WATER QUALITY
ENGG*3590
Assignment #6-2004
1)
A meat processing plant produces wastewater with a BOD5 of 1100 g/m3 @ 20C and a
kww20 of 1.15 d-1. The treated wastewater is discharged into a nearby river at a rate of 2
m3/s. The river flowrate and temperature is 95 m3/s and 6C respectively in April during
spring runoff, and only 4.4 m3/s in July with a temperature of 26C. The biodegradable
organic matter content in the river upstream of the outfall is 15 mg/L with a k20 = 0.18
1/d. If the maximum BODu value 3 d downstream of the outfall can only increase by 2%
according to the Certificate of Authorization, what are the required treatment efficiencies
during spring and summer? Assume k20 = 0.2 1/d after mixing.
2)
Due to a mechanical failure, the wastewater treatment plant in SOEVILLE is required to
by-pass untreated sewage into the Clean River. Plot the DO profile downstream of the
outfall at 500 m intervals for distance of 24 km. Are the fish safe? Given:
k = 0.11 1/d @ 15C
benthic demand = 0.7 g/m2d @ 20C
benthic = 1.065
DO in sewage = 4.5 mg/L
Upstream BODu = 3 mg/L
Pressure = 750 mm Hg
Q river = 1 m3/s
3)
CHIPS Inc. discharges partially treated wastewater at the rate of 1000 m 3/d into Small
Stream. The summer low flow in Small Stream is 6 m3/min, with a temperature of 25C.
What is the maximum value of BODu that CHIPS Inc. can discharge into Small Stream
and not endanger game fish, i.e., DO does not drop below 4 mg/L? Given:
k = 0.23 1/d @ 20C
DO in CHIPS Inc. wastewater = 2.0 mg/L
Upstream BODu = 5 mg/L
4)
k2 = 0.46 1/d @ 20C
average river depth = 3.5 m
average river width = 10 m
Upstream DO in Clean River = 8.5 mg/L
Sewage BODu = 330 mg/L
Q sewage = 0.05 m3/s
River Temp = 18C
k2 = 0.46 1/d @ 20C
Upstream DO in Small Stream = 6.1 mg/L
Pressure = 735 mm Hg
Raw wastewater having a temperature of 15C is flowing through a 450 mm trunk line to
the wastewater treatment plant. Length of the trunkline is 2,000 m. Measurements taken
show that the sewer is flowing half-full with a BOD5 of 180 mg/L with a k20=0.32 d-1 at
the start of the trunk line. Does the dissolved oxygen content increase or decrease over
the 2,000 m? Does that make sense? Given:
rB* = 27 g/m2/d @ 15C
n = 0.011
k2 
S = 0.0075
Dw = 1.6 cm2/d @ 20C (diffusion coefficient of O2 in water)
g = gravitational constant, m/s2
H = depth of water in sewer, m
k2 = reaeration constant for sewer, min-1
 = 1.024
DO concentrations: C0 = 2.5 mg/L; Cs = 8.5 mg/L
D:\Engg 359\Webfiles\359#6-ASN.doc

Dw  gSH 
0.5
/ 0.4 H
H
v
1 0.67 0.5
R S
n

0.5