Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation

Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation

Journal Pre-proof Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation Daisy Das, Barun Kumar Nandi PII: S2213...

3MB Sizes 1 Downloads 56 Views

Journal Pre-proof Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation Daisy Das, Barun Kumar Nandi

PII:

S2213-3437(19)30766-3

DOI:

https://doi.org/10.1016/j.jece.2019.103643

Reference:

JECE 103643

To appear in:

Journal of Environmental Chemical Engineering

Received Date:

9 October 2019

Revised Date:

3 December 2019

Accepted Date:

27 December 2019

Please cite this article as: Das D, Nandi BK, Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation, Journal of Environmental Chemical Engineering (2019), doi: https://doi.org/10.1016/j.jece.2019.103643

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Simultaneous removal of fluoride and Fe (II) ions from drinking water by electrocoagulation Daisy Das, Barun Kumar Nandi Department of Fuel and Mineral Engineering Indian Institute of Technology (Indian School of Mines), Dhanbad

Jo

ur

na

lP

re

-p

ro of

Dhanbad: 826004, Jharkhand, India.

*Corresponding author: E-mail: [email protected]; [email protected]; Phone: +91 3262235139; Fax: +91 3262296563

1

Graphical Abstract

DC Source

+

+

-

100

Removal efficiency of Fe(II) and Fluoride

Al Cathode

+

Al Anode

+

Simultaneous removal of Fe(II) and fluoride ion by EC

60 min EC

-

80 70 60 50

Ideal condition:

40

-1

Initial Fe(II) concentration: 20 mg L -1 Initial fluoride concentration: 10 mg L -2 Cd: 4.31 mA cm , Id : 1 cm

30 20

ro of

Al3+

Fe(II) Fluoride

90

H2O= H+ + OH-

-1

pH : 7, Csi : 0.33 g L

10

0

0

10

20

30

40

50

60

Time (min)

Treated water

+

+

lP

re

-p

TDS: 75 mg L-1, Conductivity: 685 µs cm-1, Turbidity: 0.18 NTU, Salinity: 121 mg L-1 pH: 7.64

na

Abstract

Present work reports experimental investigations on simultaneous removal of fluoride

ur

and Fe (II) ions from drinking water by electrocoagulation (EC) with aluminium electrode having submerged electrode surface area of 116 cm2. During experimental studies, effects of

Jo

pH, current density (Cd), inter-electrode distance (Id) and NaCl dose (Csi) were investigated to identify their influence on fluoride and Fe(II) ions removal efficiency. Experimental results infer that pH of 7.0, Cd of 4.31 mA cm-2, Id at 1.0 cm and Csi of 0.33 g L-1 are ideal for highest removal of fluoride and Fe(II) ions from water. Overall, 96% of fluoride ions and 98.88 % of Fe(II) ions were removed after 60 min of EC. Further it was observed that, presence of Fe (II) increases fluoride removal efficiency and fluoride ions increases Fe (II) removal efficiency. 2

Different other impurities of water such as salinity, TDS, conductivity, turbidity were also decreased in treated water. Kinetic analysis infers that, for same operating condition Fe (II) removal rate (k=0.0766 min-1) is higher compare to fluoride removal rate (k=0.0535min-1). Present study confirmed that EC is an efficient method for simultaneous removal of fluoride and Fe(II) ions along with other impurities with energy consumption of 1.716 KWh m-3. Keywords: Fluoride ion; Fe(II) ion; drinking water; electrocoagulation; aluminium electrode.

ro of

1. Introduction: Groundwater is considered as safe source of drinking water in India and in nearby countries. Various metallic and non-metallic ions like fluoride, iron, magnesium, calcium,

-p

sodium etc. with varying concentration are found in such ground water [1, 2]. Among such ions, fluoride and Fe(II) ions are considered more harmful compared to other ions above certain

re

limit. Such contamination of metallic and non-metallic ions in water bodies occur mainly due

lP

to weathering and erosion of mineral-bearing rocks, disposal of untreated industrial wastewater and human activities [1, 3]. Occurrence of such multiple harmful ions like fluoride and Fe(II) ions in ground water are serious health concern when used for direct consumption, irrigation,

na

industrial and other applications. According to WHO guidelines (summarized in Table 1) maximum 1.5 mg L-1 of fluoride ions and 0.3 mg L-1 of Fe(II) ions are permissible in drinking

ur

water [4]. Consumption of fluoride laden water above 1.5 mg L-1 prompts to several health

Jo

issues like dental and skeletal fluorosis, osteoporosis, problem in organs like lungs, nerves, kidney etc. However, consumption of fluoride between 0.5 to 1.0 mg L-1 helps in preventing dental caries and teeth deteriorations [1]. Although iron is categorized as secondary pollutant its presence in higher concentration leads to different issues like discolouration, aesthetic taste and odour, turbidity and even iron overload in some cases [5]. In rural areas as well as cities, metropolitan areas, motorized pumps are used to lift ground water to overhead tanks, which

3

further sent to domestic tap water supply network without any treatment [6]. Hence it is necessary to treat such contaminated tap water for making it drinkable. As reported by WHO, India and China has suffered severe health issues due to high fluoride contamination and almost 2.7 million population of China suffered from fluorosis in the year 2012 [2]. Similarly, Fe(II) ion contamination is a prevailing problem faced by consumers in daily life [1]. In ground water of many places, along with Fe (II) ions and fluoride ions other impurities such as TDS, salinity and turbidity exceeding WHO permissible limits (as summarized in Table 1) are also present.

ro of

Ground water contaminated with both fluoride and Fe (II) ions are extremely harmful and difficult to treat by conventional methods as optimum operating conditions for one pollutant may not be enough for removal of other pollutants. Hence, simultaneous removal of fluoride

-p

and Fe (II) ions along with other impurities from ground water needs greater attention for future water resources management, planning and development.

re

Till date significant amounts of research work have been carried out by various

lP

researcher on removal of fluoride ions as well as Fe(II) ions from water by coagulation [7], adsorption [8], membrane filtration [9], ion exchange [10], electro-chemical oxidation [11], electrofloatation [12] and electrocoagulation (EC) [1-2, 13-15] have been reported in literature.

na

Among all such methods, coagulation, adsorption, ion exchange and chemical precipitation are highly pH-sensitive, require large amount of chemicals and may generate significant amount

ur

of sludge. Similarly, membrane filtration, reverse osmosis, ion exchange demands longer

Jo

treatment time, higher operating cost and skilled manpower to operate the equipment. In this context, EC has become a promising technique in removing different types of pollutant over other conventional methods. EC has many inherent advantages such as minimum chemical consumption, faster removal rate, cost-effective and higher pollutant removal efficiency [1, 2, 15-16]. In EC process, among various electrode materials, aluminium (Al) is widely used as electrode material depending upon the types of the pollutant [16]. Considering the fact that,

4

groundwater is contaminated with fluoride and Fe (II) ions along with high TDS, salinity and turbidity, EC may be an effective methods for ground water purification. Although, significant number of research work has been published on removal of fluoride ions, Fe(II) ions as a single pollutant using EC as well as other methods, till date no research has been reported on simultaneous removal of fluoride and Fe(II) ions from drinking water. Such studies are necessary to identify the influence of other co-existing ions on fluoride and Fe(II) ions removal from drinkable tap water.

