Decolorization of azo dyes Orange G using hydrodynamic cavitation coupled with heterogeneous Fenton process

Article abstract of DOI:10.1016/j.ultsonch.2015.08.001

The present work demonstrates the application of the combination of hydrodynamic cavitation (HC) and the heterogeneous Fenton process (HF, Fe⁰/H₂O₂) for the decolorization of azo dye Orange G (OG). The effects of main affecting operation conditions such as the inlet fluid pressure, initial concentration of OG, H₂O₂ and zero valent iron (ZVI), the fixed position of ZVI, and medium pH on decolorization efficiency were discussed with guidelines for selection of optimum parameters. The results revealed that the acidic conditions are preferred for OG decolorizaiton. The decolorization rate increased with increasing H₂O₂ and ZVI concentration and decreased with increasing OG initial concentration. Besides, the decolorization rate was strongly dependent on the fixed position of ZVI. The analysis results of degradation products using liquid chromatography-ESI-TOF mass spectrometry revealed that the degradation mechanism of OG proceeds mainly via reductive cleavage of the azo linkage due to the attack of hydroxyl radical. The present work has conclusively established that the combination of HC and HF can be more energy efficient and gives higher decolorization rate of OG as compared with HC and HF alone.

Full text of DOI:10.1016/j.ultsonch.2015.08.001

Accepted Manuscript
Decolorization of azo dyes Orange G using hydrodynamic cavitation coupled
with heterogeneous Fenton process
Meiqiang Cai, Jie Su, Yizu Zhu, Xiaoqing Wei, Micong Jin, Haojie Zhang,
Chunying Dong, Zongsu Wei
PII:
S1350-4177(15)00241-2
DOI:
http://dx.doi.org/10.1016/j.ultsonch.2015.08.001
ULTSON 2961
Reference:
To appear in:
Ultrasonics Sonochemistry
Received Date:
Revised Date:
Accepted Date:
14 April 2015
30 July 2015
1 August 2015
Please cite this article as: M. Cai, J. Su, Y. Zhu, X. Wei, M. Jin, H. Zhang, C. Dong, Z. Wei, Decolorization of azo
dyes Orange G using hydrodynamic cavitation coupled with heterogeneous Fenton process, Ultrasonics
Sonochemistry (2015), doi: http://dx.doi.org/10.1016/j.ultsonch.2015.08.001
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers
we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and
review of the resulting proof before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

1
Decolorization of azo dyes Orange G using hydrodynamic cavitation
coupled with heterogeneous Fenton process
2
3
a
Meiqiang Cai , Jie Su , Yizu Zhu , Xiaoqing Wei , Micong Jin * , Haojie Zhang ,
a
a
a
b,c
a
a
Chunying Dong *, Zongsu Wei
d
4
5
6
7
8
9
0
(a School of Environmental Science and Engineering, Zhejiang Gongshang University, Hangzhou 310035; b
Zhejiang Provincial Key Laboratory of Health Risk Appraisal for Trace Toxic Chemicals, Ningbo Municipal
Center for Disease Control and Prevention, Ningbo 315010, China; c Ningbo Key Laboratory of Poison
Research and Control, Ningbo Municipal Center for Disease Control and Prevention, Ningbo 315010, China;
d Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, OH,
United States, 43210)
1
1
1
___________________________________________________________________________
1
1
1
1
1
1
1
1
2
2
2
2
2
2
3
4
5
6
7
8
9
0
1
2
3
4
Abstract: The present work demonstrates the application of the combination of hydrodynamic
0
cavitation (HC) and the heterogeneous Fenton process (HF, Fe /H
2
O
2
) for the decolorization of
azo dye Orange G (OG). The effects of main affecting operation conditions such as the inlet fluid
pressure, initial concentration of OG, H O and zero valent iron (ZVI), the fixed position of ZVI,
2
2
and medium pH on decolorization efficiency were discussed with guidelines for selection of
optimum parameters. The results revealed that the acidic conditions are preferred for OG
decolorizaiton. The decolorization rate increased with increasing H O and ZVI concentration
2
2
and decreased with increasing OG initial concentration. Besides, the decolorization rate was
strongly dependent on the fixed position of ZVI. The analysis results of degradation products
using liquid chromatography-ESI-TOF mass spectrometry revealed that the degradation
mechanism of OG proceeds mainly via reductive cleavage of the azo linkage due to the attack of
hydroxyl radical. The present work has conclusively established that the combination of HC and
HF can be more energy efficient and gives higher decolorization rate of OG as compared with
*
Corresponding author: Tel.: +86 571 28008226; Fax: +86 571 28008215.
E-mail address: dcy0915@126.com
Corresponding author: Tel.: +086-574-87274559; Fax: +086-574-87361764.
E-mail address: jmcjc@163.com
*
1

2
2
5
6
HC and HF alone.
Key words: Hydrodynamic cavitation; Zero-valent iron; Fenton process; Orange G;
2
2
7
8
Decolorization.
1. Introduction
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
Azo dyes, generally characterized by the presence of one or more azo bonds (–N=N–) in
3
association with aromatic systems and auxochromes (–OH, –SO , etc.), are important synthetic
colorants that represent the largest class of dyes in common use especially applied in textile
processing. Textile effluents have been shown to be toxic, mutagenic, carcinogenic and
non-biodegradable, making it a public health concern. Several conventional techniques including
physical, chemical, and biological processes have been developed to remove the azo dyes in the
aquatic environment, such as adsorption [1-3], coagulation [4], photo-catalysis [5,6], ozonation
[7], and biosorption [8-10]. Nevertheless, these adopted methods have proven to be costly,
time-consuming and impractical.
As these dyes are typically recalcitrant to conventional wastewater treatment, many studies
are now focused on advanced oxidation processes (AOPs). Cavitation-based AOPs have been
widely developed as a promising and efficient method for the removal of azo dyes, which are
classified as acoustic cavitation (AC), hydrodynamic cavitation (HC), optic cavitation and steam
bubble cavitation [11-13]. The AC is widely studied by sonochemical research group including
Hoffmann, Weavers, Pandit, Grieser and Asakura. The temperature (on the order of 5000 K) and
pressure (on the order of 5000 K) in collapsing microbubbles can reach extreme levels [14,15],
leading to the thermal dissociation of water vapor into reactive hydroxyl free radicals and
hydrogen atoms [15-17]. These highly reactive species are vital to the subsequent oxidization
and reduction reactions. Despite such promising information, use of acoustic cavitation reactors
in commercial scale does not appear to being progressing robustly, and only one study in
pilot-scale conducted by Hoffmann in 2001 was reported [18]. The major hindrance of using this
technique rests with efficient operation of ultrasound transducers at a commercial scale operation
due to substantially lower energy efficiencies and higher investment costs [12, 19].
Hydrodynamic cavitation, which is induced by subjecting the liquid to velocity variations
2

