WO2016035101A1

WO2016035101A1 - A process for the defluoridation of drinking water

Info

Publication number: WO2016035101A1
Application number: PCT/IN2015/050103
Authority: WO
Inventors: Rajendra Singh THAKUR; Saroj SHARMA; Chiragkumar Rameshbhai SHARMA; Akshay Rameshkumar BAVDA; Pratap Shashikant BAPAT
Original assignee: Council Of Scientific And Industrial Research
Priority date: 2014-09-02
Filing date: 2015-09-02
Publication date: 2016-03-10

Abstract

Drinking water containing higher levels of fluoride is lowered by the use of activated alumina in a column by passing the spiked water and regenerating solution from bottom of the column and collecting the output from the top of the column. Pre-treatment with KHS04 or NaHS04 delivers safe' water with a flow rate in excess of 40 LPH. Regeneration of spent activated alumina is performed with Na2C03, another safe chemical. High level of sulphate in the treated water is lowered by the use of aminated form of MMA-co-EGDMA resin, synthesized in a single vessel set up in particle size distribution controlled manner.

Description

A PROCESS FOR THE DEFLUORIDATION OF DRINKING WATER

FIELD OF THE INVENTION.

The present invention relates to process for the defluoridation of drinking water.

This invention relates to a single vessel process of activated alumina based defluoridation of water at an improved rate of uptake by using a suspended bed column and countering the in fluence of other ionic species, those present in the water. Safe chemicals were used for pre- treatment as well as for regeneration of alumina. It further relates to lowering of elevated level of sulphate in defluoridated water, owing to pre-treatment, using aminated form of a weak base resin. This invention also relates to the controlled particle size distribution synthesis of weak base resin beads in a single vessel setup.

In the field of chem ical technology, this invention relates to the integration of chem ical and mechanical aspects involved to design a domestic or other point of use defluoridation unit. Safer replacements of common ly employed chemicals and utilisation of potential energy for obtaining efficient uptake and regeneration is being demonstrated to faci l itate the ease of implementation and use. Enhanced mass transfer of dissolved species at low concentration in a solution to a reactive site on solid surface under suitable motion pattern is a known aspect. In the field of adsorbent chemistry reducing the infl uence of interfering species such as bicarbonate, hydroxide, su lphate etc. for enhanced uptake from an adsorbent-adsorbate pair (activated alumina and fluoride) during u ptake cycle and using a strong interfering species for regeneration is another known aspect. Use of safe alternatives to corrosive chemica ls is known to enhance the acceptabil ity of a process. The present invention also describes lowering of sulphate level in the defluoridated (treated) water by treatment with aminated form of methyl methacrylate - ethylene glycol dimethacrylate (MMA-co-EGDMA) resin synthesized by suspension polymerisation method in control led pa rticle size distribution manner using anchor-shaped impeller.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF PRIOR ART:

Reference may be made to US2059553 by H. V. Churchi l l wherein activated alum ina was used for defluoridation and regenerated using dilute solutions of hydrochloric acid and caustic alka li. The drawback of this method was the use of corrosive chem icals such as hydrochloric acid and caustic alkali. Reference may be made to the EPA 1984 book titled "Design Manual: Removal of Fluoride from Drinking Water Supplies by Activated Alumina" by F. Rubel wherein large scale plant for defluoridation using activated alumina was set up. Feed water was acidified to reduce the pH in the range of 5.0-6.0 enabling high amount of treated water. Regeneration was recommended using 1 % NaOH solution followed by neutralisation with H₂SO₄ acid ified water. Special containers for acid and alkali storage were discussed and skilled operators are needed to run such plants. The drawback of this method was the use of corrosive chem icals such as sulphuric acid and caustic alkali.

References may be made to the WHO 2006 book "Fluoride in Drinking Water" by J. Fawel l et al. (Chapter 2, Page 7) wherein prevalence of fluoride in ground water is noted in India, Pakistan, West Africa, Thailand, China, Sri Lanka and Southern Africa. 1GRAC has displayed maps (http://www.im-igrac.org/publications/ l 52) of higher fluoride levels in the world besides discussing various aspects of the problem. Excess amount of fluoride are known to causes dental and skeletal weakening and deformations, commonly referred as Fluorosis. WHO has suggested 1 .5 mg/L as the gu ideline value for safe level of fluoride in drinking water. WHO has summarised various removal methods of fluoride from drinking water however they are accorded the last priority owing to variety of factors e.g. use of materials of low acceptabi lity, reliability of the method, operational difficulties, and cost of equipment and/or consumables.

Reference may be made to the Ullmann's Encyclopedia of Industrial Chemistry article by L. K. Hudson et al. 2 (2012) 607-645 wherein activated alumina is described as a transition alumina however reproducib le synthesis is possible with combination of initial materials and conditions.

