Using single-chamber microbial fuel cells as renewable power sources of electro-Fenton reactors for organic pollutant treatment

Journal of Hazardous Materials 252–253 (2013) 198–203

Contents lists available at SciVerse ScienceDirect

Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat

Using single-chamber microbial fuel cells as renewable power sources of electro-Fenton reactors for organic pollutant treatment Xiuping Zhu, Bruce E. Logan ∗ Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States

h i g h l i g h t s  A new type of electro-Fenton system was developed for wastewater treatment.  Degradation efficiency of organic pollutants was substantially improved.  Operation cost was greatly reduced compared to other microbial fuel cell designs.

a r t i c l e

i n f o

Article history: Received 9 January 2013 Received in revised form 23 February 2013 Accepted 25 February 2013 Available online 5 March 2013 Keywords: Fenton Pollutant Microbial fuel cell Bioelectrochemical

a b s t r a c t Electro-Fenton reactions can be very effective for organic pollutant degradation, but they typically require non-sustainable electrical power to produce hydrogen peroxide. Two-chamber microbial fuel cells (MFCs) have been proposed for pollutant treatment using Fenton-based reactions, but these types of MFCs have low power densities and require expensive membranes. Here, more efficient dual reactor systems were developed using a single-chamber MFC as a low-voltage power source to simultaneously accomplish H2 O2 generation and Fe2+ release for the Fenton reaction. In tests using phenol, 75 ± 2% of the total organic carbon (TOC) was removed in the electro-Fenton reactor in one cycle (22 h), and phenol was completely degraded to simple and readily biodegradable organic acids. Compared to previously developed systems based on two-chamber MFCs, the degradation efficiency of organic pollutants was substantially improved. These results demonstrate that this system is an energy-efficient and cost-effective approach for industrial wastewater treatment of certain pollutants. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Fenton reactions, based on the reaction of hydrogen peroxide (H2 O2 ) with ferrous ion (Fe2+ ) to generate hydroxyl radicals, have attracted great attention for industrial wastewater treatment due to the strong oxidation potential of hydroxyl radicals. Previous studies [1–4] have demonstrated that Fenton reactions are effective in degrading many organic pollutants, including phenols, anilines, dyes, pesticides, and heteroaromatic derivatives. However, conventional chemical Fenton processes require chemical storage and transport of unstable H2 O2 and the addition of ferrous salts [5,6]. Electro-Fenton processes have been proposed to generate in situ H2 O2 and Fe2+ , which have higher reaction efficiencies and therefore are of great interest [7–10]. However, the process requires the use of electrical power, and thus the process could be more useful and sustainable by developing Fenton-based systems that do not require either chemical addition or electrical grid energy.

∗ Corresponding author. Tel.: +1 814 863 7908; fax: +1 814 863 7304. E-mail address: [email protected] (B.E. Logan). 0304-3894/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2013.02.051

Microbial fuel cells (MFCs) are bioelectrochemical systems that use bacteria to oxidize organic wastes and generate electricity [11–13]. Microorganisms on the anode oxidize organic substrates and simultaneously generate electrons and protons. The electrons are transferred to the cathode through external circuit, and protons are released into solution. At the cathode, oxygen reacts with electrons and protons to form water. In the past decade, MFCs have been extensively investigated due to the advantage of recovering green energy (electricity) from wastewaters and waste biomass sources. The power output of MFCs has increased from only a few milliwatts per square meter of electrode to 4.3 W/m2 [14–16]. These higher power densities could therefore make it practical to use MFCs as power sources for electro-Fenton systems. Two-chamber MFCs have been previously investigated as a method to degrade pollutants using electro-Fenton reactions, but these systems have had very poor performance due to the intrinsic setup of the system [17–19]. In two-chamber MFCs, the electrons generated by bacteria on the anode are used to reduce oxygen to H2 O2 on the cathode, but a membrane must be used to prevent oxygen and H2 O2 from reaching the anode. At the cathode, the H2 O2 reacts with Fe2+ (added or released from certain types of cathodes)

X. Zhu, B.E. Logan / Journal of Hazardous Materials 252–253 (2013) 198–203

Fig. 1. Schematic diagram of the electro-Fenton system powered by a singlechamber MFC.

