- Email: [email protected]
Treatment of reverse-osmosis concentrate of printing and dyeing wastewater by electro-oxidation process with controlled oxidation-reduction potential (ORP)
Accepted Manuscript Treatment of reverse-osmosis concentrate of print and dyeing wastewater by electrooxidation process with controlled oxidation-reduction potential (ORP) Jiade Wang, Tian Zhang, Yu Mei, Bingjun Pan PII:
S0045-6535(18)30465-X
DOI:
10.1016/j.chemosphere.2018.03.051
Reference:
CHEM 20995
To appear in:
ECSN
Received Date: 22 January 2018 Revised Date:
6 March 2018
Accepted Date: 7 March 2018
Please cite this article as: Wang, J., Zhang, T., Mei, Y., Pan, B., Treatment of reverse-osmosis concentrate of print and dyeing wastewater by electro-oxidation process with controlled oxidationreduction potential (ORP), Chemosphere (2018), doi: 10.1016/j.chemosphere.2018.03.051. 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.
ACCEPTED MANUSCRIPT 1
Treatment of reverse-osmosis concentrate of print and dyeing wastewater by
2
electro-oxidation process with controlled oxidation-reduction potential (ORP)
3
RI PT
Jiade Wang1, Tian Zhang1, Yu Mei2, Bingjun Pan1*
4 1
College of Environment, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
6
2
College of Biological and Environmental Engineering, Zhejiang Shuren University, Hangzhou,
7
Zhejiang 310005, China
SC
5
9
M AN U
8
10
*
11
E-mail: [email protected]
12
Tel: +86-571-88320915; Fax: +86-571-88320882
Corresponding author
TE D
13
Highlights:
15
1. Removal efficiencies of COD, TN and chroma are positively correlated with Qsp.
16
2. The optimal current efficiency can be obtained at a certain current density.
17
3. A good correlation between ORP and the COD/Cl- removal efficiencies, Qsp is found.
18
4. The developed constant-ORP system substantially increases energy-efficiency.
AC C
19
EP
14
1
ACCEPTED MANUSCRIPT 20
ABSTRACT Reverse osmosis concentrate (ROC) of printing and dyeing wastewater remains as a
22
daunting environmental issue, which is characterized by high salinity, chemical oxygen
23
demand (COD), chroma and low biodegradability. In this study electro-oxidation process
24
(PbO2/Ti electrode) coupled with oxidation-reduction potential (ORP) online monitor was
25
applied to treat such a ROC effluent. The results show that with the increase of specific
26
electrical charge (Qsp), the removal efficiencies of COD, TN and chroma increased significantly
27
at the incipience and then reached a gentle stage; the optimal total current efficiency (12.04
28
kWh m-3) was obtained with the current density of 10 mA cm-2 (Qsp, 2.45 Ah L-1). Meanwhile,
29
some inorganic ions can be simultaneously removed to varying degrees. FTIR analyses
30
indicated that the macromolecular organics were decomposed into smaller molecules. A
31
multi-parameter linear relationship between ORP and Qsp, COD and Cl- concentration was
32
established, which can quantitatively reflect the effect of current density, chloride ion
33
concentration, pollutants and reaction time on the performance of the electro-oxidation
34
system. As compared to a traditional constant-current system, the constant-ORP system
35
developed in this study (through the back-propagation neural network [BPN] model with
36
ORP monitoring) approximately reduced the energy cost by 24-29%. The present work is
37
expected to provide a potential alternative in optimizing the electro-oxidation process.
38
Keywords: reverse osmosis concentrate (ROC); printing and dyeing wastewater;
39
electro-oxidation process; oxidation-reduction potential (ORP); constant-ORP system
AC C
EP
TE D
M AN U
SC
RI PT
21
40 41 2
ACCEPTED MANUSCRIPT 42
1. Introduction Reverse osmosis process has been widely applied in printing and dyeing wastewater
44
treatment as it can effectively barrier various organic/inorganic contaminants and also
45
biological constituents (Šostar-Turk et al., 2005). After being treated, a large proportion of
46
feed stream can be reused directly in printing and dyeing process (Bagastyo et al., 2013),
47
while the residual reverse osmosis concentrate (ROC) of printing and dyeing wastewater,
48
which is characterized by recalcitrant organics, high hardness and high salinity, cannot be
49
directly discharged and still remains serious environmental risks (Combernoux et al., 2015).
M AN U
SC
RI PT
43
Lots of conventional techniques have been proposed to further treat stubborn ROC
51
effluents (Pérez-González et al., 2012). However, the physical and chemical treatments such
52
as coagulation (Chen et al., 2017), membrane distillation (Qu et al., 2009) and adsorption
53
(Zhao et al., 2012) will eventually cause secondary pollution and most of them come with a
54
high waste disposal cost. The biochemical method is also not a good choice for terminal
55
treatment because of the very low biodegradability and high salinity in ROC effluent (Ersever
56
et al., 2014). Advanced oxidation processes such as ozonation (Benner et al., 2008),
57
heterogeneous photocatalysis (Lu et al., 2013) and Fenton (Zhou et al., 2012), are not
58
economically feasible and need extra reagents. Among the existing treatment options,
59
electro-oxidation has been widely applied in ROC treatment (Pérez et al., 2010, Radjenovic et
60
al., 2013). The high content of salts in ROC effluent ensures the good conductivity and can
61
reduce the cell voltage during electrolysis (Yao et al., 2016). Moreover, massive chloride, a
62
main component in ROC effluent can serve as active chlorine resource and thus enhance the
63
indirect oxidation in electro-oxidation process (Pérez et al., 2010). Weng and Pei (2016)
AC C
EP
TE D
50
3
ACCEPTED MANUSCRIPT found that the removal efficiency of COD can reach 59.35% by using Co doped PbO2 anode at
65
a current density of 80 mA cm-2. Zhou et al. (2011) investigated the COD degradation in
66
high-salinity ROC effluent and found that it could almost be completely removed by
67
electro-oxidation at 3.0 Ah L-1 with the electrode of IrO2-RuO2/Ti. Hege et al. (2002) reported
68
that 70% of COD and 75% of ammonia nitrogen in ROC of printing and dyeing wastewater
69
was removed by using boron-doped diamond (BDD) as working electrode at a specific
70
electrical charge of 1.5 Ah L-1.
SC
RI PT
64
However, the energy cost of electro-oxidation process is still a major factor that restricts
72
its wide application in wastewater advanced treatment. Various studies have accordingly
73
carried out and found that optimizing electrode materials and developing new reactors can
74
improve the current efficiency and thus reduce the energy consumption (Raghu et al., 2009;
75
Zhu et al., 2015; Cao et al., 2016). Zou et al. (2016) also found that increasing electrolyte
76
concentration in the wastewater can improve the current efficiency and save about 32% of
77
energy consumption. Fortunately, the ROC of printing and dyeing wastewater usually comes
78
along with high electrolyte concentration. Additionally, since the current efficiency depends
79
on the current density and is affected by the composition of wastewater, the optimal current
80
density often fluctuate during operation process. Also, the electro-generated active hydroxyl
81
radicals (serving as the functional oxidizing species) in electro-oxidation process are difficult
82
to be online monitored.
AC C
EP
TE D
M AN U
71
83
Since 1980s, oxidation-reduction potential (ORP) has been reported as an important
84
indicator in some wastewater advanced treatment such as Fenton dosage control (Wu and
85
Wang, 2012), simultaneous nitrification-denitrification in oxidation ditch process (Hou et al., 4
ACCEPTED MANUSCRIPT 2006), and the nanoscale zero-valent iron process for trichloroethylene degradation (Yu et al.,
87
2015). Some quantitative relationships have been established among ORP, operating
88
parameters and treatment efficiency to optimize the dosage of chemical agents, guide the
89
operation of wastewater plant, and save the operation cost and energy consumption. As
90
compared to current density, ORP is considered to be a more suitable indicator for the
91
optimal operation of the electro Fenton process (Kishimoto et al., 2015). In electro-oxidation
92
process, ORP is also the key factor to explore the redox effect of substances at the electrode
93
surfaces or in the solution. However, until now no literature reports the relationship between
94
ORP and treatment efficiencies in electro-oxidation processes.
M AN U
SC
RI PT
86
In this study, the removal efficiencies of COD, TN and chroma for ROC effluent of a real
96
printing and dyeing wastewater by electro-oxidation process was investigated with different
97
operation parameters. Fourier transform infrared spectroscopy (FTIR) was used to analyze
98
the degradation of large organic molecules by electro-oxidation. Meanwhile, the removal of
99
the inorganic ions in ROC effluent was also inspected during electro-oxidation. Finally, the
100
optimum response interval and the quantitative relationship among ORP, Qsp, COD and
101
chloride ion concentration were established to verify the possibility of reducing energy
102
consumption.
AC C
EP
TE D
95
5
ACCEPTED MANUSCRIPT 103
2. Materials and methods
104
2.1. Characteristics of ROC effluent of printing and dyeing wastewater The ROC effluent was collected from a printing and dyeing factory (Zhejiang, China),
106
which built a wastewater treatment plant with the capacity of 12000 T d-1. With being
107
treated by microfiltration (MF) and reverse osmosis (RO), 65% of the total wastewater was
108
reused as productive water, and 35% of the total wastewater (ROC) was discharged into the
109
public wastewater treatment plant for further purification. The main characteristics of the
110
ROC effluent are listed in Table 1. Briefly, the COD value is 272±10 mg L-1, and the total
111
dissolved solids (TDS) is 8490 mg L-1, which is beyond the suitable value of 5000 mg L-1 for
112
biodegradation, although some microorganism was reported to maintain metabolic activity
113
in higher TDS concentration (He et al., 2016). Additionally, Due to nitrification in aerobic
114
reactor, the ROC effluent also contains ≈40 mg L-1 total nitrogen (TN, most of them are
115
nitrate).
TE D
M AN U
SC
RI PT
105
The dissolved solids in ROC effluent were further analyzed by ion chromatography. As
117
shown in Table 1, the main anions in ROC effluent are Cl- (1471.8 mg L-1) and SO42- (4739.9
118
mg L-1), and the major cations are Na+ (4330.5 mg L-1) and K+ (40.6 mg L-1). High
119
concentration of TDS and chloride would inhibit the biological activity in bioprocess, but are
120
in favor of the electro-oxidation process. High salinity can provide excellent conductivity to
121
reduce energy consumption, and high chlorine content promotes indirect oxidation of the
122
organic matter by increasing active chlorine (Cl2, HOCl) and consequently improves the
123
current efficiency.