Reference may be made to WHO 2006 book "Fluoride in Drinking Water" by J. Fawell et a l. (Chapter 5 page 69) wherein activated alumina defluoridation was found advantageous for high removal efficiency, easy construction with cheap and widely available material and scalabi lity. The drawbacks are regeneration by taking out the material and with subsequent treatment with 4% NaOH and 2% sulphuric acid and hence centralised setup was recommended for even household units.

Reference may be made to a paper in J. Ind. Chem . Soc. 8 1 (2004) 461 -466 by G. Karthikeyan et a l. wherein instantaneous fluoride uptake was reported from deionised and double distilled water. Strong interference of HCO₃ ^" and m ild interference of SO₄ ^2- was also reported. This study demonstrated faster defluoridation in the absence of the interference from other ionic species. The drawback of the study was lack of applicability to groundwater system.

Reference may be made to IGRAC report "Fluoride in groundwater: Probability of occurrence of excessive concentration on global scale" (http://www.un- igrac.org/publications/147) by R. Brunt et al. and wherein prevalence of high fluoride groundwaters are associated with sodium-bicarbonate water type along with lower levels of calcium and magnesium levels and pH values are high (above 7).

Reference may be made to the paper in J. Haz. Mat. B 139 (2007) 103- 107 by V. S. Chauhan et al. wherein 9- 10 L of tap water having medium alkalinity and about 10 mg/L of fluoride was passed through column containing 3 kg of activated alumina. Units were run intermittently to pass total 40 L of water per day and about 450 L of safe water having fluoride less than 1.5 ppin was obtained from 3 kg of alumina. The drawbacks are the low rate of treatment and regeneration by taking out the material and with subsequent treatment with 1 % NaOH and 1% sulphuric acid. The drawback of the method was the use of corrosive chemicals and slow treatment.

Reference may be made to the paper in In. J. Den. Adv. 3 (201 1 ) 526-533 by P. Eswar et a!. wherein multiple field studies employing activated alumina at both domestic and community levels led to palatable water however cited maintenance disadvantages in particular cumbersome and lengthy regeneration requiring trained persons.

Reference may be made to the 20^th WEDC conference paper by G. Karthikeyan et al. wherein multiple size of activated alumina was screened and higher yield was obtained for small size with lower flow rate from field water. The treated water was found to be acceptable and cost of one defluoridalion and regeneration cycle was estimated. Flow rate of 3 LPH was obtained from 2 kg activated alumina column and requirement of minimum contact time was stated. Regeneration was performed using 2% solutions of NaOH and HCl. The drawback of this method was slow treatment and the use of corrosive chemicals such as hydrochloric acid and caustic alkali.

Reference may be made to the paper in Chem. Engg. J. 98 (2004) 165- 1 73 by S. Ghorai et al. wherein mass transfer control for adsorption of fluoride on activated alumina was concluded however effects of interfering species was not considered for the process. To the best of our knowledge, no experimental data for suspended bed was reported for fluoride adsorption on activated alumina.

Reference may be made to the paper in Water SA 13 (1987) 229-234 by J. J. Schoeman et al. wherein activated alumina was used for defluoridation of Pretoria tap water. Hydroxide and bicarbonate alkalinity was found to be the most important factor affecting fluoride removal efficiency. The study pointed out the drawback of non-applicability of this method to ground (tap) water system.

Reference may be made to US2006/0086668 A l by M. V. Bhinde et al. wherein reducing fluoride content in calcium chloride slurry was demonstrated at higher rate after pre-treatment with sulphuric acid. The drawback of this method is the significantly different ionic composition to that of drinking water as the water contained high amount of chloride and calcium ions. Another drawback was the use of difficult to handle chemicals i. e. sulphuric acid for pre-treatment and NaOH for regeneration.

Reference may be made to NIOSH database (htlp://www.cdc.gov/niosh/idlh/intridl4.htinl) wherein sulphuric acid and sodium hydroxide are listed in chemical list of "Immediately Dangerous to Life or Health". International Chemical Safety Cards suggests Na₂C0₃ and KHSO₄ to be safer and easier to handle, store, transport, and spillage control than NaOH and H₂SO₄ respectively. It h ighlights the drawback of use of NaOH and H₂SO,i in a given process.

Reference may be made to a paper in Eur. J. Chem. 3 (2012) 125- 128 by B. Baghernejad wherein KHSO₄ was described as an inexpensive, eco-friendly, easy to handle and non-toxic chemical for use as a catalyst in organic transformations.

Reference may be made to a paper in Ind. Eng. Chem. Res. 36 ( 1997) 939-965 by E. V. Lima et al. wherein many advantages of suspension polymerisation is discussed however difficulties in controlling particle size distribution are noted.

