Question $4$

$($a$)$ What suitable unit processes are required to treat raw municipal wastewater to the required quality? Use a schematic diagram to show the sequence of selected unit processes in your answer. Justify the selection of each unit process by giving reasons for selecting each treatment process for the appropriate water quality parameter$($s$)$ to be improved posttreatment.

$($b$)$ Study the given diagram of the Sewage Treatment Plant $($S$.$T$.$P$)$ and answer the questions that follow:

$($a$)$ Which one of the two $\text{'}$S$.$T$.$P$.\text{'}($A$)$ or $($B$)$ will be more effective in treating the human excreta in the municipal waste?

$($b$)$ Write the steps followed in carrying the treatment of the sewage in step $($Z$),$ once the BOD of sewage is reduced significantly till it is passed on to the "anaerobic sludge digesters".