Bioresource Technology 102 (2011) 3827–3832

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Bioresource Technology

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Simultaneous degradation of refractory contaminants in both the anodeand cathode chambers of the microbial fuel cell

Yong Luo, Renduo Zhang, Guangli Liu ⇑, Jie Li, Bangyu Qin, Mingchen Li, Shanshan ChenSchool of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou, Guangdong 510275, China

a r t i c l e i n f o a b s t r a c t

Article history:Received 29 July 2010Received in revised form 25 November 2010Accepted 27 November 2010Available online 3 December 2010

Keywords:Microbial fuel cellElectricity generationFenton-like reactionAcid Orange 7Degradation

0960-8524/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.biortech.2010.11.121

⇑ Corresponding author. Tel.: +86 20 84110052; faxE-mail address: liugl@mail.sysu.edu.cn (G. Liu).

In this study, the microbial fuel cell (MFC) was combined with the Fenton-like technology to simulta-neously generate electricity and degrade refractory contaminants in both anode and cathode chambers.The maximum power density achieved was 15.9 W/m3 at an initial pH of 3.0 in the MFC. In the anodechamber, approximately 100% of furfural and 96% COD were removed at the end of a cycle. In the cathodechamber, the Fenton-like reaction with FeVO4 as a catalyst enhanced the removal of AO7 and COD. Theremoval rates of AO7 and COD reached 89% and 81%, respectively. The optimal pH value and FeVO4 dos-age toward degrading AO7 were about 3.0 and 0.8 g, respectively. Furthermore, a two-way catalyst mech-anism of FeVO4 and the contaminant degradation pathway in the MFC were explored.

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1. Introduction

The microbial fuel cell (MFC) has recently drawn wide interestsas a new method of directly generating electricity from wastewa-ters, and simultaneously treating wastewaters. It has been demon-strated that microorganisms can degrade many types of toxic andrefractory compounds, such as phenol, indole, and azo dye andgenerate electricity simultaneously (Luo et al., 2009; Zhang et al.,2009; Sun et al., 2009a). These degradation processes generally oc-cur in the anode chamber of the MFC. To our knowledge, simulta-neous degradation of toxic and refractory compounds in bothanode and cathode chambers has not been investigated yet.

The Fenton reaction is an advanced oxidation process (AOP)that generates hydroxyl radicals (�OH) from a mixture of ferrousions (Fe2+) and hydrogen peroxide (H2O2) (Pérez et al., 2002; Zazoet al., 2005). The hydroxyl radical is a non-selective, powerful oxi-dant with the ability to decompose almost all organic contami-nants into carbon dioxide and water in solutions (Li et al., 2009;Ramirez et al., 2007a). Therefore, this reaction has been employedto efficiently treat a variety of industrial wastewaters containinghazardous organic compounds, such as phenol, wood preserva-tives, and azo dye (Pimentel et al., 2008; Engwalla et al., 1999;Sun et al., 2009b). However, the homogeneous Fenton processhas some serious disadvantages. The catalyzed reactions need upto 50–80 mg/L of ferrous ions in the solution. The removal andtreatment of the excess sludge at the end of the wastewater

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treatment are expensive and need large amount of chemicals andmanpower (Ramirez et al., 2007b). Moreover, ferrous ions maybe deactivated attributable to the iron complexation with reagents,such as phosphate anions (Kuznetsova et al., 2004). To overcomethese drawbacks and attain high degradation rates, we proposeto use FeVO4 as a heterogeneous Fenton-like catalyst in the cath-ode of the MFC. FeVO4 allows a facile recovery and recycling ofthe iron regent. More importantly, FeVO4 containing iron ion andvanadate anion can be employed as a two-way Fenton-like cata-lyst. Such catalyst possesses a higher catalytic activity towardsthe degradation of refractory organic pollutants, compared withthe conventional heterogeneous Fenton-like catalysts, such as a-Fe2O3, Fe3O4, and c-FeOOH (Deng et al., 2008).

In this study, we propose to combine the MFC with the Fenton-like technology to degrade simultaneously toxic and refractorycompounds in both anode and cathode chambers. In the MFC, elec-trons and protons releasing from the biodegradation of contami-nants in the anode chamber transport to the cathode chamberthrough an external circuit and a proton exchange membrane,respectively. The oxygen reduction by the electrons in the cathoderesults in H2O2 (Zhu and Ni, 2009), which then reacts with Fe (I)and V(V) with the catalyst FeVO4 to produce �OH (Deng et al.,2008). By this process, the MFC not only can generate electricity,but also degrade refractory contaminants in the anode and cathodechambers simultaneously.

