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Bio-inspired materials for defluoridation of water: A review

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Abstract

The polluted water sources pose a serious issue concerning the various health hazards they bring along. Due to various uncontrolled anthropogenic and industrial activities, a great number of pollutants have gained entry into the water systems. Among all the emerging contaminants, anionic species such as fluoride cause a major role in polluting the water bodies because of its high reactivity with other elements. The need for water remediation has led the research community to come up with several physicochemical and electrochemical methods to remove fluoride contamination. Among the existing methods, biosorption using bio and modified biomaterials has been extensively studied for defluoridation, as they are cheap, easily available and effectively recyclable when compared to other methods for defluoridation. Adding on, these materials are non-toxic and are safe to use compared to many other synthetic materials that are toxic and require high-cost design requirements. This review focuses on the recent developments made in the defluoridation techniques by biosorption using bio and modified biomaterials and defines the current perspectives of fluoride removal specifically using biomaterials.

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... Due to anthropogenic and industrial activities, a great number of pollutant entry in water systems leading to possible concerns for wildlife and human health. Defluoridation of water may contribute in reducing the level of fluoride contamination in water and different physicochemical and electrochemical methods have been used for this purpose [129]. Among these, biosorption should be considered an easily available, recyclable and inexpensive tool [129]. ...
... Defluoridation of water may contribute in reducing the level of fluoride contamination in water and different physicochemical and electrochemical methods have been used for this purpose [129]. Among these, biosorption should be considered an easily available, recyclable and inexpensive tool [129]. ...
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Background: Perchlorate-induced natrium-iodide symporter (NIS) interference is a well-recognized thyroid disrupting mechanism. It is unclear, however, whether a chronic low-dose exposure to perchlorate delivered by food and drinks may cause thyroid dysfunction in the long term. Thus, the aim of this review was to overview and summarize literature results in order to clarify this issue. Methods: Authors searched PubMed/MEDLINE, Scopus, Web of Science, institutional websites and Google until April 2020 for relevant information about the fundamental mechanism of the thyroid NIS interference induced by orally consumed perchlorate compounds and its clinical consequences. Results: Food and drinking water should be considered relevant sources of perchlorate. Despite some controversies, cross-sectional studies demonstrated that perchlorate exposure affects thyroid hormone synthesis in infants, adolescents and adults, particularly in the case of underlying thyroid diseases and iodine insufficiency. An exaggerated exposure to perchlorate during pregnancy leads to a worse neurocognitive and behavioral development outcome in infants, regardless of maternal thyroid hormone levels. Discussion and conclusion: The effects of a chronic low-dose perchlorate exposure on thyroid homeostasis remain still unclear, leading to concerns especially for highly sensitive patients. Specific studies are needed to clarify this issue, aiming to better define strategies of detection and prevention.
... This calls for sustainable methods to preserve the available freshwater. Preservation of water resources is still a global challenge because of its limited availability, industrialization and increase in the population (Hegde et al. 2020). Several factors including anthropogenic and geological factors (Yadav et al. 2018), uncontrolled industrialization, urbanization and unskilled utilization of water contribute to the contamination of groundwater and degradation of water quality, getting them down of the World Health Organization (WHO) standards for safe drinking water (Hegde et al. 2020). ...
... Preservation of water resources is still a global challenge because of its limited availability, industrialization and increase in the population (Hegde et al. 2020). Several factors including anthropogenic and geological factors (Yadav et al. 2018), uncontrolled industrialization, urbanization and unskilled utilization of water contribute to the contamination of groundwater and degradation of water quality, getting them down of the World Health Organization (WHO) standards for safe drinking water (Hegde et al. 2020). ...
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Capacitive deionization (CDI) is among the promising technologies employed for water purification. CDI has been studied for the removal of various ionic species from water including fluoride ion (F−) with promising results. However, there is no comprehensive literature that summarizes the use of CDI for water defluoridation applications. Therefore, this review paper critically analyzes different electrode materials that have been studied for water defluoridation, their electrosorption capacities and F− removal efficiencies. It further discussed the parameters that influence CDI efficiency during defluoridation and point out the issues of F− selectivity when co-existing with other ions in the solution. We can conclude that different electrode materials have shown different abilities in electrosorption of F−. The carbon-based materials possess high surface area and good electrical conductivity which is paramount for ion adsorption but gives lack selectivity for F− removal. Metal oxides and hydroxides have been reported with improved electrosorption capacity and high selectivity to F− due to the ion exchange between the F− and the hydroxyls surface of the metal oxides/hydroxides. Apart from the good performance of these materials for defluoridation, the discovery of actual practical use of the electrode materials for defluoridation for commercial scale is still a need. HIGHLIGHTS Water defluoridation by capacitive deionization (CDI) have been reviewed.; The defluoridation efficiency of various CDI electrode materials has been reviewed.; Metal oxides/hydroxides, as well as carbon materials and metal oxides/hydroxides composites, have shown good fluoride uptake in pilot-scale experiments.; Parameters affecting the defluoridation process with CDI have been reviewed.;
... The advantages and drawbacks of various conventional defluoridation techniques are well elaborated in Table 2. It is widely documented that most of these methods are time-consuming, laborious, costintensive, and require waste disposal (Hegde et al., 2020) Thus, the adoption of a more economic, eco-friendly, and cost-effective defluoridation method is preferred. Adsorption-based defluoridation has received overwhelming attention in the last few years (Loganathan et al., 2013). ...
... However, it is pertinent to mention that temperature also plays an important role in the alteration of surface features of an adsorbent . The best-suited temperature required for the adsorption process ranges from Hegde et al., 2020;Deshmukh et al., 2018;Ravulapalli and Kunta, 2017;Singh et al., 2015;Getachew et al., 2015;Kumar et al., 2015;Dwivedi et al., 2014;Rajan and Alagumuthu, 2013;Abas et al., 2013;Sanchez-Sanchez et al., 2013). 20 to 30 • C. ...
Article
Fluoride is recognized as one of the global environmental threats because of its non-biodegradable nature and long-term persistence in the environment. This has created the dire need to explore various defluoridation techniques (membrane process, adsorption, precipitation, reverse osmosis, ion exchange, and electrocoagulation). Owing to their cost ineffectiveness and high operational costs, these technologies failed to find any practical utility in fluoride remediation. Comparatively, defluoridation techniques involving the use of low-cost plant-derived adsorbents and fluoride phytoremediators are considered better alternatives. Through this review, an attempt has been made to critically synthesize information about various plant-based bioadsorbents and hyperaccumulators from existing literature. Moreover, mechanisms underlying the fluoride adsorption and accumulation by plants have been thoroughly discussed that will invigorate the researchers to develop novel ideas about process/product modifications to further enhance the removal potential of the adsorbents and plants. Literature survey unravels that various low-cost plant-derived adsorbents have shown their efficacy in defluoridation, yet there is an urgent need to explore their pragmatic application on a commercial scale.
... Scientists have provided numerous solutions by employing various techniques for dealing with fluoride pollution in order to get potable and fluoride-free water. Defluoridation techniques involve precipitation, membrane filtration, electrochemical treatment, ion exchange, and adsorption Hegde et al., 2020;. ...
... It could be physical or chemical adsorption or it could be governed through hydrogen bonding or electrostatic forces of attraction (Yadav et al., 2018). Furthermore, this interaction also may get influenced by the physicochemical properties such as contact time, solution pH, surface area, adsorbent dose, pore size, temperature, pore-volume, particle size, initial concentration of adsorbate, and regeneration capacity of adsorbent Hegde et al., 2020;Yadav et al., 2018; (Fig. 4.1). Thus, to make the adsorption process more economical and simpler, special attention should be given to the aforementioned characteristics. ...
Chapter
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Fluoride while beneficial for human health at low concentration shows harmful impacts on skeletal fragility, kidney, nerve damage, etc., if consumed in excess. Several techniques were applied for the removal of excess fluoride from water such as adsorption, membrane separation, ion exchange, precipitation, etc. The selection of a particular technique depends on its specific advantages and disadvantages. These techniques were initially developed at a lab scale and further evolved as pilot plants. Successful pilot plant studies were subsequently developed into community-based applications for fluoride removal. Some of these processes not only removed fluoride but also other unwanted species, namely, phosphate, arsenic, bicarbonates. These plants are extremely popular in various Asian and African countries as they are useful for providing safe drinking water to underprivileged people. In such studies, adsorption was one of the popular methods that employed various adsorbents and the overall cost was about 20 USD/m³. Similarly, precipitation methods like Nalgonda technique were also successfully applied at the cost around 15 USD/m³. Electrocoagulation using aluminium electrode is also a popular method having an operational cost of about 1 USD/m³, whereas equipment cost is substantially high. On the other hand, membrane separation has the highest installation cost of about 800k USD and operational cost of about 0.2 USD/m³. This chapter is specifically discussing about the economics, cost analysis of water defluoridation, and possible applicability.
... In the case of F − adsorption, the removal efficiency was predominantly higher at acidic pH medium, which may be attributable to an increase in H + ions in the solution, creating a positive surface charge on the adsorbents. Under these conditions, the nucleophilic replacement of OH − ions with F − might be dominating, and competing OH − ions may have hampered the ion exchange phenomenon as the pH increased towards the basic range [32,37]. ...
Article
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In this study, we demonstrate the use of functionalized inter-penetrated biomaterial mesh composites (FMCs) as rapid hazardous heavy metal and emerging pollutant retention media. Varying composition of biopolymers were first functionalized to be converted into highly active hazard retention sites. Further, structural and morphological confirmation of the synthesized FMC’s were characterized using different analytical tools such as FT-IR, P-XRD, FE-SEM, XPS, DLS, and Zeta potential. Likewise, experiments were conducted to investigate the removal of toxic pollutants such Cr⁶⁺, F⁻, and series of emerging pollutants. The optimized composition among the five variant FMCs showed maximum adsorption capacity of 315.86 mg/g for Cr⁶⁺ ions, 52.75 mg/g for fluoride ions, 77.71 mg/g for Ciploflaxin and 61.5 mg/g for Diclofenac. Further, to check the practical use and robustness of the composite materials, continuous flow adsorptive membrane filters were prepared and then the adsorptive membrane was tested in continuous filtration mode for the robust removal series of pollutants both in simulated feed condition as well as real contaminated samples. In this mode, adsorptive membrane showed a flux of ∼300-900 LMH and > 98% retention efficiency for Cr⁶⁺, 92% rejection for CTAB, and 60% retention for both low molecular weight pharmaceutical pollutants and F⁻ ions. Therefore, this research demonstrates a sustainable strategy for efficiently removing Cr⁶⁺, F⁻, and emerging pollutants like active pharmaceutical ingredients (APIs) from contaminated water streams.
