Removal of brilliant green dye from aqueous solution by electrocoagulation using response surface methodology

Removal of brilliant green dye from aqueous solution by electrocoagulation using response surface methodology

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Removal of brilliant green dye from aqueous solution by electrocoagulation using response surface methodology Ghufran K. Mariah ⇑, Kamal S. Pak Chemical Engineering Department, AL-Nharain University, Baghdad, Iraq

a r t i c l e

i n f o

Article history: Received 9 July 2019 Received in revised form 18 September 2019 Accepted 29 September 2019 Available online xxxx Keywords: Electrocoagulation Iron electrode Brilliant green Response surface methodology Electrical energy consumption

a b s t r a c t This study proposed batch electrocoagulation with iron electrodes as a simple and economical method for treating aqueous solution containing 250 mg/l of brilliant green dye. Response surface methodology was performed to design experiments and to optimize the process. A total of 20 experiments were conducted to study the effect of three important process parameters: initial solution pH (5–11), current density (5–20 mA/cm2) and reaction time (10–40 min). Multiple response optimization reveals that a maximum dye removal efficiency of 96.1% with minimum electrical energy consumption of 3.857 kW h/kg dye removed was achieved at optimum conditions. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.

1. Introduction Pollution dangers of wastewater drainage and other naturalist activities threaten rivers, water passages, and other water resources in the environment [1]. The extreme use of water in the industrial activities, which drain the prime part of their waste to the environment, produces dangerous pollution effects [2]. The fast industrialization, utilize of coloring chemicals, such as dyes, increase excessively day by day. This leads to various industries such as textile, lacing, food, cosmetic, paper, pharmaceutical etc., that use a variation of synthetic dyes. These dyes are chemically, photolytically and biologically extremely stabilized and are highly persistent in nature [3]. The drainage of like dyes in the ecosystem is deemed as a prime environmental interest. The most quite used synthetic dyes are azo dyes, which include one or more azo bonds (–N N–). It has been confirmed that some azo dyes are poisonous and carcinogenic and even mutagenic across living organisms in the aquatic environment [4]. In addition, several of the Azo dyes cause bladder cancer in humans and chromosomal deviation in mammalian cells [5]. Dye effluents, are not only aesthetic pollutants by nature of their color, but may overlap light breakthrough in water annoying biological activities of aquatic life. In addition, the stabilization of their molecular framework renders them resis⇑ Corresponding author.

tant to biological or even chemical degradation. Therefore, the dye effluents should be treated before their drainage to the receiving water stream in order to meet the environmental regulations [5]. Brilliant Green (chemical formula = C27H34N2O4S, molecular weight = 482.62 g/mol) has its maximum absorbance at a wavelength of 625 nm [6]. Brilliant Green a basic (cationic) dye pertinence to aniline group include. It is exceedingly used in textile dyeing, leather, cosmetic and paper printing. It is used in the industrialization of green ink and as a staining constitutive of bacteriological media. It is used as a topical purifier and as an eclectic bacteriostatic agent in tissue-culture media. It is deemed highly poisonous for humans and animals [7]. Fig. 1 shows the molecular structure of brilliant green dye. Electrocoagulation (EC) is a potentially efficient technique utilized for processing the textile dyeing effluent. The EC process has shown many advantages over traditional chemical coagulation. It is plain, utilized low-cost equipment and is effective where the coagulant is constructed in situ through electro-oxidation of a sacrificial anode. Moreover, EC is distinguished by low sludge production and no secondary contamination, as the process is accomplished without adding any chemical coagulants [9]. The EC process typically includes three techniques: (i) product of coagulants via electro oxidation of the sacrificial anode; (ii) destabilization of the contaminants and emulsions breakage; and (iii) collecting of the destabilized stages to form flocs [10].

E-mail address: [email protected] (G.K. Mariah). https://doi.org/10.1016/j.matpr.2019.09.175 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 2nd International Conference on Materials Engineering & Science.

Please cite this article as: G. K. Mariah and K. S. Pak, Removal of brilliant green dye from aqueous solution by electrocoagulation using response surface methodology, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.175

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a DC power supply (DAZHENZ, China, type: SY 3005 D). A magnetic stirrer (Lab-Tech, Korea, type: LMS_1003) was utilized for mixing purpose. The pH of the solutions was measured by a pH meter (Microprocessor PH Meter, HANNA instruments, Canada) and adjusted by adding diluted NaOH or H2SO4 solutions. Concentrations of dye solutions were measured by UV–Vis spectrophotometer (type: UV–Vis 6800, Jenway, U.K.). 2.2. Analytical procedure A UV–Vis spectrophotometer was utilized for measuring dye concentration at wavelength of 625 nm. Eq. (4) was used to calculate the dye removal efficiency [19].