to form hydroxyl radicals that can then be used to degrade pollutants such as p-nitrophenol and various dyes (Rhodamine B and Orange II). Two-chamber MFCs have low power output (relative to single-chamber, air-cathode designs), due to the high internal resistance produced by the membrane, and the low pH produced in the anode chamber (which reduces current production by bacteria) due to the inefficient transport of protons across the membrane. Also, H2 O2 will damage the membrane, ferrous salts or specific cathodes (such as carbon nanotube/␥-FeOOH and carbon felt/Fe@Fe2 O3 ) are needed to provide Fe2+ , and membranes can become fouled by iron [20,21]. Recently, a different type of electro-Fenton process was proposed where a two-chamber MFC was used to accelerate in situ generation of Fe2+ from sacrificial iron. However, this system required the addition of H2 O2 because it could not be generated in situ in this system [22]. For these reasons, two-chambered MFCs do not appear to be a feasible approach for pollutant degradation using Fenton reactors. A modified type of electro-Fenton system is presented here that overcomes the limitations of previous systems by using a single-chamber MFC to drive H2 O2 and Fe2+ production in a second electrochemical reactor. H2 O2 is produced on a cathode made of carbon felt, while Fe2+ is released from a sacrificial iron anode in an undivided electrochemical reactor that is separate from the MFC. The feasibility of this system was examined using phenol as the model pollutant, because phenol is a typical pollutant in many industrial wastewaters [23,24]. This modified type of treatment system may provide a more energy-efficiency and cost-effective approach for industrial wastewater treatment. 2. Materials and methods

199

A carbon fiber brush (2.5 cm diameter, 2.5 cm length, 0.22 m2 total fiber area) was used as the anode, which had been heat treated at 450 ◦ C for 30 min [25]. A piece of carbon cloth with a 0.5 mg-Pt cm−2 catalyst layer on the water side was used as the air cathode (projected surface area of 7 cm2 ). No membrane was used between the anode and the cathode. To reduce oxygen diffusion to the anode, four polytetrafluoroethylene layers were coated on the air side of the cathode [26]. The brush anode was placed horizontally in the center of the cylindrical chamber and the air cathode was vertically placed on the other end of the same chamber, with the tip of the brush anode 1.25 cm from the air cathode. MFCs were inoculated using the effluent of other MFCs, and operated with an external resistance of 1000  at room temperature (about 25 ◦ C). The medium contained (per L): 1 g sodium acetate, 4.28 g Na2 HPO4 , 2.45 g NaH2 PO4 ·H2 O, 0.31 g NH4 Cl, 0.13 g KCl, 12.5 mL minerals, and 5 mL vitamins [27]. The voltages across the external resistors were recorded every 20 min using a multimeter data acquisition system (model 2700 Keithley Instruments). When reproducible cycles were obtained, these MFCs were then tested as the power source for the electro-Fenton reactors. Electro-Fenton reactors were constructed using a 100 mL bottle. An iron plate (2 cm × 2 cm) used as the anode was connected to the MFC cathode using a copper wire. A piece of carbon felt the same size as the cathode was connected to the MFC anode also using a copper wire. Carbon felt cathodes were used in this study because previous studies [17,28] have demonstrated oxygen can be effectively reduced to H2 O2 using this material, and they are relatively inexpensive. The distance between the anode and the cathode was about 2 cm, which is common in electro-Fenton systems [9,29]. For every experiment, 80 mL of phenol wastewater (1 mM phenol + 50 mM KH2 PO4 ) was added to the medium bottle and pH was adjusted to 3, 5, or 7 using 85% H3 PO4 and 0.2 M NaOH. Phosphate buffer was used here to avoid significant changes in pH during the experiments. The reactor solution was bubbled using a porous diffusor. Samples were withdrawn from the bottle and filtered through 0.22 ␮m-porosity polytetrafluoroethylene (PTFE) membranes prior to chemical analysis. Experiments were carried out under normal lab daylight and room temperatures (25–30 ◦ C). Every experiment was repeated at least two times. 2.2. Electrical power analysis The cell voltages and electrode potentials of the MFCs and the electro-Fenton reactors were recorded using a multimeter data acquisition system (model 2700 Keithley Instruments). To measure the potentials of the electrodes in the MFCs and electro-Fenton reactors, Ag/AgCl reference electrodes were inserted into the reactors. All potentials were reported here versus Ag/AgCl, which was +210 mV vs. a standard hydrogen electrode. To perform polarization tests, a resistor box was connected between the MFC anodes and the electro-Fenton cathodes (Fig. 1). The resistances were manually varied from open circuit to 5000 , 1000 , 500 , 100  and 0 , and the cell voltages and electrode potentials of the MFCs and the electro-Fenton reactors were recorded. The power output of the MFCs connected to the electroFenton reactors (P, mW/m2 ) was calculated using P = UI/A, where U is the cell voltage of MFCs (V), I is the current (A), and A is the cathode area of the electro-Fenton reactors (4 cm2 ).