5
5
5
5
5
5
5
6
6
6
6
6
6
6
6
6
6
7
7
7
7
7
7
7
7
7
7
8
8
8
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
by introducing constrictions in the flow, can be a serious contender as an alternative to AC.
Several reports appear in literature confirming that HC is better energy efficient, lower
investment costs, and higher scale-up possibilities than AC [19-21]. However, time-consuming
has proven to be a major hindrance of alone HC process. Consequently, individual HC process is
not yet considered commercially feasible due to this limitation. Moreover, the previous results
suggested that the combination of various AOPs was deemed as essential step in their further
development. Therefore, numerous research programs aimed at the combination of HC with
AOPs in order to intensify degradation rate or achieve complete mineralization, such as catalytic
oxidation, Fenton process and Fenton like processes [22,23]. Especially, the effect of
applicability of combination of HC and Fenton chemistry has been also widely studied. The
overall aim of these combined processes is to mineralize the initial organic pollutants completely
or at least lower chain compounds, obtain higher degradation rate, and convert the initial
compounds into less harmful final products than the individual techniques [23,24].
2+
Conventionally, Fenton chemistry is based on the use of Fe ions conjunction with hydrogen
peroxide (H ) to generate highly reactive hydroxyl radicals (·OH) which then oxidize the
organic pollutants to CO , H O and relatively smaller molecules [25-27]. In heterogeneous
Fenton process (HFP), it is hypothesized that initially iron metal is corroded to Fe in the
presence of H under acidic conditions, which then further reacts with H in a Fenton-like
2
O
2
2
2
2+
2
O
2
2 2
O
3+
0
3+
2+
process to generate ·OH and Fe . The Fe then reduces the Fe back to Fe and the cycle
continues [28].
The combination of HC and HFP is considered to obtain an improved degradation
efficiency attributed to the higher quantum free radicals production [29]. Researches confirmed
that the combination of HC and HFP is very energy efficient and cost effective as compared to
individual technique to treat the wastewater, such as the efficacy of combination of HC and
Fenton chemistry for the removal of p-nitrophenol studied by Pradhan et al. [30], and HC
coupled with the HFP for the treatment of real industrial wastewater reported by Bremner et al.
[31]. As was pointed out by Bagal et al. in recent literature [22], the role of sequential addition of
Fenton’s reagent on degradation efficiency of pollutant in combined process of HC and AFP
must be optimized and the heterogeneous Fenton like processes must be developed on the pilot
scale for reduction or elimination of the sludge formation [32].
3

8
8
8
8
8
8
8
9
9
9
9
9
9
9
3
4
5
6
7
8
9
0
1
2
3
4
5
6
The Orange G (OG), which is a typical symbol of azo dye and extensively used in dyeing the
textile fabrics, has been the subject of investigations. The chemical structure of OG is shown in
Fig. 1. Mostly, the degradation of OG using traditional techniques including adsorption [33,34],
2
sonolysis [35], biotransformation [36], UV/TiO [37,38], and Fenton processes [39] has been
reported. Currently, it should be noted that in spite of extensive research, very limited
information exists regarding the evaluation on OG decolorization through the combination of HC
with HFP. Cavitation is a dynamic phenomenon and its effects strongly depend on the
operational parameters. In this study, experiments on OG decolorization were conducted by
0
coupling of HC and HFP (Fe /H
2
O
2
). The objective of this study was to investigate the effects of
main affecting operation conditions such as the inlet fluid pressure, initial concentration of OG,
and ZVI, the fixed position of ZVI, and medium pH on decolorization efficiency. To our
2 2
H O
knowledge, this is the first comprehensive investigation of operation parameters on the
decolorization of OG and degradation mechanism in HC- HFP system, thus paving the way for
pilot-scale application.
9
9
9
7
8
9
2. Experimental
2.1. Chemicals and solvents
Hydrogen peroxide (30%, w/v) and ZVI powder were purchased from Kelong chem.
(ShangHai, China). HPLC grade acetonitrile and acetic acid were obtained from Merck Co.
(Darmstadt, Germany). Orange G and other reagents with analytic reagent grade were
purchased from Huipu chemical&apparatus Co. (Hangzhou, China). Solutions were prepared
using Millipore water supplied by a Milli-Q water purification system (Molsheim, France).
1
1
1
1
00
01
02
03
1
1
1
1
1
1
1
1
04
05
06
07
08
09
10
11
2.2. Apparatus setup
Schematic representation of experimental setup of hydrodynamic cavitation system and the
dimensions of the applied orifice plate are shown in Fig. 2. The system consists of a feed vessel
tank with 1.25 L capacity, a vortex pump ( 25WB-65, Shanghai Hongya Machine Pump Making
3
Co., LTD, 3 kW, 2900 rmp, 0.3 m /h ), and valves. The discharge pipe of pump is connected to
the suction side on the bottom of the tank and bifurcated into main and bypass lines. The main
line and the bypass line discharge the material back into the tank. The main line has the facility
to incorporate an orifice plate located over the pressure gauge to generate cavitation of different
4

1
1
1
1
1
1
1
1
1
12
13
14
15
16
17
18
19
20
intensities. The bypass line has a throttling valve for adjusting pressure and flow rate into the
main line. The water passes through the orifice plate, causing the central pressure at the cavity
falls below the vapor pressure of the water and generating a number of cavities. The pressure
gauges are provided and recorded both in inlet line and downstream of the orifice plate. During
the experiment, control valve (in bypass line) was left open until the pump reaches its maximum
speed, and thus the desired pressure and flow rate were obtained in the mainline.
2.3. Experimental methodology
A dimensionless parameter called cavitation number, is generally used in hydrodynamic
cavitation and is defined as
pd − pv pd
≈
pu − pd pu
1
21
σ =
(1)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
where p
d
, p
u
, and p are the downstream, upstream, and vapor pressures, respectively, and the
v
approximation holds when p ≥p ≥p as they do under this experimental conditions.
u
d
v,
All experiments were performed with reaction time of 120 min, and samples were
withdrawn from the reaction vessel every 20 min. The concentration of OG was analyzed by
measuring the absorbance of dye solution at 478 nm using a UV-spectrophotometer (TU-1901).
2+
The concentration of dissolved Fe concentration was determined using the standard
phenanthroline colorimetric method [40]. The extent of mineralization was measured on a total
organic carbon analyzer (TOC-V CPN5000 A, Shimadzu). All experiments were carried out in
triplicate to check the reproducibility and the average value for each run was calculated as the
presented data.
The temperature of the reaction mixture was maintained at 25 ℃ by circulating cooling
water through the surrounding water jacket. The optimal pH value at 3 was selected and adjusted
2 2
by sulphuric acid and sodium hydroxide considering the cavitation intensity. The H O
concentration ranging from 0.005 to 0.02 g/L was analyzed based on the rate of mineralization
and decolorization process. Four different ZVI concentrations were tested: 0.125, 0.25, 0.5 and
0.7 g/L. Besides, the effect of ZVI fixed positions was evaluated with consideration toward the
tank or the orifice plate on OG decolorization rate.
1
39
2.4. HPLC-MS Analysis
5

