Carbon yarn microbial fuel cells

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Treatment of domestic and distillery wastewater inhigh surface microbial fuel cells

Jayesh M. Sonawane a,b,1, Enrico Marsili c,d,e,f,*,Prakash Chandra Ghosh a,b,**,1

a Fuel Cell Research Facility, Department Energy Science and Engineering, Indian Institute of Technology Bombay,

Mumbai 400 076, Indiab IITB-Monash Research Academy, Indian Institute of Technology Bombay, Mumbai 400 076, Indiac School of Biotechnology, Dublin City University, Collins Avenue, Dublin 9, Irelandd National Centre for Sensor Research, Dublin City University, Collins Avenue, Dublin 9, Irelande Marine and Sensor Technology Hub, Dublin City University, Collins Avenue, Dublin 9, Irelandf Singapore Centre on Life Science Engineering (SCELSE), Nanyang Technological University, 637551, Singapore

a r t i c l e i n f o

Article history:

Received 17 April 2014

Received in revised form

25 June 2014

Accepted 17 July 2014

Available online xxx

Keywords:

Microbial fuel cell

Domestic wastewater

Distillery wastewater

Interlaced carbon yarn anode

* Corresponding author. Singapore Centre onTel.: þ65 6592 7895.** Corresponding author. Department EnergyTel.: þ91 22 2576 7896; fax: þ91 22 2576 4890

E-mail addresses: [email protected] Ghosh).

1 Tel.: þ91 22 2576 7896; fax: þ91 22 2576

Please cite this article in press as: Sonawcrobial fuel cells, International Journal o

http://dx.doi.org/10.1016/j.ijhydene.2014.07.00360-3199/Copyright © 2014, Hydrogen Ener

a b s t r a c t

Microbial fuel cells (MFCs) are bio-electrochemical devices that couple organic carbon

removal from wastewater and electricity production. Full-scale application of MFCs in a

wastewater treatment plant (WWTP) requires high surface, lowcost electrodes to maximize

microbial growth and power output. In this study, a high surface MFC anode is constructed

by interlacing carbon yarn with stainless steel. The anode is arranged in a double-air

cathode MFC configuration with 6 ± 1 U internal resistance. When closed on 100 U

external resistances in batch mode, the MFCs produce maximum power densities of

621 ± 17 and 364 ± 11 mW m�2 for domestic and distillery wastewater, respectively. The

chemical oxygen demand (COD) removal is 68% and 58% with a columbic efficiency of 47%

and 27% for domestic and distillery wastewater, respectively. The biofouling layer on the

Nafion membrane is twofold thicker in the domestic wastewater MFC, thereby suggesting

that the power output and COD removal in distillery wastewater MFC are not limited by the

cation transport across the membrane, but rather by the chemical composition of the

distillery wastewater that does not support an efficient electrochemically active microbial

community.

Copyright © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights

reserved.

Life Science Engineering (SCELSE), Nanyang Technological University, 637551, Singapore.

Science and Engineering, Indian Institute of Technology Bombay, Mumbai 400 076, India.., [email protected] (E. Marsili), [email protected], [email protected] (P.

4890.

ane JM, et al., Treatment of domestic and distillery wastewater in high surface mi-f Hydrogen Energy (2014), http://dx.doi.org/10.1016/j.ijhydene.2014.07.085

85gy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

mailto:[email protected]




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http://dx.doi.org/10.1016/j.ijhydene.2014.07.085



i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e92

Introduction

Microbial fuel cells (MFCs) convert chemical energy from

wastewater into electrical energy using viable electrochemi-

cally active microorganisms [1]. A typical MFC for energy re-

covery from wastewater is composed of an anodic chamber,

where the organic matter in the wastewater is oxidized by the

microbial biomass, and a gas-porous air cathode where at-

mospheric oxygen is reduced [2]. Other MFC architectures

have been designed to couple chemical oxygen demand (COD)

reduction with removal of nitrate [3], azo dyes [4], and drug

residues [5].