%R ¼

Fig. 1. Molecular structure of Brilliant Green Dye [8].

The varied reactions occurring at anode, cathode and solution are specified below [10]:

Co  C 100 C

ð4Þ

where: Co and C are the concentration of the dye before and after electrocoagulation, respectively. 2.3. Electrical energy consumption (EEC)

At the anode : Fe ! Feþ2 þ 2e

ð1Þ

At the cathode : 2H2 O þ 2e ! H2 þ 2OH

ð2Þ

Electrical energy consumption of the electrocoagulation experiments was calculated as follows [20]:

Overall reaction : Fe2þ þ 2H2 O ! H2 þ FeðOHÞ2

ð3Þ

EEC ¼

Different types of monomeric and polymeric iron complex are 2+ 2+ formed such as: Fe(H2O)3+ 6 , Fe(H2O)5OH , Fe(H2O)4(OH) , Fe2(H24 4+ 2+ O)8(OH)2 , Fe2(H2O)6(OH)4 and Fe(OH) [11]. Previous works discussed removing of dyes from wastewater by different techniques such as physical, biological, and chemical. Each of these techniques has many drawbacks. On the other hand, electrocoagulation proves it’s efficient in removing dyes from different wastewater sources [12–16]. Response surface methodology (RSM) combines between mathematical and statistical methods for empirical model constructing and analysis of troubles in which a response of interest is affected by different variables. Primarily, RSM was advanced to form experimental responses and then immigrate into modelling of numeral experiments [17]. RSM showed excellent advantages of optimization compared with the traditional method by reducing experimental trials to provide sufficient information for statistically right results and valuation of the proportional significance of parameters and their interactions [18]. The goal of the current study was to investigate Brilliant Green dye removal from aqueous solution by electrocoagulation process. For this purpose RSM with central composite design (CCD) was used to develop a mathematical correlation between BG dye removal efficiency and three crucial independent parameters: initial pH, applied current density and time of electrolysis. 2. Materials and methods 2.1. Experimental setup The brilliant green dye solution was obtained by dissolve solid dye in distilled water. For the preparation of sample 250 mg of the dye was dissolved per liter of distilled water which is close to real industrial dye effluent. The conductivity of the solutions was raised up and adjusted by the addition of potassium chloride salt. Batch experiments were conducted using 1.5L capacity glass beaker with 1L of dye solution at ambient temperature (25 ± 2 °C). Iron plates of dimensions 15 cm  2.5 cm  2 mm was used as anode and cathode electrodes. The distance between the anode and cathode was fixed to 2.5 cm. The effective surface area of each electrode was 20 cm2. The electrodes were connected to

IVt 1000 volDC

ð5Þ

where: EEC: Electrical energy consumption (kW h/kg BG removed), i = Applied current in Ampere (A), V = Voltage (V), t = time of electrolysis (h), vol. = volume of wastewater (liter), DC = Concentration difference (Co  Cx) mg/l. 3. Results and discussion In the present study, a preliminary experiments (screening) were conducted to determine the most crucial factors and the effective rang of these factors. Three factors (pH, i, t) were chosen to evaluate and optimize the electrocoagulation treatment process and to study the effect of variables on the removal efficiency and electrical energy consumption. A central composite design (CCD) is a widely used form with RSM, which include runs with factors at their extrema limits. The factors with their levels are shown in Table 1 Using minitab17 software. Analysis of variance (ANOVA)

Table 1 Experimental conditions and responses. Exp. No

Current density (i) (mA/cm2)

pH

Time (min)

%R

EEC (kW h/kgBG)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

12.5 12.5 12.5 12.5 5.0 5.0 12.5 20.0 20.0 12.5 20.0 5.0 5.0 20.0 12.5 12.5 12.5 20.0 12.5 5.0

8 8 8 8 5 11 8 8 5 8 5 5 8 11 11 8 8 11 5 11

25 40 10 25 40 10 25 25 10 25 40 10 25 40 25 25 25 10 25 40

97.15 99.80 85.60 96.80 86.32 77.14 96.20 98.60 81.30 97.30 97.50 74.54 84.34 99.90 94.60 98.67 96.67 88.71 91.82 84.41