2.1. Reactors construction and operation

2.3. Chemical analysis

The schematic diagram of our modified electro-Fenton system powered by a single-chamber MFC is shown in Fig. 1. MFCs were constructed from a solid cube of Lexan with a cylindrical chamber 4 cm long by 3 cm in diameter (empty bed volume of 28 mL).

Phenol and degradation intermediates were measured using a high-performance liquid chromatography (Shimadzu LC-20AT) equipped with an Allure® Organic Acids 5 ␮m column and a diode array detector set at a wavelength of 210 nm. The mobile phase was

200

X. Zhu, B.E. Logan / Journal of Hazardous Materials 252–253 (2013) 198–203

Fig. 2. Cell voltages of MFCs with 1000  external resistance and in the electroFenton system at pH 3, pH 5, and pH 7.

50 mM KH2 PO4 buffer (pH 2.31 adjusted by H3 PO4 ) at a flow rate of 1.0 mL min−1 . Total organic carbon (TOC) analysis was performed with a Shimadzu TOC-VCSN Total Organic Carbon analyzer. Hydroxyl radicals were detected through a spin trap by N,Ndimethyl-p-nitrosoaniline (RNO) [30,31]. For every test, 80 mL of 50 mM KH2 PO4 buffer (pH 3, pH 5, or pH 7) containing 200 ␮M RNO was added to the electro-Fenton reactor, and the bleaching of the yellow color (RNO) was monitored at 440 nm using a spectrophotometer (DR2700, HACH). 3. Results 3.1. Electrical performance and electron-transfer mechanisms of this system Single-chamber MFCs were incubated for about one month at an external resistance of 1000 , until reproducible cycles of voltage production were obtained (Fig. 2). These MFCs were then used as power sources for the electro-Fenton reactors to degrade phenol in solutions at three different initial pHs of 3, 5, and 7. The voltages produced by the MFCs in the system were 0.2–0.3 V at pH 3 and pH 5, and 0.5–0.6 V at pH 7 (Fig. 2). Good repeatability was exhibited for consecutive multiple cycles. The higher voltage at pH 7 was due to the larger resistance of the electro-Fenton reactors (about 750 ) compared to those at pH 3 and pH 5 (50–100 ) since the Fenton reaction and iron corrosion are slower at neutral pH. In order to examine the electrical performance of this system, we conducted polarization tests at three different pHs (Fig. 3). When the external resistance was zero (no resistor in the circuit between the MFCs and the electro-Fenton reactors), the power densities were 1746 ± 100 mW/m2 (pH 3), 1964 ± 150 mW/m2 (pH 5), and 630 ± 100 mW/m2 (pH 7). These results show that the power densities that can be produced here are much higher than those achieved in two-chamber electro-Fenton systems (300–500 mW/m2 ) [17–19]. Based on the potentials of MFC anodes, MFC cathodes, electroFenton anodes, and electro-Fenton cathodes during polarization tests (supporting information Fig. S1), the electron transfer processes in the proposed system should proceed as shown in Fig. 1. At the MFC anode, acetate is oxidized to CO2 by bacteria, and electrons and protons are produced (Eq. (1)). These electrons are transferred to the cathode of the electro-Fenton reactor through copper wires, where oxygen is reduced to H2 O2 (Eq. (2)). At the anode of the electro-Fenton reactors, iron is oxidized to Fe2+ , and electrons are released (Eq. (3)) to the cathode of the MFCs where oxygen is

