Effect of Current Induced by Density Cahnges on Performance of Sedimentation Tanks and Proposing Solutions to Eliminate its Negative Impacts

Subject Areas : Water and Environment

Seyed Mostafa Khezri ¹ ( - Assistant Professor of Water Resources, Department of Energy and Environment, Islamic Azad University, Science and Research Branch, Tehran, Iran.. )
Faranak Mirfattah ² ( MSc of Water Resources, Department of Energy and Environment, Islamic Azad University, Science and Research Branch, Tehran, Iran. *(Corresponding Author) )

Received: 2010-10-02 Accepted : 2011-04-14 Published : 2016-11-21

Keywords: Density current, intermediate and withdrawal ba, rectangular sedimentation tank, triangular weir,

Abstract :

Abstract Background and Objective: The objective of this study is to evaluate the disadvantages of density in sedimentation tanks and suggest sollutions to eliminate those disadvantages. Method: In this study, a 1:20–scale rectangular sedimentation tank, with thickness of 10 mm, was used as a pilot. The pilot was made up of plexiglass according to the Frod model. Three draw_offs in the bottom of the tank, two withdraw baffles, one intermediate baffle, one inlet baffle and effluent weir configurations were used in the experiments. Turbulence was formed by density of current and then lighter suspended solids went toward effluent weir. Results: The turbulence cused by currents lead to increase of suspended solids at effluent and decrease of the sedimentation tank efficiency. The proposed sollution for prohibition of those disadvantages is the use of baffles in different positions. Conclusion: The results indicated increases of 20% for using intermediate baffle and 23% for using withdrawal baffles within 2.2-6.8 °C temperature difference between entering current and sedimentation tank contests with suspended solid concentrations of 100- 300 mg/lit. 

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