Advanced Treatment Technologies for Fluoride Removal in Water

Water is the most crucial component and the building block of life on Earth. The world is facing water scarcity, affecting millions of people. Most of the population uses groundwater for drinking purposes. Groundwater can be contaminated by natural anthropogenic and industrial sources such as heavy metals, manganese, radioactive materials, nitrates, sulfates, iron, fluorides, arsenic, etc. In the Earth’s crust, fluorine ranks as the 13th most abundant element. Groundwater contains fluoride derived primarily from fluorspar, sedimentary rocks, cryolite, granite, fluorapatite, sellaite, dolomite, etc. The simultaneous presence of fluoride in groundwater is related to volcanic, geothermal, mining, and other activities. Although small amounts of fluorides are beneficial for dental and bone health in humans, fluoride in higher concentrations is detrimental to human health. Fluorides and other contaminants can affect health independently, synergistically, or antagonistically. The degree of leaching of crystalline minerals is directly related to the level of fluoride contamination. China, India, Mexico, and Pakistan are the countries most affected by groundwater fluoride contamination. Millions of people in China and India are at risk of fluoride. The following methods are currently used for fluoride removal: Chemical precipitation of coagulation, which also includes electrocoagulation floatation, Adsorption on special activated solids, ion exchange, and Membrane techniques, which include nanofiltration, reverse osmosis, electrodialysis methods, etc. Electrocoagulation and flotation techniques are relatively expensive due to high operational costs. Adsorption methods are the most widespread, but produce a significant amount of wastewater to recharge the adsorption beds. Based on the concentration of fluoride in water, these removal techniques can be applied sequentially to achieve the desired fluoride concentration that is safe to use. This chapter discusses in depth the global scenario of fluoride contamination in depth and briefly discusses its effects and possible ways to reduce and treat fluoride contamination.

Fluoride contamination in groundwater is one of the drinking water crisis globally. Although its presence is necessary in small quantities, it is harmful to humans with intakes of more than 1.5 mg L⁻¹ through contaminated drinking water due to geological factors and geochemical processes. A high fluoride content in drinking water results in skeletal fluorosis, as well as long-term liver, kidney, and brain damage. One of the most crucial challenges for drinking water safety is the management of fluoride pollution and fluorosis. To reduce the probability of fluorosis, it is essential to have a better understanding of the mechanisms underlying the presence of fluoride in the chemistry of subsurface water and the ability to identify high-risk locations using geographic data and remote sensing. The utilization of other sources of water or mixing should be prioritized. The development of stable technologies and integrated devices that are efficient, affordable, and manageable, as well as fundamental research on defluoridation reagents and novel materials, should receive significant amount of focus. To achieve stable gains, the design, construction, operation, and monitoring of defluoridation facilities should be thoroughly evaluated and improved. This chapter highlights the extent of fluoride contamination, the effect of fluoride contamination on human health, and the available defluoridation methods.

The lesser and excessive amounts of F⁻ ions are both unhealthy for human health. Due to an insufficient amount of F⁻, the formation and decay of teeth is observed, but excessive fluoride is linked to the diagnosis of fluorosis leading to hyperactivity, Musculoskeletal abnormalities, and brain damage due to excessive fluoride exposure during the development of tooth enamel. Before opting for the method of treatment for the fluoride-contaminated water, the chemical composition of surface and subsurface water is imperative. The presence of volcanic ash and some fertilizers in the soil also leads to an increase in the concentration of F⁻. Sometimes a low concentration of F⁻ also has effective health benefits, but F⁻ at concertation > 1 ppm can lead to several health hazards. Excessive use of it over a long period of time can cause changes in DNA structure. In order to produce usable water, numerous technologies are being used for the removal of F⁻ and its derivatives. The major technologies used for the removal of F⁻ from waste water are green nanomaterials, capacitive deionization (CDI), membrane technology, and electrocoagulation. Apart from F⁻ removal from waste water, techniques used for natural water are equally important, viz. adsorption technology using various adsorbents. Some effective adsorbents are namely zeolites, alumina, organic based, Shell based including carbon-based nanotubes and graphite, metallopolymers and variety of microspheres. The defluoridation of water using modified activated alumina, chitosan derivatives, clays and muds, composites, and various separation techniques having merits and demerits are in use. Mechanisms used in the fluoride removal techniques are generally Adsorption, Nano-adsorption, Reverse-osmosis, Coagulation-Precipitation, Electrodialysis, Electrocoagulation, Nanofiltration, Ion exchange, Membrane dialysis etc.