AC C
EP
116
124 6
ACCEPTED MANUSCRIPT 125
2.2. Electrode selection The working electrode is a key part in electro-oxidation process. Table SM-1 compares
127
the oxygen evolution potentials (OEP), the removal efficiency of pollutants and the electrode
128
life of several commercial electrodes. That is, BDD electrode has the highest OEP of 2.3 V, but
129
it is more expensive. IrO2/Ti electrode and RuO2/Ti electrode have low OEP values (1.6~1.65
130
V) with poor performance on COD removal. SnO2-Sb2O5/Ti and PbO2/Ti have the same OEP
131
value of 1.9 V. However, the working life and COD removal efficiency of SnO2-Sb2O5/Ti were
132
worse than that of PbO2/Ti. Moreover, the price of PbO2/Ti is cheaper than BDD,
133
SnO2-Sb2O5/Ti, and RuO2/Ti. Therefore, PbO2/Ti is selected as the experimental electrode.
134 135
2.3. Electro-oxidation experiment
M AN U
SC
RI PT
126
A laboratory-scale reactor with an effective volume of 1 L was built as shown in Fig. 1.
137
The anode is titanium-based lead dioxide (PbO2/Ti) and the cathode is titanium mesh-plate
138
with the same size of 10 cm × 15 cm. The effective area of the anode is 300 cm2 and the
139
electrode gap between the anode and cathode is 1.0 cm. A direct current converter (MPS
140
601, Tradex, United States) was used to deliver power to the electrodes. An ORP probe
141
(Sanxin, China) and a pH probe (Sanxin, China) were installed in the Electrolysis bath for
142
online monitoring ORP/pH during the Electro-oxidation. Both probes and direct current
143
converter were connected to a computer, and the software of Matlab was utilized for
144
acquiring data and controlling specific electrical charge input. In order to provide a good
145
mass transfer in electrolyte, a circulation system of wastewater was set up with silicone
146
rubber tube and peristaltic pump. Five current densities (5, 10, 15, 20 and 25 mA cm-2) were
AC C
EP
TE D
136
7
ACCEPTED MANUSCRIPT designed to observe the effect of the specific electrical charge on the electrolysis efficiency.
148
The removal efficiencies of COD, TN, chroma and inorganic ions were investigated for
149
evaluating the efficacy of electro-oxidation. 1000 mL of ROC effluent was continuously
150
recirculated and a 6.0 mL aliquot of supernate was sampled each time. All electrolysis
151
processes were carried out without adding any chemical reagent.
152 153
2.4. Analysis and calculation methods
RI PT
147
The COD values of samples were determined according to the standard of China EPA.
155
Specifically, sample was mixed with suitable amount of DI water, K2Cr2O7, Ag2SO4/H2SO4 and
156
HgSO4 (to eliminate the interference of chloride ion), and the mixed solution was digested at
157
150
158
spectrophotometer (DR6000, HACH). Chroma was measured by dilution method, and it
159
means the dilution times of sample by pure water when its color of the diluted sample is
160
barely visible by visual inspection. The values of conductivity and total dissolved solids (TDS)
161
were determined by Conductivity meter (Five Easy Plus, Mettler Toledo, Switzerland). The
162
concentrations of inorganic ions were measured by ion chromatography (Dionex ICS-2000,
163
USA). The molecular structures of the organics before and after electrolysis were determined
164
by Fourier transform infrared spectroscopy (FTIR, Nicole 6700, thermo, USA).
166
M AN U
EP
TE D
for 2 h and then measured at a wavelength of 440 nm by UV–visible
AC C
165
SC
154
The specific removal of pollutants in unit water (R, mg L-1) and the specific electrical
charge (Qsp, Ah L-1) were calculated by the equations (1, 2), respectively:
167
R = -
168
Qsp = j ∙ A ∙
169
(1)
(2)
Where C0 and Ct are the concentrations of samples at electrolytic time 0 and t (mg L-1), 8
ACCEPTED MANUSCRIPT 170
respectively; j is current density (A cm-2); A is the effective area of electrode (cm2); V is the
171
effective volume of the electrolysis bank (L); t is reaction time during electrolytic process (h).
173
The total energy consumption (TEC, kWh m-3) and the total current efficiency (TCE, %) were calculated using the following equations (3, 4): TEC = Qsp ∙ U
174
TCE = ∑ C ∙ Ei =(
175
)∙
RI PT
172
(3)
∑[( − ) ∙
]
(4)
Where U (V) is the cell voltage; i is pollutant (COD, NO3- and NH4+, respectively); Ci0 and
177
Cit are pollutants values measured at electrolytic time 0 and t, respectively; F (96485.3 C
178
mol-1) is the Faraday constant; ni is the number of electrons transferred; Mi (g mol-1) is the
179
molar mass.
182 183
M AN U
181
The energy consumption (EC, kWh [kg COD]-1) and the instantaneous current efficiency (ICE, %) were calculated by equations (5, 6):
TE D
180
SC
176
EC=1000 ∙ Qsp ∙
(5)
∙
= ∙ ∙ ∙
(6)
Where RCOD (mg L-1) is the specific removal of COD, which can be obtained according to Eq.
185
(1); I (A) is the current, t (s) is reaction time during electrolytic process.
AC C
186
EP
184
9
ACCEPTED MANUSCRIPT 187
3. Results and discussion
188
3.1. Effect of specific electrical charge on removal efficiencies Fig. 2 shows the removal of COD, TN and chroma in ROC effluent of printing and dyeing
190
wastewater under different specific electrical charges. The specific removal of COD, TN and
191
chroma increased with the increase of Qsp. In order to analyze the effect of specific electrical
192
charge on pollutant removal and obtain the appropriate specific electrical charge, the curve
193
fittings were conducted and the regression equations, regression coefficients and rate
194
constants are listed in Table 2. The degradations of COD, TN and chroma follow the
195
first-order kinetics, the reaction constants for COD, TN and chroma are 0.217, 0.021 and
196
0.258, respectively. As shown, 99 % of chroma can be degraded with only 2.7 Ah L-1 of Qsp,
197
and the removal efficiency of COD could reach 95.5 % (where the residual COD concentration
198
is 12.42 mg L-1) under the specific electrical charge of 13.0 Ah L-1.
SC
M AN U
TE D
199
RI PT
189
In China, the limitation of COD was set as 100 mg L-1 for printing and dyeing factory
201
effluent discharge (China EPA, 2013, Discharge standards of water pollutants for dyeing and
202
finishing of textile industry). Therefore, the residual COD value of 80 mg L-1 is set as the end
203
point of electro-oxidation reaction in this study. Fig. 3 shows the total energy consumptions
204
(TEC) and the total current efficiencies (TCE) at five current densities when the reaction end
205
point was reached. With the increase of the current density, TCE increased at first stage and
206
then decreased, while the values of TEC increased monotonously. The inflection point of TCE
207
was at the current density of 10 mA cm-2, where the TEC and TCE were 12.04 kWh m-3 and
208
27.86 %, respectively. Therefore, the suitable current density was 10mA cm-2 and the
AC C
EP
200
10
ACCEPTED MANUSCRIPT 209
electrolysis time was 40 min, with the specific electrical charge of 2.45 Ah L-1.
210 211
3.2. Evaluation of removal efficiencies of inorganic ions Fig. SM-1 shows the removal of inorganic ions in ROC effluent by electro-oxidation
213
process under the suitable operating parameters (current density: 10 mA cm-2; reaction time:
214
40 min). Comparatively, higher removal efficiencies of chloride ion (42.0 %), ammonia
215
nitrogen (54.3 %) and calcium ion (62.7 %) were observed. The removal efficiencies of nitrate
216
and magnesium were 19.1 % and 21.3 %, respectively, while only 8.2 % of potassium ion and
217
almost no sulfate and sodium removal were found.
M AN U
SC
RI PT
212
The chloride in the ROC effluent was oxidized to chlorine (Cl2) (Eq. 7) by the anodic
219
electron transfer reaction. Subsequently, the chlorine was hydrolyzed to hypochlorous acid
220
(HClO) and chloric acid (ClO3-) (Eqs. 8-9), which could greatly enhance the indirect oxidation.
TE D
218
2Cl- → Cl2 + 2e-
222
Cl2 + H2 O → HClO + HCl
(8)
223
12HClO + 6H2 O → 4HClO3 + 8HClO + 3O2 + 12H+ +12e-
(9)
EP
221
(7)
During the electro-oxidation process, the calcium ions and magnesium ions in the ROC
225
effluent moved to the cathode and deposited on the cathode due to the reaction with CO32-
226
in wastewater (Rocha et al., 2012). Standard electrode potential of Na and K are -2.7 and -2.9
227
V, respectively, which result in their insignificant removal. The sulfate might not react due to
228
its low reduction potential (S2-/SO42-, E0= 0.82 V) at cathode in alkaline environment and its
229
higher oxidation potential (SO42−/S2O82−, E0= 2.10 V) at anode (Espinoza et al., 2016). So the
230
concentration of sulfate ion almost kept stable in the whole electro-oxidation process.
AC C
224
11
ACCEPTED MANUSCRIPT 231 232
3.3. Variation of organic molecular structure The components of organics in the ROC effluent are usually complex. According to the
234
previous work (Xu, 2010), the main components of organic compounds in the ROC effluent of
235
printing and dyeing wastewater are ketone ethers (RC-O-R/R-O-R, 40.6 %), amines
236
(RNH2/RNHR'/RN[R']R'', 29.1 %); and nitriles, alkanes, esters, aromatic hydrocarbons,
237
carboxylic acids and olefin were also detected.
SC
RI PT
233
The samples before and after electro-oxidation treatment were measured by FTIR
239
instrument and the results are shown in Fig. SM-2. The peak at 1661.1 cm-1 for the untreated
240
ORC effluent (Fig. SM-2a) represents the structural vibration of C=O, and peaks at 990.7 and
241
694.1 cm-1 represent the C=C stretching. The peaks at 1362.4 and 830.7 cm-1 indicate the
242
existence of aromaticity or benzene ring, while the other peaks at 875.8 and 616.4 cm-1
243
indicate the presence of S-O stretching.
