Sulfur Treatment and Control

Two forms of sulfur are commonly found in drinking water supplies: sulfate and hydrogen sulfide. Both forms can be nuisances that usually do not pose a health risk at the concentrations found in domestic water supplies. High concentrations of dissolved hydrogen sulfide also can foul the resin bed of an ion exchange water softener. When a hydrogen sulfide odor occurs in treated water (softened or filtered) and no hydrogen sulfide is detected in the non-treated water, it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Water softeners provide a convenient environment for these bacteria to grow. A "salt-loving" bacteria, that uses sulfates as an energy source, may produce a black slime inside water softeners.

For sulfate, the most common method of treating large quantities of water is ion exchange. This process works similar to a water softener. Ion-exchange resin, contained inside the unit, adsorbs sulfate. When the resin is loaded to full capacity with sulfate, treatment ceases. The resin then must be "regenerated" with a salt (sodium chloride) brine solution before further treatment can occur. Another approach is reverse osmosis; the membranes have a porosity that permits water molecules to pass through but leaves the larger ions, like sulfate, behind in what becomes the waste water. Distillation boils water to form steam that is then cooled and then recondensed. Minerals, such as sulfate, do not vaporize with the steam and are left behind in the boiling chamber.

For hydrogen sulfide, the most common types of water treatment include: granular activated-carbon, oxidation filters, chemical oxidation, and aeration. If the hydrogen sulfide odor is associated primarily with the hot water system, a hot water heater modification may reduce the odor. Replacing the water heater's sacrificial magnesium corrosion-control rod with one made of aluminum or another metal may improve the situation.

To remove low levels of hydrogen sulfide, install an activated-carbon filter. The filter must be replaced periodically to maintain performance. Frequency of replacement will depend on daily water use and the concentration of hydrogen sulfide in the water. Hydrogen sulfide concentrations up to about 5 to 7 ppm can be removed using an oxidizing filter. These filters are similar to the units used for iron treatment . Such a filter contains sand with a manganese dioxide coating that changes hydrogen sulfide gas to tiny particles of sulfur that are trapped inside the filter. The sand filter must be backwashed regularly and treated with potassium permanganate to maintain the coating.

Hydrogen sulfide concentrations exceeding 7 to 10 ppm can be removed by injecting an oxidizing chemical such as household bleach or potassium permanganate followed up by filtration. The oxidizing chemical should enter the water upstream from the storage or mixing tank to provide at least 30-45 minutes of contact time between the chemical and water. The length of the holding time is a function of the chemical dosage, tank configuration, and water temperature. Sulfur particles can then be removed using a sediment filter and the excess chlorine can be removed by activated-carbon filtration. When potassium permanganate is used, a manganese greensand filter is recommended.

When you have a problem with sulfur and sulfate, proper water testing is critical. If you are experiencing a hydrogen sulfide odor in your cold water and you are located in an apartment complex or are using a city water drinking water source, the first recommendation is to flush your drinking water lines to see if the problem goes away and then to check the system for problems with "backflow".