Decolorization of Reactive Blue 171 Dye Using
Ozonation and UV/H2O2 and Elucidation of the
Degradation Mechanism
Namata N....
Aldrich. All solutions were prepared with distilled water.
Except in concentration optimization study, the dye concen-
group means and their associated procedures to test the null
hypothesis against an alternative hypothesis. In its simplest...
initiates decomposition of ozone thereby generating hydro-
peroxyl anion (HO2
) which further reacts with ozone yield-
Effect of Ozonation Time on COD Removal
As can be seen in Figure 4, under the optimized pH con-
ditions, within first 1 min...
conditions leading to the decrease of OH•
formation. Azbar
et al. [25] also indicated that best results on reduction of
Table 2. GC spectral details of intermediates obtained by ozonation of RB 171.
GC/MS fragments by Ozonation Details of the...
the dye structure which was found to diminish in the treated
samples. In addition, band at 1610 cm21
confirmed the pres-
HPLC spectrum of RB 171 showed one major peak at
retention time of 6.467 min and a minor peak at 6.360 min.
The spectrum f...
Authors would like to express their gratitude to UGC for
funding of this project under Major Research Proj...
of 10

Namata 1st ppr

Published on: Mar 3, 2016

Transcripts - Namata 1st ppr

  • 1. Decolorization of Reactive Blue 171 Dye Using Ozonation and UV/H2O2 and Elucidation of the Degradation Mechanism Namata N. Patil and Sanjeev R. Shukla Department of Fibres and Textile Processing Technology, Institute of Chemical Technology, (University under the Section-3 of UGC Act 1956), Nathalal Parekh Marg, Matunga, Mumbai 400019, India; or (for correspondence) Published online 00 Month 2015 in Wiley Online Library ( DOI 10.1002/ep.12171 In this report, the degradation of a commercially impor- tant dye C. I. Reactive Blue 171 (RB 171) has been investi- gated using peroxidation under UV light and ozone. The effect of operational conditions such as the dye concentra- tion, operating pH and use of the oxidants such as ozone and UV/H2O2 was studied. Complete decolorization of RB 171 (50 mg/L) was obtained using ozonation, while UV/ H2O2 showed poor decolorization efficiency. The COD removal by ozone was fair enough at 33%, whereas with UV/ H2O2 it was lower than 2%. Characterization using TLC, FTIR and HPLC indicated degradation of the organic bonds of the dye. To the best of our knowledge, for the first time a possible fate of metabolism of intact dye molecule by ozone has been proposed using GC/MS analysis, which showed the production of benzene and aliphatic/aromatic sulfonate derivatives. Phytotoxicity studies revealed extensive reduction in toxicity of RB 171 with ozone. It may be concluded that the ozonation is a promising way of rapid decolorization along with effective mineralization. VC 2015 American Institute of Chemical Engineers Environ Prog, 00: 000–000, 2015 Keywords: ozonation, UV/H2O2, HPLC, GC/MS, toxicity studies INTRODUCTION Annual worldwide production of dyes used for textile col- oration is over 10,000 tons, out of which the azo chromophore-based reactive dyes constitute a major share [1]. The presence of even ppm level concentration of dyes in the effluent streams creates aesthetic problems, hinders the photosynthesis and aquatic life [2]. The dyeing of reactive dyes produces color on cotton through strong covalent bonding and hence is in large demand. However, their pick up is poor. As a result, over 20% of unutilized dye gets dis- charged into wastewater during dyeing. Intense washing of dyed cotton further adds up due to removal of unfixed dye [3]. The conventional technique for the treatment of waste- water in the textile industry mainly includes coagulation- flocculation, which produces large amount of sludge merely transferring the contaminants from wastewater to secondary waste. The biological treatment that follows has the draw- back of system maintenance as well as treatment time [4]. Advanced