Reference may be made to US4444961 A (also EP 0051210 B l) by E. E. Timm wherein uni form size polymer beads were obtained in suspension polymerisation method. Monodispersity was induced by droplet formation achieved by vibratorialy exciting the monomer jet. Resin beads in the size range of 0.7 mm to 1 .2 mm constituted more than 94 % of the product formed. The drawback of this method was additional assembly for droplet formation of monomer mixture. Reference may be made to US4623706A by E. E. Timm et al. wherein uniform size polymer ^• beads of small size, 5 μm to 1 00 μηι, were obtained by discharging the monomer jet flow into continuous gas phase. Monomer jet possessed the laminar flow characteristics and droplets were formed by suitably sized orifice. The drawback of this method was additional assembly for droplet formation of monomer mixture.

Reference may be made to EP0046535B 1 by P. M. Lange et al. wherein uniform size polymer beads were obtained by dispersing uniform size monomer droplets into immiscible solvent leading to encapsulation. Beads in the size range of 0.8 to 1 .2 mm are 50-75%. The drawback of this method was additional assembly for droplet formation of monomer mixture.

Reference may be made to US7947748B2 by J. D. Finch el al. wherein droplets containing monomer, cross linker and initiator is discharged into water. Aqueous suspension of encapsulated droplets is transferred by a pipe at a lower temperature to another reactor wherein the polymerisation is performed. It was attempted on styrene DVB system and harmonic mean size of 435 micron was reported with uniform ity coefficient of 1 .04. The drawback of this method was additional assembly for droplet formation.

Reference may be made to US7265 I 59B2 by R. Klipper et al. wherein momomer mixture is either sp/ayed into an immiscible liquid and/or reacted with a feed containing the same acrylic compounds. The drawback of this method was additional assembly for droplet formation.

Reference may be made to US20080234398 A I by R. Klipper et al. wherein monodisperse droplets containing methacrylates, crosslinking agent, initiators and porogens are produced by alomisation are microencapsulated. Droplets are supported in aqueous phase using longitudinal oscillations and polymerized at higher temperature. The drawback of this method was additional assembly involving atomizer and oscil lator.

OBJECTS OF THE INVENTION.

The main object of the present invention is to provide a technique of defluoridation of drinking water.

Another object of the present invention is to lower the sulphate level in the treated water using the aminated form of MMA-co-EGDMA resin beads. Still another object of the present invention is to synthesize the MMA-co-EGDMA resin beads in particle size distribution controlled manner using si ngle vessel setup wherein the monomer m ixture is added to aqueous phase. Droplets are generated by anchor shaped impeller and polymerisation is performed by heating the m ixture.

BRIEF DISCRETION OF THE DRAWINGS

The present invention is ill ustrated in drawings 1 -7 accompanying this specification.

Drawi ng I represents the effect of various factors controlling the uptake of fluoride ions by activated alumina (grade DF- 101 from Siddhartha Chem Industries, Vadodara, India). The Mechanical stirring (400 rpm), ionic composition of water, and pretreatment of activated alumina were investigated for defluoridation.

Drawing 2 represents the effect of various factors control ling the uptake of fluoride ions by activated alum ina (grade DF- 1 01 from Aquaplus Techno, Salem, India). The Mechanical stirring (400 rpm), ionic composition of water, and pretreatment of activated alumina were investigated for defluoridation .

Drawing 3 represents the 50 L square tank ( 1 ) as reactor whererin m ixing was performed with closed loop distribution system. Water was drawn from the tank ( 1 ) using an inlet (2) to centrifugal pump (3) and distribution system (5) is attached to the pump outlet (4) for circulation. Flexible pipes were used for connections. Dimensions are given in mm.

Drawing 4 represents the detailed design of distri bution system (5) as described in Drawing 3. It consisted of hollow pipe (6) of length 622 mm to which the outlet (4) of centrifugal pump (3) was attached. Another end of the pipe (6) was connected to the vertica l connection of a T-shaped con nector. Two hollow pipes (7, 8) of length 200 mm were connected to the remaining two horizontal connections of the same T-shaped connector. The other ends of the pipes (7, 8) were c losed with the use of mechanical seals. 9 holes of diameter I mm were made at uniform intervals of 20 mm in pipes (7, 8). The distribution system was mechanically fixed to one of the wal l of the tan k ( 1 ) in such a way that the ho les are facing towards the interior part. Pipes used were having internal diameter of 14 mm and external diameter of 16 mm . Dimensions are given in mm.

Drawi ng 5 represents the defluoridation kinetics performed in the 50 L tank ( 1 ) with closed loop water distribution setup as described in Drawings 3 and 4. Effect of pretreatment of water (lo counter the interfering species) and pretreatment of activated alumina were investigated for defluoridation kinetics as well as cumulative effect of both pretreatments.

