Question

Wastewater from a small town is treated in a trickling filter which is preceded 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.
The maximum scouring velocity or slip velocity is 0.3 m/s and the maximum surface load or Hazen velocity is 40 m/h.

Assume 4 channels. Take a W:L ratio of 1:15

Calculate the vertical surface area Avertical in m²
Calculate the horizontal surface area Ahorizontal in m²

Dimension the rectangular sand removal channels.
Length (m):
Width (m):
Maximum water height (m):

Allow a free waterboard of 15 cm and a maximum grit accumulation height of 20 cm. Give the total height in m of the grit channel.

Calculate the liquid velocity during Qdwf (in m/s) in the channel.

Answer 1

Answer:

Wastewater from a small town is treated in a trickling filter which is preceded 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.