Combined Sewer Research Articles

Analysis of (Anti-)Oestrogenic and (Anti-)Androgenic Activities in Wastewater from the Lodz Sewer System

This article presents the results of a study on the oestrogenicity and androgenicity of urban wastewater in Lodz, and the possibility of their removal by the Group Wastewater Treatment Plant (GWWTP). Wastewater samples were taken at five points of the sewer system in the city and at the inlet and outlet of the GWWTP. The study was conducted using Yeast Oestrogen Screen (YES)/Yeast Androgen Screen (YAS) tests, which allow a general assessment of the content of compounds with (anti-)oestrogenic and (anti-)androgenic effects in wastewater, without identifying specific substances. Wastewater samples taken from the sewage network did not show (anti-)oestrogenic activity, while oestrogenic and antagonistic properties to androgens were detected in most of them. In the influent of the treatment plant, oestrogen agonistic activity was detected only in one sample (oestrogen equivalent—EEQ equal to 1.31 × 105 ng 17 β–oestradiol/L) and was 100% removed. The purification efficiencies in GWWTP for oestrogen and androgen antagonistic activity were 51.5–99.2% and 39.4–47.1%, respectively. Although no oestrogenic activity was detected in general wastewater in Lodz, observed high-antagonistic–androgenic activities may adversely affect the water body and cause, among others, the feminization of fish, especially in the case of discharge of untreated wastewater by combined sewer overflows.

Persistence of MRSA and ESBL-producing E. coli and K. oxytoca in river water

Due to climate change precipitation patterns are changing in terms of frequency and quantity in Germany. As a result, prolonged dry weather can lead to extremely low flow rates in river systems with large portions of treated wastewater. However, storm events and heavy rainfall events are increasing too, which may lead to higher frequencies of combined sewer overflows. Increased microbial pollution (e.g. coliform bacteria, clostridia, faecal streptococci) of waterbodies after heavy precipitation events was demonstrated in several studies. Pathogenic multi-resistant bacteria enter waterbodies via sewer systems. The persistence potential of such pathogens in aquatic environments is mainly still unknown. This study investigated the growth behaviour of Gram-negative extended spectrum beta-Lactamase-producing Klebsiella oxytoca and Escherichia coli and Gram-positive methicillin-resistant Staphylococcus aureus in river water. The concentrations of these antibiotic-resistant bacteria were monitored in batch experiments using river water differently impacted by wastewater. Staphylococcus aureus persisted for at least 3 days at incubation temperatures of 8 and 18 °C. The persistence of K. oxytoca and E. coli was shown for at least 37 days at both temperatures. In the river water at 8 °C, bacteria concentrations decreased slower, suggesting diminished persistence of ARB (antibiotic-resistant bacteria) with increasing temperatures. Initial concentrations of ARB and other pathogens in river water corresponded to the impact of wastewater. However, significant effects on the persistence itself by wastewater impact could not be shown for the bacteria species tested. Further studies should pursue our approaches concerning the persistence of pathogenic ARB in freshwater to assess the health risk for humans and animals.

Proximity to Combined Sewer Overflow-Impacted Waters in Philadelphia: A Geographic Information Systems Study to Explore Environmental Injustice

Background: Recreating in waterbodies impacted by combined sewer overflows (CSOs) can present health risks due to exposure to microbial pathogens. This study compares population characteristics of those living within walking distance to CSO-impacted versus nonimpacted waters in Philadelphia to determine whether these populations differ by race, ethnicity, and sociodemographic characteristics. Methods: Adults recreating at or near natural water bodies in Philadelphia completed a questionnaire that assessed the average walking distance to each site. Walking distance boundaries informed by questionnaire responses were created around each waterbody in Philadelphia, and population-level census data corresponding with block groups included within each buffer were used to characterize those living near a CSO-impacted and nonimpacted waterbodies in Philadelphia. Results: Compared with populations residing in census block groups within walking distance to a nonimpacted waterway, populations living within the same distance to a CSO-impacted waterway were more likely to comprise Hispanic residents (standardized adjusted prevalence ratio [APR] = 1.13) and those living in poverty (APR = 1.21) and less likely to comprise White residents (APR = 0.76). Conclusion: These findings suggest that communities of color and those experiencing poverty are disproportionally impacted by environmental hazards.

