An Innovative Design for a Separate Sewer System

Separate sewer systems are currently used in all new developments and are prevalent in comparison with combined sewer systems, the use of which is limited due …

Green Stormwater Infrastructure (GSI), which includes elements like green roofs, bioretentions, pervious pavement and cisterns, has proven to be a cost effective alternative that can achieve a wider range of benefits in stormwater management compared to the single-purpose grey/traditional infrastructure (Combined Sewer System or Municipal Separate Storm and Sewer System). However, the implementation of GSI as a replacement or support system for grey infrastructure faces some barriers preventing its adoption by planners/designers and decision makers, in the private as well as in the public sector. While understanding and quantifying the full costs and the benefits of GSI plans are critical for sound decision making and to facilitate its adoption, planners/designers face challenges pertaining to hydrologic calculations (including sizing of Green Stormwater Infrastructure Elements (GSIEs), cost estimation (life cycle costs) and benefit assessment). This thesis presents a proof of concept tool (prototype) that is developed to help planners/designers and different stakeholders involved in conducting a comprehensive GSI planning process. The tool generates GSI alternative solutions (combination and size of GSIEs) that meet the user’s financial and hydrologic objectives. These alternatives are generated to maximize benefits, reduce costs and account for design specifications and multi-functionality of GSI. The prototype has three modules: An Interface Module (including Input and Output Interfaces) A Process Module for hydrology, cost and benefit calculation and an optimization model for strategy generation.A Database Module for storing collected data that are used for different process module calculations. The prototype, which is developed in Ms. Excel, was successfully tested for functionality and usability on a residential development site in Pittsburgh, PA. The prototype required minimal input from the user (site specific data) and generated strategies that double the net annual benefits compared to the plan proposed by the developer. The tool also allowed generation of strategy scenarios that responded to multiple user objectives.

Separate sewer systems collect and discharge rainwater directly into surface water bodies. In residential areas covering moderate traffic load these are alternative drainage routes to avoid combined sewer overflow discharge and to keep rivers clean as required by the EU Water Framework Directive. This overflow's microbial quality, however, needs to be evaluated, since stormwater run-offs are potential pathways for pathogens into river systems. Between 2010 and 2016, two separate sewer systems in North Rhine-Westphalia (Germany) were investigated. The stormwater outflow was sampled during discharge events and microbiologically analysed. The results showed high concentrations of Escherichia coli (1,100-1,100,000 CFU/100 mL) and Clostridium perfringens (20-13,000 CFU/100 mL). Campylobacter and Salmonella were detected in 97% and 43% of the samples. Giardia cysts were more often detected (31.6%) than Cryptosporidium oocysts (10.5%). The sources of human pathogens in rainwater run-off are heterogeneous. While roads have already been declared as chemical polluters via rainwater run-off, our study detected supplementary pollution of mainly faecal microorganisms. Presumably, failed connections in the sewer system itself are important sources of human pathogens. We suggest treatment of stormwater run-offs before being discharged into the river system.

This paper presents an overview of the transport of toxic pollutants through multiple media and drainage systems in the urban watershed during wet-weather periods. It includes the origin of the toxic substances; their transport via atmospheric deposition, overland washoff, and urban sewer systems; and, their impacts on both surface and ground waters. During dry-weather periods, incompletely combusted hydrocarbons from automobiles combine with atmospheric particulates from a host of other sources and deposit on urban streets and other urban surfaces. During a storm event, these solids, in addition to solids from industrial and commercial parking lots, material storage areas, and vehicular service stations are washed off by surface runoff and drained into either separate storm sewer or combined sewer systems. Field studies have identified that a major portion of hazardous waste priority pollutants including benzene, polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides, and heavy metals (e.g., arsenic, cadmium, chromium, copper, lead, mercury, and zinc) contained in urban stormwater runoff are in particulate form or sorbed onto particles. These stormwater particulate pollutants contribute significant toxicity to receiving waters. Mortality, epidermal lesions, or fin erosion can occur in fish and other aquatic life forms that are exposed to these toxic suspended solids and sediments. Methods for intercepting the cross-media transport of toxic constituents in the urban environment include best management practices to control surface runoff pollution; steeper sewer slopeage and improved pipe bottom shapes to maintain high velocity solids-carrying capacity during low-flow periods; and upstream sewer flushing and sediment trapping to reduce clogging and sediment in sewers.

