Question

The two pond system is fed by a stream with flow rate 1.0 MGD (million gallons per day) and BOD (nonconservative pollutant) concentration of 20 mg/L. The rate of decay of BOD is 0.3/day. The volume of the first pond is 5 million gallons and the second is 3 million. Assuming complete mixing within the pond, find the BOD concentration leaving each pond.

Answer 1

Answer: First pond= 8.0 mg/L

second pond = 4.2 mg/L

Explanation:

Cn/Co = [ 1/ [ 1 + (k*t/n)]]

for the first pond

where Co into the first pond is 20mg/L,

Cn = 20*[ 1/ [ 1+ ((1 x 5)/0.3)]]

Cn = 8 mg/L

into the second pond we calculate the BOD leaving the pond of volume 3million liters

we have Cn = 4.2 mg/L