Drawing 6 represents single pass and gravity induced flow defluoridation setup wherein a given aqueous solution was filled in the aspirator bottle (9) and flown through a suspended bed column ( 10) of activated alumina and collected in a reservoir ( 1 1 ). Aspirator bottle (9) was kept at the height of 1080 mm and flow was controlled by the attached tap. Suspended bed column (10) of activated alumina was placed vertically such that the base of the column was at a height of 180 mm above the ground. The column (10) had two openings at the top and bottom and the bottom opening was connected to the bottle aspirator (9) through a flexible pipe of 10 mm internal diameter. Top opening was connected to the reservoir ( I I ) for collecting the aqueous solution passed through the column ( 10). Dimensions are given in mm.

Drawing 7 represents the anchor shaped impeller made of hollow circular glass tubes (8 mm outside diameter) used in particle size distribution controlled synthesis of MMA-EGDMA resin beads. Anchors were of 43 mm of horizontal and vertical dimensions. Three anchors were fabricated on a glass tube of length 400 mm such that they were perpendicular to adjacent anchors and base to base distance between successive anchors were 75 mm.

Dimensions are given in mm.

BRIEF DESCRIPTION OF THE INVENTION:

In an embodiment of the present invention fast defluoridation of drinking water by passing it through activated alumina column is realised after pre-treatment using suitable safe chem ical.

In another embodiment of the present invention regeneration of spent activated alumina column ach ieved by passing suitable safe chemical.

In yet another embodiment of the present invention is all steps involved in uptake and regeneration is performed inside one vessel i.e. column filled with activated alumina.

In sti ll another embodiment of the present invention is the suitability of the process for domestic or other point of use by employing smalt size of the column and safer reagents. In sti ll another embodiment of the present invention sulphate level in the low fluoride water is lowered by treatment with am inated form of the MMA -co-EGDMA resin.

In still another embodiment of the present invention MMA-co-EGDMA resin is synthesized in particle size-distribution controlled manner in a single vessel setup by employing anchor shaped impeller.

DETAILED DESCRIPTION OF THE INVENTION:

The present invention a ims to speed up fluoride uptake by activated alum ina and subsequent regeneration by tuning the influence of interfering species under suitable motion pattern. In multiple studies, OH^" and HCO₃- are considered as strong interfering ions while SO,|^2" has a moderate influence in the defluoridation of groundwater by alumina. Mass transfer is known to become rate l im iting step for sol id-solution interface of dissolved species present at ppm levels. The current development aims to enhance mass trans fer of dissolved fluoride into adsorbent by the use of suspension bed and elimination of the i nfluence of interfering species by pre-treatment with 1 % KHSO₄ (or NaHSO₄) solution. Fast and efficient regeneration is realised by passi ng 1 % Na₂CO₃ solution which can provide strongly interfering species OH^' and HCO₃- ions in solution. The faster defluoridation and subsequent regeneration by means of safer chem icals in a single vesse l operation contribute to ease of implementation and use. Higher level of su lphate in the treated water arising from pre-treatment with is lowered by treatment with aminated form of weak base ion exchange resin. Particle size distribution controlled synthesis of weak base ion exchange resin is performed by using suspension stabiliser and droplet formation is achieved by stirring applied from anchor shaped impeller made from cylindrical glass tubes. The organ ic layer in contact with impel ler gets rolled into droplets under stirring which are polymerised at higher temperature.

Past defluoridation from activated alumina shou ld be achievable by pre-treatment with acidic su lphate solution (e.g. Na₂SO₄ + H₂SO₄) and upward flow through a column. Regeneration should be achievable with any carbonate (e.g. K₂CO₃) solution. These chemica ls can also work as replacements of H₂SO₄ and NaOH for defluoridation using colum n operation at larger scale. Anchor shaped impel ler used for control partic le size distribution synthesis of resin beads can also work for other polymeric systems.

The fol lowing exam ples are given by way of i llustration and therefore should not be construed to limit the scope of the present invention . EXAMPLE- 1

Kinetics of fluoride uptake was performed for deionised as well as tap water for quite as well as stirring conditions. Fluoride uptake kinetics by activated alumina (grade DF- 101 from Siddhartha Chem Industries, Vadodara, India; BET surface area 362.9 m²/g; 6.6% weight loss upto 400 °C and 1 1 .2% npto 800 °C, particle size 0.4-1 .2 mm) is shown in Drawing 1 . Water containing about 10 ppm fluoride ( I L) was treated with 4 g activated alumina in a beaker under stirring using overhead stirrer at 400 rotations per minute (RPM) from where 20 mL fractions were collected after designated time intervals. Pre-treatment of activated alum ina was performed by washing with 200 mL of 1 % H₂SO₄ solution for 30 min under stirring conditions followed by washing with corresponding water. Stirring led to significant faster fluoride uptake for deionised as well as tap water. Fluoride uptake was faster in deionised water than tap water and acid washing further enhanced the rate of uptake in both cases. Similar observations were noted for Fluoride uptake kinetics by activated alumina (grade DF- 101 from Aquaplus Technologies, Salem, India; BET surface area 260.4 m²/g; 8.8% weight loss upto 400 °C and 13.0% upto 800 °C, particle size 0.4- 1.2 mm) and are shown in Drawing 2. Typical characteristics of tap water are pH 8. 15, conductivity 1 .1 5 mS/cm and alkalinity 2.3 mL of 0. I N HCl.

