Treatment of textile wastewater using electrofenton process

1. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
248
TREATMENT OF TEXTILE WASTEWATER USING
ELECTROFENTON PROCESS
SRUTHI K., SOSAMONY K. J.
Department of Civil Engineering, Government Engineering College Thrissur, Kerala, India
ABSTRACT
In this study, the Electrofenton process has been used for the treatment of synthetic textile wastewater. Box-
Behnken design was applied to evaluate the effects of parameters like pH, Fe2+
dosage (mM), current (mA) and
electrolysis time (min) on synthetic dye water treatment, in terms of chemical oxygen demand (COD) and dye removal
efficiencies. The result shows that, on following the optimum combination of parameters, the maximum removal of COD
is 86%, and the maximum Dye removal obtained is 70%.
Keywords: Advanced Oxidation Process, Box-Behnken Design, Electro-Fenton, Optimization
1. INTRODUCTION
Textile industry is one of the complicated industries which uses chemicals like dyes, acids, alkalies, starch and
surfactants etc., for their processes. Textile industry is a very diverse sector in terms of raw materials, processes, products
and equipment and has very complicated industrial chain [1]. The textile industry consumes large quantities of water and
generates large volume of waste water from different steps in the printing, dyeing and finishing processes. Pre-treatment
include desizing, scouring, washing etc. [2].
Dyeing mainly aims at dissolving the dye in water, which will be transferred to the fabric to produce coloured
fabrics. Printing is a type of dyeing which is confirmed to a certain portion of the fabric that constitutes the design. In
dyeing, colour is applied in the form of solutions, whereas in printing, the colour is applied in the form of a thick paste.
Finishing processes involves the use of a large number of agents for softening, crosslinking and waterproofing and is
done to improve specific properties in the fabric. Waste water from printing and dyeing units is often rich in colour and
contains residues of dyes and chemicals, such as complex compounds, many aerosols, high COD and BOD
concentration. The waste water also contains natural impurities washed off from fibres and the chemical materials used
in the various processes.
Due to their high BOD/COD, their colouration and salt content, the wastewater from dyeing cotton will be
seriously polluted. The coloured dye stuffs prevent the entry of light into the water, thereby negatively affecting the
photosynthetic activities. It also destroys the aesthetic appearance of rivers and streams [3]. Numerous physicochemical
processes like coagulation, flocculation, precipitation, oxidation, irradiation, incineration, and membrane adsorption have
been used for the treatment of dye contaminated effluents. But most of these processes become ineffective due to the
major disadvantages like high cost, sludge generation and handling difficulties of waste generated. Since biological and
physicochemical methods have been used with a low efficiency, the most promising alternative are the so called The
Advanced oxidation processes (AOPs), which are based on the free hydroxyl radicals production (*OH) as a strong
oxidant for organic compounds. Advanced Oxidation Processes are defined as a process that makes use of free *OH in
aqueous solution, produced by different means such as chemical, photochemical or electrochemical reactions, to promote
the oxidation of organic compounds present in waste water. One of the most promising method among the AOPs is the
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Volume 5, Issue 12, December (2014), pp. 248-255
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Electrofenton process [4]. The Electrofenton process involves the in-situ electrochemical generation of H2O2 which
readily decomposes in an aqueous medium catalysed with iron ions to produce the hydroxyl radical species [5]. The
relevant electrochemical reaction, described by the following equation corresponds to the 2e- reduction of dissolved
oxygen (O2) under slightly acidic conditions:
O2+ 2H+
+ 2e
-
H2O2 (1)
The presence of iron ions, which are usually introduced to the system as FeSO4, accelerates the production of
•OH radicals:
Fe2+
+ H2O2 Fe (OH)2+
+ •
OH (2)
Hydroxyl radicals are highly reactive species that are able to attack and destroy even the most persistent organic
molecules that are not oxidized by the oxidants as oxygen, ozone or chlorine. Hydroxyl radicals then react on organic
compounds to produce simple end products:
*OH + pollutants products (3)
This study made use of Response surface methodology (RSM), which enabled the use of minimum number of
experiments while simultaneously changing several variables. Response surface methodology (RSM) is a collection of
mathematical and statistical techniques useful for the modeling and analysis of problems in which a response of interest
is influenced by several variables and the objective is to optimize this response. RSM explores the relationship between
several explanatory variables and one or more response variables. The Box-Behnken design (BBD) is a type of response
surface method which is based on three-level incomplete factorial designs. It requires fewer runs when compared to other
RSM designs making its application more economical [6].
