Combined collection systems of sewage and rainfall runoff seriously affect the spatial distributions of natural estrogens and their conjugates in river water: Insights from the Pearl River of China

So far, little has been known about how the combined collection systems of sewage and rainfall runoff (CCSs) affect emerging contaminants in river water. To fill up the knowledge gap, this study was conducted to investigate the spatial distributions of three natural estrogens (NEs, i.e., estrone (E1), 17β-estradiol (E2) and estriol (E3)) and their conjugates (C-NEs) in the Pearl River in the wet and dry seasons. Results showed that the respective average concentrations of NEs and C-NEs at different locations alongside the Pearl River in the wet season were 7.3 and 1.8 times those in the dry season. Based on estrogen equivalence (EEQ), the average estimated EEQ level in the Pearl River waters in the wet season was nearly 10 times that in the dry season. These seemed to imply that the CCSs in the wet season not only cause untreated sewage into the receiving water body, but greatly decrease the removal efficiency of NEs and C-NEs in wastewater treatment plant. Furthermore, the estimated annual loads of E1, E2, and E3 to the Pearl River in the wet season accounted for about 88.6 %, 100 %, and 99.3 % of the total annual loads. Consequently, this work for the first time demonstrated that the CCSs in cities with high precipitation are unfavorable for controlling of emerging contaminants.

Microplastic accumulation in sewer sediments and its potential entering the environment via combined sewer overflows: a study case in Paris

During wet weather events, combined sewer overflows (CSOs) transfer large amount of particulate matter and associated pollutants into surrounding water bodies, thereby deteriorating the recipients' ecological health. Resuspension of sewer sediments during these events contributes significantly to pollution level of these discharges. However, how much this in-sewer process contributes to CSOs' quality regarding microplastic (MP) pollution is little known. Therefore, an investigation on sewer deposits inside the Parisian combined sewer network was carried out. The study found high MP concentrations stored in this matrix, ranging from 5 × 103 to 178 × 103 particle/kg dry weight. Polymer composition is similar to what found in raw wastewater, containing a high proportion of polyethylene and polypropylene. Thus, the results indicated the persistence of MPs in sewer network during transport during dry weather periods to treatment facilities. Once resuspension of sewer deposits happens, MPs can be released into water flow and get discharged along with CSOs. This highlights another potential pathway of MPs into freshwater environment.

Global resilience analysis of combined sewer systems under continuous hydrologic simulation

Managing and reducing combined sewer overflow (CSO) discharges is crucial for enhancing the resilience of combined sewer systems (CSS). However, the absence of a standardised resilience analysis approach poses challenges in developing effective discharge reduction strategies. To address this, our study presents a top-down method that expands the existing Global Resilience Analysis to quantify resilience performance in CSS. This approach establishes a link between threats (e.g., rainfall) and impacts (e.g., CSOs) through continuous and long-term simulation, accommodating various rainfall patterns, including extreme events. We assess CSO discharge impacts from a resilience perspective by introducing eight new metrics. We conducted a case study in Fehraltorf, Switzerland, analysing the performance of three green infrastructure (GI) types (bioretention cells, green roofs, and permeable pavements) over 38 years. The results demonstrated that GI enhanced all resilience indices, with variations observed in individual CSO performance metrics and their system locations. Notably, in Fehraltorf, green roofs emerged as the most effective GI type for improving resilience, while the downstream outfall displayed the highest resilience enhancement. Overall, our proposed method enables a shift from event-based to continuous simulation analysis, providing a standardised approach for resilience assessment. This approach informs the development of strategies for CSO discharge reduction and the enhancement of CSS resilience.

A One-Health environmental risk assessment of contaminants of emerging concern in London's waterways throughout the SARS-CoV-2 pandemic

The SARS-CoV-2 pandemic had huge impacts on global urban populations, activity and health, yet little is known about attendant consequences for urban river ecosystems. We detected significant changes in occurrence and risks from contaminants of emerging concern (CECs) in waterways across Greater London (UK) during the pandemic. We were able to rapidly identify and monitor large numbers of CECs in n = 390 samples across 2019-2021 using novel direct-injection liquid chromatography-mass spectrometry methods for scalable targeted analysis, suspect screening and prioritisation of CEC risks. A total of 10,029 measured environmental concentrations (MECs) were obtained for 66 unique CECs. Pharmaceutical MECs decreased during lockdown in 2020 in the R. Thames (p ≤ 0.001), but then increased significantly in 2021 (p ≤ 0.01). For the tributary rivers, the R. Lee, Beverley Brook, R. Wandle and R. Hogsmill were the most impacted, primarily via wastewater treatment plant effluent and combined sewer overflows. In the R. Hogsmill in particular, pharmaceutical MEC trends were generally correlated with NHS prescription statistics, likely reflecting limited wastewater dilution. Suspect screening of ∼ 1,200 compounds tentatively identified 25 additional CECs at the five most impacted sites, including metabolites such as O-desmethylvenlafaxine, an EU Watch List compound. Lastly, risk quotients (RQs) ≥ 0.1 were calculated for 21 compounds across the whole Greater London freshwater catchment, of which seven were of medium risk (RQ ≥ 1.0) and three were in the high-risk category (RQ ≥ 10), including imidacloprid (RQ = 19.6), azithromycin (15.7) and diclofenac (10.5). This is the largest spatiotemporal dataset of its kind for any major capital city globally and the first for Greater London, representing ∼ 16 % of the population of England, and delivering a foundational One-Health case study in the third largest city in Europe across a global pandemic.

