Separate Sewer Systems Research Articles

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 …

The unfulfilled promise of urban Lake Kleine Melanen (The Netherlands): Diagnostics, experiment on reduction of sediment P-release and in-lake restoration

Waajen, G, Lürling M, van de Sande R. The unfulfilled promise of urban Lake Kleine Melanen (The Netherlands): diagnostics, experiment on reduction of sediment P-release and in-lake restoration. Lake Reserv Manage. 35:8–24.Lake Kleine Melanen (The Netherlands) experienced cyanobacterial blooms during the summertime, causing public health risks, turbid water, and lack of macrophytes. To improve the situation, we determined the underlying causes of the poor water quality. Our diagnosis included the water and phosphorus (P) budget of the lake and showed the need for the reduction of both the external and internal P loads. The external P load (7.5 mg P/m2/d) exceeded the transition between the clear water state and the turbid state by 44–121%, mainly due to the discharges from the separated stormwater sewer system in the adjacent neighborhood. Due to political and financial considerations of the managing authorities, the restoration (2010–2012) was restricted to internal management. To reduce the high internal P load (3.8 mg P/m2/d), we tested 3 sediment capping options in an enclosure experiment, showing the best results when we combined sand capping with the P fixative Phoslock® and flocculant polyaluminumchloride. A 0.6–1.3 m thick layer of soft sediment was dredged from the lake. Thereafter, the sediment was capped with a 0.2 m thick layer of sand to which Phoslock® was added. Additional in-lake measures including fish removal and shoreline reconstruction were also conducted to support improvement. We compared water quality before (2008–2010) and after (2012–2014) interventions. Although the mean concentration of total P was reduced from 0.30 to 0.11 mg P/L, and cyanobacterial chlorophyll a from 52 to 6 μg/L, cyanobacterial blooms still occurred. For further water quality improvement, the reduction of the external P load caused by stormwater runoff is required.

Performance and uncertainties of TSS stormwater sampling strategies from online time series.

The event mean concentrations (EMCs) that would have been obtained by four different stormwater sampling strategies are simulated by using total suspended solids (TSS) and flowrate time series (about one minute time-step and one year of data). These EMCs are compared to the reference EMCs calculated by considering the complete time series. The sampling strategies are assessed with datasets from four catchments: (i) Berlin, Germany, combined sewer overflow (CSO); (ii) Graz, Austria, CSO; (iii) Chassieu, France, separate sewer system; and (iv) Ecully, France, CSO. A sampling strategy in which samples are collected at constant time intervals over the rainfall event and sampling volumes are pre-set as proportional to the runoff volume discharged between two consecutive sample leads to the most representative results. Recommended sampling time intervals are of 5 min for Berlin and Chassieu (resp. 100 and 185 ha area) and 10 min for Graz and Ecully (resp. 335 and 245 ha area), with relative sampling errors between 7% and 20% and uncertainties in sampling errors of about 5%. Uncertainties related to sampling volumes, TSS laboratory analyses and beginning/ending of rainstorm events are reported as the most influent sources in the uncertainties of sampling errors and EMCs.

Pollutant transport analysis and source apportionment of the entire non-point source pollution process in separate sewer systems

Understanding pollutant transport process and source apportionment is critical to urban stormwater pollution mitigation. Previous studies have investigated transport and sources of road deposited sediments (RDS) and sewer sediments individually, and most of these studies focused on stormwater pollution in combined sewer systems. However, studies about pollutant transport and source apportionment of the entire urban non-point source pollution process in separate sewer systems are lacking. This study analyzed particle size distribution and chemical pollutants in five media during the entire pollutant process including RDS, roof runoff, road runoff, sewer sediments, and sewer runoff. The outcomes found that mass percentage of fine particles became greater during pollutant transport in stormwater runoff. According to transport characteristics, particles were grouped into three types: particles <20 μm, 20–105 μm, and >105 μm. Particles <20 μm had the highest mobility capacity and particles >105 μm had the lowest mobility capacity, while mobility capacity of particles 20–105 μm was uncertain. Pollutant concentrations in road runoff were significantly influenced by rainfall intensity and pollutant concentrations in sewer runoff could become lower during rainy seasons ignoring rainfall intensity. RDS was the main contributor of heavy metals while organic matter and nutrients were primarily contributed by sewer sediments. Roof runoff, road runoff and sewer sediments contributed 5.35%, 69.24% and 25.41% particles to urban receiving water, respectively. Based on the outcomes, several suggestions were given for stormwater management.

