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REVIEW ARTICLE
Year : 2014  |  Volume : 1  |  Issue : 1  |  Page : 1-4

Defluoridation techniques: Which one to choose


1 Department of Public Health Dentistry, K. D. Dental College and Hospital, Mathura, Uttar Pradesh, India
2 Department of Orthodontics and Dentofacial Orthopaedics, K. D. Dental College and Hospital, Mathura, Uttar Pradesh, India

Date of Web Publication21-Oct-2014

Correspondence Address:
Harsh Vardhan Dubey
Dahi Wali Gali, Purohit Mohalla, Infront of Jain Temple, Bharatpur, Rajasthan
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2394-2010.143315

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  Abstract 

Water is one of the most important elements for all forms of life and is indispensable to the maintenance of life on the earth. Safe drinking water is the important need for every human being. Water may be contaminated by natural sources or by industrial effluents. One such contaminant is fluoride. The problem of excess fluoride in ground water was detected in many states of India. Till 1999, 17 states have been identified with the problem of excess fluoride in ground water sources. Several materials like aluminium salts, calcined alumina, magnesia, lime, activated carbon sulphonated carbonaceous materials, and ion exchange resins have been screened for their utility in defluoridation of water. On the basis of results and extensive investigations, different researchers had developed a simple and economical domestic defluoridation processes. This article attempts to critical review of the past work on defluoridation studies by using conventional and unconventional materials, and to compile the various pros and cons of these defluoridation methods including Nalgonda, Activated Alumina, bone char, fly ash, brick, and reverse osmosis.

Keywords: Defluoridation methods, fluorosis, India


How to cite this article:
Ingle NA, Dubey HV, Kaur N, Sharma I. Defluoridation techniques: Which one to choose. J Health Res Rev 2014;1:1-4

How to cite this URL:
Ingle NA, Dubey HV, Kaur N, Sharma I. Defluoridation techniques: Which one to choose. J Health Res Rev [serial online] 2014 [cited 2018 Dec 18];1:1-4. Available from: http://www.jhrr.org/text.asp?2014/1/1/1/143315


  Introduction Top


Water is essential for life. It is used in almost every domestic activity, from cooking to washing or for sanitation. With rapid population growth, increasing urbanization, and technological development in various fields, human dependence on water has increased tremendously. Water availability is neither adequate nor equitable for all human beings. In addition to the problem of limited availability of water, there is also the problem of water quality. For instance, the biological and chemical contamination of water is a matter of grave concern. One such chemical contaminant present in the water is flouride. [1] Defluoridation involves removal of fluoride ion in drinking water. Defluoridating methods may broadly be classified in two categories namely Additive methods and Adsorptive methods. In additive methods, certain reagents are added and optimum conditions for the defluoridation are maintained. Fluoride ion present in water reacts with the reagents added and forms an insoluble complex and was removed as ad flocs. In adsorptive methods, a bed of greater surface activity is chosen and water is passed through the bed. Due to surface activity, fluoride ions get preferentially adsorbed on the bed surface thereby causing a reduction of fluoride ion in the exit stream. The different methods used for the removal of excess fluoride from water can be broadly classified into four basic types:- [2]

  • Precipitation technique
  • Adsorption technique
  • Ion-Exchange technique
  • Miscellaneous methods.



  Precipitation technique Top


Nalgonda technique

The Nalagonda technique was developed by the National Environment Engineering Research Institute (NEERI), Nagpur, after testing of many materials Nawlakhe et al. [3] In Nalgonda Technique there is addition of aluminium salts, lime, and bleaching powder followed by rapid mixing, flocculation, sedimentation, filtration, and disinfection. Aluminium salts can be added as aluminium sulphate (alum) or aluminium chloride or combination of these two. It is responsible for removal of fluoride from water. The dose of aluminium salt increases with increase in the fluoride and alkalinity levels of the raw water. Lime facilitates forming dense flocks for rapid settling of insoluble fluoride salts. The dose of lime is empirically 1/20 th of that of the dose of aluminium salt. Bleaching powder is added in the amount of 3 mg/l for disinfection. [2] Bulusu et al. stated in 1979 that Nalgonda Technique was preferable at all levels because of the low price and ease of handling. [4] Parthasarathy et al., [5] studied the combination of calcium salts and polymeric aluminium hydroxide, for the treatment of fluoridated waste water. In this treatment, the calcium ion acts as a precipitant and polymeric aluminium hydroxide acts as a coagulant. The addition of calcium fluoride seeds (approximate 20 mg/l) results in the acceleration of the precipitation process and the residual fluoride concentrations were closed to the theoretical levels. Under the above conditions fine CaF 2 precipitate with poor ability to settle was formed. The addition of small amount of polymeric aluminium hydroxide greatly facilities the ability to settle of the precipitate. The advantage of using polymeric hydroxide over the use of alum for the removal of fluoride is that less concentration of the former is required and the results are good. Mameri et al., [6] suggested an efficient defluoridation process in which aluminium bipolar electrodes was used. In the first step, certain parameters such as inter-electrode distance fluoride concentration, temperature and the pH of the solution were investigated and optimized with synthetic water in batch mode. The electro-congratulation process with aluminium bipolar electrodes permitted the defluoridation of Sahara Water without adding soluble salts to the treated water. The aluminium fluoride weight ratio attended as 7. The technique is highly versatile and has the applications like; for large communities, fill and draw technique for small communities as well as for rural water supply, for domestic defluoridation, etc. [2]

