comprehensive review and compilation of treatment for azo dyes using microbial fuel cells
TRANSCRIPT
Comprehensive Review and Compilation ofTreatment for Azo Dyes Using Microbial Fuel Cells
V. Murali1, Soon-An Ong1*, Li-Ngee Ho2, Yee-Shian Wong1, Nasrul Hamidin1
ABSTRACT: Microbial fuel cells (MFCs) represent an emerging
technology that focuses on power generation and effluent treatment.
This review compiles articles related to MFCs using azo dye as the
substrate. The significance of the general components in MFCs and
systems of MFCs treating azo dye is depicted in this review. In addition,
degradation of azo dyes such as Congo red, methyl orange, active
brilliant red X-3B, amaranth, reactive blue 221, and acid orange 7 in
MFCs are summarized. Further exploration and operational modifica-
tion are suggested to address the challenges of complete removal of azo
dye with maximum power generation in an MFC. In addition, a
sequential treatment system with MFCs is suggested for complete
mineralization of azo dye. Water Environ. Res., 85, 270 (2013).
KEYWORDS: microbial fuel cell, azo dye, decolorization, power
generation, substrate.
doi:10.2175/106143012X13503213812481
IntroductionMicrobial fuel cells (MFCs) represent the most recent
technology to convert degradable organics into useful electrical
energy. The main components of MFCs are electrodes,
membranes, and substrate. In general, electrode materials
exhibit characteristics such as good conduction, good chemical
stability, high strength, and so on. Moreover, significant
characteristics of the electrode are good biocompatibility and
efficient electron transfer between the bacterial and electrode
surface (Wei et al., 2011).
A physical separator between the anode and cathode is called
a membrane. The main function of the membrane is to transfer
protons that have developed in the anode to the cathode. As an
optional component, one significant problem in the absence of
membrane is that when oxygen and substrate diffusion
increases, it lowers the Coulombic efficiency and biocatalytic
activity of the anode microorganisms (Hou et al., 2011a). Jang et
al. (2004) conducted a study of membrane-less MFCs and
witnessed a poor cathode reaction caused by a large quantity of
oxygen to diffuse toward the anode.
Substrate is an important factor that supports biological
activities in the MFC. Acetate, glucose, lignocellulosic biomass,
industrial wastewaters, and synthetic wastewaters are the main
substrates used in MFCs in recent years (Pant et al., 2010).
Several reviews of MFCs have been published in recent years,
each with a different emphasis. Wang et al. (2010) discussed the
advantages, characteristics, fabrication methods, and perfor-
mances of microsized MFCs including milliliter and microliter
scale. Lefebvre et al. (2011) debated the challenges of MFC
technology in relation to energy self-sufficiency. Qian and Morse
(2011) compiled the challenges and future prospects for
miniaturized MFCs. Li et al. (2011) discussed the different types
and recent advances in membranes in MFCs. Huang et al. (2011)
amassed electron transfer mechanisms and performance of
biocathode MFCs. Osman et al. (2011) studied recent develop-
ments and challenges toward the microbial activities in MFCs.
Oh et al. (2010) conferred about the various dominant
microorganisms in different MFCs treating wastewaters and its
ecology. Sharma and Kundu (2010) summarized the various
biocatalysts or microorganisms used in both anodes and
cathodes in MFCs. Pant et al. (2010) reviewed the different
substrates and the power output achieved by these substrates in
MFCs. Wei et al. (2011) summarized the performance and cost
of the different materials used for electrodes in MFCs.
Recently, efforts have been made to use the azo dye as
substrate in MFCs for color removal and electricity generation.
For color removal of azo dyes, much research has so far focused
on biological studies. Among this research, Kim et al. (2008)
conducted a study of color removal of azo dye using the
anaerobic process. The authors used an anaerobic reactor with a
mechanical stirrer. The result obtained was 94% color removal in
72 hours of retention time along with the consumption of 964
mg/L of glucose. Senthilkumar et al. (2011) conducted color
removal from textile wastewater using a biphasic upflow
anaerobic sludge blanket reactor along with sago wastewater
as co-substrate; the authors reported that maximum color
removal was 91.8% at 24 hours of hydraulic retention time
(HRT). Dos Santos et al. (2007) reviewed the advantages and
disadvantages of various color removal methods, more specif-
ically, of biological treatment methods. In terms of the trend of
treating azo dyes using biological methods, a recent upgradation
is treating azo dye using MFCs. Simultaneous power generation
and color removal can be achieved in this biochemical process.
