Combined Sewer Overflow Reduction Research Articles

Optimization of LID Strategies for Urban CSO Reduction and Cost Efficiency: A Beijing Case Study

Combined sewer overflow (CSO) can lead to serious urban water environment pollution and health risks to residents. Low Impact Development (LID) facilities are one of the important measures to alleviate CSO and have been widely applied. The rational selection of LID facility types, locations, and scales is the most important task, which can effectively improve resource utilization efficiency. Based on the NSGA-II multi-objective optimization algorithm and coupled with the SWMM sewer network hydraulic model, this study takes the combined sewer overflows and the construction cost of LID facilities as optimization objectives and optimizes the types and scales of LID layout in the study area, including eight different return periods. By using the Pareto frontier and visualizing the results of the model, the effects of different rainfall return periods on the CSO control and investment cost of LID layout schemes are compared. The results show the following: (1) the optimization model can demonstrate the relationship between CSO control volume and LID construction cost under different LID layout schemes through the Pareto frontier, showing three different trends, indicating that the relationship between overflow volume and investment cost is nonlinear; (2) with the increase in rainfall intensity, higher requirements are proposed for LID schemes to meet CSO control targets, leading to a decrease in the number of Pareto frontier solution sets. Under larger rainfall intensities, it is difficult to achieve the same overflow control effect by increasing the scale of LID construction. Therefore, considering constraining the LID construction cost between RMB 5.3 and 5.38 million is helpful to determine the most suitable solution; (3) in the optimal layout schemes under different return periods, 87.3% of the locations where LID is deployed have similar scales. Based on these locations with a relatively large proportion of deployment, it can be determined that special attention should be paid to spatial positions in LID planning and construction. This study provides valuable insights for solving combined sewer overflow problems and optimizing urban drainage management and provides guidance for future planning and decision-making processes.

Digitalisation of the European Water Sector to Foster the Green and Digital Transitions

During the Digital Decade, the European Union (EU) is facing two important challenges: the green (and energy) transition and the digital transition, which are interconnected with one another. These transitions are of high relevance in several aspects of our life, e.g., in the industry, energy sector, transports, environmental management and our daily life. Digital technologies are particularly emerging also as multi-benefit solution in the water sector, as water is becoming more and more vulnerable to climate change (e.g., droughts and floods) and human activities (e.g., pollution and depletion). Within this context, in this study we assessed some of the several economic benefits that digital solutions can bring to the water sector, with a focus on leakage reduction in water distribution networks, reduction of combined sewer overflows and improvement of hydropower generation and operation. The benefits are calculated for each EU Member State and the UK, and then aggregated at the EU scale. Benefits were quantified in EUR 5.0, 0.14 and 1.7 billion per year (EUR 13.2 per person per year, on average), respectively, excluding environmental and social benefits, which may play a non-negligible role.

The impact of stormwater management strategies on the flow regime of a peri-urban catchment facing urbanisation and climate change: a distributed modelling study in Lyon, France

ABSTRACT The relative impact of urbanisation (urban sprawl), climate change (rainfall and evapotranspiration) and stormwater disconnection strategies (implementation of green infrastructure (GI)) on a peri-urban stream in the western suburbs of Lyon, France, was investigated using a distributed, physically based model (J2000P). Results showed that ambitious catchment-scale implementation of GI has the potential to mitigate some hydrological effects of urbanisation, especially a drastic reduction of combined sewer overflows. However, GI did not have a large impact on the stream flow regime, especially in the context of climate change, as the stream is dominated by non-urban contributions. Spatially distributed models have the capacity to inform river managers about the extent of implementation of GI needed to achieve given management goals and highlight some limitations of disconnection strategies. Indeed, while GI improved the resilience of sewer networks to global change, it was not sufficient to compensate for the effects of climate change on streamflow.

Optimization of Real‐Time Control With Green and Gray Infrastructure Design for a Cost‐Effective Mitigation of Combined Sewer Overflows

AbstractAn 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.

