Combined Sewer Research Articles

Combined sewer overflows: relating event duration monitoring data to wastewater systems' capacity in England

Water pollution caused by the frequent use of combined sewer overflows (CSOs) has been attracting increased media and political coverage in England as in other places in the world.

APPLICATION OF MULTIPLE LINEAR REGRESSION MODELS TO DETERMINE MICROBIAL WATER QUALITY CHANGES ACROSS HIGHLY DISTURBED LOWER HIMALAYAN STREAM AND THE GROUNDWATER SOURCES IN THE PROXIMITY, JAMMU (INDIA)

The study investigated the microbial quality of Behlol stream- a Lower Himalayan stream and groundwater sources in its proximity areas in terms of MPN index/100 ml for total and faecal coliforms and application of statistical tools like correlation and linear regression to deduce beneficial parametric associations for easy interpretation of the data. MPN/100 ml index analysis revealed severe microbial contamination at the surface water sampling site S2 and the nearby groundwater sites G2 and G3 indicating the impact of surface water pollution on the groundwater sources. The authors observed that the rate of groundwater contamination decreased with the increase in distance from the surface water sites suggesting that the groundwater pollution is mainly contributed by the release of combined industrial and sewage wastes into the Behlol stream. The study also identified bacterial genera like Escherichia, Enterobacter, Klebsiella, Citrobacter, Proteus, Salmonella, and Shigella, belonging to the family Enterobacteriaceae via colony cultural characteristics and biochemical tests. A significant relationship obtained from an orderly linear correlation and regression in this study provides a better alternative for a systematic study over the conventional techniques; reducing the quantum of analysis and can therefore be treated as a rapid method for water quality monitoring

Study on urban combined sewer overflows and self-purification capacity load of river

Study on urban combined sewer overflows and self-purification capacity load of river

Implementing green infrastructure for stormwater management and combined sewer overflow control

Implementing green infrastructure for stormwater management and combined sewer overflow control

Optimization of Locations for Bioswales Stormwater Management Using BMP Siting Tool - Case Study of Sulaymaniyah City-KRG-Iraq

Today, urban Stormwater management is one of the main concerns of municipalities and stakeholders. Drought and water scarcity made rainwater harvesting one of the main steps toward climate change adaptation. Due to the deterioration of the quality of urban runoff and the increase of impermeable urban land use, the treatment of urban runoff is essential. Best Management Practice (BMP) and Low Impact Development (LID) approaches are necessary to combat climate change consequences by improving the quantity and quality of water resources. The application of Bioswales along urban streets and roadways can reduce the stress on water resources, recharge groundwater and prevent groundwater pollution. While Sulaymaniyah City has a combined sewer network, the application of Bioswales makes wastewater treatment possible in all seasons. This study aimed to determine suitable locations for LID as one of the methods of urban runoff management in Sulaymaniyah City, KRG Iraq. The research modeled and optimized the placement of Bioswales using the BMP Sitting Tool (BST) in the ArcGIS program. Results of the study suggested a total area of 104329 m2 in 530 locations for the installation of the Bioswale system. Also, results showed that land use parameters and soil hydrological groups could be considered important factors in selecting a suitable location for Bioswale system establishment.

The ability of reusing municipal treated water for irrigation the landscaping in Vietnam. The research in constructed wetland in municipal wastewater treatment plant, Danang city

All around the world, the constructed wetland is a variation for for reusing treated water by irrigation the landscaping. Based on the synthesis and metabolism of different plant species, nutrients, especially nitrogen and phosphorus, in wastewater has been removed. Therefore, the article evaluates the ability of reusing municipal treated water from combined sewerage system for technology constructed wetland. Based on building and operating model wetland in municipal wastewater treatment plant for 2 months, adaptability of 2 selected plant species in model include Canna generalis and Portulaca grandiflora has been determined. At first, the experiment evaluates of the growth and development of plants. After that, based on operated model with with hydraulic rention time was 48 hours and hydraulic loading rate is approximately 0.2 m3/m2/d, the efficiency transformation of Nitrogen in range 30 – 40% with Canna generalis and 20 – 30% with Portulaca grandiflora. Moreover, the preformance removing ortho phosphorus of both models in range 40 – 60%. Sumerize, the synthesis and metabolism of nutrients by these plants will reduce the loading of biological reactor in wastewater treatment plants.