Furfural is a toxic and refractory pollutant, which is used in theoil extraction unit of oil refineries and petrochemical refining toextract dienes from other hydrocarbons (Borghei and Hosseini,2008). Furfural is chosen as the objective contaminant in the anode

3828 Y. Luo et al. / Bioresource Technology 102 (2011) 3827–3832

chamber of the MFC because our recent work has demonstratedthat furfural can be utilized by microorganisms to generate elec-tricity (Luo et al., 2010). We choose Acid orange 7 (AO7) as thecathode contaminant, which is a typical toxic and refractory azodye used widely in textile, leather tanning, paper production, andprinting industries (Mu et al., 2009).

2. Methods

2.1. Preparation of catalyst

FeVO4 was prepared with a wet chemical process (Poizot et al.,2000). Under a molar ration of 1:1, a 0.26 M solution of iron nitratewas quickly poured into a 4.27 � 10�2 M solution of ammoniummetavanadate under stirring. The mixture was maintained at75 �C for 1 h. The resulting precipitate was separated by pumpingfiltration, and sequentially washed with ultrapure water and ace-tone. Finally, the precipitate was dried at 50 �C in an oven for about15 h.

2.2. MFCs set up, microbial inoculum and operation

Three different MFCs (MFC-A, MFC-B, MFC-C) were designed inthis study. The MFC-A consisted of an anode chamber and a cath-ode chamber, which were separated by a proton exchange mem-brane (PEM, Nafion 212, Dupont Co., USA). The anode electrodewas made of carbon-cloth (TGP-H-060, Toray, Japan) with an areaof 10 cm2, while the cathode electrode was made of carbon felt(5 cm � 3 cm � 0.5 cm, Xinka Co., Shanghai, China). After insertingthe electrodes, the net volumes of the anode and cathode chamberswere about 100 mL, respectively. Copper wires were used to con-nect the circuit with an external resistance of 1000 X and all wirecontacts were sealed with epoxy material. The MFC was operatedat a constant temperature (30 ± 1 �C). The anode chamber was con-nected with a brown bottle (250 mL capacity) as the anode groove.A flow rate of 20 mL/min was controlled by a peristaltic pump forsolution circulation between the brown bottle and the chamber.Batch-fed experiments were performed in the cathode of the MFC.

Anaerobic and aerobic sludge (1:1, 10 mL) was taken from LiedeMunicipal Wastewater Treatment Plant in Guangzhou City, China,and inoculated in the MFC with a glucose solution of 1000 mg/Land an anodic solution. The anodic solution contained (in 1 L deion-ized water): 4.0896 g Na2HPO4, 2.544 g NaH2PO4, 0.31 g NH4Cl,0.13 g KCl, and 12.5 mL trace metal solution and 12.5 mL vitaminsolution (Lovely and Phillips, 1988). A furfural solution of 300 mg/L was used as the sole substrate to continue incubating the activemicroorganisms that have been incubated above. The total volumeof the anode solution was 200 mL. The substrate in the MFC was re-placed when the voltage decreased below 90 mV. Before the oper-ation of each cycle, the anode compartment of the MFC wasflushed with N2 for 10 min to ensure an anaerobic environment.

The cathode solution consisted of 1 g FeVO4 powder, 50 mg/LAO7, and 20 g/L Na2SO4. The solution pH was adjusted with diluteH2SO4. An optimum pH value of 3.0 was selected to carry out theFenton-like reaction (Hwang et al., 2010). The total volume of thecathode solution was 80 mL. The solution was sonicated for30 min to be mixed uniformly before adding it into the cathodechamber. Air was continuously purged into the cathode chamber.Open-circuit experiments were conducted in the MFC-A. The pur-poses of these control experiments were to compare the removalof furfural under the open circuit and close-circuit conditions.

AO7 is likely to be reduced though accepting electrons from theanode (Mu et al., 2009). To demonstrate the AO7 removal mainlycaused by the Fenton-like reaction, we designed the MFC-B, inwhich a N2-purged cathode solution contained AO7 as the sole

electron acceptor susceptible for reduction. The lack of the dis-solved O2 prevented H2O2 generation and thus there was no theFenton-like reaction in the MFC-B. To study the adsorption effectson AO7 removal, the MFC-C with the same configuration of theMFC-B was conducted but under the open circuit condition with-out any electrochemical reaction. Other reactor configuration andoperation conditions of the MFC-B and MFC-C were the same asthe MFC-A described above. In the following sections, unless stat-ing, the MFC was referred to the MFC-A.

