Color removal of reactive dyes using microwave - Do Quang Thang

COLOR REMOVAL OF REACTIVE DYES USING MICROWAVE Do Quang Thang(1*), Bui Manh Ha(2), Bui Nghia Hiep(3) (1) Thu Dau Mot University, (2) Saigon University, (3) Baclieu University Received 14 June 2018, Accepted 5 July 2018 Email: thangdq@tdmu.edu.vn Abstract Microwave irradiation had been one of the methods for removing color of four commercial reactive dyes: Sunzol Black B 150%, Procion Red MX 5B, Remazol Brilliant Blue R and Sunzol turquoise blue G 133 in aqueous solution. The effect of irradiation time, power consumption, air flow and initial dye concentrations were investigated. The results showed that color of all fours reactive dyes were eliminated. The Jar-test compared experiment was also tested with low removal capacity. Once again, the results indicate a strong capacity of microwave technology on colors removal. Keywords: reactive dyes, coagulation, microwave irradiation 1. INTRODUCTION For a long time ago, waste water of dyeing industry has been considered as one in the seriously polluted sources. In Ho Chi Minh city, just considering particularly the Tham Luong Channel, there are thousands of cubic meters of waste water which has not been passed any treatment stages and discharged directly to environment every day. At the results, the Tham Luong Channel is currently in the list of the “dead” rivers of the city. Most of dyes which remain in the dyeing waste water are active type, because their entire extraction capacity is low, their solvent power in water is unlimited, their structural formulas are complex and containing many color-bearing radicals which are difficulty to be bio-decomposed and the absolute treatment of the active dyeing waste water by the normal methods such as coagulation, absorption and biology usually engender poor results (Abraham et. al., 1996). Therefore, seeking the new and effective method for resolution of dyeing wastewater question always attract a lot of international and domestic scientists, one among the new technologies is that the microwave process (MW). MW is defined as the electro-magnetic radiations in the range of frequency from 0.3 GHz to 30 GHz, in the range between VHF and infrared wave. Nowadays, most of household microwave ovens in the families as well as the specialized ovens work in the fixed frequency of 2,45 GHz. MW has been applied for a long time in many fields such as industry, agriculture, organic substances synthesis and so on but it is recently applied in environmental process (Gao et al. 2016). In the progress of changing direction and in the very high frequency, the material molecules will hit against and rub to each other, the heat caused by the friction progress will create a very great thermal energy. The combination between MW and some other technologies such as photochemistry (TiO2, ZnO2, etc.) which is considered as one of the advanced oxidation processes, the basis of this process is right the process of creating the powerful active oxidant radicals such as OH●, HO2●, H● and so on (Vitthal et al. 2017). In this study, it has been studied the progress of using the low-power household microwave oven (800 W- 2,42 GHz), to decolor four types of active dyes with the color-bearing radicals of azobenzen, antraquinon and ptalocianin in the absolutely hydrolysed form. 2. MATERIALS AND METHOD 2.1 Materials: The dyes in this study are dyes used in technology such as Sunzol Black B 150% (Diazobenzen), Reactive Brilliant Red 5BS (Monoazobenzen), Remazol Brilliant Blue R (Antraquinon) and, Sunzol turquoise blue G 133 (Ptalocianin), which are collected from the dying processes of the companies such as Phong Phu Corporation, the Phuoc Long garment and textile joint-stock Company, the Songwol Vina towel dyeing Company, the Panko Vina textile, dyeing and completion Company. The other used chemicals are the purified ones to limit errors in experimental progress. 