Combined Sewer Overflow Treatment Research Articles

Hydraulic fractionation of conventional water quality constituents in municipal dry- and wet-weather flow samples

The effective design of treatment processes for combined sewer overflows (CSOs) requires understanding of the CSO characteristics and treatability. Environment Canada partnered with four municipalities to evaluate water quality and treatability of wet- and dry-weather flows at local sewage or CSO treatment facilities. Chemical characterization of the samples indicates that the municipal sewage at all of the sites is of relatively weak strength, with several differences between the water quality data for dry-weather and wet-weather flows (assumed to represent CSOs). Hydraulic separation of constituents with an elutriation apparatus illustrated the removals that can be expected with conventional settling techniques and differences in settling of various constituents.

A comparative study of surface and subsurface flow constructed wetlands for treatment of combined sewer overflows: A greenhouse experiment

The use of surface flow (SFCWs) and subsurface flow constructed wetlands (SFCWs) for the treatment of combined sewer overflows was assessed at pilot scale. Synthetic wastewater was applied in three batches with decreasing concentrations to mimic concentration profiles that are obtained in the field during overflow events. Three simulated combined sewer overflows were applied on each wetland. Composite water samples (60 in total) were taken for a period of 8 days to study the removal of total nitrogen (Ntot), NH 4–N, NO 3–N, total COD (CODtot) and total phosphorus. Redox potential, which was monitored at various locations along the wetlands, was more negative in the SSFCWs. In general, removal occurred faster in the SSFCWs and the final concentrations were lower. The removal of Ntot was only 36.6 ± 3.3% in the SFCWs due to nitrification-limiting conditions. The conditions in the SSFCWs, in contrast, seemed to promote Ntot removal (removal efficiency 96.7 ± 1.9%). The removal of P was hampered in both wetland types by reducing conditions. P that was initially removed was released again from the substrates later on. First-order removal rate constants were derived for the removal of both CODtot (SSFCWs: 1.1 ± 0.3 m d −1; SFCWs: 0.17 ± 0.06 m d −1) and Ntot (SSFCWs: 0.4 ± 0.1 m d −1; SFCWs: 1.7 ± 0.5 m d −1).

Treatment of Combined Sewer Overflow Using Retention Treatment Basin Assisted with Polymer Chemical Coagulation

Pilot plant experiments were conducted to examine the performance of a retention treatment basin (RTB) with chemical coagulation using a cationic polymer in the treatment of combined sewer overflow (CSO) for the City of Windsor, Ontario, Canada. The pilot plant was operated at surface overflow rates (SORs) up to 1370 m3/m2 x d. This study demonstrated that the use of polymer coagulation improved settling characteristics of solids, and allowed the SOR in the RTB to be increased significantly. An optimum polymer dosage to achieve the discharge standards of CSO was determined from the experimental runs. The effluent quality met the Ontario Ministry of the Environment Procedure F5-5 in terms of 5-day biochemical oxygen demand and total suspended solids removals. A flushing box was successfully tested for flushing the collected floatables and sludge from the bottom of the RTB after storm events.

CSO treatment strategy based on constituent index relationships in a highly urbanised catchment

In urbanising catchments the variability of particulate matter (solids) and oxygen demanding constituents of wet weather and dry weather characteristics result in variable treatment effectiveness from physical unit operations and biological unit processes. Higher organic concentrations during dry weather flow are more amenable to biological unit processes while the higher inorganic loads generated largely by urban wet weather constituents and much larger flows can be more effectively treated or conditioned by physical unit operations, including ideally preceded by hydrologic controls. This study examines the relationships between total chemical oxygen demand (COD)(t), dissolved chemical oxygen demand (COD)(d), particulate chemical oxygen demand (COD)(p) and solids, measured as total suspended solids (TSS). Results also provide an index for selection and optimisation of treatment operations for combined sewer overflow (CSO) loads.