1
1
1
1
1
1
1
1
1
1
1
40
41
42
43
44
45
46
47
48
49
50
In our previously work, a liquid chromatography–diode array detection-mass spectrometry
system was used for identification of sonolytic degradation products of azo dye Orange G [41].
In this work, the chemical structures of the OG degradation products were elucidated using a
Triple TOF 5600+ (AB SCIEX, Framingham, MA, USA) fitted with an Agilent 1100 series LC
equipped with an UV Diode array detection (DAD). A Shim-pack XR-ODSⅡcolumn
(150mm×4.0mm, 5µm) using mobile phase acetonitrile -acetic acid 65:35 (v/v) was run at a flow
rate of 0.25 ml/min. The DAD was monitored at 210, 268, 280 and 478 nm wavelength. MS
detection was performed on the Triple TOF 5600+ mass spectrometer in both positive and
negative ESI ion modes with a full scan mass spectrum in the m/z range from 50 to500. Direct
injections of aqueous solutions were performed to elucidate the degradation products. For more
detail about analysis condition could be found in our previously work [41].
1
1
51
52
3. Results and discussion
3.1. Decolorization of OG under different treatments
1
1
1
1
1
1
1
1
1
53
54
55
56
57
58
59
60
61
The decolorization of OG with treatments of HC alone, HC coupled with hydrogen
2 2
peroxide (HC-H O ), and HC coupled with HFP (HC-HFP) was investigated and shown in Fig. 3.
All experiments were performed at temperature 25 ℃, fluid flow 0.55 L/s, and pH 3.0. Data
shown in Fig. 3 indicated that the decolorization rate was enhanced by the combination,
comparing the values 25.6%, 99.5% and 99.8% obtained at 120 min for HC alone, HC- H
HC-AFP, respectively. The significant intensifications were also obtained when HC was
combined with H [24,42,43]. This phenomenon was attributed to the more amounts available
2 2
O and
2
O
2
for hydroxyl radical generation due to the added H
2
O
2
. The reaction mechanisms occurring in
HC-H O system can be outlined below:
2
2
1
1
62
63
H
2
O
2
+ ))) → 2 ·OH
(1)
(2)
H
2
O
2
2 2
+ ·OH → H O + HO ·
1
1
1
1
64
65
66
67
The addition of the Fenton catalyst such as ZVI into HC-H
enhancement [24, 44]. In our study, although similar observations obtained for both HC- HFP
and HC-H treatments, the HC- HFP system was considered as a better choice for the
2 2
O system leads to usually significant
2
O
2
decolorization of OG in view of practice application. First, it produces hydroxyl radicals as
6

1
1
1
1
1
1
1
68
69
70
71
72
73
74
hydrogen can get scavenged by reacting with the excess hydrogen peroxide, indicated by the
slower decolorization rate at the end of the reaction shown in Fig. 3. Second, HFP utilizes ZVI
pieces as the catalyst, which considerably reduces the overall cost of the treatment compared
with hydrogen peroxide dosage and price. Third, hydrogen peroxide in aqueous bulk escaped
from the inside and interface of caviation bubble can also be utilized, enhancing the
decolorization rate. Therefore, the HC- HFP system was considered as an alternative to HC-H
for the decolorization of OG in this study.
2 2
O
1
75
3.2. Effect of flow rate
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
Inlet pressure is an important operating parameter of HC system. In order to investigate the
influence of inlet pressure on the decolorization rate of OG, experiments were conducted by
varying flow rate from 0.16 to 0.55 L/s. The OG concentration was kept constant at 40 mg/L and
the pH value was fixed at 3.0. Fig. 4 showed the effect of flow rate on decolorization rate with
respect to time. The experimental results indicated that the rate of decolorization increased with
an increase in flow rate ranging from 0.16 to 0.46 L/s, but beyond which no significant increase
in the rate of decolorization. The same trend was represented for the function of inlet pressure.
The optimum inlet pressure of 4.9 bar was observed with the consideration of the flow rate,
which was similar to the results reported in the literature by other researchers [11], and also in
accordance with the optimum value of pressure as 4-6 bar [45]. It is worth mentioning that H
concentration was only 0.02 g/L which was dramatically reduced compared with the dosage (0.5
g/L) used in experiments from section 3.1, indicating the optimal H dosage demand and cost
2 2
O
2
O
2
saving potential in HC-HFP. The velocity, cycle number and cavitation number concerning
different inlet pressure were shown in Table 1. There is no significant difference in cavitation
number with operating pressure, suggesting it may explain the difference on decolorization
efficiency.
1
1
1
1
1
92
93
94
95
96
3.3. Effect of operating pH
The effect of different initial pH of the solution on the decolorization rate of OG was carried
out for different pH values ranging from 2 to 7. Fig. 5 showed the effect of different initial pH
value on decolorization rate with respect to time. As shown in Fig. 5, an increase in pH of OG
solution caused a decrease in decolorization rate. In addition, the maximum decolorization rate at
7