State of the Practice: Assessing Water Quality Benefits from Street Sweeping

AbstractMunicipal separate storm sewer system (MS4) permittees face costly obligations to reduce pollutant of concern (POC) loadings for achieving waste load allocations (WLAs) assigned from total ...

Benchmarking of energy consumption in municipal wastewater treatment plants - a survey of over 200 plants in Italy.

One of the largest surveys in Europe about energy consumption in Italian wastewater treatment plants (WWTPs) is presented, based on 241 WWTPs and a total population equivalent (PE) of more than 9,000,000 PE. The study contributes towards standardised resilient data and benchmarking and to identify potentials for energy savings. In the energy benchmark, three indicators were used: specific energy consumption expressed per population equivalents (kWh PE-1 year-1), per cubic meter (kWh/m3), and per unit of chemical oxygen demand (COD) removed (kWh/kgCOD). The indicator kWh/m3, even though widely applied, resulted in a biased benchmark, because highly influenced by stormwater and infiltrations. Plants with combined networks (often used in Europe) showed an apparent better energy performance. Conversely, the indicator kWh PE-1 year-1 resulted in a more meaningful definition of a benchmark. High energy efficiency was associated with: (i) large capacity of the plant, (ii) higher COD concentration in wastewater, (iii) separate sewer systems, (iv) capacity utilisation over 80%, and (v) high organic loads, but without overloading. The 25th percentile was proposed as a benchmark for four size classes: 23 kWh PE-1 y-1 for large plants > 100,000 PE; 42 kWh PE-1 y-1 for capacity 10,000 < PE < 100,000, 48 kWh PE-1 y-1 for capacity 2,000 < PE < 10,000 and 76 kWh PE-1 y-1 for small plants < 2,000 PE.

Quantification of pathogens and markers of fecal contamination during storm events along popular surfing beaches in San Diego, California

Along southern California beaches, the concentrations of fecal indicator bacteria (FIB) used to quantify the potential presence of fecal contamination in coastal recreational waters have been previously documented to be higher during wet weather conditions (typically winter or spring) than those observed during summer dry weather conditions. FIB are used for management of recreational waters because measurement of the bacterial and viral pathogens that are the potential causes of illness in beachgoers exposed to stormwater can be expensive, time-consuming, and technically difficult. Here, we use droplet digital Polymerase Chain Reaction (digital PCR) and digital reverse transcriptase PCR (digital RT-PCR) assays for direct quantification of pathogenic viruses, pathogenic bacteria, and source-specific markers of fecal contamination in the stormwater discharges. We applied these assays across multiple storm events from two different watersheds that discharge to popular surfing beaches in San Diego, CA. Stormwater discharges had higher FIB concentrations as compared to proximal beaches, often by ten-fold or more during wet weather. Multiple lines of evidence indicated that the stormwater discharges contained human fecal contamination, despite the presence of separate storm sewer and sanitary sewer systems in both watersheds. Human fecal source markers (up to 100% of samples, 20-12440 HF183 copies per 100 ml) and human norovirus (up to 96% of samples, 25-495 NoV copies per 100 ml) were routinely detected in stormwater discharge samples. Potential bacterial pathogens were also detected and quantified: Campylobacter spp. (up to 100% of samples, 16-504 gene copies per 100 ml) and Salmonella (up to 25% of samples, 6-86 gene copies per 100 ml). Other viral human pathogens were also measured, but occurred at generally lower concentrations: adenovirus (detected in up to 22% of samples, 14-41 AdV copies per 100 ml); no enterovirus was detected in any stormwater discharge sample. Higher concentrations of avian source markers were noted in the stormwater discharge located immediately downstream of a large bird sanctuary along with increased Campylobacter concentrations and notably different Campylobacter species composition than the watershed that had no bird sanctuary. This study is one of the few to directly measure an array of important bacterial and viral pathogens in stormwater discharges to recreational beaches, and provides context for stormwater-based management of beaches during high risk wet-weather periods. Furthermore, the combination of culture-based and digital PCR-derived data is demonstrated to be valuable for assessing hydrographic relationships, considering delivery mechanisms, and providing foundational exposure information for risk assessment.

