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| 1.0 Introduction and Background |
| The incidence of “rotten egg”
sulfur odors and often the resulting black water in hot and cold water
lines is due to the reaction of sulfates and microorganisms in water.
This can occur in the well directly, or in the household plumbing
both hot and cold water pipes, or in only the water heater and hot
water lines. |
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| Black or rusty slime in toilet
flush tanks (above) indicate the presence of bacterial growth.
Water heaters (right) are prime sources of odors when bacteria
react with the anode rod inside. |
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| To determine the source of the odor,
it is important to first check to see whether the cold water contains
odor, or just the hot. |
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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. |
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If the hot water alone has odor, then the odor
is occurring primarily in the water heater. |
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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. |
| 1.1 Odors Caused by Bacteria |
| Some well waters contain an excessive amount of sulfates
with various strains of sulfate bacteria. These bacteria, harmless
to health, will react in stagnant water that has been depleted of
oxygen, and will produce hydrogen sulfide gas. 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. |
| 1.2 Odors Can Develop
in High in Sulfates |
| If your well water is used directly from the well, and
not aerated in a 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 odors,
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. |
| 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. |
| 2.0 Odors Present Directly
From Well Water (outside house) |
| The most common methods to eliminate
odors from well water are: |
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Periodic shock chlorination with high doses of
chlorine |
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Aeration of the water to oxidize
the hydrogen sulfide gas, combined with periodic shock |
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chlorination. |
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Continuous ozone injection to the water |
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Continuous chlorine injection to the water |
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Filtration of the odor by greensand media or
activated carbon |
| 2.1 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. When the odor returns, usually
in a couple of days to a couple of 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. |
| 2.2 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 an open 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. |
| 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 large
quantities of air with low concentrations of ozone. Aeration and residence
time allow the hydrogen sulfide gasses to be oxidized and odors eliminated. |
| Figure 1 Storage
Tank with Ozone Bubbler Aeration |
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| 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, 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. |
| Figure 2 In-line
Ozone Injection by Venturi & Contact Tank |
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