Problem No$.2($last year's exam question$)$

A wastewater containing ${10}^9$ bacteria per liter is treated with three completely$-$mixed ponds that are

arranged in parallel $($flow distributed equally among multiple reactors$).$ The volume of each pond is

$10,000m^3.$ The total flow rate of wastewater is $1200\frac{m^3}{?}$ day.

$($a$)$ Estimate the bacteria concentration and their removal efficiency after the pond treatment. The decay

rate constant, $k=1\mathrm{.}0$ day ${?}^{-1}.$

$($b$)$ Would the removal efficiency improve if three ponds were arranged in series? $($calculate the removal

efficiency$)$