2.2 Experimental model: Diagram of experimental model of treatment process using MW is described on Figure 1. In that, reaction jar has the form of glass cylinder with capacity of 250 ml and a heat-resistant lid with two holes of Ø 3 and 5 mm in diameter, respectively, to aerate and balance pressure with the 500-ml jar outside the Whirpool XT-25MS/S microwave oven. Figure 1. Diagram of experiment of microwave treated. 1) Control panel, 2) Sample jar, 3) Aerating pump, 4) Condensing unit. 2.3 Method Experimental modeling: At normal temperature, dissolubility of technical dyes is very limited. To make the dyeing solution for microwave treated process, we have performed to make the sample solution containing “absolutely” soluble dyes and dyes in solution must be in the “hydrolyzed” form. The procedure could be found in our previous study (Perng et al. 2014). Experimental method: Take 150 mL of Sunzol Black B (SBB) solution of 150% concentration (C). The initial solution is adjusted to the value of needed pH, by NaOH and HCl (0,05 N) solutions, and take 3 mL to measure the absorbability in optimum wavelength. The rest sample is measure the COD and BOD5 parameters. Pour 100 mL of above solution into sample jar, and install the MW system as same as Figure 2. Switch on the pump and adjust the aerating flow into jar to reach the value of Q. Adjust the power of microwave oven to the power of (P). Adjust the timer to record the time (t) of MW starting. After (t) minutes of radiating, stop the system, and deposit the solution in 15 minutes, use pipette to take 3 mL of sample to measure the absorbability at the optimum wavelength. Record the results. The spectrum of UV-Vis of the dyes is determined on ultraviolet spectrograph (Jenway -6505). COD and BOD5 are determined upon the standard method (APHA 1995). Discoloration efficiency of organic substances of dyes are calculated by formula: Treatment efficiency (%) With Ao: Absorbability (COD, BOD5) of the initial dying solution; A: Absorbability (COD, BOD5) of the treated dying solution 3. RESULTS AND DISCUSSION Based on the recent research documents, we chose the subject of SBB (Reactive black 5) for the experiment to survey the “appropriate” conditions for microwave-based decomposition of dyes. 3.1. Investigating the microwave-based decomposition of dyes 3.1.1 Influence of aerating flow We investigated the influence of aerating flow (Q) by fixing the initial factors: P = 156 W, C =100 mg/L (A599=2,867), pH=6,0, t = 10 minutes and changing Q from 0,2 to 1,0 L/minute. In investigation, to determine the role of aeration for microwave, we carried out the additional microwave radiated reaction of the dyeing solution in the condition of MW without aerated and only aerated (0,6 L/minute). Table 1. Results of aerating flow investigation Flow of Q (liter/minute) A599 Efficiency (%) b0,0 2.865 0.21 0,2 2.742 4.48 0,4 2.697 6.06 0,6 2.647 7.80 0,8 2.652 7.64 1,0 2.650 7.70 c0,6 2.869 0.053 b: Reaction with only microwave radiation and without aerated c: Reaction with only flow aerating of 0.6L/minute These results showed that air plays an active role in microwave-based discoloring reaction. When separated treatment of dyes, aeration showed no effect. Therefore, it’s possible to affirm that, in this case, air does not play the role of oxidant of organic substances but the aeration process creates many bubble centers, the thermal stability in system is increased, the impact process has the gradually increased effect to increase efficiency. 3.1.2. Investigation upon the microwave radiation power The power specializes for microwave energy. When energy supplied for the microwave reaction is increased, normally, reaction efficiency is increased, too (Bo et al. 2002). We carried out investigation of the MW power change by fixing the initial factors: Q=0,6 L/minute, C=100 mg/L (the correspondent absorbability of A599=2,867), pH=6,0 and changing the power radiation: 156, 270, 360, 432, 594 W in 10 minutes, respectively. Table 2. Results of power investigation Power (W) A599 Efficiency (%) 156 2.645 7.85 270 2.541 11.49 360 2.514 12.44 432  - 594  - d: Efficiency or percentage (%) of discolorization ( - ): Sample evaporates too fast From the above results, it was suggested that, the more increased level of power, the higher treatment efficiency is