A study on vortex separator technology to control combined sewer overflow

Influence of particle size on diffuse particulate pollutants in combined sewer systems

Stimulated by the recent USEPA’s green stormwater infrastructure (GSI) guidance and policies, GSI systems have been widely implemented in the municipal area to control the combined sewer overflows (CSOs), also known as low impact development (LID) approaches. To quantitatively evaluate the performance of GSI systems on CSO and urban flooding control, USEPA-Stormwater Management Model (SWMM) model was adopted in this study to simulate the behaviors of GSI systems in a well-developed urban drainage area, PSW45, under different circumstances. The impact of different percentages of stormwater runoff transported from impervious surfaces to the GSI systems on CSO and urban flooding control has also been investigated. Results show that with current buildup, GSI systems in PSW45 have the best performance for low intensity and short duration events on both volume and peak flow reductions, and have the worst performance for high intensity and long duration events. Since the low intensity and short duration events are dominant from a long-term perspective, utilizing GSI systems is considered as an effective measure of CSO control to meet the long-term control strategy for PSW45 watershed. However, GSI systems are not suitable for the flooding control purpose in PSW45 due to the high occurrence possibility of urban flooding during or after high intensity events where GSI systems have relatively poor performance no matter for a short or long duration event.

The aims of the study were to evaluate the effect of combined sewer overflows (CSO) and storm water drains (SWD) on metal bioavailability in small urban streams in Prague and to evaluate levels of metals in water, sediment, and macroinvertebrates. The following working hypotheses were adopted: (a) sites dominantly affected by SWD are less polluted by metals, and (b) sites dominantly affected by SWD have higher bioavailability of metals. Physical and chemical parameters (pH, conductivity, NO3-N, NH4-N, COD, alkalinity, and water hardness) and concentrations of the metals Cu, Zn, Pb, Ni, and Cr were determined in samples of water and sediment at five to six sites on four target streams—Zatisský Creek, Kosikovský Creek, Botic Creek, and Rokytka Creek—three to five times per year during the period 2002–2004. The sites from all studied creeks were categorized into five groups according to the prevailing type of urban drainage impact. Macroinvertebrates were sampled and analyzed for metals at each site for a period of 1 month. The concentration patterns of metals were interpreted by partition coefficient (Kd), hazard quotient (HQ), cumulative criterion unit (CCU), and biota sediment accumulation factor (BSAF). Concentrations of metals in water as well as in sediment at sites receiving water from SWD were lower than at sites where creeks receive water from CSO, except for Pb. Concentrations of Cu, Zn, and Pb in sediment were higher at sites affected by CSO. Concentrations of metals in aquatic macroinvertebrates, expressed as BSAF, indicated higher values at sites affected by SWD. Frequencies of high BSAF (>1) were lower in CSO compared to SWD. This finding was explained by (a) a decrease of pH on SWD sites compared to the increase of pH on CSO sites during rain events, (b) a greater resuspension of sediment at SWD sites during rain events, and (c) an abundance of organic matter in CSO available for sorption of metals and a corresponding reduction of their bioavailability. In the study area, the type of urban drainage affects the bioavailability of metals—while SWD increase metal bioavailability, CSO cause its decrease. The sediments in SWD sites do not indicate risk to the benthic community according to the applied environmental quality standards. Water and sediment in creeks affected by SWD are less polluted by metals. Both working hypotheses were therefore supported.

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

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

Combined-sewer overflow (CSO) must be controlled by a storage-treatment system because storm flow in the combined sewerage system is intermittent and highly variable in both pollutant concentration and flow rate. A treatment facility operating without the benefit of upstream storage would need to be very large and costly in order to handle the relatively high volume and flowrate of a CSO. Similarly, if storage is used without treatment, the storage volume required would be very large and also expensive. This paper describes a strategy to optimize CSO control system. This optimized system maximizes the use of the existing system before new construction and sizes the storage volume in concert with the wastewater treatment plant capacity to obtain the lowest-cost storage and treatment system.

In 1999, The Metropolitan Sewer District of Greater Cincinnati, Ohio (MSD) began negotiations with the United States Department of Justice, the United States Environmental Protection Agency, and the State of Ohio to create a program to address sanitary sewer overflows (SSO) and combined sewer overflows (CSO). The resulting document, the Consent Decree, formally outlined a process that MSD would follow and that government agencies could recognize and support. MSD had been addressing removal and reduction of SSOs and CSOs prior to the Consent Decree negotiations, but the Consent Decree defined a time frame as well for MSD. The Consent Decree required MSD to update the CSO Long Term Control Plan (LTCP). An important component of the CSO LTCP Update is the assessment of CSO control alternatives with respect to receiving water quality. As such, a field program was designed and implemented to support water quality modeling and CSO planning objectives. The field program would coincide with the water recreation season, starting in May and ending in October. The field program contained several components associated with dry and wet weather sampling and monitoring as outlined by the Consent Decree; Ohio River sampling, source characterization (CSO, SSO and Storm), and tributary sampling and continuous monitoring. This paper discusses the continuous monitoring component of the tributary sampling and monitoring program. Starting with the conceptual plan described by the Consent Decree, it outlines the process of converting a conceptual ideal into a workable field program including the installation, maintenance, data management and demobilization activities. Specific examples of unique site limitations are provided with the solutions tried and the resulting outcomes.

