Secondary Outlet from the Flocculator
The flow rate of the sedimentation tank is designed to be 24 L/min, but the flocculator flow rate is designed to be as high as 110 L/min. This means that excess flow needs to bypass the sedimentation tank and go directly to the existing outlet in the flocculation tank. A large outlet weir is our proposed design for this alternative exit. Because the head loss out of the sedimentation tank is relatively high (5 cm through the manifold and 13.7 cm out of the plant leveling tank) a small height variation (on the order of mm) of the water in the floc tank will have a negligible effect on the sedimentation tank flow rate.
Since the flow rate into the floc tank has been measured to be anywhere between 70 L/min to 110 L/min, It was important to check whether the height of water in the floc tank could change enough to effect the flow rate to the sedimentation tank. If the accessory weir is required to take in a smaller flow rate, the water height in the floc tank will lower. This is the equation that describes the water height above the weir as a function of the flow rate.
Unable to find DVI conversion log file.Where
Unable to find DVI conversion log file.where H is the height of water above the weir and Pw is the weir height), Q weir is the plant flow rate minus the sedimentation flow rate, and the available perimeter was set to be 120 cm. This perimeter values was chosen arbitrarily to attain a factor of safety of about 10 between the head loss coming out of the sedimentation tank and a head loss over the alternative weir in the flocculation tank. A factor of ten was not feasible because this would have required the head loss over the alternative weir to be 0.5cm which was not feasible. At 120 cm the head loss is 0.75cm. In order to minimize changes in the floc tank, the perimeter will be established by cutting a pipe laterally and letting water flow over the cut out, down into the trough and then out the existing 7.62cm (3") outlet. When this was calculated we got a water height above the weir of 7.6 mm, which is small enough when compared to the head loss in the launder to assume that it will not affect the flow rate into the sedimentation tank.