Consider a municipal water treatment plant for a small community. Waste water, $32000$ m$/$day$,$ flows through the treatment plant with a mean residence time of $8$ hr$,$ air is bubbled through the tanks and microbes in the tank attack and break down the organic material.

$($Organic Waste$)+02$

Microbes

CO$2+$ H$20$

A typical entering feed has a BOD $($biological oxygen demand$)$ of $200$ mg O$2/$litre$,$ while the effluent has a negligible BOD. Find the rate of reaction or decrease in BOD in the treatment tanks.