Estimation of the impact of combined sewer overflows on surface water quality in a sparsely monitored area

Combined sewer overflows (CSOs) can have a severe negative, local impact on surface water systems. To assure good ecological surface water quality and drinking water production that meets the demands, the impact of sewer system overflows on the surrounding water bodies for current and future climate conditions needs to be assessed. Typically, integrated, detailed hydrological and hydrodynamic water quantity and quality models are used for this purpose, but often data and computational resource requirements limit their applicability. Therefore, an alternative computationally efficient, integrated water quantity and quality model of sewer systems and their receiving surface waters is proposed to assess the impact of CSOs on surface water quality in a sparsely observed area. A conceptual model approach to estimate CSO discharges is combined with an empirical model for estimating CSO pollutant concentrations based on waste water treatment plant influent observations. Both methods are compared with observations and independent results of established reference methods as to evaluate their performance. The methodology is demonstrated by modelling the current impact of CSOs on the water abstraction area of a major drinking water production centre in Flanders, Belgium. It is concluded that the proposed conceptual models achieve similar results for daily WWTP effluent and CSO frequency, whereby the accumulated CSO volume is similar to more detailed full hydrodynamic models. Further, the estimated pollutant concentrations correspond with another dataset based on high resolution sampled overflows. As a result, the proposed computational efficient method can give insights in the impact of CSOs on the water quality at a catchment level and can be used for planning monitoring campaigns or performing analyses of e.g. the current and future water availability for a data scarce areas.

Evaluating the transmission risk of SARS-CoV-2 from sewage pollution

The presence of SARS-CoV-2 in untreated sewage has been confirmed in many countries but its incidence and infection risk in contaminated waters is poorly understood. The River Thames in the UK receives untreated sewage from 57 Combined Sewer Overflows (CSOs), with many discharging dozens of times per year. This study investigated if such discharges provide a pathway for environmental transmission of SARS-CoV-2. Samples of wastewater, surface water, and sediment collected close to six CSOs on the River Thames were assayed over eight months for SARS-CoV-2 RNA and infectious virus. Bivalves were also sampled as an indicator species of viral bioaccumulation. Sediment and water samples from the Danube and Sava rivers in Serbia, where raw sewage is also discharged in high volumes, were assayed as a positive control. No evidence of SARS-CoV-2 RNA or infectious virus was found in UK samples, in contrast to RNA positive samples from Serbia. Furthermore, this study shows that infectious SARS-CoV-2 inoculum is stable in Thames water and sediment for <3 days, while SARS-CoV-2 RNA is detectable for at least seven days. This indicates that dilution of wastewater likely limits environmental transmission, and that detection of viral RNA alone is not an indication of pathogen spillover.

Complexing characteristics between Cu(Ⅱ) ions and dissolved organic matter in combined sewer overflows: Implications for the removal of heavy metals by enhanced coagulation

Enhanced coagulation has been widely used in storm tanks to remove heavy metal ions (HMs) from combined sewer overflows (CSOs), but faces challenges on removing the HMs bound to dissolved organic matter (DOM) with small molecular weight (MW). DOM ubiquitously existing in CSOs generally contains a large distribution range of MW, which can significantly impact the MW distribution of HMs by complexing reaction, thereby adding uncertainties for the removal efficiency of coagulation. Therefore, realizing the potential MW distribution of the HMs bound to CSO-DOM is greatly important for cost-effectively removing HMs from CSOs in the coagulation process. This paper presents a comprehensive approach of ultrafiltration, fluorescence quenching titration, excitation-emission matrix parallel factor analysis, complexation model, and two-dimensional correlation fluorescence spectroscopy for exploring the MW-based complexing characteristics between Cu(II) ions and CSO-DOM components. Results show that: (1) Cu(II) ions that bound to the CSO-DOM were mainly distributed in the MW range of <5 kDa, which makes them very difficult to be removed from CSOs by coagulation technique. (2) Concentration effect and molecular composition exerted great impacts on the MW distribution of the Cu(II) ions bound to CSO-DOM. (3) The humic-like component of terrestrial origin with the MW range of 100 kDa∼0.45 μm possessed high binding stability, capacity, and priority with Cu(II) ions, and they could be used at a high concentration to promote the removal efficiency of coagulation for Cu(Ⅱ) ions of CSOs by competitive complexation and inter-molecular bridging.

Urban pathways of biocides towards surface waters during dry and wet weathers: Assessment at the Paris conurbation scale

Eighteen biocides used in building materials and domestic products were monitored in wastewater treatment plants (WWTPs) during dry weather and in combined sewer overflows (CSOs) during wet weather in the Paris conurbation. The aims of this study were to (i) acquire data on biocides in urban waters, which are very scarce up to now, (ii) identify their origins in CSOs with the perspective of reducing these contaminants at source, and (iii) compare and rank biocide pathways to the river (dry vs. wet weather) at the annual and conurbation scales. The results showed the ubiquity of the 18-targeted biocides in WWTP waters and CSOs. High concentrations of methylisothiazolinone, benzisothiazolinone (0.2-0.9 μg/L) and benzalkonium C12 (0.5-6 μg/L) were measured in wastewater. Poor WWTP removals (< 50 %) were observed for most of the biocides. Both wastewater (mainly domestic uses) and stormwater (leaching from building materials) contributed to the CSO contamination. However, benzisothiazolinone mainly came from wastewater whereas diuron, isoproturon, terbutryn, carbendazim, tebuconazole, and mecoprop mainly came from stormwater. Annual mass loads discharged by WWTPs and CSOs into the Seine River were estimated using a stochastic approach (Monte Carlo simulations) at the conurbation scale and showed that WWTP discharges are the major entry pathway.

