Combined Sewer Research Articles

Assessing stormwater control measure inventories from 23 cities in the United States

Since the 1987 Clean Water Act Section 319 amendment, the US Government has required and funded the development of nonpoint source pollution programs with about $5 billion dollars. Despite these expenditures, nonpoint source pollution from urban watersheds is still a significant cause of impaired waters in the United States. Urban stormwater management has rapidly evolved over recent decades with decision-making made at a local or city scale. To address the need for a better understanding of how stormwater management has been implemented in different cities, we used stormwater control measure (SCM) network data from 23 US cities and assessed what physical, climatic, socioeconomic, and/or regulatory explanatory variables, if any, are related to SCM assemblages at the municipal scale. Spearman’s correlation and Wilcoxon rank-sum tests were used to investigate relationships between explanatory variables and SCM types and assemblages of SCMs in each city. The results from these analyses showed that for the cities assessed, physical explanatory variables (e.g. impervious percentage and depth to water table) explained the greatest portion of variability in SCM assemblages. Additionally, it was found that cities with combined sewers favored filters, swales and strips, and infiltrators over basins, and cities that are under consent decrees with the Environmental Protection Agency tended to include filters more frequently in their SCM inventories. Future work can build on the SCM assemblages used in this study and their explanatory variables to better understand the differences and drivers of differences in SCM effectiveness across cities, improve watershed modeling, and investigate city- and watershed-scale impacts of SCM assemblages.

How much do bacterial growth properties and biodegradable dissolved organic matter control water quality at low flow?

Abstract. The development of accurate water quality modeling tools is necessary for integrated water quality management of river systems. Even though some water quality models can simulate dissolved oxygen (DO) concentrations accurately during high-flow periods and phytoplankton blooms in rivers, significant discrepancies remain during low-flow periods, when the dilution capacity of the rivers is reduced. We use the C-RIVE biogeochemical model to evaluate the influence of controlling parameters on DO simulations at low flow. Based on a coarse model pre-analysis, three sensitivity analyses (SAs) are carried out using the Sobol method. The parameters studied are related to bacterial community (e.g., bacterial growth rate), organic matter (OM; partitioning and degradation of OM into constituent fractions), and physical factors (e.g., reoxygenation of the river due to navigation and wind). Bacterial growth and mortality rates are found to be by far the two most influential parameters, followed by bacterial growth yield. More refined SA results indicate that the biodegradable fraction of dissolved organic matter (BDOM) and the bacterial growth yield are the most influential parameters under conditions of a high net bacterial growth rate (= growth rate − mortality rate), while bacterial growth yield is independently dominant in low net growth situations. Based on the results of this study, proposals are made for in situ measurement of BDOM under an urban area water quality monitoring network that provides high-frequency data. The results also indicate the need for bacterial community monitoring in order to detect potential bacterial community shifts after transient events such as combined sewer overflows and modifications in internal processes of treatment plants. Furthermore, we discuss the inclusion of BDOM in statistical water quality modeling software for improvement in the estimation of organic matter inflow from boundary conditions.

Chemical prioritization of pharmaceuticals and personal care products in an urban tributary of the Potomac River

Pharmaceuticals and personal care products (PPCPs) are incredibly diverse in terms of chemical structures, physicochemical properties, and modes of action, making their environmental impacts challenging to assess. New chemical prioritization methodologies have emerged that compare contaminant monitoring concentrations to multiple toxicity data sources, including whole organism and high-throughput data, to develop a list of “high priority” chemicals requiring further study. We applied such an approach to assess PPCPs in Hunting Creek, an urban tributary of the Potomac River near Washington, DC, which has experienced extensive human population growth. We estimated potential risks of 99 PPCPs from surface water and sediment collected upstream and downstream of a major wastewater treatment plant (WWTP), nearby combined sewer overflows (CSO), and in the adjacent Potomac River. The greatest potential risks to the aquatic ecosystem occurred near WWTP and CSO outfalls, but risk levels rapidly dropped below thresholds of concern – established by previous chemical prioritization studies – in the Potomac mainstem. These results suggest that urban tributaries, rather than larger rivers, are important to monitor because their lower or intermittent flow may not adequately dilute contaminants of concern. Common psychotropics, such as fluoxetine and venlafaxine, presented the highest potential risks, with toxicity quotients often > 10 in surface water and > 1000 in sediment, indicating the need for further field studies. Several ubiquitous chemicals such as caffeine and carbamazepine also exceeded thresholds of concern throughout our study area and point to specific neurotoxic and endocrine modes of action that warrant further investigation. Since many “high priority” chemicals in our analysis have also triggered concerns in other areas around the world, better coordination is needed among environmental monitoring programs to improve global chemical prioritization efforts.