ro of

Present work reports experimental investigations on simultaneous removal of fluoride and Fe (II) ions from drinking water by EC with aluminium electrode. Experimental investigations has been carried out to identify the influence of different parameters of EC like

-p

current density (Cd), inter-electrode distance (Id), initial pH, solution conductivity (Csi) on removal of fluoride and Fe (II) ions. Further, turbidity, TDS, salinity and conductivity of water

) during the process was also analysed to estimate the cost effectiveness of EC. Kinetic

lP

3

re

have been also studied to confirm the quality of treated water. Energy consumption (KWh m-

analysis of EC process has been carried out for a detailed understanding on importance of operating parameters of EC. Such study will be extremely helpful in evaluating the influence

na

of coexisting ions present in groundwater on removal efficiency of fluoride and Fe(II) ions by EC.

ur

2. Fluoride and Fe (II) removal mechanism by EC

Jo

In EC process, Al3+ and OH- ions are produced by various electrochemical reactions to generate numerous monomeric and polymeric hydroxyl metallic compounds and further they hydrolyses as amorphous Al(OH)3(S) [2]. These freshly produced metal hydroxide complexes have a strong affinity to adsorb the pollutant ions (fluoride and Fe(II) ions in the present study) as they are electrified in nature and having large surface area and eventually separated as sludge at the bottom of the reactor after undergoing flocculation, adsorption, coagulation and co-

5

precipitation [15, 17]. Various reaction during fluoride and Fe(II) ions removal are summarized as follows [14, 18, 19]: (1)

2𝐻2 𝑂 + 2𝑒 → 𝐻2 + 2𝑂𝐻 −

(2)

𝐴𝑙 3+ + 𝐻2 𝑂 → 𝐴𝑙(𝑂𝐻)2+ + 𝐻 +

(3)

+ 𝐴𝑙(𝑂𝐻)2+ + 𝐻2 𝑂 → 𝐴𝑙(𝑂𝐻)+ 2 +𝐻

(4)

+ 𝐴𝑙(𝑂𝐻)+ 2 + 𝐻2 𝑂 → 𝐴𝑙(𝑂𝐻)3(𝑠) + 𝐻

(5)

− Al(OH)3(s) + nF − → Al(OH)3−n Fn(s) + nOH −

(6)

ro of

𝐴𝑙 → 𝐴𝑙 +3 + 3𝑒

In the presence of OH- ions, between pH 7 and 14. Fe(II) ions hydrolyses to form various mononuclear species of FeOH+ to Fe(OH)4−2 which gets precipitates [13] along with

-p

Al(OH)3(s) flocs and removed from water.

re

To understand the removal mechanism of both the contaminants, kinetic analysis was done with different initial concentration of fluoride ions and Fe(II) ions. Removal of fluoride and

lP

Fe(II) ions were found to follow first-order kinetic models as [18, 19] 𝑑𝐶 𝑑𝑡

= −𝑘𝐶

(7)

na

After integration, Eq (7) can be modified as 𝐶

𝑙𝑛 𝐶 = −𝑘𝑡

(8)

𝑜

ur

Where C0 is the initial concentration of fluoride/ Fe, C is the concentration at any time t. Rate 𝐶0 𝐶

vs t plot.

Jo

constant k (min-1) value can be obtained from 𝑙𝑛 3. Experimental

Batch EC experiments were carried out using a 5L cylindrical glass reactor of 25 cm

height and 14 cm diameter filled with 3L of fluoride and Fe(II) ions contaminated water at room temperature ( ̴ 25ºC). A pair of aluminium (Al) electrode (thickness: 1 mm; width: 58 mm; length: 100 mm), submerged electrode surface area of 116 cm2, Id of 1.0 cm in monopolar 6

mode has been used. A DC power source (0-10 A, 0-30V) of APLAB India was used to provide the necessary electrical energy. Fluoride and Fe(II) contaminated water with desired ion concentration were prepared by diluting the analytical grade sodium fluoride salt (NaF) (Fisher Scientific) and iron sulphate heptahydrate salt (FeSO4.7H2O) salt (Merck India) in tap water which was connected to overhead tank which was filled by ground water using motorized pump. To adjust the conductivity and pH of the solution, sodium chloride (NaCl) and 1N NaOH /1N HCl were used as required. For uniform mixing of EC generated flocs and water, solution

ro of

was agitated at 200 RPM (corresponding Reynolds No 5200 [18]) using a magnetic stirrer of TARSON India. Before conducting each EC experiment, Al electrodes were rubbed using sand paper and then dipped into diluted sulphuric acid and finally rinsed with water and acetone

-p

successively to remove the impurities on its surface and weighed to calculate metal loss during EC. To increase accuracy of experimental data, all the experiments were repeated for minimum

re

three times and average values are described here. During EC experiments, approximately 5-7

lP

mL of treated sample was collected at an interval of 10 min, filtered using Whatman 1 filter paper of 110 mm diameter and analysed. Concentration of Fluoride ion was measured using a fluoride ion selective electrode (EUTECH, India) after performing standard calibration using

na

standard fluoride solution. To avoid interference of other co-existing ions, fluoride ISA from ANTECH was mixed with water as per standard fluoride ion measurement procedure. Fe(II)

ur

ions concentration were measure using Atomic Absorption Spectrometer (AAS) of Thermo

Jo

scientific (model: iCE 3000 Series). AAS analysis was carried out with flame type of airacetylene at fuel flow rate of 0.9 L min-1 using the flame method after calibration with a standard iron solution for AAS of Reagecon. The concentration of fluoride and Fe(II) ions were varied from 0 to 25 mg/L and 0 to 50 mg/L respectively. These ranges of concentration were considered based on the contamination of these ions reported in different parts of India by various investigators in the recent years [19]. Ranges of other operating parameters considered

7

during the experiments are summarized in Table 2. Conductivity, pH, salinity, TDS, turbidity and resistivity of the water were estimated using digital multimeter (EUTECH India, PC2700) and turbidity meter (Thermo Scientific, EUTECH TN-100) respectively. Fluoride and Fe(II) removal efficiency was estimated using the following equation 𝑅𝑒𝑚𝑜𝑣𝑎𝑙(%) =

𝐶𝑖0 −𝐶𝑖 𝐶𝑖0

× 100

(9)

Where 𝐶𝑖𝑂 and 𝐶𝑖 are the initial and final concentration of the contaminants. Electric energy consumption (EEC) amid the EC was interpreted using the following equation 𝑣𝑜𝑙𝑡𝑎𝑔𝑒(Ù)×𝑐𝑢𝑟𝑟𝑒𝑛𝑡(ì)×𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛 𝑡𝑖𝑚𝑒(𝑡)

ro of

Energy consumption (Kwh/m3) =

𝐹𝑢𝑛𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 (˅)

-p

4. Results and discussions

(10)

4.1 Effect of initial pH on simultaneous removal of Fluoride and Fe (II) ions

re

To assess the effect of initial pH on simultaneous removal of Fe(II) and fluoride ions,

lP

pH of water was varied from 5 to 9. Figure 1 shows the removal efficiency of both fluoride ions and Fe(II) ions at different initial pH . From figure 1 it is observed that with increase in pH from 5 to 7, fluoride and Fe(II) ions removal increases from 88.45% to 96% and 98.54% to

na

98.88%, respectively. With further increase in pH from 7 to 9, fluoride and Fe(II) ion removal efficiency decreases to 81.89% and 86.04%, respectively. Highest removal efficiency of was

ur

for both fluoride and Fe(II) ions was observed at pH of 7 after 60 minutes of EC. Lower