Fluoride is a common element found in many minerals and rocks, and its widespread distribution and high concentration in groundwater have raised serious concerns. Adsorption is one of the most efficient approaches that have been suggested for removing it from aquatic environments. Iron-based materials, such as nanoscale zerovalent iron (nZVI), modified nZVI, spinel ferrites, Fe-based metal–organic frameworks, and their composites, have recently gained a lot of attention because of their even greater fluoride removal efficiencies from an aqueous solution compared to those from other adsorbents. The most popular iron-based substances used in fluoride elimination are described in this chapter. Their methods of preparation and characterization were categorised and presented in groups. The authors also explained how these materials could be used to effectively remove fluoride from water. For a comprehensive understanding of the fluoride removal mechanisms of fluoride, commonly used adsorption isotherms, kinetic models, and thermodynamic analysis are completely described. Subsequently, research on regeneration and recycling was addressing these issues. According to the results, fluoride may be effectively removed from water using materials with an iron base. However, several current obstacles need to be addressed further to enable their actual application in fluoride removal.

From ancient times, underground water resources such as wells and bawaris have been used for drinking and other daily activities. Half of the world’s population still relies on groundwater to satisfy their drinkable water needs. Consequently, its quality is degraded due to industrialization and human interference. The most prevalent concern is groundwater contamination from sewage, industrial effluents, pesticides, and other pollutants. As a result, one of the most critical and complex environmental concerns confronting all life forms on Earth is supplying adequate clean drinking water to every human being to ensure survival. Groundwater is estimated to be the source of domestic water for 80% of the rural and 50% of its urban areas. Fluoride-rich groundwater exposure produced everything from dental fluorosis to devastating skeletal fluorosis in humans and animals. Although numerous defluoridation methods are available, including coagulation, reverse osmosis, and nanofiltration, these technologies have proven ineffective in rural areas, particularly in rural hilly areas, due to high costs and a lack of skilled operators. The present review aims to corroborate the uses of organic products, mainly from agriculture, agroforestry, and forest waste. In this chapter, we discuss the preparation of various adsorbents from these products, the efficiency of fluoride removal, the cost–benefit analysis, and market economy. The chapter provides insight into some cost-effective mitigating approaches for ground water defluoridation at the household and community level in rural hilly areas of India.

The presence of fluoride in Groundwater is a significant issue. The fluoride in the water used for human consumption does not exceed 1.5 mg/l, according to the WHO; however, many countries already exceed that limit. The human health risks of fluoride contamination are well documented, prompting widespread efforts to find effective defluoridation strategies. This study aims to investigate the efficacy of inexpensive limestone powder as an adsorbent for treating fluoride-contaminated Groundwater. The efficacy of limestone powder was investigated through batch studies with different physical and chemical parameters, including pH, contact duration, adsorbent dosage, and fluoride concentration. The removal of fluoride using limestone was most effective at a pH of 7.22, with a sorption capacity of 2.57 mg/g. It took 90 min to reach equilibrium. Groundwater samples were also used in the sorption investigation; the study revealed that limestone powder could decrease fluoride from 3.48 to 0.878 ppm. SEM and FTIR spectroscopy were used to ascertain the surface’s functional group and morphology.

