Conference Paper · December 2016
CITATIONS
0
READS
33 3 authors:
Some of the authors of this publication are also working on these related projects:
This is part of my MS thesisView project
Artificial neural network and response surface methodology modeling to assess non-thermal plasma efficiency in simultaneous removal of BTEX from waste gases View project
Elham Rahmanpour Salmani
Doctor Sheikh Hospital, Mashhad University of Medical Sciences 12PUBLICATIONS 11CITATIONS
SEE PROFILE
Mojtaba Davoudi
Torbat Heydarieh University of Medical Sciences 16PUBLICATIONS 55CITATIONS
SEE PROFILE
Ali Asghar Najafpoor
Mashhad University of Medical Sciences 34PUBLICATIONS 143CITATIONS
SEE PROFILE
All content following this page was uploaded by Elham Rahmanpour Salmani on 26 August 2017.
The user has requested enhancement of the downloaded file.
Optimization of electrochemical pathways for dyeing wastewater treatment in continuous-flow divided cell
Elham Rahmanpour Salmani 1*, Mojtaba Davoudi2, Ali Asghar Najafpoor3
1. MSc, Student Research Committee, Health School, Mashhad University of Medical Sciences, Mashhad, IR Iran, [email protected]
2. Assistant Professor, Faculty of Health, Torbat Heydariyeh University of Medical Sciences, Torbat Heydariyeh, IR Iran, [email protected]
3. Associate Professor, Faculty of Health, Mashhad University of Medical Sciences, Mashhad, IR Iran, [email protected]
Abstract
Environmental concerns have been arisen from entrance of a significant fraction of synthetic dyes by discharging textile effluents. Reactive dyes based on azo chromophores as the most common colorants used in textile industry cannot be easily removed through many of the treatment methods mainly because of their complex aromatic structure. In many studies, potentiality of electrochemistry approach to deal with industrial pollutions has been actualized. This work was focused on finding the optimum operating conditions of dye removal using continues flow electrochemical cell through oxidation and reduction mechanisms. The graphite and stainless steel were applied as anode and cathode, sodium chloride and Reactive Red 120 (RR120) were used as supporting electrolyte and model dye, respectively. Reactor was divided by cellulosic separator and operated in continuous flow mode. CCD of Design Expert7 was considered for designing the experiments, analyzing data and optimization. Accordingly, the effects of initial dye concentration (100-500 ppm), electrolysis time (20-90 min), and current intensity (0.1-0.4 A) as variables governing the efficiency of the process were studied through a set of repeated experiments. The maximum removal of color 98.14% was achieved at 90 min of electrolysis time using 0.25 A of current intensity in a solution containing 300 ppm of dye. In effluent with same concentration under same current density, decreasing reaction time from 90 to 55 min reduced the efficiency about 5%. Electrolysis time was the most influential factor on response. 1.67 to 13.2 Kwhm-3 of electrical energy was consumed in experiments. 87.6% removal rate was observed under optimum conditions with consumption of only 6.55 kwhm-3 of electrical energy. Current research confirmed that applying electrochemical mechanisms in cell proposed by this study was an effective methode for optimized removal of RR120 from simulated dyeing wastewater.
Key words: Electrochemical Oxidation, Electrochemical Reduction, Optimization, Reactive Red 120
1. Introduction
Synthetic organic dyes have been employed considerably in many branches of industry, such as textile, leather tanning, food, agricultural research, photochemical cells [1], cosmetic, pulp and paper, and pharmaceutical industries [2].
Daily extensive production of colored effluents resulted from large- scale industrial application of dyes and subsequent release of them into receiving environments is undesirable, and unsafe. The textile industry is one of the greatest producers of colored wastewater in the world. In textile industry dye fixation to fabrics fails somewhat and nearly 2-50% of unfixed dye can reach to effluent. A group of colors classified as reactive dyes have been detected in high concentrations in wastewaters mainly due to their low degree of fixation [3].