Retrofitting dense urban neighborhoods with green stormwater infrastructure (GSI) requires early and ongoing outreach to the affected public. Add in a combined sewer overflow (CSO) control project that is under a federal consent decree, giving affected neighbors little choice about the upcoming changes to their neighborhood, and a troubled history with large-scale GSI projects in the city, and public outreach takes on greater importance. The King County Wastewater Treatment Division took on its first GSI project for CSO control in two Seattle neighborhoods. Community outreach on the project design began in earnest in 2011. The project, which is nearing the completion of its first construction season, has overcome many challenges and has learned lessons about how to effectively work with the affected community on large-scale urban GSI projects. This paper focuses on the outreach tools and techniques employed during the design phase that built community acceptance of the project and enabled a smooth transition into construction and operation. Examples include taking advantage of creative educational opportunities, building relationships and trust, understanding and speaking to specific concerns about retrofit GSI projects, employing effective outreach techniques (going beyond public meetings), and building neighborhood trust in the construction team. These lessons are applicable to any agency or developer that wants to implement GSI in a dense, heavily used public space where public concerns could slow or stop the project.

Evaluation of the factors relating combined sewer overflows with sediment contamination of the lower Passaic River

Hydrodynamic modelling of the influence of stormwater and combined sewer overflows on receiving water quality: Benzo(a)pyrene and copper risks to recreational water

An innovative optimization‐simulation framework is applied to a case study of the Province of Quebec, Canada, to optimize the spatial distribution of green infrastructure (GI), the capacity and location of gray infrastructure, and the parameters specific to real‐time control (RTC) operating rules of a sewer system for reducing combined sewer overflows (CSOs) frequency and volume. GI, gray infrastructure, and RTC are applied either individually or in integration through eight optimization scenarios which are simulated over a nine‐year period of historical rainfall data. Among all scenarios, spatial optimization of GI with RTC leads to maximal CSO volume reduction (98%) and is the most cost‐effective option analyzed (70$/m3 of seasonal average CSO reduction compared to 140$/m3 for the scenario involving gray infrastructure alone). However, it requires a high GI implementation level and the CSO frequency under this scenario is sensitive to varying GI design parameters. The findings suggest that the best alternative for CSO control is the integration of the optimization of green and gray infrastructures with RTC as it still provides high CSO volume reduction (95%) and remains a cost‐effective solution (90$/m3 of CSO reduction), while providing robustness under cost and design uncertainties.

This paper presents a case study focusing on the impacts of combined sewer overflows on the water quality of the receiving water body, Hatirjheel. Hatirjheel, the largest surface water body in Dhaka City with an area of about 1.012 km2, receives discharges from nine combined sewer overflow (CSO) structures. The water quality of Hatirjheel is poor throughout the year, but particularly during the wet season (June to October) near the CSO structures through which significant rainwater-sewage overflows. The water has been found to contain high concentrations of 5-day biochemical oxygen demand (BOD5) and chemical oxygen demand; some of the BOD5 values exceed the national discharge standards for treated effluents. Total ammonia concentration in Hatirjheel water increases during the wet season, often exceeding 20 mg/l; the concentration continues to increase after the end of the wet season, most likely due to the ammonification process. Nitrate concentration in Hatirjheel water increases at the end of the wet season, possibly due to nitrification; subsequent reduction in nitrate and ammonia concentration is possibly due to incorporation of nitrogen into algal mass. Excessive phosphorus in Hatirjheel promotes eutrophication, resulting in the visible greenish color of the water. This study highlights the significant adverse impact of combined sewer overflows, particularly for a densely populated city like Dhaka, where most of the rainfall occurs within a relatively short period during monsoon.ArticleHighlightsCombined sewer overflows could significantly deteriorate the water quality of the receiving water bodies.Sewer overflows create a significant spatiotemporal variation of water quality, with higher pollution close to the overflowing combined sewer overflow structures.Because of its significant adverse impact on water quality and ecology, combined sewer systems may not be viable for high-density urban areas.

This paper presents a novel data-driven method for modeling combined sewer overflows (CSOs) in real-time. This method treats CSO event generation as a threshold process that is triggered by increasingly intense rainfall events, and predicts the likelihood of a CSO given input conditions using a Bayesian network. The fusion of relevant data from multiple agencies into a unified data stream in real time is described, and a hierarchical modeling strategy is proposed that will facilitate the exploration of the causes of CSOs and direct research into the adaptive management of combined sewer systems using the Chicago wastewater system as a case study.

Stormwater and combined sewer overflows (CSO) might represent an important source of macro and microplastics in the environment, but such fluxes are poorly investigated. In order to fill this knowledge gap, macro and microplastic concentrations were investigated (i) in stormwater and grid refusals at the outlet of a runoff water pipe located in Sucy-en-Brie (Paris suburb, France) and (ii) in CSO discharges at the Clichy outfall (Paris suburb, France). Macroplastics were sorted, weighted and classified. To study microplastics during rain events, 500 litres of water were filtered using plankton net with 80 μm mesh size. Microplastics were then extracted using H2O2 30% digestion followed by NaI density separation (d = 1.6 g.cm−3). A microscope and Fourier Transformed Infrared spectroscopy were applied to identify microplastics. Preliminary results from stormwater outlet of Sucy-en-Brie showed that macroplastic mass percentages were in the range of 1.5 to 37.5%. Moreover, 8 main plastic categories were found to contribute to 95% of total macroplastics and were identified as sanitary textiles, plastic bags or films, food packaging, bottles, cigarette buds, garbage bags, and polystyrene fragments. Macroplastic concentrations in stormwater from March to June 2018 ranged from 3 × 10−5 kg/m3 to 1 × 10−4 kg/m3. Three rain events were sampled at Sucy-en-Brie to study the concentration of microplastics. Microplastics with size of 1 to 5 mm during first rain event were analysed. Results indicated that microplastic concentrations were in the range of 4.6 × 10−2 and 9.3 × 10−3 fragments/L, in which polyamide and polyethylene predominated.

Real-time control in combined sewer systems in Germany––some case studies