Chlorination System for Hydrogen Sulfide Removal

When drinking water tastes like foul eggs and bath water smells bad, or when the laundry comes out stained, then the odds are that the water is tainted with hydrogen sulfide (H2S). As little as a 1.0 part per million (ppm) dilution of hydrogen sulfide in water makes it odoriferous, corrosive and spotty.

What is Hydrogen Sulfide?

• Hydrogen sulfide is a gaseous by-product of water-borne sulfur bacteria that feeds on sulfur from decaying plants and animals in the environment. It can also be formed by magnesium rods that manufacturers insert in water heaters to prevent water heater corrosion. The sulfur that is dissolved in the water can then react with the magnesium rod to form hydrogen sulfide. Replacing the magnesium rod with an aluminum one will prevent the formation of hydrogen sulfide but may also void the manufacturer's warranty. Generally, however, chlorination is the preferred method of removing hydrogen sulfide from drinking water.

The Chlorination Process

• When hydrogen sulfide is found in well water, the addition of regular household bleach may be sufficient to resolve the problem. Any yellow sulfur particles that remain after the hydrogen sulfide has been removed can be filtered out of the water system with a simple sand or aggregate filter. Periodically the filter will need to be back-flushed in order to remove the trapped sulfur particles.

  In water supplies where the pH is between 6.0 and 8.0, the preferred method of continuous chlorination is administered in commercial home water treatment systems as sodium hypochlorite. It will react with sulfide, hydrogen sulfide and bisulfide to form chemical compounds that will not foul drinking water and cause it to smell and taste bad. According to Mike Miller and Karen Mancl from Ohio State University, the regularly recommended dosage is 2.0 milligrams per liter (mg/l) of chlorine for every 1.0 mg/l of hydrogen sulfide. With this procedure the chlorine is added to the water before it enters the treatment system's mixing tank. Once in the tank, the water must remain in contact with the chlorine for a minimum of 20 minutes, after which it is filtered by activated carbon to remove suspended sulfur and excess chlorine.

  James R. Chastain, Jr., PhD, PE, MPH, a Diplomate of the American Academy of Environmental Engineers, points out that the oxidation of hydrogen sulfide must be performed carefully since the process forms elemental sulfur which, if not removed correctly with filtration will allow the reformation of hydrogen sulfide.

  Commercially available chlorination systems are available as pellet-drop units or as liquid-chemical feed systems which dispense their chlorine automatically.

  When other water contaminants such as iron or high levels of minerals are also dissolved in the water, the chlorination process may need to be augmented with aeration and manganese greensand or catalytic carbon filtration.