Reactive dye structure consists of two parts: that part which reacts with the fiber to be colored is obviously the reactive group while the other group responsible for the color is called chromophore [4]. On industrial scale dyes with azo chromophores (–N=N–) are the largest group of synthetic dyes annually produced all over the world [3] mostly because of comfortable and cheap production along with a brilliant shadow [2]. Complex aromatic conjugated structure of reactive azo dye raises its solubility in water, its color intensity, and its resistance to decomposition under normal conditions [5].
Discharge of colored waste streams without applying efficient and sufficient treatment methods on them threatens the health of receiving environments in the vicinity of dyeing industries. It poses serious problems to health of living beings of water bodies [6] by preventing light penetration into the water [7], and causing aesthetic and odor alterations in aquatic ecosystems [8]. To these, carcinogenic, mutagenic, and toxic nature of some dyes and substances caused by their degradation must be added [7]. Possible persistence and the ability for long-term bioaccumulation can raise dyestuffs as the risk factors for human health besides the aquatic biota [8]. Hence, adoption of suitable removal technologies for the treatment of aqueous solutions containing dyestuffs should be considered.
According to literature inquiry a broad range of conventional and novel treatment techniques have been tried by researchers for the removal of dyes from aqueous media.
Conventional biological processes are known to be ineffective for the removal of dyes mainly because of colors stability against light, temperature and biodegradation. Although azo dyes are biodegradable under anaerobic treatment, but breakdown of dye structure and subsequent formation of substances like aromatic amines which may be more toxic than color molecules are preventing factors in selecting of this method [5]. Furthermore, many physical and chemical methods have been utilized for treatment of dyeing wastewaters, but requirement to large areas of land and further treatment [9], also imposing high operational costs for treatment and disposal of residue are common recognized shortcomings which restrict application of some physicochemical pathways for discoloration [10]. Not long, electrochemical techniques have attracted a great interest for treatment of dyeing wastewaters [5]. The feasibility of on-site treatment of various pollutants in less space by controlling the desired reactions has made them distinctive [11]. In electrochemical methods classified into four main types of photoassisted, oxidation, reduction, and electrocoagulation no reagent is added and electron plays the major role [4].
Pollutant removal through electrochemical oxidation proceeds either by direct oxidation on the anode surface through the exchange of electrons or indirectly in the solution bulk by electrochemically generated reactive oxidizing species. Reactive dye degradation can occur by its chemical reaction with active hydroxyl radicals produced on the surface of anode following H2O discharge according to the below mechanisms [12]:
Here, M is the anode surface and R shows the organic molecules. In indirect electro- oxidation mechanism, the in situ generated strong oxidants such as various forms of active chlorine including free-chlorine gaseous, hypochlorous acid or hypochlorite ions oxidize dyestuffs as below [13]:
Simultaneously with oxidation reactions in the anolyte compartment, reduction reactions occur in the catholyte chamber. The most common reaction of cathode is the conversion of water to hydrogen gas [14]:
Electrochemical reduction method has been considered suitable for the treatment of strongly colored wastewaters in which reactive azo dye can be reduced fully or partially to hydrazine or amine compounds respectively [15].
So far, most studies devoted to color removal by electrochemical method were carried out using undivided cells. Two-compartment reactors separated using common membranes mainly made of asbestos or ion exchange have not received great interest for environmental purposes because of remained toxic substances in terms of asbestos or short duration along with high expense related to ion exchange membranes. However, separating the electrochemical chamber can have many benefits such as accelerate the oxidation and reduction reactions which consequently lead to shorter electrolysis time and smaller size of reactor [16], effluent disinfection under acidic conditions of anode section due to the dominance of the hypochlorous acid compared to hypochlorite ion [17], restricted formation of chlorinated by products in acidic solution [18], and faster detoxification of chlorinated organic compounds under alkaline pH of cathode chamber [16]. Therefore, a physical barrier capable to separate two aquatic environments which is environmentally friendly and low-cost can be a viable alternative to conventional membranes. Cellulose was first tried by Davoudi et al [19]. for electrochemical cell separation and its application yielded satisfactory results for low-cost removal of phenol, chromium and ammonia from synthetic tannery wastewater regarding abundance of cellulose in nature.
