|Year : 2019 | Volume
| Issue : 1 | Page : 3-8
Novel materials for defluoridation in India: A systematic review
Sreekanth Bose, R Yashoda, Manjunath P Puranik
Department of Public Health Dentistry, Government Dental College and Research Institute, Bangalore, Karnataka, India
|Date of Web Publication||23-Apr-2019|
Department of Public Health Dentistry, Government Dental College and Research Institute, Bangalore, Karnataka
Source of Support: None, Conflict of Interest: None
Background: Fluorosis is an endemic disease prevalent in 22 states in India affecting 70 million individuals. The process of removal of fluoride ions from water is known as defluoridation. Even though several defluondation techniques have been developed and implemented in India, most of these techniques have many disadvantages. Development of a newer defluoridation technique starts With laboratory experimentation of materials. Objectives: To identify recent advances in laboratory studies in India with regard to the materials used for defluoridation (published from 2010-2017). Methodology: The review was carned out according to the Joanna Briggs Institute (J81) critical appraisal guideline. A three-step search strategy was utilized which yielded twenty articles after the final step. These articles were evaluated to describe, compare and contrast the materials (Chemical, indigenous and herbal) in terms of effectiveness of fluonde removal, critical pH, cost and other factors. Results: Fluoride removal capacity varied around to 100% and optimum pH between 2 to 10 in different studies. Indigenous and herbal materials are cost effective compared to chemicals. But chemicals have better defluoridation capacity. The defluondating properties can be enhanced using certain combinations or pretreatment of these materials (eg-Heat activation). Conclusions: Indigenous and herbal products are suitable for Indian conditions because of the ease of availability and cost-effectiveness. The future research should focus on enhancing the defluoridating properties of locally available materials and field studies regarding the feasibility in real life scenarios.
Keywords: Defluoridation, India, laboratory studies, materials
|How to cite this article:|
Bose S, Yashoda R, Puranik MP. Novel materials for defluoridation in India: A systematic review. J Dent Res Rev 2019;6:3-8
|How to cite this URL:|
Bose S, Yashoda R, Puranik MP. Novel materials for defluoridation in India: A systematic review. J Dent Res Rev [serial online] 2019 [cited 2020 Aug 8];6:3-8. Available from: http://www.jdrr.org/text.asp?2019/6/1/3/256806
| Introduction|| |
Fluoride is one of the most potent ions present in groundwater which can cause endemic outcomes. According to WHO 1984 and Indian standard drinking water specification 1991, the maximum permissible limit of fluoride is 1.5 ppm and highest desirable limit is 1.0 ppm. As an extremely electronegative element, fluorine has high affinity to get attracted by positively charged ions such as calcium in mineralized tissues. Excess intake may cause fluorosis which can be dental, skeletal, and nonskeletal along with various neurological complications.
Many countries first started to inspect the harmful effects of fluoride and its elimination from drinking water in the 1930s. The process of removal of fluoride ions from water is known as defluoridation. There were many materials and techniques explored to carry out fluoride removal. However, the experiments to construct a method of defluoridation that can be used under differing environmental, social, financial, and technical constraints have not been successful. Hence, the elimination of fluoride from water is important and a challenging task among scientists.
The world's fluoride stores in ground are estimated to be 85 million tons, of which nearly 12 million tons are located in India. A hot tropical climate with comparatively more drinking water consumption creates a high prevalence of affected population. Fluorosis is an endemic disease thought to affect 70 million individuals and prevalent in 22 states of India, particularly in arid parts of the country. Skeletal fluorosis is present among 43% of these individuals with clinical presentations such as severe pain in the back bone, joints and pelvic girdle which leads to stiffness of the vertebral column, immobile joints, and terminating in a crippling condition. Although there is no treatment or solution, this disease can be prevented.
