STUDY OF HIGH RATE SEDIMENTATION TANK IN WATER TREATMENT PLANTS

Introduction: Sedimentation is considered as an important process in removing turbidity produced in water and wastewater plants. Gravity sedimentation is usually the first method considered in water treatment system. However, required overflow rates (OFRs) to remove turbidity in the conventional clarifiers are too low. Therefore, the shallow depth sedimentation concept was studied remove turbidity in order to increase OFRs of gravity setting equipment.
 Methods: Using a pilot with parallel plates with effect area 1.5 m2 and 1.5 m depth. The independent parameters such as OFRs, sludge concentration and turbidity were evaluated for turbidity removal. The pilot is located in Isfahan Water Treatment Plant.
 Results: The efficacy of pilot for turbidity 10-50 NTU is equal to 50 percent (P<0.01). The maximum removal efficiency at sludge concentration 270 ml/lit was obtained (P<0.01). A nonlinear relationship exists between removal efficiency (TR%), sludge concentration (Sc) over flowrates (OFR) and influent turbidity (Tu) in pilot.
 Discussion: By using high rate sedimentation tank in water treatment plant, detection time reduced from 3 hours to 20-30 minute, turbidity removal increased up to 30 percent in compare with conventional sedimentation. Also, it has economic benefits and high efficiency