EXAMPLE-2

Fluoride uptake by activated alumina (grade DF- 101 from Siddhartha Chem Industries, Vadodara, India) was attempted for 50 L water tank (Drawing 3 ; dimensions in mm). The water was kept in motion by means of a centri fugal pump (50 W, 230 V; 600 litres per hour { LPH} at the height of 1 5 meter) to enhance the mass transfer rate at the liquid- solid interface in the tank. The outlet of the centrifugal pump was connected to the distribution system. The distribution system was kept at the bottom of the tank (Drawing 4; dimensions in mm). The pipe, connected to the inlet of the centrifugal pump was always kept immersed in the water. Effectiveness of treatment of alumina, tap water and both are compared and the data is shown in Drawing 5. Pre-treatment of alum ina as well as that of water led to faster defluoridation of tap water by similar extent. Combination of both approaches led to cumulative effect. Acid washing of 400 g activated alumina with 2 L of 1 %% H₂SO₄ was performed in a beaker by stirring for 30 minutes using overhead stirrer followed by wash ing with tap water. 25 L tap water was treated with 20 g of slaked lime Ca(OH)₂ and another 25 L was treated with 150 mL I N HC).

EXAMPLE-3

The tap water having 9.8 ppm fluoride concentration was initially stored in an aspirator bottle of 20 L capacity. The aspirator bottle was kept at the height of 108 cm with respect to the ground level. The tap water was then passed through the column containing activated alumina particles (DF-101 Siddhartha Chem Industries). The activated alumina particles are hereafter termed as 'particles' . The total mass of the activated alumina particles kept in the column was I kg and the occupied length in the column was 220 mm.

The column was placed at the height of 1 8 cm from the ground level. The internal diameter of the column was 74 mm. The column was having two openings, one at the top and the other at the bottom. The upper open ing was covered internally with the nylon filter of mesh size 72 to avoid any escape of the particles. The liquid phase such as water containing d issolved fluoride was always passed through the bottom opening of the column and water circu lation prevented particles to drop out of lower opening. Thus, the net liquid flow was always in the upward direction in the column leading to suspended bed operation. The liquid was then allowed to come out of the column from the top opening through the pipe connections and then final ly col lected into a pot.

The outlet of the aspirator bottle was connected to the bottom open ing of the column with the help of flexible tube of internal diameter of 10 mm . As the aspirator bottle was kept at the higher vertica l level ( 108 cm) than that of the column ( 1 8 cm), water from the aspirator bottle flowed through the column under the influence of water head available and the flow rate was then controlled through the stopcock attached to the bottle aspirator (Drawing 6; dimensions in mm). Thus, no external pump was used to circulate the water. Initially, 10 L of 1 % aqueous solution of sulphuric acid was passed through the column as a pie-treatment for the activated alum ina particles.

The flow rate of the tap water through the column was 47 LPH. In itial 10 L of treated tap water was discarded as its pH level was below perm issible level for drinking water standards. The fluoride level was sampled at (he interval of 10 I , and total volume of treated water having fluoride less than 1 .5 ppm (henceforth referred as safe water) was 92 L. In the next cycle 1 1 7 L of safe water obtained for 9.5 ppm initial fluoride concentration with a flow rate 45.5 LPH .

EXAMPLE-4

The setup described in example 3 was used in d ifferent set of conditions. The tap water having 1 9.2 ppm fl uoride concentration was passed through the activated alumina column at the rate of 44 LPH after pre-treatment with 10 L of 1 % aqueous solution of su lphuric acid. Initial 10 L of treated lap water was discarded and 92 L of safe water was obtained.

EXAMPLE-5

The setup described in example 3 was used in different set of conditions. The rap water having 1 8.2 ppm fluoride concentration was passed through the activated alumina column at the rate of 46 LPH after pre- treatment with 10 L of 1 % aqueous solution of HCl. Initial 10 L of treated tap water was discarded and 1 0 L of safe water was obtained. This example has taught about limited effectiveness of HCl in the process.

EXAMPLE-6

The setup described in example 3 was used in different set of cond itions. The tap water having 10 ppm fl uoride concentration was passed through the activated alumina column at the rate of 44.4 LPH after pre-treatment with 10 L of 1 % aqueous solution of sodium hydrogen sulphate. Initial 1 0 L of treated tap water was discarded and 84 L of safe water was obtained.