2.3. Analyses and calculation

Samples from the anode and cathode solutions in the MFC weretreated by filtering through a membrane with a pore diameter of0.22 lm to remove cells and suspended particles. Chemical oxygendemand (COD) was measured according to the standard method(Clesceri et al., 1998). The furfural concentration was analyzedusing HPLC (Agilent 1100, TC-C18 reverse-phase column), in which70% methanol and 30% water were used as the mobile phase and aflow rate of 1 mL/min was maintained. A UV spectrophotometricdetector was employed with a wavelength of 275 nm. The concen-tration of AO7 was determined by a UV vis spectrophotometry(Uv957S, Shanghai, China) at 484 nm. The H2O2 concentrationwas determined spectrophotometrically using the iodide methodat 351 nm (Klassen et al., 1994). The H2O2 measurements wereconducted in cycles without AO7 and FeVO4 in the cathode solu-tion. Intermediates from AO7 degradation were analyzed usingGC/MS (Voyager, USA) with samples extracted from the cathodesolution with an equal volume of dichloromethane. The tempera-ture of the GC/MS column (BPX5, 30 m � 0.25 mm � 0.25 lm)was started at 40 �C for 3 min, increased at 20 �C/min to a finaltemperature of 250 �C for 5 min. Helium was used as the carriergas at a constant pressure of 103 kPa.

Voltages of the MFC were measured at a time interval of 30 sacross the external resistance (1000 X) using a data acquisitionsystem (DT85, Datataker Corp., Australia). The current was calcu-lated based on the voltage and the external resistance. The volu-metric power density (PV, W/m3) were calculated as follows:

PV ¼UIV

ð1Þ

where I is the current (A), U is the voltage (V), V is the available vol-ume of anodic compartment (m3). The volumetric power densityindicates how much power is generated from unit volume ofwastewater.

Polarization curves were generated by changing the externalresistances from 20 to 8000 X. For each resistance, at least two cy-cles of the MFC were operated to ensure that repeatable voltageoutputs were achieved. Averaged voltages from the outputs wereused to calculate the power density (W/m3). The internal resis-tance (Rint) was calculated from the slope of plots of U vs. I asfollows:

U ¼ Ecell � IRint ð2Þ

where Ecell is the electromotive force of the MFC (Logan et al., 2006).Coulombic efficiency (CE) is defined as the ratio of total cou-

lombs actually transferred to the anode from the substrate to themaximum possible coulombs if all substrate removal produceselectricity. The CE (%) is calculated by:

CE ¼ 100%

Pn

i¼1Uiti

RFbDSVM ð3Þ

Here Ui is the output voltage of MFC at time ti (V), R is the exter-nal resistance (1000 X), F is Faraday’s constant (96,485 C/mol elec-trons), b is the number of moles of electrons produced per mol of

Table 1The removal rates of furfural and COD obtained from the MFC with 300 mg/L furfuralas the sole fuel under close circuit and open circuit situations.

Y. Luo et al. / Bioresource Technology 102 (2011) 3827–3832 3829

the COD (4 mol e�/mol COD), DS is the removal of COD concentra-tion (g/L), V is the liquid volume (L), and M is the molecular weightof oxygen (32 g/mol).

Time(h)

Opened circuit Closed circuit

Furfuralremoval (%)

COD removal(%)

Furfuralremoval (%)

COD removal(%)

0 0 0 0 01 31 ± 1.3a 20 ± 3.4 43 ± 0.9 35 ± 4.32 51 ± 0.7 35 ± 2.5 65 ± 0.8 54 ± 3.63 70 ± 1.1 57 ± 3.1 82 ± 1.2 69 ± 3.37 79 ± 1.2 71 ± 4.3 93 ± 1.4 87 ± 2.6

60 100 ± 0.0 92 ± 2.8 100 ± 0.1 96 ± 2.7

a The mean value and standard deviation of multiple cycles (n = 3).

