VII. Water Treatment

1. VII. Water Treatment C. Supplementation (fluoridation) of drinking water treatment, D. Special processes of drinking water treatment

2. Objectives: • Describe the process of fluoridation, the different forms of fluoride used, and justify the use of fluoride as a drinking water supplement. • List, define, and distinguish special water treatment processes relating to taste, odor, color, solids, and point-of-use treatments.

3. Fluoridation: • The addition of fluoride significantly reduces dental caries (cavities) in children. • Fluoride also reduces the prevalence of osteoporosis and hardening of the arteries. • Optimum fluoride level has been established at 1 ppm to prevent tooth decay

4. Fluoridation: (Cont’d) • Fluoride concentrations higher than 2.0 ppm can lead to tooth mottling (dental fluorosis), and possibly bone damage. • The benefits of fluoride last a lifetime. • Fluoride in the concentration recommended for dental health does not cause allergic reactions.

5. Three common forms of fluoride: • Sodium fluoride (NaF) - crystalline form that may be added manually or with mechanical feeders. • Sodium silicofluoride (Na2SiF6) - also commercially available in various grades for dry feeding. • Fluosilic acid (H2SiF6) - corrosive liquid acid, must be handled with care.

6. Fluoridation system design: • Smaller systems often choose liquid systems that are prepared in batches. • Larger systems use either mechanical dry feeders or solution feeders to inject full-strength fluosilic acid directly from the shipping drum. • Automatic systems use flow meters and recorders to adjust the flow rate.

7. Fluoride addition and removal: • Fluoride application is best in a channel or water main coming directly from the filters, or directly into the clear well after filtration. • Excess fluoride removal (defluoridation) can be accomplished by filtering water through insoluble activated alumina or bone char.

8. Special processes (taste, odor, color, dissolved solids): • Contaminants like algae, hydrogen sulfide, methane, inorganic salts or metal ions can cause taste and odor problems. • Oxidizing agents like chlorine, ozone, and potassium permanganate can reduce taste, odor, color, and dissolved solids.

9. Special treatment processes: • Aeration is used to remove volatile compounds, and oxidize some metal ions. • Activated carbon adsorption in powdered (PAC) or granulated (GAC) forms can be used prior to (or during) filtration to improve taste, odor, and color. • UV radiation can also be used to improve taste and odor problems.

10. Point-of-use treatments: • These treatments are used to modify water quality once it has reached homes or businesses and includes: • In-home water softening systems, and • Activated carbon filters (either whole-house unit or drinking tap units should be changed regularly to avoid bacterial concentration).

11. Summary: • Supplementation of water with fluoride reduces cavities in children, and osteoporosis and arterial plaque formation in adults (but may be toxic at high levels). • Special treatment processes include activated carbon adsorption, oxidation, aeration, and water softening, both at treatment plants and point-of-use.