Evaluation of the adsorption characteristics of dissolved organic matter using granular activated carbon (GAC) and the regeneration efficiency of denitrification, Electro-Fenton, and Sono-Fenton oxidation

This research explored the use of a granular activated carbon (GAC) column to treat dissolved organics in Combined Sewer Overflows (CSOs), a major river pollutant. The regeneration efficiency of spent GAC was assessed utilizing three distinct methods: biological denitrification, electro-Fenton oxidation, and Sono-Fenton oxidation. Among the six organics tested, sucrose and raw sewage demonstrated the most comparable adsorption characteristics. GAC adsorption factors are multifaceted, involving pore size, surface functional groups, and competing solution substances, rather than just organic matter hydrophobicity. The biological denitrification enabled the utilization of the adsorbed organic matter on spent GAC, consequently reducing the initial NO3-N concentration from 99 mg/L to 8 mg/L over a period of 48 hours. Electro-Fenton treatment revealed marginal performance differences between SUS-SUS and Ti/Pt-Ti/Pt; however, the latter proved superior in terms of electrode stability over prolonged use. A combined strategy employing ultrasound and Fenton treatment at a frequency of 40 kHz yielded marginally higher GAC regeneration efficiency (68.5%) as compared to that at 750 kHz (67.8%). Among all regeneration techniques applied in this investigation, the Sono-Fenton method showed the highest efficiency.

Denitrification Potential of Surface Soils of Constructed Wetlands in Newtown Creek, an Urban Superfund Site.

Denitrification, the anaerobic microbial conversion of nitrate (NO3 - ), a common water pollutant, to nitrogen (N) gases, is often high in the soil of natural wetlands. In areas where natural wetlands have been degraded or destroyed, constructed and restored wetlands have been used to restore ecosystem services like denitrification. Thus, denitrification in restored and constructed wetlands could play an important role in treating anthropogenic N sources such as combined sewer overflow (CSO) discharges which can be high in NO3 - . In this study, we measured denitrification potential using an anaerobic slurry assay and made a suite of ancillary measurements (soil moisture content, microbial biomass carbon (C) and N content, potential net N mineralization and nitrification, soil inorganic N pools and soil respiration) in four constructed salt marsh wetlands, and a series of wetland habitat basins in Newtown Creek, NY, an urban superfund site. Samples were also taken from natural salt marshes located at Paerdegat Basin, Jamaica Bay, NY. Our results show that constructed Spartina alterniflora marshes in ultra-urban Newtown Creek support denitrification potential equivalent to rates of natural marshes in Jamaica Bay and reference marshes in other urban estuaries. There were significant positive correlations between microbial biomass C and N content and organic matter content and denitrification potential. Results suggest that constructed wetlandscan support wetland vegetation, soils, and microbial life and contribute to N removal under ultra-urban conditions. This article is protected by copyright. All rights reserved.

Modeled predictions of human-associated and fecal-indicator bacteria concentrations and loadings in the Menomonee River, Wisconsin using in-situ optical sensors.

Human sewage contamination of waterways is a major issue in the United States and throughout the world. Models were developed for estimation of two human-associated fecal-indicator and three general fecal-indicator bacteria (HIB and FIB) using in situ optical field-sensor data for estimating concentrations and loads of HIB and FIB and the extent of sewage contamination in the Menomonee River in Milwaukee, Wisconsin. Three commercially available optical sensor platforms were installed into an unfiltered custom-designed flow-through system along with a refrigerated automatic sampler at the Menomonee River sampling location. Ten-minute optical sensor measurements were made from November 2017 to December 2018 along with the collection of 153 flow-weighted discrete water samples (samples) for HIB, FIB, dissolved organic carbon (DOC), and optical properties of water. Of those 153 samples, 119 samples were from event-runoff periods, and 34 were collected during low-flow periods. Of the 119 event-runoff samples, 43 samples were from event-runoff combined sewer overflow (CSO) influenced periods (event-CSO periods). Models included optical sensor measurements as explanatory variables with a seasonal variable as an interaction term. In some cases, separate models for event-CSO periods and non CSO-periods generally improved model performance, as compared to using all the data combined for estimates of FIB and HIB. Therefore, the CSO and non-CSO models were used in final estimations for CSO and non-CSO time periods, respectively. Estimated continuous concentrations for all bacteria markers varied over six orders of magnitude during the study period. The greatest concentrations, loads, and proportion of sewage contamination occurred during event-runoff and event-CSO periods. Comparison to water quality standards and microbial risk assessment benchmarks indicated that estimated bacteria levels exceeded recreational water quality criteria between 34 and 96% of the entire monitoring period, highlighting the benefits of high-frequency monitoring compared to traditional grab sample collection. The application of optical sensors for estimation of HIB and FIB markers provided a thorough assessment of bacterial presence and human health risk in the Menomonee River.

