Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2024 Sep 11;9(38):39997–40009. doi: 10.1021/acsomega.4c05815

Synergistic Degradation of Methylene Blue by Hydrodynamic Cavitation Combined with Hydrogen Peroxide/Vitamin C System

Yan Cao †,‡,*, Guoqiang Wu †, Yongchun Huang †,‡, Chengdu Huang †,‡
PMCID: PMC11425821  PMID: 39346872

Abstract

graphic file with name ao4c05815_0016.jpg

In this study, a new combined process of hydrodynamic cavitation (HC) and a hydrogen peroxide/vitamin C (H2O2/Vc) system was proposed for the degradation of methylene blue (MB) in wastewater. An impact-jet hydraulic cavitator was used as the cavitation generation equipment, and H2O2/Vc was selected as a homogeneous oxidation system. The degradation characteristics of MB were investigated. The results showed that the degradation effect of HC in combination with the H2O2/Vc system was more effective than that of the individual HC or H2O2/Vc system. A maximum degradation rate of 87.8% was achieved under the following conditions: H2O2 concentration of 0.03 mol/L, Vc concentration of 0.021 mol/L, inlet pressure of 0.3 MPa, initial solution concentration of 4 μmol/L, solution volume of 150 mL, and reaction time of 10 min. The synergy index was 1.615, indicating a synergistic effect between the HC and H2O2/Vc system. The data of the hydroxyl radical (·OH) yield under the conditions of HC, the H2O2/Vc system, and the HC + H2O2/Vc system were fitted and analyzed. A correlation equation for ·OH yield was established, further revealing the synergistic mechanism of the HC and H2O2/Vc system. The intermediate products of MB degradation were detected based on LC-MS, and three possible degradation pathways of MB degradation were proposed. The combined process of HC and H2O2/Vc systems exhibited relatively low energy efficiency and operating cost, indicating that it was in line with the development direction of wastewater treatment.

1. Introduction

Methylene blue (MB) is an organic alkaline dye in printing and dyeing wastewater and poses significant harm to the environment and human health. Traditional methods for dye removal include chemical coagulation,1 adsorption,2 biochemical oxidation,3 etc. However, these methods have problems, such as high cost, long degradation cycle, and susceptibility to secondary pollution. In recent years, advanced oxidation processes (AOPs) applied to eliminate harmful substances in wastewater have become popular. It involves the production of hydroxyl radicals (·OH) with high oxidation activity, which oxidize organic matter into H2O, CO2, and some small molecules to achieve efficient degradation of dye wastewater. AOPs have the advantages of high efficiency, low environmental impact, and low cost in decomposing toxic pollutants. It is regarded as a green and powerful treatment technology for dye degradation. AOPs include electrochemical oxidation,4 Fenton and Fenton-like oxidation,5,6 photocatalytic oxidation,7 and cavitation,8 etc. In addition, microbial degradation9 was also recognized as a promising method, which utilized random mutagenesis for the bioremediation of dyes, leading to dye degradation. The combination of two AOPs or one AOP with other methods has attracted the attention of many researchers due to its higher efficiency compared to a single method.10−12

Hydrodynamic cavitation (HC) is considered as one of the AOPs. In the process of HC, pressure changes cause the growth, contraction, and collapse of cavitation bubbles, resulting in a strong chemical effect (free radical effect) and mechanical effect.13 Since HC has the advantages of low cost, low energy consumption, and no secondary contamination problems, it is favored by researchers and has been widely used in wastewater treatment,14 biodiesel synthesis,15 preparation of nanoemulsion,16 sterilization,17 polymer degradation,18 etc. HC is regarded as a very promising technology for the degradation of water pollutants.19 Many researchers have studied the degradation of organic compounds in wastewater by HC technology. Rajoriya et al.20 studied the degradation mechanism of Rhodamine 6G under the action of HC using two types of cavitation devices, slit and circular venturi, and pointed out that ·OH was the main factor affecting the degradation effect. Dhanke et al.21 utilized an HC reactor to treat fish processing wastewater. The biochemical oxygen demand (BOD), chemical oxygen demand (COD), total organic carbon (TOC), odor, and color of this wastewater have been reduced promisingly. It was pointed out that this wastewater can be degraded effectively by HC. Although HC has unique advantages in wastewater treatment, the use of HC alone poses problems such as insufficient cavitation intensity and low degradation efficiency of organic matter.

H2O2 has strong oxidizing properties and can decompose to produce ·OH.22 However, in the absence of a catalyst, the rate of H2O2 decomposition to produce ·OH is very slow. Generally, H2O2 is combined with Fe2+ to form a Fenton reagent. Under the catalysis of Fe2+, H2O2 can rapidly decompose to produce highly active ·OH, greatly accelerating the reaction rate. The Fenton process is one of the AOPs. It was reported that the combination of HC and AOPs can significantly improve the degradation efficiency of organic matter,23 and the combination of HC and Fenton has been widely studied. Rajoriya et al.24 reported four combined processes (HC + air, HC + O2, HC + O3, HC + Fenton) for the treatment of textile dyeing industry effluent. It was pointed out that the combination of HC and Fenton was the most effective for the treatment of this wastewater, resulting in a 48% reduction in TOC and a 38% reduction in COD. Askarniya et al.25 investigated the decolorization of Congo red using the hybrid process of HC with H2O2, FeSO4, and Fenton. It was pointed out that the combination of HC and Fenton can achieve a maximum decolorization rate of 70% within 60 min, and the hybrid process has a more effective decolorization effect than the individual process. However, a major drawback with the use of Fenton reagents was the generation of a large amount of sludge during the process of treating wastewater, resulting in new pollution issues.26

Vitamin C (Vc), also known as l-ascorbic acid, is an acidic polyhydroxy compound containing 6 carbon atoms, mainly derived from fresh fruits and vegetables. It is an essential nutrient for higher primates and a few other organisms and has strong reducibility. In the presence of Vc, H2O2 can easily decompose to produce ·OH. Yan et al.27 pointed out that the degradation mechanism of Vc and H2O2 was similar to that of Fe2+ and H2O2 in Fenton’s reagent. The combination reagent (H2O2 + Vc) was considered as one of Fenton’s reagents. Both Vc and Fe2+ tended to promote the decomposition of H2O2 to generate ·OH,28 thereby leading to the degradation of organic compounds. The H2O2 + Vc composite reagent is an environmentally friendly redox reaction system, and its use will not cause secondary pollution. Currently, this composite reagent is commonly used for the degradation of polysaccharides in food. Li et al.29 reported the degradation of polysaccharides from Passiflora edulis peel by the Vc-H2O2 system. After degradation, the molecular weight and intrinsic viscosity of the Passiflora edulis peel were significantly reduced. It was pointed out that the Vc-H2O2 system was effective in the degradation of Passiflora fruit peel. Yan et al.27 studied the degradation of codium cylindricum polysaccharides by combined processes of H2O2 + Vc + ultrasonic and H2O2 + Fe2+ + ultrasonic. It was pointed out that many ·OH that affected positive antioxidant activity were produced in both processes. The combined process of H2O2 + Fe2+ + ultrasound has stronger antioxidant activity, while the combined process of H2O2 + Vc + ultrasound had a mild reaction and higher recovery rate. In addition, the application of the H2O2–Vc composite reagent has been extended to the field of wastewater treatment. Li et al.30 used the H2O2–Vc system to treat azo dye wastewater which contained a high concentration of methyl orange. The results showed that this system can effectively degrade methyl orange with a decolorization rate of over 98%. However, there is currently no research on the use of H2O2–Vc composite reagent for the treatment of MB in wastewater.