Throughout the years, several defluoridation procedures have been developed and actualized in India. Nalgonda technique developed by National Environmental Engineering Research Institute, based on combined use of alum and lime in a two-step process, is the most widely used. However, the technique has a lot of disadvantages such as the undesirable taste of treated water, high maintenance cost need of large space, the requirement of a regular attendant looking after-treatment process, temperature, and presence of silicate ions affect the efficacy. The purified water can produce adverse health outcomes such as dementia due to residual aluminum, the cathartic effect due to sulfate ion, and toxicity due to a soluble aluminum fluoride complex ion which does not form the sledge.
Prasanti technology developed by Satya Sai University for Higher Learning, Puttaparthy use activated alumina. The limitations of this method include high expense, need for trained persons for reactivation of filter material, and formation of moderately high residual aluminum byproduct ranging from 0.1 to 0.3 ppm.
While reverse osmosis which is considered as most effective in terms of fluoride removal also holds certain disadvantages such as economic burden, large waste volumes, extensive pretreatments, and chance of chemical attacks, plugging, and fouling by particulate matter in the units. Besides, this method removes all the ions present in water, essential for human growth and development. Hence, there is a need for the development of a better method of defluoridation with fewer limitations.
Development of new defluoridation technique is a stepwise and complex process including laboratory testing of the material, bench scale test, pilot scale, and field scale demonstrations.
Laboratory experiments enable many parameters to be inspected in detail and a significant understanding about the performance of materials in various conditions. The information obtained from these studies is very useful in formulating and implementing newer methods of defluoridation. Much laboratory research has been done on materials in this decade in India.
Hence, there is a need to evaluate the results of these studies by means of a systematic review.
Hence, the objective of this review was to identify recent advances in laboratory studies in India with regard to the materials used for defluoridation (published from 2010 to 2017) to critically evaluate the effectiveness of newer chemical, indigenous, and herbal materials studied for defluoridation in terms of effectiveness of fluoride removal, critical pH, cost, and other factors.
| Materials and Methods|| |
The review was carried out according to the standards of Joanna Briggs Institute guidelines for systematic review. A three-step search strategy was used in this review. An initial literature search of publications indexed in the English language was performed through core databases (MEDLINE and Google scholar), with the following keywords: effectiveness of materials, defluoridation, laboratory studies, and India. In the second step, articles describing laboratory investigations that evaluated material effectiveness for defluoridation done in India which were published over a period of 7 years (2010–2017) were retrieved for the study. Third, the reference list of all identified reports and articles was searched for additional studies. Gray literature was not included in the study. The date limitation in the search strategy might have excluded the potentially relevant studies. However, the objective was to find recent advances in defluoridation which could be achieved only through the time period restriction. Primary search and screening were conducted by the first reviewer. Inclusion and exclusion of the studies were decided by consensus among all reviewers.
The search yielded 127 articles. A total of sixteen articles were eliminated due to duplication while 22 articles were excluded because full-length articles were not available. Thus, 89 articles were retrieved at the second stage and critically assessed for inclusion by the team consisting of the three reviewers. A total of 62 articles were excluded at the second level, as they were not related to the main outcome of this study. Finally, based on the interpretations of the team, seven articles were excluded due to lack of clarity in the literature. Thus, a total of twenty articles were included in this systematic review, as shown in [Figure 1].
|Figure 1: These 20 articles were critically assessed by all the reviewers. The assessment was focused to describe, compare, and contrast the materials (chemical, indigenous, and herbal) in terms of effectiveness of fluoride removal, critical pH, cost, and other factors|
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| Results|| |
A total of 20 studies conducted over 7 years (2007–2017) were included in this systematic review. The analysis of literature revealed that laboratory studies are being carried out on different types of materials which can be chemical, indigenous, or herbal. Most of the studies modified the material to achieve better fluoride removal properties. The studies included three major defluoridation techniques – adsorption, precipitation, and ion exchange [Table 1]. Maximum number of studies (seventeen) described materials using adsorption technique. Among them, ten studies were on herbal materials.
