filtration || the removal of excess fluoride from drinking water by activated alumina

The Removal of Excess Fluoride From Drinking Water by Activated AluminaAuthor(s): Frederick Rubel Jr. and R. Dale WoosleySource: Journal (American Water Works Association), Vol. 71, No. 1, Filtration (January1979), pp. 45-49Published by: American Water Works AssociationStable URL: http://www.jstor.org/stable/41269576 .

Accessed: 30/09/2013 07:59

Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp

.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact [email protected].

.

American Water Works Association is collaborating with JSTOR to digitize, preserve and extend access toJournal (American Water Works Association).

http://www.jstor.org

This content downloaded from 139.80.2.185 on Mon, 30 Sep 2013 07:59:40 AMAll use subject to JSTOR Terms and Conditions

http://www.jstor.org/action/showPublisher?publisherCode=awwa

http://www.jstor.org/stable/41269576?origin=JSTOR-pdf

http://www.jstor.org/page/info/about/policies/terms.jsp


Simple Apparatus for On-Site Contin- uous Liquid-Liquid Extraction of Or- ganic Compounds from Natural Waters. Anal. Chem., 46:6:658 (May 1974).

2. Draft Analytical Report-New Orleans Area Water Supply Study. USEPA 906/ 10-74-002. Lower Mississippi River Facili- ty, Slidell, La. Surveillance and Analysis Div., Region 6, Dallas, Tex. (1974).

3. McNeil, Edward E. et al. Determination of Chlorinated Pesticides in Potable Water. Jour. Chromatogr., 132:2:277 (Feb. 1977).

4. Buelow, Ralph, W.; Carswell, Keith, J.; & Symons, James M. An Improved Method for Determining Organice by Activated Carbon Adsorption and Solvent Extrac- tion-Part 2 (Test Method), /our. AWWA,

65:3:195 (Mar. 1973). 5. Standard Methods for the Examination of

Water and Wastewater. APHA, AWWA, & WPCF, New York, N.Y. (14th ed., 1975).

6. Bottom, Carey B. et al. The Interference of Elemental Sulfur in the Determination of Trace Organice in Drinking Water by the Carbon Adsorption Method. Jour. Envir. Sci. Health, All:6:409 (1976).

7. Cappelli, Frank P. et al. Measurement of Organice in Some Treated and Untreated Water Supplies of Southern Ontario. Environmental Analysis (Galen W. Ew- ing, editor). Academic Press, Inc., New York, N.Y. (1977).

8. Cappelli, Frank P. et al. Determination of the Adsorption Efficiency of the "Or-

ganics-Carbon Adsorbable" Standard Method by Dissolved Organic Carbon Analysis. Jour. Envir. Sci. Health A13:2:167 (1978).

9. Barlett, J.K. & Skoog, D.A. Colorimetrie Determination of Elemental Sulfur in Hydrocarbons. Anal. Chem., 26:6:1008 (Jun. 1954).

A paper contributed to and selected by the Journal, authored by Rein Otson (Active Member, AWWA), chemist; Peter D. Bothwell, technician; and David T. Williams (Active Member, AWWA), head; all of the organic chemistry sect., bur. of chemical hazards, health protection br., Health & Welfare Canada, Ottawa, Ont.

53575 4130,4140

The Removal of Excess Fluoride From Drinking Water by Activated Alumina

Frederick Rubel Jr. and R. Dale Woosley Described here are cost-effective operating practices developed at three water treatment plants for removing excess fluoride from drinking water by activated alumina. By use of these methods the fluoride removal capacity of alumina was increased by a factor of five.

Under the national Interim Primary Drinking Water Regulations maximum contaminant levels (MCL) in potable water supplies have been established for ten inorganic chemicals, including fluoride. The MCL for fluoride varies from 1.4 to 2.4 mg/L depending upon the annual average of the maximum daily air temperatures (Table 1). If the prescribed maximum level is to be enforced, its achievement must be technically and economically feasible.

Since it became known that excess fluoride in drinking water caused mot- tled teeth in children,1 many methods of removing fluoride have been developed. One of them employs activated alumina to defluoridate water supplies. Although many investigators have found that activated alumina is quite effective in reduc- ing fluoride to very low levels in treated water, there is an abundance of confu- sion as to the useful capacity of activated alumina.