Groundwater contamination with excess fluoride concentration is a serious concern for various nations around the world. Consumption of drinking water with excess fluoride poses a serious threat to human health through dental/skeletal fluorosis. Therefore, defluoridation of water has attracted global attention and different techniques have been developed to ensure its safety for human consumption. However, the higher operating costs and low efficiency of these techniques make them difficult to use for field applications. Among the various techniques for water defluoridation. Adsorption is widely adopted as a result of its low cost, ease of availability, easy utilization, high efficiency, and simple physical technique. Although activated carbon has been widely used for the removal of various contaminants, including fluoride, it is sometimes restricted due to its higher cost. Recently, efforts to develop low-cost adsorbents from waste materials have led to the development of bio-sorbents from plants and animal waste that have shown considerable potential for water defluoridation. The main emphasis of this chapter is to gather in-depth knowledge concerning the utilization of inexpensive adsorbents for water defluoridation.

Fluoride, a naturally occurring element, is released from rocks into the land, water, and air. The WHO recommends 1 mg/L of fluoride in drinking water as the ideal or recommended amount. An abundance of fluoride ions can cause dental/skeletal fluorosis, muscular and bone damage, chronicle issues, inhibit the photosynthesis process, and enzymatic and metabolic activities in aquatic organisms. Membrane filtration processes, reverse osmosis, electrodialysis are widely used treatment processes for the removal of fluoride; however, they are expensive and complex. The adsorption method is considered to be an effective technique because of the low operating costs, the capacity to hold metal ions at low concentrations, and the availability of a variety of adsorbents for treatment applications, which makes it an attractive option. If there are opposing anions present including chloride, iodide, and sulfate, then the iron oxide-hydroxide nanoparticles demonstrate their effectiveness as a repeatable and efficient adsorbent medium for defluoridating water. This chapter deals with adsorptive removal of fluoride removal using iron-based adsorption techniques and highlights different parameters affecting the performance of adsorption.

In recent years, the environmental sector has become interested in electrochemical-based techniques due to their environmental compatibility, sustainability, versatility, low cost, efficiency, and a small amount of sludge production. Fluoride in drinking water at high levels has been associated with a number of health problems, including skeletal, dental, and various forms of fluorosis. Among the various available de-fluoridation methods, the electrocoagulation procedure was tested experimentally and optimized to increase removal effectiveness while using the least amount of energy possible. The electrocoagulation process with Fe as sacrificial electrodes was used at domestic, industrial, and commercial levels. The Fe ions have a great affinity for fluoride ions, leading to a higher removal efficiency of fluoride from the water. The removal efficiency also depends on factors such as the applied current, the initial fluoride content, the electrode spacing, the electrolysis time, pH, the contact surface area, etc. This chapter deals with the removal of fluoride contents through Fe-based ion electrodes by electrocoagulation (EC). We further discuss the mechanism of CE, the different shapes of Fe electrodes, and the geometry of reactors in contrast to the efficiency of F removal from the water.

In precipitation, fluoride-rich water is treated with aluminum salts and lime, which is then taken through filtration or sedimentation. Lime reacts with the free fluorides, originating from salts such as NaF and HF (acids released by industries), forming calcium fluoride (CaF₂), an insoluble impurity that can be eliminated. Since aluminum acts as a coagulant, its salts Aluminium Chloride (AlCl₃) or Aluminium sulfate (Al₂(SO₄)₃) are used for the viable removal of fluorides. This leads to the formation of Aluminium Hydroxide (Al(OH)₃) with the introduction of alum. This leads to the accumulation of all fluoride impurities, which makes it easier to eliminate them. This coagulation process can also be carried out using Ferric salts (Fe salts) as an alternative to aluminum salts. An improvement in this is electrocoagulation (EC), which involves electric current passed through an aqueous medium wherein sacrificial electrodes are used. An aluminum anode is used, which breaks the metal into ions that react with the free fluoride ions in the aqueous solution to form an Aluminium Hydroxide-Fluoride complex. It coagulates, thus increasing the speed of impurity elimination. These complexes need to be filtered to further reduce the fluoride content of the water; carbon, or gravel filters can be used. Here, a layer of a sand filter is used along with layers of gravel. Thus, chemical precipitation (coagulation) is utilized to reduce the fluoride concentration from a high bulk level to a few milligrams per L. This is further reduced below the critical limit of minerals/elements with filtration and sedimentation. Thus, this chapter discusses methods of removal of fluoride impurities through chemical precipitation using coagulation, electrocoagulation, and filtration, including membrane filtration. Explores recent technology and methods that have been developed to improve the efficiency and cost-effectiveness of precipitation and filtration methods.

