Question

An effluent at a flow rate of $2760m^3/d$ from a sewage treatment plant is to be disinfected. The laboratory data of disinfection studies with a chlorine dose of $15mg/l$ yields the model $N_t=N_0{e}^{-0.145t}$ Where $N_t$= no. of micro-organism surviving at time t (in min) and $N_o$ = no. of micro­ organism present Initially (at t = 0) the volume of disinfection unit (in $m^3$) required to achieve a 98% kill of micro-organism is.

• A. 51.71

Answer 1

The correct option is A 51.71
$Q=2760m^3/day$

Chlorine dose= $15mg/l$

$N_t=N_o{e}^{-0.145t}$

If 98% micro – organism are killed, 2% are surviving

$\Rightarrow 0.02=e^{-0.145t}$

$\Rightarrow t=26.979min$

Vol. of tank= $Q{t}_d$

$=\frac{2760m^3}{24\times 60min}\times 26.979min$

$=51.71m^3$