Is flow control in a space-constrained drainage network effective? A performance assessment for combined sewer overflow reduction

Recurring combined sewer overflows (CSOs) can have a significant impact on the ecological condition of receiving water bodies. There are several structural measures, like adding retention basins and switching to low impact development solutions, that have been proposed to reduce the number of sewage overflows. Besides, several flow control strategies have been discussed in scientific literature that take advantage of the space within urban drainage networks, which is assumed to be adequate, for temporary storage. The adequacy of such storage space, however, is not a universally valid assumption as a large fraction of drainage networks frequently operate close to their design discharge. In this paper, we investigate the efficacy of flow control for a space-constrained drainage network. We employ a low-cost, heuristic real time control strategy with the use of flow control devices (FCDs) and available in-sewer space to reduce the magnitude of CSOs. We consider the performance of the proposed control strategy and discuss the effect of FCD location on CSO reduction. Our results, based on over 300 rainfall-event simulations, show that the flow control strategy using limited sewer capacity is more efficient during relatively small rainfall events, where the CSO is large enough to enable reduction using the chosen control rules. The CSO is reduced, to varying degrees, for around 80% of rainfall events with peak intensity between 10 and 20 mm h−1. For larger rainfall events, the flow control is more unstable in response to abrupt water release during control operation, which seems to be unavoidable because of the water accumulation effect and the transition to pressurized pipe flow in space-constrained networks. We also found that the flow control performance is highly sensitive to the FCD location – as it depends on the interplay of the peak rainfall intensity and the water level condition immediately upstream of the FCD. The efficacy of a location for flow control is determined by the unfilled capacity (i.e., effective in-sewer storage potential) in the pipe upstream of the FCD during the rainfall peak; furthermore, the location also has to be resistant to the water accumulation effect. Using our analysis, we substantiate two anticipated caveats to flow control strategies when the storage space is limited in a drainage network: diminished performance in CSO reduction and the appearance of additional control-related challenges, which are otherwise mitigated in more spacious networks.

Not all SuDS are created equal: Impact of different approaches on combined sewer overflows

Sustainable urban drainage systems (SuDS) help in stormwater management by reducing runoff volume, increasing runoff concentration time and thereby improving the drainage system capacity. This study investigated the potential and cost-effectiveness of SuDS in reducing combined sewer overflows (CSOs). We simulated the performance of four SuDS techniques (bioretention cell, permeable pavement, rain barrel and green roof) at incremental levels of spatial coverage for a small urban catchment with a combined sewer system. We also used an Analytic Hierarchy Process (AHP) considering end-point CSO, land use, imperviousness, slope and elevation criteria to identify priority areas for SuDS deployment. Results showed that CSO volume attenuation ranged a maximum of 50–99% for the catchment, depending on the deployment strategy and underlying mechanisms of each technology. We also found that deployment of SuDS in AHP-selected sub-catchments improved CSO reduction only for rain barrels and green roofs, but not for bioretention cells and permeable pavements. SuDS were also a cost-effective retrofit option: for a 40% volume reduction, the SuDS cost, at most, 25% of the equivalent cost required for a large CSO tank. Outcomes of this study demonstrate the efficacy of SuDS in controlling CSOs, adding yet another tangible benefit to their increasingly recognised multi-functionality.

Sustainable urban drainage systems in established city developments: Modelling the potential for CSO reduction and river impact mitigation

Sustainable urban drainage systems (SUDS) can significantly reduce runoff from urban areas. However, their potential to mitigate acute river impacts of combined sewer overflows (CSO) is largely unknown. To close this gap, a novel coupled model approach was deployed that simulates the effect of realistic SUDS strategies, developed for an established city quarter, on acute oxygen depressions in the receiving river. Results show that for an average rainfall year the SUDS strategies reduce total runoff by 28%–39% and peak runoff by 31%–48%. Resulting relative reduction in total CSO volume ranges from 45%–58%, exceeding annual runoff reduction from SUDS by a factor of 1.5. Negative impacts in the form of fish-critical dissolved oxygen (DO) conditions in the receiving river (<2 mg DO L−1) can be completely prevented with the SUDS strategies for an average rainfall year. The realistic SUDS strategies were compared with a simpler simulation approach which consists in globally downscaling runoff from all impervious areas. It indicates that such a simple approach does not completely account for the positive effect of SUDS, underestimating CSO volumes for specific rain events by up to 13%. Accordingly, global downscaling is only recommended for preliminary planning purposes.

