Defluoridation of drinkable water “Comparative study and parameter influent”

El-Oued is known for some diseases caused by fluoride concentration in drinkable water. To reduce it, a sample with the biggest content among many sources was chosen. A comparative study between the precipitation with calcium salts [Ca(OH) 2 , CaCl 2 , CaSO 4 ] and the coagulation with the following salts [Al 2 (SO 4 ) 2 ·18H 2 O, Fe 2 (SO 4 ) 2 ·H 2 O, FeSO 4 ] was done. Finely we studied the parameters influencing (the mass , pH, temperature) to choose the best conditions in order to get better reduction yield.


INTRODUCTION
The concentration of fluoride in drinkable water depends on the geological characteristics, and chemical properties of rocks and climate of the region. Fluoride content in the groundwater of northern Algerian desert often exceeds the world Health Organization standards, which indicated that the consumption of high fluoride water for long periods causes health complications from discolored teeth to fluoride poisoning bone. When concentration between (0.5-1.5 mg / l), it gives good protection against tooth decay, and if it exceeds 1.5 mg / l, defect occurs in teeth enamel but at a concentration between 4 and 8 mg / l, it leads to the risk of fluorosis skeletal [1]. The water of El Oued is characterized by high concentrations of fluoride, associated with severely high and excessive total mineralization. This water is the only source of drinking. The hot and dry climate has forced people to consume a lot of water which leads to raise the daily consumption rate of fluoride, in addition the large consumption of dates and tea leads to the spread of fluorosis disease which is characterized by the yellowish of tooth enamel according to the classification of the national program of school health [2,3]. To prevent these diseases from happening or reduce them, many defluoridation techniques are used such as: membrane technologies, precipitation and adsorption. A comparative study between precipitation and coagulation has been done with different salts, then determination of optimal conditions of factors affecting the reduction of fluoride in the studied water.

1. Preparation of curve witness fluoride
To determine the concentration of fluoride in Various samples, a potentiometer method was used (Rodier2005) [4]. Different standard concentration solutions were prepared from NaF salt in cups of plastic. Then their potential are measured by using specific fluoride pole (ISE15381/1) and a pH-meter model (pH211), using a solution of TISAB (12) . The graph E = f (log C F ) is presented in Figure 1.

Determination of fluoride concentration in some samples of the study area
The concentration of fluoride has been determined in some water sources of the study area in order to determine and treat the largest content of fluoride. The results are presented in Table 1. The selected sample (cold water of Shuhada) has a concentration of fluoride 2.61 mg / l.

3. Determination of the predominant concentration of ions in the studied water
The study was done according to (Rodier2005) [4] on cold water of Shuhada as follows:

4. 1. 1. Effect of cathion concentration
Based on the adsorption of Fˉ on both Al(OH) 3 and Fe(OH) 3 according to equilibriums (1), (2), (3) and (4) [8][9][10]. 100 ml of Shuhada water was put in each cup of plastic then the pH and temperature T were measured, after that different amount of the same salt was added to each cup. After stirring for three minutes, they are left for a while then filtered, finally the amount of fluoride in the filtrate was measured. The results were presented in Table 3.

2. 1. 2. Effect of pH
Based on the adsorption of fluoride ion on cathion hydroxides [Al(OH) 3 and Fe(OH) 3 ] which is related to the pH of the studied water according to equilibriums (5) and (6) for Al 3+ [8], equilibriums (7) and (8) for Fe 3+ [9] and equilibrium (9) for Fe 2+ [10]. We repeat the same steps of the previous experiment as mentioned in (2.4.1) by fixing the temperature and the added optimal concentration of each cathion separately but changing the pH by buffer solutions. The results are presented in Figure 2 and Table 4.

2. 1. 3. Effect of temperature T
The same steps of the experiment are repeated as mentioned in (2.4.2) by fixing the concerned added salt and the optimal pH, but changing the temperature. The results were presented in Table 5 and Figure 3 [5].

4. 1. Effect of calcium concentration
Based on the precipitation of fluoride in the form of CaF 2 ,low soluble according to equilibrium (10). 100 ml of Shuhada water was put in each cup of plastic then the pH and temperature T were measured, after that different amount of the same salt was added to each cup. After stirring for three minutes, they are left for a while then filtered, finally the amount of fluoride in the filtrate was measured. The results were presented in Table 6 and Figure 4.

