Hydrogen sulphide removal from drinking water

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Dear friends,

We have wells in sandstone area and recently we increased the depth of these bore wells from 600 ft to 700 ft. Since then, we have started getting smelly water and the pipe infrastructure is also corroding.

When we did the chemical analysis we found out that the drinking water has hydrogen sulfide at the level of 4 mg/l. Some naturally found anaerobic bacteria are forming this in soil and we can not stop it. So the best way is to remove the H2S from the water.

Our technical guide has asked us to opt for aeration, but your suggestions about some other options as well are welcomed. 

We have only these three wells as the water source for a village, and we need to solve the problem asap.

Also the recommended method should be very economical... :)

Thanks,
Anita.

 

 

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33 Answers

  4. The water network's editors and research team has consolidated an answer to the above question. More inputs from members are welcomed and appreciated.

    Occurance of hydrogen sulphide

    Sulfates are a combination of sulfur and oxygen and are a part of naturally occurring minerals in some soil and rock formations that contain groundwater. The mineral dissolves over time and is released into groundwater.

    Sulfur-reducing bacteria, which use sulfur as an energy source, are the primary producers of large quantities of hydrogen sulfide. These bacteria chemically change natural sulfates in water to hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners and water heaters.

    Hydrogen sulfide gas also occurs naturally in some groundwater. It is formed from decomposing underground deposits of organic matter such as decaying plant material. It is found in deep or shallow wells and also can enter surface water through springs, although it quickly escapes to the atmosphere. Hydrogen sulfide often is present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.

    Treatment methods for removal of hydrogen sulphide

    The removal methods vary according to the concentrations of hydrogen sulphide present in the well.

    Using activated carbon filters (For Hydrogen sulphide trace amounts of 0.05-0.3 mg/l)

    Activated carbon is used as a granular form in tank-type filters (Figure 1) and as finely divided powder in a cartridge. The hydrogen sulfide is adsorbed onto the surface of the carbon particles. A granular filter must be backwashed periodically; a cartridge filter must be cleaned or replaced periodically. Cleaning frequency depends on the amount of hydrogen sulfide in the water and the volume of water treated. Moderate to high levels of hydrogen sulfide will require frequent filter replacement.

    Aeration Method (less than 2mg/l hydrogen sulphide concentration)

    Aeration (adding air to the water) is a treatment option that is commonly used by city water treatment systems. Oxygen in the air reacts with hydrogen sulfide to form an odorless, dissolved form of sulfur called sulfate. Several types of aeration systems are available. Type 1: compressed air is injected into the water system. The air then must be removed from the water to prevent knocking or air-blocks in the system and to reduce the corrosion potential caused by dissolved oxygen. Type 2: water is sprayed into a non-pressurized storage tank. A second pump is needed to re-pressurize the water. The storage tank provides 6 to 8 hours holding time for oxidation of hydrogen sulfide, iron and manganese. The storage tank and aerator must remain secure to prevent contamination of the water supply, or the system must be chlorinated. This process usually produces a strong hydrogen sulfide odor near the aerator, and may not always reduce the hydrogen sulfide to non-detectable levels. In such cases, a carbon filter can be used to remove some of the remaining trace amounts of hydrogen sulphide.

    Using Iron removal filter with manganese greensand pressure filtration system

    An iron removal filter containing manganese greensand can remove low to moderate levels of hydrogen sulfide in addition to iron and manganese. This process oxidizes hydrogen sulfide into sulfate; iron and manganese form precipitates that are filtered out (Figure 2). Manganese greensand filters must be recharged with a solution of potassium permanganate when the oxygen is depleted. This process is very similar to the regeneration process used in water softeners, and must be performed at regular intervals of 1 to 4 weeks depending on the chemical composition of the water, size of the unit and amount of water processed. Water with a pH below 6.7 could require acid neutralization, increasing the pH to 7.5 to 8.3, before iron removal will be effective.

    Figure 2 Manganese greensand pressure filtration system for removal of hydrogen sulfide, iron and manganese

    Continuous chlorination method (Up to 75 mg/l)

    Continuous chlorination using an automatic chemical feed pump can effectively remove medium to high levels of hydrogen sulfide (Figure 3). Chlorine quickly oxidizes hydrogen sulfide into a tasteless, odorless form. Continuous chlorination also effectively removes iron and manganese that can occur in association with hydrogen sulfide. Chlorine demand (concentration) and contact time are very important to successful chlorination. The amount of chlorine needed to react with organic and inorganic materials in the water can range from 1 mg/l to more than 10 mg/l if the water is high in sulfide, ammonia, iron or manganese. For removal of hydrogen sulphide, the chlorine dosage needs to be 2.2 times H2S concentration (mg/l). Contact time (exposure) depends on the concentration of chlorine in the water, water temperature and pH. Oxidation of iron and hydrogen sulfide is instantaneous, while manganese oxidizes more slowly. Chlorine should be introduced into the system before it reaches the storage tank. The tank must have sufficient volume to provide a 20-minute contact time between the water and the chemical. In addition, a fine-retention sediment filter can be used to remove any oxidized iron and manganese. Excess free chlorine is undesirable and can produce an objectionable taste in the water. An activated carbon filter can be used to obtain chlorine-free water for cooking and drinking.

