Surface Environment, Mine Ventilation and Underground Hazards · Surface Environment · 2 marks · Multiple choice
A 10 mL wastewater sample is diluted to 300 mL with BOD-free water. Initial dissolved oxygen is 9.0 mg/L and the original wastewater’s BOD₅ is 60 mg/L. Find final DO of the diluted sample, in mg/L.
The sample fraction is 10/300=1/30. Oxygen depletion in the diluted bottle is 60/30=2 mg/L. Final DO is 9−2=7.0 mg/L, C. The original-sample BOD must be multiplied by its dilution fraction, not subtracted directly.
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