This article presents a review of azo dye treatment using MFCs.
Microbial Fuel Cell System Using Azo Dye as SubstrateDimensions and materials for electrodes and membranes
differ from one another in a MFC system using azo dye as
substrate. The various materials used as electrodes and
membranes are summarized in Table 1. Li et al. (2008)
conducted anaerobic and aerobic systems of treatment for azo
dyes using two-chambered MFCs. In this study, the authors
1* School of Environmental Engineering, University of Malaysia,Perlis, 02600, Arau, Perlis, Malaysia; e-mail: [email protected] School of Materials Engineering, University of Malaysia, Perlis;Arau, Perlis, Malaysia
270 Water Environment Research, Volume 85, Number 3
conducted two different MFCs with different electrodes. In the
first reactor, the electrodes were carbon felt in both the anode
and cathode. The second reactor was fixed with carbon felt in
the anode and graphite granule in the cathode. In both reactors,
known concentrations of glucose with anaerobic and aerobic
sludge were inoculated in the anode and cathode, respectively.
After the initial run, Congo red was introduced to the anode and
the treated effluent transferred to the cathode to remove
aromatic amines generated from azo dye reduction. The study
suggested that the second reactor with different electrodes was
more efficient compared to the first reactor. Moreover, the study
was conducted with different concentrations of glucose and
different HRT. The authors observed that the maximum power
density obtained at 1000 mg/L of glucose concentration and the
optimized HRT for electricity production was 14.8 hours.
Ding et al. (2010) conducted a study based on azo dye removal
using two-chambered MFCs with rutile cathode. The anodic
electrode was an unpolished graphite electrode and the cathode
was a polished graphite electrode. A cation exchange membrane
was used as a separator. Another set of experiments was
conducted by replacing the polished graphite electrode with the
rutile cathode. Rutile cathode is a semiconductor mineral
(TiO2)-coated cathode. During startup, the anodic chamber of
the MFC was inoculated with the anaerobic sludge. The cathodic
chamber was initially filled with electrolyte and then replaced
with methyl orange before monitoring started. Visible light
responsiveness was selected as the cathodic catalyst. Rutile
electrode irradiated by visible light shows maximum power
generation and color removal.
Fu et al. (2010) investigated the combination of the two-
chambered MFC and Fenton system using amaranth as the
substrate. Granular graphite and spectrographic pure graphite
were used as the anode and cathode electrodes. The separator
between the anode and the cathode was the proton exchange
membrane. Two types of experiments were conducted: one was a
conventional Fenton system with MFC and the other was an
electrochemical Fenton system with the MFC. In the conven-
tional system, after the production of hydrogen peroxide caused
Table 1—Electrodes, membranes, and performance of MFCs.
Type of MFC Anode material Cathode material Type of membrane
Two-chamber Carbon felt R1, carbon felt; R2, graphite granule PEM
Two-chamber Unpolished Graphite electrode Rutile cathode electrode andgraphite electrode
Cation exchange membrane
Two-chamber Granular graphite Spectrographic pure graphite PEM
Two-chamber Porous carbon papers (withoutwaterproofing)
Porous carbon papers (withoutwaterproofing)
PEM
Two-chamber Graphite bars Graphite bars PEMTwo-chamber Granular activated carbon packed in
a cylindrical stainless cage meshused as anode. A graphite rodwas inserted in the anode.
Granular activated carbon packed ina cylindrical stainless cage meshused as electrode. A graphite rodwas inserted in the cathode.
The bottles are joined by a glassbridge containing a glass wool(Pyrex; Corning Incorporated,Corning, New York)
Two- chamber Carbon felt Carbon felt Cation exchange membrane
Two-chamber Activated carbon fiber withelectrochemical active bacteria
Carbon paper (4 3 4 cm2; TorayIndustries, Inc., Tokyo, Japan) orthionine-modified carbon paper
PEM (Nafion 117; DuPont,Wilmington, Delaware)
Single- chamberair cathode
Porous carbon papers projectedsurface area of 6x 6 cm2
Air cathode consisted of a catalystlayer (containing 0.5 mg /cm2 ofPt) on the water-facing side and aPTFE diffusion layer on the air-facing side
MFM (0.22 lm in pore size) wasapplied directly onto thewater-facing side of thecathode.