Advantages

  • It can be used at domestic and community level
  • It is cost effective
  • Simplicity of design, construction, operation and maintenance
  • Low technology, adaptable at point of use and point of source level
  • Beside fluoride turbidity, colour, odour, pesticides and organic substance are also removed in this method.


Disadvantages

  • The daily operations require a trained operator
  • There is a possibility of excess aluminium contaminating the water. The maximum concentration of aluminium permitted is 0.03 mg to 0.2 mg/litre of water according to Bureau of Indian Standards (BIS), as an excess is suspected to cause Alzheimer's disease
  • Discarding the sludge from the Nalgonda process is a serious environmental health problem. The sludge is toxic as it contains the removed fluoride in a concentrated form and therefore, sludge disposal is a problem
  • Periodic analysis of feed and treated water is required to calculate the correct dose of chemicals to be added. [7]



  Adsorption technique Top


Many adsorbent materials have been tried in the past to find out an efficient and economical defluoridating agent. Activated alumina, activated carbon, activated alumina coated silica gel, calcite, activated saw dust, activated coconut shell carbon, and activated fly ash, groundnut shell, coffee husk, rice husk, magnesia, serpentine, tricalcium phosphate, bone charcoal, activated soil sorbent, carbion, defluoron-1, defluoron-2, etc., are different adsorbent materials reported in the literatures. The most commonly used adsorbents are activated alumina and activated carbon. [8] The fluoride removing efficiency of activated alumina is affected by hardness and surface loading that is. the ratio of total fluoride concentration to activated alumina dosage. Chloride does not affect the defluoridation capacity of activated alumina. The process is pH specific, so pH of the solution should be between 5.0-6.0 because at pH > 7, silicate and hydroxide become stronger competitor of the fluoride ions for exchange sites on activated alumina and at pH less than 5; activated alumina gets dissolved in acidic environment leading to loss of adsorbing media. The process is highly selective but it has low adsorption capacity, poor physical integrity, requires acidification, and pre-treatment and its effectiveness for fluoride removal reduces after each regeneration. [7] Mckee and Johnston 1934, investigated the use of powdered activated carbon for fluoride removal and achieved good results. [9] The process is pH dependent with good results only at pH 3.0 or less. Therefore, the use of this material is expensive due to need of pH adjustment. Patil and Kulkarni [10] studied the ion exchange resin and activated alumina as defluoridating media and found that equilibrium adsorption capacity of ion exchange resin on Indeon A-100 was 1.54 gm/Kg of resin. Two hundred bed volumes of water can be treated with initial fluoride concentration of 2.2 mg/1 to obtain an effluent concentration of less than 1 mg/1 at the optimized fluid flow rate of 35 l/hr. No appreciable change was observed in the test of water. The defluoridation by catalyst grade activated alumina of type AC 101 was found that equilibrium adsorption was more than 15 mg/gm of Al 2 O 3 . Activated alumina technique for defluoridation is started in several villages by the voluntary organizations funded by UNICEF or other agencies in order to provide safe drinking water. [7]

Advantages

  • This process can remove fluoride up to 90%
  • Effective and economical
  • It requires minimum contact time for maximum defluoridation
  • It is indigenously available and cheap
  • Percentage of regeneration is considerably high.


