Combined Sewer Systems Research Articles

Different erosion characteristics of sediment deposits in combined and storm sewers.

To investigate the different erosion patterns of sediments in combined and storm sewers, sediments from three separate sewer systems and two combined sewer systems in urban Shanghai were collected for the flushing experiments. These experiments were conducted with different consolidation periods and shear velocities. As the consolidation period increases, dissolved oxygen exhibits a positive effect on the microbial transformations of organic substrates. Potential structural changes and separations of the surface and bottom layers of sediments are observed. The results also reveal that the organic matter, particle size and moisture have different effects on the erosion resistance of sediments. Furthermore, illicit connections behaved as an important factor affecting the viscosity and static friction force of particles, which directly alter the erosion resistance of sewer sediments.

Improved understanding of combined sewer systems using the Illinois Conveyance Analysis Program (ICAP)

Understanding the conveyance of sewer networks is vital, especially in cases of great variability in flow rates, such as in combined sanitary and storm sewer systems. Conventional conveyance studies in sewer systems often have extended computation times due to complexity of the solution, or alternatively make assumptions that ignore the water-surface profile within a pipe. In previous research, the hydraulic performance graph (HPG) was successfully used for open-channel capacity determination. The HPG summarizes the results of many backwater calculations for a reach so that these calculations do not need to be repeated. This article describes algorithms utilized by the Illinois Conveyance Analysis Program that uses the HPGs to describe the conveyance of a system, identify bottlenecks for varying conditions, conserve mass by tracking outflow and overflows under stepwise steady flow conditions. The software is freely available at https://github.com/obergshavefun/icap/wiki.

The determination of petroleum hydrocarbons in sewer sediment

Based on the available standards it is possible to analyze the concentration of petroleum hydrocarbons in sewer sediment. Guidelines included in the standard PN-EN 14039:2008 – Characterization of waste – Determination of hydrocarbon content in the range of C10 to C40 by gas chromatography and in standard PN-EN ISO 16703:2011 – Soil quality – Determination of content of hydrocarbon in the range C10 to C40 by gas chromatography are useful here. The results of analysis concerning elaboration of the methodology of petroleum hydrocarbons determination in sewer sediment based on available literature are presented in the article. According to carried out literature review and the possibilities of available data use, five temperature programs were initially selected. All temperature programs were tested on a standard sample (oil mixture). In the next stage one of prepared method to determine the amount of petroleum hydrocarbons in sewer sediment was applied for sewer sediment come from the combined sewer system. The verification of the sample preparation procedures according to available standards on real sediment revealed the difficulties. Finally, preliminary value of petroleum hydrocarbons concentrations in sewer sediment from the combined sewage system was determined.

Quantification of nonpoint source pollutants discharged from the combined sewer system in the Nakdong River basin, Korea, using SWMM

Quantification of nonpoint source pollutants discharged from the combined sewer system in the Nakdong River basin, Korea, using SWMM

The protection of urban areas from surface wastewater pollutions

In this paper it considered the problem of collection, treatment and discharge into waters of rain and melted wastewater. To reduce the load on the combined sewer system, there are engineering solutions collect rain and melt water for use in the irrigation of lawns and green spaces. Research carried out at the department “Water supply and sanitation”, (Russia), confirm the high pollution concentrations of meltwater and rainfall in urban arias. Series of measurements of heavy metal in rainwater runoff carried out in Hungary demonstrates clearly the differences in concentrations in the function of distance from the edge of the road. Also differences are introduced between pollution concentrations in runoff water from within and outside urban traffic roads. The quality of snow cover, forming meltwater is observed to be changing in dependence on roadway location. Quality characteristics of surface runoff and its sediments can be effectively improved with super-high frequency radiation (SHF) treatment which is presented in this paper.

