Optimization of CSO Storage and Treatment Systems

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

A combined-sewer overflow (CSO) is a significant contributor of contamination to surface waters. During a rain event, the flow in a combined sewer system (CSS) may exceed the capacity of the intercepting sewer leading to a wastewater treatment plant, thus releasing a mixture of storm water and raw sanitary wastewater into the receiving water. As CSOs contain untreated domestic, commercial, and industrial wastes, as well as surface runoff, many different types of contaminants can be present. Because of these contaminants and the volume of the flows, CSOs can cause a variety of adverse impacts on the physical characteristics of surface water, impair the viability of aquatic habitats, and pose a potential threat to drinking water supplies. The resulting short-term problems are poor aesthetics (floatables, turbidity, oil and grease), and beach closure due to increased harmful bacteria levels. The long term impacts include reduced dissolved oxygen in receiving waters, eutrophication and sediment contamination. Since CSO is considered to be a major source of water quality impairment for the receiving waters, much attention has been directed to reducing the quantity and quality of CSO discharged to meet the Ministry of Environment guidelines. There are several approaches to control the quantity and quality of CSO. The selection of a particular treatment technology depends on various factors such as site conditions, CSO characteristics, receiving water requirements. One of the emerging options is the vortex separator technology for High Rate Treatment (HRT) facilities at overflow location. There are many devices for CSO control in different trade names where vortex separator technology has been used (e.g. EPA Swirl Concentration, FluidSep(TM), Storm King(TM), CDS®). This study articulates the different CSO control technologies with emphasized [sic] on vortex separator technology. The City of Niagara Falls HRT pilot project for CSO control to the Niagara River is presented as a case study in this report. The performance of two HRT devices - Storm King(TM) and CDS® are evaluated in the pilot project. Analytical Probabilistic Model has been used a a tool in this study to evaluate the potential pollution reduction at the Niagara Falls CSO system.

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

In this study, the generation characteristics of the Combined Sewer Overflows (CSOs) that occur in urban areas were investigated. In addition, performance evaluation of the CSO treatment efficiency was conducted through the field application of a high-speed filtering apparatus using a fibrous filter medium for the treatment of the CSOs that occurred in an urban area. The study site, a city located in Seoul, South Korea, was one that included the typical residential and commercial districts. The daily average flow rate of the Eungbong drainage area, which was the study site, was 92.5 m 3 /hr during the dry season, and the daily average flow rate ranged from 70.2 to 129.2 m 3 /hr, indicating a wide daily-average-flow-rate range. The highest flow rate was shown at around 9 a.m. on weekdays and at around 11 a.m. on weekends. The average influent concentrations that occurred during the dry season were 19.0 mg/L (BOD), 15.9 mg/L (COD), 10.9 mg/L (SS), 33.9 mg/L (TN), and 0.5mg/L (TP), and the hourly concentration ranges turned out to be 4.1~43.5 mg/L (BOD), 9.5~26.8 mg/L (COD), 3.6~33.0 mg/L (SS), 25.5~52.2 mg/L (TN), and 0.4~0.9 mg/L (TP). The results of the field application of a high-speed filtering apparatus using a fibrous filter medium showed that the average treatment efficiency of SS was 63.7% during the dry season. The average treatment efficiency of SS during rainfall was 84.2% (1 st ), 88.0% (2 nd ), 87.5% (3 rd ), 85.8% (4 th ), 75.8% (5 th ), 75.5% (6 th ), and 90.3% (7 th ), and exhibiting more than 80% treatment efficiency. In the case of organic contaminants like BOD, however, low treatment efficiency (less than 30%) appeared. Judging from the above results, it is difficult to expect a treatment effect if the influent concentration is less than 30 mg/L in the case of an organic material when the high-speed filtering apparatus is applied to the site, and even in the case of an influent concentration of more than 30 mg/L, the treatment efficiency is about 30% on average. The treatment effect of the particulate material (SS) remained quite high, however, without significant restrictions on the filtering liner velocity and influent concentration. The results of the analysis of the characteristics of the CSOs in urban areas and of the application of a highspeed filtering apparatus using a fibrous filter medium are expected to be utilized as basic data for management alternatives to reduce rainfall runoff loads with respect to overflows that occur during rainfall.

