Investigation of Defluoridation Options for Rural and

Research Report 41

Investigation of Defluoridation Options for Rural and Remote Communities

Research Report 41

Investigation of Defluoridation Options for Rural and Remote Communities

Amy Dysart

Power Water Corporation

Research Report No 41

INVESTIGATION OF DEFLUORIDATION OPTIONS FOR RURAL AND REMOTE COMMUNITIES

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© CRC for Water Quality and Treatment 2008

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Cooperative Research Centre for Water Quality and Treatment Private Mail Bag 3 Salisbury SA 5108 AUSTRALIA Telephone: +61 8 8259 0351 Fax: +61 8 8259 0228 E-mail: [email protected] Web site: www.waterquality.crc.org.au Investigation of Defluoridation Options for Rural and Remote Communities Research Report 41 ISBN 18766 16679

CRC FOR WATER QUALITY AND TREATMENT – RESEARCH REPORT 41

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FOREWORD

Research Report Title: Investigation of Defluoridation Options for Rural and Remote Communities Research Officers: Amy Dysart Research Nodes: Power Water Corporation CRC for Water Quality and Treatment Project No. 3.3.0.8 – Investigation of the Defluoridation of Water Supplies in Rural and Remote Communities


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ABSTRACT

Fluoride primarily produces effects on skeletal tissues (bones and teeth) and has a narrow range between intakes that cause beneficial and detrimental health effects. Elevated levels of fluoride (>1.5 mg/L) in the drinking water occur in a number of parts of the world and often have significant adverse impacts on public health. In the Northern Territory elevated levels occur in a limited number of groundwater supplies, resulting in an increase in the prevalence of dental fluorosis in the affected population.

The investigation focused on the identification of a cost effective, robust and low maintenance defluoridation system that may be implemented in these rural and remote communities. Batch adsorption experiments utilising activated alumina, bauxite and hydrotalcite were carried out, resulting in the successful removal of fluoride from natural water samples. Activated alumina displayed the highest removal rate, greatest capacity for fluoride and the smallest impact on the other water quality characteristics, of the three media and was utilised for further equilibrium isotherms and column studies.

Activated alumina equilibrium isotherms were correlated to the Langmuir and Freundlich equations indicating appropriate levels of fluoride adsorption from natural waters could be achieved. Water from two communities in the Northern Territory, Tennant Creek and Ali Curung, was successfully treated through column studies, achieving adsorption capacities for fluoride of 875 mg/kg and 1268 mg/kg respectively. The regeneration (and reactivation) of the column was carried out using 0.1 M NaOH and 0.1 M HCl, which resulted in a decrease in adsorption capacity of the activated alumina with each regeneration.


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TABLE OF CONTENTS

Foreward................................................................................................................................................. 3

Abstract .................................................................................................................................................. 4

1 Introduction......................................................................................................................................... 9 1.1 Fluoride .......................................................................................................................................... 9

1.1.1 Environmental Occurrence...................................................................................................... 9 1.1.2 Distribution and Exposure ....................................................................................................... 9 1.1.3 Human Health Effects ........................................................................................................... 10 1.1.4 Drinking Water Levels ........................................................................................................... 11 1.1.5 Guidelines and Standards in Drinking Water ........................................................................ 14

1.2 Defluoridation Techniques ........................................................................................................... 14 1.2.1 Advanced Treatment Technologies ...................................................................................... 15 1.2.2 Chemical Treatment .............................................................................................................. 15 1.2.3 Sorption Media ...................................................................................................................... 16

1.3 Evaluation and Selection of Technique ....................................................................................... 21 1.3.1 Northern Territory Situation................................................................................................... 22

1.4 Objectives of the Research.......................................................................................................... 27 1.4.1 Specific Objectives ................................................................................................................ 27

2 Methods ............................................................................................................................................. 28 2.1 Media Preparation and Supplier .................................................................................................. 28

2.1.1 Activated Alumina.................................................................................................................. 28 2.1.2 Bauxite................................................................................................................................... 28 2.1.3 Hydrotalcite ........................................................................................................................... 28

2.2 Batch Adsorption Experiments..................................................................................................... 28 2.2.1 Procedure.............................................................................................................................. 28

2.3 Equilibrium Isotherms (Batch)...................................................................................................... 29 2.3.1 Procedure.............................................................................................................................. 29

2.4 Column Studies............................................................................................................................ 30 2.4.1 Procedure.............................................................................................................................. 30 2.4.2 Regeneration (and Reactivation) .......................................................................................... 31

3 Results and discussion ................................................................................................................... 32 3.1 Batch Adsorption Experiments..................................................................................................... 32

3.1.1 Activated Alumina (A-2 and CPN)......................................................................................... 32 3.1.2 Bauxite................................................................................................................................... 33 3.1.3 Hydrotalcite ........................................................................................................................... 34 3.1.4 Water Quality Analysis .......................................................................................................... 34 3.1.5 Assessment of media ............................................................................................................ 38

3.2 Equilibrium Isotherms (batch) ...................................................................................................... 39 3.2.1 Activated Alumina (A-2 and CPN)......................................................................................... 39 3.2.2 Langmuir Isotherm ................................................................................................................ 41 3.2.3 Freundlich Isotherm............................................................................................................... 41 3.2.4 Isotherm interpretation (A-2 and CPN).................................................................................. 42

3.3 Column Studies............................................................................................................................ 44 3.3.1 Column System ..................................................................................................................... 44


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3.3.2 Media Replacement .............................................................................................................. 45 3.3.3 Regeneration (and Reactivation) .......................................................................................... 46

3.4 Pilot Plant ..................................................................................................................................... 47

4 Conclusion ........................................................................................................................................ 48

5 References ........................................................................................................................................ 49

6 Appendices ....................................................................................................................................... 54 Appendix A: Northern Territory Community Water Quality Characteristics ....................................... 54 Appendix B: Fluorosis Data - Tennant Creek Children 2001/2002.................................................... 55 Appendix C: Media specifications Activated Alumina and Bauxite.................................................... 58 Appendix D: Results of Batch Adsoption Experiments ...................................................................... 59 Appendix E: Water Quality Analysis from batch adsorption experiments.......................................... 62 Appendix F: Adsorption Isotherms Data ............................................................................................ 65 Appendix G: Column Studies Data .................................................................................................... 68


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LIST OF FIGURES

Figure 1 Naturally elevated fluoride levels identified in Northern Territory water supplies managed by Power and Water (Power and Water Corporation 2002)..................................................................................... 13

Figure 2 Illustration describing the structural state transformation upon calcination and rehydration of layered double hydroxide compound showing its structural memory effect (Wong and Buchheit 2004). ............ 19

Figure 3 Decision process for appropriate action in relation to elevated concentrations of fluoride in water sources. .................................................................................................................................................... 22

Figure 4 Australia classified according to the Remoteness area (ABS 2001)................................................ 23

Figure 5 Typical batch adsorption experiments conducted in conical flasks (500 mL) with 20 g/L of adsorbent, with 500 mL of the three water samples (Spiked RO, Tennant Creek and Ali Curung), at ambient temperature and with constant stirring. ...................................................................................... 29

Figure 6 Typical equilibrium isotherms experiments conducted in conical flasks (500 mL) with known amounts of AA, with 500 mL of the three water samples (Spiked RO, Tennant Creek and Ali Curung), at ambient temperature and with constant stirring. ...................................................................................... 29

Figure 7 Schematic diagram of the AA experimental design of the column studies ...................................... 30

Figure 8 Experimental activated alumina column (PVC column on RHS) utilised for column studies........... 30

Figure 9 Adsorption studies of Activated Alumina (a) A-2 (b) CPN, using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data)................................................................................................................................................. 32

Figure 10 Adsorption studies of bauxite using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data). ....... 33

Figure 11 Adsorption studies of hydrotalcite using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data). ....... 34

Figure 12 Chloride concentrations, prior to batch adsorption experiments (initial) and the treated water (final), with 2mg/L F- spiked RO water (a) natural water samples from Tennant Creek 1.4 mg/L F- (b) and Ali Curung 2.4 mg/L F- (c) (Appendix E)................................................................................................... 36

Figure 13 Adsorption studies with Activated Alumina A-2 and CPN, Spiked RO at 2 mg/L fluoride at pH 6.1(a,d) Tennant Creek at 1.4 mg/L fluoride at pH 7.3 (b,e) and Ali Curung 2.5 mg/L fluoride at pH 7.5 (c,f) at ambient temperature 23+/- 1°C (Average n=2 see Appendix F for data). .................................... 40

Figure 14 Langmuir plot for Activated Alumina A-2 (a) and CPN (b) and Freundlich plot for A-2 (c) and CPN (d) (Appendix F)........................................................................................................................................ 42

Figure 15 Experimental breakthrough curve from treatment with the Tennant Creek water (a) and Ali Curung water (b) (Appendix G). ............................................................................................................................ 45

Figure 16 The fluoride removed during CPN AA column studies with treatment of the Ali Curung water following regeneration of the media (Appendix G). .................................................................................. 46


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LIST OF TABLES

Table 1 Typical fluoride concentrations in natural water sources (Fawell et. al. 2006; IPCS 2002; WHO 2004b) ...................................................................................................................................................... 10

Table 2 Typical fluoride concentrations in drinking water and the associated health effects (Fawell et al. 2006; IPCS 2002; WHO 2004b) ............................................................................................................... 11

Table 3 Fluoridation of Public Water Supplies Regulation 1998 recommended fluoridation levels (Queensland 1999)................................................................................................................................... 12

Table 4 Summary of reported fluoride levels in a number of countries (Fawell et al. 2006)........................... 12

Table 5 Guidelines and standards for fluoride levels in drinking water........................................................... 14

Table 6 Summary of high-risk fluoride levels in communities managed by Power and Water (Power and Water Corporation 2002).......................................................................................................................... 24

Table 7 Summary of the prevalence of fluorosis in children residing in Tennant Creek (TC) in 2001/2002 (Appendix B)............................................................................................................................................. 24

Table 8 Summary of the defluoridation techniques and their application to the remote communities in the Northern Territory ..................................................................................................................................... 25

Table 9 Physical water quality analysis at the completion of the batch adsorption experiments using Activated Alumina (AA) Bauxite and Hydrotalcite to remove fluoride from spiked RO water 2 mg/L F- and natural water samples from Tennant Creek 1.4 mg/L F- and Ali Curung 2.4 mg/L F- (Appendix E). ....... 35

Table 10 Concentration of metals (mg/L) influenced during the batch adsorption experiments using Activated Alumina (AA), Bauxite and Hydrotalcite to remove fluoride from spiked RO water 2 mg/L F- and natural water samples from Tennant Creek 1.4 mg/L F- and Ali Curung 2.4 mg/L F- (Appendix E). ................... 37

Table 11 Results from the Langmuir and Freundlich equilibrium isotherms for A-2 and CPN (Appendix F). 43

Table 12 Summary of batch Langmuir and Freundlich equilibrium isotherm data for previous investigations (Ghorai and Pant 2004; Ghorai and Pant 2005; Pietrelli 2005). .............................................................. 43

Table 13 Advantages and Disadvantages of AA column systems with either regeneration or media replacement (Rubel 2003)........................................................................................................................ 45


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1 INTRODUCTION

1.1 Fluoride

Fluoride is one of the very few chemicals for which significant health effects have been correlated to exposure through drinking water. At low concentrations in drinking water, fluoride has beneficial effects on teeth, but excessive exposure to fluoride in drinking water, or in combination with fluoride from other sources can give rise to a number of adverse effects (Fawell et al. 2006). Elevated levels of fluoride in drinking water occur in a number of parts of the world and these often have significant adverse impacts on public health. As a result, a number of technological solutions to remove fluoride have been proposed, tested and proven.

1.1.1 Environmental Occurrence

Fluorine (F) is the lightest member of the halogen group and is the most reactive of all chemical elements. Consequently, fluorine does not occur in the elemental state in the environment and instead acquires a negative charge to form fluoride (Fawell et al. 2006). Fluoride is common in the environment, accounting for about 300 mg/kg of the Earth’s crust, principally in the form of fluorite and fluorapatite and is naturally released into the environment through the weathering and dissolution of minerals, emissions from volcanoes and in marine aerosols. Anthropogenic sources of fluoride include coal combustion, process water and waste from various industrial processes, including steel manufacture, primary aluminium, copper and nickel production, phosphate ore processing, phosphate fertiliser production and use, glass, brick and ceramic manufacturing, and glue and adhesive production. The use of fluoride-containing pesticides and the controlled fluoridation of drinking-water supplies also contribute to the release of fluoride into the environment (IPCS 2002).

1.1.2 Distribution and Exposure

1.1.2.1 Air

The distribution of fluoride in the atmosphere is principally due to dust, industrial production of fertilisers, coal ash from the burning of coal and volcanic activity (Fawell et. al. 2006). In non-industrial areas, the mean concentrations of fluoride in ambient air are typically quite low (<1 µg/m3), although the levels may be slightly higher in urban (2 – 3 µg/m3) than rural locations. In areas in the direct vicinity of emission sources, reported fluoride concentrations are higher (>6 µg/m3) leading to increased exposure through the inhalation route (IPCS 2002). However, air is typically responsible for only a small fraction of total fluoride exposure (Fawell et al. 2006).

1.1.2.2 Food

Virtually all foodstuffs contain at least trace amounts of fluoride (IPCS 2002). Vegetables and fruits normally have low levels of fluoride (0.1 - 0.4 g/kg) although higher levels (2 mg/kg) have been reported in certain field grown vegetables, particularly rice and barley. In general, the levels of fluoride in meat (0.2 - 1.0 mg/kg) and fish (2 - 5 mg/kg) are relatively low, although certain types of fish contain protein concentrates with high levels (up to 370 mg/kg). Tea leaves contain high levels of fluoride (up to 400 mg/kg dry weight) although fluoride exposure due to ingestion of tea ranges from 0.04 - 2.7 mg per person (Fawell et al. 2006).

1.1.2.3 Dental Products

A number of dental products, used to reduce dental decay, contain fluoride, including toothpaste (1 - 1.5 g/kg), fluoride solutions and gels for topical treatment (0.25 - 24.0 g/kg), and fluoride tablets (0.25, 0.50 or 1.00 mg/tablet). The contribution of these sources to the total fluoride exposure varies, although the swallowing of toothpaste by some children has been estimated to contribute 0.50-0.75 mg per child per day (Fawell et al. 2006).

1.1.2.4 Water

All natural water systems contain some concentration of fluoride (Fawell et al. 2006). Seawater contains relatively consistent fluoride concentrations (1.2 - 1.5 mg/L), while the amount of fluoride naturally occurring in freshwater is highly variable, depending upon the geological environment of the source (Benefield et al.


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1982; IPCS 2002). Generally, surface water has relatively low fluoride concentrations (<0.5 mg/L), whereas fluoride concentrations in groundwater can vary significantly (0 - 50 mg/L) (Table 1). However, extremely high fluoride concentrations (2,800 mg/L) have been documented in the lakes associated with volcanic activity along the East African Rift system (Fawell et al. 2006).

Table 1 Typical fluoride concentrations in natural water sources (Fawell et. al. 2006; IPCS 2002; WHO 2004b)

Water source Fluoride concentration (mg/L) Seawater 1.2 – 1.5 Surface water (rivers) < 0.5 Groundwater 0.0 – 50.0

Typically, drinking water is the largest single contributor to daily fluoride intake; however, this can vary greatly between locations and individuals, depending on the fluoride level in the drinking water and daily water consumption (Fawell et al. 2006; IPCS 2002).

1.1.2.5 Total Fluoride Exposure

Although for adults, the individual exposure to fluoride is likely to be highly variable, the inhalation of airborne fluoride generally contributes a minor amount to the total intake and the consumption of food and drinking water are the principal routes of exposure (IPCS 2002). The estimate of total daily fluoride exposure in temperate climates is approximately 0.6 mg/adult/day in areas that do not contain fluoride in the drinking water and 2 mg/adult/day in fluoridated areas. However, this may be significantly higher for children, from the use of dental products and for all individuals because of the environment, such as the consumption of water and food (Fawell et al. 2006).

1.1.3 Human Health Effects

Fluoride is yet to be explicitly demonstrated as an essential element for humans and there is no data indicating the minimum nutritional requirement of the element (WHO 2004b). Nevertheless, it has been well established that fluoride primarily produces effects on skeletal tissues and has a narrow range between intakes that cause beneficial and detrimental health effects (Fawell et al. 2006; Rao 2003; WHO 2004b).

1.1.3.1 Fluoride Metabolism

Predominantly, ingested fluoride is absorbed from the stomach and the intestine, the mechanism and the rate of gastric absorption relates to gastric acidity. Acidity of the stomach converts fluoride into hydrogen fluoride (HF) for adsorption, which can markedly decrease with high concentrations of cations that form insoluble complexes with fluoride, including calcium, magnesium and aluminium. Once absorbed in the blood, fluoride readily distributes throughout the body, with approximately 99% of the fluoride retained in the calcium rich areas of the bone and teeth. The selective affinity of fluoride for these mineralised tissues is initially due to uptake on the surface of the bone crystallites. In the long term, fluoride is incorporated into the crystal lattice structure of teeth and skeletal tissue by replacing some hydroxyl ions within the unit cells of hydroxyapatite, producing partially fluoridated hydroxyapatite. A higher portion of the ingested fluoride is absorbed into the growth phase of the skeleton and therefore infants and children retain a higher percent of the absorbed fluoride than adults. Fluoride is primarily excreted via the urine, where the urinary fluoride clearance increases with urine pH, due to an increase in the HF concentration (Fawell et al. 2006; IPCS 2002).

1.1.3.2 Teeth and Skeletal Tissues

The regular consumption of drinking water with low levels of fluoride (0 - 0.3 mg/L) during childhood is linked with the occurrence of preventable dental caries in latter years (Fawell et al. 2006; Ncube and Schutte 2005). The consumption of drinking water containing ‘optimal’ amounts of fluoride (0.3 - 1.2 mg/L) has beneficial effects on the teeth by hardening enamel and reducing the incidence of caries (Fawell et al. 2006; HDR Engineering 2001; WHO 2004b). This has led to the worldwide fluoridation of water supplies with ‘optimal’ amounts of fluoride as a pubic health measure aimed at reducing the incidence of dental caries (Fletcher and Smith 2003).


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However, as the fluoride concentration increases (>1.5 mg/L), the benefits are replaced with the negative effects of fluorosis (Table 2). Dental fluorosis is characterised by effects on developing teeth. The effects vary from mildly chalky-white teeth, to marked staining and discolouration, to pitting of the teeth in severe forms. It is caused by the elevated levels of fluoride in or adjacent to the developing enamel and therefore only develops in children (Fawell et al. 2006). The concentration at which dental fluorosis becomes apparent varies between studies, although in general, it does not occur in temperate areas at concentrations below 1.5 - 2.0 mg/L of fluoride in the drinking water. However, in warmer areas, due to the increased consumption of water, and areas where fluoride intake via routes other than drinking water are elevated, dental fluorosis can occur at concentrations in the drinking water below 1.5 mg/L (WHO 2004b).