Assessment of Rainfall Intensity Equations Enlisted in the Egyptian Code for Designing Potable Water and Sewage Networks

The design of combined sewage system networks is based on the sanitary discharge (domestic, industrial) and the runoff generated by rainfall. The Egyptian code of practice for designing potable water and sewage networks gives two Intensity-Duration-Frequency (IDF) equations to calculate the intensity of rainfall to be applied to all cities of Egypt. The purpose of this research is to study and assess the adequacy of the rainfall intensity equations suggested by the aforementioned Egyptian code. This is carried out taking into consideration the available rainfall ground station measurements and remote sensing Tropical Rainfall Measurement Mission (TRMM) satellite rainfall estimates. This assessment leads to the following results. For the Mediterranean coastal cities, the code of practice equations significantly underestimates the rainfall intensities for all storm durations, which may lead to road networks damage and accidents due to hydroplaning and road flooding. On the contrary, for many other southern cities along the Nile Valley, the code equations significantly overestimate the rainfall intensities, which affects the economical aspect of the sewage network. Consequently, the current research suggests new rainfall intensity equations instead of the code equations.

Assessment of total suspended solids (TSS) event load and its uncertainties in combined sewer system from continuous turbidity measurements

This paper presents a methodology for assessing TSS wet weather event load along with the associated uncertainties from continuous turbidity measurements. The proposed method is applied to dozens of rainfall events sampled on various urban catchments in the cities of Paris and Nantes. This method takes into account the dependency between the residual errors made by converting the turbidity values into TSS concentrations using an average TSS-turbidity relationship. Results obtained indicate that the inter-event variations of TSS-turbidity relationships induce significant systematic errors on TSS event loads which can reach ±30% of the average TSS event load.

Post Construction Green Infrastructure Performance Monitoring Parameters and Their Functional Components

Drainage system infrastructures in most urbanized cities have reached or exceeded their design life cycle and are characterized by running with inadequate capacity. These highly degraded infrastructures are already overwhelmed and continued to impose a significant challenge to the quality of water and ecological systems. With predicted urban growth and climate change the situation is only going to get worse. As a result, municipalities are increasingly considering the concept of retrofitting existing stormwater drainage systems with green infrastructure practices as the first and an important step to reduce stormwater runoff volume and pollutant load inputs into combined sewer systems (CSO) and wastewater facilities. Green infrastructure practices include an open green space that can absorb stormwater runoff, ranging from small-scale naturally existing pocket of lands, right-of-way bioswales, and trees planted along the sidewalk as well as large-scale public parks. Despite the growing municipalities’ interest to retrofit existing stormwater drainage systems with green infrastructure, few studies and relevant information are available on their performance and cost-effectiveness. Therefore, this paper aims to help professionals learn about and become familiar with green infrastructure, decrease implementation barriers, and provide guidance for monitoring green infrastructure using the combination of survey questionnaires, meta-narrative and systematic literature review techniques.

Experimental and Numerical Analysis of Egg-Shaped Sewer Pipes Flow Performance

A Computational Fluid Dynamics (CFD) model was developed to analyze the open-channel flow in a new set of egg-shaped pipes for small combined sewer systems. The egg-shaped cross-section was selected after studying several geometries under different flow conditions. Once the egg-shaped cross-section was defined, a real-scale physical model was built and a series of partial-full flow experiments were performed in order to validate the numerical simulations. Furthermore, the numerical velocity distributions were compared with an experimental formulation for analytic geometries, with comparison results indicating a satisfactory concordance. After the hydraulic performance of the egg-shaped pipe was analyzed, the numerical model was used to compare the average velocity and shear stress against an equivalent area circular pipe under low flow conditions. The proposed egg shape showed a better flow performance up to a filling ratio of h/H = 0.25.

Community participation and sustainable investment in city projects: The Berlin Water Consumer Stock Ownership Plan

