treatment of organic content at high total dissolved solids by electrochemical oxidation

8/11/2019 Treatment of organic content at high Total Dissolved Solids By Electrochemical Oxidation

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I JSRD - I nternational Journal for Scientifi c Research & Development| Vol. 1, I ssue 10, 2013 | ISSN (onli ne): 2321-0613

All rights reserved by www.ijsrd.com 2217

Abstract--- The electrochemical treatment of synthetic

wastewater with salinity of 330 g NaCl/L and organic load

of up to 3200 mg COD/L was investigated. The effects of

important parameters like pH, temperature, potential,

current, reaction time, and initial organic concentration were

studied using graphite electrodes. Tween80 and phenol were

used as organic pollutants for the preparation of the

synthetic wastewater. The best reduction in COD was

observed at pH 6.0 for phenol and 6.4 for tween80,

temperature of 10°C, potential of 4.0V(tween80) and

3.0V(phenol), current of 0.2A(tween80) and 0.3A(phenol),and reaction time of 60 minutes. The variations were

depicted using State-Ease® Design Expert software trail

version 8.0.6 and response surface methodology (RSM).

Total current efficiency (TCE), anode efficiency (AE) and

energy consumption (EC) were also most desirable at these

optimum conditions. Reaction kinetics reveal that the

electro-oxidation here follow the pseudo-first-order model.

Negative values of ΔSº and ΔHº for both phenol and

tween80 indicate that at lower temperatures the reaction is

feasible and spontaneous so as to make ΔGº negative. Using

these optimized parameters, significant reduction in COD of

up to 100% was achieved in a real saline wastewater withCOD of up to 1100 mg/L.

Keywords: Electrochemical treatment of synthetic saline

wastewater, Modified method, real saline sample, Response

surface methodology.

I. INTRODUCTION

Saline wastewater is generated from many industrial sectors

like textile, petroleum, petrochemical, leather etc. All these

sectors generate very large amount of saline wastewater,

rich in both salt (NaCl) and organic matter. When this

wastewater is discharged into the environment without prior

treatment, it can cause severe damage to the aquatic life,water potability and agriculture by contamination of soil,

surface and groundwater [1]. Biological treatment of saline

wastewater results in poor removal of chemical oxygen

demand (COD) due to the inhibition by high salt content

[2]-[5]. Due to high conductivity in saline wastewater with

the presence of anions and cations, electro-oxidation

treatment might be a favorable route [6]. Several studies

have been carried out on the electro-oxidation of different

organic compounds and anode materials [7], [8]. This

method also has been successfully applied for the treatment

of saline wastewater in textile industry, tannery, distillery,

domestic sewage and landfill leachate [9]-[16]. Graphite

electrodes have been widely used recently, for organic

removal because of its low cost. It has large surface area and

high current efficiency compared to other electrodes [10]. In

graphite electrodes, oxidation is dominated mainly by

physisorbed active oxygen hydroxyl radicals. These

hydroxyl radicals cause the complete destruction of organic

matters. However, the relatively poor service life due to

surface corrosion especially when the electro-oxidation is

conducted at high potential is the notable short-coming of

graphite electrode. But here since the potential for the

operation is optimized to 3 - 4V only, the short-coming can

be neglected.

In the electrochemical oxidation, organic pollutants areremoved by electro-generated oxidizing agents like chlorine

and hypochlorite [17]. In general, the following reaction

takes place during electro-oxidation using graphite

electrodes in the presence of sodium chloride, magnesium

chloride, calcium chloride and ammonium chloride.

At the anode:

2Cl- → Cl2 + 2e

- (1)

4OH- → O2 + 2H2O + 4e

- (2)

At the cathode:

2H2O + 2e- → H2 + 2OH

-(3)

In the undivided cell, chlorine formed at the anode and

hydroxides formed at the cathode react to form chloride and

hypo chlorites. Both the hypochlorite and free chlorine are

chemically reactive and oxidize the organic pollutants in the

effluent to carbon dioxide and water [14].

