Combined Sewer Systems Research Articles

Simulation Analysis of Annual Pollution Load of Combined Sewer Overflow in Wuhan City Based on SWMM

With the acceleration of urbanization, the urban water environment problem has become increasingly severe. The combined sewer overflow(CSO) pollution control has become the focus and problem which urgently needed to be solved in China’s sponge city construction and black smelly water treatment. Simulating and calculating the annual pollution load of the CSO is of great significance for the quantitative analysis of the cause of the water environment pollution. In this paper, the improved SWMM model coupled with the module for scouring the silting on the bottom of the pipes was used to simulate the combined sewer system with a drainage area of 1666ha. The results show that under the same drainage area, the larger the interception ratio is, the smaller the annual pollution load of CSO is; under the same interception ratio, the larger the drainage area is, the smaller the annual pollution load of CSO is. For the combined sewer system in Wuhan, the annual COD, TN and TP load of CSO can be calculated by three formulas: WcoD=378.58-33.71lnF, WTN=51.032-5.7871/lnF and WTP=13.667F-0.404, respectively when the interception ratio is equal to 1.0.

A systematic review of the human health and social well-being outcomes of green infrastructure for stormwater and flood management.

The increase in frequency and intensity of urban flooding is a global challenge. Flooding directly impacts residents of industrialized cities with aging combined sewer systems, as well as cities with less centralized infrastructure to manage stormwater, fecal sludge, and wastewater. Green infrastructure is growing in popularity as a sustainable strategy to mimic nature-based flood management. Although its technical performance has been extensively studied, little is known about the effects of green stormwater infrastructure on human health and social well-being. We conducted a multidisciplinary systematic review of peer-reviewed and gray literature on the effects of green infrastructure for stormwater and flood management on individuals', households', and communities' a) physical health; b) mental health; c) economic well-being; and d) flood resilience and social acceptance of green infrastructure. We systematically searched databases such as PubMed, Web of Science, and Scopus; the first 300 results in Google Scholar; and websites of key organizations including the United States Environmental Protection Agency. Study quality and strength of evidence was assessed for included studies, and descriptive data were extracted for a narrative summary. Out of 21,213 initial results, only 18 studies reported health or social well-being outcomes. Seven of these studies used primary data, and none allowed for causal inference. No studies connected green infrastructure for stormwater and flood management to mental or physical health outcomes. Thirteen studies were identified on economic outcomes, largely reporting a positive association between green infrastructure and property values. Five studies assessed changes in perceptions about green infrastructure, but with mixed results. Nearly half of all included studies were from Portland, Oregon. This global systematic review highlights the minimal evidence on human health and social well-being relating to green infrastructure for stormwater and flood management. To enable scale-up of this type of infrastructure to reduce flooding and improve ecological and human well-being, widespread acceptance of green infrastructure will be essential. Policymakers and planners need evidence on the full range of benefits from different contexts to enable financing and implementation of instfrastructure options, especially in highly urbanized, flood-prone settings around the world. Therefore, experts in social science, public health, and program evaluation must be integrated into interdisciplinary green infrastructure research to better relate infrastructure design to tangible human outcomes.

Pollutant Transport Analysis and Source Apportionment of the Entire Non-point Source Pollution Process in Combined Sewer Systems