2. MATERIALS AND METHODS
2.1 Sampling of real textile wastewater
Three samples of untreated real textile wastewater were collected at different intervals from Augustan Textile
colours Ltd. Palakkad. They were stored at 4o
C and analysis was done for all the samples collected. The average values
of the characteristics of untreated real textile wastewater are shown in the table 1.
TABLE 1: Characteristics of real wastewater
Analytical Parameters Real sample (avg.)
COD (mg/l) 750
BOD (mg/l) 192
Turbidity (NTU) 119
Sulphide (mg/l) 126
Chloride (mg/l) 1200
Hardness (mg/l) 410
Alkalinity (mg/l) 1140
Total Suspended Solids (mg/l) 460
Total Dissolved Solids (mg/l) 2180
2.2 Preparation of Synthetic Wastewater
The synthetic wastewater was simulated towards the characteristics of a real textile dyeing effluent. Dyes were
mixed in distilled water along with various chemicals like levelling agent, lubricant and wetting agent. The composition
of the dye and various chemicals used in the synthetic sample preparation are given in the table 2.

3. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
30 – 31, December 2014, Ernakulam, India
250
TABLE 2: Composition of chemicals used in synthetic sample preparation
After the preparation of synthetic sample, the parameters like Chemical Oxygen Demand (COD), Biochemical
Oxygen Demand (BOD), turbidity, sulphide, chloride, hardness, alkalinity, Total Suspended Solids (TSS), and Total
Dissolved Solids (TDS) were experimentally found out in the laboratory.
2.3 Chemicals
The reactive dye Chemifix Ultra Red 3D was provided by Augustan textile industry in Palakkad, and was used
without further purification. All the chemical substances used in the experiment, heptahydrated ferrous sulfate,
Anhydrous sodium sulfate and sulphuric acid were of reagent grade. Sulphuric acid was used to adjust the initial solution
pH. All of the solutions were prepared from the deionized water and the experiments were conducted at room conditions.
2.4 Experimental design
The Design-Expert software Minitab version 16 was used to design the number of experiments to be performed,
calculate the experimental data and to evaluate the experimental results. In order to investigate the effects of significant
factors and to obtain the optimum condition, the Box-Behnken statistical design was used. The optimization procedure
involves studying the response of statistically designed combination, estimating the coefficients by fitting experimental
data to the response functions and predicting the response of fit model.
2.5 Electrofenton Experimental setup
The performance of Electrofenton process for treating synthetic wastewater was evaluated in lab scale. Reactor
is a glass beaker having a size of 9.5cm diameter and 15cm height. Four identical bipolar graphite electrodes, immersed
in a solution in the beaker act as cathode and anode respectively. The size of the graphite rods are 1.5cm diameter and
15cm height. Aeration was done using an aerator, which was pumped into the bottom of the reactor at a flow rate of 10
L/ min.
2.6 Electrofenton Experimental method
The graphite rods used in this experiment were pretreated before the experiments. They were first immersed in
dilute nitric acid solution; then they were subjected to oven drying. Experiments were performed in a reactor which is
glass beaker of 1000 ml capacity. In each experiment, 700 ml of synthetic wastewater was used. 0.5 M Na2SO4 was used
as the supporting electrolyte. The synthetic wastewater in the reactor was aerated as soon as the reactor was started. All
the runs were performed at room temperature. After the reaction, the samples were allowed to settle in the reactor for 60
minutes. The laboratory experimental setup is shown in the Fig. 1.