4.375 6.817 1.986 4.391 1.453 0.424 4.418 9.669 4.560 4.368 15.214 0.420 1.008 15.063 4.449 4.308 4.397 4.239 4.493 1.549

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was utilized to evaluate the data. The total of 20 experiments were performed including six center points. Where S, NS indicates significant and insignificant respectively. Based on the experimental results of BG removal efficiency and EC and regression analysis for CCD, the full quadratic model is given by Eqs. (6) and (7):

%R ¼ 34:23 þ 2:167 I þ 5:43 PH þ 1:233 t  0:0805 I  I  0:3101 PH  PH  0:01467 t  t þ 0:0507 I  PH þ 0:00927 I  t  0:02644PH

ð6Þ

EEC ¼ 1:964  0:3387 I  0:100 PH  0:0825 t þ 0:01651 I  I þ 0:0067PH  PH  0:000038 t  t  0:00318 I  PH þ 0:021467 I  t þ 0:00073 PH  t

ð7Þ

F-value is hypothesis where the F-value greater than F-critical indicate the model is significant. The models F-values of 92.91, 742.84 and F-critical is 4.256 for %R and EEC respectively implies that the model is significant, the p-value related to the F-value used to show whether the F-value is large enough or not. In other words, p-values lower than 0.05 confirm that the regression model is statistically significant (Tables 2 and 3). These models take into account linear effects, quadratic effects and two-way interactions between the studied factors. The empir-

ical correlation represented in Eqs. (6) and (7) that involved factors produced the actual values of these factors, the quality and adequacy of the model are evaluated by the correlation coefficient value (R2), adjusted and predicted R2. The R2-values present a measure of how the experimental factors and their interactions can explain much variability in the experimental response values. The R2-value is always between 0 and 1. The closer R2-value to 1 better fit [19]. In this study, the value of the determination coefficient (R2) for both %R and EEC are 0.9882 and 0.9985 respectively, also, the adjusted R2 is a standard for how well the model is improved if an extra variable is added, whereas predicted R2 is an expression of the model’s ability to predict a new point, the adjusted determination coefficients R2 adj for both response (R2 adj %R = 0.9775 and R2 adj EEC = 0.9972) which indicate to the model is significant, The R2 pred. was in reasonable agreement with the R2 adj, where R2 pred. for both responses are 0.9399 and 0.9886 respectively (Fig. 2).

3.1. Effect of variables on removal efficiency Figs. 3 to 5 are surface plots and contour plots show the effect of the studied process parameters on removal efficiency. Also, these figures display the interaction between process parameters on the removal efficiency (%R).

Table 2 Analysis of variance (ANOVA) table for the full quadratic model of BG removal efficiency (%R). Source

DF

Adj SS

Adj MS

F-Value

p-Value

Remarks

Model Linear Current(I) pH Time(t) Error Lack-of-Fit

9 3 1 1 1 10 5

1183.80 736.53 351.17 17.64 367.72 14.16 2.114

131.533 245.511 351.175 17.636 367.721 1.416 2.114

92.91 173.42 248.05 12.46 259.74

0.000 0.000 0.000 0.005 0.000

S S S S S

2.95

0.130

Table 3 Analysis of variance (ANOVA) table for the full quadratic model of electrical energy consumption (EEC). Source

DF

Adj SS

Adj MS

F-Value

p-Value

Remarks

model Linear Current(I) pH Time(t) Error Lack-of-Fit

9 3 1 1 1 10 5

325.027 273.703 192.657 0.017 81.029 0.486 0.479

36.114 91.234 192.657 0.017 81.029 0.049 0.096

742.84 1876.63 3962.82 0.36 1666.72

0.000 0.000 0.000 0.563 0.000

S S S NS S

66.81

0.000

Fig. 2. 3D surface plot and 2D contour plot as function of pH and t (min) for removal efficiency (%R) at constant i = 12.5 mA/cm2.

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Fig. 3. 3D surface plot and 2D contour plot as function of t (min) and current (i) for removal efficiency (%R) Effect at constant pH = 8.

