Combined Sewer Overflow Treatment Research Articles

Treatment of combined sewer overflows using ferrate (VI).

This paper presents the results of a study conducted on the treatment of combined sewer overflows using ferrate (VI) [Fe (VI)]. At a Fe (VI) dose of 0.24 mg/L, total chemical oxygen demand (TCOD), soluble chemical oxygen demand (SCOD), total biochemical oxygen demand (TBOD5), soluble biochemical oxygen demand (SBOD5), total suspended solids (TSS), volatile suspended solids (VSS), total phosphorus (TP), total nitrogen (TN), and soluble TN removal efficiencies of 71, 75, 69, 68, 72, 83, 64, 38, and 36%, respectively, were achieved. Kinetic studies revealed that a contact time of only 15 minutes is sufficient to achieve secondary effluent criteria. An innovative technique of using primary sludge (PS) and thickened waste activated sludge as a source for the in situ synthesis of ferrate was developed. A comparative study of treatment efficiencies achieved by Fe (VI) generated from different sources was done. At 0.1 mg/L dose of Fe (VI) synthesized from PS, TCOD, SCOD, TSS, VSS, TP, and TN removal efficiencies of 60, 62, 63, 67, 30, and 25%, respectively, were achieved.

소독제 농도, pH, 온도, 암모니아 농도, 부유물질이 강우 월류수 염소 소독에 미치는 영향

The treatment of combined sewer overflow (CSO) is one of potential concerns in domestic wastewater treatment in Korea due to the pre-announce of CSO regulations. This work investigated the effects of disinfectant (NaOCl) concentration (0.11 to 4.0 mg Cl2/L), pH (6.5 to 8.0), temperature (15 to 25°C), ammonia (10 to 41 mg N/L), and suspended solids (91 to 271 mg SS/L) on the chlorine disinfection of CSO. The effect of NaOCl concentration on the pseudo-1 order reaction rate for total coliform inactivation was described well with a saturation-type model with the half-velocity constant of 1.212 mg/L. The total coliform inactivation reaction rate decreased with SS and pH, and increased with temperature. Ammonia in the examined range did not affect the disinfection kinetics. A chlorine contact tank with the injection chlorine level of 1 mg Cl2/L and the hydraulic retention time of 1.25 min is estimated to reduce total coliform from 1 × 10 MPN/mL to 1,000 MPN/mL at 271 mg SS/L, 15°C, and pH 8.0. Chlorine would be a proper option for the disinfection of CSO.

RSF_Sim – A simulation tool to support the design of constructed wetlands for combined sewer overflow treatment

Treatment of combined sewer overflow (CSO) in constructed wetlands (CWs) has proven to be highly efficient in reducing negative impacts on receiving water bodies. In Germany retention soil filters (RSFs) were developed for this purpose. RSFs are basically vertical subsurface flow constructed wetlands combined with retention basins. So far dimensioning of RSF is based only on long term rainfall-runoff simulations. Effluent quality is not considered. This paper presents a simple phenomenological model for RSF. In combination with sewer quality models it can predict the long term emissions from a particular RSF. The model will support the design of filters to meet specific emission requirements. First results of calibrating and validating simulation outputs on measurement data show, that simple mass and volume balances with only few input parameters can be sufficient for the given purpose.

Particle size distributions in combined sewer overflows in a high-intensity urban catchment in Shanghai, China

To determine the dissolved-phase chemicals and solid-phase particulate matter (PM) in a combined sewer overflow (CSO), the event mean concentrations of typical particulate-band and dissolved-band contaminants were analyzed. Particulate-band chemical oxygen demand and total phosphorous formed the majority of particles, while only around 50% of the total nitrogen was found in the particulate-band. Particle size distributions (PSDs) for PM in 49 CSO samples collected during seven rainfall events, and 18 run-off samples collected during two rainfall events, were analyzed. Variation in PSDs in both CSO and dry weather flow samples occurred with sample storage time. Mean values of particle size in CSO samples were not significantly different from median values for particles within the size range from 0.41 to 3,080 μm, at a 95% confidence level. Values for D50 and D90 for PSDs of PM in both CSO and run-off samples were higher than for previous studies. It was caused by high flow rates during the operation of storm water lifting pumps. The first flush of particles in different size ranges was quantitatively evaluated using PSDs and total suspended solids in each sample. Given the prevalence of CSOs in China and other countries, knowledge of the PSD, and its variation with time, facilitates both the design of CSO treatment procedures and optimization of wastewater treatment plants; it also provides important input for modeling water treatment operations.

