Title of Invention	PROCESS FOR THE TREATMENT OF FLUORIDE CONTAMINATED WATER AND A DOMESTIC DE-FLUORIDATION UNIT
Abstract	Disclosed herein is a physico-chemical process for treating fluoride-contaminated groundwater and a device for carrying out the said process as de-fluoridation is important in ensuring acceptable levels of fluoride in water that is consumed by humans to avoid flour sis a crippling bone disease.

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This invention relates to a physico-chemical process for treating fluoride-contaminated groundwater and a device for carrying out the said process as de-fluoridation is important in ensuring acceptable levels of fluoride in water that is consumed by humans to avoid flourosis, a crippling bone disease. Background High levels of fluoride in drinking water (>1,5 ppm) lead to fluorosis, a crippling bone disease. Fluorosis is caused by the ingestion of excess fluoride over a long period of time. It affects multiple tissues, organs and systems of the body and results in a variety of clinical manifestations. Prevention is the only solution, provided the disease is detected in the early stages (Susheela, 1992), The Indian Standard (IS 10500: 1991) specifies the desirable and permissible limits for fluoride in drinking water as 1.0 and L5 ppm ! I respectively. In India, the fluorosis problem is quite severe as almost 80 percent of the rural population depends on untreated groundwater for potable water supplies. It is estimated that about 62 million people in India suffer from fluorosis. Seventeen Indian states have been identified with the problem of excess fluoride in groundwater resources till 1999. The states of Andhra Pradesh, Kamataka, Tamil Nadu, Uttar Pradesh, Punjab, Rajasthan and Gujarat have reported the effects of high fluoride levels since 1937, when fluorosis was first discovered in the Nalagonda district in Andhra Pradesh. The occurrence of fluorosis in India is linked to the state of the natural environment. Three major sources of fluoride in India are fluorspars, rock phosphates and phosphorities. Because of differences in geographical, chemical and physical characteristics of aquifers and differences in contact period between groundwater and fluoride-bearing rocks, the fluoride content in groundwater varies from up of fluoride in the aquifers (Handa, 1975; Jacks et. al,, 2005). This motivates the necessity to experiment with and improve existing methods of de-flouridation. Discussion of prior art Fluoride removal from drinking water in India is usually achieved by the Nalagonda technique and activated alumina process (Susheela, 1992). The Nalagonda technique was developed by National Environment Engineering Research Institute (NEERI), Nagpur, after extensive testing of many materials and processes (Nawlakhe et.al., 1975). The Nalgonda technique involves addition of aluminum salts, lime and bleaching powder followed by rapid mixing, flocculation, sedimentation, filtration and disinfection. Aluminum salt may be added as aluminum sulfate or aluminum chloride or combination of these two. Aluminum salt is only responsible for removal of fluoride from water. The dose of aluminum salt increases with increase in the fluoride and alkalinity levels of the raw water. The selection of either aluminum sulfate or aluminum chloride also depends on sulfate and chloride contents of the raw water to avoid them exceeding their permissible limits. The dose of lime is empirically l/20th that of the dose of aluminum salt. Lime facilitates formation of dense floe for rs^id settling. Bleaching powder is added to the raw water at the rate of 3 mg/1 for disinfection. Activated alumina was proposed for de-fluoridation of water for domestic use in 1930's (Boruff, 1934; Fink and Lindsay, 1936), Since then the activated alumina has become one of the most advocated de-fluoridation methods. In India, Indian Institute of Technology, Kanpur and Satya Sai University, Anantpur have developed activated alumina process for fluoride removal. Experiments have demonstrated that magnesium oxide removes fluoride from fluoride-spiked water. The mechanism of removal of fluoride ions from water by magnesium oxide is as follows (Lisle, 1967; Mamatha, 2003; Zettelemoyer et.al., 1947; Booster et.al., 2003). On addition to fluoride spiked water, magnesium oxide (MgO) hydrates to brucite [Mg(0H)2] as: MgO + H20 => Mg(OH)2 (1) During brucite formation, fluoride ions (F) in the spiked water samples are incorporated into the brucite lattice by isomorphous substitution of hydroxyl ions by fluoride ions. The isomorphous substitution reaction leads to the formation of the Mg(0H)2-y.Fy phase. The rate of magnesium oxide hydration constitutes the rate determining step in the formation of Mg(0H)2.y.Fy phase. Magnesium oxide exhibited more than 86 % retention efficiency for fluoride ions at a range of fluoride concentrations (2 to 20 ppm) generally encountered in groundwater conditions* Elvove (1940) patented the removal of fluoride from water containing about 5 ppm of fluoride, relatively low mineral content and pH of approximately near neutrality. For these conditions, Elvove (1940) recommends addition of very high dosage of finely powdered magnesium oxide (15 g per liter of water) and shaking of the suspension for half hour. The suspension is allowed to settle for 48 hours and the clear supernatant water siphoned off The magnesium oxide charge of 15 g per liter could be used over again several times for treating additional lots of the water before its activity as fluoride remover gets exhausted. 1 Lisle (1967) patented a method for de-fluoridation of water using magnesium oxide. Fluoride bearing water is introduced into a first container where mixing of magnesium oxide and fluoride bearing water is facilitated by upward movement of air or by means of an electrical stirrer. The suspension is directed to a second chamber, where the magnesium oxide sludge settles. The clear water is directed through plurality of first and second chambers in series imtil the fluoride concentration in the water is reduced to desirable limits. The second container has an inlet for addition of alum used as a settling agent. The first container has an inlet for addition of lime for the purpose of reacting or precipitating excess magnesium in the solution to reduce alkalinity and thereby render it potable in a pH range between 7.2 and 7.4. Venkateshwarlu and Narayana Rao report, two research studies (Venkateshwarlu and Narayana Rao 1953, 1954) on the removal of fluoride from water using magnesium i 1 oxide. In the first study (Venkateshwarlu and Narayana Rao, 1953), one liter of city tap water samples were spiked with fluoride ions using sodiimi fluoride salt to yield tap water samples containing 5, 15 and 20 ppm of fluoride ions. The one liter of fluoride bearing water sample was brought to boiling, 5 g of light magnesixmi oxide was added, stirred and set aside. Boiling is discontinued after 5 minutes. The magnesium oxide with the adsorbed fluoride settles to the bottom. The clear supernatant water free from toxic amoimts of fluoride is decanted for use. The fluoride bearing water sample was brought to boiling to allow efficient contact between magnesixun oxide and fluoride ions. The water after the above treatment had a pH of 10.5, In their second study on the removal of fluoride from water using magnesium oxide, Venkateshwarlu and Narayana Rao (1954) spiked city tap water samples with 5, 10 and 20 ppm fluoride ions. 200 ml of the fluoride bearing water sample was placed in a beaker, raised to the desired temperature, a definite amount of magnesium oxide was added and kept in suspension using electric stirrer. Aliquots of the water were pipetted periodically, immediately filtered and analysed for fluoride content. Their study was able to discern the temperature at which the maximum adsorption of fluoride by magnesium occurs, the influence of time on fluoride adsorption related to period of contact, the increase in fluoride adsorption when the amount of magnesium oxide is kept constant while increasing the concentration of fluoride ions and the increase in the amount of fluoride removed when the adsorbent used is varied and finally the difference in adsorption between light and heavy magnesium oxide. Viswanadham et al. (1974) at Chemical Laboratory of Geological Survey of India, Hyderabad used magnesium oxide for the removal of fluoride from water. The defluoriding capacity of magnesixmi oxide obtained by heating L.R. grade magnesium carbonate to 900^C is higher than the commercial grade magnesium oxide obtained by calcinations of magnesite. Treatment of natural waters with magnesium oxide increases pH, magnesixmi content and conductivity and converts large proportion of bicarbonates into carbonates. Increase in pH of treated water can be lowered by aeration and passage of carbon dioxide. Though the earlier works succeeded in establishing the fluoride removing ability of magnesium oxide, vital issues necessary for successful field implementation of the method were not addressed. For example, the dosages of magnesium oxide required for treating water containing different fluoride and dissolved salts concentrations is not specified, the issue of lowering the pH of magnesixmi oxide treated water within potable water limits are not comprehensively addressed, the optimxmi conditions for mixing the magnesium oxide-water suspension is not defined. Failure to address the above issues i has impeded the commercial success of the magnesium oxide treatment method for fluoride removal from water. The limitations in the earlier works are