On Optimizing the Conditional Value-at-Risk of a Maximum Cost for Risk-Averse Safety Analysis

The popularity of Conditional Value-at-Risk (CVaR), a risk functional from finance, has been growing in the control systems community due to its intuitive interpretation and axiomatic foundation. We consider a nonstandard optimal control problem in which the goal is to minimize the CVaR of a maximum random cost subject to a Borel-space Markov decision process. The objective represents the maximum departure from a desired operating region averaged over a given fraction of the worst cases. This problem provides a safety criterion for a stochastic system that is informed by both the <i>probability</i> and <i>severity</i> of the potential consequences of the system&#x0027;s behavior. In contrast, existing safety analysis frameworks apply stage-wise risk constraints or assess the probability of constraint violation without quantifying the potential severity of the violation. To the best of our knowledge, the problem of interest has not been solved. To solve the problem, we propose and study a family of stochastic dynamic programs on an augmented state space. We prove that the optimal CVaR of a maximum random cost enjoys an equivalent representation in terms of the solutions to these dynamic programs under appropriate assumptions. For each dynamic program, we show the existence of an optimal policy that depends on the dynamics of an augmented state under the assumptions. In a numerical example, we illustrate how our safety analysis framework is useful for assessing the severity of combined sewer overflows under precipitation uncertainty.

A simplified approach for the hydrological simulation of urban drainage systems with SWMM

The management of an Urban Drainage System (UDS) is a complex task, as it requires extensive knowledge about precipitation regime, hydrological features of the catchment, hydraulic characteristics of the drainage network, and information about the water use by the served inhabitants. Complex semi-distributed hydrological and physically based hydraulic models are nowadays available to summarise such information and run simulations. However, in many cases, the uncertainty of the available hydrological information hampers the use of complex models. Hence, simple models with few parameters and small computational effort may be preferable, especially for UDS management problems requiring the execution of many simulations. This paper proposes a convenient approach to define effective lumped Simplified Models (SMs) of UDSs, the parameters of which can be estimated directly from cartographic information. For several case studies of UDS with different morphological and topological characteristics, SMs were built, capable of reproducing the hydrographs provided by available semi-distributed Detailed Models (DMs), assumed as benchmark in absence of measured hydrographs. To this aim, the SWMM simulation software was used, and the SM lumped parameters were calibrated by maximising the goodness of fit between the hydrograph of the DM and of the SM. The results show that SMs satisfactorily predict the hydrographs for all the case studies, and that robust relationships between the calibrated parameters and morphological and topological characteristics of the UDS can be established. This suggests that SMs can be used by decision makers for preliminary design, planning studies and management problems of UDSs, as their parameters can be soundly estimated from cartographic information. An example of application of SMs to Combined Sewer Overflow prediction is also presented.

Constructed wetlands for the treatment of combined sewer overflow upstream of centralized wastewater treatment plants

Combined sewer overflows (CSOs) constitute nowadays a major environmental concern, representing one of the main untreated sources of pollution for receiving water bodies. Additional, in recent years, the frequency and intensity of CSOs have increased due to the growing urbanisation and climate change. Although there is no single effective strategy, one of the most promising approaches for the control and treatment of CSOs can be found in nature-based solutions (NBS), such as constructed wetlands (CWs). Despite the demonstrated potential of CWs to treat CSOs, the only data reported in the literature refer to CSO-CW systems located along the sewerage network. This research represents, to the best of our knowledge, the first monitoring of a full-scale CSO-CW designed to treat the combined sewer overflow upstream of the WWTP located in Carimate, in the province of Como (Italy). The system is a multistage CW, composed by a 1st vertical subsurface flow (VF) stage (total area of 8500 m2) and a 2nd free water surface (FWS) stage (total area of 4500 m2). The observed removal rates during the 3 years monitoring campaign (mean values equal to 83.2%, 64.6%, 63.8% for COD, TP, and N-NH4+ respectively) confirmed the treatment efficiency of CW system for all the investigated parameters, consistent with literature data for CSO-CWs in line with the sewerage network, despite its large scale and different hydraulic characteristics. Furthermore, the system also provides additional ecosystem services such as flood mitigation (average CSO interception of 82%), enhancement of biodiversity and a low operational and maintenance cost.

