Coomassie Brilliant Blue (CBB) degradation using hydrodynamic cavitation, hydrogen peroxide and activated persulfate (HC-H2O2-KPS) combined process

Journal Pre-proof Coomassie Brilliant Blue (CBB) Degradation using Hydrodynamic Cavitation, Hydrogen Peroxide and Activated Persulfate (HC-H2 O2 -KPS) Combined Process Soroush Baradaran, Mohammad-Taghi Sadeghi

PII:

S0255-2701(19)30703-2

DOI:

https://doi.org/10.1016/j.cep.2019.107674

Reference:

CEP 107674

To appear in:

Chemical Engineering and Processing - Process Intensification

Received Date:

23 June 2019

Revised Date:

25 September 2019

Accepted Date:

26 September 2019

Please cite this article as: Baradaran S, Sadeghi M-Taghi, Coomassie Brilliant Blue (CBB) Degradation using Hydrodynamic Cavitation, Hydrogen Peroxide and Activated Persulfate (HC-H2 O2 -KPS) Combined Process, Chemical Engineering and Processing - Process Intensification (2019), doi: https://doi.org/10.1016/j.cep.2019.107674

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Coomassie Brilliant Blue (CBB) Degradation using Hydrodynamic Cavitation, Hydrogen Peroxide and Activated Persulfate (HC-H2O2-KPS) Combined Process Soroush Baradaran and Mohammad-Taghi Sadeghi * Author’s Address: Department of Chemical, Oil and Gas Engineering, Iran University of Science

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and Technology (IUST), Tehran, Iran

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Corresponding Author’s E-mail: [email protected]

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Graphical abstract

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Research Highlights Hybrid process using HC and dual oxidation system for CBB decolorization is introduced.

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Single and interactive effects of parameters are investigated using RSM.

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An accurate correlation is developed for CBB decolorization.

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Kinetics and synergistic effects of HC, H2O2 and KPS is revealed.

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Abstract

Emerging combination of hydrodynamic cavitation and dual oxidant chemical system (HC-KPS-

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H2O2), was used for decolorization and mineralization of Coomassie Brilliant Blue (CBB) in wastewater. Investigation were conducted on the effect of HC inlet pressure (4-8 bar), hydrogen

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peroxide (H2O2) concentration (0-1000 mg L-1) and potassium persulfate (KPS) concentration (0-

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1000 mg L-1) via experimental design using Box-Behnken Design (BBD). Furthermore, synergistic effects of various combinations (HC-KPS, HC-H2O2, KPS-H2O2, and HC-H2O2-KPS) was

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determined through decolorization kinetics as well as mineralization tests. Beneficial effects for simultaneous utilization of H2O2 and KPS in combination with HC were addressed. A remarkable 92% decolorization and 73.2% mineralization in 60 min was attained at HC inlet pressure, H2O2 concentration and KPS concentration equal to 7.1 bar, 676.1 mg L-1 and 541.1 mg L-1, respectively.

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The maximum obtained first order rate constant was 9.2 × 10−3 min−1 leading to a synergistic coefficient of 3.04 using HC-H2O2-KPS combined process. Keywords: Hydrodynamic Cavitation (HC); Advanced Oxidation Process (AOP); Coomassie Brilliant Blue (CBB); Hydrogen peroxide; Potassium persulfate;

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1. Introduction A number of industries such as plastics, food, pharmaceutical, textile, dying are using organic dyes, that in turn impose environmental issues in the industry effluents as well as health effects even at very low concentrations [1]. Hydrodynamic Cavitation (HC) generated through formation and collapse of bubbles resulting from depressurization at relatively constant temperature, has proved its ability in altering the

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chemical processes with respect to its physico-chemical effects [2]. Thus, HC can be considered

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as a substantial effective technology for advanced oxidation of various pollutants, through in situ production of hydroxyl radicals [3]. Moreover, HC plays a crucial role in process intensification

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and mass transfer acceleration.

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Coomassie Brilliant Blue (CBB) is a non azo dye that belongs to the group of triphenyl methane dyes. This organic dye is frequently used in textile industry, gel electrophoresis and other

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biological applications [4]. Various processes have been developed so far to handle the problems associated with brilliant blue to the environment. Adsorption based processes are considered using

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variety of synthetic adsorbents [5-7]. Among these efforts, nanocomposite hydrogel coupled with photocatalytic process for CBB oxidation has been utilized leading to 88.6% decolorization in 240 min [8]. Photocatalytic degradation along with adsorption via TiO2/BC composite has also resulted in 99.71% conversion in 60 min [9]. TiO2/BC composite with hydrogen peroxide in adjusted pH

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also led to 97.7% decolorization in 3h [10]. Recently, a remarkable 95% decolorization of Remazol Brilliant Blue R in aqueous medium is reported in 10min through a novel acyltransferase-ISCO (in situ chemical oxidation) coupled system [11]. Along with these techniques, acoustic cavitation and ultrasonic utilization as a well-known advanced oxidation technique has been in center of attentions for brilliant blue degradation. Sonocatalytic degradation of this dye resulted in 90%

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decolorization in 40min. In this case, application of WO3 and WO3-ZnO, hydrogen peroxide (H2O2) and Zinc acetate dehydrate enhanced the reaction efficiency [12]. Effect of periodate in sonochemical degradation of brilliant blue is also investigated resulting in 97% degradation in 20min [13]. Effects of ultrasonic frequency, power density, pH and various additives such as ferrous ion, hydrogen peroxide and peroxodisulphate are studied and optimized in degradation of CBB. The authors introduced 13 transformed products in a certain sonication time. A maximum

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conversion of 93% in 30 min is achieved via the optimum conditions [4]. Photocatalytic

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degradation of CBB has also been investigated in literature through UV and TiO2 [14], visible light and Bi2WO6/H2O2, as well as UV/V and ZnO-GO [15]. Almost total decolorization in 30 min

