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 k2 = 0.46 1/d @ 20C

benthic demand = 0.7 g/m2d @ 20C average river depth = 3.5 m

benthic = 1.065 average river width = 10 m

DO in sewage = 4.5 mg/LUpstream DO in Clean River = 8.5 mg/L

Upstream BODu = 3 mg/LSewage BODu = 330 mg/L

Pressure = 750 mm HgQ sewage = 0.05 m3/s

Q river = 1 m3/sRiver Temp = 18C

3)CHIPS Inc. discharges partially treated wastewater at the rate of 1000 m3/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 k2 = 0.46 1/d @ 20C

DO in CHIPS Inc. wastewater = 2.0 mg/LUpstream DO in Small Stream = 6.1 mg/L

Upstream BODu = 5 mg/LPressure = 735 mm Hg

4)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

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