Scholarly article on topic 'A Comparative Study of Homogeneous and Heterogeneous Photo-fenton Process for Textile Wastewater Treatment'

A Comparative Study of Homogeneous and Heterogeneous Photo-fenton Process for Textile Wastewater Treatment Academic research paper on "Chemical sciences"

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{"Textile wastewater" / "Homogeneous photo-Fenton process" / "Heterogeneous photo- Fenton process" / "Taguchi's experimental design"}

Abstract of research paper on Chemical sciences, author of scientific article — P.H. Sreeja, K.J. Sosamony

Abstract In this study, the COD removal and Dye removal efficiencies of homogeneous and heterogeneous photo-Fenton process are compared for the treatment of synthetic textile wastewater. The effect of parameters like pH, catalyst dosage, H2O2 dosage and U V power are evaluated using Taguchi's experimental design. In heterogeneous photo-Fenton process copper modified iron oxide is used as the catalyst. The heterogeneous process showed the highest removal efficiencies under optimum condition with COD removal of 62% and Dye removal of 85%.For homogeneous photo-Fenton process COD removal and Dye removal are 47% and 82% respectively.

Academic research paper on topic "A Comparative Study of Homogeneous and Heterogeneous Photo-fenton Process for Textile Wastewater Treatment"

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Procedia Technology 24 (2016) 217 - 223

International Conference on Emerging Trends in Engineering, Science and Technology (ICETEST

- 2015)

A Comparative Study of Homogeneous and Heterogeneous Photo-Fenton Process for Textile Wastewater Treatment

Sreeja P H a*, Sosamony K J b

aPG student, Department of Civil Engineering, Government Engineering College, Thrissur, 680009, India b Associate professor, Department of Civil Engineering, Government Engineering College, Thrissur, 680009,India

Abstract

In this study, the COD removal and Dye removal efficiencies of homogeneous and heterogeneous photo-Fenton process are compared for the treatment of synthetic textile wastewater. The effect of parameters like pH, catalyst dosage, H2O2 dosage and U V power are evaluated using Taguchi's experimental design. In heterogeneous photo-Fenton process copper modified iron oxide is used as the catalyst. The heterogeneous process showed the highest removal efficiencies under optimum condition with COD removal of 62% and Dye removal of 85%.For homogeneous photo-Fenton process COD removal and Dye removal are 47% and 82% respectively.

© 2016 The Authors.PublishedbyElsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICETEST - 2015

Keywords: Textile wastewater; Homogeneous photo-Fenton process; Heterogeneous photo- Fenton process; Taguchi's experimental design

1. Introduction

Textile industry is one among the various industries having very diverse sector and has a very complicated industrial chain. The major impacts caused by textile industries include pollutants discharge, water consumption and energy consumption. The discharged wastewater is the main environmental problem caused by the textile industry. The major processes in textile industries are sizing, weaving, desizing, scouring, bleaching, mercerizing, fulling, dyeing and finishing. Dyeing and finishing processes contribute the major portion of pollution [1].

* Corresponding author. Tel.:+0 890 757 89 75;

E-mail address:sreejaotp@gmail. com

2212-0173 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of ICETEST - 2015 doi:10.1016/j.protcy.2016.05.065

Various chemicals and dyes of complex structures are used for the different processes in the textile industries. The presence of textile dyes in water bodies affects the photosynthetic activity, aesthetic appearance, makes water unfit for drinking and for the use of domestic and irrigation purposes [2].

Various physico-chemical processes are used for the dye contaminated effluent treatment. But, these processes are ineffective due to their various disadvantages like high cost, high sludge and difficulty in handling. Advanced oxidation processes (AOPs) is a most promising alternative which overcomes these disadvantages. Advanced oxidation processes deals with the generation of hydroxyl radicals. The hydroxyl radical oxidizes organic contaminants into carbon dioxide and water rapidly and as a result it can effectively degrade the pollutants. The most important AOP is the Fenton's system, which consist of the reaction between H2O2 and Fe2+ in an acidic solution to produce free *OH.

The Fenton process that takes place in presence of U V light or visible light is called the Photo-Fenton process. In this method *OH is released by the molecular fragmentation of water molecule to oxidize the organic compounds. Photo-Fenton process in presence of U V light is found to be an effective method for wastewater treatment.