    Figure 3 Chlorine injection system for removal of hydrogen sulphide.


    Source: Texas A&M AgriLife Extension Service http://AgriLifeExtension.tamu.edu


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  7. @ Anita, may i know the flow rate you are looking for; 4 mg/l H2S concentration is not much here. Better install Carbon Adsorber (no of adsorber will depends on flow rate) with the carbon having iodine value greater that 800 IV. The velocity to be maintained within the vessel should be less that 9 M/hr.

  10. Love the comments but most of the solutions are very expensive for a rural village.

    Answered on by

  12. As I read all the previous solutions, they involve getting the water to the surface before treatment. This means that the pumping assembly (lineshaft and turbines, or submersible motor-driven, and piping) is still vulnerable. Pulling pumps and replacing components is expensive, and can result in temporary insufficiency of system capacity. Feeding chemicals down to the pump bowl inlet is possible, but frought with too many risks. You might consider sealing the portion of the aquifer producing the undesirable water, and drilling more wells if the aquifer will supply the required volume of water. Also, consider drilling a test well to see if there is better water in a lower formation. If the latter, you could install a liner through the undesirable formation to seal it off. Good luck. Please let us know how you wind up dealing with this problem.

  13. More analysis

    I second Ralf's comments. A more detailed analysis of what else is in the water is needed. Aeration is usually the first and simplest option to consider, but, the presence of significant levels of iron, manganese, organic carbon, etc may require additional or alternative treatment solution(s) to be adopted. There are plenty of comments about alternative processes that have their place (ie application), but, you want to be sure that you really need to use them as they all involve additional complexity and cost (both in terms of capital as well as operating and maintenance).

  14. Our company produces a well aerator operated via either wind or solar power. Its simple and typically there is no need for extra chemical addition if properly sized based on a chemical analysis. I totally agree with all those that have indicated the importance of locating the source of the contamination if at all possible.

  15. Hossein

    As you indicated rural area, therefore maintenance and supply could be a challenge. In my opinion the most cost and labour effective solution could be chlorination and then filtration thru pressurized sand filter+ Granular Activated carbon. The issue with filter is wasted water that should be consider according to water availability. Chlorination up to breaking point could minimize the health related risks of chlorine.
     

  16. Solution

    I'll advise  you dose the water with  hydrogen peroxide, an oxidizing agent and a disinfectant, hydrogen peroxide will oxidize the hydrogen sulfide to an elemental sulfur, which can be removed by passing the water through activated carbon media tank..H2O2 also stop the growth of  anaerobic organisms

    H2O2 + H2S    =  2H2O + S
     

    H2O2 = H2O +  1/2 O2

  17. There is a new methode of cleaning water, using an old formula: Chlorine Dioxide. It used to be complicated to make, but now available in small up to large pills, under the brand name "AquaProve" A very effective water purification product that exceeds all chlorine type disinfectants. Eliminates harmful parasites and pathogens including E-coli, Salmonella, Guardia, Staphylococcus and Listeria. Aquaprove also takes care of odour causing bacteria. You simply drop the pills into the water and wait for half an hour. Try a few "shock-treatments"(overdose) and watch the results, you will be amazed.

  18. I would recommend simple splash tray aeration (cascade) for this application, it is effective and very simple and inexpensive.

    Answered on by

  19. the apporche is simple. while digging you have penetrate in a vein of liquid in putrefaction which can come from a flow of waste waters. this liquid element in putrefaction does not have anything any more biological. It is impossible to think of being able to eliminate all micro the pollutant correctly chemical which is diluted in this water. it is necessary to close this puît.

  20. Most of the colleagues have suggested diferent alternatives and I agreed with most of them but I believe it should investigate origin of this contaminant in the water because it can mean that some other problems can be associated.

