Question Two $(6$ points$)$

A completely mixed activated sludge system receives wastewater with the following characteristics.

$\backslash$table$[[$Item$,$unit,$],[$Flow$,\frac{m^3}{d},10,000],[$Influent BOD,$\frac{g}{m^3},150],[$Influent nbvss$,\frac{g}{m^3},120],[$Influent TKN$,\frac{g}{m^3},30],[$Temperature$,C,10],[$bCOD$/$BOD$,$ratio,$1\mathrm{.}6]]$

The system is designed for BOD removal and nitrification to achieve an effluent $N{H}_4-N$ concentration of $0\mathrm{.}50\frac{g}{m^3}$ and an effluent BOD concentration of $2\frac{g}{m^3}.$ For reactor DO concentration of $2\mathrm{.}7\frac{g}{m^3}$ and peak$/$average TKN load of $1\mathrm{.}8,$

i$.$ An appropriate solids retention time $(c)$ is:

A$.15\mathrm{.}5$ days

B$.21\mathrm{.}0$ days

C$.8\mathrm{.}6$ days

D$.12\mathrm{.}5$ days

ii$.$ If nitrogen oxidized $($NOx$)$ is considered to be $80\%$ of influent TKN and if the net waste activated sludge produced each day is $1700KgVS\frac{S}{d},$ the oxygen demand is expected to be:

A$.48\mathrm{.}6K\frac{g}{h}$

B$.120\mathrm{.}0K\frac{g}{h}$

C$.112\mathrm{.}4K\frac{g}{h}$

D$.82\mathrm{.}7K\frac{g}{h}$

The biokinetic coefficients for $N{H}_4$ oxidation at $20C$ are:

$\backslash$table$[[{}_{mn}=0\mathrm{.}75gVS\frac{S}{g}VSS.d,{}_T$ value for ${}_{mn}=1\mathrm{.}07$