Interaction of oxygen concentration and retention of pollutants in vertical flow constructed wetlands for CSO treatment

The EU Water Framework Directive (WFD) calls for a good quality of all water bodies. Retention soil filters (RSF) have been developed to treat discharges from combined sewers systems. RSF have proved over the past 15 years to be the most effective measure to meet the EU WFD standards, especially for small or particularly sensitive receiving waters, which require an enhanced reduction of emissions from combined sewer overflows (CSOs). The paper presents results from laboratory-scale experiments, in which the oxygen measurement in the filter plays a main role. The results show remarkable differences in oxygen concentrations in different filter depths. The highest oxygen consumption takes place in the upper part of the filter. In the lower part the re-aeration of sewage from the soil air dominates. This indicates that the biological activity is limited to the upper part of the filter. The availability of oxygen in the filter is a sign for degradation of wastewater compounds (ammonium, COD) under certain conditions and already takes place during the filter operation. The removal of ammonium especially cannot be strictly divided into phases of sorption during the loading and oxidation during the dry period any more.

Effectiveness of combined sewer overflow treatment for dissolved oxygen improvement in the Chicago Waterways

An Use Attainability Analysis (UAA) has been initiated to evaluate what water-quality standards can be achieved in the Chicago Waterway System (CWS). There are nearly 200 combined sewer overflow (CSO) locations discharging to the CWS by gravity. Three CSO pumping stations also drain approximately 140 km2. Because of the dynamic nature of the CWS the DUFLOW model that is capable of simulating hydraulics and water-quality processes under unsteady-flow conditions was used to evaluate the effectiveness of water-quality improvement techniques identified by the UAA including CSO treatment. Several CSO treatment levels were applied at gravity flow CSOs to evaluate improvement in dissolved oxygen (DO). The results show that pollutant removal at CSOs improves DO to a certain degree, but it still was not sufficient to bring DO concentrations to 5 mg/L or higher for 90% of the time during wet weather at most locations on the CWS. Flow from the pumping stations results in substantial stress on DO since a huge amount of un-treated water with a high pollution load is discharged into the CWS in a short period of time at a certain location. The simulation results indicate that CSO treatment does not effectively improve DO during wet-weather periods on the CWS.

Sewer solids separation by sedimentation – the problem of modeling, validation and transferability

Sedimentation of sewer solids in tanks, ponds and similar devices is the most relevant process for the treatment of stormwater and combined sewer overflows in urban collecting systems. In the past a lot of research work was done to develop deterministic models for the description of this separation process. But these modern models are not commonly accepted in Germany until today. Water Authorities are sceptical with regard to model validation and transferability. Within this paper it is checked whether this scepticism is reasonable. A framework-proposal for the validation of mathematical models with zero or one dimensional spatial resolution for particle separation processes for stormwater and combined sewer overflow treatment is presented. This proposal was applied to publications of repute on sewer solids separation by sedimentation. The result was that none of the investigated models described in literature passed the validation entirely. There is an urgent need for future research in sewer solids sedimentation and remobilization!

Modelling of organic matter degradation in constructed wetlands for treatment of combined sewer overflow

Subsurface vertical flow constructed wetlands (CWs) have been found to be a useful system to treat combined sewer overflow (CSO). The study presented uses numerical simulation to increase the understanding of the fundamental processes of COD degradation in CWs for CSO treatment. The multi-component reactive transport module CW2D was used for the simulation study. The simulation results showed that the measured behaviour of the system can only be modelled when COD adsorption is considered as additional process. A new parameter set for CW2D for modelling CSO treatment is presented. A range of values for COD adsorption parameters, COD fractionation and bacteria concentrations were estimated by an identifiability analysis. For the simulation a step wise approach was developed. On the one hand a lysimeter study was used for calibration and validation, and on the other hand field and lab-scale experiments were used for validation. Single-event simulations as well as long-term simulations were carried out. For the single-event simulations (lysimeter and field studies) a good match between measured and simulated data could be achieved. However, the long-term simulations showed that there is a need for further investigations mainly due to the uncertainties during long dry periods between the loadings.