Table 2 Typical fluoride concentrations in drinking water and the associated health effects (Fawell et al. 2006; IPCS 2002; WHO 2004b)

F- conc. (mg/L) in drinking water Health effect < 0.5 Minimal effect in prevention of dental carries

0.5 - 1.0 Beneficial effect in preventing dental carries 1.5 – 2.5 Dental fluorosis 3.0 – 6.0 Skeletal fluorosis

>10 Crippling fluorosis

The chronic ingestion of excessive fluoride can lead to severe effects on skeletal tissues. The consumption of drinking water with excessive fluoride levels (3 - 6 mg/L) can lead to skeletal fluorosis, characterised by adverse changes in the bone structure (WHO 2004b) although exposure to fluoride through additional sources is also potentially important (Fawell et al. 2006). The consumption of drinking water with even higher fluoride concentrations (10 mg/L) can lead to crippling fluorosis, which causes the hardening and calcifying of the bones (WHO 2004b).

The severity of fluorosis has a definite relationship with the following factors (IPCS 2002):

1. Fluoride concentration in drinking water

2. Period of exposure

3. Climatic factors (temperature)

4. Fluoride exposure from other sources

5. Nutritional status

6. Chemical constituents of drinking water other than fluoride

In addition to these well-documented effects, there are a number of epidemiology studies that attempt to draw links between fluoride in drinking water and other health issues, however, the World Health Organisation concludes that at this stage the data is too limited to make such associations (WHO 2004b).

1.1.4 Drinking Water Levels

Generally, fluoride enrichment of groundwater results from prolonged water - geology interactions making geology an important factor in determining the fluoride concentration of groundwater. Previous studies show that fluoride enrichment of groundwater occurs where the water is contained within bedrock aquifers of alkali granites and metamorphic rocks. More recent, studies have concluded that various factors including geochemistry, residence time, well depth, preferential pathways for the upward movement of deep groundwater, and hydrologic condition of the pathways also control the fluoride level (Kim and Jeong 2005). Fluorine occurs mainly as free fluoride ions in natural waters and fluoride concentrations typically increase where calcium is absent and where the cation exchange of sodium for calcium occurs (Rukah and Alsokhny 2004). Therefore, high fluoride concentrations are mostly associated with calcium-deficient groundwater in areas where fluoride-bearing minerals are common (Fawell et al. 2006).

1.1.4.1 Fluoridation

Water fluoridation is defined as the deliberate adjustment of the fluoride levels of a water supply to maximise the benefits of ‘optimal’ levels of fluoride (Muller et al. 1998). Fluoridation of water supplies that are deficient in natural fluoride has been an accepted practice by water and health authorities since the 1950’s (HDR Engineering 2001). The ‘optimal’ amount of fluoride is specific for the location and reflects factors that


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influence the overall intake of fluoride in the population. Primarily, recommended fluoridation levels decrease with increasing temperature, due to the assumption that there is higher water consumption during warm weather than cool weather (Fawell et al. 2006; NHMRC 2004). The Australian Drinking Water Guidelines (ADWG) recommend the fluoridation of supplies at 0.7 - 1 mg/L, with the lower concentration applying where the climate is hot (NHMRC 2004). The various states and Territories in Australia provide their own specific guidance on the level to fluoridate water supplies, the Territory does not have specific guidance on the fluoridation level and Queensland has been used as an example of the Fluoridation of Public Water Supplies Regulation 1998, which indicates the fluoride levels based on the average maximum air temperature of the community (Table 3).

Table 3 Fluoridation of Public Water Supplies Regulation 1998 recommended fluoridation levels (Queensland 1999)

Average maximum air temp. (ºC) F- conc. (mg/L) in drinking water 32.6 and over 0.5 - 0.6 26.3 – 32.5 0.6 - 0.7 21.5 – 26.2 0.7 - 0.8 17.7 –21.4 0.7 - 0.9

1.1.4.2 International

Groundwaters with high fluoride concentrations occur in many areas of the world including large parts of Africa, China, the Eastern Mediterranean and Southern Asia (India, Sri Lanka) and is a serious problem in developing countries (Table 4). Generally, in the USA and in Central Europe, the fluoride concentration of natural water is at the lower end of the range (Fletcher and Smith 2003).

Table 4 Summary of reported fluoride levels in a number of countries (Fawell et al. 2006) Country Reported F- levels (mg/L) Comments Argentina 0.9 – 18.2 Mean of 3.8 mg/L, only 2.9% below guideline Brazil 0.1 – 3.0 Mostly rural communities Canada 0.1 – 4.3 Isolated communities China 2.0 – 17.0 Mainly arid and semi-arid regions Eritrea 0.2 – 3.7 Around 15,000 at risk of high fluoride level Ethiopia 1.2 – 36.0 High fluoride concentrations clustered in the centre Germany 0.1 – 8.8 Rural regions India 0.2 – 20.0 Estimated 25 million suffering from fluorosis Indonesia 0.1 – 4.2 Associated with local volcanos Japan 0.1 – 1.4 15% indicated fluorosis from exposure 1.1-1.4mg/L Kenya 2.0 – 50.0 60% exceed 1 mg/L Mexico 1.5 – 7.8 Estimated 5 million exposed to elevated fluoride Niger 0.1 – 1.6 Alternative sources has keep levels low Nigeria 0.5 – 4.0 Highest from stream sources Norway 0.02 – 10.0 Increased use of groundwater Pakistan 0.1 – 13.5 Most acceptable levels, except in the North Saudi Arabia 0.5 – 2.8 Mostly rural areas South Africa 0.1 – 57.0 Elevated levels from the geology, Northern communities Spain 0.1 – 4.6 Mainly to the North of the Island Sir Lanka 0.1 – 10.0 Relatively recent with increased use of groundwater Sudan 0.7 – 3.2 Isolated regions Thailand 0.1 – >10.0 Northern and Western parts Turkey 1.9 – 13.7 Middle and Eastern parts Uganda 0.5 – 2.5 Severity of fluorosis increases with age UR Tanzania 0.2 – 65.0 Fluoride rich water is associated with volcanic activity USA 0.3 – 13.7 Elevated fluoride concentrations mostly 2-4 mg/L


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1.1.4.3 Australia

Within the global context, Australia has relatively low natural fluoride concentrations in drinking water. However, in a number of regional areas that rely on groundwater as the primary source of reticulated water, elevated concentrations occur. This is particularly so in arid regions where the recharge to groundwater aquifers is slow and sporadic and residence times are long, giving rise to increased salinity and ‘rich’ water chemistry (Fitzgerald et al. 1999). In a large survey of groundwater sources in Northern South Australia, one half of the supplies contained fluoride levels exceeding 1.5 mg/L, with several in the range of 3 - 9 mg/L (Fitzgerald et al. 1999). Similarly, in the central desert region of the Northern Territory, there are a number of minor centres and remote Indigenous communities with natural fluoride in the drinking water approaching and in some cases exceeding 1.5 mg/L (Figure 1).

Figure 1 Naturally elevated fluoride levels identified in Northern Territory water supplies managed by Power and Water (Power and Water Corporation 2002).

Power and Water Corporation provide essential services (electricity, water and sanitation) to seventeen major and minor centres and eighty Indigenous communities across the Northern Territory (Power and Water Corporation 2002). In addition to the communities serviced by Power and Water, there are approximately 500 small communities in the Northern Territory with populations of less than fifty people, referred to as outstations, which are currently serviced through the Federal Government (Bailie et al. 2004). The quality of the water in these outstation communities is not fully documented; however communities in close proximity or utilising similar aquifer systems to those supplied through Power and Water Corporation with elevated fluoride concentrations are likely to have similar water quality characteristics.


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1.1.5 Guidelines and Standards in Drinking Water

Based on health considerations, ADWG recommend that the concentration of fluoride in the drinking water should not exceed 1.5 mg/L. This guideline value is to protect children from the risk of dental fluorosis, although it is not the recommended level for fluoridation of water supplies (NHMRC 2004).

The World Health Organisation also recommends a guideline value of 1.5 mg/L, which is based on the level at which the occurrence of dental fluorosis is minimal. This guideline level was set in 1984 and through two re-evaluations in 1996 and 2004, it was concluded that there was no evidence to suggest that the value should be revised (WHO 2004b). Similarly, 1.5 mg/L is higher than recommended for the artificial fluoridation of water supplies (WHO 2004a) and is not a ‘fixed’ value but intended to be adapted to take into account the local conditions, such as diet and water consumption (Fawell et al. 2006).

The Environmental Protection Authority (EPA) set the United States (US) Standards for fluoride in drinking water. The standards for fluoride were established in 1986 and include a Maximum Contaminant Level Goal (MCLG) of 4 mg/L, a Secondary Maximum Contaminant Level (SMCL) of 2 mg/L and a Maximum Contaminant Level (MCL) of 4 mg/L. The MCLG and SMCL are target levels that are not legally enforceable, while the MCL is a legally enforceable level. These standards apply to naturally occurring fluoride from geological sources, not to fluoridated supplies (US EPA 1996). Recently, the US National Research Council (NRC) released a major report reviewing the US EPA’s standards on fluoride in drinking water. Although the report recommendations are broad on the appropriateness of the current standards, there was a greater level of confidence in 2 mg/L providing the beneficial effects of fluoride without introducing negative effects, compared to 4 mg/L (National Research Council 2006).

Table 5 Guidelines and standards for fluoride levels in drinking water F- level (mg/L)) Guideline/Standard

1.5 Australian Drinking Water Guidelines (NHMRC 2004) 1.5 Drinking Water Standards for NZ (Ministry of Health 2005) 1.5 Guidelines for Drinking Water Quality (WHO 2004a)

2.0, 4.0 Safe Drinking Water Act (US EPA 1996)

Achieving the ‘optimal’ fluoride level in drinking water is a careful balance between levels that maximise the benefits and minimise the negative effects of fluoride. The ‘optimal’ level is specific for the local conditions and varies by region or country. In most cases, drinking water is the primary route of fluoride exposure and therefore the amount of water consumed can significantly affect this balance. In hot, arid climates where the amount of water consumed is greater than in temperate climates, total fluoride intake may be excessive even if the groundwater conforms to the guideline value of 1.5 mg/L (Fitzgerald et al. 1999). Consequently, there are specific guideline values for fluoride that consider the mean temperature of the local area. These include empirical formulae that estimate safe limits of fluoride for drinking water as a function of temperature (Foss and Pittman 1986) and the recommendation of lower maximum safe fluoride levels (0.6 - 0.7 mg/L) in higher ambient temperature, arid and semi-arid areas (Brouwer et al. 1988; EPA 1997).

1.2 Defluoridation Techniques

The first preference, when considering the mitigation of elevated fluoride concentrations is treatment avoidance techniques. This may include the abandonment of water sources in favour of other water supplies with lower fluoride concentrations. Alternatively, combining (blending) multiple water sources can ensure the water entering the distribution system meets the guideline values (Fawell et. al. 2006).

Assessing the total fluoride intake for the affected population may also provide an opportunity to manage fluoride exposure. This may include minimising exposure from other sources, such as access to unfluoridated toothpaste, milk and salt (Fawell et al. 2006) and ensuring adequate levels of nutrition, such as intakes of calcium and vitamin C that are directly associated with reducing the risks of dental fluorosis (Dinesh 1998).

However, if alternatives are unavailable the selection of a suitable defluoridation technique is dependent on a number of factors. Fluoride removal is complicated by the presence of other ions in the water that compete for removal and the water quality characteristics and initial fluoride concentration can influence the effectiveness of various techniques (HDR Engineering 2001). The community context for the system will also


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influence selection; small point-of-use systems may not be appropriate in communities serviced by municipal suppliers. Consequently, techniques are more suited to certain situations (HDR Engineering 2001).

Defluoridation techniques are based on the principals of:

• Advanced Treatment Technologies

• Chemical Treatment

• Sorption Media

1.2.1 Advanced Treatment Technologies

Advanced treatment technologies are those based on membrane filtration processes. Membrane separation technology has been utilised for many years in small volume treatment of pure and ultra-pure water for many industries and is increasingly being utilised for the treatment of drinking water (HDR Engineering 2001).

1.2.1.1 Reverse Osmosis and Nanofiltration

Reverse Osmosis (RO) membranes first became commercially available in the 1960s for treating seawater/brackish water and today are the most common type of membrane processes used in potable water treatment in the US. Nanofiltration (NF) is a much newer type of membrane filtration with relatively few installations, although interest and popularity of the technology is growing. Both processes are capable of removing a large spectrum of contaminants from water, including turbidity, pathogens, salts, hardness, heavy metals and natural and synthetic organics, although NF membranes exhibit lower removal capabilities and operate at lower pressures than RO membranes (HDR Engineering 2001). RO is a well-established technique for the removal of fluoride from water and the US EPA recommends RO as one of two options for the ‘Best Available Technologies’ for the removal of fluoride (US EPA 2003b; HDR Engineering 2001).

RO and NF processes are highly effective for fluoride removal, producing consistent high quality water that includes the disinfection of the water during treatment (Maheshwari 2006). However, the systems require special equipment, electrical energy and specifically trained operators, which leads to relatively high capital and operational costs. RO systems may also have significant water losses, typically 10-35%, which can have further implications on aquifer stores and water conservation measures (Sincero and Sincero 2003).

1.2.2 Chemical Treatment

There are a number of chemicals, and various combinations of chemicals, that are added to fluoride-contaminated water to remove or decrease the fluoride concentration. The majority of these systems utilise chemical agents (coagulants) to destroy the forces that stabilise the fluoride particles in solution and promote the aggregation of the molecules, through mixing and flocculation. The subsequent insoluble fluoride precipitates are then removed by sedimentation and filtration (Benefield et al. 1982).

1.2.2.1 Alum and Lime (Nalgonda)

Aluminium sulfate (Alum) was one of the first chemicals investigated for use in removing fluoride from drinking water supplies and is commonly used in isolation or in combination with other chemicals as a defluoridating agent. When alum is added to water, it reacts with the alkalinity in the water to produce insoluble aluminium hydroxide. The removal of fluoride is due to the adsorption of the fluoride onto the aluminium hydroxide particles that are separated from the water by sedimentation (Benefield et al. 1982).

Al2(SO4)3. 18.3H20 + 3Ca(HCO3)2 2Al(OH)3 + 3CaSO4 + 18.3H20 + 6CO2

Alum Reaction (Benefield et al. 1982)


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Nalgonda is named after the village in India where the method was pioneered and developed by the National Environment Engineering Research Institute (Fawell et al. 2006; Sushella et al. 1992). The Nalgonda technique involves addition of alum and lime followed by rapid mixing, flocculation, sedimentation and filtration. The dose of alum increases with an increase in the fluoride and alkalinity levels of the raw water (Rao and Mamatha 2004). The technique involves the dissolution of the alum in the raw water under efficient mixing conditions to ensure complete mixing, which induces the development of aluminium hydroxide flocs, which are removed by sedimentation. During this flocculation process, a number of micro-particles and negatively charged ions including fluoride are partially removed by electrostatic attachment to the flocs. As the alum solution is acidic, simultaneous addition of lime is required to ensure a neutral pH and complete precipitation of the aluminium. The treated water is decanted, although filtration is required as a polishing stage in order to ensure that no sludge particles escape with the treated water (Fawell et al. 2006).

Al2(SO4)3 .18H2O 2Al3+ + 3SO42- + 18H2O Dissolution Alum

2Al3+ + 6H2O 2Al(OH)3 + 6H+ Precipitation Aluminium (acidic) F- + Al(OH)3 Al-F complex + undefined product Co-precipitation 6Ca(OH)2 + 12H+ 6Ca2+ + 12H2O pH adjustment

Nalgonda Reaction (Fawell et al. 2006)

1.2.2.2 Magnesium Oxide

The Indian Institute of Science developed a method to treat fluoride-contaminated water using magnesium oxide, calcium hydroxide and bisulfate. The method relies on precipitation, sedimentation and filtration techniques and is efficient for a range of groundwater chemistry conditions. The addition of magnesium oxide to raw water results in the formation of magnesium hydroxide that then combines with fluoride ions to form insoluble magnesium fluoride (Rao and Mamatha 2004).

MgO + H2O Mg(OH)2 Dissolution of magnesium oxide 2NaF + Mg(OH)2 MgF2 + 2NaOH Precipitation of magnesium fluoride

Magnesium Oxide Reaction (Rao and Mamatha 2004)

Often, lime is used in conjunction with the magnesium oxide to reduce the consumption of bisulfate for pH adjustment and chemical stabilisation of the precipitate. The successful application of the technique is limited to raw water concentrations of fluoride 1.5 - 5.0 mg/L, bicarbonate 0-400 mg/L and calcium 0-160 mg/L (Rao and Mamatha 2004).

1.2.3 Sorption Media

Sorption media refers to insoluble media that remove fluoride based on either one or a combination of absorption, adsorption and ion exchange. Although these interactions are complex, absorption is defined as the physical or chemical processes where molecules in solution ‘attach’ to the external surface of the media and adsorption where the molecules ‘attach’ to the internal and external surface of the media (Benefield et al. 1982). Ion exchange involves the reversible exchange of ions of the same charge between the solution and the media, (HDR Engineering 2001). In practical applications, these processes, primarily adsorption and ion exchange, are grouped together and referred to as sorption for treatment processes (Inglezakis and Poulopoulos 2006). Sorption based defluoridation systems are all based on the removal of fluoride by providing contact between the water and the media which binds the fluoride (Zevenbergen et al. 1996).

1.2.3.1 Activated Alumina

Activated Alumina (AA) is a well-established technique for the removal of fluoride from water and is recommended by the US EPA as one of the ‘Best Available Techniques’ for fluoride removal (HDR Engineering 2001; Susheela 1992; US EPA 2003b). AA was first proposed for defluoridation of water for domestic use in the 1930’s (Boruff 1934; Fink and Lindsay 1936) and today is the method of choice in many industrialised countries. AA is prepared by controlled thermal treatment of granules of hydrated alumina to produce a highly porous media consisting essentially of a mixture of amorphous and crystalline phases of aluminium oxide, described as aluminium trihydrate (Benefield et al. 1982; Frankel and Juergens 1980). Compared to most oxide materials, alumina has a high pH zero-point-of-charge (pHzpc ~8.2) indicating that it has an adsorption affinity for many negatively charged constituents and the crystalline structure means that


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it is selective for specific anions. The removal mechanism is complex, involving the exchange of hydroxyl ions (OH-) for dissolved species (ion exchange) and partially an adsorption process (HDR Engineering 2001). The majority of equilibrium isotherm studies conclude that AA correlates to the Langmuir and Freundlich isotherms (Ghorai and Pant 2004; Ghorai and Pant 2005; Pietrelli 2005).

AA systems are designed with the AA media packed in a column, where the raw water is passed through the column in either an up-flow or down-flow direction, and the fluoride is removed from solution by ‘attaching’ to the AA. Eventually, the column is saturated with fluoride, indicated initially by a low residual fluoride concentration in the effluent water, until it gradually increases to total saturation, where the influent concentration equals the effluent concentration (Fawell et al. 2006). Regeneration of the saturated AA involves passing an alkaline solution through the column, typically sodium hydroxide, to strip fluoride from the column and restore the removal capacity of the AA. The fluoride removal capacity is strongly dependent on pH and an acid solution, typically sulfuric acid or hydrochloric acid, is passed through the column to neutralise and reactivate the system (HDR Engineering 2001). During this process 5 - 10 % of the alumina is lost, which typically results in a loss of capacity in the media by 30 - 40% and is replaced after regenerating 3 - 4 times (Fawell et al. 2006). Therefore, the regeneration process requires disposal of a waste stream and eventually the media will also need to be disposed of.