Fe2+ + H2O2^ Fe3+ + *OH + OH-

Fe2+ + H2O2 ^ Fe (OH) 2+ + *OH

Fe (OH)2+ + hv ^ Fe2+ + *OH

(1) (2) (3)

Eq.1 represents the Fenton reaction. In this equation Fe2+ reacts with hydrogen peroxide and produces Fe3+ and *OH. The reaction also produces iron aqua complex, Fe (H2O)5(OH)2+ represented as Fe(OH)2+(Eq.2). It is the new important source of *OH. The reaction of Fe (OH)2+ with UV light regenerates Fe2+ and *OH(Eq.3). Thus compared to Fenton process, photo-Fenton process requires less Fe2+ concentration. A cyclic mechanism takes place when this UV regenerated Fe 2+ reacts with the H2O2 in the solution [3].

The photo-Fenton process can be both homogeneous and heterogeneous. The type of interaction between the Fenton's reagent and the compounds to be degraded is mainly considered in the homogeneous process. But the major disadvantages of this process are sludge generation due to post treatment process, limited pH range, high iron discharge to environment and difficulty in iron ion recovery [4].

These disadvantages made heterogeneous process superior to homogeneous process. In heterogeneous phase, the physical steps in addition to chemical changes take place on the surface of the catalyst at the active sites where mass transfer limited adsorption of reactant molecules occurs. At the end of the reaction, the product molecules are desorbed and leave the active sites available for a new set of reactant molecules to attach to the surface and react. The main advantages of heterogeneous process are less iron production, environment friendly, easy separation of catalyst from the solution.

In this study comparison of homogeneous photo-Fenton process and heterogeneous photo-Fenton process using photo-Fenton process is conducted. The optimum process parameters are found out using Taguchi method. Taguchi's method is used to find out the most significant factor in the process. An orthogonal array is used to find out the factors. The main advantage of this method is the lesser number of experiments. An orthogonal array means the design is balanced so that factor levels are weighted equally. Because of this, each factor can be evaluated independently of all the other factors, so the effect of one factor does not influence the estimation of another factor. The analysis of variance (ANOVA) is also used to find out the significant factors [5, 6].

2. Materials and methods

2.1. Characteristics of textile wastewater

Collection of real textile wastewater was done at different intervals from Augustan Textile colours Ltd. Palakkad. The collected samples were stored at an appropriate temperature (4°C) and they were analyzed to find out the characteristics. Table 1 gives the average values of the characteristics of untreated textile wastewater.

Table 1. Characteristics of untreated textile wastewater

Analytical parameters Concentration

pH 10-11

Total dissolved solids(mg/L) 2000-3000

Total suspended solid(mg/L) 40-100

Total alkalinity as CaCO3(mg/L) 700-1200

Turbidity(NTU) 70-120

Total Hardness as CaCO3(mg/L) 250-420

Sulphide(mg/L) 100-140

Chloride(mg/L) 1200-1600

BOD(3 day 27°C)(mg/L) 180-240

COD(mg/L) 600-800

2.2. Synthetic wastewater preparation

Synthetic wastewater was prepared using various chemicals like levelling agent, lubricant and wetting agent along with the dye used. The chemicals were mixed in de-ionized water suitably based on their composition given in table 2.

Table 2.Composition of chemicals used in synthetic sample preparation

Chemicals

Quantity

Chemistar Turq Blue (Dye) Sorbecol (levelling agent) Nylube C(Lubricant) Salt

20 % Caustic soda Wetsoft (Softener)

100mg/L

20ml/L

After the synthetic wastewater preparation its characteristics were analysed experimentally in the laboratory. The characteristics are given in the table 3.

Table 3. Characteristics of synthetic wastewater

Parameter Concentration

COD 780mg/L

BOD 198mg/L

pH 10.85

TSS 48mg/L

TDS 2603mg/L

Alkalinity 700mg/L

Turbidity 72NTU

Sulphides 110mg/L

Chlorides 1575mg/L

Hardness 297mg/L

2.3. Chemical used

The dye used in the study was provided from the industry. The other chemicals used like heptahydrated ferrous sulphate, anhydrous sodium sulphate, sulphuric acid were of reagent grade. The experiments were conducted at room temperature and sulphuric acid was used to adjust the pH of the solution.

2.4. Design of experiments

To find out the number of experiments to be carried out, experimental data calculation and experimental results evaluation were done using software Minitab version 16.To obtain the significant factors and to find out the optimum parameters, the Taguchi method was used. Taguchi's orthogonal array (OA) analysis helps to find out the best optimum parameters by considering least number of experiments. By using this method, lesser experiments are needed to study different levels of all parameters. Signal-to-noise (S/N) ratio is used to find out the parameter variability in this method. The S/N ratio is defined as ratio between desirable results (signal) to undesirable results (noise).The optimum condition is given by the maximum S/N ratio [7].