The presence and significance of microplastics in surface water in the Lower Hudson River Estuary 2016-2019: A research note

Microplastics are a major environmental issue of concern. Since 2016, Hudson River Park has collaborated with Brooklyn College to survey microplastics within Park waters between Chambers and 59th Streets in Manhattan. It was hypothesized that microplastic concentration is influenced by proximity to combined sewer overflow (CSO) points, precipitation, and tides. Samples were collected at channel and near-shore locations at downtown and midtown sites. Microplastics were analyzed following NOAA methods via stereo microscope. Concentrations in 2018 were higher than in 2016, 2017 and 2019 ((ANOVA F (1,70) = 5.2, p < 0.03*; post hoc Tukey test p < 0.009*)), and near-shore sites tended to exhibit higher concentrations than channel sites (ANOVA and post-hoc Tukey: p < 0.03*). Microfibers were not fully accounted for and fragments were highly prevalent in all samples (~70%). Additional data will improve the understanding of the presence of microplastics in the Lower Hudson and elucidate the effects of wet weather on plastic concentrations.

London's river of plastic: High levels of microplastics in the Thames water column

This opportunistic study focussed on the quantification of microplastics in the River Thames water column, the catchment responsible for draining Greater London. Two sites on the tidal Thames were sampled; one upstream of the City of London at Putney, and the other downstream at Greenwich. Water column samples were collected from June through to October 2017, being taken on the ebb and flood tides, at the surface and a depth of 2 m. Microplastics (excluding microfibres) were identified to test whether the load varied between the two sites in relation to tide, depth and season. Secondary microplastics, films and fragments, contributed 93.5% of all those found at Putney and Greenwich. Site, tide, depth and month affected density, with the combined interaction of month and site found to have the greatest influence on microplastics. Fourier Transform Infrared Spectroscopy analysis showed that polyethylene and polypropylene were the most common polymers collected from the River, suggesting broken down packaging was the primary source of microplastics in these samples. Excluding microfibres, the estimate of microplastics in the water column was 24.8 per m³ at Putney and 14.2 per m³ at Greenwich. These levels are comparable to some of the highest recorded in the world.

Assessing the role of microbial communities in the performance of constructed wetlands used to treat combined sewer overflows

Combined sewer overflows are contaminated with various micropollutants which pose risk to both environmental and human health. Some micropollutants, such as carbamazepine and sulfamethoxazole, are very persistent and difficult to remove from wastewater. Event loaded vertical-flow constructed wetlands (retention soil filters; RSFs) have proven to be effective in the treatment of combined sewer overflows for a wide range of pollutants. However, little is known about how microbial communities contribute to the treatment efficiency, specifically to the reduction of micropollutants. To the best of our knowledge, this is the first study attempting to close this gap. Microbial communities in pilot-scale RSFs were investigated, which showed explicit grouping of metabolic activity at different filter depths with some differential abundance of identified genera. The highest microbial activity was found in the top layer of 0.75 m deep filters, whereas homogeneous activity dominated in a 0.50 m deep filter, indicating oxygen availability to be a limiting factor of the metabolic activity in RSFs. The removal efficiencies of all investigated organic trace substances were correlated to the utilization of specific carbon sources. Most notable is the correlation between the carbon source glucose-1-phosphate and the removal of metoprolol. The strongest correlations for other substances were the removal of diclofenac to the utilization of the carbohydrate i-erythritole; bisphenol A to carbohydrate α-d-lactose, and 1-H-benzotriazole to carbonic acid D-galacturonic acid. Those results are supported by positive correlations of specific microbial genera with both the utilization of the above mentioned carbon sources and the removal efficiency for the respective micropollutants. Most notable is correlation of Tetrasphaera and the removal of benzotriazole and diclofenac.

Tracking the contribution of multiple raw and treated wastewater discharges at an urban drinking water supply using near real-time monitoring of β-d-glucuronidase activity

Past waterborne outbreaks have demonstrated that informed vulnerability assessment of drinking water supplies is paramount for the provision of safe drinking water. Although current monitoring frameworks are not designed to account for short-term peak concentrations of fecal microorganisms in source waters, the recent development of online microbial monitoring technologies is expected to fill this knowledge gap. In this study, online near real-time monitoring of β-d-glucuronidase (GLUC) activity was conducted for 1.5 years at an urban drinking water intake impacted by multiple point sources of fecal pollution. Parallel routine and event-based monitoring of E. coli and online measurement of physico-chemistry were performed at the intake and their dynamics compared over time. GLUC activity fluctuations ranged from seasonal to hourly time scales. All peak contamination episodes occurred between late fall and early spring following intense rainfall and/or snowmelt. In the absence of rainfall, recurrent daily fluctuations in GLUC activity and culturable E. coli were observed at the intake, a pattern otherwise ignored by regulatory monitoring. Cross-correlation analysis of time series retrieved from the drinking water intake and an upstream Water Resource Recovery Facility (WRRF) demonstrated a hydraulic connection between the two sites. Sewage by-passes from the same WRRF were the main drivers of intermittent GLUC activity and E. coli peaks at the drinking water intake following intense precipitation and/or snowmelt. Near real-time monitoring of fecal pollution through GLUC activity enabled a thorough characterization of the frequency, duration and amplitude of peak contamination periods at the urban drinking water intake while providing crucial information for the identification of the dominant upstream fecal pollution sources. To the best of our knowledge, this is the first characterization of a hydraulic connection between a WRRF and a downstream drinking water intake across hourly to seasonal timescales using high frequency microbial monitoring data. Ultimately, this should help improve source water protection through catchment mitigation actions, especially in a context of de facto wastewater reuse.

