Direction: In a rapid sand filter, the time for reaching particle breakthrough (TB) is defined as the time elapsed from start of filter run to the time at which the turbidity of the effluent from the filter is greater than 2.5 NTU. The time for reaching terminal head loss (TH) is defined as the time elapsed from the start of the filter run to the time when head loss across the filter is greater than 3m.
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The effect of increasing the filter depth (while keeping all other conditions same) on TB and TH is
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- TB increases and TH decreases
- Both TB and TH increases
- TB decreases and TH increases
- Both TB and TH decreases
Correct Option: C
When filter depth increases, velocity decreases. Therefore, TH increases. Since the area in bed increases, time to reach break through TB decreases.
