In wastewater treatment, dimension the following pre-treatment unit for a wastewater treatment plant receiving a dry weather flow (dwf) of 18,000 m3/day. Assume that flow doubles during rain. A bar screen is used to remove the coarse waste. The rain water flow velocity in the screen channel (v) is 0.5 m/s and the flow-through velocity of the clean screen (V) is 0.9 m/s. What is the required open screen area (m2) for reaching this screen velocity during treatment of the rain weather flow?
0.46
To calculate the required open screen area for reaching the desired screen velocity during treatment of the rain weather flow, you'll need to follow these steps:
Step 1: Determine the flow rate during rain.
Given that the dry weather flow (dwf) is 18,000 m3/day, and the flow doubles during rain, the flow rate during rain would be 2 * 18,000 = 36,000 m3/day.
Step 2: Calculate the required screen channel width.
The screen channel width (B) can be calculated using the following formula:
B = Q / (v * H)
Where:
Q = Flow rate in m3/day (36,000 m3/day in this case)
v = Flow velocity in m/s (0.5 m/s in this case)
H = Height of the screen in meters (Assumed to be 1 meter in this case)
Thus, B = (36,000 m3/day) / (0.5 m/s * 1 m) = 72,000 m2/day/m
Step 3: Determine the effective screen length.
The effective screen length can be calculated using the formula:
L = V / v * B
Where:
V = Flow-through velocity of the clean screen in m/s (0.9 m/s in this case)
B = Screen channel width calculated in Step 2 (72,000 m2/day/m)
Thus, L = (0.9 m/s) / (0.5 m/s) * (72,000 m2/day/m) = 129,600 m
Step 4: Calculate the required open screen area.
The required open screen area (A) can be calculated using the formula:
A = L * B
Where:
L = Effective screen length calculated in Step 3 (129,600 m)
B = Screen channel width calculated in Step 2 (72,000 m2/day/m)
Thus, A = (129,600 m) * (72,000 m2/day/m) = 9,331,200,000 m2/day
Therefore, the required open screen area for reaching the desired screen velocity during treatment of the rain weather flow is approximately 9,331,200,000 m2/day.