Churchill,2 in his 1936 patent on the use of activated alumina for fluoride removal, states that a pH of 5 to 6.5 should be used during treatment for best results. There is no stated capacity in his patent. E.A. Savinelli and A.R. Black,3 in their 1958 bench experiments, showed that a capacity of 7800 g/m3 (3400 grains/ cu ft) was achieved when treated water pH was 5.6. Their studies were made with tap water to which sodium fluoride had been added. Yeun C. Wu,4 in a recent article, again shows that treatment pH is quite important for high removal capaci-

ties. He reports maximum removals of 9600 g/m3 (4200 grains/cu ft) with treatment at pH 5 on pure sodium fluoride solutions. Other investigators510 who have made bench, pilot, or commercial installation studies report much lower capacities because they have not under- stood or chosen to operate at optimum pH conditions.

Two plants that have had several years of low-cost experience in producing waters with fluoride concentrations re- duced to acceptable levels are the Lake Tamarisk plant at Desert Center, Calif., with nine years of operation, and the Rincón Water Co. plant at Vail, Ariz., with six years of operation. A third plant began operation in Gila Bend, Ariz., in May 1978. By paying close attention to pH control, the three plants are able to operate routinely with removal capacities exceeding 4600 g/m3 (2000 grains/cu ft). Removal capacities exceeding 7000 g/m3 (3200 grains/cu ft) were observed during the pilot work done at Gila Bend, Ariz., to confirm that the developed operating practices would work on that water supply.

Development work with pilot-plant equipment on a continuing basis has perfected the water treatment and alumina regeneration processes at each of these locations. This article outlines the operating practices developed for removing fluoride to acceptable levels.

Fluoride Removal Technology This article is based on pilot-plant

experiments and plant data for which granular activated alumina* (mesh size 28 to 48) was used.

The basic principles of fluoride removal technology are

1. Optimizing the environment for sorbing of fluoride ions to activated alumina surfaces

2. Preventing competing ions from occupying alumina surfaces that should be reserved for fluoride ions

3. Upon regeneration of an expended treatment bed, taking all steps necessary to remove all fluoride ions from the bed before returning it to treatment.

There are also many "common sense" principles that apply to the process which, though important, are not as crit- ical as the three listed.

There are four modes of operation: treatment, backwash, regeneration, and neutralization. Operating details for each mode are discussed here.

Treatment mode for virgin or regenerated treatment bed. The optimum environment for fluoride removal exists when raw water pH is adjusted to 5.0-6.0 by sulfuric acid injection. Because acid feed rates are a function of the raw water alkalinity, they vary from one water to another. The best results obtained to date have occurred when the raw water pH has been held carefully at 5.5. In this environment the attraction of the fluoride ion to the activated alumina surface is most favorable and interference by competing ions is minimal. Adsorption is the most probable mechanism for fluoride ion removal from water, but because work in this area is still in progress, discussion of mechanism is premature. In applications

*F-1, Alcoa, Pittsburgh, Pa.

JANUARY 1979 F. RUBEL JR. & R.D. WOOSLEY 45



TABLE 1 Maximum Contaminant Levels For Fluoride

Average Maximum Daily Temperature Fluoride 1

Level °F °C mg/L

<12.0 <53.7 2.4 12.1-14.6 53.8-58.3 2.2 14.7-17.6 58.4-63.8 2.0 17.7-21.4 63.9-70.6 1.8 21.5-26.2 70.7-79.2 1.6 26.3-32.5 79.3-90.5 1.4

TABLE 2 Water Analyses At Existing Operations

Facility

Lake Rincón Town of Parameter Tamarisk Water Co. Gila Bend

Ca-mg/L 11 51 31 Mg-mg/L 0.5 5.8 <1 Na-mg/L 58 151 396 SO.-mg/L 40 261 160 Cl-mg/L 67 22 540 Hardness (as

