pH & Alkalinity – How are they related?

ACTI-Mag for alkalinity & pH control

A safe and cost effective alternative to the use of sodium hydroxide (caustic soda) or other chemicals for wastewater alkalinity and pH adjustment.

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What does this mean for pH control?   Take home messages:
  1. There are only 2 ways to move pH:

Add or remove alkalinity

  •  to raise pH add an alkali (caustic or MHL – Mg(OH)­2 + CO2(aq) => Mg++ + 2HCO3)
  •  to lower pH add an acid (H+ + HCO3 => H2O + CO2^(g)) remove alkalinity & also adds CO2

Add or remove dissolved CO2

  •  dissolve or strip CO2 to decrease or increase pH (increase or decrease bottom line)

Note: in a treatment plant CO2 generation is a ‘given’ as BOD/COD is oxidized to CO2

=> pH will always come down spontaneously even if we dose all influent to >pH 8.5

=> system self-corrects – high pH influent can’t upset the plant unless greatly overdosed

=> excess CO2 generation is normally stripped by aeration

  1. The higher the water alkalinity
  •  the greater the acid or alkali dose required to move pH up or down
  •  the more stable the pH (that’s why you need to maintain adequate alkalinity in your pool)

pH  vs Alkalinity presentation

There is a direct correlation, but pH and alkalinity are not the same.

pH is a measure of the amount of hydrogen ions (H+, acid) in the water.

M Alkalinity is a measure of the bicarbonate (HCO3) concentration.

Think of M Alkalinity and bicarbonate as dissolved limestone (CaCO3).

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