b$)$ A trickling filter has been recommended instead to treat the wastewater in $($a$).$ Given factor a $=0\mathrm{.}332,$ Now rate of $8\mathrm{.}000$ m$\text{'}/$d and that the effluent quality should be maintained at $20$BOD mg$/$L$,$ using the NRC formula, for a filter depth of $3$ metres, determine the filter area if:$($i$)$ Recirculation is only for maintaining the hydraulic load onto the filters. $($il$)$ A recirculation factor of $3$ is used.