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is reported [16]. Furthermore, photoelectrocatalytic degradation [17] and utilization of a

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continuous-flow tubular reactor coated with thin layer of PdO [18] are among the other solutions tested for such purposes. However, despite all this valuable researches, HC based advanced

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oxidations have been rarely used for decolorization/degradation of brilliant blue category. Recently, persulfates are gaining more attentions due to its appropriate solubility in water,

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convenient utilization, stability at room temperature, relatively low cost and accessibility, as well as, wide operative pH range [19]. Activation of persulfate ion (S2O82-) leads to generation of highly reactive sulfate free radicals (SO4-). It can take place through cleavage of O-O bond via various methods such as thermal activation, UV radiation, ferrous activating systems, photolysis and

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radiation [20, 21]. However, uncertainties exists regarding simultaneous using of KPS along with H2O2, since they are typically used independently. Recently, the dual oxidation system using KPS and H2O2 have been examined in carbofuran photodegradation [22], absorption of NO [23], bisphenol removal [24] and in-situ chemical oxidation (ISCO) process for soil and groundwater remediation [25]. While, up to date no research study have been set out to verify the effectiveness

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of combination of hydrodynamic cavitation, hydrogen peroxide and activated persulfate (HCH2O2-KPS). In the present study, the aim is to evaluate the novel combination of HC, KPS and H2O2 in decolorization and mineralization of CBB. The parameters evaluation as well as optimization is carried out using experimental design methodology and the synergy of various possible combinations (HC-KPS, HC-H2O2, KPS-H2O2, and HC-H2O2-KPS) is investigated through

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decolorization kinetics.

2. Materials and methods

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Experimental HC setup

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HC experimental setup was designed and fabricated as schematized in Fig.1a. A centrifugal pump (PENTAX CBT600/00, 5.5 HP) was operated to provide determined pressure and flowrate.

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Holding tank was also provided equipped with a cooling coils to maintain the temperature. The setup was constructed in a way to be capable of regulating flow and pressure through a bypass line

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and manual valves on each branch. A single hole circular orifice with conical opening was considered as the cavitating device with thickness of 5 mm, inlet hole diameter of 4 mm and bevel angle of 45° following a sharp edge. This beveled orifice enables flow increment as well as faster pressure recovery that can exhibit beneficial effect on the HC. Fig.1b demonstrates the schematic

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of this cavitating device. Cavitation reactor was made of Plexiglas to enable visual observation of the macroscopic phenomena and is shown in Fig.1c. All the experiments were performed in aqueous solution at initial dye concentration of 20 mg L-1. The operating temperature was maintained at 30±2 °C. Materials and analytical methods

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Coomassie Brilliant Blue (CBB) was provided from a well-known commercial producer. Hydrogen peroxide (H2O2 50% wt.) and potassium persulfate (KPS: K2S2O8) were both purchased from viable domestic resources. UV–visible spectroscopy was performed by a UV-VIS Spectrophotometer (Hach DR/2010) to determine the concentration of CBB. To verify the extent of mineralization following oxidation process, total organic carbon (TOC) was measured using a TOC analyzer (Analytik Jena,

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Germany).

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Experimental design

Response Surface Methodology (RSM) was applied for investigation on the effects of parameters.

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It enables quantitative assessment of parameters and those contribution on the response as well as

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determination of the parameters significance and mutual interaction. It also provides models for exact optimization according to the desired objective. Box-Behnken design (BBD) was selected

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for such purpose. Design Expert 10.0.7 software was applied for modelling and optimization using the numerical methods, based on desirability function. The target was set to maximize CBB

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decolorization in the simulated wastewater. Selected parameters and the corresponding values are reported in Table 2. HC inlet pressure was selected to evaluate HC contribution in CBB decolorization. Hydrogen peroxide (H2O2) was used to stimulate oxidation of the dye within the concentration range of 0 to 1000 mg L-1. Besides, potassium persulfate (KPS) in the same range

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of concentration was applied for the study. All the experiments were carried out in constant temperature of 30°C with initial dye concentration of 20 ppm in aqueous solution. Decolorization kinetics and synergistic coefficients

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In order to evaluate the kinetics of CBB decolorization using different processes a pseudo first order reaction kinetic equation was applied to fit the obtained data. The apparent rate constants were calculated via following Eq. (1): 𝑙𝑛 𝐶⁄𝐶 = −𝑘𝑡

(1)

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Where parameter k represents the apparent first order rate constant, C is the CBB concentration at

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time t during oxidation, C0 denotes to the initial concentration of CBB and t is the treatment time. Based on the kinetics, synergistic coefficients have been computed to reveal the efficacy of hybrid

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processes (i.e., HC-KPS, HC-H2O2, KPS-H2O2, HC-H2O2-KPS). Eq. (2) is the basis for evaluation

simplified equation. 𝑘(𝐻𝐶−𝐾𝑃𝑆−𝐻2𝑂2)

3. Results and Discussion Statistical analysis

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(𝐻𝐶) +𝑘(𝐾𝑃𝑆) + 𝑘(𝐻2𝑂2)

(2)

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𝑠𝑦𝑛𝑒𝑟𝑔𝑖𝑠𝑡𝑖𝑐 𝑐𝑜𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑡 = 𝑘

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of HC-H2O2-KPS hybrid scheme. Other combinations also could be verified through a similar

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The obtained values for all the experiment are reported in Table 3. A range of responses from 18% to 89% extent of degradation for CBB is observed. Analysis of variance (ANOVA) determines the model competency and significance of parameters affecting the CBB extent of decolorization.