CaCOJ-mg/L 30 152 78 Total alkalinity (as

CaCO,)-mg/L, 77 171 30 Phenolphthalein alkalin-

ity (as CaCO,)-mg/L, 0 0 2 Fe-mg/L 0.2 <0.05 0.2 SiO2-mg/L 22 55 21 F-mg/L 7.5 4.5 6.0 Total dissolved sol-

ids-mg/L 409 650 1121 pH 7.9 7.5 8.3

13 m - |

8

' Treatment Bed: 11 щЗ 380 cu ft Activated Alumina. 28-48 Mesh 11 - j' Raw Water: 6 mg/L F, pH 8.3

l' Usable Water: 14 050 m3 3.72 mil gal' With Average F- Concentration of 10 mg/L

10 - I ' ~ 6

I 7 _ I ^S^reated Water pH - 4 ^

Raw Water pH ТД. ' 8

2 - ^^^ Treated Water F Content ф^^ -

^•- ^ ' -^ Ш^*^ , I I I I I ̂ ^T+^-f- ^ - t- -^ I I I I I I I U о

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Water Flow Through Treatment Bed- ЮЗтЗ

Fig. 1. Typical Operational Run at Gila Bend, Ariz.

to date, treatment bed capacities consis- tently have exceeded 4600 g/m3 (2000 grains/cu ft), and some runs have exceeded 9200 g/m3 (4000 grains/cu ft).

As raw water pH moves above 6.0 or below 5.0, fluoride removal capacity deteriorates at an increasing rate. For example, from previous experiments it has been shown that at pH 7.0 bed capacity is about 1100 g/m3 (500 grains/cu ft). Though efficiency might appear to be the same, breakthrough occurs earlier and treatment runs are shorter. Fluoride removal efficiency at optimal pH ap- proaches 100 percent, as indicated by treated water fluoride concentration well below 0.1 mg/L during portions of the treatment run at each installation. This efficiency is achieved in waters with different chemistries including varying fluoride levels (Table 2). Superfi- cial residence time (flow time through the bed neglecting the volume of bed material) is also a limiting factor; a 5-min minimum is a practical limit for maximum removal efficiency. Best results occur with flow directed down through the bed. Care must be taken to prevent a wall effect or channeling.

The initial effluent pH is high, with no fluoride removal, as explained in the discussion on neutralization mode. After a short period both pH level and residual fluoride drop to acceptable levels. At that point usable water can be directed to storage or distribution. Fluoride level

drops rapidly to a very low level and remains there until breakthrough begins, at which point it increases gradually until the treatment run is terminated.

Treated water pH drops below 6. Because water of this pH is corrosive, the treated water pH must be adjusted to a desirable level (about 7.5) by injection of sodium hydroxide or by blending.

Backwash mode. For two reasons it is important that the bed be backwashed with raw water before each regeneration: first, any suspended solids that have been filtered from the raw water by the treatment bed tend to blind the bed and must be removed; second, even though filtration may not have taken place, the downward flow tends to pack the bed. Therefore, an upflow backwash expands the bed, breaking up any tendency toward wall effects or channeling. A backwash rate of 5-6 mm/s will expand the bed about 50 percent, which is adequate. Care must be taken to avoid backwashing granular bed material out of the treatment unit. Normally, backwash is completed within 10 min.

Regeneration mode. The object of regeneration is the removal of all fluoride ions from the bed before any part of the bed is returned to the treatment mode. The most successful regeneration is accomplished in two steps: the first is upflow immediately after backwash while the bed is still expanded, followed by an upflow rinse. The unit is then drained to

the top of the treatment bed. The second regeneration step is downflow immediately followed by the neutralization mode. Regeneration steps employ 1 percent (by weight) sodium hydroxide solution flowing at a rate of 1.7 mm/s. With a standard treatment bed depth of 1.5 m, each regeneration step takes 35 min. Chemical consumption in each regeneration step is 27 L of 50 percent NaOH per cubic metre of treatment media (0.2 gal/cu ft). The intermediate upflow rinse flows at a rate of 3.4 mm/s for a period of 30 min. If the treatment bed depth varies from standard, flow rates and times must be adjusted. The régénérant solution is usually an in-line dilution of 50 percent sodium hydroxide with raw water, with the sodium hydroxide maintained at or above 21° С to prevent freezing.