  22. As others have noted/suggested, Aeration & Chlorination are the standard/basic Rx methods of removal: But for Chlorination to work properly, treated water needs to be held - in a pipe or enclosed area - long enough for the chem process to fully interact. Aeration of Bore Hole water could prove both technically & cost difficult; with results depending on extent/source of the H2S tainting. To reinforce other recommendations, you REALLY need to try to determine the natural causal source of this chemical: E.g., in deepening the bore holes, you may have hit some volcanic rock formations. Grasses/weeds can also be a source; but whatever, there's a bacterial factor in the mix. Cautionary Note: "Chlorine" use is the "default" antidote; but this chem has been used for pathogenic "purification" purposes for over half a century now. However, what those "hooked" on this so-called panacea are totally ignoring are these now well known facts: 1) Chlorine is now a well known/recognized CARCINOGEN, with extended/heavy use!; 2) It's ingestion can also cause a number of potentially very negative health side-effects, with even short-term use; some people being HIGHLY sensitive! (NB: I've personally witnessed people go into convulsions, after ingesting heavily chlorine treated "raw" water.); 3) Chlorine has a very short "shelf/use life", & thereby easily loses whatever bacteria conversion/elimination powers it has at full strength. Bottom Line: You first need to determine the causative source creating the H2S condition/problem. Just keep in mind, as you review/consider all those "chemistry" change suggestions/formulae posted above: When one starts mixing chemicals, it's easy to arrive at "unanticipated/unwanted" results: INCLUDING THE CREATION OF POISONOUS/EXPLOSIVE GASES & WATER!!

  25. Possible solutions for hydrogen sulphide removal

    Dear Anita

    How much water has to be treated?

    Generally I can see following possibilities:

    1. Sulfides, such as other inorganic compounds are easily oxidable. Thereby sulfate will be produced. You need 4 Mol O3 for 1 Mol Sulfide. The reaction is as follows: S2- + 4O3 = SO42- + 4O2 

    Treatment would include:

    - Ozone generator
    - Piping
    - Domeaerators
    - Residual ozone destruction
    - Tanks
    - Valves, metering devices and automation

    2. You could use granulate (catalyticly acitve) filter medium, with high manganese oxide content. This filter medium is normally used for iron and manganese removal as well as hydrosulphides.

    This kind of treatment would be a lot cheaper and also easier to maintain.

    If you send us a sample of your water, we can try it out, having some of these filter media at hand in our laboratory.

    3. You apply a lot of chemicals. Iron chemical produces a disgusting, stinking, black  sludge, which has to be disposed of properly. Chlorine has already been discussed in other answers. I wouldn't go for this option if I was to produce drinking water...

    Best regards

    Christoph
    WABAG Water Technology Ltd., Switzerland

     

  30. You need to do the following tests the water COD & BOD You must know the type of bacteria present in the water to be treated water knowledge Must be examined within the water pipelines and wells to make sure of the safety of the pumps in terms of the absence of any leak because the leak is working on the introduction of the air here, where it is to be a good environment for bacteria After testing the water to make sure the well can be treated substance (hydrogen peroxide) is a hypertext killer bacteria

  31. Dear Madam, In my knowledge, Aeration is normally not used for about more than 2.0 mg/l H2S concentration. As the water from well is going to be used for drinking purpose and the nearby soil contains anaerobic bacteria, the best way to remove H2S may be chlorine dosing with activated carbon filter before its consumption. ONLY IF WATER HAS NO SIGNIFICANT AMOUNT OF IRON. Considering 4.0 mg/l of H2S concentration, you will need 8.0 mg/l of chlorine dosing with approximately 20 minutes of retention time. In the given retention time chlorine will oxidize H2S where as the activated carbon filter will removes the insoluble sulphide particles as well as residual chlorine left after the oxidization of the H2S. Best Regards, Sameer Dohare

  32. When chlorine enters water, it immediately begins to react with compounds found in the water. The chlorine will react with organic compounds and form trihalomethanes. It will also react with reducing agents such as hydrogen sulfide, ferrous ions, manganous ions, and nitrite ions. Let's consider one example, in which chlorine reacts with hydrogen sulfide in water. Two different reactions can occur: Hydrogen Sulfide + Chlorine + Oxygen Ion → Elemental Sulfur + Water + Chloride Ions H2S + Cl2 + O2- → S + H2O + 2Cl- Hydrogen Sulfide + Chlorine + Water → Sulfuric Acid + Hydrochloric Acid H2S + 4Cl2 + 4 H2O → H2SO4 + 8 HCl I have written each reaction using both the chemical formula and the English name of each compound. In the first reaction, hydrogen sulfide reacts with chlorine and oxygen to create elemental sulfur, water, and chloride ions. The elemental sulfur precipitates out of the water and can cause odor problems. In the second reaction, hydrogen sulfide reactions with chlorine and water to create sulfuric acid and hydrochloric acid. Each of these reactions uses up the chlorine in the water, producing chloride ions or hydrochloric acid which have no disinfecting properties. The total amount of chlorine which is used up in reactions with compounds in the water is known as the chlorine demand. A sufficient quantity of chlorine must be added to the water so that, after the chlorine demand is met, there is still some chlorine left to kill microorganisms in the water.