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