Neutralization mode. The object of this step is to return the bed to the treatment mode as rapidly as possible without dissolving the treatment media. As soon as the second (downflow) regeneration step has been completed, all of the fluoride should have been removed from the bed. At this point the bed is drained again to the top of the treatment media. Raw water with pH adjusted to 2.5 is then fed downflow at the normal treatment flow rate (Fig. 1). Sulfuric acid concentrations again vary with the alkalinity of the specific raw water. The entire bed has a pH range from 12.5 to 13.0, and as the top of the bed begins to

46 WATER TECHNOLOGY/QUALITY JOURNAL AWWA



TABLE 3 Operating Costs At Existing Treatment

Plants

Location

Lake Rincón Tamarisk Water Co. Gila Bend c/ c/ c/ c/ c/ c/

1000 1000 1000 1000 1000 1000 Item L да] L gai L ga/

Treatment chemicals 2.2 8.3 1.3 5.1 1.0 3.7 Operating labor 1.3 5.0 1.1 4.1 1.6 6.0 Electric utility 0.1 0.5 0.1 0.4 0.1 0.6 Media replacement 0.2 0.7 - - - -

Spare parts & misc. 0.1 0.3 0.2 0.8 0.2 0.8 Total 3.9 14.8 2.7 10.4 2.9 11.1

Pilot-Plant Equipment in Use at Gila Bend, Arii

Aerial View of Rincón Water Co. Treatment Plant, Vail, Ariz.

neutralize and enter a treatment mode, the fluoride level in the treated water starts to drop below that of the raw water. Treated water pH also begins to drop. As the fluoride level drops below the mandatory limit, the water becomes usable and can be directed to storage or distribution. pH may still be high (9.0-9.5) in the treated water; however, this water can be blended with treated water of lower pH from other treatment units. When the pH is 9.0 to 9.5, the raw water pH is adjusted to 4.0 as the bed rapidly neutralizes. When the treated water pH drops to 7.5, the raw water pH is adjusted to 5.5, where it is maintained throughout the remainder of the run.

Initial Start-Up Procedures When the bed material is first placed

into the treatment unit, the vessel should be half filled with water. As the activated alumina is poured into the bed from above, the water dissipates the heat generated by the heat of wetting of the activated alumina, thereby preventing cementing of the bed. The water also aids in separating fines from the granular material; protects the underdrain assem- bly from impact; and initiates stratifica- tion of bed material. Once the bed is in place, it must be backwashed for an extended period until all of the alumina fines are flushed from the virgin bed. The flow is then reversed and downflow treatment begins for the virgin run.

Blending of Treated Water Blending can take place in either large

reservoirs or the treated water main. During a treatment run there is a long period when the fluoride level of the treated water is well below desired levels. As breakthrough occurs there is a long period of slowly increasing fluoride concentration in the treated water. It has been found that treated water can continue to flow to storage or distribution until the fluoride concentration reaches one and one half to two times the maximum allowable level; the resulting total average fluoride level continues to meet the prescribed fluoride level (one half the maximum allowable level).

When there is a large reservoir in which the major portion of a treatment run can be stored, blending takes place there. At locations where the reservoir is not large and there are two or more treatment units, staggered regenerations accomplish the same result; that is, a regenerated treatment unit will produce water of very low fluoride content while a second unit in the later stages of its treatment run may be producing water of a higher fluoride level. By mixing the effluent from the two units in the treated water main, an average fluoride concentration near the prescribed level can be maintained. Similarly, the treated water of high pH occurring early in the run for one unit can be blended with the low pH effluent of another unit in a later stage.

The benefit of this blending is short- lived; soon the pH of the blended streams requires adjustment.

Disposal of Wastewater The wastewaters resulting from back-

wash, regeneration, and the early part of neutralization are not suitable for consumption and must be discarded. The backwash water, which is only raw water, can be discharged to existing storm water disposal systems. The only objectionable feature of the regeneration waste is the high concentration of fluoride ions that cannot be returned to the groundwater aquifer. Its high pH can be neutralized. Disposal of waste of high fluoride concentration must comply with local wastewater discharge standards, which vary. Existing plants concentrate the waste in lined evaporation ponds; eventually the concentrated waste must be transferred to an acceptable disposal site or the fluoride must be reclaimed.