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Table 4 reports the analysis results. Quadratic model was fairly adopted to the available dataset. Based on that, a polynomial second-order quadratic equation for representing an empirical relation between the response and significant parameters, HC pressure (A), H2O2 concentration (B) and KPS concentration(C) at constant temperature of 30°C in term of coded factors is as Eq. (3): Extent of Decolorization (%) =

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86.5800 +17.9375A +14.48751B +4.6000C -6.1000AB +1.4750AC -5.2250BC -19.2650A213.4650B2 -9.6400C2

(3)

According to the statistical study, model F-Value of 156.33 confirmed the appropriate selection and significance of the selected model. It is calculated based on the ratio between the mean square due to regression and the mean square due to error term [26]. The attained lack of fit for the model was 1.33. This value is not significant relative to the pure error so that the model can be used for

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the prediction and optimization purposes [27].

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In the experimental design analysis, the terms with P-Value of less than 0.05 exhibits their significance effect on the response. Meanwhile, for any parameter the probability value higher

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than 0.10 implies that the parameter contribution is not significant in the model. According to the

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results, all the three studied parameters are significant while the factor contribution reduces in the order of pressure, H2O2 and KPS concentration, respectively.

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Table 5 represents the statistical parameters calculated based on the assumed model. Coefficient of variation (C.V) is 3.51% that implies model high reliability and reproducibility of the data. High

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value for R-squared (0.995) and adjusted R-Squared (0.9887) are obtained. These are also in reasonable agreement with the predicted R-Squared (0.9566). Diagnostic plots are presented in Fig.2. According to the normal plot of residuals that is demonstrated in Fig.2a, despite the existence of some scatter, straight line is followed that implies

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normal distribution of residuals. Graph of amounts of actual response values against the predicted ones is depicted in Fig.2b. The illustration is provided for detection of values that are improperly predicted through the prediction model.

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Fig.2c belongs to plot of the residual versus the ascending predicted response values that verifies the assumption of constant variance. The points are located in a range of ±2 that and follow a random scatter. Single effect analysis Fig.3 represents the single effect analysis of the parameters at fixed values for the rest of the parameters. As demonstrated in Fig.3a, effect of HC inlet pressure on the CBB degradation at KPS

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and H2O2 concentration of 500 mg L-1 is highly pronounced. Initially with increasing pressure

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from 4 bar to 7 bar, CBB decolorization improves from 50.1% up to 90%. In this area, the response is highly sensitive and the changes are drastic. Within the aforementioned range, increasing the

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HC pressure drop, stimulates expansion of bubbles and generation of intense collapses leading to

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extreme local effects (i.e., temperature, pressure). Furthermore, cavitation zone is also affected that provides more active volume for oxidation reaction [28]. Moreover, due to the subsequent

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flow rate increment with pressure, the number of passes into reactive cavitation zone would increase. This could also result in improving yield, despite the negative effect on residence time

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of reactive species in the reaction zone. On the other side, decreasing cavitation number leads to higher number of cavitating bubbles where the turbulence phenomena is also empowered [29]. Typically, oxidation pathway of the dyes in presence of HC and other agents can be attributed to several types of reactions. In this regards, two credible degradation pathways exist for the

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degradation of CBB. One could be considered as the pyrolytic decomposition of the CBB accompanied with aromatic hydroxylation and demethylation [4]. Such a pathway is related to the hydrophobic interaction of CBB with the cavitating bubbles. This can take place inside the cavity interior due to the local pressure and temperature exhibited subsequent to bubble collapses. It can also happen to the other molecules that are exposed to the extreme conditions in the interface

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region. Therefore, due to the HC mechanical effects, breakage of chromophore group (C=N) may occur [4, 30]. Increasing pressure stimulate this mechanism through reinforcing HC intensity up to a certain threshold. Another pathway is a result of pyrolysis of water and oxidizing agents leading to generation of active radicals (i.e., •OH, •SO4-) that subsequently react with the dye molecules. During the decolorization of CBB, breakage of chromophore group (C=N) is the main step while destruction of the chromosphere bounds through hydroxyl and persulfate radical’s

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attack, takes place at bubble interfaces or within the bulk medium [31]. This pathway could be the

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dominant mechanism due to high efficiency of radical attacks as well as presence of larger number of molecules that are recognized as the radical sources. These would favor the pyrolysis of these

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compounds having lower required energy compared to the first mechanism.

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These can contribute to formation of more active oxidizing species mainly as a consequence of the higher temperature of gas phase inside the bubbles at the final stage of collapsing process

H2O → •OH + •H

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through pyrolysis dissociation of water molecules according to Eq.(4): (4)

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Meanwhile, for HC pressure values of above 7 bar, appearance of a maximum is observed. It could be attributed to the choked cavitation or super cavitation phenomenon. The phenomenon may lead to completely filled cavitation zone with large number of cavities, where contains generally water vapor molecules, coalescing to form cloud of cavitation. Subsequently, despite decreasing

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cavitation number and increasing cavitational events resulted from increased pressure drop, large cavity cloud escapes the liquid without collapsing. Hence, a decline in overall cavitation intensity occurs due to the incomplete or cushioned collapse of the cavities [32, 33]. This has led to decay in CBB degradation from 90% in 7 bar to 85% in 8 bar. In case of HC standalone without using KPS and H2O2, a maximum degradation of 45% could be achieved in 60 min at HC inlet pressure

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of 7 bar. It is also worth mentioning that HC combination with KPS (500 mg L-1) will result in 65% degradation, while its combination with H2O2 (500 mg L-1) will lead to 75% extent of decolorization. The single effect analysis of H2O2 concentration on the decolorization could be assessed through Fig.3b. H2O2 is a conventional oxidizing agent with high oxidation potential (1.78 V) [34]. Dissociation of this agent under HC leads to produce reactive •OH that is a strong oxidizing agent

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with high oxidation potential (2.8 V) according to Eq. (5) and Eq. (6). The active radical can diffuse

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among bulk of fluid and degrade pollutant molecules [35]. H2O2 → •OH + •OH

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H2O2 + •OH → •HO2 + H2O

(5) (6)

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As demonstrated in Fig.3b, increase of H2O2 loading from 0 to 750 mg L-1, is accompanied with 58% to 90.5% extent of decolorization at 6 bar HC inlet pressure with 500 mg L-1 KPS loading.