Disadvantages

  • The process is highly pH dependent and works only in a pH range of 5-6
  • High concentration of total dissolved salts (TDS) can result in fouling of the alumina bed
  • Presence of sulphate, phosphate or carbonate results in ionic competition
  • The process has low adsorption capacity, poor integrity and needs pre treatment
  • The regeneration is required after every 4-5 months
  • Disposal of fluoride laden sludge is also a problem
  • Skilled personnel are required for plant operation
  • Suitable grades may not be indigenously available in less developed countries
  • This treatment is not effective if TDS exceeds 1500 mg/L
  • It requires time to time regeneration as after some time activated alumina is exhausted. [8]



  Ion exchange technique Top


Synthetic chemicals, namely, anion and cation exchange resins have been used for fluoride removal. Some of these are Polyanion (NCL), Tul-sion A-27, Deacedite FF (IP), Amberllte IRA 400, Lewatit MIH-59, and Amberlite XE-75. These resins have been used in chloride and hydroxy form. The fluoride exchange capacity of these resins depends upon the ratio of fluoride to total anions in water. The capacity of Amberlite XE 75 was found to be approximately 88 g/m 3 when fluoride to total anion ratio was 0.05. The capacity increased with increasing ratio. Polyanion removed fluoride at the rate of 862 mg/kg and 1040 mg/kg with initial fluoride concentration of 2.8 and 8.1 mg/L, respectively. Deacedite FF (IP) and Tulsion A-27 could treat 2270 L and 570 L of water bringing fluoride level from 2.2-1.0 mg/L. [2] Related studies was carried by Mohan Rao and Bhaskaran [11] in Andhra Pradesh where he experimented several materials including aluminium salts, calcium alumina, magnesium, lime, activated carbon, sulphonated carbonaceous materials, and ion exchange resins have been screen for their utility in defluoridation of water. In this study, he observed that sulphonated carbonaceous materials and ion exchange resins removes fluoride from 5 mg/1 to 1.5 mg/1. Popat et al., [12] used aluminium form of the amino methyl phosphonic type ion exchange for fluoride removal. However, the presence of sulphates (100 mg/L) and bicarbonates (200 mg/L) reduced the fluoride removal capacity of the resins to 33%. The resins increased the concentration of chloride in treated water, which can cause corrosion of the water storage utensils. The treated water also had high pH. [2]

Advantages

  • Removes fluoride up to 90-95%
  • It helps in the retention of taste and colour of water intact.


Disadvantages

  • Its efficiency is reduced in presence of other ions like sulphate, carbonate, phosphate and alkalinity
  • Regeneration of resin is a problem because it leads to fluoride rich waste, which has to be treated separately before final disposal
  • The technique is expensive because of the cost of resin
  • Treated water has a very low pH and high levels of chloride. [8]



  Miscellaneous methods Top


Reverse osmosis and electro dialysis

In reverse osmosis, the hydraulic pressure is exerted on one side of the semi permeable membrane which forces the water across the membrane leaving the salts behind. The relative size of the pollutants left behind depends on the pressure exerted on the membrane. In electro dialysis, the membranes allow the ions to pass but not the water. The driving force is an electric current which carries the ions through the membranes. The removal of fluoride in the reverse osmosis process has been reported to vary from 45-90% as the pH of the water is raised from 5.5-7. The membranes are very sensitive to pH and temperature. The economics of the approach also deserves evaluation under specific circumstances. The units are also subject to chemical attacks, plugging, fouling by particulate matter, and concentrated and large quantity of wastes. The waste volumes are even larger than the ion exchange process. Sometimes, the pre-treatment requirements are extensive. Electro dialysis is highly energy intensive and expensive. [2] Few investigators have studied reverse for arsenic and fluoride removal. However, recent work by Fox, 1981 [13] and Huxstep, 1981 [14] has shown reverse osmosis to be effective in reducing traced concentration of these contaminants. The improvements in design and materials of the membranes have made the water treatment process economically competitive and highly reliable. [15] Thus with improved management; this new technology for drinking water production might be the best option. Furthermore, membrane processes have several advantages as compared with other treatment methods. [16]

Advantages

  • The process is highly effective for fluoride removal
  • The process permits the treatment and disinfection of water in one step
  • It ensures constant water quality
  • No chemicals are required and very little maintenance is needed
  • Life of membrane is sufficiently long, so problem of regeneration or replacement is encountered less frequently
  • It works under wide pH range
  • No interference by other ions is observed
  • The process works in a simple, reliable automated operating regime with minimal manpower using compact modular model.