The power output of wastewater MFC depends on

numerous factors, including the concentration of electro-

chemically active microorganisms [6], cathode and

anode electrode assembly [7,8], the composition and the

thickness of the ion-selective membrane between the two

electrodes [9], the reactor design [10], the organic load, the

Fig. 1 e A schematic design of the MFC used in this study: (a) M

overall experimental setup.

Please cite this article in press as: Sonawane JM, et al., Treatmecrobial fuel cells, International Journal of Hydrogen Energy (2014

operating temperature, and the value of external resistance

(Rext) [11].

Reactor cost and operative costs should be considered for

scale-up and practical application in WWTPs [12]. Recent

research has singled out reactor configurations that allow

high energy recovery when used in conjunction with actual

domestic or industrial wastewater. For example, a low-cost,

tubular MFC stack removed more than 90% of COD and 80%

of total nitrogen from domestic wastewater [13]. Tubular

MFCs installed in municipal wastewater remove 65e70% of

the initial COD, although sulphate reduction scavenges elec-

trons and reduces the overall power output [3]. High surface

anode materials, like carbon based sponges, cloths, and fibres

increase immobilisation of electrochemically active microor-

ganisms, which have resulted in power output improvement

[14]. However, the scale-up of high surface MFCs is not

straightforward. For example, MFCs based on high surface

graphite brush anode produce 75e150 Wm�3 power output at

laboratory conditions, but freely floating graphite fibres

FC assembly; (b) details of interlaced yarn anode; and (c)

nt of domestic and distillery wastewater in high surface mi-), http://dx.doi.org/10.1016/j.ijhydene.2014.07.085



i n t e rn a t i o n a l j o u rn a l o f h y d r o g e n en e r g y x x x ( 2 0 1 4 ) 1e9 3

require supporters to maintain the shape of larger electrodes

[15]. Increasing the anode surface with nanoparticles or

implanting functional groups by plasma or chemical treat-

ment determines rapid biofilm attachment and fast electron

transfer rate at the interface biofilm/electrode [16e17].

However, as the anodic biofilm grows, the anode surface is

covered and the biofilm layer close to the bulk liquid show

slower electron transfer rate than those closer to themodified

surface [18].

To achieve high power output, internal resistance Rint

should be very low. Dense biofilms formed by rod shaped

microorganisms have Rint as low as 10 U [19], whereas mi-

croorganisms on the high surface anode that are based on

graphite brush have Rint as low as 8 U [20]. These designs

provide efficiency at the laboratory scale and may be suitable

for pilot-scale or large-scale implementation like retrofitting

of existing WWTPs.

Despite these recent results, there is still a need for high

surface MFC assemblies that are suitable to treat raw waste-

water with minimal pretreatment. This study reports an

anode design based on interlaced carbon yarn that provides a

large accessible surface for biofilm attachment and is suitable

for the scale-up and deployment in conventional WWTP. The

cell was equipped with a double air-breathing cathode to

minimize cathode limitations and to further increase the

power output.

Materials and methods

Microbial fuel cells configuration

Two identical MFCs with interlaced carbon yarn anode and

porous air cathodes were fabricated with 0.8 cm thick acrylic

sheet (Fig. 1(a)). Each MFC had a 0.7 L anodic chamber

(12.5� 7� 8 cm)with two openings on the front and rear sides,

where two identical air cathodesweremounted, plus inlet and

outlet for recirculation and sampling. Recirculation at a rate of

0.45 L min�1 was achieved by a mini fountain pump and the

recirculated wastewater was evenly distributed in the vicinity

of the cathodes.

Electrode fabrication

The anodewas designed using a perforated stainless steel (SS-

308) sheet, which was folded to form a frame with a dimen-

sion of 12.2 � 6.7 � 7.7 cm. The 0.2 cm thick carbon yarn was

purchased at 12 USD/Kg (Y2100, Aiflon, China) and was woven

alternately through the holes on the SS sheet in horizontal

and vertical threading (Fig. 1(b)), leading to a projected anode

surface of 0.1018 m2. The interlaced carbon yarn anode as-

sembly was placed in the anode chamber and connected with

the electrical circuit through two stainless steel rods.