TE D
M AN U
238
After electro-oxidation, the components of organics in ROC effluent changed
245
significantly. The new peak in Fig. SM-2b appears at 1419.9 cm-1, indicating the production of
246
carboxylic acids (-COO-). while the peaks of 1362.4, 990.7, 830.7 and 694.1 cm-1 completely
247
disappear and the peaks of 1661.1, 875.8 and 616.4 cm-1 shift to 1637.1, 876.6 and 614.6
248
cm-1, respectively. After being treated by eletro-oxidation, the macromolecular components
249
in ROC was degraded to small molecular matters such as organic acids. The above results
250
show that electro-oxidation process has a destructive function for complex structures of
251
organics and thus is an effective way to treat ROC of printing and dyeing wastewater.
AC C
EP
244
252 12
ACCEPTED MANUSCRIPT 253
3.4. Relationship among ORP, Qsp, COD and chloride ion concentration Electro-oxidation/reduction is essentially the process of electronic gain/loss at electrode
255
surfaces. The relative oxidizing or reducing strength of solution can be expressed using ORP
256
(oxidation-reduction potential) to explore the redox interaction effect of substances at a
257
macroscopic level. Qsp and the concentration of Cl- are two major factors which influence the
258
removal of pollutants in wastewater during the electro-oxidation process. Fig. 4 shows the
259
dependences of the values of ORP, pH, COD and Cl- on Qsp during the electro-oxidation
260
process. The ORP value decreased from 260 ± 25 mV to -75 mV in 2min of electrolyzing and
261
then increased rapidly to reach a steady stage at 720 ± 10 mV. In contrast, the pH value kept
262
relatively stable throughout the reaction process (increasing from 8.3 to 8.9). Meanwhile,
263
the values of COD and Cl- decreased obviously with the increase of specific electrical charge;
264
and their values can be reduced to 77 mg L-1 and 866 mg L-1, respectively, at the specific
265
electrical charge of 3.0 Ah L-1.
TE D
M AN U
SC
RI PT
254
According to the previous analysis, ORP has a close correlation with chloride ion
267
concentration and the specific electrical charge during the electro-oxidation process, and can
268
affect the COD removal efficiency. In order to find out the relationship among ORP, Qsp, COD
269
and chloride ion concentration under the suitable operating parameters, multiple regression
270
was conducted using Origin 8.0 software (Wu and Wang, 2012), their relationships can be
271
expressed as following:
272
AC C
EP
266
ORP = -699.35 + 112.01 Qsp - 5.70 COD + 1.75 Cl-
(10)
273
The regression coefficient (R2) is 0.976, reflecting a good correlation among ORP, Qsp,
274
COD and Cl-. The ORP value is in a positive correlation with Cl- content and Qsp, which 13
ACCEPTED MANUSCRIPT presents oxidizing power; and in a negative correlation with COD value, which presents
276
reduction power. The good correlation shows that the ORP value gives a comprehensive
277
indicator to the effect of current density, chloride ion concentration, pollutants and reaction
278
time on the performance of the electro-oxidation system. Therefore, the ORP value can be
279
used as an effective controlling factor to optimize the electro-oxidation process.
280
3.5. The optimization of specific electrical charge (Qsp) control
SC
281
RI PT
275
Fig. 5 shows the relationship between energy consumption (EC), instantaneous current
283
efficiency (ICE) and ORP during the electro-oxidation. As shown, ORP has significant effect on
284
the values of EC and ICE, and their relation curves look like two opposite waves along with
285
the increase of ORP value. It can be found that, in the ORP ranger of 690 to 740 mV, the
286
maximum value of ICE (≈33 %) and the minimum value of EC (≈50 kWh [kg COD]-1) are
287
simultaneously achieved at 721±3mV, which can be considered as the optimum response
288
interval for electro-oxidation. Note that when ORP ≤ 690 mV the residual COD value of the
289
treated ROC was still larger than the target concentration (80 mg L-1).
291 292 293
TE D
EP
By converting Eq. (10), the relationship between Qsp and ORP, COD and chloride ion
AC C
290
M AN U
282
concentration can be obtained: !"# = 6.24 + 0.0009 ORP + 0.05 COD - 0.015 Cl-
(11)
Thus, to maintain a relatively constant ORP value, we can accordingly adjust the input of
294
Qsp by Eq. (11) when providing different concentrations of COD and chloride ion. A computer
295
control procedure based on back-propagation neural network (BPN) model was developed
296
with Matlab software to optimize the input of Qsp according to the content of residual 14
ACCEPTED MANUSCRIPT pollutants (Yu et al., 2013). The desired residual value of COD and the constant ORP value are
298
the two objective parameters to control. The initial content of pollutants in wastewater,
299
temperature, pH value and Chroma are the original parameters. The Qsp value was optimized
300
by the computer control procedure to control the ORP at a stable value, and the energy
301
consumption could be calculated at this constant ORP system during electro-oxidation
302
process. With the target residual COD value (80 mg L-1), the total energy consumption (TEC)
303
in constant-ORP system was 9.06 kWh m-3, while that for constant-current system was
304
12.04kWh m-3. Thus, the developed constant-ORP system can save the energy consumption
305
by 24.75% as compared to the constant-current system. Consequently, monitoring of ORP
306
has high potential to effectively optimize the electro-oxidation process.
M AN U
SC
RI PT
297
307
309
4． ．Conclusions
TE D
308
The electro-oxidation technique can be considered as an effective, feasible and robust
311
treatment method for ROC effluent in printing and dyeing factory by using PbO2/Ti electrode.
312
With a suitable specific electrical charge of 2.45 Ah L-1, high removal efficiencies of COD
313
(72 %), TN (18 %) and chroma (99 %) were achieved. FTIR analyses show that the
314
electro-oxidation technique has a significant degradation effects to the organic matters of
315
complex structures in ROC effluent. Additionally, the electro-oxidation process can also
316
simultaneously remove some inorganic ions. The quantitative relationship among ORP, Qsp,
317
COD and chloride ion concentration was established. This good correlation shows that the
318
ORP value gives a comprehensive indicator to the effect of current density, chloride ions,
AC C
EP
310
15
ACCEPTED MANUSCRIPT 319
pollutants and reaction time on the performance of electro-oxidation system. The developed
320
constant-ORP system showed the success of online monitoring of ORP in optimizing the
321
electro-oxidation process.
323
RI PT
322
Acknowledgements
The authors are grateful for the financial support provided by the National Natural
325
Science Foundation of China (Grant No.51278465) and the Transformation Projects in the
326
Science & Technology Pillar Program of Zhejiang Province (Grant No.20130176).
SC
324
AC C
EP
TE D
M AN U
327
16
ACCEPTED MANUSCRIPT 328
References
329 330 331
Bagastyo, A.Y., Batstone, D.J., Rabaey, K., Radjenovic, J., 2013. Electrochemical oxidation of
332 333
Benner, J., Salhi, E., Ternes, T., Von, G.U., 2008. Ozonation of reverse osmosis concentrate: kinetics and
334 335 336
Bonfatti, F., Ferro, S., Lavezzo, F., Malacarne, M., Lodi, G., Battisti, A.D., 2000. Electrochemical
337 338
Cao, J.L., Zhao, H.Y., Cao, F.H., Zhang, J.Q., Cao, CN., 2009. Electrocatalytic degradation of
339 340 341
Cao, Z., Wen, D.N., Chen, H., Wang, J.D., 2016. Simultaneous Removal of COD and Ammonia Nitrogen
342 343 344
Chatzisymeon, E., Dimou, A., Mantzavinos, D., Katsaounis, A., 2009. Electrochemical oxidation of
345 346
Chen, G.H., Hung, Y.T., 2007. Electrochemical Wastewater Treatment Processes. Humana Press. pp
347 348 349
Chen, Y.Y., Baygents, J.C., Farrell, J., 2017. Evaluating electrocoagulation and chemical coagulation for
350 351 352
Combernoux, N., Schrive, L., Labed, V., Wyart, Y., Carretier, E., Benony-Rhodier, A., Moulin, P., 2015.
353 354
Correa-Lozano, B., Comninellis, C., Battisti, A.D., 1997. Service life of Ti/SnO2–Sb2O5 anodes. J. Appl.
355 356 357
Ersever, I., Ravindran, V., Tsai, H.H., Pirbazari, M., 2014. Modeling and design of anaerobic fluidized
358 359 360
Espinoza, J.D.G., Drogui, P., Zolfaghari, M., Dirany, A., Ledesma, M.T.O., Gortáres-Moroyoqui, P., Buelna,
361 362 363
Fryda, M., Herrmann, D., Schafer, L., Klages, C.P., Perret, A., Haenni, W., Comninellis, C., Gandini, D.,
electrodialysed reverse osmosis concentrate on Ti/Pt-IrO2, Ti/SnO2-Sb and boron-doped diamond
efficiency of beta blocker oxidation. Water Res. 42, 3003-12.
RI PT
electrodes. Water Res. 47, 242-250.
Incineration of Glucose as a Model Organic Substrate. I. Role of the Electrode Material. J. Electrochem. Soc. 146, 2175-2179.
SC
4-chlorophenol on F-doped PbO2 anodes. Electrochim. Acta. 54, 2595-2602.
Electrochem. Soc. 11, 4018-4026.
M AN U
Using a Novel Electro-Oxidation Reactor: A Technical and Economic Feasibility Study. Int. J.
model compounds and olive mill wastewater over DSA electrodes: 1. The case of Ti/IrO2 anode. J. Hazard. Mater. 167, 268-274.
TE D
866-8.
removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions. J. Water Process. Eng. 16, 50-55.
EP
Study of polyamide composite reverse osmosis membrane degradation in water under gamma
AC C
rays. J. Membr. Sci. 480, 64-73.
Electrochem. 27, 970-974.
bed reactor with recycling for denitrification of reverse osmosis concentrates. Chem. Eng. Sci. 108, 111-122.
G., 2016. Performance of electrochemical oxidation process for removal of di (2-ethylhexyl) phthalate. Environ. Sci. Pollut. R. 23, 12164-12173.