MULTI-OBJECTIVE OPTIMIZATION OF COMBINEDSEWER OVERFLOW CONTROL SYSTEM

How to reduce the construction cost while increasing the reduction rate of combined sewer overflow (CSO) control system has been widely concerned by the planning & decision makers. In this study, the multi-objective optimization model of CSO system construction cost and CSO reduction rate was established by using Matlab, Python and SWMM. A series of Pareto solution sets were obtained using non-dominant sorting genetic algorithm (NSGA-Ⅱ), so different options were put forward to planning decision makers. For the 3-year storm events, the optimization results showed that the proportion of the construction cost was highest for constructing source low impact development (LID) facilities, followed by constructing the detention tanks and retrofitting the midway pipes. Among the three types of facilities, the contribution of the CSO reduction rate of the detention tanks was the highest, followed by the source LID facilities and the midway pipes.

Studying the effect of bioswales on nutrient pollution in urban combined sewer systems

The objective of this study was to evaluate the impact of bioswales on nutrient pollution in an urban combined sewershed. This evaluation was based on two criteria: the ability of bioswales to (1) remove nutrient pollution from stormwater runoff directly and (2) decrease sewer overflow volumes, which indirectly reduces total sewershed nutrient pollution during a storm event. Bioswales' direct nutrient removal was determined by analyzing nitrogen and phosphorus levels in water samples at seven bioswales located in the Bronx, New York City (NYC) over 42 storm events, while a bioswale's indirect nutrient removal through combined sewer overflow reduction was estimated by quantifying water retention at one of the bioswales. The study results indicated that: 1) the bioswale retained about 40% of stormwater conveyed to it from a drainage area 231 times its size, 2) bioswales leach nutrients into the subsurface, and 3) nitrogen leaching from bioswales varied seasonally, while phosphorus leaching decreased steadily over the study period. Although the studied bioswales leached a median 1.3 kg nitrogen per year into the subsurface, they provided an aggregate decrease in watershed nutrient pollution, from 7.7 to 6 kg nitrogen per year, due to their reduction of combined sewer overflow via stormwater retention.

Energy optimization of the urban drainage system by integrated real-time control during wet and dry weather conditions

ABSTRACTAn extension of the frequently applied equal filling degree control algorithm is proposed for integrated control of sewer system and wastewater treatment plant (WWTP). Under dry weather conditions (DWC), this control synchronizes sewer storage volume activation at pumping stations (PS) throughout the sewer system with the intermittent aeration at the WWTP. This is in contrast with the frequently advocated influent load equalization at WWTPs. The concept is demonstrated on a case study using an integrated system composed of detailed models for sewer system and WWTP where it reveals considerable potential for energy savings and effluent quality improvement. Moreover, the integrated control allows for the reduction of combined sewer overflows during wet weather events and decreased sedimentation potential in the sewer system. Neither weather predictions nor structural changes at the WWTP or in the sewer system are required. The control concept is applicable to about 50 Flemish WWTPs.

A Framework for Multifunctional Green Infrastructure Investment in Camden, NJ

This study demonstrates a decision-support framework for planning Green Infrastructure (GI) systems that maximize urban ecosystem services in Camden, NJ. Seven key ecosystem services are evaluated (urban agriculture expansion, combined sewer overflow reduction, heat island reduction, flooding reduction, capacity building/green jobs expansion, fitness expansion, and stress reduction), to produce a normalized value for each service for each drainage sub-basin within the city. Gaps in ecosystem services are then mapped and utilized to geographically prioritize different kinds of multifunctional GI. Conceptual designs are developed for four site typologies: parks, schools, vacant lots, and brownfield sites. For one demonstration site, additional analysis is presented on urban engagement, life cycle cost reduction, and new sources of funding. What results is an integrated, long-term vision where multifunctional GI systems can be readily customized to meet multiple needs within urban communities. This study provides a portable and replicable framework for leveraging the regulatory requirement to manage stormwater to meet broader urban revitalization goals, all through a decentralized network of green infrastructure assets.