State Selection and Cost Estimation for Deep Reinforcement Learning-Based Real-Time Control of Urban Drainage System

In recent years, a real-time control method based on deep reinforcement learning (DRL) has been developed for urban combined sewer overflow (CSO) and flooding mitigation and is more advantageous than traditional methods in the context of urban drainage systems (UDSs). Since current studies mainly focus on analyzing the feasibility of DRL methods and comparing them with traditional methods, there is still a need to optimize the design and cost of DRL methods. In this study, state selection and cost estimation are employed to analyze the influence of the different states on the performance of DRL methods and provide relevant suggestions for practical applications. A real-world combined UDS is used as an example to develop DRL models with different states. Their control effect and data monitoring costs are then compared. According to the results, the training process for DRL is difficult when using fewer nodes information or water level as the input state. Using both upstream and downstream nodes information as input improves the control effect of DRL. Also, using the information on upstream nodes as the input state is more effective than using downstream nodes; using flow as input is more likely to have a better control effect than using water level, while using both flow and water level cannot significantly further improve the control effect. Because the cost of flow monitoring is higher than water level monitoring, the number of monitoring nodes and the use of flow/water level need to be balanced based on cost-effectiveness.

The impact of combined sewer outflows on urban water quality: Spatio-temporal patterns of fecal coliform in indianapolis

Many urban waterways with older stormwater drainage systems receive a significant amount of untreated or poorly treated waste from Combined Sewer Outflow (CSO) systems during precipitation events. The input of effluent waste from CSO to urban water streams during storm events often leads to elevated fecal coliform, specifically Escherichia Coli (E. Coli) in these waterways. The aim of the study is to examine fecal coliform concentration, water chemistry, and water quality parameters to better understand spatio-temporal patterns of fecal coliform associated with CSO events in three waterways from Indianapolis, Indiana (USA). The waterways are Pleasant Run Creek (PRW), Fall Creek (FC) and White River (WR). The sampling occurred biweekly over one year for PRW, nine months for FC, and an intense (∼every three days) sub-analysis of the presumed peak period of fecal coliform growth (July) for WR. All PRW and FC sampling sites significantly exceeded the EPA contact standard limit of 200 CFU/100 mL for fecal coliform concentrations during the sampling period. We found no relationship between fecal coliform levels and the number or density of CSO outfalls above a given site. The most significant predictors of increased fecal coliform concentrations were precipitation on the sampling day and cumulative degree days. The most significant predictors of decreased fecal coliform were maximum precipitation during the ten-day window prior to sampling and median discharge during a three-day window prior to sampling. These findings suggest a push-pull balance within the system where CSO activation and seasonal gradients replenish and promote fecal coliform growth. At the same time, large hydrologic events act to flush and dilute fecal coliform concentrations. The results from this study help us to better understand how different drivers influence fecal coliform growth and how this information can be potentially used to predict and remediate the conditions of urban water streams.

Regulating the in situ generation of active chlorine species in a photoelectrochemical system for the efficient simultaneous removal of ammonia nitrogen and refractory pharmaceuticals