obtained. This may be explained that when changing, the more increased radiation power, the more microwave energy is supplied for reaction, which combines with the “intrinsic” energy produced in radiation process. As a result, the impact effect and the treatment efficiency are increased. Though, when energy is increased too high, solvent (water) reaches fast to boiling point, evaporates and brings about the undecomposed pollutants. This decreases the effect of reaction by chance. On the other hand, for the treatment system, it’s necessary to consider the great energy consumption for not high result. Therefore, we decided to choose the power level of 270 W for the next experiments. 3.1.3. Influence of pH pH influences to dissolubility of air and dyes in solution, thus influences to reaction efficiency (Brittany 2002). To study this influence, we chose the investigated wide range of pH from: acidity, neutrality to alkalinity with the variant values of 1, 2, 3, 4, 6, 8, 10, 12, respectively when fixing the factors of P=270W, Q = 0,6 L/minute and C =100 mg/L, in 10 minutes with microwave radiation exposure. The investigation results are presented in Table 3. The results showed that pH has the very great influence on the color treatment efficiency in microwave-radiated reaction. In comparison of pH 4, the discoloration efficiency at pH of 3 is higher by far. Table 3. Results of pH investigation pH A599 input A599 output Efficiency (%) 1 2.861 0 100.00 2 2.863 0 100.00 3 2.867 0 100.00 4 2.868 0.418 85.42 6 2.869 1.331 53.61 8 2.870 2.207 23.12 10 2.871 2.359 17.82 12 2.871 2.514 12.43 This may be due to the solvent ability of dyeing substances at organic phase is increased at low pH because they can not split their molecules. These dyes, by chance, are swept by the impact directions of polarized molecules in magnetic field. The higher pH is, the more reaction efficiency is decreased. This showed that the microwave-based discoloration reaction only has effect in low range of pH (Campanella et al., 2004; Ha 2008) and so on. Although the lower pH is, the higher efficiency is, but in fact, it’s needed a very great amount of neutralizing acids consumption to make pH from 11 (normal value of waste water source after the active dyeing processes) down to pH of 1 or 2. Furthermore, with the very acid environment, the likelihood of corrosion of microwave oven is very high. Therefore, we chose pH =3 as appropriate condition for other investigations. 3.1.4. Influence of dye concentration So far, we determined the factors to get the highest efficiency currently as: P=270 W; Q=0,6 L/minutes; C=100 mg/L; pH=3,0; t= 10 minutes. To investigate the MW radiation efficiency in dye treatment at the different concentrations, we varied C as: 50, 100, 150, 200, 300, 400, 1000 mg/L, respectively and obtained the results as following: In a fixed time (10 minutes), at the concentration level of ordinary sewage water (<100 mg/L), treatment efficiency of microwave reaches optimum level, dyes most likely are decomposed absolutely. At the greater concentration, efficiency of microwave is decreased gradually. This is easily explained that at a certain level of energy provided in a certain time, the higher concentration of particles is, the more decreased level of energy which is provided for each particles is, and efficiency is low, too (Chen et al., 2001; Sanz (2003). 3.1.5 Influence of reaction time Beside the optimized parameters in the system which are investigated quite sufficiently, we carried out investigation of reaction time to know what the time of most efficient reaction is, when the factors of P=270 W, Q= 0,6 L/minutes, C=100 mg/L and pH=3,0 are fixed. Table 5. Dye decomposition upon time Time (minute) pH (-) A599 COD (mg/l) BOD5 (mg/l) 0 3.01 2.867 352 88 10 3.12 0.000 251 84 20 3.06 0.000 221 82 30 3.45 0.000 187 81 40 2.98 0.000 175 81 50 3.24 0.000 168 80 60 3.53 0.000 159 80 Table 6. Discoloration, COD and BOD5 when SBB microwave radiation exposure Time (min) % Discolor % COD reduced % BOD5 reduced BOD5/ COD (%) 0 0.00 0.00 0.00 25.00 10 100.00 28.69 4.55 33.47 20 100.00 37.22 6.82 37.10 30 