The outlet in the form of overflow weir can also be used to control the water level in the basin. In addition, a good outlet will ensure that only well-settled water leaves the basin and enters the filter. Like the inlet zone, the outlet zone is designed to prevent short-circuiting of water in the basin. The outlet zone controls the amount of water flowing out of the sedimentation basin. The settling zone may be simply a large area of open water. For optimal performance, the settling zone requires a slow, even flow of water. This is where the bulk of settling occurs and this zone will make up the largest volume of the sedimentation basin. The combination of channel and baffle serves to evenly distribute the incoming water.Īfter passing through the inlet zone, water enters the settling zone where water velocity is greatly reduced. The second type of inlet allows water to enter the basin by first flowing through the holes evenly spaced across the bottom of the channel and then by flowing under the baffle in front of the channel.
Water leaves the inlet and enters the settling zone of the sedimentation basin by flowing through the holes evenly spaced across the stilling wall. The stilling wall, also known as a perforated baffle wall, spans the entire basin from top to bottom and from side to side. The inlet of rectangular basin is shown in Fig. Inlet arrangement for a rectangular basin Breakup of floes in the sedimentation basin will make settling much less efficient. If the water velocity is greater than 0.15 m/ see, then floes in the water will break up due to agitation of the water. In addition to preventing short-circuiting, inlets control the velocity of the incoming flow.
Short-circuiting is a problematic circumstance in which water bypasses the normal flow path through the basin and reaches the outlet in less than the normal detention time. The incoming flow in a sedimentation basin must be evenly distributed across the width of the basin to prevent short-circuiting. In addition, inlet devices act to prevent turbulence of the water. The two primary purposes of the inlet zone of a sedimentation basin are to distribute the water and to control the water’s velocity as it enters the basin. But the four zones can still be found within the clarifier the above figure. In a square or circular basin (clarifier), water typically enters the basin from the center rather than from one end and flows out to outlets located around the edges of the basin.
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