A Point Source of a Different Color: Identifying a Gap in United States Regulatory Policy for “Green” CSO Treatment Using Constructed Wetlands

Up to 850 billion gallons of untreated combined sewer overflow (CSO) is discharged into waters of the United States each year. Recent changes in CSO management policy support green infrastructure (GI) technologies as “front of the pipe” approaches to discharge mitigation by detention/reduction of urban stormwater runoff. Constructed wetlands for CSO treatment have been considered among suites of GI solutions. However, these wetlands differ fundamentally from other GI technologies in that they are “end of the pipe” treatment systems that discharge from a point source, and are therefore regulated in the U.S. under the National Pollution Discharge Elimination System (NPDES). We use a comparative regulatory analysis to examine the U.S. policy framework for CSO treatment wetlands. We find in all cases that permitting authorities have used best professional judgment to determine effluent limits and compliance monitoring requirements, referencing technology and water quality-based standards originally developed for traditional “grey” treatment systems. A qualitative comparison with Europe shows less stringent regulatory requirements, perhaps due to institutionalized design parameters. We recommend that permitting authorities develop technical guidance documents for evaluation of “green” CSO treatment systems that account for their unique operational concerns and benefits with respect to sustainable development.

Methods to accompany and evaluate planning of combined sewer overflow treatment concepts for complex sewer systems

Simulation tools are in common use to evaluate combined sewer overflow (CSO) treatment concepts in complex sewer systems. However, the planning of CSO structures in a sewer system is a matter of local constraints, expert knowledge and trial and error. Common standards only provide general recommendations to plan CSO structures and work out management strategies. Additionally, modelling the emissions of complex sewer systems tends to result in comprehensive findings. Although, it is essential to understand local behaviour and interaction of CSO structures in a system to improve local and overall performance there is a lack of tools to illustrate comprehensive simulation results in a simple way. In this context the methods presented here are developed. These include clear illustrations of the as-is state in the catchment using Sankey diagrams to show relevant volume and pollutant flows. Furthermore, loading and treatment indicators are suggested to illustrate local loading conditions and treatment capabilities of CSO structures in relation to the overall system. Additional emission indicators provide information on local emissions and show interactions of CSO structures. The results indicate that the suggested methods contribute to an efficient evaluation of interactions and performances to improve treatment strategies in the planning phase.

Constructed wetlands for treatment of combined sewer overflow in the US: a review of design challenges and application status

Constructed wetlands for treatment of combined sewer overflow in the US: a review of design challenges and application status

Constructed wetlands for combined sewer overflow treatment in a Mediterranean country, Portugal

The use of constructed wetlands as a valuable and attractive method for combined sewer overflow (CSO) treatment has been demonstrated in several studies. In Portugal, a Mediterranean country having usually a long dry period, there are still no applications of this technology. The purpose of this research is to gather information and know-how required for the design and management of this type of infrastructure. A pilot-scale experimental setup for CSO treatment was installed and evaluated in situ, in terms of organic matter, total suspended solids and microorganism removal with emphasis on the results of the start-up. After 1 day of retention average removal efficiencies of 73-79% and 82-89% were obtained in terms of chemical oxygen demand (COD) and total suspended solids (TSS), respectively. During the remaining retention time a slower removal was observed. After 7 days, the COD removal efficiencies reached 86-91% and the TSS removal efficiencies reached 93-97%. On average, after 1 day, reductions of 1.2-2.0 log and 1.9-2.4 log, respectively, for total coliforms and Enterococcus were observed. For a retention time of 7 days these reductions attained 4.0-4.9 log and 4.4-5.3 log, respectively.