oxidation processes (AOPs) have gained attention as a clean and efficient technology. The key AOPs, UV/ H2O2, and ozonation are based on the generation of OH• , which act as a powerful oxidizing agent (2.8 V), destroying various organic and inorganic compounds nonselectively [5]. The decolorization of reactive dyes is marked by the cleav- age of the chromophoric system; however, the generated intermediates/by-products may or may not be toxic. Ideally, the decolorized water used for recycling should not adversely affect the dyeing process and should have reduced toxicity. Considering these requirements, the study of inter- mediate compounds formed during degradation process seems to be crucial. Recently, the identification of intermedi- ates formed during the degradation process of reactive dyes has been reported [6,7]. Degradation mechanism involving ZnO-mediated photocatalytic treatment of Reactive Blue 160 was revealed by using GC/MS and IC techniques [6]. Agrawal et al. [7] have studied the degradation of Acid Black 210 by using the enzyme Providencia sp. SRS82 with different char- acterization techniques such as FTIR, HPTLC, HPLC, GC/MS, and LCMS. C. I. Reactive Blue 171 (RB 171) dye, based on azo chro- mophore, is largely used for dyeing of cotton textiles. How- ever, only a few studies on its degradation have been reported [8,9]. Sun et al. adsorbed RB 171 on fly ash [8]. Khan and Husain have decolorized the same dye by using potato (Solanum tuberosum) soluble and immobilized poly- phenol oxidase [9]. This work explores the degradation of RB 171 by UV/H2O2 and O3. Operating parameters like pH, reagent dosage and time of treatment of dye solution were optimized. Characterization of degradation products through FTIR, TLC and HPLC confirmed the fragmentation of dye structure into smaller components, which were further sub- jected to the toxicity studies followed by GC/MS analysis for their identification so as to predict the probable mechanistic pathway of the dye degradation. MATERIALS C. I. Reactive Blue 171 (RB 171) dye, procured from Atul Ltd., India, was used without further purification. The struc- tural details of the selected dye are shown in Figure 1. All the chemicals were of LR grade and purchased from SigmaVC 2015 American Institute of Chemical Engineers Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2015 1
  • 2. Aldrich. All solutions were prepared with distilled water. Except in concentration optimization study, the dye concen- tration was kept at 50 mg/L. pH of the solution was adjusted by using 0.1 M HCl/0.1 M Na2CO3/NaOH. METHODS Ozonation Ozonation of 50 mL dye solution was carried out at alka- line pH in a semi-batch lab scale 100 mL glass reactor with ozone dose of 72 mg/L. Ozone was generated from pure oxygen at an input current of 0.3A with a flow rate of 3 L/ min by ozone generator unit (A. M. Ozonics Pvt. Ltd., India) having an ozone production capacity of 10 g/h. The excess ozone gas coming out from the reactor outlet was passed into a column of activated carbon to quench it. Most of the test runs lasted for 3 min. UV/H2o2 Process The photolytic oxidation setup consists of a closed wooden chamber with a single low pressure UV tube (UVC) with a power rating of 36 W, which was procured from Philips, India. The power output was 15.3 W, which was 35–40% of the input power. The UV tube was placed above the 100 mL reactor, at a distance of 13 cm. The reac- tor was filled with 50 mL dye solution of known concentra- tions. Runs were carried out at pH 4, 7, 9 and 10.5 with H2O2 dosing varied up to 8% (v/v). The treatment time was fixed at 30 min and the sample was collected after every 5 min. The dye solution was mechanically agitated using a magnetic stirrer at a speed of 400 rpm, so that H2O2 is uni- formly mixed. The studies were performed at room temperature (30 6 28 C), with pH varying between 4 and 10.5, repeated twice to ensure data reproducibility. The experimental errors were within 