Disadvantages

  • It removes all the ions present in water. Since though some minerals are essential for proper growth therefore, remineralisation is required after treatment
  • The process is expensive in comparison to other options
  • The water becomes acidic and needs pH correction
  • Lots of water gets wasted as brine
  • Disposal of brine is a problem. [8]



  Conclusion Top


Fluorosis is an important public health problem in India. Drinking water is the main source of ingestion of fluoride. The various manifestations of chronic fluoride toxicity are mild to severe dental fluorosis and skeletal fluorosis. Though not life threatening, this disease causes impairment of dental aesthetics, derangement of skeletal system which results in compromised quality of life. There is no cure to the disease and prevention is the only solution. The first and foremost preventive measure is drinking fluoride-safe water. This can be accomplished by defluoridation of fluoride-contaminated drinking water. Defluoridation should be taken up where there is no alternate source of safe drinking water. It has been observed that many methods are used for removal of excess of fluoride in the drinking water but every method have their advantages and disadvantages. The fluoride removal ability varies according to many site-specific chemical, geographical and economical conditions, so actual applications may vary from the generalizations made. Some particular process, which is suitable at a particular region, may not meet the requirements at some other place. Therefore, any technology to be used should be treated before implementation in the field.

 
  References Top

1.Social Inclusion: A Case Study of the Rajasthan Integrated Fluorosis Mitigation Programme. Available from: http://www.kcci.org.in rajasthan.pdf. [Last accessed on 2013 Nov 07].  Back to cited text no. 1
    
2.Piddennavar R, Krishnappa P. Review on Defluoridation techniques of water. Int J Eng Sci 2013;2:86-94.  Back to cited text no. 2
    
3.Nawlakhe WG, Kulkarni DN, Pathak BN, Bulusu KR. De-fluoridation of water by Nalgonda technique. Indian J Environ Health 1975;17:26-65.  Back to cited text no. 3
    
4.Bulusu KR, Sundaresan BB, Pathak BN, Nawlakhe WG, Kulkarni DN, Thergaonkar VP. Fluorides in water-defl uoridation methods and their limitations. J Inst Eng (India) 1979;60:1-25.  Back to cited text no. 4
    
5.Parthasarathy N, Buttle J, Haeridi W. Combined used of calcium salts and polymeric aluminium hydroxide for deluoridation of waste water. J Water Resour 1986;20:443-8.  Back to cited text no. 5
    
6.Mameri N, Yeddou AR, Lounicih, Belhiccine D, Garib H, Bariou B. Defluoridation of septentrional sahara water of North Afrika by electro coagulation process using bipolar aluminium electrodes. J Water Resour 1998;32:1604-32.  Back to cited text no. 6
    
7.Modi S, Soni R. Merits and demerits of different technologies of defluoridation for drinking water. J Environ Sci Toxicol Food Technol 2013;3:24-7.  Back to cited text no. 7
    
8.Razbe N, Kumar R, Pratima, Kumar R. Various options for removal of fluoride from drinking water. Int Organ Sci Res J Appl Phys 2013;3:40-7.  Back to cited text no. 8
    
9.Mckee R, Johnston WS. Removal of fluorides from drinking water using low-cost adsorbent. Indian J Environ Health 1999;41:53-8.  Back to cited text no. 9
    
10.Patil AR, Kulkarni BM. Study of ion exchange regime and activated alumina as defluoridation media. J Inst Eng (India) 1989;03:14-6.  Back to cited text no. 10
    
11.Mohan Rao NV, Bhaskaran CS. Studies on defluoridation of water. J Fluor Chem 1998;41:17-24.  Back to cited text no. 11
    
12.Popat KM, Anand PS, Dasare BD. Selective removal of fluoride ion from water by the aluminium, from the aminomethyl phosphonic acid type ion exchange resin. React Funct Polym 1994;23:23-32.  Back to cited text no. 12
    
13.Fox KR. "Removal of inorganic contaminants from drinking water by reverse osmosis'' EPA- 600/2-81-115, Municipal environmental research laboratory, U.S. Environmental Protection Agency, Cincinnati, OH; 1981.  Back to cited text no. 13
    
14.Huxstep MR. "Inorganic contaminants removal from drinking water by reverse osmosis''EPA-600/2-81 Offi ce of research and development, U.S. Environmental Protection Agency, Cincinnati, OH; 1981.  Back to cited text no. 14
    
15.Babra D, Caputi P, Cifoni DS. Drinking water supply in Italy. Desalination 1997;113:111-7.  Back to cited text no. 15
    
16.Meenakshi, Maheshwari RC, Jain SK, Gupta A. Use of membrane technique for potable water production. Desalination 2004;170:105-12.  Back to cited text no. 16
    



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Abstract
Introduction
Precipitation te...
Adsorption technique
Ion exchange tec...
Miscellaneous me...
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