The removal of chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) is always a critical problem in combined polluted sewage treatment. To simultaneously treat NH4+-N and refractory organics, a WO3/BiVO4-cobalt borate (WO3/BiVO4-CoBi) photoanode was applied in a photoelectrochemical (PEC) system. It used Cl- in highly-saline wastewater to generate strongly-oxidizing active chlorine species in situ, which were responsible for the system’s NH4+-N directional oxidation and simultaneous degradation ability. Thus, the PEC system with Cl- (PEC-Cl) simultaneously removed 99% of carbamazepine (CBZ) within 40 min and 75.4% of NH4+-N within 120 min. It also selectively converted NH4+-N into N2 (10% NO3–-N production rate). The {010} facet-oriented array of decahedral BiVO4 and WO3/BiVO4 heterostructure contributed to the effective separation of photo-generated electron-hole pairs. Coupled with the reduced charge-transfer resistance of the photoanode/solution interface and the greater conversion of photo-generated holes into redox equivalents by the CoBi co-catalyst, the system demonstrated efficient carrier transfer. Active chlorine species (Cl2, HClO, Cl•, and •ClO) were produced with the participation of photo-generated holes and •OH and could be regulated by controlling the system potential, Cl- concentration, and solution pH. This study provides a feasible method for the simultaneous removal of NH4+-N and refractory organics with a high efficiency and stability.

Operational guidance for aeration and flow augmentation for the Chicago Area Waterway System—A case study

The Chicago Area Waterway System (CAWS) is a 133.9 km branching network of navigable waterways controlled by hydraulic structures, in which the majority of the flow is treated wastewater effluent and there are periods of substantial combined sewer overflows. The CAWS comprises a network of effluent dominated streams. More stringent dissolved oxygen (DO) standards and a reduced flow augmentation allowance have been recently applied to the CAWS. Therefore, a carefully calibrated and verified one-dimensional flow and water quality model was applied to the CAWS to determine emission-based real-time control guidelines for the operation of flow augmentation and aeration stations. The goal of these guidelines was to attain DO standards at least 95% of the time. The “optimal” guidelines were tested for representative normal, dry, and wet years. The finally proposed guidelines were found in the simulations to attain the 95% target for nearly all locations in the CAWS for the three test years. The developed operational guidelines have been applied since 2018 and have shown improved attainment of the DO standards throughout the CAWS while at the same time achieving similar energy use at the aeration stations on the Calumet River system, greatly lowered energy use on the Chicago River system, and greatly lowered discretionary diversion from Lake Michigan, meeting the recently enacted lower amount of allowed annual discretionary diversion. This case study indicates that emission-based real-time control developed from a well calibrated model holds potential to help many receiving water bodies achieve high attainment of water quality standards.

Reducing antimicrobial resistances by source separation of domestic wastewater

Antimicrobial resistances (AMR) are ranked among the top ten threats to public health and societal development worldwide. Toilet wastewater contained in domestic wastewater is a significant source of AMR entering the aquatic environment. The current commonly implemented combined sewer systems at times cause overflows during rain events, resulting in the discharge of untreated wastewater into the aquatic environment, thus promoting AMR. In this short research article, we describe an approach to transform combined sewer systems into source separation-modified combined sewer systems that separately treat toilet wastewater. We employ simulations for demonstrating that source separation-modified combined sewer systems reduce the emission of AMR-causing substances by up to 11.5 logarithm levels. Thus, source separation-modified combined sewer systems are amongst the most effective means of combating AMR.

Monitoring organic micropollutants in stormwater runoff with the method of fingerprinting

The ecological state of receiving water bodies can be significantly influenced by organic micropollutants that are emitted via stormwater runoff. Reported efforts to quantify the emission of micropollutants mainly focus on sampling at combined sewer overflows and storm sewer outfalls, which can be challenging. An alternative method, called fingerprinting, was developed and tested in this study. The fingerprinting method utilizes wastewater treatment plant (WWTP) influent samples and derives the proportion of stormwater in a sample. This is achieved by comparing the wet weather vs dry weather concentrations of substances-tracers which are present only in wastewater. It is then possible to estimate the concentration of organic micropollutants in stormwater runoff from measurements in the influent of a WWTP based on a mass balance. In this research, the fingerprinting method was applied in influent samples obtained in five WWTPs in the Netherlands. In total, 28 DWF and 22 WWF samples were used. The chosen tracers were ibuprofen, 2-hydroxyibuprofen, naproxen and diclofenac. Subsequently, the concentration in stormwater runoff of 403 organic micropollutants was estimated via the WWF samples. The substances that were present and analyzed included glyphosate and AMPA, 24 out of 254 pesticides, 6 out of 28 organochlorine pesticides, 45 out of 63 pharmaceuticals, 15 out of 15 PAHs, 2 of the 7 PCBs, and 20 of 33 other substances (e.g. bisphenol-A). A comparison with findings from other studies suggested that the fingerprinting method yields trustworthy results. It was also noted that a representative and stable dry weather flow reference concentration is a strict requirement for the successful application of the proposed method.

