Q: A city of 200,000 people disposes of 1.05 ms of treated sewage that
still has a BODu of 28.0 mg . L and 1.8 mg. Ll of Do into a river.
Upstream from the outfall
, the river has a flow rate of 7.08 ms and
velocity of 0.37 m. st. At this point, the BODu and Do in the river are 3.6
and 7.6 mg . L , respectively. The saturation value of Do ( at the
temperature of the river ) is 8.5 mg. L. The deoxygenation coefficient, ka
is 0.61 day, and the reaction coefficient k is 0.76 day! Assume
complete mixing and that the velocity in the river is the same upstream and
downstream of the outfall.
1- What is the oxygen deficit and the BODu just downstream from the
outfall (just after mixing, before any reaction can occur)?
2- What is the DO 16 km downstream?
3- Calculate the critical time and distance.
4- What is the minimum DO?​