2. Objectives
The aim of present work was investigating the efficiency of electrochemical oxidation and reduction of reactive red 120 on graphite and stainless steel electrodes by taking advantage of a cellulosic separator in a continuous-flow system. Effective parameters on discoloration efficiency are optimized and reported through this study.
3. Materials and Methods
3.1. Reactor setup, dye solution and measurement method
The electrochemical system used in this study was in bench scale consisted of a rectangular reactor made of plexiglass sheets in the volume of 0.27 Litre, a DC power supply (Iran Pars), a digital multimeter (DT700D), a cellulosic separator made of cotton between reticular PVC sheets, one rod of graphite as anode, one sheet of stainless steel cathode, pump and reservoir (figure1).
Figure 1: Diagram of divided electrochemical cell used for studying simultaneous anodic and cathodic removal reactions of RR120: DPS, DC power supply; M, multimeter; R, reservoir; P,
pump; C, cellulosic separator; G, graphite electrode; and S, stainless steel electrode
Stock solution of color was prepared by dissolving 1 g of reactive red 120 into 1 Litre of distilled water and mixed thoroughly using a magnetic stirrer (DELTA HM-101 IKA- WERKE). Reactive red 120 (RR 120) was chosen as a model of reactive azo dyes since it is the most common colorant used for dyeing of cotton fibers. Its molecular structure and properties are shown in table 1 [20].
Table1: RR 120 structure and properties
Charge Functional group Color structure
Negative Diazo Bright red
M.W C.I No. CAS No.
1673.3g/mol 25810 61951-82-
4
Working solutions were prepared according to the experiments by diluting of stock solution. For each experiment 0.5 Litre solution of specified dye concentration containing 7500 ppm of analytical grade sodium chloride (NaCl) was prepared and 0.3 Litre of that was transferred into the pump reservoir. The electrochemical reactor was operated in continuous mode from anode compartment to cathode in the net reaction volume of 0.2 Litre. The flow
rate from pump to inlet of reactor was set for each run based on dye solution retention time inside the reactor and it was calculated by simple fraction of reaction volume (0.2 Litre) to electrolysis time. After each test, separator and electrodes were removed from the chamber, and cellulosic membrane was placed in 10% NaCl solution to be regenerated. Also, prior experiments, electrodes and reaction chamber were manually cleaned using sponge, and tap water. At the end of each run, a 30ml sample was taken from the catholyte compartment and centrifuged at 3000 rpm for 15 min to obtain a supernatant prior measurement. Absorbance of raw and treated experimental samples was measured at the maximum wavelength of 511 nm using T80UV/VIS Spectrophotometer. To illustrate samples concentrations, a standard curve was plotted by measuring the absorbance of solutions having specified dye concentrations. The system performance in decolorization was then calculated by following expression:
Where C shows the color concentration of solution at times t=0 (initial time) and t (time t).
3.2. Experimental conditions
Operating conditions in terms of most influential factors were chosen on the basis of our primary assays, as well as scientific papers reports. For optimizing responses through smaller number of tests Response Surface Methodology (RSM) of Design-Expert 7 trial version was used. Theory and steps for RSM application is thoroughly explained by Bezerra et al [21]. For empirical modeling of RR 120 removal efficiency CCD the most popular second order design of RSM was selected. CCD designed twenty experiments considering of eight factorial points, six axial points and six central points to study single and interaction effects of initial color concentration, electrolysis time and current density on percentage of color removal. Table 2 shows the independent variables at five coded levels some in rounded values for ease of experiments, whereas, table 3 represents designated experiments. Considering equal outputs of tests repeated at least in double, results presented in this research are reliable.
