Question

A filter with a surface area of 80 m2, a filter run time of 72 hours, and a filtration rate of 5 m/h is backwashed for 20 minutes with a backwash rate of 50 m/h. In addition, the filter is not operating for 20 minutes due to drainage of the supernatant water. • Calculate the amount of water filtered. • Calculate the amount of water used for backwashing.

Answer 1

a)Filter surface area = A = 80 m²

Filtration rate = v = 5 m/h

Rate of flitration per hour(Q) = Av = 80x5 = 400 m³/h

Operation time during which water is filtered = t = 72 - 20/60 - 20/60

= 71.34 hours

Amount of water filtered = Qt

= 400 x 71.34

= 28536 m³

b) Backwashing rate = v_b = 50 m/h

Rate of water used during backwashing(Q_b) = Av_b = 80 x 50 = 4000 m³/h

Backwashing time = t_b = 20 min = 20/60 hours

Amount of water used for backwashing = Q_bxt_b = 4000x20/60

= 1333.34 m³