1.5% of the reported values of dye degradation. Analysis of Aqueous and Extracted Dye Solutions and Their Degradation Products The concentration of dissolved ozone was determined using iodometric procedure [10]. Concentration of RB 171 was measured by using UV-VIS Spectrophotometer (Model 8500, TECHCOMP, Hong Kong) at the characteristic kmax of 605 nm of the dye. Some of the samples were also analyzed for the extent of chemical oxygen demand (COD) removal. The samples were digested using closed reflux micro method and analyzed on Hach colorimeter (model DR/850) at a filter value 610 nm [11]. After these measurements, initial and ozone treated aque- ous dye solutions were filtered. The supernatant obtained was used to extract metabolites with an equal volume of ethyl acetate; dried over anhydrous Na2SO4, concentrated in a rotary vacuum evaporator followed by its dissolution in the HPLC grade methanol and was further used for characteriza- tion by FTIR, TLC, HPLC and GC/MS. The changes in functional groups were investigated using FTIR spectrum 2000 Perkin-Elmer spectrophotometer in the mid IR region of 750 2 4000 cm21 with 16 scan speed at a resolution of 4/cm. The dye was analyzed in powder form, whereas the dye degradation products were analyzed in the form of their methanol extracts [12]. TLC is considered as an easy and confirmatory test before moving on to the HPLC analysis. The extracts mounted on silica gel TLC plates (Merck) were run in the trough chamber previously saturated with mobile phase consisting of hex- ane/ethyl acetate/methanol (5:3:2 v/v). The resolved chroma- tograms were observed under UV light (254 nm) and were developed using iodine chamber. HPLC was performed on Agilent 1100 Series model, equipped with an auto sampler. Water Hypersil C18, 5 lm (4.6 m 3 250 mm) reverse phase column was used to sepa- rate individual components that were detected using Diode Array Detector. The mobile phase consisted of HPLC grade methanol. The column was run at a flow rate 1 mL/min for 10 min without controlling the temperature and the eluate was monitored at wavelength 254 nm using isocratic elution. The metabolites formed after degradation were subjected to identification using GC/MS (Shimadzu 2010 MS). The ioni- zation voltage was 70 eV. Gas chromatography was con- ducted in the temperature programming mode with a Restek column (0.25 mm id, 60 m long, nonpolar; XTI-5). The initial column temperature was 808C for 2 min, raised linearly at 108C/min to 2808C, and held for 7 min. The temperature of the injection port was 2808C and the GC/MS interface was maintained at 2908C. Helium was used as a carrier gas with a flow rate of 1.0 mL/min. Degradation products were identi- fied by comparison of retention time and fragmentation pat- tern, as well as with the mass spectra in the NIST spectral library support stored in the GC/MS solution software (ver- sion 1.10 beta, Shimadzu) [12]. Toxicity Studies Establishing the toxicity levels of the dye and its degrada- tion products is important to decide the mode of recycling of decolorized solution. Two types of crops, Phaseolus mungo (dicot) and Triticum aestivum (monocot) were selected for phytotoxicity analysis as they are regularly consumed in India. Solutions of the dye RB 171 (500 mg/L) and methanol extracts of the treated solutions (obtained by using each AOP), all were adjusted to pH 7, were prepared in distilled water. Ten healthy seeds of each crop were separately sowed into pots containing sand. The toxicity study was car- ried out at room temperature i.e., 328C by daily watering 5 mL for each using distilled water (as control)/mineralized wastewater [13]. Germination and the lengths of plumule (shoot) and radicle (root) were recorded after 8 days of growth. Germination (%) was estimated using the formula given below: Germination %ð Þ 5 ðNo: of seeds germinated 3100=No: of seeds sowedÞ Statistical Analysis Analysis of variance (ANOVA) is a collection of statistical models used in order to analyze the differences between Figure 1. C. I. Reactive Blue 171 (RB 171). Environmental Progress & Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep2 Month 2015