Fig. 3. Power density curves of MFCs in the electro-Fenton system at pH 3, pH 5, and pH 7.

reduced to water (Eq. (4)). In the electro-Fenton reactors, H2 O2 reacts with Fe2+ to produce hydroxyl radicals to oxidize organic pollutants (Eq. (5)). Only the primary reactions were considered here. Other reactions might also occur in the electro-Fenton reactors, such as the oxidation of Fe2+ to Fe3+ by oxygen (Eq. (6)) and the reduction of Fe3+ to Fe2+ at the cathode (Eq. (7)). At pH 3, the cathode potentials of electro-Fenton reactors were very low (−0.72 V) when MFC was directly connected, which would improve the efficiency of H2 O2 generation. On the other hand, the anode potentials of electro-Fenton reactors increased from −0.6 V to −0.4 V with a decrease in the external resistance, which would enhance iron corrosion and performance. CH3 COO− + 2H2 O → 2CO2 + 7H+ + 8e

(1)

O2 + 2H+ + 2e → H2 O2

(2)

Fe → Fe

2+

+ 2e

(3)

+

O2 + 4H + 4e → H2 O 2+

Fe

2+

Fe

3+

Fe

(4) −

+ H2 O2 → OH + OH + Fe +

+ O2 + 4H → Fe + e → Fe

3+

3+

+ 2H2 O

2+

(5) (6) (7)

In order to confirm the generation of hydroxyl radicals by a Fenton reaction, hydroxyl radical concentrations in the electroFenton reactors powered by the MFCs were measured after 4 h (Fig. 4). The measured concentrations were 166 ± 8 ␮M (pH 3), 107 ± 40 ␮M (pH 5), and 12 ± 10 ␮M (pH 7). The highest concentrations of hydroxyl radicals were generated at pH 3, in agreement with the power output of MFCs at different pHs and the expected optimum conditions for Fenton reactions [1,10,32]. 3.2. Phenol degradation rate and pathway The concentrations of phenol and TOC were monitored over time during a fed batch cycle (22 h) (Fig. 5). When MFCs were connected to power the electro-Fenton reactors, the removal rates of phenol and TOC were significantly enhanced for the pH 3 and pH 5 conditions, with little change at pH 7. The optimal pH condition was pH 3, consistent with the electric performance of this system and known ideal conditions for Fenton-based reactions. After 22 h, phenol was completely removed and TOC was reduced by 75 ± 2%. Controls (no power added) were also conducted under the same conditions to examine phenol losses due to adsorption, volatilization, and precipitation. For the control experiment at pH 3, there was appreciable removal of phenol and TOC, which was likely due

X. Zhu, B.E. Logan / Journal of Hazardous Materials 252–253 (2013) 198–203

201

Fig. 4. Hydroxyl radical concentration in electro-Fenton reactors at pH 3, pH 5, and pH 7 after powered by MFCs for 4 h.

to increased rates of iron corrosion and consequently more effective precipitation than at pH 5 and pH 7. To investigate the stability of the electro-Fenton system for degradation, experiments were conducted at these different pHs over multiple cycles (5 times). Each time MFCs were replenished with fresh medium, the electro-Fenton reactors were rinsed using DI water and refilled with solutions containing phenol at the indicated pH. The extent of phenol removal showed good repeatability for each condition. After 6 h treatment, the phenol removals were maintained at 95% (pH 3), 80% (pH 5), and 35% (pH 7) (Fig. 6a). TOC removals during a cycle had larger variations, especially for pH 5 and pH 7 conditions (Fig. 6b). These variations could be partly a

Fig. 6. (A) Phenol removal after 6 h and (B) TOC removal after 22 h in the electroFenton system for five repeated experiments, under different pH conditions (pH 3, pH 5, and pH 7).