Application of Radial Type Multifiber Media Filtration Process for Combined Sewer Overflow Treatment

Fiber media filtration for combined sewer overflow (CSO) treatment was evaluated in this work. Pilot-scale experiments of CSO treatment involve seven layers that form radial-type fiber media filters. The fiber media filter was characterized using analysis techniques and exhibited extremely high hydrophobicity and negative charge. The results obtained for a sewer treatment plant at Tancheon in Seoul revealed potential for suspended solid, total organic carbon, and biochemical oxygen demand removal with efficiencies of 89.6%, 56%, and 42%, respectively. The results are consistent with the sieving effects and electrostatic repulsion between fiber media and pollutants. Head loss was induced by organic pollutants and was 10.5 cm after 20 h of operation. To mitigate the head loss induced by organic pollutants on the fiber media filter, sodium hypochlorite (NaClO) was used as a chemical backwashing agent. An NaClO concentration of 2000 mg/L with a soaking time of 24 h yielded an optimal head loss recovery of 96.2% of the initial head loss obtained for the virgin fiber media filter without media filter degradation. The result of the present study will provide practical insight and act as a technical guide for CSO treatment plant engineers.

Assessment and Actions to Support Integrated Water Resources Management of Seville (Spain)

AbstractIntegrated Water Resources Management (IWRM) of the city of Seville, Spain, located in the southern Guadalquivir River Basin is assessed applying the city blueprint approach (CBA). The trends and pressures framework identifies five major indicators reflecting ‘concern’ for Seville’s urban water management: heat island effect, urban drainage flooding, river peak discharges, unemployment rate and economic pressure. The results indicate increased daytime and night-time temperatures and increased urban flooding due to sealed soil, and river rise from regional precipitation under climate change. The financial pressures are driven by the high unemployment rate and the low per capita income compared to other cities assessed. The city blueprint framework identifies three categories reflecting ‘poor’ performance for the urban water management of Seville: water infrastructure, solid waste and climate adaptation. An aging sewer network, low operational cost recovery and combined-sewer overflow systems dominate. Solid waste management is characterized by high waste generation, low recycling rate and minimal energy recovery. The percentage of green space is low, but growing. The Governance Capacity Framework identifies five conditions reflecting ‘limited’ governance of water scarcity: awareness, useful knowledge, continuous learning, agents of change and financial viability. The assessment of water governance reflects a low citizens’ sense of urgency. Integrating citizens and stakeholders in a more participative governance will result in increased awareness of economic efforts required to face water scarcity, renewal of water infrastructure and climate adaptation. The blue city index (BCI) of Seville is 5.8/10, placing it highly among other Mediterranean cities, and in the top 20% of 125 cities assessed worldwide. Application of the CBA to the urban water resources of cities allows clear definition of water and resource management challenges and is the first step to becoming a ‘water smart’ city.

A Deep Rock Cavern Captures Stormwater

In many sewer systems in the northeast and midwestern U.S., stormwater and sewage flows are collected together and then delivered for treatment in a single piping system, which means treatment flows can increase substantially during storm events. Annually, over 9 billion gallons of combined stormwater and sewage were discharged to Lake Erie in the 1970s. The volume was cut in half through the construction of new water treatment plants and improvements to the existing ones. Untreated sewage discharged to the lake continues to be a major contributing factor to the water quality issues, such as algae blooms.

Predictive heuristic control: Inferring risks from heterogeneous nowcast accuracy

Urban Drainage Systems can cause ecological and public health issues by releasing untreated contaminated water into the environment. Real-time control (RTC), augmented with rainfall nowcast, can effectively reduce these pollution loads. This research aims to identify key dynamics in the nowcast accuracies and relate those to the performance of nowcast-informed rule-based (RB)-RTC procedures. The developed procedures are tested in the case study of Rotterdam, the Netherlands. Using perfect nowcast data, all developed procedures showed a reduction in combined sewer overflow volumes of up to 14.6%. Considering real nowcast data, it showed a strong ability to predict if no more rain was expected, whilst performing poorly in quantifying rainfall depths. No relation was found in the nowcast accuracy and the consistency of the predicted rainfall using a moving horizon. Using the real nowcast data, all procedures, with the exception of the one predicting the end of the rainfall event, showed a significant risk of operative deterioration (performing worse than the baseline RB-RTC), linked to the relative performance of the nowcast algorithm. Understanding the strengths of a nowcast algorithm can ensure the reliability of the RB-RTC procedure and can negate the need for detailed modelling studies by inferring risks from nowcast data.

