# Math Help - Chemical engineering...

1. ## Chemical engineering...

20million litres per day (MLD) of a conservative substance, with a concentration of 10mg/L is released into a stream having an upstream flow of 50 MLD and a substance concentration of 3mg/L. Assumin g complete mixing:

what is the concentration in ppm just downstream?
what is the mass flow rate of the substance in kg/day passing just downstream?

2. Originally Posted by Haris
20million litres per day (MLD) of a conservative substance, with a concentration of 10mg/L is released into a stream having an upstream flow of 50 MLD and a substance concentration of 3mg/L. Assumin g complete mixing:

what is the concentration in ppm just downstream?
what is the mass flow rate of the substance in kg/day passing just downstream?
The concentration just down stream is a weighted average of the two flows (upstream and released)

$c = \frac{20\times 10 + 50\times 3}{70} = 5$ mg/L

For part 2 you just need to multiply flow by concentration

$m = (50 + 20) \times 10^6 \times 5 = 350 \times 10^6$ mg/day

Now there are 10^6 mg in a kg so the mass flow just downstream is 350 kg per day.

Hope this helps.