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

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

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

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

Three common forms of fluoride: l Sodium fluoride (NaF) - crystalline form that may be added manually or with mechanical feeders. l Sodium silicofluoride (Na 2 SiF 6 ) - also commercially available in various grades for dry feeding. l Fluosilic acid (H 2 SiF 6 ) - corrosive liquid acid, must be handled with care.

Fluoridation system design: l Smaller systems often choose liquid systems that are prepared in batches. l 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.

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

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

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

Point-of-use treatments: l 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).

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