... The presence of specific functional groups in biological materials facilitates surface modification to achieve higher fluoride removal efficiencies (Raveendra M. Hegde et al., 2020). Functional groups such as hydroxyl, thiol, amine and carboxyl groups can be easily modified to obtain effective fluoride complexes. ...
Article
Fluoride is one of the essential trace elements for the human body, but excessive fluoride will cause serious environmental and health problems. This paper summarizes researches on the removal of fluoride from aqueous solutions using newly developed or improved biomass materials and biomass-like organic materials in recent years. These biomass materials are classified into chitosan, microorganisms, lignocellulose plant materials, animal attribute materials, biological carbonized materials and biomass-like organic materials, which are explained and analyzed. By comparing adsorption performance and mechanism of adsorbents for removing fluoride, it is found that carbonizing materials and modifying adsorbents with metal ions are more beneficial to improving adsorption efficiency and the adsorption mechanisms are various. The adsorption capacities are still considerable after regeneration. This paper not only reviews the properties of these materials for fluoride removal, but also focuses on the comparison of materials performance and fluoride removal mechanism. Herein, by discussing the improved adsorption performance and research technology development of biomass materials and biomass-like organic materials, various innovative ideas are provided for adsorbing and removing contaminants.
... Recently, importance has been given to nanoscale-based materials for water treatment as they can help in tuning properties such as scale matter, surface properties, and morphology [39,117,118]. Nickel oxide (NiO) nanomaterial is a transition metal oxide and an effective adsorbent that can be used for water treatment due to low-cost, ease of synthesis, high porosity, and high surface area. Recently, Abukhadra et al. developed Ni/NiO modified DE by using a co-precipitation method for the adsorption of MG from aqueous solution at pH 5 [119]. ...
Article
The presence of toxic pollutants such as dyes and metal ions at higher concentrations in water is very harmful to the environment. Removal of these pollutants using diatomaceous earth or diatomite (DE) and surface-modified DE has been extensively explored due to their excellent physio-chemical properties and low cost. Therefore, naturally available DE being inexpensive, their surface modified adsorbents could be one of the potential candidates for the wastewater treatment in the future. In this context, the current review has been summarized for the removal of both pollutants i.e., dyes and metal ions by surface-modified DE using the facile adsorption process. In addition, this review is prominently focused on the various modification process of DE, their cost-effectiveness; the physio-chemical characteristics and their maximum adsorption capacity. Further, real-time scenarios of reported adsorbents were tabulated based on the cost of the process along with the adsorption capacity of these adsorbents.
... Industrial effluents are mainly composed by environmental relevance metals (ERM) among others metalloids and organic contaminants that inflicted serious damage on ecosystems [3,4].Environmental relevance metals' pollution is a serious concern due to the negative impact at even very small concentrations [5]. It is a direct consequence of processes as tannery [6], electroplating [7], dyeing or mining [8], and also of agriculture, sewage sludge [9] or waste treatment plants [10]. Certain industrial activities such as electroplating, mining, and metal-processing operations have been increasing in the last decades according to the improvement needs of specific characteristics in metallic products, such as oxidation polluted environments in an eco-friendly approach with low cost compared to conventional techniques. ...
Article
Non treated Copper-loaded effluents disposed in water-bodies can cause severe damage in biota, so its removal before discharge is required. The aim of this work was to study the interaction of free and immobilised Pseudomonas veronii 2E with Copper, together with the design of biotreatment systems. Free cell sorption kinetics showed a 24 h-maximal retention of 0.330 mmol/g biomass, from 1 mM copper at 32 °C. Sorption isotherms revealed a specific maximal retention capacity 0.523 mmol/g. Optimal sorption achieved with biomass immobilised on vegetable sponge was 71.4% at 24 h. A reactor with recirculation and 3 continuous reactors in series were designed, obtaining final sorption of 78.3 and 56.0% at 9 and 1 days respectively. Copper desorption using hydrochloric acid was evaluated in both reactors. This work presents alternatives of applicable biotreatments of copper-loaded effluents, characterized by a combination of metal removal and recovery with low cost.
... Fluorine is one of the necessary trace elements for human health, and appropriate fluorine can prevent dental caries and maintain the stability of calcium and phosphorus metabolism (Hegde et al. 2020). However, both insufficient and excessive fluorine will cause harmful effect on human health. ...
Article
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Aluminum hydroxide is an eye-catching and extensively researched adsorbent for fluoride removal and its defluoridation performance is closely related to the preparation method and crystalline phase. In this research, the defluoridation performances of aluminum hydroxides with different crystalline phases are compared and evaluated in terms of fluoride removal capacity, sensitivity to pH values and residual Al contents after defluoridation. It is found that the defluoridation performance of different aluminum hydroxides follows the order of boehmite > bayerite > gibbsite. The fluoride adsorption on aluminum hydroxides follows the pseudo-second-order kinetic model and Langmuir isotherm model, and the maximum defluoridation capacities of boehmite, bayerite and gibbsite are 42.08, 2.97 and 2.74 mg m−2, respectively. The pH values and FTIR analyses reveal that the ligand exchange between fluoride and surface hydroxyl groups is the fluoride removal mechanism. Different aluminum hydroxides have different surface hydroxyl group densities, which results in the different defluoridation capacities. This work provides a new idea to prepare aluminum hydroxide with outstanding defluoridation performance. HIGHLIGHTS The defluoridation performance of boehmite, bayerite and gibbsite is compared.; Boehmite exhibits better defluoridation performance than bayerite and gibbsite.; Fluoride removal mechanism was revealed through pH value and FTIR analyses.; Adsorption capacity of aluminum hydroxide depends on surface hydroxyl group density.;
... Water is considered as the origin of life and it is the critical source for human well-beings and social development [1]. Water quality is very important for water resource usage, agricultural activities, industrial production, aquaculture, and regional safety [2][3][4][5][6]. However, water has been frequently contaminated by diverse pollutants such as heavy metals [7], endocrine disrupting chemicals [8], antibiotic resistance genes [9], microplastics [9], and other emerging chemicals in recent decades. ...
Article
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The Yellow River is very important for human health and social development in China to require good water quality. This study selected the Ningxia section of the Yellow River as the study area to investigate the water quality variation in 2016–2020. A total of 9 water quality parameters were monitored, and 8 parameters including pH, dissolved oxygen, biological oxygen demand, chemical oxygen demand, total phosphate, fluoride, ammonia-nitrogen, and permanganate index were in the range of Class II standard requirement. Dissolved oxygen concentrations ranged from 7.5 to 9.4 mg/L. However, total nitrogen concentrations in 2018–2020 ranged from 1.87 to 2.8 mg/L to cause the pollution. Both the Nemerow index method and the contamination degree method showed that total nitrogen with high concentration exerted the water pollution. Principal component analysis also proved this. Stricter environmental management strategies for controlling total nitrogen should be taken in the future. The findings provided some useful information for water pollution of the Ningxia section of the Yellow River.
... Thus, exploring environmentally safe routes for sludge disposal or using this F − -bearing sludge for alternate use needs to be considered while evaluating an adsorption technique for defluoridation of drinking water. In addition, this methodology is also pH and temperature-sensitive (Alkurdi et al., 2019;Alhassan et al., 2020;Hegde et al., 2020). The ion-exchange process is another high-performance (95%) defluoridation technique that uses ion-exchange resin for the removal of F − . ...
Article
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Fluoride contamination in drinking water is a global issue. Frequent over-exposure to fluoride causes several health problems such as fluorosis, neurological, thyroid, osteoporosis, etc. The guideline values prescribed by the WHO and other nationals for fluoride in drinking water are reasonable but mostly relevant to fluorosis. However, these guideline values cannot be satisfied in some regions due to economic and financial shortcomings. Several fluorosis management techniques were suggested to address excess fluoride in drinking water, but each has specific drawbacks. Defluoridation techniques like the Nalgonda technique, reverse osmosis (RO), and adsorption using activated alumina have found to be promising to reduce fluoride concentration within the prescribed limits, and RO water is most widely used for drinking in fluorosis affected regions. However, these techniques are still associated with certain drawbacks, and prior research on this theme has focused on one dimension of removing excess fluoride from water. Hence, it is essential to understand the basic problems associated with fluoride contamination, such as sources of fluoride exposure, adverse health effects and defluoridation techniques feasibility. Furthermore, perception of the effect of co-existing ions with fluoride in drinking water is crucial in deciding fluoride toxicity level and developing efficient strategies for fluorosis mitigation.
... Fermentation based wastes (microbial residue, molasses, etc.) are used as cheap biomass for biochar production process (Maroušek et al., 2020a). These raw biomass cannot be directly utilized as adsorbent owing to their low carbon content, porosity, surface area and surface functionality (Fernández et al., 2018;Hegde et al., 2020). However, these biomass have been utilized as a precursor for synthesis of novel-low cost adsorbents via appropriate processing technology such as pyrolysis, hydrothermal carbonization and liquefaction (Arun et al., 2021;Dai et al., 2018). ...
Article
Excessive phosphate run-off with total phosphorus concentration greater than 20 μg P L ⁻¹ triggers the growth of harmful algal species in waterbodies and potentially leads to eutrophication. This has severe negative implications on aquatic environment and impacts human health. The annual economic impact of harmful algal blooms is reported to be as high as $25 million for public health and commercial fishery sector, $29 million for recreation/tourism sector and $2 million for monitoring and management. Adsorption is widely considered as an effective and economic strategy to achieve extremely low concentration of phosphorus. The char produced by valorizing various waste biomasses have been gaining attention in phosphorus remediation owing to their availability, their ability to regenerate and reuse. This review paper exclusively focuses on utilizing hydrochar and biochar synthesized from waste biomass, respectively, through hydrothermal carbonization and slow pyrolysis to mitigate phosphorus concentration and potential strategies for handling the spent char. The key mechanisms involved in phosphate adsorption are electrostatic interaction, ion exchange and complexation. The maximum adsorption capacity of hydrochar and biochar ranges from 14 - 386 mg g⁻¹ and 3–887 mg g ⁻¹, respectively. Hydrochar and biochar are cost-effective alternative to commercial activated carbon and spent char can be used for multiple adsorption cycles. Furthermore, extensive research studies on optimizing the feedstock, reaction and activation conditions coupled with technoeconomic analysis and life cycle assessment could pave way for commercialization of char-based adsorption technology.
