Question

10) Determine the size of two stage trickling filter using the NRC equations. Assume both filters have the same efficiency BOD removal and the same recirculation ratio. Other conditions are as follows o Wastewater temperature 20 C o Wastewater flow, Q 3785 n/d o Influent BODs 195 mg/l Design effluent BOD = 20mg/ o Depth of each filter 2m o Recirculation for filters 1 and 2, r 218

Answer 1

Step 1:

y_in=195 mg/l

y_eff=20 mg/l

Assuming that the removal efficiency is 30%

y_in=136.5 (195x0.7=136.5)

E=y_in-y_eff/y_in

E=136.5-20/136.5=0.85

Step 2:

Assume E1=0.75

E=E1+E2(1-E1)

0.85=0.75+E2(0.3)

E2=0.33

Step 3:

E=100/(1+0.4432(W/VF)^0.5)

W=3785x195x0.7=516.652kg/day

75=100/(1+0.4432(516.652/Vx1.8)^0.5)

V=524m³

Depth=2m

Area=524/2=262m²

0.785d²=262

d=18.2m, provide 18.5m diameter filter

Step 4:

For the second stage using the same NRC equation

W2=W1x0.25(because 75% of the efficiency is acheived in 1st stage only)

W2=129.163

E2=100/(1+0.4432/(1-E1)(W2/VF)^0.5)

33=100/(1+0.4432/0.25)(129.163/Vx1.8)^0.5

V=54m³

0.785d²=54

d=8.29m, provide 8.5m diameter filter