The Environmental Protection Agency (EPA) has stated that what was considered state-of-the-art pollution control a century ago is no longer valid today. Designers of new sewer systems must identify the problems inherited from old design concepts and try to use new technology to revisit and upgrade traditional urban drainage management. Separate sewer systems are currently used in all new developments. They are more prevalent than combined sewer systems, the use of which is limited due to numerous environmental regulations. However, the narrow streets commonly found in the UK, Europe and other densely populated areas, are usually occupied by a complex network of infrastructure services, making providing space to place a traditional separate sewer system is therefore challenging. This research presents an innovative design for manholes, created to overcome the challenges associated with the installation of separate sewer systems in narrow streets. The proposed manhole combines two traditional manholes into one structure with two separate chambers, allowing storm flow and foul flow to pass through the same manhole without mixing. The structural performance and hydraulic properties of the new design have been tested using mathematical modelling, finite element (FE) and computational fluid dynamic modelling (CFD), validated by experimental testing. The results have been compared with the performance of conventional manholes. Testing of the new manhole when buried in soil revealed high stability and resistance under applied traffic loads. With regards to the hydraulic performance of the new manhole, the head loss coefficient and pattern of shockwaves were studied for both manholes (new and conventional), under the same conditions, using independent, dimensionless parameters for each manhole. The new manhole generates higher head losses, about twice the head loss generated in a conventional manhole. Four shockwaves were identified in the storm chamber of the new manhole, the locations and characteristics of these also determined. The new manhole required a new configuration to setup the two pipes in one trench, the storm pipe over the sanitary pipe. The behaviours of these two flexible pipes were tested using a 3D finite element (FE) model, validated against experimental data from a laboratory investigation. A modified Drucker–Prager soil constitutive model was used to simulate elasto-plastic soil behaviour. The results show that this approach, using a large-diameter flexible pipe set above a small-diameter flexible pipe, mitigates the strain on the smaller pipe and decreases the total deflection of both pipes and the soil. These results led to further development of the Iowa Formula so that is can calculate the deflections of two flexible pipes set in one trench. The Improved Iowa formula was tested and compared with the experimental results. The use of the new system promises to reduce construction costs, footprint and construction time. The storage capacity and retention time increased by 280% and 200%, respectively. This new system is an attempt to improve the concept of the design of traditional sewer systems which have been in use for approximately one hundred years. The new system design can be used to install a new separate sewer system or used to separate existing combined sewer systems.

Combined sewer overflows (CSOs) degrade water quality through the release of microbial contaminants in CSO effluent. Improved understanding of the partitioning of microbial contaminants onto settleable particles can provide insight into their fate in end-of-pipe treatment systems or following release during CSO events. Sampling was performed across the hydrograph for three storm events as well as during baseflow and wet weather in three surface waters impacted by CSO. qPCR was performed for select antibiotic resistance genes (ARG) and a marker gene for human fecal indicator organisms (BacHum) in samples processed the partitioning of microbial contaminants on settleable particles versus suspended in the aqueous phase. Amplicon sequencing was performed on both fractions of storm samples to further define the timing and partitioning of microbial contaminants released during CSO events. Samples collected at the CSO outfall exhibited microbial community signatures of wastewater at select time points early or late in the storm events. CSOs were found to be a source of ARG. In surrounding surface waters, sul1 was higher in samples from select locations during wet weather compared to baseflow. Otherwise, ARG concentrations were variable with no differences between baseflow and wet weather conditions. The majority of ARG at the CSO outfall were observed on the attached fraction of samples: 64–79% of sul1 and 59–88% of tet(G). However, the timing of peak ARG and human fecal indicator marker gene BacHum did not necessarily coincide with observation of the microbial signature of wastewater in CSO effluent. Therefore, unit processes that remove settleable particles (e.g., hydrodynamic separators) operated throughout a CSO event would achieve up to (0.5–0.9)-log removal of ARG and fecal indicators by removing the attached fraction of measured genes. Secondary treatment would be required if greater removal of these targets is needed.