Design and evaluation of control strategies in urban drainage systems in Kunming city

Real time control (RTC) of urban drainage systems (UDSs) is an important measure to reduce combined sewer overflow (CSO) and urban flooding, helping achieve the aims of ‘Sponge City’. Application of RTC requires three main steps: strategy design, simulation-based evaluation and field test. But many of published RTC studies are system-specific, lacking discussions on how to design a strategy step by step. In addition, the existing studies are prone to use hydrologic model to evaluated strategies, but a more precise and dynamic insight into strategy performance is needed. To fill these knowledge gaps, based on a case UDS in Kunming city, a study on RTC strategy design and simulation-based evaluation is performed. Two off-line volume-based RTC strategy design principles, Maximize WWTP inflow and Make full use of space, are emphasized. Following these principles, a detailed design procedure is shown for the case UDS resulting in three RTC strategies: static, constant and equal filling. The proposed strategies are evaluated based on a hydrodynamic model- StormWater Management Model (SWMM) - under four typical rainfall events characterized by different return periods (1-year or 0.5 year) and different spatial distributions (uniform or uneven). The equal filling strategy outperforms other two strategies and it can achieve 10% more CSO reduction and 5% more flooding reduction relative to the no-tank case.

Improving the microbiological quality of the Ruhr River near Essen: comparing costs and effects for the reduction of Escherichia coli and intestinal enterococci.

After rain events in densely populated areas, combined sewer overflows (CSOs) can have severe health-related effects upon surface water quality, as well as diffuse overland runoff and wastewater treatment plants (WWTPs). All of these sources emit pathogens and fecal indicator bacteria into the surface water, which the EU Bathing Water Directive addresses by giving threshold values for the indicators Escherichia coli and intestinal enterococci. This study presents a comparison between 21 scenarios of costs for processes that reduce the load of Escherichia coli and intestinal enterococci into the Ruhr River during and shortly after rain events. The methods examined include UV irradiation for WWTPs, integrated sewer management and treatment of CSOs with vertical flow constructed wetlands or performic acid. For pollution by diffuse overland flow, we evaluated organizational measures. The treatment of only diffuse pollution shows merely a slight effect on intestinal enterococci, but none on Escherichia coli and hence, was not considered further. Combining all three CSO reduction methods with the irradiation of WWTP effluent provides the best simulation results in terms of reducing both indicator bacteria.

Evolutionary and Holistic Assessment of Green-Grey Infrastructure for CSO Reduction

Recent research suggests future alterations in rainfall patterns due to climate variability, affecting public safety and health in urban areas. Urban growth, one of the main drivers of change in the current century, will also affect these conditions. Traditional drainage approaches using grey infrastructure offer low adaptation to an uncertain future. New methodologies of stormwater management focus on decentralized approaches in a long-term planning framework, including the use of Green Infrastructure (GI). This work presents a novel methodology to select, evaluate, and place different green-grey practices (or measures) for retrofitting urban drainage systems. The methodology uses a hydrodynamic model and multi-objective optimization to design solutions at a watershed level. The method proposed in this study was applied in a highly urbanized watershed to evaluate the effect of these measures on Combined Sewer Overflows (CSO) quantity. This approach produced promising results and may become a useful tool for planning and decision making of drainage systems.

Decentralized Stormwater Controls for Urban Retrofit and Combined Sewer Overflow Reduction

Phase 1 of this project demonstrated the technical feasibility of using decentralized stormwater controls in urban areas for retrofits and controlling combined sewer overflows. This technical feasibility was illustrated by a number of early adopters using decentralized controls to complement their existing municipal stormwater and wastewater infrastructure. However, institutional and programmatic issues required further study to broaden the use of a distributed, decentralized stormwater approach. This research evaluates implementation strategies for incorporating decentralized controls into an infrastructure management system. The distributed nature and multiple environmental benefits of decentralized controls necessitate an integrated and inter-departmental management approach. The results of this research identify various implementation strategies for incorporating decentralized controls into urban infrastructure management programs. Case studies and programmatic and regulatory examples detail alternatives to expedite the adoption of decentralized controls. Managing infrastructure by limiting demand is explored in the context of distributed controls. In addition, an evaluation of economic methods appropriate for assessing environmental costs and benefits is included to more fully capture the financial consideration of decentralized controls. Guidance for modeling decentralized controls with commonly used stormwater models is also provided. This title belongs to WERF Research Report Series . ISBN: 9781843393535 (Print) ISBN: 9781780403588 (eBook)

Combined sewer overflow control with LID based on SWMM: an example in Shanghai, China.