Fig. 5. Evolution of (A) phenol and (B) TOC concentration over time in the electroFenton system under different pH conditions (pH 3, pH 5, and pH 7).

consequence of the measurement method. For TOC analyses, samples were highly diluted (10×) in order to measure TOC concentrations in the range of the instrument (0 to 10 mg L−1 ), making the low TOC of the dilution water (0.2–0.5 mg/L) and dissolved CO2 (especially at pH 5 and 7) a greater contributor to variations in the calculated TOC changes. The intermediates formed during phenol degradation at different pHs were also monitored (Fig. 7). Five main intermediates were identified: hydroquinone, fumaric acid, maleic acid, oxalic acid, and formic acid. After 3 h, approximately 85% of removed phenol was degraded to intermediates based on carbon balance, consistent with Fenton reactions being important in this system. The remaining 15% of the phenol was likely lost to adsorption, volatilization, and precipitation. Many more intermediates were produced at pH 3 than at the other two pH conditions, due to the faster phenol degradation rate (Fig. 7). Complex intermediates (hydroquinone, fumaric acid, and maleic acid) were gradually degraded to simple carboxylic acids, and finally mineralized to CO2 . After one cycle (22 h), little simple carboxylic acids (oxalic acid and formic acid) remained in the system. These end products are similar to those formed from phenol by other advanced oxidation processes, such as ozonation, electrochemical oxidation, and photocatalysis [33–35]. In general, phenol degradation proceeded in three steps. First, aromatic intermediates (e.g., hydroquinone) were formed through a series of radical reactions initiated by hydroxyl radicals. Second, aromatic intermediates were degraded with ring breakage to various carboxylic acids (i.e., fumaric acid, maleic acid, oxalic acid, and formic acid). Finally, carboxylic acids were completely mineralized

202

X. Zhu, B.E. Logan / Journal of Hazardous Materials 252–253 (2013) 198–203

TOC was removed by 70–80% after 22 h. The anode and cathode (electro-Fenton) chamber volumes in previous two-chamber MFC electro-Fenton systems were usually the same, but here the electroFenton reactor volume (80 mL) was about three times that of the MFC volume, allowing for a treatment of a larger volume of wastewater per volume of solution used in the MFC. This situation allows more efficient degradation of pollutants than previous systems, which was due to the improved power densities produced by using the single-chamber MFCs. Moreover, previous systems contained expensive membranes and chemically-amended cathodes (such as carbon nanotube/␥-FeOOH and carbon felt/Fe@Fe2 O3 ), or required Fe2+ addition. The modified electro-Fenton system here has circumvented these disadvantages. Compared to previous electro-Fenton systems that required addition of H2 O2 and Fe2+ release from iron driven by a MFC [22], the operation costs of the electro-Fenton system here should be much less due to the lack of a need for H2 O2 or expensive membranes. For example, in a previous test 0.63 kg of H2 O2 solution was needed to treat 1000 kg of industrial wastewater [22], and the current price of industrial grade H2 O2 is $390–500 per ton. Proton exchange membranes can cost about $100 per square meter or more. One disadvantage of the proposed electro-Fenton system here is that it needs to be operated under acidic conditions, so it is best suited for treating acidic industrial wastewaters, or the wastewater pH would need to be adjusted. Additionally, acetate was used as the substrate in MFCs. If other biodegradable wastewaters were used, or the effluents of electro-Fenton reactors with simple organic acids were utilized to feed the MFCs, the overall process would become more energy-efficient and cost-effective. 5. Conclusions A modified two-reactor electro-Fenton system based on using the power produced by a single-chamber MFC to drive a Fenton reactor was shown to be an effective method for phenol degradation under acidic conditions. After one cycle (22 h), phenol was completely degraded to simple organic acids (such as oxalic acid and formic acid) and 75% of the TOC was removed. Compared to previous electro-Fenton systems with two-chamber MFCs, the degradation efficiency of organic pollutants was substantially improved and the operation cost was greatly reduced. This process is therefore a very promising method for treating acidic industrial wastewaters containing organic pollutants that can be degraded using Fenton reactions. Acknowledgement Fig. 7. Intermediates formed during phenol degradation in the electro-Fenton system under different pH conditions: (A) pH 3, (B) pH 5, and (C) pH 7.

to CO2 . These results suggested that the electro-Fenton system will be useful to pretreat industrial wastewaters, and that the effluent of this treatment could be used as influent for power production in MFCs. 4. Discussion The use of a single-chamber MFC for providing power to an electro-Fenton reactor can be an effective method for phenol degradation. The pollutant degradation rates were similar to previous electro-Fenton systems using two-chamber MFCs where H2 O2 was generated at the cathodes (requiring Fe2+ addition or ironamended cathodes) [17–19]. Phenol was 95% degraded within 6 h here, compared to 70–90% removals for p-nitrophenol, Rhodamine B, and Orange II in previous systems within the same time (6 h).