The impact of stormwater management strategies on the flow regime of a peri-urban catchment facing urbanisation and climate change: a distributed modelling study in Lyon, France

ABSTRACT The relative impact of urbanisation (urban sprawl), climate change (rainfall and evapotranspiration) and stormwater disconnection strategies (implementation of green infrastructure (GI)) on a peri-urban stream in the western suburbs of Lyon, France, was investigated using a distributed, physically based model (J2000P). Results showed that ambitious catchment-scale implementation of GI has the potential to mitigate some hydrological effects of urbanisation, especially a drastic reduction of combined sewer overflows. However, GI did not have a large impact on the stream flow regime, especially in the context of climate change, as the stream is dominated by non-urban contributions. Spatially distributed models have the capacity to inform river managers about the extent of implementation of GI needed to achieve given management goals and highlight some limitations of disconnection strategies. Indeed, while GI improved the resilience of sewer networks to global change, it was not sufficient to compensate for the effects of climate change on streamflow.

Comparative study of deterministic and probabilistic assessments of microbial risk associated with combined sewer overflows upstream of drinking water intakes

Combined sewer overflows (CSOs) are a source of microbial contamination of drinking water intakes located downstream from their discharge. To safeguard the quality of the source water, it is essential to evaluate the risk levels associated with these municipal structures. This study compares two risk assessment approaches to test their applicability for assessing the risk of CSOs to drinking water intakes in a highly urbanized watershed. The first approach was based on a deterministic equation that combines the characteristics of an overflow structure allowing the risk to be rated as very low, low, medium, high, or very high. The second probabilistic risk assessment approach yielded findings that are probabilistically distributed across the five levels of risk. This approach was developed by constructing a novel Bayesian network to probabilistically link the different factors defining the exposure of water intakes to the hazards of CSOs. The comparison between the results of these two approaches highlighted the importance of simultaneously considering many scenarios for assessing the risk of contamination of source waters. It was possible to use the Bayesian network rather than the deterministic equation, which only supports one scenario at a time. It was also shown that the deterministic approach often overestimated risk levels for CSO outfalls close to the water intake. This occurred because the assessment process emphasized the distance factor between the discharge point and the water intake, while neglecting other crucial characteristics of the overflow, such as duration and frequency. In particular, the deterministic approach tended to underestimate risk for CSOs associated with low overflow frequencies as it did not support scenarios of overflow duration, unlike the probabilistic approach. The validation and sensitivity analysis of the Bayesian model revealed that the population residing in the CSO's drainage basin, along with the frequency and duration of the overflows, exerted the greatest influence on the resulting risk levels. These factors outweighed other variables utilized in the risk assessment, including vulnerability of the drinking water intake, the type of overflow recorder, pipe diameter, and variables defining the exposure of the water intake to the discharge. In the context of implementing action plans, the Bayesian network is estimated as a cost-effective technique as it prioritized overflow structures needing special attention in a highly urbanized watershed, where the same CSOs were deterministically rated as having the same risk level. The results also demonstrated the effectiveness of the Bayesian model in addressing data gaps faced by water managers and stakeholders. The Bayesian model proved capable of assessing risks with uncertainties for CSOs, even with limited input data available. These findings can assist managers in identifying problematic structures by considering various scenarios, unlike the deterministic approach, which left almost half (n = 42) of the study site's overflow structures unassessed due to data limitations.

Environmental DNA clarifies impacts of combined sewer overflows on the bacteriology of an urban river and resulting risks to public health