Figure 1: Laboratory experimental setup of Electrofenton process
Chemicals Quantity
Chemifix ultra red dye 80 mg/l
Sorbecol (levelling agent) 1ml
Nylube c ( lubricant) 0.5ml
Monosodium phosphate 5.5 ml
Salt solution(25%) 9.6 ml
Caustic soda(20%) 6.0 ml
Wetsoft (softener) 50 ml

4. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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2.7 Analysis of treated sample
The chemical oxygen demand (COD) of dye solution was measured according to the standard methods for
examination of water and wastewater by closed reflux methods. The dye concentration was determined from the
absorbance characteristics in the UV–Vis range with the calibration method. A Hach UV–Vis spectrophotometer was
used. For the measurement the maximum absorption (λmax=600 nm) wavelength of dye was determined by
measurement of it absorbance at various wavelengths.
3. RESULTS AND DISCUSSION
Four important factors affecting Electrofenton process; namely, pH, Fe2+
dosage, current intensity, and
electrolysis time were selected as factors in the Box- Behnken statistical design. COD and dye removal efficiencies were
represented by a response function.
TABLE 3: The levels of the four factors on Box- Behnken statistical design
Variables Symbol
Variable level
Low High
pH A 2 4
Fe2+
(mM) B 0.1 0.15
Current (mA) C 50 250
Electrolysis time(min) D 30 120
The total number of experiment with four variables and two levels in Box- Behnken design were 27
experimental runs. The results shows that the maximum removal of COD is 86%, and the maximum Dye removal
efficiency is 70%. From the experiments the maximum COD removal was achieved when the pH was 3, Fe2+
0.15mM,
current 250 mA, and time 75 minutes. But the dye removal efficiency corresponding to this combination of parameters
was only 67%. The maximum dye removal efficiency of 70% was obtained for the following combination, pH 3, Fe2+
0.125 mM, current 250 mA, electrolysis time 120 minutes. The regression coefficients for COD and dye removal is
given in the table 4.
TABLE 4: The regression coefficients for COD removal and dye removal.
3.1 Effect of each parameter on COD removal efficiency
The parameter which affects COD removal the most, is the current having regression coefficients of 9.4167,
followed by electrolysis time and ferrous sulfate dosage. pH has a lesser effect on COD removal with a regression value
of 0.0833.Thus current have significant effect on the COD removal efficiency, and time and Fe2+
have lesser significance.
Fig. 2, shows a positive effect of current and time for the maximum COD removal. From the graph it is clear that using
60mA current for 30 min time, the percentage COD removal is 55%. On increasing the reaction time to 120 min and
current to 240 mA, there is considerable increase in COD removal efficiency to 85%. This is because, more the current,
more H2O2 is supplied to the solution from the two electron reduction of O2 at the electrodes.
Variable
Regression coefficients
COD % DR%
pH 0.0833 -1.1667
Fe2+
(mM) 5.2500 4.4167
Current (mA) 6.4167 6.8333
Electrolysis time(min) 9.4167 16.2500

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Figure 2: Response Surface plot of COD% vs current, time
Fig. 3, shows the response surface plot of COD % vs current and Fe. The graph shows that using 0.1 mM of
Fe2+
at maximum current of 250 mA gives 70% COD removal. While on increasing the Fe2+
ion to 0.15 mM, there is
85% COD removal. This is due to the reason that increase in the amount of Fe2+
ion promotes the reaction of H2O2 with
Fe2+
, thereby increasing the production of *OH, which is responsible for the efficient COD removal from the synthetic
wastewater.
Figure 3: Response Surface plot of COD% vs current, Fe
Fig. 4, shows the positive effect of current and the optimum value of pH for the efficient COD removal. pH is an
important parameter for fenton reactions which controls the rate of generation of *OH radical. From the graph it is clear
that, the increase in pH value shows same effect at various currents. At maximum current when the pH value is 2, the
COD removal efficiency is around 65%.
