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This study was conducted to evaluate the effects of longitudinal baffles on particles settling performance within a full-scale sedimentation basin with a flow rate of 1,000 m3/hr. Comparative experiments on turbidity removal efficiency and sludge deposit distribution were performed in longitudinally baffled and non-baffled sedimentation basins. The turbidity removal rate in the baffled sedimentation basin was observed to be higher than that in the non-baffled basin. In addition, the depth of the sludge deposit in the baffled sedimentation basin was approximately 20% less than that in the non-baffled sedimentation basin, and the sludge concentration was 10% higher. To explain these results and to further investigate the effects of longitudinal baffles, the authors performed computational fluid dynamics (CFD) simulation for both basin types. The results of this CFD simulation indicated that the flow, particularly near the outlet orifice, was more stable in the longitudinally baffled sedimentation basin. Moreover, it could be concluded that the longitudinal baffle enables a fully developed flow and is thus more effective for sedimentation. [ABSTRACT FROM AUTHOR]

Dissolved air flotation (DAF) is a solid-liquid separation system that uses fine bubbles rising from the bottom to remove particles in water. In this study, we investigated the effect of L/W (L; length, W; width) on the hydrodynamic behavior in a DAF system using CFD (computational fluid dynamics) and ADV (acoustic Doppler velocimetry) technique. The factual full-scale DAF system, L/W ratio of 1:1, was selected and various L/W ratio conditions (2:1, 3:1, 4:1 and 5:1) were simulated with CFD. For modelling, 2-phase (gas-liquid) flow equations for the conservation of mass, momentum and turbulence quantities were solved using a Eulerian-Eulerian approach based on the assumption that a very small particle is applied in the DAF system. Also, for verification of CFD simulation results, we measured the actual velocity at some points in the full-scale DAF system with the ADV technique. Both the simulation and the measurement results were in good accordance with each other. We concluded that the L/W ratio and outlet geometry play an important role for flow pattern and fine bubble distribution in the flotation zone. In the ratio of 1:1, the dead zone is less than those in other cases. On the other hand, in the ratio of 5:1, the fine bubbles were more evenly distributed. [ABSTRACT FROM AUTHOR]

A DAF (Dissolved-Air-Flotation) process has been designed considering raw water quality characteristics in Korea. Although direct filtration is usually operated, DAF is operated when freshwater algae blooms occur or raw water turbidity becomes high. Pre-sedimentation is operated in case when the raw water turbidity is very high due to rainstorms. A main feature of this plant is that the operation mode can be changed (controlled) based on the characteristics of the raw water to optimize the effluent quality and the operation costs. Treatment capacity (surface loading rate) and efficiency of DAF was found to be better than the conventional sedimentation process. Moreover, low-density particles (algae and alum flocs) are easily separated while the removal of them by sedimentation is more difficult. One of the main concerns for DAF operation is a high raw water turbidity. DAF is not adequate for raw water, which is more turbid than 100 NTU. In order to avoid this problem, pre-sedimentation basins are installed in the DAF plant to decrease the turbidity of the DAF inflow. For simulation of the actual operation, bench and full-scale tests were performed for highly turbid water conditions. Consequently, it is suggested that pre-sedimentation with optimum coagulation prior to DAF is the appropriate treatment scheme. [ABSTRACT FROM AUTHOR]

The major objective of this research is to determine engineering GAC adsorber design criteria for removal of various organic contaminants found in the 3 drinking water sources in the Keum river basin. Dissolved Organic Carbon (DOC) and UV absorbance at 254 mm were chosen as parameters for overall organics level in raw and owed water. Removal of micropollutants including organophosphorus pesticides, MBAS, volatile organic chemicals (VOCs), phenol and NH3-N were also taken into consideration in bench and/or pilot studies, Treatment efficiencies for target contaminants in three different pilot plants with different raw water quality in the same Keum river basin were compared. Identification and decision of the treatment objectives were found to be important factors for determining design parameters such as GAC bed depth. Range of appropriate bed depth and reactivationfrequency for different treatment levels were suggested based on pilot studies. [ABSTRACT FROM AUTHOR]