Hydrogen Sulfide in Well Water
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 very difficult to measure because it is a gas and escapes very quickly from the water. Because lab or on-site testing is unreliable, odor is really the best way to tell if it is present. Concentrations as low as .5ppm can be detected by smell. Concentrations above 2-3 ppm 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 it is present. 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 cannot nor does it attempt to detect this. Our recommendation is for the buyer to run the water at the house and smell the water themselves.
WHAT CAUSES THE 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.
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 -Oxygen System
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.) We generally do not use air injection because the venturi is easily fouled and rendered ineffective by oxidized mineral.
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 chlorine is used, it is often desirable to remove it with carbon.
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 Systems
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 properly with the flows available from most residential pumps.