Answer: Coefficient= 0.35 per day
Explanation:
To find the bio degradation reaction rate coefficient, we have
k= 
Here, the C lagoon= 20 mg/L
Q in= Q out= 8640 m³/d
C in= 100 mg/L
C out= 20 mg/L
V= 10 ha* 1* 10
V= 10⁵ m³
So, k= 
k= 0.35 per day
That is a thread ball valves