In Australia, there is an AA based treatment plant designed exclusively to remove fluoride from the drinking water at Dunsborough in Western Australia. The full-scale treatment plant is capable of treating 4.5 ML/day of high fluoride water from 3 mg/L to zero and successfully produces water quality within guideline values through a blending strategy. The full-scale defluoridation plant consists of four AA reactors in an up-flow configuration and pH adjustment, which involves the addition of sulphuric acid to lower the pH from 8 - 8.9 to 5.5. The full-scale plant was extrapolated from a pilot plant and demonstrates that AA is a practical and cost effective method for removing fluoride from groundwater in Australia with the installed plant reported to be performing better than expectations (Broom et al. 2005).

The utilisation of AA in industrialised countries for the removal of anions, including fluoride, from drinking water and wastewater has resulted in a number of guidance documents on the design and operation of treatment plants (Rubel 2003; US EPA 2000; US EPA 2002; US EPA 2003b; Wang et al. 2000; Washington State Department of Health 2005). These discuss the various options available to remove anions and the advantages and disadvantages of systems design options. The AA process is sensitive to pH and system designs include consideration of the ‘natural’ pH of the raw water and the optimum pH range of AA. Generally, the adsorption of anions by AA is more effective below pH 8.2, as below this pH the AA surface has a net positive charge that can be balanced by adsorbing anions. Generally, optimum removal of anions with AA occurs in the range of pH 5.5 - 6.0 (López Valdivieso et al. 2006; Pietrelli 2005; US EPA 2000) although appreciable removal has been achieved at a neutral pH (Ghorai and Pant 2004). A decrease in fluoride adsorption below pH 5 can be associated with dissolution of alumina in the acidic environment leading to a loss of adsorbing media (Maheshwari 2006; Nordin et al. 1999). Above pH 7, fluoride adsorption decreases, as the exchange reactions between surface hydroxide groups and the adsorbing fluoride ion are less favourable, as the silicate and hydroxide become a stronger competitor of the fluoride ions for the exchange sites on the AA (Maheshwari 2006). Increasing the pH also favours the electrostatic repulsion between the negatively charged surface of alumina and the anionic fluoride (López Valdivieso et al. 2006). Fluoride-contaminated water typically has pH in the range of 7 - 9 and systems are frequently operated with pH adjustment to maximise the absorption capacity of AA. Often smaller systems are operated without pH adjustment, which usually leads to the AA being utilised without regeneration to avoid the requirements of chemicals, appropriate storage facilities and disposal of waste streams (Wang et al. 2000).

The technologies and market for alumina-based adsorptive media is continuing to expand, and there are several emerging proprietary media that are advancing conventional AA treatment and often contain alumina in a mixture with other substances (US EPA 2003a). AA has been modified by impregnation with alum, which has a high fluoride adsorption capacity, to enhance the adsorption efficiency. The efficacy of impregnated alum AA to remove fluoride from water is found to be 99% at pH 6.5 with a contact time for 3 h at a dose of 8 g/L (Tripathy et al. 2006). Similarly, the study of the defluoridation potential of manganese-oxide-coated alumina (MOCA) recorded a maximum fluoride capacity of 2850 mg per kg of MOCA compared to 1080 mg per kg conventional AA (Maliyekkal et al. 2005). A new activation technique for alumina based on the application of an electric field on the adsorbent rather than thermal activation, demonstrated that the electro-sorption process achieved 55% greater adsorption of fluoride than the conventional AA (Lounici et al. 2004).


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Constituents in the water, other than fluoride, can interfere with the AA adsorption process, either by competing for adsorption sites or by clogging the media with particulate matter. AA preferences for certain ions are indicated by the general selectivity sequence:

OH- > H2AsO4- > Si(OH)3O- > F- > HSeO3

- > TOC > SO42- > H3AsO3

General selectivity sequence for AA (US EPA 2003b)

Hardness, silica, iron, bicarbonate/carbonate and phosphate have also been identified as interfering with the fluoride removal system and reducing the effectiveness of AA (HDR Engineering 2001; Maheshwari 2006; Rao 2003). In addition, the ability of AA to remove fluoride depends on the flow rate, raw water fluoride concentration and media depth (Ghorai and Pant 2004) with media depth forming one of the critical factors in the design of systems (Chauhan et al. 2007). Typical of exothermic adsorption processes, the adsorption capacity of AA deceases as temperature increases (López Valdivieso et al. 2006).

AA remains a popular choice for defluoridation, as the system is specific for fluoride removal, has a relatively high adsorption capacity, requires minimum contact time for maximum defluoridation, low water loss, low energy consumption and generally the media is readily available and relatively cost effective (Veressinina et al. 2001). The percentage of regeneration is also considerably higher, the system is relatively low maintenance and the sludge produced is typically non-hazardous (US EPA 2002; US EPA 2003b). However, the system requires careful design, system efficiency is dependent on source water characteristics and can require chemical handling and storage and waste stream disposal for pH adjustment and or regeneration (US EPA 2003b).

1.2.3.2 Bone Charcoal

Bone Charcoal (BC) was used for defluoridation in the Unites States during the 1940s -1960s, when BC was commercially widely available from large-scale uses in the sugar industry. BC is a blackish porous granular material composed primarily of calcium phosphate 57 - 80%, calcium carbonate 6 - 10%, and activated carbon 7 - 10%. BC is able, to absorb a wide range of pollutants such as colour, taste and odour components and fluoride. The preparation of BC is crucial for its properties as a defluoridation agent and unless carried out properly, the bone charring process may result in a product of low defluoridation capacity and/or deterioration in water quality (Fawell et al. 2006). The removal capability of BC is believed to be due to its chemical composition, mainly as hydroxyapatite where one or both the hydroxyl-groups can be replaced with fluoride, or the reaction between calcium phosphate and fluorine or the replacement of the carbonate by fluoride to form an insoluble fluorapatite (Abe et al. 2004; Fawell et al. 2006; Rao 2003).

Today the commercial distribution of BC is much more limited than in the past and the application of the technique in developing countries at the domestic level relies on the community preparing the BC locally. Similar to most sorption processes the BC is able to be regenerated by treating with an alkaline solution followed by neutralisation, although this is typically only cost effective at large scale treatment level or in the case of a shortage in the media. However, the cost of BC may be significant, depending on the method of manufacture and today large scale BC systems have been replaced by the use of ion-exchange resins and AA. At a domestic level, BC defluoridation appears to be suited to Thailand and Africa, but so far there is no experience in wide scale implementation (Fawell et al. 2006).

1.2.3.3 Hydrotalcite

Hydrotalcite, also known as hydrotalcite like compounds, layered double hydroxides, mixed metal hydroxides and anionic clays, are important classes of readily produced natural and synthetic compounds that are growing as potential anion exchange and adsorption materials (Hou et al. 2002; Wang et al. 2001a). Hydrotalcite’s crystal structure consists of positively charged layers of mixed metal hydroxides sheets separated by interlayers, containing exchangeable anions and water molecules (Erickson et al. 2005; Hou et al. 2002; Wong and Buchheit 2004). A wide range of compositions are possible for synthetic hydrotalcites, based on the general formula [M2+

1-x M3+x (OH)2]b+[An-]b/n . mH2O, where M2+

and M3+ are the divalent and trivalent cations in the octahedral positions within the hydroxide layers; An- is an interlayer anion with a negative charge; b, n is the charge of the layer; and m is the number of water molecules (Frost and Musumeci 2006; Kloprogge et al. 2004; Parida et al. 2006, Zhang et al. 2004).


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The ability of hydrotalcite to adsorb anions from aqueous solutions is due to the ‘memory effect’. The ‘memory effect’ results from the thermal activation (calcination) of the hydrotalcite, which removes the water, hydroxyl and anions from the interlayer structure, forming an atomic mixture of metal oxides. When this calcined hydrotalcite is exposed to water and anions, it returns to its original structure by absorbing the water and reforming the hydroxyl layers (Figure 2). This results in the anions and water being absorbed into the interlayer, although the anion may not necessarily be the same as in the original hydrotalcite (Erickson et al. 2005; Frost and Musumeci 2006).

Figure 2 Illustration describing the structural state transformation upon calcination and rehydration of layered double hydroxide compound showing its structural memory effect (Wong and Buchheit 2004). 1.2.3.4 Ion Exchange Resins

Ion exchange is a physico-chemical process in which ions are swapped between a solution phase and solid resin phase. The solid resin is typically an elastic three-dimensional hydrocarbon network containing a large number of ionisable groups electrostatically bound to the resin, which are exchanged for ions of similar charge in solution that have a stronger exchange affinity for the resin (US EPA 2003b). Ion exchange resins have been shown to be effective in the defluoridation of drinking water and are recommended by the US EPA as one of the ‘Best Available Techniques’ for fluoride removal (US EPA 2003b).

However, ion exchange resins often require pre-treatment of the raw water to ensure the effectiveness of the systems. Suspended solids should be low (zero is possible) and turbidity should be less than 1 NTU to prevent bed plugging. Ferrous ion should be removed prior to ion exchange treatment, as it can oxidise to the ferric form within the bed if oxygen is present, although if oxygen is not present the process will effectively remove ferrous and manganous ions. Chlorine should not be present in the raw water and the presence of organic matter will result in resin fouling. In general, the ion exchange process is not an economically viable treatment technology if source water contains over 500 mg/L of TDS, >50 mg/L of sulfate carbonate, phosphate and alkalinity (Maheshwari 2006; US EPA 2003b; Wang et al. 2000). The technique is relatively expensive due to the cost of the resin, pre-treatment required, regeneration and waste disposal (Maheshwari 2006).

1.2.3.5 Natural and Low Cost Materials

The development of defluoridation techniques that are simple, effective and economically viable has led to the use of natural materials that are readily available, relatively cost effective and may be more readily accepted by the community. The first comprehensive study of the fluoride adsorption onto minerals and soils was released in the late 1960’s and since then there have been a number of fluoride adsorption studies on a variety of natural low cost materials (Coetzee et al. 2003).

Bauxite

Bauxite ores occur naturally across the globe and are abundantly available in Australia, containing predominantly oxides/oxyhydroxides. The use of bauxite for defluoridation typically involves thermal activation to increase the adsorption capacity of the media (Das et al. 2005). The use of bauxite and bauxite


20

derivatives for the treatment of water has been further developed by commercial companies. The Virotec technology, trademark Bauxsol, is derived from bauxite refinery residues and is used for the treatment of wastewater. The BauxsolTM pellets are able to remove a range of contaminants including fluoride to the theoretical limit of 1.5 mg/L although there is potential to modify the pellet to remove fluoride down to 0.7 mg/L.

Calcite (Limestone)

Limestone is composed of calcite (calcium carbonate CaCO3) with some sediment. Calcite is primarily involved in defluoridation and the removal is based on adsorption and precipitation. Calcite systems are traditionally designed to treat wastewater, which have relatively high fluoride concentrations compared to drinking water. A two-column reactor designed to reduce fluoride concentrations to 4 mg/L, functions by forcing calcite to dissolve and fluorite (CaF2) to precipitate in the fist column, the second column is used to precipitate the calcite dissolved in the first, returning the treated water to its approximate initial composition. The system successfully reduces the fluoride level from 109 mg/L to 4 mg/L with a pore-water residence time of 2 hours (Reardon and Wang 2000).

Calcite occurs naturally across the globe and is abundantly available in Australia where the medium is readily available and relatively cheap. Column system operations are favourable as the system monitoring is minimal, regular column regeneration is not required and chemicals are not permanently added to the water (Reardon and Wang 2000). However, although the calcite is able to dramatically reduce fluoride levels, when fluoride is in high concentrations, the technique is unable to reduce levels to 1 mg/L as required for the treatment of drinking water.

Clays and Soils

There are a number of investigations that utilise soils and clays in the defluoridation of drinking water. The term clay is often used in a non-specific description of either a soil consisting of a range of small particles or very fine-grained earthy substances comprising a combination of minerals, inorganic amorphous material and organic matter or a specific clay mineral (Coetzee et al. 2003).

Numerous investigations of clay and soil materials demonstrate appreciable defluoridation capacities (Karthikeyan et al. 2005b; Masamba et al. 2005; Moges et al. 1995; Wang and Reardon 2001). Batch experiments using local Kenyan soil derived from volcanic ash achieved significantly larger fluoride adsorption capacity than those reported in the literature for other soil types (Zevenbergen et al. 1996). A novel technique for the defluoridation of water in India trialled the modification of existing locally constructed clay vessels, common in rural India and other developing countries for storing water, in water defluoridation (Agarwal et al. 2003). Comparison of twenty five South African clays types, grouped according to the major clay types of bauxite, laterite, palygorskite, bentonite and kaolinite, revealed that high adsorption is correlated with the bauxite and lateritic samples and the lowest adsorption recorded for kaolin samples (Coetzee et al. 2003). Although locally available materials are often utilised, commercially available clay materials such as Kaolin (hydrated aluminium silicate) have also been examined for their defluoridation efficiency (Karthikeyan et al. 2005a). The comparison of commercial kaolin and bentonite clays suggested that the bentonite possessed properties more suitable for retaining fluoride with a higher modelled sorption capacity and lower effective diffusion than the kaolin (Kau et al. 1999). Another investigation examined the defluoridation capabilities of kaolin clay liners in storage of fluoride contaminated waste. Batch experiments revealing that the optimum removal occurs at pH 5.0 to 5.5 with 3480 mg of fluoride per kg of clay, at pH 6.0 (Kau et al. 1997).

Hydroxyapatite

Hydroxyapatite (HAP) is naturally abundant, as a common accessory mineral in many types of rock, and has been used for the removal of fluoride from drinking water. Apatites (Ca10(PO4)6(F,Cl,OH)2) are a complex and diverse class of materials, which in the geological environment are the most abundant in phosphorus-bearing minerals found extensively in igneous, metamorphic and sedimentary rocks (De Leeuw 2004). The apatite structure is an ionic crystal, where the phosphate and hydroxide groups behave like poly-anions, removing the fluoride by initially adsorbing onto the hydroxyapatite surfaces and then exchanging with hydroxide groups within the hydroxyapatite lattice (De Leeuw 2004; Fan et al. 2003). The use of hydroxyapatite for the defluoridation of drinking water appears promising, as it seems to be able to successfully remove low raw water fluoride concentrations, is found naturally in the environment and relatively cost effective.


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KRASS Process

Research in India has developed the KRASS process for defluoridation of drinking water (Gupta et al. 1998). The medium used for the process is made of inorganic substances with a spherical shape, 0.08mm, uniformity coefficient of 2 and specific gravity of 2.6 (under patent). Investigations of the technique include the use of PVC columns in continuous down flow mode, where the fluoride water was kept at a constant level above the surface of the media and 10% alum solution was used for recharging (Agarwal et al. 1999). Successful operations of domestic KRASS systems have been trialled in rural Indian communities. The process decreases fluoride levels below the acceptable range, maintains aluminium levels well within the permissible range, does not increase the TDS levels and maintains the pH, colour and turbidity levels in the output (Gupta et al. 1998). The system differs from other defluoridation techniques in its simplicity, cost effectiveness and results in traces of residual aluminium in treated water. Also the process is independent of fluoride concentration, temperature, pH, alkalinity and TDS of the input water (Agarwal et al. 1999). However, the system relies on patented media that has been developed in India, potentially creating logistical limitations in the sourcing of the media in Australia and confining sources.

Waste Products

The utilisation of waste products for the removal of fluoride from water is a cost effective alternative to acquiring specific media for sorption-based processes. Alum sludge generated during the manufacture of alum from bauxite by the sulphuric acid process has been used for the defluoridation of wastewater. The sludge mainly consists of oxides of aluminium and titanium with small amounts of undecomposed silicates, which are known to possess adsorption and ion exchange properties. Adsorption experiments on raw and treated alum sludge, concluded that the alum sludge shows superior adsorption capacity for the fluoride ion and that this adsorption seems to be a surface phenomenon (Cinarli at al. 2005; Sujana et al. 1998).

Summary

The various investigations conducted using local materials for the removal of fluoride have proven to be relatively successful, although in general it was found that the adsorption capacity of soils and clays was low and the kinetics slow (Coetzee et al. 2003). The application of local materials requires identification, analysis, extraction and activation to develop and trial the appropriateness of the technique, which may be outside the scope for many small systems.

1.3 Evaluation and Selection of Technique

Although there are a number of techniques that may be implemented to defluoridate drinking water, there is not a universal method that is appropriate under all social, financial, economic, environmental and technical conditions. Therefore, when considering appropriate actions in relation to elevated concentrations of fluoride in water sources, a decision process should be followed (Figure 3).


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Figure 3 Decision process for appropriate action in relation to elevated concentrations of fluoride in water sources.

1.3.1 Northern Territory Situation

Australia is generally considered an urban country, with the majority of the population living in the large cities and towns in temperate climates (ABS 2001). The water supply and sanitation infrastructure provided in these large population areas is sophisticated and reliable such that people typically receive a safe, reliable and adequate water supply to their homes (Henderson and Wade 1996). Water utilities and suppliers in these urban centres are relatively well resourced and are able to have appropriately qualified people oversee the water treatment processes and monitor water quality to ensure the protection of public health.

However, the Australian population inhabits many different geographical locations, apart from the large coastal cities, including regional and remote communities (ABS 2004). The remoteness structure is used to define these vastly different areas and classifies Australia into regions, which share common characteristics of remoteness (Figure 4).


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Figure 4 Australia classified according to the Remoteness area (ABS 2001).

The Northern Territory covers approximately one fifth of Australia and supports a population of approximately 250,000 people, who predominantly reside in Darwin, Alice Springs and Katherine, with the remainder dispersed in minor centres and remote communities across the Territory. The relatively large area and small population results in the majority of the Territory being classified as very remote and the communities that have elevated fluoride concentrations in the water supply are located in the very remote areas (Figure 4). In remote communities, distance, accessibility, climate variability and service difficulties typically impede the delivery of water supply services, often further complicated by the lack of local technical capacity, expertise and resources.

The water quality characteristics of groundwater with elevated levels of fluoride in the Northern Territory vary, although can generally be described as hard water, with a neutral pH and a ‘rich’ water chemistry (Appendix A). The fluoride levels may be classified into two categories based on their relative health risks (Table 2):

1. High risk: Communities with fluoride levels ≥1.5 mg/L (defined in the ADWG) (NHMRC 2004)

2. Moderate risk: Communities with fluoride levels between 0.7-1.5 mg/L. Although the levels do not exceed the guideline value, locations in areas with average mean temperatures above 30°C increases the fluoride exposure that may have adverse impacts on the health of the community.

Power and Water has identified seventeen communities with elevated fluoride levels and the assessment to decide on the appropriate action to minimise risks will be based on the potential impacts on public health.

1.3.1.1 Moderate Risk (0.7-1.5 mg/L F)

Fourteen communities have fluoride levels between 0.7-1.5 mg/L and although these levels are below the guideline, the relatively high mean temperature of the region suggests that more water would be consumed than in temperate regions (Fawell et al. 2006; NHMRC 2004). Therefore, the ‘optimum’ fluoride concentration


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in the drinking water in many of these affected communities is 0.6-0.8 mg/L rather than 1.5 mg/L as suggested as the guideline value.

