Combined Sewer Research Articles

Contribution of different land use catchments on the microplastic pollution in detention basin sediments

The assessment of microplastic (MP) pollution in urban areas is essential considering its abundance in freshwater, particularly due to urban wet weather discharge. The precise sources of MPs must be identified to better understand its characteristics. This study examines the relationship between MP pollution in detention basin sediments and land use in the investigated catchments. The study of stormwater management infrastructure, mainly in detention basins, has enabled the quantification of MP abundance in sediments conveyed by stormwater in urban areas. Sediment sampling was conducted in ten detention basins and one combined sewer overflow (CSO) structure in the Lyon metropolitan area, France. These basins correspond to stormwater outlets of representative urban catchment areas. MP extraction involves densimetric separation and organic matter degradation. MPs were then characterized using micro-Fourier infrared spectroscopy and siMPle software. This protocol identified MPs between 50 and 500 μm in the study sites. This study highlights the high abundance in the collected sediment samples, ranging from 2,525 to 1,218,82 MP kg−1 by dry weight sediment. The MPs found have a median size around 115 μm, making them very small MPs that are mainly composed of polypropylene followed by polyethylene and polystyrene or polyethylene terephthalate. The abundance of MPs in sediments is associated with the land use type. Catchments in predominantly industrial and commercial zones were more significantly polluted with MPs compared with those in predominantly agricultural or heterogeneous zones. Finally, statistical analyses revealed links between sedimentary and urban parameters and MPs concentrations. Several recommendations are given for future research, notably concerning the analyzing of stormwater sediments to understand the sources of MP pollution.

Operation Risk Simulation and Interaction Impact of Stormwater and Sewage Systems Based on Storm Water Management Model

With the increasing urbanization rate, higher demand is placed on drainage systems, necessitating analysis of their risk profiles. While many studies focus on the individual hydraulic modeling of stormwater and wastewater systems when considering operational risks, they often overlook the exacerbating effects of combined stormwater and wastewater flows on each other’s risks. In this study, we constructed a model of the combined stormwater and wastewater drainage system in Lijiao, Guangdong Province. We analyzed the operational risks of both stormwater and sewage networks in different scenarios, focusing on full-load pipes, overload pipes, node overflows, and minimum flow velocities. Furthermore, we compared the exacerbating effects of sewage and stormwater on each other’s network operational risks. Simulation results indicated that, for sewage networks with combined sewer sections, the lengths of full-load pipes and overload pipes increased by an average of 27.4% and 16.3%, respectively, during rainy weather scenarios compared to dry weather. After considering the inflow of sewage into combined sewer sections, the average length of full-load pipes increased by 3.8 km, overload pipe length increased by 1.1 km, and overflow volume increased by 2.26 × 104 m3. As the return period of rainfall events increases, these inter-system impacts gradually diminish. Therefore, when modeling drainage systems and assessing operational risks, particularly during low return period rainfall events, the inclusion of both stormwater and sewage in combined sewer networks should be comprehensively considered.

Investigating First Flush Occurrence in Agro-Urban Environments in Northern Italy

The first flush (FF) phenomenon is commonly associated with a relevant load of pollutants, raising concerns about water quality and environmental management in agro-urban areas. An FF event can potentially transport contaminated water into a receiving water body by activating combined sewer overflow (CSO) systems present in the drainage urban network. Therefore, accurately characterizing FF events is crucial for the effective management of sewer systems and for limiting environmental degradation. Given the ongoing controversy in the literature regarding the delineation of FF event occurrences, there is an unavoidable necessity for further investigations, especially experimental-based ones. This study presents the outcomes of an almost two-year field campaign focused on assessing the water quantity and quality of two combined sewer systems in Northern Italy. For this purpose, various hydro-meteorological variables, including precipitation, flow rate, temperature, and solar radiation, in addition to water quality analytics, were measured continuously to capture stormwater events. Throughout the monitoring period, sixteen stormwater events were identified and analyzed using five indices usually adopted in the literature to identify FF occurrences. The results indicate that there is a strong positive correlation between the mass first flush ratios calculated for nutrients and three factors, including maximum rainfall intensity, maximum flow rate, and antecedent dry weather period. Furthermore, rainfall duration was found to possess a strong negative correlation with the mass first flush ratios calculated for nutrients. However, for the same rainfall event, the occurrence of FF has never been unanimously confirmed by the indices examined in this study. Moreover, different macro-groups of pollutants can behave differently. Thus, it becomes apparent that relying solely on a priori analyses, without the support of data from experimental monitoring campaigns, poses a risk when designing actions for the mitigation of FF occurrences.

