461
of the c5 component is from the agitated sump deposit. (2) These indicated
462
relationships demonstrate the feasibility and capability of analyzing the DOM with page 24 / 42
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the EEM-PARAFAC method to be used for dynamic monitoring of the primary
464
pollutant sources within urban drainage systems. (3) The input of the newly increased
465
sanitary sewage has a dominant influence on the quality and yield of WWF DOM,
466
compared to the paved runoff. To our knowledge, this work is pioneering the linkage
467
of the WWF DOM with the EEM-PARAFAC method to identify the primary pollution
468
sources, overflow types and illicit connection problems in the completely artificial
469
urban drainage systems. These ideas and approaches regarding the WWF DOM
470
deliver a significant potential to provide supplementary and effective methods for the
471
assessment and reconstruction of urban drainage systems, particularly for those have
472
serious problems regarding sanitary sewage inputs or illicit connections.
473
Furthermore, there remains limitations of the tool for monitoring paved runoff
474
and sanitary sewage in urban systems, especially the constraining requirement of the
475
fluorescence method on sample nature or content. The Delaunay triangulation
476
interpolation algorithm was used to preprocess the raw EEM data before PARAFAC,
477
yet this algorithm was applicable only to the samples that have relatively high scatter
478
signals in the EEM. Nevertheless, the algorithm can be adapted in terms of the actual
479
nature of the samples. In addition, the tool identifies the overflow pollutant source is
480
in a semi-quantitative way, and a quantitative resolution should be the subject of a
481
future research expansion.
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ACKNOWLEDGMENT
483
This study was financially supported by the National Natural Science Foundation of
484
China (Grant No. 51578396), the National Water Pollution Control and Treatment
485
Science and Technology Major Project (Grant No. 2013ZX07304002-1), and the
486
German BMBF (Bundesministerium für Bildung und Forschung, Federal Ministry of
487
Education and Research) CLIENT project “Managing Water Resources for Urban
488
Catchments” in the framework of the Sino-German “Innovation Cluster Major Water”
489
(Grant NO. 02WCL1337A). We would also like to acknowledge the substantial
490
supports from Shanghai Municipal Sewerage Co. Ltd and Changzhou drainage
491
management office.
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SUPPORTING INFORMATION
493
Additional details about study sites, raining conditions, condition parameters of
494
methods, plots of DOM component degradation, loading data of PCAs,
495
EEM-PARAFAC dynamic monitoring, Linear regression analysis. This information is
496
available free of charge via the Internet at http://pubs.acs.org.
497 498
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FIGURES
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Figure 1
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Figure 1. Fmax percentage distributions of the EEM-PARAFAC fitted DOM
794
components (c1, c2, c3, c4 and c5) in a humic acid solution (2 mg/L) and samples of
795
runoff, DWF and WWF. Each batch of samples was totally included for each
796
PARAFAC fitting.
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Figure 2
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Figure 2. PCA of DOM compositions of a humic acid solution (2 mg/L) and samples
805
of terrestrial runoff, paved runoff, DWF and WWF as measured by the Fmax
806
percentages of EEM-PARAFAC fitted components (c1, c2, c3, c4 and c5). (a) square
807
cosines for c1, c2, c3, c4 and c5 on PC1 and PC2; (b) PCA of DOM compositions of a
808
humic acid solution (2 mg/L) and samples of terrestrial runoff, paved runoff, DWF
809
and WWF. Loading panels are described in SI Table S5. The percentages in axis titles
810
indicate the percentage variance explained by each principal component. Coordinate
811
position of each sample point in panel b indicates its loadings on the 2 principal
812
components.
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813
Figure 3
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Figure 3. Dynamic EEM monitoring of the WWF batches of COM1-Rf1, COM2-Rf1, page 38 / 42
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COM2-Rf2, SEP4-Rf1 and SEP4-Rf2. Continuous collection of samples was started
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at the beginning of the overflow process (stormwater pump launch) and stopped at the
818
end with a 15 min interval. Fluorescence intensity: Raman units.
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Figure 4
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Figure 4. EEM-PARAFAC fitted tyrosine-like components in DWF samples (left
822
column) and sump deposit leachates (right column) from sites COM1, COM2 and
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SEP1 to SEP4. Left column: short emission wavelength peak at ex: 280 nm and em:
824
302~313 nm; right column: longer emission wavelength peak at ex: 280 nm and em:
825
321~325 nm. Normalized fluorescence intensity: Raman units.
826 827 828 829 830
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Figure 5
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Figure 5. Linear regression analysis of the average values of WWF and paved runoff
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sample variables. (a) percent c4 to MW (Da), (b) percent c4 to ρ, (c) percent c4 to
835
SUVA254 (L/mgC·m), (d) percent c4 to DOC (mgC/L), (e) percent c3 to MW, (f)
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percent c3 to NH3-N (mg/L), (g) percent c4 to CODCr (mg/L), (h) impervious cover
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ratio to SUVA254, (i) SUVA254 to MW. Error bars represent standard error of the
838
average by each batch. Statistical parameters of linear fitted curves are described in SI
839
Table S7.
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