This paper proposed a new combined process of the HC and H2O2/Vc system, both of which were green and environmentally friendly AOPs. In the present work, the degradation characteristics of MB by the combined process of the HC and H2O2/Vc system were investigated. First, the effects of various factors on the degradation rate of MB and the yield of ·OH were studied. In addition, the synergistic effect of HC and H2O2/Vc and the degradation mechanism of MB were explored. This study attempts to explore a new green method for the efficient degradation of MB in wastewater.

2. Experimental Section

2.1. Materials

Methylene blue (AR grade) was obtained from Tianjin Zhiyuan Chemical Reagent Co., Ltd., Tianjin, China. Hydrogen peroxide (30%, AR grade) and l-ascorbic acid (AR grade) were provided by Xilong Scientific Co., Ltd., Shantou, China. All of the solutions were prepared with pure water produced by a Milli-Q system (Millipore Co., Ltd., Billerica, MA, USA).

2.2. Experimental Process Parameters

The MB solution was preheated to a reaction temperature of 30 °C before carrying out the experiment. Appropriate amounts of H2O2 and Vc were added sequentially to the MB solution. Two gear pumps were started simultaneously, and the flow rate could be controlled by adjusting the speed of the pumps. When the reaction was complete, sampling and analysis were carried out immediately. The parameters and conditions selected in the experiments were as follows: H2O2 concentration, 0.01–0.05 mol/L; Vc concentration, 0–0.035 mol/L; inlet pressure, 0.1–0.5 MPa; initial concentration of MB solution, 4–20 μmol/L; volume of solution, 120–240 mL; time, 2.5–12.5 min. In all experiments, the pH of the simulated MB wastewater was maintained at 6.23, and the reaction temperature was set at 30 °C.

2.3. Experimental Setup

The schematic diagram of the experimental setup is shown in Figure 1. The setup included a constant-temperature water bath (DF-101S, Gongyi Yuhua Instrument Co., Ltd., Zhengzhou, China), a beaker, two gear pumps (WT3000-1JB, Longer Precision Pump Co., Ltd., Baoding, China), and a reactor. These devices were connected by silicone tubes to form a circulation loop. The pressure gauges (Y-40Z, Hongqi Instrument Co., Ltd., Leqing, China) were installed in the two inlet sections of the reactor to display the real-time pressure. Two types of reactors were used in this experiment. Reactor 1 and reactor 2 were the devices with and without venturi on the outlet, respectively.

Figure 1.

Figure 1

Open in a new tab

Schematic diagram of experimental setup (Photograph courtesy of Yan Cao).

The structures of reactors 1 and 2 are shown in Figure 2. The reactor 1 was an impact-jet hydraulic cavitator, which had two inlets and one outlet. The inner diameters of the inlet and outlet were 5 and 6 mm, respectively. A venturi with a throat diameter of 0.5 mm was placed in the outlet section. The inlet cone angle and outlet cone angle of the venturi were 40 and 32°, respectively. The reactor 2 was an impact reactor, which had the same structure as the reactor 1, except for the absence of a venturi in the outlet section. The reactor 1 was used to study the degradation of MB under two conditions, HC alone and HC in combination with the HC + H2O2/Vc system. The effect of the H2O2/Vc system alone on MB degradation was investigated using reactor 2, in which the influence of cavitation on MB degradation can be eliminated.

Figure 2.

Figure 2

Open in a new tab

Structures of the reactors used in this study: (a) reactor 1, (b) reactor 2.

2.4. Experimental Analysis

An ultraviolet–visible spectrometer (UV-2600, Shimadzu Co., Ltd., Suzhou, China) was used to measure the absorbance of the MB solution. The absorption spectrum of the MB solution was acquired within the wavelength range of 400–800 nm, as shown in Figure 3. The maximum absorption peak was observed at a wavelength of 664 nm. Therefore, the absorbance of the MB solution in this study was measured at a maximum wavelength of 664 nm. The concentration of MB can be determined based on the MB standard curve, as shown in Figure 4, obtained from Beer–Lambert Law. The degradation products of MB were detected with liquid chromatography–mass spectrometry (LC-MS, Agilent LC1290-QQQ-6470, USA). The mass spectrometric conditions included positive ion acquisition mode, a dry gas temperature of 150 °C, a dry gas flow rate of 12 L/min, an atomized gas pressure of 30 Psi, a capillary voltage of 3500 V, and a quality detection range set to m/z from 50 to 400. The chromatographic conditions consisted of a flow rate of 0.35 mL/min and a mobile phase composed of acetonitrile and 0.1% formic acid. The TOC was measured by using a TOC analyzer (Elementar vario TOC, Germany).

Figure 3.

Figure 3

Open in a new tab

Absorption spectrum of the MB solution.

Figure 4.

Figure 4

Open in a new tab

Standard curve of the MB solution.

In order to reduce the influence of experimental errors on the experimental results, each experiment was repeated three times. The experimental data in the figures were expressed as the mean or mean ± standard deviation.

3. Results and Discussion

In this study, ·OH was mainly derived from the HC process and the reaction between H2O2 and Vc. In the process of HC, when the fluid passed through a constriction (such as orifice plate, venture, etc.), cavitation bubbles underwent the process of formation, growth, and collapses due to pressure changes. At the moment when the cavitation bubble collapsed, an extreme environment of high temperature (500–15,000 K) and high pressure (100–5000 bar) was generated. In this extreme environment, water molecules were decomposed into species with high oxidative activity, such as ·OH, ·OOH, etc. The energy required for dissociation of the OH bond in H2O2 was 388 kJ/mol.31 The presence of catalysts (such as Fe2+, Vc, etc.) reduced the energy barrier for H2O2 decomposition and promoted the cleavage of the OH bond.

·OH reacts with MB to generate various degradation products, and the reaction process can be described as follows:

3. 1

Under the attack of a large number of ·OH, a series of reactions occur, such as demethylation, hydroxylation, bond cleavage, etc. Hydroxylation is the process of introducing ·OH into a molecular structure to form compounds with hydroxyl groups. However, the degradation pathways of MB are usually more than one, and the degree of hydroxylation of intermediate products varies in different degradation pathways. It was found in various degradation pathways reported in the literature32−34 that in most cases intermediate products containing one hydroxyl radical were usually formed. Similar findings were found in our study (as shown in Section 3.4). There are three possible pathways for MB degradation. The intermediate products containing one hydroxyl radical were formed in pathways 1 and 2, while polyhydroxy compounds were only formed in pathway 3. Therefore, in order to achieve quantitative analysis of the yield of ·OH captured, the degradation process of MB has been simplified, and a hypothesis was proposed that the hydroxyl radical reacted equimolarly with MB (n = 1 in eq 1). A similar method for obtaining the yield of· OH was reported by Zhang et al.35 Therefore, the concentration of ·OH captured can be calculated as follows:

3. 2

Where CMB,o and CMB are the concentrations before and after MB degradation, respectively.

