Endocrine disruptive estrogens role in electron transfer: bio-electrochemical remediation with microbial mediated electrogenesis.
ABSTRACT Bioremediation of selected endocrine disrupting compounds (EDCs)/estrogens viz. estriol (E3) and ethynylestradiol (EE2) was evaluated in bio-electrochemical treatment (BET) system with simultaneous power generation. Estrogens supplementation along with wastewater documented enhanced electrogenic activity indicating their function in electron transfer between biocatalyst and anode as electron shuttler. EE2 addition showed more positive impact on the electrogenic activity compared to E3 supplementation. Higher estrogen concentration showed inhibitory effect on the BET performance. Poising potential during start up phase showed a marginal influence on the power output. The electrons generated during substrate degradation might have been utilized for the EDCs break down. Fuel cell behavior and anodic oxidation potential supported the observed electrogenic activity with the function of estrogens removal. Voltammetric profiles, dehydrogenase and phosphatase enzyme activities were also found to be in agreement with the power generation, electron discharge and estrogens removal.
- SourceAvailable from: Chandrasekhar Kuppam[Show abstract] [Hide abstract]
ABSTRACT: A novel bio-electrohydrolysis system (BEH) based on self-inducing electrogenic activity was designed as pretreatment device to enhance biohydrogen (H2) production efficiency from food waste. Two-stage hybrid operation with hydrolysis in the initial stage and acidogenic fermentation of the resulting hydrolysate (after hydrolysis) for H2 production in the second stage was evaluated. Application of variable external resistances viz., 10Ω, 100Ω, 1000Ω and closed circuit (CC) influenced the hydrolysis of substrate in BEH system and hydrogen production in acidogenic reactor compared to control. Pretreated substrate at 100Ω documented higher H2 production (1.05l) than 10Ω (0.93l), CC (0.91l), 1000Ω (0.88l) and control operation (0.68l). Comparatively, 10Ω documented higher substrate degradation (53.4%) followed by CC (52.42%), 100Ω (49.51%), 1000Ω (47.57%) and control (43.68%). Voltammetric profiles were in agreement with the observed bio-electrohydrolysis and H2 production efficiency.Bioresource Technology 02/2014; 165:372-382. · 5.04 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The feasibility of removing estrogens including 17β-estradiol (E2) and 17α-ethynyl-estradiol (EE2) was studied in a bio-electro-Fenton (BEF) system equipped with a Fe@Fe2O3/non-catalyzed carbon felt (NCF) composite cathode. E2 and EE2 were removed by reactive oxidants, produced by bio-electro-Fenton system and zero-valent iron/O2 system, as well as adsorption. Under closed-circuit condition, 81% of E2 and 56% of EE2 were removed within 10h in the system, in which the highest concentration of total iron ions and H2O2 reached 81 and 1.2mg/L, respectively. The maximum power density of BEF system equipped with Fe@Fe2O3/NCF electrode was 4.35W/m(3). Two intermediates of E1 and 6-OH-E2 were identified during Fenton oxidation of E2. This study demonstrates the degradation fate of E2 and EE2 in a BEF system equipped with Fe@Fe2O3/NCF electrodes, which provides a promising and cost-effective solution for the removal of recalcitrant contaminants with simultaneous power generation.Bioresource Technology 04/2013; 138C:136-140. · 5.04 Impact Factor
- Bioresource Technology 03/2014; 165:355-364. · 5.04 Impact Factor
Endocrine disruptive estrogens role in electron transfer: Bio-electrochemical
remediation with microbial mediated electrogenesis
A. Kiran Kumarb, M. Venkateswar Reddya, K. Chandrasekhara, S. Srikantha, S. Venkata Mohana,⇑
aBioengineering and Environmental Center (BEEC), Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 607, India
bIICT-CCMB Dispensary, Indian Institute of Chemical Technology (CSIR-IICT), Hyderabad 500 607, India
a r t i c l ei n f o
Received 24 June 2011
Received in revised form 12 October 2011
Accepted 12 October 2011
Available online 20 October 2011
Bio-electrochemical treatment (BET)
Microbial fuel cell (MFC)
a b s t r a c t
Bioremediation of selected endocrine disrupting compounds (EDCs)/estrogens viz. estriol (E3) and ethy-
nylestradiol (EE2) was evaluated in bio-electrochemical treatment (BET) system with simultaneous
power generation. Estrogens supplementation along with wastewater documented enhanced electro-
genic activity indicating their function in electron transfer between biocatalyst and anode as electron
shuttler. EE2 addition showed more positive impact on the electrogenic activity compared to E3 supple-
mentation. Higher estrogen concentration showed inhibitory effect on the BET performance. Poising
potential during start up phase showed a marginal influence on the power output. The electrons gener-
ated during substrate degradation might have been utilized for the EDCs break down. Fuel cell behavior
and anodic oxidation potential supported the observed electrogenic activity with the function of estro-
gens removal. Voltammetric profiles, dehydrogenase and phosphatase enzyme activities were also found
to be in agreement with the power generation, electron discharge and estrogens removal.