Single-chamberair cathode
Non-wet proofing carbon papers Cathode was prepared by coating0.5 mg cm2 of Pt on a wetproofing carbon paper
MFM (0.22 lm in pore size)
Single- chamberair cathode
Non-wet proofed porous carbonpapers (no catalyst) with aprojected surface area of 3 3 3cm on one side
Dim similar to anode prepared bycoating 0.5 mg/cm2 of Pt on wet-proofed porous carbon papers
MFM, PEM, UFM-1K,UFM-5K,UFM-10K
Single-chamberair cathode
Plain porous carbon papers (3 3 3cm, without wet proofing orcatalyst)
Coating 0.5 mg/cm2 of Pt on 3 3 3-cm wet-proofed porous carbonpaper
MFM (0.22 lm in pore size)
Single-chamberair cathode
25 g granular graphite with agraphite rod (8 mm in diameter)
Carbon paper Catalyst layer (containing 0.5mg/cm2 of Pt)
Murali et al.
March 2013 271
by the neutral catholyte, the dye effluent transferred to the
Fenton reaction. In the electrochemical Fenton system, Fe3þwas
introduced as a catalyst inside the cathode after the production
of hydrogen peroxide. Based on the results of the experiment,
power production was higher in the electrochemical Fenton
system (28.3 W/m3) than the conventional Fenton system (11.1
W/m3). Amaranth dye removal efficiency was higher in the
conventional Fenton system (82.59%) than the electrochemical
Fenton system (76.43%).
Sun et al. (2011a) used porous carbon papers as the electrodes
in both the anode and cathode. A proton exchange membrane
was used as a separator in this two-chambered MFC. Aerobic
biocathode and anaerobic anode MFC was used with active
brilliant red X-3B as substrate. The maximum power density
obtained was 50.74 mW/m2 and 81.56% of the color was
removed from the source.
In a study by Bakhshian et al. (2011), graphite bars were used
as electrodes and proton exchange membrane as separator.
Experiments performed with molasses as the energy source in
the anaerobic anode and commercial laccase with phosphate
buffer and reactive blue 221 were added in the cathode of the
two-chambered MFC. Color removal and chemical oxygen
demand (COD) reduction from molasses were monitored. After
the addition of molasses, the maximum voltage observed was
305 mV; it was stable for 30 hours. A color removal rate of 87%
was achieved in the cathode chamber and 84% COD removal
was observed in the anode chamber.
Granular activated carbon was packed in a cylindrical stainless
steel mesh cage and a graphite rod was inserted. This
combination was used as an electrode, and glass wool was used
as a membrane in a two-chambered MFC used by Kalathil et al.
(2011). The experiment was conducted using real dye wastewa-
ter on both the anode and cathode. The high power density
observed was 1.7 W/m3. Color removal was 73% in the anode
and 77% in the cathode at a duration of 48 hours.
Liu et al. (2009) used carbon felt as an electrode and cation
exchange membrane as a separator for a two-chambered MFC.
Glucose was added to the anode chamber and catholyte
Table 1—Extended.
Dye used Color removal Electricity generated References
Congo red 69.3 to 92.7% at a glucose concentration of4000 mg/L
387 mW/m2 at a glucose concentration of1000 mg/L
Li et al., 2008
Methyl orange Graphite electrode, 37.8%; Rutile cathodeelectrode, 47.4%; rutile cathode electrodeirradiated by visible light, 73.4%;disconnected circuit, 17.8%; connectedcircuit, 73.4%
Highest current density obtained in theirradiated rutile cathode electrode
Ding et al., 2010
Amaranth Conventional Fenton system, 82.59%,electrochemical Fenton system, 76.43%
Electrochemical Fenton system, maximumpower density of 28.3 W/m3; conventionalFenton system, 11.1 W/m3
Fu et al., 2010
Active brilliant red X-3B 81.56% In 38 days, 0.35V (R 500X); maximumpower, 50.74 mW/m2
Sun et al., 2011a
Reactive blue 221 83% 305 mV Bakhshian et al., 2011Real wastewater Anode 73% at 48 hours, cathode 77% at 48
hoursHigh power density 1.7 W/m3 Kalathil et al., 2011
Orange I, acid orange 7,and methyl orange
Nearly 99% 250 6 15 mV Liu et al., 2009
Methyl orange 99% 1.4 mW/m2 Liu et al., 2011
Active brilliant red X-3B MFC (48 hours), 100%; anaerobic reactor,80.1%
Glucose produced the highest powerdensity, followed by sucrose and dilutedconfectionery wastewater. The lowestpower density was observed in theacetate-fed MFC.