The database management framework for combined sewerage system of Phu Loc river basin in Danang city by GIS

Nowadays, Geographic Information Systems (GIS) applications have provided tools to integrate information, visualize scenarios, present powerful ideas, and develop effective solutions like never before so that it supports strategic decision making. Based on the advantages of GIS applications, the main goal of database management framework is simulation and visualization combined sewerage system and water quality data of Phu Loc river, Da Nang city via QGIS software. Although the length of the river is only 1.9 km, the Phu Loc river was discharge point of drainage basin in the northwest area of Da Nang city with a total area of more than 3500 hectars, which included 5 urban lakes, the municipal wastewater treatment plant with capacity over 40000 m3/d. After transform and organize data from other source to QGIS, the researchers created a database management framework for sewerage system with relation model for each group of data. Based on process digitalization data of water quality, QGIS software should presented type of digital map of Phuloc basin area with construction of combined sewerage system for basin area and water quality index for river and urban lakes.

Optimal siting of rainwater harvesting systems for reducing combined sewer overflows at city scale

The installation of green infrastructure (GI) is an effective approach to manage urban stormwater and combined sewer overflow (CSO) by restoring pre-development conditions in urban areas. Research on simulation-optimization techniques to aid with GI planning decision-making is expanding. However, due to high computational expense, the simulation-optimization methods are often based on design storm events, and it is unclear how much different rainfall scenarios (i.e., design storm events vs. long-term historical rainfall data) impact the optimal siting of GI. The Parallel Pareto Archived Dynamically Dimensioned Search (ParaPADDS) algorithm in a novel simulation-optimization tool OSTRICH-SWMM was used to leverage distributed computing resources. A case study was conducted to optimally site rainwater harvesting cisterns within 897 potential subcatchments throughout the City of Buffalo, New York. Seven design storm events with different return periods and rainfall durations and a one-month historical rainfall time series were considered. The results showed that the optimal solutions of siting cisterns using event-based scenarios, though less computationally expensive, may not perform well under continuous rainfall scenarios, suggesting design rainfall scenarios should be carefully considered for optimizing GI planning. The impact of rainfall scenarios was particularly significant in the middle region of the Pareto front of multi-objective optimization. Utilizing high-performance parallel computing, OSTRICH-SWMM is a promising tool to optimize GI at large spatial and temporal scales.

Application of iron–carbon microbial galvanic activated sludge combined with MBR process in the treatment of wastewater from comprehensive railway station

The application of iron–carbon microbial cell activated sludge (ICMC-AS) was carried out in a membrane bioreactor (MBR) processor to treat wastewater from an integrated railway station. Results showed that the chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) removal efficiencies of the original MBR processor increased from 80%, 30%, and 10% to 92%, 93.5%, and 92%, respectively. Further research showed that the combined sewage treatment system also had a strong impact resistance ability. The combined sewage treatment system ran stably when the COD, TN, and TP concentrations changed greatly. The in-depth analysis of the reaction process and reaction rate of the combined sewage treatment system revealed that the combined system is dominated by COD removal with high nitrogen removal efficiency. The removal rate constants of various pollutants were in the order: KCOD (0.647 ± 0.017) > KNO3−−N (0.416 ± 0.044) > KNH4+−N (0.275 ± 0.014) > KTN (0.258 ± 0.083). Calculations of the energy saving and carbon emission reduction of the combined system showed that the system’s annual carbon emission reduction could reach more than 388,203.55 kg CO2e, which remarkably improves the carbon emission reduction effect and obtains a good green effect. The results indicate that adding ICMC-AS to the MBR processor for combined wastewater treatment can substantially improve the efficiency of wastewater treatment and obtain better energy-saving and emission-reducing effects. This combined application provides an effective way for the transformation and upgrading of small- and medium-scale water treatment systems.

