Question

A municipal wastewater treatment plant is designed for COD removal and nitrification. The wastewater characteristics and kinetic coefficients are described in the table below. The aeration tank DO concentration is 2.0 mg/L and MLSS concentration is 2500 mg/L. The temperature is 15C. Assume that the concentration of influent NH4-N that is nitrified accounts for 80% of influent TKN. Calculate the following parameters as a function of SRT (i.e., derive mathematical expressions of the following parameters as a function of SRT, respectively, and show your calculation in detailed steps), and plot them as a function of SRT by varying SRT from 3 to 20 days.

(a) Effluent COD concentration (mg/L);

(b) Effluent NH4-N concentration (mg/L);

(c) Aeration tank volume (m3);

(d) Hydraulic retention time t (hours);

(e) Solids production as kg TSS/d;

(f) Oxygen requirement as kg/d.

Wastewater characteristics

Flow rate = 20,000 m3/d

VSS = 200 mg/L

COD = 352 mg/L

TKN = 40 mg/L

nbVSS = 100 mg/L

Temperature = 15 oC TSS = 220 mg/L

Kinetic coefficients of heterotrophic bacteria at 20 C

µm=6 g VSS/g VSS d

Theta for µm = 1.07

Ks=20 mg COD/L

Theta for Ks= 1.00

Y=0.4 g VSS/g VSS

Theta for kd =1.04

kd=0.12 g VSS/g VSSd

fd=0.15 g VSS/g VSS

Kinetic coefficients of nitrification at 20 C

µnm=0.75 g VSS/g VSSd

Theta for µnm = 1.07

Kn=0.74 mg NH4-N/L

Theta for Kn = 1.053

Yn=0.12 g VSS/g NH4-N

Theta for kdn =1.04

kdn=0.08 g VSS/g VSSd

Theta for Ko = 1.00

Ko=0.5 mg O2/L

Answer 1