highlighted in details. • The magnesium oxide treatment method of Elvove (1940), Lisle (1967) and Venkateshwaralu and Narayana Rao (1953, 1954) did not carry out studies on natural, fluoride bearing water. Such a study is necessary to establish the applicability of laboratory results to field conditions, • Groundwater can vary greatly in chemical composition. For example, data available for fluoride bearing groxmdwater in Kamataka (Private communication, Department of Mines and Geology) show that fluoride concentrations generally range between 2 and 5 ppm. The studies of Elvove (1940), Lisle (1967), Venkateshwaralu and Narayana Rao (1953, 1954) and Viswanadham et al, (1974) does not specify any dosages of magnesium oxide required for treating groundwater containing different fluoride concentrations. Establishing the correct magnesium oxide dosage to treat fluoride contaminated water is necessary to produce treated water that contains fluoride within permissible limits and save chemical costs. • Addition of magnesium oxide to water increases the pH of water between 10 and 11 from magnesiiun hydroxide formation. Indian Standards code for drinking water (IS 10500: 1991) specifies that the pH of drinking water should • • range between 6.5 and 8.5, as beyond this range the water will affect the mucous system. The magnesium oxide treatment method of Elvove (1940), Lisle (1967) and Venkateshwaralu and Narayana Rao (1953, 1954) does not dwell on methods to lower the pH of magnesium oxide treated water within limits recommended for potable drinking water, while, the proposal of Viswanadham et al. (1974) to lower the pH of treated water by aeration and passage of carbon dioxide cannot be easily adopted by unskilled rural populace. Lowering the pH of magnesium oxide treated water within potable water limits (6.5 to 8.5) is essential to safeguard health of persons consuming water treated with magnesium oxide. The total dissolved salts concentration of fluoride bearing groundwater (1.5 to 5 ppm range) in Kamataka ranges between 100 and 1500 ppm and are mainly comprised of sodium, calcium, magnesium, potassium, chloride, bicarbonate and sulfate ions. Elvove (1940), Lisle (1967) and Venkateshwaralu and Narayana Rao (1953, 1954) did not examine the impact of dissolved salts concentrations on the fluoride removing efficiency of magnesium oxide. Knowledge of the impact of variations in dissolved salts concentrations on the fluoride removing efficiency of magnesium oxide is essential to arrive at the correct dosage of magnesium oxide needed to treat natural waters containing varied fluoride and dissolved salts concentration. Such a study again will save chemical costs and provide treated water that contains fluoride within permissible limits. The magnesium oxide treatment method of Elvove (1940), Lisle (1967) and Venkateshwaralu and Narayana Rao (1953, 1954) did not carry out studies to examine how the magnesium oxide treatment affects the dissolved salts composition of water. Such a study is relevant, as treatment with magnesium oxide should not deteriorate the water quality with respect to dissolved salts concentration. This is again essential to safeguard health of persons consuming the water. The magnesium oxide treatment method of Venkateshwarlu and Narayana Rao (1953, 1954) reconunends the use of boiling and use of electric stirrer to facilitate efficient contact between fluoride ions and magnesium oxide. Boling of water will consume additional energy. Further, their method would be i difficult to implement in rural domestic households that have no electricity. Lisle (1967) recommends the use of air current or electric motor to mix magnesium oxide and fluoride bearing water that may not be feasible in rural parts of the country that do not have electricity. Though Viswanadham et al, (1974) recommend manual stirring of magnesium oxide-water suspension, they do not specify the duration and speed of stirring. It is essential to establish proper stirring procedures that are feasible in rural Indian communities for efficient contact between magnesium oxide particles and fluoride ions. This will again save chemical costs and provide treated water that contains fluoride within allowable limits. Summary of the invention The present work provides solutions for a range of issues that were not addressed by earUer works and are necessary to design an efficient, cost-effective and environment friendly process for fluoride removal from groimdwater using magnesium oxide. Here we present an invention that addresses the following limitations: • Ensuring that the laboratory samples represent the chemical composition of the field water samples. • • • Determining dosages of magnesium oxide are needed for treating water containing different fluoride and dissolved salts concentrations. The