|Table 1: Description of literature based on the type of material and technique of defluoridation|
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The most important properties evaluated in most of the studies were fluoride removal capacity and optimum pH of materials. Fluoride removal capacity varied around 40%–100% and optimum pH between 2 and 10 in different studies as shown in [Table 2], [Table 3], [Table 4].
|Table 2: Description of the defluoridating capacity of chemical materials based on technique and optimum pH|
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|Table 3: Description of the defluoridating capacity of indigenous materials based on technique and optimum pH|
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|Table 4: Description of the defluoridating capacity of herbal materials based on technique and optimum pH|
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Very few studies, have focused on cost of the materials. Certain indigenous materials such as bentonite clay, rice husk ash, and shale were shown to have good economic viability. All the herbal materials under investigation are very much cost-effective and easily available in rural regions. Typha angustata cost only around US $25/ton.
Regeneration of material after the process is useful in reuse, limiting the total amount of material needed for fluoride removal. Some studies,,,,,, have reported regeneration capacity of respective materials. Zirconium chitosan nanoparticles, chitosan composite modified with lanthanum complex, lanthanum-impregnated bauxite, aluminum hydroxide derived from hydrated aluminum sulfate, bentonite clay, tamarind, and T. angustata have regeneration capacity.
Hardness of water which is due to the presence of a wide variety of ions affects the adsorption capacity of the sorbent. Lanthanum-modified chitosan, bentonite clay, and tamarind seeds showed lower defluoridation capacity in the presence of bicarbonate ions. The inhibitory effect of Shale was in the order of carbonate, nitrate, chloride, and phosphate while it was carbonate, sulfate, chloride, nitrate for lanthanum-impregnated bauxite, and Phyllanthus emblica. Activated alumina proved to have no ionic interactions.
| Discussion|| |
Air, water, and food are the three fundamental requirements for the survival of individuals. Hence, the drinking water must be safe and potable. Groundwater, which aquifers below the surface of the Earth, is one of the most important sources of drinking water. Groundwater frequently contains high amount of inorganic minerals such as fluoride which can cause risk to the well-being.
Various techniques and materials were used for defluoridation of drinking water. Precipitation, adsorption, ion exchange, and membrane methods are the most important techniques used. This review showed that most of the recent laboratory investigations are using the method of adsorption. The materials are either chemicals, indigenous, or herbal. Different materials such as alumina, alum, and activated charcoal are used traditionally depending on the techniques. The present day investigations focus on modifications of chemicals with known defluoridation properties to enhance the efficacy or finding newer indigenous/herbal materials with better fluoride removal capacity.
Laboratory studies have the role of paving the path for new techniques. It will provide considerable insight and quantitative information about many of the physical properties of materials used for defluoridation. Recent advances in defluoridation of water in India are clustered around innovative laboratory experiments done for novel effective material. Chemicals such as alumina, limestone, and alum are used for defluoridation of water since early days. A systematic review done by Dubey et al. reported the use of chemicals, especially aluminum compounds in the ongoing field programs.
Chitosan modified with lanthanum, lanthanum-impregnated bauxite, and aluminum hydroxide are new chemicals with their modifications under investigation which shows promising results in fluoride removal capacity. They exhibited fluoride removal capacity of 17.50 mg/g, 18.18 mg/g, and 25.8 mg/g, respectively.,, Chitosan composite modified with nano zirconium was able to remove around 99% of fluoride from water. These chemical compounds work around neutral pH. It was observed that acidic conditions produced by addition of phosphoric acid can give better defluoridation with limestone. Chemicals such as aluminum compounds are proved to be better candidates for the defluoridation process in the application, and this observation is in line with the review on emerging adsorbents by Jadhav et al.