1999. Properties of Diamond Electrodes for Wastewater Treatment. New Diam. Front. C. Technol. 9, 229-240. 17
ACCEPTED MANUSCRIPT 364 365
He, H.J., Chen, Y.J., Li, X., Cheng, Y., Yang, C.P., Zeng, G.M., 2016. Influence of salinity on
366 367 368
Hege, K.V., Verhaege, M., Verstraete, W., 2002. Indirect electrochemical oxidation of reverse osmosis
369 370
Hou, H.X., Chen, L.Q., Wang, S.Y., Mino, T., Satoh, H., 2006. Use ORP to control simultaneous
371 372
Kishimoto, N., Yu, N., Kato, M., Otsu, H., 2015. Effect of oxidation–reduction potential on an
373 374 375
Lu, J., Fan, L.H., Roddick, F.A., 2013. Potential of BAC combined with UVC/H2O2 for reducing organic
376 377
Pérez-González, A., Urtiaga, A.M., Ibáñez, R., Ortiz, I., 2012. State of the art and review on the
378 379
Pérez-González, A., Fernández-Alba, A.R., Urtiaga, A.M., Ortiz, I., 2010. Electro-oxidation of reverse
380 381 382
Qu, D., Wang, J., Wang, L.L., Hou, D.Y., Luan, Z.K., Wang, B.Q., 2009. Integration of accelerated
383 384
Radjenovic, J., Bagastyo, A., Batstone, D., Keller, J., 2013. Electrochemical Treatment of Reverse
385 386 387
Cossu, R., Polcaro, A.M., Lavagnolo, M.C., Mascia, M., Palmas, S., Renoldi, F., 1998. Electrochemical
388 389 390
Raghu, S., Chang, W.L., Chellammal, S., Palanichamy, S., Basha, C.A., 2009. Evaluation of
391 392 393
Rocha, J.H.B., Gomes, M.M.S., Fernandes, N.S., Silva, D.R.D., Martínez-Huitle, C.A., 2012. Application
394 395
Santos, I.D., Dezotti, M., Dutra, A.J.B., 2013. Electrochemical treatment of effluents from petroleum
396 397 398
Silva, L.M.D., Faria, L.A.D., Boodts, J.F.C., 2002. Electrochemical impedance spectroscopic (EIS)
399 400
Šostar-Turk, S., Simonič, M., Petrinić, I., 2005. Wastewater treatment after reactive printing. Dyes and
microorganisms in activated sludge processes: A review. Int. Biodeter. Biodegr. 119, 520-527.
membrane concentrates at boron-doped diamond electrodes. Electrochem. Commun. 4, 296-300.
electrochemical Fenton-type process. Chem. Eng. J. 260, 590-595.
RI PT
nitrification and denitrification in oxidation ditch process. J. B. Univ. Technol. 32, 1093-1096.
reclamation. Chemosphere 93, 683-688.
SC
matter from highly saline reverse osmosis concentrate produced from municipal wastewater
M AN U
treatment technologies of water reverse osmosis concentrates. Water Res. 46, 267-283.
osmosis concentrates generated in tertiary water treatment. Water Res. 44, 2763-2772.
precipitation softening with membrane distillation for high-recovery desalination of primary
TE D
reverse osmosis concentrate. Sep. Purif. Technol. 67, 21-25.
Osmosis Concentrates. Anal. Chem. 86, 3764-72.
Treatment of Landfill Leachate: Oxidation at Ti/PbO2 and Ti/SnO2 Anodes. Environ. Sci. Technol.
EP
32, 3570-3573.
electrochemical oxidation techniques for degradation of dye effluents—A comparative approach.
AC C
J. Hazard. Mater. 171, 748-754.
of electrochemical oxidation as alternative treatment of produced water generated by Brazilian petrochemical industry. Fuel Process. Technol. 96, 80-87.
industry using a Ti/RuO 2 anode. Chem. Eng. J. 226, 293-299.
investigation of the deactivation mechanism, surface and electrocatalytic properties of Ti/RuO2(x)+Co3O4(1−x) electrodes. J. Electroanal. Chem. 532, 141-150.
Pigments 64, 147-152. 18
ACCEPTED MANUSCRIPT 401 402
Xu, Q.K., 2010. Study on advanced treatment of textile wastewater. Dissertation, South China Normal
403 404
Weng, M.L., Pei, J.C., 2016. Electrochemical oxidation of reverse osmosis concentrate using a novel
405 406 407
Wu, H., Wang, S., 2012. Impacts of operating parameters on oxidation-reduction potential and
408 409
Yao, J.C., Wen, D.N., Shen, J.N., Wang, J.D., 2016. Zero discharge process for dyeing wastewater
410 411 412
Yu, R.F., Lin, C.H., Chen, H.W., Cheng, W.P., Kao, M.C., 2013. Possible control approaches of the
413 414
Yu, R.F., Chi, F.H., Cheng, W.P., Wang, M.H., 2015. Online monitoring of the nanoscale zero-valent iron
415 416
Zhao, C.X., Gu, P., Cui, H.Y., Zhang, G.H., 2012. Reverse osmosis concentrate treatment via a PAC-MF
417 418 419
Zhou, M.H., Liu, L., Jiao, Y.L., Wang, Q., Tan, Q.Q., 2011. Treatment of high-salinity reverse osmosis
420 421
Zhou, M.H., Tan, Q.Q., Wang, Q., Jiao, Y.L., Oturan, N., Oturan, M.A., 2012. Degradation of organics in
422 423
Zhu, R.Y., Yang, C.Y., Zhou, M.M., Wang, J.D. 2015. Industrial park wastewater deeply treated and
424 425 426 427
Zou, J., Peng, X., Miao, L., Ying, X., Bing, W., Dong, F., Wang, B., 2016. Electrochemical oxidation of COD
University (in Chinese).
electrode: Parameter optimization and kinetics study. Desalination 399, 21-28.
J. Hazard. Mater. 243, 86-94.
treatment. J. Water Process. Eng. 11, 98-103.
RI PT
pretreatment efficacy in the pretreatment of printing and dyeing wastewater by Fenton process.
Electro-Fenton process for textile wastewater treatment using on-line monitoring of DO and ORP.
SC
Chem. Eng. J. 218, 341-349.
M AN U
process for trichloroethylene wastewater treatment. Int. J. Environ. Sci. Technol. 12, 1647-1656.
accumulative countercurrent adsorption process. Water Res. 46, 218-226.
concentrate by electrochemical oxidation on BDD and DSA electrodes. Desalination 277,
TE D
201-206.
reverse osmosis concentrate by electro-Fenton process. J. Hazard. Mater. 287, 215-216.
EP
reused by a novel electrochemical oxidation reactor. Chem. Eng. J. 260, 427-433.
from real textile wastewaters: Kinetic study and energy consumption. Chemosphere 171,
AC C
332-338.
19
ACCEPTED MANUSCRIPT 428
Tables and Figures
429
Table 1. General characteristics of the ROC effluent. Physical-chemical properties COD
272±10 mg L-1 -1
Inorganic ions Na+
40.6 mg L-1
40.8 mg L
TP
1.8 mg L-1
Ca2+
26.9 mg L-1
pH
8.3
Mg2+
7.5 mg L-1
Chroma
160 times
NH4+
4.0 mg L-1
Conductivity
17.0 ms cm-1
SO42-
4739.9 mg L-1
TDS
8.49 g L-1
Cl-
1471.8 mg L-1
NO3F-
430 431
TN
TE D
COD
0.6 mg L-1
RCOD = -203.6 exp(-Qsp/1.993) + 241.6
0.948
0.217
RTN = -9.78 exp(-Qsp /5.913) + 11.6
0.931
0.021
0.898
0.258
RCOD (mg L-1), RTN (mg L-1) and RChroma (times) are the specific removal of COD, TN and chroma, respectively; Qsp is the specific electrical charge (Ah L-1).
AC C
a
EP
Chroma RChroma = -85.9 exp(-Qsp /0.879) + 156.5
436 437
1.3 mg L-1
Table 2. Regression equations, coefficients and rate constants for the dependences of the special removals of COD, TN and chroma on the specific electrical charge. rate constants regression equationa regression coefficient (R2) (k,s-1)
432 433
434 435
24.9 mg L-1
M AN U
PO43-
RI PT
TN
SC
K
4330.5 mg/L
+
20
438
Fig.1. Diagram of experimental setup of eletro-oxidation.
440
RTN (mg L
-1
)
12 9
TN RTN
6
TE D
) -1
EP
Chroma RChroma
135
AC C
RChroma (Times)
150
120
45 30 15
105
0 0
3
6
9
-1
Qsp (Ah L
12
Chroma (Times)
0 60
)
75
90 45
442 443 444
150
-1
RCOD (mg L
135
COD (mg L
225 COD RCOD
180
441
30 300
225
90
33
)
270
36
-1
3
39
TN (mg L
M AN U
439
SC
RI PT
ACCEPTED MANUSCRIPT
15
)
Fig.2. Effect of specific electric charge on COD, TN and chroma removal efficiencies; the initial values of COD, TN and chroma were 272 mg L-1, 40.82 mg L-1, and 160 Times, respectively.
445 446 21
ACCEPTED MANUSCRIPT 447 29 TCE
18
TEC
28
RI PT
TCE (%)
27
TEC (kWh m )
15
12
-3
26
25
5
10
15
20
SC
9
25
-2
current density (mA cm )
Fig. 3. The influence of current density on the total current efficiency (TCE) and the total energy consumption (TEC); the residual COD value was set as 80 mg L-1.
451 800
400 200 0 -200
EP
8
453 454 455
AC C
452
0
200 150 100 50 1400
pH
1200
-
Cl
7 6
250
1000 1
2
3
Cl- (mg L-1)
9
pH
ORP COD
TE D
ORP (mV)
600
300
COD (mg L-1)
M AN U
448 449 450
800
-1
Qsp (Ah L )
Fig. 4. The effect of Qsp on the values of ORP, pH, COD and chloride ion concentration; current density: 10 mA cm-2, reaction time: 40 min.