The volume of wastewater is approxi- mately 4 percent of the total throughput. Materials of Construction

The cost of a treatment plant is a function of the quality of the construction materials in its design. Trouble-free, low-cost plant operation can be achieved only by proper selection of materials to meet the service requirements of the process. Without considering the materials for concentrated acid and caustic

JANUARY 1979 F. RUBEL JR. & R.D. WOOSLEY 47



Treatment Units at Gila Bend, Ariz. Treatment Plant at Gila Bend, Ariz.

Lake Tamarisk Treatment Plant at Desert Center, Calif. Rincón Treatment Unit: Acid Line in Foreground

systems, treatment system materials must be suitable for service under the following conditions: (1) potable water system; (2) ambient temperatures (provi- sion for thermal expansion); (3) exposure to sunlight (or protected); (4) pH 2-13; and (5) ease of maintenance (remove and replace with minimum logistics). Materi- als for the chemical storage and handling systems should comply with chemical manufacturers' guidelines.

Operator Requirements A qualified operator for a fluoride

removal water treatment plant requires

thorough fluoride removal process train- ing, preferably at an existing treatment plant. The operator must be able to service pumps, piping systems, instru- mentation, and electrical accessories. The operator must be totally informed about the characteristics of sulfuric acid in all concentrations and sodium hydroxide in all concentrations. Safety requirements as to clothing, equipment, and antidotes must be thoroughly under- stood and executed. The operator must be trained to run routine water analyses including at least two methods for determining fluoride levels. He needs simple

mathematics for record keeping during a treatment run and for operation cost accounting. Above all, the operator must be dependable and conscientious.

Cost of Operation The cost of operating an alumina fluo-

ride removal system including chemicals, electricity, bed replacement, replacement parts, and labor currently falls in the range of 2-5c/kL (8-20С/Ю00 gal) of treated water. Individual plant operating costs vary as functions of raw water fluoride level, plant capacity, treated water consumption, electric utili-

48 WATER TECHNOLOGY/QUALITY JOURNAL AWWA



ty rate, labor costs, delivered chemical costs, and so forth. The low operating costs at the three operational plants discussed in this article are shown in Table 3. The 1977-78 materials and construction costs for the plant at Gila Bend were less than $200 000. The plant was designed for 2.8 X 103-mVday (0.75- mgd) average production with peak capacity of 4.8 X 103m Vday (1.3 mgd). Conclusion

Low operating costs for removing fluoride from potable water can be achieved with an activated alumina system. Reliability of plant equipment, materials, and operational costs have been docu- mented through nine years of commercial field experience. Installation and operating costs are compatible with limited

public budgets and funding programs. All materials and equipment are available, and there is existing technology to assist in designing a plant to meet fluoride MCLs.

References 1. Dean, L.T.; Arnold, F.A. Jr.; & Elvove, E.

Domestic Water and Dental Caries. Pub. Health Rep. 57:1155 (1942).

2. Churchill, H.V. US Patent 2,059,553 (Nov. 3, 1936).

3. Savinelli, E.A. & Black, A.P. Defluorida- tion of Water with Activated Alumina. Jour. AWWA, 50:33 (1958).

4. Wu, Yeun C. Activated Alumina Removes Fluoride Ions from Water. Wtr. Er Sewage Works, 125:6:76 (Jun. 78).

5. Boruff, C.S. Removal of Fluorides from Drinking Waters. IEC, 26:69 (1934).

6. Goetz, P.C. US Patent 2,179,227 (Dec. 6,

1938). 7. Maier, F.J. Defluoridation of Municipal

Water Supplies. Jour. AWWA, 45:879 (1953).

8. Swope, H.G. & Hess, R.H. Removal of Fluorides from Natural Waters by De- fluorite. JEC, 29:424 (1937).

9. Zabban, Walter & Helrick, R. Defluori- dation of Waste Water. Proc. 30th Ann. Purdue Industr. Waste Conf. (1975).

10. Zabban, Walter & Jewett, N.W. The Treatment of Fluoride Wastes. Proc. 22nd Ann. Purdue Industr. Waste Conf., Engrs. Bull. No. 129 (1967).

