PE Exam Practice Problem #87: Environmental | Dissolved Oxygen Concentration - Streeter Phelps Eq

Welcome to SolvedIn6: Free practice problems for the Professional Engineering Exam! Each question is styled after those created by the NCEES, and is usually solved in under 6 minutes, which is the average time you will have to solve each question on the Professional Engineering Exam.

This problem takes longer to read and to pull information out of than it takes to actually solve. We are given a case where a treated effluent is discharging into a stream and mixing. Many pieces of information are provided about the river and the effluent, but only some of it is needed.

Searching the Environmental reference manual for "Dissolved Oxygen" will lead to a section called Stream Modeling and specifically to the Streeter Phelps equation. There are a few different forms provided for this equation. We only need one of the more simple versions to complete this problem.
Plug in the following information into the equation terms and you will solve for your answer:
k1 will be the deoxygenation rate constant
k2 will be the reaeration rate constant
L0 will be the initial Ultimate BOD value in the mixing zone.
3 days will be the tc value, or the time at which the minimum dissolved oxygen occurs.
We will solve for Dc.

If you would like more practice problems, please check out the rest of the playlist which this video is part of. Please note that newer versions of the reference manual may have been released since this video was recorded. The search terms are usually still correct, but the page numbers listed in the video will be different."

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