CEE 370 
Spring 1997 
Exam #2
April 15, 1997
Closed book, 2 sheets of notes allowed.
Please answer all of questions #1 through #5 and one of either #6 or #7. Show all work. Be neat, and boxin your answer.
Answer #1#5
The Northampton wastewater treatment plant discharges 4.5 MGD of treated wastewater with a BOD_{5} of 7.5 mg/L. What is the loading in lb of ultimate BOD per day (i.e., lbBOD_{u}/d). Assume a BOD rate constant (k) of 0.18 d^{1}.
Solution to #1
First calculate the ultimate BOD in the effluent
then multiply this by the flow with the appropriate conversion factor.
You have designed a batch diffused aeration system for transferring oxygen into a groundwater. The tank holds 5000 gal, and it has a gas transfer coefficient (K_{L}a) of 0.12 min^{1}. If the raw groundwater has a DO of 1.5 mg/L and the treated water must have a DO of 7.5 mg/L how may gallons per day can be treated by this system? Assume that the saturation value (C_{s}) is 10.2 mg/L. Ignore the time required to fill and drain the tank.
Solution to #2
First calculate the time required to process one batch of 5000 gal.
Now calculate the number of batches per day and the total volume treated:
# batches = 24hrs(60min)/9.75min = 147.7
Volume treated = 147.7 batches/day * 5000 gal/batch
= 738,000 gal/day
= 0.74 MGD
A conventional water treatment plant is to be constructed to process 185,000 m^{3}/d. Pilotplant analysis indicates that an overflow rate of 5 m/hr will be acceptable in the gravity settling tanks. Assuming a surface configuration of approximately 12x30 m, how many settling tanks will be required? Allow one unit out of service for cleaning.
Solution to #3
Thus, a minimum of 5 settling tanks are needed, and allowing 1 to be continually out of service for backwash, means that 6 tanks are required.
How many mg/L of hypochlorous acid are required to oxidize 0.8 mg/L ferrous iron?
Solution to #4
First balance the equation:
Next calculate the mass requirements
Since most forms of chlorine are expressed as Cl_{2}, the more accepted answer would be:
Answer to a:
Total hardness: sum of calcium and magnesium concentration in a water
Carbonate hardness: portion of the total hardness that is matched by the anions, carbonate and bicarbonate
Answer to b:
The product of concentration (C ) times time (t) that gives a certain degree of kill of a given organisms with a specific disinfectant.
Answer to c:
Includes rapid mix, coagulation, flocculation, settling, filtration.
Nonconventional processes may include, GAC adsorption, biological filtration, flotation, membrane processes, intermediate ozonation.
Answer either #6 or #7
A settling tank has a width of 20 ft, a depth of 10 ft and a length of 60 ft. It receives 0.60 ft^{3}/s of flow. What fraction of all 0.10 mm diameter alum floc particles will be removed at 5^{o}C (assume 1.04 g/mL floc density)?
Solution to 6:
The Intercontinental Paper Co. is discharging its wastewater directly into the Mill River. The discharge flow is 3.8 ft^{3}/s (cfs) the discharge D.O. is 8.5 mg/L and the discharge ultimate BOD (BOD_{u}) is 35 mg/L. They obtain half of this water from an intake 0.5 miles upstream of the wastewater outfall, and half from groundwater via a nearby well field. On average, the Mill River water upstream of the IPC outfall has an ultimate BOD (BOD_{u}) of 2.5 mg/L and a D.O. of 8.5 mg/L. If the Mill River has a flow of 12 cfs upstream of the IPC intake, and if the state permits a minimum DO of 7.5 mg/L in the Mill River, will the state have to further restrict the BOD in IPC's wastewater (i.e., is the stream out of compliance)? Calculate the minimum stream D.O. expected as a result of the IPC discharge.
Additional assumptions: BOD deoxygenation rate: k_{1} = 0.23 d^{1}
reaeration rate constant (k_{2}) of 0.82 d^{1}
D.O saturation concentration = 9.5 mg/L
River flow velocity = 0.5 ft/s
Solution to #7
First the downstream flow is:
The solve for the instream BOD_{u} concentration at the point of discharge using a mass balance:
Now determine the critical travel time:
Yes, the stream will be out of compliance.
Appendix
Some physical constants of Water:
Temp., ^{o}C 
Density, kg/m^{3} 
Viscosity, Ns/m^{2} 
Kinematic Viscosity, m^{2}/s 
0 
999.8 
1.781x10^{3} 
1.785x10^{6} 
5 
1000.0 
1.518 x10^{3} 
1.519x10^{6} 
10 
999.7 
1.307 x10^{3} 
1.306 x10^{6} 
15 
999.1 
1.139 x10^{3} 
1.139 x10^{6} 
20 
998.2 
1.002 x10^{3} 
1.003 x10^{6} 
25 
997.0 
0.890 x10^{3} 
0.893 x10^{6} 
30 
995.7 
0.798 x10^{3} 
0.800 x10^{6} 
35 
994.0 
0.725 x10^{3} 
0.729 x10^{6} 
40 
992.2 
0.653 x10^{3} 
0.658 x10^{6} 
Selected Chemical Constants
Element 
Symbol 
Atomic # 
Atomic Wt. 
Valence 
Electronegativity 

Aluminum 
Al 
13 
26.98 
3 
1.47 

Boron 
B 
5 
10.81 
3 
2.01 

Calcium 
Ca 
20 
40.08 
2 
1.04 

Carbon 
C 
6 
12.01 
2,4 
2.50 

Cerium 
Ce 
58 
140.12 
3,4 
1.06 

Chlorine 
Cl 
17 
35.453 
1 

Holmiuum 
Ho 
67 
164.93 
3 
1.10 

Hydrogen 
H 
1 
1.01 
1 
2.20 

Magnesium 
Mg 
12 
24.31 
2 
1.23 

Manganese 
Mn 
25 
54.94 
2,3,4,6,7 
1.60 

Osmium 
Os 
76 
190.2 
2,3,4,8 
1.52 

Oxygen 
O 
8 
16.00 
2 
3.50 

Potassium 
K 
19 
39.10 
1 
0.91 

Sodium 
Na 
11 
22.99 
1 
1.01 

Sulfur 
S 
16 
32.06 
2,4,6 
2.44 
Useful conversion factors
1 ft = 0.305 m