fluoride removal from aqueous solutions using ...

© by PSP Volume 24 – No 4. 2015

Fresenius Environmental Bulletin

FLUORIDE REMOVAL FROM AQUEOUS SOLUTIONS USING MORINGA OLEIFERA SEED ASH AS AN ENVIRONMENTAL FRIENDLY AND CHEAP BIOSORBENT Sina Dobaradaran1,2,3,*, Maryam Kakuee4, Iraj Nabipour5, Abdolrahim Pazira4, Mohammad Ali Zazouli6, Mozhgan Keshtkar2 and Maryam Khorsand4 1

The Persian Gulf Marine Biotechnology Research Center, Bushehr University of Medical Sciences, Bushehr, Iran Department of Environmental Health Engineering, Faculty of Health, Bushehr University of Medical Sciences, Bushehr, Iran 3 Systems Environmental Health, Oil, Gas and Energy Research Center, Bushehr University of Medical Sciences, Bushehr, Iran 4 Islamic Azad University, Bushehr Branch, Iran 5 The Persian Gulf Tropical Medicine and Infectious Research Center, Bushehr University of Medical Sciences, Bushehr, Iran 6 Department of Environmental Health Engineering, Faculty of Health, Health Sciences Research Center, Mazandaran University of Medical Sciences, Sari, Iran 2

ABSTRACT Adsorption is considered as the most promising treatment technology for fluoride (F) removal from aqueous solutions. The aim of this study was to determine the efficiency of seed Moringa oleifera ash in removal of F from aqueous solutions. After determining optimum pH (pH=7) and ashing temperature (650º C) by pretests, the adsorption experiments were studied in batch systems at room temperature. The effects of experimental parameters such as adsorbent dose (0.8 – 64 g/l), contact time (5 -120 min) and initial F concentration (2 -8 mg/l) were studied. The highest removal adsorption was at 64 g/l adsorbent, 10 min contact time and initial F concentration at 8 mg/l (81.14 % F removal). The results showed that the Moringa Oleifera ash can be used as an environmental friendly, cheap and effective adsorbent from aqueous solutions.

KEYWORDS: Moringa oleifera seed; biosorption; Fluoride removal; Environmentally friendly.

fects in soft tissues [4-7]. With view to the special concerns of F, various studies have been done in relation to F concentrations in drinking water, air, tea, fish, and sea as well as in connection with its removal from high-F waters [6-23]. Different methods such as adsorption, precipitation, ionexchange, electro-dialysis and electro-chemical, were developed to remove extra F from water [24] that among these processes, adsorption is a widely used method for F removal of water [25]. Currently, considerable interests were observed on the utilization of biosorbent materials for removal of different pollutants [26]. Biosorption advantages over conventional treatment methods include low cost, less sludge production, high efficiency in dilute effluents, no nutrient needs, regeneration of biosorbent, and environmental favorable and economical viable [26-27]. Moringa oleifera is grown in tropical areas and has been consumed as food in some African regions. The Coagulating demeanor of its seed powder has been studied for different aspects of water treatment such as turbidity, alkalinity, total dissolved solids and hardness [28] but very small studies have been directed towards its sorption demeanor for the removal of pollution from water. In the present study, the efficiency of Moringa oleifera seed as a biosorbent for F removal of aqueous solution was studied and the results can be useful in areas suffering from high F levels that mainly located in rural and remote areas.

1. INTRODUCTION In the environment, fluoride (F) occurs naturally through the earth’s crust and anthropogenic activities such as steel, semiconductor, electroplating, aluminum, bricks, glass, ceramic and fertilizers industry. These industries play an important role in increasing water pollution by F [1-3]. F can cause a wide range of adverse health effects including teeth and damaging and bone, as well as adverse health ef* Corresponding author

2. MATERIALS AND METHODS 2.1 Adsorbent preparation

After collection and transfer to laboratory, the Moringa oleifera seeds were washed by tap water and then two times washed by distillated water to remove sand, clay, and other impurities. The washed Moringa Oleifera seeds were heated in an oven at 650 ˚C, and finally ground and sieved through a 0.71mm screen.

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value of 7 has been selected as the optimum pH to perform all experiments.