Assessment of input of organic micropollutants and microplastics into the Baltic Sea by urban waters

We assess how different micropollutants and microplastics, connected to wastewater are introduced into the Baltic Sea. The relevance of untreated wastewater, treated wastewater, treated and untreated rain runoff, as well as combined sewer overflow (CSO), is assessed in respect to mass balance, as well as relative inflows of micropollutants and -plastics into the Baltic Sea. To achieve this, modelling based on data on exemplary sewer systems and measured micropollutant concentrations in the single sources were used. Most compounds reach the receiving Baltic Sea via treated wastewater. A few exceptions are compounds that are removed to a very high extent in wastewater treatment plants. For these compounds, the emissions with stormwater (e.g., terbutryn) or untreated wastewater (e.g., triclosan) are dominating. Additionally, compounds that are discharged with the water that is running off urban surfaces are introduced into marine areas via rain runoff. These data are used to forecast a total mass load and concentrations that can be expected in the Baltic Sea. Massloads are expected to be between 0.1 and 5.9 t/a for triclosan and TCPP (tris (2-chloropropyl) phosphate) and 0.2 t/a for microplastic particles. The expected concentrations in open Baltic Sea waters range from 0.01 to 26 ng/L.

Normalized dynamic behavior of combined sewer overflow discharges for source water characterization and management

As one of the major sources of surface water quality impairments, Combined Sewer Overflows (CSOs) are of concern when receiving waters are used for drinking water supplies. Given the large number and variability in CSO discharges and loads, there is a need for a general methodology for estimating discharges for environmental planning and source water protection. Detailed data on CSO flowrates, contaminant concentrations including Total Suspended Solids (TSS), Escherichia coli (E. coli), caffeine (CAF) and acetaminophen (ACE) were used to develop a simple loading model that was then verified using discharge and concentration data from other CSO and stormwater events in the literature. The variability of the parameters within each event was analyzed by normalizing flowrate, concentration and event duration to their respective peak values. The normalized flowrate data indicate that the second decile of the discharge periods was associated with peak flowrates. The dynamic behavior of CSO flowrates can be characterized by a linearly increasing trend and then a logarithmically decreasing trend in terms of normalized values. The samples captured during the first decile of the events were illustrated to be a better representation of peak concentrations of all four contaminants. By analyzing the discharge period in three sections (i.e. 1st decile, 2nd decile and remainder), a semi-probabilistic CSO loading model is proposed for the entire discharge period taking into account the variability of the phenomena. Findings can help water managers and utilities to characterize their source waters for better planning and to more efficiently design sampling campaigns for capturing peak concentrations at drinking water treatment plants.

Acute toxicity and risk evaluation of the CSO disinfectants performic acid, peracetic acid, chlorine dioxide and their by-products hydrogen peroxide and chlorite

The ecotoxicological evaluation of combined sewer overflow (CSO) disinfectants, with their degradation products, is important for ensuring safe use. For this form of toxicity, data for organisms representing different trophic levels are needed. We studied the toxicity of the alternative disinfectants peracetic acid (PAA), performic acid (PFA) and chlorine dioxide (ClO₂) and their degradation products hydrogen peroxide (H₂O₂) and chlorite (ClO₂^-) on Vibrio fischeri and Daphnia magna. ClO₂ was more toxic to D. magna (EC₅₀ < 0.09 mg/L) and PFA was most toxic to V. fischeri (EC₅₀ 0.24 mg/L). EC₅₀ of PFA, PAA, ClO₂, H₂O₂ and ClO₂^- on D. magna were 0.85, 0.78, <0.09, 3.46 and 0.36 mg/L, respectively. Similarly, EC₅₀ of PFA, PAA, ClO₂, H₂O₂ and ClO₂^- on V. fischeri were 0.24, 0.42, 1.10, 5.67 and 30.93 mg/L, respectively. For both PFA and ClO₂, the degradation in water was faster than for PAA, H₂O₂ and chlorite. Using these data together with literature values, we derived environmental quality standards. By combining these with typical concentrations of disinfectants used for CSOs, we estimated the dilution required for discharging CSOs after disinfection, which can be used for quick assessment of the environmental feasibility of disinfection systems at specific CSO sites. Minimal dilutions in the receiving water, in the orders of 44, 70 or 138-fold, are needed for ClO₂, PFA and PAA, respectively. This highlights PFA as the most widely applicable disinfectant, taking into account both its efficiency and the lower risk of unwanted environmental effects.

Assessment of 34 dissolved and particulate organic and metallic micropollutants discharged at the outlet of two contrasted urban catchments

The assessment of micropollutants in urban wet weather discharges is essential to improve the knowledge of the impact of such discharges on receiving waters. This study assessed the quality of combined sewer overflows (CSOs) in Ecully (residential catchment) and stormwater runoff in Chassieu (industrial catchment) during rain events by providing data on occurrence and total event mean concentrations (EMC_t) of 34 priority substances (PS) (9 metals, 13 pesticides, 6 PAHs, 4 alkylphenols and 2 chlorobenzenes) in dissolved and particulate fractions. Over 34 substances monitored, 23 were quantified in urban wet weather discharges of both catchments. For both catchments, 9 metals and 6 PAHs monitored were always quantified, reflecting their ubiquitous presence. For other organic pollutants, only 5 pesticides were quantified and only 2 alkyphenols were measured solely in dissolved fraction. A significant site-to-site difference was observed for metals, PAHs and alkylphenols. The highest concentrations were measured in stormwater runoff in Chassieu vs. Ecully. On the contrary, the diuron concentrations were highest in CSO discharges in Ecully. Distribution of the PS between particulate and dissolved fractions provides information for urban stormwater practitioners. Most PS in urban wet weather discharges were mainly linked to particles (PAHs, Pb, Ti for example). The comparison between daily flows of wastewater treatment plants during dry weather and CSOs daily flows in Ecully showed that stormwater was the most important source of contamination for fluoranthene, benzo(b)fluoranthene and benzo(k)fluoranthene and 7 metals (As, Cr, Co, Cu, Pb, Ti and Zn) in receiving water bodies, but not for pesticides and alkylphenols.

