In a certain situation, wastewater discharged into a river,mixes

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In a certain situation, wastewater discharged into a river,mixes with the river water instantaneously and completely. Following is the data available:
Wastewater: DO = 2.00 mg/L
Discharge rate = 1.10 m³/s
River water DO = 8.3 mg/L
Flow rate = 8.70 m³/s
Temperature = 20°C
Initial amount of DO in the mixture of waste and river shall be

1. 5.3 mg/L
2. 6.5 mg/L
3. 7.6 mg/L
4. 8.4 mg/L

Correct Option: C

DO of mixture is given by

DO^mix =	A_s × DO_s + A_R × DO_R
	A_s + A_R

=	(1.1 × 2) + (8.7 × 8.3)
	1.1 + 8.7

= 7.6 mg/l