The degree of MB degradation is reflected by the degradation rate (η),36 which can be calculated as follows:

3. 3

In HC devices, the degradation of MB was closely related to the cavitation intensity, which can be evaluated by the cavitation number (Cv). Generally, cavitation occurs when Cv ≤ 1. A smaller Cv value indicates a higher cavitation intensity. Cv is a dimensionless parameter,37 which can be defined as follows:

3. 4

Where Pr denotes the outlet pressure of the hydraulic cavitator, Pv denotes the vapor pressure of the liquid, ρ denotes the density of liquid, and v denotes the average velocity of the liquid at the venturi throat.

3.1. Effect of H2O2 Concentration on Degradation of MB by the HC + H2O2/Vc System

In the process of synergistic degradation of MB by HC and the H2O2/Vc system, H2O2 was the main source of ·OH. The amount of H2O2 had a significant impact on the production of ·OH, which further affected the degradation efficiency of MB. In this experiment, the influence of H2O2 concentration on the degradation of MB was studied using reactor 1. The results are shown in Figure 5.

Figure 5.

Figure 5

Open in a new tab

Effect of H2O2 concentration on degradation of MB by the HC + H2O2/Vc system (conditions: Pin = 0.3 MPa, CMB,o = 20 μmol/L, t = 10 min, V = 150 mL, CVc = 0.021 mol/L).

With the increase in H2O2 concentration from 0.01 to 0.05 mol/L (corresponding to a molar ratio of H2O2/MB ranging from 500 to 2500), the degradation rate of MB gradually increased, reached a plateau, and then slightly decreased. The Cv did not change with the variation of the H2O2 concentration, and its value was 0.210. A constant Cv indicated that the amount of ·OH generated by HC remained unchanged, and the change in the ·OH yield was mainly contributed by the reaction between H2O2 and Vc. The increase in H2O2 concentration led to an increase in the ·OH yield, thereby accelerating the degradation rate of MB. However, when there is an excess of H2O2, the excess H2O2 can react with ·OH, leading to a slight decrease in the ·OH yield.38 Consequently, the degradation rate of MB also slightly decreased. Excess H2O2 not only hindered the degradation of MB but also posed a risk of damage to the reaction equipment.39 Therefore, it was necessary to control the amount of H2O2 added at the appropriate level. It was considered that the appropriate H2O2 concentration was 0.03 mol/L, with a molar ratio of H2O2/MB at 1500.

3.2. Effect of Vc Concentration on Degradation of MB by the HC + H2O2/Vc System

Vc exhibited strong reducibility and can form a strong redox system with H2O2. Vc can accelerate the decomposition of H2O2 to produce ·OH. The amount of Vc added had a significant impact on the production of ·OH in the system, which affected the degradation of MB.

Figure 6 shows the influence of Vc concentration on the degradation of MB. When the Vc concentration increased from 0 to 0.014 mol/L, the degradation rate of MB increased significantly from 53.0 to 76.6%. However, the degradation rate of MB only increased by about 4% with the increase of the Vc concentration from 0.014 to 0.035 mol/L. The larger the amount of Vc added in the system, the more ·OH generated by the reaction between H2O2 and Vc, which can significantly improve the degradation rate of MB. The change in Vc concentration did not cause a change in cavitation intensity. A constant Cv indicated that the change in the ·OH yield was mainly contributed by the reaction between H2O2 and Vc. The ·OH was mainly derived from the decomposition of H2O2. In this experiment, the amount of H2O2 was constant, so the amount of Vc required in the redox reaction should also be constant. Excess Vc cannot generate more ·OH in the system. Thus, it was taken into consideration of a cost saving, the appropriate Vc concentration was 0.021 mol/L.

Figure 6.

Figure 6

Open in a new tab

Effect of Vc concentration on degradation of MB by the HC + H2O2/Vc system (conditions: Pin = 0.3 MPa, CMB,o = 20 μmol/L, t = 10 min, V = 150 mL, CH2O2 = 0.03 mol/L).

3.3. Synergistic Effect of HC and H2O2/Vc System

In Sections 3.1 and 3.2, the concentrations of H 2O 2 and Vc were determined to be 0.03 and 0.021 mol/L, respectively. In this study, in order to obtain the synergistic mechanism of HC and H 2O 2/Vc system on the degradation of MB, the influence of various factors (inlet pressure, initial solution concentration, solution volume, and time) on the degradation rate of MB was investigated under different conditions, namely HC alone, H 2O 2/Vc system alone, and combined process of HC + H 2O 2/Vc system.

3.3.1. Effect of Inlet Pressure on Degradation of MB

The change in the inlet pressure can cause a change in the fluid velocity. According to eq 4, changes in fluid velocity can lead to changes in Cv. Thus, the inlet pressure was an important factor affecting the cavitation intensity. In this study, the influence of the inlet pressure or pump speeds on the degradation of MB was studied. The results are shown in Figure 7.

Figure 7.

Figure 7

Open in a new tab

Effect of the inlet pressure on the degradation of MB. (a) Degradation rate of MB; (b) ·OH yield (conditions: t = 10 min, CMB,o = 20 μmol/L, V = 150 mL).

The degradation rate of MB increased with the increase of inlet pressure under the conditions of individual HC and the HC combined with the H2O2/Vc system. As the inlet pressure increased from 0.1 to 0.5 MPa, the Cv value decreased from 0.829 to 0.109, indicating an enhanced cavitation effect.40 Therefore, more ·OH could be generated. In addition, the fluid velocity increased with an increase in inlet pressure. The increase in fluid velocity can result in an increase in the number of passes of fluids (N = Qt/V)41 through the hydraulic cavitator within the same cavitation time. Thus, more opportunities to generate ·OH can be obtained. Wang et al.26 pointed out that pressure not only affected cavitation behavior but also affected the number of passes of fluids. Higher inlet pressure contributed to the degradation of the organic matter.

Figure 7 shows that in the individual H2O2/Vc system, the degradation rate of MB increased with the increase of pump speed, but the trend of increase was very slow, only rising from 53.3 to 55.5%. An increase in the pump speed can increase the collision velocity and the number of collisions of the two fluids. The mixing of H2O2 and Vc was enhanced, leading to the generation of more ·OH. However, the effect of improving the impact velocity of fluids to enhance the degradation rate of MB was not very significant.

When the inlet pressure was 0.3 MPa, the degradation rates of MB under the conditions of HC, H2O2/Vc system, and HC + H2O2/Vc system were 7.9, 54.9, and 74.2%, respectively. The decolorization effect of MB is shown in Figure 8. The degradation rate of MB by the H2O2/Vc system was significantly higher than that by HC alone, indicating that the ·OH generated by the decomposition of H2O2 mainly contributed to the degradation of MB. On the basis of the H2O2/Vc system, the utilization of HC can significantly improve the degradation rate of MB, which is mainly due to the combined effects of free radical effect and mechanical effect generated during the process of HC. In the process of HC, the strong shock wave and high-speed microjet flow generated by the collapse of cavitation bubbles can greatly enhance the mixing of H2O2 and Vc. The reaction process between Vc and H2O2 was strengthened, leading to the production of more ·OH. Therefore, the degradation rate of MB could be improved. It can be seen that the method of the HC-assisted H2O2/Vc system was a promising method for the degradation of MB. In consideration of energy saving and safety, an inlet pressure of 0.3 MPa was selected for the following research.