1
1
1
2
2
2
2
2
2
2
2
2
2
2
2
2
2
97
98
99
00
01
02
03
04
05
06
07
08
09
10
11
12
13
pH value 2.0, 3.0 and 5.0 in 120 min was 98.8%, 93.2% and 86.1%, respectively. The
decolorization rate of OG at neutral pH, only 12.3% in 120 min, was disadvantageous compared
with that at pH for 2.0, 3.0 and 5.0, indicating that the acidic condition is preferred for the
decolorization of OG in HC- HFP. The pKa value of OG is 11.5 and 1.0 for the deprotonation of
3
the naphthalene OH and the two SO H group from the literature [35], respectively. The
estimated log Kow and solubility of OG in water is -4.56 and 80 mg/ml, respectively. This
indicates that the driving mechanism on decolorization of hydrophilic OG occurs mainly in the
bulk solution. Iron powder used in HFP can be easily dissolved in acid solution producing
ferrous ions. The produced ferrous ions further react with hydrogen peroxide to generate •OH. A
similar observation was also reported for the degradation of various pollutant including
Rhodamine B [7] and acid Red 88 [46], Dichlorvos [47], Methyl Parathion [48], in which HC
combined with Fenton process was favored at low pH. For instance, the extent of removal of
p-nitrophenol was demonstrated similar trends, as evidenced by the fluctuation of removal rate,
5.7% at pH 8.0 and 63.2% under acidic conditions [24]. The difference in the extent of
decolorization at pH 2.0 and 3.0 was attributed to the optimal pH condition was observed
between 3.0 to 4.0 in Fenton’s process for decolorization[49], depending on ZVI and H
concentrations.
2 2
O
2
14
3.4. Effect of initial OG concentration
2
2
2
2
2
2
2
2
2
2
2
15
16
17
18
19
20
21
22
23
24
25
The effect of initial OG concentration on decolorization rate was depicted in Fig. 6 at
temperature 25 ℃, flow rate 0.55 L/s, and pH 3.0. The figure presented the means of
decolorization rate for all of the initial OG concentration tested over the entire experimental
period. It was not difficult to find that the decolorization rate by the 10 mg/L initial OG
concentration treatment was somewhat on par with the 20 mg/L treatment during the same period.
This observation in decolorization rate was consistent with the pattern for ultrasonic irradiation
combined with zero-valent aluminum (ZVAl) process at 5 and 10 mg/L initial concentration of
azo dye Acid Orange 7 within 30 min [50]. But for initial concentration of OG between 10 to 100
mg/L, the fluctuation in decolorization rate became progressively conspicuous, jumping from
90.4 to 47.3% within 20 min. The observed lower decolorization rate at initial concentration of
OG higher than 10 mg/L in this study could be attributed to the insufficient production of •OH to
8

2
2
2
2
2
2
2
2
2
2
26
27
28
29
30
31
32
33
34
35
destruct the hydrophilic OG completely, indicating that the appropriate proportion of total
amount of molecules and the total amount of ·OH radicals is an important parameter. The
driving mechanisms for the decolorization of OG was the oxidization of ·OH radicals coming
2 2
from the decomposition of H O from original introduction and recombination both in gas phase
toward gaseous bubble and in solution. In HC alone, H
2
2
O from sonochemical recombination is
unavailable for pollutant destruction, while the pollutants are inherently reactive with hydrogen
peroxide and produce •OH in HC-AFP. The decolorization rate was significantly raised in the
2 2
beginning of the experiment, indicating the conversion H O to •OH occurred within the first 20
min. It should be noted that the decolorization only indicated the concentration of parent azo dye
OG or azo bonds more strictly.
2
36
3.5. Effect of concentration of ZVI
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
The effect of ZVI concentration on decolorization rate was investigated at temperature
25 ℃, fluid flow 0.55 L/s, and pH 3.0. Experiments were carried out for different ZVI
concentration ranging from 0.125 to 0.7 g/L. As presented in Fig. 7, it was clearly shown that
0
increasing the initial Fe concentration could increase the decolorization rate during the operation,
0
with decolorization rate being 65.2 and 74.6% at 20 min for the Fe treatments of 0.125 and 0.7
2 2
g/L, respectively, as reached to the maximum. The ratio of OG:H O :Fe in our study was
1:3.33:0.025, 1: 3.33:0.05, 1: 3.338:0.10, and 1: 3.33:0.14 , which was in range of from 1:1:1 to
1:4:4 for triazophos :H O :FeSO in convention Fenton [35], and was about 1:7.82:1.955 for
2
2
4
imidacloprid:H
heterogeneous Fenton may indicate that the ZVI plays a reduction role in the decolorization
process for lower ratio of H :Fe [52]. It may be explained by the enhanced surface area of ZVI,
leading to favorable generation of ·OH radical through direct electron transfer from ZVI surface
to H in acid conditions. Moreover, it is interesting to note that the decolorization rates were,
2 2
O : Fe [51]. This difference of iron amount used between convention Fenton and
2
O
2
2
O
2
in general, similar for all treatments at ZVI concentrations greater than 0.5 g/L, indicating that
the optimum iron content in the solution was achieved due to continuous leaching and also with
2
+
operating pressure and initial concentration of OG. The Fe concentration determined was
about 1.12 mg/L after 1 h treatment. About 0.2 g solid waste were obtained for 0.7 g/L of ZVI
concentration by the immersion of magnetic-iron into the feed vessel tank at the end of
9

2
2
55
56
experiment.
3.6. Effect of hydrogen peroxide concentration
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
The concentration of hydrogen peroxide plays a crucial role in determining the overall
efficacy of decolorization process. The formation of ·OH in the combination of HC and HFP can
2+
be classified into two pathways. One pathway is that the ZVI dissolution generates Fe ions in
2+
solution under acidic conditions. Another pathway is that the sonochemical combination of Fe
2 2
produced and H additive yields hydroxyl radicals. The experiments on the effect of H O
2
O
2
concentration on the decolorization rate of OG were conducted by varying concentrations from
0.005 to 0.02 g/L under initial pH 3, flow rate 0.55 L/s and temperature 25 ℃. The Fig. 8
documented the performance of different treatments in decolorization rate. It was clearly shown
2 2
that increasing the H O concentration could increase the decolorization rate during the operation
and maximum decolorization rate was determined at 0.02 g/L in the first 20 min of the
experiment. The trend was consistent with other study [29]. Hydrogen peroxide is dissociated
2 2
into ·OH radicals under sonication as shown in Eqn (1). H O can be effectively used in the
formation of hydroxyl radicals in HC- HFP, and also acts a scavenger for the generated ·OH
radicals, as expressed in Eqn (2). In addition, the residual H O contributes to COD and also is
2
2
harmful to microorganisms of conventional biological oxidation. A similar observation was also
reported, in which a sharp drop in degradation rate was observed for all AOPs with H
additive as external resources of ·OH radical after maximum degradation rate appeared, with the
2
O
2
2 2.
effect becoming more pronounce as the excessive amounts of H O
2
2
2
2
2
2
2
2
2
75
76
77
78
79
80
81
82
83
3.7. Effect of the fixed position of zero valent iron
The effect of the fixed position of ZVI on decolorization rate was investigated at
temperature 25 ℃, fluid flow 0.55 L/s, and pH 3.0. Experiments were carried out in a sequential
manner as described above toward two different fixed positions, in the tank and 35 cm away
from the orifice plate. For the treatment of 35 cm away from the orifice plate, the decolorization
rate increased sharply at the beginning (within 20 min), and then raised slightly before being
caught up with other treatment. As shown in Fig. 9, the maximum decolorization rate for both
treatments was obtained as 99.8% after 60 min operation. A result reported by Bremner showed
that a slight difference in TOC removal rate at two different catalyst bed location, 23 and 50 cm
1
0

