• Journal of Korean Society of Water and Wastewater
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• v.23 no.5
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• pp.647-654
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• 2009

Since the end of the 1990s, sewer pipe improvement works have been going on: most septic tanks have been thrown away and discarded. These discarded septic tanks amounts up to 370,000 based on the project plan 2005-2008: it is a serious squander of nation's resources, a contaminating means that buries toxins under soil, and a cause of a expensive waste. Research on recycling of discarded septic tank as a new resource is in urgent need. This research suggests plans to recycle discarded septic tank as a rainwater management facility, solutions to water cycle recovery in the limelight, and economic analysis of the plan. In the case of a recycling discarded septic tank as a rainwater management facility will socially benefit to support economical adequacy, discard cost saving of septic tank and water supply and sewage cost reduction will come out. Consequently a rainwater management facility converted from a discarded septic tank leads to decentralization of the rainwater management system, which anticipates a positive effect on recovery of urban water cycle.

• Journal of Korean Society of Water and Wastewater
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• v.34 no.3
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• pp.211-220
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• 2020

When domestic sewage and rainwater runoff are discharged into a single sewer pipe, it is called a "combined sewer system." The sewage design standards in Korea specify the flow velocity based only on the volume of rainfall; therefore, sedimentation occurs on non-rainy days owing to the reduced flow rate and velocity. This sedimentation reduces the discharge capacity, causes unpleasant odors, and exacerbates the problem of combined sewer overflow concentration. To address this problem, the amount of sewage on non-rainy days, not just the volume of rainfall, should also be considered. There are various theories on sedimentation in sewer movement. This study introduces a self-cleansing velocity based on tractive force theory. By applying a self-cleansing velocity equivalent to the critical shear stress of a sand particle, sedimentation can be reduced on non-rainy days. The amount of sewage changes according to the water use pattern of citizens. The design hourly maximum wastewater flow was considered as a representative value, and the velocity of this flow should be more than the self-cleansing velocity. This design method requires a steeper gradient than existing design criteria. Therefore, the existing sewer pipelines need to be improved and repaired accordingly. In this study, five types of improvement and repair methods that can maximize the use of existing pipelines and minimize the depth of excavation are proposed. The key technologies utilized are trenchless sewer rehabilitation and complex cross-section pipes. Trenchless sewer rehabilitation is a popular sewage repair method. However, it is complex because the cross-section pipes do not have a universal design and require continuous research and development. In an old metropolis with a combined sewer system, it is difficult to carry out excavation work; hence, the methods presented in this study may be useful in the future.