There is no reference of microbiological water quality in the European Union's Water Framework Directive, adapted into English law, and consequently microbial water quality is not routinely monitored in English rivers, except for two recently designated bathing water sites. To address this knowledge gap, we developed an innovative monitoring approach for quantitative assessment of combined sewer overflow (CSO) impacts on the bacteriology of receiving rivers. Our approach combines conventional and environmental DNA (eDNA) based methods to generate multiple lines of evidence for assessing risks to public health. We demonstrated this approach by investigating spatiotemporal variation in the bacteriology of the Ouseburn in northeast England for different weather conditions in the summer and early autumn of the year 2021 across eight sampling locations that comprised rural, urban, and recreational land use settings. We characterized pollution source attributes by collecting sewage from treatment works and CSO discharge at the peak of a storm event. CSO discharge was characterized by log10 values per 100 mL (average ± stdev) of 5.12 ± 0.03 and 4.90 ± 0.03 for faecal coliforms and faecal streptococci, and 6.00 ± 0.11 and 7.78 ± 0.04 for rodA and HF183 genetic markers, for E. coli and human host associated Bacteroides, respectively, indicating about 5 % sewage content. SourceTracker analysis of sequencing data attributed 72–77 % of bacteria in the downstream section of the river during a storm event to CSO discharge sources, versus only 4–6 % to rural upstream sources. Data from sixteen summer sampling events in a public park exceeded various guideline values for recreational water quality. Quantitative microbial risk assessment (QMRA) predicted a median and 95th percentile risk of 0.03 and 0.39, respectively, of contracting a bacterial gastrointestinal disease when wading and splashing around in the Ouseburn. We show clearly why microbial water quality should be monitored where rivers flow through public parks, irrespective of their bathing water designation.

Storm-event Dynamics of Nitrogen and Dissolved Oxygen in Urban River: The Upper Tame, Birmingham

Nitrogen (N) and dissolved oxygen (DO) are essential indicators of urban water pollution, with excess nitrogen causing eutrophication and low dissolved oxygen damaging the living environment of aquatic organisms and affecting biodiversity. Urban areas cover a high proportion of impervious areas. When heavy rainfall occurs, it rapidly generates surface runoff in urban areas and carries nitrogen into river systems. This study aims to assess the water quality of the river tame through the Birmingham metropolitan area over the last 15 years, investigate whether excess nitrogen input during storm events causes significant changes in dissolved oxygen, and find a linear relationship between nitrogen and dissolved oxygen. By comparing the water quality at the Sandwell Park sample point, which does not flow through urban Birmingham, with the water quality at the Minworth sample point, which is the final outlet of Birmingham, it was found that the nitrogen content of the river Tame increased from 4.17 mg/L to 13.09 mg/L, indicating a decline in water quality after the river Tame flowed through urban Birmingham. The correlation coefficient between nitrogen and dissolved oxygen increases from 0.65 to 0.8 between the rainfall event and the storm event, which is highly correlated, suggesting that combined sewer overflow (CSO) events coincided with peak nitrogen and strengthened the correlation between nitrogen and dissolved oxygen in the river Tame. A regular and continuous monitoring program should be established for the Tame catchment through urban Birmingham to prevent overflows as a priority and to enhance the treatment capacity of the sewage treatment plant.

Per- and polyfluorinated alkyl substances (PFAS) in Pennsylvania surface waters: A statewide assessment, associated sources, and land-use relations

The objectives of this study are to identify per- and polyfluoroalkyl substances (PFAS) in Pennsylvania surface waters, corresponding associations with potential sources of PFAS contamination (PSOC) and other parameters, and compare raw surface water concentrations to human and ecological benchmarks. Surface water samples from 161 streams were collected in September 2019 and were analyzed for 33 target PFAS and water chemistry. Land use and physical attributes in upstream catchments and geospatial counts of PSOC in local catchments are summarized. The hydrologic yield of the sum of 33 PFAS (∑PFAS) for each stream was computed by normalizing each site's load by the drainage area of the upstream catchment. Utilizing conditional inference tree analysis, the percentage of development (>7.58 %) was identified as a primary driver of the ∑PFAS hydrologic yields. When percentage of development was removed from analysis, ∑PFAS yields were closely related to surface water chemistry associated with landscape alteration (e.g., development or agricultural cropland), such as concentrations of total nitrogen, chloride, and ammonia, but also to count of water pollution control facilities (agricultural, industrial, stormwater, and/or municipal waste pollution abatement facilities). In oil and gas development regions, ∑PFAS yields were associated with combined sewage outfalls. Sites surrounded by ≥2 electronic manufacturing facilities had elevated ∑PFAS yields (median = 241 ng/s/km2). Study results are critical to guide future research, regulatory policy, best practices that will mitigate PFAS contamination, and the communication of human health and ecological risks associated with PFAS exposure from surface waters.

