QF
Description
Wastewater from a small town is treated in a trickling filter which is preceeded by a screen, sand-removal and primary clarification. The maximum hydraulic capacity, or peak flow, of the treatment plant is
1,500 m3/h. The dry weather flow (Qdwf) amounts 7,500 m3/day, with a BOD concentration of 300 mg/l.
Additional information
After this pre-treatment the water is fed to a trickling filter. The diameter of this trickling filter is 30 m and its height is 3 m.
Assume for the next question no BOD removal in the pre-treatment, so influent BOD concentration is 300 mg/l.
1.Calculate the loading rate (kg/m3/day) of the trickling filter.
[Due to the low BOD loading rate the biomass growth will be too little. Methanol needs to be dosed to keep the biomass alive.]
[ Due to the high BOD loading rate the filter might clog. This can be prevented by effluent recycling in order to increase the shear stress on the biofilm.]
[ Due to the high BOD loading rate the filter might clog. Because the hydraulic loading is also high, one should build an additional trickling filter to increase the filter volume.]
[ Due to the high hydraulic loading, the biomass will shear off and problems with the conversion processes and effluent quality will occur. This can only be prevented by building an additional filter.]
Correct answer to "Which is correct for this trickling filter?"
- Due to the high BOD loading rate the filter might clog. This can be prevented by effluent recycling in order to increase the shear stress on the biofilm.
In wastewater treatment, what is the required open screen area (m2) for reaching this screen velocity during treatment of the rain weather flow when dimension of the pre-treatment unit for the wastewater treatment plant is receiving a dry weather flow (dwf) of 18000 m3/day, and assuming that the flow doubles during rain, where the bar screen is used to remove the coarse waste with the rain water flow velocity in the screen channel is 0.5 m/s and the flow -through velocity of the clean screen (V) is 0.9 m/s?
To calculate the loading rate (kg/m3/day) of the trickling filter, we need to determine the BOD loading rate and the filter volume.
1. BOD Loading Rate:
The BOD loading rate can be calculated using the formula:
BOD Loading Rate = Qdwf * BOD Concentration
where Qdwf is the dry weather flow and BOD Concentration is the BOD concentration in the wastewater.
Given:
Qdwf = 7,500 m3/day
BOD Concentration = 300 mg/l
BOD Loading Rate = 7,500 * 300 * 10^-3
BOD Loading Rate = 2,250 kg/day
2. Filter Volume:
The filter volume can be calculated using the formula:
Filter Volume = π * (diameter/2)^2 * height
where the diameter and height are given.
Given:
Diameter = 30 m
Height = 3 m
Filter Volume = π * (30/2)^2 * 3
Filter Volume = 1,590 m3
3. Loading Rate Calculation:
Loading Rate = BOD Loading Rate / Filter Volume
Loading Rate = 2,250 / 1,590
Loading Rate = 1.415 kg/m3/day
Therefore, the loading rate of the trickling filter is 1.415 kg/m3/day.
Note: The loading rate helps to determine if the filter will be able to handle the BOD load effectively. If the loading rate is too low, additional measures like dosing methanol should be considered to maintain the biomass. If the loading rate is too high, measures like effluent recycling or building an additional filter may be necessary to prevent clogging and maintain the efficiency of the trickling filter.