? 2011 Elsevier Ltd. All rights reserved.
Endocrine disrupting compounds (EDCs)/estrogens are exoge-
nous substances that interferes and alters the functions of endo-
crine system and consequently causes adverse health effects in
an intact organism, or its progeny or (sub) populations (Damstra
et al., 2002). Estrogens indirectly interact with the endocrine sys-
tem that regulates the body’s function resulting in excessive secre-
tion or suppression of hormones by the phenomenon called
endocrine disruption, which may involve the appearance of infer-
tility, sexual under development, altered or reduced sexual behav-
ior, attention deficit or hyperactivity, altered thyroid or adrenal
cortical function, increased incidents of certain cancers, birth de-
fects, etc. (Vogel, 2005). Even at nanogram levels these compounds
increase the risk of cancer and decrease egg and sperm production,
reduce gamete quality and tend to complete feminization of male
fish (Notch et al., 2007). Occurrence of EDCs in the aquatic water
bodies including fresh water environment and their possible dis-
ruptive effects on indigenous fauna was reported in many of the
countries (Damstra et al., 2002). From the recent past, concern
about the environmental fate and behavior of natural and synthetic
organic chemicals detected in water has been increased. Natural or
synthetic estrogens exhibit two or three orders of magnitude high-
er estrogenic activity than the chemical compounds and are con-
sidered to be dominant contributors to estrogenic activity in the
treated wastewater (Barnes et al., 2008). Estrogens are considered
as pseudo persistent pollutants due to their continuous entry into
the environment through sewage/domestic wastewater. Removal
of estrogens is extremely important to reduce the potential risk
caused by them in treated wastewater. Various treatment method-
ologies have been reported for the removal of estrogens, viz. en-
zyme mediated, ultrasound destruction, ozonation, adsorption,
potassium ferrate treatment, membrane bioreactors, and reverse
osmosis, etc. in the literature (Huang et al., 2005; Auriol et al.,
2006, 2008; Sei et al., 2008; Mao et al., 2009; Kiran Kumar et al.,
2009, 2011). Estrogens degradation efficiency with biocatalyst
was reported but with lower concentrations (Jobling et al., 1998).
However, the removal efficiencies strongly dependent on the type
0960-8524/$ - see front matter ? 2011 Elsevier Ltd. All rights reserved.
Abbreviations: AO, activation over-potentials; BET, bio-electrochemical treat-
ment; C, control operation; C1, concentration 1 (500 lg/L); C2, concentration 2
(1000 lg/L); C3, concentration 3 (2000 lg/L); COD, chemical oxygen demand; CP,
concentration polarization; CV, cyclic voltammetry; DH, dehydrogenase; DSW,
designed synthetic wastewater; DSWE, DSW and E3; e-, electrons; E0
anodic potential; Eanodic, anodic potential at resistance; EDCs, endocrine disruptive
estrogens compounds; E3, estriol; EE2, ethynylestradiol; EIA, enzymatic immuno-
assay; ELISA, enzyme-linked immunosorbent assay; FAD+, flavin adenine dinucle-
otide; FADH2, flavin adenine dinucleotide (reduced); H+, protons; I, current; LSV,
linear sweep voltammetry; MFC, microbial fuel cells; NAD+, nicotinamide adenine
dinucleotide; NADH + H+, nicotinamide adenine dinucleotide (reduced); OCV,
potential difference/open circuit voltage; OL, ohmic losses; OLR, organic loading
rate; PEM, proton exchange membrane; PT, phosphatase; RDAP, relative decrease in
the anode potential; SDR, substrate degradation rate; TF, triphenyl formazan; TTC,
2,3,5-triphenyltetrazolium chloride; UASB, upflow anaerobic sludge blanket; VFA,
volatile fatty acids; % I, percentage inhibition.