Jo

removal efficiency at lower pH between 5 to 7 may be due to presence of excess of H+ ions in the solution which hinders production of Al(OH)3 and thus results in inadequate removal of fluoride and Fe(II) ions [2]. At higher pH of above 7, more than sufficient amount of hydroxide anions (OH-) are generated which prompts to the formation of stable insoluble aluminium hydroxide flocs [ Al(OH)3(s)] which tends to slow down the further coagulation process [2, 18]. Removal efficiency of Fe(II) ions was found to be higher compared to fluoride ions for all the

8

pH. This was due to the fact that Fe2+ions have more affinity towards Al(OH)3 flocs produced than fluoride ions and readily gets adsorbed. Moreover, due to presence of OH- ions in the solution, reduced Fe3+ ions tends to react with it and forms amorphous ferric hydroxide flocs which gets precipitates easily [14]. Table 3 represents the variation in conductivity, turbidity, TDS, salinity of the sample before and after 60 minutes of EC treatment and final pH of the solution after 60 min at various initial pH. It can be observed from Table 3 that when pH increased from 5 to 7, conductivity decreased from 740.6 µs cm-1 to 692.7µs cm-1, turbidity

ro of

decreased from 49.60±0.2 NTU to 0.24±0.02 NTU, TDS decreased from 285.06±1.0 mg L-1 to 80.10±1.0 mg L-1 and salinity decreased from 240.3 ±1.2 mg L-1 to 127.8 ±0.5 mg L-1 after 60 min of EC and the final pH slightly increased to 7.64±0.01. Any further increase in pH from

-p

7.0 results increase in values for all the parameters. For initial pH of 7, final values of all the parameters are lowest compared to the other pH values. This infers that pH 7 is ideal for

re

reduction of conductivity TDS, turbidity, salinity along with fluoride and Fe(II) ions. Overall,

lP

all the parameters i.e. conductivity, turbidity, TDS, salinity post-treatment was found to be within an acceptable range of drinking water quality as mentioned in Table 1. Also, the highest removal efficiency for both the ions was seen at pH 7. Considering all the above facts, further

na

experiments were performed at an initial pH of 7.

4.2 Effect of current density on simultaneous removal of Fluoride and Fe (II)

ur

Figure 2a and 2b shows the variations in removal efficiency of fluoride and Fe(II) ions

Jo

when Cd varied from 1.5 mA cm-2 to 12.93 mA cm-2 at constant initial concentration of 10 mg L-1 and 20 mg L-1, respectively. From Figure 2a it is observed that with the increase in Cd from 1.5 mA cm-2 to 12.93 mA cm-2, residual Fe(II) concentration decreases from 0.67 to 0.008 mg L-1 after 60 min of EC. Corresponding removal efficiencies varied from 96.66% to 99.99%. For similar current densities residual fluoride ions concentration decreases from 1.54 to 0.13 mg L-1 with corresponding removal efficiencies varied from 84.6% to 98.77%. For values of

9

Cd i.e., 1.5 to 2.0 mA cm-2, permissible limit of fluoride and Fe(II) ion concentration i.e. 1.5 mg L-1 and 0.3 mg L-1(WHO, 2004) was not achieved even after 60 min of EC. For Cd of 4.31, 8.62 and 12.93 mA cm-2 the permissible limit of fluoride and Fe(II) ion concentration was achieved after 60, 50, 30 min and 50, 40, 30 minutes of EC. With increase in Cd, fluoride and Fe(II) ion removal efficiency increases due to excessive dissolution of the sacrificial anode and high sweep coagulation process. Such phenomenon helps in faster entrapment of the contaminant ions by the flocs at higher Cd and enhances the ions removal process [18].

ro of

Moreover, it is also observed that Fe(II) ions are more easily removed than fluoride ions for the same Cd. This is due to the higher adsorption capacity of the aluminium hydroxide flocs towards Fe3+ ions. It is also to be noted that Cd controls other factors like sludge production,

-p

the energy consumption and operating cost of the EC.

Table 4 shows variations of conductivity, TDS, turbidity, salinity, final pH and energy

re

consumption for different Cd during EC. It is observed from Table 4 that for Cd of 4.31 mA

lP

cm-2, conductivity decreases from 740.6±1.5 µs cm-1 to 685±1.0 µs cm-1, turbidity reduces from 49.20±0.2 NTU to 0.18±0.01 NTU, TDS decreases from 285.06± 1.0 mg L-1 to 75.73±1.2 mg L-1 salinity reduces from 240.3±1.2 mg L-1 to 121.1±1.0 mg L-1, whereas pH is lightly increased

na

to 7.64±0.01. Similar trends were also observed for Cd of 1.5, 2.0, 8.62 and 12.93 mA m-2. Such decrease in conductivity, turbidity, salinity and TDS were due to simultaneous removal

ur

of other impurities like soluble solids, other ions etc. (expressed as TDS, turbidity, salinity etc.)

Jo

present in water during EC. Insignificant increase in pH of the supernatant was due to the rise in no of hydroxyl ions in water. With increase in Cd from 1.5 to 12.93 mA cm-2, energy consumption increases from 0.2668 to 13.9 KWh m-3. This was due to the fact that with increase in the applied current results in an increase in voltage also which leads to higher consumption of energy during the process. Considering all the factors, moderate Cd of 4.31 mA cm-2 was considered as ideal for further experiments as the suggested limit of Fe(II) ion (0.3

10

mg L-1) and fluoride ions (1.5 mg L-1) in drinking water according to WHO (as mentioned in Table 1) was achieved within 60 min of EC. 4.3 Electrochemical kinetics Figure 3a and 3b shows the first order plot corresponding to Eq. 4 for different Cd on removal of Fe(II) and fluoride ions. From Figure 3a it can be observed that as the Cd increases from 1.5 mA cm-2 to 12.93 mA cm-2, Fe(II) ion removal rate constant (k) increases from 0.0563 to 0.1739 min-1. Similarly from figure 3b, the rate constant for fluoride removal was found to

ro of

increase from 0.0317 to 0.0721 min-1 as Cd increases from 1.5 mA cm-2 to 12.93 mA cm-2. Increase in k with increase in Cd is due to higher availability of Al(OH)3 flocs in the solution, which leads to higher removal of Fe(II) and fluoride ions. Removal rate of Fe(II) ions is found

-p

to be higher compared to fluoride ions at all Cd due to better ionic attraction between Fe(II) ions and Al(OH)3 flocs as mentioned earlier. Based on the observed values of rate constant (k)

re

at different Cd for removal of Fe(II) and fluoride ions rate constant (k) for Fe(II) and fluoride

Eq.11 and 12 as

lP

ions at varying Cd are shown in figure 3c and found to follow linear equations summarized in

𝑘 = 0.0095. 𝐶𝑑 + 0.0385

For Fe(II) ions,

𝑘 = 0.0033. 𝐶𝑑 + 0.0319

na

For fluoride ions,

at Cd = 1.5 to 12.93 mA cm-2

(11)

at Cd = 1.5 to 12.93 mA cm-2

(12)

