To determine the BOD5 of a waste water sample, 5, 10 and

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To determine the BOD5 of a waste water sample, 5, 10 and 50 ml aliquots of the waste water were diluted to 300 ml and incubated at 20°C in BOD bottles for 5 days.

Based on the data, the average BOD₅ of the wastewater is equal to

1. 139.5 mg/l
2. 126.5 mg/l
3. 109.8 mg/l
4. 72.2 mg/l

Correct Option: C

BOD₅ = Oxygen consumed × Dilution factor
Sample 1: BOD₅ = (9.2 – 6.9) × 300/5 = 138 mg/l
Sample 2: BOD₅ = (9.1 – 4.4) × 300/10 = 141 mg/l
Sample 3: BOD₅ = (8.4 – 0) × 300/50 = 50.4 mg/l

Average BOD =	138 + 141 + 50.4	= 109.8 mg/l
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