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Hydrogen Sulfide Removal 1

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caraibes

caraibes

Chemical
Aug 26, 2009
3
Hello all, and thank you for future responses they would be greatly appreciated.

A small municipality that I work for has an H2S level that exceeds agencies standards for simple treatment by chlorination. Due to budget and operational restraints the only solutions to lowering the H2S levels are pH adjustments before aeration (to lower the pH), then corrosion inhibitors or another pH adjustment to readjust the pH of the water before distribution to the system. Does anybody know how to calculate the amount of acid to add to lower the pH of the water (with sulfuric acid) in order to favor the production of H2S before aeration, or know of spreadsheets that would do it (I have some chemical data for the water such as alkalinity, Ca, etc.).
 
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The removal of hydrogen sulfide by aeration is usually unsatisfactory unless the water is acidic. Most sulfur waters contain appreciable amounts of alkalinity. You will have to remove the alkalinity with acid. 1 mg/l of 98% Sulfuric Acid will remove 1 mg/l of alkalinty.

At a pH of 5, 98% of the sulfide is present as hydrogen sulfide. At that pH, the alkalinity is also gone.

Even when the sulfur water contains free carbon dioxide, the carbon dioxide comes out faster than the hydrogen sulfide.
 
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bimr,

Thanks for your reply. The pH of the water is about 7.6, I just want to lower it a tad at about 7.2 or 7 so that the aeration is more effecient. Did you use stoechiometric amounts to come up with the result? I would have to have the calculation more detailed for the health dept report. Do you know of a spreadsheet where i could get the equations from? Or could you develop?

Thanks!
 
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The reaction of sulfuric acid with alkalinity follows:

H2SO4 + 2NaHCO3 --> 2H2O + Na2SO4 + 2CO2 or
H2SO4 + Ca(HC03)2 --> 2H2O + CaSO4 + 2CO2

Destruction of bicarbonate alkalinity creates carbon dioxide.

The stoechiometric amount of sulfuric acid required is 1 mg/l of 98% Sulfuric Acid to remove 1 mg/l of alkalinty.

If you know the concentrations of CO2 and alkalinity in the raw water, you can use Fig.1 in the linked article to determine the pH.


Refer to Chemistry for Sanitary Engineers, McGraw Hill.

At a pH of 7, 39% of the sulfide will be present as hydrogen sulfide.
 
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Bimr,

Thanks for the reply! It was very helpfull. I unfortyunately do not have a value for CO2. I have however found a calculator and am trying to understand the calculations: Do you know of any other way without the CO2? I will try to get the book. Thanks again!
 
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You can assume that the CO2 concentration in the effluent of an aerator is approximately 10 mg/l.

If you know the alkalinity and pH, you can also calculate the CO2 with Fig. 1.
 
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