A wastewater treatment operator has been fined because the DO at a point 6 km downstream is below the permit limit of 5 mg/L. Determine the highest BODu concentration possible in the effluent which can still achieve the permitted requirement of a DO greater than 5 mg/L year round.
QR = 13.8 m3/s
QW = 4.4 m3/s
TW Summer = 30°C
TR Summer = 22°C
TW Winter = 13°C
TR Winter = 7°C
kBOD@20° = 0.4 d-1 (assume KBOD is the same for the river and effluent)
H =4 m (assume no change due to wastewater flow)
V = 0.03 m/s (assume no change due to wastewater flow)
DOR = 7 mg/L
DOW = 1 mg/L
BODR = 5 mg/L
n = 0.4