Water supply issues and sustainable urban development are inextricably linked in cities across the world and are becoming even more urgent given the everincreasing scale and nature of demand. As with many large cities across the world, Berlin is situated along a river, the Spree. What regularly causes massive fish death is not emission-intensive industries or citizens illegally disposing of waste. During heavy rainfall as the sewers threaten to become overburdened, the combined sewage system discharges its contents directly into the river to prevent an overflow into the streets. This problem is common to countless metropolitan regions. The measures implemented by the city of Berlin to date — underground concrete basins as buffers and an intelligent canal control system — remain insufficient to capture the 3–4 million cubic metres of untreated wastewater still discharged into the river each year. LURITEC, a new system of pre-manufactured, modular synthetic glass fibre tubes that are placed in the river instead of underground, can make a cost-efficient contribution towards closing this gap. The system is complementary to traditional concrete tanks. Two major obstacles have so far hindered implementation of the €60m LURITEC pilot project: first, a lack of financing; and secondly, a lack of political support. Here, citizens’ financial participation can lower public costs while providing a grassroots democratic backbone. A Consumer Stock Ownership Plan (CSOP) offers low-risk loan financing of a significant share of the project while requiring only a small financial contribution from the CSOP participants. Combining different revenue sources, the redemption period for repaying the €12.4m debt is 8.5 years. Community participation, in particular citizen capital participation as proposed in this article, anchors the citywide project in the citizenry, thus strengthening its democratic legitimacy and facilitating sustainable urban development.

Calibration of hydrodynamic model-driven sewer maintenance

Sewer performance is typically assessed using hydrodynamic models assuming the absence of in-sewer defects. As a consequence, hydraulic performance calculated by models is likely to be overestimated, while the real hydraulic performance of the sewer system remains unknown. This article introduces the concept of ‘hydraulic fingerprinting’ based on model calibration to identify in-sewer defects affecting hydraulic performance. Model calibration enables detection of changes in hydraulic properties of the sewer system. Each model calibration results in a set of model parameter values, their uncertainties and residuals. The model parameter values also incorporate the antecedent condition of the catchment of the event calibrated and are therefore less suitable to identify in-sewer defects. The residuals on the other hand, and more specifically their absolute values, statistical properties and the correlation between residuals at different monitoring locations are suitable as indicators of the occurrence of in-sewer defects. This allows the application of ‘hydraulic fingerprinting’ based on model calibration, where the ‘fingerprint’ is defined by the model parameters and the residuals. The concept of ‘fingerprinting’ is demonstrated for the combined sewer system ‘Tuindorp’ (Utrecht, the Netherlands). The results show that ‘hydraulic fingerprinting’ can be a powerful tool for directing sewer asset management actions.

Fish recolonization of a lowland river with non-buffered storm water discharges but with abated pollution from a large municipality

Water pollution from industrial Metro Łódź (ML), Poland, made the Ner River almost fishless in its middle-lower course for most of the 19th and 20th century. The new sewage treatment plant of ML and reduction of industry have caused pollution abatement there since the 1990s. As a result, the Ner became repopulated, which was shown by fish samples collected along its course in 2000–2012. Multivariate statistical methods helped distinguish unpolluted (I and II, in the upper course), and recovered (III, IV and V, in the middle-lower course) sections of the river. Historical and present data indicated that section III (downstream of ML) recovered least, both before and during the study. Section V (outflow one) recovered most and its fish fauna (almost exclusively native) now displays high and stable biomass, abundance and species richness, including those of obligatory riverine species. Non-native Prussian carp's dominance followed the river degradation gradient, i.e. was highest in section III, and in section V declined to almost absence. This study shows that the revival of native fish fauna seems to be a method of restricting the dominance of this highly tolerant species. Despite the abatement, storm events are very harmful to fish (mostly in section III), because the Ner discharge may then increase manifold and all storm water is drained by the ML combined sewer system to the Ner in several hours. Other stressors are numerous dams and desorption of pollutants from sediment in the middle Ner, and perhaps pollutant inflow from agriculture or local urban areas. Some moderation of storm impact on water entering the Ner from ML by constructing buffer reservoirs would probably cause further fish recovery in section III.

Modelling the impacts of global change on concentrations of Escherichia coli in an urban river