This study shows how fluoride can be removed from drinking water using a lot of techniques. For instance, membrane separation process, ion exchange, adsorption procedures, coagulation-precipitation and the numerically technique magneto-hydrodynamics model. The problem is taken into consideration for two-dimensional planer parallel flow in the magneto-hydrodynamics model. The behaviour of finely dispersed impurities contaminants is illustrated using the drift–diffusion approximation. Because of the high establishment and maintenance cost, membrane and ion exchange techniques are not so common. In India, two more methods are frequently used. The Nalgonda method is one of well-known approaches widely employed in underdeveloped nations, such as India, Kenya, Senegal and Tanzania, for DE fluoridating water. The adsorption technique is widely employed, produces positive results and is undoubtedly a more appealing approach for fluoride removal in the form of cost, simplicity of concept and operation among the several ways for DE fluoridating water. Environmental Protection Agency data show that fluoride is a contaminant that encourages pollution in public drinking water and can be harmful to human health. As per World Health Organization and Water Conservation Agency, maximum pollution of fluoride that has few negative effects has been set at 1.5 mg fluoride per litre. Fluoride can be found both naturally and chemically, however leading sources of fluoride in the human body are pesticides, drinking water, and dental products. Fluoride can influence the human body in a variety of ways, including metabolic and nutritional problems. Fluoride has a number of negative health effects on humans, including dental effects, musculoskeletal effects such as bone fractures and skeletal fluorosis, reproductive and development effects, neurobehavioral and neurotoxicity effects, endocrine effects, as well as some effects on the kidneys and immune system.

Living beings are affected by fluoride (present in soil, water, and air). In the halogen family, fluorine is a naturally abundant element. It has no biological purpose and is exceedingly harmful to humans, animals, and the environment when it is present in large amounts. Fluorine is an extremely reactive element that does not exist in nature in its pure form. It is found as fluoride ion (F⁻), which makes up approximately 0.3 g/kg of the Earth’s crust. Its pollution has a significant negative impact on 200 million people in 29 nations, including India. It is released into the soil naturally by the breakdown of minerals such as apatite, fluorspar, topaz, and mica. It is transferred to crops, vegetables, and fruits during irrigation using fluoride-contaminated water. This bioaccumulation increases the risk to the population already affected by fluoride poisoning since it adds more fluoride to the food chain in addition to the route through drinking water. Emphasis must be placed on educating people about fluorosis and limiting their use of fluoride-contaminated irrigation water. High levels of F⁻ may have a negative impact on human health over time by reducing thyroid function, allowing kidney stones to form, causing bone fractures, skeletal fluorosis, dental fluorosis, and impairment of IQ, especially in young children. In this chapter, we focus on the effects of F⁻ in the living beings through the water.

The issue of fluoride exceeding permissible limits in drinking water (DW) and its associated problems has been extensively documented, both within and outside India. The excessive presence of fluoride in DW causes detrimental effects on human health. Challenges related to elevated fluoride levels in DW are particularly prevalent in countries such as India. Fluorosis, an illness caused by the assimilation of fluoride, is a serious health problem. This chapter discusses various health issues that arise due to the increased fluoride concentration in water such as impaired joint mobility, neuropathic effects, decreased thyroid function, lower intelligence levels in children, hindered mental growth, elevated risk of kidney stone risk, and potential carcinogenicity. The leaching of fluoride from minerals in the earth's crust is the primary source of fluoride in groundwater. Many rivers in various regions of India have recorded different concentrations of fluoride, ranging from 0.1 to 12.0 ppm. Several countries, including India, China, Ethiopia, Pakistan, Senegal, Sri Lanka, Algeria, Ghana, Kenya, Ivory Coast, Uganda, Tanzania, Mexico, and Argentina, are among the nations severely affected by fluoride contamination. Various solutions have been proposed in the literature to address these issues. Techniques such as ion exchange/adsorption, and coagulation/precipitation are effective in fluoride removal from water or wastewater. The ion exchange/adsorption processes are effective for both concentrated and diluted solutions, ensuring complete removal when applied under appropriate conditions. The selection of the most suitable method for a particular situation should be done carefully, considering various factors. This chapter provides a wide-ranging summary of fluoride, mainly its presence in the atmosphere, sources of origin, impact on human health, and methods for defluoridation.