Article
Diatomite, composed of amorphous macroporous hydrated silica, has generated increasing attention as an attractive raw material for elimination of heavy metal, while suffering low surface activity. Herein, easily separable diatomite adsorbents modified by Zn compounds are developed for effective adsorption of Pb(II), Cu(II) and Cd(II) ions and sunlight photoreduction of toxic Cr(VI) to low-toxic Cr(III). The micro-structure and functionality are characterized through energy spectrum and spectroscopic analysis. Sulfion S²⁻ or carbonyl COO⁻ interlinked networks on the modified diatomite are effective for capturing Pb(II), Cu(II) and Cd(II) ions, and are capable of being oxidized to generate [email protected] directly at 450 °C in air atmosphere. Significantly, by recycling the used [email protected] ([email protected]) adsorbents loaded by Cu(II) and Cd(II) ions, Cu or Cd doped ZnO photocatalysts can be fabricated on diatomite to vary band gap energy of ZnO for more efficient absorption of visible light for Cr(VI) photoreduction under sunlight irradiation. Although the derivatives exhibit weakened Cr(VI) photoreduction capacity compared with [email protected] precursor, probably owing to the influence of surface deposits of Cu(II) or Cd(II) on doping efficiency and light absorption, this idea offers a promising solution to convert the used adsorbents loaded by poisonous heavy metals into photocatalysts for secondary utilization in waste water purification, thus making it possible to produce tailor-made materials for specific requirements alternative by the reutilization of discarded heavy metal adsorbents.
Article
Herein, we demonstrate the use of cerium (Ce)-UiO-66 metal organic framework (MOF) for the removal of a variety of potentially toxic pollutants. The Ce-UiO-66 MOF, with similar framework topologies to Zr-UiO-66, has not been explored for its adsorptive properties in water remediation. The replacement of Zr metal center with Ce yields a MOF that can be synthesized in shorter durations with lesser energy consumptions and with excellent multipollutant adsorption properties. Further, the Ce-UiO-66 MOF was also studied for its adsorption abilities in the binary component system. Interestingly, the adsorbent showed higher adsorption capacities in the presence of other pollutants. Removal studies for other potentially toxic anionic and cationic dyes showed that the Ce-UiO-66 MOF has a wide range of contaminant removal abilities. Investigations of individual adsorption capacities revealed that the Ce-UiO-66 MOF has a maximum adsorption capacity of 793.7 mg/g for congo red (CR), 110 mg/g for methylene blue (MB), 66.1 mg/g for fluoride (F⁻), 30 mg/g for Cr⁶⁺ and 485.4 mg/g for the pharmaceutical waste diclofenac sodium (DCF). To imply the practical applications of the Ce-UiO-66 MOF we have also demonstrated an adaptable filter that could separate all the potentially toxic pollutants.
Article
Hydrofluoric acid is used in large volumes during solar panels manufacturing for cleaning purpose. It results in the generation of wastewater containing high concentrations of fluoride. Chemical precipitation is commonly used to remove most of fluoride from the wastewater. It reduces fluoride concentration to ~ 20 mg/L, whereas the discharge standard is set to 2 mg/L. Adsorption is preferable when dealing with diluted wastewater. This study evaluated the adsorption of fluoride using two low-cost adsorbents: granular palm shell activated carbon and its modification with the prepared chitosan of prawn shells. The effects of pH, dosage, contact time and initial fluoride concentration were studied in batch mode adsorption experiments. The highest removal efficiencies of fluoride by two adsorbents comprised 46% and 55%, respectively, at pH 2 and pH 7. The contrasting behavior of the two adsorbents in relation to pH is attributed by the adsorbents surface charge associated with the surface functional groups identified by FTIR. The adsorption isotherm modeling showed better fit to the Langmuir model for both adsorbents. Adsorption kinetics results fitted well into the pseudo-second-order kinetics model suggesting chemisorption mechanism of fluoride removal.
Chapter
Natural and anthropogenic activities bring about a wide-scale influx of several organic and inorganic contaminants into the groundwater matrix. Amongst these, fluoride constitutes one of the major contaminants, and consumption of fluoride-laden water for prolonged periods leads to serious health ailments such as dental fluorosis and skeletal fluorosis. Of the various methods available for defluoridation, adsorption is very popular owing to its cost-effectiveness, ready availability, and ease in handling. This book chapter deals with an in-depth analysis of the different classes of adsorbents employed for deflouridation, namely agricultural waste, carbon-based, industrial waste-based, biopolymers-based, algal, and fungal-based along with nanoparticles and nanocomposite-based adsorbents. Moreover, prominent methods employed for desorption and regeneration of adsorbents along with their performance in terms of adsorption capacity have been summarized.
Chapter
Dyes are extensively used as colouring agents and are significantly beneficial to a variety of textile, leather, plastic, and paper manufacturing industries. However, dyes belong to a major class of organic molecules that are commonly contaminating water sources triggering major environmental hazards. The poor biodegradation abilities of these dyes due to the complex molecular structure make them pseudo-persistent in the environment. Additionally, exposure to dyes can be hazardous to human health and can cause carcinogenic and mutagenic effects. Therefore, the elimination of such toxic dyes from contaminated wastewater is of great prominence. Nevertheless, advances in water treatment techniques have steered several evolutionary methods for the removal of dyes from water. Several techniques such as adsorption, membrane separation, photocatalytic, biological treatment, and many others are routinely explored for water decontamination. However, such new-generation dye removal techniques mandate novel materials to reprocess contaminated water. Aerogels are one such advanced class of ultralight porous materials that are lately used for dye adsorption. Constructed by open porous networks, aerogels offer extremely low densities, large empty spaces, and macroporous structures. Such intriguing properties provide relaxed diffusion kinetics and admittance to the active sites for adsorption. Additionally, by coupling various porous materials, lightweight aerogels are fabricated to resolve handling and recovery issues from contaminated wastewaters. This chapter proposes to highlight some of the major progressions made towards the use of ultralight aerogels for the removal of various toxic dyes. Eventually, this review categorises aerogels developed for dye elimination into two main classifications, specifically, the biopolymer-based aerogels, and carbon-based aerogels. Progressions made by these categories have been thoroughly reviewed with special emphasis on the advantages and future perspectives have been proposed.
Chapter
One of the adverse environmental impacts of anthropogenic activities is the occurrence of toxic pollutants in freshwater sources. Fluoride is one such persistent pollutant causing serious hazards to living organisms, humans in particular. Ingestion of fluoride in higher concentrations over prolonged durations is said to cause possibilities of dental and skeletal fluorosis and can also lead to lesions of the organs. Unfortunately, above 200 million people worldwide are at the risk of consuming fluoride-contaminated water above the acceptable and tolerable levels. To mitigate such precarious impacts, several physical, chemical, and biological defluoridation techniques have been explored and implemented around the globe. Adsorption is one of the most steadfast techniques employed as it is simple in operation, reliable, and cost-effective. Further, this technique provides a wider choice of material sources known as adsorbents which can be rationally designed to suit the application. To this degree, nature provides a greener choice of several adsorbents which are readily available and do not require high-end synthetic requirements. These green sorbents are inclusive of natural materials, biomaterials, or biosorbents, carbonaceous materials from wastes, agricultural, and industrial by-products. These materials are cheap, eco-friendly, and do not pose secondary toxicity concerns compared to many other synthetic adsorbents. Additionally, these adsorbents can be modified with physical and chemical treatments to enhance their defluoridation performance. This chapter intends to highlight the recent progress made toward the use of naturally available green adsorbents for the adsorption of fluoride ions in an eco-friendly manner.
Article
Aim: To perform a 10-year scientometric analysis of the characteristics of the worldwide publication on the toxic effects of fluoride. Materials and methods: A bibliometric study of the worldwide scientific production on the toxic effects of fluoride during the years 2011-2020 was performed. All metadata from the Scopus database were evaluated. These were then exported to SciVal (Elsevier) for analysis of quantity, collaboration, and impact indicators. Results: We found that the "Biological Trace Element Research" was the most productive journal with 22 published manuscripts and that the most productive universities on the systemic toxic effects of fluoride on the body were Shanxi Agricultural University, Guizhou Medical University, and Huazhong University of Science and Technology with 31, 11, and 10 manuscripts, respectively. In addition, it was found that most of the world scientific production on the toxic effects of fluoride was published in Q1 level journals (top 25%). Conclusion: Finally, it was concluded that most of the total production on this topic was published in high-impact Q1 journals, with China being the leading country in terms of number and impact of publications. Finally, there was evidence of collaboration between the United States, China, and India, being the countries that led in co-authorship by country. Clinical significance: This research is of clinical importance as it allows the identification of the most productive institutions, authors, and countries in this field. In this way, strategic alliances can be established to enhance the development of research.
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Herein, low-cost diatomite (DE) and bentonite (BE) materials were surface modified with Ni–Fe layered double hydroxide (LDHs) (represented as NFD and NFB respectively), using a simple co-precipitation procedure for the removal of methyl orange (MO) dye from water. The adsorbents of both before and after MO adsorption have been studied by XRD, N2 adsorption-desorption isotherm, FTIR, FESEM-EDX and XPS characterization. The zeta potential analysis was used to observe the surface charge of adsorbents within the pH ranges of 4–10. The MO removal efficiency was significantly improved after LDHs modification, showing a 94.7% and 92.6% efficiency for NFD and NFB at pH 6, respectively. Whereas bare DE and BE have shown removal efficiency of 15.5% and 4.9% respectively. The maximum adsorption capacities of NFD and NFB using the Langmuir isotherm model were found to be 246.9 mgg⁻¹ and 215.9 mgg⁻¹ respectively. The designed NFD showed high selectivity towards anionic-based dyes from water and also the effect of salts shows the dye removal percentage was increased and decreased for the addition of Na2SO4 and NaCl, respectively. The reusability of NFD and NFB have been studied for a maximum of five cycles and they can remove MO up to four cycles. Therefore, the designed adsorbents can be very effective towards the removal of MO from water and they may be useful for dye-based wastewater treatment.
