An existing $6m$ deep bio tower cannot meet the effluent standard of less than $10m\frac{g}{L}.$

The plant influent BOD is $220m\frac{g}{L},$ the primary effluent BOD is $150m\frac{g}{L},$ the plant

final effluent is $30m\frac{g}{L}$ and the recirculation ratio is $1\mathrm{.}5$ of the wastewater flow

entering the plant. One proposal is to change the recirculation ratio, to reduce the

effluent BOD from $30$ to $10m\frac{g}{L}.$ The constants for the random plastic media, $n$ is

$0\mathrm{.}44$ and $k_{20}$ is $\frac{0\mathrm{.}055}{m}in.$ Design temperature is $25C.$

a$)$ Calculate the hydraulic loading

b$)$ By using the recirculation ratio $=2\mathrm{.}0,$ check whether the plant effluent meet the

standard

c$)$ What recirculation should we have to maintain to meet the standard