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Hydrogen sulfide is a naturally occurring gas that causes an odor that
can be described as anything from rotten eggs to that of tidal flats at low tide. At high concentrations, it will
oxidize in the water when it is released from a faucet and will cause a black stain. It is a very difficult contaminate
to quantify (measure) because it is a gas and escapes very quickly from the water. Because lab or on-site testing
are so unreliable, we consider these types of tests useless. Odor is really the best way to tell if you have any
or not. Concentrations as low as .5ppm can be detected by smell. Concentrations above 2-3ppm will all smell the
same. Because of this lack of difference in smell at high concentrations, odor is not a good indication of how
much is in the water but only whether or not there is some there. If the odor in the water is described as medicinal,
like band-aide adhesive or dirt it is not hydrogen sulfide and can not be treated in the same way as hydrogen sulfide would be.
Hydrogen sulfide is not tested for in standard mortgage test. This gives rise to many problems in real estate transactions.
Buyers have test results that don't tell them the water smells. They move into the house and discover this terrible
odor and get very upset. They think someone has not tested properly. The testing may have been done properly but
the test simply can't nor does it try to detect this. Our recommendation is for the buyer to run the water at the
house and smell the water themselves.
What causes this problem?
The gas can be generated in a number of different ways. Decaying organic
matter, like that which forms coal or peat moss, can create this gas. A second way to generate this gas is from
the reaction of acidic water with aquifer that has a sulfur content. The third way is from the by products of bacteria
that use iron or manganese as part of their diet. These bacteria are sometimes referred to as iron bacteria. No
matter how the gas is generated, once formed, it can be treated the same way.
The only time it is not practical to treat the gas with standard water treatment techniques is when the source
of the problem is not in the source water. Sometimes a reaction between the sulfites in the water and the anode
in the hot water heater causes hydrogen sulfide gas to be formed. This is easily determined by checking for odor
in the cold and hot water supply. The odor in the hot water side will always be stronger because the gas wants
to escape from hot water faster than it does from cold water. As a matter of fact, it is a good idea to check the
odor on the cold water side first so that your sense of smell does not get overwhelmed with the odor from the hot
water side. The best way to do this is to smell the water as you fill a five gallon pail with water directly from
the pressure tank.
Sometimes it is recommended that the well
be shock treated with a high concentration (>100ppm) of chlorine
to cure an iron bacteria problem. We have not found this to be very successful and generally do not recommend it
unless the well has never been disinfected with chlorine.
Treatment
The only practical treatment of hydrogen sulfide is with oxidation filtration.
The gas is actually oxidized into elemental sulfur and then the sulfur is mechanically removed with a filter. Some
companies recommend carbon. Carbon is not practical because it will only work for a few days or weeks. There are
catalytic carbons (Centar) that claim to treat hydrogen sulfide very successfully. This will only be true in water
with sufficient oxygen to cause the oxidation of the hydrogen sulfide. Our local waters do not provide this much
oxygen and the systems will fail quickly.
Air Injection
- Oxygen in the air is used to oxidize the hydrogen sulfide. The system requires the use of a venturi to inject
the air. The system is therefore called an air injection system. There are many brand names for this type of system
but they all require a minimum flow (usually at least 5 gpm) from the well pump to make the venturi work. This
flow must be tested before this type of system can be used. Good systems will consist of 3 parts- venturi, air
release tank, and filter tank. The air release tank removes any undissolved air and allows for the retention of
the water. If the air is not released, severe spitting will result at the faucet. The retention allows time for
the oxidation reaction to take place. The filter tank removes the precipitated sulfur that was formed by the oxidation
process. (THIS PROCESS DOES NOT WORK WELL AT HIGH pH)
Chlorination systems (OUR
FIRST CHOICE)
- Chlorine is introduced into the water by one of two methods. The chlorine can be pumped in with a solution feed
pump or it can be dropped in tablet form directly into the well. The water is then either sent to a retention tank
and then to a filter or it can be sent directly to a filter. The choice of methods will be determined by the severity
of the hydrogen sulfide problem and the type of media chosen for the filter tank. If chorine is used, it may be
desirable to remove it with carbon. The chlorine should be able to be regulated so that it is of no higher a concentration
than that found in city water. CARBON IS NOT TO BE USED UNTIL
THE WATER IS CHECKED FOR RADON BECAUSE THE CARBON CAN BECOME A RADIOACTIVE SOURCE.
Greensand systems (NOT
USED BY US)-
This method uses a catalytic media (called greensand) coated with manganese that is treated periodically (like
the regeneration of a softener) with potassium permanganate. The potassium permanganate acts as an oxidant (like
the chlorine or air). When the hydrogen sulfide in the water comes in contact with the surface of media it oxidizes
and the sulfur is then filtered out by sticking to the media before it finds it way through the filter. We do not
use this method because these systems can easily bleed manganese into the water and the potassium permanganate
is not only poisonous, but, if spilled, stains badly. The manganese that bleeds into the water can get to levels
high enough to be toxic. You will hear these filters referred to as manganese filters, greensand filters or potassium
permanganate filters.
Catalytic Media (NOT
USED BY US) This method of treatment uses a media similar
to greensand. The media has many different trade names but is usually a naturally occurring mineral called pyrolucite
(manganese dioxide). This method of treatment counts on there being enough air in the water to provide the oxygen
necessary to turn the hydrogen sulfide into sulfur. This media can also bleed manganese into the water. It doesn't
work to remove hydrogen sulfide in the water we find locally because there is not enough naturally dissolved oxygen.
A second major draw back is that the media is so heavy it is very difficult to back wash(clean see filter operation)
properly with the flows available from most residential pumps.
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