Article
Metal-organic frameworks (MOFs) are a versatile class of porous materials offering unprecedented scope for chemical and structural tunability. On account of their synthetic versatility, tunable and exceptional host-guest chemistry they are widely utilized in many prominent water remediation techniques. However, some of the MOFs present low structural stabilities specifically in aqueous and harsh chemical conditions which impedes their potential application in the field. Among the currently explored MOFs, UiO-66 exhibits structural robustness and has gained immense scientific popularity. Built with a zirconium-terephthalate framework, the strong Zr–O bond coordination contributes to its stability in aqueous, chemical, and thermal conditions. Moreover, other exceptional features such as high surface area and uniform pore size add to the grand arena of porous nanomaterials. As a result of its stable nature, UiO-66 offers relaxed admittance towards various functionalization, including synthetic and post-synthetic modifications. Consequently, the adsorptive properties of these highly stable frameworks have been modulated by the addition of various functionalities. Moreover, due to the presence of catalytically active sites, the use of UiO-66 has also been extended towards the degradation of pollutants. Furthermore, to solve the practical handling issues of the crystalline powdered forms, UiO-66 has been incorporated into various membrane supports. The incorporation of UiO-66 in various matrices has enhanced the rejection, permeate flux, and anti-fouling properties of membranes. The combination of such exceptional characteristics of UiO-66 MOF has expanded its scope in targeted purification techniques. Subsequently, this review highlights the role of UiO-66 in major water purification techniques such as adsorption, photocatalytic degradation, and membrane separation. This comprehensive review is expected to shed light on the existing developments and guide the inexhaustible futuristic scope of UiO-66 MOF.
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Excess fluoride in drinking water endangers the health of human being. Nowadays, a lot of efforts have been made for defluoridation to guarantee drinking water safety. Absorption is proved to be the safe, effective and environment friendly method to remove excess fluoride in water. In this work, a simple synthetic method was applied to successfully fabricate the zirconium based MOFs (metal organic frameworks), namely MOF 1. Following investigation showed that the as-synthetized material was highly stable and had significantly effective fluoride adsorption performance over a wide range of pH from 3 to 10. What's more, the maximum adsorption capacity (mg·g⁻¹) for Langmuir isotherms is 204.08. To the best of our knowledge, it is the best performance so far for Zr based MOFs. Besides, the as-synthetized adsorbent was used for fluoride remove from real water sample. The result manifested that the adsorbent had effective fluoride adsorption on real ground water.
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Environmental pollution has drawn forth advanced materials and progressive techniques concentrating on sustainable development. Metal-organic frameworks (MOFs) have aroused vast interest resulting from their excellent property in structure and function. Conversely, powdery MOFs in highly crystalline follow with fragility, poor processability and recoverability. Aerogels distinguished by the unique three-dimensional (3D) interconnected pore structures with high porosity and accessible surface area are promising carriers for MOFs. Given these, combining MOFs with aerogels at molecule level to obtain advanced composites is excepted to further enhance their performance with higher practicability. Herein, we focus on the latest studies on the [email protected] composites. The construction of [email protected] with different synthetic routes and drying methods are discussed. To explore the connection between structure and performance, pore structure engineering and quantitation of MOFs content are outlined. Furthermore, various types of [email protected] composites and their carbonized derivatives are reviewed, as well as the applications of [email protected] for environmental remediation referring to water purification and air clearing. More importantly, outlooks towards these emerging advanced composites have been presented from the perspective of practical application and future development.
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Water is termed a ‘prime natural resource’ and ‘basic human need’. It is worthwhile to ensure access to a good quality of life or enhance life expectancy. Water is considered the ingredient essential to human advancement. The biggest challenge encountered in dealing with water contaminants around the magnitude of the health hazard. Fluoride is a common ion that creates health problems for humans depending on their ingested qualities. The fluoride contamination in water, excess fluoride-related diseases, and the features of different defluoridation techniques are covered. The membrane is the key to tackling water contamination and the world's challenges today. In membrane separation, various influencing factors (viz. nature of membranes, the effect of ions, pH, feed concentration, applied pressure) are reviewed. The hybrid processes related to the membranes and membrane-linked other approaches are also emphasized. The strategic approaches to tackling the rejected water are also narrated.
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Elevated fluoride concentration in water can trigger several health-related problems. In this study, the influence of post pyrolysis hydrothermal activation on defluoridation has been investigated to check their interacting effect using response surface methodology. Amongst the various optimizing factors which were investigated, temperature and time emerged as the most significant factors (p-value < 0.05). The Fe–Zn (2:1) binary metal hydrochar composite synthesized from optimized hydrochar demonstrated an optimum dose, contact time, initial concentration and solution pH of 0.8 g/L, 120 min, 5 mg/L and 7 respectively. The isotherm and kinetic results indicated that experimental data best fitted to Langmuir and pseudo-second order, with a determination coefficient approaching one (R² = 0.99). Maximum monolayer adsorption capacity for this composite was found to be 28.41 mg/g. Thermodynamic parameters corroborate that defluoridation was chemisorption in nature (ΔH⁰ >10 kJ/mol) and was favoured at lower temperature (30 °C). An extensive characterization was employed to explain the adsorption mechanism, and confirmed occurrence of Lewis acid-base interactions, ion-exchange processes and electrostatic interactions. The performance of a fixed bed column was assessed based on breakthrough curve analysis. This novel composite could therefore serve as an efficient fluoride adsorbent because of enhanced sorption at neutral pH and reusability, thereby ensuring a sustainable and practical solution for low-cost defluoridation of drinking water.
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Exposure of heavy metals in the environment especially in aquatic bodies is one of the major environmental issues. Heavy metals are non bio-degradable and accumulated in human body through food chains. Some heavy metals are essential for the growth and development of living organisms but most of them are very harmful even at very low concentrations. Addition of such metals into the waters may due to natural or anthropogenic activities. Various methods cited in the literature used for the removal of heavy metals are chemical precipitation, evaporation, electroplating, ion exchange, membrane filtration, carbon adsorption, phytoremediation etc. Among these biosorption is relatively new, cheap and efficient technique. This brief review discuss the effect of heavy metals and their sources, biosorption techniques, different parameters of biosorption and introduction of isotherm models and kinetic parameters for the suitability of biosorption of heavy metals on biosorbents.
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Despite WHO standards, waterborne diseases among the human being are rising alarmingly. It is known that the prolong exposure to contaminated water has major impact on public health. The effect of chemical contaminations in drinking water on human being is found to be chronic rather than acute and hence can be defined “consumption of contaminated drinking water could be a silent killer”. As the WHO recommended water quality standards are only for individual element and synergic effects of trace metals and anions have not been considered, investigation of synergic effects of trace metals and anions and their effect on human being is of prime important research. By an animal trial, we investigated the synergic effect(s) of heavy metals, aluminium, arsenic, fluoride and hardness in drinking water on kidney tissues of mice. Our investigation strongly suggests existing of a synergic effect especially among Cd, F and hardness of water which could lead to severe kidney damage in mice, even at WHO maximum recommended levels. Hence, the synergic effect(s) of trace metals, fluoride and hardness present in drinking water should be investigated meticulously when stipulating the water quality at WHO maximum recommended levels.
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This study presents a new type of biomass material for defluoridation from water; the material was prepared by loading tetravalent zirconium ions onto grape pomace produced from grape juicing and wine factories.
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For about the past eight decades, high concentrations of naturally occurring fluoride have been detected in groundwater in different parts of India. The chronic consumption of fluoride in high concentrations is recognized to cause dental and skeletal fluorosis. We have used the random forest machine-learning algorithm to model a dataset of 12,600 groundwater fluoride concentrations from throughout India along with spatially continuous predictor variables of predominantly geology, climate and soil parameters. Despite only surface parameters being available to describe a subsurface phenomenon, this has produced a highly accurate prediction map of fluoride concentrations exceeding 1.5 mg/L at 1 km resolution throughout the country. The most affected areas are the northwestern states/territories of Delhi, Gujarat, Haryana, Punjab and Rajasthan and the southern states of Andhra Pradesh, Karnataka, Tamil Nadu and Telangana. The total number of people at risk of fluorosis due to fluoride in groundwater is predicted to be around 120 million, or 9% of the population. This number is based on rural populations and accounts for average rates of groundwater consumption from non-managed sources. The new fluoride hazard and risk maps can be used by authorities in conjunction with detailed groundwater utilization information to prioritize areas in need of mitigation measures.
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The preparation of carbons in virgin and Ti-modified forms under controlled conditions at low temperature from plantain pseudo-stem (Musa paradisiaca) was achieved. These prepared carbons were characterized for instrumental studies such as BET, FTIR, XRD, SEM with EDS and TGA to understand the chemistry and modification. The determination of IEP and pHZPC established the presence of positive surface sites on the virgin (VMPC) and Ti-modified (TiMPC) carbons to facilitate the sorption of fluoride. The fluoride removal efficiency as a function of time, pH, dose, initial fluoride concentration, temperature, and co-ion intervention was studied. The maximum fluoride removal of about 81.2 and 97.7% was achievable with VMPC and TiMPC, respectively, after 20 min at the pH of 2.04 and continued for the equilibrium of 60 min. Temperature was found to be influential both by way of initial increase followed by a decrease in the fluoride uptake of MPCs. Regeneration was very consistent up to 7 cycles with the residual fluoride concentration below the WHO guide line of 1.5 mg L-1. Highest intervention due to hydrogen carbonate ions was observed during the fluoride removal process. Kinetic (pseudo-first-order, pseudo-second-order, and intra-particle diffusion) and isotherm models (Langmuir, Freundlich, and DKR) were checked for their compliance with the present sorption system. These low temperature synthesized MPCs are found to be effective candidates in the process of fluoride abatement in water.
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Contamination of underground water with fluoride (F) is a tremendous health hazard. Excessive F (> 1.5 mg/L) in drinking water can cause both dental and skeletal fluorosis. A fixed-bed column experiments were carried out with the operating variables such as different initial F concentrations, bed depths, pH and flow rates. Results revealed that the breakthrough time and exhaustion time decrease with increasing flow rate, decreasing bed depth and increasing influent fluoride concentration. The optimized conditions are: 10 mg/L initial fluoride concentration; flow rate 3.4 mL/min, bed depth 3.5 and pH 5. The bed depth service time model and the Thomas model were applied to the experimental results. Both the models were in good agreement with the experimental data for all the process parameters studied except flow rate, indicating that the models were appropriate for removal of F by natural banana peel dust in fix-bed design. Moreover, column adsorption was reversible and the regeneration was accomplished by pumping of 0.1 M NaOH through the loaded banana peel dust column. On the other hand, field water sample analysis data revealed that 86.5% fluoride can be removed under such optimized conditions. From the experimental results, it may be inferred that natural banana peel dust is an effective adsorbent for defluoridation of water.