A comprehensive and scientific understanding of non-point source pollutant transport pathways and source apportionment in combined sewer systems is essential for managing and improving the urban water environment. This study analyzed build-up and wash-off processes of pollutants on road surfaces and in sewers within a catchment of combined sewer systems in a typical old district in Zhuhai. Besides, source apportionment of the entire urban non-point source pollution was investigated by using the mass conservation method. The outcomes revealed that the build-up load of road deposited sediments in the study area was (28.81±10.69) g·m-2. The average wash-off load of road deposited sediments during five different rainfall events was (19.27±10.90) g·m-2 and the wash-off percentage was (52.69±13.3)%. The event mean concentrations of suspended solids (SS) in road runoff were 52-109 mg·L-1, and the event mean concentrations of SS in sewer runoff were 68-158 mg·L-1. Source apportionment analysis showed that road runoff, domestic wastewater, and sewer sediments contributed 39%-72%, <20%, and 13%-56% to SS, respectively. The thickness of sewer sediments increased by 1-14 cm during light and moderate rains, and the thickness decreased by 7-17 cm during heavy rains. It was found that rainfall characteristics affected the contribution percentages of pollution sources. The contribution of pollution from road runoff, domestic sewage, and sewer sediments in combined sewer systems were 2%-52%, 9%-65%, and 8%-81%, respectively. The derived outcomes should be useful for developing recommendations to control non-point source pollution in combined sewer systems and improve urban receiving water quality in China.

\u201cSickenin\u2019 in the rain\u201d \u2013 increased risk of gastrointestinal and respiratory infections after urban pluvial flooding in a population-based cross-sectional study in the Netherlands

BackgroundClimate change is expected to increase the chance of extreme rainfall events in the Northern Hemisphere and herewith, there is an increased chance of urban pluvial flooding. Urban pluvial flooding often consists of street flooding and/or flooding of combined sewerage systems, leading to contamination of the floodwater with several gastrointestinal and/or respiratory pathogens. An increase in flooding events therefore pose a health risk to those exposed to urban floodwater. We studied the association between exposure to pluvial floodwater and acute gastroenteritis (AGE) and acute respiratory infection (ARI).MethodsWe performed a retrospective, cross-sectional survey during the summer of 2015 in 60 locations in the Netherlands with reported flooding. Two weeks after the flooding, questionnaires were sent to households in these locations, collecting data on self-reported AGE and ARI and information on floodwater exposure in the previous 2 weeks. Multivariable generalized estimating equations (GEE) regression models, accounting for the clustered data structure, were used to identify risk factors for AGE and ARI.ResultsIn total, 699 households with 1,656 participants (response rate 21%) returned the questionnaire. Contact with floodwater was significantly associated with AGE (aOR 4.2, 95%CI 2.1–8.4) and ARI (aOR 3.3, 95%CI 2.0–5.4). Risk factors for AGE were skin contact with floodwater (aOR 4.0, 95%CI 1.8-9.0), performing post-flooding cleaning operations (aOR 8.6, 95%CI 3.5-20.9) and cycling through floodwater (aOR 2.3, 95%CI 1.0-5.0). Skin contact with floodwater (aOR 3.6, 95%CI 1.9-6.9) and performing post-flooding cleaning operations (aOR 5.5, 95%CI 3.0-10.3) were identified as risk factors for ARI.ConclusionsResults suggest an association between direct exposure to pluvial floodwater and AGE and ARI. As it is predicted that the frequency of pluvial flooding events will increase in the future, there is a need for flood-proof solutions in urban development and increased awareness among stakeholders and the public about the potential health risks. Future prospective studies are recommended to confirm our results.

Developing a stochastic sewer model to support sewer design under water conservation measures

Population growth and climate change place a strain on water resources; hence, there are growing initiatives to reduce household water use. UKWIR (2016) have a stated aim to halve water abstraction by 2050. This will significantly reduce inflow to sewer systems and increase wastewater concentration. This work presents a new stochastic sewer model that can be used to predict both hydraulic and pollutant loading for various water saving scenarios. The stochastic sewer model is based on integration of the stochastic water demand model SIMDEUM® with the InfoWorks ICM® (Sewer Edition) hydraulic model and software. This model has been developed using foul sewer networks, i.e. where household discharges are the dominant inflow; however, it could also be used in combined sewage systems where rainwater flows would add to the stochastic dry weather flow (DWF). The stochastic sewer model was tested and validated on several real catchments in the Wessex Water area of the UK. Calibration was carried out using metered consumption data. The stochastic sewer model gives an accurate prediction of the diurnal patterns of sewage discharge at a household level and was validated using real flow measurements within the catchment. The results obtained indicate that this model can be used to accurately predict changes in flow due to water conservation. A preliminary study for the impact of low water use on this validated network model has been conducted and it was found that overnight and daytime flow was reduced by up to 80% whereas evening flows remained largely similar. Extended stagnation times were observed in the street scale pipes (150 mm) in the low water use scenario.

Modelling engineered nanomaterials in wet-weather discharges

The impacts of the unintended release of engineered nanomaterials (ENMs) and the resulting exposure to the ecosystems are still poorly understood and intensively debated. In current mass flow models, a global transfer coefficient is used to account for ENMs discharged from sewer systems to surface waters during rain events. However, different types of sewer systems and specific ENM applications likely require a more elaborate approach to quantify ENM loads entering surface waters during rain events.Therefore, we evaluated the impact of distinguishing between different application areas of ENMs (indoor/outdoor) and different types of sewer systems (combined/separate) on the loads of selected ENMs passing through wastewater systems and reaching the surface water. We applied a dynamic mass flow analysis to eight substances (TiO2, ZnO, Ag, SiO2, FeOx, CuO, CeO2 and carbon black) for six different sewer system configurations. To estimate the runoff from streets and facades, we used a hydrological model developed for dissolved substances. For areas with separate sewer systems only and ENMs predominantly used in and released from outdoor applications (e.g. CuO, carbon black), up to ~80% of the annual loads entering the sewer systems never reach a sewage treatment plant. Those ENMs are directly discharged to surface waters via stormwater outlets. For combined sewer systems and ENMs mainly applied indoors (e.g. Ag, ZnO), the percentage of ENM bypassing sewage treatment plants remains below 2%. Although the model is setup for Switzerland and other geographical areas will show for example different rain characteristics, the relative importance of the different release pathways will broadly remain the same and the results should, therefore, be transferrable to other countries.

Deep tunnel sewerage system phase 2 – hydraulics

Abstract The Deep Tunnel Sewerage System (DTSS) is aimed at providing a robust and efficient means of catering to Singapore's used-water needs. DTSS2 is the second phase of this project, comprising an approximately 30-km long South Tunnel, a 10-km long Industrial Tunnel, 60-km of Link Sewers and a new Water Reclamation Plant integrated with a NEWater facility. In contrast with tunnels designed to store overflows in combined sewer systems, the DTSS tunnels convey used-water all the time from Singapore's separated system. This paper describes hydraulic analyses that were conducted during the feasibility study and preliminary design. The topics covered include hydraulic modelling of the entire system with the main goal of ensuring system resilience, air management to avoid odours at ground level, and isolation of tunnel section using gates for potential maintenance or repair. The resilience analyses concentrated on the system functionality in case of a failure, to ensure that used-water can be safely conveyed to a treatment plant. The air management system included several odour control facilities and air jumpers to avoid escape of odorous air from the system and the isolation gates requires detailed hydraulic analyses to cater to the high heads involved.

Development of a scenario-based stormwater management planning support system for reducing combined sewer overflows (CSOs)

Using combined sewer systems to handle excess stormwater runoff is common in older urban areas. Combined sewer overflow (CSO) events occur when hydraulic capacity is exceeded, and untreated wastewater discharges to surface waters. As urban population density increases, and more demand is placed on infrastructure, CSO events happen more often and cause serious environmental problems and public-health risks. Recently, green infrastructure (GI) has been integrated with existing gray infrastructure (GrayI) to reduce CSO events. However, there lacks a goal-oriented planning framework for eliminating CSOs at a watershed/sewershed scale. Moreover, existing stormwater simulations based on catchments or other geographic units, do not consider spatial variation within the unit, such as distribution, attribution, ownership, and management of GI. We propose a scenario-based Stormwater Management Planning Support System for CSOs (SMPSS-CSO) to provide a platform for reducing CSO events by coordinating parcel-based installations of GI. We applied the SMPSS-CSO to a sewershed with a single CSO location in Cincinnati, Ohio and developed four scenarios representing increased use of GI (rain barrels, green roofs, porous pavements, and detention basin) based on its cost, difficulty of installation, and property ownership. Runoff quantity, time of concentration, and peak flow rate were simulated using the curve number method. Our analysis shows a 41% reduction in stormwater runoff is necessary to eliminate CSO events for a two-year rainfall, required 97.25% of private and 27.59% of public parcels to install GI. GI alone cannot eliminate CSO events in this sewershed and must be incorporated with additional GrayI (e.g., storage tanks, pipes). The SMPSS-CSO has the potential for including multiple stakeholders' preferences and concerns in the searching for preferable scenarios.