Characterizing heavy metals in combined sewer overflows and its influence on microbial diversity

This study characterized the pollution levels and potential ecological risk of heavy metals in combined sewer overflows (CSOs) and their effects on microbial diversity in nearby riparian sediments. The chemical fractionations of Zn, Cd, Cr, and Cu in dry-weather flows, wet-weather flows (CSO discharges), sewer sediments, and surface runoffs were determined. Geo-accumulation (I_geo) and ecological risk (RI) indexes were employed for metal risk assessment. DNA extraction and polymerase chain reaction (PCR) amplification on the Illumina MiSeq platform were conducted. The results show that heavy metals contents in fine-sized fractions have higher values than those in coarse-sized fractions. Chemical fractionation analysis suggests that Zn and Cd are two of the most bioavailable metals impacted by anthropogenic activities. Cr and Cu contents in CSOs are relatively stable and could exist for extended periods. According to the RI analysis, CSOs pose a considerable risk (RI-G2) to receiving waters due to the higher bioavailability of Cd, which was consistent with the I_geo index. Furthermore, under the stress of the highly-bioavailable Cd and Cu, Gram +ves in the riparian benthic sediment gradually became dominant with metal-tolerance property. Therefore, long-term exposure to highly bioavailable metals could exhibit great impacts on microbial diversity.

DSM-flux: A new technology for reliable Combined Sewer Overflow discharge monitoring with low uncertainties

In the past ten years, governments from the European Union have been encouraged to collect volume and quality data for all the effluent overflows from separated stormwater and combined sewer systems that result in a significant environmental impact on receiving water bodies. Methods to monitor and control these flows require improvements, particularly for complex Combined Sewer Overflow (CSO) structures. The DSM-flux (Device for Stormwater and combined sewer flows Monitoring and the control of pollutant fluxes) is a new pre-designed and pre-calibrated channel that provides appropriate hydraulic conditions suitable for measurement of overflow rates and volumes by means of one water level gauge. In this paper, a stage-discharge relation for the DSM-flux is obtained experimentally and validated for multiple inflow hydraulic configurations. Uncertainties in CSO discharges and volumes are estimated within the Guide to the expression of Uncertainty in Measurement (GUM) framework. Whatever the upstream hydraulic conditions are, relative uncertainties are lower than 15% and 2% for the investigated discharges and volumes, respectively.

Impacts from urban water systems on receiving waters - How to account for severe wet-weather events in LCA?

Sewage systems are a vital part of the urban infrastructure in most cities. They provide drainage, which protects public health, prevents the flooding of property and protects the water environment around urban areas. On some occasions sewers will overflow into the water environment during heavy rain potentially causing unacceptable impacts from releases of untreated sewage into the environment. In typical Life Cycle Assessment (LCA) studies of urban wastewater systems (UWS), average dry-weather conditions are modelled while wet-weather flows from UWS, presenting a high temporal variability, are not currently accounted for. In this context, the loads from several storm events could be important contributors to the impact categories freshwater eutrophication and ecotoxicity. In this study we investigated the contributions of these wet-weather-induced discharges relative to average dry-weather conditions in the life cycle inventory for UWS. In collaboration with the Paris public sanitation service (SIAAP) and Observatory of Urban Pollutants (OPUR) program researchers, this work aimed at identifying and comparing contributing flows from the UWS in the Paris area by a selection of routine wastewater parameters and priority pollutants. This collected data is organized according to archetypal weather days during a reference year. Then, for each archetypal weather day and its associated flows to the receiving river waters (Seine), the parameters of pollutant loads (statistical distribution of concentrations and volumes) were determined. The resulting inventory flows (i.e. the potential loads from the UWS) were used as LCA input data to assess the associated impacts. This allowed investigating the relative importance of episodic wet-weather versus "continuous" dry-weather loads with a probabilistic approach to account for pollutant variability within the urban flows. The analysis at the scale of one year showed that storm events are significant contributors to the impacts of freshwater eutrophication and ecotoxicity compared to those arising from treated effluents. At the rain event scale the wet-weather contributions to these impacts are even more significant, accounting for example for up to 62% of the total impact on freshwater ecotoxicity. This also allowed investigating and discussing the ecotoxicity contribution of each class of pollutants among the broad range of inventoried substances. Finally, with such significant contributions of pollutant loads and associated impacts from wet-weather events, further research is required to better include temporally-differentiated emissions when evaluating eutrophication and ecotoxicity. This will provide a better understanding of how the performance of an UWS system affects the receiving environment for given local weather conditions.