  • 3. group means and their associated procedures to test the null hypothesis against an alternative hypothesis. In its simplest form, ANOVA provides a statistical test of whether or not the means of several groups are equal. The effect of ozonation and UV/H2O2 treatments was studied on two types of seeds and the null hypothesis would be that all treatments have the same effect. Rejecting the null hypothesis (F FCritical) would imply that the two treatments result in different effects. Statistical summary reviews the values of variance, average, sum and count obtained by applying ANOVA to phytotoxicity study and gives the sum of squares of residuals (SS) together with the corresponding degrees of freedom (df), F-values, P-values. F-value is the ratio of variation asso- ciated with the model and variation associated with the experimental error about its mean. Greater F-value indicates that the components explain the variation [14]. The critical value of F is a function of the degrees of freedom (df) in the numerator and the significance level (a) in the denominator. Adjusted mean square (MS) is the ratio of sum of squares (SS) to degree of freedom (df). P-values assist in understand- ing the pattern of the mutual interactions between the test variables. The smaller the P-value, the more significant the corresponding coefficient is. RESULTS AND DISCUSSION Ozone Treatment Effect of Ozonation Time and Various Dye Concentrations on Extent of Decolorization RB 171 dye solutions of various concentrations (50– 200 mg/L) were ozonated for 3 min. As can be seen from Figure 2, the extent of decolorization decreased as the con- centration of dye was increased to 200 mg/L. This may be attributed to the insufficiency of OH• with respect to the higher amount of dye molecules present in solution and the competition of dye degradation products with the virgin dye molecules for the available OH• to get further oxidized [15,16]. It can be seen from UV-Vis spectra of 50 mg/L aque- ous RB 171 solution (Figure 3) that maximum absorbance for RB 171 at k 5 605 nm decreases as a function of ozonation time, which could be correlated to more population of OH• that becomes available for dye degradation with longer time of ozonation. In order to compare the degradation efficiency, the con- centration of dye solution was kept constant at 50 mg/L with a volume of 50 mL. Effect of pH on Decolorization For optimization, pH of the dye solutions was adjusted to 4, 7, 9, and 10.5 and each one was subjected to ozonation for 1 min. Decolorization was found to be the maximum at the alkaline pH of 10.5. Ozonation experiments were con- ducted under alkaline pH using NaOH/Na2CO3 for pH adjustment. From Figure 4, it may be observed that using NaOH, decolorization enhanced by 7% (for 1 min ozonation) at pH 10.5. However, reactive dyeing on cotton is carried out under alkaline conditions using Na2CO3 and not NaOH. For this reason, we have not chosen NaOH to maintain the pH, although carbonate ions are known to scavenge OH• [17]. At alkaline pH, ozone undergoes self-decomposition to generate much powerful OH• (E0 5 2.8 V) that attack the dye pollutant nonselectively [18]. Mechanism for enhanced decolorization of RB 171 solution could be explained by higher concentration of hydroxide ions at alkaline pH that Figure 2. Effect of ozonation time on decolorization and COD removal at different dye concentration. Figure 3. UV-Vis spectra of RB 171 solution at different ozo- nation time. Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2015 3
