Help with H2S Odor in Water Supply 1

[ccbailey]

The H2O from my well smells like rotten eggs (H2S). From the well, the H2O goes into a large pressure tank (~50 gallons), and a larger fiberglass retention vessel (~80 gallons). Chlorine is injected immediately before the pressure tank. From the rentention tank, the H2O enters a carbon filter, and then off to the hot water tank/rest of the house.

The cold water has almost no smell, but I can't get rid of the hot water smell. I recently removed the anode from the hot water tank and flushed it. The odor was reduced for a day or two, but it returned. Can Sulphide Reducing Bacteria (SRB's) still thrive in a water tank even without the anode present? Why chlorine level is required to kill them?

Typically, when I take a shower, I can turn the hot water on for 30 seconds before it gets hot. The first 30 seconds of water does not stink even though it comes from the hot water tank. If there are SRB's, why would this cold water not stink? I suspect that the chlorine is not getting all of the H2S out of the retention tank. What would you suggest as a means of addressing this problem?

The Chlorine is added at about 4 ppm, and the water coming out of the retention tank is at about 0.5 ppm. The pH of the water is around 8.5.

Any thoughts/suggestions would be appreciated.

 

[GarySCWSVI]

First, you need to super chlorinate the water heater. Just flushing it will not rid it of the SRB the likely causer of the H2S.

Second, it is likely that your 2 tanks do not have sufficient capacity to give enough contact time between the water and the chlorine. For H2S, 30 minutes of contact time is best. If the water is flowing at 5 gpm that is 150 gallons of capacity. There are likely times when the flow rate exceeds 5 gpm. The retention tank should be sized for the peak flow rate.

Third, you can also raise the temperature of your hot water. Increase it to 140 degrees F. However, caution should be excersized in the shower to be sure to blend enough cold water to prevent scalding. Also, let other users know that the water is extremely hot. You can also installed a valve on the shower to control the water temperature during showering.

Finally, yes, Sulfate Reducing Bacteria (SRB) can survive and cause the odor even with the anode removed.



Gary Schreiber, CWS VI
The Purolite Co.

 

[ccbailey]

Thanks Gary,

Your response generated four questions:

1) What level of chlorine kills SRB's? I'm assuming 4 ppm only removes H2S, but doesn't kill them? I'm wondering if I can just turn up my chlorine pump, or if I should be removing the anode and dumping a pail of bleach in? Any description on the best way to do this would be appreciated.
2) I was under the impression the carbon filter should remove any sulphur from the water. What are the SRB's surviving on?
3) Assuming they can survive in my hot water tank (or retention tanks), how regularly will I have to kill them off? I know that if I flush my tank with water, the odor is reduced for a day or two.
4) The first 30 seconds of hot water in my shower is cold. It has no odour despite the fact it did come from the hot water tank. If it has no odour, is it possible that my cold water that I think is "clean" of H2S actually has odour, but I'm not detecting it at the cooler temperatures. If so, wouldn't this imply the problem is not with the hot water tank, but that the chlorine isn't adequately removing the H2S?

Thank you,
Chris

 

[TBP]

Your water may be reacting with the standard anode rod material in the water heater. If I remember correctly (it's been a while...) the standard rod is magnesium. Try switching to an aluminum one - that will often get rid of the smell.

 

[GarySCWSVI]

Answers:

1. SRB is just one constituent in water that has chlorine demand. You don't dose with chlorine for just SRB. You need to dose at whatever level will leave 0.5 ppm after 30 minutes of contact time. The SRB create H2S. Therefore those 2 alone would likely require a chlorine dose of 7 ppm for 30 minutes. We don't know what else is in the water that will add to that chlorine demand. It could be iron or manganese or any of a large number of organics that could be present. SRB are difficult to overcome with chlorine because of that. Try increasing the dose, increasing the contact time with a larger retention tank and increasing the temperature of your hot water. Without doing all that some SRB could survive and recontaminate.

2. Carbon has very little capacity for H2S removal. It does not remove sulfur. The SRB are surviving on the sulfates in the water and other organic nutrients. Carbon is also a great growing ground for any form of bacteria.

3. "Regularly" is not applicable here. Continuously is more applicable. Continuous chlorine feed, retention and high hot water temperature are the primary effective means.

4. The odor is always more prominent in hot water. When it cools the odor is very much less. SRB is in your cold water. As they multiply to high levels without any treatment the odor will eventually be detectable in the cold unheated water.

Gary Schreiber, CWS VI
The Purolite Co.

 

[ccbailey]

Thank you,

There was a sticker on one of the vessels, so I contacted the installer of the system. They indicated that I shouldn't have any more than 1 ppm of chlorine coming out of the retention tanks, or I would rapidly deplete the carbon (I don't know if deplete is the right word)? Regardless, if my hot water tank is downstream of the carbon filter (which it is), what is to prevent SRB's from growing there? The chlorine level downstream of the carbon filter is zero.

Somewhere, I read that at my pH level (8.5), there is a difference in the chemical state of the H2S. Does this affect it's ability to react with the chlorine?

Chris

 

[GarySCWSVI]

Levels of chlorine greater than 1 ppm will deplete and also damage the carbon.

After the carbon filter has removed the chlorine there is nothing to prevent SRB's from multiplying nor is there anything that will prevent recontamination from sources after the carbon filter. I should say here also that SRB's will develop a "cocoon" or shell around itself to protect it against chlorine. They will go right through the bed of carbon and then continue multiplication. That is another reason to increase the hot water temperature.

Yes, high pH will reduce the ability of the chlorine and will also cause precipitation of the H2S gas to a sulfur precipitate. Best to reduce the pH to 7.2 to 7.5. Talk more with the installer of your system. They are right there and can see what all needs to be done.

Gary Schreiber, CWS VI
The Purolite Co.

 

[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.

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 blowing 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.

H2S will come out of solution much more readily as the temperature of the water is increased.

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.

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