"Bio-Filtration as a Solution for the Detrimental Health Effect of Excess Fluoride in Drinking Water"

One of the main importance of water filtration is to prevent water-related illnesses and diseases. To this day, various explored methods were used in the remediation of water of different types of contaminants such as flocculation [1,2], coagulation [3], solventextraction [4], co-precipitation [5], precipitation [6], ion-exchange [7], photo catalysis [8], adsorption-desorption [9], reverse-osmosis [10], nano-membrane filtration [11]. The adsorption technique is considered one of the attractive and commercial options to eliminate of the most pollutant substances whether macroor microorganic/inorganic ions from water, due to its simplicity of steps and high activity. Moreover, the purification of water by using adsorption technique has been applied to several matter as absorbent such as agricultural residues and industrial residues, and biomaterials wastes, which are modified and applied in biosorption of contaminants from water [7,9-12]. Fluoride is an ionic form of fluorine and can be found in food and numerous sources of drinking water. It can be also purchased as a dietary supplement [12]. Many kinds of toothpastes contain fluoride because these ions serve as an armor against tooth decay [13]. Approximately 80% of the fluoride taken orally is absorbed. Humans retain around 50% of the fluoride they consume, and most of this amount is deposited in teeth and bones (Graphical Abstracts 1 & 2). The remaining 50% is excreted in the urine.


Introduction
One of the main importance of water filtration is to prevent water-related illnesses and diseases. To this day, various explored methods were used in the remediation of water of different types of contaminants such as flocculation [1,2], coagulation [3], solventextraction [4], co-precipitation [5], precipitation [6], ion-exchange [7], photo catalysis [8], adsorption-desorption [9], reverse-osmosis [10], nano-membrane filtration [11]. The adsorption technique is considered one of the attractive and commercial options to eliminate of the most pollutant substances whether macro-or micro-organic/inorganic ions from water, due to its simplicity of steps and high activity. Moreover, the purification of water by using adsorption technique has been applied to several matter as absorbent such as agricultural residues and industrial residues, and biomaterials wastes, which are modified and applied in biosorption of contaminants from water [7,[9][10][11][12]. Fluoride is an ionic form of fluorine and can be found in food and numerous sources of drinking water. It can be also purchased as a dietary supplement Graphical Abstract 2: Solution.
However, young children can retain an especially high percentage of the consumed fluoride, because their bones and teeth absorb more fluoride than those of adults [14]. The principle and mechanism of pollutants removal by adsorption technology from different types of water based on forms layer of condensate pollutants (called adsorbate) which is migrated from aqueous solution to the surface of solid (called adsorbent) as either in the form of liquid-solid interface [11,15]. Excess fluoride is harmful to human health. Groundwater wells worldwide have been reported to contain water with fluoride concentrations exceeding the acceptable level of 1.5 mg/L. This fact was attributed to local ground stones exhibiting high percentages of fluoride in their composition [14]. Excessive fluoride consumption can lead to several health issues, such as skeletal fluorosis, a disorder marked by bone and joint pain as well as joint tenderness. The overconsumption of fluoride during the formative years of tooth enamel can also lead to dental fluorosis, which leads to tooth discoloration, and/or tooth pitting [15]. Many researchers have attempted to develop water filtration strategies to lower the levels of fluoride or metals that contaminate water [16]. Biomaterials have shown great promise in water filtration because of their environmentally favorable properties, high filtering efficiency, and low cost [17].
Charcoal, which may be manufactured from a variety of biomaterials, is one of the most commonly used bio-filters. Water contaminated with heavy metals can be treated using different processes, which include ion exchange, precipitation, reverse osmosis, catalysis, coagulation, and adsorption [18,19]. Heavy metal adsorption is dependent on the nature of the adsorbents, which can be composed of natural or man-made mate-rials including clay [10], sludge [11], industrial waste, activated carbon, and plants [12]. Bone char is an adsorbent made up of 90% calcium phosphate and 10% carbon. It can be created using one of the two methods: treatment with chemicals and physical treatment leading to carbonization of bones [20,21]. Cow bone char is com-monly used to purify water contaminated with heavy metals, as shown in (Table 1). The aim of the current study was to produce a lowcost, effective, and environmentally friendly biochar adsorbent from cow bone through physical activation (carbonization), and subsequently use it to remove fluoride from the polluted water [22]. Furthermore, it was also proposed to enhance this bio-filter by adding nanocomposites. Nanocomposites have very high surfaceto-volume ratios, which makes them ideal components for the adsorption process [23,24]. in the parts-per-million (ppm) range. Ion chromatography can also be used to determine the concentrations of organic acid [26].
The surface structure of cow bone charcoal was studied by using a scanning electron microscope (SEM) (Model: JSM-7100F) at 10000 × magnification [27]. In conjunction with SEM, the energy dispersive X-ray (EDX) analysis technique was used to perform the elemental analysis and chemical characterization of the material. EDX utilizes an electron beam that strikes the surface of a conducting sample (placed under SEM) to determine its elemental content [28].

Results and Discussion
The SEM micrographs of the cow bone biochar explained the sample morphology by analyzing the microstructure of the bone powder, as shown in (Figure 1a). The corresponding EDX graph is presented in (Figure 1b). A close look at (Figure 1a)   The surface morphology of the cow bone is particularly distinctive in terms of the hard appearance and the distribution of pores, which are of critical importance in filtering large species from water ( Figure 2). Hence, the surface geometry and the source of adsorbent provided different types of active sites onto surface of adsorbent [29][30][31][32][33][34][35] (Table 2).

Conclusion
The examined cow bone charcoal filter achieved maximal fluoride adsorption of 93.6%, which can be attributed to its porous nature. The prepared bio-filter has a very high adsorption capacity and is energy-efficient as it works at room temperature and does not require energy consumption. It means that using cow bone charcoal is a cost-effective filtration technique that should be further investigated to optimize the performance of nanocomposites and to set up measures for its widespread manufacturing.