Optimisation of urban-rural nature-based solutions for integrated catchment water management

Nature-based solutions (NBS) have co-benefits for water availability, water quality, and flood management. However, searching for optimal integrated urban-rural NBS planning to maximise co-benefits at a catchment scale is still limited by fragmented evaluation. This study develops an integrated urban-rural NBS planning optimisation framework based on the CatchWat-SD model, which is developed to simulate a multi-catchment integrated water cycle in the Norfolk region, UK. Three rural (runoff attenuation features, regenerative farming, floodplain) and two urban (urban green space, constructed wastewater wetlands) NBS interventions are integrated into the model at a range of implementation scales. A many-objective optimisation problem with seven water management objectives to account for flow, quality and cost indicators is formulated, and the NSGAII algorithm is adopted to search for optimal NBS portfolios. Results show that rural NBS have more significant impacts across the catchment, which increase with the scale of implementation. Integrated urban-rural NBS planning can improve water availability, water quality, and flood management simultaneously, though trade-offs exist between different objectives. Runoff attenuation features and floodplains provide the greatest benefits for water availability. Regenerative farming is most effective for water quality and flood management, though it decreases water availability by up to 15% because it retains more water in the soil. Phosphorus levels are best reduced by expansion of urban green space to decrease loading on combined sewer systems, though this trades off against water availability, flood, nitrogen and suspended solids. The proposed framework enables spatial prioritisation of NBS, which may ultimately guide multi-stakeholder decision-making, bridging the urban-rural divide in catchment water management.

Assessing the impact of climate change on Combined Sewer Overflows based on small time step future rainfall timeseries and long-term continuous sewer network modelling

The evolution of the climate in the future will probably lead to an increase in extreme rainfall events, particularly in the Mediterranean regions. This change in rainfall patterns will have impacts on combined sewer systems operation with a possible increase of spilled flows, leading to an increase of untreated water volumes released to the receiving water. Due to the impact of overflows on the water cycle, local authorities managing combined sewer systems are wondering about the extent of these changes and the possibility of taking it into account in stormwater management structure design. To do this, rainfall data with a fine time step are required to better master the shape of the hyetographs that are crucial to get a relevant rainfall/runoff relationship in an urban environment. However, there are currently no simulations of future rainfall series available at a time step compatible with the needs in urban drainage field. In this work, future rainfall time series with a fine time step are elaborated with the aim to be used in urban hydrology. The proposed approach is based on simulations results from five regional climate models in the framework of the Euro-Cordex program. It consists in a spatial downscaling step followed by a temporal disaggregation. The rainfall time series obtained are then used as input for a calibrated and validated hydrological model to investigate the evolution of annual CSO volumes and frequencies by 2100. The results show an increase of annual spilled volumes between 13% and 52% according to the considered climate model. This increase will most likely be a problem regarding compliance of sewer networks in line with the water framework directive, particularly the current French regulations. No clear trends were observed on the CSO frequencies. If there is a consensus for all the carried-out simulations to conclude that the CSO volumes will increase, we must remember that actual regional climate models suffer from limited spatial and temporal resolution and don't explicitly solve convection processes. Due to this point uncertainty concerning the evolution rate remains important particularly for intense rainfall episodes. New generations of climate models are needed to accurately predict intense episodes.