  • 4. initiates decomposition of ozone thereby generating hydro- peroxyl anion (HO2 - ) which further reacts with ozone yield- ing super-oxide anion radical (O2 -• ) as follows: O3 1 OH- ! HO- 21 O2 O3 1 HO- 2 ! OH• 1 O-• 2 1 O2 In the propagation step, ozone further reacts with gener- ated super-oxide anion radical to generate ozonide anion radical (O3 -• ), which is immediately decomposed to OH• at alkaline pH. O31 O-• 2 ! O-• 3 1 O2 O-• 3 $ O-• 1 O2 O-• 1 H2O ! OH• 1 OH- The termination stage comprises of radicals which react among themselves to form another molecule as described by Cremaso and Mochi [19]. The rate of the attack by OH• is normally 106 to 109 times faster than the corresponding reac- tion rate for molecular ozone. Thus, the concentration of OH• and molecular ozone can be controlled by adjusting the solution pH to 10.5 and 4, respectively. It is worth mentioning here that the pH of the spent reac- tive dye bath is essentially alkaline favoring alkaline ozona- tion and eliminating the pH adjustment step. This is an additional advantage of the ozone treatment for decoloriza- tion of reactive dye baths, which dominates the market of various types of dye classes applicable on cotton fabric. Effect of Various Concentrations of Chloride and Sulfate Ions on Decolorization Efficiency Dyeing with reactive dyes requires the addition of consid- erably large quantities of salts (sodium chloride or sodium sulfate) to the dye bath for enhanced pick up of dye on cot- ton. However, the solubility of ozone is readily affected by pH and presence of radical scavengers in the liquor. Hence, this parameter was studied under optimized conditions (RB 171 dye concentration 50 mg/L, solution pH 10.5 and volume 50 mL) at various salt concentrations (60, 500, and 1000 mg/ L) to evaluate the efficiency of ozone in decolorizing reactive dye bath (Figure 5). Decolorization efficiency was found to decrease marginally after 1 min of ozonation, more so with the higher concentration (1000 mg/L) of NaCl/Na2SO4. This negative effect of salt on RB 171 decolorization was possibly due to the depletion of OH• at alkaline pH as the salt anions and dye compete for OH• [20] as shown below: Cl- 1 OH• ! Cl• 1 OH- Cl- 1 Cl• ! Cl2 1 e- Addition of Na2SO4 also had similar effect, which could be explained by the reaction mentioned below: SO2- 4 1 OH• ! SO-• 4 1 OH- Muthukumar and Selvakumar [20] reported that higher the chloride and sulfate ion content, longer is the time required for complete decolorization. This is in agreement with our observations. Figure 4. Effect of pH on the decolorization of RB 171 in the ozonation treatment. Figure 5. Effect of chloride ions on the extent of decoloriza- tion by ozonation. Table 1. Decolorization of RB 171 using UV/H2O2. Decolorization (%) H2O2 In absence of UV In presence of UV 15 min at pH 30 min at pH (%, v/v) 4 7 9 10.5 4 7 9 10.5 0 0 1.4 0.5 0.4 0 1.9 0.6 0 0 1 0.6 9.3 3.7 2 2.8 22.1 6.1 4.3 3.9 2 1.4 12.4 5.4 3.5 5.2 22.1 6.9 4.9 5.7 4 1.9 14.4 9.5 5.9 8.0 23.5 10.8 6.9 9.6 6 2.3 16.9 10.3 6.4 7.4 24.4 10.8 5.9 6.5 8 3.1 17 12.3 7.9 6.9 23.9 12.8 8.3 8.7 Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep4 Month 2015
  • 5. Effect of Ozonation Time on COD Removal As can be seen in Figure 4, under the optimized pH con- ditions, within first 1 min of ozonation, more than 80% dye solution was decolorized, but COD removal (Figure 2) was not even 10%. At the end of 3 min ozone treatment, the COD removal increased, but only to 33%. Thus a longer duration of treatment is essential to achieve better minerali- zation of the dye. Perhaps, in the first 1 min, the OH• cre- ated by ozone in alkaline medium attack the azo chromophore of dye thereby loosing the color. Mineraliza- tion was found to be poor with respect to decolorization, as decolorization was rapid than COD reduction, which depends essentially on the smaller size products of dye deg- radation [21]. UV/H2O2 Treatment Effect of UV Exposure on Decolorization The data given in Table 1 indicates insignificant decolor- ization by UV or H2O2 alone. Li et al. also observed the same [15]. When the treatment under UV was combined with 6% H2O2, the extent of decolorization increased with UV expo- sure time, perhaps due to increased population of active OH• , by extended duration of photolysis [22]. H2O21UV ! 