A complete$-$mix activated sludge system is used to treat $6750$ m$3/$d of sewage. The

system consist of $2$ rectangular tanks, arranged in parallel. Dimension of EACH

aeration tank is $20$ m $($long$)$ x $9$ m $($width$)$ x $3$ m $($depth$).$

Sewage with $350$ mg$/$L BOD flows in a primary clarifier, and reduces to $210$ mg$/$L

at the effluent of the PRIMARY clarifier. The effluent BOD after FINAL clarifier

must comply with Standard A$.$

Underflow sludge concentration is $10,000$ mg$/$L$,$ MLSS concentration in the

aeration tank is $3,000$ mg$/$L; and SRT is $10$ days

Based on the above information, determine:

$($i$)$

The HRT of aeration tank

$($ii$)$

F$/$M ratio

$($iii$)$

Volumetric loading rate

$($iv$)$

Quantity of wasted sludge daily $($for both tanks$)$

$($v$)$

Recycle ratio $($show mass balance around final clarifier$)$

$($vi$)$

BOD removal efficiencies for primary clarifier and activated sludge

systems