A lagoon is to be designed to accommodate an input flow of $0\mathrm{.}10$ m$3/$s of nonconservative pollutant with concentration $30\mathrm{.}0$ mg$/$L and reaction rate constant $0\mathrm{.}20/$day$.$ The effluent from the lagoon must have pollutant concentration less than $10\mathrm{.}0$ mg$/$L$.$ Assuming the lagoon is designed as a PFR$,$ how large must the lagoon be$?$