Comparing peracetic acid and hypochlorite for disinfection of combined sewer overflows: Effects of suspended-solids and pH

Peracetic acid (PAA) is an alternative disinfectant that may be effective for combined sewer overflow (CSO) disinfection, but little is known about the effect of particle size on PAA disinfection efficiency. In this work, PAA and hypochlorite were compared as disinfectants, with a focus on the effect of wastewater particles. Inactivation experiments were conducted on suspended cultures of Escherichia coli and wastewater suspended solids. Tested size fractions included particle diameters <10μm, <100μm, and raw wastewater. Chlorine disinfection efficiency decreased with increasing solids size. However, solids size had little effect on PAA disinfection. The PAA disinfection efficiency decreased at pH values above 7.5. Live/dead staining revealed that PAA disinfection leaves most cells in a viable but non-culturable condition. Fourier transform infrared spectroscopy (FTIR) analyses suggests that PAA and hypochlorite may inactivate E. coli bacteria by similar mechanisms.

Three-dimensional model to capture the fate and transport of combined sewer overflow discharges: A case study in the Chicago Area Waterway System

We used a numerical model to analyze the impact of combined sewer overflows (CSOs) in the hydrodynamics and water quality of the Chicago Area Waterway System (CAWS). We coupled the Environmental Fluid Dynamics Code (EFDC) with the Water Quality Analysis Simulation Program (WASP) to perform three-dimensional simulations of the hydrodynamics and water quality in CAWS. The analysis was performed for two different storms: (i) May 6, 2009 representing a 6-hour duration 4-month return period, and (ii) September 12, 2008 representing a 48-hour duration 100-year return period. Results from the simulations show distinct differences between the two storms. During the May 2009 storm there was only one major CSO pumping event with negligible impact on the water quality of CAWS. During the September 2008 storm there were several CSOs that impacted the hydrodynamics and water quality of CAWS. In particular, CSOs during the September 2008 event induced a reversal flow in CAWS, with a plume of constituents that traveled in the opposite direction as water does under normal conditions. However, the simulation results show that CSOs events in CAWS take place during periods of high rainfall, thus the discharge of CSOs is significantly diluted along the CAWS. As a result, the concentrations of organic matter and inorganic nutrients observed at the downstream boundary in CAWS were significantly lower than those recorded at the CSOs outfalls and are within the limits established in the regulation for regular effluents. These results suggest that even during storms events with significant CSOs into the CAWS there is a significant dilution that reduce the impact in the water quality at the system boundaries.

Organic micropollutants discharged by combined sewer overflows - Characterisation of pollutant sources and stormwater-related processes

To characterise emissions from combined sewer overflows (CSOs) regarding organic micropollutants, a monitoring study was undertaken in an urban catchment in southwest Stuttgart, Germany. The occurrence of 69 organic micropollutants was assessed at one CSO outfall during seven rain events as well as in the sewage network at the influent of the wastewater treatment plant (WWTP) and in the receiving water. Several pollutant groups like pharmaceuticals and personal care products (PPCPs), urban biocides and pesticides, industrial chemicals, organophosphorus flame retardants, plasticisers and polycyclic aromatic hydrocarbons (PAHs) were chosen for analysis. Out of the 69 monitored substances, 60 were detected in CSO discharges. The results of this study show that CSOs represent an important pathway for a wide range of organic micropollutants from wastewater systems to urban receiving waters. For most compounds detected in CSO samples, event mean concentrations varied between the different events in about one order of magnitude range. When comparing CSO concentrations with median wastewater concentrations during dry weather, two main patterns could be observed depending on the source of the pollutant: (i) wastewater is diluted by stormwater; (ii) stormwater is the most important source of a pollutant. Both wastewater and stormwater only play an important role in pollutant concentration for a few compounds. The proportion of stormwater calculated with the conductivity is a suitable indicator for the evaluation of emitted loads of dissolved wastewater pollutants, but not for all compounds. In fact, this study demonstrates that remobilisation of in-sewer deposits contributed from 10% to 65% to emissions of carbamazepine in CSO events. The contribution of stormwater to CSO emitted loads was higher than 90% for all herbicides as well as for PAHs. Regarding the priority substance di(2-ethylhexyl)phthalate (DEHP), this contribution varied between 39% and 85%. The PAH concentrations found along the river indicate environmental risk, especially during rainfall events.

Cumulative effects of fecal contamination from combined sewer overflows: Management for source water protection

The quality of a drinking water source depends largely on upstream contaminant discharges. Sewer overflows can have a large influence on downstream drinking water intakes as they discharge untreated or partially treated wastewaters that may be contaminated with pathogens. This study focuses on the quantification of Escherichia coli discharges from combined sewer overflows (CSOs) and the dispersion and diffusion in receiving waters in order to prioritize actions for source water protection. E. coli concentrations from CSOs were estimated from monitoring data at a series of overflow structures and then applied to the 42 active overflow structures between 2009 and 2012 using a simple relationship based upon the population within the drainage network. From these estimates, a transport-dispersion model was calibrated with data from a monitoring program from both overflow structures and downstream drinking water intakes. The model was validated with 15 extreme events such as a large number of overflows (n > 8) or high concentrations at drinking water intakes. Model results demonstrated the importance of the cumulative effects of CSOs on the degradation of water quality downstream. However, permits are typically issued on a discharge point basis and do not consider cumulative effects. Source water protection plans must consider the cumulative effects of discharges and their concentrations because the simultaneous discharge of multiple overflows can lead to elevated E. coli concentrations at a drinking water intake. In addition, some CSOs have a disproportionate impact on peak concentrations at drinking water intakes. As such, it is recommended that the management of CSOs move away from frequency based permitting at the discharge point to focus on the development of comprehensive strategies to reduce cumulative and peak discharges from CSOs upstream of drinking water intakes.