optimum mixing and settling conditions for fluoride-bearing water treated with magnesium oxide. Methods and specifications to lower the pH of magnesium oxide treated water within potable water liinits Determining how the proposed treatment affect the chemical composition of treated water • The methods adopted to determine the concentrations of chemical constituents of the water samples • Methods for safe disposal of fluoride bearing magnesium oxide sludge In this specification, the method of the present invention will be referred to as the "IISc treatment" method. Detailed description of the preferred embodiments 1.0 Proposed solution with examples The present work provides solutions for a range of issues that were not addressed by earlier workers and which, are necessary to design an efficient, cost-effective and environment friendly process for fluoride removal from groundwater using magnesium oxide* We provide a point-wise description of the invention, based on the limiters it addresses. 1.1 Accurate representation of the chemical composition of the field water samples in the laboratory samples used in experimentation: In the present work, studies are performed on laboratory prepared, fluoride spiked water samples and fluoride-bearing natural waters from Kolar District in Kamataka. The fluoride spiked water samples were prepared in the laboratory by dissolution of laboratory reagent (LR) grade sodium fluoride salt in distilled water. The fluoride concentrations in the spiked water samples corresponded to 2 and 5 ppm and are based on the fluoride concentrations in natural groundwater samples from Kamataka determined over a period of 8 years from 1994-2001 (Ifrivate commimication, Department of Mines and Geology), The fluoride spiked water samples were also spiked with commonly present ions in natural groundwater samples such as calcium, magnesium, sodium, sulfate, chloride and bicarbonate ions (Tables 1 and 2). The concentrations of these dissolved salt ions in the spiked water samples were based on the concentrations of these ions in the groundwater samples of Kamataka determined over a period of 8 years from 1994-2001 (Private communication, Department of Mines and Geology), The fluoride- contaminated groundwater samples from Kolar District, Kamataka used in the studies had total dissolved salts concentration ranging from 584 to 720 ppm and fluoride concentrations ranging from L9 to 3.1 ppm (Table 3), The detailed chemical composition of the groundwater samples from Kolar District, Kamataka are also provided in Table 3. 1.2 Dosages of magnesium oxide that are needed for treating water containing different fluoride and dissolved salts concentrations: I The present study specifies the dosage of magnesium oxide needed for treating water containing fluoride concentrations of up to 5 ppm in presence of dissolved salts commonly encountered in fluoride-contaminated groundwater samples. Studies with spiked water samples containing fluoride concentrations of 2 and 5 ppm, total dissolved salts concentration of 295 to 890 ppm and host of other cations and anions commonly found in fluoride-contaminated groundwater revealed that dosage of 1.0 g magnesixmi oxide (light variety, IP grade) per litre of fluoride spiked water reduces the fluoride level below permissible (1.5 ppm) limit (Tables 1 and 2). The magnesium oxide dosage of Ig/L for fluoride-contaminated water containing 1,5 to 5 ppm fluoride is arrived from the studies of Mamatha (2005). 1*3 The optimal mixing and settling conditions for fluoride-bearing water treated with magnesium oxide; Efficient contact between magnesium oxide and fluoride ions in water is achieved by manually stirring the fluoride^contaminated water for 5 to 10 minutes at a speed of 90 to 100 rpm. Stirring period of 5 minutes is recommended for water samples containing fluoride concentrations 1.4 The methods and specifications to lower the pH of magnesium oxide treated water within potable water limits: Treatment of fluoride-bearing water samples with magnesium oxide increases the pH of the treated water samples to about 10.5 (Tables 1 and 2)* Sodium bisulfate is commonly used to neutralize the pH of alkaline water. Addition of sodium bisulfate lowers the alkaline pH of water as : HS04+0H- => S04^" + H20 (2) When bicarbonates ions are present in the fluoride-bearing water samples, they convert to carbonate ions in the alkaline pH created by magnesium oxide addition according to the reaction; HCO3* "H OH" => COs^" + H2O (3) The carbonate ions formed in reaction 3, in turn consume additional sodium bisulfate according to the reaction: COi^' 4- HSO4' => HCOs" + S04^" (4) Laboratory results of Mamatha (2005) illustrated that interference from bicarbonate ions towards pH neutralization (i.e., lower the pH of treated water samples between 6.5 and 