2.5. Photo-Fenton process

The performance of photo-Fenton 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. 1 litre of the sample was taken for treatment. A magnetic stirrer provides a continuous mixing effect for the solution.8W, 16W, 24W monochromatic U V lamps were used as the source of light respectively. The Experimental setup is shown in the figure 1.

2.6. Preparation of Copper Modified Iron Oxide

A modified iron oxide catalyst was prepared by mixing together 50.0 g FeSO4.7H2O dissolved in 250 mL of water and 25.0g of CuSO4.5H2O dissolved in 250 mL of water. Aqueous NaOH was added drop-wise to adjust the pH to 9.0. The content was agitated for 40 minutes. The precipitate was filtered, washed with water to ensure complete removal of the NaOH and sulphate ions (SO4 ) and air dried. The precipitate was kept in a muffle furnace at 400°C for 2 hour [8, 9].

2.7. Photo-Fenton experiment

In photo-Fenton experiment 1L of the sample is taken in the beaker. pH of the solution is adjusted using H2SO4 and NaOH. Experiments were conducted at room temperature for different combinations of parameters designed using Taguchi method. The reaction starts when Fe2+ and H2O2 are added to the sample. The sample is mixed well with a magnetic stirrer. After 15 minutes the U V lamp of required power is switched on. The setup is covered with aluminium foil in order to avoid the U V radiation. Photo-Fenton experiment is conducted in both homogeneous and heterogeneous way by replacing Fe2+ by copper modified iron oxide.

Fig.1 The experimental setup of photo-Fenton process

2.8. Analysis of treated sample

A closed reflux method was used to measure the chemical oxygen demand of wastewater. Calibration method was used to determine the absorbance characteristics. A Hatch UV-Vis spectrophotometer was used. Absorbance at various wavelengths was determined to measure the maximum absorption wavelength (600nm).

3. Results and discussions

In order to investigate the factors (pH, catalyst dosage, H2O2 dosage and U V power) involved in the photo-Fenton process, 16 sets of experiments with operating conditions according to the Taguchi's experimental design were performed. The variables and the values of their levels selected are shown in table 4.

Table 4.Variables and the values of their levels

Parameter Level 1 Level 2 Level 3 Level 4

pH 2 3 4 5

Catalyst dosage (mg/l) 5 10 15 20

H2O2 dosage(mM) 50 100 150 200

UV power (W) 0 8 16 24

3.1. Result of homogeneous photo-Fenton Process and Heterogeneous Photo-Fenton Process

Four important factors affecting photo-Fenton process are pH, catalyst dosage, hydrogen peroxide dosage, and the U V power. The total number of experiments with four variables and four levels in Taguchi design are 16 experimental runs. The results shows that for homogeneous photo-Fenton process the maximum removal of COD is 47%, and the maximum Dye removal efficiency is 80%.For heterogeneous photo-Fenton process the maximum removal of COD is 58%, and the maximum Dye removal efficiency is 90%.

3.2. Determination of optimum parametric levels for COD removal and Dye removal

The effects of experimental parameters on the S/N ratio for COD removal and Dye removal is shown in Figure 2(a, b). For both process, the optimum level for pH is 3, catalyst dosage is 10mg/L, H2O2 dosage is150mM and U V power is 16 W respectively.

3.3. Effect of each parameter on COD removal and Dye removal

From figures 2(a,b), it can be seen that as pH increases the COD removal rate and Dye removal rate first increases and later it decreases. This is because at high pH iron precipitates as hydroxide (Fe(OH3)).In this form iron decomposes H2O2 into water and oxygen. So less hydroxyl radicals are available. At lesser pH, formation of oxonium ion (H3O)+ enhances the stability of H2O2 and restricts the generation of *OH radical. This results in less degradation. As H2O2 dosage increases the removal rates increases. This is due to the scavenging effect of H2O2. The removal % decreases with the increase in ferrous dosage (catalyst). This is due to the catalytic effect of Fe2+ on H2O2.When Fe2+ concentration increases the formation of Fe (OH) 2+ increases. Fe (OH) 2+ absorbs U V light, this results in decrease in strength of U V light. In heterogeneous process the amount of catalyst would increase the number of iron ions and copper ions in which case there is a possibility of short circuiting of Ferrous, Ferric, cuprous and cupric ions. As a result, lesser number of hydroxyl radicals would be formed which decreases the reaction rate .An increase during the initial stage is due to the increase in surface area of the catalyst as its dosage increases. When light intensity increases the removal rate increases. This is due to the increased number of photons reacting with the Fe2+ ions which results in hydroxyl radical increase and increase in reaction rate. A decrease in later stage is due to the external thermal effect.

