Hydrogen Sulfide Sources
Hydrogen sulfide, or H2S, is a gas common to many groundwater systems across the United States. Hydrogen sulfide gas is insoluble in water. It is released into groundwater from the rock formations it passes through, or occurs as a byproduct from sulfur-reducing bacteria. Hydrogen sulfide gas is flammable, colorless, and readily escapes water giving off a distinct rotten egg or swampy odor. Hydrogen sulfide is most often present in high iron bearing water and low or acidic pH waters, but also occurs naturally in crude oil, natural gas, and geologically active areas like volcanoes and hot springs. Most people can smell hydrogen sulfide in water with a concentration of as little as 0.25 parts per million (ppm) or 0.25 mg/L. The odor may be noticeable only when the water is initially turned on or when hot water is running. Because hydrogen sulfide readily escapes from water, the best way to sample for it is directly at the source, or by following strict sampling guidelines. Said guidelines include specialized sampling equipment that requires the addition of certain chemicals to keep the gas in solution, so that it may be tested in a certified testing laboratory. Moving surface waters typically contain little to no hydrogen sulfide because of natural aeration. However, still bodies of water like bogs or swamps may contain considerable levels of hydrogen sulfide from the decay of organic materials by sulfur reducing bacteria.
Hydrogen sulfide can also be produced in home water heaters that contain elevated levels of sulfate and sulfate reducing bacteria in the water, either from public water supplies or private water wells. Sulfate reducing bacteria are harmless and thrive in anaerobic, oxygen-free, environments like water heaters. Water heaters also provide an abundance of free electrons, which are crucial for sulfur reducing bacteria, thanks in part to the anode rod. Hot water is naturally more corrosive and would attack the walls and heating elements of the water heater if not for the sacrificial anode rod. The anode rod is added to a water heater to concentrate corrosion and to prevent the water heater from essentially corroding itself. Standard anode rods are made of magnesium, which allows the anode rod to corrode before the water heater itself. In the presence of sulfate reducing bacteria, the natural corrosion of the anode rod creates an abundance of free electrons in the water heater. Sulfate reducing bacteria use the free electrons to reduce the sulfate into elemental sulfur, which it uses as an energy source. The byproduct of this process is the production of hydrogen sulfide gas. Replacing the magnesium anode rod with an aluminum-zinc based anode rod instead will help prevent this from happening. Water heater manufacturers have strict warranty guidelines for checking and replacing the anode rod, so always contact the manufacturer before attempting this process.
Health Concerns
Hydrogen sulfide is a secondary water contaminant with an MCL of zero. There are no major health concerns related to hydrogen sulfide as it is mostly a nuisance compound. Even at low levels, hydrogen sulfide will produce foul enough tastes and odors that would prevent anyone from consuming enough of it to get sick. However, it can cause nausea and headaches from drinking water or breathing air that contains the gas. Hydrogen sulfide is corrosive to metals, piping and plumbing fixtures, tarnishes silverware, and results in yellow or black staining in some cases. The lower the pH, the more rapidly the hydrogen sulfide will come out of solution. The higher the pH, the more likely the hydrogen sulfide is to stay in solution.
There is no mistaking the presence of hydrogen sulfide because of the rotten egg/sulfur odor. Even at low concentrations, hydrogen sulfide can still give a strong odor and is the first indicator that it is present in your water supply.
Treatment Options
Hydrogen sulfide can be a tricky contaminant to troubleshoot and fix if you don't know what you're looking for. First, it is important to determine the source of the hydrogen sulfide gas, whether it is present on hot and cold water fixtures, or if it is present only on hot water fixtures. The answer can dictate the appropriate course of treatment. If the sulfur odor is present on hot water only, disinifection through chlorination of a water heater and home plumbing system in combination with anode rod replacement can often be the solution for getting rid of the hydrogen sulfide odor. Hydrogen sulfide is typically not present on public or city water systems which are chlorinated.
The primary mechanism for removing hydrogen sulfide is chemical or catalytic oxidation and filtration. Master Water Conditioning offers a number of treatment options for hydrogen sulfide removal. Before recommending any treatment options, it is important to have a full water analysis performed. The presence of other contaminants like iron, manganese, or both can complicate the treatment process and dictate which treatment option is most appropriate. pH plays a large role in determining what treatment option is best as well.
The first option is our CSIMPLUS and SIMPLUS series. These units use Simplus media, which is a granular manganese oxide filter material used for the removal of hydrogen sulfide, iron, and manganese. It is generally effective on water that has a pH in the 6.5-7.8 range. Simplus acts as a catalyst to create a reaction between dissolved oxygen and the hydrogen sulfide. We always recommend that a water softener be installed after the filter if iron or manganese is present. Simplus can be regenerated with sodium hypochlorite (5.25% bleach) to clean precipitate from the filter material. Regenerating with chlorine helps to disinfect the system and to reactivate the oxidation capabilities of the media. You can learn more about our SIMPLUS units at this link.
The second option is either the FUSIONC or FUSIONS units from our Master Fusion Series. Our FUSION units use a valve mounted ozone generator, and do not require an additional tank for regenerant storage. Instead of regenerating with chlorine, ozone is created by a corona cell discharge generator, and the process leaves no residual taste or odor that can occur with chlorine based systems. The FUSIONS uses the same granular manganese oxide Simplus media that is used in our SIMPLUS units. The FUSIONC uses coconut shell based, catalytic carbon which is unique in that it concentrates reactants via adsorption and then promotes their reaction on the surface of the pores. You can learn more about ozone and its advantages here. The FUSION series are an excellent chemical free option that you can learn more about at this link.
Chemical feed pump systems for injecting chlorine or hydrogen peroxide work well for treating hydrogen sulfide as well. A chemical feed pump system typically consists of the feed pump itself, a solution tank for mixing the appropriate chemical concentration, a retention tank to achieve the necessary contact time between the chemical and the contaminants, and some means of activating the pump, such as an in-line meter. The most common post-filter used with such a setup is a backwashing activated carbon filter, such as the Master Clarifier AC units. However, depending on the specific water quality for the application, additional filtration may be required.