8.5) by sodium bisulfate addition becomes apparent when the bicarbonate ion concentration in fluoride bearing water samples exceed 100 ppm. Laboratory results of Mamatha (2005) also demonstrated that addition of calcium hydroxide minimizes the interference from bicarbonate ions to pH neutralization by sodium bisulfate according to the following reactions. Calcium hydroxide ionizes in water as: Ca (0H)2 => Ca^^ + 20H' (5) The ionization products from reaction 5, transforms the soluble bicarbonates to insoluble calcium carbonates (reaction 6) thereby making them unavailable for participation in reaction 3. The transformation of soluble bicarbonates to insoluble calcium carbonates is represented as: HCOs" + Ca^^ -f OH" => t CaCOs + H2O (6) To examine the efficiency of calcium hydroxide in reducing the interference of bicarbonate ions towards neutralizing the pH of the magnesium oxide treated water samples (i.e., reducing their pH between 6.5 and 8,5), laboratory experiments were performed with 5 ppm fluoride spiked water samples containing a range of bicarbonate (100 to 400 ppm), calcium (30 to 120 ppm) and magnesium (approximately 5 to 40 ppm) ion concentrations. Fluoride-spiked water samples containing 10 ppm calcium concentration belong to FSW-30 series (Table 4). Similarly, fluoride-spiked water samples containing 60 and 120 ppm calcium concentrations belong to FSW-60 (Table 5) and FSW-120 (Table 6) series respectively. The fluoride-spiked water samples of each series contain other ions commonly found in fluoride bearing groundwater samples (Tables 4 to 6). All experiments were performed with 2 liters of water sample. Each (fluoride spiked) water sample of a series was treated with IP grade magnesium oxide at the rate of 1 g of magnesium oxide per liter of water sample. Based on preliminary experimental results, varying dosages of calcium hydroxide (0.1 to 0.25 g of calcium hydroxide per liter of fluoride spiked water sample) were also added along with magnesium oxide to the water sample. The magnesium oxide + calcium hydroxide mix was manually stirred (rate of stirring = 90-100 rpm) for 10 minutes and allowed to settle for 16 hours. At the end of 16 hours, the clear supematant was filtered through Whatman 1 filter paper. The pH of the filtrate (10.5) was adjusted to potable water limits (6.5 to 8.5) by controlled addition of 2.5 % laboratory reagent grade sodium bisulfate solution. The various cation and anion concentrations of the pH adjusted water samples were determined by standard analytical procedxires. The results are summarized in Tables 4 to 6. The salient observations of the studies are follows: • The efficiency of fluoride removal by the selected dosage of magnesium oxide (Ig per liter of fluoride contaminated water) is independent of the initial cation and anion composition of the fluoride spiked water samples. In all laboratory experiments, treatment with magnesium oxide reduces the fluoride concentration of the water samples below the permissible limit of 1.5 ppm. • At calcium ion concentrations sodium bisulfate solution to neutralize (pH = 7 to 8.5) the alkaline pH of magnesium oxide treated water samples. • For a given initial bicarbonate concentration and calcium hydroxide dosage, water samples with higher calcium ion concentrations need smaller volumes of sodium bisulfate solution to lower the pH of the magnesium oxide treated water between 7 and 8.5. The experimental resxilts illustrate that the efficiency of fluoride removal for the selected dosage of magnesium oxide is unaffected by variations in the initial chemical composition of the fluoride-spiked water samples. Despite the addition of calcium hydroxide, the volume of bisulfate solution required to neutralize the pH of the magnesium oxide treated water samples within potable water limits (pH = 7 to 8,5) is strongly dependant on the initial bicarbonate concentration of the water samples at initial calcium ion concentrations 100 ppm. Similarly, calcium chloride solution addition becomes necessary at calcium ion concentration 1*5* Examples of application of nSc treatment method to fluoride-contaminated water samples: To illustrate the working of the IISc method (outlined m Table 7), results of laboratory experiments performed with fluoride-spiked water samples and fluoride-contaminated groundwater samples using the IISc method are discussed. Two series of fluoride-spiked water samples were prepared. Samples of series FSW-10 contains fluoride concentration of 5 ppm, calcium ion concentration of 10 ppm, magnesiimi ion concentration of 8 ppm and bicarbonates concentrations of 100,200,250, 300 and 400, ppm respectively (Table 8). Similarly, samples belonging to series FSW-60 contain fluoride concentration of 5 ppm, calcium ion concentration of 60 ppm, magnesium ion concentration of 38 ppm and