3. Results and discussion

3.1. Power generation

After operation for 15 d under the close-circuit condition, weobtained consistent and repeatable cycles of power generation inthe MFC with 300 mg/L furfural as the sole fuel. Three representa-tive cycles are shown in Fig. 1. When the anodic and cathodic solu-tions were replaced with fresh solutions, voltage outputs began toincrease quickly and reached the maximum voltage output about820 mV, and then decreased to about 250 mV within 15 h, and sub-sequently decreased gradually. Correspondingly, the averageoperation period per cycle was about 60 h. Fig. 2 shows the rela-tionships between the voltage and power density vs. the currentdensity. The voltages decreased linearly with the current densities.A maximum power density of 15.9 W/m3 was obtained at a currentdensity of 39.9 A/m3 in the MFC, and the internal resistance of theMFC was around 129 X.

3.2. Furfural degradation in the anode chamber

Biodegradation rates of furfural and COD in the close circuit andopen-circuit experiments are shown in Table 1. When using a con-

0 30 60 90 120 150 180 2100

150

300

450

600

750

900

Vol

tage

(m

V)

Time (h)

Fig. 1. Electricity voltage outputs of the MFC using 300 mg/L furfural as the solefuel. The arrows show the time of anode solution replacement.

0 10 20 30 40 50 60 700

200

400

600

800

1000

Voltage Power density

Current density (A/m3)

Vol

tage

(m

V)

0

4

8

12

16

20

Pow

er d

ensi

ty (

W/m

3 )

Fig. 2. Power density and cell voltage as a function of current density for the MFC.

centration of 300 mg/L furfural as the sole fuel in the MFC under theclosed-circuit condition, 93% furfural was removed within 7 h, andthe COD removal was 87%. Nearly 100% of furfural and 96% of CODwere removed at the end of the cycle (around 60 h) (Table 1). Re-sults from Fig. 1 and Table 1 showed that the MFC could degradefurfural and generate electricity simultaneously. It was indicatedthat the electrons and protons were released from furfural biodeg-radation in the anode chamber and transferred to the cathodechamber. In the cathode chamber, O2 reduction by these electronsproduced H2O2, which drove the Fenton-like reaction.

Compared with the open-circuit experiments, the removal ratesof furfural and COD within 7 h were 14% and 16% higher in theclose-circuit condition of the MFC (Table 1). The results demon-strated that the MFC could enhance furfural and COD degradation.A similar result was also reported by Luo et al. (2009) that the MFCenhanced phenol degradation under the closed-circuit condition.

3.3. AO7 degradation in the cathode chamber

The removal rate of AO7 in the MFC-C indicated that AO7adsorption by the cathode electrode was 8.2–9.5%. In the MFC-A,about 50% of AO7 and 32% of COD were removed within 1 h, and82% of AO7 and 74% of COD were removed within 3 h. The removalrates of AO7 and COD reached 89% and 81%, respectively, at the endof a cycle (about 60 h). However, in the MFC-B, only 42% of AO7and 28% of COD were removed at the end of the cycle. The lowerremoval rates of AO7 and COD in the MFC-B indicated that electro-chemical reduction of AO7 through accepting electrons from theanode on the cathode electrode was not high. Furthermore, sinceair was continuously purged into the cathode chamber of theMFC-A, the dissolved O2 in the MFC could obtain more electronsthan AO7, which inhibited the electrochemical reduction of AO7.Therefore, the electrochemical reduction and Fenton-like reactionwere probably simultaneously available in the process of degrad-ing AO7 in the MFC-A, but the AO7 removal was mainly attributedto the Fenton-like reaction.

Feng et al. (2010) characterize the generation of H2O2 on thecathode with three stages: a static stage when there is weaklydetectable H2O2, a fast-grown stage when H2O2 is progressivelyproduced, and an equilibrium stage when the H2O2 generation rateand its decomposition rate are equivalent. However, in this study, astatic stage seemed not to exist and H2O2 generated quickly in ashort time in the MFC. H2O2 reached a maximum concentrationof 2.1 mg/L within 1 h, and then gradually decreased. At the endof the operation cycle, the concentration of H2O2 decreased to0.94 mg/L. The concentration change of H2O2 was most probablyattributable to the electricity generation. Voltages quickly in-creased up to 820 mV when the anodic and cathodic solutionswere replaced with fresh substrates (Fig. 1). Correspondingly, theelectrons and protons quickly transferred to the cathode chamberand reacted with O2, thus resulted in H2O2 formation. Afterward,

70

80

90

100

7 re

mov

al (

%)

12

14

16

18

20

pow

er d

ensi

ty (

W/m

3 )

3830 Y. Luo et al. / Bioresource Technology 102 (2011) 3827–3832

the voltage output was noticeably decreased, which led to thegradual decrease in H2O2 concentrations vs. time. Furthermore,H2O2 could be consumed through receiving electrons, which alsoresulted in decrease of the H2O2 yield. The removal rates of AO7 in-creased with the H2O2 concentrations. For example, with the larg-est H2O2 amount (2.1 mg/L), more than 50% of AO7 (25.3 mg/L)was removed within 1 h. The results confirmed that the H2O2 con-centration played an important role in the��OH generation towardsdegrading AO7.