Performance of a high-rate sedimentation process for combined sewerage treatment in wet weather

A novel high-rate sedimentation process has been developed for directly treating combined sewer overflows (CSOs). This was done using a test facility at an actual wastewater treatment plant in Tokyo. Pilot test results, carried out 13 times, from December 2002 to July 2003 in wet weather, suggested that the process was suitable for treatment of CSOs. The performance of the process was favorable at 50 m3/(m2 ·h) up to 880 mg/L influent TSS, removing between 78 % and 91 % of TSS at loading and between 64 % and 85 % of BOD5 also at loading. The pilot testing clarified that a decrease in the influent alkalinity due to rain water caused a drop in the pH after FeCl3 addition and thus improved coagulation, with a significant decrease in the effluent TSS. Mixing, coagulation and flocculation were carried out in a baffling type mixing tank to enable uniform mixing without any short-passes. Coagulation conditions in this mixing method were evaluated and results clarified that rapid mixing was required momentarily after each addition of FeCl3 and polymer, i.e. to diffuse these additives into the influent.

Effectiveness of Fine Screens in Meeting CSO Treatment Requirements for Identifiable Sanitary Materials

Effectiveness of Fine Screens in Meeting CSO Treatment Requirements for Identifiable Sanitary MaterialsRemoval of identifiable sanitary material is a necessary component required to achieve adequate treatment of combined sewer overflows (CSO) by the Michigan Department of Environmental Quality (MDEQ). As part of the demonstrative approach that the city of Detroit is using to develop a Long-Term CSO Control Plan for the Detroit River outfalls, the city constructed two pilot facilities to test the...Author(s)Mirza A. RabbaigTerrance MooreImad A. SalimWade TrimJennifer R. FansonMark J. TenBroekClayton E. McCormackWade TrimSourceProceedings of the Water Environment FederationSubjectSession 5: Tunnels and Treatment – Unique Approaches to Store and Treat CSOsDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2006ISSN1938-6478SICI1938-6478(20060101)2006:4L.261;1-DOI10.2175/193864706783796295Volume / Issue2006 / 4Content sourceCollection Systems ConferenceFirst / last page(s)261 - 277Copyright2006Word count493

The Use of Computational Flow Modeling to determine Disinfection Efficacy of an Advanced Hydrodynamic Vortex combined Sewer Overflow Treatment System

The Use of Computational Flow Modeling to determine Disinfection Efficacy of an Advanced Hydrodynamic Vortex combined Sewer Overflow Treatment System

Simulation of a subsurface vertical flow constructed wetland for CSO treatment

Constructed wetlands (CWs) have proved to be a highly effective measure to reduce the ecological impact of combined sewer overflows (CSOs) on receiving waters. Due to the stochastic nature of the loading regime and the multitude of environmental influences, assessment of the performance of such plants requires detailed mathematical modelling. A multi-component reactive transport module (CW2D) was applied to simulate the flow, transport and degradation processes occurring in a CW for CSO treatment. CW2D was originally developed to simulate the treatment of municipal wastewater in subsurface flow CWs. Loading and operational conditions in CSO treatment differ fundamentally from the conditions occurring for wastewater treatment. Despite these differences, first results from the simulation of lab-scale experiments show, that the model is generally applicable to this type of plant. Modelling of adsorption, degradation processes, and influent fractionation, however, require further research.

Planning and Design of Combined Sewer Overflow Treatment

Abstract A newly produced (2004) Combined Sewer Overflow (CSO) Treatment Technologies Manual provides an overview of practices in, and guidance for, planning, design and implementation of CSO treatment. Towards this end, the manual first addresses CSO abatement program planning in order to provide an overall framework within which the application and design of CSO treatment facilities may be considered. Following the establishment of a planning framework, guidance is provided for CSO treatment facility preliminary design, which encompasses such steps as the development of CSO control and treatment objectives, assessment of design flows, development of a treatment process train, site-specific considerations, and costs and operating and maintenance (O&M) factors. Finally, preliminary design considerations are developed in more detail for CSO retention treatment basins (RTBs), which are commonly applied to control and treat CSOs in the Great Lakes municipalities. Well-designed RTBs can meet the Ontario requirements for CSO pollution abatement and thereby contribute to the remedial action in the Great Lakes Areas of Concern.

