Question

In a rapid sand filter, the time for reaching particle break through ($T_B$) 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 $2.5NTU$. The time for reaching terminal head loss $\left(T_H\right)$ 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 3 m.
The effect of increasing the filter depth (while keeping all other conditions same) on $T_B$ and $T_H$ is

• A. $T_{B}increasesand{T}_{H}decreases$
• B. $T_{B}decreasesand{T}_{H}increases$
• C. $both{T}_{B}and{T}_{H}increases$
• D. $both{T}_{B}and{T}_{H}decreases$

Answer 1

The correct option is A $T_{B}increasesand{T}_{H}decreases$

$T_B$ will increase since particles in water will have the opportunity to potentially interact with more collectors and hence the chance of particle attachment to collector is more.

$T_H$: Since bed depth is more, water is encountered more resistance in passing through the bed. Hence $T_H$ will decrease.