Environmental Engineering FOURTH EDITION

78 ENVIRONMENTALENGINEE~G

4.6 The temperature soundings and dissolved oxygen measurements for a lake

are as follows:

Depth (ft) Temperature ("F) oxygen (mg/L)

0 (surface)

10

20

30

40

50

60

70

70

70

50

40

40

40

9.5

9.5

9.5

4.0

2.0

0.0

0.0

Plot depth vs temperature and depth vs oxygen. Label the hypolimnion, epilimnion,

and thermocline. Is this lake oligotrophic or eutrophic?

4.7 Draw the dissolved oxygen sag curves you would expect in a stream from

the following wastes. Assume the stream flow equals the flow of wastewater. (Do not

calculate.)

Waste

source

Dairv 2000 100 40

Brick manufacturing 5 100 10

Fertilizer manufacturing 25 5 200

Electroplating plant 0 100 10

4.8 Starting with nitrogenous dead organic matter, follow N around the aerobic

4.9 Describe what is occurring in the following process. Is this process aerobic

2NH4 + 302 + 2N0, + H20 + 4H'

2N0, + 02 + 2N0,

4.10 Suppose a stream with a velocity of 1 ft/s, a flow of 10 million gallons per day

(mgd), and an ultimate BOD of 5 mg/L was hit with treated sewage at 5 mgd with an

ultimate BOD (Lo) of 60 ma. The temperature of the stream water is 20"C, at the point

of the sewage discharge the stream is 90% saturated with oxygen, and the wastewater

is at 30°C and has no oxygen (see Table 4-1). Measurements show the deoxygenation

constant ki = 0.5 and the reoxygenation ki = 0.6, both as days-'. Calculate: (a) the

oxygen deficit 1 mile downstream, (b) the minimum dissolved oxygen (the lowest part

of the sag curve), and (c) the minimum dissolved oxygen (or maximum deficit) if the

ultimate BOD of the treatment plant's effluent was 10 mg/L. You may write a computer

program or use a spreadsheet program to solve this problem.

and anaerobic cycles by writing down all the various forms of nitrogen.

or anaerobic? Where might you expect this process to occur?