Sun et al., 2009
Congo red Congo red decolorization resulted in a largechange in the oxidation peak position ofthe bioanode.
Addition of Congo red did not result in anynoticeable decrease in the peak catalyticcurrent until a Congo red concentrationup to 900 mg/L.
Sun et al., 2011b
Congo red UFM-10K ¼ 4.77 mg/L�h; MFM ¼ 3.61 mg/L�h; UFM-5K ¼ 2.38 mg/L�h; UFM-1K ¼2.02 mg/L�h; PEM ¼ 1.72 mg/L�h
Highest power UFM-1K ¼ 324 mW/m2 Hou et al., 2011b
Congo red More than 90% decolorization at a dyeconcentration of 300 mg/L was achievedwithin 170 hours.
MFCs simultaneously ¼ 192 mW/m2; MFCssequentially ¼ 110 mW/m2
Hou et al., 2011a
Acid orange 7 Degradation (97%) was achieved after 168hours of operation.
Power density obtained was 5.0 W/m3 Zhang and Zhu, 2011
Murali et al.
272 Water Environment Research, Volume 85, Number 3
containing azo dyes was added to the cathode chamber. Azo dyes
used in this investigation were orange I, acid orange 7, and
methyl orange. The MFC produced a relatively stable voltage of
250 6 15 mV for about 2.7 hours and, beyond this period, a
sharp drop in voltage was noticed. Three dyes were completely
reduced to amines in the cathode.
Liu et al. (2011) used an activated carbon fiber with
electrochemical active bacteria as the anode electrode, carbon
paper as the cathode electrode, and the proton exchange
membrane as a separator in a two-chambered MFC. Phosphate
buffer containing methyl orange was filled in the cathode and
autoclaved medium and methyl orange was filled in the anode.
Higher color removal efficiency (99%) was obtained in the
cathode chamber than the anode chamber. Maximum power
density was determined as 1.4 mW/m2.
The single chamber air cathode consisted of a catalyst layer
(containing 0.5 mg/cm2 of Pt) on the water-facing side and a
polytetrafluoroethylene (PTFE) diffusion layer on the air-facing
side. The anode electrode was porous carbon paper and
microfiltration was applied directly onto the water-facing side
of the cathode in a MFC used by Sun et al. (2009). In addition to
active brilliant red X-3B (ABRX3), glucose, acetate, sucrose, and
confectionery wastewater with an initial concentration of 500
mg/L COD were used in co-metabolism. The following series of
experiments were conducted: (a) comparison of the color
removal performance of MFC, autoclaved sludge containing
MFC, and the anaerobic batch reactor; (b) the MFC was further
tested at different dye concentrations and with different external
resistance; (c) suspended solids were removed from the anodic
chamber of the MFC at the end of one batch test for evaluation
of suspended solids contribution to dye decolorization and
electricity generation; and (d) 300 mg/L of ABRX3 was added to
three individual MFCs along with different organic carbon
sources like acetate, sucrose, and confectionery wastewater,
respectively, to investigate the effect of the organic carbon
source on dye decolorization and electricity generation in the
MFC. Glucose produced the highest power density, followed by
sucrose, diluted confectionery wastewater, and acetate-fed MFC.
Color removal obtained in the anaerobic reactor was 80.1% and
anaerobic autoclaved sludge MFC was 11.2%. Dye concentra-
tions of 300 mg/L and 600 mg/L obtained 100% color removal
compared to other concentrations. Among the organic carbon
sources used, maximum color removal was obtained in glucose
and the minimum was obtained in acetate.
Sun et al. (2011b) used the air cathode single chamber with
non-wet proofing carbon papers as the anode; the cathode was
prepared by coating 0.5 mg/cm2 of Pt on a wet proofing carbon
paper. A microfiltration membrane was used as the separator
and Congo red was used in the bioanode. Results show that
Congo red did not affect the peak catalytic current up to 900
mg/L among the various concentrations.
