Hydrogen sulfide gas and the resulting “rotten egg” sulfur odors are typically caused by the reaction of sulfates and microorganisms in ground water. In some areas the hydrogen sulfide gas is a result of decaying vegetation and organic matter. This gas and odor can occur in the well directly, or in the household plumbing in both hot and cold water pipes, or in only the water heater and hot water lines. 

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. These bacteria usually flourish on the hot water side of a water distribution system, and in some cases the water heater itself is the source of the hydrogen sulfide.

A gray or black color is often associated with hydrogen sulfide gas in water and it can tarnish fixtures and corrode metals such as copper, brass and iron. Hydrogen sulfide can affect the taste and color of cooked food, tea and other beverages.

Cold Water Odor or Hot Water Odor?

To determine the source of the odor and decide on the type of treatment required, it is important to first check to see whether the cold water contains odor, or just the hot.

• Run the hot water to notice the odor. Then move to another faucet and run the cold water. If the cold water has an odor, then the source is in the cold water.

• If the hot water alone has odor, then the odor is occurring primarily in the water heater.

• Next go outside and determine if the well water contains odors directly from the well by running water outside the home, before it enters the home piping.


Odors Caused by Bacteria & Sulfates

Some well waters contain an excessive amount of sulfates with various strains of sulfate bacteria. These bacteria, while harmless to health, will react in stagnant water that has been depleted of oxygen, and will produce hydrogen sulfide gas.

If your well water is used directly from the well, and not aerated in an atmospheric (non-pressurized) storage tank, then the odors are most likely caused by anaerobic bacteria. These types of bacteria thrive in oxygen-deprived environments, and often on waters high in sulfates. If the cold water entering the home contains no odor, odor can still develop in cold water piping in the home, especially in galvanized iron piping. Often iron piping in the house is of an older age and can be corroded, providing a good environment for the bacteria to grow and odors to develop.

If there is an odor in the cold water inside the home, but not directly from the well, see if the piping is iron piping, and then replace it with copper. As a first step to this process, one can shock-chlorinate the piping and sanitize it, and see if the odor can be eliminated.


Water Heater Odors

If the water is in the hot water only, then a shock-chlorination of the water heater and servicing or replacing the anode rod in the water heater can eliminate this problem.

Almost all water heaters have “anode rods” which in a cathode-anode reaction, produce excess ions that wear off the anode rod and adhere to the inside glass lining of the water heater, preventing corrosion. These bacteria (typically the “desulfovibrio” or a related species) can be killed with adequate amounts of chlorine by periodic shock chlorination, or by continuous ozone or chlorination, or by turning up the water heater to extremely high (often dangerous) temperatures.


Odors Present Directly From Well Water (outside house)

One of the following methods is typically used to remove hydrogen sulfide gas from well water:

• Periodic shock chlorination with high doses of chlorine

• Aeration of the water to oxidize the hydrogen sulfide gas, combined with periodic shock chlorination.

• Chlorine, hydrogen peroxide, or ozone injection alone

• Filtration of the odor by greensand media, activated carbon or other filter media

• Chlorine, hydrogen peroxide, or ozone injection followed by filtration with greensand, activated carbon or other media.


Periodic shock chlorination with high doses of chlorine

This involves injecting into the well, pump system and piping a 50 to 200 ppm dose of chlorine. The chlorine residual is allowed to sit in the well for 6 to 24 hours, and then the water is pumped out until the chlorine residual is gone. This will typically eliminate the odor problem temporarily. If the odor returns, often within a couple of days to a few weeks, the procedure can be repeated. If after a couple of repeated shock-chlorination procedures, the odor is still present, one of the other methods will need to be used.


Aeration of the water to oxidize the hydrogen sulfide gas, combined with periodic shock chlorination.

Since the bacteria that create the hydrogen sulfide odor are usually anaerobic, or bacteria that cannot thrive in oxygen rich environments, often aeration in a non-pressurized vented holding tank is beneficial to eliminate and drive off the gas into atmosphere. This works best if the pH is low (less than 7.0) since the hydrogen sulfide gas at pH higher than 7.0 will not easily gas off completely.


Continuous Chlorine Injection

Odors can be controlled in water by chlorination, followed by retention or contact time and aeration. See Fig. 1. Chlorine is a powerful oxidizer, and while not as powerful as ozone by weight, is less expensive to install and operate than ozone systems.