4. 2.Effect of pH
Based on displacing the equilibrium towards the precipitation of fluoride in the form of CaF 2 according to the relation (1). We repeat the same steps of the previous experiment as mentioned in (2.4.1) by fixing the temperature and the added optimal concentration of either CaSO 4 , CaCl 2 and Ca(OH) 2 ,but changing the pH by buffer solutions. The results are presented in Table 7 and Figure 5. Table 7. Relation between the pH and the residual fluoride  International Letters of Chemistry, Physics and Astronomy Vol. 15

4. 3. Effect of temperature T
Based on displacing the equilibrium towards the precipitation of fluoride in the form of CaF 2 according to the relation (1). We repeat the same steps of the previous experiment as mentioned in (2.4.1) by fixing the pH and the added optimal concentration of either CaSO 4 ,CaCl 2 and Ca(OH) 2 ,but changing the temperature by buffer solutions. The results are presented in Table 8 and Figure 6 [5].

1. Coagulation
 According to the results of Table 2 we observe that the high concentrations of (Ca 2+ , Mg 2+ , SO 4 2ˉ, Clˉ) exceed the WHO (10) standards of water . This related to the geological characteristics and the structure of rocks .  According to the results of Table 3 , defluoridation by the use of Al 2 (SO 4 ) 3 is the best. This can be explained by the adsorption of fluoride on the flocks of Al(OH) 3 (equilibrium 1). The optimal concentrations of cathions resulting from both Al 2 (SO 4 ) 3 ·18H 2 O, Fe 2 (SO 4 ) 3 ·H 2 O and FeSO 4 are 0.0024 g/l , 0.08 g/l and 1.55 g/l respectively.  According to the results of Table 4, the optimal pH resulting by the addition of both Al 2 (SO 4 ) 3 ·18H 2 O, Fe 2 (SO 4 ) 3 ·H 2 O and FeSO 4 are 8.0, 7.6 and 7.5 respectively.  According to the results of The optimal conditions for coagulation by the previous salts are presented in Table  9.

2. Precipitation
 According to the results of Table 7, defluoridation by the use of Ca(OH) 2 is the best. This can be explained by the precipitation of CaF 2 (equilibrium 10) and the adsorption of fluoride on the flocks of Mg(OH) 2 which is formed according to the equilibrium (11) [6]. The optimal concentrations of Ca 2+ resulting from both Ca(OH) 2 , CaCl 2 and CaSO 4 are 0.054 g/l, 3.6 g/l and 0.93 g/l respectively.  The results of Table 8 indicate that the concentrations of residual fluoride are decreased when the values of pH are increased. The use of Ca(OH) 2 is the best because it has a basic nature which rise the pH of the solution. As a result, the concentration of residual fluoride is decreased which is fitted to equation (4). The optimal pH resulting from both Ca(OH) 2 , CaCl 2 and CaSO 4 are 7.40, 8.00 and 8.00 respectively.

ILCPA Volume 15
 The results of Table 9 indicate that the concentration of residual fluoride are decreased when the values of temperature are increased which is not expected theoretically, but fits to the results reached by (SAOUD 2009) [5]. The optimal temperatures resulting from both Ca(OH) 2 , CaCl 2 and CaSO 4 are 22 °C, 29 °C and 22.4° crespectively. The optimal conditions for precipitation by the previous salts are presented in Table 10.

CONCLUSIONS
 According to this study on the water of some region of El-Oued, it appear that most of them Contain a high quantity of fluoride exceeds the standard value of (WHO) (10) with a high total hardness.
 This lead us to look for the best way to reduce the amount of fluoride by comparative study between precipitation and coagulation treatments suit the characteristics of the studied water .
 Through this research, it appear that the precipitation is better the coagulation for the defluoridation of water.
 The present investigation indicates that reducing fluoride from water by using Ca(OH) 2 is economic and decreases the hardness of the treated water .
 Through the study of factors affecting (concentration, pH, temperature) it is possible to choose the best conditions for a reduction process with Ca(OH) 2 by adding an amount at a concentration of 0.1 g/l, pH = 7 and a temperature of 22 °C. International Letters of Chemistry, Physics and Astronomy Vol. 15 59 [Fˉ] Fe 2+ (   7   ) : concentration of fluoride residual after adding FeSO 4 to water. MO (8) : methyl orange Ph.Ph (9) : phenolphthalein TA (10) : alkalimetric title TAC (11) : The complete alkalimetric title. TISAB (12) : total ionic strength adjustment buffer WHO (13) : World Health Organization.