Most of the places endemic to fluorosis in India are remote areas where chemicals are not easily available. Indigenous materials are very useful in defluoridation because of the local availability and low cost. If defluoridation can be carried out efficiently by locally available indigenous materials, there will be lesser barriers in rural India for the implementation of such programs. Materials such as rice husk ash, bentonite clay, brick powder, and coal mine wastes have defluoridating capacity in the adsorption process. The defluoridating capacity was 9–10 mg/g for rice husk ash while coal mine waste and bentonite clay showed 88% and 97% fluoride removal., Under precipitation method, the brick powder had 50%–55% fluoride removal capacity which increased by 4%–5% when impregnated with alum., Generally, indigenous materials work around acidic pH. Eggshell waste has ion exchange properties which are useful for fluoride removal from water. Modifications of these materials can increase the efficiency.
Herbal materials are observed to collect fluoride with the process of adsorption, and hence, application as defluoridating agents has been proposed. Acceptability of herbal materials among Indians make them good candidates for the process. Seeds of tamarind and moringa, charcoal obtained from neem, banana peel and coffee husk and T. angustata plant, Indian gooseberry Tulsi have promising fluoride removal characteristics.,,,,,,,,, The defluoridation capacities were 91% and 76% for tamarind and moringa seeds, respectively, 94% and 84% for neem and banana peel and coffee husk charcoals, respectively, and 82.1% and 42% for Indian gooseberry and Tulsi leaves, respectively.,,,,, Herbal materials work efficiently around a wide spectrum of pH. Optimum pH for charcoal obtained from the banana peel and coffee husk is 2 while it is 8 for moringa seeds., Most of the plant extracts and compounds give desirable odor to the treated water, and medicinal properties of herbs will promote rural population to use it for defluoridation. Studies are aiming to increase the effectiveness of these compounds.
The Indian government is striving to provide people with safe drinking water provisions. India is a large country with huge population which makes it hard to address the issue of overabundance of fluoride in water through public-aided community-based treatment units. The absence of proprietorship by user communities and the consequent hesitance to take over the responsibility were also observed in many villages. Hence, domestic defluoridation techniques are best for Indian conditions. It will reduce the burden of huge government investment to meet the needs of millions of endemic rural population. Domestic units are the “point of use” units with a higher level of individual possession. This might make sure better utilization and maintenance of these units. Past experience with domestic units with the assistance of United Nations Children's Fund has not been generally encouraging due to higher material cost. Indigenous and herbal materials are most suitable in this scenario. They are locally available and cost-effective.
Studies are conducted on a variety of materials for their defluoridation capacity. Limitations of these studies include scarcity of literature regarding field applications. This can create a void in the practicability of use of materials about amount of workforce required, quality, and acceptability of purified water. Studies are not providing information about the cost of materials. The ability of methods to be converted into large scale or household water defluoridating units is also not discussed in the earlier studies. These factors were reflected on the results of this review and can be considered as limitation.
Indigenous and herbal products for fluoride removal are suitable methods in the Indian scenario. Cultural habits in India will promote using herbal materials for water treatments, and the purified water will have acceptable odor and taste. The low cost and availability are the factors which favor the use. Adsorption which has a tremendous potential for defluoridation because of its effectiveness, ease of operation, and ability to reuse the adsorbent (regeneration) is used for it. However, generally, these materials have very low fluoride removing capacity. The defluoridating properties can be enhanced using certain combinations, pretreatment (e.g., heat activation) of these materials before the defluoridation process. Hence, this systematic review recommends researchers to focus on enhancing the defluoridating properties of locally available materials and conduct field studies regarding the feasibility of models in real-life scenarios.
| Conclusions|| |
Recent advances in developing effective materials for defluoridation in India show promising research in the development of novel materials. Effective, easily available, and low-cost materials (chemicals, indigenous products, and herbal materials) are the core of investigations. Modifications of known materials used for fluoride removal can also produce good results. Adsorption is proved to be the most studied method of defluoridation. It is the most appropriate mechanism while using indigenous and herbal products. These materials are suitable for Indian conditions because of the ease of availability and cost-effectiveness. Field studies are suggested to test the applicability of these materials.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]