The authors acknowledge support from the King Abdullah University of Science and Technology (KAUST) by Award KUS-I1003-13. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jhazmat. 2013.02.051. References [1] J.J. Pignatello, E. Oliveros, A. MacKay, Advanced oxidation processes for organic contaminant destruction based on the Fenton reaction and related chemistry, Crit. Rev. Environ Sci. Technol. 36 (2006) 1–84. [2] E. Brillas, I. Sires, M.A. Oturan, Electro-Fenton process and related electrochemical technologies based on Fenton’s reaction chemistry, Chem. Rev. 109 (2009) 6570–6631.

X. Zhu, B.E. Logan / Journal of Hazardous Materials 252–253 (2013) 198–203 [3] R.C. Martins, A.F. Rossi, R.M. Quinta-Ferreira, Fenton’s oxidation process for phenolic wastewater remediation and biodegradability enhancement, J. Hazard. Mater. 180 (2010) 716–721. [4] N. Masomboon, C. Ratanatamskul, M.C. Lu, Kinetics of 2,6-dimethylaniline oxidation by various Fenton processes, J. Hazard. Mater. 192 (2011) 347–353. [5] C.C. Jiang, J.F. Zhang, Personal review: progress and prospect in electro-Fenton process for wastewater treatment, J. Zhejiang Univ. -Sc. A 8 (2007) 1118–1125. [6] M. Umar, H.A. Aziz, M.S. Yusoff, Trends in the use of Fenton, electro-Fenton and photo-Fenton for the treatment of landfill leachate, Waste Manage. 30 (2010) 2113–2121. [7] H. Zhang, C.Z. Fei, D.B. Zhang, F. Tang, Degradation of 4-nitrophenol in aqueous medium by electro-Fenton method, J. Hazard. Mater. 145 (2007) 227–232. [8] H. Liu, C. Wang, X.Z. Li, X.L. Xuan, C.C. Jiang, H.N. Cui, A novel electro-Fenton process for water treatment: reaction-controlled pH adjustment and performance assessment, Environ. Sci. Technol. 41 (2007) 2937–2942. [9] M.H. Zhou, Q.Q. Tan, Q. Wang, Y.L. Jiao, N. Oturan, M.A. Oturan, Degradation of organics in reverse osmosis concentrate by electro-Fenton process, J. Hazard. Mater. 215 (2012) 287–293. [10] M. Panizza, G. Cerisola, Electro-Fenton degradation of synthetic dyes, Water Res. 43 (2009) 339–344. [11] B.E. Logan, B. Hamelers, R.A. Rozendal, U. Schrorder, J. Keller, S. Freguia, P. Aelterman, W. Verstraete, K. Rabaey, Microbial fuel cells: methodology and technology, Environ. Sci. Technol. 40 (2006) 5181–5192. [12] A.E. Franks, K.P. Nevin, Microbial fuel cells, a current review, Energies 3 (2010) 899–919. [13] K. Rabaey, W. Verstraete, Microbial fuel cells: novel biotechnology for energy generation, Trends Biotechnol. 23 (2005) 291–298. [14] S.K. Chaudhuri, D.R. Lovley, Electricity generation by direct oxidation of glucose in mediatorless microbial fuel cells, Nat. Biotechnol. 21 (2003) 1229–1232. [15] B.H. Kim, H.S. Park, H.J. Kim, G.T. Kim, I.S. Chang, J. Lee, N.T. Phung, Enrichment of microbial community generating electricity using a fuel-cell-type electrochemical cell, Appl. Microbiol. Biotechnol. 63 (2004) 672–681. [16] Y.Z. Fan, S.K. Han, H. Liu, Improved performance of CEA microbial fuel cells with increased reactor size, Energy Environ. Sci. 5 (2012) 8273–8280. [17] X.P. Zhu, J.R. Ni, Simultaneous processes of electricity generation and pnitrophenol degradation in a microbial fuel cell, Electrochem. Commun. 11 (2009) 274–277. [18] L. Zhuang, S.G. Zhou, Y. Yuan, M. Liu, Y.D. Wang, A novel bioelectro-Fenton system for coupling anodic COD removal with cathodic dye degradation, Chem. Eng. J. 163 (2010) 160–163. [19] C.H. Feng, F.B. Li, H.J. Mai, X.Z. Li, Bio-electro-Fenton process driven by microbial fuel cell for wastewater treatment, Environ. Sci. Technol. 44 (2010) 1875–1880. [20] K.H. Choo, H. Lee, S.J. Choi, Iron and manganese removal and membrane fouling during UF in conjunction with prechlorination for drinking water treatment, J. Membr. Sci. 267 (2005) 18–26.