4.4 Effect of fluoride ions on Fe (II) ion removal

ur

To understand the influence of fluoride ions on Fe(II) ions removal, fluoride ions

Jo

concentrations were varied from 0 to 25 mg L-1, Fe(II) ions concentration were kept constant at 20 mg L-1 and results are shown in Figure 4a. It can be seen from Figure 4a that, presence of fluoride ion influences Fe(II) ions removal significantly. Fe(II) ions decreases from 20 mg L-1 to 0.384 mg L-1 at the end of 60 min of EC when fluoride ion was not added to the solution. But with addition of fluoride ions of 10, 15, 20 and 25 mg L-1, residual Fe(II) ions decreases to 0.223, 0.120, 0.0851 and 0.40 mg L-1, respectively. As fluoride ion concentration increased

11

from 0 to 25 mg L-1, the time required to reduce Fe(II) ions to permissible limit (0.3 mg L-1) reduces from 60 min to 40 min. This infers that presence of fluoride ion enhances the removal of Fe(II) significantly. Such phenomena can be explained based on removal mechanism of fluoride ions (Eqn. 6) which occurs by substitution of hydroxide groups present in Al(OH)3 flocs by the fluoride ions dissolved in the solution [2]. Moreover, removal of fluoride involves generation of higher amount of OH- which is observed from the experimental results (Table 5), as for higher dosage of fluoride concentration the final pH increases significantly. Such

ro of

increase in pH leads to increase in generation of Fe(OH)3 as precipitates and easily getting removed from solution [14]. As a result, removal rate of Fe(II) ions increases in present of fluoride ions. Figure 4b shows the first-order plot for Fe(II) ions removal with varying fluoride

-p

concentration. The rate constant (k) in min-1 for Fe(II) concentration of 20 mg L-1 for 0, 10, 15, 20 and 25 mg L-1 of fluoride ions are 0.0674, 0.0766, 0.0871, 0.0931 and 0.1055 min-1

re

respectively. This may be due to an increase in removal rate as a consequence of adequate

lP

entrapment of pollutant ions at constant Cd. The observed values of k for Fe(II) ion removal can be summarized in Eq.13 as:

𝑘 = 0.0019. 𝐶𝑓𝑙𝑢𝑜𝑟𝑖𝑑𝑒 + 0.0333

(13)

na

for Cfluoride = 0 to 25mg L-1

Table 5 demonstrates the conductivity, TDS, salinity, turbidity and final pH of the sample before and after treatment for the various concentration of fluoride. It is observed that increase

ur

in initial fluoride concentration from 0 to 25 mg L-1, the TDS and turbidity of the sample

Jo

increase from 275±1.2 to 298±1.0 mg L-1 and 47.20±0.2 to 53.90±0.3 NTU respectively. Such increase in TDS, turbidity were due increase in dissolved ions in the solution. Overall, TDS and turbidity values are within allowable limit of drinking water (Table 1). 4.5 Effect of Fe (II) ions on Fluoride ions removal To understand the influence of Fe(II) ions on fluoride ions removal, Fe(II) ions concentrations were varied from 0 to 50 mg L-1, fluoride ions concentration were kept constant

12

at 10 mg L-1 and results are shown in Figure 5a. It is observed from Figure 5a that, with increase in concentration of Fe(II) ions from 0 to 50 mg L-1, residual fluoride ion concentration decreases from 1.36 to 0.09 mg L-1. This results infers that presence of Fe(II) ions increases fluoride ions removal efficiency. Such increase in removal rate of fluoride ions in presence of Fe(II) ions can be explained by the formation of Fe(OH)3 flocs during EC due to presence of Fe(II) ions in the solution. Newly generated Fe(OH)3 flocs has larger surface area with higher adsorption capacity to entraps fluoride anion present in the solution due to sweep coagulation

ro of

[20]. As a result, overall fluoride ion removal increases in the presence of Fe(II) ions. Various reaction of ferric hydride flocs with fluoride ion is summarized as [20]: 𝐹𝑒 3+ + 3𝑂𝐻 − → 𝐹𝑒(𝑂𝐻)3(𝑠)

(14)

-p

3𝐹𝑒 3+ + (3 − 𝑥)𝑂𝐻 − + 𝑥𝐹 − → 𝐹𝑒(𝑂𝐻)(3−𝑥) 𝐹 ↓ 𝑦𝐹𝑒(𝑂𝐻)3(𝑠) + 𝑥𝐹 − → 𝐹𝑒(𝑂𝐻)(3−𝑥) 𝐹 ↓ +(𝑂𝐻)𝑥

(16)

re

𝑦

(15)

Figure 5b shows the first-order kinetic model for different concentration combination of

lP

fluoride and Fe(II) ions. The rate constant (k) in min -1 for various initial Fe(II) concentration of 0, 20,30, 40 and 50 mg L-1 are 0.2143, 0.3495, 0.4008, 0.4909 and 0.5251 min-1 respectively.

na

The rate constant is found to increase with the increase in dosage of Fe(II) ions as the removal becomes faster with increasing Fe ions. The observed value of k for fluoride removal at various

ur

Fe(II) concentration can be summarized as Eq.17 as: 𝑘 = 0.0064. 𝐶𝐹𝑒(𝐼𝐼) + 0.2174

for CFe(II) = 0 to 50mgL-1 (17)

Jo

Table 6 represents the conductivity, TDS, salinity, turbidity and final pH of the treated water at varying Fe(II) ions. It was observed from Table 6 that, with the increase in Fe(II) concentration from 0 to 50 mgL-1, the final TDS and turbidity increases slightly from 62.44±1.0mg L-1 to 79.90±1.5 mg L-1 and 0.17±0.02 NTU to 0.37±0.02 NTU, respectively. Such decrease in removal of both the parameters is due to increase in dissolved ions in the solution with higher amount of initial Fe(II) concentration. However, final values of all the 13

parameters are found to be within the permissible values as mentioned in Table 1 for all the cases. 4.6 Effect of inter-electrode distance on fluoride and Fe (II) ions removal To study the impact of inter-electrode distance on simultaneous removal of fluoride and Fe(II) ions in EC process, varying Id of 1, 1.5, 2 and 2.5 cm were considered and results are shown in Figure 6. It is observed from figure 6 that when Id increased from 1 to 2.5 cm, fluoride ions and Fe(II) ions removal decreases from 96% to 87.9% and 99.88% to 95.9%, respectively

ro of

after 60 min of EC. Corresponding residual fluoride and Fe(II) ions concentrations are 0.40, 0.81, 1.03, 1.20 mg L-1 and 0.23, 0.41, 0.61 and 0.80 mg L-1, respectively for Id of 1, 1.5, 2 and 2.5 cm after 60 min of EC. Decrease in fluoride and Fe(II) ions removal with increase in the

-p

Id is due to decrease in interaction between electrodes and less generation rate of Al(OH)3 flocs. With increase in Id, electrical resistance between electrodes increased, interaction among the

re

electrodes becomes tough. As a result, overall flocs generation rate decreases and pollutant ion

lP

removal rate decreases. To keep required flocs production rate, applied voltage needs to be increased from 6.7 to 9.4 Volt which results in higher energy consumption. Removal efficiency of Fe(II) ions was found higher than fluoride for the same Id as the readily oxidized Fe3+ ions

na

are more likely to get adsorbed to the coagulant flocs produced in the bulk solution as discussed in the previous section.

