A $20000$ m$^3/$d municipal activated sludge plant is presently operating at an F$/$M of $0\mathrm{.}5$ d$^-1$ with soluble influent BOD$5$ of $120$ mg$/$L$.$ A chemical industry has asked for permission to discharge $4000$ m$3/$d of wastewater with a soluble BOD$5$ of $1500$ mg$/$L$.$ What reduction in BOD$5$ should the industry provide before discharging into the municipal sewers so that BOD$5$ removal efficiency will remain the same, and effluent soluble BOD$5$ will not exceed $20$ mg$/$L$?($The Y $=0\mathrm{.}4$ mg biomass$/$mg BOD$5,$ kd$=0\mathrm{.}10$ d$^-1,$ k$=6\mathrm{.}0$ d$^-1,$ Ks$=100$mg$/$L$)$A $20,000\frac{m^3}{d}$ municipal activated sludge plant is presently operating at an $\frac{F}{M}$ of $0\mathrm{.}5d^{-1}$ with soluble

influent $BO{D}_5$ of $120m\frac{g}{L}.$ A chemical industry has asked for permission to discharge $4000\frac{m^3}{d}$ of

wastewater with a soluble $BO{D}_5$ of $1500m\frac{g}{L}.$ What reduction in $BO{D}_5$ should the industry provide

before discharging into the municipal sewers so that $BO{D}_5$ removal efficiency will remain the same, and

effluent soluble $BO{D}_5$ will not exceed $20m\frac{g}{L}?$

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