Fluoride is largely consumed by people all around the world through drinking water. Fluorosis is caused by largely through high level of fluoride in consumable water, lowering the quality of human life. This becomes crucial considering that fluoride intake primarily comes from water. According to estimates, bones and teeth hold 99% of the fluoride that is absorbed by humans. Children retain 80% of the fluoride they have received, compared to adults who retain only 50%. The typical dietary fluoride in adults ranges from 0.020 to 0.048 mg/kg (living in places with water fluoride values of 1.0 mg/L). At a water fluoridation level of 1 mg/L, the prevalence of dental fluorosis has remained calculated to be 48% in fluoridated areas and 15% in non-fluoridated parts. Due to its global proliferation into further than 40 countries, mainly in mid-latitude zones, fluorosis has turned out to be endemic in numerous areas of the world. Typically, fluorosis in tooth tissues is considered a more severe form as a result of the increased intake of fluoride through water. Additionally, consuming vegetables and cereals full-grown in fluoridated zones increase the incidence of fluorosis in kids among the ages of 3 and 14 years. Established on different sources of water consumption between different communities, nutritional deficiency can be seen that leads to dental fluorosis in different concentration can be seen. The community fluoride index is used to measure the load of dental fluorosis in designated population. Nutritional status in children can be improved through preventive programs that are targeted at subpopulations that live in regions with high concentrations of fluoride in water. These programs are designed to prevent children from consuming an excessive amount of fluoride. Policymakers in the field of public health could target these subpopulations.

Fluorine is an element that can be discovered in water, soil, rocks, minerals, and other natural surroundings. It is a naturally occurring substance. Fluoride’s effects on plant health may be both beneficial and detrimental depending on how it’s used. Gaseous hydrogen fluorides (HF) are the most phytotoxic air pollutants because they accumulate in the leaves of fragile plants against a concentration gradient and harm them at very low concentrations. This is because they harm plants even at extremely low concentrations. The most damaging effect that HF has on plants is caused when it enters their systems in the form of gas and disrupts many physiological processes. As HF accumulates in plant leaves, it has the potential to negatively impact human and animal health as it moves up the food chain. Fluoride is transferred from the fluoridated water used for irrigation to the crops, vegetables, and fruits that are being grown. Because additional fluoride is added to the food chain in addition to entering the body through drinking water, the risk of fluoride poisoning to the population already at risk from fluoride poisoning increases as a result of bioaccumulation. The condition known as fluorosis should be brought to people's attention, and it should be prevented from using fluoridated irrigation water. The purpose of this review, in its entirety, is to bring attention to the following points:

Due to pollution and rapid resource depletion, the availability of clean water is decreasing at an alarming rate. Different techniques have been devised to utilize available polluted water to produce potable water. Most desalination systems use high-grade energy. Solar energy is a very large and inexhaustible source of energy. Solar desalination reduces the amount of energy used. The success of Solar still is dependent not only on the enhancement of its yield, but also the quality of distilled output. The objective of the present study is to examine the performance of solar energy with the addition of phase change material (PCM) to the bottom of it and affects energy storage capacity. The presence of fluoride may cause several health issues such as dental and skeleton fluorosis, bone rupture, muscle damage, neurological and thyroid damage, etc. Today, the removal and reduction from drinking water is a global concern. Solar energy is still one of the most suitable and economical techniques for reducing the level of fluoride in the water. A total of seven synthetic samples of fluoride-contaminated water were prepared as a feed for solar distillation. The concentration of fluoride was assessed in the distillate samples and it was found that the removal efficiency of passive solar still was greater than 90%.