Figure 8.

Figure 8

Open in a new tab

Image of MB decolorization effect (Photograph courtesy of Yan Cao).

3.3.2. Effect of Initial Solution Concentration on Degradation of MB

The initial concentration of organic matter in the solution was an important factor affecting its degradation rate. It can be seen from Figure 9 that with the increase of the initial concentration of MB, the degradation rate of MB decreased while the yield of ·OH increased. Since the HC conditions and the amounts of H2O2 and Vc added were constant, the yield of ·OH in the system would be constant. However, the total amount of MB increased with the increase of the initial concentration of MB, so more ·OH will be captured by MB.14,42 The maximum amount of ·OH was generated under the conditions of the HC + H2O2/Vc system compared with that of HC alone and the H2O2/Vc system alone. As the concentration of organic matter in the solution increased, the probability of ·OH being captured was higher. Therefore, under the condition of the HC + H2O2/Vc system, the increased amount of ·OH was the largest, which was 11.913 μmol/L. However, due to the fact that the increase in the number of ·OH captured was less than the increase in the number of MB, the degradation rate of MB decreased. This result was similar to that obtained by Wang et al.43 using swirling jet-induced cavitation combined with H2O2 to degrade rhodamine B in aqueous solution.

Figure 9.

Figure 9

Open in a new tab

Effect of initial solution concentration on degradation of MB and ·OH yield. (a) Degradation rate of MB; (b) ·OH yield (conditions: Pin = 0.3 MPa, t = 10 min, V = 150 mL).

3.3.3. Effect of Solution Volume on Degradation of MB

In our previous research, it was found that the solution volume had a significant impact on the generation of ·OH.44 Therefore, the influence of solution volume on the degradation of MB was studied in this study. The results are shown in Figure 10.

Figure 10.

Figure 10

Open in a new tab

Effect of the solution volume on the degradation of MB. (a) Degradation rate of MB; (b) ·OH yield (conditions: Pin = 0.3 MPa, t = 10 min, CMB,o = 20 μmol/L).

Under the conditions of HC, H2O2/Vc system, and HC + H2O2/Vc system, the degradation rate of MB decreased with the increase of solution volume, and HC in combination with the H2O2/Vc system maintained the best degradation effect. Although a change in solution volume did not cause a change in cavitation intensity, it can lead to a change in the number of passes of fluids. The larger the solution volume, the smaller the number of passes of fluids, and the less ·OH can be generated. Moreover, the total amount of organic matter in the solution increased with increasing the solution volume. Therefore, the degradation rate of MB would inevitably decreased. Similarly, the number of cyclic impacts decreased with a decrease in solution volume. The reaction between Vc and H2O2 was weakened, and the yield of ·OH decreased.

3.3.4. Effect of Time on Degradation of MB and Synergistic Factor

The effect of time on the degradation of MB was investigated in this study under the conditions of the HC, H2O2/Vc system, and HC + H2O2/Vc system. Furthermore, the kinetic constants under these three conditions were determined by measuring the concentration of MB at different times. The kinetic rate constant (k)45 can be calculated as follows:

3.3.4. 5

Where t is the degradation time, and c is a constant.

Figure 11a illustrates that the degradation rate of MB increased with the increase of time under the conditions of HC, H2O2/Vc system, and HC + H2O2/Vc system. Although the increase in time did not cause a change in cavitation intensity, a longer time meant that the more times the fluid underwent cavitation and impact, and the more ·OH was generated.46 Consequently, the degradation rate of MB increased. It can be seen from Figure 11b that ln(CMB,0/CMB) versus time showed reasonable linearity, which indicated that the degradation of MB conformed to first-order kinetics. The kinetic rate constants under the conditions of HC, H2O2/Vc system, and HC + H2O2/Vc system were 0.005, 0.0646, and 0.1124 min–1, respectively. This result indicated that MB had the fastest degradation rate under HC in combination with the H2O2/Vc system.

Figure 11.

Figure 11

Open in a new tab

Effect of time on degradation of MB and first-order kinetic ftting of MB degradation. (a) Degradation rate of MB; (b) degradation kinetics curve (conditions: Pin = 0.3 MPa, CMB,o = 20 μmol/L, V = 150 mL).

In order to explore the synergistic effect between HC and H2O2/Vc system, the synergy index SI was introduced, and it can be calculated according to the following equation47:

3.3.4. 6

Where kHC, kH2O2/Vc, and kHC+H2O2/Vc were the kinetic rate constants under the conditions of HC alone, H2O2/Vc system alone, and HC in combination with H2O2/Vc system, respectively. Usually, an SI value greater than 1 indicates the presence of synergistic effects in the studied system or process.

In this study, the value of SI calculated was 1.615, which was greater than 1, indicating a synergistic effect between HC and the H2O2/Vc system. This also confirmed that the combination of the HC and H2O2/Vc system was an effective method for improving the degradation of MB.

3.3.5. Correlation Equation of ·OH

·OH was a significant free radical for the degradation of MB. The yield of ·OH was closely related to the effect of MB degradation. Therefore, research on the yield of ·OH was of great significance. According to the discussion in Section 3.3.4, it was known that there was a synergistic effect between the HC and H2O2/Vc system. This synergistic relationship can be reflected by a certain correlation between the concentrations of ·OH under different conditions.

In order to further investigate the synergistic effect between HC and the H2O2/Vc system, the yield of ·OH under different conditions was investigated, as shown in Figure 12.

Figure 12.

Figure 12

Open in a new tab

Yield of ·OH under different conditions (experimental points: 1–5 for inlet pressure, 0.1–0.5 MPa; 6–10 for solution volume, 120–240 mL; 11–15 for time, 2.5–12.5 min; 16–20 for initial solution concentration, 4–20 μmol/L).

It can be seen from Figure 12 that the order of ·OH yield was C·OH (HC + H2O2/Vc system) > C·OH (H2O2/Vc system) > C·OH (HC), and the ·OH yield of HC + H2O2/Vc system was greater than the sum of the ·OH yield of HC alone and ·OH yield of H2O2/Vc system alone. This further confirmed the synergistic effect between HC and the H2O2/Vc system. During the process of HC, an extreme environment of high temperature and pressure was formed, along with a strong shock wave and high-speed microjet flow. The ability of H2O2 decomposition to produce ·OH can be enhanced in the high-temperature and high-pressure environments.11 In addition, the reaction between H2O2 and Vc was enhanced under the conditions of a strong shock wave and high-speed microjet flow. It was the synergistic effect between HC and the oxidant system that led to the generation of more ·OH.

Zhang et al.35 proposed a correlation equation between collapse pressure (Pc) and the concentration of ·OH based on data fitting and pointed out that Pc was an exponential function of the concentration of ·OH. A correlation equation used to describe the effect of independent variables on the residence time of the liquid in the rotor-stator cavity was established by Wang et al.48 This correlation equation was obtained by the Levenberg–Marquardt algorithm. Similarly, three models of ·OH yield were proposed based on the ·OH yield data obtained in this study, as shown in Table 1. The parameters and correlation coefficient R2 of these three models were obtained by the optimization method of Levenberg–Marquardt and Universal Global Optimization in the software 1stOpt 1.5. Table 1 shows that the R2 value of the regression equation obtained in model 3 was the maximum, with a value of 0.9549, which indicated that the correlation between the concentrations of ·OH was the best in this model.