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.

Demonstration of energy-saving membrane bioreactor (MBR) systems.

Membrane bioreactors (MBRs) have the advantages of achieving excellent effluent quality, a small footprint and smooth operation and maintenance. On the other hand, its high energy consumption remains a critical challenge for MBR application. Japan Sewage Works Agency has conducted a series of joint researches with several private companies since 2012 and developed four kinds of energy-saving MBR systems. Based on the results of long-term pilot-scale demonstrations, specific energy consumption (SEC) per unit treated effluent volume was calculated for each MBR system, resulting in all systems achieving SEC of 0.4 kWh/m3 or less. To meet an additional requirement for expanding MBR application, it is also necessary to establish the applicability of MBR systems to combined sewer systems, suffering from occasional inflow fluctuation caused by rainfall. The capability of temporary higher flux operation during and after rainy weather was also demonstrated with three of the four developed systems.

Analysis of the residual nutrient load from a combined sewer system in a watershed of a deep Italian lake

This paper investigates the residual nutrient load from a combined sewer system along the shore of a deep Italian lake, to provide data that can help explaining the contribution of combined sewers to lakes eutrophication. To this purpose, a stochastic methodology is applied to the analysis of the combined sewer overflows and pollutants, that provides reliable estimates, with related uncertainties, of the storage capacity to be supplied in order to mitigate the impact on the quality of receiving waters. The sewer is modeled by SWMM and two terminal combined sewer weirs are modeled in detail and instrumented for calibration purposes. A year-long campaign was accomplished, allowing to study the occurrence and relevance of the first flush. The calibrated model of the sewer network was used to extrapolate the results to a 10-years period, thus providing a statistically reliable estimate of the residual load delivered from this watershed to the lake. A conservative evaluation shows that up to 22% of phosphorus and up to 41% of nitrogen delivered to the sewer are still discharged into the environment. However, the results also show that in this case a relatively small capture volume would obtain a target pollution reduction, thus providing insights on the feasibility of this structural practice in similar watersheds along the shore of endangered lakes.

Field Study of Suspended Solid Discharge from Combined Sewerage System of a Highly Urbanized Area

Field Study of Suspended Solid Discharge from Combined Sewerage System of a Highly Urbanized Area

An Innovative Method for Installing a Separate Sewer System in Narrow Streets

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 …

Influence of the amount of inflowing wastewater on concentrations of pollutions contained in the wastewater in the Nowy Targ sewerage system

This study presents the results of the analysis concerning the influence of the amount of inflowing wastewater on concentrations of organic and biogenic pollutants, as well as chromium ions in wastewater flowing into the collective sewage treatment plant in Nowy Targ. The research was carried out in 2016 and 2017, where in the period of 24 months a total number of 87 wastewater samples were collected in order to determine the concentration of the analyzed pollution indicators. During this period, the average daily inflow of wastewater to the sewage treatment plant was also analyzed. Based on the analysis of linear correlation, it was stated that there is a high dependence of concentrations of organic and biogenic pollutants on the amount of inflowing raw wastewater. Furthermore, it was found that there is an average dependence of chromium ion concentrations in raw wastewater on the amount of inflowing wastewater. In order to minimize the high variability of the concentration of pollutants in raw wastewater, it is recommended to reconstruct the sewerage system from the combined sewer system to the distribution system. Additionally, it is recommended to monitor the sewerage network in order to eliminate illegal inflows of rainwater and industrial wastewater from furrier’s production facility.

