• Journal of Korean Society of Water and Wastewater
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• v.22 no.1
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• pp.105-112
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• 2008

Disinfection is a basic and effective microorganism inactivation method and historically contributed a decrease in waterborne diseases. To guarantee the disinfection ability, improving T in CT value is important. Many indexes are used to estimate the hydraulic efficiency, however, these are black-box analysis. Therefore it is need to develope new estimation method. In this study, internal short-circuiting estimation method (ISEM) is developed using CFD and we inquire into the factor which causes increase of $T_{10}/T$ value as LW ratio increases. And the effect of shape on the relation of LW ratio and $T_{10}/T$ is analyzed. As LW ratio increases, internal short-circuiting index (ISI) of influent and effluent zone is rapidly reduced and recirculation and dead zone are reduced in channel zone. Therefore, as the $T_{10}/T$ value converges maximum value, ISI curve is changed from "V" shape to "U" shape and hydraulic efficiency is improved especially in downstream portion of clearwell. The less the shape ratio(width/length of clearwell) is the less the $T_{10}/T$ value is at a same LW ratio because the portion of turning zone increases as shape ration decreases, therefore more boundary separation is generated.

• Journal of Korean Society of Water and Wastewater
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• v.22 no.1
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• pp.113-120
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• 2008

A large majority of clearwell must be modified with maintaining the present baffles since they were underground built with the material like concrete. Therefore it is unreasonable to apply the previous research in clearwell modification which is studied with the assumption that distance between baffles is constant. In this study, internal short-circuiting estimation method (ISEM), which has the advantage of being applied at any condition, is applied to evaluate modification of A clearwell and modify B and C clerwell which have unusual characteristics. After analyzing the hydraulic efficiency at current state, modifications, where baffles, intra basins and diffuser walls are additionally installed, are considered and evaluate using ISEM. And the effect of intra basin and diffuser wall on $T_{10}/T$ is estimated and application feasibility of ISEM is evaluated. The improvement of intra basins is almost same with that of baffles. Also, short-circuiting in effluent zone can be reduced with the same level of channel zone if intra basin is added in effluent zone. However, effect range is restricted to the next channel zone. Diffuser wall can obtain the lower ISI than minimum ISI of cases where baffles and intra basins are installed. Therefore, additional improvement of $T_{10}/T$ value can be expected after $T_{10}/T$ value converges maximum only using baffles