Review: The application of source analysis methods in tracing urban non-point source pollution: categorization, hotspots, and future prospects.

The contribution of urban non-point source (NPS) pollution to surface water pollution has gradually increased, analyzing the sources of urban NPS pollution is of great significance for precisely controlling surface water pollution. A bibliometric analysis of relevant research literature from 2000 to 2021 reveals that the main methods used in the source analysis research of urban NPS pollution include the emission inventory approach, entry-exit mass balance approach, principal component analysis (PCA), positive matrix factorization (PMF) model, etc. These methods are primarily applied in three aspects: source analysis of rainfall-runoff pollution, source analysis of wet weather flow (WWF) pollution in combined sewers, and analysis of the contribution of urban NPS to the surface water pollution load. The application of source analysis methods in urban NPS pollution research has demonstrated an evolution from qualitative to quantitative, and further towards precise quantification. This progression has transitioned from predominantly relying on on-site monitoring to incorporating model simulations and employing mathematical statistical analyses for traceability. This paper reviews the principles, advantages, disadvantages, and the scope of application of these methods. It also aims to address existing problems and analyze potential future development directions, providing valuable references for subsequent related research.

Water depth prediction in combined sewer networks, application of generative adversarial networks

This paper addresses the pressing issue of combined sewer overflows (CSOs) in urban areas, which pose significant environmental and public health threats. CSOs occur when combined sewer systems become overwhelmed during heavy rainfall, leading to untreated sewage and stormwater being discharged into nearby water bodies. To effectively manage and mitigate CSO effects, accurate predictions of CSOs are crucial for real-time control measures. This study introduces an innovative approach that utilizes Generative Adversarial Networks (GANs) to augment data and improve the accuracy of data-driven models for predicting water depth in combined sewer systems. Apart from data augmentation, the paper addresses scenarios where rare patterns, such as extreme events, are infrequently observed regardless of dataset size. It proposes a specialized generative model based on GANs designed to augment datasets targeting these rare patterns. This innovation involves adding a tail-focused loss function to the adversarial objective of the GAN training pipeline. The research is exemplified through a case study in Kaiserslautern, Germany. The results indicate an improvement in water depth predictions. Also, it was found that the model trained solely with synthetic data is comparable to that trained with real data.Graphical

Bibliometric analysis of global performance and trends of research on combined sewer overflows (CSOs) from 1990 to 2022.

Combined sewer overflows (CSOs) are one of the main sources of pollution in urban water systems and significantly impede the restoration of water body functionalities within urban rivers and lakes. To understand the research and frontier trends of CSOs comprehensively and systematically, a visual statistical analysis of the literature related to CSOs in the Web of Science core database from 1990 to 2022 was conducted using the bibliometric method using HistCite Pro and VOSviewer. The results reveal a total of 1,209 pertinent publications related to CSOs from 1990 to 2022, and the quantity of CSOs-related publications indicated an increasing trend. Investigations of the distribution and fate of typical pollutants in CSOs and their ecological effects on receiving waters and studies on pollution control technologies (source reduction, process control, and end-of-pipe treatment) are the current focus of CSOs research. CSOs pollution control technologies based on source reduction and the monitoring and control of emerging contaminants are at the forefront of scientific investigations on CSOs. This study systematically and comprehensively summarized current research topics and future research directions of CSOs, thus providing a reference for CSOs control and water environment management research.

