Figure below shows a modified activated$-$sludge biological wastewater treatment system. It consists of $4$ completely mixed bioreactors with equal volume in series. Influent flow after mixing with recycled flow is split evenly into $4$ bioreactors. The system is operated under steady state condition. using the parameter below to determine the biomass concentrations in Bioreactors $1$ and $2($X$1$ and X$2).$ S$0=250$mg$/$L$,$ S$1=4$mg$/$L$,$ S$2=6$mg$/$L$,$ S$3=8$mg$/$L$,$ S$4=10$mg$/$L$,$ Se$=$S$4,$ X$0=0$mg$/$L$,$ Xu$=12500$mg$/$L$,$ Q$0=4000$m$^3/$d$,$ Qr$=800$m$^3/$d$,$ kd$=0\mathrm{.}05$d$^-1,$ Y$=0\mathrm{.}65,$ and volume of each reactor is $240$ m$3.80\%$ of biomass is volatile.Figure below shows a modified activated$-$sludge biological wastewater treatment system. It consists of

$4$ completely mixed bioreactors with equal volume in series. Influent flow after mixing with recycled

flow is split evenly into $4$ bioreactors. The system is operated under steady state condition. Using the

parameters below to determine the biomass concentrations in Bioreactors $1$ and and $\{$:$x_2).$

$S_0=250m\frac{g}{L},S_1=4m\frac{g}{L},S_2=6m\frac{g}{L},S_3=8m\frac{g}{L},S_4=10m\frac{g}{L},S_e=S_4,x_0=0m\frac{g}{L},x_u=12500$

$m\frac{g}{L},Q_0=4000\frac{m^3}{d},Q_r=800\frac{m^3}{d},k_d=0\mathrm{.}05d^{-1},Y=0\mathrm{.}65,$ and volume of each reactor is $240m^3\mathrm{.}80\%$

of biomass is volatile.

$Q_0,S_0,x_0$