ur

Table 7 summarizes the initial and final values of conductivity, TDS, salinity, turbidity,

Jo

final pH as well as energy consumption at various Id. It is observed that when Id increased from 1.0 to 2.0 cm, the energy consumption (KWhm-3) increased from 1.7167 to 3.15 KWh m-3. Such an escalation in energy consumption was due to the higher voltage requirement from 6.7 to 9.4 Volt at constant Cd. It is also observed that with the increase in Id, final conductivity at the end of 60 min of EC increases from 685±1.0 to 689.5±1.0 µs cm-1, turbidity from 0.18±0.01 to 0.22±0.01 NTU, salinity from 121.1±1.0 to 127.9±1.0 and final pH of the solution from

14

7.64±0.01 to 7.71±0.03. All these final values of the parameters are found within permissible limit. Considering all the above factors as well from the point of highest removal efficiency at lower Id i.e. 1 cm is considered as ideal Id to ensure minimum energy consumption and better pollutant removal efficiency. 4.7 Effect of NaCl dose on fluoride and Fe (II) ions removal To understand the influence of NaCl on simultaneous removal of fluoride and Fe (II) ions, experiments were carried out with varying NaCl dose from 0.33 to 0.83 g L-1. Figure 7

ro of

shows the variations in fluoride and Fe (II) ions removal for different NaCl dose after 60 min EC. It is observed from figure 7 that with, as dose of NaCl increased from 0.33 to 0.83 g L-1, fluoride and Fe(II) ions removal improved from 96% to 98.14% and 98.88% to 99.90%,

-p

respectively. Such trivial increase in removal of both the ions was due to better transport of Fe(II) and fluoride ions to the generated flocs, which results in better interaction among

re

between them and better removal rate from water [19]. Table 8 summarizes the variation in

lP

salinity, conductivity, pH, TDS and EEC for varying NaCl dose after 60 min EC. From Table 8, it may be observed that with rise in initial NaCl dose from 0.33 to 0.83 gL-1, final conductivity surges from 685±1.0 to 1125±1.2 µs cm-1, TDS reduces from 75.73±1.2 to

na

71.93±1.0 mg L-1 and turbidity reduces from 0.18±0.01 to 0.13±0.03 NTU. The increase in final conductivity values are due to insufficient adsorption of the excess Na+ or Cl- ions in the

ur

solution at constant Cd. Energy consumption of the process was found to decrease from 1.7167

Jo

to 0.9 KWh m-3 with increase in NaCl dose from 0.33 to 0.83 g L-1. Decrease in energy consumption for higher NaCl dose was due to increase in electrical conductivity of the solution at higher NaCl dose. Hence, to maintain necessary current density, inter electrode voltage decreases and finally energy consumption decreases. Further, experimental result infers that, higher dose of NaCl improves the pollutant removal. Considering the fact that higher dose of NaCl may modify the taste of treated with traces of with Na+ ions may not be accepted in

15

drinking water, lower NaCl dose of 0.33 g L-1 should be considered as desirable NaCl dose for EC. Hence, considering the economic aspect of the process, lower concentration of NaCl i.e. 0.33 g L-1 may be considered as ideal dose for EC treatment. 4.8 Comparison of the present work with other work available in literature Table 9 summarizes the comparison between results of the present work on fluoride and Fe(II) ions removal by EC using Al electrode data available in literature. In EC process, current density and electric energy consumption plays a crucial role as it directly deals with the

ro of

operating cost and performance of the process. From table 9, it can be observed that, energy consumption (EEC) for simultaneous fluoride and Fe(II) ions removal (1.719 KWh m-3) reported in this work are lower compare to individual fluoride and Fe(II) removal reported in

-p

our previous work [18,19]. This observation infers that presence of both fluoride and Fe(II) ions not only increases their individual removal efficiency as reported in section 4.4 and 4.5,

re

also decreases energy consumption. Further it can be observed that, energy consumption

lP

reported by Hashim et al., [15] for Fe(II) removal is significantly higher (10.14 KWh m-3) compare to the present work as well as other work, may be due to use of very less quantity of sample water (0.5 L). So based on the data available in Table 9, it is evident that simultaneous

na

removal of fluoride and Fee(II) ions by EC gives better pollutant removal efficiency and needs

ur

to carried out with higher volume of water to reduce energy consumption. 5. Conclusions

Jo

In this work, simultaneous removal of fluoride and Fe(II) ions by EC are studied to

identify the influence of coexisting ions on their removal efficiency. During experiment, 10 mg/L of fluoride ions and 20 mg/L Fe(II) ions were considered to study their simultaneous removal with varying pH, Cd, inter-electrode distance and NaCl dose. Highest removal efficiency of 96% for fluoride ions and 98.88% for Fe(II) ions was achieved after 60 min EC at 0.431 mA cm-2 Cd, 1 cm Id, 0.33 g L-1 NaCl dose and 7.0 pH. During experiment it was 16

observed that with increase in Cd from 1.5 mA cm-2 to 12.93 mA cm-2, Fe(II) and fluoride ions removal efficiency increases from 96.66% to 99.99% and 84.6% to 98.78% respectively due to higher electro-dissolution. However, with increase in Cd from 1.5 mA cm-2 to 12.93 mA cm2

, the energy consumption of the system increases from 0.2668 to 13.9 KWh m-3. It is also

observed that with the increase in initial Fe(II) concentration from 0 to 50 mg/L, fluoride ions removal increases from 86.38% to 99.1% due to affinity of fluoride ions towards the ferric hydroxide flocs. Further, it was observed that presence of fluoride ion in the solution also

ro of

enhances Fe(II) ions removal process. First order rate constant for fluoride and Fe(II) ion removal was found to increase from 0.0317 to 0.0721 min-1 and 0.0563 to 0.1739 min-1 as Cd increases from 1.5 mA cm-2 to 12.93 mA cm-2 respectively. Such trends in result is due to higher

-p

removal rate of pollutant at higher Cd because of availability of more flocs in the solution. It was observed that after 60 minutes of EC almost 99.63% of turbidity was removed. The range

re

of TDS, conductivity, salinity and pH were also found to be in the range of satisfactory drinking

lP

water quality. Based on experimental results, the present study determines that EC is an effective remediation method for concurrent removal of Fe(II) and fluoride ions from water.

na

Authors Contribution:

ur

Ms. Daisy Das has performed all the experimental work reported in this work. She also has prepared the manuscript draft.

Jo

Dr. Barun Kumar Nandi, is the Project Investigator of the work and Doctoral thesis supervisor for Ms. Daisy Das. He has instructed the sequence of experiments, analysis methods and significantly contributed in interpretation of experimental results, kinetic analysis. Finally manuscript has been prepared by both the authors.

Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

17

Acknowledgements: This work is partially supported by a grant (INNO-INDIGO/27/MKP/2015-16

dated

26.11.2015) from the Department of Biotechnology (DBT), New Delhi, under DBT - INNO INDIGO joint call. Any opinions, findings and conclusions expressed in this paper are those of the authors and do not necessarily reflect the views of DBT (New Delhi) - INNO INDIGO.

ro of

References: [1] V. L. Dhadge, C.R. Medhi, M. Changmai, M. K. Purkait, House hold unit for the treatment of fluoride, iron, arsenic and microorganism contaminated drinking water, Chemosphere 199

-p

(2018) 728-736.

[2] J. F.A. Silva, N. S. Graca, A. M. Ribeiro, A.E. Rodrigies, Electrocoagulation process for

re

the removal of co-existent fluoride, arsenic and iron from contaminated drinking water,

lP

Separation and Purification Technology 197 (2018) 237-243.

[3] M. A. Sandoval, R. Fuentes, J.L. Nava, O. Coreño, Y. Li, J. H. Hernández, Simultaneous removal of arsenic and fluoride from groundwater by electrocoagulation using a filter-press

na

flow reactor with a three-cell stack, Separation and Purification Technology 208 (2019) 208216.

ur

[4]World Health Organization, Guidelines for drinking water quality, Recommendations, 3rd

Jo

ed., World Health Organization. Geneva, 2004. [5] N. Khatri, S. Tyagi, D. Rawtani, Recent strategies for removal of iron from water: A review, Journal of Water Process Engineering. 19 (2017) 291-304. [6] D. Das, B. K. Nandi, Arsenic removal from tap water by electrocoagulation: Investigation of process parameters, kinetic analysis and operating cost , Journal of Dispersion Science and Technology, (2019) DOI: 10.1080/01932691.2019.1681280.

18

[7] Y. Gan, X. Wang, Li Zhang, B. Wu, G. Zhang, S. Zhnag, Coagulation removal of fluoride by zirconium tetrachloride: Performance evaluation and mechanism analysis, Chemosphere 218 (2019) 860-868. [8] R. F. P. M. Moreira, V. S. Madeira, H. J. José, E. Humeres, Removal of Iron from Water Using Adsorbent Carbon, Separation Science and Technology 39 (2005) 271-285. [9] R. Mandal, S. Pal, D.V. Bhalani, V. Bhadja, U. Chatterjee, S. K. Jewrajka, Preparation of polyvinylidene fluoride blend anion exchange membranes via non-solvent induced phase

ro of

inversion for desalination and fluoride removal, Desalination 445 (2018) 85-94. [10] J. N. Pereira, R. Lima, G. Choudhary, P.R. Sharma, S. Ferdov, G. Botelho, R. K. Sharma, S. L. Mendez, Highly efficient removal of fluoride from aqueous media through polymer

-p

composite membranes, Separation and Purification Technology 205 (2018) 1-10.

[11] M. Mohapatra, S. Anand, B.K. Mishra, D. E. Giles, P. Singh, Review of fluoride removal

re

from drinking water, Journal of Environment Management 91 (2009) 67-77.

lP

[12] S. V. Jadhav, E. Bringas, G. D. Yadav, V. K. Rathod, I. Ortiz, K.V. Marathe, Arsenic and fluoride contaminated groundwaters: A review of current technologies for contaminants removal, Journal of Environment Management 162 (2015) 306-325.

na

[13] M. Behbahani, M. R. Alavi Moghaddam, Techno-economical evaluation of fluoride removal by electrocoagulation process: Optimization through response surface methodology,

ur

Desalination 271 (2011) 209-218.

Jo

[14] D. Ghosh, H. Solanki, M.K. Purkait, Removal of Fe(II) from tap water by electrocoagulation technique, Journal of Hazardous Materials 155 (2008) 135-143. [15] K.S. Hashim, A. Shaw, R. Al Khaddar, M.O. Pedrola, Iron Removal, energy consumption and operating cost of electrocoagulation of drinking water using a new flow column reactor, Journal of Environment Management 189(2017) 98-108.

19

[16] B.K. Nandi, S. Patel, Effects of operational parameters on the removal of brilliant green dye from aqueous solutions by electrocoagulation, Arabian Journal of Chemistry 10 (2017) S2961-S2968. [17] A. Doggaz, A. Attour, M.L.P Mostefa, M. Tlili, F.Lapicque, Iron removal from waters by electrocoagulation: Investigations of the various physicochemical phenomena involved, Separation and Purification Technology 203 (2018) 217-225. [18] D. Das, B.K. Nandi, Defluoridization of drinking water by electrocoagulation (EC):

ro of

process optimization and kinetic study, Journal of Dispersion Science and Technology 40 (2018) 1136-1146.

[19] D. Das, B.K. Nandi, Removal of Fe(II) ions from drinking water using Electrocoagulation

-p

process: Parametric optimization and kinetic study, Journal of Environmental Chemical Engineering 7 (2019) 103116.

re

[20] A.A.G.D. Amarasooriya, T. Kawakami, Electrolysis removal of fluoride by magnesium

lP

ion-assisted sacrificial iron electrode and the effect of coexisting ions, Journal of

na

Environmental Chemical Engineering 7 (2019) 103084.

100

Fluoride Fe(II)

98

ur

96

Removal %

Jo

94 92 90 88

Initial Fe(II) concentration: 20 mgL -1 Initial F concentration: 10 mgL -2 Id: 1 cm, Cd: 4.31 mAcm -1 EC time: 60 min, Csi :0.33 gL

86 84 82

-1

80 5

6

7

8

9

pH

Figure 1: Effect of pH of water on removal of fluoride and Fe (II) ions. 20

10

20

-1

Initial F concentration: 10 mg L -1 Id: 1 cm, pH:7, Csi: 0.33 g L

-1

16

EC time: 60 min

14 12

-2 Cd-12.93 mAcm

10 8 6 4

WHO permissible limit

2

8 -1

-

Initial Fe(II) concentration: 20 mg L -1 Initial F concentration: 10 mg L -1 Id: 1 cm, pH:7, Csi: 0.33 g L

[b]

9

Concentration of Fluoride, mg L

18

Concentration of Fe(II), m gL

-2 Cd-1.5 mAcm -2 Cd-2.0 mAcm -2 Cd-4.31 mAcm -2 Cd-8.62 mAcm

[a] Initial Fe(II) concentration: 20 mg L-1

-1

EC time: 60 min

7

-2 Cd- 1.5 mA cm -2 Cd- 2.0 mA cm -2 Cd- 4.31 mA cm -2 Cd- 8.62 mA cm -2 Cd- 12.93 mA cm

6 5 4 3 2 WHO permissible limit

1 0

0 10

20

30

40

50

0

60

10

20

30

40

50

60

Time (min)

ro of

0

Time (min)

Figure 2: Effect of Cd on simultaneous removal of fluoride and Fe (II). (a) Variation in residual

-p

Fe(II) concentration (b) variation residual of fluoride concentration. 5

[a]

Fe(II) removal rate -2 -1 Cd- 1.5 mA cm , k=0.0563min

10

-2

Cd- 2.0 mA cm , k=0.0637 min -2

-2

re

-2

-1

-2

Cd- 8.62 mA cm , k=0.0618 min

-1

Cd- 12.93 mA cm , k=0.1739min

ln Co/C

-1

-2

Cd- 12.93 mA cm , k=0.0727 min

3

6

-1

-1

lP

ln Co/C

-1

-2

Cd- 4.31 mA cm , k=0.0535 min

Cd- 8.62 mA cm , k=0.1009 min -2

Cd- 2.0 mA cm , k=0.038 min

4

-1

Cd- 4.31 mA cm , k=0.0766 min

8

[b]