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

Integration of life cycle assessment and statistical analysis to understand the influence of rainfall on WWTPs with combined sewer systems

One of the most common methods of combined sewer overflow (CSO) treatment is by conventional settling, the efficiency of which depends on the properties of solid particles and the characteristics of the flow transporting these solids. Since the geometry and hydraulics of CSO facilities are often very complex, traditional design methods based on many simplifying assumptions may not predict well the actual operational performance. Therefore, there is a growing need for new tools assisting engineers in design or operation of CSO storage and treatment facilities. In a study of such a CSO facility, a commercial computational fluid dynamics (CFD) model (FLUENT) was used to investigate flow and sediment behaviour, and to explore the ways of optimizing the overall facility performance by adding flow conditioning baffles to improve particle settling. A two-stage approach was adopted; flow patterns were simulated first by means of a volume of fluid (VOF) model and subsequently formed a basis for simulating particle transport by the discrete phase (DP) model. The simulation results for water surface, flow fields in different structure configurations, and particle capture rates in three parallel CSO storage/treatment tanks are presented for various flow conditions.

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.

Each year in the United States, combined sewer overflow (CSO) events result in the release of 850 billion gallons of untreated wastewater into lakes and rivers, causing drinking water contamination, human illness, animal and fish kills, and eutrophication. This paper examines the ability of an embedded sensor network to reduce the frequency and severity of CSO events by maximizing the existing storage capacity in the combined sewer system (CSS). This novel network system is called combined sewer overflow network (CSONet). CSONet uses data gathered from a distributed network of sensors to provide decentralized, distributed, real-time control of the CSS's storage capacity using automated valves called smart valves. One pilot CSONet was deployed in South Bend, IN, during the summer of 2005. It controlled the storage of storm water runoff in a large retention basin using level data from sensors within the basin and at the CSO outfall, 3.2 miles away. Once there was no longer a threat of a CSO event, CSONet au...

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.

A generic model is introduced that represents the combined sewer infrastructure of a settlement quantitatively. A catchment area module first calculates the length and size distribution of the required sewer pipes on the basis of rain patterns, housing densities and area size. These results are fed into the sewer-cost module in order to estimate the combined sewer costs of the entire catchment area. A detailed analysis of the relevant input parameters for Swiss settlements is used to identify the influence of size on costs. The simulation results confirm that an economy of scale exists for combined sewer systems. This is the result of two main opposing cost factors: (i) increased construction costs for larger sewer systems due to larger pipes and increased rain runoff in larger settlements, and (ii) lower costs due to higher population and building densities in larger towns. In Switzerland, the more or less organically grown settlement structures and limited land availability emphasise the second factor to show an apparent economy of scale. This modelling approach proved to be a powerful tool for understanding the underlying factors affecting the cost structure for water infrastructures.

While conventional rule based, real time flow control of sewer systems is in common use, control systems based on fuzzy logic have been used only rarely, but successfully. The intention of this study is to compare a conventional rule based control of a combined sewer system with a fuzzy logic control by using hydrodynamic simulation. The objective of both control strategies is to reduce the combined sewer overflow volume by an optimization of the utilized storage capacities of four combined sewer overflow tanks. The control systems affect the outflow of four combined sewer overflow tanks depending on the water levels inside the structures. Both systems use an identical rule base. The developed control systems are tested and optimized for a single storm event which affects heterogeneously hydraulic load conditions and local discharge. Finally the efficiencies of the two different control systems are compared for two more storm events. The results indicate that the conventional rule based control and the fuzzy control similarly reach the objective of the control strategy. In spite of the higher expense to design the fuzzy control system its use provides no advantages in this case.

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