Table 1. Models of ·OH Yielda.
model correlation equation parameters R2 relative deviation
model 1 C = a(C1 + C2) a = 1.171 0.9282 ±15%
model 2 C = aC1 + bC2 a = 0.569, b = 1.272 0.9413 ±12%
model 3
graphic file with name ao4c05815_m012.jpg
 k = 5.146, a = 670.869 0.9549 ±10%
b = 3.422, c = 0.045
d = 5.904, h = −9.960
Open in a new tab
a

C, C1, and C2 denoted the yield of ·OH generated in the HC + H2O2/Vc system, HC alone, and H2O2/Vc system alone, respectively.

The experimental values of ·OH yield were compared with the theoretical values of ·OH yield calculated by these three models, and the results are shown in Figure13. It can be seen that almost all data points in model 3 were within ±10% deviation lines. The relative deviations of model 1, model 2, and model 3 were ±15, ± 12, and ±10%, respectively. The model 3 had the smallest relative deviation, which indicated that it was more reasonable to use this model to reflect the intrinsic correlation of ·OH yield under the conditions of the HC, H2O2/Vc system, and HC + H2O2/Vc system in the range of the present study. Therefore, the correlation equation for ·OH yield established in this study was as follows:

3.3.5. 7
Figure 13.

Figure 13

Open in a new tab

Comparison of experimental and calculated values for ·OH yield.

The model 3 represented a complex exponential and logarithmic relationship among C, C1, and C2, rather than the simple multiple and additive relationships shown in model 1 or model 2. It was indicated that there were complex interactions between HC and the H2O2/Vc system. In model 3, the coefficient of C2 at 0.045 was much smaller than the coefficient of C1 at 670.869. However, the value of C2 was much larger than that of C1, and the exponent of C2 was greater than that of C1. Consequently, the calculation result of 0.045C25.904 was greater than that of 670.869C13.422. It was indicated that compared with HC, the H2O2/Vc system contributed more to the production of ·OH in the synergistic process. This was consistent with the experimental results. Therefore, the construction of model 3 was reasonable.

3.4. Degradation Pathways of MB

LC-MS technology was used to identify the intermediate products of MB degradation under the condition of HC combined with the H2O2/Vc system. Multiple peaks of different intensities are observed in Figure 14a, indicating the destruction of the MB molecule and the production of intermediate products with diverse compositions and concentrations. These intermediates were usually formed through processes such as hydroxylation and demethylation.49 Due to their similar structures, they exhibited similar polarity, resulting in the elution of multiple intermediates within a narrow time range (2.0–2.5 min). From Figure 14b, it can be seen that some fragment peaks appeared at m/z = 366, 350, 333, 301, 285, 270, 262, 242, 218, 197, 169, 132, 104, and 91. By studying the mass of the eluted intermediates and their cracking law, it can be concluded that 14 main intermediate products were generated. On the m/z values detected with LC-MS, the molecular structure of the main intermediates can be confirmed. Therefore, three possible degradation pathways of MB were proposed, as shown in Figure15.

Figure 14.

Figure 14

Open in a new tab

LC-MS of intermediate products of MB degradation. (a) LC chromatogram. (b) MS spectrum.

Figure 15.

Figure 15

Open in a new tab

Degradation path of MB by HC combined with the H2O2/Vc system.

In path 1, some MB molecules were isomerized to form the intermediate product M1. The methyl group connected to N was easily attacked by ·OH, and the strong shock wave in the process of HC contributed to the detachment of the methyl group.50 Under the action of ·OH and a strong shock wave, product M2 was formed. Under the same action, some M2 continued to demethylate (two CH2−) to form product M3, while others were isomerized and demethylated (one CH2−) to form product M4. The main chromophore of MB was −CH3 on the N–CH3 bond. Therefore, the main reason for MB decolorization was demethylation.51 Due to the weak binding force of the C–S bond in intermediate products, they were easily attacked and broken by ·OH, leading to ring opening.52 Furthermore, during the process of HC, the collapse of cavitation bubbles would generate an instantaneous high temperature and pressure. This extreme environment can lead to a series of reactions, such as bond breakage, hydroxylation, demethylation, etc., ultimately forming the product M6. Our findings were similar to those reported by Wang et al.53 Subsequently, ·OH further attacked the benzene ring, causing its structure to be destroyed and resulting in the formation of products M12, M13, and M14. Ultimately, these products were mineralized to form simple inorganic molecules, such as CO2, NO3–, H2O, and SO42–.

Due to the synergistic effect of the HC and H2O2/Vc system, a large number of ·OH were instantly generated, which fiercely attacked MB molecules. As a result, MB molecules were highly hydroxylated and produced various polyhydroxy compounds such as products M10 and M11 in Path 3. Wang et al.53 reported a similar finding that a polyhydroxy compound with m/z = 364 was obtained in the degradation of MB. Furthermore, under the continuous action of ·OH, the C–S bonds were destroyed, and the intermediate products would undergo nitration and demethylation, ultimately forming the product M6 or M9. These products were further destroyed by ·OH, and their rings were opened to form low molecular weight organic compounds, which were ultimately decomposed into simple inorganic molecules, as obtained in Path 1.

In order to further understand the mineralization degree of MB, a TOC analysis was carried out. The mineralization degree of MB can be reflected by the mineralization efficiency (η(TOC)), which was calculated according to the following equation52:

3.4. 8

where TOC0 and TOC1 were the organic carbon content of the initial and degraded MB solution, respectively. Based on the measured TOC data, the η(TOC) was 76.13% under the conditions of inlet pressure of 0.3 MPa, initial solution concentration of 20 μmol/L, solution volume of 150 mL, and reaction time of 10 min. Under the same conditions, the degradation rate of MB was 77.30%, which was close to the mineralization efficiency value. Therefore, it was proved that MB molecules were degraded and effectively mineralized.

3.5. Energy Efficiency

Energy efficiency (Ef) is the energy required to treat 1 L of wastewater, and it can be calculated as follows:

3.5. 9

Where ε is the cavitation yield, mg/J. Cavitation yield (ε) can reflect the change of the treatment effect per unit of energy consumed in the wastewater treatment process. It can be expressed as follows39:

3.5. 10

Where Pm is the power of the pump, t is the treatment time, and V is the solution volume.

In this study, the pumps were the main source of energy dissipation, with a total power of 300 W. Under the specific conditions: the treatment time was 10 min, the solution volume was 150 mL, and the initial solution concentration was 20 μmol/L; the cavitation yield and energy efficiency were calculated to be 4.11 × 10–6 mg/J and 0.43 kWh/L, respectively. Furthermore, the cost estimation for wastewater treatment using the HC combined with the H2O2/Vc system was completed. The electricity price per kilowatt-hour was 0.50 CNY in China. Therefore, the operating cost was 0.22 CNY/L (0.03 USD/L).