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This paper presents a comparative review of arsenite (As(III)), arsenate (As(V)), and fluoride (F ⁻ ) for a better understanding of the conditions and factors during their adsorption with focus on (i) the isotherm adsorption models, (ii) effects of pH, (iii) effects of ionic strength, and (iv) effects of coexisting substances such as anions, cations, and natural organics matter. It provides an in-depth analysis of various methods of arsenite (As(III)), arsenate (As(V)), and fluoride (F ⁻ ) removal by adsorption and the anions’ characteristics during the adsorption process. The surface area of the adsorbents does not contribute to the adsorption capacity of these anions but rather a combination of other physical and chemical properties. The adsorption capacity for the anions depends on the combination of all the factors: pH, ionic strength, coexisting substances, pore volume and particles size, surface modification, pretreatment of the adsorbents, and so forth. Extreme higher adsorption capacity can be obtained by the modification of the adsorbents. In general, pH has a greater influence on adsorption capacity at large, since it affects the ionic strength, coexisting anions such as bicarbonate, sulfate, and silica, the surface charges of the adsorbents, and the ionic species which can be present in the solution.
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The main aim of this experimental investigation was to develop inexpensive and safe method of fluoride removal. The adsorbents used in this investigation are amla powder, coconut shell powder, neem powder and turmeric powder. All adsorbents used are inexpensive and nontoxic materials, available easily in nature and locally at village/rural level. Some of the adsorbents are very effective in removal of fluoride ion& can be used a defluoridating agents but they impart color and turbidity to the treated drinking water. Among all adsorbents used, amla powder was found to be the most and cost effective in adsorbing fluorine ions. Coconut shell powder was also found to be an efficient adsorbent to certain extent. Turmeric powder was also capable of adsorbing fluoride ions at lower pH value. Batch experiments were conducted, fluoride removal capacity was studied with respect to time and flow rates lit/day respectively. Finally, it has been observed that adsorbents were definitely having good adsorbent capacity and fluoride concentrations are well within permissible limits.
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The adsorption behavior and mechanism for the uptake of fluoride ions by untreated and desugared reed residues (roots, stems and leaves) were studied through adsorption experiments, elemental analysis, infrared spectroscopy and surface area analysis. The results showed that the adsorption capacity of untreated and desugared reeds followed the order: desugared roots 2136 mg/kg > desugared leaves 1825 mg/kg > desugared stems 1551 mg/kg > untreated roots 191 mg/kg > untreated stems 175 mg/kg > untreated leaves 150 mg/kg, so adsorption capacity of desugared reeds was larger than that of the untreated reeds. The adsorption kinetic of fluoride ions followed a pseudo-first-order model. A Langmuir model could be used to fit the isothermal adsorption process which was a spontaneous endothermic reaction involving mainly physical adsorption. The ΔG for the uptake of fluoride by the desugared reeds was more negative, so the degree of spontaneity was higher than for the use of the untreated reeds. After samples were desugared, the specific surface area and aromaticity of the reed increased, while the polarity and hydrophilicity decreased, which explained the adsorption amount of desugared reed was higher than that of the untreated. This study enriches techniques and methods of removing fluoride ions from water.
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Calcium phosphate adsorbents, derived from prawns and crabs shell biomass wastes have been developed using wet chemistry and low temperature treatment. The adsorbents were characterized by X-ray diffractometry and Fourier transform infrared spectroscopy. Batch adsorption test were carried out to investigate their effectiveness in adsorption of fluoride from ground and surface waters. Adsorption capacities were compared with bone char and synthetic hydroxyapatite (CCHA). Results indicate that prawns derived adsorbent (PHA) formed hexagonal structure with phases identifiable with hydroxyapatite while crabs based adsorbent (CHA) formed predominantly monoclinic structure with crystalline phase characteristic of brushite. Vibrational analysis and kinetic studies predicted defluoridation occurred mainly by ion exchange and ion adsorption mechanisms. Defluoridation capacity of the adsorbents was found to be superior compared to bone char and CCHA. CHA was the most effective with efficiencies above 92% and highest capacity of 13.6 mg/g in field water with fluoride concentration of 5-70 mg/L. PHA had highest capacity of 8.5 mg/g which was still better than 2.6 mg/g recorded by CCHA and bone char. Adsorption was best described by pseudo 2nd order kinetics. The findings indicate that crustacean derived calcium phosphate systems have better potential for defluoridation than traditional bone char and synthetic systems.
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Background: Fluorosis being irreversible should be prevented by providing water with optimal fluoride concentration. Due to certain limitations of routinely used defluoridation methods, exploration of indigenous products for the prevention of fluorosis calls for. Hence the study was designed with an aim to compare the defluoridation efficacy of tea ash in water at various concentrations. Materials & Method: Specifically treated tea residue was used. Fluoride level was measured using fluoride ion selective electrode at National Environmental Engineering Research Institute (NEERI), Nagpur, India. Testing samples of 2 different particle sizes were added in 50ml of water containing 4ppm of fluoride. The concentration of fluoride remaining in the filtrate was analyzed after 60 and 90 minutes and 24 hours. Following initial results, varying quantities of tea ash (105 µm) were added in 50ml of water containing fluoride of different concentrations. The concentration of fluoride remaining in the filtrate was analyzed after 30 and 60 minutes. Results: Tea ash exhibited defluoridation capacity at both particle sizes. Tea ash (105µm) weighing 0.5, 0.75, 1, 1.25, 1.5 gm was found to be effective to reduce water fluoride content from 2, 3, 4, 5, 6 ppm to an almost optimum fluoride concentration. Conclusion: Tea ash can be advocated as an efficient, cost-effective domestic defluoridating agent. © 2018, Indian Journal of Public Health Research and Development. All rights reserved.
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The defluoridation from aquatic medium by raw marine algae, Ulva lactuca, was investigated. The element components and adsorbent’s properties were determined. The influence of pH, contact period, and Ulva sp. weight on the deflouridation was achieved. The complete defluoridation of 10 mg F⁻/l solution was obtained within 10 min at definite pHs. Fourteen adsorption isotherms and four kinetic models (pseudo-first order and pseudo-second order, Elovich, and intraparticle diffusivity) were studied. The most adequate model was performed by using five error functions. The application of chi-squared test indicated that the nonlinear isotherm models (two and three parameters) were more applicable than the linear ones. The adsorption kinetic proceeded by pseudo-first-order model. The adsorption mechanism was very complex; thus, the solute distribution step was not the only dominant one during the process. The adsorption seemed to be a physical negative binding cooperative type with activation energy and free energy of 3.16 and − 1.672 kJ/mol, respectively. Thus, raw marine algae, Ulva lactuca, can be used as an adsorbent in solving the fluoridation problem in aquatic mediums throughout the world due to their fast procedure, high efficiency, low effort, and high economic value.
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Possotia leaf powder (PLP), a novel biosorbent obtained from a locally available wild plant with environment friendly and low cost nature, has found to be effective to remove fluoride from fluoride contaminated drinking water. The kinetic and thermodynamic parameters for the adsorption have been studied. Its fluorideabsorption efficiency is found to be nearly 75% at natural pH range and is affected by the parameters likecontact time, absorbent dose, solution temperature and initial fluoride concentration. The optimum contact time and absorbent dose were found to be 120 min and 3gm/L, respectively.Langmuir, Freundlich and Temkin isotherm are studied through this experimental data and found to be well followed. The adsorption kinetics data were fitted to pseudo first order, pseudo second order, and intraparticle diffusion models and was best fitted for pseudo second order model. The thermodynamic study points out the efficiency of this bio-adsorbent at low temperatureindicating the physical nature of adsorption with weak adsorbent-adsorbate force of attraction. By studyingenthalpy, entropy and Gibb’s free energy via van’t Hoff plot, it was observed that the adsorption process wasfavorable and exothermic in nature.
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The current worldwide issue of fluoride contamination in groundwater has resulted in an increased demand for efficient adsorbents. Meanwhile discard and landfill of bone waste has led to environmental pollution. In order to achieve bone waste recycling and enhance the efficiency of fluoride removal, a lanthanum-modified bone waste (LBW) composite was synthesized and tested to remove fluoride from contaminated groundwater. The adsorbent characterization was conducted by SEM, BET, XRD, FTIR and XPS. The fluoride adsorption performance was evaluated by batch experiments. SEM and BET revealed that the introduction of lanthanum could modify the porous structure of the adsorbent and enhance its specific surface area. The LBW composite had a high pHzpc of 11.4 and the fluoride adsorption was barely affected by the solution pH over a wide pH range of 2.5–10.0. The influence of common co-existing oxygen anions in the range of 0–100 mg L⁻¹ was not significant. The fluoride adsorption was a typical chemisorption process and followed PSO and F-L PSO equations. The FVER model provided a more accurate prediction of a larger surface coverage degree with respect to equilibrium at the initial stage during adsorption of fluoride. Isotherm studies revealed that the reaction obeyed the Langmuir model, indicating that this process was monolayer adsorption. Possible defluoridation and regeneration were proposed. The fluoride adsorption was mainly controlled by the processes of electrostatic attraction on the LBW surface with a positive charge and ion exchange between fluoride and hydroxide ions. This research provides an alternative method for fluoride removal from contaminated groundwater in practical applications.
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Batch-type experiments were used to study As(V), Cr(VI), F − , and Ni 2+ sorption/desorption on wheat straw. For the lowest concentration added (0.5 mmol·L −1), the sorption sequence was F − > Ni 2+ > Cr(VI) >> As(V) (93%, 61%, 29%, 0.3%), but changed to Ni 2+ > F − > Cr(VI) >> As(V) when 3.0 and 6.0 mmol·L −1 were added (with 65%, 54%, 25%, 0%, and 68%, 52%, 27%, 0% sorption, respectively). Overall, As(V) showed the lowest sorption, whereas it was 25–37% for Cr(VI), 61–68% for Ni 2+ , and 52–93% for F −. For As(V), pH in the equilibrium solution was always above the pH of the point of zero charge (pH PZC) for wheat straw, decreasing sorption efficiency. For Cr(VI), pH was below pH PZC , but not enough to reach high sorption. For F − , pH in the equilibrium was above pH PZC , which could reduce sorption. For Ni 2+ , pH in the equilibrium was always below pH PZC , which made sorption difficult. The satisfactory fitting of Cr(VI), F − , and Ni 2+ data to the Freundlich model suggests multilayer-type adsorption. Desorption was high for F − , whereas Ni 2+ showed the lowest desorption. This research could be especially relevant when focusing on the use of wheat straw as a bio-sorbent, and in cases where straw mulching is used.