⇑Corresponding author. Tel./fax: +91 40 27191664.
E-mail address: firstname.lastname@example.org (S. Venkata Mohan).
Bioresource Technology 104 (2012) 547–556
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/biortech
of treatment applied and the physicochemical properties of the
estrogens (Kiran Kumar et al., 2009, 2011).
Microbial fuel cell (MFC) is a hybrid bio-electrochemical system
which directly transforms chemical energy stored in chemical
bonds of substrate into electrical energy via electrochemical reac-
tions involving biochemical pathways where microorganisms
serve as biocatalyst (Lefebvre et al., 2011; More and Ghangrekar,
2010; Oh et al., 2010; Venkata Mohan et al., 2008b,c, 2009;
Hamelers et al., 2010). The bio-potential developed between the
bacterial metabolic activity [redox reactions generating electrons
(e-) and protons (H+)] and electron acceptor conditions (separated
by a membrane) leads to generate bioelectricity in MFC. Exploiting
wastewater as substrate to harness electricity is considered as a
sustainable approach and is the present age of energy research.
More recently, MFC function as bioelectrochemical treatment sys-
tem (BET) was established where several pollutants viz. azo dyes,
phenol, nitrates, sulphates, chloroaniline, petroleum sludge, etc.
have been reported through the anodic oxidation or cathodic
reduction reactions (Luo et al., 2009; Mu et al., 2009a,b; Butler
et al., 2010; Hamelers et al., 2010; Mohanakrishna et al., 2010;
Venkata Mohan et al., 2010b; Venkata Mohan and Chandrasekhar,
2011). Anode chamber of MFC/BET resembles anaerobic treatment
unit where substrates gets metabolized into its products through
redox reactions and enzyme activities. Enzyme catalyzed transfer
of electrons from an intracellular electron carrier molecule (redox
mediator) to proton (H+) will occur as a part of metabolic activity
during fermentation process (Venkata Mohan et al., 2010a;
Venkateswar Reddy et al., 2010). Oxidation of substrate in order
to obtain energy and synthesis of cellular components from carbon
source through energy coupling mechanisms is a general process
during bacterial metabolic activities. The pollutants present in
wastewater can also act as mediators between the fuel cell compo-
nents, especially electrodes and biocatalyst, and get reduced.
In this context, detailed studies were performed to evaluate the
function of BET system in remediation of selected estrogen com-
pounds with simultaneous power generation. The functional role
of estrogens in electron discharge during BET operation was also
studied. Phosphatase (PT) and dehydrogenase (DH) are important
enzymes involved in the carbon degradation and redox reactions
for the inter-conversion of metabolic intermediates. PT and DH
activities were also evaluated during estrogens bioremediation un-
der microbial electrogenesis. Synergistic interaction of biochemical
and electrochemical oxidation processes during estrogens removal
was discussed in detail.
2. Experimental design
2.1. Endocrine disruptive compound (EDC)
Estriol [E3, C18H24O3; 1,3,5 (10)-estratriene-3,16a,17b-triol;
Sigma–Aldrich] and 17a-ethynylestradiol [EE2; C20H24O2, 17-ethy-
phenanthrene-3,17-diol; Sigma–Aldrich] were used as model
estrogen compounds after diluting to the required concentrations
Anaerobic consortia from operating full scale UASB reactor
treating wastewater was used as biocatalyst (Venkata Mohan
et al., 2008a). Parent culture was enriched under anaerobic micro-
environment at pH 6.0 in designed synthetic wastewater (DSW)
constituting glucose (3 g/L) as carbon source along with the other
nutrients such as, NH4Cl (0.5 g/L), KH2PO4 (0.25 g/L), K2HPO4
(0.25 g/L), MgCl2(0.3 g/L), CoCl2(25 g/L), ZnCl2(11.5 mg/L), CuCl2
(10.5 mg/L), CaCl2 (5 mg/L), MnCl2 (15 mg/L), NiSO4 (16 mg/L)
and FeCl3(25 mg/L), with a chemical oxygen demand (COD) of
3600 mg/L (80 rpm; 48 h).