Nafion NE 1135 (thickness 89 mm) was used as cationic

exchange membrane. The cathodes were fabricated adapting

a previously described method [21]. In brief, fine platinized

Vulcan XC-72carbon powder (Pt content 20% wt.) (Sigma

Aldrich, India) was coated on a 12.5 cm � 8 cm Toray TGP-H-

060 carbon Paper (Fuel Cell Etc., USA), to fabricate the cath-

ode. The platinum loading in the electrode was 0.5 mg cm_2


using 5%wt. Nafion solution as a binder (SigmaAldrich, India).

Subsequently, the electrode was hot-pressed on one side of

89 mm Nafion NRE-1135 (Sigma Aldrich, India) under

10 kg cm�2 pressure at 140 �C for 2 min. The resulting mem-

brane electrode assembly was then inserted in the MFC. Two

identical membrane-cathode assemblies were mounted in

each MFC (Fig. 1(a)). The cathodes were connected to the

external electrical circuit through silver paste and copper

wires (Fig. 1(c)).

Inoculation of MFCs

One of the MFCs was fed with domestic wastewater, the

other with distillery wastewater. The experiments were

conducted simultaneously at ambient temperature. The

initial pH and COD of domestic wastewater collected from

the primary clarifier of the Mumbai municipal WWTP were 8

and 1650 mg L�1, respectively. Secondary treated distillery

wastewater with pH 7.8 and COD 2303 mg L�1 was obtained

from a local distillery. The relatively low COD value for the

distillery wastewater might be due to abundant rains in the

days before wastewater collection. Each wastewater amount

was divided in three jars, which were maintained at 4 �Cprior to the inoculation in the MFC. At the beginning of each

cycle (three cycles for each wastewater, for a total of six

experiments), the wastewaters were sparged with N2 for

30 min prior to inoculation, and the MFCs were sparged for

10 min after inoculation, to increase the initial activity of

obligate anaerobes and minimize aerobic oxidation of

organic matter.

Operation of MFCs

The temperature of the anodic compartment was measured

by a thermocouple. The ambient temperature varied between

23 �C in the night and 33 �C in the day. Such temperature

variation is typical of MFC run in tropical environment with

no temperature control. However, the current output in

the week-long experiments did not change significantly

within a day, likely because the mixed microbial consortia in

the MFC was adapted to these variation of temperature. Both

the MFCs were operated for three different cycles of 7e8 days

duration. In the first cycle, the Rext was disconnected and the

open circuit potential (OCV) was recorded. The first run

ensured the acclimatization of the inoculum and the forma-

tion of a healthy biofilm on the anode surface. Following

removal of spent wastewater, the MFCs were re-inoculated

with new wastewater and closed on a 100 U Rext. The polar-

isation curveswere recorded under recirculating and stagnant

conditions on day 3 and 4, respectively. The third cycle was

carried out with recirculation and the polarisation curves

were recorded on day 3.

Analytics and calculations

COD concentration in each cell was measured daily. The two

cathodes were connected to the common anode and the MFC

potential was continuously monitored in a two-electrode

mode every 10 min using a data logger (Graphtec GL800,

Japan). The values of the potential were averaged on 36 data





points (6 h). The current output was calculated by Ohms' lawacross the Rext [22]. The power density, normalised to the

projected cathode surface area, was calculated by P ¼ E2/

(Rext.A), where A [m2] is the projected cathode surface, Rext [U]

the external resistance, E [Volts] the MFC potential. The

polarisation curve was obtained by changing the Rext step-

wise from 100 U to 1 U. Each value of the Rext was main-

tained for 15 min and the total procedure required 6 h. The

internal resistance of the MFCs was measured through elec-

trochemical impedance spectroscopy (EIS) with a potentiostat

(VSP, Bio-Logic, France) and the slope of the polarization

curve, as previously described [22]. The EIS measure were

conducted in three-electrode configuration, with a Ag/AgCl

reference electrode inserted in the anodic chamber.

