S E P

SAMPLE EXAM
PROBLEM 1: WATER TREATMENT
For the overflow basin below, determine the hydraulic retention time (in hours), the average vertical velocity (in
m/d), and the flow of water over the weirs.
D = 15 m
H=3m
v = 0.28 m/s
Feeder pipe diameter 30 cm
PROBLEM 2: AIR POLLUTION
Two acres of soil are contaminated with toluene, and the estimated release (flux) from the soil to the atmosphere
is 5.7 x 10-6 g/cm2-s. Prevailing wind velocity is 5.5 m/sec and the area is characterized by slight incoming solar
radiation during the day. Determine the exposure to a person 2 km downwind, and 1 km to the right of the
centerline (i.e. x = 2 km and y = 1 km). Report your answer as g/m3.
8
2
Note: 2 acres = 8.09 x 10 cm .
PROBLEM 3: WASTEWATER TREATMENT DESIGN
Use the typical design values in the table below to estimate the size (both diameter and depth) for two circular
clarifiers used to treat wastewater at a design flow of 30 MGD. Each clarifier is to treat half the flow. Note: 7.48
3
gal = ft
Check the weir loading at peak flow.
Parameter
Design Range At Average Flow
Surface overflow rate (gal/ft2-day)
Average detention time (hr)
Weir loading (gal/ft-day)
800-1200
1.5-2.5
10,000 - 40,000
Typical
Values
1000
2.0
20,000
Design
PROBLEM 4: WATER TREATMENT
What is the total hardness, carbonate hardness and noncarbonate hardness in mg/L as CaCO 3 of the water
analyzed below?
CONSTITUENT
Bicarbonate
Calcium
Carbon dioxide
Carbonate
Fluoride
Iron
Magnesium
Manganese
Copper
Sodium
mg/L as CaCO3
98.2
69.3
23.7
102.8
8.9
7.2
132.8
12.8
3.7
3.2
PROBLEM 5: MASS BALANCE
The purpose of a sedimentation basin is to remove solids from a water or wastewater flow through concentration
at the bottom of the tank. In our operation, we are given several key parameters, such as the influent flow and
concentration. As engineers, we need to design a system to maintain effluent concentration below a legal limit
acceptable in our receiving water. Determine the returns solids pumping rate (Qr) given the following:
3
influent flow Qi = 0.25 m /s
influent concentration Ci = 250 mg/L
effluent concentration Ce = 6.2 mg/L
return flow concentration Cr = 2500 mg/L
PROBLEM 6: TYPE II SETTLING
Given the following isoconcentration chart, determine the theoretical removal efficiency of a settling basin with a
3
depth of 3.5 m, a volume of 1300 m3 and an inflow of 14,000 m /d.
R  ro  
rZ i
Zo
PROBLEM 7: WASTEWATER TREATMENT DESIGN
The town of Stockton, Ohio has been directed to upgrade its primary WWTP to a secondary plant that can meet an
effluent standard of 35 mg/L BOD5 and 30 mg/L SS.
Assuming that the BOD5 of the SS may be estimated as equal to 69% of the SS concentration, estimate the required
volume of the aeration tank. The following data are available from the existing primary plant.
Existing plant effluent characteristics:
3
Flow = 0.2m /s
BOD5 = 240 mg/L
Assume a value of 1800 mg/L for the MLVSS.
S
Ks 1  k d  c 
 c   m  kd   1
X
 c Y  So  S 
 1  k d  c 
Typical values of growth constants for domestic wastewater
Parameter
Ks
m
kd
Y
Value
100 mg BOD5/L
-1
2.5 d
-1
0.05 d
0.05 mg/mg BOD5