2 OH• Effect of pH on Decolorization Maximum decolorization was obtained at pH 4 for each H2O2 dosage studied (Table 1). Decreased decolorization at alkaline pH might be a consequence of the following possi- ble reasons. The concentration of the conjugate base of H2O2 (HO2 - ) increases at alkaline pH which reacts with a nondissociated molecule of H2O2 resulting in oxygen and water, in place of producing OH• under UV radiation as shown below [23]: H2O2 ! HO- 21 H1 pKa ¼ 11:6ð Þ HO- 21 H2O2 ! H2O1 O21 OH- Hence, the instantaneous concentration of OH• becomes lower than expected. Secondly, the reaction of OH• with HO2 - is approximately 100 times faster than its reaction with H2O2 that has been very well explained by Mitrovic et al. [24]. Furthermore, the self-decomposition rate of hydrogen peroxide has been observed to increase in alkaline Figure 6. FTIR spectra of the RB 171 (a) and its degradation products by ozonataion (b). Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2015 5
  • 6. conditions leading to the decrease of OH• formation. Azbar et al. [25] also indicated that best results on reduction of COD and color were obtained when the treatment was per- formed under acidic pH rather than an alkaline pH. Reduc- tion in pH after the treatment from initial 4 to nearly 2.5 can be attributed to the formation of organic and inorganic acids [26]. Effect of H2O2 Dosage on Decolorization and Extent of COD Removal The extent of RB 171 decolorization increased to 24.4% (Table 1) till an optimum H2O2 dosage of 6% (v/v). How- ever, higher dosage of H2O2 [8% (v/v)] resulted in the inhibi- tion of decolorization limiting it to 23.9%, which may be attributed to further increase in OH• , scavenging H2O2 itself [27] as follows: H2O2 1 OH• ! HO• 2 1 H2O HO• 2 1 HO• ! H2O1 O2 Even after 30 min of the reaction, the COD removal was very poor (less than 2%). UV/H2O2 treated samples were not considered for elucidation of degradation due to poor decol- orization and COD removal, however, those were considered for the toxicity studies. Analysis of methanol extracts to study degradation by FTIR, TLC, HPLC, and GC/MS Figure 6a shows the appearance of hump in the region of 3330 2 3550 cm21 confirming the presence of primary, sec- ondary and tertiary amines (aliphatic as well as aromatic) in Figure 7. GC/MS spectra obtained after the degradation of RB 171 by ozonation. Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep6 Month 2015
  • 7. Table 2. GC spectral details of intermediates obtained by ozonation of RB 171. GC/MS fragments by Ozonation Details of the intermediate Structure a Chemical Formula: C9H7ClN5NaO3S sodium 3-(4-amino-6-chloro-1,3,5-triazin-2-ylamino) benzenesulfonate b Chemical Formula: C10H9N4NaO4S sodium 5,6-diamino-3-diazenyl-4-hydroxynaphthalene-2- sulfonate c Chemical Formula: C9H7N4NaO2S sodium 3-(1,3,5-triazin-2-ylamino)benzenesulfinate (1) Chemical Formula: C31H18ClN10Na5O16S5sodium 4-amino-3-((E)-(5-(4-chloro-6-(3-sulfonatophenylamino)-1, 3,5-triazin-2-ylamino)22-sulfonatophenyl)diazenyl)- 5-hydroxy-6-((E)-(2-sulfonatophenyl)diazenyl) naphthalene-2,7-disulfonate (2) Chemical Formula: C15H10ClN5Na2O6S2 sodium 3, 40 -(6-chloro-1,3,5-triazine-2,4diyl)bis(azanediyl) dibenzenesulfonate (3) Other fragments like sodium hydroxide, sodium benzenesulfonateand SO3 ions (4) Chemical Formula: C6H6NNaO3S sodium 4-aminobenzenesulfonate Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2015 7