The CODwasmeasured through standardmethod [23]. The

cumulative COD removal efficiency and the Coulombic effi-

ciency h were calculated as previously described [22]:

DCODcu

�t

�¼ COD0 � CODðtÞ

COD0� 100 (1)

where DCODcu% (t) [mg L�1] is the cumulative COD removal

efficiency at time t, COD0 [mg L�1] is the initial COD and COD (t)

[mg L�1] is the COD at time t;

h�t� ¼

MZ t

0

idt

F$n$V$DCODcuðtÞ (2)

Fig. 2 e SEM images of the well-developed anodic biofilm imm

magnification. Panel (b) shows microorganisms not embedded

domestic wastewater MFC at (c) 1000£ and (d) 10000£ magnifi

extracellular polymeric matrix is more abundant than in distill


where M [g] ¼ 32 is the molecular weight of O2, F [C

(Me�)�1] ¼ 96,485 is Faraday's constant, n ¼ 4 is the number of

electrons exchanged per molecule of oxygen reduced, and V

[L] ¼ 0.7 is the anode volume.

Scanning electron microscopy

A small section of each anode with the electrochemically

active biofilm was prepared for electron microscopy by fixing

the electrode piece in 3% glutaraldehyde buffered with 0.1 M

phosphate buffer at room temperature for 24 h. After fixation,

the sample was rinsed with a the same buffer, and then

dehydrated step-wise with 30%, 40%, 50%, up to 100% in

ethanol, for 15 min at each ethanol concentration. Samples

were mounted on aluminium stubs, sputtered with gold and

examined in a DSM 940A (Zeiss, Germany). The resolution

range used for microscopy varied from 700� to 3000�. At the

end of the experiments, the dry Nafion membranes were

mounted on aluminium stubs, sputtered with platinum, and

examined by energy dispersive spectroscopy (EDS) in the

scanning electron microscope (SEM).

Results

The OCV for bothMFCs reached themaximumvalue of 788 ± 3

and 516 ± 5 mV 6 h after inoculation. However, the OCV of the

distillery wastewater MFC decreased rapidly with time,

ersed in distillery wastewater (a) 1000£ and (b) 10000£in extracellular polymeric matrix. Anodic biofilm from

cation. Electrode coverage is less homogeneous and

ery wastewater biofilm.





indicating fast depletion of organic carbon substrate (Fig. 3).

Following MFC treatment, the color of distillery wastewater

changed from dark brown to malt brown. When closed on a

100 U Rext in the second and third cycles, the domestic

wastewater MFC exhibited a similar sustainable current of

approximately 297.1 ± 3.8 and 298.1 ± 2.8 mA m�2 for six days

until substrate depletion occurred on day seven (Fig. 4(a)).

The sustainable power produced from the domestic

wastewater MFC was 170.3 ± 1.5 mW m�2. However, the

maximum current and power in the short-term polarization

curves was recorded at Rint ¼ 6 U is 2204 ± 30 mA m�2 and

621 ± 17 mW m�2, respectively, with little difference between

the second and third cycle (Fig. 5(a)). The maximum power

output under stagnant conditions was approximately 20%

lower, indicating that diffusional limitations have a limited

effect when Rext ¼ 100 U.

The difference between the short-term maximum power

output and the sustainable power output indicated that the

MFC could be operated sustainably at lower Rext [24]. The

sustainable current output of the distillery wastewater MFC

was 261.4 ± 12.7 mA m�2, without significant difference be-

tween the two cycles. The sustainable power output was

128.1 ± 6.2 mW m�2. Differently from the domestic waste-

water MFC, the current output was less stable and decreased

rapidly after two days (Fig. 4(b)). The maximum current and

power output at Rint ¼ 6 U were 1815 ± 189 mA m�2 and

364 ± 11 mW m�2, respectively (Fig. 5(b)).

