Given the following nitrified effluent flow and characteristics from an upstream activated sludge process, design a post anoxic suspended growth (activated sludge) system to achieve a residual effluent NO3- - N of 2.0 mg/L.

Wastewater characteristics: Influent flow rate Q=5000 m³/d; Influent NO₃^- - N=30 mg/L; TSS=25 mg/L; temperature=15^oC.

The stoichiometric relationship for BOD_L used for NO₃N removal is : g BOD_L/g NO₃^- -N=2.86/(1-1.42 Y_obs).

Design assumptions:

Using the following denitrification kinetics coefficients at 15 degree C.

Y=0.18 g VSS/g COD used, b=0.05d^-1, q=6.7 mg BOD_L/mg VSS_a-d, and K=10.9 mg BOD_L/L.

In the anoxic bioreactor, MLSS=2500 mg/L.

Feed TSS is not significantly degraded (and BOD from the upstream nitrification reactor is negligible)

Designed SRT in the anoxic bioreactor is SRT=5 days.

determine the following with explanations and formulas:

(1) the required methanol dose (mg methanol/L) that includes both the needed methanol for denitrification and residual methanol in the effluent

(2) the anoxic bioreactor volume and hydraulic retention time

(3) the waste sludge production rate