Abstract
Double perforated baffles in rectangular secondary clarifiers were studied to determine whether they contribute to producing high-quality effluents. The Computational Fluid Dynamics (CFD) simulations indicated that bio-flocculation occurred at the front of the baffle and the longitudinal movement of the settled sludge was hampered whenever the clarifier had high inflow. Simulation results showed that the rectangular clarifier with the double perforated baffle produced an effluent with lower suspended solid (SS) concentrations than the effluent from the clarifier without the baffle. To verify the simulation results, a double perforated baffle was installed in two of the 48 rectangular clarifiers in a 300,000 m3/d-capacity wastewater treatment plant. To study the effect of the baffle on solid removal, the effluent turbidity of the clarifier with and without the double perforated baffle was measured simultaneously. Experimental data showed that the double perforated baffle played a significant role in reducing effluent turbidity. The effluent turbidity reduction ratio with the baffle decreased when the Sludge Volume Index (SVI) of the Mixed Liquor Suspended Solids (MLSS) was below 100 mL/g. The overall average reduction ratio was 24.3% for SVI < 100 mL/g and 45.1% for SVI > 100 mL/g. The results of this study suggest that double perforated baffles must be installed in secondary rectangular clarifiers to produce high-quality effluent regardless of the operational conditions.
Highlights
Water reuse is the global demand, and secondary effluent filtration has been commonly adapted to meet this demand
Two double perforated baffles were installed in two of the 48 rectangular secondary clarifiers in the Suwon Wastewater Treatment Plant located in Hwaseong City, South Korea, and a double perforated baffle was elected for each clarifier
The performance of rectangular secondary clarifiers with double perforated baffles was evaluated by Computational Fluid Dynamics (CFD) simulations and field tests
Summary
Water reuse is the global demand, and secondary effluent filtration has been commonly adapted to meet this demand. The backwashing water is sent back to head work of the wastewater treatment facility. Since frequent backwashing entails high operational costs and high hydraulic loads for the treatment facility, the frequency should be decreased by lowering the concentration of solids in the secondary effluent that is the influent to the filtration facility. Many researchers studied the bio-flocculation of MLSS (Mixed Liquor Suspended Solid) to reduce the solids in the secondary effluent. The center well within the clarifier was modified to a flocculation well to promote bio-flocculation [1]. The MLSS was slow-mixed before being introduced into the clarifier to promote bio-flocculation [2]
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