The role of macroinvertebrate taxonomic resolution in bioassessment of urban streams: A case study from the City of Lodz, Poland

Benthic macroinvertebrates were sampled at 28 sites situated on ten urban streams (Łódź, Poland) representative of a wide range of anthropogenic modifications of water chemistry and bed structure. A total of 5,043 individuals, comprising 121 species belonging to 37 families and 15 orders, were collected. Diptera (35.8 %) and Ephemeroptera (31.8 %) were dominant.The studied sites were grouped into clusters based on separately-analyzed environmental parameters, various levels of taxonomic diversity, and bioassessment variables. All analyses demonstrated similar trends of anthropogenic modification, intensifying concentrically from the suburbs towards the city centre. The first cluster included the upper section of streams; less polluted, richer in ecotone zones and natural stream bed substrate. The second cluster comprised streams demonstrating the influence of moderate human pressure. The third cluster included streams flowing through the city center in concreted beds and which were connected to a combined sewage system in which sewage and rain water are transported through a single canal system and enters the nearest stream. Modification of stream beds was significantly negatively correlated with the number of species, families and orders, but not with total abundance.The number of species, the number of families and the number of orders were highly mutually correlated. Moreover, they were similarly correlated with biodiversity and biotic indices, which are used to assess the ecological status of the aquatic environment. Hence, different levels of taxonomic identification demonstrate similar effectiveness in assessment, i.e. higher taxa of aquatic macroinvertebrates may be suitable for simplified ecological monitoring of urban watercourses.

A Unique Monitoring Method for Fecal and Sewage-Derived Chemical Pollution Utilizing International Pellet Watch Approach.

This study established a unique approach to assess fecal contamination by measuring fecal sterols, especially coprostanol (5β-cholestanol-3β-ol, 5β) and cholestanol (5α-cholestan-3β-ol, 5α) and their ratio 5β/(5β + 5α) alongside triclosan (TCS) and methyl-triclosan (MTC) in beached plastic pellets across 40 countries. Coprostanol concentrations ranged from 3.6 to 8190 ng/g pellet with extremely high levels in densely populated areas in African countries. The 5β/(5β + 5α) ratio was not affected by the difference in residence time of pellets in aquatic environments, and their spatial pattern showed a positive correlation with that of sedimentary sterols, demonstrating its reliability as an indicator of fecal contamination. Pellets from populated areas of economically developing countries, i.e., Africa and Asia, with lower coverage of wastewater treatment exhibited higher 5β/(5β + 5α) ratios (∼0.7) corresponding to ∼1% sewage in seawater, while pellets from developed countries, i.e., the USA, Canada, Japan, and Europe, with higher coverage of modern wastewater treatment displayed lower ratios (∼0.5), corresponding to the first contact limit. Triclosan levels were higher in developing countries (0.4-1298 ng/g pellet), whereas developed countries showed higher methyl-triclosan levels (0.5-70 ng/g pellet) due to TCS conversion during secondary treatment. However, some samples from Japan and Europe displayed higher TCS levels, suggesting contributions from combined sewage overflow (CSO). Combination of 5β/(5β + 5α) and MTC/TCS ratios revealed extreme fecal contamination from direct input of raw sewage due to inadequate treatment facilities in some African and South and Southeast Asian countries.

Optimal distribution of green and grey infrastructures coupled with real time control of the sewer for combined sewer overflows control as an adaptation measure to climate change

ABSTRACT Optimization of the spatial distribution of green infrastructures (GIs) was performed for a combined sewer system located in the Province of Quebec, Canada, using a simulation-optimization tool with the aim of reducing seasonal combined sewer overflows (CSOs). The performance of four CSOs control alternatives involving the individual and integrated implementation of GIs with storage tanks and real time control (RTC) of the sewer was evaluated for a nine-year simulation period of historical rainfall data and for 20%-increased rainfall data (representative of potential climate change impact). The integration of GIs with RTC of the sewer (with or without storage tanks) lowered the total CSO volume by 95% to 99% under historical rainfall data and by 93% to 96% under increased rainfall intensities when compared to the reference scenario. Adapting GI’s number and location for optimal CSO control rather than according to space availability criteria reduced CSO frequency but had only a slight impact on CSO volume reduction.