The majority of the communities have relatively consistent fluoride levels in the groundwater sources and thus blending strategies will not greatly influence the final concentration delivered to the consumers (Appendix A). The most effective way of ensuring that the risk to the consumers is minimised is by continuing to monitor health, especially in children for the presentation of fluorosis, and minimising the total fluoride intake in the community. This may include minimising exposure from other sources, such as limiting access to fluoridated toothpaste, milk and salt and ensuring adequate levels of nutrition, such as intakes of calcium and vitamin C that are directly associated with reducing the risks of dental fluorosis (Fawell et al. 2006)

1.3.1.2 High Risk (≥1.5 mg/L F) (Table 6)

Four communities have fluoride levels that are ≥1.5 mg/L (Table 6). The levels of fluoride may be minimised at Robinson River through the implementation of blending strategies, although the fluoride will remain above the guideline levels. Tennant Creek’s fluoride levels are similar to the guideline level and blending strategies may be implemented to ensure that the water delivered to the consumers is below the guideline level. However, the levels in the other communities are relatively consistent and blending will not lower risks.

Table 6 Summary of high-risk fluoride levels in communities managed by Power and Water (Power and Water Corporation 2002)

Community Bore No. Fluoride (mg/L) Community Bore No. Fluoride

(mg/L) RN5778 1.9 RN01736 1.2 RN10744 2.3 RN10273 1.5 RN10744 2.3 RN10622 1.5 Ali Curung

RN5788 1.8 RN10623 1.5 RN13830 2.0 RN12603 1.3 RN13831 2.0 RN12604 1.4 RN16227 2.0 RN12605 1.4 Alpurrurulam

RN16927 2.0 RN12609 1.5 New 2.0 RN12910 1.3 RN26478 1.3

Tennant Creek

RN12790 1.4 RN27845 1.1

Robinson River

RN32158 1.9

Applying the circumstances in Ali Curung and Alpurrurulam to the decision process (Figure 3) reveals that both water supplies have fluoride levels above the guideline and the prevalence of dental fluorosis needs to be examined. There is very little data on dental fluorosis within these communities, although a limited study was conducted with Tennant Creek children in 2001-02 (Appendix B). The Northern Territory Government, Department of Health and Community Services conducted the study of the upper four permanent teeth of a number of children aged between 8-13 years old residing in Tennant Creek, using Dean’s (Fluorosis) Index. The study suggests that there is a measurable degree of difference in the prevalence of dental fluorosis between children who have resided in Tennant Creek for an extended amount of time compared to those who have not (Table 7). The levels of fluoride in Tennant Creek are lower than Ali Curung and Alpurrurulam. As a result it is presumed that there would be a higher prevalence of dental fluorosis in the communities with higher fluoride concentrations and management strategies to minimise the risks are required.

Table 7 Summary of the prevalence of fluorosis in children residing in Tennant Creek (TC) in 2001/2002 (Appendix B).

Dean’s Fluorosis Index (% of children effected) TC children examined

(No.)

Average Fluorosis

Score Severe

(5) Moderate (4) Mild (3)

Very Mild (2)

Questionable (1)

Normal (0)

Born TC (28) 2.9 4 18 36 36 7 0 >1yr in TC (16) 2.7 0 6 44 38 13 0 <1yr in TC (9) 1.6 0 0 11 33 22 33 Average (53) 2.6 2 11 34 36 11 6


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Unfortunately, there are no alternative sources of water in the vicinity of these communities that are feasible to develop or have lower fluoride levels and therefore defluoridation options should be considered for these communities (Table 7).

Table 8 Summary of the defluoridation techniques and their application to the remote communities in the Northern Territory

Technique Suitability for the Northern Territory situation Further Analysis

Membrane Processes

Reverse Osmosis Nanofiltration Electrodialysis

Although membrane systems are becoming relatively more cost competitive, especially for smaller systems, the system complexity, high maintenance and requirements for skilled operators remain the primary barriers to their application in rural and remote communities.

Chemical Treatment

Alum and Lime (Nalgonda)

Despite Nalgonda being utilised in many cases and places, it has not yet been demonstrated to be the method of choice. The primary barriers to its application in rural and remote communities is the requirement of continual correct chemical dosing and close monitoring to ensure effective fluoride removal; system effectiveness is influenced by the raw water quality; potential to increase the TDS of the treated water; and continuously produces a sludge that requires appropriate disposal.

Magnesium Oxide

Similar to most chemical treatments, the removal is relatively complex requiring continual chemical dosing and controlled monitoring. Also the raw water quality in the communities approaches, and in some instances exceeds, the boundary conditions that can successfully be treated with this technique and is therefore not appropriate for application in remote communities.

Sorption media

Activated alumina

AA is a widely accepted technique for defluoridation in many industrialised countries and appears appropriate for use in rural and remote communities. The systems may be implemented with or without pre-treatment or regeneration and feasibility analysis of the different options should be investigated to ascertain its fluoride removing capacity for NT waters.

Bone Charcoal (BC)

The feasibility of the BC system depends on the local availability of bones, production and price of the BC especially for a large-scale community plant. In the Northern Territory there are a limited number of abattoirs, limiting the availability of animal bones; also there is limited capacity to effectively calcine the bones for large-scale treatment for the application of the technique to rural and remote communities.

Hydrotalcite

Hydrotalcite is a relatively new material used for the removal of fluoride, although the media has not been demonstrated on a large scale the technique is promising as the media can be prepared relatively easily and economically.

Ion Exchange

The primary barrier to the application of this technique in remote communities is the relative expense of ion exchange resins. Also the water quality characteristics in the rural and remote communities have relatively high hardness, TDS and some iron and therefore ion exchange would not be suited to this technique without pre-treatment of the water.


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Table 8 continued

Technique Suitability for the Northern Territory situation Further Analysis

Low Cost Materials

Bauxite

Bauxite appears to be a potential defluoridation media for treating drinking water and may be sourced locally, relatively economically and warrants further investigation to effectively treat water in the remote communities.

Bricks Although the utilisation of bricks is promising, bricks are not generally locally available in the remote communities and therefore the economic benefits of the technique are minimised.

Calcite (limestone)

Calcite is locally available at quarries and is therefore readily obtainable and relatively cheap. However, although calcite is an effective defluoridator, the technique is unable to reduce levels to 1 mg/L as required for the treatment of drinking water.

Clays and Soils

The various investigations conducted using local materials for the removal of fluoride has proven to be relatively successful, although in general it was found that the adsorption capacity of soils and clays was low and the kinetics slow. The primary barrier on the use of a local material is the identification, analysis, extraction and activation required to develop an appropriate material. The commercial production of kaolin and bentonite clays separates it from many of the techniques using natural materials as a consistent reproducible product can be obtained. However the sorption capacity of the kaolin clay is relatively low and this may restrict the application of the technique at community scale.

Hydroxyapatite

The use of hydroxyapatite for the defluoridation of drinking water appears promising as it seems able to successfully remove low raw water fluoride concentrations. However a further investigation into the source of the material revealed that there are limited natural sources (impure forms) available and the high grade material found was too expensive (approx $1000/kg)

KRASS

Unfortunately the system relies on patented media that has been developed in India that may create logistical limitations in the sourcing of the media in Australia. The patent on the media also limits the supply and availability and possibly increases the cost of the media. Consequently although the technique appears promising in terms of removal with the water quality characteristics in remote communities sourcing of the media may prevent its application.

Waste products

There are a number of waste products that are generated locally many of these require a level of pre-treatment to ensure that the drinking water is not contaminated. Although at laboratory scale the pre-treatment could be easily achieved, the complexity of establishing pre-treatment at a larger scale limits the application of this technique.

The techniques based on sorption media are likely to be most appropriate for implementation within the rural and remote communities in the Northern Territory (Table 8). This is primarily due to the relatively simple operation of the systems as ‘filtration columns’ that can be designed such that the systems are reasonably robust, require minimal maintenance and the principles of removal are also easy to understand. However, there is a large degree of variance in the efficiencies of various media and the selection and trial of a number of different media for further investigation will help ensure an appropriate media is chosen. Consequently, three media have been identified for further investigation, including AA, bauxite and hydrotalcite. AA has been widely demonstrated to be successful in minimising the fluoride concentrations in drinking water and there are a number of different products available, thus two types of AA were selected, which vary in manufacturer, composition and price.


27

As adsorption is influenced by the characteristics of the water, the defluoridation capacity will be assessed using three different water samples. Water from two of the communities, Tennant Creek and Ali Curung will be utilised as they represent a range of water qualities in the communities. A spiked RO sample with a fluoride concentration of 2 mg/L will also be investigated to indicate the adsorption capacity without competing anions and at a lower pH of approximately 6.

1.4 Objectives of the Research

The research aims to identify a cost effective, robust and low maintenance defluoridation system that may be implemented at the community level within rural and remote communities in Australia.

1.4.1 Specific Objectives

To effectively achieve the objectives of the research a number of more specific objectives have been identified:

• Identify a relatively simple system that may be piloted in rural and remote communities in the coming year

• Minimise the maintenance and skills required for system operation

• Assess the feasibility of piloting the system in a rural and remote community


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2 METHODS

2.1 Media Preparation and Supplier

2.1.1 Activated Alumina

A-2 28x48 was manufactured by UOP LLC, Des Plaines, United States. The Australian supplier for the A-2 was Alchemy Trading Company Pty Ltd. CPN 28x48 was manufactured by Engelhard Corporation, Iselin, United States. The Australian supplier for the CPN was Unimin Australia Ltd (Appendix C). Both the AA samples were washed prior to utilisation in the batch experiments to remove fine particles, which may have the potential to contaminate the output water.

2.1.2 Bauxite

The bauxite was manufactured by Alcan, Gove, Australia and product was sourced directly from Alcan Gove Pty Limited (Appendix C). The raw grade bauxite produced at Alcan varied in size and there were fine particles that had the potential to contaminate the output water. Consequently, the media was sieved at >500 µm to remove the fine particles, this was considered the smallest media size that Alcan could supply on a large scale.

2.1.3 Hydrotalcite

Laboratory - The hydrotalcite used for the batch adsorption experiments was prepared in the laboratory following the coprecipitation method. 1 M sodium aluminate (NaAl(OH)4) solution was prepared by dissolving aluminium foil (13.5 g) in sodium hydroxide (120 g) using 1 L RO water. Then 1 M magnesium chloride solution was prepared by dissolving magnesium chloride hexahydrate (206 g) in 1 L of RO water, which was added to the sodium aluminate in sufficient quantities to maintain a pH in excess of 12. The hydrotalcite formed was then filtered through Whatman 0.45 µm membrane and washed with RO water to a stable pH of about 8, covered and dried at 60ºC overnight.

Waste Product - The hydrotalcite waste product is formed when the supernatant liquor from the Bayer process plant is mixed in a release pond with seawater from Melville Bay, which then settles by gravity. The waste hydrotalcite was roughly ground (approx. 1 cm – 1 µm) prior to use in batch experiments.

2.2 Batch Adsorption Experiments

Batch adsorption experiments were carried out using AA, bauxite and hydrotalcite

2.2.1 Procedure

The initial batch adsorption experiments were conducted in conical flasks (500 mL) with 20 g/L of adsorbent, with three water samples (Spiked RO, Tennant Creek and Ali Curung) at ambient temperature and with constant stirring. The experiments were carried out in duplicate plus a control (water sample with no media) and a blank (RO water and media). Samples were taken at time intervals over 5 hours (0, 15, 30, 45, 60, 90, 150 and 300 minutes) and the fluoride concentration determined.


29

Figure 5 Typical batch adsorption experiments conducted in conical flasks (500 mL) with 20 g/L of adsorbent, with 500 mL of the three water samples (Spiked RO, Tennant Creek and Ali Curung), at ambient temperature and with constant stirring.

At the completion of the batch experiments, the pH and conductivity were determined before centrifugation at 3000 rpm for 5 minutes, filtration (0.45 µm) and storage at 4ºC for water quality analysis.

2.3 Equilibrium Isotherms (Batch)

Equilibrium isotherms were carried out with the two types of AA.

2.3.1 Procedure

The equilibrium isotherm experiments (Benefield et al. 1982) were conducted in conical flasks (500 mL) with known amounts of AA, with 500 mL of the three water samples (Spiked RO, Tennant Creek and Ali Curung), at ambient temperature and with constant stirring. The experiments were carried out in duplicate plus a control (water sample with no media) and a blank (RO water and media). Samples were taken at time intervals over 90 minutes (0, 5, 10, 15, 30, 60, and 90 minutes) and the fluoride concentration determined.

Figure 6 Typical equilibrium isotherms experiments conducted in conical flasks (500 mL) with known amounts of AA, with 500 mL of the three water samples (Spiked RO, Tennant Creek and Ali Curung), at ambient temperature and with constant stirring.


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2.4 Column Studies

Column experiments were carried out with AA (CPN) with the three water samples.

2.4.1 Procedure

The column experiments were conducted using a cylindrical PVC column. The column was constructed of 100mm PVC pipe (internal diameter of 94 mm) with two screw caps and a total height of 300 mm. The AA (1 kg) was contained in the column approximately 50 mm off the bottom of the column on a support with a 200 μm screen. The pump, with flow controller, directed the water from the influent reservoir in an upward flow through the column (Figure 7). Samples of the outlet solution were collected at various time intervals, fluoride levels were determined immediately.

Figure 7 Schematic diagram of the AA experimental design of the column studies

Figure 8 Experimental activated alumina column (PVC column on RHS) utilised for column studies

1 Kg Activated Alumina

(CPN)

PUMP

Influent Reservoir

Defluoridated Water

Fluoride Contaminated Water

PVC Column

Screen


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2.4.2 Regeneration (and Reactivation)

The exhausted AA was regenerated and reactivated for the next defluoridation cycle with sodium hydroxide (NaOH) and hydrochloric acid (HCl). When the outlet fluoride concentration was ≥0.8 mg/L, 0.1M NaOH was added to the system, followed by 0.1M HCl. Then the fluoride contaminated water was introduced through the system, however the initial volume of water that passed though the system was diverted to waste until the pH of the outlet solution rose to above 5 and the fluoride concentration was zero. RO water was not used to rinse the media as this would not be available to the communities in sufficient quantities) This procedure was used to regenerate the exhausted AA after each cycle and continued for up to 3 cycles to determine the fluoride absorption capacity following regeneration and reactivation. The 1st regeneration and reactivation was conducted using approximately 5 bed volumes of the NaOH and HCl, however the subsequent regeneration and reactivation used 3 bed volumes of each.


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3 RESULTS AND DISCUSSION

Adsorption is influenced by water quality, where constituents of the water, other than fluoride, can interfere with the adsorption process either by competing for adsorption sites or clogging the media with particulate matter. Consequently, the adsorption efficiency was investigated using three water samples:

• Fluoride spiked RO water – 2 mg/L F

• ‘Natural’ water samples from Tennant Creek – 1.5 mg/L F

• ‘Natural’ water samples from Ali Curung - 2.5 mg/L F.

The spiked RO represents ‘optimal’ adsorption conditions, without the presence of competing ions at a pH 6, while the ‘natural’ water samples represent the typical range of water qualities in Northern Territory water supplies with elevated fluoride. Adsorption is primarily affected by pH and the optimum pH for fluoride removal is pH 5-7 for the different media (Das et al. 2005; Ghorai and Pant 2004; Wang et al. 2007). The water supplied with elevated fluoride concentrations in the Northern Territory has a pH around 7 and has a relatively high alkalinity (Appendix A). The adjustment of pH prior to treatment requires daily monitoring and the storage of chemical on site; therefore it is preferred to operate the treatment system without pH adjustment and the investigations were conducted at the natural pH of the groundwater and the spiked RO sample.

The results of the batch adsorption experiments and the water quality analysis were used to identify the media that was most appropriate for further extensive investigation by way of equilibrium isotherms and column studies.

3.1 Batch Adsorption Experiments

The fluoride removal capacity of the selected media is a function of the pH, contact time, adsorbate concentration, adsorbent dose and temperature, therefore batch experiments often involve an investigation of the removal capacities based on these functions (Ghorai and Pant 2004; Mohapatra et al. 2004; Wang et al. 2007). Without concentrating on all aspects that influence the fluoride adsorption, batch adsorption experiments were used to establish the ability of the different media to remove fluoride using the three water samples. The experiments were conducted over 300 minutes, considered sufficient for completion of the adsorption process and the adsorption dose was estimated based on previous studies that indicated the ratio sufficient to effectively remove fluoride from water (Das et al. 2005; Ghorai and Pant 2004; Veressinina et al. 2001; Wang et al. 2007).

3.1.1 Activated Alumina (A-2 and CPN)

Prior to batch adsorption experiments both types of AA were washed to remove fine particles and prevent contamination of the treated water. The A-2 required significantly more washing than the CPN.

Figure 9 Adsorption studies of Activated Alumina (a) A-2 (b) CPN, using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data).

(b) (a)

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33

The general trends of the adsorption kinetics show that the removal mechanism for the fluoride primarily occurs in the initial 45 minutes of the reaction (Figure 9) reflecting classic Langmuir Adsorption Isotherm shape curve. Both the A-2 and CPN show similar fluoride removal capabilities, the spiked RO sample achieving the greatest removal efficiency, followed by Tennant Creek and then Ali Curung. This is typical of adsorption processes, where the absence of competing ions allows the fastest removal efficiency to be achieved with the spiked RO, followed by the natural water with the lower fluoride concentration and then the natural water with the higher fluoride concentration. The A-2 appears to release a minor amount of fluoride over time with the three different water samples (Figure 9a). The CPN appears to have reached saturation with the Ali Curung water sample, as it did not achieve 100% removal after 300 minutes (Figure 9b). This may be attributed to the higher fluoride concentration of the Ali Curung water compared to the Tennant Creek water and the relatively high concentration of competing anions and alkalinity (Appendix A). The CPN has higher specific surface area; therefore the saturation of the media suggests that there are a lower number of sites available to bind the fluoride than the A-2 assuming that the ratio of sites is 1:1.

3.1.2 Bauxite

Initially the raw bauxite product is of low quality and varies in size, resulting in a portion of very fine material contaminating the treated water, which was removed by sieving (500 µm) and pre-washing.

Figure 10 Adsorption studies of bauxite using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data).

The adsorption of the fluoride by the bauxite is consistent with the classical Freundlich Adsorption Isotherm shape curve. At the same adsorbent dose, the bauxite displays a lower capacity to remove fluoride from all three samples than the AA and the removal is steady (Figure 10). The adsorption efficiency with the spiked RO is markedly higher than with the natural water, indicating that the bauxite is less selective for fluoride and the other constituents in the water have a greater influence on the removal efficiency, compared to the AA. Although the removal is less efficient than AA at the same adsorbent dose, the product is locally available and more cost effective and thus may be more appropriate based on economical and logistical considerations.

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3.1.3 Hydrotalcite

Similar to the AA, the hydrotalcite adsorption efficiency is highest with the spiked RO sample followed by the ‘natural’ water samples, consistent with the fluoride concentration of the water (Figure 11).

