Question

An effluent discharge with a flow of 1.5 m3/s and an ammonium-N concentration of 2 mg/L is released to a river with a flow of 12 m3/s and an ammonium-N concentration of 0.015 mg/L. What is the concentration of this mixture after they have become perfectly mixed downstream?

Answer 1

To find the concentration of the mixture after becoming perfectly mixed downstream, we can use the principle of mass conservation.

Step-by-step explanation:

To find the concentration of the mixture after becoming perfectly mixed downstream, we can use the principle of mass conservation. The total mass of ammonium-N in the effluent discharge is given by the product of its concentration and flow rate, while the total mass of ammonium-N in the river is given by the product of its concentration and flow rate. When the effluent discharge and river mix together, the total mass of ammonium-N remains constant.

We can use the equation:

(flow rate of effluent discharge * concentration of effluent discharge) + (flow rate of river * concentration of river) = (flow rate of mixture * concentration of mixture)

Plugging in the given values:

(1.5 m³/s * 2 mg/L) + (12 m³/s * 0.015 mg/L) = (flow rate of mixture * concentration of mixture)

Solving this equation will give us the concentration of the mixture after they have become perfectly mixed downstream.

Answer 2

the final concentration is C=0.235 mg/L

Step-by-step explanation:

doing a mass balance

ammonium mass outflow = ammonium inflow from river+ effluent discharge of ammonium = 12000 L/s* 0.015 mg/L + 1500 L /s * 2 mg/L = 3180 mg/s

outflow rate = 12000 L/s+ 1500 L /s = 13500 L/s

then the final concentration is

C= ammonium mass outflow/outflow rate = 3180 mg/s/13500 L/s= 0.235 mg/L