Fig. 4. 3D surface plot and 2D contour plot as function of pH and current(i) for removal efficiency (%R) at constant t = 25 min.

pH is an important operating factor influencing the performance of the electrocoagulation process. To examine its effect on the treatment efficiency experiments was carried out at room tem-

perature (25 ± 2 OC), initial solution pH was varied from 5 to 11by adding drops of diluted NaOH or H2SO4 solution and the results are shown in Figs. 3 and 5. When pH increase from 5 to 8 the removal efficiency was increased from about 74 to 99%, it is found that the percentage of color removal was increased with increasing pH up to 8. This can be explained by the fact that when the pH is in the range of 5–8, the dominant ferric species in the form of Fe (OH)3(s) acts as a coagulating agent, which increases color removal efficiency. pH increases the dissolved iron weight during the electrocoagulation process increases due to the formation of iron hydroxide species which adsorb the dye molecules and cause hydrogen evolution at cathodes (reaction (8)) which leads to the increase of the removal efficiency.

2H2 O þ 3e ! H2ðgÞ þ 2OHðaq:Þ

ð8Þ

The applied current density influences the performance and economy of the electrocoagulation process. In order to investigate its effect on dye removal efficiency, a series of experiments were conducted at current density range from 5 to 20 mA/cm2 and the results are shown in Figures (4) and (5). It has been found that when current density increases to 20 mA/cm2, removal efficiency increase to value to 99%. This behavior is due to the fact that applied current density that determines the coagulant dosage rate, the bubble production rate and size of flocs growth resulting in faster removal of pollutants as presented in Eq. (7) [21]. Fig. 5. Multiresponse optimization plot for maximizing %R, and minimizing EEC.

4Feþ2 þ O2 þ 4Hþ ! 4Feþ3 þ 2H2 O

ð9Þ

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Another influential factor in electrocoagulation performance is reaction time. The effect of reaction time on the removal efficiency of the dye is shown in Figs. 3 and 4. It can be noticed that the decolonization efficiency increases by increasing reaction time. BG removal efficiency increased from 74% to 99% when increasing reaction time from 10 to 40 min. Higher reaction time leads to form extra hydroxyl ions and iron cations, which consequently result in more and stronger floc production. Energy consumption increases reaction time. In fact, the amount of electrical energy consumption (EEC) is doubled by doubling the reaction time [13]. 3.2. Optimization and validation of process variables Response surface methodology (RSM) was performed for numerical optimization to determine the optimum parameters to maximize removal efficiency (%R) and minimize electrical energy consumption (EEC). Fig. 5 shows that multiresponse optimization predicts the following parameters: time of operation; 27.878 min., current density; 10.757 mA/cm2 and pH; 8.45. The predicted removal efficiency was 96.116% and EEC was 3.857 kW h/kg BG at composite desirability of 0.8082. An experiment was performed at the optimum conditions (t = 27.878 min, pH = 8.45 and i = 10.75 mA/cm2), and the results show that %R = 97.78 and EEC = 3.30988 kW h/kg BG, which agrees with the optimization predication. 4. Conclusion The performance of electrocoagulation process for the treatment of brilliant green dye from wastewater was investigated. It was found that electrocoagulation treatment is rapid and effective method for the removal to BG dye. The BG removal efficiency depends on the initial pH of the solution, applied current density and time of electrolysis. Multiple response optimization for maximizing BG removal efficiency and minimizing electrical energy consumption reveals that the optimum condition was time of electrolysis is 27.878 min, pH of 8.45, and the current density of 10.757 mA/cm2. At these conditions, the removal efficiency and EEC was 96.11% and 3.857 kW h/kg BG removed respectively. References [1] B. Merzouk, B. Gourich, A. Sekki, K. Madani, M. Chibane, Removal turbidity and separation of heavy metals using electrocoagulation-electroflotation technique. A case study, J. Hazard. Mater. 164 (1) (2009) 215–222, https:// doi.org/10.1016/j.jhazmat.2008.07.144. [2] Erik Jorgensen, Industrial Wastewater Management, seventh ed., Elsevier Scientific Publishing Comp., 1979, pp. 309–312. [3] D. Suteu, D. Bilba, Equilibrium and kinetic study of reactive dye Brilliant Red HE-3B adsorption by activated charcoal, Acta Chim. Slov. 52 (1) (2005) 73–79. [4] S. Aoudj, A. Khelifa, N. Drouiche, M. Hecini, H. Hamitouche, Electrocoagulation process applied to wastewater containing dyes from textile industry, Chem. Eng. Process. Process Intensif. 49 (11) (2010) 1176–1182.

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Please cite this article as: G. K. Mariah and K. S. Pak, Removal of brilliant green dye from aqueous solution by electrocoagulation using response surface methodology, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.175