456 457 458 459 22
ACCEPTED MANUSCRIPT
M AN U
461 462 463
SC
RI PT
460
Fig. 5. The relationship between energy consumption (EC), instantaneous current efficiency (ICE) and ORP during the electro-oxidation process.
AC C
EP
TE D
464
23
S0045-6535(18)30465-X
DOI:
10.1016/j.chemosphere.2018.03.051
Reference:
CHEM 20995
To appear in:
ECSN
Received Date: 22 January 2018 Revised Date:
6 March 2018
Accepted Date: 7 March 2018
Please cite this article as: Wang, J., Zhang, T., Mei, Y., Pan, B., Treatment of reverse-osmosis concentrate of print and dyeing wastewater by electro-oxidation process with controlled oxidationreduction potential (ORP), Chemosphere (2018), doi: 10.1016/j.chemosphere.2018.03.051. 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.
ACCEPTED MANUSCRIPT 1
Treatment of reverse-osmosis concentrate of print and dyeing wastewater by
2
electro-oxidation process with controlled oxidation-reduction potential (ORP)
3
RI PT
Jiade Wang1, Tian Zhang1, Yu Mei2, Bingjun Pan1*
4 1
College of Environment, Zhejiang University of Technology, Hangzhou, Zhejiang 310014, China
6
2
College of Biological and Environmental Engineering, Zhejiang Shuren University, Hangzhou,
7
Zhejiang 310005, China
SC
5
9
M AN U
8
10
*
11
E-mail: [email protected]
12
Tel: +86-571-88320915; Fax: +86-571-88320882
Corresponding author
TE D
13
Highlights:
15
1. Removal efficiencies of COD, TN and chroma are positively correlated with Qsp.
16
2. The optimal current efficiency can be obtained at a certain current density.
17
3. A good correlation between ORP and the COD/Cl- removal efficiencies, Qsp is found.
18
4. The developed constant-ORP system substantially increases energy-efficiency.
AC C
19
EP
14
1
ACCEPTED MANUSCRIPT 20
ABSTRACT Reverse osmosis concentrate (ROC) of printing and dyeing wastewater remains as a
22
daunting environmental issue, which is characterized by high salinity, chemical oxygen
23
demand (COD), chroma and low biodegradability. In this study electro-oxidation process
24
(PbO2/Ti electrode) coupled with oxidation-reduction potential (ORP) online monitor was
25
applied to treat such a ROC effluent. The results show that with the increase of specific
26
electrical charge (Qsp), the removal efficiencies of COD, TN and chroma increased significantly
27
at the incipience and then reached a gentle stage; the optimal total current efficiency (12.04
28
kWh m-3) was obtained with the current density of 10 mA cm-2 (Qsp, 2.45 Ah L-1). Meanwhile,
29
some inorganic ions can be simultaneously removed to varying degrees. FTIR analyses
30
indicated that the macromolecular organics were decomposed into smaller molecules. A
31
multi-parameter linear relationship between ORP and Qsp, COD and Cl- concentration was
32
established, which can quantitatively reflect the effect of current density, chloride ion
33
concentration, pollutants and reaction time on the performance of the electro-oxidation
34
system. As compared to a traditional constant-current system, the constant-ORP system
35
developed in this study (through the back-propagation neural network [BPN] model with
36
ORP monitoring) approximately reduced the energy cost by 24-29%. The present work is
37
expected to provide a potential alternative in optimizing the electro-oxidation process.
38
Keywords: reverse osmosis concentrate (ROC); printing and dyeing wastewater;
39
electro-oxidation process; oxidation-reduction potential (ORP); constant-ORP system
AC C
EP
TE D
M AN U
SC
RI PT
21
40 41 2
ACCEPTED MANUSCRIPT 42
1. Introduction Reverse osmosis process has been widely applied in printing and dyeing wastewater
44
treatment as it can effectively barrier various organic/inorganic contaminants and also
45
biological constituents (Šostar-Turk et al., 2005). After being treated, a large proportion of
46
feed stream can be reused directly in printing and dyeing process (Bagastyo et al., 2013),
47
while the residual reverse osmosis concentrate (ROC) of printing and dyeing wastewater,
48
which is characterized by recalcitrant organics, high hardness and high salinity, cannot be
49
directly discharged and still remains serious environmental risks (Combernoux et al., 2015).
M AN U
SC
RI PT
43
Lots of conventional techniques have been proposed to further treat stubborn ROC
51
effluents (Pérez-González et al., 2012). However, the physical and chemical treatments such
52
as coagulation (Chen et al., 2017), membrane distillation (Qu et al., 2009) and adsorption
53
(Zhao et al., 2012) will eventually cause secondary pollution and most of them come with a
54
high waste disposal cost. The biochemical method is also not a good choice for terminal
55
treatment because of the very low biodegradability and high salinity in ROC effluent (Ersever
56
et al., 2014). Advanced oxidation processes such as ozonation (Benner et al., 2008),
57
heterogeneous photocatalysis (Lu et al., 2013) and Fenton (Zhou et al., 2012), are not
58
economically feasible and need extra reagents. Among the existing treatment options,
59
electro-oxidation has been widely applied in ROC treatment (Pérez et al., 2010, Radjenovic et
60
al., 2013). The high content of salts in ROC effluent ensures the good conductivity and can
61
reduce the cell voltage during electrolysis (Yao et al., 2016). Moreover, massive chloride, a
62
main component in ROC effluent can serve as active chlorine resource and thus enhance the
63
indirect oxidation in electro-oxidation process (Pérez et al., 2010). Weng and Pei (2016)
AC C
EP
TE D
50
3
ACCEPTED MANUSCRIPT found that the removal efficiency of COD can reach 59.35% by using Co doped PbO2 anode at
65
a current density of 80 mA cm-2. Zhou et al. (2011) investigated the COD degradation in
66
high-salinity ROC effluent and found that it could almost be completely removed by
67
electro-oxidation at 3.0 Ah L-1 with the electrode of IrO2-RuO2/Ti. Hege et al. (2002) reported
68
that 70% of COD and 75% of ammonia nitrogen in ROC of printing and dyeing wastewater
69
was removed by using boron-doped diamond (BDD) as working electrode at a specific
70
electrical charge of 1.5 Ah L-1.
SC
RI PT
64
However, the energy cost of electro-oxidation process is still a major factor that restricts
72
its wide application in wastewater advanced treatment. Various studies have accordingly
73
carried out and found that optimizing electrode materials and developing new reactors can
74
improve the current efficiency and thus reduce the energy consumption (Raghu et al., 2009;
75
Zhu et al., 2015; Cao et al., 2016). Zou et al. (2016) also found that increasing electrolyte
76
concentration in the wastewater can improve the current efficiency and save about 32% of
77
energy consumption. Fortunately, the ROC of printing and dyeing wastewater usually comes
78
along with high electrolyte concentration. Additionally, since the current efficiency depends
79
on the current density and is affected by the composition of wastewater, the optimal current
80
density often fluctuate during operation process. Also, the electro-generated active hydroxyl
81
radicals (serving as the functional oxidizing species) in electro-oxidation process are difficult
82
to be online monitored.
AC C
EP
TE D
M AN U
71
83
Since 1980s, oxidation-reduction potential (ORP) has been reported as an important
84
indicator in some wastewater advanced treatment such as Fenton dosage control (Wu and
85
Wang, 2012), simultaneous nitrification-denitrification in oxidation ditch process (Hou et al., 4
ACCEPTED MANUSCRIPT 2006), and the nanoscale zero-valent iron process for trichloroethylene degradation (Yu et al.,
87
2015). Some quantitative relationships have been established among ORP, operating
88
parameters and treatment efficiency to optimize the dosage of chemical agents, guide the
89
operation of wastewater plant, and save the operation cost and energy consumption. As
90
compared to current density, ORP is considered to be a more suitable indicator for the
91
optimal operation of the electro Fenton process (Kishimoto et al., 2015). In electro-oxidation
92
process, ORP is also the key factor to explore the redox effect of substances at the electrode
93
surfaces or in the solution. However, until now no literature reports the relationship between
94
ORP and treatment efficiencies in electro-oxidation processes.
M AN U
SC
RI PT
86
In this study, the removal efficiencies of COD, TN and chroma for ROC effluent of a real
96
printing and dyeing wastewater by electro-oxidation process was investigated with different
97
operation parameters. Fourier transform infrared spectroscopy (FTIR) was used to analyze
98
the degradation of large organic molecules by electro-oxidation. Meanwhile, the removal of
99
the inorganic ions in ROC effluent was also inspected during electro-oxidation. Finally, the
100
optimum response interval and the quantitative relationship among ORP, Qsp, COD and
101
chloride ion concentration were established to verify the possibility of reducing energy
102
consumption.
AC C
EP
TE D
95
5
ACCEPTED MANUSCRIPT 103
2. Materials and methods
104
2.1. Characteristics of ROC effluent of printing and dyeing wastewater The ROC effluent was collected from a printing and dyeing factory (Zhejiang, China),
106
which built a wastewater treatment plant with the capacity of 12000 T d-1. With being
107
treated by microfiltration (MF) and reverse osmosis (RO), 65% of the total wastewater was
108
reused as productive water, and 35% of the total wastewater (ROC) was discharged into the
109
public wastewater treatment plant for further purification. The main characteristics of the
110
ROC effluent are listed in Table 1. Briefly, the COD value is 272±10 mg L-1, and the total
111
dissolved solids (TDS) is 8490 mg L-1, which is beyond the suitable value of 5000 mg L-1 for
112
biodegradation, although some microorganism was reported to maintain metabolic activity
113
in higher TDS concentration (He et al., 2016). Additionally, Due to nitrification in aerobic
114
reactor, the ROC effluent also contains ≈40 mg L-1 total nitrogen (TN, most of them are
115
nitrate).
TE D
M AN U
SC
RI PT
105
The dissolved solids in ROC effluent were further analyzed by ion chromatography. As
117
shown in Table 1, the main anions in ROC effluent are Cl- (1471.8 mg L-1) and SO42- (4739.9
118
mg L-1), and the major cations are Na+ (4330.5 mg L-1) and K+ (40.6 mg L-1). High
119
concentration of TDS and chloride would inhibit the biological activity in bioprocess, but are
120
in favor of the electro-oxidation process. High salinity can provide excellent conductivity to
121
reduce energy consumption, and high chlorine content promotes indirect oxidation of the
122
organic matter by increasing active chlorine (Cl2, HOCl) and consequently improves the
123
current efficiency.