The power output determined from both polarization and

one-week experiments were higher for the domestic waste-

water MFC, despite the higher COD concentration in distillery

wastewater. This finding confirms that COD concentration

alone does not allow estimation of power production in any

given wastewater, although it serves for rapid comparison

Fig. 3 e Open circuit potential (OCV) for distillery

wastewater and domestic wastewater MFCs. OCV remains

approximately constant in domestic wastewater, while the

OCV of distillery wastewater decreases nearly 30% over

seven days, likely because of partial COD removal by non-

electrochemically active microorganisms. Low OCV value

confirms that distillery wastewater is not an optimal

substrate for bioelectricity production.


between different MFCs fed with the same wastewater. It is

also likely that distillery wastewater contains a small alcohol

concentration and trace of toxic chemicals that might inhibit

electrochemically active microorganisms.

Anodic biofilms

The carbon fibres of the anode are colonized by biomass after

24 days (Fig. 2). The biofilm in the domestic wastewater MFC is

less dense and distributed in large clusters, while part of the

fibres appears free from biomass (Fig. 2(a)). The biofilm on the

anode of distillery wastewater MFC covers most of the carbon

fibre surface (Fig. 2(c)). The biofilm matrix in the domestic

wastewater MFC is more evident than in the distillery MFC

(Fig. 2(c)). Individual cells were observed only in the distillery

wastewater MFC (Fig. 2(d)). As the matrix of electrochemically

active biofilms is usually conductive [25], the lower concen-

tration of biofilm matrix in the distillery wastewater MFC

might explain the lower power output of the latter with

respect to the domestic wastewater MFC.

COD removal and coulombic efficiency

The cumulative COD removal was 74.3 and 57.8% with a h of

47% and 27% for domestic and distillery wastewater, respec-

tively. The cumulative COD removal and the h were plotted in

Fig. 6(a and b), respectively. The COD removal rate decreased

in the last five days for distillery wastewater. As both MFCs

were operated at Rext higher than the maximum sustainable

resistance, it was likely that COD removal rate can be

improved by lowering Rext. The h increased with time for both

MFCs, indicating adaptation of the electrochemically active

consortia. The low h for distillery wastewater confirmed the

prevalence of fermentative microbial over electrochemically

active consortia at the anode.

Biofouling layer and elemental composition

The biofouling of the Nafion membranes at the end of the

three cycleswas characterised by Zeta 2Dmicroscopy (Fig. S1).

The average thicknesses of the biofouling layers were

approximately 30 mm and 60 mm in distillery and domestic

wastewater, respectively (Fig. S1(a and b)). The effect of the

biofouling layer was evident in the mass transfer-limited re-

gion of the polarisation curve, where the cell potential of the

domestic wastewater MFC (Fig. 5(a)) decreased faster than the

in the distillery wastewater MFC (Fig. 5(b)). Interestingly, the

mass transfer limitation region of the domestic wastewater

MFC (Fig. 5(a)) overlapped partially with the maximum power

output region, indicating that the biofouling layer should be

reduced to increase the power output of the system.

Conversely, the organic load or the flow rate of the distillery

wastewater MFC can be further increased before the power

output is controlled by the mass transfer at the cationic

membrane.

During the operation of the systems, bacterial debris and

suspended solids settled on a Nafion membrane and formed

multiple layers. SEM-EDS analysis showed that the elemental

composition of the biofouling layers were different for do-

mestic and distillery wastewater (Fig. S2). The carbon content




Fig. 4 e (a) Current density in the domestic wastewater MFC at Rext ¼ 100 U. The current output is similar in both 2nd and

3rd cycle and it remains constant for about six days, indicating that the Rext is sustainable; (b) current density in the

distillery wastewater MFC at Rext ¼ 100U. The current output is similar in 2nd and 3rd cycle, and it decreases following MFC

inoculation.


was higher on the membrane exposed to distillery waste-

water, as expected from the higher COD concentration with

respect to domestic wastewater. Trace metals were found on

the membrane exposed to domestic wastewater. This may

partly explain its better performance as opposed to the dis-

tillery wastewater MFC, as trace metals are needed for the

overall fitness of the electrochemically active microbial

consortia.

