Municipal Water Treatment > Chlorination and Other Additives

In order to make the contaminated ground water and treated wastewater that municipal water systems must use safe for consumption, many chemical additives are introduced during the process. Surprisingly, many of these additives are actually designed to counter-act the effects of others. The result is a chemical "cocktail" that can impact both the body as well as our environment.

Chlorination

The most common disinfection method in municipal water treatment is some form of chlorine or its compounds such as chloramine or chlorine dioxide. Chlorine is a strong oxidant that rapidly kills many harmful microorganisms. Because chlorine is a toxic gas, there is a danger of a release associated with its use. This problem is avoided by the use of sodium hypochlorite, which is a relatively inexpensive solution that releases free chlorine when dissolved in water.

All forms of chlorine are widely used despite their respective drawbacks. One drawback is that chlorine from any source reacts with natural organic compounds in the water to form potentially harmful chemical by-products trihalomethanes (THMs) and haloacetic acids (HAAs), both of which are carcinogenic in large quantities and regulated by the United States Environmental Protection Agency (EPA). The formation of THMs and haloacetic acids may be minimized by effective removal of as many organics from the water as possible prior to chlorine addition.

Although chlorine is effective in killing bacteria, it has limited effectiveness against protozoans that form cysts in water (Giardia lamblia and Cryptosporidium, both of which are pathogenic). Although chloramine is not as strong of an oxidant as Chlorine, it does provide a longer-lasting residual, and it won't form THMs or haloacetic acids. Chlorine is often converted to chloramine by adding ammonia to the water after addition chlorine. Water distribution systems disinfected with chloramines may experience nitrification, wherein ammonia is used a nutrient for bacterial growth, with nitrates being generated as a byproduct.

Additional Treatment Additives and Options

Water Fluoridation: In many areas, fluoride is added to water for the purpose of preventing tooth decay. Fluoride is usually added after the disinfection process. In the U.S., fluoridation is usually accomplished by the addition of hexafluorosilicic acid, which decomposes in water, yielding fluoride ions.

Water Conditioning: This is a method of reducing the effects of hard water, in which hardness salts are created during the water treatment method as a result of heating. Water with high concentrations of hardness salts can be treated with soda ash (sodium carbonate), which precipitates out the excess salts, through the common-ion effect, producing calcium carbonate of very high purity.

Plumbo-Solvency Reduction: In areas with naturally acidic waters of low conductivity, the water may be capable of dissolving lead from any lead pipes that it is carried in. The addition of small quantities of phosphate ion and increasing the pH slightly both assist in greatly reducing plumbo-solvency by creating insoluble lead salts on the inner surfaces of the pipes.

Radium Removal: Some groundwater sources contain radium, a radioactive chemical element. Typical sources include many groundwater sources north of the Illinois River in Illinois. Radium can be removed by ion exchange, or by water conditioning. The back flush or sludge that is produced is, however, a low-level radioactive waste.

Fluoride Removal: Although fluoride is added to water in many areas, some areas of the world have excessive levels of natural fluoride in the source water. Excessive levels can be toxic or cause undesirable cosmetic effects such as staining of teeth. One method of reducing fluoride levels is through treatment with activated alumina.

Below is a list of just a few of the approved additives (chemical as well as mineral) that are used in the Water Treatment Process:

Aluminum Sulfate - Make it clear (remove turbidity), but has been linked to Alzheimer's and associated with some allergies (peanut).

Ammonium Hydroxide - Algaecide.

Ferric Chloride - Basically Iron, used to remove cloudiness in the water.

Flousillsic Acid - Flouride, for dental "health," but has been linked to all kinds of problems such as bone brittleness, etc.

Sodium Carbonate - (Baking Soda) - used to neutralize all of the acids that have been added for other reasons. When combined with Calcium it becomes Calcium Carbonate, which when heated in home water heaters, creates calcium deposits that can build up in water heaters, thus requiring more energy to heat water and increases electrical bills. ¼ inch build up on a heating coil has been proven to increase electricity costs by 20-30%. (Ohio State University, Water Quality Association).

Sodium Hydroxide - Added to raise the pH balance on acidic water, but increases the sodium content of the water after the acidity has been neutralized.

Sodium Hypochlorite - Bleach used for disinfectant and whitening agent.

Sodium Permanganate - An extremely high oxidizer, is used to remove organic gases - such as sulfur, which can create "rotten egg" smell and taste.

Calcium - Added to increase "hardness" in water. Hard water contains larger amounts of minerals, ranging as low as 30 PPM, but very hard water is considered 200 PPM. This is a stabilizer that neutralizes the naturally aggressive properties of water, as well as the effects of the chemical additives mentioned above used for sanitation.