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As expected, increasing the amount of H2O2 results in positive influence on generation of radicals and acceleration of pollutant degradation rate [36]. However, decay in degradation is observed

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with further H2O2 concentration of around 750 mg L-1 to 1000 mg L-1. Despite the reinforcement of the radical generation, this contradictory behavior is a result of consumption of hydroxyl radicals by H2O2 according to Eq. (6) leading to production of water and •HOO[37]. The optimum concentration of H2O2 is based on type of pollutant and intensity of cavitation [38] and the trend

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is also observed in other reports such as oxidation of 2,4-dinitrophenol [39]. Fig.3c shows the effect of KPS considering HC inlet pressure at 6 bar and 500 mg L-1 of H2O2 concentration. The data indicate that a maximum for extent of decolorization (87%) within the aforementioned range could be achieved by the KPS loading of 683 mg L-1. The activity of KPS is substantially dependent on the mechanism of its activation. Following reactions (Eq.(7) and

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Eq.(8)) can take place for the activation and generation of active radicals due to the thermal effects of cavitating bubble collapses in liquid-vapor interface [40]: S2O82- → 2•SO4-

(7)

•

(8)

•

(9)

•

(10)

SO4- + H2O → SO42− + •OH + H+ SO4- + •SO4- → S2O82SO4- + S2O82- → SO42− + •S2O8-

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Meanwhile, above the aforementioned threshold, a negative effect is exerted by further loading of

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KPS. It could be concluded that at high extent of KPS loadings, the decay in activity takes place probably due to the PS radical scavenging by itself based on Eq. (9) or reacting with S2O82-

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according to Eq. (10), instead of reacting with CBB. Scavenging of the active radicals of PS is also

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mentioned by the others [4].

However, this trend is not similar to what was previously reported for KPS loading in degradation

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of orange acid-II via HC and acoustic cavitation, where increasing concentration of PS resulted in increasing the conversion up to a maximum and then remained approximately unfazed by further

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increments in loadings, from 90 mg L-1 to 1600 mg L-1[41]. Therefore, it seems that the PS behavior and the optimum value aside from type of pollutant and the amount of loading, depends on other processes that are simultaneously take part in oxidation mechanism (i.e., HC intensity and H2O2).

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Response surface analysis

Descriptions of the output from validated models could be empowered through response surface model graphs since the obtained results of single factor analysis imply the existence of parameters mutual effects. Hence, each parameter effect is dependent upon the settings of the others. In such cases there might be some missing points on the contribution of the parameters (i.e., HC pressure,

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H2O2 and KPS). Graphical representations of 3-D dimensional response surface plots are depicted

in Fig.4. Each plot is drawn at a fixed value for one parameter in center point of the studied range and variation of two other factors in the experimental investigation ranges. The interactive effects of HC pressure and H2O2 in constant KPS concentration of 500 mg L-1 is represented via Fig.4a. As illustrated, in low values for HC inlet pressure, increase of H2O2 loading resulted in a continuously increase of CBB decolonization from 17.3% to 57.4%. Meanwhile, at

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constant H2O2 loadings, increasing the HC inlet pressure has resulted in dramatic increase of

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degradation. The same trend has been repeated at high values for HC inlet pressure (6-8 bar) and H2O2 loading (600-1000 mg L-1). In this region, an optimum is appeared. The synergistic

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combination of HC and H2O2 could be described by various aspects. One is the chemical aspects

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that radical generation through pyrolytic dissociation of water molecules according to Eq. (4), HC facilitates the dissociation of H2O2 based on Eq. (5). Therefore, the active radicals are formed from

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dissociation of both water and H2O2. The synergistic effect of HC and H2O2 in formation of hydroxyl radicals is well known and reported in featured researches [42]. Another aspect is the

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physical influence of this combination. Enhanced cavitation zone and increasing number of cavitation events consequently, could be occurred due to presence of H2O2. In fact, H2O2 can act as initial nuclei for bubble formation. The contribution of H2O2 can even impact the regime of HC [43, 44]. Hence, the interactive effects of HC and H2O2 appears in both chemical and physical

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features to influence the CBB overall decolorization. However, the synergistic effect of HC-H2O2 combination is not sustained at high values of the parameters. In this case, enhanced HC inlet pressure could result in super cavitation phenomenon that diminishes the bubble collapses and limits hydroxyl formation. High concentration of H2O2 and its physical contributions on the phenomenon can facilitate occurrence of the super cavitation phenomenon. Another possible event

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is surplus accumulation of •OH radicals and its recombination that results in formation of water and H2O2 molecules leading to deceleration of degradation rate. In order to evaluate the relation of HC pressure (A) and KPS (C) at constant H2O2 concentration of 500 mg L-1, the 3-D graph response surface is illustrated in Fig.4b. Potassium persulfate dissociates in aqueous solutions to form the persulfate anion (S2O8)2-. According to the obtained results, activation of (S2O8)2- to generate highly reactive sulfate radicals (SO4)- is enhanced through

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increasing the overall cavitation intensity. It leads to enhancement of CBB decolorization.

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However, this effect is limited at high HC inlet pressure values due to appearance of super cavitation. It damps the cavitation overall intensity and subsequently hinders persulfate activation.

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This fact, highlights the role of HC in thermal activation of KPS. Subsequent to water and H2O2

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pyrolysis by HC, the released local heat empowers generation of free •SO4-. Besides, in addition to the energy released due to the collapse of bubbles, chemical effect of pyrolysis reactions (Eq.