Do baseline assumptions alter the efficacy of green stormwater infrastructure to reduce combined sewer overflows?

Green stormwater infrastructure (GSI) is growing in popularity to reduce combined sewer overflows (CSOs) and hydrologic simulation models are a tool to assess their reduction potential. Given the numerous and interacting water flows that contribute to CSOs, such as evapotranspiration (ET) and groundwater (GW), these models should ideally account for them. However, due to the complexity, simplified models are often used, and it is currently unknown how these assumptions affect estimates of CSOs, GSI effectiveness, and ultimately planning guidance. This study evaluates the effect on estimates of CSOs and GSI effectiveness when different flows and hydrologic processes are neglected. We modified an existing EPA SWMM model of a combined sewer system in Switzerland to include ET, GW, and upstream inflows. Historical rainfall data over 30 years are used to assess volume and duration of CSOs with and without three types of GSI (bioretention basins, permeable pavements and green roofs). Results demonstrate that neglect of certain flows in modelling can alter CSO volumes from -15 % to 40 %. GSI effectiveness also varies considerably, resulting in differences in simulated percent of CSO volume reduced from 8 % to 35 %, depending on the GSI type and modeled flow or process. Representation of GW within models is particularly crucial when infiltrating GSI are present, as CSOs could increase in certain subcatchments due to higher GW levels from increased infiltration. When basing GSI planning decisions on modeled estimates of CSOs, all relevant hydrologic processes should be included to the extent possible, and uncertainty and assumptions should always be considered.

Data-driven methodological approach for modeling rainfall-induced infiltration effects on combined sewer overflow in urban catchments

Combined sewer system deterioration poses significant challenges, especially as it leads to substantial volumes of Permanent Infiltration Inflow (PII) and Rain-Induced Infiltration (RII) to percolate into sewer pipes. This infiltration increases the risk of Combined Sewer Overflow (CSO) events and reduces the treatment plant's efficiency by diluting raw effluent. To effectively decrease CSO volumes, it is crucial to identify the various flow components and their contribution to overflow volumes. In this study, a data-driven hydrological model was developed, conceptualizing the surface hydrological processes as well as the interactions between soil water and the sewer system, based on long-term monitoring. Four flow components at the outlet of the catchment were identified and characterized: wastewater, surface runoff, PII, and RII. The model was applied and evaluated using monitored data from the Ecully catchment in France. The model demonstrated its suitability in replicating the observed hydrograph and estimating CSO volumes. Two sewer system scenarios were proposed, investigating the effect of partial and complete reduction of PII and RII on CSO volumes. The results showed a reduction of the annual CSO volume by 5 % to 7.5 %, and 12 % to 17 %, in the first and second scenario, respectively. To compare the performance of these scenarios with stormwater management strategies, two other scenarios were considered where source control measures allowed infiltration of the first 5 and 10 mm of rainfall. The results demonstrated that these measures could, respectively, reduce CSO volumes by 13 % to 48 % and completely eliminate CSO for half of the events. This study highlights the limitations of relying solely on PII and RII strategies to eliminate CSO events and emphasizes the necessity of considering stormwater management strategies.

