Alum water treatment

The same questions about the safety of organic flocculants have been raised ia other countries. The most drastic response has occurred ia Japan (7,77) and Swit2edand (77) where the use of any synthetic polymers for drinking water treatment is not permitted. Alum and PAC are the principal chemicals used ia Japan (7). Chitin, a biopolymer derived from marine animals, has been used ia Japan (80,81). Maximum allowed polymer doses have been set ia Prance and Germany (77). 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

Most of the floeculation agent is removed with the floe, nevertheless, some question the safety of using alum due to the toxicity of the aluminum in it. There is little to no seientific evidence to back this up. Virtually all municipal plants in the US dose the water with alum. In bulk water treatment, the alum dose can be varied untU the idea dose is found. The needed dose varies with the pH of the water and the size of the particles. Increase turbidity makes the floes easier to produce not harder, due to the increased number of eollisions between partieles. 

Water treatment by either direct or contact filtration has become common practice for raw water with low turbidity [<3NTU] and low colour. Simple metal salts such as alum or ferric chloride are added to plant inlet water. Hydrolysis takes place with the formation of hydroxylated species, which adsorb, reducing or neutralizing the charge on the colloidal particles in the raw water, promoting their collision and the formation of floes that settle or can be filtered out. 

Alum AI2(S04)3-XH20 electrolytic and coagulation water treatment 5-10 15 ppm 2(5 inorganic chemical manufacturers... 

Aluminum compounds are used in many diverse and important industrial applications such as alums in water-treatment and alumina in abrasives and furnace linings. They are found in consumer products such as antacids, astringents, buffered aspirin, food additives, and antiperspirants. Powdered aluminum metal is often used in explosives and fireworks. To learn more about the properties and uses of aluminum, see Chapters 3 and 4. 

Background levels of aluminum in rural air typically range from 0.005 to 0.18 ng/m3, whereas levels in urban and industrial areas can be considerably higher, ranging from 0.4 to 10 ng/m3. Concentrations of aluminum are highly variable in drinking water, ranging from <1 ppb to 1,029 ppb (Schenck et al. 1989). The use of alum (aluminum sulfate) as a flocculent in water treatment facilities is the usual cause of... 

Figure 9.4 Illustration ofZeta potentials and coagulation of solids in New York City water treatment through sequential additions of aluminum sulfate (alum), cationic polyelectrolyte, and anionic polymer. Adapted from Zeta-Meter [544]. Courtesy L.A. Ravina, Zeta-Meter, Inc., Staunton, Va.

The aluminum chloride catalyst used in the alkylation is finally rejected from the system as an acidic aqueous solution. This by-product AICI3 is usually best used for waste water treatment. Sale or use of this material is often as an alum or copperas substitute in water clarification. It is also used in U.S. municipal sewage treatment plants, where a valuable side effect is phosphate removal. In Japan it is converted to polyaluminum chloride (PAC) and used for water treatment. Other uses for this aqueous aluminum chloride stream exist. 

Example 6.1 A turbine with six blades is installed centrally in a baffled vessel. The vessel is 2.0 m in diameter. The turbine, 61 cm in diameter, is positioned 60 cm from the bottom of the vessel. The tank is filled to a depth of 2.0 m and is mixing alum with raw water in a water treatment plant. The water is at a temperature of 25°C and the turbine is running at 100 rpm. What horsepower will be required to operate the mixer ... 

Example 6.2 By considering the criterion for effective mixing, the volume of a rapid-mix tank used to rapidly mix an alum coagulant in a water treatment plant was found to be 6.28 m with a power dissipation of 3.24 hp. Assume air is being provided at a rate of 1.12 m per m of water treated and that the detention time of the tank is 2.2 min. Calculate the pressure at which air is forced into the diffuser. Assume barometric pressure as 101,300 nW, the depth from the surface to the diffuser as 2 m, and the temperature of water as 25°C. 

Example 6.3 A hydraulic-jump mixer similar to the one shown in Figure 6.9 is used to mix alum in a water treatment plant. The height of the bottom of the sluice gate to the bottom of the channel is 5 cm. The rate of flow into the mixer is 0.048 mVs and the width of the channel is 10 cm. Calculate the mixing power developed in the jump. 

A hydraulic-jump mixer similar to the one shown in Figure 6.9 is used to mix alum in a water treatment plant. The mixing power developed is... 

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