2
2
2
2
2
2
2
2
2
2
2
2
84
85
86
87
88
89
90
91
92
93
94
95
from the orifice, implying that active cavitation zone is expected to be maintained over a
distance of 50 cm away from the point of orifice [53]. The performance toward to the fixed
0
position is due to the continuous cleaning of the Fe surface by the impingement of the liquid jet
stream with high force at the iron metal surface and also by the collapsing microbubbles on the
0
0
Fe surface generated by the HC. In addition, the liquid velocity was higher when Fe located
away from the orifice plate as compared to that observed in the tank under the same operating
0
pressure. Besides, the Fe located away from the orifice plate has easier access to cavitation
bubbles, which generate more free radicals upon rapid collapse of cavitation bubbles, being
conductive to the decolorization of OG. The results of TOC content was also shown in Fig. 9.
The TOC content decreased significantly in the first 20 min and then slower rate of reduction
was observed, indicating the primary products and intermediates were not easily to be
2 2
mineralized into CO and H O, which was validated by the following HPLC-MS analysis.
2
96
3.8 Degradation mechanism of Orange G in the HC-HFP
2
2
2
3
3
3
3
3
3
3
3
3
3
3
3
3
97
98
99
00
01
02
03
04
05
06
07
08
09
10
11
12
The best separation with a Shim-pack XR-ODSⅡcolumn obtained using 0.2% acetic
acid/acetonitrile (35/65, v/v) as mobile phase was run at a flow rate of 0.25 ml/min. The run time
of analysis was 20 min. A representative chromatogram of the OG and its degradation products
at 268 nm was shown in Fig. 10, 13 main peaks including OG were found in the chromatogram,
the retention times were 3.25, 3.75, 4.87, 5.90, 6.75, 7.40, 7.75, 8.20, 12.87, 13.25, 14.12, 14.75
and17.37 min, respectively. Here, we identified the compounds of the 13 main peaks by
comparison the observed mass and calculated mass, eight of them were found in our previous
study using LC–ESI–MS. A summary of the identification of degradation products is presented
in Table 2.
On the basis of the HPLC-DAD-ESI- TOF results, plausible mechanisms of degradation for
OG by the HC-HFP were proposed in Fig. 10. The degradation of the dye appears to involve
primarily oxidative steps, the cleavage of the C-N bond resulting in aniline (peak 11) which were
not detected without preconctration in our previously work [41] and 1-hydroxylamine-2-
naphthol-6,8- disulfonic acid (peak 12), indicating different generation rate of hydroxyl radical
between the sonolysis and HC-HFP. The hydroxy products of 7-hydroxy-8-(hydroxyamino)
naphthalene-1,3-disulfonic acid as the cosequence of •OH hydroxyl radical attack including peak
11

3
3
3
3
3
3
3
3
3
3
3
3
13
14
15
16
17
18
19
20
21
22
23
24
7, peak 9, peak 8, and peak 1 were also detected. The similar degradation products have also
been earlier reported for methyl orange [54] and AO7 [55]. The another probable degradation
pathway of the dye is the reactions of hydroxyl radicals with the N=N bond with generation of
benzene and 2- naphthol-6,8- disulfonic acid (peak 10) and its hydroxy products (peak 11) . This
reaction involves initial attack by the •H radical generated from ZVI, •OH radical and the •H
radical on the nitrogen atom. The third probable pathway is shown in Fig. 10. This reaction
involves intermolecular dehydration forms 7,8-epoxyazo-naphthalene- 1,3- disulfonic acid (peak
3), which was also reported by Muruganandham et al. [56] in the degradation process of
2
Reactive Orange 4 using TiO -P25. The detected 7 -hydroxy- 8- azophenyl-naphthalene-
1-sulfonic acid (peak 6) and 7-oxy-8-azo-naphthalene-(1’- oxy-2’- azo-phenyl)- 1-sulfonic acid
(peak 4) also idicated the reactions of desulfonation of sulfuric acid and the intermolecular
dehydration.
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
4. Conclusion
The present work reports the effectively use of HC coupled with HFP on the decolorization
of OG. The efficacy treatment scheme is affected by operating parameters including fluid
pressure, initial concentration of OG, H O additive dosage, ZVI concentration and fixed position,
2
2
and medium pH. The conclusions drawn from this study can be summarized as follows: (1) Use
of Fenton chemistry in combination with HC enhances the decolorization rate of OG
0
significantly. The fixed position of Fe is also important and it should be in the orifice plate
0
which can accelerate the decolorization rate efficiently. Increasing the concentration of Fe at a
fixed H
2
O
2
concentration for the treatment is conductive to the overall extent of decolorization,
0
and the optimal Fe concentration is 0.7 g/L. (2) The combination of HC and advanced Fenton
oxidation is favored under acidic condition and sensitive to the solution pH and the OG initial
concentration. Moreover, no significant influence of inlet fluid pressure on OG decolorization
2 2
was found from this study. (3) The addition of H O increases the extent of OG decolorization
due to excessive hydroxyl radicals available for the oxidation of OG. The optimization of H O2
2
dosage is 0.02 g/L with decolorization rate at 93.7%. In addition, on the basis of the detected 13
degradation products using HPLC-DAD-ESI-TOF, different pathways including the reductive
cleavage of azo linkage, intermolecular dehydration and desulfonation may lead to various
1
2

