Hydrogen sulfide removal in well water 5

[UtahWater]

We have a client with a 2700 gpm well that produces water with a strong "rotten egg" smell at the source and a "musty" smell in the distribution system. What technologies are availabel to treat the water? We've completed some rudimentary tests with chlorox and it would take about 5 ppm Cl2 to treat the water with chlorine. Any advice would be appreciated.

 

[semo]

Aeration is typically used (forced draft aerator); however, aeration also requires a basin/tank with high service pumps to put the water into the system.

Chemical means for a direct (well to system) source include CL2 and KMNO4. The dosage for CL2 is 8.33 ppm per 1 part H2S removed. The dosage for KMNO4 is 12.37 ppm per 1 part H2S removed.

 

[UtahWater]

Thanks, semo. Is there a situation where the smell can't be eliminated through mechanical means? A preliminary evaluation by an air stripping tower manafacturer indicated that the problem is "in solution" rather than "gaseous" and can't be stripped. Is there another mechanical means (sand bed filtration or the like) out there that might help us.

 

[orenda1168]

UtahWater:

An electrolytic-catalytic system (ECP) available from ECP International, LLC at water@infoecp.com can easily and economically remove H2S to zero concentration by oxidation. You may want to contact them if this is of interest.

At your flow rate, chemical removal will probably be cost-prohibitive.

Orenda

R. J. Kersey

http://www.infoecp.com

 

[hydrae]

UtahWater

The hydrogen sulfide can be reduced to elemental sulfur by dosing the chlorine at 2.1 ppm per ppm of sulfide, then the elemental sulfur can be filtered in a variety of media filters (sand, garnet, anthracite, cartridge, DE) Dosing the bleach to just 2.1 can be tricky since the contaminate concentration can vary in a pump run or by seasons.

Dosing to 8.3 ppm per ppm is easier to control since with an online monitor, when a free chlorine residual appears the dose is correct.

Use of air will also work, what is happening is the oxygen is reacting with the sulfide and again reducing the sulfide to sulfate, lighter dosing will reduce it to just sulfur requiring a filter. The air is typically added using a basin with a bubbler, but there is no reason why a tower would not do the trick other than the extra cost. Sometimes the water will require a filter aid, pH, and/or alkalinity adjustment to fine tune the treatment. A pilot study would be called for to test the treatment techniques to find out which best performs with the water in question. Interactions of other in-organics if present may complicate treatment for just sulfide, again the pilot study will help this.

Caution:
Using just air in an un-chlorinated groundwater system may lead to positive chloroform samples requiring the installation of a disinfectant system.

I disagree with Orenda on the cost prohibitive comment, not treating rotten egg odor can lead to very dissatisfied customers, resulting in one of two choices treat the water or shut off that large well. At $5 per gallon of 12.5% bleach this will cost about $0.21 per 1000 gallons. Odds are you will get a lower price when purchased in larger quantities.
The lowest capital cost system would be straight bleach treatment, at that point the addition of more capital structures such as the use of gas instead of bleach, aeration basin, ECP or lower dose with a filter can be evaluated on a capital verses O&M costs.

Hydrae

 

[sbush]

To remove hydrogen sulfide from well water you must first reduce the pH of the water to 5.5 in order to shift all of the ionic hydrogen sulfide to the gaseous state. Then strip the gas using a packed tower constructed entirely of corosion resistant materials such as fiberglass, polypropylene and PVC. As Semo suggested, the forced draft method is best. Add alkali to the tower sump or clearwell to raise the finished water pH to acceptable levels for distribution to the system and chlorinate.

This is how sulfur is removed from municipal water systems throughout the country. It has been proven for years and it works. Just don't try it without acid or carbon dioxide, you'll end up with tiny white feathers in your water.

S. Bush

http://www.water-eg.com

 

[semo]

Sorry I was out for the weekend.

Hydrae and sbush have both given the same info I could. As Hydrae mentioned, I would do some pilot studies.

I've seen several instances where pH adjustment wasn't necessary; however, if your aerator manufacturer is stating that it is in "solution" (ie it has been ionized), it will probably require a reduction in pH as Sbush stated. If the water has a higher pH or there is CO2 in the raw water, straight aeration will increase the pH by stripping the CO2 quicker and could ionize some of the H2S.

At high H2S levels, aeration and/or chlorination can also drop elemental sulfur which will require additional treatment (coagulation/filtration).

Basically what I am saying is to do some pilot studies on the water and see what works more efficiently and cost effectively.

 

[bimr]

You have not presented enough information to make a detailed recommendation. You need to obtain a water analysis that specifically includes field measurements of carbon dioxide and H2S. Some observations regarding H2S removal can be made

While the chlorination of raw waters containing high concentrations of sulfides is rather expensive, chlorination is of great value in eliminating the small residuals from the effluents of other sulfide removal processes. The amount of chlorine required to oxidize 1 ppm of H2S to the sulfate is over 8 ppm.

I disagree with Hydrae in that it is not possible to selectively convert the sulfide to elemental sulfur. A competing reaction will convert the H2S to sulfate.

The amount of chlorine required to oxidize 1 ppm of H2S to water and sulfur is only 2 ppm. However, either all or a great part of the sulfides are oxidized to sulfates and this oxidation takes place to a great extent even when a deficiency of chlorine is added. So, it is not practical to expect the oxidation of H2S to only sulfur to occur and you can expect the chlorine dosage to be over 8 ppm to one part of H2S.

Both H2S and CO2, when dissolved in water, are very feebly ionized, and it is possible to displace either one of these substances from its alkaline salt by blow a stream of the other gas through the solution. In treating sulfur waters, though, the important and unfortunate fact is that the CO2 comes out much more easily than the more soluble H2S. Also, as the CO2 comes out, the pH value (assuming a normally alkaline water) rises, and this upsets the equilibrium between alkaline sulfides and H2S so that the reaction proceeds in the wrong direction for the removal as H2S.

At a pH of 5, 98% of the H2S will air strip. At a pH of 6, 86% of the H2S will air strip. At a pH of 7, 39% of the H2S will air strip. If the pH value of 9, only a little over one-half of one percent would be present as H2S, and the remained would be present as an alkaline or alkaline earth sulfide.

Lowering the water pH of a 2,700 gpm stream will be an expensive proposition, especially if your water analysis shows high levels of alkalinity.

In summary, the cost effective of any H2S treatment is going to depend greatly on the chemical analysis of your water analysis.

 

[bimr]

I should have added that the use of air for oxidation of sulfides is not practical because of the rather slow sulfide oxidation reaction. I have read of experiments where after two hours of standing time, no measurable degree of oxidation occurred.

In fact, most aerators and aerated water reservoirs, after operating for some time on waters containing sulfide, show growths of sulfur bacteria which frequently play an important role in reducing the sulfide content.

I am not convinced that a pilot test is warranted. The wheel does not have to be reinvented. The design parameters to prepare a treatment process to treat this water are available. The first step is to obtain a complete water analysis. With a proper water analysis, one should be able to develop the most cost effective treatment process.

 

[semo]

Note that the testing for the H2S and CO2 will have to be done at the well head. You can't bottle the sample and send it off. Some of the H2S and CO2 will offgas in the bottle and give a false reading at the lab.

 

[pareshcvora]

Utahwater

May be the guys at the link below may provide a suitable solution.
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