Application of coagulation process for the treatment of combined sewer overflows (CSOs)

Nonpoint source pollutions discharged with stormwater runoff during rainfall events degrade public waterbodies. Because combined sewer overflows (CSOs) especially affect public waterbodies, necessary measures must be taken for CSOs. Therefore, this study treated CSOs using the ultra-rapid coagulation (URC) process. More than 50% of the study site was comprised of an industrial area, followed by forest, farmland and residential areas at 21.3, 2.6, and 23.5%, respectively. The 30,000 ton capacity URC process was used to treat CSOs generated from the catchment. Monitoring was conducted over 8 rainfall events, and the samples were analyzed for pollutant parameters such as total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (CODcr), total nitrogen (TN), total phosphorus (TP), and heavy metals. At the beginning of the rainfall, the first flash effect was observed, but was not observed 20 min later. The concentration of TSS and BOD increased as the rainfall intensity became stronger in the middle stage of the rainfall. The treatment efficiency of the pollutants by the URC process was analyzed as TSS 94.4%, BOD 70.8%, CODcr 77.6%, TN 36.1%, and TP 83.5%. These treatment efficiencies were higher than those of other nonpoint pollution control facilities. Meanwhile, the removed particle size ranged from 0.1 to 10μm or from 80 to 300μm.

CSOs 처리를 위한 실증규모 응집침전시스템의 설계평가

도시유역에서 강우시에 발생되는 합류식 하수관거 월류수(CSOs; Combined Sewer Overflows)을 처리하기 위해 물리화학적 처리기법을 적용한 실증규모의 응집침전시스템을 개발하였다. 이에 앞서 응집침전시스템은 lab-test를 통해 도출된 최적의 설계조건이 실증규모로 증설할 시에 설계인자가 제대로 반영되었는지 평가가 필요하며, 최적조건에 따라 설계에 반영하였다 하더라도 대상원수의 유입특성에 따라서도 처리결과에 대한 평가가 다를 수가 있다. 이에 본 연구에서는 청주하수 처리장에 유입되는 CSOs를 대상으로 각각 <TEX>$1m^3$</TEX>/일과 <TEX>$100m^3$</TEX>/일의 CSOs를 처리할 수 있는 실험실규모 및 실증규모의 장치를 통해 실험을 수행하였다. 실증규모의 시스템을 운전하여 lab-test에서 도출된 설계인자와의 상사성을 검토하고, 이를 바탕으로 높은 처리효율을 유지하기 위한 운전인자를 적용하여 CSOs를 처리함에 있어 그 가능성을 평가하였다. 그 결과, 실험실 규모의 설계조건과 상사성을 만족하는 인라인믹서와 응집반응조의 조건을 도출할 수 있었으며, pilot-test를 운전하기 위한 적정 응집제 주입량을 도출하였고, 결과적으로 실증규모의 시스템에서도 CSOs를 대상으로 높은 효율의 응집침전처리를 가능하게 할 수 있었다. A pilot scale coagulation system, which has a function of physicochemical treatment, was developed to treat Combined sewer overflows(CSOs). This coagulation system requires evaluation of optimum design factors whether it has reflected those of lab scale system, moreover, the pilot scale system can be evaluated differently according to the characteristics of influent CSOs even though it has reflected lab scale's design factors. We conducted an experiment using lab scale system that could treat <TEX>$1m^3$</TEX> of CSOs in a day, and also pilot-scale system with <TEX>$100m^3/day$</TEX> CSOs flowed into the Cheongju sewage treatment plant. Therefore the aim of this study is to evaluate a hydraulic similarity between the design factors of pilot scale and those of lab scale coagulation system, and to evaluate feasibility of the coagulation system for the CSOs treatment with optimum operation conditions. From the result of pilot-test, we drew the optimum operation factors of in line mixer and flocculator having similarities with those of lab scale system as well as the optimum coagulant dose. Finally we confirmed that the coagulation system has feasibility to treat the CSOs with high removal efficiency.

A Coagulant Survey for Chemically Enhanced Primary Treatment of Synthetic CSOs

Combined sewer overflow (CSO) wastewaters tend to be highly variable in composition, presenting a challenge to effective treatment. The robustness of various coagulants and flocculants was studied in terms of their ability to bring about efficient contaminant removal under variable conditions. To accomplish this, the effects of total suspended solids (TSS) and dissolved organic carbon (DOC) concentrations on chemically enhanced settling of synthetic CSO wastewater were evaluated using various inorganic salt and organic polyelectrolyte products. The evaluated products varied in their responses to changes in solids and organics concentrations, particularly in terms of sensitivity to DOC concentration and ability to bring about its removal. The required dosages of the coagulants (both inorganic and organic) were quite sensitive to DOC concentration, but good to excellent TSS and DOC removals were obtained. In comparison, the polymer flocculants displayed good TSS removal but poor reduction of DOC under all conditions, in spite of sensitivity to initial DOC concentration. The coagulants and flocculants studied also varied in tendency to overdosing and effect on pH. While no coagulant or flocculant is universally applicable, understanding the trends in treatment efficiency can help in choosing the type of product that is most suitable for treatment under given wastewater quality conditions.

Constructed Wetlands for Combined Sewer Overflow Treatment—Comparison of German, French and Italian Approaches

Combined sewer systems are designed to transport stormwater surface run off in addition to the dry weather flows up to defined limits. In most European countries, hydraulic loads greater than the design flow are discharged directly into receiving water bodies, with minimal treatment (screening, sedimentation), or with no treatment at all. One feasible solution to prevent receiving waters from strong negative impacts seems to be the application of vertical flow constructed wetlands. In Germany, first attempts to use this ecological technology were recognized in early 1990s. Since then, further development continued until a high level of treatment performance was reached. During recent years the national “state-of-the-art” (defined in 2005) was adapted in other European countries, including France and Italy. Against the background of differing national requirements in combined sewer system design, substantial developmental steps were taken. The use of coarser filter media in combination with alternating loadings of separated filter beds allows direct feedings with untreated combined runoff. Permanent water storage in deep layers of the wetland improves the system’s robustness against extended dry periods, but contains operational risks. Besides similar functions (but different designs and layouts), correct dimensioning of all approaches suffers from uncertainties in long-term rainfall predictions as well as inside sewer system simulation tools.

Carbon footprint and life cycle assessment of centralised and decentralised handling of wastewater during rain

The most widely used approaches for handling of combined sewer overflows (CSOs) are: (1) storage in smaller retention basins and local decentralised treatment; and (2) storage in larger retention basins and treatment at a central wastewater treatment plant. This paper compares the environmental impact including carbon footprint for these two approaches using the life cycle assessment (LCA) method, and provides a holistic view of how CSO is to be treated considering technical, economic and environmental issues. The analysis is based on the results of the EU-financed LotWater project and 9 years of operational data from wastewater treatment in Copenhagen. All technologies are analysed for handling of 1 m3 of CSO. However, costs are compared based on cost per reduced area. The study showed that decentralised treatment of CSO is the cheapest method and the power consumption for the decentralised treatment is five times less than that for central treatment of CSO. However, central treatment of CSO appeared to be most efficient in reducing discharge of nutrients and environmental toxics. The LCA showed that the largest environmental impacts from handling CSOs are eutrophication and aquatic ecotoxicity. This study concludes that focusing on global warming alone in the form of reduced energy consumption could result in negative impacts on recipient waters.

Treatment of combined sewer overflows by ballasted flocculation: Removal study of a large broad spectrum of pollutants

This study aims at examining the performance of the ballasted flocculation unit (BFU) on treating combined sewer overflows (CSOs) and the evaluation depends on the values obtained of routine wastewater parameters and on the contents of a large broad spectrum of pollutants. Accordingly, the full-scale BFU at the largest wastewater treatment plant in Europe (Seine Aval plant near Paris, France) is investigated during three sampling campaigns. Of the 97 molecules targeted, 57 substances including 18 priority substances and 11 priority hazardous substances were detected in the BFU influents confirming that wet weather flow (WWF) treatment has definitively proven to be necessary. The WWF treatment by ballasted flocculation appears as a promising but not a fully adapted technology for use in densely urbanized areas to considerably mitigate the CSO impacts. On operating at the optimal chemical and sand doses, this process appears to be a suitable technology to remove particles, carbonaceous and phosphorous pollutants, particulate metals and most of hydrophobic organic compounds whilst nitrogenous pollutants and most of hydrophilic compounds are from poorly (<20%) to moderately (<50%) removed. The BFU appeared less sensitive to the influent concentration fluctuations and hydraulic peak load (at the scale of the campaigns considered) than to the adjustments of chemical doses and sand injection. Investigating the performance of such process, could serve to develop management strategies that enable mitigating the impacts of CSOs on receiving water in compliance with the Water Framework Directive objectives.

Frequency analysis of river water quality using integrated urban wastewater models

In recent years integrated models have been developed to simulate the entire urban wastewater system, including urban drainage systems, wastewater treatment plants, and receiving waterbodies. This paper uses such an integrated urban wastewater model to analyze the frequency of receiving water quality in an urban wastewater system with the aim of assessing the overall system performance during rainfall events. The receiving water quality is represented by two indicators: event mean dissolved oxygen (DO) concentration and event mean ammonium concentration. The compliance probability of the water quality indicators satisfying a specific threshold is used to represent the system performance, and is derived using the rainfall events from a series of 10 years' rainfall data. A strong correlation between the depth of each rainfall event and the associated volume of combined sewer overflow (CSO) discharges is revealed for the case study catchment, while there is a low correlation between the intensity/duration of the rainfall event and the volume of the CSO discharges. The frequency analysis results obtained suggest that the event mean DO and ammonium concentrations have very different characteristics in terms of compliance probabilities at two discharging points for CSO and wastewater treatment plant effluent, respectively. In general, the simulation results provide an understanding of the performance of the integrated urban wastewater system and can provide useful information to support water quality management.

Variability of Settling Characteristics of Solids in Dry and Wet Weather Flows in Combined Sewers: Implications for CSO Treatment

Four devices developed for measuring settling velocity distributions of combined sewer overflow (CSO) solids were applied to dry and wet weather flow samples from an urban area serviced by combined sewers (Welland, ON, Canada). The settling column-based methods (the Aston, Brombach and US Environmental Protection Agency columns) produced comparable results indicating minimal differences in settleability of dry and wet weather samples. The elutriation apparatus, which assessed settling velocities in a flowing medium, indicated higher settleabilities than the column methods. This was attributed to enhanced opportunities for particle coalescence in the flowing medium, which should better approximate actual sedimentation conditions. While the elutriation apparatus also indicated larger differences in settleabilities between dry and wet weather samples than the column methods, this difference was not statistically significant. Experimental distributions of particle settling velocities were approximated by a mathematical function, which was then used to estimate partial settling of total suspended solids (TSS) with settling velocities smaller than the clarifier overflow rate. The TSS removal target of 50%, which is applicable to CSOs in Ontario, could be met for overflow rates ranging from 4.7 to 6.8 m/h, for dry and wet weather flows, respectively, based on the average settling velocities measured. Experimental data collected in the study indicate that the design of CSO storage and settling facilities is affected, among other factors, by both the apparatus used to assess CSO settleability and the inter-event variability of CSO settling characteristics.

Water management in cities of the future using emission control strategies for priority hazardous substances

Cities of the future face challenges with respect to the quantity and quality of water resources, and multiple managerial options need to be considered in order to safeguard urban surface water quality. In a recently completed project on 'Source control options for reducing emissions of Priority Pollutants' (ScorePP), seven emission control strategies (ECSs) were developed and tested within a semi-hypothetical case city (SHCC) to evaluate their potential to reduce the emission of selected European priority hazardous substances (PHSs) to surface waters. The ECSs included (1) business-as-usual, (2) full implementation of relevant European (EU) directives, (3) ECS2 in combination with voluntary options for household, municipalities and industry, (4) ECS2 combined with industrial treatment and best available technologies (BAT), (5) ECS2 in combination with stormwater and combined sewer overflow treatment, (6) ECS2 in combination with advanced wastewater treatment, and (7) combinations of ECS3-6. The SHCC approach was chosen to facilitate transparency, to allow compensating for data gaps and to decrease the level of uncertainty in the results. The selected PHSs: cadmium (Cd), hexachlorobenzene (HCB), nonylphenol (NP) and pentabromodiphenyl ether (PBDE) differ in their uses and environmental fate and therefore accumulate in surface waters to differing extents in response to the application of alternative ECS. To achieve the required reduction in PHS levels in urban waters the full implementation of existing EU regulation is prioritised and feasible combinations of managerial and technological options (source control and treatment) can be highly relevant for mitigating releases.

Distribution and Mobilization of Pollutants in the Sediment of a Constructed Floating Wetland Used for Treatment of Combined Sewer Overflow Events

Sediments in combined sewer overflow treatment systems may exhibit elevated pollutant concentrations. Concentrations measured in the sediment of a floating treatment wetland ranged from 0.17 to 1.6 (cadmium), 28 to 142 (copper), 10 to 33 (chromium), 50 to 141 (manganese), 5 to 20 (nickel), 50 to 203 (lead), and 185 to 804 (zinc) mg/kg dry matter and 7.4 to 17 (iron), 2 to 8 (total nitrogen), and 1.3 to 4.4 (total phosphorus) g/kg dry matter. During overflow events, the entering water volumes can disturb the sediments. A greenhouse experiment was set up to evaluate the possible mobilization of pollutants through disturbation. The disturbation did not result in an increased mobilization of cadmium, copper, chromium, nickel, lead, zinc, nitrogen, phosphorus, and organic carbon towards the pore and surface water. Calcium concentrations in the surface water increased for all sediments, as a result of release from the exchangeable sediment pool and dissolution of carbonates. Geochemical speciation modeling indicated that, in the pore water, the free ion form was the most abundant for calcium, iron, manganese, cadmium, and nickel, with its fraction increasing with time.

The Development of Solid Fabric Filter for CSOs Treatment

The cost for nonpoint source in urban area tends to increase as it's distanced farther from the pollution source. Thus it's more effective to dispose of the pollution at the pollution source. It becomes more difficult when nonpoint source is flowed into the surface water by stormwater. In case of combined sewer, increasing stormwater on impermeable surface causes the Combined Sewer Overflows (CSOs) containing the high level of pollutants which runs into the water system through the storm overflow diverging tank without treatment process. A huge amount of CSOs is generated instantly and as it carries the pollutants on impermeable surface as well as the deposits in sewage pipe, it's necessary to develop the technology for treatment of CSOs. This study was intended to develop the solid fabric filter which will be suitable for treatment of CSOs and the characteristic and performance of solid fabric filter were evaluated.

Diurnal fluctuation of indicator microorganisms and intestinal viruses in combined sewer system

Combined sewer overflow (CSO) has been considered to be a source of pathogenic microorganisms for aquatic environment. For the effective control and treatment of CSOs, the microbial behavior in combined sewer system (CSS) needs to be investigated. In this study, whole-day extensive monitoring of indicator microorganisms and intestinal viruses in dry weather flow (DWF) was conducted at a small residential urban drainage area with CSS. All indicator bacteria represented similar diurnal variations in the two different monitoring campaigns; their concentrations gradually decreased to the minimum at the dawn (around 5 a.m.), increased sharply to the maximum around 7 to 8 a.m., and remained rather constant from noon to midnight. On the other hand, neither coliphages nor intestinal viruses showed any concentration peaks in the morning. The maximum/minimum load ratios ranged from 18 to 42 for total coliforms, fecal coliforms and E. coli, whereas those ratios for coliphages, enteroviruses and noroviruses G2 showed greater values than those for indicator bacteria. These results indicate that the diurnal variation patterns of bacterial and viral concentrations in DWF should be considered, which affect the discharge characteristics of each microorganism and the loads of bacteria and viruses in CSOs significantly vary with the overflow time as well.