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Fluoride is a naturally occurring element in water systems and enters food chain mostly through drinking water. The WHO permissible limit of fluoride in water is 1.0 mg/l. At < 1.0 mg/l, it inhibits dental caries, at > 1.0 mg/l causes molting of teeth, lesion of endocrine glands, thyroid, liver and other organs. At still higher concentration (3-6 mg/l), it causes skeletal fluorosis. Existing fluoride removal techniques haven’t been very effective as these remove fluoride only up to 2 mg/l. Therefore, an economically viable, eco-friendly and easy method for defluoridation of drinking water is highly desirable. In the present investigation, Ocimum sp. leaves along with ragi seed husk was used as natural fluoride adsorbents and the process parameters such as absorbent dosage (1-10 g/l), pH (3-12) and contact time (10-150 min) were optimized using Central Composite Design (CCD) of Response Surface Methodology (RSM). The fluoride content in the water was quantitatively determined by UV spectrophotometric analysis and the presence of fluoride in the treated Ocimum sp. leaves were identified with EDAX analysis. RSM design optimized conditions i.e - 5.5 g/l each of Ocimum sp. leaves and ragi seed husk, 6.0 pH and 50 min contact time gave the end values of 0.43 mg/l of fluoride. The optimized values of RSM with respect to the end fluoride content (0.43 mg/l) after treatment process were validated using feed forward model of Artificial Neural Network (ANN). ANN predicted value (0.4250 mg/l) was very close to the optimized experimental value of RSM design (0.43 mg/l) and the error was 0.049. In conclusion, an optimized process was developed for the removal of fluoride from the drinking water using Ocimum sp. leaves and Ragi seed husk as natural fluoride adsorbents. Final concentration of 0.43 mg/l of fluoride was achieved from initial concentration of 10mg/l. Key Words : Fluoride removal, Adsorption, Ocimum sp. leaves and Ragi seed husk, Response Surface Methodology (RSM), Artificial Neural Network (ANN), EDAX analysis
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Over the course of the past decade, there has been growing interest in the development of different types of membranes composed of carbon nanotubes (CNTs), including buckypapers and composite materials, for an ever-widening range of filtration applications. This article provides an overview of how different types of CNT membranes are prepared and the results obtained from investigations into their suitability for different applications. The latter involve the removal of small particles from air samples, the filtration of aqueous solutions containing organic compounds and/or bacteria, and the separation of individual liquids present in mixtures. A growing number of reports have demonstrated that the incorporation of CNTs into composite membranes confers an improved resistance to fouling caused by biomacromolecules and bacteria. These results are discussed, along with evidence that demonstrates it is possible to further reduce fouling by taking advantage of the inherent conductivity of composite membranes containing CNTs, as well as by using different types of electrochemical stimuli.
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This paper concerns simultaneous removal of fluoride and hydrated silica from groundwater (4.08 mg L-1 fluoride, 90 mg L-1 hydrated silica, 50 mg L-1 sulfate, 0.23 mg L-1 phosphate, pH 7.38 and 450 μS cm-1 conductivity) by electrocoagulation (EC), using an up-flow EC reactor, with a six-cell stack in a serpentine array, opened at the top of the cell to favor gas release. Aluminum plates were used as sacrificial electrodes. The effect of current density (4 ≤ j ≤ 7 mA cm-2) and mean linear flow rate (1.2 ≤ u ≤ 4.8 cm s-1), applied to the EC reactor, on the elimination of fluoride and hydrated silica was analyzed. The removal of fluoride followed the WHO guideline (<1.5 mg L-1), while the hydrated silica was abated at 7 mA cm-2 and 1.2 cm s-1, with energy consumption of 2.48 kWh m-3 and an overall operational cost of 0.441 USD m-3. Spectroscopic analyses of the flocs by XRD, XRF-EDS, SEM-EDS, and FTIR indicated that hydrated silica reacted with the coagulant forming aluminosilicates, and fluoride replaced a hydroxide from aluminum aggregates, while sulfates and phosphates were removed by adsorption process onto the flocs. The well-engineered EC reactor allowed the simultaneous removal of fluoride and hydrated silica.
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Nrf2 is a crucial transcription factor that regulates the expression of cytoprotective enzymes and controls cellular redox homeostasis. Both arsenic and fluoride are potent toxicants that are known to induce Nrf2. They are reported to coexist in many areas of the world leading to complex mixture effects in exposed organisms. The present study investigated the expression of Nrf2 and related xenobiotic metabolizing enzymes along with other stress markers such as histopathological alterations, catalase activity, reduced glutathione content and lipid peroxidation in zebrafish liver as a function of combined exposure to environmentally relevant concentrations of arsenic (37.87 μgL−1 or 5.05×10−7 M) and fluoride (6.8mgL−1 or 3.57×10−4 M) for 60 days. The decrease in the total reduced glutathione level was evident in all treatment conditions. Hyperactivity of catalase along with conspicuous elevation in reactive oxygen species, malondialdehyde content and histo-architectural anomalies signified the presence of oxidative stress in the treatment groups. Nrf2 was seen to be induced at both transcriptional and translational levels in case of both individual and co-exposure. The same pattern was observed in case of its nuclear translocation also. From the results of qRT-PCR it was evident that at each time point co-exposure to arsenic and fluoride seemed to alter the gene expression of Cu/Zn Sod, Mn Sod, Gpx and Nqo1 just like their individual exposure but at a very low magnitude. In conclusion, this study demonstrates for the first time the differential expression and activity of Nrf2 and other stress response genes in the zebrafish liver following individual and combined exposure to arsenic and fluoride.
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Contamination of the ground water with fluoride is a great problem worldwide. Removal of fluoride (F⁻) ions from simulated natural waters containing fluoride by electrocoagulation (EC) using aluminum electrodes, has been investigated in a discontinuous lab cell. Two types of water have been studied: local tap water and deionized water-based luoride solutions of sodium fluoride with addition of sodium chloride to reach the desired conductivity. The effect of four operating parameters has been followed for a current density fixed at 5 mA/cm² within the following ranges: fluoride concentration (5–50 mg/L), temperature (25–55 °C), conductivity (1–6 mS/cm) and initial pH (4–8.5). In accordance with published data, the presence of 61 mg/L buffering hydrogencarbonate ions in the tap water was found to substantially reduce the Al(III) amount required for a given abatement in comparison with deionized water. Performance comparison of the discontinuous electrocoagulation treatment between the two types of water has been discussed for 90% abatement of F⁻ introduced, in terms of the amount of Al(III) dissolved over the initial fluoride concentration, the parameters of a previous adsorption model and the fraction of Al(III) flocs not involved in the adsorption. EC performances were shown to be governed by the solution pH for the two types of water, with little effect of the other operating conditions: at initial pH 6, F⁻ abatement was found to require two or three times less trivalent aluminium than at initial pH 8.5.
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In this study, biogenic activated carbon were successfully synthesized from Citrus limetta pulp residue, and applied to remove fluoride from an aqueous solution. For the synthesis activated carbon of biosorbents, raw materials were heated in muffle furnace at two different temperatures i.e. (250 °C and 500 °C) and were noted as ACP-250 and ACP-500. The prepared biosorbents were characterized through scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD). Batch adsorption studies were performed with varying temperature, dosage, pH, and various initial concentrations. Adsorption isotherms and the reaction kinetics were also analyzed in order to understand the adsorption mechanism. The results of this study shows that the maximum removal achieved was approximately (86 and 82) % of ACP-500 and ACP-250, respectively. The isotherm results show that the Langmuir isotherm model fitted better, with monolayer adsorption capacity of 12.6 mg/g of fluoride. However, for kinetic study, the pseudo-second-order kinetics fitted well. The synthesized materials at different temperature were highly effective for the removal of fluoride from water, with reusability of three to four times.
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In this study, Aspergillus niger (FS18) was used to remove the fluoride from aqueous medium. Batch and column mode studies were carried out to investigate the effect of different conditions such as live biomass, dead biomass, various pretreated biomass and immobilized fungal biomass on the removal of fluoride removal. The results showed that the maximum removal of fluoride was attained at 30–80 min using dead fungal biomass when compared to live and various pretreated biomass. The fluoride removal was noted somewhat in the aqueous medium using formaldehyde and acid treated biomass when compared to calcium treated fungal biomass. The experimental data was fitted with pseudo second order when compared to pseudo first order. In column study, the maximum fluoride adsorption capacity of 89% was observed. Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDXA) techniques were used to elucidate the adsorption mechanism of dead fungal biosorbent. Findings of this work suggested that dead fungal biomass could be a suitable sorbent for the removal of fluoride in aqueous solution.
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The importance of water pollutants on human health has been the subject of intense study and constitutes perhaps the most significant grand challenge for the future of human society. Water remediation faces many challenges in effectively combating pollution, especially for low income populations where poor water sanitation and little to no access to technically competent and cost effective remediation are nearly insurmountable issues. In an effort to provide low-cost adsorbents, research over the last few years has focused on biological residual materials from plants and animal biomass to not only to add value, but to remediate water at a lower cost with the same or improved efficiency as commercially available option. Crustacean shells are among a class of biological residues that are commonly treated as a waste product of the sea food industry. However, potential valorization by remediation of heavy metal ions, organic matter, and anionic species is a topic of high interest in the current eco-friendly environment. The aim of this review is to provide insight on the state of the art of crustacean shells for addressing water remediation and to offer some perspective regarding challenges and the future of this type of biomass.
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This article focuses on the application of clay, kaolinite, for the removal of fluoride ion from Saharan groundwater located in the Tindouf region (Algeria) because high concentrations are detected in potable water. Adsorption tests show that fluoride ion removal was efficient when the pH varies from 4.5 to 6. Under these conditions, the adsorption capacities were 0.442 and 0.448 mg/g, respectively. Kinetic and isotherm adsorption correlations were applied to describe the adsorption process. The results showed that the pseudo-second-order kinetic model and Freundlich isotherm fit well the experimental data. Thermodynamic calculation indicated that fluoride sorption into clay increased with increasing temperature from 30 to 55 °C, indicating the endothermic nature of sorption process. The investigation of the removal of fluoride from simulated potable water shows that the presence of nitrate and chloride ions did not influence the fluoride uptake. However, sulfate and carbonate ions decrease the adsorption capacity. Such results show that these ions may enter in competition with each other that may result in electrostatic repulsive forces between fluoride and clay surface. From this study, it can be concluded that the kaolinite is an effective and low-cost material for the removal of fluoride ions from groundwater.