Characterization and risk assessment of seasonal and weather dynamics in organic pollutant mixtures from discharge of a separate sewer system

Sites of wastewater discharge are hotspots for pollution of freshwaters with organic micropollutants and are often associated with adverse effects to aquatic organisms. The assessment, monitoring and managment of these hotspots is challenged by variations in the pollutant mixture composition due to season, weather conditions and random spills. In this study, we unraveled temporal exposure patterns in organic micropollutant mixtures from wastewater discharge and analyzed respective acute and sublethal risks for aquatic organisms. Samples were taken from two components of a separate sewer system i) a wastewater treatment plant (WWTP) and ii) a rain sewer of a medium size town as well as from the receiving river in different seasons. Rain sewer samples were separately collected for rain and dry - weather conditions. We analyzed 149 compounds by liquid chromatography-tandem mass spectrometry (LC-MS/MS). By considering the pollution dynamics in the point sources, we reduced the complexity of pollutant mixtures by k-means clustering to a few emission groups representing temporal and weather-related pollution patterns. From these groups, we derived biological quality element (BQE) - specific risk patterns. In most cases, one main risk driving emission group and a few individual risk driving compounds were identified for each BQE. While acute risk for fish was quite low, algae were exposed to seasonally emitted herbicides (terbuthylazine, spiroxamine) and crustaceans to randomly spilled insecticides (diazinon, dimethoate). Sublethal risks for all BQE were strongly influenced by constantly emitted pollutants, above all, pharmaceuticals. Variability of risks in the river was mainly driven by water discharge of the river rather than by season or peak events. Overall, the studied WWTP represented the major pollution source with a specific emission of agricultural compounds. However, the investigated rain sewer showed to be a constant pollution source due to illicit connections and was an important entry route for high loads of insecticides and biocides due to spills or incorrect disposal. By considering these pollution and risk dynamics, monitoring strategies may be optimized with a special focus on times of low flow conditions in the river, rain events and seasonally emitted risk drivers.

An effective and comprehensive model for optimal rehabilitation of separate sanitary sewer systems

In the field of rehabilitation of separate sanitary sewer systems, a large number of technical, environmental, and economic aspects are often relevant in the decision-making process, which may be modelled as a multi-objective optimization problem. Examples are those related with the operation and assessment of networks, optimization of structural, hydraulic, sanitary, and environmental performance, rehabilitation programmes, and execution works. In particular, the cost of investment, operation and maintenance needed to reduce or eliminate Infiltration from the underground water table and Inflows of storm water surface runoff (I/I) using rehabilitation techniques or related methods can be significantly lower than the cost of transporting and treating these flows throughout the lifespan of the systems or period studied.This paper presents a comprehensive I/I cost–benefit approach for rehabilitation that explicitly considers all elements of the systems and shows how the approximation is incorporated as an objective function in a general evolutionary multi-objective optimization model. It takes into account network performance and wastewater treatment costs, average values of several input variables, and rates that can reflect the adoption of different predictable or limiting scenarios. The approach can be used as a practical and fast tool to support decision-making in sewer network rehabilitation in any phase of a project. The fundamental aspects, modelling, implementation details and preliminary results of a two-objective optimization rehabilitation model using a genetic algorithm, with a second objective function related to the structural condition of the network and the service failure risk, are presented. The basic approach is applied to three real world cases studies of sanitary sewerage systems in Coimbra and the results show the simplicity, suitability, effectiveness, and usefulness of the approximation implemented and of the objective function proposed.