HOCl is then formed.

Cl2 + H2O → H+ + Cl

- + HOCl (4)

The HOCl dissociates into OCl− and H

+ ions.

HOCl ↔ H+

+ OCl-

(5)

These hypochlorite ions act as the main oxidizing agent in

the organic degradation.

The overall desired reaction of electrolysis is:

Organic matter + OCl- → Intermediates (6)

Intermediates → CO2 + Cl- + H2O (7)

The other important products of electrolysis include Cl2,

ClO2, O3, OH., O

., ClOH

., H2O2, O2, H2 and CO2. Due to the

high oxidation potential of the radicals, they may undergo

decomposition to produce other oxidants which may oxidize

the organic compounds. This process is called direct

oxidation. The primary (Cl2 and O2) and secondary (ClO2,

O3 and H2O2) oxidants have long life. They are capable of

diffusing into the areas away from the electrodes andcontinue to oxidize the pollutants [18].

Treatment of organic content at high Total Dissolved Solids

By Electrochemical OxidationImranul Islam Laskar

1 Deepak Ramachandran O.

2

1,2Dept. of Chemical Engineering, Sathyabama University, Chennai, India



Treatment of organic content at high Total Dissolved Solids By Electrochemical Oxidation

(IJSRD/Vol. 1/Issue 10/2013/0041)


In the classical method of optimization one parameter is

varied at a time while the other being constant. However,

the classical method is unable to understand the complex

interactions between the variables and the response.

Response surface methodology (RSM) is an effective

statistical tool for collection of mathematical and statistical

information useful for developing, improving and

optimizing processes and can be used to evaluate the relativesignificance of several parameters in complex interactions

[19]. Here, after the parameters have been optimized, RSM

was used for graphical representation and generation of

mathematical relation of the parameters with the response.

Present work investigates the effectiveness of the critical

parameters such as pH, current, potential, temperature and

reaction time in chemical oxygen demand (COD) reduction

by electro-oxidation of synthetic saline wastewater using

graphite electrodes and the variations in total current

efficiency (TCE), anode efficiency (AE) and energy

consumption (EC). Scope of this work also includes

optimization of the process using RSM; finding a modifiedmethod suitable for COD analysis of sample with salt

content of 330g NaCl/L and COD of up to 3200 mg/L; study

of reaction kinetics and thermodynamic parameters of the

process; and electro-oxidation of a real saline reject water

using the optimized conditions.

II. MATERIALS AND METHODS

A. Electro-oxidation cell

A cylindrical vessel of 100 mL working volume

(Length=5cm, Breadth=3.5cm, Height=8cm) was used as

the electro-oxidation cell as in Fig. 1. Graphite electrode

with a diameter of 1 cm was used as an anode and stainless

steel (SS304) of same diameter as the cathode. The

electrodes were arranged parallel to each other with a

constant electrode gap of 1 cm. The electric power supply

was provided by laboratory A.C. to D.C. convertor power

source equipped with current – voltage monitoring. For

temperature studies, a separate electro-oxidation cell was

used with a provision for jacketed water flow at varying

temperature.

B. Synthetic wastewater

Fig. 1: Schematic diagram of electro-oxidation cell.

The synthetic wastewater prepared here was a prototype of

reverse osmosis (RO) reject in leather industry with COD in

the range of 2800-3200 mg/L and inorganic composition as

follows: NaCl: 330 g/L, CaCl2: 16.5 g/L, MgCl

2: 6.624 g/L,

and NH4Cl: 0.486 g/L. The organic compounds taken in this

study were: phenol and tween80 as both are major organic

pollutant in the RO reject stream. For pH studies, the pH of

the synthetic salt was altered using either NaOH or HCl. The

salts used here were from Hi-Media Laboratories and of

analytical (AR) grade.

Fig. 2: Electro-oxidation cell for temperature studies.