Effect of microbial network complexity and stability on nitrogen and sulfur pollutant removal during sediment remediation in rivers affected by combined sewer overflows

Discovering the complexity and improving the stability of microbial networks in urban rivers affected by combined sewer overflows (CSOs) is essential for restoring the ecological functions of urban rivers, especially to improve their ability to resist CSO impacts. In this study, the effects of sediment remediation on the complexity and stability of microbial networks was investigated. The results revealed that the restored microbial community structure using different approaches in the river sediments differed significantly, and random matrix theory showed that sediment remediation significantly affected microbial networks and topological properties; the average path distance, average clustering coefficient, connectedness, and other network topological properties positively correlated with remediation time and weakened the small-world characteristics of the original microbial networks. Compared with other sediment remediation methods, regulating low dissolved oxygen (DO) shifts the microbial network module hubs from Actinobacteria and Bacteroidetes to Chloroflexi and Proteobacteria. This decreases the positive association of networks by 17%–18%, which intensifies the competitiveness among microorganisms, further weakening the influence and transmission of external pressure across the entire microbial network. Compared with that of the original sediment, the vulnerability of the restored network was reduced by more than 36%, while the compositional stability was improved by more than 12%, with reduced fluctuation in natural connectivity. This microbial network succession substantially increased the number of key enzyme-producing genes involved in nitrogen and sulfur metabolism, enhancing nitrification, denitrification, and assimilatory sulfate reduction, thereby increasing the removal rates of ammonia, nitrate, and acid volatile sulfide by 43.42%, 250.68% and 2.66%, respectively. This study comprehensively analyzed the succession patterns of microbial networks in urban rivers affected by CSOs before and after sediment remediation, which may provide a reference for reducing the impact of CSO pollution on urban rivers in the subsequent stages.

Precipitation and discharge changes drive increases in Escherichia coli concentrations in an urban stream

Determining the driving factors of E. coli dynamics and predicting future E. coli changes in urban aquatic systems are important for regulating water quality. In this study, data from 6985 measurements of E. coli from 1999 to 2019 in an urban waterway Pleasant Run in Indianapolis, Indiana (USA) were statistically analyzed by Mann-Kendall and multiple linear regression to assess the long-term trends in E. coli concentrations and to project E. coli concentrations under future climate change scenarios. E. coli concentrations monotonically increased over the last two decades, with the value increasing from 111 Most Probable Number (MPN)/100 mL in 1999 to 911 MPN/100 mL in 2019. E. coli concentrations have exceeded the Indiana standard of 235 MPN/100 mL since 1998. E. coli showed peak concentration in summer and higher concentration in sites with combined sewer overflows (CSOs) relative to those without. Precipitation had both direct and indirect impacts on E. coli concentrations meditated by stream discharge. Multiple linear regression results showed that annual precipitation and discharge accounted for 60 % of E. coli concentration variability. Based on the observed precipitation-discharge-E. coli concentration relationship, the projected results showed that, in the highest emission representative concentration pathways (RCP) 8.5 climate scenario, E. coli concentrations in the 2020s, 2050s, and 2080s will be 1350 ± 563 MPN/100 mL, 1386 ± 528 MPN/100 mL, and 1443 ± 479 MPN/100 mL, respectively. This study illustrates that climate change can impact E. coli concentrations by altering temperature, precipitation patterns, and stream flow in an urban stream and predicts an undesired future situation under a high CO2 emission scenario.

How reliable – and (net) beneficial – is the green in green infrastructure

AbstractThe idea of green infrastructure (GI) has generated great interest and creativity in addressing a range of challenging and expensive environmental problems, from coastal resilience to control of combined sewer overflows (CSOs). The appeal of GI stems from its cost savings compared to traditional “gray” infrastructure and the multiple benefits it provides, including biodiversity, aesthetics, and carbon sequestration. For example, a “green” approach to controlling CSOs in New York City saved $1.5 billion compared to a “gray” approach. Despite these advantages, GI still does not have detailed design and reliability specifications as compared to engineered gray infrastructure, potentially hindering its adoption. In this paper, we review some of the potential applications of GI in modern environmental science and discuss how reliability and associated (un)certainty in net benefits need to be addressed to realize the potential of this new approach.