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(5) and Eq. (6)) shall be taken into account. Based on Eq. (8), the PS radical can take part in reaction with water to generate •OH. The PS radical can also react with OH- (Eq. (11)). The

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generated •OH from Eq. (3), Eq. (4) or Eq. (11) may get subject of further transformation with SO42− to produce •SO4- and OH-. Hence, based on the mentioned events, the synergic chemical effect of HC and PS is postulated [40]. SO4- + OH- → SO42− + •OH

(11)

SO42− + •OH → •SO4- + OH-

(12)

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Interactive effect of H2O2 and KPS at constant 6 bar HC inlet pressure could be addressed from Fig.4c. At high H2O2 concentration, decreased efficiency of CBB degradation can be seen. This effect is more pronounced at higher concentration of persulfate. Therefore, in order to attain 90%

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decolorization, the oxidants concentration should be set in the range of 650 mg L-1 to 850 mg L-1 for H2O2 and 400 mg L-1 to 670 mg L-1 for KPS. Combination of these oxidizing agents might seem to be independent of each other due to different types of primary radicals generated. Gogate et al. suggested that inter-conversion of radicals can take place leading to formation of hydroxyl radicals as a consequence of persulfate and sulfate ion presence in water [41, 45]. As a remark, it could be stated that due to multi-step and unselective

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pathways of the radicals and their scavenging effect, increase in concentration of the two chemical

efficiency.

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Parameters optimization and validation of results

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oxidizers leads to suppression of radicals diffusion and consequently termination of decolorization

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According to the modeling results a highly desirable optimum value for HC inlet pressure, H2O2 concentration and KPS concertation could be 7.1 bar, 676.1 mg L-1 and 541.1 mg L-1, respectively.

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It results in 92.27% decolorization within the proposed operating condition and initial concentration of the dye. Verification of the predicted point was experimentally examined. In the

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desired optimum condition, slight difference (less than 5%) between experimental and predicted response, implies a reliable modelling and approves the applied methodology. Kinetics and synergistic effects Kinetics of the understudying processes were elucidated in both standalone mode (HC, KPS and

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H2O2) and hybrid mode (HC-KPS, HC-H2O2, KPS-H2O2, HC-H2O2-KPS). In order to determine the exact contribution of HC, a set of experiments were performed using the setup with the HC reactor bypass line. This enables evaluation of the KPS and H2O2 degradation performance in the absence of HC. The Fig.5 shows the experimental data obtained following sampling and analysis performed within time interval of 10 min during the treatment process at temperature of 30°C. The

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values for each parameter as well as apparent first order rate constants and synergistic coefficient based on Eq. (1) and Eq. (2) are reported in Table 6. According to the results, the reaction first order rate constants is equal to 9.2 × 10−3 min−1 using HC (7 bar pressure drop) standalone mode in CBB decolorization. Besides, addition of H2O2 (676 mg L-1) has been accompanied with synergistic coefficient of 2.11 and rate constant of 9.2 × 10−3 min−1. Eventually, a synergistic coefficient of 3.04 could be achieved by addition of KPS (541 mg L-1) resulting in rate constant of

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9.2 × 10−3 min−1. The findings indicate the beneficial effect of hybrid process using HC and the

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dual oxidation system (H2O2 and KPS). According to the Table 6, limited oxidizing capability of H2O2 alone resulted in rate constant of 3.6 × 10−3 min−1. Meanwhile its combination with HC

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accelerated the degradation ending up with 27× 10−3 min−1 rate constant. Synergistic coefficient of

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2.11 implies the gainful combination of the two effects. It should be also noted that, no significant activity was exhibited by KPS in the absence of HC wither in standalone (k=0.9× 10−3 min−1) or

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in combination with H2O2 (k=3.8× 10−3 min−1). It highlights the role of the latter in activation of KPS through the aforementioned reactions.

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Mineralization Study

Efficacy of the treatment process for dissolved natural organic matters (NOM) was evaluated through analyzing the percentage removal total organic carbon (TOC) from aqueous solution. The performance of various processes and changes in TOC with time of the process are displayed in

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Fig.6. Accordingly, a continual decreasing trend is observed in all the experiments. Hence the time has beneficial effect on the TOC removal. Using HC (7 bar pressure drop), H2O2 (676 mg L-1) and KPS (541 mg L-1) individually resulted in TOC removal of 27.1 %, 30.2 % and 4.1 %. Low changes of TOC implies that although the CBB is degraded through decolorization process, it has been transferred to other organic compounds. In this combined process, active radicals are formed due

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to pyrolysis reaction of water, H2O2 and K2S2O8 activation. Next, the initial attack of active radicals to destroy the CBB chromophore bounds occurs via hydrogen abstraction and addition. Eventually, the subsequent attacks take place lead to abolishing the conjugate structure of CBB where the color of the dye solution disappears. Mineralization of the CBB indicates its transfer to water, CO2 and other degradation products. Based on the optimized hybrid scheme (HC-H2O2-KPS), maximum mineralization of 73.2 % in 60 min is achieved that highlights the effectiveness of the process in

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degradation and mineralization. The obtained synergistic coefficient for the hybrid process is equal

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to 1.16. The results indicate high capability of the optimized process in both decolorization and mineralization. Additionally, further investigation on the treatment time using the optimum

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conditions revealed a slight increment in TOC removal that leads to 76.1% of the mineralization

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at 90 min.

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4. Conclusion

A hybrid scheme for CBB as a non azo organic dye was optimized. Experimental investigations

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were performed on the basis of experimental design using Box-Behnken design (BBD) method. According to the analysis of variance, accurate modelling for the observed values was performed that enables acceptable prediction and optimization. Evaluation of the significance of operating inlet pressure and dual oxidizing system (KPS and H2O2) highlighted their interactive effect,

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leading to an optimum of 92% decolorization and 73.2% TOC removal within the reaction time of 60 min. HC presence and its intensity should be considered in finding the optimum for the chemical system because of the mutual interactions and dependency of the values. Furthermore, according to the kinetic study of the different configuration of the three proposed techniques, utilization of the dual oxidant system in presence of HC exhibited synergistic effect in the optimum range of concentrations and deterrent effect in high loadings on the decolorization yield. 17

