1. ## Percentage and blending

Hi I need help on a question but I will post a similar example as then I am not cheating.

A water treatment plant is used to supply 10 million litres a day by treating a portion and blending it with untreated water.

The quality needed is that the water have a salt content of 50 mg per liter
The untreated water has a salt content of 500 mg per liter and the treated has a salt content of 5 mg per liter.

Calculate the throughput of the treatment plant assuming 25% of the feed to the plant is reject.

Thanks

3. I have no idea what this - "the throughput of the treatment plant assuming 25% of the feed to the plant is reject" - means.

The question is phrased really poorly, which is probably leading people to not bother.

Nevertheless, here's what I think part of the question is asking.

You've got untreated water that has 500 mg of salt per liter.

You've got treated water that has 5 mg of salt per liter.

You want to mix the two to get water that has 50mg of salt per liter.

So I'll just deal with that - nothing about throughputs, rejects, etc., here.

Note that MOST of your water will have to be treated water, as 50 mg is a lot closer to the 5 mg of the treater water than the 500 mg of the untreated.

To determine what fraction of the total water must be from each part, note that 50 is $\frac{50 - 5}{500 - 5} = \frac{45}{495} = \frac{1}{11}$ of the way from 5 to 500. This means one-eleventh of the water used must be untreated, and the other ten-elevenths of the water must be treated.

If you want 10,000,000 liters of water, you'll want to use about 909,091 liters of untreated water and 9,090,909 liters of treated water.

Again, I have no idea if this information is helpful, and it certainly isn't the entire answer, as I don't know what you mean by the business I quoted above. Maybe this is totally irrelevant, but it's a shot.

4. Thanks maybe I did'nt word it too well I was on a night shift when I posted it.

Reject

Treatment plant = 10 million liters

Untreated water

My attempt at a diagram is not very clear the untreated water does not go through the treatment plant but is blended with treated water however the treatment plant is not 100% efficient as 25% is reject I hope this makes it clear then the throughput will be all water that has gone through the plant