The new German standard on constructed wetland systems for treatment of domestic and municipal wastewater.

The German Association for Water, Wastewater and Waste e.V. (DWA) has published a new standard for the dimensioning, construction, and operation of constructed wetlands for treatment of domestic and municipal wastewater. The changes to the standard are based on a wide range of experience gained in recent years in Germany and Europe. For the first time ever, the standard has been officially translated and published in English. This paper summarizes the new standard for secondary treatment of domestic wastewater with classical one-stage unsaturated vertical flow (VF) wetlands, VF wetlands with lava sand for treatment of wastewater from combined sewer systems, and actively aerated VF and horizontal flow (HF) flow wetlands. Two-stage unsaturated VF wetlands treating raw wastewater (French VF wetlands), are also included in the new standard. HF wetlands are no longer described in the standard for secondary treatment of domestic wastewater. This does not exclude their application. Existing HF wetland systems in Germany may continue to be operated so long as effluent parameters are met and proper operations and maintenance is ensured. This paper gives an overview of the new design standard, including key information on wastewater type and loading, as well as primary attributes of each wetland design.

Exploring the performances of a new integrated approach of grey, green and blue infrastructures for combined sewer overflows remediation in high-density urban areas

Most sewage collection systems designed between 19th and early to mid-20th century use single-pipe systems that collect both sewage and urban runoff from streets, roofs and other impervious surfaces. This type of collection system is referred to as a combined sewer system. During storms, the flow capacity of the sewers may be exceeded and the overflow discharged into a receiving water body (RWB) through spillways without any control and remediation. Combined sewer overflows (CSOs) may, therefore, produce serious water pollution and flooding problems in downstream RWBs. Methodologies for a rational management of CSOs quantity and quality share many commonalities, and these two aspects should be considered together in order to maximize benefits and promote local distributed actions, especially in high urban density areas where the space availability for the construction of CSO storage tanks is often a limiting factor. In this paper, a novel strategy to control downstream flow propagation of a CSO as well as to improve its quality is tested on a real case study in the area of the metropolitan city of Milan. The approach is based on the combination of grey, green and blue infrastructures and exploits the integrated storage and self-depuration capacities of a firstflush tank, a constructed wetland and a natural stream to obtain admissible flow rates and adequate water quality in the RWB. The results, evaluated through a modelling framework based on simplified equations of water and pollutants dynamics, show excellent performances for the integrated system, both in terms of flow control and pollution mitigation. The pollution, using biological oxygen demand concentration as a proxy of the whole load, was decreased by more than 90% and downstream flooding situations were avoided, despite the spillway was not regulated. Concerning the economic point of view, from a rough estimate of the costs, the system allows reducing the investment of 30 to 50% in respect to the traditional CSO controls based solely on flow detention tanks. The proposed approach, as well as the modelling framework for its effective implementation, appear strongly scalable in different world contexts and aim to fill the gap between urban and rural environments in the management of stormwater and CSOs, promoting the involvement of the water managers, the irrigation-reclamation agencies and regional authorities.

Sewer Sediment Bacterial Communities Suggest Potential to Transform Persistent Organic Pollutants.

Sediments of combined sewers are seeded with microbes from a variety of sources, and experience varying biogeochemical conditions. A variety of redox processes have been demonstrated to occur within sewer systems, as well as transformation of several recalcitrant xenobiotic contaminants. Illumina sequencing of the 16S ribosomal RNA gene from sediments of three combined sewer systems in the northeastern United States resulted in 10 000 to 47 000 operational taxonomic units per sample. Whereas orders Clostridiales and Bacteroidales, considered human fecal indicators, were dominant in one city's sediments; other cities had communities suggestive of diverse redox processes, including reductive dechlorination of chlorinated organic compounds. Collection systems previously associated with polychlorinated biphenyl (PCB) biotransformation, and those with elevated in situ PCB concentrations, had high abundances of Dehalococcoidetes. The results suggest that wastewater collection systems have intrinsic passive treatment capacity, reducing contaminant loads on water resource recovery facilities and, ultimately, on receiving waters.