Discussion

The first cycle under OCV conditions ensures the formation of

active biofilm on the anode. It is well-known that transfer of

anodic biofilm from already exposed to electrogenic condi-

tions shortens acclimation time and speeds up power output

production [26,27]. However, acclimation time decreases also

when biofilm grown under non-electrogenic conditions is

Fig. 5 e (a) Polarization curves of the domestic wastewater MFC

obtained at Rext ¼ 6 ± 1 U. Recirculation of the anolyte increase

distillery wastewater MFC. The maximum power output of abo


exposed to anodic potential [28]. In this study, power output

started immediately after replacement of spent wastewater

with fresh wastewater and exposure to anodic potential.

The biosolids contained in domestic wastewater deposited

on the MFC anode and on the cationic membrane, resulting in

a complex biofilm structure. On the other hand, the biofilm

observed in the anode and cationic membrane immersed in

distillery wastewater show lower biosolids concentration. It is

likely that the different power output of the two MFCs studied

here is due to the different microbial ecology of the anodic

communities. A recent study on high-strength synthetic

wastewater MFCs show biofilm formation on the electrodes

and the membrane [29]. The presence of numerous metals

and oligo-nutrients on the domestic wastewater MFC mem-

brane suggests that the microbial community in this MFC can

harbour a larger concentration of electrochemically active

bacteria, which result in a higher power output. A recent study

on MFC fed with high-strength molasses wastewater shows

. The maximum power output of about 600 mW m¡2 is

s power output of about 20%; (b) polarization curves of the

ut 350 mW m¡2 is obtained at Rext ¼ 7 ± 1 U.




Fig. 6 e Energy recovery from domestic and distillery wastewater: (a) cumulative COD removal at Rext ¼ 100 U; the COD

removal is faster in the domestic wastewater MFC; (b) the coulombic efficiency is much higher in the domestic wastewater

MFC.


that most of the bacteria present in the inoculum are also

found in the biofilm after 5-months operation. The enrich-

ment in electrochemically active strains however was not

fully demonstrated [30].

The Rint is probably the single most important electrode

parameter for power output [19]. The Rint of a MFC depends

upon the electrode material [31], electrode spacing, and

system architecture [32]. A recent review on microfluidic

MFCs analyses the adverse effects of internal resistance on

power production in MFCs and show that electrode topology

and electrode surface area/volume ratio [19]. The Rint

calculated by the slope of the polarization curve

was7.3 ± 0.3 U and was dependent on the wastewater used

or the recirculation conditions. The Rint calculated from

impedance data was 6 ± 1 U, thus inferring the two methods

are in good agreement. The low Rint measured in this MFC

assembly is very promising for effective energy recovery

from wastewater.

The two wastewaters tested in this study yielded very

different power output and, most importantly, showed the

different power output as a function of time. In fact, domestic

wastewater produces a near-constant power output, while the

Table 1 e Comparison with other MFCs with distillery and dom

WW Reactor vol.(mL)

pH Anode Cat

Distillery 501 6 Graphite plate Graphi

7270 7e8 Carbon paper Carbon

700 7.8 Interlaced carbon yarn Carbon

Domestic 28 e Carbon paper Carbon

28 e Carbon paper Carbon

21 7.5 Carbon cloth Carbon

150 7 CNT sponge CNT sp

700 8 Interlaced carbon yarn Carbon

Synthetic 26 e Graphite fibre brush-small

(C-MFC)

Carbon

300 e Graphite fibre brush-large

(B-MFC)

Carbon


power output of the distillery wastewater MFC decreases

rapidly with time. This unusual behaviour of distillery

wastewater MFCs has not been observed in previous litera-

ture, where continuous flow MFCs were used [19,33,34]. It

should be noted that distillery wastewater produces a low

power output despite its high COD. Biological oxygen demand

(BOD) should be used instead of COD to obtain a meaningful

correlation between bioavailable substrates and power

output.