Cost to society from infiltration and inflow to wastewater systems

Water from infiltration and inflow to wastewater systems is an extensive problem causing costs to society in various ways. Comprehensive methods for supporting decisions on how to efficiently mitigate the problems in a sustainable manner are, however, missing today. This paper presents a novel risk-based model to assess the cost to society from infiltration and inflow to wastewater systems by monetising effects related to treatment of wastewater, pumping, combined sewer overflows, and basement flooding. The present value is calculated for a specified time horizon and discount rate, using a cost-benefit analysis approach. To acknowledge the various uncertainties, a probabilistic approach is applied where probability distributions represent the input variables. The model is shown to be applicable by illustrating its use in a case study area in Gothenburg, Sweden. Main results from the case study show that most of the costs are related to investments at the wastewater treatment plant and restoration due to basement flooding events. Sensitivity analyses show that the result is highly dependent on factors such as the volume of infiltration and inflow water, the share of basement flooding, and the discount rate. Using expert elicitation to quantify input data is also illustrated and shown to be a valuable method. The presented model fills an important research knowledge gap and will facilitate a more sustainable and comprehensive handling of water from infiltration and inflow.

Towards coordinated and robust real-time control: a decentralized approach for combined sewer overflow and urban flooding reduction based on multi-agent reinforcement learning

The real-time control (RTC) of urban drainage systems can make full use of the capabilities of existing infrastructures to mitigate combined sewer overflow (CSO) and urban flooding. Despite the benefits of RTC, it may encounter potential risks and failures, which need further consideration to enhance its robustness. Besides failures of hardware components such as sensors and actuators, the RTC performance is also sensitive to communication failures between the devices that are spatially distributed in a catchment-scale system. This paper proposes a decentralized control strategy based on multi-agent reinforcement learning to enhance communication robustness and coordinate the decentralized control agents through centralized training. To investigate different control structures, a centralized and a fully decentralized strategy are also developed based on reinforcement learning (RL) for comparison. A benchmark drainage model and a real-world drainage model are formulated as two cases, and the control agents are trained to control the orifices or pumps for CSO or flooding mitigation in each case. The three RL strategies reduce the CSO volume by 5.62-9.30% compared with a static baseline in historical rainfalls of the benchmark case and reduce the CSO and flooding volume by 14.39-21.36% compared with currently-used rule-based control in synthetic rainfalls of the real-world case. Benefitting from centralized training, the decentralized agents can achieve similar performance to the centralized agent. The decentralized control also enhances the communication robustness with smaller performance loss than the centralized control when observation communication fails, and provides a robust backup at the local level to limit the uncertainties when action commands from the centralized agent are lost. The results and findings indicate that multi-agent RL contributes to a coordinated and robust solution for RTC of urban drainage systems.

Real-time control of combined sewer systems: Risks associated with uncertainties

Model Predictive Control (MPC) of combined sewer systems can reduce environmental degradation caused by uncontrolled overflows. However, practical uncertainties are often neglected when assessing the potential of MPC strategies. This paper aims to understand the risks associated with using a non-perfect internal MPC-model, real precipitation forecast, and realistic dynamic system capacity fluctuations. An MPC with the objective to reduce the total combined sewer overflow (CSO) volume was implemented in the case study of Eindhoven in the Netherlands where highly sensitive waterways receive the sewer overflows. Two types of risks were identified: relative system performance loss and operative deterioration. The former entails a practical decrease in efficacy of controlling CSO spills compared to the theoretical situation, whereas the latter describes the aggravation of environmental pollution compared to a static form of system operation. The results obtained demonstrate that precipitation forecast uncertainty is associated with a small relative system performance loss. Opposite to this, significant performance loss was observed as a consequence of uncertainties in the internal MPC model and the actual sewer system capacity available. The latter caused additional combined sewer overflows compared to a statically optimised control for smaller precipitation events.