2.2 Batch studies

A stock solution of 100 mg/L F was prepared by dissolving sodium fluoride (NaF) in ultrapure water. F solutions were prepared at 2, 3, 5 and 8 mg/L concentrations. At each stage of the experiments, 100 ml of F solution with a specific initial F concentration at neutral pH (pH=7) was agitated at 120 rpm. The effects of five contact times (5, 10, 25, 60, and 120 min), four initial F concentration (2, 3, 5, and 8 mg/L), and various ratios of bio-sorbent to the F levels (five ratios within the range of 400-8000) were investigated in the batch experiments. The standard SPANDS method was used by using a spectrophotometer (Model CAM Spec M501) for analysis of the remaining F concentration in the aqueous solution after each run.

3.2 Effect of ashing temperature

In order to determine the optimal activation temperature for adsorbent, pretests of the experiment were performed at different temperatures (350, 450, 500, 550, 600, 650˚C), two adsorbent doses (1, and 2 g/L), three contact times (30, 45, and 60 min), and initial F concentration of 2 mg/L. The results showed that by increasing temperature, the F removing efficiency will be increased so 650˚C temperature was selected as the ashing temperature to perform all experiments. 3.3 Effect of adsorbent dose

The effect of biomass dosage on the F removal by adsorbent was studied using various biomass doses of Moringa oleifera seed in the range of 2– 40 g/L (Fig. 1). The results showed that the adsorption efficiency depend on the increasing biomass dosage in the solution. The maximum adsorption of F was obtained at biomass dosage of 30 g/L. This trend could be elucidated as a consequence of a partial compression of biomass at higher biomass concentration, which results in a decrease in effective surface area for the adsorption [31]. Similarly, Jagtap et al. [32] found that F removal capacity distinctly increases from 19 to 81.98% with the increasing adsorbent dosage from 0.2 to 1 g/L and after a dose of 1 g/L there was no significant improvement in the F removal. In another study, Dobaradaran et al. [20] reported that for an initial F level of 8 mg/L, the F removal

3. RESULTS AND DISCUSSION 3.1 Effect of pH

The effect of pH on F adsorption in a range from 5 to 11 (5, 7, 9, 11) was investigated as pretests. In the pretest experiments, adsorbent dose of 2 g/L, contact time of 35 min and initial F concentration of 2 mg/L were used to determine the effect of pH. The results suggested a pH value of 7 as the best pH value for removal of F by Moringa oleifera seed. Decrease in F removal at lower pH value in this study (pH=5) may be due to the formation of the weakly ionised HF (pKa = 3.2) and because of the competitiveness of the OH− and F− ions at higher pH values (pH values of 9 and 11) [24]. The same results have been reported for F removal by different adsorbents [24, 29, 30]. Therefore a pH

100 90

Removal efficiency (%)

80 70 60

5 min

50

10 min

40

25 min

30 60 min

20 10 0 0

5

10

15

20

25

30

35

40

Biomass dosage (g/l) FIGURE 1 - F adsorption as a function of adsorbent dose (initial F concentration = 5 mg/L).

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100

Removal efficiency (%)

90 80 70 60

2 mg/l

50

3 mg/l

40

5 mg/l

30

8 mg/l

20 10 0 0

20

40

60

80

100

120

Time (min) FIGURE 2- F adsorption, using a fixed mass ratio of biosorbent to initial F concentration, as a function of initial F concentration (g L-1 biomass/g L-1 F=1000)

percentage increased with increasing shrimp shell waste dose as biosorbent from 3.2 g/L to 64 g/L but there were no significant differences in the F removal percentage between adsorbent doses of 48 and 64 g/L. Sivasankar et al. [24] examined F removal with MnO2-coated Tamarind Fruit (Tamarindus indica) shell at various doses and observed that the percentage removal increased with increasing dosage of the adsorbent and then remained constant. In contrast, Thakre et al. [33] reported that biomass dosage chitosan has no significant F removal capacity.

where qe is the mass of F adsorbed per unit weight of the sorbent (mg/g), kF is the Freundlich capacity factor and a measure of adsorption capacity, 1/n is the Freundlich intensity parameter, and Ce is the equilibrium concentration of F in solution (mg/l) after adsorption. The linear plot of log qe vs log Ce show the applicability of Freundlich isotherm. The values of 1/n and kF for the sorbent were accounted from the slope and the intercept of the linear plot of log qe vs log Ce. The Langmuir adsorption isotherm is defined as:

3.4 Effect of contact time and initial F concentration

The effect of initial F concentration on the removal of F is shown in Fig.2. It was observed that by increasing the F concentration from 2 to 8 mg/L the removal efficiency increased from 33.14 to 80.84 percent. This could be due to high adsorption capacity of Moringa olifera ash. Viswanathan et al. [29] and Mahramanlioglu et al. [34] reported similar results in the defluoridation of aqueous solutions by protonated chitosan beads and poly aluminum chloride, respectively. In contrast, Ramanaiah et al. [35] found that the removal efficiency of F by waste fungus decrease with increasing initial F concentration.

qe =

(3)

and can be rewritten as [30]:

(4)

where qe is the mass of F per unit mass of sorbent (mg/g), qmax is the monolayer sorption capacity, b is the Langmuir constant related to the free energy of sorption equilibrium concentration of F in solution (mg/l) after adsorption. The Langmuir constant can be determined by versus Ce. plotting

3.5. Sorption isotherms

To quantify the sorption capacity of Moringa Oleifera for the removal of F from aqueous solutions, two usually used isotherms like Freundlich and Langmuir have been adopted. The Freundlich isoterm can be written as: qe= kf ce1/n

3.6.1. Biosorption kinetics and modeling

(1)

and written in linear form as [30]: log qe = log kF +

logCe

Figure 3 shows that Langmuir model is better fitted than Freundlich model. Langmuir isotherm assumes monolayer adsorption on homogenous flat surface; due to the greater tendency of F to be adsorbed onto the adsorbent surface instead undergo heterogeneous adsorption.

(2)

The sorption kinetics is important in the treatment of aqeous solution, as it presents valuable insights into reacion and mechanisms of sorption reactions. The experimental biosorption kinetic were defined by using pseudo-

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FIGURE 3- (a) Freundlich and (b) Langmuir isotherm investigation of F adsorption by Moringa Oleifera.

FIGURE 4- (a) Pseudo-first-order model and (b) Pseudo-second-order model of F adsorption by Moringa Oleifera.

first and pseudo-second- order kinetics. These kinetics can be represented in their nonlinear forms, as follows: Pseudo-first- order model, log(qe − qt ) = log qe −

,

.

t,

(5)

Pseudo-second- order model, ,

+ ,

(6)

Where qe is the mass of solute sorbed at equilibrium (mg/g), qt the mass of solute sorbed at time t (mg/g), K1 the first-order equilibrium rate constant (g/g/min), and K2 is the second-order equilibrium rate constant (g/g/min). The first-order equilibrium rate constant (K1) for F sorption was calculated from the slop of the linear plot of log (qe − qt) versus time. In the case of the seconed-order equilibrium rate constant (K2), kinetic data were plotted between t/qt against time. As show in Fig.4, it can be concluded that F sorption onto Moringa Oleifera seed ash seems to be pseudo-second- order.

4. CONCLUSION Biosorption is an effective method for removal of excess F from water or wastewater. This study showed that Moringa Oleifera seed ash is a suitable adsorbent for the removal of F from aqueous solutions. The removal percentage of F was in the range of 7.23 –81.14 % and it was depended on the initial F concentration, pH, ashing temperature, contact time and the biomass dosage. The highest removal was reached only after 10 min contact time in optimum operation condition. The applied biosorbent in this study, Moringa Oleifera seed, is easy to source, inexpensive, and renewable. Finally, it should be noted that Moringa Oleifera seed can be used as an environmental friendly, effective and cheap adsorbent for removal of F from water especially in rural and remote areas due to its easy operation as well as it can be used for removal of F from industrial effluent containing high level of F.

ACKNOWLEDGMENTS The authors are grateful to the Bushehr University of Medical Sciences for their financial support.

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[18] Ostovar, A. Dobaradaran, S. Ravanipour, M. Khajeian, A. (2013) Correlation between fluoride level in drinking water and the prevalence of hypertension: an ecological correlation study. Int J Occup Environ Med 494, 216-7.

The authors have declared no conflict of interest.

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Received: August 10, 2014 Revised: October 28, 2014 Accepted: December 08, 2014

CORRESPONDING AUTHOR Sina Dobaradaran The Persian Gulf Marine Biotechnology Research Center Bushehr University of Medical Sciences Faculty of Health Department of Environmental Health Engineering Bushehr IRAN Phone/ Fax: +987733450134 E-mail: [email protected] FEB/ Vol 24/ No 4/ 2015 – pages 1269 - 1274

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