QF

Question

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.]

Answer 1

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.

Answer 2

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?