C. Analysis of wastewater

COD is the main pollution parameter and was analyzed

following the standard procedure as reported by American

Public Health Association [20]. Mercuric sulphate is used to

mask the chloride interference in COD estimation. However,

there are limitations when measuring the organic matter in

wastewater samples with chlorides higher than 2000 mg/L

using the standard method. This is due to the oxidation of

chloride ions expressed by the following equation:

Cr 2O72-

+ 6Cl- + 14H

+ → 3Cl2 + 2Cr

3+ + 7H2O (8)

The standard method suggests the use of a HgSO4: Cl ratio

of 10:1 when the chloride concentration is up to 2000 mg/L

in order to mask the excess of chloride by the formation of

HgCl2. However, many researchers have found that this

ratio (10:1) in samples with chlorides more than 2000 mg/L

contributed to a significant error at low and moderate CODs

[21]-[24]. Here with chlorides higher than 330 g/L, even ahigh dilution of the samples does not eliminate the problem

as the organics are diluted accordingly. These existing

methods have substantial errors, mainly in the range of low

organic concentrations with high salinity. A modified

method, which will enable the range of the standard method

to be extended up to 40 g NaCl/L with low COD values

(less than 230 mg COD/L), with error less than 10% in

contrast to an error of about 50-85% with the standard

method, was applied here [25]. However, this only solves

the problem for low organic concentrations with high

salinity. Here the synthetic saline wastewater contains both

the inorganic and organic matter in high amount. We foundthat following the modified procedure together with dilution

of the sample and ferrous ammonium sulphate (FAS), error

was minimized to 1%.

D. Experimental Design

Central composite design (CCD) and RSM has been used to

design the experiments. Five factors were used in this study

based on RSM and a total of 50 experiments were

summarized by the trail version of Stat-Ease Design®

Expert V8.0.6 Software. Here, we conducted experiments

based on our assumptions, then optimized each parameter

step by step. Later, the software was run and the response

for COD was given in accordance with the experimental

results. Analysis Of Variance (ANOVA) was done for the




(IJSRD/Vol. 1/Issue 10/2013/0041)


justification of the model. Five factors: current, potential,

initial organic concentration per liter of the synthetic

wastewater, time and pH were selected as variables,

whereas, COD removal efficiency from the synthetic

wastewater was the response.

E. Anode efficiency, total current efficiency (TCE), and

energy consumption

Using (9), (10), and (11), we calculated anode efficiency,

TCE, and energy consumption at optimum conditions for

COD removal [26], [27].

(9)

[]

(10)

where CODt and CODt+Δt are chemical oxygen demands at

time t and t+Δt in gram of O2 per dm3 respectively; F is

Faraday‘s constant (96,487 Cmol-1

); V is the volume of

electrolyte in liters and I is the current in Ampere and 8 is

the oxygen equivalent mass (g/equiv. -1).

(11)

where t is the time of electrolysis in hours, V is the average

cell voltage, I is the current in Ampere, S v is sample volume

in litres and ΔCOD is the difference in COD in time t in

mg/L.

F. Reaction kinetics

In order to investigate the electrochemical oxidation of the

prepared synthetic wastewater, pseudo-first-order and

pseudo-second-order integral equations were used [28].

The integral pseudo-first-order equation is given as:

(12)

where r t is the COD reduction capacity at time t (mg/L), r e is

the COD reduction capacity at equilibrium (mg/L), k f is the

pseudo-first-order rate constant (min-1

), and t is the

electrolysis time (min).

The pseudo-second-order model is represented as:

(13)

where k s is the pseudo-second-order rate constant

(L/mg

.

min).G. Estimation of thermodynamic parameters

The Gibbs free energy change of the electrochemical

process is related to the equilibrium constant by the classic

Van’t Hoff’s equation:

(14)

According to thermodynamics, the Gibbs free energy

change of the electrochemical process is also related to the

entropy change and heat of reaction at constant temperature

by the following equation:

(15)

Combining the above two equations, we get

(16)

where ∆G˚ is the free energy change (kJ/mol), ∆H˚ is the

change in enthalpy (kJ/mol), ∆S˚ is the entropy change

(kJ/mol K), T is the absolute temperature (K) and R is the

universal gas constant (8.314 J/mol.K). The above equation

can be plotted using lnK as y-axis and 1/T as x-axis; hence

∆H˚ and ∆S˚ are then calculated.