EXAM PLE-7

The setup described in example 3 was used in different set of conditions. 800 g of activated alumina (DF- 101 from Aquaplus Technologies) with a fill height of 207 mm was taken in the column. The lap water having 19.2 ppm fluoride concentration was passed through the activated alumina column at the rate of 42 LPH after pre-treatment with 10 L of 1 % aqueous solution of sulphuric acid. Initial 10 L of treated tap water was discarded and 60 L of safe water was obtained. EXAMPLE-8

The setup described in example 7 was used in different set of conditions. The tap water having 1 9.2 ppm fluoride concentration was passed through the activated alumina column at the rate of 44 LPH after pre-treatment with 10 L of 1 % aqueous solution of potassium hydrogen sulphate. Initial 1 0 L of treated tap water was discarded and 70 L of safe water was obtained. The average yield of subsequent 4 cycles was 57.5 L for similar flow rates. This example has taught about partial regeneration with potassium hydrogen sulphate solution.

EXAMPLE-9

The setup described example 7 was used to regenerate column by passing 20 L solution of 2% sodium carbonate followed by washing with 20 L tap water. Pre-treatment was performed by passing 1 0 L of 1 % sodium hydrogen su lphate. 70 L of safe water was obtained upon passing J 0.4 ppm fl uoride solution at a rate of 44 LPH through regenerated alumina column.

EXAMPLE- 10

The setup described example 7 was used to regenerate column by passing 20 L solution of 1% sodium carbonate followed by washing with 2 L tap water. Pre-treatment was performed by passing 10 L of 1 % sodium hydrogen sulphate. 50 L of safe water was obtained upon passing 1 1.2 ppm fl uoride solution at a rate of 40 LPH through regenerated alumina column.

EXAMPLE- 1 1

Water passed through column (500 mL pH ~ 5) was treated with aminated weak base resin under stirring at 400 RPM using an overhead stirrer for 1 hour. In itial sulphate level (precipitated as BaS0₄ from 300 m L water) of 387.0 mg/L (282 nig BaSO₄ ) was lowered to 5.5 mg/L (4 mg BaS0₄) for 20 and 10 mL of weak base resin and 90.3 mg/L for 5 mL (66 mg BaSO.») of weak base resin. Tap water contained about 96 mg/L (70 mg BaSO^) of sulphate level. In another attempt, lowering of sulphate level from 293 mg/L to 9.9 mg/L was observed by ion-chromatography wherein 500 m L of water passed through column was treated with 20 m L of am inated weak base resin under stirring at 400 RPM using an overhead stirrer for 1 hour. Chloride level was found to increase from 340 mg/L to 620 mg/L. Animation of MMA-co-EGDMA resin was performed by heating 200 m L of resin with 1400 mL of trielhylenetetram ine at a temperature of 190°C for around 8 hours. EXAMPLE- 12

Weak base resin from example 1 1 was synthesized to 94.5% of beads (w/w) in the particle size range of 420-840 μηι. Crosslinked porous polymer of MMA-co-EGDMA was synthesized by rad ical suspension polymerization technique using n-heptane as porogen . The polymerization was carried out in three necked 3 L round bottom flask equipped with mechanical stirrer, thermometer and reflux condenser. Stirring at 240 RPM was provided from a heavy duty stirrer using anchor shaped impeller (Drawing 7; dimensions in mm) made of hollow glass tube. The organic mixture comprise of 80% (w/w) monomer mixture and 20% (w/w) n-heptane. The monomer mixture comprise of 80% (w/w) monomer (MMA), and 20% (w/w) crosslinking agent (EGDMA), initiator (benzoyl peroxide, BPO 1 % w/w of the monomer). The organic m ixture ( 150 mL) was added into 1500 mL water containing suspension stabi lizer (polyvinyl alcohol PVA cold 1 .5%) and 0. 1 5% NaCl at 65°C under stirring. After fully d ischarging the organic mixture slowly inside the water the whole system was allowed to remain for 10-20 mins during which smal l droplets of organic mixture are formed. Thereafter, the temperature of the syatem was increased to 80°C at the rate of ] °C/ min and al lowed to remain at 80°C for polymerization. After 4 hrs the resulting polymeric beads were fi ltered out from the reaction vessel and washed 3-4 times with hot water to remove the unreacted monomers and adhering PVA. The washed polymeric beads were dried in air followed by soxhlet extraction using n-hexane. The total weight of beads formed was 77.7 g. Beads of the 420-840 μm particle size were separated using the sieves of mesh size 20 and 40. The beads outside this size range were larger than 840 μm.