3
42
potentially more toxic and difficult-mineralized products than OG.
3
3
43
44
Acknowledgements
This work was supported by the National Natural Science Foundation of China (NO.
3
3
3
3
3
45
46
47
48
49
20906080, 20977083), the Analyzing and Testing Foundation of Zhejiang Province, China (NO.
2009F70014), the Youth Fund Zhejiang Gongshang University, the Zhejiang Xinmiao Talents
Program (NO. 2015R408031), the Science and Technology Innovation Team Project of Ningbo
City (2015C110019), and the Zhejiang Provincial Program for the Cultivation of High-level
Innovative Health Talents.
3
50
References
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
[1] V.K. Gupta, B. Gupta, A. Rastogi, S. Agarwal, A. Nayak, A comparative investigation on
adsorption performances of mesoporous activated carbon prepared from waste rubber tire
and activated carbon for a hazardous azo dye-Acid Blue, J. Hazard. Mater. 186 (2011)
891-901.
[2] S. Papic, N. Koprivanac, A. Loncaric Bozic, A. Metes, Removal of some reactive dyes from
synthetic wastewater by combined Al(III) coagulation/carbon adsorption process, Dyes
Pigm. 62 (2004) 291-298.
[3] C.L. Yang, J. McGarrahan, Electrochemical coagulation for textile effluent decolorization, J.
Hazard. Mater. 127 (2005) 40-47.
[4] E. Ellouze, D. Ellouze, A. Jrad, R. Ben Amar, Treatment of synthetic textile wastewater by
combined chemical coagulation/membrane processes, Desalination Water Treat. 33 (2011)
118-124.
[5] T.A. Saleh, V.K. Gupta, Photo-catalyzed degradation of hazardous dye methyl orange by use
of a composite catalyst consisting of multi-walled carbon nanotubes and titanium dioxide, J.
Colloid. Interface. Sci. 371 (2012) 101-106.
[6] A.R. Khataee, M.N. Pons, O. Zahraa, Photocatalytic degradation of three azo dyes using
2
immobilized TiO nanoparticles on glass plates activated by UV light irradiation: Influence
of dye molecular structure, J. Hazard. Mater. 168 (2009) 451-457.
[7] C.P. Bai, X.F. Xiong, W.Q. Gong, D.X. Feng, M. Xian, Z.X. Ge, N.A. Xu, Removal of
rhodamine B by ozone-based advanced oxidation process, Desalination 278 (2011) 84-90.
1
3

3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
4
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
00
[8] A.H. Chen, S.M. Chen, Biosorption of azo dyes from aqueous solution by
glutaraldehyde-crosslinked chitosans, J. Hazard. Mater. 172 (2009) 1111-1121.
[9] F. Elisangela, Z. Andrea, D.G. Fabio, R.D.M. Cristiano, D.L. Regina, C.P. Artur,
Biodegradation of textile azo dyes by a facultative Staphylococcus arlettae strain VN-11
using a sequential microaerophilic/aerobic process, Int. Biodeterior. Biodegrad. 63 (2009)
280-288.
[10] O. Türgay, G. Ersöz, S. Atalay, J. Forss, U. Welander, The treatment of azo dyes found in
textile industry wastewater by anaerobic biological method and chemical oxidation, Sep.
Purif. Technol. 79 (2011) 26-33.
[11] V.K. Saharan, A.B. Pandit, P.S.S. Kumar, S. Anandan, Hydrodynamic Cavitation as an
Advanced Oxidation Technique for the Degradation of Acid Red 88 Dye, Ind. Eng. Chem.
Res. 51 (2012) 1981-1989.
[12] K.P. Mishra, P.P. Gogate, Intensification of degradation of Rhodamine B using
hydrodynamic cavitation in the presence of additives, Sep. Purif. Technol. 75 (2010)
385-391.
[13] C.G. Joseph, G.L. Puma, A. Bono, D. Krishnaiah, Sonophotocatalysis in advanced
oxidation process: A short review, Ultrason. Sonochem. 16 (2009) 583-589.
[14] C. Balaji, V.S. Moholkar, A.B. Pandit, M. Ashokkumar, Mechanistic Investigations on
Sonophotocatalytic Degradation of Textile Dyes with Surface Active Solutes, Ind. Eng.
Chem. Res. 50 (2011) 11485-11494.
[15] S. Merouani, O. Hamdaoui, F. Saoudi, M. Chiha, Influence of experimental parameters on
2 2
sonochemistry dosimetries: KI oxidation, Fricke reaction and H O production, J. Hazard.
Mater. 178 (2010) 1007-1014.
[16] H. Ghodbane, O. Hamdaoui, Degradation of Acid Blue 25 in aqueous media using 1700
2 2
kHz ultrasonic irradiation: ultrasound/Fe(II) and ultrasound/H O combinations, Ultrason.
Sonochem. 16 (2009) 593-598.
[17] H. Zhang, J.H. Zhang, C.Y. Zhang, F. Liu, D.B. Zhang, Degradation of C.I. Acid Orange 7
by the advanced Fenton process in combination with ultrasonic irradiation, Ultrason.
Sonochem. 16 (2009) 325-330.
[18] H. Destaillats , T.M. Lesko, M. Knowlton, H. Wallace, M.R. Hoffmann, Scale-up of
1
4

4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
sonochemical reactors for water treatment, Ind. Eng. Chem. Res. 40 (2001) 3855–3860.
[19] P. Braeutigam, M. Franke, R.J. Schneider, A. Lehmann, A. Stolle, B. Ondruschka,
Degradation of carbamazepine in environmentally relevant concentrations in water by
Hydrodynamic-Acoustic-Cavitation (HAC), Water Res. 46 (2012) 2469-2477.
[20] M. Zupanc, T. Kosjek, M. Petkovšek, M. Dular, B. Kompare, B. Širok, Z. Blazeka, E. Heath,
Removal of pharmaceuticals from wastewater by biological processes, hydrodynamic
cavitation and UV treatment, Ultrason. Sonochem. 20 (2013) 1104-1112.
[21] L.P. Amin, P.R. Gogate, A.E. Burgess, D.H. Bremner, Optimization of a hydrodynamic
cavitation reactor using salicylic acid dosimetry, Chem. Eng. J. 156 (2010) 165-169.
[22] M.V. Bagal, P.R. Gogate, Degradation of 2,4-dinitrophenol using a combination of
hydrodynamic cavitation, chemical and advanced oxidation processes, Ultrason. Sonochem.
20 (2013) 1226-1235.
[23] A.G. Chakinala, P.R. Gogate, A.E. Burgess, D.H. Bremner, Industrial wastewater treatment
using hydrodynamic cavitation and heterogeneous advanced Fenton processing, Chem. Eng.
J. 152 (2009) 498-502.
[24] A.A. Pradhan, P.R. Gogate, Removal of p-nitrophenol using hydrodynamic cavitation and
fenton chemistry at pilot scale operation, Chem. Eng. J. 156 (2010) 77–82.
[25] J.H. Sun, S.H. Shi, Y.F. Lee, S.P. Sun, Fenton oxidative decolorization of the azo dye Direct
Blue 15 in aqueous solution, Chem. Eng. J. 155 (2009) 680-683.
[26] Y.S. Ma, C.F. Sung, J.G. Lin, Degradation of carbofuran in aqueous solution by ultrasound
and Fenton processes: Effect of system parameters and kinetic study, J. Hazard. Mater. 178
(2010) 320-325.
[27] L.B. Chu, J.L. Wang, J. Dong, H.Y. Liu, X.L. Sun, Treatment of coking wastewater by an
advanced Fenton oxidation process using iron powder and hydrogen peroxide, Chemosphere
86 (2012) 409-414.
[28] A.G. Chakinala, D.H. Bremner, A.E. Burgess, A modified advanced Fenton process for
industrial wastewater treatment, Water Sci. Technol. 55 (2007) 59-65.
[29] A.G. Chakinala, D.H. Bremner, P.R. Gogate, K. Namkung, A.E. Burgess, Multivariate
analysis of phenol mineralization by combined hydrodynamic cavitation and heterogeneous
advanced Fenton processing, Appl Catal B-Environ. 78(2008) 11-18.
1
5