  • 8. the dye structure which was found to diminish in the treated samples. In addition, band at 1610 cm21 confirmed the pres- ence of AN@NA linkage while the bands between 1530 and 1560 cm21 indicated aromatic C@C stretching [28], followed by the band between 550 and 850 cm21 thus marking CACl stretching. All the above mentioned bands were found to be absent in the spectra of the ozone treated sample Figure 6b, confirming the degradation of dye to different species. The FTIR spectra of the treated samples showed two peaks between each 2800 2 2900 cm21 , 1400 2 1450 cm21 and 1000 2 1120 cm21 regions representing CAH stretching, CAH bending, and CAN stretching vibrations of aliphatic amines, respectively, thus indicating the production of ali- phatic saturated compounds due to oxidation of RB 171 by ozonation. In the case of TLC analysis, the Rf value for the parent dye RB 171 was much higher (0.87) in comparison with that for ozone treated sample (0.45). The same has been con- firmed by Sahasrabudhe and Pathade [29] and Zope et al. [30]. Table 3. Phytotoxicity study of the dye RB 171 and the metabolites obtained after AOP treatments for the Phaseolus mungo and Triticum aestivum. (Dicot) Phaseolus mungo (Monocot) Triticum aestivum 5 mL/Day Germination (%) Shoot length (cm) Root length (cm) Germination (%) Shoot length (cm) Root length (cm) Dist. Water 100 20.3 6 0.8 7 6 0.6 100 16.4 6 0.8 4 6 0.5 500 ppm RB 171 70 14.4 6 0.9 3 6 0.7 60 11.3 6 0.6 1.8 6 0.2 UV/H2O2 70 15.2 6 0.8 3.1 6 0.4 70 13.3 6 0.4 2.7 6 0.4 Ozonated 90 17.8 6 0.4 4.2 6 0.4 90 14.8 6 0.4 3.1 6 0.3 Data was analyzed by one-way analysis of variance (ANOVA) with Tukey-Kramer Multiple Comparison Test and mentioned values are the mean of ten germinated seeds of four sets SEM (6). Figure 8. Proposed degradation pathway for the dye RB 171 by ozonation. Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep8 Month 2015
  • 9. HPLC spectrum of RB 171 showed one major peak at retention time of 6.467 min and a minor peak at 6.360 min. The spectrum for ozone treated sample showed the peaks at 2.413 and 3.393 min. This difference in the retention times of the original dye and the fragments formed by ozone treat- ment confirms the dye degradation into different small organic fragments by ozonation, further to cleavage of azo linkage that is responsible for decolorization. The GC/MS spectrum of ozone treated sample is shown in Figure 7. The details of intermediates detected by GC/MS were labeled alphabetically and those undetected-but- reorganized as necessary intermediates were labelled numeri- cally and are given in Table 2. Inferring Figure 8, it could be assumed that the dye structure was attacked by OH• , leading to asymmetric azo bond cleavage and yielded intermediate (a); (m/z 5 322) followed by the formation of a unidentified reactive intermediate (1). It might have further cleaved at sec- ond azo position by OH• giving two intermediates, one of them was labeled as Intermediate (b); (m/z) 5 304) and sec- ond as Intermediate (2). Oxidative cleavage of this intermedi- ate (2) between N and C of the triazine ring led to the formation of intermediate (c); (m/z) 5 258 and intermediate (3 and 4). Thus, probable degradation mechanism showed the production of benzene and aliphatic/aromatic sulfonate deriv- atives. Similar were the observations by Bansal and Sud [6]. Toxicity Studies Toxicity of 500 mg/L of the dye RB 171 solution before and after the treatments was confirmed by inhibition in ger- mination for Phaseolus mungo (dicot) and Triticum aestivum (monocot), as against distilled water. This untreated solution adversely affected both shoot and root lengths (Table 3). However UV/H2O2 and ozone treated set showed excellent results comparable to distilled water, thus indicating exten- sive reduction in toxicity by the treatment order ozone UV/ H2O2. This study paved the route for the treated water towards its reuse for irrigation purpose as well. Kurade et al. [14] also acknowledged similar reduction in toxicity of Scarlet RR dye after Consortium BL-GG treatment. Statistical Analysis Higher difference in variance values (Table 4) between ozone and UV/H2O2 treated samples with respect to that between ozone and control (distilled water) samples confirms that ANOVA result is in agreement with the experimental data stating higher reduction