Enhanced removal of typical odor compounds in constructed wetlands integrated with iron carbon and tidal flow

The use of constructed wetlands (CWs) has become increasingly popular in pollutant removal in combined sewer overflows, while the performance in dealing with odor compounds in CWs has remained an open question. In this study, Tidal flow Wetland (TW), Iron-carbon Wetland (IW) and Tidal flow Iron-carbon Wetland (TIW) were parallel constructed, where novel substrates modified with iron-carbon and different hydrodynamics in optimizing removal efficiency were compared. The degradation kinetics of geosmin (GSM), a typical kind of odor compounds, were selected to indicate the removal efficiency. The biological features in different constructed wetlands were investigated, in terms of microbial community distribution, functional genes and metabolic pathways. In contrast to TW, IW and TIW exhibited enhanced performance in degrading of GSM. At the steady stage, 19.74 % and 23.19 % of the GSM was removed in a 24-h cycle for IW and TIW respectively. The degradation process followed the pseudo-first-order kinetics. Cyanobacteria, which produced GSM as parts of their metabolites, and Flavobacterium and Sphingomonas, which acted as the degrader on the other hand, together contributed to the variation of GSM concentration in the constructed wetlands. The adding of iron-carbon in the substrates increased the abundance of Flavobacterium and Sphingomonas, while decreased the growth of Cyanobacteria, and weakened the biosynthetic pathway of terpenoids. Tidal flow further enhanced the aerobic environment of the wetland and stimulates the metabolic activities of microorganisms, therefore enhanced the pathway of metabolism and degradation of odor compounds. Consequently, such combination further favored the degradation of GSM and the final removal efficiency.

Impact of model structure on radionuclide transport in urban stormwater

This paper compared simulation results from different SWMM model constructions after radiological contamination from a hypothetical dirty bomb. The model constructions included a utility-provided combined sewer model, a high-resolution mesh surface flow model, and a hybrid of the two. The models were run under three different rainfall configurations including a 3-h event, a 24-h event, and a 24-h event with 48 h of drainage to investigate the influence that model structure had on transport of 137Cs. Model structure was found to impact the contaminant loading of the stormwater model from the air modeling. It was also found to impact the amount of contaminant washoff (high resolution modeling produced more washoff), flow of contamination through outfalls (more contamination through outfalls connected to underground pipes), and 137Cs levels per pipe. The implications of these findings are that few stormwater models are considered ready to aid in response and recovery as originally designed.

Characteristics of antibiotic resistance gene distribution in rainfall runoff and combined sewer overflow.

Rainfall runoff and combined sewer overflow (CSO) converge with organic waste, nutrients, and microbes from the ground and wastewater. These pollutants promote the spread and transformation of antibiotic resistance genes (ARGs). In this study, four rainfall runoff and one CSO outfall were chosen, and samples were collected to explore the occurrence and distribution of ARGs. The ARGs were extracted from suspended solids and analyzed using metagenomic sequencing. A total of 888 ARG subtypes, belonging to 17 ARG types, were detected in all samples. Eleven ARG types were shared by all the samples. Multidrug resistance genes had the highest relative abundance. Their total relative abundance reached 1.07 ratio (ARG copy number/16S rRNA gene copy number) and comprised 46.6% of all the ARGs. In all samples, the CSO outfall had the highest total relative abundance (8.25 × 10-1 ratio) of ARGs, with a ratio ranging ND (not detected)-3.78 × 10-1 ratio. Furthermore, the relationship between ARG types and environmental factors was determined using redundancy analysis. The results showed that chemical organic demand (COD) and bacterial abundance were positively correlated with most ARG types, including multidrug, bacitracin, aminoglycoside, β-lactam, tetracycline, and sulfonamide. NH3-N, TN, and TP were positively correlated with rifamycin, fosmidomycin, and vancomycin resistance genes. The relationship among the ARG subtypes was investigated using network analyses. The multidrug resistance gene subtypes had the highest frequency of co-occurrence. This study provides insights into the occurrence and distribution of ARGs under non-point source pollution and may contribute to the control of ARGs.