4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[30] A.A. Pradhan, P.R. Gogate, Degradation of p-nitrophenol using acoustic cavitation and
Fenton chemistry, J. Hazard. Mater. 173 (2010) 517-522.
[31] D.H. Bremner, S.D. Carlo, A.G. Chakinala, G. Cravotto, Mineralization of
2,4-dichlorophenoxyacetic acid by acoustic or hydrodynamic cavitation in conjunction with
the advanced Fenton process, Ultrason. Sonochem. 15 (2008) 416-419.
[32] M.V. Bagal, P. R. Gogate, Wastewater treatment using hybrid treatment schemes based on
cavitation and Fenton chemistry: A review, Ultrason. Sonochem. 21 (2014) 1-14.
[33] M. Arulkumar, P. Sathishkumar, T. Palvannan, Optimization of Orange G dye adsorption by
activated carbon of Thespesia populnea pods using response surface methodology, J. Hazard.
Mater. 186 (2010) 827-834.
[34] I.D. Mall, V.C. Srivastava, N.K. Agarwal, Removal of Orange-G and Methyl Violet dyes by
adsorption onto bagasse fly ash dkinetic study and equilibrium isotherm analyses, Dyes
Pigments 69 (2006) 210-223.
[35] J. Madhavan, F. Grieser, M. Ashokkumar, Degradation of orange-G by advanced oxidation
processes, Ultrason. Sonochem. 17 (2009) 338-343.
[36] L. Pereira, A.V. Coelho, C.A. Viegas, M.M.C. dos Santos, M.P. Robalo, L.O. Martins,
Enzymatic biotransformation of the azo dye Sudan Orange G with bacterial CotA-laccase, J.
Biotechnol. 139 (2009) 68-77.
[37] H. Lachheb, E. Puzenat, A. Houas, M. Ksibi, E. Elaloui, C. Guillard, J.M. Herrmann,
Photocatalytic degradation of various types of dyes (Alizarin S, Crocein Orange G, Methyl
Red, Congo Red, Methylene Blue) in water by UV-irradiated titania, Appl. Catal. B:
Environ. 39 (2002) 75-90.
[38] J.H. Sun, L.P. Qiao, S.P. Sun, G.L. Wang, Photocatalytic degradation of Orange G on
nitrogen-doped TiO
2
catalysts under visible light and sunlight irradiation, J. Hazard. Mater.
155 (2008) 312-319.
[39] S.P. Sun, C.J. Li, J.H. Sun, S.H. Shi, M.H. Fan, Q. Zhou, Decolorization of an azo dye
Orange G in aqueous solution by Fenton oxidation process: Effect of system parameters and
kinetic study, J. Hazard. Mater. 161 (2009) 1052-1057.
[40] C.C. Jiang, S.Y. Pang, F. Ouyang, J. Ma, J. Jiang, A new insight into Fenton and Fenton-like
processes for water treatment, J. Hazard. Mater. 174 (2010) 813–817.
1
6

4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
[41] M.Q Cai, M.C. Jin, L.K. Weavers, Analysis of sonolytic degradation products of azo dye
spectrometry, Ultrason. Sonochem., 18 (2011) 1068-1076.
[42] M.M. Gore, V.K. Saharan, D.V. Pinjari, P.V. Chavan, A.B. Pandit, Degradation of reactive
orange 4 dye using hydrodynamic cavitation based hybrid techniques, Ultrason. Sonochem.
21 (2014) 1075–1082.
[43] S. Raut-Jadhav, V. K. Saharan, D. Pinjari, S. Sonawane, D. Saini, A. Pandit, Synergetic
2 2
effect of combination of AOP’s (hydrodynamic cavitation and H O ) on the degradation of
neonicotinoid class of insecticide, J. Hazard. Mater. 261 (2013) 139–147.
[44] P. Li, Y. Song, S. Wang, Z. Tao, S.L. Yu, Y.N. Liu, Enhanced decolorization of methyl
orange using zero-valent copper nanoparticles under assistance of hydrodynamic cavitation,
Ultrason. Sonochem. 22 (2015) 132–138.
[45] P.R. Gogate, P. N. Patil, Combined treatment technology based on synergism between
hydrodynamic cavitation and advanced oxidation processes, Ultrason. Sonochem. 25 (2015)
60–69.
[46] Y.L. Song, J.T. Li, H. Chen, Degradation of CI Acid Red 88 aqueous solution by
combination of Fenton’s reagent & ultrasound irradiation, J. Chem. Technol. Biotechnol. 84
(2009) 578-583.
[47] R.K. Joshi, P.R. Gogate, Degradation of dichlorvos using hydrodynamic cavitation based
treatment strategies, Ultrason. Sonochem. 19 (2012) 532–539.
[48] J.J. Pignatello, Y. F. Sun, Complete oxidation of metolachlor and methyl parathion in water
by the photoassisted fenton reaction, Water Res. 29 (1995) 1837-1844.
[49] B.G. Kwon, D.S. Lee, N. Kang, J. Yoon, Characteristics of p-chlorophenol oxidation by
Fenton’s reagent, Water Res. 33 (1999) 2110-2118.
[50] A.Q. Wang, W.L. Guo, F.F. Hao, X.X. Yue, Y.Q. Leng, Degradation of Acid Orange 7 in
aqueous solution by zero-valent aluminum under ultrasonic irradiation, Ultrason. Sonochem.
21 (2014) 572-575.
[51] M.T. Angaji, R. Ghiaee, Decontamination of unsymmetrical dimethylhydrazine waste water
by hydrodynamic cavitation-induced advanced Fenton process, Ultrason. Sonochem. 21
(2014) 1170–1177.
[52] I. Hua, M.R. Hoffmann, Optimization of ultrasonic irradiation as an advanced oxidation
1
7