A geyser in a closed conduit system is characterized by an explosive release of a mixture of air and water through a drop shaft. Geysers are often observed in combined sewer systems (CSSs) as an explosive form of combined sewer overflows (CSOs). In the present work, the flow characteristics of sewer geyser phenomenon are studied numerically using a three-dimensional computational fluid dynamics (CFD) model for the first time. Traditionally, investigations of flow processes associated with sewer geysers are conducted through physical experiments and one or two-dimensional numerical models. However, sewer geysers are undeniably three-dimensional, hence 3D models are necessary to gain further understanding of the phenomena. The CFD model was calibrated using an experiment that exhibit characteristics of sewer geysers.

The FURBAS project (Forecasting urban floods and strong rainfall events, 2022-2025) aims at establishing a real-time pluvial flood forecast system for the city of Hanover in Germany with a total catchment area of 260 km². The forecast system consists of radar rainfall with nowcasting  and an Artificial Neuronal Network (ANN) to forecast the dynamical evolution of surface water levels in the city with a spatial resolution of 5x5 meter and a temporal resolution of 5 minutes (Berkhahn & Neuweiler, 2023). The ANN is trained based on results of a physically based hydrodynamic model (HYSTEM EXTRAN 2D) with bi-directional coupled storm-sewer (1d) to surface (2d) domain.The terrain has a slight gradient which causes a long travel time in the sewer system. The pipe network is partially built as combined sewer and separate sewer system. In the latter, rainfall is partially routed via trenches that are modelled as part of the 2d surface. These trenches are required to get an impression of the overall extent of the flooding and the interaction with the sewer system. In classical modelling approaches the drainage volume vanishes when reaching the outlets of the pipe network which leads to an underestimation of the flood level. We show the effects of modelling trenches as elements of the surface and provide tips for the correct arrangement of trenches.The underground transport tunnels of a city are a rarely modelled factor in the flooding of a city. The underground stations are connected to the public drainage system where it can lead to a drainage delay, due to underground storage tanks. Flooding or overload of the drainage pipes along the underground tunnels have an important influence on the operability of the trains because the inflowing water is pumped into the regular drainage network. The fill level of the pipes is therefore the decisive limit value. We show the effects of station entrances and tunnel ramps to the water level at the surface and how the precipitation intensity is decisive for the operation of the trains.Funding:The FURBAS research project is a cooperation of the Institute for Technical and Scientific Hydrology (itwh) GmbH, the Institute of Fluid Mechanics and Environmental Physics in Civil Engineering, Leibniz University of Hanover, and the municipal operation for Hanover city drainage. The project is funded by the German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection under grand number 67DAS224.Literature: Berkhahn, S., & Neuweiler, I. (2023). Data driven real-time prediction of urban floods with spatial and temporal distribution. Journal of Hydrology X, 100167.

'Classical' real-time control (RTC) strategies in sewer systems are based on water level and flow measurements with the goal of activation of retention volume. The control system rule of 'clean (storm water) runoff into the receiving water - polluted runoff into the treatment plant' has been thwarted by rough operating conditions and lack of measurements. Due to the specific boundary conditions in the city of Wuppertal's separate sewer system (clean stream water is mixed with polluted storm water runoff) a more sophisticated--pollution-based--approach was needed. In addition the requirements to be met by the treatment of storm water runoff have become more stringent in recent years. To separate the highly-polluted storm water runoff during rain events from the cleaner stream flow a pollution-based real-time control (P-RTC) system was developed and installed. This paper describes the measurement and P-RTC equipment, the definition of total suspended solids as the pollution-indicating parameter, the serviceability of the system, and also gives a cost assessment. A sensitivity analysis and pollution load calculations have been carried out in order to improve the P-RTC algorithm. An examination of actual measurements clearly shows the ecological and economic advantages of the P-RTC strategy.