203

[21] R.A. Assink, Fouling mechanism of separator membranes for the iron chromium redox battery, J. Membr. Sci. 17 (1984) 205–217. [22] X. Liu, X. Sun, D. Li, W. Li, Y. Huang, G. Sheng, H. Yu, Anodic Fenton process assisted by a microbial fuel cell for enhanced degradation of organic pollutants, Water Res. 46 (2012) 4371–4378. [23] D. Rajkumar, K. Palanivelu, Electrochemical treatment of industrial wastewater, J. Hazard. Mater. 113 (2004) 123–129. [24] J. Iniesta, E. Exposito, J. Gonzalez-Garcia, V. Montiel, A. Aldaz, Electrochemical treatment of industrial wastewater containing phenols, J. Electrochem. Soc. 149 (2002) D57–D62. [25] Y. Feng, Q. Yang, X. Wang, B.E. Logan, Treatment of carbon fiber brush anodes for improving power generation in air-cathode microbial fuel cells, J. Power Sources 195 (2010) 1841–1844. [26] S. Cheng, H. Liu, B.E. Logan, Increased performance of single-chamber microbial fuel cells using an improved cathode structure, Electrochem. Commun. 8 (2006) 489–494. [27] S. Cheng, D. Xing, D.F. Call, B.E. Logan, Direct biological conversion of electrical current into methane by electromethanogenesis, Environ. Sci. Technol. 43 (2009) 3953–3958. [28] S. Irmak, H.I. Yavuz, O. Erbatur, Degradation of 4-chloro-2-methylphenol in aqueous solution by electro-Fenton and photoelectro-Fenton processes, Appl. Catal. B: Environ. 63 (2006) 243–248. [29] K. Cruz-Gonzalez, O. Torres-Lopez, A. Garcia-Leon, J.L. Guzman-Mar, L.H. Reyes, A. Hernandez-Ramirez, J.M. Peralta-Hernandez, Determination of optimum operating parameters for Acid Yellow 36 decolorization by electro-Fenton process using BDD cathode, Chem. Eng. J. 160 (2010) 199–206. [30] C. Comninellis, Electrocatalysis in the electrochemical conversion/combustion of organic pollutants for waste-water treatment, Electrochim. Acta 39 (1994) 1857–1862. [31] X.P. Zhu, M.P. Tong, S.Y. Shi, H.Z. Zhao, J.R. Ni, Essential explanation of the strong mineralization performance of boron-doped diamond electrodes, Environ. Sci. Technol. 42 (2008) 4914–4920. [32] A. El-Ghenymy, S. Garcia-Segura, R.M. Rodriguez, E. Brillas, M.S. El Begrani, B. Abdelouahid, Optimization of the electro-Fenton and solar photoelectroFenton treatments of sulfanilic acid solutions using a pre-pilot flow plant by response surface methodology, J. Hazard. Mater. 221 (2012) 288–297. [33] X.Y. Li, Y.H. Cui, Y.J. Feng, Z.M. Xie, J.D. Gu, Reaction pathways and mechanisms of the electrochemical degradation of phenol on different electrodes, Water Res. 39 (2005) 1972–1981. [34] P. Canizares, J. Lobato, R. Paz, M.A. Rodrigo, C. Saez, Electrochemical oxidation of phenolic wastes with boron-doped diamond anodes, Water Res. 39 (2005) 2687–2703. [35] C.A. Emilio, M.I. Litter, M. Kunst, M. Bouchard, C. Colbeau-Justin, Phenol photodegradation on platinized-TiO2 photocatalysts related to charge-carrier dynamics, Langmuir 22 (2006) 3606–3613.