4
4
4
4
4
4
4
4
4
5
5
5
5
91
92
93
94
95
96
97
98
99
00
01
02
03
technology, Environ. Sci. Technol. 31 (1997) 2237-2243.
[53] A.G. Chakinala, D.H. Bremner, P.R. Gogate, K.C. Namkung, A.E. Burgess, Ultivariate
analysis of phenol mineralisation by combined hydrodynamic cavitation and heterogeneous
advanced Fenton processing, Appl. Catal. B-Environ. 78 (2008) 11-18.
[54] C. Baiocchi, M.C. Brussino, E. Pramauro, A. B. Prevot, L. Palmisano, G. Marci,
Characterization of methyl orange and its photocatalytic degradationproducts by
HPLC/UV–VIS diode array and atmospheric pressure ionization quadrupole iontrap
massspectrometry Int. J. Mass Spectrom. 214(2002) 247-256.
[55] P. Bansal, D. Singh, D. Sud, Photocatalytic degradation of azo dye in aqueous TiO
2
suspension: Reaction pathway and identification of intermediates products by LC/MS, Sep.
Puri. Technol. 72(2010) 357-365.
[56] M. Muruganandham, M. Swaminathan, Photochemical oxidation of reactive azo dye with
UV–H O process, Dyes. Pigm.68 (2006) 133-142.
2
2
5
04
1
8

5
5
5
05
06
07
Table title
Table. 1 Hydrodynamic characteristics and cavitation number of the experimental setup
Table. 2 The information of OG and the identified OG degradation products
5
08
Caption to the figures
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
Fig. 1 Molecular structure of OG
Fig. 2 Schematic representation of experimental setup with expanded view of orifice
Fig. 3 Effect of three treatment methods on the decolorization rate of Orange G. Conditions:
volume of solution, 1.25 L; OG concentration, 20 mg/L; pH of solution, 3.0; fluid flow, 0.55 L/s;
H O concentration, 0.5 g/L; zero valent iron concentration, 0.5 g/L.
2
2
Fig. 4 Effect of flow rate on the decolorization rate of Orange G. Conditions: volume of solution,
1.25 L; OG concentration, 40 mg/L; pH of solution, 3.0; H
valent iron concentration, 0.5 g/L.
2 2
O concentration, 0.02 g/L; zero
Fig. 5 Effect of operating pH on the decolorization rate of Orange G. Conditions: volume of
solution, 1.25 L; OG concentration, 40 mg/L; inlet fluid pressure, 0.55 L/s; H
0.02 g/L; zero valent iron concentration, 0.5 g/L.
2 2
O concentration,
Fig. 6 Effect of initial concentration of Orange G on the decolorization rate. Conditions: volume
of solution, 1.25 L; pH of solution, 3.0; inlet fluid pressure, 0.55 L/s; H
2 2
O concentration, 0.01
g/L; zero valent iron concentration, 0.5 g/L.
Fig. 7 Effect of zero valent iron concentration on the decolorization rate of OG. Conditions:
volume of solution, 1.25 L; OG concentration, 40 mg/L; pH of solution, 3.0; inlet fluid pressure,
2 2
0.55 L/s; H O concentration, 0.01 g/L.
Fig. 8 Effect of H
2
2
O concentration on the degradation rate of OG. Conditions: volume of
solution, 1.25 L; OG concentration, 40 mg/L; pH of solution, 3.0; inlet fluid pressure, 0.55 L/s;
zero valent iron concentration, 0.5 g/L.
Fig. 9 Effect of the fixed position of zero valent iron on the decolorization rate and TOC of OG.
Conditions: volume of solution, 1.25 L; OG concentration, 20 mg/L; pH of solution, 3.0; inlet
2 2
fluid pressure, 0.55 L/s; H O concentration, 0.5 g/L; zero valent iron concentration, 0.5 g/L.
Fig. 10 Representative chromatograms of the OG degradation products at 268 nm.
Chromatographic condition: column: Shim-pack XR-ODSⅡ(75 mm×2.0 mm i.d., 2.2 µm),
1
9

5
5
5
5
5
34
35
36
37
38
mobile phase: 0.2% acetic acid/acetonitrile (35/65, v/v), flow rate: 0.25 ml/min, column
º
temperature: 40 C.
Fig. 11 Proposed degradation pathways of Orange G by the combination of hydrodynamic
cavitation (HC) with heterogeneous Fenton process (HFP).
2
0

5
39
Inlet pressure
bar)
Flow rate
(L/min)
0.16
Velocity
(m/s)
2.26
Cavitation
number
0.28
Cycle number
(/min)
0.16
(
3
4
4
5
.1
.1
.9
.4
0.25
3.54
0.37
0.25
0.46
6.51
0.39
0.46
0.55
7.78
0.39
0.55
5
5
40
41
Table1
5
42
2
1

5
43
Peak
number
Retention time
(min)
Observed
mass
Proposed molecular
formula
Calculated mass
1
2
3.25
3.75
368.9379
285.0642
C
10
H
8
S
2
O
11
368.9581
285.0758
C
16
12 5
H O
3
4
4.87
5.90
330.9568
327.0427
C H S O N
330.9689
327.0434
10
6
2
7
2
2
C
16
16
16
H
10SO
4
N
5
6
6.75
7.40
381.0108
329.0478
C
H
12
S
2
O
7
381.0097
329.0591
C
H
12SO
4
N
2
7
8
9
7.75
8.20
320.9811
352.9657
336.9669
304.9769
110.0969
335.9759
409.0149
C H S O
320.9733
352.9632
336.9683
304.9784
110.0964
335.9842
409.0158
10
8
2
8
C
10
10
10
H
8
O
10
S
2
12.87
13.25
14.12
14.75
17.37
C
H
H
8
8
O
9
7
S
2
1
0
1
C
O
S
2
1
7 11
C H N
1
1
2
3
C
10
H
9
NO
8
S
2
C
16
H
12
S
2
O
7
N
2
5
5
44
45
Table 2
5
46
2
2

Figure1
ONa
N
O S
O N
OH
O
S
NaO
O

Figure2

Figure3

Figure4

Figure5

Figure6

Figure7