bicarbonate concentrations of 100, 250, 300 and 400, ppm respectively (Table 9), The calcium ion concentrations in series FSW-10 samples are below 50 ppm. Hence, 4 ml/liter of 7.5 % calcium chloride solution are added to each of the water samples belonging to FSW-10 series (Table 8). The calcium ion concentrations in series FSW-60 are > 50 ppm, but FSW-10 series samples is attributed to their lower initial magnesium ion concentrations. Despite these slight discrepancies, the sodium bisulfate consumption by samples of both series complies with the recommendations in Table 7. The pH and chemical parameters of the pH adjusted samples are given in Tables 8 and 9. Fluoride contaminated groundwater samples were collected from Yellodu village in Kolar District in Kamataka. The calcium ion concentration in the Yellodu sample is below 50 ppm. Hence, 4 ml/liter of 7.5 % calcium chloride solution was added to the water sample. Magnesium oxide at the rate of Ig/L and calcium hydroxide at the rate of 0.25 g/L (based on the bicarbonate concentration of 337 ppm) were added to the raw water. The chemical-water mix was manually stirred for 10 minutes at the rate of 90-100 rpm. After stirring, the mix was allowed to settle for 16 hours. After 16 hours, the clear supernatant was filtered through Whatman 1 filter paper. 2.5 % sodium bisulfate solution was added at the rate of 4 ml/L. The fluoride concentration of the water sample reduces to 0.8 ppm that falls below the desirable limit. The pH of the treated water (7.0) also conforms to the potable water limit. The detailed chemical analysis of the treated water sample is given in Table 10. 1*6 Determining how the proposed treatment affects the chemical composition of treated water: Tables 8 to 11 details the chemical compositions of the water samples (both spiked and natural water samples) after treatment by the proposed method. Addition of magnesium oxide + calcium hydroxide mix to fluoride bearing water and buffered with sodium bisulfate meets the water quality (Table 12) parameters as specified by the Indian Standards for drinking water (IS 10500: 1991). 1.7. The methods adopted to determine the concentrations of chemical constituents of the water samples: The chloride and fluoride concentrations in the water -samples were determined using respective ion selective electrodes. Sulfate concentrations in the water samples were determmed by turbidity method. Sodium and calcium ion concentrations in the water samples were determined by flame photometer. Magnesium and alkalinity (bicarbonates and carbonates) were determined by standard titration procedures. The TDS of the water samples were determined from electrical conductivity measurements. To check the reproducibility of the treatment method, laboratory tests were repeated on identical water samples in dupUcate. Experiments showed that fluoride concentrations of the repeat samples varied within ± 5 % after treatment. 1.8 Methods for safe disposal of fluoride bearing magnesium oxide sludge Magnesium oxide in conjunction with calcium oxide (lime) is commonly used for chemical stabilization of soils (Purushothama Raj, 1999). The cementitious nature of magnesium oxide + lime mix provides an environmentally safe route for re-use of fluoride bearing magnesium oxide sludge in soil based building materials, such as, stabilized soil blocks, tiles etc. The fluoride encapsulated soil-stabilized blocks are suited for constructing walls of buildings, protected by a plaster layer and are generally dry. Exposure to moisture and inundation is very minimal. The possible re-use of fluoride bearing magnesium oxide sludge in environmentally safe modes is a key factor to adopt magnesium oxide based process for fluoride removal from drinking water for domestic purposes. 1.9 Advantages of IISc method • The method specifies a single dosage of magnesium oxide (1 g/L) for a range of fluoride concentration (1.5 -5 ppm) in the raw water. • The method is mdependent of the initial pH and speed of stirring, • All the chemicals used are non-toxic and easily available. • pH of the treated water is easily adjusted by addition of soluble sodium bisulfate. • The method does not mvolve any recharge process and thus avoids generation of corrosive and toxic wastes. • The re-use of fluoride bearing magnesium oxide sludge in environmentally safe modes is possible. 1.10 Costs The costs of treating 15 liters of fluoride contaminated groundwater containing fluoride concentrations ranging from 1.5 to 5 ppm using commercial grade and laboratory reagent grade chemicals are detailed in Table 11. 