A community generates $1$ million litres/day (MLD) of wastewater. This wastewater is treated using activated sludge process (ASP). The working volume of the aeration tank of the ASP is $250 \mathrm{~m}^{3}$, and the biomass concentration in the tank is $3000 \: \mathrm{mg} / \mathrm{L}$. Analyses results showed that a biomass concentration of $10 \: \mathrm{mg} / \mathrm{L}$ is present in the treated effluent from the secondary sedimentation tank of the ASP. Sludge wastage from the system is at a rate of $5000 \mathrm{~L} / \text{day}$ with a biomass concentration of $10000 \: \mathrm{mg} / \mathrm{L}$. The system is in steady state condition.
The biological sludge residence time (BSRT) of the system (in days) is $\_\_\_\_\_\_\_\_\_\_$ (round off to one decimal place).