Optimal Positioning of RTC Actuators and SuDS for Sewer Overflow Mitigation in Urban Drainage Systems

Real-time control (RTC) and sustainable drainage systems (SuDS) can be implemented simultaneously to enhance the performance of existing urban drainage systems (UDS). However, significant challenges arise when choosing the optimal locations due to hydraulic interactions between the different interventions and the high number of possible configurations. This paper presents a novel optimization–simulation framework to optimize the spatial allocation of flow control devices (FCDs) combined with SuDS for combined sewer overflow (CSO) spill mitigation within UDS. Optimal intervention schemes were identified by a genetic algorithm (GA), combining different numbers of FCDs installed in existing manholes with simplified SuDS implemented in different portions of the catchment. The methodology was tested on two case-study catchments with different characteristics to mitigate CSO spills during synthetic storm events. FCD-SuDS configurations were then validated during continuous rainfall series, resulting in CSO spill volumes reduction ranging between 11% and 45% compared to the baseline networks. The results demonstrate how the GA-based method can efficiently identify optimal placement schemes within UDS characterized by different distributions of in-pipe storage potential as well as hydrological responses to rainfall-runoff events, enhancing the combined benefits of the two decentralized solutions for mitigating CSO spills.

Optimization of in-pipe storage capacity use in urban drainage systems with improved DP considering the time lag of flow routing

The active control of urban drainage systems (UDSs) is playing an increasingly important role in the world threatened by urban flooding and associated disasters caused by insufficient drainage capacity. However, little research has recognized the importance of the optimal use of in-pipe storage space. To address this issue, the use of the in-pipe storage capacity was optimized in this study. A novel approach, that is, dynamic programming with successive approximation considering the time lag of flow routing (DPSA-TL), was developed to determine the control policies, in addition to the commonly used passive, rule-based control (RBC), and evolutionary algorithm (EA) strategies. A real-life urban catchment considering flooding control and combined sewer overflow (CSO) reduction was used as the case study. First of all, the potential benefit of maximizing the use of in-pipe storage space was tested using the four control strategies in three storm events, including a 3-year, 2-hour design (46.5 mm), a 5-year, 2-hour design (56.0 mm) and a 7-h historical (152.5 mm) storm events. Results indicate that DPSA-TL performed best in all cases. Without compromising the goal of flooding control, it provided 16.5%, 12.6%, and 3.0% reductions in CSO volume for the three storm events when compared with the passive strategy. Due to the limited capacity of in-pipe storage, the relative improvement diminished as the total rainfall depth increased. Then, control strategies were further applicated to the real-time operation. DPSA-TL was found to be the best alternative for CSO control, with the CSO volume reduced by 14.7%, 11.4%, and 2.5% in the three storm events, respectively. The findings suggest that the performance of UDS can be significantly improved by optimizing the use of in-pipe storage capacity, and the proposed method is effective in the offline optimization and real-time control of UDSs.

Evaluation of SWMM-LID Modeling Applicability Considering Regional Characteristics for Optimal Management of Non-Point Pollutant Sources

Urbanization and climate change have deteriorated the runoff water circulation and quality in urban areas worldwide. Consequently, low-impact development (LID) and green infrastructure (GI) techniques have been applied to manage impermeable land and non-point source pollutants. Herein, the impacts of urban characteristics, sewer system type, and precipitation intensity on surface runoff were analyzed using the Storm Water Management Model (SWMM) to derive an effective water circulation strategy for urban and complex areas through the optimal allocation of LID/GI strategies. The runoff rates were estimated to be 77.9%, 37.8%, and 61.7% for urban areas with separated and combined sewer systems and complex areas with combined sewer systems, respectively. During low rainfall, runoff was intercepted in areas with combined sewer systems, and runoff and pollutant load were lower than that in areas with separated sewer system. In contrast, wastewater was diluted during heavy rainfall; however, the total pollutant load was higher than in separated areas. The analysis of scenarios according to the regional distribution of each LID type resulted in high efficiency when combined sewers were applied during the distributed placement of catchment areas. Additionally, LID infrastructure was applied in areas with separated sewers when the placement was concentrated at the end of the basin.