CEE 370 Spring 1996

Exam #1

March 11, 1996

Each problem is worth 20 points.

1.The ultimate BOD (BODU) of a wastewater is 300 mg/L; K=0.25 days-1 at 20 C.

1. What is the 5-day BOD at 20 C?
2. How much oxygen is utilized between the end of day 2 and day 4 (20 C)?
3. What is the 5-day BOD if the temperature were 25 C?
4. What is the ultimate BOD if the temperature were 25 C?

2. Two input streams are joined in a mixing box as shown below:

What is the flowrate of stream 2 if the output concentration (Cout) = 150 mg/L?

3. For the same situation as problem three, what would Cout be if conversion occurred in the mixing box and C were converted to a product? Assume that a first order reaction is applicable (with K = 0.25 hrs-1), that the reactor is completely mixed, and the reactor retention time is 2 hours.

4. Sketch an oxygen-sag curve and label Do, Dc, DOmin and td. Also indicate on the curve:

• The stretch of the river for which the rate of deoxygenation exceeds the rate of reaeration
• The stretch of the river for which the rate of reaeration exceeds the rate of deoxygenation.
• The point where the two rates are equal to one another.

1. What is meant by the indicator organism concept (e.g., coliform organisms)?
2. Why (under what circumstances) would nutrients (N and P) be a water quality concern?
3. What is vector transmission?
4. What are chemosynthesis and photosynthesis?