Figure 11 Adsorption studies of hydrotalcite using three water samples at the natural pH, natural fluoride concentrations and adsorbent concentration of 20 g/L (Average of n=2 see Appendix D for data). The hydrotalcite fluoride adsorption process is relatively rapid, with the majority of the adsorption process occurring in the initial 15 minutes, although it did not achieve removal efficiencies of AA with the natural waters (Figure 11). Similar to the bauxite, the hydrotalcite is markedly less efficient at removing the fluoride with the relatively ‘complex’ natural waters compared to the spiked RO, as the other constituents of the water compete for adsorption sites on the medium. The primary reason for the lower adsorption at the pH>7 (as with the ‘natural’ water) is due to the silicates and the hydroxyl ions that would compete more strongly with the fluoride ions for adsorption exchange sites on the alumina. Although the hydrotalcite was prepared in the laboratory relatively cheaply, further investigation into the commercial production of hydrotalcite revealed that sources are limited and the cost was more than anticipated, significantly affecting the application of the medium in the field.

As the hydrotalcite appears to have potential for defluoridation, an alternative source of hydrotalcite waste product from a local bauxite refinery was identified. Initially batch adsorption experiments were carried out, however this resulted in increase in the fluoride concentration, which was due to the release of fluoride that was incorporated into the hydrotalcite during interaction with seawater. Consequently, a number of pretreatment options were trialled to remove the impurities of the roughly ground waste hydrotalcite; continuous washing, calcining at 500°C and washing of the calcined product with 0.1 M sodium hydroxide, however experiments utilising the waste product still released fluoride. Therefore no further investigation or adsorption studies were conducted with this medium

3.1.4 Water Quality Analysis

Water quality analysis was carried out on the water samples prior (initial) to batch experiments and with the treated water, to ensure that the final water quality characteristics were compliant with the ADWG and that the media would not contaminate the drinking water supply. The water quality characteristics that were analysed were those likely to be influenced by the adsorption process.

The treatment of the spiked RO water sample with the hydrotalcite (laboratory grade) resulted in the final water being contaminated with very fine particles of hydrotalcite that couldn’t be removed with a 0.45µm filter and thus the water quality analysis was not carried out on these samples.

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3.1.4.1 Physicochemical

The different media had varying impacts on the physical characteristics of the water treated (Table 9) and were consistent with the reactions observed in the adsorption curves. The treatment of the ‘natural’ water with the two types of AA did not have a significant impact on the pH of the water although the treatment with AA resulted in a significant decrease in some of the other physiochemical parameters. Following the treatment of the Ali Curung water there was a significant decrease of 28-33% in the alkalinity, corresponding to the significant decrease in hardness and >10% decrease in Total Dissolved Solids (TDS). The decrease in alkalinity (hardness and TDS) is due to some other ions interfering with the fluoride adsorption process, either by competition for adsorption sites or accumulating on the surface of the AA by forming magnesium and calcium carbonates (Maheshwari 2006, Rao 2003).

The treatment of the water with bauxite resulted in an increase in the alkalinity and TDS, which is due to the interference of ions with the fluoride removal efficiency, although there was no significant change in the pH or hardness. The increase in alkalinity is attributed to the exchange of fluoride for hydroxyl ions on the surface that are released in to the treated water. In contrast, the hydrotalcite (laboratory grade) significantly influenced the final physical water quality, resulting in a slightly lower alkalinity, a higher pH and hardness and appreciably higher TDS. The significant increase in TDS indicates that ions from the hydrotalcite are being exchanged for the fluoride and contaminating the final water quality. The physical characteristics of the spiked RO, Tennant Creek and Ali Curung water samples prior to treatment with the three media indicates the differences in the water quality. The spiked RO is relatively ‘pure’, the Tennant Creek water is relatively ‘complex’ containing a high alkalinity and moderate hardness, while the Ali Curung water is more ‘complex’ with a approximately double the alkalinity and hardness of the Tennant Creek water. The media display similar removal efficiencies that decrease with the increasing complexity of the water samples (Figures 9-11).

Table 9 Physical water quality analysis at the completion of the batch adsorption experiments using Activated Alumina (AA) Bauxite and Hydrotalcite to remove fluoride from spiked RO water 2 mg/L F- and natural water samples from Tennant Creek 1.4 mg/L F- and Ali Curung 2.4 mg/L F- (Appendix E).

Final Characteristics Physical Characteristics

ADWG (mg/L) Initial

AA (A-2) AA (CPN) Bauxite Hydrotalcite Alkalinity N/A Spiked RO <20 <20 40 <20 N/A Tennant Creek 220 200 200 260 160 Ali Curung 420 280 300 350 280 pH 6.5-8.5 Spiked RO 6.1 6.6 6.7 5.8 7.7 Tennant Creek 7.3 7.2 7.2 7.3 8.1 Ali Curung 7.5 7.3 7.4 7.3 8.0 TDS 500 Spiked RO 8 26 26 13 486 Tennant Creek 594 461 531 627 2426 Ali Curung 970 851 832 1005 2803 Hardness 200 Spiked RO 4 0.06 0.05 1.17 N/A Tennant Creek 99 23 34 60 105 Ali Curung 123 39 45 126 168 Bicarbonate N/A Spiked RO <20 <20 40 <20 N/A Tennant Creek 220 200 200 260 160 Ali Curung 420 280 300 350 280 Carbonate N/A Spiked RO <D.L. <D.L. <D.L. <D.L. <D.L. Tennant Creek <D.L. <D.L. <D.L. <D.L. <D.L. Ali Curung <D.L. <D.L. <D.L. <D.L. <D.L.

<D.L = Less than Detection Limit see Appendix E


36

3.1.4.2 Inorganic

The batch experiments using the AA and bauxite with the three water samples did not influence the chloride concentrations in the final water, which remained constant throughout the experiments, although there is a slight increase in the final concentrations with the Ali Curung water samples (Figure 12).

(a) (b)

Figure 12 Chloride concentrations, prior to batch adsorption experiments (initial) and the treated water (final), with 2mg/L F- spiked RO water (a) natural water samples from Tennant Creek 1.4 mg/L F- (b) and Ali Curung 2.4 mg/L F- (c) (Appendix E).

However, the treatment using hydrotalcite resulted in a significant increase in the chloride concentrations (Figure 12). The release of chloride is due to the exchange of chloride ions, within the hydrotalcite structure, for the fluoride ions in the solution. Although the guideline value for chloride is based on aesthetic considerations and not a health-based guideline, the significant increase in chloride levels will influence the appropriateness of this media for the treatment of drinking water. The final chloride levels with the spiked RO remained below the guideline of 250 mg/L, while the levels in both ‘natural’ water samples increased significantly (Figure 12).

3.1.4.3 Metals

The selection of the metals analysed were based on constituents of the media and likely adsorption interactions with constituents of the water, therefore relatively inert metals were not included in the analyses (Table 10). Depending on the media, there were various impacts of the final metal concentrations in the treated water.

>250

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37

Table 10 Concentration of metals (mg/L) influenced during the batch adsorption experiments using Activated Alumina (AA), Bauxite and Hydrotalcite to remove fluoride from spiked RO water 2 mg/L F- and natural water samples from Tennant Creek 1.4 mg/L F- and Ali Curung 2.4 mg/L F- (Appendix E).

Final Characteristics Metals ADWG (mg/L) Initial

AA (A-2) AA (CPN) Bauxite Hydrotalcite Na 180 Spiked RO 5.8 16.2 15.7 2.85 N/A Tennant Creek 129 129 135 126 940 Ali Curung 223 226 235 225 1160 Mg N/A Spiked RO 1.24 0.06 0.05 0.28 N/A Tennant Creek 27.1 14.3 23.2 25.4 62.3 Ali Curung 42.2 22.8 26.5 42.4 72.4 Al 0.2 Spiked RO 0.01 0.16 0.17 <D.L N/A Tennant Creek <R.L. 0.11 0.095 0.13 0.01 Ali Curung <R.L. 0.21 0.09 0.12 0.01 Ca N/A Spiked RO 2.4 <D.L <D.L 0.89 N/A Tennant Creek 72.1 8.80 10.6 34.9 42.2 Ali Curung 80.5 16.6 18.3 83.1 95.1 Zn 3 Spiked RO 0.01 0.01 0.01 0.01 N/A Tennant Creek 0.01 0.01 0.01 0.02 <D.L. Ali Curung 0.01 0.02 0.02 0.01 <D.L. Sr N/A Spiked RO <D.L. <D.L. <D.L. <D.L. N/A Tennant Creek 0.44 0.22 0.04 0.39 0.42 Ali Curung 0.83 0.06 0.08 0.79 0.80

<D.L = Less than Detection Limit see Appendix E N/A = Sample not analysed

Both types of AA performed similarly and were relatively selective for fluoride with limited influence on the other metal constituents in the water (Table 10). As discussed under the physical qualities, the treatment with AA resulted in a decrease in hardness, which is reflected through the decrease in the calcium and magnesium concentrations. There is also a slight decrease in the strontium (Sr) concentration after treatment, although this metal is not included in the ADWG. However, there was a slight increase in sodium concentrations, which was released from the AA matrix during treatment. One of the duplicate samples from treatment with the A-2 AA recorded elevated aluminium levels at the ADWG value, although the other samples were elevated the levels remained below ADWG values.

The sieved (500 µm) and pre-washed bauxite performed competitively with the more refined AA product, in terms of the influence on the metal constituents of the water. While, the treatment with bauxite resulted in an increase in the aluminium levels in the product water, the levels remained under ADWG value with both ‘natural’ waters. Also the treatment of the Tennant Creek water with the bauxite resulted in a slight increase in the zinc concentration in the product water, although again the levels were still below the ADWG value (Table 10).

Treatment of the water samples using hydrotalcite resulted in a significant increase in the sodium concentrations in the final product water. The sodium levels were at least five times the ADWG value, while sodium is not a health parameter the elevated concentrations will adversely effect the aesthetic quality of the water. The treatment also resulted in a significant increase in the magnesium concentrations in the treated water (Table 10).


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3.1.5 Assessment of media

The performances of the media were assessed based on the batch adsorption experiments and the results of the water quality analysis.

3.1.5.1 Activated Alumina (A-2 and CPN)

The two types of AA performed similarly during the batch adsorption experiments, both displaying promising defluoridation efficiencies, although the A-2 appeared slightly more efficient than the CPN (Figure 8). Both media are consistent products that are relatively easy to handle, although when transferring the media a ‘cloud’ of fine activated alumina particles was produced, which requires suitable personal protection equipment to ensure the health and safety of operators. The A-2 contained significantly more fine particles than the CPN and required approximately 10 times more washing to remove these particles and prevent contamination of the treated water. This poses a significant challenge in the field as RO water would need to be either used to wash the media on site or prior to transport to site, added additional transport and complexity to the system. Neither media resulted in a significant change in the water quality characteristics following treatment with the AA, except the slight decrease in the alkalinity, hardness and TDS (Table 9) and one of the duplicate samples from the A-2 showed aluminium levels at the ADWG value (Table 10). Overall, the use of AA for the defluoridation of water in the Northern Territory appears promising and further investigation of both types of media was carried out to determine the adsorption efficiency in a continuous flow column regime.

3.1.5.2 Bauxite

The use of bauxite to remove fluoride from the three water samples appears promising, especially considering that the bauxite is less than one tenth the cost of AA and is available locally (Appendix C). However, the removal mechanism is significantly slower than the AA and the utilisation of the media in a column system would require a very large system with a long contact time to achieve similar adsorption capacities to AA (Figure 8 and 9).

Although the bauxite is produced locally in the Northern Territory and in a number of other locations in Australia, the markets for the product are already established and current production has already been negotiated and sold in advance. In addition, the raw product is of a low quality and varies in size, resulting in a portion of very fine material that contaminates the final water. Although the fine material may be removed by sieving (500 µm) and pre-washing, negotiation to carry out this pre-treatment is required to produce a product suitable for the treatment of drinking water. The batch experiments also revealed that the treatment of the water samples with bauxite resulted in an increase in alkalinity and TDS, though the pH remained constant (Table 9). The treatment also resulted in an increase in the aluminium and zinc concentration in the product water with the Tennant Creek water, although the levels remained under ADWG value (Table 10). However, investigations with bauxite will not be continued at this stage, although there may be potential for the development of the media in the future. Although the removal efficiencies were relatively low and slow compared to the AA future investigations are warranted due to the significantly cheaper alternative that bauxite offers.

3.1.5.3 Hydrotalcite

Hydrotalcite shows some potential for use as a defluoridation medium for the treatment of drinking water. Consistent with the adsorption process the hydrotalcite adsorption efficiency is highest with the spiked RO sample followed by the natural water samples based on fluoride concentration (Figure 11). While the efficiency of the hydrotalcite appears promising the media significantly affects the final water quality. The use of the media significantly decreases the alkalinity (25-50%), increases pH and appreciably increases TDS (Table 9) and chloride levels (Figure 12). The hydrotalcite is very fine and the utilisation of such a fine media has a number of practical limitations in the field, and the product is not available on a commercial scale at a cost-effective price.

Investigations were continued using the locally made waste hydrotalcite product, although the removal efficiencies were not expected to be as high as the laboratory grade hydrotalcite, as the waste hydrotalcite is not pure and is complexed with calcium carbonate. The initial batch experiments with the waste product resulted in an increase in the fluoride concentration rather than a decrease, after a number of unsuccessful trials to remove the fluoride, the differential particle size was presumed to be the cause of the retention and


39

release of fluoride. However the treatment process believed to be required to ‘clean’ the hydrotalcite to an appropriate level for effective fluoride removal is complex. It would likely require the media to be effectively ground to a consistent size of between 500-1000 µm, treatment with strong solution of sodium carbonate (5M Na2CO3), followed by washing and then drying. However this process will be difficult to achieve on a large scale for use in the treatment of drinking water. Consequently, investigations with the two forms of hydrotalcite will not be continued at this stage, although there may be potential for the development of the media in the future.

3.2 Equilibrium Isotherms (batch)

While bauxite and hydrotalcite appeared promising for the treatment of drinking water there were a number of supplier, preparation and field application limitations that would impede the implementation of these media in the communities in the Northern Territory for the removal of fluoride from water supplies. Therefore, equilibrium isotherm studies were conducted with the two types of AA to understand the performance of the media and yield valuable information on the adsorption mechanisms and capacity of the two types of AA (Benefield et al. 1982).

3.2.1 Activated Alumina (A-2 and CPN)

Equilibrium studies were carried out to determine the fluoride removal on AA. It was observed that the adsorption reaches equilibrium when there is negligible change in the residual fluoride concentration. The distribution of fluoride between the liquid phase and the solid phase is a measure of the equilibrium in the adsorption process and can be expressed by the Langmuir and Freundlich equations (Ghorai and Pant 2005).


40

Figure 13 Adsorption studies with Activated Alumina A-2 and CPN, Spiked RO at 2 mg/L fluoride at pH 6.1(a,d) Tennant Creek at 1.4 mg/L fluoride at pH 7.3 (b,e) and Ali Curung 2.5 mg/L fluoride at pH 7.5 (c,f) at ambient temperature 23+/- 1°C (Average n=2 see Appendix F for data).

The fluoride removal efficiency of the A-2 and CPN are similar, although generally the A-2 appears to be more efficient than the CPN (Figure 13). Again, the adsorption efficiencies are consistent with the complexity of the water samples, the spiked RO samples being most efficient followed by the Tennant Creek and lastly Ali Curung, which has the highest fluoride concentration, alkalinity TDS and hardness. In general, the percentage of fluoride removed increased with increasing absorbent dose due to increasing the available adsorption sites. The results from the batch experiments are consistent with this process as the smaller amounts of media recorded lower removal efficiencies compared to the larger amounts of media, although there is a degree of variance in the efficiency of the different amounts of media due to experimental and instrumental error.

The results of the equilibrium isotherms can be used to describe the equilibrium distribution of the adsorbate between the liquid and solid phases through mathematical relationships (Benefield et al. 1982). These equilibrium isotherms describe adsorption by illustrating the relationship between the bulk aqueous activity (concentration) of the adsorbate and the amount adsorbed at a constant temperature (Stumm 1992). The two most common that correlate with the adsorption of fluoride are the Langmuir and Freundlich isotherms.

(a)

(b)

(c)

(d)

(e)

(f)

0

20

40

60

80

100

0 20 40 60 80Time (min)

Fluo

ride

rem

oval

(%)

1g CPN 3g CPN5g CPN 7g CPN

0

20

40

60

80

100

0 20 40 60 80Time (min)

Fluo

ride

rem

oval

(%)


0

20

40

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80

100

0 20 40 60 80Time (min)

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ride

rem

oval

(%)


0

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40

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80

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0 5 10 15 20 25 30Time (min)

Fluo

ride

rem

oval

(%)

3g A-2 4g A-25g A-2 6g A-2

0

20

40

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100

0 5 10 15 20 25 30Time (min)

Fluo

ride

rem

oval

(%)

8g A-2 9g A-210g A-2 11g A-2

0

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40

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80

100

0 5 10 15 20 25 30Time (min)

Fluo

ride

rem

oval

(%)

9g A-2 10g A-211g A-2 12g A-2


41

3.2.2 Langmuir Isotherm

The Langmuir isotherm is based on the assumption that adsorption sites on the surface of the adsorbent become occupied by a monolayer of adsorbate from the solution (Stumm and Morgan 1996). Furthermore, the isotherm assumes that all the adsorption sites have equal affinities for molecules of the adsorbate and that the presence of adsorbed molecules at one site will not affect the adsorption of molecules at an adjacent site (Benefield et al. 1982). The Langmuir equation is expressed as:

qa = Q° bCeq / (1+bCeq) or 1/qa = ( 1/Q° bCeq) + 1/Q°

Where: qa = amount of adsorbate absorbed (mg) Ceq = equilibrium concentration of adsorbate in solution (mg/L) Q° = limiting adsorption capacity b = empirical coefficient related to affinity binding sites

3.2.3 Freundlich Isotherm

The Freundlich isotherm is based on the assumption that the adsorbent had a heterogeneous surface composed of different classes of adsorption sites (Benefield et al. 1982). The Freundlich equation is empirically derived and assumes a straight logarithmic isotherm, described by the following equation:

qa = kCeq 1/n or log qa = log k + 1/n log Ceq

Where: qa = amount of adsorbate absorbed (mg) Ceq = equilibrium concentration of adsorbate in solution (mg/L)

k = sorption capacity 1/n = adsorption intensity

The Freundlich relation differs from the Langmuir in that not all sites on the surface are considered equal but rather that adsorption becomes progressively more difficult as more and more adsorbate accumulates. Furthermore, it is assumed that once the surface is covered, additional adsorption species can be accommodated, thus no maximum (monolayer) adsorption is predicted by this relation. The equation does not imply any particular mechanism of adsorption, it is purely empirical and has been found to be most satisfactory in the low concentration range (vanLoon and Duffy 2000).


42

3.2.4 Isotherm interpretation (A-2 and CPN)

The adsorption verses time plots for the A-2 are consistent with previous batch experiments, the spiked RO sample displaying a greater adsorption capacity than with the natural water samples, the Ali Curung water resulting in the lowest capacity (Figure 14).

Figure 14 Langmuir plot for Activated Alumina A-2 (a) and CPN (b) and Freundlich plot for A-2 (c) and CPN (d) (Appendix F). However, the results for the CPN are not consistent with previous results, as the CPN AA displays a greater adsorption capacity with the Ali Curung than with Tennant Creek. This is not expected as the Ali Curung water has a higher fluoride concentration and higher concentrations of competing ions than the Tennant Creek (Appendix A). These results may be due to the relatively similar performance of the CPN with the three water samples, where the adsorption range is larger than with the A-2. Also the higher fluoride concentrations in the Ali Curung water may favour greater adsorption, although this is generally correlated with significantly higher fluoride concentrations (Chauhan et al. 2007). The isotherm plots were analysed to determine the performance of the media and to compare the different media. Both the A-2 and CPN AA show a strong correlation to both equilibrium isotherms, although generally there appears to be a higher correlation with the Freundlich isotherm, indicated by the higher R2 values (Table 11).