Water quality parameters were predicted by many methods in the past, but the application of the best subset method is yet to be explored much. This method is unique in its application as it adopts the statistical regression modeling procedure to fit a separate model for every combination of any number of predictors while selecting the best subset for making the optimal decision. The present chapter demonstrates the application of the best subset model for the prediction of fluoride in river water by developing the regression equations for various combinations of other physicochemical parameters of the water quality of the Godavari River, the second largest river in India. The desired fluoride concentrations were evaluated using the concentrations of 16 other water quality parameters data collected for a period of 13 years (1993–2005) from 13 monitoring sites during the Monsoon (June-October) and Post-Monsoon (November-February) periods in the study region. Several best subsets of independent variables are chosen based on the percentage variation in the dependent variable, with a gradual increase in the number of predictors using various combinations of water quality parameters, and the best models are selected in agreement with the highest R² value and the lowest RSS value. The final best subset regression model is selected among the various best models using F-value statistics criteria. The best subset regression model is successful in explaining 90% variation in fluoride concentrations for both seasons in the study area. It would be interesting to try this method for the study of both surface water and groundwater quality parameters.

The growth of the economy is highly dependent on industrial development, and most industries discharge their effluent into streams or lakes. Due to industries growing at a very fast rate, the rate of pollution increased several times. Various industries discharge their effluent into the mainstream of water. As a result, the water becomes polluted and humans, aquatic animals, and even plants are affected. Fluoride is a chemical contaminant. It is toxic to plants and animals, including humans. This chapter explores the impact of fluoride contamination on the environment and contaminations in drinking water that can harm human health and various species at high levels. We also examine strategies to prevent and treat fluorosis, both globally and in India, and recent advances in fluoride remediation, as well as review various methods for fluoride removal from drinking water, such as coagulation-precipitation, membrane separation process, ion exchange, adsorption techniques, hybrid technology, and others. However, membrane and ion exchange processes are not widely adopted due to high installation and maintenance costs. Coagulation-precipitation and adsorption techniques are more prevalent in India. Among the different methods for water defluoridation, the adsorption technique is widely used and provides satisfactory results. It is also a more attractive method in terms of cost, design, and operation simplicity. The literature survey reveals that various methods have demonstrated novel potential for fluoride removal. However, it is still a need to evaluate the feasibility of such methods on a commercial scale, leading to improved pollution control.

In recent years, there has been intensification in community discernment of the damaging possessions of fluoride to human health (because of its effects on teeth and bones), as well as effects on the environment. Artificial activities are one of the biggest issues in the world today. It is crucial to develop efficient and reliable solutions to remove excess fluoride from water environments. The fluoride parameter stands out among the others. The goals included describing the framework for monitoring water quality, defining a proposed set of indicators, and informing the public about fluoride content. It is still essential to effectively clean fluoride-contaminated water. Metal–organic framework (MOF) materials are thought to be one of the several attractive adsorption materials for the various technologies used to remove fluoride from water. This article reviews current developments in the synthesis of MOFs and their use in aquatic defluoridation. MOFs are classified as the core metal ions. The mechanism of adsorption and an assessment of potential real-world uses of fluoride removal by various MOFs are explained. The practice of artificial water fluoridation should be reviewed globally as part of efforts to prevent harmful fluoride consumption, and industrial safety regulations should be improved to reduce the unethical release of fluoride compounds into the environment. The practice of artificial water fluoridation should be reviewed globally as part of efforts to prevent harmful fluoride consumption, and industrial safety regulations should be improved in order to reduce the unethical release of fluoride compounds into the environment. Public health strategies to reduce dental caries without relying on systemic fluoride intake.