$($b$)$ An activated sludge process is used to treat a combined wastewater from two

separate sources of seafood processing and raw sugar refining, respectively.

The seafood processing produces a wastewater stream of $200\frac{m^3}{d}$ with $550$

$BO\frac{D_5}{L},$ and the sugar refinery produces another wastewater stream of $320$

$\frac{m^3}{d}$ with $650BO\frac{D_5}{L}.$ The activated sludge reactor is operating at an organic

loading rate of $4$kgBO$\frac{D}{m^3}.$d$.$

$($i$)$ Calculate the volume of the reactor and the hydraulic retention time

based on the combined wastewater flow and $BO{D}_5$ concentration.

$(6$ marks$)$

$($ii$)$ For a Food$/$Microorganism ratio of $0\mathrm{.}6$kgBO$\frac{D_5}{k}g$ MLVSS$.$d$,$ what MLVSS

concentration should be maintained in the aeration tank?

$(3$ marks$)$

$($iii$)$ Estimate the mean cell residence time, assuming an effluent volatile solids

concentration of $20m\frac{g}{L}$ and the daily amount of waste sludge is $95m^3$

that contains $1\%$ of volatile solids.