(a) (b)

(d) (c)

y = 0.5654x + 3.4188R2 = 0.9006

y = 0.3406x + 7.9219R2 = 0.8979

y = 0.6099x + 9.754R2 = 0.9645

0

2

4

6

8

10

12

14

0 2 4 6 8 10 121/Ceq (mg/L)

1/qa

(mg/

g)

Spiked RO Tennant CreekAli Curung

y = 0.246x + 0.1065R2 = 0.9852

y = 0.1699x + 0.0704R2 = 0.9843 y = 0.0332x + 0.0743

R2 = 0.8739

0.01

0.10

1.000.01 0.10 1.00

Log Ceq (mg/L)

LOG

qa

(mg/

g)

Spiked ROTennant CreekAli Curung

y = 0.2508x + 2.5576R2 = 0.9397

y = 0.3934x + 4.6626R2 = 0.9585

y = 0.1995x + 4.5289R2 = 0.9232

0

5

10

15

0 5 10 15 201/Ceq (mg/L)

1/qa

(mg/

g)

Spiked ROTennant CreekAli Curung

y = 0.5649x + 0.1207R2 = 0.9989

y = 0.151x + 0.0958R2 = 0.9591 y = 0.1936x + 0.1194

R2 = 0.9787

0.01

0.1

10.01 0.1 1

Log Ceq (mg/L)

Log

qa (m

g/g)

Spiked RO

Tennant CreekAli Curung


43

Table 11 Results from the Langmuir and Freundlich equilibrium isotherms for A-2 and CPN (Appendix F). Langmuir Freundlich Activated

Alumina Q� mg/kg b R2 k mg/kg 1/n R2

A-2 Spiked RO 299 0.517 0.900 106 0.246 0.985 Tennant Creek 128 0.370 0.897 70.4 0.169 0.984 Ali Curung 102 0.168 0.964 74.3 0.033 0.873 CPN Spiked RO 391 1.559 0.939 565 0.120 0.998 Tennant Creek 224 0.545 0.958 194 0.193 0.978 Ali Curung 221 1.106 0.923 259 0.151 0.959

The results from the equilibrium isotherms are more consistent and relatively higher with the CPN rather than the A-2 (Table 11), although they are significantly lower than similar batch studies (Table 12). The large difference in adsorption capacities in this study compared to those in the literature is primarily due to the surface structures of AA and their respective specific surface areas. Equilibrium determinations vary considerably depending on the experimental conditions, especially the pH, the initial fluoride concentration and other experimental conditions. Characteristics of the AA utilised for experiments, including quality, physical properties and the degree of activation, will also influence the efficiencies.

Table 12 Summary of batch Langmuir and Freundlich equilibrium isotherm data for previous investigations (Ghorai and Pant 2004; Ghorai and Pant 2005; Pietrelli 2005).

Langmuir Freundlich AA batch investigation

Type of Water

pH of water Q� mg/kg b R2 k mg/kg 1/n R2

Ghorai and Pant 2005 Spiked RO 7 2410 0.31 0.999 1780 0.32 N/A Pietrelli 2005 (MGA) Waste 6.5 12570 0.023 0.991 630 0.197 0.982Pietrelli 2005 (AA) Waste 6.5 7090 0.048 0.993 6190 0.019 0.823

Higher fluoride adsorption capacities are generally reported either from spiked water without competing ions or when the pH is at the ‘optimum range of 5–6, which results in favourable conditions for fluoride exchange (Pietrelli 2005). Fluoride removal by AA has been shown to be highly concentration dependent and adsorption capacity increases with the increase in initial fluoride concentration (Chauhan et al. 2007). The relatively low initial fluoride concentrations in the natural water samples in the Northern Territory at the natural pH with competing ions will significantly influence the adsorption capacities. Although higher adsorption capacities were achieved with the spiked RO sample, these remained significantly lower than expected (Table 11 and 13). This may be partially attributed to the stronger correlation to the Freundlich isotherm, compared to previous results that have greater correlation to the Langmuir equation (Table 12). For the Freundlich equation the adsorption suggested by k is not a maximum adsorption and additional adsorbed species can be accommodated (vanLoon and Duffy 2000) indicating a minimum rather than a maximum capacity. This suggests that the adsorption of fluoride onto AA (in this case) was not only restricted to the formation of a monolayer of adsorbate on the surface and also involved the adsorption or diffusion of the adsorbate into the pores of the AA. Variance will always remain due to AA quality, variable experimental conditions and instrumental and experimental error, emphasising the need to carry out batch, column and field trials to determine the applicability of the media.

While equilibrium isotherms are useful in providing an indication of the performance of the adsorption media under static test conditions, they do not give accurate scale-up data in a fixed bed system (Ghorai and Pant 2005). In order to ensure successful practical applicability of the activated alumina additional column studies are required to evaluate the performance of the systems in continuous flow system (Benefield et al. 1982).


44

3.3 Column Studies

The column studies were conducted using the CPN AA. The CPN was selected as the performance of the media in the equilibrium isotherms was more favourable and the media required significantly less pre-washing. Also the manufacturer of A-2 recently restructured and has withdrawn from the water treatment market, therefore product is no longer available. The column studies were undertaken in order to determine the efficiency of the system in the laboratory to allow a pilot-scale trial in the field in the future and therefore were carried out with natural water samples.

3.3.1 Column System

Primarily the AA physical properties, bed height and flow rate determine the efficiency of AA defluoridation systems (Chauhan et al. 2007; Ghorai and Pant 2004; Ghorai and Pant 2005; Pietrelli 2005). While the AA properties were based on the product available in the market (Appendix C), the bed height and flow rate were determined based on previous studies. Investigations were carried out using a cylindrical column, as this is accepted as the most suitable for adsorption systems (Chauhan et al. 2007). Bed depth of the AA is an important determinant of column efficiency, requiring a critical minimum depth to ensure that there is sufficient depth to remove the fluoride and avoid premature increases in the effluent fluoride concentration (Chauhan et al. 2007). Previous studies indicated that tall narrow columns achieve high removal efficiencies, however the application of these in the field is often not practical and the dimensions selected for this investigation were based on the column height that is twice the width (Veressinina 2001). It is reported that 5 minutes is sufficient Empty Bed Contact Time (EBCT) to remove fluoride from solution at pH 6 (Broom et al. 2005; Chauhan et al. 2007; HDR Engineering 2001). At this pH, the effect of bicarbonate, which is one of the primary competing anions for fluoride binding to the AA surface, is eliminated due to protonation. However, at the natural groundwater pH of 7-8, longer EBCT are beneficial to ensure complete binding of fluoride, consequently 20 – 30 minutes EBCTs were investigated (Chauhan et al. 2007).

Initially, the AA will adsorb the fluoride ions and the fluoride concentration of the effluent will be very low. As adsorption continues, the effluent concentration rises, slowly at first but then abruptly (Ghorai and Pant 2004). The increase in fluoride concentration in the effluent is referred to as the breakthrough curve, which reaches the breakthrough point when the fluoride concentration exceeds a predetermined value, which was 0.8 mg/L for this investigation. This value is considered the maximum fluoride concentration in the drinking water that ensures the protection from the negative effects of fluoride for the relatively high average mean temperature of the region (Table 3). The time between the start of operation and reaching the breakthrough point is the accumulated volume of the treated water. This allows the calculation of the number of Bed Volumes (BV), which is an expression of the capacity of treatment before the column needs to be regenerated (Fawell et al. 2006).

AA can either be regenerated or replaced with new media when the selected breakthrough point is reached. The adsorptive capacity of AA is pH sensitive and employing pH adjustment generally provides cost advantages whether the media is regenerated or replaced. As the pH adjustment chemicals are usually the same chemicals that are used for regeneration, it is generally advantageous to couple regeneration with pH adjustment systems. There are a number of advantages and disadvantage of operating adsorptive systems with pH adjustment and regeneration or the replacement of spent media (Table 13).


45

Table 13 Advantages and Disadvantages of AA column systems with either regeneration or media replacement (Rubel 2003).

Column System Advantages Disadvantages

Regeneration (including pH adjustment and regeneration)

1. Low-cost &simple to operate. 2. Requires minimal operator attention during treatment. 3. Can employ either manual or automatic operation. 4. AA media has longer treatment runs (greatest removal capacity)

1. Requires chemical feed equipment, storage & handling of corrosive chemicals (acid and caustic) for pH adjustment of raw water and re-adjustment of treated water. 2. pH adjustment chemicals increase inorganic ions & TDS in the treated water. 3. Regeneration of spent media requires disposal of wastewater.

Media Replacement (without pH adjustment or regeneration)

1. Inexpensive to install & depending on water quality characteristics operational cost may be low. 2. Does not require chemical feed, storage equipment & handling. 3. Requires minimal operator attention during treatment. 4. Can employ either manual or automatic operation. 6. Disposal of spent AA can be as a non-hazardous waste

1. Lower adsorptive removal capacity resulting in much shorter treatment runs. 2. Other ions in the water may compete with adsorption sites and interfere with the adsorption efficiently when not operated at the ‘optimum’ pH. 3. Requires more frequent media replacement. Expensive materials could result in costly operation.

Regeneration including the pH adjustment requires chemical (acid and caustic) dosing, handling and storage and is likely to be economically justified for systems with high flow rates and fluoride concentrations, due to the rapid consumption of adsorption capacity. Media replacement may be appropriate to avoid the use of chemicals, especially those that may degrade the quality of the potable water, or for other economical, technical, or aesthetic concerns. Therefore each evaluation should include considerations of both operational modes of the column systems (Rubel 2003).

3.3.2 Media Replacement

Column studies based on media replacement were carried out with the CPN AA with the natural water samples from Tennant Creek and Ali Curung.

Small systems typically conduct AA treatment under natural pH conditions. As such these systems operate without regeneration, and the savings in capital and chemical costs required for pH adjustment and media regeneration offset against the costs associated with decreased efficiency of the AA system. The exhausted media that is replaced is considered non-toxic and may be disposed of in municipal solid waste landfill (US EPA 2003b). Although the toxicity of the exhausted media may need to be verified by testing as other possibly toxic contaminants may also be absorbed this can easily be remobilised. Therefore if the exhausted media is classified as hazardous it requires proper disposal that will add additional costs to the systems.

Figure 15 Experimental breakthrough curve from treatment with the Tennant Creek water (a) and Ali Curung water (b) (Appendix G).

0.0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500 600 700

Bed Volumes (L)

Ct/C

o

Tennant Creek, 1.4 mg/L fluoride, EBCT 31 min

0.0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400 500Bed Volumes (L)

Ct/C

o

Ali Curung, 2.2 mg/L fluoride, EBCT 22 minAli Curung, 2.3 mg/L fluoride, EBCT 21 min

(a) (b)


46

The breakthrough curves for the natural water samples indicate that initially the AA absorbs all of the fluoride leaving no residual in the treated water, although after a number of bed volumes (BV=1050 mL) the fluoride residual gradually increases until it reaches the breakthrough point (Benefield et al. 1982). The breakthrough point of 0.7 mg/L fluoride was below the initial fluoride concentration and the curves do not plateau as would be expected if the columns were to continue operation (Ghorai and Pant 2005; Pietrelli 2005). Consistent with the equilibrium isotherm results, the treatment of the Tennant Creek water achieved a fluoride adsorption capacity of 935 mg per kg of AA, which is lower than the average fluoride adsorption capacity of 1268 for the treatment of the Ali Curung water (Figure 16). The results from the column studies are significantly higher than those predicted by the equilibrium isotherm with the column system being approximately 10 times more efficient based on the contact time. The column results are similar to results reported by Fawell et al. (2006). A study of the treatment of natural water with a fluoride concentration of 3 mg/L and alkalinity of 432 mg/L achieved a comparable adsorption capacity of 1140 mg/kg (Karthikeyan et al. 1994). Similarly, sample water representing typical natural water characteristics was used with a number of AA columns and recorded an adsorption capacity of 1788 mg/kg, although the initial fluoride concentration was higher at 10.5 mg/L (Chauhan et al. 2007).

3.3.3 Regeneration (and Reactivation)

Column studies based on regeneration (and reactivation) were carried out with the CPN AA with the natural water sample from Ali Curung.

Although the investigations have been carried out without pH adjustment, an assessment of the feasibility of regeneration will be carried out. This is primarily based on the limitations of pH adjustments on site at the individual communities, which relates to availability of personnel and appropriate skills and the regular transport of chemicals to remote locations. Regeneration may be carried out at a central regeneration location, increasing the feasibility of the treatment. However, the regeneration treatment increases the pH and dissolves some of the AA media, resulting in elevated concentrations of TDS, aluminium and fluoride in the waste solution produced (US EPA 2003b).

Figure 16 The fluoride removed during CPN AA column studies with treatment of the Ali Curung water following regeneration of the media (Appendix G).

The results of the fluoride removal efficiency following regeneration are consistent with previous results, with the efficiency decreasing with increasing number of regeneration cycles (Fawell et al. 2006; Ghorai and Pant 2005; US EPA 2003b). The first regeneration resulted in a loss of over 36% of the initial fluoride removal efficiency, although the second regeneration only resulted a further 16% loss and the third a further 6% (Figure 16). This decrease in efficiency is typical of regeneration processes, although the initial loss may have been exaggerated through the excess use of regeneration (and reactivation) solution during the process that was subsequently decreased with the second and third regeneration cycles. Also flushing the system with the fluoride contaminated water to raise the pH following regeneration may have resulted in the

0

250

500

750

1000

1250

1500

Initial 1st 2nd 3rd

Regeneration Cycle

Fluo

ride

Rem

oved

(mg) Ali Curung 2.3 mg/L fluoride


47

uptake of fluoride ions on the available adsorption sites and reduced the efficiency of the media prior to use. However, as discussed the transport of large quantities of RO water to site is prohibitive and thus in the field it was more likely that the fluoride contaminated water would be used and the low pH of the water was less likely to favour adsorption of fluoride during washing.

3.4 Pilot Plant

The column studies indicate that the AA system is capable of successfully treating water supplies in the Northern Territory and therefore a pilot plant is recommended to treat the Tennant Creek water supply. This will allow assessment of the system operation and maintenance requirements prior to implementation into more remote locations. The pilot plant would be designed to treat drinking water delivered to the Primary school(s) at Tennant Creek through an on-site treatment system. This will target the population group at highest risk from exposure to elevated levels of fluoride; that is, children who have lost baby teeth and have not finished growing their adult teeth (notionally 5-12 yrs old). The AA system recommended for the pilot trial consists of a number of AA columns in series, which allows higher flow rates through the columns, while still maintaining sufficient contact time with the AA to effectively remove the fluoride from the water. The columns may be constructed using PVC pipe (4 x width 40 cm, height 155 cm), each containing approximately 125 kg AA. The system may be operated with replacement of the media and may require additional pumps and water storage depending on the pressures available in the existing system.


48

4 CONCLUSION

Batch adsorption experiments utilising AA, bauxite and hydrotalcite successfully removed fluoride from natural groundwater samples. AA displayed the highest removal rate, greatest capacity for fluoride and the smallest impact on the other water quality characteristics of the three media and was utilised for further equilibrium isotherms and column studies.

Equilibrium isotherms and column studies confirmed the defluoridation potential of AA in treating the natural groundwater supplied in communities in the Northern Territory. The AA equilibrium isotherms were correlated to the Langmuir and Freundlich equations indicating that fluoride adsorption was favourable. While, the equilibrium isotherms underestimated the adsorption capacity of the AA, the column studies correlated closely with previous investigations and confirmed the capacity of AA in a continuous system. Water from two communities in the Northern Territory, Tennant Creek and Ali Curung, was successfully treated through column studies, achieving adsorption capacities for fluoride of 875 mg/kg and 1268 mg/kg respectively. AA regeneration investigations revealed that the fluoride removal efficiency following regeneration decreases with increasing number of regeneration cycles, although the reduction in capacity decreases with each regeneration cycle.

Implementation of systems based on bauxite and hydrotalcite requires additional research to refine the raw product and determine system design appropriate for effective treatment. Bauxite is particularly interesting as it is readily available and relatively cheap and further investigation into the refinement of the raw product including activation temperature, regeneration capacity, medium preparation and design of the treatment system will provide a greater assessment of the treatment potential. Similarly, the utilisation of the hydrotalcite waste product for the treatment of drinking water may have potential and further investigation into the refinement of the raw product to ensure effective removal of fluoride and the regeneration capacity will provide a greater indication of the defluoridation capabilities.