Development and application of a mathematical model for calculating the discharge of non-standard thin-plate weirs in urban combined sewer overflow systems: a case study

Abstract The aim of this study is to address the issue of difficulty in evaluating the combined sewer overflow (CSO) pollution effectively, especially for the monitoring of overflow from non-standard thin-plate weirs (NTPWs). In order to construct a discharge calculation mathematical model (DCMM) of NTPWs in an urban combined sewer overflow system (UCSOS), which can be used to construct a real-time monitoring and early warning system, a physical model constructed firstly for obtaining hydraulic characteristic sets under three flow conditions (free, submerged, pressurized flow). Then, the coefficient function expressions are obtained under three flow conditions through genetic algorithm (GA) fitting, and a DCMM of UCSOS is established subsequently. The results indicate that DCMM exhibits high accuracy, with mean relative error (MRE) at 0.0326, root mean square error (RMSE) at 1.569, and Nash–Sutcliffe efficiency (NSE) coefficient at 0.9387. The DCMM can not only evaluate the discharge capacity under different flow conditions, but also be used to realize reliable and convenient discharge monitoring. Although the DCMM constructed in this case is not universal, the modeling method of combining physical models with GA is an effective new approach to evaluate the discharge capacity of NTPW, which also holds value for application in other cities.

Sitting in our own soup? Combined sewers, climate change and nature-based solutions for urban water management in Berlin

Traditionally, the planning, investment, management, and evaluation of combined sewer networks has been the domain of hydraulic modelling using narrowly defined indicators associated with spill frequencies, flows and waterbody environmental quality standards. Due to concerns about the increasing frequency and impact of combined sewer overflow (CSO) ‘spill’ events, many cities and citizens are realising or reassessing the problems that accompany these systems, and considering alternatives including nature-based solutions (NBS). We report on an investigation of the impacts of urban stormwater management and CSOs, addressing key issues of framing, assessment and measures of success. With increasing interest being directed towards NBS for urban water management, we asked the questions: Which additional or alternative measures of success might be applied to judge the success or otherwise of different approaches? What outcomes are viewed as beneficial or problematic, what benefits should be optimised and what adverse impacts should be designed out? Reflecting on recent impact assessment guidance and drawing on research in a city with a globally leading reputation for innovation and ecological sustainability practices (Berlin), we explore how the conceptual, practical and methodological frameworks might evolve over time. Factors affecting investments in stormwater management, whether involving conventional hard infrastructure or using NBS, go well beyond simple measures of flow, storage, volume and frequency. Public notions of value and legitimacy in urban water management are changing fast. We conclude with recommendations as to how city stakeholders may together develop more comprehensive assessments of combined sewer impacts and stormwater management practices.

Optimizing Formic Acid-Assisted Co-HTL of Digested Sewage Sludge and Lignocellulosic Waste for Enhanced Bio-Crude Yield and Energy Recovery

In recent years, hydrothermal liquefaction (HTL) has gained attention as a means of enhancing and increasing the production of biofuels from biomass. Co-HTL involves the simultaneous processing of two or more feedstocks, with the potential for interactions that can affect the overall yield and quality of the resulting biofuels. This study investigates the bio-crude yield, chemical composition, and energy content of bio-crudes obtained through formic acid-assisted hydrothermal liquefaction of combined digested sewage sludge (DSS) and lignocellulose (LC). The bio-crude yields are in the range of 26.8–58.9 wt%, with a higher heating value (HHV) of approximately 32 MJ/kg. The best experiment shows that mixtures with more DSS and high levels of process condition variables (350 °C, formic acid present, and 50 wt% EtOH) give high bio-crude yields with a maximum value of 58.9 wt%. For comparison, pure DSS and LC run at these process conditions resulted in a bio-crude yield of 52.5 wt% and 48.3 wt%, respectively. Partial least squares (PLS) regression reveals a synergistic effect from mixing the feedstocks, as the quadratic term of the regression equation for mixture ratio shows a negative coefficient. GC–MS data show that combining feedstocks results in the formation of new compounds, mostly phenols, that are not present in the bio-crudes from the separate feedstocks. Thus, combining feedstocks will not only increase the resource availability for hydrothermal liquefaction and streamline the process but will also increase the overall production of bio-crude with its synergistic effect.