Fluoride removal rate -2 -1 Cd- 1.5 mA cm , k=0.0317 min

-1

4

2

2

0 0

10

20

na

1

30

40

50

0

60

0

Time (min)

10

20

30

Jo

ur

Time (min)

21

40

50

60

0.18

Fe(II) Fluoride

0.16

(c)

85

0.14

.03

k, min

-1

0.12

k=

0.10

0 0.0

0.08

.C

95

+0 d

+0 033C d k=0.0

0.06

.0319

0.04 0.02 0

2

4

6

8

10

12

14

-2

ro of

Cd, mA cm

Figure 3: (a) 1st order plot for removal of Fe(II) ions at various Cd. (b) 1st order kinetic model for removal of fluoride ions at various Cd. (c) Variation in rate constant (k) for removal of

-p

fluoride and Fe(II) ions at different Cd. 20

-1

[Fe/F]- [20/0] mg L , k= 0.0674 min

6

re

-1

16 14

-1

[b]

-1 [Fe/F]- [20/10] mg L ,k=0.0766 min -1 -1 [Fe/F]- [20/15] mg L ,k=0.0871 min -1 -1 [Fe/F]- [20/20 ]mg L , k=0.0931 min -1 -1 [Fe/F]- [20/25] mg L ,k=0.1055 min

5

-1

4

lP

12 10

Initial Fe(II) concentration: 20 mg L -2 Cd: 4.31 mAcm , Id : 1 cm

8

-1

-1

ln Co/C

Residual Fe (II) concentration (mg L )

7

-1 F concentration: 0 mg L -1 F concentration: 10 mg L -1 F concentration: 15 mg L -1 F concentration: 20 mg L -1 F concentration: 25 mg L

[a]

18

3

Csi : 0.33 gL , pH:7

6

2

na

4

1

WHO permissible limit

2 0 0

10

20

30

40

50

0

60

0

10

Time (min)

20

30

40

50

60

ur

Time (min)

Figure 4: (a) Effect of fluoride ion concentration on removal of Fe(II) ions. (b) 1st order plot

Jo

for Fe(II) ion removal at varying fluoride ion concentrations.

22

Fe(II) concentration: 0 mg L

-1

Residual Fluoride concentration (mg L )

[a] 9 8

-1

5.0

Fe(II) concentration: 20 mg L

-1

Fe(II) concentration: 30 mg L

-1

Fe(II) concentration: 40 mg L

-1

7

Fe(II) concentration: 50 mg L

-1

6

Initial F concentration: 10 mg L -2 Cd: 4.31 mA cm , Id: 1 cm

-

5

pH: 7, Csi: 0.33 g L

-1

4

-

-1

[b]

[Fe/F ]-[0/10] mg L-1, k= 0.2143 min

4.5

-

-1 [Fe/F ]-[20/10] mg L ,k= 0.3495 min -1 [Fe/F ]-[30/10] mg L-1, k= 0.4008 min -1 [Fe/F ]-[40/10] mg L-1,k= 0.4909min -1 [Fe/F ]-[50/10] mg L-1, k= 0.5251 min

4.0 3.5

-1

-1

3.0

lnCo/C

10

3

2.5 2.0 1.5

2

1.0 WHO permissible limit

1

0.5

0 0

10

20

30

40

50

0.0

60

0

10

20

30

40

50

60

Time (min)

Time(min)

ro of

Figure 5: (a) Effect of Fe(II) ion concentration on removal of fluoride ions. (b) 1st order plot

-p

for fluoride ion removal at varying Fe(II) ion concentrations.

re

100

98

92

lP

94

Initial Fe(II) concentration: 20 mg L -1 Initial F concentration: 10 mg L -2 -1 Cd: 4.31 mA cm , Csi: 0.33 g L

-1

pH: 7, EC time: 60 min

na

Removal %

96

Fluoride Fe (II)

90

88

ur

0.5

1.0

1.5

2.0

2.5

3.0

Id(cm)

Jo

Figure 6: Effect of inter-electrode distance on simultaneous removal of fluoride and Fe (II) ions.

23

100

Removal %

99

98

97

Initial Fe(II) concentration: 20 mg L -1 Initial F concentration: 10 mg L -2 C : 4.31 mA cm , I : 1 cm d d

-1

pH: 7, EC time: 60 min

96

Fluoride Fe (II)

95 0.3

0.4

0.5

0.6

0.7

0.9

ro of

NaCl concentration, g L

0.8

-1

Figure 7: Effect of initial NaCl concentration on simultaneous removal of fluoride and Fe (II)

lP

re

-p

ions.

Parameters

na

Table 1: Characterization of tap water, synthetic solution and WHO [4] permissible values. Tap water

Synthetic solution

WHO Permissible values

BDL

20 mgL-1

0.3 mg L-1

Fluoride ion

BDL

10 mgL-1

1.5 mg L-1

TDS

201

285.06±1.0

500-700 mg L-1

Turbidity (NTU)

1.50

49.60±0.2

<1 NTU

Conductivity

225

740.6±1.5

200-2000 µs cm-1

pH

7.02

7.02±0.01

6.5-8.5

Jo

ur

Fe (II) ion

#BDL- below detection level

24

Table 2: Various experimental parameters considered during simultaneous removal of fluoride and Fe (II) ions.

Initia

parameters

l pH

studied Effect of initial

5,6,7,

pH

8,9

Effect of Cd

7.0

Effect of initial

EC

Density (mA

duration

cm-2)

(min)

4.31

60

1.0

60

60

1.5, 2.0, 4.31, 8.62, 12.93

7.0

conc.

Current

4.31

NaCl

Id

dose (g

(cm)

4.31

60

fluoride ion

(II) ion

(mg L-1)

on (mg L-1)

0.33

10

20

1.0

0.33

10

20

1.0

0.33

0,10,15,20,25

0.33

10

20

10

20

1.5,2,

-p

7.0

Initial Fe

concentration concentrati

L-1)

1, Effect of Id

Initial

ro of

Effect of

0,20,30,40, 50

2.5

Effect of NaCl

7.0

re

0.33,0.5

4.31

60

1.0

0,0.66,

lP

0.83

na

Table 3: Variations in conductivity, TDS, salinity, turbidity and pH of the treated water at different initial pH after 60 min EC. [Initial values before EC: conductivity- 740.6±1.5 µs cm, turbidity- 49.60±0.2 NTU, TDS- 285.06±1.0 mg L-1, salinity- 240.3±1.2 mg L-1]

ur

1

Conductivity

Turbidity

(µs cm-1)

(NTU)

5.0

692.7±1.2

0.24±0.02

80.10±1.0

127.8±0.5

5.78±0.02

6.0

690.6±1.0

0.22±0.05

77.80±1.5

125.1±1.5

6.91±0.05

7.0

685.0±1.0

0.18±0.01

75.73±1.2

121.1±1.0

7.64±0.01

8.0

697.4±1.5

0.26±0.05

82.34±0.5

129.0±0.5

8.78±0.03

9.0

701.3±0.5

0.29±0.01

84.42±1.0

134.5±1.0

9.76±0.05

Jo

Initial pH

TDS(mg L-1)