in toxicity by ozonation than UV/ H2O2 treatment. In all cases, P value 0.05 (Table 5) along with F FCritical for a certain number of degrees of freedom at level of 95% significance a (a 5 0.05) proves that null hypoth- esis is rejected (Both treatments have different efficiency in toxicity removal). Much lower P value for Phaseolus mungo with respect to Triticum aestivum indicate that among both the prior resulted in good germination and better growth. CONCLUSIONS From this study the following conclusions may be drawn: 1. The fastest decolorization (100% within 2 min) and high- est COD removal (33% within 3 min) was achieved by ozonation at pH 10.5. However, UV/H2O2 was found to be time consuming (30 min) leading to only 24.4% decol- orization at acidic pH 4. COD removal was poor with both the AOPs. 2. FTIR, TLC, and HPLC analysis of ozone-treated samples confirmed the structural changes in the large dye mole- cule in terms of shift/disappearance of IR peaks, retention time and elution peaks, respectively. 3. Probable degradation illustrated the production of ben- zene and aliphatic/aromatic sulfonate derivatives. This might be attributed to lower COD removal values. 4. Toxicity studies revealed possible reuse of treated dye solution for irrigation purpose. 5. It may be concluded therefore that ozonation is most promising technique for abatement of the pollution caused by the presence of color in the wastewater. Table 4. Statistical summary indicating the values corresponding to “Sum,” obtained by summation of shoot and root length values (from Table 3), for Phaseolus mungo and Triticum aestivum. Phaseolus mungo (Dicot) Triticum aestivum (Monocot) Variance Average Sum Count Summary Count Sum Average Variance 89.2448 13.63 27.26 2 D.W 2 20.37 10.185 76.26125 64.65469 8.671429 17.34286 2 RB 171 2 13.06667 6.533333 45.125 72.68735 9.171429 18.34286 2 UV/H2O2 2 16.07143 8.035714 56.02867 92.54477 10.96905 21.9381 2 Ozonated 2 17.96667 8.983333 68.18525 7.247746 16.90964 67.63857 4 Shoot length 4 55.79413 13.94853 4.688716 3.368698 4.31131 17.24524 4 Root length 4 11.68063 2.920159 0.853955 Average values are function of “Sum” in numerator to “Count” in denominator. Variance calculated by ANOVA measures the variability from an average or mean. Table 5. ANOVA analysis confirms that seeds germinated in RB 171 solution are significantly different from those germinated in metabolites at P 0.05. Better germination and growth was obtained for Phaseolus mungo at P 0.0001 than Triticum aestivum. Phaseolus mungo (Dicot) Triticum aestivum (Monocot) F crit P-value F MS df SS Source of Variation SS df MS F P-value F crit 9.276628 0.020518 17.7834 10.0512 3 30.1537 Treatments 14.278 3 4.75929 16.0753 0.00863 9.2766 10.12796 0.000165 561.632 317.436 1 317.436 Shoot root lengths 243.25 1 243.25 310.51 0.0004 10.128 Environmental Progress Sustainable Energy (Vol.00, No.00) DOI 10.1002/ep Month 2015 9
  • 10. ACKNOWLEDGMENTS Authors would like to express their gratitude to UGC for funding of this project under Major Research Project grant. Thanks are also due to Mr. A. Moolji (Director, M/S A. M. Ozonics Pvt. Ltd., Mumbai) for his timely and valuable inputs. Ms. Namata Patil is also grateful for UGC-SAP fellow- ship under CAS. LITERATURE CITED 1. Forgacs, E., Cserhati, T., Oros, G. (2004). Removal of synthetic dyes from wastewaters: A review, Environment International, 30, 953–971. 2. Allegre, C., Moulin, P., Maisseu, M., Charbit, F. (2006). Treatment and reuse of reactive dyeing effluents, Journal of Membrane Science, 269, 15–34. 3. Solıs, M., Solıs, A., Manjarrez, N., Flores, M. (2012). Microbial decolouration of azo dyes: A review, Process Biochemistry, 47, 1723–1748. 4. Beyerbach, A., Rothman, N., Bhatnagar, V., Kashyap, R., Sabbioni, G. (2006). Hemoglobin adducts in workers exposed to benzidine and azo dyes, Carcinogensis, 27, 1600–1606. 5. Glaze, W., Kang, J. D.H. (1987). 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