Q$4(25$ marks$)$

A conventional activated sludge based wastewater treatment plant $($WWTP$)$ has an average flow of $10,000\frac{m^3}{d}.$ The system is operated at an SRT of $10$ days.

a$.$ If the aeration tank in the WWTP is operated at an MLSS of $3,500m\frac{g}{L},$ and the system has a waste sludge production rate of $100\frac{m^3}{d}$ at waste sludge MLSS of $10,000m\frac{g}{L},$ calculate the volume and HRT of the aeration tank. $(10$ marks$)$

b$.$ If the total secondary clarifier volume is $3,500m^3$ with a side water depth of $3\mathrm{.}5m,$ calculate the surface overflow rate and solids loading rate for the secondary clarifiers. $(7$ marks$)$

c$.$ For a primary clarifier effluent $BO{D}_5$ of $150m\frac{g}{L},$ calculate the oxygen demand in $k\frac{g}{d}$ for BOD removal. $(8$ marks$)$