Coordinated management of combined sewer overflows by means of environmental decision support systems

During heavy rainfall, the capacity of sewer systems and wastewater treatment plants may be surcharged producing uncontrolled wastewater discharges and a depletion of the environmental quality. Therefore there is a need of advanced management tools to tackle with these complex problems. In this paper an environmental decision support system (EDSS), based on the integration of mathematical modeling and knowledge-based systems, has been developed for the coordinated management of urban wastewater systems (UWS) to control and minimize uncontrolled wastewater spills. Effectiveness of the EDSS has been tested in a specially designed virtual UWS, including two sewers systems, two WWTP and one river subjected to typical Mediterranean rain conditions. Results show that sewer systems, retention tanks and wastewater treatment plants improve their performance under wet weather conditions and that EDSS can be very effective tools to improve the management and prevent the system from possible uncontrolled wastewater discharges.

The effects of combined sewer overflow events on riverine sources of drinking water

This study was set out to investigate the impacts of Combined Sewer Overflows (CSOs) on the microbiological water quality of a river used as a source of drinking water treatment plants. Escherichia coli concentrations were monitored at various stations of a river segment located in the Greater Montreal Area including two Drinking Water Intakes (DWIs) in different weather conditions (dry weather and wet weather (precipitation and snowmelt period)). Long-term monitoring data (2002-2011) at DWIs revealed good microbiological water quality with E. coli median concentrations of 20 and 30 CFU/100 mL for DWI-1 and DWI-2 respectively. However, E. coli concentration peaks reached up to 510 and 1000 CFU/100 mL for both DWIs respectively. Statistical Process Control (SPC) analysis allowed the identification of E. coli concentration peaks in almost a decade of routine monitoring data at DWIs. Almost 80% of these concentrations were linked to CSO discharges caused by precipitation exceeding 10 mm or spring snowmelt. Dry weather monitoring confirmed good microbiological water quality. Wet weather monitoring showed an increase of approximately 1.5 log of E. coli concentrations at DWIs. Cumulative impacts of CSO discharges were quantified at the river center with an increase of approximately 0.5 log of E. coli concentrations. Caffeine (CAF) was tested as a potential chemical indicator of CSO discharges in the river and CAF concentrations fell within the range of previous measurements performed for surface waters in the same area (∼20 ng/L). However, no significant differences were observed between CAF concentrations in dry and wet weather, as the dilution potential of the river was too high. CSO event based monitoring demonstrated that current bi-monthly or weekly compliance monitoring at DWIs underestimate E. coli concentrations entering DWIs and thus, should not be used to quantify the risk at DWIs. High frequency event-based monitoring is a desirable approach to establish the importance and duration of E. coli peak concentrations entering DWIs.

Impacts of global change on the concentrations and dilution of combined sewer overflows in a drinking water source

This study presents an analysis of climate change impacts on a large river located in Québec (Canada) used as a drinking water source. Combined sewer overflow (CSO) effluents are the primary source of fecal contamination of the river. An analysis of river flowrates was conducted using historical data and predicted flows from a future climate scenario. A spatio-temporal analysis of water quality trends with regard to fecal contamination was performed and the effects of changing flowrates on the dilution of fecal contaminants were analyzed. Along the river, there was a significant spatial trend for increasing fecal pollution downstream of CSO outfalls. Escherichia coli concentrations (upper 95th percentile) increased linearly from 2002 to 2012 at one drinking water treatment plant intake. Two critical periods in the current climate were identified for the drinking water intakes considering both potential contaminant loads and flowrates: local spring snowmelt that precedes river peak flow and extra-tropical storm events that occur during low flows. Regionally, climate change is expected to increase the intensity of the impacts of hydrological conditions on water quality in the studied basin. Based on climate projections, it is expected that spring snowmelt will occur earlier and extreme spring flowrates will increase and low flows will generally decrease. High and low flows are major factors related to the potential degradation of water quality of the river. However, the observed degradation of water quality over the past 10 years suggests that urban development and population growth may have played a greater role than climate. However, climate change impacts will likely be observed over a longer period. Source water protection plans should consider climate change impacts on the dilution of contaminants in addition to local land uses changes in order to maintain or improve water quality.

Evaluating rain gardens as a method to reduce the impact of sewer overflows in sources of drinking water

The implications of climate change and changing precipitation patterns need to be investigated to evaluate mitigation measures for source water protection. Potential solutions need first to be evaluated under present climate conditions to determine their utility as climate change adaptation strategies. An urban drainage network receiving both stormwater and wastewater was studied to evaluate potential solutions to reduce the impact of combined sewer overflows (CSOs) in a drinking water source. A detailed hydraulic model was applied to the drainage basin to model the implementation of best management practices at a drainage basin scale. The model was calibrated and validated with field data of CSO flows for seven events from a survey conducted in 2009 and 2010. Rain gardens were evaluated for their reduction of volumes of water entering the drainage network and of CSOs. Scenarios with different levels of implementation were considered and evaluated. Of the total impervious area within the basin directly connected to the sewer system, a maximum of 21% could be alternately directed towards rain gardens. The runoff reductions for the entire catchment ranged from 12.7% to 19.4% depending on the event considered. The maximum discharged volume reduction ranged from 13% to 62% and the maximum peak flow rate reduction ranged from 7% to 56%. Of concern is that in-sewer sediment resuspension is an important process to consider with regard to the efficacy of best management practices aimed at reducing extreme loads and concentrations. Rain gardens were less effective for large events, which are of greater importance for drinking water sources. These practices could increase peak instantaneous loads as a result of greater in-sewer resuspension during large events. Multiple interventions would be required to achieve the objectives of reducing the number, total volumes and peak contaminant loads of overflows upstream of drinking water intakes.

