of fluorosis
Providing nutritional supplement of calcium and other vitamins (like C, E, and D)
Addition of calcium‐, vitamin C‐, and vitamin D‐rich food to diet and avoid chewing supari, gutka, etc.
Awareness, motivation and training of the community.
2.5.3.5 Reverse Osmosis
A tank divided into two parts with the help of a semipermeable membrane comprises a reverse osmosis system. Fluoride‐contaminated water passes via semipermeable membrane with the help of hydraulic pressure on a side of tank. Along with water, few impurities also cross the semipermeable membrane, whereas salts and other impurities cannot cross the membrane (Dubey et al. 2018). Successful filtration of various impurities with different sizes has been reported while crossing the semipermeable membranes by exerting pressure. In the process of reverse osmosis oman‐induced pressure toward the contaminated water side of the membrane proved to be advantageous to overcome the naturally occurring osmotic pressure that flows in the opposite direction. In order to enhance the reaction speed of the process some more osmotic pressure has been added by forcing water across the semipermeable membrane toward the opposite, clean side (Demeuse 2009; Water Professionals 2018). According to reports, reverse osmosis results in accessing a better quality of drinking water, having salinity less than 0.1 g salts/L (Mazighi et al. 2015). Ions residing in water could be carried via membranes with the help of electric currents in the electrodialysis process. The two major parameters affecting the performance of membrane are pH and temperature. The ability to remove fluoride via the reverse osmosis process varies from 45 to 90% by increasing the pH level from 5.5 to 7. Some problems associated with reverse osmosis are chemical attacks, fouling due to particulate matter, plugging of membrane, and producing large quantities of waste. The waste generated by this process is much more than in the ion exchange process. Pretreatment of raw water must be carried out before introduction into the production unit if the raw water condition is not optimal. Another demerit is eliminating all the ions of contaminated water. As we all know, humans require minerals for proper growth and metabolism thus remineralization of reverse osmosis‐treated water is required, hence increasing the cost of the process in comparison to other options. This method involves more financial input as the purification process makes water more acidic, thus several pH corrections are required, generating lots of brine waste (Kumar and Gopal 2000). The important points of consideration for the reverse osmosis membrane selection method are recovery of purified water, raw water composition, pretreatment steps, cost, rejection properties, etc. (Jagtap et al. 2012; Yadav et al. 2017; Yadav et al. 2018).
2.5.3.6 Nanofiltration
One more removal method for fluoride is nanofiltration which decreases hardness of water with the help of membranes having high retention capacities for charged particles like bivalent ions. Nanofiltration has been considered as the optimum membrane process for eliminating fluoride having this inherent property of specific membrane selectivity (Tahaikt et al. 2007). Many researchers have shown successful elimination of fluoride with the help of the nanofiltration method. Reports suggest that nanofiltration membranes have better success in elimination of fluoride from polluted drinking water in comparison to LPRO (low‐pressure reverse osmosis) membranes. One study reported two commercially available nanofiltration membranes: NF‐90 and NF‐270, in which NF‐270 reduces the concentration of fluoride from 10 to 1.5 mg/L whereas NF‐90 decreases the concentration from 20 to 0.5 mg/L. The presence of anions like bicarbonates exert no noticeable negative effects on the purification process whereas the elimination of fluoride reduces under acidic condition (Hoinkis et al. 2011). According to the study of Bejaoui et al. (2014), successful elimination of fluoride has been reported utilizing reverse osmosis comparing against NF‐90 considering different parameters like pH, ionic strength, feed pressure, and fluoride concentration, as well as nature of cations present along with fluoride. The results revealed that optimization of fluoride removal was done at higher pH as enhancing overall negative charges of membrane has been tested (Bejaoui et al. 2014). The study of Emamjomeh et al. (2018) shows a lab‐scale study of nanofiltration membrane (FILMTEC‐NF90‐4040) using a pilot plant: fluoride removal from contaminated water with concentration lying between 1.50 and 2.17 mg/L. The effectively considered parameters were pressure (between 4 and 12 bars) and temperature (between 10 and 30 °C). Results revealed minimum and maximum removal percentage of fluoride, i.e. 30 and 70%, respectively. One other point brought into light was that increasing pressure and temperature enhanced the performance of fluoride removal and membrane permeate flow rate (Emamjomeh et al. 2018).
According to the study of Van der Bruggen et al. (2008), membrane fouling, chemical resistance, and insufficient separation limited lifetimes, as well as rejection, are some significant disadvantages of the nanofiltration method that increase the financial input of the method. The production of fouling that should be collected and disposed off is also considered as one main disadvantage of this method. One study shows the comparison between NF5 and NF9, two commercial nanofiltration membranes for removing fluoride from groundwater (Nasr et al. 2013). The concentration of fluoride in purified water using NF5 and NF9 nanofiltration membrane was found to be 1.45 and 0.38 mg/L, respectively. Mainly, NF5 and NF9 membranes successfully removed higher amounts of divalent anions from water but smaller ions could be removed more effectively in comparison to others. The reason behind this could be the salvation energy of smaller ions. Results also revealed that chlorine ions penetrate the NF5 and NF9 nanofiltration membrane faster than fluoride. BW30 and NF90 nanofiltration membrane can successfully eliminate fluoride, reducing the concentration from 417.9 to 1.5 mg/L (Shen and Schäfer 2014). According to the reports, calcium carbonate is the main fouling component on membranes of nanofiltration. Recovery of nanofiltration membranes could be achieved by using the citric acid and ammonia cleaning method (Wei‐fang et al. 2009).
2.5.3.7 Electrocoagulation
Electrocoagulation (EC) is another filtration method removing suspended solids (fluorides) to μm level from water (Noling 2004). Electrocoagulation is a type of electrolytic method in which metallic cation synthesis occurs at sacrificial anodes (Kobya et al. 2016). The electrocoagulation utilization has been enhanced in the last decade. This method is introduced as one of the suitable methods for elimination of fluoride from contaminated drinking water. It can effectively remove a wide range of pollutants such as oil, heavy metals, dye, and fluoride (Hu et al. 2005; Malakootian et al. 2011). The electrocoagulation method does not release secondary pollutants and retain beneficial components of raw water during defluoridation. According to the report of Sinha et al. (2012), the electrocoagulation successfully eliminates fluoride and aluminum simultaneously under the condition of 230 V DC using aluminum electrodes. Better fluoride removal from drinking water can be achieved by providing longer retention time. One of the most important parameters in this method is charge loading for controlling EC reaction rates that ultimately decides coagulation rates (Kobya et al. 2016). The fluoride depletion and charge loading performance do not have a linear relationship. Despite being the important parameter for EC, charge loading is not considered a critical parameter in fluoride removal from drinking water. Enhanced charge loading reduces fluoride concentration initially in treated water, whereas after a critical point the fluoride concentration decrease was not significant (Sinha et al. 2012). The electrocoagulation method releases less aluminum from water in comparison to the active aluminum process and the Nalgonda technique. Data revealed that aluminum concentration in treated water is enhanced when input energy has been enhanced (Sinha et al. 2012). From steel industry wastewater, successful removal of fluoride has been done using the electrocoagulation method. The fluoride removal has been optimized under several conditions like “hydraulic retention time, pH, temperature, voltage, number of aluminum plates between anode and cathode to assess the performance of this method. Results revealed that increase in hydraulic retention time by 5 min shows enhanced fluoride removal performance”. The concentration of fluoride reduces from 4 to 6 mg/L to less than 0.5 mg/L (Khatibikamal et al. 2010). According to the study of Emamjomeh and Sivakumar (2006) the performance