MB in wastewater can be effectively degraded by various methods. Our work has been compared with other methods in terms of degradation rate, energy efficiency, cost, etc., as shown in Table 2. It can be inferred that the combination of two methods exhibited a higher extraction rate and lower operating cost than a single method. The combination process of the HC + H2O2/Vc system exhibited the maximum k value of 0.1124 min–1, indicating that this method had a faster reaction rate compared to other methods. Additionally, this method exhibited a relatively low energy efficiency and operating cost. This indicated that the combined process of the HC and H2O2/Vc system conformed to the development direction of wastewater treatment.

Table 2. Comparison of the Different Treatment Methods for MB.

method conditions degradation rate (%) k × 103 (min–1) cavitation yield (mg/J) energy efficiency (kWh/L) operating cost (CNY/L) ref
NPV-HC (orifce plate) pressure: 5 bar; time: 150 min 28.13   4.15 × 10–6 0.66 0.37 (45,52)
HC (venturi) pressure: 5 bar; time: 120 min 32.32 3.41 3.08 × 10–6 1.1 0.61 (54)
HC + photocatalytic pressure: 5 bar; time: 120 min; catalyst: 200 mg/L 64.58 8.62       (54)
HC + H2O2 pressure: 3 bar; time: 60 min; [H2O2]:0.1 g/L 94.64 42.91 5.99 × 10–6     (54)
HC + H2O2/Vc pressure: 3 bar; time: 10 min; [H2O2]:0.9 g/L 87.8 112.40 4.11 × 10–6 0.43 0.22 our study
Open in a new tab

4. Conclusions

A new combined process of HC and the H2O2/Vc system was proposed for the degradation of MB in wastewater. This study focused on investigating the degradation characteristics of MB using this new combined process. The effects of various parameters, such as H2O2 concentration, Vc concentration, inlet pressure, initial solution concentration, solution volume, and reaction time, on the degradation rate of MB were investigated. The intrinsic correlation of ·OH yield under the conditions of the HC, H2O2/Vc system, and HC + H2O2/Vc system was explored. The degradation pathways of MB were discussed. The main conclusions were as follows:

  • 1.

    The increase in inlet pressure and time, the decrease in initial solution concentration and solution volume were beneficial for improving the degradation rate of MB. A maximum degradation rate of 87.8% was achieved under the following conditions: H2O2 concentration of 0.03 mol/L, Vc concentration of 0.021 mol/L, inlet pressure of 0.3 MPa, initial solution concentration of 4 μmol/L, solution volume of 150 mL, and reaction time of 10 min.

  • 2.

    The degradation effects of the combination process of the HC + H2O2/Vc system can be greatly improved compared to only HC or only H2O2/Vc system. The synergy index was 1.615, indicating a synergistic effect between HC and H2O2/Vc system.

  • 3.
    The order of ·OH yield was C·OH (HC + H2O2/Vc system) > C·OH (H2O2/Vc system) > C·OH (HC). A correlation equation for ·OH yield was established as follows:
    graphic file with name ao4c05815_m011.jpg

    The value of the correlation coefficient R2 was 0.9549. The relative deviations between the experimental and calculated values of the ·OH yield were basically within 10% of the yield by this model.

  • 4.

    Based on LC-MS, the molecular structure of 14 main intermediates was confirmed, and three possible degradation pathways of MB were proposed. It was demonstrated that the action of ·OH and strong shock wave acted together on MB molecules, which ultimately decomposed into simple inorganic molecules. A mineralization efficiency of 76.13%, indicating that MB molecules were degraded and effectively mineralized.

  • 5.

    The combined process of the HC and H2O2/Vc system exhibited a relatively low energy efficiency of 0.43 kWh/L and a relatively low operating cost of 0.03 USD/L. The method of HC-assisted H2O2/Vc system was a promising method for the degradation of MB.

Acknowledgments

The authors gratefully acknowledge the financial support of the Specific Research Project of Guangxi for Research Bases and Talents (No. Guike AD20238033).

The authors declare no competing financial interest.