0.0 0.5 1.0 1.5 2.0 2.550

60

AO7 removal Maximum power density

FeVO4 dosage (g)

AO

8

10

Max

imum

Fig. 3. Maximum power densities and AO7 degradation rates as a function of FeVO4

dosage.

3.4. Effect of the initial pH on AO7 degradation and power generation

The effect of the initial pH of the cathode solution on AO7 deg-radation and power generation was examined in the MFC. Asshown in Table 2, pH had a significant effect on AO7 degradationand power generation. With the initial pH value of 3.0, the maxi-mum AO7 degradation rate of 89% was achieved in the MFC. Athigh pH values (pH > 4.0), the formation of ferrous/ferric hydroxidecomplexes led to catalyst deactivation, which resulted in decreaseof the �OH amount (Daud and Hameed, 2010). Therefore, the effi-ciency of AO7 degradation was low. At the initial pH of 7.0, the re-moval rate of AO7 was only 62%. With pH values lower than 3.0,the efficiency of AO7 degradation also decreased. With the initialpH of 2.0, the removal rate of AO7 was 85% (Table 2). The resultwas probably attributable to the H2O2 reaction with excessive H+

to form oxonium ion (H3O2+), which is stable and difficult to react

with Fe (III) and V(V) to form �OH (Daud and Hameed, 2010; Ramir-ez et al., 2007b). At the same time, �OH can also be scavenged byexcessive H+ (Kwon et al., 1999). Therefore, the optimum pH wasabout 3.0.

In addition to influence the efficiency of AO7 degradation, theinitial pH also affected significantly the power output (Table 2).Decrease in pH values from 7.0 to 2.0 resulted in increase in themaximum power densities from 9.5 to 16.8 W/m3. The higher max-imum power density achieved at a lower pH value was due to twofactors: thermodynamically, the MFC took advantage of the pH dif-ference between anode and cathode, and kinetically, the acidiccatholyte reduced the cathode over-potential (Erable et al., 2009).

3.5. Effect of FeVO4 dosage on AO7 degradation and power generation

The relationships between the catalyst dosage vs. AO7 degrada-tion and electricity generation at the initial pH of 3.0 are illustratedin Fig. 3. The results indicated that AO7 degradation was greatlyinfluenced by the dosage of FeVO4 and the optimum dosage of0.8 g of the catalyst resulted in the maximum AO7 degradation rate(91%). The highest degradation rate achieved at this catalyst dosagemight be attributed to the highest production of �OH in the Fenton-like reaction.

The FeVO4 dosage influenced the maximum power density lesssignificantly than the AO7 degradation rate. When the FeVO4 dos-age increased from 0.2 to 2 g, the maximum power densitiesachieved in the MFC changed somewhat in the range of 15.3–16.1 W/m3 (Fig. 3).

Table 2Maximum power densities and AO7 degradation rates as a function of the initial pHvalues.

pH value Maximum power density (W/m3) AO7 degradation rate (%)

2 17 ± 1.7a 85 ± 2.13 16 ± 1.6 89 ± 0.74 14 ± 1.1 80 ± 3.25 11 ± 1.4 71 ± 4.56 11 ± 0.4 64 ± 5.17 10 ± 0.7 62 ± 5.8

a The mean value and standard deviation of multiple cycles (n = 3).

3.6. The catalytic mechanism of Fenton-like reaction employing FeVO4

as the catalyst

In the cathode chamber, oxygen was adsorbed on the surface ofthe carbon felt. H2O2 was then continuously produced in the solu-tion from the two-electron reduction of dissolved O2 on the carbonfelt surface (Zhu and Ni, 2009):

O2 þ 2Hþ þ 2e� ! H2O2

The reaction was evidenced from the detectable amount ofH2O2 present in the cathodic solution. In the next step, the ionsof Fe (I) and V(V) from FeVO4, like many other compounds con-taining Fe (III) and V(V), could activate H2O2 to generate �OH (Denget al., 2008). Although the mechanism of the Fenton-like reaction isstill far from being fully understood, the most possible pathways toactivate H2O2 by Fe (III) are involved in the following tworeactions:

FeðIIIÞ þH2O2 ! FeðIIÞ þ �OOHþHþ

FeðIIÞ þH2O2 ! FeðIIIÞ þ �OHþ OH�

Similarly, the activation of V (V) compound towards H2O2 is be-lieved to follow the two steps below:

VðVÞ þH2O2 ! VðIVÞ þ �OOHþHþ

VðIVÞ þH2O2 ! VðVÞ þ �OHþ OH�

Based on the above reactions, Fe (III) and V(V) can be employedas a two-way Fenton-like catalyst that leads to the production ofmore �OH, which is in accordance with the observations in the lit-erature (Deng et al., 2008; Zhang et al., 2010). Consequently, AO7 isquickly oxidized by �OH in the cathode chamber of the MFC.

3.7. Mechanism of electron transfer and contaminant degradation

GC/MS analyses of the cathode solutions indicated some inter-mediates, such as benzaldehyde, naphthalene, and phenol, amongwhich phenol was main intermediate. Based on the intermediates,the possible mechanism of electron transfer and contaminant deg-radation in the MFC was as follows. In the MFC anode, furfural wasutilized by electrochemically active microorganisms to releaseelectrons and protons (Luo et al., 2010). After the electrons andprotons were transferred to the cathode chamber, AO7 was proba-bly reduced by two different reactions: the electrochemicalreduction and the Fenton-like reaction (Feng et al., 2010). The

Y. Luo et al. / Bioresource Technology 102 (2011) 3827–3832 3831

mechanism of electrochemical reduction of AO7 was that the azobond of AO7 was broken by protons and electrons, resulting in col-orless products of sulfanilic acid and 1-amino-2-naphthol (Muet al., 2009). However, a majority of AO7 was degraded by the Fen-ton-like reaction. The reaction evidenced from the detectable H2O2

and FeVO4 present in the cathode generated �OH. The �OH withhighly oxidative capability resulted in the cleavage of the azo bandof AO7, which then produced some aromatic intermediates, such asphenol, benzaldehyde, and naphthalene. Further oxidation of thearomatic intermediates resulted in ring opening product, and final-ly mineralized into CO2 and H2O (Hammami et al., 2008; Ozcanet al., 2009).

3.8. Practical significance and considerations

The results in this study demonstrated for the first time that theMFC can simultaneously generate electricity and remove refractorycompounds in both anode and cathode chambers. Three processes(i.e., bioelectricity generation, biodegradation, and Fenton-likereaction degradation for contaminants) were involved in theMFC. To drive the Fenton-like reaction toward contaminant degra-dation in the cathode, the contaminant used as the fuel in the an-ode chamber should have the ability of efficiently generatingelectricity. Besides furfural, some toxic and refractory compounds,such as phenol and 1,2-dichloroethane, are also likely to achievethe objective because these compounds have been shown to gener-ate high voltage outputs in the MFC (Luo et al., 2009; Pham et al.,2009). In the cathode chamber of the MFC, a broader range of non-degradable contaminants can be degraded due to the presence ofthe Fenton-like reaction, which has the potential to decomposemany organic contaminants.

The CE achieved in the MFC was only 1.9%. The low CE from theMFC might be mainly attributable to the non-electricity-generat-ing microbes (e.g., methanogens) existing in the anode groove,which consumed the majority of COD (He et al., 2005; Li et al.,2010). Further research is needed to improve the CE. Althoughthe repeated experiment of Fenton-like degradation towards AO7confirm that this FeVO4 catalyst can be used for a long time andreusable, the separation and reuse of FeVO4 after each cycle is stilla problem. The immobilization of FeVO4 on the carbon felt elec-trode may be a major issue for the practical application of thisprocess.

4. Conclusions

Our study clearly showed that the MFC could degrade furfuraland AO7 in the anode and cathode chambers, respectively, andgenerate relatively high power outputs. The removal rates of furfu-ral reached 100% at the end of the cycle. The initial pH was animportant factor that affected the power output and the AO7 deg-radation efficiency. The electrons and protons were released fromthe biodegradation of furfural in the anode chamber and trans-ported to the cathode chamber to drive the Fenton-like reaction to-ward degrading AO7.

Acknowledgements

This work was partially supported by grants from the NaturalScience Foundation of China (Nos. 50608070 and 50779080), theFundamental Research Funds for the Central Universities, and theResearch Fund Program of Guangdong Provincial Key Laboratoryof Environmental Pollution Control and Remediation Technology(No. 2006K0007).

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