Discharges of combined sewer system overflows (CSOs) affect water quality in drinking water sources despite increasing regulation and discharge restrictions. A hydrodynamic model was applied to simulate the transport and dispersion of fecal contaminants from CSO discharges and to quantify the impacts of climate and population changes on the water quality of the river used as a drinking water source in Québec, Canada. The dispersion model was used to quantify Escherichia coli (E. coli) concentrations at drinking water intakes. Extreme flows during high and low water events were based on a frequency analysis in current and future climate scenarios. The increase of the number of discharges was quantified in current and future climate scenarios with regards to the frequency of overflows observed between 2009 and 2012. For future climate scenarios, effects of an increase of population were estimated according to current population growth statistics, independently of local changes in precipitation that are more difficult to predict than changes to regional scale hydrology. Under “business-as-usual” scenarios restricting increases in CSO discharge frequency, mean E. coli concentrations at downstream drinking water intakes are expected to increase by up to 87% depending on the future climate scenario and could lead to changes in drinking water treatment requirements for the worst case scenarios. The greatest uncertainties are related to future local discharge loads. Climate change adaptation with regards to drinking water quality must focus on characterizing the impacts of global change at a local scale. Source water protection planning must consider the impacts of climate and population change to avoid further degradation of water quality.

Accelerating Flood Relief

To expedite flood relief in two neighborhoods, the District of Columbia Water and Sewer Authority accelerated the design and construction of the approximately 2,700 ft long First Street Tunnel, which can store up to 9 million gallons of stormwater and wastewater that otherwise would overwhelm the city’s combined sewer system. To be completed this month, construction of the tunnel and its appurtenant facilities included ground freezing in several locations to minimize untoward effects on the dense urban neighborhood above.

Cesium and strontium loads into a combined sewer system from rainwater runoff

In this study, combined sewage samples were taken with time in several rain events and sanitary sewage samples were taken with time in dry weather to calculate Cs and Sr loads to sewers from rainwater runoff. Cs and Sr in rainwater were present as particulate forms at first flush and the particulate Cs and Sr were mainly bound with inorganic suspended solids such as clay minerals in combined sewage samples. In addition, multiple linear regression analysis showed Cs and Sr loads from rainwater runoff could be estimated by the total amount of rainfall and antecedent dry weather days. The variation of the Sr load from rainwater to sewers was more sensitive to total amount of rainfall and antecedent dry weather days than that of the Cs load.

Implementing sustainable drainage systems for urban surface water management within the regulatory framework in England and Wales

The UK 2007 floods resulted in damages estimated to exceed over £4 billion. This triggered a national review of strategic flood risk management (Pitt, 2008) with its recommendations informing and implemented by the Flood and Water Management, Act (FWMA, 2010). Estimating that up to two-thirds of properties flooded in the 2007 event as a direct result of overloaded sewer systems, the FWMA set out an ambitious overhaul of flood risk management approaches including identifying bodies responsible for the management of local flood risk (local municipalities) and the development of over-arching Lead Local Flood Authorities (LLFAs) at a regional level. LLFAs duties include developing local flood risk management strategies and, aligned with this, many LLFAs and local municipalities produced sustainable drainage system (SUDS) guidance notes. In parallel, changes to the national planning policy framework (NPPF) in England give priority to the use of SUDS in new major developments, as does the related Town and Country Planning Order (2015). However, whilst all three pieces of legislation refer to the preferential use of SUDs, these requirements remain “economically proportionate” and thus the inclusion of SUDS within development controls remain desirable - but not mandatory - obligations. Within this dynamic policy context, reignited most recently by the December 2015 floods, this paper examines some of the challenges to the implementation of SUDS in England and Wales posed by the new regulatory frameworks. In particular, it examines how emerging organisational procedures and processes are likely to impact on future SUDS implementation, and highlights the need for further cross-sectoral working to ensure opportunities for cross-sectoral benefits– such as that accrued by reducing stormwater flows within combined sewer systems for water companies, property developers and environmental protection – are not lost.

Predictors of urban variable source area: a cross‐sectional analysis of urbanized catchments in the United States