AC C
EP
116
124 6
ACCEPTED MANUSCRIPT 125
2.2. Electrode selection The working electrode is a key part in electro-oxidation process. Table SM-1 compares
127
the oxygen evolution potentials (OEP), the removal efficiency of pollutants and the electrode
128
life of several commercial electrodes. That is, BDD electrode has the highest OEP of 2.3 V, but
129
it is more expensive. IrO2/Ti electrode and RuO2/Ti electrode have low OEP values (1.6~1.65
130
V) with poor performance on COD removal. SnO2-Sb2O5/Ti and PbO2/Ti have the same OEP
131
value of 1.9 V. However, the working life and COD removal efficiency of SnO2-Sb2O5/Ti were
132
worse than that of PbO2/Ti. Moreover, the price of PbO2/Ti is cheaper than BDD,
133
SnO2-Sb2O5/Ti, and RuO2/Ti. Therefore, PbO2/Ti is selected as the experimental electrode.
134 135
2.3. Electro-oxidation experiment
M AN U
SC
RI PT
126
A laboratory-scale reactor with an effective volume of 1 L was built as shown in Fig. 1.
137
The anode is titanium-based lead dioxide (PbO2/Ti) and the cathode is titanium mesh-plate
138
with the same size of 10 cm × 15 cm. The effective area of the anode is 300 cm2 and the
139
electrode gap between the anode and cathode is 1.0 cm. A direct current converter (MPS
140
601, Tradex, United States) was used to deliver power to the electrodes. An ORP probe
141
(Sanxin, China) and a pH probe (Sanxin, China) were installed in the Electrolysis bath for
142
online monitoring ORP/pH during the Electro-oxidation. Both probes and direct current
143
converter were connected to a computer, and the software of Matlab was utilized for
144
acquiring data and controlling specific electrical charge input. In order to provide a good
145
mass transfer in electrolyte, a circulation system of wastewater was set up with silicone
146
rubber tube and peristaltic pump. Five current densities (5, 10, 15, 20 and 25 mA cm-2) were
AC C
EP
TE D
136
7
ACCEPTED MANUSCRIPT designed to observe the effect of the specific electrical charge on the electrolysis efficiency.
148
The removal efficiencies of COD, TN, chroma and inorganic ions were investigated for
149
evaluating the efficacy of electro-oxidation. 1000 mL of ROC effluent was continuously
150
recirculated and a 6.0 mL aliquot of supernate was sampled each time. All electrolysis
151
processes were carried out without adding any chemical reagent.
152 153
2.4. Analysis and calculation methods
RI PT
147
The COD values of samples were determined according to the standard of China EPA.
155
Specifically, sample was mixed with suitable amount of DI water, K2Cr2O7, Ag2SO4/H2SO4 and
156
HgSO4 (to eliminate the interference of chloride ion), and the mixed solution was digested at
157
150
158
spectrophotometer (DR6000, HACH). Chroma was measured by dilution method, and it
159
means the dilution times of sample by pure water when its color of the diluted sample is
160
barely visible by visual inspection. The values of conductivity and total dissolved solids (TDS)
161
were determined by Conductivity meter (Five Easy Plus, Mettler Toledo, Switzerland). The
162
concentrations of inorganic ions were measured by ion chromatography (Dionex ICS-2000,
163
USA). The molecular structures of the organics before and after electrolysis were determined
164
by Fourier transform infrared spectroscopy (FTIR, Nicole 6700, thermo, USA).
166
M AN U
EP
TE D
for 2 h and then measured at a wavelength of 440 nm by UV–visible
AC C
165
SC
154
The specific removal of pollutants in unit water (R, mg L-1) and the specific electrical
charge (Qsp, Ah L-1) were calculated by the equations (1, 2), respectively:
167
R = -
168
Qsp = j ∙ A ∙
169
(1)
(2)
Where C0 and Ct are the concentrations of samples at electrolytic time 0 and t (mg L-1), 8
ACCEPTED MANUSCRIPT 170
respectively; j is current density (A cm-2); A is the effective area of electrode (cm2); V is the
171
effective volume of the electrolysis bank (L); t is reaction time during electrolytic process (h).
173
The total energy consumption (TEC, kWh m-3) and the total current efficiency (TCE, %) were calculated using the following equations (3, 4): TEC = Qsp ∙ U
174
TCE = ∑ C ∙ Ei =(
175
)∙
RI PT
172
(3)
∑[( − ) ∙
]
(4)
Where U (V) is the cell voltage; i is pollutant (COD, NO3- and NH4+, respectively); Ci0 and
177
Cit are pollutants values measured at electrolytic time 0 and t, respectively; F (96485.3 C
178
mol-1) is the Faraday constant; ni is the number of electrons transferred; Mi (g mol-1) is the
179
molar mass.
182 183
M AN U
181
The energy consumption (EC, kWh [kg COD]-1) and the instantaneous current efficiency (ICE, %) were calculated by equations (5, 6):
TE D
180
SC
176
EC=1000 ∙ Qsp ∙
(5)
∙
= ∙ ∙ ∙
(6)
Where RCOD (mg L-1) is the specific removal of COD, which can be obtained according to Eq.
185
(1); I (A) is the current, t (s) is reaction time during electrolytic process.
AC C
186
EP
184
9
ACCEPTED MANUSCRIPT 187
3. Results and discussion
188
3.1. Effect of specific electrical charge on removal efficiencies Fig. 2 shows the removal of COD, TN and chroma in ROC effluent of printing and dyeing
190
wastewater under different specific electrical charges. The specific removal of COD, TN and
191
chroma increased with the increase of Qsp. In order to analyze the effect of specific electrical
192
charge on pollutant removal and obtain the appropriate specific electrical charge, the curve
193
fittings were conducted and the regression equations, regression coefficients and rate
194
constants are listed in Table 2. The degradations of COD, TN and chroma follow the
195
first-order kinetics, the reaction constants for COD, TN and chroma are 0.217, 0.021 and
196
0.258, respectively. As shown, 99 % of chroma can be degraded with only 2.7 Ah L-1 of Qsp,
197
and the removal efficiency of COD could reach 95.5 % (where the residual COD concentration
198
is 12.42 mg L-1) under the specific electrical charge of 13.0 Ah L-1.
SC
M AN U
TE D
199
RI PT
189
In China, the limitation of COD was set as 100 mg L-1 for printing and dyeing factory
201
effluent discharge (China EPA, 2013, Discharge standards of water pollutants for dyeing and
202
finishing of textile industry). Therefore, the residual COD value of 80 mg L-1 is set as the end
203
point of electro-oxidation reaction in this study. Fig. 3 shows the total energy consumptions
204
(TEC) and the total current efficiencies (TCE) at five current densities when the reaction end
205
point was reached. With the increase of the current density, TCE increased at first stage and
206
then decreased, while the values of TEC increased monotonously. The inflection point of TCE
207
was at the current density of 10 mA cm-2, where the TEC and TCE were 12.04 kWh m-3 and
208
27.86 %, respectively. Therefore, the suitable current density was 10mA cm-2 and the
AC C
EP
200
10
ACCEPTED MANUSCRIPT 209
electrolysis time was 40 min, with the specific electrical charge of 2.45 Ah L-1.
210 211
3.2. Evaluation of removal efficiencies of inorganic ions Fig. SM-1 shows the removal of inorganic ions in ROC effluent by electro-oxidation
213
process under the suitable operating parameters (current density: 10 mA cm-2; reaction time:
214
40 min). Comparatively, higher removal efficiencies of chloride ion (42.0 %), ammonia
215
nitrogen (54.3 %) and calcium ion (62.7 %) were observed. The removal efficiencies of nitrate
216
and magnesium were 19.1 % and 21.3 %, respectively, while only 8.2 % of potassium ion and
217
almost no sulfate and sodium removal were found.
M AN U
SC
RI PT
212
The chloride in the ROC effluent was oxidized to chlorine (Cl2) (Eq. 7) by the anodic
219
electron transfer reaction. Subsequently, the chlorine was hydrolyzed to hypochlorous acid
220
(HClO) and chloric acid (ClO3-) (Eqs. 8-9), which could greatly enhance the indirect oxidation.
TE D
218
2Cl- → Cl2 + 2e-
222
Cl2 + H2 O → HClO + HCl
(8)
223
12HClO + 6H2 O → 4HClO3 + 8HClO + 3O2 + 12H+ +12e-
(9)
EP
221
(7)
During the electro-oxidation process, the calcium ions and magnesium ions in the ROC
225
effluent moved to the cathode and deposited on the cathode due to the reaction with CO32-
226
in wastewater (Rocha et al., 2012). Standard electrode potential of Na and K are -2.7 and -2.9
227
V, respectively, which result in their insignificant removal. The sulfate might not react due to
228
its low reduction potential (S2-/SO42-, E0= 0.82 V) at cathode in alkaline environment and its
229
higher oxidation potential (SO42−/S2O82−, E0= 2.10 V) at anode (Espinoza et al., 2016). So the
230
concentration of sulfate ion almost kept stable in the whole electro-oxidation process.
AC C
224
11
ACCEPTED MANUSCRIPT 231 232
3.3. Variation of organic molecular structure The components of organics in the ROC effluent are usually complex. According to the
234
previous work (Xu, 2010), the main components of organic compounds in the ROC effluent of
235
printing and dyeing wastewater are ketone ethers (RC-O-R/R-O-R, 40.6 %), amines
236
(RNH2/RNHR'/RN[R']R'', 29.1 %); and nitriles, alkanes, esters, aromatic hydrocarbons,
237
carboxylic acids and olefin were also detected.
SC
RI PT
233
The samples before and after electro-oxidation treatment were measured by FTIR
239
instrument and the results are shown in Fig. SM-2. The peak at 1661.1 cm-1 for the untreated
240
ORC effluent (Fig. SM-2a) represents the structural vibration of C=O, and peaks at 990.7 and
241
694.1 cm-1 represent the C=C stretching. The peaks at 1362.4 and 830.7 cm-1 indicate the
242
existence of aromaticity or benzene ring, while the other peaks at 875.8 and 616.4 cm-1
243
indicate the presence of S-O stretching.