25

Salinity (mg L-1)

pH

Table 4: Variations in conductivity, TDS, salinity, turbidity and pH of treated water along with energy consumption ((KWh/m3) after 60 min of EC at various Cd. [Initial values before EC: conductivity- 740.6±1.5 µs cm-1, turbidity- 49.60±0.2 NTU, TDS- 285.06±1.0 mg L-1, salinity240.3±1.2 mg L-1] EEC

Cd (mA

Conductivity

Turbidity

TDS(mg L-

Salinity

cm-2)

(µs cm-1)

(NTU)

1)

(mg L-1)

1.5

700.2±1.0

0.28±0.02

82.99±1.0

133.5±1.5

7.71±0.02

0.2668

2.0

691.4±1.2

0.21±0.05

78.72±1.5

128.6±0.5

7.68±0.05

0.4408

4.31

685.0±1.0

0.18±0.01

75.73±1.2

121.1±1.0

7.64±0.01

1.7167

8.62

678.6±1.5

0.12±0.03

71.20±1.0

117.4±1.5

7.60±0.03

6.5

12.93

671.7±0.5

0.08±0.01

65.21±0.5

102.3±1.0

7.60±0.02

13.9

pH

(KWh

lP

re

-p

ro of

m-3)

na

Table 5: Variations in conductivity, TDS, salinity, turbidity and pH of treated water at different concentration of Fluoride ions after 60 minutes of EC. [Initial values before EC: conductivity740.6±1.5 µs cm-1, turbidity- 49.60±0.2 NTU, TDS- 285.06±1.0 mg L-1, salinity- 240.3±1.2

ur

mg L-1, initial Fe(II) concentration- 20 mg L-1]

Jo

Initial

Conductivity

Turbidity

TDS(mg L-

Salinity(mg L-

(µs cm-1)

(NTU)

1)

1)

[F/Fe]-0/20

684.9±1.5

0.17±0.02

48.27±1.0

123.9±1.0

7.44±0.02

[F/Fe]-10/20

685.0±1.0

0.18±0.01

55.73±1.2

121.1±1.0

7.49±0.01

[F/Fe]-15/20

685.1±0.5

0.70±0.05

58.90±1.5

121.4±1.5

7.52±0.03

[F/Fe]-20/20

683.8±1.5

0.81±0.03

59.89±1.0

123.8±1.2

7.56±0.04

[F+Fe(II)]

conc.(mg L-1)

26

pH

[F/Fe]-25/20

685.0±1.0

0.87±0.01

61.26±1.2

124.8±0.5

7.63±0.02

Table 6: Variations in conductivity, TDS, salinity, turbidity and pH of treated water at different Fe(II) ion concentration after 60 min of EC. [Initial values before EC: conductivity- 740.6±1.5 µs cm-1, turbidity- 49.60±0.2 NTU, TDS- 285.06±1.0 mg L-1, salinity- 240.3±1.2 mg L-1, initial fluoride concentration- 10 mg L-1]

[Fe(II)+F]

Conductivity

Turbidity

TDS(mg

conc.(mg L-

(µs cm-1)

(NTU)

L-1)

[Fe/F]-0/10

684.2±1.5

0.10±0.02

62.44±1.0

[Fe/F]-20/10

685.0±1.0

0.18±0.01

75.73±1.2

[Fe/F]-30/10

684.8±12

1.22±0.05

76.23±0.5

122.3±1.2

7.67±0.05

[Fe/F]-40/10

683.6±0.5

1.23±0.04

78.45±1.0

122.0±1.0

7.59±0.02

[Fe/F]-50/10

685.4±1.0

re

Initial

1.37±0.02

123.3±0.5

7.63±0.03

L-1)

124.2±1.5

7.60±0.02

121.1±1.0

7.64±0.01

-p

1)

pH

ro of

Salinity(mg

lP

79.90±1.5

na

Table 7: Variations in conductivity, TDS, salinity, turbidity and pH of treated water along with energy consumption ((KWh/m3) after 60 min of EC for different Id .[ Initial values before EC:

ur

conductivity- 740.6±1.5 µs cm-1, turbidity- 49.60±0.2 NTU, TDS- 285.06±1.0 mg L-1, salinity-

Jo

240.3±1.2 mg L-1]

Id

Conductivity cm-1)

Turbidity (NTU)

TDS(mg L-1)

Salinity

pH

(KWh m-3

(cm)

(µs

1.0

685.0±1.0

0.18±0.01

75.73±1.2

121.1±1.0

7.64±0.01

1.716

1.5

686.9±1.5

0.19±0.02

77.86±1.5

123.4±1.2

7.67±0.05

2.2

2.0

687.4±1.5

0.20±0.03

79.23±1.0

125.9±1.5

7.69±0.02

2.75

2.5

689.5±1.0

0.22±0.01

80.99±1.2

127.9±1.0

7.71±0.03

3.15

27

(mg

L-1)

EEC

)

Table 8: Variations in conductivity, TDS, salinity, turbidity and pH of treated water along with energy consumption ((KWh m-3) after 60 min of EC for different NaCl dose (Csi). [Initial values before EC: conductivity- 740.6±1.5 to 1485±1.0 µs cm-1, turbidity- 49.60±0.2 NTU, TDS285.06±1.0 mg L-1, salinity- 240.3±1.2 mg L-1] EEC

Csi (g L-

Conductivit

Turbidity

TDS

Salinity

1)

y (µs cm-1)

(NTU)

(mg L-1)

(mg L-1)

0.33

685.0±1.0

0.18±0.01

75.73±1.2

121.1±1.0

7.64±0.01

1.7167

0.50

879.3±1.5

0.17±0.02

74.10±1.5

184.4±1.5

7.62±0.05

1.25

0.66

1107±2.0

0.15±0.05

73.24±2.0

155.3±2.0

7.61±0.06

1.1

0.83

1125±1.2

0.13±0.03

71.93±1.0

167.8±1.2

7.60±0.03

0.9

pH

lP

re

-p

ro of

(KWh m-3)

EC

Sample

Initial

time

Volume

concentration

(min)

(L)

(mg L-1)

ur

Optimum

na

Table 9: Comparison of the present work with other work available in literature.

Condition

pH- 7; Id- 1 cm

Cd: 12.93 mA cm2

; pH- 7; Id- 1 cm

Cd: 2 mA cm-2; pH- 6.34; Id- 1 cm

EEC (KWh m-3)

Reference

Fluoride : 10

Fluoride: 96 %

Fe(II) : 20

Fe(II) : 98.88%

3

Fluoride : 10

97.1%

12.66

[17]

3

Fe(II) : 20

98.6%

0.3828

[18]

60

3

40

45

Jo

Cd: 4.31 mA cm-2;

Removal %

28

1.719

Present study

Cd: 16.7 mA cm-2; pH- 7; Id- 3 cm Cd: 1.5 mA cm-2; pH- 6; Id- 0.5 cm

25

2

Fluoride : 25

94.5%

-

[12]

20

0.5

Fe(II) : 20

98.5%

10.14

[15]

2

Fe(II) : 25

98.4%

1.02

[16]

Cd: 10 mA cm-2;

Jo

ur

na

lP

re

-p

ro of

pH- 7; Id- 1 cm

29