AbstractMany studies have empirically confirmed the relationship between urbanization and changes to the hydrologic cycle and degraded aquatic habitats. While much of the literature focuses on extent and configuration of impervious area as a causal determinant of degradation, in this article, I do not attribute causes of decreased watershed storage on impervious area a priori. Rather, adapting the concept of variable source area (VSA) and its relationship to incremental storage to the particular conditions of urbanized catchments, I develop a statistically robust linear regression‐based methodology to detect evidence of VSA‐dominant response. Using the physical and meteorological characteristics of the catchments as explanatory variables, I then use logistic regression to statistically analyze significant predictors of the VSA classification. I find that the strongest predictor of VSA‐type response is the percent of undeveloped area in the catchment. Characteristics of developed areas, including total impervious area, percent‐developed open space and the type of drainage infrastructure, do not add to the explanatory power of undeveloped land in predicting VSA‐type response. Within only developed areas, I find that total impervious area and percent‐developed open space both decrease the odds of a catchment exhibiting evidence of VSA‐type response and the effect of developed open space is more similar to that of total impervious area than undeveloped land in predicting VSA response. Different types of stormwater management infrastructure, including combined sewer systems and infiltration, retention and detention infrastructure are not found to have strong statistically significant effects on probability of VSA‐type response. VSA‐type response is also found to be stronger during the growing season than the dormant season. These findings are consistent across a national cross‐section of urbanized watersheds, a higher resolution dataset of Baltimore Metropolitan Area watersheds and a subsample of watersheds confirmed not to be served by (combined sewer systems). Copyright © 2016 John Wiley & Sons, Ltd.

Anaerobic digestion of sludge differing in inorganic solids content: performance comparison and the effect of inorganic suspended solids content on degradation.

High inorganic suspended solids (ISS) content of sludge in many areas (especially with combined sewage systems) results in low VS/TS (volatile solids, VS; total solids, TS) levels and raises concerns about its effect on anaerobic digestion. The performances of sludge anaerobic digestion with different feeding VS/TS levels as well as the effect of ISS content on the anaerobic degradation process were investigated in completely stirred tank reactors by semi-continuous and batch experiments. In semi-continuous experiment with sludge at VS/TS of 61.4%, 45.0, 30.0% and 15.0%, biogas yield, VS reduction and methane content decreased logarithmically with the feeding VS/TS decreasing; slightly higher volatile fatty acid concentration was observed at VS/TS 15%. Results of the batch experiments suggested that acetogenesis and methanogenesis are obviously affected by high ISS addition, while hydrolysis is less affected. The retardment of substrate conversion rate is probably attributed to decreased mass transfer efficiency at high ISS content.

Assessment of pollutant load emission from combined sewer overflows based on the online monitoring.

Cities equipped with combined sewer systems discharge during wet weather a lot of pollutants into receiving waters by combined storm overflows (CSOs). According to the Polish legislation, CSOs should be activated no more than ten times per year, but in Lodz, most of the 18 existing CSOs operate much more frequently. To assess the pollutant load emitted by one of the existing CSOs, the sensors for measuring the concentration of total suspended solids (SOLITAX sc) and dissolved chemical oxygen demand (UVAS plus) installed in the overflow chamber as well as two flowmeters placed in the outflow sewer were used. In order to check the data from sensors, laboratory tests of combined wastewater quality were conducted simultaneously. For the analysis of the total pollutant load emitted from the overflow, the raw data was denoised using the Savitzky-Golay method. Comparing the load calculated from the analytical results to online smoothed measurements, negligible differences were found, which confirms the usefulness of applying the sensors in the combined sewer system. Online monitoring of the quantity and quality of wastewater emitted by the combined sewer overflows to water receivers, provides a considerable amount of data very useful for combined sewerage upgrading based on computer modelling, and allows for a significant reduction of laboratory analysis.

Urban stormwater forecasting model and drainage optimization based on water environmental capacity

Drainage systems in China are currently being transformed from combined sewer systems into separate sewer systems; newly built areas generally use the latter for sewage and stormwater treatment. Polluted stormwater runoff is discharged directly into rivers through pipelines, thereby deteriorating the water quality of rivers. In this work, an urban stormwater system model was built with Infoworks Integrated Catchment Modeling and validated by measured data. The loads at the pipe outlets during rainstorms were analyzed as well. Stormwater system was transformed by using mathematical models under the conditions of meeting river water quality standards and preventing damage to water environmental capacity. The relative errors of volume and peak runoff of model calibration were from −2.33 to +12.06 % and −13.43 to +8.7 %, respectively. The study indicates that the stormwater system model can be used in scenario analysis, and the stormwater system can accommodate floods over a recurring interval of 10 years. Moreover, stormwater can be directly discharged into water bodies without exceeding the carrying capacity of the water environment with the transformation of the stormwater system.