III. RESULTS AND DISCUSSION

A. Model fitting and ANOVA

The response(y) of COD by electro-oxidation experimental

data were fitted to quadratic model to obtain the

regression equations, sequential model sum of

squares, model summary statistics and subsequent

ANOVA were tested and it was found that the

quadratic model most suitably described the COD

values obtained from the experiments. The quadratic

equation obtained in terms of coded factors is given

below:

For phenol synthetic saline solution:

y = 916.75 + 717.74X1 + 38.25X2 – 656.37X3 – 76.89X4

– 64.18X5 + 99.38X1X2 – 70.63X1X3 – 44.38X1X4

– 43.12X1X5 + 104.38X2X3 – 21.87X2X4 +

6.88X2X5 – 11.87X3X4 – 75.62X3X5 – 84.37X4X5+ 274.11X12 + 109.71X22 + 231.69X32 + 54.91X42

+ 61.98X52. (17)

For tween80 synthetic saline solution:

y = 806.5608164 + 261.0501133X1 – 163.259299X2 –

335.9547309X3 + 192.3746207X4 – 116.6477117X5

– 83.75X1X2 – 127.5X1X3 – 30.625X1X4 – 93.125X1X5 + 47.5X2X3 + 75.625X2X4 –

24.375X2X5 – 5.625X3X4 – 5.625X3X5 +

22.5X4X6 + 41.25829025X12 – 29.45238787X22 +

233.9448881X32 + 48.32935806X42 +

1.483533804X52.

(18)

The ANOVA of COD values with respect to various

parameters after electro chemical oxidation showed model

‗F‘ value of 13.21(phenol) and 14.28(tween80) for the

quadratic model, implying that the model is significant as

shown in Table I and II. A ―prob>F‖ lower than 0.0500 forthe quadratic model indicates that the model terms are

significant. The ANOVA table for phenol saline solution

obtained from the response surface quadratic model shows

that the parameters concentration, time, (concentration)2

and (time)2 are the significant terms and for tween80,

concentration, time, pH,voltage,current,concentration*pH,concentration*current, concentration*time and (time)2 are

the significant terms. ―Adequate Precision‖ measures the

signal to noise ratio. A ratio more than 4 is desirable. For the

present study signal to noise ratio was found to be 14.578

for phenol and 17.530 for tween80 indicating adequate

signal. Therefore quadratic model can be used to navigate

the design space to optimize the operational parameters.

According to normal probability, studentized residuals and

outer-t residual plots which are not shown here, the

quadratic model well satisfied the ANOVA. R 2 is a

statistical measure of how well the regression lineapproximates the real data points. An R

2 of 1.0 indicates that




(IJSRD/Vol. 1/Issue 10/2013/0041)


the regression line perfectly fits the data. The R 2 value

obtained here is 0.9011 for phenol and 0.9078 for tween80

which indicates that there is a good co-relation between the

observed and predicted values of COD.

SourceSum of

squares

D

F

Mean

squareF value

p-value

Prob

>F

Model493422

00.420

2467110.02

13.2132575

<0.0001

Significant

X1 –

concentration

223133

93.41

223133

93.4

119.505

255

<0.00

01

Signifi

cant

X2 – pH63370.6

2591

63370.6

259

0.33939

808

0.564

7

X3 – time186604

98.81

18660498.8

99.9412162

<0.0001

Significant

X4 –

potential

256055.

6361

256055.

636

1.37137

34

0.251

1

X5 – current

178428.499

1178428.

4990.95562

0830.336

4

X1X2 316012.

51

316012.

5

1.69248

818

0.203

5

X1X3 159612.5 1 159612.5 0.85484679 0.3628

X1X4 63012.5 1 63012.50.33748

004

0.565

8

X1X5 59512.5 1 59512.50.31873

4870.576

7

X2X3348612.