49

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54

6 APPENDICES

Appendix A: Northern Territory Community Water Quality Characteristics


55

Appendix B: Fluorosis Data - Tennant Creek Children 2001/2002

Fluorosis levels Average Fluorosis Index Fluorosis in Children born in Tennant Creek

Selected teeth Fluorosis Severe Moderate Mild Very Mild Questionable Normal

YOB Indigenous Born TC # yrs TC 12 11 21 22 Score (5) (4) (3) (2) (1) (0) 92 Y Y 2 3 3 3 2.75 0 0 0 1 0 0 92 N Y 9 1 1 9 1 0 0 0 0 1 0 92 Y Y 3 3 3 3 3 0 0 1 0 0 0 92 N Y 2 3 3 2 2.5 0 0 0 1 0 0 92 N Y 4 4 4 4 4 0 1 0 0 0 0 89 Y Y 9 2 2 2 2 0 0 0 1 0 0 92 N Y 2 2 2 9 2 0 0 0 1 0 0 92 Y Y 3 4 4 3 3.5 0 0 1 0 0 0 92 Y Y 4 4 4 4 4 0 1 0 0 0 0 91 N Y 1 1 0 1 0.75 0 0 0 1 0 0 93 Y Y 2 2 2 2 2 0 0 0 1 0 0 94 Y Y 9 4 4 9 4 0 1 0 0 0 0 90 Y Y 3 4 4 3 3.5 0 0 1 0 0 0 89 Y Y 5 5 5 5 5 1 0 0 0 0 0 92 N Y 9 3 3 9 3 0 0 1 0 0 0 93 N Y 9 2 2 1 3.5 0 0 1 0 0 0 91 N Y 2 3 3 3 2.75 0 0 0 1 0 0 90 N Y 3 2 2 3 2.5 0 0 0 1 0 0 90 Y Y 3 3 3 3 3 0 0 1 0 0 0 91 N Y 3 3 3 3 3 0 0 1 0 0 0 91 N Y 3 3 3 3 3 0 0 1 0 0 0 91 Y Y 3 3 3 3 3 0 0 1 0 0 0 92 Y Y 2 2 2 2 2 0 0 0 1 0 0 91 Y Y 2 1 1 2 1.5 0 0 0 0 1 0 94 N Y 9 4 4 9 4 0 1 0 0 0 0 90 N Y 4 4 4 4 4 0 1 0 0 0 0 91 Y Y 3 4 4 3 3.5 0 0 1 0 0 0 92 N Y 2 3 3 2 2.5 0 0 0 1 0 0 Total 2.9 1 5 10 10 2 0 4% 18% 36% 36% 7% 0%


56

Appendix B continued

Fluorosis levels Average Fluorosis Index Fluorosis in Children residing in Tennant Creek longer than 1 year Selected teeth Fluorosis Severe Moderate Mild Very Mild Questionable Normal

YOB Indigenous Born TC # years TC 12 11 21 22 Score (5) (4) (3) (2) (1) (0)

94 Y N Most of life 9 3 3 3 3 0 0 1 0 0 0 89 N N Most of life 2 2 2 2 2 0 0 0 1 0 0 91 Y N Most of life 3 3 3 3 3 0 0 1 0 0 0 90 N N 9 3 4 4 3 3.5 0 0 1 0 0 0 91 N N 9 3 4 4 3 3.5 0 0 1 0 0 0

92 N N 8 (from

Adelaide) 3 4 4 3 3.5 0 0 1 0 0 0 92 N N 7 2 3 3 2 2.5 0 0 0 1 0 0 91 Y N 6 4 4 4 4 4 0 1 0 0 0 0 90 Y N 6 2 2 2 2 2 0 0 0 1 0 0

92 N N 5 (from

Adelaide) 2 3 3 2 2.5 0 0 0 1 0 0

92 Y N 5 (from Pt August) 2 3 3 2 2.5 0 0 0 1 0 0

92 N N 4 3 3 3 3 3 0 0 1 0 0 0

92 N N 4 (from

Katherine) 0 1 1 0 0.5 0 0 0 0 1 0 92 N N 3 2 2 2 2 2 0 0 0 1 0 0 92 Y N 3 (from Alice) 2 1 1 2 1.5 0 0 0 0 1 0

90 N N 3 (from

Adelaide) 3 4 4 3 3.5 0 0 1 0 0 0 Total 2.7 0 1 7 6 2 0 0% 6% 44% 38% 13% 0%


57

Appendix B continued

Fluorosis levels Average Fluorosis Index Fluorosis in Children residing in Tennant Creek less than 1 year Selected teeth Fluorosis Severe Moderate Mild Very Mild Questionable Normal

YOB Indigenous Born TC

# years in TC 12 11 21 22 Score (5) (4) (3) (2) (1) (0)

93 Y N 1 3 3 3 3 3 0 0 1 0 0 0 91 N N 1 3 3 2 2 2.5 0 0 0 1 0 0 93 Y N 1 1 1 1 1 1 0 0 0 0 1 0 93 Y N 1 (from QLD) 0 0 0 0 0 0 0 0 0 0 1 92 N N 1 (from PNG) 0 0 0 0 0 0 0 0 0 0 1

92 Y N 1 (from

Melbourne) 9 0 0 9 0 0 0 0 0 0 1

91 N N 1 (from

Melbourne) 2 2 2 2 2 0 0 0 1 0 0

90 N N 1 (from

Melbourne) 2 2 2 2 2 0 0 0 1 0 0

93 Y N 1 (from

Katherine) 1 1 1 1 1 0 0 0 0 1 0 Total 1.6 0 0 1 3 2 3 0% 0% 11% 33% 22% 33% The enamel surface is smooth glossy and usually a pale creamy white colour The enamel shows slight aberrations from the translucency of normal, which may range from a few white flecks to occasional spots Small, opaque, paper white areas scattered irregularly over the tooth but involving less than 25% of the labial tooth surface The white opacity of the enamel of the tooth is more extensive than for 2, but covers less than 50% of the tooth surface The enamel surfaces of the teeth show marked wear and brown stain is frequently a disfiguring feature The enamel surfaces are badly affected and hypoplasia is so marked that the general form of the tooth may be affected. There are pitted of worn areas and Brown stains are wide spread, the teeth often have a corroded appearance Non-fluorotic defects recorded


58

Appendix C: Media specifications Activated Alumina and Bauxite

Typical chemical and physical properties of Activated Alumina A-2 and CPN

Properties A-2 28x48 CPN 28x48 Chemical (%) Al2O3 93.6 92.0 SiO2 0.02 0.02 Fe2O3 0.02 0.03 Na2O 0.35 0.30 TiO2 0.002 - Loss on ignition 6.0 7.0 Physical Surface area (m2/g) 300 315 Total pore volume (cc/g) - 5 Packed bulk density (kg/m3) 697 752 Feasibility Estimated cost (per kg) 8.0 10.0

(Engelhard Corporation 2005 and UOP LLC 1999)

Engelhard Corporation (2005) CPN Granular Activated Alumina – Arsenic and fluoride removal. Engelhard Corporation, United States

UOP LLC. 1999, A-2 Activated Alumina. UOP LLC, United States.

Typical specification of physical, chemical and mineralogy properties of Alcan bauxite (Alcan Gove Pty Limited)

Properties Alcan Bauxite Chemical (%) Al2O3 49.7 SiO2 4.7 Fe2O3 16.3 TiO2 3.1 CaO <0.01 P2O5 0.06 K2O 0.02 Cr2O3 0.03 V2O5 0.06 MnO 0.01 ZrO2 0.16 ZnO <0.01 MgO 0.10 SO3 0.10 OrgC 0.28 Physical Loss o ignition 25.6 Mineralogy Gibbsite 67.0 Boehmite 2.8 Kaolinite 8.5 Hematite 15.1 Quartz 0.7 Feasibility Estimated cost ($/kg) 1.0


59

Appendix D: Results of Batch Adsoption Experiments

Results of Batch Adsoption Experiments

Activated Alumina A-2 Raw Data - Spiked RO

0 15 30 45 60 90 150 300 Test 1.88 0.25 0.01 <DL 0.02 0.02 <DL <DL

Duplicate 1.82 0.22 0.1 <DL <DL 0.02 <DL <DL STDEVControl 1.93 2.11 2.12 2.16 2.1 2.07 1.94 1.94 0.09 Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percentage removal 0 15 30 45 60 90 150 300

Test 0 86.7 99.5 100.0 98.9 98.9 100.0 100.0 Duplicate 0 87.9 94.5 100.0 100.0 98.9 100.0 100.0

Mean 0 87.3 97.0 100.0 99.5 98.9 100.0 100.0 Range 0 0.60 2.48 0.00 0.53 0.00 0.00 0.00

Raw Data - Tennant Creek 0 15 30 45 60 90 150 300

Test 1.28 0.3 0.18 0.04 <DL 0.05 0.02 <DL Duplicate 1.32 0.26 0.16 <DL <DL 0.04 0.01 <DL STDEVControl 1.41 1.36 1.43 1.47 1.45 1.4 1.33 1.39 0.05 Blank <DL <DL <DL <DL <DL <DL <DL <DL


Test 0 76.6 85.9 96.9 100.0 96.1 98.4 100.0 Duplicate 0 80.3 87.9 100.0 100.0 97.0 99.2 100.0

Mean 0 78.4 86.9 98.4 100.0 96.5 98.8 100.0 Range 0 1.87 0.97 1.56 0.00 0.44 0.40 0.00

Raw Data - Ali Curung 0 15 30 45 60 90 150 300

Test 2.31 0.62 0.39 0.25 0.04 <DL <DL <DL Duplicate 2.47 0.57 0.32 0.15 <DL <DL <DL <DL STDEVControl 2.3 2.29 2.41 2.07 2.13 1.94 1.96 2 0.18Blank <DL <DL <DL <DL <DL <DL <DL <DL


Test 0 73.2 83.1 89.2 98.3 100.0 100.0 100.0 Duplicate 0 76.9 87.0 93.9 100.0 100.0 100.0 100.0

Mean 0 75.0 85.1 91.6 99.1 100.0 100.0 100.0 Range 0 1.88 1.96 2.37 0.87 0.00 0.00 0.00 Activated Alumina CPN

Raw Data - Spiked RO 0 15 30 45 60 90 150 300

Test 1.89 0.16 <DL <DL <DL <DL <DL <DL Duplicate 1.87 0.11 <DL <DL <DL <DL <DL <DL STDEVControl 1.89 1.82 1.82 1.94 1.97 1.93 1.89 1.91 0.05 Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 91.5 100.0 100.0 100.0 100.0 100.0 100.0 Duplicate 0 94.1 100.0 100.0 100.0 100.0 100.0 100.0

Mean 0 92.8 100.0 100.0 100.0 100.0 100.0 100.0 Range 0 1.29 0.00 0.00 0.00 0.00 0.00 0.00


60

Appendix D continued


Test 1.3 0.19 <DL <DL <DL <DL <DL <DL Duplicate 1.29 0.24 0.04 <DL <DL <DL <DL <DL STDEVControl 1.29 1.33 1.35 1.3 1.29 1.17 1.09 1.34 0.09 Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 85.4 100.0 100.0 100.0 100.0 100.0 100.0 Duplicate 0 81.4 96.9 100.0 100.0 100.0 100.0 100.0

Mean 0 83.4 98.4 100.0 100.0 100.0 100.0 100.0 Range 0 1.99 1.55 0.00 0.00 0.00 0.00 0.00


Test 2.42 0.98 0.71 0.37 0.29 0.21 0.08 0.07 Duplicate 2.51 0.78 0.5 0.32 0.41 0.21 0.1 0.04 STDEVControl 2.41 2.39 2.35 2.35 2.21 2.28 2.18 2.37 0.08 Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 59.5 70.7 84.7 88.0 91.3 96.7 97.1 Duplicate 0 68.9 80.1 87.3 83.7 91.6 96.0 98.4

Mean 0 64.2 75.4 86.0 85.8 91.5 96.4 97.8 Range 0 4.71 4.71 1.27 2.18 0.16 0.34 0.65 Bauxite

Raw Data - Spiked RO 0 15 30 45 60 90 150 300

Test 1.98 1.65 1.46 1.34 1.17 1.14 1.05 0.77 Duplicate 1.96 1.65 1.56 1.38 1.32 1.18 0.97 0.86 STDEVControl 2.14 1.92 1.87 1.94 1.82 1.81 1.85 1.87 0.11Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 16.7 26.3 32.3 40.9 42.4 47.0 61.1 Duplicate 0 15.8 20.4 29.6 32.7 39.8 50.5 56.1

Mean 0 16.2 23.3 31.0 36.8 41.1 48.7 58.6 Range 0 0.43 2.93 1.37 4.13 1.31 1.77 2.49


Test 1.36 1.28 1.29 1.22 1.29 1.2 1.15 1.02 Duplicate 1.34 1.34 1.36 1.35 1.25 1.19 1.12 0.9 STDEVControl 1.4 1.31 1.42 -0.08 1.31 1.37 1.23 1.24 0.50Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 5.9 5.1 10.3 5.1 11.8 15.4 25.0 Duplicate 0 0.0 -1.5 -0.7 6.7 11.2 16.4 32.8

Mean 0 2.9 1.8 4.8 5.9 11.5 15.9 28.9 Range 0 2.94 3.32 5.52 0.78 0.29 0.49 3.92


61

Appendix D continued


Test 2.29 2.14 2.11 2.08 2.26 2.24 1.94 1.96 Duplicate 2.27 2.15 2.19 2.17 2.09 2.09 2.02 1.82 STDEVControl 2.26 2.21 2.29 2.22 2.24 2.34 2.3 2.13 0.06Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 6.6 7.9 9.2 1.3 2.2 15.3 14.4 Duplicate 0 5.3 3.5 4.4 7.9 7.9 11.0 19.8

Mean 0 5.9 5.7 6.8 4.6 5.1 13.1 17.1 Range 0 0.63 2.17 2.38 3.31 2.87 2.14 2.71

Hydrotalcite Raw Data - Spiked RO

0 15 30 45 60 90 150 300 Test 1.96 <DL <DL <DL <DL <DL <DL <DL

Duplicate 1.95 <DL <DL <DL <DL <DL <DL <DL STDEVControl 1.97 1.96 2.01 2.04 1.97 1.98 2.07 1.93 0.05 Blank <DL <DL <DL <DL <DL <DL <DL <DL

Percent removal 0 15 30 45 60 90 150 300

Test 0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Duplicate 0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

Mean 0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Range 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00



Percent removal 0 15 30 45 60 90 150 300

Test 0 53.2 56.8 71.2 72.7 75.5 81.3 77.7 Duplicate 0 61.4 62.9 65.0 69.3 79.3 75.7 76.4

Mean 0 57.3 59.8 68.1 71.0 77.4 78.5 77.1 Range 0 4.10 3.01 3.11 1.69 1.87 2.79 0.63



Percent removal 0 15 30 45 60 90 150 300

Test 0 46.4 49.8 54.1 53.6 59.2 58.4 63.1 Duplicate 0 53.1 54.4 55.6 60.2 60.2 65.6 63.9

Mean 0 49.7 52.1 54.8 56.9 59.7 62.0 63.5 Range 0 3.38 2.29 0.76 3.26 0.47 3.60 0.41


62

Appendix E: Water Quality Analysis from batch adsorption experiments

Water Quality Analysis from batch adsorption experiments Final Characteristics

Physical ADWG (mg/L) R.L.* Initial

AA (A-2)

AA (CPN) Bauxite Hydrotalcite

Alkalinity N/A 2.00E+01 Spiked RO <20 <20 40 <20 N/A Tennant Creek 220 200 200 260 160 Ali Curung 420 280 300 350 280 pH 6.5-8.5 1.00E-01 Spiked RO 6.1 6.6 6.7 5.8 7.7 Tennant Creek 7.3 7.2 7.2 7.3 8.1 Ali Curung 7.5 7.3 7.4 7.3 8.0 TDS 500 1.00E-03 Spiked RO 8 26 26 13 486 Tennant Creek 594 461 531 627 2426 Ali Curung 970 851 832 1005 2803 Hardness 200 5.30E-01 Spiked RO 4 0.06 0.05 1.17 N/A Tennant Creek 99 23 34 60 105 Ali Curung 123 39 45 126 168 Bicarbonate N/A 2.00E+01 Spiked RO 20 20 40 20 N/A Tennant Creek 220 200 200 260 160 Ali Curung 420 280 300 350 280 Carbonate N/A 2.00E+01 Spiked RO <R.L. <R.L. <R.L. <R.L. <R.L. Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L.

Inorganic R.L. InitialAA (A-

2) AA

(CPN) Bauxite HydrotalciteChloride 250 1.00E-03 Spiked RO <R.L. <R.L. <R.L. <R.L. 172 Tennant Creek 105 105 100 105 >250 Ali Curung 155 165 165 165 >250


63

Appendix E continued

Final Characteristics

Metals ADWG (mg/L) R.L. Initial

AA (A-2)

AA (CPN) Bauxite Hydrotalcite

Na 180 6.34E-02 Spiked RO 5.8 16.2 15.7 2.85 N/A Tennant Creek 129 129 135 126 940 Ali Curung 223 226 235 225 1160 Mg N/A 6.50E-03 Spiked RO 1.24 0.06 0.05 0.28 N/A Tennant Creek 27.1 14.3 23.2 25.4 62.3 Ali Curung 42.2 22.8 26.5 42.4 72.4 Al 0.2 1.00E-03 Spiked RO 0.01 0.16 0.17 <R.L. N/A Tennant Creek <R.L. 0.11 0.095 0.13 0.01 Ali Curung <R.L. 0.21 0.09 0.12 0.01 K N/A 3.35E-02 Spiked RO 0.95 0.16 0.14 0.19 N/A Tennant Creek 30.2 31.2 30.5 30.7 31.6 Ali Curung 52.2 53.9 54.9 56.7 55.8 Ca N/A 5.30E-01 Spiked RO 2.4 <R.L <R.L 0.89 N/A Tennant Creek 72.1 8.80 10.6 34.9 42.2 Ali Curung 80.5 16.6 18.3 83.1 95.1 V N/A 5.00E-04 Spiked RO <R.L <R.L <R.L <R.L N/A Tennant Creek 0.02 <R.L <R.L 0.01 0.01 Ali Curung 0.03 <R.L <R.L 0.015 0.01 Fe 0.3 2.80E-03 Spiked RO <R.L <R.L <R.L <R.L N/A Tennant Creek <R.L 0.01 0.01 <R.L. 0.01 Ali Curung <R.L <R.L <R.L. 0.01 0.02 Mn 0.1 2.00E-05 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L. Zn 0.003 2.00E-04 Spiked RO 0.01 0.01 0.01 0.01 N/A Tennant Creek 0.01 0.01 0.01 0.02 <R.L. Ali Curung 0.01 0.02 0.02 0.01 <R.L. As 0.01 2.20E-04 Spiked RO <R.L. <R.L <R.L <R.L N/A Tennant Creek <R.L. <R.L <R.L <R.L <R.L Ali Curung <R.L. <R.L <R.L <R.L 0.01 Se 0.01 4.00E-05 Spiked RO <R.L. <R.L. <R.L <R.L N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L Ali Curung 0.01 0.01 0.01 0.01 <R.L


64

Appendix E continued

Sr 0.02 4.00E-05 Spiked RO <R.L. <R.L. <R.L <R.L N/A Tennant Creek 0.44 0.22 0.04 0.39 0.42 Ali Curung 0.83 0.06 0.08 0.79 0.80 Cd 0.002 3.00E-05 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L. Sb 0.003 2.00E-04 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L. Ba 0.7 2.00E-05 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. 0.004 <R.L. 0.04 0.06 Ali Curung <R.L. <R.L. <R.L. 0.06 0.07 Pb 0.01 8.00E-05 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L. Th N/A 2.00E-05 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek <R.L. <R.L. <R.L. <R.L. <R.L. Ali Curung <R.L. <R.L. <R.L. <R.L. <R.L. U 0.02 1.00E-06 Spiked RO <R.L. <R.L. <R.L. <R.L. N/A Tennant Creek 0.01 0.01 <R.L. 0.01 <R.L. Ali Curung 0.01 <R.L. <R.L. 0.01 <R.L. * R.L. Reporting Limit


65

Appendix F: Adsorption Isotherms Data

Results Adsorption Isotherms

Activated Alumina A-2 Spiked RO Tennant Creek Ali Curung

3g Time interval (min) 8g Time interval (min) 9g Time interval (min) Water Sample 0 5 10 15 30 0 5 10 15 30 0 5 10 15 30

Test [F-] 2 0.98 0.83 0.69 0.54 1.42 0.42 0.32 0.28 0.24 2.38 1.1 0.77 0.62 0.54Dup. [F-] 2 1.05 0.65 0.71 0.54 1.34 0.5 0.43 0.26 0.22 2.53 1.05 0.72 0.7 0.54Mean [F-] 2 1.02 0.74 0.70 0.54 1.38 0.46 0.38 0.27 0.23 2.46 1.08 0.75 0.66 0.54

Range 0 0.07 0.18 0.02 0 0.06 0.08 0.11 0.02 0.02 0.15 0.05 0.05 0.08 0 % Removal Test 0 51.0 58.5 65.5 73.0 0 69.6 76.8 79.7 82.6 0 55.2 68.6 74.7 78.0% Removal Dup. 0 47.5 67.5 64.5 73.0 0 63.8 68.8 81.2 84.1 0 57.2 70.7 71.5 78.0Mean % Removal 0 49.3 63.0 65.0 73.0 0 66.7 72.8 80.4 83.3 0 56.2 69.7 73.1 78.0