Case study on the use of a combined system as an intermediate solution in Brazil: cost estimate

AbstractAs a developing country, Brazil has to deal with a lack of basic sanitation. One of the major challenges is the treatment of wastewater. While 94% of Brazilian municipalities have stormwater systems, only 55% are connected to a wastewater system. To help improve the current situation, this study estimates the costs for implementing an intermediate solution, which is designed to ease the transition towards a separate wastewater treatment system. This solution utilizes a combined sewer system approach in areas where stormwater systems have already been implemented. A case study was carried out assessing two possible alternatives for a wastewater treatment system with data from the city of Joinville. Both alternatives are separate systems but one has a combined system as an intermediate solution. The results show that the alternative with an intermediate combined system will reduce the short‐term financial burden on governments in comparison to the separate sewer system approach.

Detection and quantification of lateral, illicit connections and infiltration in sewers with Infra-Red camera: Conclusions after a wide experimental plan

Separate sewer systems are sensitive to illegal or mis-connections. Several techniques (including the Distributed Temperature Sensor) are now available to identify and locate those connections. Based on thermal fingerprints, DTS allows the localization of each lateral connection along a reach. The use of Infra-Red camera has been investigated with 748 laboratory experiments (artificial connections along a flume). The tested connections vary in diameters (from 75 to 200 mm), lengths of intrusion (from 0 to 200 m), shapes (circular or linear i.e. cracks), depths, discharge rates between the lateral connection and the main flume, and temperatures. IR frame analysis (for detection) and 2D temperature mapping (at the free water surface, for quantification) demonstrate that: i) the detection limit is very low (ratio between lateral and main discharges: 0.025) and ii) the quantification of the lateral discharge is impossible. Application of an IR camera seems to be a promising technique to detect lateral connections.

Parametric investigation in Malaysian separate sewer systems

Flow characteristics are significant in the design of sewerage systems in that poor analysis of the flow design parameters may influence the capacity of a sewerage system, causing health and environmental problems. The aim of this study is to verify the design parameters in the peak flow factor equation in Malaysian Standard Code of Practice MS 1228:1991. Data collection was conducted in a residential area at Taman Lepar Hilir Saujana, Kuantan, Pahang. ISCO 2150 Area Velocity Flow Meter and ISCO 674 Rain Gauge were used in this study to collect flow rate and rainfall intensity data, respectively. The resultant analysis shows that the flow design parameters, per capita flow and design criterion, were unexpectedly 42·2 and 16% lower than the value of per capita flow and design criterion described in MS 1228:1991, respectively. This indicates that the separate sewer systems in Malaysia may be overdesigned if using the flow design parameters recommended in MS 1228:1991. Thus, a revision of the flow design parameters may be necessary, taking into account the rising cost of materials around the world.

Effects of submerged zone, media aging, and antecedent dry period on the performance of biochar-amended biofilters in removing fecal indicators and nutrients from natural stormwater

Biochar has demonstrated promising performance as an amendment to biofilter soil media in removing fecal indicator bacteria (FIB) from simulated stormwater. However, there is no study that investigates its efficacy in treating natural stormwater runoff. Additional information, including the effects of antecedent dry period, microbial biofilm, and presence of a saturation zone on the performance of biochar-augmented biofilters are needed to inform their field implementation. This study uses laboratory column experiments to monitor FIB (enterococci and Escherichia coli) and nutrient removal capacity of biochar-amended biofilters for 140days using natural stormwater. Our study also investigates the effects of antecedent dry days (ADD) and the presence of a saturation zone (SZ) on the performance of lab-scale biochar-amended biofilters. The results suggest insignificant influence of the ADD and SZ on FIB removal performance, however biofilters with a SZ perform significantly better in removing nitrate-nitrogen compared to those without a SZ. In addition, it appears that the presence of biofilm augments nutrient removal capacity but reduces FIB removal capacity. Our observations indicate that biochar-amended biofilters are able to treat (to comply with recreational water quality standard for FIB) urban stormwater runoff for the duration of the experiment. Nitrate- and ammonium-nitrogen removal in the biologically aged biofilters is found to be 50–60% while the total dissolved phosphorus and the organic nitrogen removal is 20–30%. Our results inform full-scale design of biochar-amended biofilters in order to meet the total maximum daily load (TMDL) and municipal separate storm sewer system (MS4) permitting requirement for FIB and nutrients.

