Effluent from a wastewater-treatment plant is discharged to a surface stream. Th

Question

Effluent from a wastewater-treatment plant is discharged to a surface stream. The characteristics of the effluent and the stream are given in the table below. Determine the stream characteristics after mixing has occurred.

Parameter

Effluent

Stream

Flow,

8500 m3/day

1.5 m3/sec

BOD5, mg/L

25.0

2.0

Ammonia, mg/L

10.0

0.0

Nitrate, mg/L

7.0

3.0

Chloride, mg/l

15

5.0

Parameter

Effluent

Stream

Flow,

8500 m3/day

1.5 m3/sec

BOD5, mg/L

25.0

2.0

Ammonia, mg/L

10.0

0.0

Nitrate, mg/L

7.0

3.0

Chloride, mg/l

15

5.0

Explanation / Answer

a) The combined rate = effulent + stream = 8500 + 1.5 = 8501.5 m^3 / sec

b) Biological oxygen demand = flow rate of effulent X BOD of effulent +flow rate of stream x BOD of stream / total flow

BOD = 8500 X 25 + 1.5 X 2 / 8500 + 1.5 = 212500 + 3 / 8501.5 = 24.99 mg / L

C) Total ammonia = flow rate of effulent X ammonia +flow rate of stream x ammonia / total flow

Ammonia = 8500 X 10 + 0 / 8501.5 = 9.99 mg / L

D) Total nitrate = flow rate of effulent X nitrate of effulent +flow rate of stream x nitrate stream / total flow

Nitrate = 8500 X 7 + 1.5 X 3 / 8501.5 = 6.99 mg / L

E ) Total Chloride = flow rate of effulent X BOD of effulent +flow rate of stream x BOD of stream / total flow

Total chloride = 8500 X 15 + 5 X 1.5 / 8501.5 = 14.99 mg ./ L

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