TE D
M AN U
238
After electro-oxidation, the components of organics in ROC effluent changed
245
significantly. The new peak in Fig. SM-2b appears at 1419.9 cm-1, indicating the production of
246
carboxylic acids (-COO-). while the peaks of 1362.4, 990.7, 830.7 and 694.1 cm-1 completely
247
disappear and the peaks of 1661.1, 875.8 and 616.4 cm-1 shift to 1637.1, 876.6 and 614.6
248
cm-1, respectively. After being treated by eletro-oxidation, the macromolecular components
249
in ROC was degraded to small molecular matters such as organic acids. The above results
250
show that electro-oxidation process has a destructive function for complex structures of
251
organics and thus is an effective way to treat ROC of printing and dyeing wastewater.
AC C
EP
244
252 12
ACCEPTED MANUSCRIPT 253
3.4. Relationship among ORP, Qsp, COD and chloride ion concentration Electro-oxidation/reduction is essentially the process of electronic gain/loss at electrode
255
surfaces. The relative oxidizing or reducing strength of solution can be expressed using ORP
256
(oxidation-reduction potential) to explore the redox interaction effect of substances at a
257
macroscopic level. Qsp and the concentration of Cl- are two major factors which influence the
258
removal of pollutants in wastewater during the electro-oxidation process. Fig. 4 shows the
259
dependences of the values of ORP, pH, COD and Cl- on Qsp during the electro-oxidation
260
process. The ORP value decreased from 260 ± 25 mV to -75 mV in 2min of electrolyzing and
261
then increased rapidly to reach a steady stage at 720 ± 10 mV. In contrast, the pH value kept
262
relatively stable throughout the reaction process (increasing from 8.3 to 8.9). Meanwhile,
263
the values of COD and Cl- decreased obviously with the increase of specific electrical charge;
264
and their values can be reduced to 77 mg L-1 and 866 mg L-1, respectively, at the specific
265
electrical charge of 3.0 Ah L-1.
TE D
M AN U
SC
RI PT
254
According to the previous analysis, ORP has a close correlation with chloride ion
267
concentration and the specific electrical charge during the electro-oxidation process, and can
268
affect the COD removal efficiency. In order to find out the relationship among ORP, Qsp, COD
269
and chloride ion concentration under the suitable operating parameters, multiple regression
270
was conducted using Origin 8.0 software (Wu and Wang, 2012), their relationships can be
271
expressed as following:
272
AC C
EP
266
ORP = -699.35 + 112.01 Qsp - 5.70 COD + 1.75 Cl-
(10)
273
The regression coefficient (R2) is 0.976, reflecting a good correlation among ORP, Qsp,
274
COD and Cl-. The ORP value is in a positive correlation with Cl- content and Qsp, which 13
ACCEPTED MANUSCRIPT presents oxidizing power; and in a negative correlation with COD value, which presents
276
reduction power. The good correlation shows that the ORP value gives a comprehensive
277
indicator to the effect of current density, chloride ion concentration, pollutants and reaction
278
time on the performance of the electro-oxidation system. Therefore, the ORP value can be
279
used as an effective controlling factor to optimize the electro-oxidation process.
280
3.5. The optimization of specific electrical charge (Qsp) control
SC
281
RI PT
275
Fig. 5 shows the relationship between energy consumption (EC), instantaneous current
283
efficiency (ICE) and ORP during the electro-oxidation. As shown, ORP has significant effect on
284
the values of EC and ICE, and their relation curves look like two opposite waves along with
285
the increase of ORP value. It can be found that, in the ORP ranger of 690 to 740 mV, the
286
maximum value of ICE (≈33 %) and the minimum value of EC (≈50 kWh [kg COD]-1) are
287
simultaneously achieved at 721±3mV, which can be considered as the optimum response
288
interval for electro-oxidation. Note that when ORP ≤ 690 mV the residual COD value of the
289
treated ROC was still larger than the target concentration (80 mg L-1).
291 292 293
TE D
EP
By converting Eq. (10), the relationship between Qsp and ORP, COD and chloride ion
AC C
290
M AN U
282
concentration can be obtained: !"# = 6.24 + 0.0009 ORP + 0.05 COD - 0.015 Cl-
(11)
Thus, to maintain a relatively constant ORP value, we can accordingly adjust the input of
294
Qsp by Eq. (11) when providing different concentrations of COD and chloride ion. A computer
295
control procedure based on back-propagation neural network (BPN) model was developed
296
with Matlab software to optimize the input of Qsp according to the content of residual 14
ACCEPTED MANUSCRIPT pollutants (Yu et al., 2013). The desired residual value of COD and the constant ORP value are
298
the two objective parameters to control. The initial content of pollutants in wastewater,
299
temperature, pH value and Chroma are the original parameters. The Qsp value was optimized
300
by the computer control procedure to control the ORP at a stable value, and the energy
301
consumption could be calculated at this constant ORP system during electro-oxidation
302
process. With the target residual COD value (80 mg L-1), the total energy consumption (TEC)
303
in constant-ORP system was 9.06 kWh m-3, while that for constant-current system was
304
12.04kWh m-3. Thus, the developed constant-ORP system can save the energy consumption
305
by 24.75% as compared to the constant-current system. Consequently, monitoring of ORP
306
has high potential to effectively optimize the electro-oxidation process.
M AN U
SC
RI PT
297
307
309
4． ．Conclusions
TE D
308
The electro-oxidation technique can be considered as an effective, feasible and robust
311
treatment method for ROC effluent in printing and dyeing factory by using PbO2/Ti electrode.
312
With a suitable specific electrical charge of 2.45 Ah L-1, high removal efficiencies of COD
313
(72 %), TN (18 %) and chroma (99 %) were achieved. FTIR analyses show that the
314
electro-oxidation technique has a significant degradation effects to the organic matters of
315
complex structures in ROC effluent. Additionally, the electro-oxidation process can also
316
simultaneously remove some inorganic ions. The quantitative relationship among ORP, Qsp,
317
COD and chloride ion concentration was established. This good correlation shows that the
318
ORP value gives a comprehensive indicator to the effect of current density, chloride ions,
AC C
EP
310
15
ACCEPTED MANUSCRIPT 319
pollutants and reaction time on the performance of electro-oxidation system. The developed
320
constant-ORP system showed the success of online monitoring of ORP in optimizing the
321
electro-oxidation process.
323
RI PT
322
Acknowledgements
The authors are grateful for the financial support provided by the National Natural
325
Science Foundation of China (Grant No.51278465) and the Transformation Projects in the
326
Science & Technology Pillar Program of Zhejiang Province (Grant No.20130176).
SC
324
AC C
EP
TE D
M AN U
327
16
ACCEPTED MANUSCRIPT 328
References
329 330 331
Bagastyo, A.Y., Batstone, D.J., Rabaey, K., Radjenovic, J., 2013. Electrochemical oxidation of
332 333
Benner, J., Salhi, E., Ternes, T., Von, G.U., 2008. Ozonation of reverse osmosis concentrate: kinetics and
334 335 336
Bonfatti, F., Ferro, S., Lavezzo, F., Malacarne, M., Lodi, G., Battisti, A.D., 2000. Electrochemical
337 338
Cao, J.L., Zhao, H.Y., Cao, F.H., Zhang, J.Q., Cao, CN., 2009. Electrocatalytic degradation of
339 340 341
Cao, Z., Wen, D.N., Chen, H., Wang, J.D., 2016. Simultaneous Removal of COD and Ammonia Nitrogen
342 343 344
Chatzisymeon, E., Dimou, A., Mantzavinos, D., Katsaounis, A., 2009. Electrochemical oxidation of
345 346
Chen, G.H., Hung, Y.T., 2007. Electrochemical Wastewater Treatment Processes. Humana Press. pp
347 348 349
Chen, Y.Y., Baygents, J.C., Farrell, J., 2017. Evaluating electrocoagulation and chemical coagulation for
350 351 352
Combernoux, N., Schrive, L., Labed, V., Wyart, Y., Carretier, E., Benony-Rhodier, A., Moulin, P., 2015.
353 354
Correa-Lozano, B., Comninellis, C., Battisti, A.D., 1997. Service life of Ti/SnO2–Sb2O5 anodes. J. Appl.
355 356 357
Ersever, I., Ravindran, V., Tsai, H.H., Pirbazari, M., 2014. Modeling and design of anaerobic fluidized
358 359 360
Espinoza, J.D.G., Drogui, P., Zolfaghari, M., Dirany, A., Ledesma, M.T.O., Gortáres-Moroyoqui, P., Buelna,
361 362 363
Fryda, M., Herrmann, D., Schafer, L., Klages, C.P., Perret, A., Haenni, W., Comninellis, C., Gandini, D.,
electrodialysed reverse osmosis concentrate on Ti/Pt-IrO2, Ti/SnO2-Sb and boron-doped diamond
efficiency of beta blocker oxidation. Water Res. 42, 3003-12.
RI PT
electrodes. Water Res. 47, 242-250.
Incineration of Glucose as a Model Organic Substrate. I. Role of the Electrode Material. J. Electrochem. Soc. 146, 2175-2179.
SC
4-chlorophenol on F-doped PbO2 anodes. Electrochim. Acta. 54, 2595-2602.
Electrochem. Soc. 11, 4018-4026.
M AN U
Using a Novel Electro-Oxidation Reactor: A Technical and Economic Feasibility Study. Int. J.
model compounds and olive mill wastewater over DSA electrodes: 1. The case of Ti/IrO2 anode. J. Hazard. Mater. 167, 268-274.
TE D
866-8.
removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions. J. Water Process. Eng. 16, 50-55.
EP
Study of polyamide composite reverse osmosis membrane degradation in water under gamma
AC C
rays. J. Membr. Sci. 480, 64-73.
Electrochem. 27, 970-974.
bed reactor with recycling for denitrification of reverse osmosis concentrates. Chem. Eng. Sci. 108, 111-122.
G., 2016. Performance of electrochemical oxidation process for removal of di (2-ethylhexyl) phthalate. Environ. Sci. Pollut. R. 23, 12164-12173.