References

  1. Zodia S.; Merzoukb B.; Potiera O.; Lapicquea F.; Leclerc J. P. Direct red 81 dye removal by a continuous flow electrocoagulation/flotation reactor. Sep. Purif. Technol. 2013, 108, 215–222. 10.1016/j.seppur.2013.01.052. [DOI] [Google Scholar]
  2. Hethnawi A.; Nassar N. N.; Manasrah A. D.; Vitale G. Polyethylenimine-functionalized pyroxene nanoparticles embedded on diatomite for adsorptive removal of dye from textile wastewater in a fixed-bed column. Chem. Eng. J. 2017, 320, 389–404. 10.1016/j.cej.2017.03.057. [DOI] [Google Scholar]
  3. Choi Y.; Koo M. S.; Bokare A. D.; Kim D. H.; Bahnemann D. W.; Choi W. Sequential process combination of photocatalytic oxidation and daik reduction for tlie removal of organic pollutants and Cr (VI) using Ag/TiO2. Environ. Sci. Technol. 2017, 51, 3973–3981. 10.1021/acs.est.6b06303. [DOI] [PubMed] [Google Scholar]
  4. Soltani R. D. C.; Mashayekhi M. Decomposition of ibuprofen in water via an electrochemical process with nano-sized carbon black-coated carbon cloth as oxygen-permeable cathode integrated with ultrasound. Chemosphere 2018, 194, 471–480. 10.1016/j.chemosphere.2017.12.033. [DOI] [PubMed] [Google Scholar]
  5. Du X. D.; Wang S.; Ye F.; Zhang Q. R. Derivatives of metal-organic frameworks for heterogeneous Fenton-like processes: from preparation to performance and mechanisms in wastewater purification - A mini review. Environ. Res. 2022, 206, 112414 10.1016/j.envres.2021.112414. [DOI] [PubMed] [Google Scholar]
  6. Li L.; Guo R. N.; Zhang S.; Yuan Y. M. Sustainable and effective degradation of aniline by sodium percarbonate activated with UV in aqueous solution: Kinetics, mechanism and identification of reactive species. Environ. Res. 2022, 207, 112176 10.1016/j.envres.2021.112176. [DOI] [PubMed] [Google Scholar]
  7. Mishra A.; Panigrahi A.; Mai P.; Penta S.; Padmaja G.; Bera G.; Das P.; Rambabu P.; Turpu G. R. Rapid photodegradation of methylene blue dye by rGO-V2O5 nano composite. J. Alloys Compd. 2020, 842, 155746 10.1016/j.jallcom.2020.155746. [DOI] [Google Scholar]
  8. Mohod A. V.; Teixeira A. C. S. C.; Bagal M. V.; Gogate P. R.; Giudici R. Degradation of organic pollutants from wastewater using hydrodynamic cavitation: A review. J. Environ. Chem. Eng. 2023, 11, 109773 10.1016/j.jece.2023.109773. [DOI] [Google Scholar]
  9. Bhayana T.; Saxena A.; Gupta S.; Dubey A. K. Enhanced decolourisation and degradation of azo dyes using wild versus mutagenic improved bacterial strain: a review. Vegetos 2023, 36, 28–37. 10.1007/s42535-022-00496-y. [DOI] [Google Scholar]
  10. Andia J. P. M.; Cayte A. E. T.; Rodriguez J. M. I.; Belón L. L.; Málaga M. A. C.; Teixeira L. A. C. Combined treatment based on synergism between hydrodynamic cavitation and H2O2 for degradation of cyanide in effluents. Miner. Eng. 2021, 171, 107119 10.1016/j.mineng.2021.107119. [DOI] [Google Scholar]
  11. Fedorov K.; Dinesh K.; Sun X.; Soltanic R. D. C.; Wangd Z. H.; Sonawane S.; Boczkaja G. Synergistic effects of hybrid advanced oxidation processes (AOPs) based on hydrodynamic cavitation phenomenon-A review. Chem. Eng. J. 2022, 432, 134191 10.1016/j.cej.2021.134191. [DOI] [Google Scholar]
  12. Ledakowicz S.; Paździor K. Recent achievements in dyes removal focused on advanced oxidation processes integrated with biological methods. Molecules 2021, 26, 870. 10.3390/molecules26040870. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Panda D.; Saharan V. K.; Manickam S. Controlled hydrodynamic cavitation: A review of recent advances and perspectives for greener processing. Processes. 2020, 8, 220. 10.3390/pr8020220. [DOI] [Google Scholar]
  14. Tao Y. Q.; Cai J.; Huai X. L.; Liu B.; Guo Z. X. Application of hydrodynamic cavitation to wastewater treatment. Chem. Eng. Technol. 2016, 39, 1363–1376. 10.1002/ceat.201500362. [DOI] [Google Scholar]
  15. Baradaran S.; Sadeghi M. T. Intensification of diesel oxidative desulfurization via hydrodynamic cavitation. Ultrason. Sonochem. 2019, 58, 104698 10.1016/j.ultsonch.2019.104698. [DOI] [PubMed] [Google Scholar]
  16. Carpenter J.; George S.; Saharan V. K. Low pressure hydrodynamic cavitating device for producing highly stable oil in water emulsion: Effect of geometry and cavitation number. Chem. Eng. Process. - Process Intensif. 2017, 116, 97–104. 10.1016/j.cep.2017.02.013. [DOI] [Google Scholar]
  17. Burzio E.; Bersani F.; Caridi G. C. A.; Vesipa R.; Ridolfi L.; Manes C. Water disinfection by orifice-induced hydrodynamic cavitation. Ultrason. Sonochem. 2020, 60, 104740 10.1016/j.ultsonch.2019.104740. [DOI] [PubMed] [Google Scholar]
  18. Prajapat A. L.; Gogate P. R. Intensifed depolymerization of aqueous polyacrylamide solution using combined processes based on hydrodynamic cavitation, ozone, ultraviolet light and hydrogen peroxide. Ultrason. Sonochem. 2016, 31, 371–382. 10.1016/j.ultsonch.2016.01.021. [DOI] [PubMed] [Google Scholar]
  19. Mancuso G.; Langone M.; Andreottola G. A critical review of the current technologies in wastewater treatment plants by using hydrodynamic cavitation process: principles and applications. J. Environ. Health Sci. 2020, 18, 311–333. 10.1007/s40201-020-00444-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Rajoriya S.; Bargole S.; Saharan V. K. Degradation of a cationic dye (Rhodamine 6G) using hydrodynamic cavitation coupled with other oxidative agents: Reaction mechanism and pathway. Ultrason. Sonochem. 2017, 34, 183–194. 10.1016/j.ultsonch.2016.05.028. [DOI] [PubMed] [Google Scholar]
  21. Dhankea P.; Waghb S.; Kanse N. Degradation of fish processing industry wastewater in hydro-cavitation reactor. Mater. Today: Proc. 2018, 5, 3699–3703. 10.1016/j.matpr.2017.11.621. [DOI] [Google Scholar]
  22. Boczkaj G.; Gągol M.; Klein M.; Przyjazny A. Effective method of treatment of effluents from production of bitumens under basic pH conditions using hydrodynamic cavitation aided by external oxidants. Ultrason. Sonochem. 2018, 40, 969–979. 10.1016/j.ultsonch.2017.08.032. [DOI] [PubMed] [Google Scholar]
  23. Randhavane Shrikant B.; Khambete A. K. Hydrodynamic cavitation: a novel treatment approach. Mater. Today. Proc. 2017, 4, 9680–9684. 10.1016/j.matpr.2017.06.246. [DOI] [Google Scholar]
  24. Rajoriya S.; Bargole S.; George S.; Saharan V. K. Treatment of textile dyeing industry effluent using hydrodynamic cavitation in combination with advanced oxidation reagents. J. Hazard. Mater. 2018, 344, 1109–1115. 10.1016/j.jhazmat.2017.12.005. [DOI] [PubMed] [Google Scholar]
  25. Askarniya Z.; Sadeghi M. T.; Baradaran S. Decolorization of Congo red via hydrodynamic cavitation in combination with Fenton’s reagent. Chem. Eng. Process. - Process Intensif. 2020, 150, 107874 10.1016/j.cep.2020.107874. [DOI] [Google Scholar]
  26. Wang B. W.; Su H. J.; Zhang B. Hydrodynamic cavitation as a promising route for wastewater treatment-A review. Chem. Eng. J. 2021, 412, 128685 10.1016/j.cej.2021.128685. [DOI] [Google Scholar]
  27. Yan S. L.; Pan C.; Yang X. Q.; Chen S. J.; Qi B.; Huang H. Degradation of Codium cylindricum polysaccharides by H2O2-Vc-ultrasonic and H2O2-Fe2+-ultrasonic treatment: Structural characterization and antioxidant activity. Int. J. Biol. Macromol. 2021, 182, 129–135. 10.1016/j.ijbiomac.2021.03.193. [DOI] [PubMed] [Google Scholar]