51

348612.

5

1.86708

607

0.182

3

X2X4 15312.5 1 15312.50.08201

0130.776

6

X2X5 1512.5 1 1512.50.00810

059

0.928

9

X3X4 4512.5 1 4512.50.02416

7880.877

5

X3X5183012.

51

183012.

5

0.98017

165

0.330

3

X4X5 227812.5

1 227812.5

1.22010985

0.2784

X12

417528

9.561

417528

9.56

22.3618

63

<0.00

01

Signifi

cant

X22

668833.86

1668833.

863.58211

5910.068

4

X32

298282

8.641

298282

8.64

15.9753

245

0.000

4

Signifi

cant

X42

167536.

8611

167536.

861

0.89728

779

0.351

3

X52

213465.

8361

213465.

836

1.14327

251

0.293

8

Residual541472

7.62

2

9

186714.

745

Lack of

fit

540192

7.62

2

2

245542.

165

134.280

871

<0.00

01

Signifi

cant

Pureerror

12800 7 1828.57143

Table 1: ANOVA for Response Surface Quadratic Model

(Phenol)

B. Effect of various parameters

The effects of various parameters on COD removal were

analyzed using 3-D graphs with contour plot. Fig. 3 shows

the effect of time(X3) and concentration(X1) on COD

reduction for phenol. At higher concentrations of phenol,

COD increased expectedly from 2800mg/L for 1.5ml/L to

1200mg/L for 0.5ml/L after 5 min. reaction time. From Fig.3 it can be noted that there is a drastic reduction in COD

until 60 min., no appreciable removal of COD happens afterthat period. With 2 hour electrolysis time, COD reaches only

up to 320mg/L where after an hour it is 380mg/L for an

initial phenol concentration of 0.5ml/L. It follows the same

trend for tween80. As time increases, more OCl- and other

radicals are formed for oxidation, thereby reducing COD.

These variations were noted by keeping the other parameters

like current, potential, temperature and pH at their optimized

values. However, the reaction time was optimized at 1 hour

so as to reduce power consumption since beyond that period

COD reduction was found to be minimal.

SourceSum of

squares

D

F

Mean

squareF value

p-

value

Prob>F

Model158662

0420

793310

.2

14.284

49

<0.000

1

Significa

nt

X1 –

concentrati

on

2951706

12951706

53.14897

<0.0001

Significant

X2 – pH1154466

11154466

20.78753

<0.0001

Significant

X3 – time4888627

14888627

88.02552

<0.0001

Significant

X4 –

potential

160295

31

160295

3

28.863

08

<0.000

1

Significa

nt

X5 –

current

589356.

11

589356

.1

10.612

060.0029

Significa

nt

X1X2 224450 1 2244504.0414

880.0538

X1X3 520200 1 5202009.366818

0.0047Significant

X1X4 30012.5 130012.5

0.540411

0.4682

X1X5 277512.

51

277512

.5

4.9969

420.0333

Significa

nt

X2X3 72200 1 72200 1.300047 0.2635

X2X4 183012.

51

183012

.5

3.2953

570.0798

X2X5 19012.5 119012.

5

0.3423

430.5630

X3X4 1012.5 1 1012.50.018231

0.8935

X3X5 1012.5 1 1012.50.018231

0.8935

X4X5 16200 1 16200 0.2917 0.5933

X12

94591.99

194591.99

1.703241

0.2021

X22 48202.8

71 48202.

870.86795

0.3592

X32

304129

81

304129

8

54.762

18

<0.000

1

Significa

nt

X42

129793.

81

129793

.8

2.3370

910.1372

X52

122.3001

1122.3001

0.002202

0.9629

Residual1610558

2955536.47

Lack of fit161055

822

73207.

17

Pure error 0 7 0

Table 2: ANOVA for Response Surface Quadratic Model

(Tween80)




(IJSRD/Vol. 1/Issue 10/2013/0041)


Fig. 3: COD removal response plot between time and

concentration (phenol).