Usually 2.0 to 3.0 ppm of chlorine is injected for every 1 ppm of sulfide, however if the pH is over 7.8 it can take up to 5 to 10 ppm of chlorine per 1 ppm of sulfide to treat hydrogen sulfide. If the pH is over 8.0 we usually recommend ozone or hydrogen peroxide injection instead of chlorine bleach.

With chorine, as ozone, contact time and concentration of the chlorine is critical. The chlorine can be injected either in before an open atmospheric holding tank (Figure 3) or injected under pressure using a metering pump and a contact tank or pressure tank. Chlorine injection followed by a contact tank and a good backwash filter system is the more thorough approach.


Fig. 1 Chlorine Injection with non-pressurized tank




Ozone

There are two main methods for injecting ozone into water. In Method 1, (see Figure 1) an open holding tank of at least a 200-gallon capacity is used. Larger holding tanks up to 5000 gallons work better. A compressor or blower is set up on a timer, or wired in so that when the well pump runs, the ozone blower system runs. The air compressor is hooked up to a ceramic diffuser stone, creating a large volume of tiny air bubbles.

If sufficient air is used, and the hydrogen sulfide levels are low, this method, combined with periodic shock chlorination works well. Shock chlorination is required to keep the levels of bacteria down in the well and holding tank.

In the open bubbler tank design, a UV generated ozone generator can be used. The UV-generated ozone systems produce lower concentrations of ozone but lots of aeration is used, and these ozone generators cost a lot less than corona-discharge generators. Aeration and residence time allow the hydrogen sulfide gasses to be oxidized and odors eliminated.

In the second method (Figure 2) , ozone is injected via a venturi under pressure, as the water flows through a contact tank. This type of ozone injection usually requires higher concentrations of ozone and typically a corona-discharge generator with dry air or oxygen feed gas is used.

Since there is less residence time and the ozone is under pressure, as the water is flowing through the contact column. This type of ozone injection does not require an open holding tank and second booster pump. It does require an ozone generator capable of putting out a much more concentrated level of ozone gas, and stainless steel tanks, or ozone-resistant plastic tank must be used to avoid corrosion problems.

Usually, after either types of ozone injection, in Figure 1 or Figure 2, filtration is required. Depending on the water chemistry, filtration by greensand, sand and anthracite, or activated carbon filters are used. These types of filters are periodically backwashed to keep the media clean and free of trapped sulfides, iron or manganese oxides.


Fig. 2 Ozone injection and contact tank



Removal of Odors by Filtration

Hydrogen sulfide gas odors can be removed by filtration but results vary, and usually filtration alone is not effective. The reasons for this are that typically odors and hydrogen sulfide gas are the result of bacterial action. Often the odors can be removed at point of entry to the home or business, and then develop again in the piping system and water heater.

It is more effective to use filtration after aeration, ozone, peroxide or chlorine injection for best results. In some applications, with low levels of hydrogen sulfide gas odors, greensand media filters, regenerated with potassium permanganate are the very effective in removing hydrogen sulfide or rotten egg odors.

Activated carbon is less effective and the life of activated carbon media beds are short, and often require frequent replacing, sometimes within a few weeks after installing the carbon filter.

A very effective and low cost method of hydrogen sulfide gas removal is by injecting chlorine or hydrogen peroxide, followed by a Greensand-Plus filter. Greensand-Plus is an improved type of greensand filter media that does not require potassium permanganate. A slight chlorine residual can be left in the water after the filter, so that the pipes and water heater are kept disinfected, eliminating any chance for odors redeveloping in the household piping.


Figure 3


Greensand Plus Iron & Odor Filtration System

See Figure 3. The booster pump is controlled by pressure switch. When pressure in pressure tank drops below the cut-in point on the pressure switch the booster pump and metering pump turn on. As water is pumped through the system, a small amount of chlorine or hydrogen peroxide is pumped into the water by the metering pump.

As the water flows into the contact tank, the chlorine is thoroughly mixed in the water, allowing contact time to kill any bacteria and oxidize any iron, manganese or hydrogen sulfide gas. Precipitated oxidized particles of iron, sulfides and manganese are filtered out of the water by the greensand-plus media filtration system.

Periodically the filter is backwashed automatically and these oxidized particles are flushed down the drain to a drain pit or septic system. Unlike regular greensand systems, no potassium permanganate powder is required.