Hou et al. (2011a) investigated different separators used in a
single-air-cathode MFC. Non-wet-proofed porous carbon paper
was used for the anode electrode and a coating of 0.5 mg/cm2 of
Pt on wet-proofed porous carbon papers was used in the
cathode. Experiments were conducted to assess the performance
of color removal and power generation using the following
different membranes: microfiltration membrane (MFM), proton
exchange membrane (PEM), and ultrafiltration membranes
(UFMs) with different molecular cutoff weights of 1 K (UFM-
1K), 5 K (UFM-5K), and 10 K (UFM-10K). Results showed that
the MFC with an UFM-1K produced the highest power density
of 324 mW/m2. The MFC with UFM-10K achieved the fastest
decolorization rate for Congo red. Hou et al. (2011b) also
published another paper using the same MFC setup. Two
different experiments were conducted with glucose and Congo
red in which glucose and Congo red were added to the MFCs
sequentially (EP1) or simultaneously (EP2) and were tested.
Results showed that the experimental procedures had a
negligible effect on color removal. Both the test achieved more
than 90% color removal at dye concentration of 300 mg/L within
170 h. Maximum power production obtained in EP2 and EP1
was 192 mW/m2 and 110 mW/m2, respectively.
Zhang and Zhu (2011) conducted a study in a single-
chambered air cathode MFC using 25 g of granular graphite
with a graphite rod as the anode and carbon paper as the
cathode. A catalyst layer containing 0.5 mg/cm2 of Pt was used
as the separator. The maximum power density obtained was 5.0
W/m3 for single-chamber MFCs using glucose with acid orange
7. Nearly complete color removal (97%) was achieved after 168
hours.
The aforementioned research was conducted using two- or
single-chambered MFCs. They differentiated with each other in
dimensions and type of materials used as electrodes and
separators. Each study targeted color removal of various azo
dyes and simultaneous energy recovery.
Azo Dye Removal in Microbial Fuel CellsCongo red, methyl orange, amaranth, active brilliant red X-
3B, reactive blue 221, orange I, and acid orange 7 were the azo
dyes used in MFC treatment. This section reviews the general
degradation of azo dye and degradation using MFC. Table 2
shows the chemical structures of these azo dyes.
Congo Red. Congo red is a diazo dye with two numbers of
sulfoante groups that ensure high aqueous solubility (Dos Santos
et al., 2007). Gopinath et al. (2009) studied biological
degradation of Congo red using Bacillus sp. This mutated
Bacillus sp. was more effective at the degradation of Congo red
compared to the wild species. Telke et al. (2009) also studied the
biological degradation of congo red using bacterium Pseudomo-
nas sp. Namasivayam and Arasi (1997) conducted an adsorption
study for the removal of Congo red. Waste red mud, an
industrial byproduct, generated during the processing of bauxite
ore was recycled for the adsorption of Congo red from aqueous
solution. Somasekhara Reddy et al. (2011) also conducted a
study of the removal of Congo red using physical adsorbent.
Indian Jujuba seeds were used as adsorbent in this study and
results show that the maximum adsorption capacity was 55.56
mg/g.
Li and Jia (2008) studied color removal of Congo red dye
using two systems: decolorization by Schizophyllum sp. and
biosorption by rice hull. Sansiviero et al. (2011) investigated
photodegradation of Congo red using various layers of thin TiO2
films. Isik and Sponza (2005) studied decolorization of Congo
red through an upflow anaerobic sludge blanket (UASB) reactor.
Reactor performance in terms of color, COD, and total aromatic
amine (TAA) removal was evaluated. Results of the experiment
show that 58% COD, 100% color, and 39% TAA removal
efficiencies were obtained in a 100 mg/L COD concentration
with glucose as co-substrate, while 25% COD, 99% color, and
40% TAA removal efficiencies were observed in a 100 mg/L
COD concentration without co-substrate. These aforementioned
Murali et al.
March 2013 273
Table 2—Dyes and their structure (dye structure drawn using ChemSketch software).
Dye Structure
Congo red
Methyl orange
Amaranth
Active brilliant red X-3B
Reactive blue 221
Acid orange 7
Orange I
Murali et al.
274 Water Environment Research, Volume 85, Number 3
studies and articles are examples of degradation of Congo red
using different methods.