Surrogate measures for providing high frequency estimates of total phosphorus concentrations in urban watersheds

Until robust in situ sensors for total phosphorus (TP) are developed, continuous water quality measurements have the potential to be used as surrogates for generating high frequency estimates. Their use has widespread implications for water quality monitoring programmes considering that TP, in particular, is generally recognised as the limiting factor in the process of eutrophication. Surrogate measures for TP concentration, such as turbidity, have proved useful within natural and agricultural contexts, but their predictive capability for urban watersheds is considered more difficult, due to the different sources of TP, though a strict relationship with turbidity/suspended matter has been clearly described even for these environments. In this context, we investigated this still unresolved problem for high frequency estimation of TP concentration in urban environments by monitoring a medium-sized (71 km(2)) urban watershed (Lambro River watershed, north Italy) in which we detected 60 active combined sewer overflows, and an its natural sub-basin for comparison. We found two different relationships between turbidity and TP concentration in the investigated urban watershed that differently describe the prevalence of TP from point sources (domestic wastewaters) or diffuse origin (surface runoff). In this regard, we first characterise the prevailing sources of TP by using a marker for detecting domestic wastewater contamination (caffeine), then we describe the mutual relationships amongst the continuously monitored variables (in our case the occurrence of the First Flush and the clockwise turbidity/discharge hysteresis). Afterwards we discriminate, by observing variables that are continuously monitored (in our case, the discharge and the turbidity), amongst the continuous surrogate records according to their sources. In conclusion, we are able to apply the relevant turbidity/TP regression equations to each turbidity record and, thus, estimate the respective TP concentrations with high frequency. If traditional grab sampling techniques had been employed, the contributions of point sources (up to 34% across 237 monitored days) to the total estimated loads would not have been correctly evaluated, whilst the high frequency monitoring is able to catch the dynamics that occur over time scales of a few hours. We conclude that the reasonable uncertainty obtained in this study can be achieved in other urban watersheds, but further studies are required for watersheds of differing sizes and degrees of urbanisation.

Surrogate measures for providing high frequency estimates of total phosphorus concentrations in urban watersheds

Until robust in situ sensors for total phosphorus (TP) are developed, continuous water quality measurements have the potential to be used as surrogates for generating high frequency estimates. Their use has widespread implications for water quality monitoring programmes considering that TP, in particular, is generally recognised as the limiting factor in the process of eutrophication. Surrogate measures for TP concentration, such as turbidity, have proved useful within natural and agricultural contexts, but their predictive capability for urban watersheds is considered more difficult, due to the different sources of TP, though a strict relationship with turbidity/suspended matter has been clearly described even for these environments. In this context, we investigated this still unresolved problem for high frequency estimation of TP concentration in urban environments by monitoring a medium-sized (71 km(2)) urban watershed (Lambro River watershed, north Italy) in which we detected 60 active combined sewer overflows, and an its natural sub-basin for comparison. We found two different relationships between turbidity and TP concentration in the investigated urban watershed that differently describe the prevalence of TP from point sources (domestic wastewaters) or diffuse origin (surface runoff). In this regard, we first characterise the prevailing sources of TP by using a marker for detecting domestic wastewater contamination (caffeine), then we describe the mutual relationships amongst the continuously monitored variables (in our case the occurrence of the First Flush and the clockwise turbidity/discharge hysteresis). Afterwards we discriminate, by observing variables that are continuously monitored (in our case, the discharge and the turbidity), amongst the continuous surrogate records according to their sources. In conclusion, we are able to apply the relevant turbidity/TP regression equations to each turbidity record and, thus, estimate the respective TP concentrations with high frequency. If traditional grab sampling techniques had been employed, the contributions of point sources (up to 34% across 237 monitored days) to the total estimated loads would not have been correctly evaluated, whilst the high frequency monitoring is able to catch the dynamics that occur over time scales of a few hours. We conclude that the reasonable uncertainty obtained in this study can be achieved in other urban watersheds, but further studies are required for watersheds of differing sizes and degrees of urbanisation.

Temporal variability of combined sewer overflow contaminants: evaluation of wastewater micropollutants as tracers of fecal contamination

A monitoring program was initiated for two sewage outfalls (OA and OB) with different land uses (mainly residential versus institutional) over the course of a year. Eleven CSO events resulting from fall and summer precipitations and a mixture of snowmelt and precipitation in late winter and early spring were monitored. Median concentrations measured in CSOs were 1.5 × 10(6)Escherichia coli/100 mL, 136.0 mg/L of Total Suspended Solids (TSS), 4599.0 ng/L of caffeine (CAF), 158.9 ng/L of carbamazepine (CBZ), in outfall OA and 5.1 × 10(4)E. coli/100 mL, 167.0 mg TSS/L, 300.8 ng CAF/L, 4.1 ng CBZ/L, in outfall OB. Concentration dynamics in CSOs were mostly related to the dilution by stormwater and the time of day of the onset of overflows. Snowmelt was identified as a critical period with regards to the protection of drinking water sources given the high contaminant concentrations and long duration of events in addition to a lack of restrictions on overflows during this period. Correlations among measured parameters reflected the origins and transport pathways of the contaminants, with E. coli being correlated with CBZ. TSS were not correlated with E. coli because E. coli was found to be mostly associated with raw sewage whereas TSS were additionally from the resuspension of in-sewer deposits and surface runoff. In receiving waters, E. coli remained the best indicator of fecal contamination in strongly diluted water samples as compared to WWMPs because WWMPs can be diluted to below their detection limits.