High-Rate Retention Treatment Basins for CSO Control in Windsor, Ontario

Abstract Experimental investigations were conducted to evaluate the effectiveness of a retention treatment basin (RTB) with polymer coagulation for the treatment of combined sewer overflows (CSO) at high hydraulic loading rates. The TSS removal efficiency of the pilot-scale RTB at a surface overflow rate (SOR) of 11 m/h was approximately 35% without chemical addition, and 80% with a polymer dosage range of 5 to 10 milligrams per gram of influent TSS. The results demonstrated that the use of polymer coagulation significantly improved TSS removal and allowed the SOR in the RTB to be significantly increased, resulting in smaller treatment units. An empirical relationship was established to estimate removal efficiencies as a function of overflow rate. The results also compared settling characteristics of CSO, obtained from long column tests, to removal efficiencies in the high-rate RTB.

Numerical Modelling of Enhancing Suspended Solids Removal in a CSO Facility

Abstract One of the most common methods of combined sewer overflow (CSO) treatment is by conventional settling, the efficiency of which depends on the properties of solid particles and the characteristics of the flow transporting these solids. Since the geometry and hydraulics of CSO facilities are often very complex, traditional design methods based on many simplifying assumptions may not predict well the actual operational performance. Therefore, there is a growing need for new tools assisting engineers in design or operation of CSO storage and treatment facilities. In a study of such a CSO facility, a commercial computational fluid dynamics (CFD) model (FLUENT) was used to investigate flow and sediment behaviour, and to explore the ways of optimizing the overall facility performance by adding flow conditioning baffles to improve particle settling. A two-stage approach was adopted; flow patterns were simulated first by means of a volume of fluid (VOF) model and subsequently formed a basis for simulating particle transport by the discrete phase (DP) model. The simulation results for water surface, flow fields in different structure configurations, and particle capture rates in three parallel CSO storage/treatment tanks are presented for various flow conditions.

URBAN WET-WEATHER FLOWS: SOURCES OF FECAL CONTAMINATION IMPACTING ON RECREATIONAL WATERS AND THREATENING DRINKING-WATER SOURCES

Discharges of urban stormwater and combined sewer overflows (CSOs) contribute to fecal contamination of urban waters and need to be considered in planning the protection of recreational waters and sources of drinking water. Stormwater characterization indicates that Escherichia coli counts in stormwater typically range from 103 to 104 units per 100 ml. Higher counts (105 units/100 ml) suggest the presence of cross-connections with sanitary sewers, and such connections should be identified and corrected. Fecal contamination of stormwater may be attenuated prior to discharge into surface waters by stormwater management measures, which typically remove suspended solids and attached bacteria. Exceptionally, stormwater discharges in the vicinity of swimming beaches are disinfected. The levels of indicator bacteria in CSOs can be as high as 106 E. coli per 100 ml. Consequently, the abatement of fecal contamination of CSOs is now considered in the design of CSO control and treatment, as for example stipulated in the Ontario Procedure F-5-5. CSO abatement options comprise combin ations of storage and treatment, in which the CSO treatment generally includes disinfection by ultraviolet (UV) irradiation. Finally, indicator bacteria data from Sarnia (Ontario) were used to demonstrate some fecal contamination impacts of wet-weather flows. In wet weather, the microbiological quality of riverine water worsened as a result of CSO and stormwater discharges, and the recreational water guidelines for indicator organisms were exceeded most of the time. Local improvements in water quality were feasible by source controls and diversion of polluted water.

IMPLEMENTATION OF A COMPUTERIZED MAINTENANCE MANAGEMENT SYSTEM FOR THE CITY OF ATLANTA

IMPLEMENTATION OF A COMPUTERIZED MAINTENANCE MANAGEMENT SYSTEM FOR THE CITY OF ATLANTAThis paper describes the activities performed to implement a Computerized Maintenance Management System (CMMS) at three water reclamation centers (WRCs), seven combined sewer overflow (CSO) treatment facilities, and fourteen pump stations for the City of Atlanta. The City of Atlanta was under a Consent Decree to install and implement a maintenance management system for the R.M. Clayton, Utoy...Author(s)Samuel O. Atere-RobertsScott A. BashSourceProceedings of the Water Environment FederationSubjectSession 01: Asset ManagementDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2002ISSN1938-6478SICI1938-6478(20020101)2002:4L.34;1-DOI10.2175/193864702785301826Volume / Issue2002 / 4Content sourceUtility Management ConferenceFirst / last page(s)34 - 44Copyright2002Word count193