1999. Properties of Diamond Electrodes for Wastewater Treatment. New Diam. Front. C. Technol. 9, 229-240. 17
ACCEPTED MANUSCRIPT 364 365
He, H.J., Chen, Y.J., Li, X., Cheng, Y., Yang, C.P., Zeng, G.M., 2016. Influence of salinity on
366 367 368
Hege, K.V., Verhaege, M., Verstraete, W., 2002. Indirect electrochemical oxidation of reverse osmosis
369 370
Hou, H.X., Chen, L.Q., Wang, S.Y., Mino, T., Satoh, H., 2006. Use ORP to control simultaneous
371 372
Kishimoto, N., Yu, N., Kato, M., Otsu, H., 2015. Effect of oxidation–reduction potential on an
373 374 375
Lu, J., Fan, L.H., Roddick, F.A., 2013. Potential of BAC combined with UVC/H2O2 for reducing organic
376 377
Pérez-González, A., Urtiaga, A.M., Ibáñez, R., Ortiz, I., 2012. State of the art and review on the
378 379
Pérez-González, A., Fernández-Alba, A.R., Urtiaga, A.M., Ortiz, I., 2010. Electro-oxidation of reverse
380 381 382
Qu, D., Wang, J., Wang, L.L., Hou, D.Y., Luan, Z.K., Wang, B.Q., 2009. Integration of accelerated
383 384
Radjenovic, J., Bagastyo, A., Batstone, D., Keller, J., 2013. Electrochemical Treatment of Reverse
385 386 387
Cossu, R., Polcaro, A.M., Lavagnolo, M.C., Mascia, M., Palmas, S., Renoldi, F., 1998. Electrochemical
388 389 390
Raghu, S., Chang, W.L., Chellammal, S., Palanichamy, S., Basha, C.A., 2009. Evaluation of
391 392 393
Rocha, J.H.B., Gomes, M.M.S., Fernandes, N.S., Silva, D.R.D., Martínez-Huitle, C.A., 2012. Application
394 395
Santos, I.D., Dezotti, M., Dutra, A.J.B., 2013. Electrochemical treatment of effluents from petroleum
396 397 398
Silva, L.M.D., Faria, L.A.D., Boodts, J.F.C., 2002. Electrochemical impedance spectroscopic (EIS)
399 400
Šostar-Turk, S., Simonič, M., Petrinić, I., 2005. Wastewater treatment after reactive printing. Dyes and
microorganisms in activated sludge processes: A review. Int. Biodeter. Biodegr. 119, 520-527.
membrane concentrates at boron-doped diamond electrodes. Electrochem. Commun. 4, 296-300.
electrochemical Fenton-type process. Chem. Eng. J. 260, 590-595.
RI PT
nitrification and denitrification in oxidation ditch process. J. B. Univ. Technol. 32, 1093-1096.
reclamation. Chemosphere 93, 683-688.
SC
matter from highly saline reverse osmosis concentrate produced from municipal wastewater
M AN U
treatment technologies of water reverse osmosis concentrates. Water Res. 46, 267-283.
osmosis concentrates generated in tertiary water treatment. Water Res. 44, 2763-2772.
precipitation softening with membrane distillation for high-recovery desalination of primary
TE D
reverse osmosis concentrate. Sep. Purif. Technol. 67, 21-25.
Osmosis Concentrates. Anal. Chem. 86, 3764-72.
Treatment of Landfill Leachate: Oxidation at Ti/PbO2 and Ti/SnO2 Anodes. Environ. Sci. Technol.
EP
32, 3570-3573.
electrochemical oxidation techniques for degradation of dye effluents—A comparative approach.
AC C
J. Hazard. Mater. 171, 748-754.
of electrochemical oxidation as alternative treatment of produced water generated by Brazilian petrochemical industry. Fuel Process. Technol. 96, 80-87.
industry using a Ti/RuO 2 anode. Chem. Eng. J. 226, 293-299.
investigation of the deactivation mechanism, surface and electrocatalytic properties of Ti/RuO2(x)+Co3O4(1−x) electrodes. J. Electroanal. Chem. 532, 141-150.
Pigments 64, 147-152. 18
ACCEPTED MANUSCRIPT 401 402
Xu, Q.K., 2010. Study on advanced treatment of textile wastewater. Dissertation, South China Normal
403 404
Weng, M.L., Pei, J.C., 2016. Electrochemical oxidation of reverse osmosis concentrate using a novel
405 406 407
Wu, H., Wang, S., 2012. Impacts of operating parameters on oxidation-reduction potential and
408 409
Yao, J.C., Wen, D.N., Shen, J.N., Wang, J.D., 2016. Zero discharge process for dyeing wastewater
410 411 412
Yu, R.F., Lin, C.H., Chen, H.W., Cheng, W.P., Kao, M.C., 2013. Possible control approaches of the
413 414
Yu, R.F., Chi, F.H., Cheng, W.P., Wang, M.H., 2015. Online monitoring of the nanoscale zero-valent iron
415 416
Zhao, C.X., Gu, P., Cui, H.Y., Zhang, G.H., 2012. Reverse osmosis concentrate treatment via a PAC-MF
417 418 419
Zhou, M.H., Liu, L., Jiao, Y.L., Wang, Q., Tan, Q.Q., 2011. Treatment of high-salinity reverse osmosis
420 421
Zhou, M.H., Tan, Q.Q., Wang, Q., Jiao, Y.L., Oturan, N., Oturan, M.A., 2012. Degradation of organics in
422 423
Zhu, R.Y., Yang, C.Y., Zhou, M.M., Wang, J.D. 2015. Industrial park wastewater deeply treated and
424 425 426 427
Zou, J., Peng, X., Miao, L., Ying, X., Bing, W., Dong, F., Wang, B., 2016. Electrochemical oxidation of COD
University (in Chinese).
electrode: Parameter optimization and kinetics study. Desalination 399, 21-28.
J. Hazard. Mater. 243, 86-94.
treatment. J. Water Process. Eng. 11, 98-103.
RI PT
pretreatment efficacy in the pretreatment of printing and dyeing wastewater by Fenton process.
Electro-Fenton process for textile wastewater treatment using on-line monitoring of DO and ORP.
SC
Chem. Eng. J. 218, 341-349.
M AN U
process for trichloroethylene wastewater treatment. Int. J. Environ. Sci. Technol. 12, 1647-1656.
accumulative countercurrent adsorption process. Water Res. 46, 218-226.
concentrate by electrochemical oxidation on BDD and DSA electrodes. Desalination 277,
TE D
201-206.
reverse osmosis concentrate by electro-Fenton process. J. Hazard. Mater. 287, 215-216.
EP
reused by a novel electrochemical oxidation reactor. Chem. Eng. J. 260, 427-433.
from real textile wastewaters: Kinetic study and energy consumption. Chemosphere 171,
AC C
332-338.
19
ACCEPTED MANUSCRIPT 428
Tables and Figures
429
Table 1. General characteristics of the ROC effluent. Physical-chemical properties COD
272±10 mg L-1 -1
Inorganic ions Na+
40.6 mg L-1
40.8 mg L
TP
1.8 mg L-1
Ca2+
26.9 mg L-1
pH
8.3
Mg2+
7.5 mg L-1
Chroma
160 times
NH4+
4.0 mg L-1
Conductivity
17.0 ms cm-1
SO42-
4739.9 mg L-1
TDS
8.49 g L-1
Cl-
1471.8 mg L-1
NO3F-
430 431
TN
TE D
COD
0.6 mg L-1
RCOD = -203.6 exp(-Qsp/1.993) + 241.6
0.948
0.217
RTN = -9.78 exp(-Qsp /5.913) + 11.6
0.931
0.021
0.898
0.258
RCOD (mg L-1), RTN (mg L-1) and RChroma (times) are the specific removal of COD, TN and chroma, respectively; Qsp is the specific electrical charge (Ah L-1).
AC C
a
EP
Chroma RChroma = -85.9 exp(-Qsp /0.879) + 156.5
436 437
1.3 mg L-1
Table 2. Regression equations, coefficients and rate constants for the dependences of the special removals of COD, TN and chroma on the specific electrical charge. rate constants regression equationa regression coefficient (R2) (k,s-1)
432 433
434 435
24.9 mg L-1
M AN U
PO43-
RI PT
TN
SC
K
4330.5 mg/L
+
20
438
Fig.1. Diagram of experimental setup of eletro-oxidation.
440
RTN (mg L
-1
)
12 9
TN RTN
6
TE D
) -1
EP
Chroma RChroma
135
AC C
RChroma (Times)
150
120
45 30 15
105
0 0
3
6
9
-1
Qsp (Ah L
12
Chroma (Times)
0 60
)
75
90 45
442 443 444
150
-1
RCOD (mg L
135
COD (mg L
225 COD RCOD
180
441
30 300
225
90
33
)
270
36
-1
3
39
TN (mg L
M AN U
439
SC
RI PT
ACCEPTED MANUSCRIPT
15
)
Fig.2. Effect of specific electric charge on COD, TN and chroma removal efficiencies; the initial values of COD, TN and chroma were 272 mg L-1, 40.82 mg L-1, and 160 Times, respectively.
445 446 21
ACCEPTED MANUSCRIPT 447 29 TCE
18
TEC
28
RI PT
TCE (%)
27
TEC (kWh m )
15
12
-3
26
25
5
10
15
20
SC
9
25
-2
current density (mA cm )
Fig. 3. The influence of current density on the total current efficiency (TCE) and the total energy consumption (TEC); the residual COD value was set as 80 mg L-1.
451 800
400 200 0 -200
EP
8
453 454 455
AC C
452
0
200 150 100 50 1400
pH
1200
-
Cl
7 6
250
1000 1
2
3
Cl- (mg L-1)
9
pH
ORP COD
TE D
ORP (mV)
600
300
COD (mg L-1)
M AN U
448 449 450
800
-1
Qsp (Ah L )
Fig. 4. The effect of Qsp on the values of ORP, pH, COD and chloride ion concentration; current density: 10 mA cm-2, reaction time: 40 min.
456 457 458 459 22
ACCEPTED MANUSCRIPT
M AN U
461 462 463
SC
RI PT
460
Fig. 5. The relationship between energy consumption (EC), instantaneous current efficiency (ICE) and ORP during the electro-oxidation process.
AC C
EP
TE D
464
23