Table 2: Experimental levels of independent variables
Factor Variable Actual values of variables under coded levels
1 0 1
A Initial dye concentration (mg/l) 100 181 300 419 500
B Retention time (min) 20 34.2 55 75.8 90
C Current density (A) 0.1 0.16 0.25 0.34 0.4
4. Results and Discussion
To find the optimal operating region of parameters affecting the electrochemical decolorization of reactive azo dyes, a series of assays was done for electrolysis of 0.2 Litre working solutions of RR120 in a two-compartment reactor using graphite anode and stainless steel cathode. While, not many studies are available on decolorization by divided cells, present research applied an abundant cheap membrane made of cellulose for this purpose.
Random measuring of test solutions pH endorsed the impact of membrane on complete separation of solution as pH was showed to be acidic in one side and alkaline in the other side of membrane. All experiments were performed in the presence of 7500 ppm of NaCl supporting electrolyte. The minimum concentration of NaCl in the real wastewater of reactive
dye bath of textile industry is determined 15000 ppm, while it gets diluted in combination with effluent of the rest processing units [22]. Numerous studies have supported the role of chloride in acceleration of decolorization [3]. Table 3 shows dye removal efficiencies obtained under various operating conditions. 41.13% of the difference between the minimum 57.01% and maximum 98.14% values of dye removal efficiency presented in table 3, can indicate that independent variables were selected at appropriate range.
Table 3: Color removal percentage at observed and predicted values corresponding to CCD Standard order Operational conditions Dye removal percent
A (mg/l) B (min) C (A) observed predicted
1 181 34.2 0.16 89.494 85.249
2 419 34.2 0.16 57.016 58.418
3 181 75.8 0.16 94.026 94.021
4 419 75.8 0.16 82.618 81.476
5 181 34.2 0.34 89.961 90.781
6 419 34.2 0.34 77.980 77.663
7 181 75.8 0.34 97.785 96.061
8 419 75.8 0.34 93.306 97.229
9 100 55 0.25 94.5 97.409
10 500 55 0.25 78.282 75.828
11 300 20 0.25 72.296 73.532
12 300 90 0.25 98.142 97.361
13 300 55 0.1 73.459 75.677
14 300 55 0.4 95.338 93.576
15 300 55 0.25 92.774 93
16 300 55 0.25 94.454 93
17 300 55 0.25 93.726 93
18 300 55 0.25 92.522 93
19 300 55 0.25 93.361 93
20 300 55 0.25 91.281 93
Calculating the electrical energy consumption was not neglected in current study. It was shown to be in fluctuations between 1.67 to 13.2 Kwhm-3 and it was observed that power consuming was more proportional to the applied current.
4.1. Development of regression model
RSM suggested a mathematical relationship between the response function and factors affecting that. The experimental response is represented by a polynomial equation as a function of principle, interaction and quadratic effects of independent variables:
93
Here Y is the dye removal efficacy, while x1, x2, x3 correspond to independent factors inclusive initial dye concentration, electrolysis time, and current intensity respectively.
Coefficients provided in the above equation are determined using Analysis of Variance (ANOVA) of Design-Expert software at confidence level of 95%. The constant term of 93 represents the average percent of dye removal obtained from 20 assays. The regression
coefficient R2 of 0.967 signifies the competency of quadratic model for the fitting of experimental data. It means developed model is unable to explain only 3.3% of the total variations. Hence it depicts a good correlation between results provided by experiments and model predictions. Besides, according to ANOVA, adjusted and predicted R-squared values were in reasonable agreement. Values of P>F were less than 0.0001 for model and all three linear effects and lower than 0.05 for two first interaction effects and all second order effects, all indicating that model and eight of model terms were significant. Normal plot of residuals (not shown) was a straight line implied on normal distribution of data. A satisfactory agreement of predicted Vs. actual data can be observed on Figure 2.
