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.
QUESTION 2C-1
After a while the screen gets clogged. The automated cleaning starts at a head loss of 10 cm. Calculate what percentage of the clean free space is clogged at this head loss. For the calculation: take the impact of clogging on the friction factor into account.
Calculate V in m/s.
QUESTION 2C-2
Calculate at which open screen area (m2) this velocity is reached.
Calculate what percentage of the clean free space is clogged at this head loss.
QUESTION 2D-2
Assume 4 channels. Take a W:L ratio of 1:15
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.
3 answers
QUESTION 2C-2: Calculate at which open screen area (m2) this velocity is reached - 0.34
Calculate what percentage of the clean free space is clogged ... 32
QUESTION 2D-1: Determine how many parallel channels 4
What is a common W:L ratio? 1:10
To prevent settling of organic matter a Vs should be > 0.03 m/s
Calculate Qdwf in m3/s.0.087
Calculate Qrwf in m3/s.0.42
QUESTION 2D-2: L-12, W-0.8, Max Water Height 0.44, grit Channel 0.8 m