Clarifier collection channel at output of activated sludge plant
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Can you tell me how to determine the width of a collection channel that conveys treated water discharged by the clarifier?
We have a problem in our plant. The collection channel around the clarifier is 30 cm wide (for inflow of 260 m3/h) and on occasion, there is an increase in hydraulic head with submergence of the exit pipe.
A width of 30 cm is sufficient for 260 m3/h (especially since this corresponds to 130 m3/h for each side of the clarifier). So the problem lies either in the slope of the bottom of the channel, or as tet2lar suggests, the discharge pipe is not big enough.
We looked into that possibility. I just wanted to check the width of the channel. Indeed, the flow is divided in 2. For the flow rate, if I start with a speed of 0.5 m/s, how do I calculate the height of the water it generates?
Q (m3/s) = V (m/s) x S (m2)
130 m3/h corresponds to 0.0361 m3/s; and if V = 0.5 m/s, your surface area will be 0.072 m2. If the width is 0.3 m, the height will be 0.24 m.
But the velocity depends on the slope of the channel: the smaller the gradient, the lower the speed and the greater the surface area. So you will want to check the collection channel and distribution slope and make sure that water flows properly on both sides of the clarifier (each half of the channel). MOST IMPORTANT: check that the channel discharge is properly sized and sloped. Otherwise it will cause a significant increase of the level upstream.
Hydraulic loading probably comes from an under sized discharge pipe, especially if the output of the treated water is circular, and depending on whether it is positioned in the channel invert or laterally.