Main Effects Plot for S/N ratios for COD removal and Dye removal

Data Means

pH Catalyst dosage

33- -----^

« S 32- IS \ \

(Л 2 3 4 5 5 10 15 20

0 H2O2 dosage U V power

£ 34-

t— N y

32- У

50 100 150 200 0 8 16 24

Signal-tto-noise: Larger is better

Main Effects Plot for S/N ratios for COD removal and Dye removal

Data Means

pH catalyst

35.4 y\

34.8 / \

» 34'2' S 33.6 IQ ' \ \

z 33.0

1Л 2 3 4 5 5 10 15 20

О H2O2 U V power

£ 35.4

E 34.8

33.6 /

33.0 /

50 100 150 200 0 8 16 24

Signal-to-noise: Larger is better

Fig.2 Effects of experimental parameters on COD removal and Dye removal (a) for homogeneous process ;(b) for heterogeneous process

3.4. ANOVA and significance of parameter

Analysis of variance was used to find out the significance of the experimental parameters .The analysis was evaluated for a confidence level 95%, that is for significance level of a=0.05 .The ratio of individual sum of squares of a particular independent variable to the total sum of squares of all the variables gives the percentage contribution (P%) of the independent variable on the response.

For homogeneous process the most significant factor for COD removal is pH followed by U V power. For Dye removal the significant factors are pH, U V power and catalyst dosage. For heterogeneous process the most significant factor for COD removal is pH followed by U V power. The most significant factor for Dye removal is pH followed by U V power and catalyst dosage.

3.5. Confirmation test

The final step in the Taguchi's experimental design is the experimental confirmation test. The confirmation experiments were conducted with the optimum parameters obtained and the results were compared with the predicted results obtained using the multiple linear regression models. The regression equations developed are:

• For homogeneous photo-Fenton process

COD removal% =47.087-1.925 pH-0.325 catalyst dosage+.0015 H2O2 dosage+0.247 U V power Dye removal % =78.275-2.15 pH-0.37 catalyst dosage+0.009 H2O2 dosage+0.5687 U V power

• For heterogeneous photo-Fenton process

COD removal% =50.387-1.025 pH-0.395 catalyst dosage-0.006 H2O2 dosage+0.835 U V power Dye removal% =94.2-4.25 pH-0.5 catalyst dosage-0.019 H2O2 dosage +0.275U V power

The Predicted values of the responses obtained using optimized parameters can be computed using the above equations. This equation considers only the significant parameters. The regression equations thus establish a correlation between the significant terms obtained from ANOVA. The predicted and the actual values obtained as a result of the confirmation test are given in table 5.

For homogeneous photo-Fenton process the actual values from confirmation test for COD removal is 47% and Dye removal is 82%.The predicted results for COD removal and Dye removal are 45% and 85% respectively. For heterogeneous photo-Fenton process the actual values from confirmation test for COD removal is 62% and Dye

Table 5.Result of confirmation experiment for photo-Fenton process

pH catalyst dosage(mg/L) H2O2 dosage(mM) U V power (W) COD removal % Dye removal %

Actual predicted Actual predicted

Homogeneous photo-Fenton process 3 10 150 16 47 45 82 85

Heterogeneous photo-Fenton process 3 10 150 16 62 61 85 86

removal is 85%.The predicted results for COD removal and Dye removal are 61% and 86% respectively. 4. Conclusion

Photo-Fenton process was used to investigate the treatment of synthetic textile wastewater. In photo-Fenton process both homogeneous photo-Fenton process and heterogeneous photo-Fenton process were studied and it was found that heterogeneous photo-Fenton process is more efficient than homogeneous for COD removal and colour removal. The optimum condition obtained from Taguchi experiment for homogeneous photo-Fenton process and heterogeneous photo-Fenton process were pH of 3, catalyst dosage 10mg/L, H2O2 dosage 150mM and UV power 16W.With these optimum condition, the actual removal efficiency for COD and colour are 47% and 82% for homogeneous process and 62% and 85% for heterogeneous process respectively. The predicted removal efficiency for COD and colour, obtained using regression model are 45% and 81% for homogeneous process and 61% and 86% for heterogeneous process respectively. Also it is found that the sludge formation is less in heterogeneous photo-Fenton process compared to homogeneous method. From this result it is clear that heterogeneous photo-Fenton process is efficient process for removal of COD and colour from textile wastewater with less sludge formation.

Acknowledgements

The author would like to thank Augustan Textile colours Pvt Ltd.Palakkad,Kerala for providing the chemicals needed for the study and also Polluchem Laboratories Pvt Ltd,North Kalamassery,Ernakulam,kerala.

References

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