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[1] S. Rajoriya, S. Bargole, S. George, V.K. Saharan, Treatment of textile dyeing industry effluent using hydrodynamic cavitation in combination with advanced oxidation reagents, Journal of Hazardous Materials 344 (2018) 1109-1115. [2] S. Baradaran, M.T. Sadeghi, Intensification of Diesel Oxidative Desulfurization via Hydrodynamic Cavitation, Ultrasonics sonochemistry (2019) 104698. [3] M. Torabi Angaji, R. Ghiaee, Decontamination of unsymmetrical dimethylhydrazine waste water by hydrodynamic cavitation-induced advanced Fenton process, Ultrasonics sonochemistry 23 (2015) 257-265. [4] M.P. Rayaroth, U.K. Aravind, C.T. Aravindakumar, Sonochemical degradation of Coomassie Brilliant Blue: Effect of frequency, power density, pH and various additives, Chemosphere 119 (2015) 848-855. [5] G. Torgut, M. Tanyol, F. Biryan, G. Pihtili, K. Demirelli, Application of response surface methodology for optimization of Remazol Brilliant Blue R removal onto a novel polymeric adsorbent, Journal of the Taiwan Institute of Chemical Engineers 80 (2017) 406-414. [6] G. Sharma, M. Naushad, A. Kumar, S. Rana, S. Sharma, A. Bhatnagar, F. J. Stadler, A.A. Ghfar, M.R. Khan, Efficient removal of coomassie brilliant blue R-250 dye using starch/poly(alginic acid-cl-acrylamide) nanohydrogel, Process Safety and Environmental Protection 109 (2017) 301-310. [7] T.L. Silva, A. Ronix, O. Pezoti, L.S. Souza, P.K.T. Leandro, K.C. Bedin, K.K. Beltrame, A.L. Cazetta, V.C. Almeida, Mesoporous activated carbon from industrial laundry sewage sludge: Adsorption studies of reactive dye Remazol Brilliant Blue R, Chemical Engineering Journal 303 (2016) 467-476. [8] Priya, B.S. Kaith, U. Shanker, B. Gupta, J.K. Bhatia, RSM-CCD optimized In-air synthesis of photocatalytic nanocomposite: Application in removal-degradation of toxic brilliant blue, Reactive and Functional Polymers 131 (2018) 107-122. [9] S. Zhang, X. Lu, Treatment of wastewater containing Reactive Brilliant Blue KN-R using TiO2/BC composite as heterogeneous photocatalyst and adsorbent, Chemosphere 206 (2018) 777783. [10] Y. Liu, L. Hua, S. Li, Photocatalytic degradation of Reactive Brilliant Blue KN-R by TiO2/UV process, Desalination 258 (2010) 48-53. [11] Z. Shu, H. Wu, H. Lin, T. Li, Y. Liu, F. Ye, X. Mu, X. Li, X. Jiang, J. Huang, Decolorization of Remazol Brilliant Blue R using a novel acyltransferase-ISCO (in situ chemical oxidation) coupled system, Biochemical Engineering Journal 115 (2016) 56-63. [12] Y.M. Hunge, A.A. Yadav, V.L. Mathe, Ultrasound assisted synthesis of WO3-ZnO nanocomposites for brilliant blue dye degradation, Ultrasonics sonochemistry 45 (2018) 116-122. [13] O. Hamdaoui, S. Merouani, Improvement of sonochemical degradation of Brilliant blue R in water using periodate ions: Implication of iodine radicals in the oxidation process, Ultrasonics sonochemistry 37 (2017) 344-350. [14] S.B. Bukallah, M. Rauf, S.S. Ashraf, Photocatalytic decoloration of Coomassie Brilliant Blue with titanium oxide, Dyes and Pigments 72 (2007) 353-356. [15] L. Kashinath, K. Namratha, K. Byrappa, Microwave Assisted Synthesis and Characterization of Nanostructure Zinc Oxide-Graphene Oxide and Photo Degradation of Brilliant Blue, Materials Today: Proceedings 3 (2016) 74-83.