Smart management of combined sewer overflows: From an ancient technology to artificial intelligence

AbstractSewer systems are an essential part of sanitation infrastructure for protecting human and ecosystem health. Initially, they were used to solely convey stormwater, but over time municipal sewage was discharged to these conduits and transformed them into combined sewer systems (CSS). Due to climate change and rapid urbanization, these systems are no longer sufficient and overflow in wet weather conditions. Mechanistic and data‐driven models have been frequently used in research on combined sewer overflow (CSO) management integrating low‐impact development and gray‐green infrastructures. Recent advances in measurement, communication, and computation technologies have simplified data collection methods. As a result, technologies such as artificial intelligence (AI), geographic information system, and remote sensing can be integrated into CSO and stormwater management as a part of the smart city and digital twin concepts to build climate‐resilient infrastructures and services. Therefore, smart management of CSS is now both technically and economically feasible to tackle the challenges ahead. This review article explores CSO characteristics and associated impact on receiving waterbodies, evaluates suitable models for CSO management, and presents studies including above‐mentioned technologies in the context of smart CSO and stormwater management. Although integration of all these technologies has a big potential, further research is required to achieve AI‐controlled CSS for robust and agile CSO mitigation.This article is categorized under: Engineering Water > Sustainable Engineering of Water Science of Water > Water and Environmental Change

Identification of microplastic pathways within a typical European urban wastewater system

AbstractIn recent years, thermoextraction/desorption‐gas chromatography/mass spectrometry (TED‐GC/MS) has been developed as a rapid detection method for the determination of microplastics (MP) mass contents in numerous environmentally relevant matrices and, in particular, for the measurement of polymers in water samples without time‐consuming sample preparation. The TED‐GC/MS method was applied to investigate a typical European municipal wastewater system for possible MP masses. Such investigations are important in view of the recent revision of the Urban Wastewater Treatment Directive. Four different representative sampling sites were selected: greywater (domestic wastewater without toilet), combined sewer, and influent and effluent of a wastewater treatment plant (WWTP). All samples were collected by fractional filtration. Filtration was carried out over mesh sizes of 500, 100, 50, and in some cases, 5 µm. Polyethylene (PE), polypropylene (PP), and polystyrene (PS) were detected in all samples, with the PE fraction dominating in all cases. Styrene‐butadiene rubber which serves as an indication of tire abrasion, was only found in the influent of the WWTP. The highest MP mass contents were found in the combined sewer, so MP can become a source of pollution during heavy rain events when the capacity limits of the effluent are reached, and the polluted effluent is released uncontrolled into the environment. Based on the studies, MP retention from the WWTP could be estimated to be approximately 96%. Few trends in polymer type or mass contents were detected within the different fractions of the samples or when comparing samples to each other.

Microbial community composition and function in an urban waterway with combined sewer overflows before and after implementation of a stormwater storage pipe.

When the wastewater volume exceeds the sewer pipe capacity during extreme rainfall events, untreated sewage discharges directly into rivers as combined sewer overflow (CSO). To compare the impacts of CSOs and stormwater on urban waterways, we assessed physicochemical water quality, the 16S rRNA gene-based bacterial community structure, and EcoPlate-based microbial functions during rainfall periods in an urban waterway before and after a stormwater storage pipe was commissioned. A temporal variation analysis showed that CSOs have significant impacts on microbial function and bacterial community structure, while their contributions to physicochemical parameters, bacterial abundance, and chlorophyll a were not confirmed. Heat map analysis showed that the impact of CSO on the waterway bacterial community structure was temporal and the bacterial community composition in CSO is distinct from that in sewers. Hierarchical clustering analysis revealed that the waterway physicochemical water qualities, bacterial community composition, and microbial community function were distinguishable from the upper reach of the river, rather than between CSO and stormwater. Changes in the relative abundance of tetracycline resistance (tet) genes-especially tet(M)-were observed after CSOs but did not coincide with changes in the microbial community composition, suggesting that the parameters affecting the microbial community composition and relative abundance of tet genes differ. After pipe implementation, however, stormwater did not contribute to the abundance of tet genes in the waterway. These results indicate that CSO-induced acute microbial disturbances in the urban waterway were alleviated by the implementation of a stormwater storage pipe and will support the efficiency of storage pipe operation for waterway management in urban areas.