Fig. 4: COD removal response plot between potential and

concentration (phenol).

Fig. 4 shows the effect of potential(X4) and

concentration(X1) on COD removal for phenol. The

concentration variations is similar to Fig. 3. Effect of

potential in COD removal is negligible for 1ml phenol/L.Current and potential was optimized at 3V and 0.3A for

phenol since the power consumption would be less and also

desirable COD level was attained. For tween80, optimized

potential and current were 4V and 0.2A respectively.

Fig. 5: COD removal response plot between current and

concentration (tween80).

From Fig. 5, it can be noted that higher pH favors COD

Removal. This is due to the release of more OCl- ions atalkaline medium and also increased rate in (5) in the

forward direction. Same variation was also observed in [29].

Increase in current also led to an increase in COD reduction

due to the release of chlorine gas at the anode and

subsequent formation of hydroxides at the cathode. Both

react to form hypo chlorites which oxidize the organic pollutants to CO2 and H2O. Other oxidizing agents formed

here are: ClOH., ClO2. Native pH of 6.0 for phenol and 6.4

for tween80 in the synthetic saline wastewater was

optimized here since it gave a favorable COD reduction.

From an economic point of view, current optimization at

0.3A for phenol was done.

Fig. 6: COD removal response plot between current and

time (tween80).

Fig. 6 depicts a similar response for tween80 with CODreduction being negligible at reaction time more than 60

minutes and current being directly proportional with COD

removal due to increased rate of hypo chlorites at higher

current, therefore better reduction but was optimized at 0.2A

for the process to be economically viable.

C. Thermodynamic studies

The thermodynamic parameters ∆S˚ and ∆H˚ were found to

be -26.1891kJ/mol.K (phenol), -15.71kJ/mol.K (tween80)

and -7045.2836kJ/mol (phenol), -3926.536kJ/mol (tween80)

from the graph‘s intercept and slope as shown in Fig. 7 and

8. Since both the parameters are negative, therefore for the

system and the electro-oxidation to be spontaneous, lower

temperature is favorable as higher temperature results in

non-spontaneity.

These can be noted from (12) and (13) where the TΔSº term

must be greater than the ΔHº term for ΔGº to be negative. A

negative ΔGº indicates the feasibility and spontaneity of the

process. Also, according to Le Chatelier‘s principle, since

the process here is exothermic (ΔHº negative), lowertemperature is favorable.




(IJSRD/Vol. 1/Issue 10/2013/0041)


1/T (K -1) →

Fig. 7: Thermodynamic analysis of degradation of phenol.

1/T (K -1) →

Fig. 8: Thermodynamic analysis of degradation of tween80.

A. Effect of temperature

For temperature studies, all the other parameters were kept

constant at their optimized values, current: 0.3A (phenol)

and 0.2A (tween80), voltage: 3V (phenol) and 4V

(tween80), pH: 6(phenol) and 6.4(tween80), concentration:

1ml/L (phenol) and 2.1ml/L (tween80), and reaction time:

60 min. Electrochemical treatment was carried out at

varying temperatures ranging from 10ºC to 70ºC as shown

in Fig. 9 and 10 for phenol and tween80 respectively. It can

be noted that at 10ºC COD reduction was maximum for both

phenol and tween80 after 60 minutes of electrolysis. Thus,

the thermodynamic results can be verified here as according

to Le Chatelier’s principle and thermodynamic stability, a

lower temperature was suggested for spontaneity of the

electrochemical process. For phenol, at 10ºC and 20ºC,

93.33% and 80% of COD reduction was achieved

respectively. In case of tween80, we achieved 81.25% and75% COD reduction at 10ºC and 20ºC respectively.

Fig. 9: Effect of temperature on COD reduction (phenol).

Fig. 10: Effect of temperature on COD reduction (tween80).

Fig. 11: Effect of temperature on anode efficiency

Temperature (ºC) → Fig. 12: Effect of temperature on energy consumption.