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[16] N.A. Shad, M. Zahoor, K. Bano, S.Z. Bajwa, N. Amin, A. Ihsan, R.A. Soomro, A. Ali, M. Imran Arshad, A. Wu, M.Z. Iqbal, W.S. Khan, Synthesis of flake-like bismuth tungstate (Bi2WO6) for photocatalytic degradation of coomassie brilliant blue (CBB), Inorganic Chemistry Communications 86 (2017) 213-217. [17] Y. Hunge, A. Yadav, M. Mahadik, V. Mathe, C. Bhosale, A highly efficient visible-light responsive sprayed WO3/FTO photoanode for photoelectrocatalytic degradation of brilliant blue, Journal of the Taiwan Institute of Chemical Engineers 85 (2018) 273-281. [18] R. Javaid, U.Y. Qazi, S.-I. Kawasaki, Highly efficient decomposition of Remazol Brilliant Blue R using tubular reactor coated with thin layer of PdO, Journal of Environmental Management 180 (2016) 551-556. [19] F. Ji, C. Li, X. Wei, J. Yu, Efficient performance of porous Fe2O3 in heterogeneous activation of peroxymonosulfate for decolorization of Rhodamine B, Chemical engineering journal 231 (2013) 434-440. [20] Y.-q. Gao, N.-y. Gao, Y. Deng, Y.-q. Yang, Y. Ma, Ultraviolet (UV) light-activated persulfate oxidation of sulfamethazine in water, Chemical Engineering Journal 195 (2012) 248-253. [21] Z.-H. Diao, X.-R. Xu, H. Chen, D. Jiang, Y.-X. Yang, L.-J. Kong, Y.-X. Sun, Y.-X. Hu, Q.W. Hao, L. Liu, Simultaneous removal of Cr (VI) and phenol by persulfate activated with bentonite-supported nanoscale zero-valent iron: reactivity and mechanism, Journal of hazardous materials 316 (2016) 186-193. [22] W. Chu, T.K. Lau, S.C. Fung, Effects of Combined and Sequential Addition of Dual Oxidants (H2O2/S2O82-) on the Aqueous Carbofuran Photodegradation, Journal of Agricultural and Food Chemistry 54 (2006) 10047-10052. [23] Z. Wang, Z. Wang, Mass Transfer-Reaction Kinetics Study on Absorption of NO with Dual Oxidants (H2O2/S2O82–), Industrial & Engineering Chemistry Research 54 (2015) 9905-9912. [24] S.A. Mokhtari, M. Farzadkia, A. Esrafili, R.R. Kalantari, A.J. Jafari, M. Kermani, M. Gholami, Bisphenol A removal from aqueous solutions using novel UV/persulfate/H 2 O 2/Cu system: optimization and modelling with central composite design and response surface methodology, Journal of Environmental Health Science and Engineering 14 (2016) 19. [25] C. Liang, B. He, A titration method for determining individual oxidant concentration in the dual sodium persulfate and hydrogen peroxide oxidation system, Chemosphere 198 (2018) 297302. [26] M. Jafarikojour, B. Dabir, M. Sohrabi, S.J. Royaee, Evaluation and optimization of a new design photocatalytic reactor using impinging jet stream on a TiO 2 coated disc, Chemical Engineering and Processing: Process Intensification 121 (2017) 215-223. [27] S.-N. Nam, H. Cho, J. Han, N. Her, J. Yoon, Photocatalytic degradation of acesulfame K: Optimization using the Box–Behnken design (BBD), Process Safety and Environmental Protection 113 (2018) 10-21. [28] H. Soyama, J. Hoshino, Enhancing the aggressive intensity of hydrodynamic cavitation through a Venturi tube by increasing the pressure in the region where the bubbles collapse, AIP Advances 6 (2016) 045113. [29] M. Capocelli, M. Prisciandaro, A. Lancia, D. Musmarra, Hydrodynamic cavitation of pnitrophenol: A theoretical and experimental insight, Chemical Engineering Journal 254 (2014) 18. [30] G. Boczkaj, A. Fernandes, Wastewater treatment by means of advanced oxidation processes at basic pH conditions: a review, Chemical Engineering Journal 320 (2017) 608-633.

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[31] Y. Çalışkan, H.C. Yatmaz, N. Bektaş, Photocatalytic oxidation of high concentrated dye solutions enhanced by hydrodynamic cavitation in a pilot reactor, Process Safety and Environmental Protection 111 (2017) 428-438. [32] M.V. Bagal, P.R. Gogate, Degradation of diclofenac sodium using combined processes based on hydrodynamic cavitation and heterogeneous photocatalysis, Ultrasonics sonochemistry 21 (2014) 1035-1043. [33] M. Gągol, A. Przyjazny, G. Boczkaj, Wastewater treatment by means of advanced oxidation processes based on cavitation–a review, Chemical Engineering Journal (2018). [34] S. Rajoriya, S. Bargole, V.K. Saharan, Degradation of reactive blue 13 using hydrodynamic cavitation: Effect of geometrical parameters and different oxidizing additives, Ultrasonics sonochemistry 37 (2017) 192-202. [35] T. Sruthi, R. Gandhimathi, S. Ramesh, P. Nidheesh, Stabilized landfill leachate treatment using heterogeneous Fenton and electro-Fenton processes, Chemosphere 210 (2018) 38-43. [36] S. Raut-Jadhav, D. Saini, S. Sonawane, A. Pandit, Effect of process intensifying parameters on the hydrodynamic cavitation based degradation of commercial pesticide (methomyl) in the aqueous solution, Ultrasonics sonochemistry 28 (2016) 283-293. [37] P. Thanekar, M. Panda, P.R. Gogate, Degradation of carbamazepine using hydrodynamic cavitation combined with advanced oxidation processes, Ultrasonics sonochemistry 40 (2018) 567-576. [38] P.R. Gogate, P.N. Patil, Combined treatment technology based on synergism between hydrodynamic cavitation and advanced oxidation processes, Ultrasonics sonochemistry 25 (2015) 60-69. [39] M.V. Bagal, P.R. Gogate, Degradation of 2, 4-dinitrophenol using a combination of hydrodynamic cavitation, chemical and advanced oxidation processes, Ultrasonics sonochemistry 20 (2013) 1226-1235. [40] J. Choi, M. Cui, Y. Lee, J. Kim, Y. Son, J. Khim, Hydrodynamic cavitation and activated persulfate oxidation for degradation of bisphenol A: Kinetics and mechanism, Chemical Engineering Journal 338 (2018) 323-332. [41] P.R. Gogate, G.S. Bhosale, Comparison of effectiveness of acoustic and hydrodynamic cavitation in combined treatment schemes for degradation of dye wastewaters, Chemical Engineering and Processing: Process Intensification 71 (2013) 59-69. [42] S. Raut-Jadhav, V.K. Saharan, D. Pinjari, S. Sonawane, D. Saini, A. Pandit, Synergetic effect of combination of AOP's (hydrodynamic cavitation and H(2)O(2)) on the degradation of neonicotinoid class of insecticide, J Hazard Mater 261 (2013) 139-147. [43] H. Sayyaadi, Enhanced cavitation–oxidation process of non-VOC aqueous solution using hydrodynamic cavitation reactor, Chemical Engineering Journal 272 (2015) 79-91. [44] H. Sayyaadi, Assessment of tandem venturi on enhancement of cavitational chemical reaction, Journal of Fluids Engineering 131 (2009) 011301. [45] M.V. Bagal, P.R. Gogate, Degradation of 2,4-dinitrophenol using a combination of hydrodynamic cavitation, chemical and advanced oxidation processes, Ultrasonics sonochemistry 20 (2013) 1226-1235.

20

of ro -p re lP ur na Jo Fig.1. Hydrodynamic cavitation experimental setup (a), cavitation device (b) and cavitation reactor (c).