Isotopic tracing and quantitative assessment of rainwater in a separate sewer system in Tiszavasvári, Hungary

도시 우수 배수 시스템에서 우수 관거는 개수로 흐름 상태로 가정하여 설계되었기 때문에 맨홀에서의 에너지 손실은 일반적으로 중요하게 고려되지 않았다. 그러나 과부하흐름에서 에너지 손실은 관거의 배수능력을 저하시켜 도심지역의 침수피해를 가중시키는 요인이 된다. 그러므로 과부하 맨홀 내에서의 수두 손실을 분석할 필요가 있다. 본 연구에서는 맨홀에 대한 문헌조사 및 현장조사를 실시하여 실험장치 제작과 실험조건을 선정하였다. 선정된 실험조건인 인버트 형상 조건(CASE A, B, C), 단차 조건(CASE I, II, III) 및 실험 유량(<TEX>$1.0\;{\sim}\;5.6\;{\ell}/sec$</TEX>)을 변화시키면서 실험을 실시하였다. 맨홀 직경(<TEX>$D_m$</TEX>)과 유입관경(<TEX>$D_{in}$</TEX>)의 비(<TEX>$D_m/D_{in}$</TEX>)가 증가할수록 손실계수가 증가하였으며, 맨홀 수심(<TEX>$h_m$</TEX>)과 유입관거 직경(<TEX>$D_{in}$</TEX>)의 비(<TEX>$h_m/D_{in}$</TEX>)가 <TEX>$1.0{\sim}1.5$</TEX>일 때 손실계수가 가장 크게 산정되었다. 또한, CASE A, B, C의 평균 손실계수는 각각 0.45, 0.37, 0.3으로 산정되었다. 맨홀에 U자형 인버트를 설치하면, 원형 맨홀에서 에너지 손실을 저감시킬 수 있다. 또한 산정된 맨홀에서의 손실계수는 과부하흐름을 고려한 우수 관거 설계에 활용될 수 있다고 판단된다. Urban sewer systems are designed to operate in open-channel flow regime and energy loss at circular manholes are usually not significant. However, the energy loss at manholes, often exceeding the friction loss of pipes under surcharge flow, is considered as one of the major causes of inundation in urban area. Therefore, it is necessary to analyze the head loss associated with manholes, especially in surcharge flow. Hydraulic experimental apparatus which can be changed the invert type(CASE A, B, C) and step height(CASE I, II, III) was installed for this study. The range of the experimental discharges were from <TEX>$1.0{\ell}/sec$</TEX> to <TEX>$5.6\;{\ell}/sec$</TEX>. As the manhole diameter ratio(<TEX>$D_m/D_{in}$</TEX>) increases, head loss coefficient increases due to strong horizontal swirl motion. Head loss coefficient was maximum because of strong oscillation of water surface when the range of manhole depth ratios(<TEX>$h_m/D_{in}$</TEX>) were from 1.0 to 1.5. The average head loss coefficients for CASE A, B, and C were 0.45, 0.37, and 0.30, respectively. Accordingly, U-invert is most effective for energy loss reduction at circular manhole. This head loss coefficients could be available to design the urban sewer system with surcharge flow.

