Problem $11-11($the solids in the effluent Xe is taken as negligible$)$

a$.$ wasting activated sludge from the aeration basin

b$.$ wasting activated sludge from the recycle line.

$11\mathrm{.}11$ Sludge age $($sometimes called mean cell residence time$)$ is defined as the mass of sludge in the aeration tank divided by the mass of sludge wasted per day. Calculate the sludge age if the aeration tank has a hydraulic retention time of $2$ hr $,$ a suspended solids concentration of $2000*m\frac{g}{L},$ the flow rate of wastewater to the aeration basin is $1\mathrm{.}5\frac{m^3}{m}in,$ the return sludge solids concentration is $12,000m\frac{g}{L},$ and the flow rate of waste activated sludge is $0\mathrm{.}02\frac{m^3}{m}in.$

$Q_0=1,5\frac{m^3}{m}in$

$t_n=2hr=120$min

$t_n=\frac{v}{Q_0}$

$180=\frac{v}{1\mathrm{.}5}=>v=180m^3$