In the studies and articles reviewed in this paper, most MFCs
used Congo red as a substrate. Li et al. (2008) investigated the
removal of azo dye in both the anode and cathode for anaerobic
and aerobic treatment. By using two-chambered MFCs, the azo
bond cleaved under the anaerobic anode chamber and aerobic
cathode chamber. The aromatic amine was removed from the
aerobic cathode chamber. Hou et al. (2011a) used a single-
chamber air cathode MFC to investigate the interception of
Congo red dye decolorization on power generation. The results
showed that Congo red decolorization did not have exhibit a
noticeable decrease in peak catalytic current until concentra-
tions of dye up to 900 mg/L. Hou et al. (2011b) used different
single-chamber air cathodes to assess the performance of
various membranes for removing Congo red. The authors
observed the following points in their research: the diffusion
coefficient of oxygen and diffusion coefficient of substrate were
two important factors needed to consider the performance of
different membranes for the color removal of azo dye; if the
diffusion coefficient of oxygen is high, it affects the anaerobic
condition of the anode chamber; because the diffusion
coefficient of oxygen transfers oxygen from the cathode to the
anode, this may not be a favorable condition for decolorization
in the anode chamber; and, if the diffusion coefficient substrate
is high, it supports decolorization resulting in a lower internal
resistance, which may increase the substrate conversion rate.
Results obtained with respect to these factors show that UFMs
with molecular cutoff weights of 10 K (UFM-10K) could be the
most suitable membranes in terms of Congo red decolorization.
The same authors (Hou et al., 2011b) conducted experiments
using an MFM as a separator in a single-chamber air cathode
MFC for Congo red decolorization. Microbial species that were
responsible for the decolorization of Congo red in MFCs were
identified.
Methyl Orange. Methyl orange belongs to the mono azo dye
group. Most of the studies on degradation of methyl orange were
based on the photocatalyst method. Chen et al. (2006) studied
the degradation of methyl orange by the photocatalyst method
using pelagite as the source material; pelagite is the ore of
manganese obtained from deep-sea beds. Jiang et al. (2011) used
monoclinic bismuth vanadate, a metallic element, as a
photacatalyst. Lin et al. (2008) used bi-based photocatalyst
Bi3SbO7 for the degradation of methyl orange. Guettai and Ait
Amar (2005) used titanium oxide as a photocatalyst for the
degradation of methyl orange. Activated carbon, nanosized
cadmium sulfide, and chitosan composite were used for
adsorption of methyl orange and visible light photocatalyst as
used for the removal of methyl orange. Chitosan is a substance
derived from the chitin of crab and other crustaceans (Jiang et
al., 2010). Decolorization of methyl orange using two-cham-
bered MFCs along with the photocatalytical effect was studied
by Ding et al. (2010). In this study, electrons from the anode
were transferred to the cathode, which contained methyl orange
as the electron acceptor. The conduction band potential of rutile
material used as the electrode was much more negative than
methyl orange; rather, it was favorable to the reduction of methyl
orange. Liu et al. (2011) conducted a study using two-chambered
MFCs. In the aerobic cathode chamber, 90% of the methyl
orange decolorized in 2 days, increasing to 99% in 4 days. In an
anaerobic anode, methyl orange remains as it. Liu et al. (2009)
used three different azo dyes (methyl orange, orange I, and
orange II) in a two-chambered MFC. Experiments were
conducted with each dye in cathode chambers. The final
products obtained after the reduction of these dyes were
identified in their study.
Active Brilliant Red X-3B. Active brilliant Red X-3B also
belongs to the mono azo dye group. The articles cited herein are
about the removal of active brilliant red X-3B using different
methods. Tao et al. (2010) conducted a study on photocatalytic
degradation of active brilliant red X-3B using a composite
material of titanium doped molecular sieves. Decomposition of
Fe (IV) results in a composite ferrate solution that was used for
the degradation of active brilliant red X-3B by Xu et al. (2009).
Dong et al. (2007) conducted a study on the removal of active
brilliant red X-3B using catalytic ozonation. Sun et al. (2009)
used a single-chamber air cathode MFC for the removal of
Active brilliant red X-3B. Bioadsorption and biodegradation are
reasons for color removal in biological systems. In this study,
biodegradation was the cause of color removal. Anaerobic
biodegradation is intercepted by aniline and sulfonated aromatic
amines. Sun et al. (2011a) conducted a study of the removal of
active brilliant red X-3B in a biocathode using a two-chambered
MFC. The authors reported that dissolved oxygen plays an
important role in the complete removal of this azo dye.