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.

Analysis of pollution characteristics and first flush effect in rainfall runoff in separate storm sewer system in upstream of Tangxi River,Chaohu Catchment

Analysis of pollution characteristics and first flush effect in rainfall runoff in separate storm sewer system in upstream of Tangxi River,Chaohu Catchment

An Analysis of Patterns and Trends in United States Stormwater Utility Systems

AbstractSeveral factors, such as municipality location and population, are thought to influence trends among stormwater utilities (SWUs); however, no analysis of the relationship between these factors andSWUcharacteristics has been performed. This article corroborates hypothesized relationships and identifies trends and patterns in the establishment, funding mechanism, and magnitude ofSWUs by analyzing location, population density, home value, and year of establishment for a comprehensive nationalSWUdatabase with data for 1,490SWUs. The equivalent residential unit (ERU), aSWUthat charges based on impervious area, was the most prevalent funding mechanism in all National Oceanic and Atmospheric Administration Climate Regions of the United States except the West and West‐North‐Central. TheERUwas also found in larger cities with high population densities, whereas the Flat Fee, aSWUthat charges a single rate for all properties, was found in smaller towns. Higher home values were correlated with higher monthly fees for 28% of the municipalities analyzed. The residential equivalence factor, aSWUthat charges based on runoff produced, was popular in municipalities with higher home values, whereas the Flat Fee was popular in municipalities with lower home values. The number ofSWUs established increased with Phase I municipal separate stormwater and sewer system (MS4) permit and PhaseIIsmallMS4 permit deadlines. Summary tables provide guidance to aid municipalities considering aSWU.

Monitoring micropollutants in the Swist river basin.

Micropollutant pathways were studied for the Swist river basin (Western Germany). The aim was to verify the effectiveness of a monitoring approach to detect micropollutants entering the river. In a separate sewer system, water was frequently found to be contaminated with micropollutants. Improper connections of sewage canals to the stormwater network seemed to be the cause of pollution. Wastewater treatment plants (WWTPs) exerted the largest influence on micropollutants for the receiving river. During a flu outbreak, antibiotics in the Swist stemming from WWTPs increased remarkably. Elevated levels of pharmaceuticals were measured in discharges from a combined sewer overflow (CSO). The study showed that the pharmaceutical load of a CSO was significantly reduced by advanced treatment with a retention soil filter. Painkillers, an anticonvulsant and beta blockers were the most often detected pharmaceuticals in the sewage of urban areas. Herbicides, flame retardants and industrial compounds were also observed frequently. On cropland, Chloridazon and Terbuthylazine compounds were often found in landscape runoff. Fungicides and insecticides were the most frequent positive findings in runoff from orchards. The paper shows that a coherent approach to collecting valid information regarding micropollutants and to addressing relevant pathways as a basis for appropriate management strategies could be established.

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.

Analysis and integrated modelling of groundwater infiltration to sewer networks

AbstractInfiltration of groundwater to sewer systems is a problem for the capacity of the system as well as for treatment processes at waste water treatment plants. This paper quantifies the infiltration of groundwater to a sewer system in Frederikshavn Municipality, Denmark, by measurements of sewer flow and novel model set‐up, which simulates the interaction between groundwater and sewer flow.The study area has a separate waste water sewer system, but the discharged volumes from the system are approximately twice the volumes from a tight system without infiltration. The model set‐up makes use of two commercial models: mike she for simulation of groundwater transport and mike urban (mouse) [DHI, Hørsholm, Denmark] for simulation of sewer flow. By simulating the groundwater level and calibrating infiltration coefficients against sewer flow measurements, it has been possible to estimate the average infiltration to the sewer system with satisfying results. The infiltration processes are indeed complicated and to a large degree heterogeneous throughout the sewer system. The paper shows contribution from both saturated and unsaturated groundwater zones, which makes the modelling process complex. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Detection of Wastewater Discharges into Stormwater Sewers: Effects of Travel Distance on Parameters

In separate sewer systems, there is a risk that wastewater from illicit connections may enter a stormwater sewer and ultimately outfall into receiving waters, adversely affecting receiving water qu ...