1.11 This invention also provides a simple to use Domestic Defluoridation unit (DDU): (a) Brief description of drawings: Fig. 1 illustrates the Domestic de-flouridation unit and Fig. 2 illustrates the Field performance of DDU. (b) Detailed description of the DDU: The device comprises of two cylindrical units 1, 2, each of 20 liters capacity. The upper and lower units are 380 mm high. The inner diameter (ID) and outer diameter (OD) of the upper unit are 280 and 305 mm respectively. The lower imit 2 has slightly larger OD of 330 mm to support the upper container L The upper unit serves as a mixing cum sedimentation unit, vfhile, the lower unit serves as treated water collection unit. The upper, mixing cum sedimentation unit is equipped with a manually operated, geared mechanical stirring device 3 for efficient mixing of required dosage of magnesixmi oxide + calcium hydroxide mix and 15 liters of fluoride contaminated water at the rate of 90 to 100 rpm. The stirrer 3 is provided with a handle 4 and the same is operated through the gear box 5 attached therein. A tap 6 is fixed 107 mm above the base of the upper container to drain the clear water to the lower unit through inlet 10, The position of the tap 6 in the upper unit creates a dead storage space of 3 liters of water that contains magnesium oxide sludge 7. The adequate dead storage volume ensures occurrence of no turbulence effect when the water is drained to the lower unit. To trap any escaping magnesium oxide sludge particles from the upper unit, 15 micron filter 8 is attached to the tap 6 of the upper unit that allows a water flow rate of 0.18 to 0.24 liters/minute. A tap 9 is fitted 51 mm above the base of lower unit to collect potable water. The 3 liters of water containing magnesium oxide sludge and present as dead storage in the upper unit of DDU is transferred to 200 liters capacity sludge storage bin on alternate days. Upon storage in the bin, magnesium oxide particles settle to the bottom of the container in a few hours and the clear supernatant water is discarded, chemical analysis of the clear supernatant water in the storage bin showed only 0.4 ppm fluoride presence that is much smaller than the desirable limit of fluoride in drinking water ( Ippm, IS 10500, 1991), After decantation of clear supernatant water, 300 ml (or 0.31iters) of magnesium oxide sludge remained in the sludge storage bin which represents the smout of sludge generation from trating 16 liters of 2-5 ppm fluoride-contaminated water. Treating 100 liters of 2-5 ppm fluoride-contaminated water will generate 1.9 liters of sludge or 2% sludge on volume basis. Samples were acquired at six points in time of the year and the amount of Flouride in the water was measured. It can be noted that the levels stayed well below the permissible limits from Fig. 2. References 1. Booster, J. L., Van Sandwijk, A,, Renter, M. A. (2003), Conversion of magnesium fluoride to magnesium hydroxide. Minerals Engineering, 16,273-281. 2. Boruff, C. S. (1934), Removal of fluorides from drinking waters. Industrial Engineering Chemistry, 26,69. 3. Elvove, E. (1940), Removal of fluoride from drinking water. United States Patent No. 2,207,725. 4. Fink, G.J. and Lindsay, F.K. (1936). Activated Alumina for Removing Fluorides from Drinking Water. Industrial Engineering Chemistry, 28, 947-948. 5. Handa, B. K, (1975). Geochemistry and genesis of fluoride containing groundwaters in India. Groundwater 13,275-281 6. IS 10500 (1991). Indian standards drinking water speciflcations. 7. Jacks, G., Bhattachatya, P., Chaudhary, V. and Singh, K. P. (2005). Control on the genesis of some high fluoride groimdwaters in India. Applied Geochemistry 20,221-228. 8. Lisle, De. A, L, (1967). Means and methods of defluoridation of water. United States Patent No, 3,337,453. 9. Mamatha, P. (2003). Laboratory studies on use of mineral filters to treat fluoride contaminated water. M.Sc.(Engg.) dissertation, Indian Institute of Science, Bangalore. Mamatha, P. (2005). De-fluoridation of groundwater and re-use of sludge (Ph.D. Dissertation xmder progress). lO.Nawlakhe, W. G., Kulkami, D. N.^ Pathak, B. N., and Bulusu, K. R. (1975). De-fluoridation of water by Nalgonda technique. Indian Journal of Environmental Health, 17,26-65. 11, Private Commxmication. Department of Mines and Geology, Government of Kamataka, Groundwater data from 1994-2001. 12, Purushothama Raj, P. (1999), Ground improvement techniques.Laxmi Publications, New Delhi. 13. Susheela, A.K., Das, T.K„ Gupta, LP,, Tandon, R.K., Kacker, S.K., Ghosh, P. and Deka, R.C. (1992). Fluoride ingestion and its correlation with gastro-intestinal discomfort. Fluoride, 25, 7-12. 14. Susheela, A.K., (1992). Defluoridation of drinking water: Merits of alternative technologies. http://www.nutritionfoundationofindia.org/ARCHIVES/JUL92C.html 15. Venkateswarlu, P. and Narayana R^o, D. (1953). Investigations on the fluoride removal from water : Rapid removal of fluoride with magnesium oxide. Indian Journal of Medical Research 41,473^477. 