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[popay73]

Hi, I came across one article relating pH control of waste water. It's batch neutralization (pharmaceutical waste waters, from different types of API).

It says:

1. bring pH to 14 (with 20% NaOH)
2. heat the Reactor (for neutralization) to 80 °C for 30 minunets
3. cool it to 40 °C
4. adjust pH to 5,5-9,5 (20% HCl)

My first question is: why do we increase pH to 14 and heat the system up ?


Then it says: Reagent (NaOH or HCl) demand is 10^-6 mol/L.

Calculation is as follows: To change pH of 1 L of waste water from 7 to 12 we need 10^4 * 10^-6 mol of Reagent.
I understand this 10^4 is range of H+ ions. One pH unit changes H+ concentration by factor of 10 (logarithmic scale)

My question is: where this 10^-6 mol/L comes from ?

Thx in advance, regards !