Microorganisms rapidly foul cationic exchange mem-

branes during MFC operations. After 90 days, fouling slows

down cation diffusing, thus increasing pH gradient and the

corresponding potential loss, which in turn decreases the

maximum power output to 30% in a synthetic wastewater

MFC. The fouling layer was composed of attached microor-

ganisms and inorganic salts precipitated from the anodic

medium. However, the thickness of the fouling layer was

not measured [33]. Long-term membrane fouling (250 days)

reported more than 50% decrease in power output of mi-

crobial desalination cells. The fouling seems to affect pref-

erentially cationic over anionic exchange membranes [35].

However, biofouling may be an indirect indicator of

estic wastewater as a substrate.

hode Max. power density(mW/m2)

COD removal(%)

Reference

te plate 124 72.8 [33]

paper 124 80e90 [34]

paper 348 57 Present work

paper 72 42 [41]

cloth 103 71 [42]

cloth 464 89e93 [21]

onge 1240 90 [16]

paper 594 68 Present work

cloth 2400 e [20]

cloth 1430 e [20]





membrane efficiency. In fact, a study on membrane fouling

in two-chamber synthetic wastewater MFCs showed that

the internal resistance of a Nafion membrane is due not to

biofouling but to the increase of other cations from the

anodic solution replacing the sulfonate groups of the

membrane [36].

The results presented here show that membrane fouling is

much higher in the membrane exposed to domestic waste-

water than in that exposed to distillery wastewater. However,

the Coulombic efficiency in the earlier is higher than in the

latter, suggesting that cation transfer across the membrane is

not a rate-limiting step for the overall energy conversion

process.

Energy recovery from distillery wastewater varies

depending on its actual chemistry (raw or partially degraded)

and the MFC configuration. Post-methanation distillery

wastewater yields 0.5 W m�3 in two-chambered MFC [37] A

continuous flow two-chambered- MFCs fed with raw distillery

wastewater removed 80e90% of the influent COD with

124 mW m�2 of power output [38]. Two-chambered thermo-

philic MFCs with graphite-felt electrodes produce nearly

1 W m�2 when fed with distillery wastewater with ~80% COD

removal and ~80% Coulombic efficiency [29]. The power

output of the MFC presented here is comparable to those re-

ported in previous studies (Table 1).

Treatment of distillery wastewater is routinely carried

out with fungal treatment. A recent study reports 61%

color removal and 65% COD removal in approximately 14 days

[39]. Extracellular ligninolitic enzymes secreted by fungi

are the main responsible for distillery wastewater decolouri-

zation [40].

Conclusions

Batch MFCs with interlaced carbon yarn anode and air-

breathing cathode were used to treat raw domestic and dis-

tillery wastewaters. The recorded power output of

621 ± 17 mW m�2 for domestic wastewater is consistent with

previous MFC studies. However, the power output measured

for distillery wastewater was much lower, 364 ± 11 mW m�2.

Coulombic efficiency and COD removal were much higher for

the domestic wastewater MFC than the distillery wastewater

MFC. Analysis of the biofouling layer on the Nafionmembrane

showed that the low energy recovery from distillery waste-

water at Rext ¼ 100 U was not due to cation diffusional limi-

tations through the membrane. The rapid decrease of current

with time in the distillery wastewater MFC suggests that dis-

tillery wastewater alone does not support efficient electro-

chemically active microbial communities.

Acknowledgements

Enrico Marsili was supported by the EU-FP7 Marie Curie In-

ternational Reintegration Grant P.N. 231072.We thank Amruta

Bhave for her help with MFC operation and Dr Sharon Long-

ford and Dr Seratna Guadarrama for their help with the edit-

ing of the manuscript.


Appendix A. Supplementary data

Supplementary data related to this article can be found at

http://dx.doi.org/10.1016/j.ijhydene.2014.07.085.

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Carbon yarn microbial fuel cells

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