An effluent at a flow rate of $2670 \mathrm{~m}^{3} / \mathrm{d}$ from a sewage treatment plant is to be disinfected. The laboratory data of disinfection studies with a chlorine dosage of $15 \mathrm{mg} / 1$ yield the model $N_{t}=N_{o} e^{-0.145 t}$ where $N_{t}=$ number of micro-organisms surviving at time $t$ (in min.) and $N_{o}=$ number of micro-organisms present initially (at $\left.t=0\right)$. The volume of disinfection unit (in $\mathrm{m}^{3}$ ) required to achieve a $98 \%$ kill of micro-organisms is

An effluent at a flow rate of $2670 \mathrm{~m}^{3} / \mathrm{d}$ from a sewage treatment plant is to be disinfected. The laboratory data of disinfection studies with a chlorine dosage of $15 \mathrm{mg} / 1$ yield the model $N_{t}=N_{o} e^{-0.145 t}$ where $N_{t}=$ number of micro-organisms surviving at time $t$ (in min.) and $N_{o}=$ number of micro-organisms present initially (at $\left.t=0\right)$. The volume of disinfection unit (in $\mathrm{m}^{3}$ ) required to achieve a $98 \%$ kill of micro-organisms is

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