EXAMPLE- ) 3

Weak base resin from example 1 1 was synthesized to 93.4-95%) of beads (w/w) in the particle size range of 420-840 μm . Crosslinked porous polymer of MMA-co-EGDMA was synthesized by radical suspension polymerization technique using n-heptane as porogen. The polymerization was carried out in three necked 3 L round bottom flask equ ipped with mechanical stirrer, thermometer and reflux condenser. Stirring at 240 RPM was provided from a heavy duty stirrer using anchor shaped impel ler made of ho llow glass tube. The organic m ixture comprise of 80% (w/w) monomer mixture and 20% (w/w) n-heptane. The monomer mixture comprise of 80% (w/w) monomer (MMA), and 20% (w/w) crosslinking agent (EGDMA), initiator (BPO 1 % w/w of the monomer). The organic mixture ( 150 mL) was added into 1 500 mL water containing suspension stabi lizer ( 1 -2% PVA) and 0. 1 -0.2% NaCl at 65°C under stirring. After fully discharging the organ ic mixture slowly inside the water the whole system was al lowed to remain for 10-20 mins during which small droplets of organic mixture are formed. Thereafter, the temperature of the system was increased to 80°C at the rate of 1°Cl min and allowed to remain at 80°C for polymerization. After 4 hrs the resulting polymeric beads were filtered out from the reaction vessel and washed 3-4 times with hot water to remove the unreacted monomers and adhering PVA. The washed polymeric beads were dried in air followed by soxhlet extraction using n-hexane. The total weight of beads formed was 77.7 - 84.3 g. Beads of the 420-840 μm particle size were separated using the sieves of mesh size 20 and 40. The beads outside this size range were larger than 840 μm. The ion exchange capacity of the aminated beads was 7-8 milliequivalents per gram (meq/g) as determined by acid-base titration using 0. 1 N solutions of HCl and NaOH.

EXAMPLE- 14

Weak base resin from example 12 was synthesized to 96.3% of beads (w/w) in the particle size range of 420-840 μιτι . Crossfmked porous polymer of MMA-co-EGDMA was synthesized by radical suspension polymerization technique using n-heplane as porogen. The polymerization was carried out in three necked 3 L round bottom flask equipped with mechanical stirrer, thermometer and reflux condenser. Stirring at 220 RPM was provided from a heavy duty stirrer using anchor shaped impeller made of hollow glass tube. The organic mixture comprise of 80% (w/w) monomer mixture and 20% (w/w) n-heptane. The monomer mixture comprise of 80% (w/w) monomer (MMA), and 20% (w/w) crosslinking agent (EGDMA), initiator (BPO 1 % w/w of the monomer). The organic mixture ( 150 mL) was added into 1 500 mL water containing suspension stabilizer (2% PVA) and 0.2% NaCI at 65°C under stirring. After fully discharging the organic mixture slowly inside the water the whole system was allowed to remain for 10-20 mins during which small droplets of organic mixture are formed. Thereafter, the temperature of the syatem was increased to 80°C at the rate of 1°Cl min and al lowed to remain at 80°C for polymerization. After 4 hrs the resulting polymeric beads were filtered out from the reaction vessel and washed 3-4 times with hot water to remove the unreacted monomers and adhering PVA. The washed polymeric beads were dried in air followed by soxhlet extraction using n-hexane. The total weight of beads formed was 76.8 g. Beads of the 420-840 μm particle size were separated using the sieves of mesh size 20 and 40. The beads outside this size range were larger than 840 μιτι.

EXAMPLE- 15 Weak base resin from example, 12 was synthesized to 55.7% of beads (w/w) in the particle size range of 420-840 μm . Crossl inked porous polymer of MMA-co-EGDMA was synthesized by radical suspension polymerization technique using n-heptane as porogen. The polymerization was carried out in three necked 3 L round bottom flask equipped with mechanical stirrer, thermometer and reflux condenser. Stirring at 210 RPM was provided from a heavy duly stirrer using anchor shaped impe ller made of hollow glass tube. The organic mixture comprise of 80% (w/w) monomer mixture and 20% (w/w) n-heptane. The monomer mixture comprise of 80% (w/w) monomer (MMA), and 20% (w/w) crosslinking agent (EGDMA), initiator (BPO 1 % w/w of the monomer). The organic mixture (150 mL) was added into 1500 mL water containing suspension stabilizer (2% PVA) and 0.2% NaCI at 65°C under stirring. After fully discharging the organic mixture slowly inside the water the whole system was allowed to remain for 10-20 mins during which small droplets of organic mixture are formed. Thereafter, the temperature of the syatem was increased to 80°C at the rate of 1°C/ min and allowed to remain at 80°C for polymerization. After 4 hrs the resulting polymeric beads were filtered out from the reaction vessel and washed 3-4 times with hot water to remove the unreacted monomers and adhering PVA. The washed polymeric beads were dried in air fol lowed by soxhlet extraction using n-hexane. The total weight of beads formed was 77.7 g. Beads of the 420-840 μm particle size were separated using the sieves of mesh size 20 and 40. The beads larger than 840 μm constituted 9.9% and smaller than 420 μm was around 34.3% of the total weight of the beads formed.