Quantifying Mixing in Sewer Networks for Source Localization

There has been a recent increase of interest in sewer network water quality, both for pollutants and wastewater epidemiology. Of particular interest is the ability to perform cost-effective small-scale monitoring to understand the sewer network and perform source localization (the process of identifying the sources of materials of interest within the network), enabling prioritization of combined sewer overflow (CSO) interventions and targeted response to the detection of infectious diseases. Rhodamine WT fluorescent dye tracing was carried out in the combined sewer networks of four UK cities, for which network geometries were available. Over 100 dye concentration profiles were recorded, from which discharge, travel time (velocity), and dispersion were quantified. A simplified hydraulic and water quality (conservative solute transport) modeling approach was used to investigate dispersion further. A theoretical method for calculating dispersion over a reach with nonuniform properties was derived and used with the models and recorded data to develop a method for estimating the dispersion coefficient in sewers. Novel simultaneous injections into multiple manholes within one sewer network were conducted. Modeling of these injections validated the modeling approach and explained the measured concentration profiles, demonstrating both the potential of hydraulic and solute transport modeling and the new dispersion coefficient predictor for source localization. Such modeling can be used to develop sewer network “fingerprints” and source location probability plots based on residence time distribution (RTD) theory to maximize information from limited water quality monitoring. This will aid managers and operators in identifying potential intermittent sources of material within the network.

Capacity Assessment of Urban Green Space for Mitigating Combined Sewer Overflows in the Tokyo Metropolitan Area

Among the countermeasures against combined sewer overflow (CSO), urban green space (UGS) has been proven effective. However, few studies have examined the effects of UGS on CSO at the municipal scale. Therefore, this study aimed to develop a novel method for estimating the relation of the area of UGS to CSO based on a case study in the Tokyo metropolitan area, which includes 10 sewersheds. This method integrates surface runoff modeling, sewer network analysis, and response analysis for estimating CSO and its response to the UGS proportion in each sewershed. This method is based on public data of topographic features, land-related data, and rainfall characteristics. Specifically, the CSO discharge is estimated to be the difference between the rainwater inflow to a terminal treatment plant and the maximum capacity of the sewer systems in each sewershed. The results revealed that the amount of CSO increases exponentially with the intensity of rainfall. In addition, a response analysis showed that the increase in UGS proportion would mitigate CSO in all sewersheds, particularly in the case where the UGS proportion increased from 5% to 10%. Overall, the present method allows us to estimate CSO in relation to rainfall pattern and the distribution of UGS in a sewershed without actual CSO records.

Particle-associated organic contaminant and cytotoxicity transport in a river during storm events

Storm events lead to mobilization of particles as well as organic contaminants that can pose a risk to river ecosystems. Assessment of total loads of particle-bound and dissolved contaminants in rivers is challenging, especially during rain events since multiple, often unknown contamination sources may be triggered, among them tributaries, combined sewer overflows, direct soil and road runoff, and the riverbed sediment. We investigated whether cytotoxicity (i.e., reduction of the cell viability of human cell lines) could be used as a proxy for the total chemical mixture to assess the transport of organic contaminant mixtures either in particle-associated form or in the aqueous phase. Time-proportional composite samples were collected in the Ammer River (Southwestern Germany) during two storm events in June 2021. All samples were screened for 127 organic contaminants and cytotoxicity in the water and particle phase separately. In total, 56 organic compounds were found, of which 14 and 34 were detected only in the water and particle extracts, respectively, and eight compounds were present in both phases. Thermodynamic equilibrium between the aqueous phase and suspended solids was observed for four compounds namely triphenyl phosphate, octocrylene, galaxolide, and p-chlorocresol. Substances that were not in equilibrium were mainly constituents of plastics and tire rubber, and their high concentrations in the particle phase were probably due to extractions from the particles themselves. Linear correlations between TSS and total compound concentrations were found for 17 PAHs and two musk fragrances, suggesting stable particle loadings and aqueous concentrations over the course of the rain event, most likely due to particle delivery from a particle source with a constant degree of contamination. The total cytotoxicity of water plus particles in the river correlated linearly with TSS during storm events. Inflowing water and particles from all sources appeared to be integrated, such that the total cytotoxicity of all contaminants per mass of particles and volume of water in the river was stable throughout storm events. From this relationship, a threshold of 0.5 g L-1 TSS was derived, above which particle-facilitated transport exceeded dissolved cumulative contaminant transport in the Ammer River, indicating the relevance of particle-facilitated contaminant transport.