Although low impact development (LID) has been commonly applied across the developed countries for mitigating the negative impacts of combined sewer overflows (CSOs) on urban hydrological environment, it has not been widely used in developing countries yet. In this paper, a typical combined sewer system in an urbanized area of Shanghai, China was used to demonstrate how to design and choose CSO control solutions with LID using stormwater management model. We constructed and simulated three types of CSO control scenarios. Our findings support the notion that LID measures possess favorable capability on CSO reduction. Nevertheless, the green scenarios which are completely comprised by LID measures fail to achieve the maximal effectiveness on CSO reduction, while the gray-green scenarios (LID measure combined with gray measures) achieve it. The unit cost-effectiveness of each type of scenario sorts as: green scenario > gray-green scenario > gray scenario. Actually, as the storage tank is built in the case catchment, a complete application of green scenario is inaccessible here. Through comprehensive evaluation and comparison, the gray-green scenario F which used the combination of storage tank, bio-retention and rain barrels is considered as the most feasible one in this case.

Speed of discrete optimization solvers for real time sewer control

In the project ‘Integrale sturing afvalwater en oppervlakte water Hoeksche Waard’ (integral management of the drainage and sewer system on the island ‘Hoeksche Waard’) in the southwestern Netherlands a central controller was developed for small sewer systems. The aim was the improvement of water quality through the reduction of combined sewer overflows. Two field tests of the controller went very well. Extension to a larger system resulted in timing problems. This paper investigates these problems. The controller minimizes the deviation from proportional distribution of the volume of sewage over the system. The pumping stations contain several pumps that can be either on or off, so the variables to be optimized do not vary continuously, but are only allowed to have integer values. The computational cost is investigated for different solvers. This cost determines the applicability of a solver for a given system size and time step.

Re-establishing Hydrological and Ecological Benefits as part of Sewer Separation in Cincinnati, Ohio

Re-establishing Hydrological and Ecological Benefits as part of Sewer Separation in Cincinnati, OhioAs part of a combined sewer overflow (CSO) reduction strategy to reduce approximately 800 million gallons of CSO volume per year from CSO 5 by 2018, the Metropolitan Sewer District of Greater Cincinnati (MSDGC) has initiated a series of sewer separation design projects in the Lick Run sewershed that incorporate green infrastructure as part of the CSO reduction strategy. Within the Lick Run...Author(s)Matt BooneSharon Jean-BaptisteKellie HebertPaul BahsJohn ShadySourceProceedings of the Water Environment FederationDocument typeConference PaperPublisherWater Environment FederationPrint publication date Sep, 2012ISSN1938-6478DOI10.2175/193864712811704576Volume / Issue2012 / 6Content sourceWEFTECCopyright2012Word count172

Decentralized Stormwater Controls for Urban Retrofit and Combined Sewer Overflow Reduction, Phase 2

Decentralized Stormwater Controls for Urban Retrofit and Combined Sewer Overflow Reduction, Phase 2

Rapid assessment of the cost-effectiveness of low impact development for CSO control

This paper presents a simple model for assessing the cost-effectiveness of investments in low impact development (LID) for reducing combined sewer overflows (CSOs) in urban watersheds. LID systems, including green roofs, porous pavement, and stormwater treatment wetlands, are site-specific controls for stormwater runoff. If applied throughout a watershed, LID systems like these can reduce the amount of runoff entering the sewer system and reduce CSOs. To be conservative, we focus solely on the function of LID systems as stormwater management techniques, neglecting the other environmental benefits commonly associated with these technologies. A model is presented that can be used to simulate the cost-effectiveness of reducing CSOs through incremental installation of LID technologies across urban watersheds, when they are introduced alone, or in combination with conventional CSO abatement technologies. The potential reduction in CSOs resulting from various levels of LID adoption is simulated using a modified Rational Method. A life-cycle cost analysis is used to compare LID with other alternatives. Given that LID implementation on private property leads to reduced CSOs, a cost sharing scheme is presented that divides the total LID cost into a private cost fraction (born by the property owner) and a public cost fraction (provided by a public agency). The implications of such a policy are discussed with reference to a CSO-shed that drains to the Gowanus Canal (Brooklyn, NY). The results indicate that individual LID systems have differing levels of cost-effectiveness in terms of CSO reduction, but that under a variety of performance and cost scenarios a public subsidy to encourage LID installation represents a cost-effective alternative for public agencies to consider in their efforts to reduce CSOs. Future areas of research in this field are outlined.