Odor
Source of Odor
Taste and odor problems of many different types can be encountered in drinking water. Troublesome compounds may result from biological growth or industrial activities. The tastes and odors may be, produced in the water supply, in the water treatment plant from reactions with treatment chemicals, in the distribution system, and/or in the plumbing of consumers. Tastes and odors can be caused by mineral contaminants in the water, such as the salty taste of water when chlorides are 500 mg/i or above, or the rotten egg odor caused by hydrogen sulfide. Odor in the drinking water is usually caused by blue-green algae. Moderate concentrations of algae in the water can cause it to have a grassy, rnusty or spicy odor. Large quantities can cause the water to have a rotten , septic, fishy or medicinal odor. Decaying vegetation is probably the most common cause for taste and odor in surface water supplies. In treated water supplies chlorine can react with organics and cause odor problems. The US EPA lists odor in the Secondary Drinking Water Standards. The contaminant effects are strictly aesthetic and a suggested Threshold Odor Number (TON) of 3 is recommended.
Treatment of Odor
Odor can be removed by oxidation-reduction or by activated carbon adsorption. Aeration can be utilized if the contaminant is in the form of a gas, such as H
2S (hydrogen sulfide). Chlorine is the most common oxidant used in water treatment, but is only partially effective on taste and odor. Potassium permanganate and oxygen are also only partially effective. Chloramines are not at all effective for the treatment of taste and odor. The most effective oxidizers for treating taste and odor are chlorine dioxide and ozone. Activated carbon has an excellent history of success in treating taste and odor problems. The life of the carbon depends on the presence of organics competing for sites and the concentration of the odor-causing compound.