100.00 46.88 7.95 43.32 40 100.00 50.28 7.95 46.29 50 100.00 52.27 9.09 47.62 60 100.00 54.83 9.09 50.31 The table of results showed that in the post-radiated solution, there is a change of pH. The radiation process produced the change of the particles in environment and the dye decomposition. After about first 10 minutes of microwave-based radiation process, the discoloration efficiency is nearly absolute. The COD and BOD5 elimination efficiency are ~ 29 and 5%, respectively. In next 50 minutes of the radiation process, the absorbability at the maximum absorb wavelength of 599 still does not show the remaining existence of SBB dyes, and the MW radiation process is absolute, the dye particles can not reunite to become the original particles. 3.2. Microwave application in treatment of the rest dyes From the study results as above in item 3.1, we have found the appropriate condition to investigate the microwave-based dye decomposition as following: Dyes solution (100 ppm), V= 100mL, input pH: 3,0÷0,2, Aerating flow (Q): 0,6 L/minute, Microwave radiating time (t): 60 minutes, Power (P): 270 W. From this appropriate condition, the method of MW is applied on three rest subjects of dyes and the results are as Table 7 and Figure 2. In general, the dyes have the organic substance contents (COD and BOD5) which are not high but very difficult for decomposition. Even though for the different structure of the color-bearing groups of azobenzen, antraquinon and phtalocianin, MW showed its nearly absolute discoloration efficiency. Table 7. Results of the RBB, RBR and STB dyes decomposition Figure 2. Efficiencies of the RBB, RBR and STB dyes decomposition 3.3. Comparison with flocculation method To comparison the MW discoloration efficiency with other methods, we carried out study the treatment capability of these dyes by ferric alum coagulation method - Jar-test. Firstly, we carried out investigate the treatment capability of 10 mg/L diluted dyes solution in the range pH of 4, 5, 6, 7, 8, respectively and the fixed concentration of alum as 1000 mg/L. After the optimum point of pH was found, we carried out fix the pH factor and change the dosage of alum as 600, 800, 1000, 1200 and 1400 mg/L, respectively to find out the optimum alum dosage. All above types of dyes have the optimum treatment point of pH of 6, in that, the range of pH from 4 to 6 showed appropriateness with the treatment process. At alkaline (8) or acidity pH (3), it’s not appropriate for flocculation process. The obtained optimum amount of alum is 800 mg/L, although the dosage of alum does not influence on the flocculation efficiency as strongly as pH, the very high or very low concentration does not result in the good results. Table 8. Treatment efficiency in pH changing Dye SBB RBR RBB STB pH 4 14.65 16.53 15.89 30.09 5 15.31 19.98 16.80 40.32 6 16.14 20.46 17.87 46.74 7 11.39 12.64 11.01 41.32 8 6.32 8.09 6.17 34.21 Table 9. Treatment efficiency in alum dosage changing Dye SBB RBR RBB STB Alum (mg/L) 600 14.30 18.26 16.73 31.12 800 18.54 21.79 18.9 51.73 1000 16.13 20.45 17.87 46.75 1200 15.73 17.35 15.71 44.21 1400 14.94 16.87 13.84 39.95 The active dyes at high concentration (chromaticity) are very difficult to be absolutely treated by using alum, the poor treatment results for the four active colors affirmed this all the more. 4. CONCLUSION At the first step, the appropriate condition for the absolute elimination reaction of dyes and a part of organic substances of the active dyes by microwave radiation process was found. The Jar-test showed that dyes containing the reactive blue 21 solution (ptalocianin group) may be discolored quite well with coagulation and flocculation process (52%). But the dyes of other groups (azobenzen and antraquinon) showed the very poor results. It affirms the dominance of microwave-based dye treatment in comparison with flocculation method. Although, this subject investigated so thoroughly some of factors which influence on the microwave-based discoloration process, the reactive kinetics still has not been studied sufficiently yet. 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