Infiltration and Inflow (I/I) to Wastewater Systems in Norway, Sweden, Denmark, and Finland

Infiltration and inflow of non-sewer water to the wastewater network (I/I-water) may have a number of both financial and environmental consequences. In Norway, there are two commonly used methods for calculating the volume of I/I-water, The Dilution method (DM) and the Water Balance Method (WBM). When comparing the methods, the WBM gives a lower value of I/I-water than the DM. Analysis shows that the volume of I/I-water for some large Norwegian wastewater plants is decreasing. From 2009 to 2016, the average value has decreased from 70% to 66% of the total annual flow. For investigated Danish districts the average amount of I/I-water is stable, on about 30%. Calculations performed by the Finnish Water Utilities Association shows a stable percentage of I/I-water on about 40% in Finland from 2010 to 2016. Calculations on Swedish wastewater plants show a reduction in I/I-water from 58% to 46% from 2010 to 2016. For the districts Asker, Bærum, and Drammen in Norway, the amount of I/I-water is increasing with increasing percentage of combined sewer systems. This is also the case for investigated plants in Norway, Sweden, and Finland. The exception is Denmark, with a high percentage of combined systems, but a low percentage of I/I-water. Investigations done for Asker, Bærum, Drammen, and the two Danish districts Randers and Esbjerg vest, show a correlation between rainfall and I/I-water only for Asker and Esbjerg vest.

Static optimal control of combined sewer networks under enhanced cost functions to minimize the adverse environmental effects

ABSTRACT Capacity limitations of combined sewer systems lead overflows (CSOs) especially under intensified rain events. The socio-economic damage due to these CSOs on receiving water is immeasurable. Structural measures include enhancing the existing pipe network and introducing new sewer systems lead extra burden on the inhabitants due to new constructions. In addition, the taxpayers have to bear the construction cost. Optimal control of existing combined sewer systems is one of the non-structural solutions in minimizing the adverse impacts of CSOs; however, a holistic control algorithm based on water quality of the receiving water is yet to be developed. This paper develops an enhanced control algorithm based on the pollution load to the receiving water from CSOs. Unlike the previous studies, this paper looks at an enhanced cost function for one of the objective functions, which includes the pumping cost of combined sewer network. The control algorithm is generic; however, it is tested against a real world combined sewer network in Liverpool, United Kingdom. Optimal control settings of the combined sewer systems are found and further analysis shows that algorithm gives feasible solutions. Therefore, the results have proved the applicability of the newly developed optimization algorithm in control of combined sewer systems.

Removal of organic matter in stormwater ponds: a plug-flow model generalisation from waste stabilisation ponds to shallow rivers

ABSTRACTThis study investigates the effect of flow conditions on the organic matter concentration, removal efficiency, and reaction kinetics in a stormwater pond in Fortaleza, Brazil. As a result of unauthorized sewage discharges, BOD and COD concentrations were similar to those of combined sewer systems. The concentrations remained roughly the same during the rainy season, which was attributed to sewage network overflow. Removal efficiencies ranged from 70–90%, similar to primary facultative ponds. Fitting different hydraulic models to the field data, it was possible to obtain BOD and COD removal rates that could be described as functions of the Reynolds number. The best fit was achieved considering the plug-flow assumption, and a general BOD model including data reported in the literature for waste stabilisation ponds, stormwater ponds and shallow rivers was derived. Lastly, simulations with this general model were performed to assess the impact of remediation measures on the studied pond.