Article
Reaction of fluoride with waste oyster shell was studied. To enhance the stability and adsorption capacity, oyster shell was coated with Al(OH)3 and the adsorption behaviors were compared with the uncoated one. When at low fluoride concentration (<30 mg/L), fluoride removal efficiency decreased with increasing pH, and the adsorption could be modeled by Langmuir isotherm. At high fluoride concentration (>100 mg/L), linear adsorption isotherm fitted better, in which the adsorption capacity of fluoride increased linearly with increasing equilibrium fluoride concentration. The coated oyster shell showed higher adsorption capacity and wider workable pH range. From XPS analysis, the presence of CaF2 was confirmed by the peak at 684.7 eV when fluoride concentration increased. It was noted that magnesium content of waste oyster shell reacted with fluoride to form significant fractions of MgF2 whose corresponding peak was detected at 685.6–685.8 eV. For coated oyster shell, fluoride reacted with Ca, Mg, and Al. The reaction mechanism was mainly adsorption at low initial concentration, and precipitation-dominated at higher concentration.
Article
Phosphate is a vital nutrient but its presence in surface waters even at very low concentrations can lead to eutrophication. Adsorption is often suggested as a step for reducing phosphate down to very low concentrations. Porous metal oxides can be used as granular adsorbents that have a high surface area and hence a high adsorption capacity. But from a practical point of view, these adsorbents also need to have good adsorption kinetics. The surface area of such adsorbents comes from pores of varying pore size and the pore size distribution (PSD) of the adsorbents can affect the phosphate adsorption kinetics. In this study, the PSD of 4 different adsorbents was correlated with their phosphate adsorption kinetics. The adsorbents based on iron and aluminium (hydr)oxide were grinded and the adsorption performance was studied as a function of their particle size. This was done to identify diffusion limitations due to the PSD of the adsorbents. The phosphate adsorption kinetics were similar for small particles of all the adsorbents. For larger particles, the adsorbents having pores larger than 10 nm (FSP and DD6) showed faster adsorption than adsorbents with smaller pores (GEH and CFH). Even though micropores (pores < 2 nm) contributed to a higher portion of the adsorbent surface area, pores bigger than 10 nm were needed to increase the rate of adsorption.
Article
Bone loss in women accelerates during perimenopause, and continues into old age. To-date, there has been little progress made in stratifying fracture risk in premenopausal and early postmenopausal women. Epidemiologic data suggests that changes in serum FSH could predict decrements in bone mass during peri- and postmenopause. In bone, FSH interacts with immune receptor complexes, increases the expression of receptor activator of nuclear factor kappa B (RANK), and stimulates osteoclast formation by releasing osteoclastogenic cytokines. Here, we address the evidence for bone loss across menopause, discuss strategies for detection and treatment of postmenopausal osteoporosis, and describe the role FSH plays in the physiology and pathophysiology of postmenopausal bone loss.
Article
Water pollution by industrial and anthropogenic actives has become a serious threat to the environment. World Health Organization (WHO) has identified that lead and fluoride amid the environmental pollutants are most poisonous water contaminants with devastating impact on the human race. The present work proposes a study on economical bio-adsorbent based technique using exhausted coffee grounds in the removal of lead and fluoride contaminants from water. The exhausted coffee grounds gathered from industrial wastes have been acid-activated and examined for their adsorption capacity. The surface morphology and elemental characterization of pre-and-post adsorption operations by FESEM, EDX and FTIR spectral analysis confirmed the potential of the exhausted coffee ground as successful bio-sorbent. However, thermodynamic analysis confirmed the adsorption to be spontaneous physisorption with Langmuir mode of homogenous monolayer deposition. The kinetics of adsorption is well defined by pseudo second order model for both lead and fluoride. A significant quantity of lead and fluoride is removed from the synthetic contaminated water by the proposed bio-sorbent with the respective sorption capabilities of 61.6 mg/g and 9.05 mg/g. However, the developed bio-sorbent is also recyclable and is capable of removing the lead and fluoride from the domestic and industrial waste-water sources with an overall removal efficiency of about 90%.
Article
We report the synthesis of a novel Fe-La composite adsorbent by one-pot hydrothermal method for removing fluoride and phosphate simultaneously. The as-obtained adsorbent shows rod-like morphology and large specific surface area of 113.13 m²/g. A series of adsorption experiments were carried out to investigate the influence of various factors on the simultaneous adsorption of fluoride and phosphate, such as different adsorbent dosage, pH, temperature and co-existing anion. The results demonstrate that the Fe-La adsorbent exhibited high adsorption capacity for fluoride and phosphate in a wide pH range (3.8–7.1). The adsorption kinetics of fluoride and phosphate by Fe-La composite could be well described by the Langmuir model and the pseudo-second-order model. The simultaneous removal of fluoride and phosphate by Fe-La composite could be ascribed to ion exchange between fluoride and La-OH groups, as well as the formation of metal phosphates precipitation, respectively. Our results may provide some insight to develop new adsorbents for removing fluoride and phosphate simultaneously.
Article
A potential feedstock, de-oiled Pongamia-pinnata seed cake is used to prepare engineered Bio-char (EBC) for the removal of fluoride from ground water. EBC was characterized and batch biosorption studies were conducted at different initial fluoride concentrations, EBC dosages and pH values. A maximum fluoride adsorption occurred at pH-7 with an equilibrium time of 90 min and EBC dosage of 10 mg/L. Different isotherm models were investigated, among which Langmuir was found to best fit with a maximum adsorption capacity of 0.985 ± 0.025 mg/g. The chemisorption was defined by Ritchie-pseudo-second-order kinetics with intra-particle diffusion contributing to the rate determining step. Column studies with variable operating conditions (initial fluoride concentration, bed depth, flow rate) and modeling of the breakthrough curves showed modified dose response model in excellent agreement with a maximum uptake of 1.12 ± 0.025 mg/g. EBC regeneration, comparison with contemporary sorbents and its real time application are also explored in the present study.
Article
Accumulation of excess fluoride in the environment poses serious health risks to plants, animals, and humans. This endangers human health, affects organism growth and development, and negatively impacts the food chain, thereby affecting ecological balance. In recent years, numerous studies focused on the molecular mechanisms associated with fluoride toxicity. These studies have demonstrated that fluoride can induce oxidative stress, regulate intracellular redox homeostasis, and lead to mitochondrial damage, endoplasmic reticulum stress and alter gene expression. This paper reviews the present research on the potential adverse effects of overdose fluoride on various organisms and aims to improve our understanding of fluoride toxicity.
Article
Biosorption is considered to be one of the favourable remediation techniques for fluoride removal from aqueous solutions. Other conventional techniques such as precipitation, reverse osmosis, ion exchange, nanofiltration etc, have several demerits such as huge initial costs, higher electricity consumption, generation of sludge, etc. The process of biosorption has become an economically feasible and environmentally benign alternative technique in the treatment of water and wastewater industries owing to the disadvantages associated with above-mentioned techniques. In this regard, numerous biosorbents have been developed for their successful implementation on defluoridation. Due to various technical barriers in the biosorption process which hinder its commercialization, there has been a steadily growing interest in this area of research. Of late more attention is being paid towards the development of cost-effective adsorbents using various agricultural wastes, plant biomass, bacteria, algae and fungi. This review paper highlights the use of various biosorbents, sorption isotherm, and kinetics. Literature review indicates the potentiality of such wastes as biosorbents for fluoride removal. Maximum fluoride removal of 91% was obtained by lanthanum-modified bone waste with a biosorption capacity of 8.96 mg/g which is reportedly the highest till date. However, it is important to determine whether these biosorbents could be used on the commercial scale which, in turn, might result in controlling pollution.
Article
Fluoride contamination of groundwater has become a major concern worldwide, resulting in serious medical conditions such as dental and skeletal fluorosis. Consequently, the WHO recommends that drinking water should not contain more than 1.5 mg/l of fluoride. Various defluoridation techniques such as coagulation, reverse osmosis, activated alumina adsorption, and biosorbent adsorption have been developed. Adsorption through the activated alumina and biosorbent process is not cost effective and has regeneration problems, and the reverse osmosis process has the high initial cost which makes it unacceptable for developing countries. Coagulation is a commonly employed field technology for defluoridation, which involves the addition of aluminum salts, lime, and bleaching powder followed by rapid mixing, flocculation, sedimentation, and filtration but suffers from a limitation of high residual aluminum in treated water. This paper critically reviews the recent developments in the coagulation technique for defluoridation along with its comparison to other defluoridation techniques. The review describes the pertinent gaps in the process and throws open suggestions for extending research by citing the recent studies which may lead to the revival of the process. The description about the suspension of alumino-fluoro complexes that constitute a substantial part of the residual aluminum after alum treatment has been narrated in the paper that helps in a deeper understanding of the defluoridation mechanism. To make the process highly suitable for communities, appropriate technological interventions, such as converting it to a continuous mode of operation, replacing alum with poly-aluminum chloride (PAC), and attaching a micro-filtration unit in series of the existing process, can be done. Also, using PAC as a coagulant with sand filtration has to be considered for making the process more efficient.
Chapter
Presence of high fluorides in groundwater has caused systemic fluorosis to become an endemic problem in many countries of the developing world, namely, India, Sri Lanka and many African nations. It is a conclusive fact that higher concentration of fluoride (beyond 1.5 mg/L) can cause teeth mottling and still higher concentrations may lead to different major health hazards including skeletal and neurological problems. The fluoride level in water in India ranges from 2 to 29 ppm, whereas the permissible level in drinking water according to WHO standard is 1.5 ppm and BIS 10500 permits only 1 ppm fluoride in drinking water. Various defluoridation techniques in India have been developed for maintaining the concentration of fluoride in water up to the permissible limit like Nalgonda Technique, reverse osmosis, activated alumina adsorption, Bio-F process, etc. Nalgonda Technique involves addition of Aluminium salts, lime and bleaching powder followed by rapid mixing, flocculation, sedimentation, filtration and disinfection and the acceptable limit of water of 1 mg/l has been achieved. Defluoridation using activated alumina as adsorbent is not cost-effective. Hence, development of community-based defluoridation unit is needed with a technique which is cost-effective, technologically simple in operation while being able to keep the fluoride level in permissible limit. The paper critically discusses the recent developments in various defluoridation processes, identifies the pertinent gaps in them and offers plausible solutions by summarizing the ongoing research at MNIT Jaipur in order to obviate these gaps through appropriate technological interventions.