Design-Expert® Software dye removal efficiency Color points by value of dye removal efficiency:
98.1419 57.016
Actual
Predicted
Predicted v s. Actual
57.00 67.50 78.00 88.50 99.00
57.02 67.30 77.58 87.86 98.14
Figure 2: Comparison of observed and predicted values for RR120 removal percent To better understand the importance and contribution percentage of principal and interventional effects of factors on response, Pareto analysis was performed (figure 3) using follow relation:
Ci represents the coefficients belong to the linear, interaction and second order effects.
From figure 3 and with respect to positive or negative signs assigned to each term of polynomial model, it can be seen that time of electrolysis has the most positive effect on response followed by current intensity.
Figure 3: Graphical Pareto analysis to determine the exact share of each linear, interaction or second order effect of parameters: initial dye concentration (A), electrolysis time (B), and
current intensity (C) on process efficacy
Table 4: Inputs and anticipated outputs to determine the optimum operating region of the factors on the basis of a cost driven approach
Parameter Variable Goal Lower
Limit
Upper
Limit Importance Inputs
A (mg/l) maximize 181.079 418.921 3
B (min) maximize 34.1889 75.8111 3
C (A) minimize 0.160809 0.339191 3
Predicted outputs
Dye Removal (%) maximize 57.016 98.1419 5
3)
Power Consumption (kwhm- target = 7 1.67292 13.2 5 4.2. Optimization
For maximizing removal efficiency while minimizing power consumption, multi response optimization technique of RSM was applied. The optimization procedure was conducted under boundaries set for both dependent and independent variables shown in table 4.
Accordingly five solutions were proposed by RSM as the optimal operating conditions.
Solution number1 predicted 88.9% of dye removal by use of 7 kwhm-3 of power under the following conditions: 418.92 mg/l of color, 75.8 min of reaction time, and 0.22 A of current density. Based on point prediction, the prediction interval with confidense level of 95% was 81.9 – 95.9% for process efficiency, and 5.98 – 8 kwhm-3 for energy consumption.
Confirmation experiment on the basis of solution number1 showed the consistency of experimental results (87.6% of dye removal, and 6.55 kwhm-3 of energy consumption) with the foreseen values by point prediction.
5. Conclusions
The results of current research confirmed high performance of the designed system for decolorization. Hence, applying electrochemical oxidation and reduction mechanisms in proposed cell was an effective methode for optimized treatment of dyeing wastewater.
Acknowledgments
Authrs are grateful for all supports conducted by Mashhad University of Medical Sciences.
References
[1] De Oliveira GR, Fernandes NS, de Melo JV, da Silva DR, Urgeghe C, Martínez-Huitle C.
Electrocatalytic properties of Ti-supported Pt for decolorizing and removing dye from synthetic textile wastewaters. Chemical engineering journal;168(1): 208-14, 2011.
[2] Thiam A, Sirés I, Garrido JA, Rodríguez RM, Brillas E. Effect of anions on electrochemical degradation of azo dye Carmoisine (Acid Red 14) using a BDD anode and air-diffusion cathode.
Separation and Purification Technology;140:43-52, 2015.
[3] Maljaei A, Arami M, Mahmoodi NM. Decolorization and aromatic ring degradation of colored textile wastewater using indirect electrochemical oxidation method. Desalination ;249(3):1074-8, 2009.
[4] Sala M, Gutiérrez-Bouzán MC. Electrochemical techniques in textile processes and wastewater treatment. International Journal of Photoenergy ;2012.
[5] Kariyajjanavar P, Jogttappa N, Nayaka YA. Studies on degradation of reactive textile dyes solution by electrochemical method. Journal of hazardous materials;190(1):952-61, 2011.
[6] Tavares MG, da Silva LV, Solano AMS, Tonholo J, Martínez-Huitle CA, Zanta CL.
Electrochemical oxidation of methyl red using Ti/Ru 0.3 Ti 0.7 O 2 and Ti/Pt anodes. Chemical Engineering Journal; 204:141-50, 2012.