(IJSRD/Vol. 1/Issue 10/2013/0041)


Temperature (ºC) →

Fig. 13: Effect of temperature on total current efficiency.

At 10ºC, anode efficiency (AE), energy consumption (EC)

and total current efficiency (TCE) were also the most

desired for both phenol and tween80 as shown in Fig. 11, 12

and 13 respectively. This is due to the better performance in

COD reduction at that temperature. At 10ºC, AE was the

highest for both phenol and tween80 at 0.743

KgCOD/A.m

2.h and 0.6897 KgCOD/A

.m

2.h respectively.

Similarly, TCE peaked at 4.69% (phenol) and 4.35%

(tween80) at the same temperature as shown in Fig. 13.Energy consumption was the lowest at 10ºC measuring

2.857 kWh/KgCOD for phenol and 3.08 kWh/KgCOD for

tween80.

A. Kinetics studies

The regression coefficient (R-squared) values were found

to be closer to unity at most temperatures for pseudo-first-

order kinetics than that for the pseudo-second-order kinetics

model. Therefore, the electro-oxidation of the synthetic

phenol/tween80 saline solution can be approximated more

appropriately by the pseudo-first-order kinetic model than

the second order kinetic model.

Temperature

(ºC)

K 1

(min-1

)

R-

squared

(1st

order)

K 2

(10-6

L/mg.min)

R-

squared

(2nd

order)

10 0.034 0.9973 10.123 0.9522

20 0.0414 0.9834 16.075 0.9556

30 0.0426 0.969 17.075 0.9375

40 0.0428 0.9857 29.8 0.9857

50 0.058 0.9513 23.8 0.9857

60 0.052 0.9578 41.35 0.9822

70 0.05 0.9887 17.17 0.996

Table 3: Reaction Kinetics Data (Phenol)

Temperature

(ºC)

K 1

(min-1

)

R-

square

d

(1st

order)

K 2

(10-6

L/mg.min)

R-

squared

(2nd

order)

10 0.0327 0.9883 8.6 0.9511

20 0.0405 0.9867 11.13 0.9

30 0.0394 0.9966 15.36 0.9866

40 0.0283 0.9944 6.35 0.765

50 0.0329 0.9632 13.23 0.323

60 0.0355 0.9872 13.23 0.982

70 0.0385 0.9902 30.46 0.901

Table 4: Reaction Kinetics Data (Tween80)

A. Real sample analysis

Current(A)

Volta

ge

(V)

Electroly

sistime

(min.)

Initial

COD

(mg/L)

Final

COD

(mg/L)

0.2 3 60 400 Nil

0.2 3.1 90 1110 Nil

0.2 3.1 30 768 160.2 3.1 30 203 Nil

Table 4: COD Analysis in a Real Saline Sample

A real saline wastewater from petrochemical industry was

electrochemically treated using the optimized current 0.2A.

We achieved a COD reduction of up to 100% with the pH

being native, since the sample was alkaline and therefore

favored (5) in the forward direction and subsequent release

of hypo chlorites for oxidizing the organic matter.

IV. CONCLUSION

Electro oxidation of organic content under high saline

condition (330 g NaCl/L) was studied using phenol andtween80 as model system and graphite as the anode. The

standard method for COD analysis was modified for better precision and the parameters such as current of

0.2A(tween80) and 0.3A(phenol), potential of 4V(tween80)

and 3V(phenol), pH of 6.4(tween80) and 6.0(phenol),

temperature of 10ºC and reaction time of 60 minutes were

optimized with respect to pollution reduction and energy

consumption. RSM has been successfully employed for the

electrochemical treatment of phenol and tween80. The

reaction kinetics of this process was found to follow pseudo-

first-order rate expression. It gave about a positive value for

ΔGº which indicates non-spontaneity. ΔSº and ΔHº values

from the thermo dynamical analysis were found to be

negative for both phenol and tween80. Therefore for

spontaneity, lower temperature was preferred and COD

removal of up to 93.33 % was achieved.

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treatment of organic content at high total dissolved solids by electrochemical oxidation

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