Characterisation of storm runoff contamination from a tropical urban residential area in Malaysia

It has been quite a long time since the Malaysian government endorsed the Urban Storm Water Management Manual (USWMM) in 2000. Until now, there is no proper and detailed database on the non-point source contamination characteristics from various land uses in tropical regions of Malaysia. As such this study was conducted to fill part of the information gap pertaining to the nature of runoff quality in the tropical regions. The combined sewer outfall of a 6.14 ha residential area in Malaysia was studied to characterise the urban runoff quality generated due to tropical rain. As the drainage outlet discharges sullage and storm runoff through the same drainage network, hourly flow pattern and contaminant concentrations were determined both for sullage and storm runoff. Basic statistical analysis was conducted to determine the mean, standard deviation and event mean concentration values for the study area, for which such data was not available. It was observed that the runoff generated from the area is polluted due to high total suspended solids (TSS), biochemical oxygen demand (BOD) and chemical oxygen demand (COD). The runoff contained more total organic carbon (TOC) than total inorganic carbon (TIC). The EMC values of BOD, COD, TSS, TOC, total Kjeldhal nitrogen, ammoniacal nitrogen and orthophosphate were 35, 168, 177, 11, 0.32, 0.54, 0.16 mg/L, respectively. The presence of heavy metals in the runoff was low. The EMC values of lead, zinc, nickel, cadmium, chromium and copper were 0.061, 0.358, 0.002, 0.002, 0.025 and 0.022 mg/L, respectively. Due to the high quantity of rainfall, a significant amount of annual contamination loading is generated from the nonpoint sources of the residential area.

Opportunities for Leveraging Existing Hydrologic and Hydraulic Models Developed for Water Quantity Management to Mitigate Flooding Due to Extreme Precipitation

With a focus on a specific flood-prone community in Camden, NJ, this research utilizes a detailed hydraulic and hydrologic (H&H) model to assesses the impacts of climate change on Combined Sewer Overflows (CSOs) and localized flooding under two different infrastructure scenarios. In the US, the Clean Water Act compels regulated utilities to develop Long-Term Control Plans to reduce combined sewer overflows (CSOs), but there is no parallel mandate to simultaneously reduce flooding within the associated service areas. With different control measures in place, H&H models are frequently used to evaluate CSO volumes and frequencies under historical climate conditions. However, precipitation intensification and sea level rise (SLR) will also modify CSO volumes. This study uses a calibrated and validated 1D and 2D Personal Computer Stormwater Management Model (PCSWMM) simulation to predict both CSO discharges and flooding under different climate and infrastructure scenarios. A total of ten climate change scenarios comprising a range of plausible climate futures are considered. The infrastructure scenario that is tested would divert stormwater generated in an upstream municipality (Pennsauken, NJ) away from Camden’s combined sewer system. Without the disconnection, increases in precipitation will increase CSOs, whereas SLR primarily increases flooding. The proposed mitigation strategy can immediately reduce both CSOs and flooding, but with diminishing effectiveness over time, as climate change demonstrates the need for supplemental measures. Areas for further analysis regarding alternative mitigation methods and future research are outlined.

First report of components responsible for odor sensation from a vertical flow constructed wetland treating combined sewer overflow

A VF CW exhibited low-level production of the components responsible for odor sensation and were similar whether or not VF was operational. VOCs are the only component related to some odor sensation and were higher in the morning.

Measuring heat transfer processes in gully pots for real-time estimation of accumulated sediment depths

The accumulation of sediments in stormwater systems negatively affects their functioning. For example, the re-suspension of these sediments can lead to serious pollution of surface water bodies through combined sewer...

Study on urban combined sewer overflows and self-purification capacity load of river

Study on urban combined sewer overflows and self-purification capacity load of river

Enhanced combined sewer overflow treatment by rapid magnetic flocculation–magnetic sedimentation: efficiency and mechanism

Rapid magnetic flocculation required a reaction time of only 2 minutes to achieve the ideal pollutant removal efficiency.