With the increase in pH value to 3, the percentage COD removal increases to about 80%. But on further
increasing the pH to 4, the COD removal efficiency decreases to 70%. Therefore the acidic pH level around 3 is optimum
for Fenton oxidation. This is due to the fact that, at low pH condition the reaction between H2O2 and Fe2+
is significantly
affected, causing the reduction in *OH production. Whereas at high pH condition, the deactivation of Fe2+
causes the
reduction of *OH due to the formation of ferric hydroxide precipitate resulting in low COD removal efficiency [7].
Figure 4: Response Surface plot of COD % vs current, pH

6. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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3.2 Effect of each parameter on the Dye removal efficiency
The current is the parameter which has the most significant effect on dye removal. The regression coefficient is
16.25. Time and Fe2+
have slight effect on dye removal with value 6.833 and 4.4167 respectively. While pH has a
negative effect on dye removal with regression value of -1.1667. Fig. 5, shows the positive effect of time and current on
the efficient dye removal. Increase in reaction time and current enhances the dye removal efficiency to about 70%. In
this graph the pH value and Fe2+
is kept as hold values. The pH value is kept as 3 and the Fe2+
dosage is kept constant as
0.125 mM.
Figure 5: Surface plot of DR% vs current, time.
Fig. 6, shows the surface plot of DR % vs current and Fe. The graph shows that using 0.1 mM of Fe2+
at
maximum current of 250 mA gives 55% Dye removal. While on increasing the Fe2+
dosage to 0.15mM, there is 70%
Dye removal.
Figure 6: Response Surface plot of DR% vs current, Fe
Fig. 7, shows the response surface plot of Dye Removal % vs time and pH. At maximum time when the pH
value is 2, the dye removal efficiency is around 50%. With the increase in pH value to 3, the percentage dye removal
increases to about 70%. But on further increasing the pH to 4, the percentage dye removal decreases to 60%. Therefore
the acidic pH level around 3 is optimum for the efficient dye removal.
Figure 7: Surface plot of DR% vs time, pH

7. Proceedings of the International Conference on Emerging Trends in Engineering and Management (ICETEM14)
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4. OPTIMIZATION
The main objective of the optimization process is to determine the optimum conditions favourable for the
removal of dye and COD concentration from the synthetic wastewater, by Electrofenton process. The optimization
module in Response surface methodology searches for a combination of factor levels that simultaneously satisfy the
requirements placed on each of the responses.
The Fig. 8, shows the optimization conditions or optimized combination of parameters favourable for maximum
COD removal and dye removal efficiency by Electro fenton process. From the graph, it is clear that the sample treated
with an initial pH of 2.82, Fe2+
dosage 0.14 mM, with a current 227 mA for 108 minutes gives maximum efficiency for
the process.
Figure 8: Optimization plot for Electrofenton process
The actual removal efficiencies when followed these predicted optimum conditions were 87% COD removal
and 70% Dye removal. Hence it can be summarized that the experimental results obtained under optimized conditions
were close to the predicted results in terms of COD and Dye removal, thus proving the reliability of the methodology
used within the range of concentration investigated [7].
5. CONCLUSION
The treatment of synthetic textile wastewater was investigated using Electrofenton process. The effect of
various operational parameters like applied current, pH, electrolysis time and ferrous ion dosage was studied. From the
experiments the maximum COD removal was 86% and this was obtained when the pH was 3, Fe2+
0.15mM, current 250
mA, and time 75 minutes. The maximum dye removal was 70% and this was obtained for the following combination of
pH 3, Fe2+
0.125 mM, current 250 mA, electrolysis time 120 minutes. The effect of each parameter was studied by
analysing the response surface design, and the parameter which has most significant effect on both COD removal and
dye removal was current. The optimised condition favourable for the maximum dye and COD removal was obtained
using response optimiser in Box- behnken design. The optimum conditions was pH 2.82, Fe2+
dosage 0.14 mM, current
227 mA and electrolysis time 108 minutes. When followed these predicted optimum conditions the removal efficiencies
obtained for COD and dye removal was 87% and 70% respectively.
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