Challenges of Combined Sewer Overflow Disinfection by Ultraviolet Light Irradiation

This article examines the performance and effectiveness of ultraviolet (UV) irradiation for disinfection of combined sewer overflow (CSO). Due to the negative impact of conventional water disinfectants on aquatic life, new agents (e.g., UV light) are being investigated for CSO. This low-quality water with high flow rates, volumes, and suspended solids content requires the use of high-rate techniques for its disinfection. Although many pilot-scale studies have investigated UV irradiation as an alternative technology, to date no full-scale CSO treatment facilities in the United States are using UV light. A survey of the major pilot-scale studies investigating UV light as a CSO disinfectant suggests that UV light irradiation, correctly applied, is an effective alternative to chlorination for CSO. The success of disinfecting with UV light seems to be strongly dependent on water quality. Thus, pretreatment of CSO prior to disinfection is a major prerequisite to ensure UV light effectiveness.

The Urban Drainage Program of Canada’s Great Lakes 2000 Cleanup Fund

Abstract Since 1990, Canada’s Great Lakes 2000 Cleanup Fund, which is administered by Environment Canada, has been supporting the development and implementation of cleanup technologies to control municipal pollution sources, to clean up contaminated sediments, and to rehabilitate fish and wildlife habitats. These efforts are focused on Canada’s 16 Great Lakes Areas of Concern (AOCs) identified by the International Joint Commission for priority cleanup action and restoration of beneficial uses. Remedial Action Plans (RAPs) developed by federal/provincial teams and the public provide the strategy for restoring the beneficial uses of the AOCs. Impairments in beneficial uses in the AOCs have been, in part, caused by discharges from combined sewer overflows (CSOs), Stormwater and sewage treatment plants (STPs). To assist municipalities in addressing the problems posed by urban drainage (CSOs and Stormwater), the Cleanup Fund’s Urban Drainage Program has been supporting the development and demonstration of innovative, cost-effective technologies and approaches. These projects include high-rate treatment of CSOs, real-time control of CSOs, performance assessment of Stormwater treatment technologies, pollution prevention and control plans, and development of Stormwater management planning tools for urban areas. These projects are carried out in collaboration with the Ontario Ministry of the Environment, municipalities, professional groups, universities and conservation authorities and other Environment Canada’s facilities (National Water Research Institute and Wastewater Technology Centre). The Urban Drainage Program has been instrumental in advancing the state of the art in CSO and Stormwater management in Ontario. Projects supported under the program have quantified pollutant loadings from municipal wastewater sources in several Ontario Areas of Concern, provided hard data on the performance of best management practices for Stormwater treatment, identified and evaluated new cost-effective technologies for CSO reduction and Stormwater treatment, and developed strategies and decision-making tools for Stormwater management The work done through the Urban Drainage Program is making it possible for Great Lakes communities to achieve important environmental objectives at significantly lower cost As a result, the communities should be able to achieve many of these objectives much earlier than they would have if their choices had been limited to more conventional and capital-intensive solutions. Although the program has focused on the needs of Areas of Concern in the Great Lakes basin, the lessons learned there can easily be applied to communities in other parts of the country and around the world.

Combined sewer overflow treatment – knowledge or speculation

The stochastic behaviour of rainfall and the uncertainties in land use development as well as the limited knowledge on efficiency of CSO-treatment measures yield the most difficult conditions for design. Therefore less emphasis should be given to regulations for sizing individual structures and more ingenuity must be used for flexible designs and integration of CSO-facilities in the overall system. More emphasis should be paid to observe and monitor the effectiveness of constructed facilities. The greatest potential in achieving more protection for less money is seen in better using the tradeoff potential between decentral and central treatment and between storage and treatment level.