[7] Basha CA, Sendhil J, Selvakumar K, Muniswaran P, Lee CW. Electrochemical degradation of textile dyeing industry effluent in batch and flow reactor systems. Desalination; 285:188-97, 2012.
[8] Méndez-Martínez AJ, Dávila-Jiménez MM, Ornelas-Dávila O, Elizalde-González MP, Arroyo- Abad U, Sirés I, et al. Electrochemical reduction and oxidation pathways for Reactive Black 5 dye using nickel electrodes in divided and undivided cells. Electrochimica Acta; 59:140-9, 2012.
[9] Mukimin A, Vistanty H, Zen N. Oxidation of textile wastewater using cylinder Ti/β-PbO2 electrode in electrocatalytic tube reactor. Chemical Engineering Journal; 259:430-7, 2015.
[10] Santana MHP, Da Silva LM, Freitas AC, Boodts JFC, Fernandes KC, De Faria LA. Application of electrochemically generated ozone to the discoloration and degradation of solutions containing the dye Reactive Orange 122. Journal of Hazardous Materials;164(1):10-7, 2009.
[11] Wang C-T, Chou W-L, Kuo Y-M, Chang F-L. Paired removal of color and COD from textile dyeing wastewater by simultaneous anodic and indirect cathodic oxidation. Journal of Hazardous Materials;169(1–3):16-22, 2009.
[12] Martínez-Huitle CA, Brillas E. Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods: a general review. Applied Catalysis B: Environmental; 87(3):105- 45, 2009.
[13] Daneshvar N, Aber S, Vatanpour V, Rasoulifard MH. Electro-Fenton treatment of dye solution containing Orange II: Influence of operational parameters. Journal of Electroanalytical Chemistry;615(2):165-74, 2008.
[14] Radha K, Sridevi V, Kalaivani K. Electrochemical oxidation for the treatment of textile industry wastewater. Bioresource Technology;100(2):987-90, 2009.
[15] Bechtold T, Mader C, Mader J. Cathodic decolourization of textile dyebaths: Tests with full scale plant. Journal of applied electrochemistry;32(9):943-50, 2002.
[16] Hastie J, Bejan D, Teutli-León M, Bunce NJ. Electrochemical methods for degradation of Orange II (sodium 4-(2-hydroxy-1-naphthylazo) benzenesulfonate). Industrial & engineering chemistry research;45(14):4898-904, 2006.
[17] Hou Y-T, Ren J, Liu H-J, Li F-D. Efficiency of electrolyzed water (EW) on inhibition of Phytophthora parasitica var. nicotianae growth in vitro. Crop Protection;42:128-33, 2012.
[18] Sadiq R, Rodriguez MJ. Disinfection by-products (DBPs) in drinking water and predictive models for their occurrence: a review. Science of The Total Environment;321(1–3):21-46, 2004.
[19] Davoudi M, Gholami M, Naseri S, Mahvi AH, Farzadkia M, Esrafili A, et al. Application of electrochemical reactor divided by cellulosic membrane for optimized simultaneous removal of phenols, chromium, and ammonia from tannery effluents. Toxicological & Environmental Chemistry;96(9):1310-32, 2014.
[20] Ananthashankar R. Treatment of Textile Effluent Containing Reactive Red 120 dye using Advanced Oxidation. Halifax, Nova Scotia: Dalhousie University; 2012.
[21] Bezerra MA, Santelli RE, Oliveira EP, Villar LS, Escaleira LA. Response surface methodology (RSM) as a tool for optimization in analytical chemistry. Talanta;76(5):965-77, 2008.
[22] Rajkumar D, Kim JG. Oxidation of various reactive dyes with in situ electro-generated active chlorine for textile dyeing industry wastewater treatment. Journal of Hazardous Materials;136(2):203- 12, 2006.
View publication stats View publication stats