Amaranth. Amaranth is a mono azo dye with high aqueous
solubility. A recent study of the degradation of amaranth dye was
conducted by Chan et al. (2012). Inoculating specified micro-
organisms with amaranth dye in microaerophilic condition and
consecutive aerobic biodegradation. Fu et al. (2010) investigated
a double-chambered MFC for the removal of this mono azo dye.
In this study, the Fenton system was accompanied by MFC for
color removal. Degradation of this azo dye was carried out by
hydroxyl radicals in two steps. In the first step, cleavage of the
azo bond to form aromatic ring molecules by hydroxyl radicals
and the aromatic ring was broken by the oxidative ring opening
reaction. In the second step, carboxylic acid formed in the
previous step was oxidized by hydroxyl radicals produced in the
Fenton reaction. Fu et al. (2010) determined a maximum
amaranth removal of 82.59% and a power density of 28.3 W/m3.
Reactive Blue 221. Alkan et al. (2005) studied the adsorption
reactive blue 221 using sepiolite mineral and reported that the
adsorption was high with respect to ionic strength and
temperature. The optimum calcination temperature of this
mineral for the highest adsorption capacity was 200 8C. Another
adsorption study was conducted by Karaoglu et al. (2010) for
Reactive Blue 221 using kaolinite. Bakhshian et al. (2011)
conducted a biocathode study in a two-chambered MFC
performing enzymatic decolorization using commercial laccase
without any mediators. Laccase acts as a catalyst for oxygen
reduction in color removal and achieved 87% decolorization.
The article reported that power density increased up to 30%
using enzymatic decolorization.
Acid Orange 7. Elias et al. (2012) used the titanium doped
molecular sieves for the photodegradation of acid orange 7. Hu
et al. (2011) investigated another photodegradation using Cu2O/
CeO2 under visible light irradiation. Konsowa et al. (2011) used
the aerobic bioreactor for the degradation of this azo dye. The
experimental setup consisted of a bioreactor with air diffuser
and submerged microfiltration. Yang et al. (2010) conducted
oxidation using persulfate and granular activated carbon as the
catalysts for degradation of acid orange 7. Chou et al. (2011)
Murali et al.
March 2013 275
conducted electrooxidation for the removal of this mono azo
dye. Zhang and Zhu (2011) used a single-chamber air cathode
MFC for the removal of acid orange 7. This study concludes that
the single-chamber MFC was more advantageous compared to
the two-chamber MFC for color removal of acid orange 7. This
could be attributed to the fact that the electrons generated in the
anode transferred to acid orange 7 easily in the single chamber.
ConclusionsAvailable literature shows that researchers are targeted to
treat the azo dye with simultaneous power generation. The
anaerobic and aerobic biological methods may be appropriate
for the treatment of azo dye containing wastewaters (Pandey et
al., 2007). Anaerobic and aerobic environment is available in a
two-chambered MFC, which can be used for the complete
mineralization of azo dye. Reduction of azo bond in the azo dye
may be performed in the anaerobic chamber (anode) and the
degradation of aromatic amine may be carried out in the aerobic
chamber (cathode). Some specific articles focused towards bio-
cathode MFC and the challenges need to overcome is lower
power production of bio-cathode MFC comparatively chemi-
cally catalyzed cathode. In a single chamber MFC sequential
with aerobic treatment may perform the complete mineraliza-
tion of the azo dye.
In this review, it is difficult to compare with each other. The
reason behind this is, all the articles differentiate to each other in
the type of materials used for the electrodes and membrane, co-
substrate and the substrate used. The substrate used in each
MFC may come under the major classification of azo dye. A
further exploration are needed to focus about the MFC using
azo dye reduction using same type of MFC in dimension and
materials along with the same co-substrate for the different azo
dyes as substrate is hopeful to address the challenges in the azo
dye reduction MFC along with maximum power generation.
AcknowledgmentsThis research work was funded by the Fundamental Research
Grand Scheme provided by the Ministry of Higher Education
Malaysia. The authors would like to thank them for their
support.
Submitted for publication February 18, 2012; accepted for
publication July 26, 2012.
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