  28. Zou M. Y.; Nie S. P.; Yin J. Y.; Xie M. Y. Ascorbic acid induced degradation of polysaccharide from natural products: a review. Int. J. Biol. Macromol. 2020, 151, 483–491. 10.1016/j.ijbiomac.2020.02.193. [DOI] [PubMed] [Google Scholar]
  29. Li X.; Zhang G. Z.; Li J.; Jiang T. M.; Chen H. Y.; Li P. J. Degradation by Vc-H2O2, characterization and antioxidant activity of polysaccharides from Passiflora edulis peel. J. Food Process Pres. 2021, 45, el6074 10.1111/jfpp.16074. [DOI] [Google Scholar]
  30. Li G. Q.; Chen K. H.; Zhang W. J. Treatment of methyl orange by homogeneous catalysis oxidation using hydrogen peroxide and ascorbic acid. J. Putian U. 2007, 14, 79–82. [Google Scholar]; URL https://www.nstl.gov.cn/paper_detail.html?id=f90e255eaa385a8e0d56a9140ac8564e (In Chinese)
  31. Sumpter B. G.; Thompson D. L. Studies of the intramolecular dynamics of model polyatomic molecules. J. Chem. Phys. 1987, 86, 2805–2817. 10.1063/1.452082. [DOI] [Google Scholar]
  32. Yulizar E. Y.; Apriandanu D. O. B.; Marcony Surya R. Fabrication of novel SnWO4/ZnO using Muntingia calabura L. leaf extract with enhanced photocatalytic methylene blue degradation under visible light irradiation. Ceram. Int. 2022, 48, 3564–3577. 10.1016/j.ceramint.2021.10.135. [DOI] [Google Scholar]
  33. Yao X. M.; Fang Y. B.; Guo Y. X.; Xu M. H. Degradation of methylene blue using a novel gas-liquid hybrid DDBD reactor: Performance and pathways. Chemosphere 2023, 336, 139172 10.1016/j.chemosphere.2023.139172. [DOI] [PubMed] [Google Scholar]
  34. Awais M.; Khursheed S.; Tehreem Rida; Sirajuddin; Mok Y. S.; Siddiqui G. U. pH regulated rapid photocatalytic degradation of methylene blue dye via niobium-nitrogen co-doped titanium dioxide nanostructures under sunlight. Appl. Catal. A-Gen. 2022, 643, 118764 10.1016/j.apcata.2022.118764. [DOI] [Google Scholar]
  35. Zhang X. D.; Fu Y.; Li Z. Y.; Zhao Z. C. The collapse intensity of cavities and the concentration of free hydroxyl radical released in cavitation flow. Chin. J. Chem. Eng. 2008, 16, 547–551. 10.1016/S1004-9541(08)60119-6. [DOI] [Google Scholar]
  36. Tang S. F.; Zhao M. Z.; Yuan D. L.; Li X.; Wang Z. T.; Zhang X. Y.; Jiao T. F.; Ke J. Fe3O4 nanoparticles three-dimensional electro-peroxydisulfate for improving tetracycline degradation. Chemosphere 2021, 268, 129315 10.1016/j.chemosphere.2020.129315. [DOI] [PubMed] [Google Scholar]
  37. Li M. D.; Bussonnière A.; Bronson M.; Xu Z. H.; Liu Q. X. Study of venturi tube geometry on the hydrodynamic cavitation for the generation of microbubbles. Miner. Eng. 2019, 132, 268–274. 10.1016/j.mineng.2018.11.001. [DOI] [Google Scholar]
  38. Luo H. W.; Zeng Y. F.; He D. Q.; Pan X. L. Application of iron-based materials in heterogeneous advanced oxidation processes for wastewater treatment: a review. Chem. Eng. J. 2021, 407, 127191 10.1016/j.cej.2020.127191. [DOI] [Google Scholar]
  39. Qin T. T.; Nie S. L.; Ji H.; Xie Z. F. Synergistic degradation and degradation pathways of methylene blue by plasma process combined with cavitation impinging stream reactor based on hydrodynamic cavitation. J. Environ. Chem. Eng. 2023, 11, 110356 10.1016/j.jece.2023.110356. [DOI] [Google Scholar]
  40. Amin L. P.; Gogate P. R.; Burgess A. E.; Bremner D. H. Optimization of a hydrodynamic cavitation reactor using salicylic acid dosimetry. Chem. Eng. J. 2010, 156, 165–169. 10.1016/j.cej.2009.09.043. [DOI] [Google Scholar]
  41. Nikolić I.; Jovanović J.; Koturević B.; Adnadjević B. Transesterifcation of sunfower oil in the presence of the cosolvent assisted by hydrodynamic cavitation. BioEnergy Res. 2022, 15, 1568–1578. 10.1007/s12155-021-10387-w. [DOI] [Google Scholar]
  42. Zhai L.; Dong S. P.; Feng G. P.; Ma H. L.; Geng D. Influencing factors of hydroxyl production in orifice-typed cavitation reactor. Sci. Technol. Rev. 2010, 28, 46–50. [Google Scholar]; URL https://www.oalib.com/paper/4633283 (In Chinese)
  43. Wang X. K.; Wang J. G.; Guo P. Q.; Guo W. L.; Wang C. Degradation of rhodamine B in aqueous solution by using swirling jet-induced cavitation combined with H2O2. J. Hazard. Mater. 2009, 169, 486–491. 10.1016/j.jhazmat.2009.03.122. [DOI] [PubMed] [Google Scholar]
  44. Cao Y.; Xie D. D.; Huang Y. C.; Huang C. D.; Zhang K. M.; Zhang X. Y.; Wang S. J. Investigation of hydroxyl radical yield in an impact-jet hydraulic cavitator. Processes 2022, 10, 2194. 10.3390/pr10112194. [DOI] [Google Scholar]
  45. Ji H.; Lan Y.; Nie S.; Qin T. T.; Nie S. L.; Zhou J. K. Synergistic effect of hydrodynamic cavitation characteristics of self-excited oscillation cavity for degradation of dye wastewater. J. Clean. Prod. 2022, 380, 135116 10.1016/j.jclepro.2022.135116. [DOI] [Google Scholar]
  46. Randhavane S. B.; Khambete A. K. Harnessing hydroxyl radicals generated by hydrodynamic cavitation reactor in simultaneous removal of chlorpyrifos pesticide and COD from aqueous solution. Desalin. Water Treat. 2017, 82, 346–354. 10.5004/dwt.2017.20965. [DOI] [Google Scholar]
  47. Saxena S.; Saharan V. K.; George S. Enhanced synergistic degradation efficiency using hybrid hydrodynamic cavitation for treatment of tannery waste effluent. J. Clean. Prod. 2018, 198, 1406–1421. 10.1016/j.jclepro.2018.07.135. [DOI] [Google Scholar]
  48. Wang Y. B.; Li J.; Jin Y.; Luo J. H.; Chen M.; Yan C. Mixing efficiency of a rotor-stator spinning disc extractor. Chem. Eng. J. 2019, 362, 357–363. 10.1016/j.cej.2018.12.179. [DOI] [Google Scholar]
  49. Rauf M. A.; Meetani M. A.; Khaleel A.; Ahmed A. Photocatalytic degradation of Methylene Blue using a mixed catalyst and product analysis by LC/MS. Chem. Eng. J. 2010, 157, 373–378. 10.1016/j.cej.2009.11.017. [DOI] [Google Scholar]
  50. Wang H.; Wang H.; Yan Q. Peroxymonosulfate activation by algal carbocatalyst for organic dye oxidation: insights into experimental and theoretical. Sci. Total Environ. 2022, 816, 151611 10.1016/j.scitotenv.2021.151611. [DOI] [PubMed] [Google Scholar]
  51. Moholkar V. S.; Pandit A. B. Modeling of hydrodynamic cavitation reactors: a unified approach. Chem. Eng. Sci. 2001, 56, 6295–6302. 10.1016/S0009-2509(01)00253-6. [DOI] [Google Scholar]
  52. Sun H. S.; Qin J.; Yi L. D.; Ruan Y. H.; Sun Y. A.; Wang J.; Fang D. W. Study on negative pressure assisted hydrodynamic cavitation (NPA-HC) degradation of methylene blue in dye wastewater. Chem. Eng. Res. Des. 2022, 181, 1–13. 10.1016/j.cherd.2022.03.003. [DOI] [Google Scholar]
  53. Wang B. W.; Wang T. T.; Su H. J. A dye-methylene blue (MB)-degraded by hydrodynamic cavitation (HC) and combined with other oxidants. J. Environ. Chem. Eng. 2022, 10, 107877 10.1016/j.jece.2022.107877. [DOI] [Google Scholar]
  54. Kumar M. S.; Sonawane S. H.; Pandit A. B. Degradation of methylene blue dye in aqueous solution using hydrodynamic cavitation based hybrid advanced oxidation processes. Chem. Eng. Process. - Process Intensif. 2017, 122, 288–295. 10.1016/j.cep.2017.09.009. [DOI] [Google Scholar]

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES