• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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• pp.313-324
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• 2013

It is widely known that untreated Combined Sewer Overflows (CSOs) that directly discharged from receiving water have a negative impact. Recent concerns on the CSO problem have produced several large scale constructions of treatment facilities, but the facilities are normally designed under empirical design criteria. In this study, several criteria for defining CSOs (e.g. determination of effective rainfall, sampling time, minimum duration of data used for rainfall-runoff simulation and so on) were investigated. Then this study suggested a standard methodology for the CSO calculation and support formalized standard on the design criteria for CSO facilities. Criteria decided for an effective rainfall was over 0.5 mm of total rainfall depth and at least 4 hours should be exist between two different events. An Antecedent dry weather period prior to storm event to satisfy the effective rainfall criteria was over 3 days. Sampling time for the rainfall-runoff model simulation was suggested as 1 hour. A duration of long-term simulation CSO overflow and frequency calculation should be at least recent 10 year data. A Management plan for the CSOs should be established under a phase-in of the plan. That should reflect site-specific conditions of different catchments, and formalized criteria for defining CSOs should be used to examine the management plans.

• Journal of Korean Society on Water Environment
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• v.33 no.1
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• pp.97-106
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• 2017

In this study, the characteristics of nonpoint source pollutant loads from separate sewer overflow (SSO) and combined sewer overflow (CSO) were evaluated during 2016 in Namyangju city, Korea. Five rainfall events were monitored during 2016 with ranging from 14.5 mm to 121.5 mm. The runoff ratio of CSO was higher than that of SSO because only design volume of maximum sanitary sewer ($1Q_h$) was transported and treated and $2Q_h$ was overflowed to waterbody during rainy day although combined sewer system was designed to transport $3Q_h$ to treatment system. The event mean concentrations (EMCs) and pollutant loads from CSO were higher than those from SSO. BOD and COD of CSO, and TOC and TN of SSO represented distinct first flush phenomena. The inadequate management in combined sewer system from which the untreated $2Q_h$ from CSO was overflowed to waterbody during rainy day could influence on high pollutant loads and first flushing. Treating $2Q_h$ from CSO, source control such as low impact development, and treating outflow from SSO were strongly recommended to control non-point source pollution in urban area.

• Journal of Korean Society on Water Environment
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• v.27 no.5
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• pp.654-660
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• 2011

One of the best way to control Combined Sewer Overflow (CSO) is proposed to construct first flush storage tank. But there is little known parameters for optimum design of these facilities. This study was conducted to get optimum design parameters for a first flush storage tank construction. The optimization of the tank is generally based upon some measure of SS(Suspended Solid) mass holding efficiency. Water quality deterioration of receiving water body happened right after first time occurring rainfall in dry weather seasons. So, design rainfall intensity is used at 2 mm/hr for peak of monthly average intensities of dry seasons. The capacities for each evaluated catchment are designed from 14.4 min to 16.1 min HRT of CSOs flow at design rainfall intensity. Owing to all storage tanks are connected to interception sewer having a redundancy, the suggested volume could be cut down.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.3
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• pp.171-178
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• 2013

In this study, the sludge that occurs in the initial operation of coagulation system developed for the treatment of CSOs were returned to the flocculation reactor. The purposes of this study were to analyze the Characteristics of flocs that are generated through the recycling sludge and settling characteristics of sludge, and to evaluate the possibility that high concentrations of particulate matter in the initial inflow of CSOs could be used as an weighted coagulant additive. As a result, the concentration of treated CSOs pollutants at the beginning of the CSOs influent with a large amount of particulate matter over 20 ${\mu}m$ was low, after gradually increasing the concentrations of them. The flocs generated from the sludge return were similar in size compared to flocs generated through injection of micro sands, and settling velocity in case of return sludge injection was decreased from 55.1 cm/min to 21.5 cm/min. SVI value of the sludge accumulated at the bottom of the sedimentation tank was 72, and settled sludge volume decreased rapidly due to the consolidation of sludge to the time it takes to 10 minutes. these mean that sludge used for recycling has good settling characteristic. A condition of returned sludge which is 0.1% return of 0.3% extraction was formed in the balance of settlement and extraction. In this case, This condition was to be adequate to maintain the proper concentration such as 100~200 mg/L of TS and 50~100 mg/L of VS in the flocculation reactor. The usage of the return sludge containing particulate matters of CSOs as an weighted coagulant additive was able to secure a stable treated water quality despite the change of influent water quality dynamically. Furthermore, it can be expected to reduce the alum dosage along with the sludge production.