An article contributed to and selected by the Journal, authored by Frederick Rubel Jr., consult, engr., Rubel and Hager, Inc., Tucson, Ariz., and R. Dale Woosley, sr. scientist, Aluminum Co. of America, St. Louis, Mo.

75383 4260

Methods for Disinfecting Tanks and Reservoirs

Committee Report Standard D1 02-64, for the Painting and Repainting of Steel Tanks, contained a section on "Disinfection Methods for Tanks and Reservoirs." When this standard V/as revised in 1978, the Standards Council and the Standards Committee for Steel Tanks decided that the disinfection methods should be contained in a separate standard and expanded to include disinfection practices for use on tanks constructed of all types of material, including concrete and fiberglass, as well as coated steel tanks. This new standard was to be published at the same time as the revised edition of D102. The work on D1 02-78 was completed and approved by the AWWA Board of Directors in 1978, but delays occurred in the development of the new standard on Disinfection of Tanks.

It now appears that the new standard will not be published before the end of 1979, and, therefore, three recommended methods of tank disinfection are listed below to give some guidance until D1 04-79 becomes available. Notice of the availability of D1 04-79, Standard for the Disinfection of Tanks, will appear in the Journal AWWA at the appropriate time.

General Information All new tanks and reservoirs should

be disinfected before they are placed in service. All tanks and reservoirs taken out of service for painting, repairing, cleaning, or any other activity which may contaminate the water, should be disinfected before they are returned to service.

Cleaning The walls and bottoms of all tanks

should be cleaned prior to disinfection to remove all dirt and loose material. If water, under pressure, is available, cleaning may be accomplished by a jet of water from a hose nozzle. Otherwise, these surfaces should be cleaned by thorough sweeping or scrubbing. Care should be taken to remove any scaffold- ing, planks, tools, rags, or any other material not a part of the structure.

Because wood will support growths of coliform bacteria, any submerged wooden surface (columns, baffles, lad- ders, etc.) should be coated with approved epoxy or other equally imper- meable paint. (See Jones & Greenberg. JAWWA 56:11:489, November 1964) Selection of Method

Three methods are given. The first method is wasteful of chemicals and requires the disposal of water containing a high chlorine residual equal to the volume of the reservoir. This may not be feasible in many instances. The second method is usually satisfactory, but cannot be used in inflatable reservoirs or those with floating covers. The third method does not expose the upper surface of the walls to a strong chlorine solution and should be used only where other methods cannot be used.

First method. The tank shall be filled to the overflow level with potable water, to which enough chlorine has been added to produce a concentration of 50 mg/L in the full tank.* The chlorine, either as high-test calcium hypochlorite, sodium hypochlorite, or liquid chlorine, shall be introduced into the water as early during the filling operation as possible. A simple and effective method of adding the disinfec- tant is to pour it through the cleanout or inspection manhole in the lower course of a standpipe shell, or in the base of the riser pipe of an elevated tank. The inspection manhole cover should then be bolted into place and the filling of the tank started. If liquid chlorine is used, a special tap may be provided in the cleanout manhole cover and the gas- water mixture pumped into the tank as the filling is started. Filling the tank will provide a thorough mix of the chlorine with the water and assure contact with all surfaces for disinfection. If no bottom manhole is available, the chlorine powder or chlorine and water mixture shall be scattered over the water surface in the partly filled tank, working from the roof manhole. After the tank has been filled to overflow level, it shall stand full for 24 hr, if

*It will normally require 41.5 lb of liquid chlorine (supplied under pressure in steel containers) to produce a concentration of 55 ppm in 100 000 gal of water. If high-test hypochlorites (powder containing 70 percent available chlorine) are used, it will require 60 lb of powder to produce the same concentration in the same amount of water.

JANUARY 1979 0003-1 50X/79/010049-02$01 .00 COMMITTEE REPORT 49 ©1979 American Water Works Association



filtration || the removal of excess fluoride from drinking water by activated alumina

Documents