Range 0 3.5 9.0 1.0 0 0 5.8 8.0 1.4 1.4 0 2.0 2.0 3.3 0 4g 9g 10g

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 0.95 0.61 0.62 0.36 1.36 0.38 0.37 0.26 0.19 2.38 0.91 0.62 0.56 0.33Dup. [F-] 2 1.06 0.67 0.71 0.44 1.42 0.53 0.25 0.26 0.18 2.53 1.22 0.85 0.62 0.46Mean [F-] 2 1.01 0.64 0.67 0.40 1.39 0.46 0.31 0.26 0.185 2.46 1.07 0.74 0.59 0.40

Range 0 0.11 0.06 0.09 0.08 0.06 0.15 0.12 0.00 -0.01 0.15 0.31 0.23 0.06 0.13% Removal Test 0 52.5 69.5 69.0 82.0 0 72.5 73.2 81.2 86.2 0 62.9 74.7 77.2 86.6% Removal Dup. 0 47.0 66.5 64.5 78.0 0 61.6 81.9 81.2 87.0 0 50.3 65.4 74.7 81.3Mean % Removal 0 49.8 68.0 66.8 80.0 0 67.0 77.5 81.2 86.6 0 56.6 70.1 76.0 83.9

Range 0 5.5 3.0 4.5 4.0 0 10.9 8.7 0 0.7 0 12.6 9.4 2.4 5.3 5g 10g 11g

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 0.92 0.57 0.46 0.26 1.42 0.36 0.29 0.24 0.18 2.38 0.87 0.57 0.68 0.27Dup. [F-] 2 0.89 0.71 0.51 0.3 1.42 0.49 0.38 0.22 0.09 2.53 0.95 0.77 0.49 0.31Mean [F-] 2 0.91 0.64 0.49 0.28 1.42 0.43 0.34 0.23 0.14 2.46 0.91 0.67 0.59 0.29

Range 0 0.03 0.14 0.05 0.04 0 0.13 0.09 0.02 0.09 0.15 0.08 0.20 0.19 0.04% Removal Test 0 54.0 71.5 77.0 87.0 0 73.9 79.0 82.6 87.0 0 64.6 76.8 72.3 89.0% Removal Dup. 0 55.5 64.5 74.5 85.0 0 64.5 72.5 84.1 93.5 0 61.3 68.6 80.0 87.4Mean % Removal 0 54.8 68.0 75.8 86.0 0 69.2 75.7 83.3 90.2 0 62.9 72.7 76.2 88.2

Range 0 1.5 7.0 2.5 2.0 0 9.4 6.5 1.4 6.5 0 3.3 8.1 7.7 1.6 6g 11g 12g


66

Appendix F continued

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 0.87 0.45 0.3 0.15 1.42 0.42 0.34 0.24 0.11 2.38 0.77 0.68 0.47 0.25Dup. [F-] 2 0.94 0.55 0.48 0.19 1.42 0.46 0.39 0.23 0.07 2.53 0.85 0.52 0.49 0.22Mean [F-] 2 0.91 0.50 0.39 0.17 1.42 0.44 0.37 0.24 0.09 2.46 0.81 0.6 0.48 0.24


Range 0 3.5 5.0 9.0 2.0 0 2.9 3.6 0.7 2.9 0 3.3 6.5 0.8 1.2 Activated Alumina CPN

Spiked RO Tennant Creek Ali Curung 6g Time interval (min) 6g Time interval (min) 11g Time interval (min) Water Sample

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 1.36 0.99 0.99 0.63 1.34 0.88 0.63 0.67 0.48 2.53 1.39 1.01 0.76 0.58Dup. [F-] 2 1.23 1.08 0.81 0.69 1.34 1.01 0.73 0.63 0.54 2.38 1.53 1.05 0.82 0.56Mean [F-] 2.00 1.30 1.04 0.90 0.66 1.34 0.95 0.68 0.65 0.51 2.46 1.46 1.03 0.79 0.57


Range 0 6.5 4.5 9.0 3.0 0 9.7 7.5 3.0 4.5 0 5.7 1.6 2.4 0.8 Raw Data 7g 7g 12g

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 1.23 0.95 0.75 0.5 1.34 0.93 0.59 0.62 0.46 2.53 1.23 1.06 0.71 0.53Dup. [F-] 2 1.31 1.1 0.78 0.6 1.34 1.04 0.68 0.57 0.33 2.38 1.39 0.97 0.85 0.46Mean [F-] 2 1.27 1.03 0.77 0.55 1.34 0.99 0.64 0.60 0.40 2.46 1.31 1.02 0.78 0.50




67

Appendix F continued

0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 1.21 0.92 0.8 0.4 1.34 0.81 0.58 0.54 0.32 2.53 1.3 0.94 0.72 0.49Dup. [F-] 2 1.33 1.01 0.87 0.64 1.34 0.94 0.63 0.59 0.29 2.38 1.34 0.96 0.72 0.41Mean [F-] 2 1.27 0.97 0.84 0.52 1.34 0.88 0.61 0.57 0.31 2.46 1.32 0.95 0.72 0.45

Range 0 0.12 0.09 0.07 0.24 0 0.13 0.05 0.05 0.03 0.15 0.04 0.02 0 0.08% Removal Test 0 39.5 54.0 60.0 80.0 0 39.6 56.7 59.7 76.1 0 47.0 61.7 70.7 80.0% Removal Dup. 0 33.5 49.5 56.5 68.0 0 29.9 53.0 56.0 78.4 0 45.4 60.9 70.7 83.3Mean % Removal 0 36.5 51.8 58.3 74.0 0 34.7 54.9 57.8 77.2 0 46.2 61.3 70.7 81.7


0 5 10 15 30 0 5 10 15 30 0 5 10 15 30 Test [F-] 2 1 0.79 0.65 0.51 1.34 0.82 0.58 0.43 0.23 2.53 1.31 0.89 0.66 0.44Dup. [F-] 2 1.28 0.93 0.52 0.34 1.34 0.85 0.43 0.35 0.27 2.38 1.22 0.99 0.54 0.3 Mean [F-] 2 1.14 0.86 0.59 0.43 1.34 0.84 0.51 0.39 0.25 2.46 1.27 0.94 0.60 0.37


Range 0 14.0 7.0 6.5 8.5 0 2.2 11.2 6.0 3.0 0 3.7 4.1 4.9 5.7


68

Appendix G: Column Studies Data

Tennant Creek Inlet Conc. Time Hours Volume Flow Outlet Conc.

Fluoride removed

Date 1 2 Avg. Start Finish Batch Cum. Batch Cum. Rate/hr 1 2 Avg. Batch Cum. Ct/Co BV 18-Mar 1.28 1.37 1.33 1200 1800 6.00 6 14 14 2.33 0 0 0 19 19 0.000 13 18-Mar 1.47 1.51 1.49 1800 645 12.75 19 28 42 2.20 0 0 0 42 60 0.000 40 19-Mar 1.40 1.38 1.39 645 1815 11.50 30 25 67 2.17 0 0 0 35 95 0.000 64 19-Mar 1.27 1.25 1.26 1815 730 13.25 44 29 96 2.19 0 0 0 37 132 0.000 91 20-Mar 1.26 1.3 1.28 730 1800 10.50 54 23 119 2.19 0 0 0 29 161 0.000 113 20-Mar 1.26 1.28 1.27 1800 630 12.50 67 28 147 2.24 0 0 0 36 197 0.000 140 21-Mar 1.25 1.2 1.23 630 1800 11.50 78 25 172 2.17 0 0 0 31 227 0.000 164 21-Mar 1.15 1.16 1.16 1800 700 13.00 91 27 199 2.08 0 0 0 31 258 0.000 190 22-Mar 1.25 1.23 1.24 700 1715 10.25 101 22 221 2.15 0 0 0 27 286 0.000 210 22-Mar 1.29 1.33 1.31 1715 645 13.50 115 28 249 2.07 0 0 0 37 322 0.000 237 23-Mar 1.15 1.18 1.17 700 2030 13.50 128 29 278 2.15 0 0 0 34 356 0.000 265 23-Mar 1.31 1.29 1.30 2030 1030 14.00 142 30 308 2.14 0 0 0 39 395 0.000 293 24-Mar 1.32 1.43 1.38 1030 2300 12.50 155 26 334 2.08 0 0 0 36 431 0.000 318 24-Mar 1.38 1.37 1.38 2300 1200 13.00 168 27 361 2.08 0 0 0 37 468 0.000 344 25-Mar 1.19 1.22 1.21 1200 1700 5.00 173 10 371 2.00 0 0 0 12 480 0.000 353 25-Mar 1.32 1.35 1.34 1700 500 12.00 185 24 395 2.00 0 0 0 32 512 0.000 376 30-Apr 1.50 1.51 1.51 2000 715 11.25 196 20 415 1.78 0 0 0 30 542 0.000 395 1-May 1.39 1.43 1.41 715 1900 11.75 208 20 435 1.70 0 0 0 28 570 0.000 414 1-May 1.27 1.26 1.27 1900 715 12.25 220 22 457 1.80 0 0 0 28 598 0.000 435 2-May 1.35 1.38 1.37 715 1730 10.25 230 19 476 1.85 0 0 0 26 624 0.000 453 2-May 1.43 1.48 1.46 1730 700 13.50 244 25 501 1.85 0 0 0 36 661 0.000 477 3-May 1.49 1.56 1.53 700 2000 13.00 257 26 527 2.00 0 0 0 40 700 0.000 502 3-May 1.52 1.54 1.53 2000 700 11.00 268 22 549 2.00 0.02 0.04 0.03 34 734 0.020 523 4-May 1.44 1.46 1.45 700 1930 12.50 280 24 573 1.92 0.06 0.06 0.06 35 769 0.041 546 4-May 1.46 1.48 1.47 1930 800 12.50 293 24 597 1.92 0.11 0.15 0.13 35 804 0.088 569 5-May 1.56 1.54 1.55 800 2000 12.00 305 24 621 2.00 0.18 0.21 0.195 37 841 0.126 591 5-May 1.49 1.48 1.49 2000 700 11.00 316 22 643 2.00 0.27 0.29 0.28 33 874 0.189 612 6-May 1.35 1.39 1.37 700 1800 11.00 327 23 666 2.09 0.37 0.4 0.385 32 905 0.281 634 6-May 1.42 1.4 1.41 1800 700 13.00 340 26 692 2.00 0.55 0.53 0.54 37 942 0.383 659 5-May 1.49 1.48 1.49 700 1730 10.50 337 20 712 1.90 0.71 0.73 0.72 30 935 0.485 678

1.4 Average 34 ml/min EBCT 31 min


69

Appendix G continued

Ali Curung Inlet Conc. Time Hours Volume Flow Outlet Conc. Fluoride removed

Date 1 2 Avg. Start Finish Batch Cum. Batch Cum. Rate/hr 1 2 Avg. Batch Cum. Ct/Co BV 5-Apr 2.07 2.37 2.22 2030 930 13.00 13 46 46 0.28 0 0 0 102 102 0.000 44 6-Apr 2.38 2.58 2.48 1330 2130 8.00 21 26 72 3.25 0 0 0 64 167 0.000 69 6-Apr 2.29 2.31 2.30 2045 915 11.50 33 38 110 3.30 0 0 0 87 254 0.000 105 7-Apr 2.26 2.3 2.28 915 2015 11.00 44 37 147 3.36 0 0 0 84 338 0.000 140 7-Apr 2.36 2.21 2.29 2030 1015 13.75 57 37 184 2.69 0 0 0 85 423 0.000 175 8-Apr 2.15 2.11 2.13 1015 1945 9.50 67 25 209 2.63 0 0 0 53 476 0.000 199 8-Apr 2.14 2.04 2.09 1945 1215 16.50 83 44 253 2.67 0 0 0 92 568 0.000 241 9-Apr 2.10 2.16 2.13 1215 2015 8.00 91 20 273 2.50 0 0 0 43 611 0.000 260 9-Apr 2.15 2.22 2.19 2030 830 12.00 103 38 311 3.17 0 0 0 83 694 0.000 296 10-Apr 2.15 2.22 2.19 845 1630 7.75 111 24 335 3.10 0 0.02 0.01 52 746 0.005 319 10-Apr 2.38 2.37 2.38 1630 800 15.50 127 48 383 3.10 0.03 0.05 0.04 114 860 0.017 365 11-Apr 2.26 2.21 2.24 800 1745 9.75 136 30 413 3.08 0.05 0.09 0.07 67 927 0.031 393 11-Apr 2.20 2.26 2.23 1745 815 14.50 151 45 458 3.10 0.11 0.15 0.13 100 1028 0.058 436 12-Apr 2.36 2.14 2.25 815 1615 8.00 159 25 483 3.13 0.21 0.18 0.195 56 1084 0.087 460 12-Apr 2.22 2.39 2.31 1615 700 14.75 174 46 529 3.12 0.46 0.51 0.485 106 1190 0.210 504 13-Apr 2.28 2.22 2.25 700 1315 6.25 180 19 548 3.04 0.6 0.68 0.64 43 1233 0.284 522 13-Apr 2.28 2.22 2.25 1615 1915 6.00 186 19 567 3.17 0.76 0.86 0.81 43 1275 0.360 540



70


Media Replacement - Repeat initial experiment

25-Apr 2.34 2.27 2.31 1030 1830 8.00 8 24 24 3.00 0 0 0 55 55 0.000 23 25-Apr 2.32 2.3 2.31 1830 730 13.00 21 41 65 3.15 0 0 0 95 150 0.000 62 26-Apr 2.28 2.3 2.29 730 1900 11.50 33 36 101 3.13 0 0 0 82 232 0.000 96 26-Apr 2.36 2.34 2.35 1900 700 12.00 45 38 139 3.17 0 0 0 89 322 0.000 132 27-Apr 2.37 2.35 2.36 700 2230 15.50 60 46 185 2.97 0 0 0 109 430 0.000 176 27-Apr 2.30 2.3 2.30 2230 900 10.50 71 30 215 2.86 0 0 0 69 499 0.000 205 28-Apr 2.30 2.32 2.31 900 1615 7.25 78 23 238 3.17 0 0 0 53 552 0.000 227 28-Apr 2.28 2.34 2.31 1615 900 17.75 96 52 290 2.93 0 0 0 120 673 0.000 276 29-Apr 2.46 2.43 2.45 945 2000 10.25 106 31 321 3.02 0 0 0 76 748 0.000 306 29-Apr 2.32 2.32 2.32 2000 800 12.00 118 38 359 3.17 0.08 0.06 0.07 88 837 0.030 342 30-Apr 2.35 2.33 2.34 800 1930 11.50 129 34 393 2.96 0.1 0.13 0.115 80 916 0.049 374 30-Apr 2.32 2.34 2.33 1930 700 11.50 141 36 429 3.13 0.17 0.19 0.18 84 1000 0.077 409 1-May 2.30 2.31 2.31 700 1900 12.00 153 34 463 2.83 0.28 0.25 0.265 78 1078 0.115 441 1-May 2.32 2.34 2.33 1900 715 12.25 165 39 502 3.18 0.42 0.39 0.405 91 1169 0.174 478 2-May 2.30 2.32 2.31 715 2030 13.25 178 40 542 3.02 0.85 0.83 0.84 92 1262 0.364 516


1st Regeneration 14-Apr 2.26 2.31 2.29 1200 1430 2.50 188 8 8 3.20 0 0 0 18 18 0.000 8 14-Apr 2.26 2.31 2.29 1430 1900 4.50 193 14 22 3.11 0 0 0 32 50 0.000 21 14-Apr 2.23 2.22 2.23 1900 1030 15.50 208 48 70 3.10 0 0 0 107 157 0.000 67 15-Apr 2.35 2.36 2.36 1030 1700 6.50 215 20 90 3.08 0 0 0 47 204 0.000 86 15-Apr 2.30 2.28 2.29 1700 2200 5.00 220 15 105 3.00 0 0 0 34 239 0.000 100 15-Apr 2.30 2.28 2.29 2200 745 9.75 230 30 135 3.08 0.05 0 0 69 307 0.000 129 16-Apr 2.34 2.39 2.37 745 1730 9.75 239 29 164 2.97 0.18 0.08 0.06 69 376 0.025 156 16-Apr 2.32 2.37 2.35 1730 700 13.50 253 42 206 3.11 0.13 0.15 0.14 98 474 0.060 196 17-Apr 2.43 2.45 2.44 700 1915 12.25 265 38 244 3.10 0.27 0.23 0.25 93 567 0.102 232 17-Apr 2.30 2.28 2.29 1915 700 11.75 277 35 279 2.98 0.35 0.29 0.32 80 647 0.140 266 18-Apr 2.34 2.38 2.36 700 1700 10.00 287 30 309 3.00 0.45 0.50 0.48 71 718 0.201 294 18-Apr 2.28 2.32 2.30 1700 2200 5.00 292 16 325 3.20 0.65 0.57 0.61 37 755 0.265 310 18-Apr 2.34 2.36 2.35 2200 700 9.00 301 27 352 3.00 0.86 0.82 0.84 63 818 0.357 335



71


2nd Regeneration 21/4 2.26 2.28 2.27 1545 1800 2.25 2 7 7 3.11 0 0 0 16 16 0.000 7 21/4 2.30 2.24 2.27 1800 900 15.00 17 46 53 3.07 0 0 0 104 120 0.000 50 22/4 2.34 2.38 2.36 900 1400 5.00 22 15 68 3.00 0 0 0 35 156 0.000 65 22/4 2.31 2.33 2.32 1400 1800 4.00 26 12 80 3.00 0 0 0 28 184 0.000 76 22/4 2.26 2.28 2.27 1800 730 13.50 40 41 121 3.04 0.08 0.04 0.05 93 277 0.022 115 23/4 2.35 2.39 2.37 730 1830 11.00 51 34 155 3.09 0.13 0.15 0.13 81 357 0.055 148 23/4 2.32 2.34 2.33 1830 700 12.50 63 38 193 3.04 0.27 0.31 0.29 89 446 0.124 184

24-Apr 2.37 2.39 2.38 700 1730 10.50 74 32 225 3.05 0.53 0.55 0.54 76 522 0.227 214 24-Apr 2.35 2.37 2.36 1730 2200 4.50 78 14 239 3.11 0.68 0.65 0.665 33 555 0.282 228 24-Apr 2.35 2.37 2.36 2200 600 8.00 86 24 263 3.00 0.81 0.83 0.82 57 612 0.347 250


3rd Regeneration 7-May 2.38 2.35 2.37 1430 1900 4.50 5 13 13 2.89 0 0 0 31 31 0.000 12 7-May 2.45 2.4 2.43 1900 700 12.00 17 33 46 2.75 0 0 0 80 111 0.000 44 8-May 2.28 2.31 2.30 700 2030 13.50 30 41 87 3.04 0.08 0.098 0.089 94 205 0.039 83 8-May 2.32 2.34 2.33 2030 600 9.50 40 29 116 3.05 0.2 0.18 0.19 68 272 0.082 110 9-May 2.34 2.3 2.32 600 1700 11.00 51 35 151 3.18 0.24 0.3 0.27 81 354 0.116 144 9-May 2.30 2.31 2.31 1700 800 15.00 66 36 187 2.40 0.44 0.43 0.435 83 437 0.189 178 10-May 2.30 2.32 2.31 800 1630 8.50 74 26 213 3.06 0.63 0.65 0.64 60 497 0.277 203 10-May 2.35 2.37 2.36 1630 2230 6.00 80 18 231 3.00 0.85 0.83 0.84 42 539 0.356 220


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