Fate of ofloxacin in rural wastewater treatment facility: Removal performance, pathways and microbial characteristics

Ofloxacin (OFL) with high biological activity and antimicrobial degradation is a kind of the typical high concentration and environmental risk antibiotics in rural sewage. In this paper, a combined rural sewage treatment facility based on anaerobic baffled reactor and integrated constructed wetlands was built and the removal performance, pathway and mechanism for OFL and conventional pollutants were evaluated. Results showed that the OFL and TN removal efficiency achieved 91.78 ± 3.93 % and 91.44 ± 4.15 %, respectively. Sludge adsorption was the primary removal pathway of OFL. Metagenomics analysis revealed that Proteobacteria was crucial in OFL removal. baca was the dominated antibiotic resistance genes (ARGs). Moreover, carbon metabolism with a high abundance was conductive to detoxify OFL to enhance system stability and performance. Co-occurrence network analysis further elucidated that mutualism was the main survival mode of microorganisms. Denitrifers Microbacterium, Geobacter and Ignavibacterium, were the host of ARGs and participated in OFL biodegradation.

A bilevel data-driven method for sewer deposit prediction under uncertainty

Deposit accumulation is one of the predominant causes of sewer blockage and overflow. Nevertheless, the traditional detection methods are costly and time-consuming, and the accuracy of the mathematical models for deposit prediction is usually affected by some uncertain factors (e.g., pipe properties and flow velocity of water). This paper proposes a framework of global sensitivity analysis (GSA) to identify the most sensitive indicators for sewer deposit prediction by (i) developing a data-driven bilevel (i.e., catchment level and segment level) model to map the relation between input and output indicators and (ii) employing three different GSA methods, namely, the Morris method, Sobol method, and Borgonovo index method to identify the indicators as important or unimportant (insensitive). The results show that the likelihood of combined sewer overflow occurrences (LCSOO), pipe age (PA), and pipe material (PM) are influential parameters for the thickness of deposits. Here, we pay close attention to the most influential parameters, which can help improve forecast prediction accuracy.

A Longitudinal Assessment of Benthic Macroinvertebrate Diversity and Water Quality along the Bronx River

The Bronx River is an urban waterway with a long history of anthropogenic disturbance. We conducted a longitudinal assessment of the Bronx River's water quality by measuring benthic macroinvertebrate diversity at 6 sites along the river. We integrated long-term water-quality data collected by the New York State Department of Environmental Conservation. We found that the overall water quality of the river has remained moderately impacted over different timepoints throughout the past 22 years. The study site upstream of combined sewage overflows and municipal separate stormwater systems exhibited healthier biological profiles, whereas the most-downstream sites exhibited slight declines in water quality. The most recent survey of the Bronx River (2020) revealed that high invasive species dominance was associated with benthic macroinvertebrate communities that were less healthy. Notably, one invasive species not documented in historical surveys, Corbicula fluminea (Asian Clam), was sampled in 5 of 6 study sites during the 2020 surveys. Moreover, no species were sampled from the order Ephemeroptera (mayflies) in 2020 despite being present in previous surveys. These results can be used to guide the management of urban rivers.

Study on Combined Sewer Overflow (CSO) Pollution and Its Control Method Based on Sewage Interception Along Rivers

Combined sewer overflow (CSO) pollution is the main factor that plagues the water environment in the area with combined sewer system in most cities of China. This paper analyzed CSO pollution, and reviewed the measures to solve CSO pollution and the latest research progress. The problems of traditional river interception projects were analyzed, and optimization and improvement ideas were proposed. Finally, a combined optimization scheme of source reduction-process control-end storage was proposed to control CSO pollution, which could provide reference for urban CSO pollution control in China.