| Sedimentation basin is one of the most common and important units in the conventional water treatment plant. It plays an important role in removing the floc formed in mixing and coagulation basin, and then has a great impact on the backwash cycle of filtration process. Plug flow pattern in sedimentation basin which is the most desirable, never exists on its own in a real basin. It is always accompanied by a certain degree of mixing and dead space. Structures such as the inlet and outlet of basin, the location of baffle wall, the installation of sludge collector may be the obstacles to the horizontal flow when it is poorly designed. Therefore, to know how these structures in the settling basin have an influence on the characteristics of hydraulic flow is beneficial to improve the settling efficiency of the floc. The hydraulic characteristics of the sedimentation basin in the three real WTPs(B, K, I) which have the different structural characteristics inside the settling basin were qualitatively investigated by the tracer test. Quantitative evaluation was not attempted due to the poor recovery of tracer chemical. First plant(B plant) has a plate settler. Second plant(K plant) has baffle wall cut about 60 cm in the bottom for the purpose of installation of the sludge collector. Third plant (I plant) does not have any structure in the basin. It was found that structures such as plate settler(B plant) and baffle wall cut in the bottom had an profound undesirable impact on the horizontal flow in the settling basin. Tracer distributions clearly indicated that any space occupied by plate settler in B plant was the complete dead zone, on the contrary to its intended role. Also, the baffle wall cut in the bottom in K plant was not as good as the plate settler in B plant in having the horizontal flow in the sedimentation basin. Even for I plant which has no structure in the basin, the limited horizontal flow was observed, though showing the best hydraulic performance among the three plants. |
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