EXAMPLE- 16

Weak base resin from example 12 was synthesized to 83% of beads (w/w) in the particle size range of 420-840 μm. Crosslinked porous polymer of MMA-co-EGDMA was synthesized by radical suspension polymerization technique using n-heptane as porogen. The polymerization was carried out in three necked 3 L round bottom flask equipped with mechanical stirrer, thermometer and reflux condenser. Stirring at around 190 RPM was provided from a low duty stirrer using anchor shaped impeller made of hollow glass tube. The organic mixture comprise of 80% (w/w ) monomer mixture and 20% (w/w) n-heptane. The monomer mixture comprise of 80% (vivW) monomer (MMA), and 20% (w/w) cross linking agent (EGDMA), initiator (BPO 1 % w/w of the monomer). The organic mixture (1 50 mL) was added into 1500 mL water containing suspension stabilizer (1.5% PVA) and 0.1 5% NaCI at 65°C under stirring. After ful ly discharging the organic mixture slowly inside the water the whole system was allowed to remain for 10-20 mins during which small droplets of organic mixture are formed. Thereafter, the temperature of the syatem was increased to 80°C at the rate of 1 °C/ min and allowed to remain at 80°C for polymerization. After 4 hrs the resulting polymeric beads were filtered out from the reaction vessel and washed 3-4 times with hot water to remove the unreacted monomers and adhering PVA. The washed polymeric beads were dried in air followed by soxhlet extraction using n-hexane. The total weight of beads formed was 76.6 g. Beads of the 420-840 μιτι particle size were separated using the sieves of mesh size 20 and 40. The beads larger than 840 μιτι constituted 3.7% and smaller than 420 μιτι was around 1 3.3% of the total weight of the beads formed.

The main advantages of the present invention are:

1. Fast defluoridation of drinking water by pre-treatment of activated alumina inside the column.

2. Easy and fast regeneration of exhausted activated alumina by passing regenerating agent inside the column.

3. Set up for defluoridation and regeneration is easy to construct and operates under spontaneous flow.

4. Safe chemicals for pre-treatment and regeneration ensuring ease of transport, storage, and handling leading to ease of operation.

5. Particle size distribution controlled synthesis of resin beads leads to higher yield in the particle size range of 420-840 μm with dispensability of the separation step.

6. Single vessel setup used for synthesis of resin beads is easy to run and maintain.

Claims

1 : A process for the defluoridation of drinking water which comprises of:

(i) pre-treatment of activated alumina inside column by passing aqueous solution of KHSO₄ (or NaHSO₄) followed by passing of fluoride containing water,

(ii) regeneration of spent activated alumina inside column by passing aqueous solution of Na₂CO₃,

(iii) lowering the sulphate level in the water generated in the step (i) with the aminated form of MMA-co-EGDMA (Methyl Methacrylate-Ethylene Glycol Dimethacrylate) resin.

2: A process for defluoridation of drinking water, as claimed in claim 1 , wherein the activated alumina column is pre-treated by passing 10 L of 1 % potassium (or sodium) bisuiphate solution through suspended bed column followed by passing the tap water containing fluoride at a rate of around 40 LPH (Litre per hour).

3. A process for regeneration of spent activated alumina, as claimed in claim 1 , wherein 20 L of 1 % sodium carbonate solution is passed through suspended bed column followed by passing 20 L of tap water,

4. A process for l owering the sulphate level in water obtained after defluoridation, as claimed in claim 1 and 2, by treatment with aminated MMA-co-EGDMA (Methyl Methacrylate-Ethylene Glycol Dimethacrylate) resin beads.

5. A process for particle size distribution controlled synthesis of resin beads, for lowering the sulphate level as described in claim 4, in single vessel setup comprises the steps of;

(i) heating 2 L aqueous solution of polyvinyl alcohol ( 1 -2%) and sodium chloride (0, 1 -0.2%) in in 3 L round bottom flask upto 60 °C,

(ti) charging organic mixture containing monomer mixture (64% MM A, 16% EGDMA and benzoyl peroxide 1% of the monomers) and n-hexane (20 %) in water filled round bottom flask stirred with anchor shaped impeller at a rate of ca. 220 RPM causing formation of droplets over a period of 10-20 minutes,

(iii) polymerisation of droplets by raising the temperature to 80°C, maintained for 4 hours, (iv) beads formed are filtered and washed with hot water for 3-4 times followed by air drying and soxhiet extraction using n-hexane,

(v) beads in the particle size range of 0.42-0.84 mm are separated by sieves of mesh sizes 20 and 40,

(vi) amination of the beads by reaction with excess of triethylenetetramine at 190°C for 8 hours.