Article
Excessive fluoride (above 1.5 mg/L) containing water consumption for prolonged periods could pose health hazards, for example, dental fluorosis. Longer exposure could also cause skeletal fluorosis leading to the permanent deformity to skeleton. In the current context, use of biomasses for defluoridation would be a most economic and sustainable option for water defluoridation over the available alternatives. This article presents a brief summary of processes used biomasses for fluoride removal from aqueous solutions. This article also discusses the theoretical and instrumental approaches used by the researchers till date to understand the defluoridation mechanisms. The literature survey pointed that theoretical models such as Langmuir and Freundlich isotherms, pseudo-first-order and second-order kinetic models, and different thermodynamic equations were also used to define the defluoridation by biomasses. Apart from the theoretical modeling, several researchers have also tried to understand the biomass-based defluoridation by applying advanced instruments, for example, FTIR, XPS, NMR, TG, FESEM, and Raman spectroscopic analysis. © 2018 American Institute of Chemical Engineers Environ Prog, 2018
Article
Fluoride contamination of groundwater is a serious problem in several countries of the world because of the intake of excessive fluoride caused by the drinking of the contaminated groundwater. Geological and anthropogenic factors are responsible for the contamination of groundwater with fluoride. Excess amounts of fluoride in potable water may cause irreversible demineralisation of bone and tooth tissues, a condition called fluorosis, and long-term damage to the brain, liver, thyroid, and kidney. There has long been a need for fluoride removal from potable water to make it safe for human use. From among several defluoridation technologies, adsorption is the technology most commonly used due to its cost-effectiveness, ease of operation, and simple physical process. In this paper, the adsorption capacities and fluoride removal efficiencies of different types of adsorbents are compiled from relevant published data available in the literature and represented graphically. The most promising adsorbents tested so far from each category of adsorbents are also highlighted. There is still a need to discover the actual feasibility of usage of adsorbents in the field on a commercial scale and to define the reusability of adsorbents to reduce cost and the waste produced from the adsorption process. The present paper reviews the currently available methods and emerging approaches for defluoridation of water.
Article
Removal of fluoride was done by adsorbent prepared from leaves of Syzygium cumini. Adsorbent preparation was done by calcination (500°C) and characterized by multiple physiochemical, and micro-analytical techniques including EDS, FT-IR, TGA and XRD. The adsorbent was mainly composed of calcium carbonate and calcium oxide/hydroxide. Adsorption study revealed a maximum fluoride removal efficiency of 77.8% with uptake capacity 4.56mgg⁻¹, within 60min of contact time from an initial 6mgL⁻¹ fluoride solution with adsorbent dose 6.5gL⁻¹ at pH 6.5 and temperature 300K. Fluoride adsorption data obtained best fitted to the Freundlich isotherm model, signified a multilayer adsorption process. Additionally, the mean calculated adsorption energy (1kJmol⁻¹) from the Dubinin-Radushkevich model suggested a physical adsorption process. The kinetic adsorption data showed agreement to the pseudo-second-order and intraparticle diffusion model, both signifying that the removal of fluoride involved boundary layer effect and intraparticle diffusion. Spontaneous and exothermic nature of the adsorption process was revealed by the thermodynamic parameters. Finally, the adsorbent successfully purified two real water samples contaminated with fluoride. The results suggested that physical adsorption with some effect of electrostatic interaction and anion exchange was also involved in the fluoride adsorption. This study will be useful in designing new calcium based low-cost adsorbent from biological wastes for removing fluoride from contaminated water.
Article
High concentrations of fluoride in drinking water can cause the disease fluorosis. Our scope goal is to develop an effective biopolymeric adsorbent for the removal of fluoride to below a specific safety limit set by the World Health Organization. In this study, the natural adsorbent material cellulose was impregnated with lanthanum chloride and effectiveness in adsorbing fluoride was confirmed by FT-IR, XRD, and SEM coupled with EDX techniques. The adsorption data were analyzed by Freundlich, Langmuir, and Redlich-Peterson isotherms. The adsorption on cellulose and Lanthanum impregnated Cellulose (LaC) obeyed the pseudo second order kinetic model and thermodynamic parameters were shows the adsorption process was spontaneous and feasible. The high adsorption capacity of LaC was developed from waste materials through an easy procedure, has potential for application to efficient defluoridation. In future, the potential LaC adsorbent will be used for designing of household defluoridation unit for effective and economical fluoride removal.
Article
Spent strongly acidic cation exchange resin was effectively used for the removal of trace concentration of fluoride ions. For this purpose, the spent resins were pulverized into fine powders to be used together with inorganic coagulation agent consisting of iron, aluminum, and calcium in batchwise operation. Prior to this operation, the pulverized resins were loaded with Zr(IV) ions to develop adsorption sites which effectively and selectively adsorb fluoride ions over other coexisting anionic species such as chloride and sulfate ions. The fluoride uptake capacity of the Zr(IV)-loaded resin powder was negligibly affected by the coagulation agent. This combined process of adsorption and coagulation was proven to be used for at least six repeated cycles of adsorption followed by desorption using dilute alkaline solution without lowering the uptake capacity for fluoride ion. Quantitative removal of trace concentration of fluoride was successfully achieved from actual waste plating solution by this process.
Article
The aim of this work was to synthesize iron-oxide nanoparticles (NPsFeO) via a non-polluting method (green synthesis), using Moringa oleífera leaf extract, and evaluate its fluoride ion adsorption potential, comparing its efficiency with a commercially available adsorbent (activated carbon of bone [BGAC]). The adsorbent materials were characterized using X-ray diffraction, transmission, and scanning electronic microscopy, X-ray dispersive energy spectrometry, and N2 adsorption/desorption. The results showed that the fluoride ion adsorption is favorable in neutral pH values, with maximum adsorption at pH 7 for NPsFeO, and pH 5 for the BGAC. Adsorption kinetics tests showed that the equilibrium was reached in 40 min for the NPsFeO, and 90 min for BGAC, with adsorption potential of 1.40 mg g(-1) and 1.20 mg g(-1), respectively. The model that best described the kinetic data was pseudo-first-order for NPsFeO and pseudo-second-order for BGAC. The Langmuir isotherm had a better fit for both adsorbents. The thermodynamic parameters indicated spontaneous and endothermic adsorption at 30, 40, and 50° C for BGAC, and at 30°C for NPsFeO. The regeneration process showed that is possible to reuse NPsFeO three times in the fluoride ion adsorption process. As a result of its adsorption capabilities and the shortest contact time to achieve equilibrium, the synthesized nanoparticles in this work are a highly promising material for fluoride ion removal.
Article
Phytoremediation is a proven low-cost and sustainable method for the removal of toxic pollutants from water. This green technology has been practiced for the past several years all over the world. In the present study, the interaction of fluoride on the surface of the floating aquatic plant water lettuce (Pistia stratiotes) during fluoride removal was investigated. Batch kinetic studies were performed to examine the fluoride uptake capacity of the plant with different initial fluoride concentrations such as 3, 5, 10, and 20 mg/L. The effects of various process parameters on fluoride uptake dynamics such as pH, plant biomass, initial fluoride concentration, and time were examined. Freundlich’s isotherm model was found to (R² = 0.957) fit well to the experimental data. The nature of reaction order followed pseudo-first-order kinetics, when the initial fluoride level in the solution was 5 mg/L. The experimental findings showed that the removal mechanism was driven by biosorption phenomenon. High fluoride concentration in the solution reduced the growth ratio of P. stratiotes. The lowest growth ratio of this aquatic macrophyte was found to be 76.80 ± 3.73% at 20 mg/L fluoride concentration. At lower fluoride concentrations such as 3 and 5 mg/L, the growth ratio of the plant was not reduced significantly.
Article
Fluoride in drinking water plays a vital role in dental health. Due to excessive fluoride in water, enamel loses its luster. At lower concentration, it guards our teeth against cavities but at higher concentrations imparts fluorosis in varying concentrations. Excess fluoride in drinking water is reported from more than 35 countries around the globe with India and China. In countries like India, the severe contamination of drinking water with excess fluoride acquired the dimensions of a social economic rather than a public health problem triggering defluoridation research.
Article
A novel iron oxide adsorbent with a high fluoride adsorption capacity was prepared by a facile wet-chemical precipitation method and ethanol treatment. The ethanol-treated adsorbent was amorphous and had a high specific surface area. The adsorption capacity of the treated adsorbent was much higher than that of untreated adsorbent. The Langmuir maximum adsorption capacity of the adsorbent prepared at a low final precipitation pH (≤9.0) and treated with ethanol reached 60.8 mg/g. A fast adsorption rate was obtained, and 80% of the adsorption equilibrium capacity was achieved within 2 min. The adsorbent had high fluoride-removal efficiency for water in a wide initial pH range of 3.5–10.3 and had a high affinity for fluoride in the presence of common co-anions. The ethanol treatment resulted in structure transformation of the adsorbent by inhibiting the crystallization of the nano-precipitates. The adsorption was confirmed to be ion exchange between fluoride ions and the hydroxyl groups on the adsorbent surface.
Article
Finding appropriate adsorbent may improve the quality of drinking water in those regions where arsenic (As) and fluoride (F⁻) are present in geological formations. In this study, we evaluated the efficiency of potato peel and rice husk ash (PPRH-ash) derived adsorbent for the removal of arsenic and fluoride from contaminated water. Evaluation was done in batch adsorption experiments and the effect of pH, initial adsorbate concentration, contact time and adsorbent dose were studied. The characterization of adsorbents were done using scanning electron micropcope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Both the Langmuir and Freundlich isotherm models fitted well for F⁻ and As sorption process. The maximum adsorption capacity of adsorbent for As and F⁻ were 2.17 μg g⁻¹ and 2.91 mg g⁻¹ respectively. The optimum As and F⁻ removal was observed between pH 7 and 9. The sorption process was well explained with pseudo-second order kinetic model. The As adsorption was not decreased in the presence of carbonate and sulfate. Results from this study demonstrated potential utility of this agricultural biowaste which could be developed into a viable filtration technology for As and F⁻ removal in As- and F-contaminated water streams.