Qualitative measurements in combined sewer systems lead to high demands on the measurement equipment. This paper describes the application of a newly developed measuring device for continuous measurements in combined sewer systems. First results with a prototype tested in municipal waste water show a very good representation and correlation of the physical parameters measured by the online-probe and the chemical analysis of samples in the laboratory. Measurements in industrial waste water with varying colors and concentrations made it necessary to develop a specialized calibration model. Finally, the paper describes an improved version of the measuring device, that was developed during a research project. In the future, this device will be used for continuous measurements of the parameters COD, SS and SAC in a stormwater overflow. Introduction Continuous measurements in sewer systems are a special challenge for the implementation of measurement equipment and it’s operators. Until recently, they were limited to physical parameters like water level, temperature, and flow. For control purposes, however, bio-chemical parameters are measured over a limited period of time. For these measurements, bottle sampling devices with subsequent chemical analysis are commonly used. Nevertheless, bottle sampling devices are unfit to supply continuous measurements for the purpose of online-monitoring and load-dependent control of combined sewer systems. Probes in combined sewer systems allow to directly record changes in the composition of the waste water and to record data for online control purposes. Bogaczyk, D. (2000) divided measurement systems into continuous and discontinuous systems. For discontinuous measurements, a separate flow was split from the combined sewer system and pumped through a bypass into a black box (i.e. a small storage tank). The latter contained the probes. The time needed to fill and empty the black box determined the time needed for a measurement-cycle. The signal from the probe showed a time-lag, because some time was passing between the extraction of the sample from the sewer and the subsequent measurement with a probe. For continuous measurements, the probe is located directly in the sewer. Under these conditions the probe was sending a dense signal with minimal time-lag.

210Pb chronology assessing the historical microplastics dynamics and aging effects in urban areas with separate sewer systems and multiple-use reservoir.

Low bar spacing trash racks have been widely investigated in order to guide fish toward bypasses. In addition to this biological function, the formulae to predict head losses, for hydropower plants, are still being discussed. This paper investigates and models the global head losses generated by inclined trash racks with six different bar shapes and two different supports, in an open channel for six angles and two low bar spacings. The girders that supported the trash racks were U-shaped and different profile shapes. In addition to the previously studied rectangular and “hydrodynamic” bars, four new bar shapes, combining different leading and trailing edges, were investigated. Water depths were measured upstream and downstream of the rack for each configuration, and head loss coefficients were characterized and modeled. Three of these new bar shapes generated lower head losses than the hydrodynamic bar shape. The most efficient bar profile reduced the shape coefficient by 40% compared to the hydrodynamic profile and by 67% compared to the conventional rectangular profile. Concerning the supports, the use of a profiled girder to replace a conventional U-shaped girder also significantly reduced the head losses. The addition of the girder effect in a global formula increased its accuracy in predicting head losses of inclined trash racks upstream of hydropower plants.

Grit removal is a process required in both separate and combined sewer systems, and at wastewater treatment plants. The bulk of grit in collection systems results from surface water runoff from impervious areas especially during the early stages of a storm. Industrial activities and construction also generate large volumes of grit that finds its way into collection systems. This paper reviews processes for grit removal in collection systems and at wastewater treatment plants and discusses the key optimal arrangements and configurations for effective and efficient grit removal and handling. Grit characteristics and grit removal data from a number of operational sites in the US are presented together with important design features that need to be taken into account in the implementation of grit removal schemes.

A new software package has been developed for use in real-time control of the flow in combined sewer systems (CSS). A central feature of the new package is forecast modelling of the flows and volumes in the sewer system. Based upon the forecast model predictions, an expert system or an optimisation module determines the set-points for all regulators in the system. The new software package includes a comprehensive tool-set for use in the design of on-line control systems, including a model-based real-time simulator, which can be applied in the testing of control strategies. The first practical application of the software package for a sewer system in the city of Aalborg is described.

As the flow expands at expansions, generation of turbulence by shear layers results in the dissipation of energy of the mean flow. Based on simplified momentum equations, this head loss was previously estimated to be comparable to the velocity head of the incoming flow. In this paper, an approach based on turbulent jet theories is used to more accurately evaluate head loss at outlets. This approach is based on the similarity between the generation of a shear layer at an outlet to that of a turbulent jet at its origin. A general equation is derived for the variation of the kinetic energy of the flow from outlets of any geometry and the corresponding head loss coefficient. The equation is simplified for rectangular outlets, which are more common in practice.