16. Venkateswarlu, P. and Narayana Rao, D. (1954). Investigations on the fluoride removal from water : Factors governing the adsorption of fluoride by magnesium oxide. Indian Journal of Medical Research 42,135-140. 17. Viswanadham, C. R., Purushottam, D., Rao, G. R., Vaidyanadhan, D. and Francis, P. G. (1974). Defluoridation of water with magnesium oxide. Symposium on Fluorosis, September 74, Hyderabad, IS.Zettlemoyer, A. C, Zettlemoyer, E. A. and Walker, W. C. (1947). Active magnesia II: Adsorption of fluoride from aqueous solution. Journal of American Chemical Society 69,1312-1315. We claim: 1. A physico-chemical process for treating fluoride-contaminated groundwater having a realistic fluoride ion concentration which comprises of the steps of: a. Adding Calcium Chloride solution to known volume of raw water sample depending on its initial calcium concentration; b. Adding Magnesium Oxide and Calcium Hydroxide mix to the fluoride- bearing water of step (a); c. Ensuring efficient contact between the mix of Magnesium Oxide, Calcium Hydroxide and fluoride-contaminated water by manual stirring; d. Allowing the water to settle which leads to the magnesium oxide sludge settling at the bottom of the container; e. Filtering the clear water into a separate container; t Adding sodium bisulfate to the treated water for pH adjustment rendering the water is fit for human consumption and. g. Removing and Storing the magnesium oxide sludge as a by-product for further use. 2. A physico-chemical process as claimed in claim 1, where fluoride-contaminated groundwater having 1.5 to 5 ppm fluoride ion concentration is treated, the pH of the treated water results in a value between 7 and 8.5, 3. A physico-chemical process as claimed in claim 1, where a required volume of 7,5% of calcixun chloride solution is added to known volume of raw water sample depending on its initial calcium concentration 4. A physico-chemical process as claimed in claim 1, where 1.0 g magnesium oxide and 0.1 to 0.25 g calcium hydroxide mix per liter of fluoride-bearing water (the calcium hydroxide dosage is determined by the initial bicarbonate concentration of raw water sample) is added in step lab. 5. A physico-chemical process as claimed in claim 1, where efficient contact between magnesium oxide + calcium hydroxide mix and fluoride-contaminated water is achieved by manual stirring for 5 minutes (for fluoride concentrations 5. A physico-chemical process as claimed in claim 1, where after stirring, water is allowed to settle for 16 hours at the end of which the magnesium oxide sludge settees at the bottom of the container where the clear water is filtered into a separate container (through filter material having 15 micron sized pores) and 2 to 6 ml of 2,5 % sodium bisulfate is added per liter of treated water for pH adjustment rendering the water fit for human consumption. 7, A physico-chemical process as claimed in claim 1, where calcium hydroxide addition becomes necessary at bicarbonate concentrations > 100 ppm, calcium chloride solution addition becomes necessary at calcium ion concentration ppm where the extraneous addition of calcium ions (as calcium chloride solution) is designed to maintain minimum and maximum calcium ion concentrations of 110 and 160 ppm before the addition of magnesium oxide + calcium hydroxide mix. 8. A physico-chemical process as claimed in claim 1, where the boundary conditions of the raw water to be treated reside between the following parameters: a. Fluoride concentration: 1.5-5 ppm b. Bicarbonate concentration: 0 - 400 ppm c. Calcium concentration: 0-160 ppm 9. A Domestic De-fluoridation Unit that is to treat fluoride-contaminated water using the process as claimed in claim 1, which comprises of two cylindrical units, whose upper unit serves as a mixing cum sedimentation unit, while, the lower unit serves as treated water collection unit, a manually operated, geared mechanical stirring means/device being provided on the upper xmit for efficient mixing of required dosage of magnesium oxide, calcium hydroxide mix and fluoride contaminated water at a desired rate, a tap that is fixed above the base of the upper container to drain the clear water to the lower unit through a funnel shaped inlet, a filter being attached to the tap of the upper amity to trap any escaping magnesium oxide sludge particles from the upper unit, a second tap is fitted above the base of lower unit to collect potable water.

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614-che-2004-claims granted.pdf

614-che-2004-correspondnece-others.pdf

614-che-2004-correspondnece-po.pdf

614-che-2004-description(complete)filed.pdf

614-che-2004-description(complete)granted.pdf

614-che-2004-description(provisional).pdf

614-che-2004-drawings.pdf

614-che-2004-form 1.pdf

614-che-2004-form 18.pdf

614-che-2004-form 26.pdf

614-che-2004-form 5.pdf