21

Design-Expert® Software CBB Degradation

Normal Plot of Residuals

Color points by value of CBB Degradation: 89

99

17.3

90 80 70 50 30

of

Normal % Probability

95

20 10 5

-2.00

-1.00

0.00

ro

1

1.00

Jo

ur na

lP

re

-p

Internally Studentized Residuals

22

2.00

Design-Expert® Software CBB Degradation

Predicted vs. Actual

Color points by value of CBB Degradation: 89

100

17.3

80

Predicted

60

40

20

0

20

40

60

80

Design-Expert® Software CBB Degradation

Residuals vs. Predicted

-p

2.00

1.00

0.00

0

-1.00

lP

Internally Studentized Residuals

17.3

3.00

3

re

Color points by value of CBB Degradation: 89

100

ro

Actual

of

0

-2.00

-3.00

-3

ur na

0

20

40

60

80

100

Predicted

Jo

Fig.2. Model diagnostic plots for CBB decolorization; (a) Normal plot of residuals, (b) Predicted vs actual plot, (c) plot of the Residual versus predicted.

23

of ro -p re lP ur na Jo

Fig.3. Single effect analysis of HC pressure (A), H2O2 concentration (B) and KPS concentration (C) on CBB decolorization.

24

of ro -p re lP ur na Jo 25 Fig.4. Response surface 3-D graph of CBB decolorization; the interactive effect of HC pressure (A), H2O2 (B) and KPS (C) concentration.

2.5

ro

2

of

HC KPS H2O2 HC+KPS HC+H2O2 KPS+H2O2 HC+KPS+H2O2

re

ln (C0/C)

-p

1.5

Jo

0.5

ur na

lP

1

0

0

10

20

30

40

50

Time (min)

Fig.5. Kinetics of CBB decolorization using HC, H2O2, KPS and various hybrid processes.

26

60

80 HC KPS

70

H2O2 HC+KPS HC+H2O2

of

HC+KPS+H2O2

ro

50

40

-p

TOC Reduction (%)

60

30

10

0 10

ur na

0

lP

re

20

20

30

40

50

Time (min)

Jo

Fig.6. TOC reduction as a function of time for various processes (HC, H2O2, KPS, HC- KPS, HCH2O2 and HC- KPS- H2O2).

27

60

Table 1. Operating parameters and corresponding cavitation number.

Flowrate (LPM)

Cavitation Number (Cv)

4

15

0.47

5

19

0.31

6

22

0.23

7

26

0.16

Jo

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-p

ro

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Inlet Pressure (bar)

28

Table 2. Parameters level and experimental window.

Parameters

Unit

-1

0

+1

A

HC inlet pressure

bar

4

6

8

B

H2O2 concentration

mg L-1

0

500

1000

C

KPS concentration

mg L-1

0

500

1000

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Symbol

29

Table 3. Box-Behnken experiments and the experimental values for response.

Std.

Run

Factor 1

Factor 2

Factor 3

Extent of

A: P[bar]

B: H2O2[mgL-1]

C: K2S2O8

Decolorization

[mgL-1]

(%)

6

500

500

88.1

5

2

4

500

0

35.0

13

3

6

500

500

83.3

17

4

6

500

500

6

5

8

500

0

8

6

8

500

2

7

8

0

9

8

6

0

3

9

4

10

10

6

14

11

6

15

12

6

12 1

11

ro

86.4 70.8 83.3

500

62.5

0

38.8

1000

500

57.4

1000

0

79.3

500

500

89.0

500

500

86.1

lP

re

-p

1000

13

4

500

1000

41.6

14

6

1000

1000

77.7

15

4

0

500

17.3

16

8

1000

500

78.2

17

6

0

1000

58.1

Jo

4

ur na

7

of

1

16

30

Table 4. ANOVA results of the response surface quadratic model for CBB extent of degradation (%).

Source

Sum of Squares df

Mean Square

F Value

p-value Prob > F

Model

7693.07

9

854.79

156.33

< 0.0001

A-P

2574.03

1 2574.03

470.75

< 0.0001

B-H2O2

1679.10

1 1679.10

307.08

< 0.0001

169.28

1

169.28

30.96

0.0008

AB

148.84

1

148.84

27.22

0.0012

AC

8.70

1

8.70

1.59

0.2475

BC

109.20

1

109.20

19.97

A2

1562.70

B2

763.39

1

C2

391.28

1

38.28

7

Lack of Fit

19.09

3

6.36

Pure Error

19.19

4

4.80

ro

-p

0.0029

285.79

< 0.0001

139.61

< 0.0001

re 391.28

71.56

< 0.0001

5.47

7731.34 16

Jo

Cor Total

763.39

lP

ur na

Residual

1 1562.70

of

C-PS

significant

31

1.33

0.3830 not significant

Table 5. Statistical parameters of the model from ANOVA.

Value 2.34 66.64 3.51 335.38 62.04

Parameter R-Squared Adj R-Squared Pred R-Squared Adeq Precision BIC AICc

Value 0.9950 0.9887 0.9566 39.731 90.37 118.71

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Parameter Std. Dev. Mean C.V. % PRESS -2 Log Likelihood

32

Table 6. The rate constants of CBB decolorization using HC, H 2O2 , KPS and various hybrid processes.

R2

Synergistic Coefficient

HC

7

0

0

9.2

0.978

-

KPS

*

0

540

0.9

0.966

-

H2O2

*

676

0

3.6

0.963

-

HC + KPS

7

0

540

18.2

0.986

1.80

HC + H2O2

7

676

0

27

0.981

2.11

KPS + H2O2

*

676

540

7

676

540

re

H2O2

3.8

-p

HC + KPS +

41.6

Jo

ur na

lP

* Experiments were carried out using HC reactor bypass mode.

33

of

Process Type

ro

H2O2 KPS Concentration Concentration [mgL-1] [mgL-1]

Pseudo first order rate constant (k × 103 min−1)

HC Pressure [bar]

0.967

0.84

0.987

3.04