2.3. System configuration
Single chambered MFC/BET was fabricated with open-air cath-
ode using ‘perspex’ material (total/working volume: 0.5/0.42 L).
Non-catalyzed graphite plates [5 ? 5 cm; 10 mm thick; surface
area 70 cm2(plain cathode) and 83.5 cm2(perforated anode;
0.1 cm diameter)] were used as electrodes. Prior to use, electrodes
were soaked overnight in deionized water (?18 h). Proton ex-
change membrane (Nafion 117; Sigma–Aldrich) was fixed between
anode and cathode. Top portion of the cathode was exposed to air
while bottom portion was fixed to PEM and was in contact with
wastewater. Anode was completely submerged in the anolyte (Sfig.
1). Copper wires were used for contact with electrodes after sealing
with epoxy sealant. Provisions were made in the design for sam-
pling ports, wire input points (top), inlet and outlet ports and gas
outlet. Leak proof sealing was provided at joints to maintain anaer-
obic microenvironment in the anode compartment.
Anodic chamber was inoculated with enriched anaerobic cul-
ture (0.04 L) by dissolving in DSW (0.38 L). Prior to feeding, pH of
the wastewater was adjusted to 6 (acidophilic) using concentrated
orthophosphoric acid (88%) or 1 N NaOH. Wastewater was fed to
reactor from inlet provided at the bottom of anode chamber to
facilitate the flow in upward direction passing through anode to-
wards cathode (advective flow). Anolyte was continuously stirred
at 80 rpm to eliminate concentration gradient during operation.
BET was operated in fed batch mode at room temperature
(29 ± 2 ?C). Before every feeding event, inoculum was allowed to
settle down (30 min; settling) and exhausted feed (0.38 L) was re-
moved (decanted; 15 min) under anaerobic conditions. Settled
inoculum (?0.04 L by volume) was used for subsequent opera-
tions. Feeding, decanting and recirculation operations were per-
formed using peristaltic pumps controlled by electronic timer.
After every feeding event, anode chamber was sparged with oxy-
gen free N2gas for 2 min to maintain anaerobic microenvironment.
Initially, BET was operated at an OLR of 0.195 kg COD/m3day for
stabilized performance with respect to power generation and sub-
strate removal. After obtaining stable performance the anode
chamber was fed with EDC compounds dissolved in DSW. OLR
was maintained constantly (0.458 kg COD/m3day) throughout
the operation and the concentration of EDCs was varied. Different
concentrations of E3 was dissolved in DSW and fed to reactor [C1,
500 lg/L; C2, 1000 lg/L; C3, 2000 lg/L]. Remediation of E3 was
also evaluated under 2000 mV poised potential (PP) with C2 con-
centration. 2000 mV was selected as external potential based on
the observations made in previous study where increased treat-
ment efficiencies were observed (Srikanth et al., 2010). Remedia-
tion of EE2 was also evaluated at C2 [1000 lg/L] concentration.
Operation details along with the performance were as depicted
in Table 1.
Power output and substrate degradation were considered to as-
sess the performance of BET during operation with varying nature
and concentrations of estrogens. Potential difference/open circuit
voltage (OCV) and current (I) (in series; 100 X) measurements
were recorded by digital multi-meter. Power (mW) was calculated
using P = IV. Power density (mW/m2) and current density (mA/m2)
were calculated by relating the obtained power and current with
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
the surface area (m2) of the anode. Fuel cell behavior of BET was
evaluated in terms of polarization under varying external resis-
tance (30–0.05 kO). The anodic oxidation potential, its relative
change with external resistance and cell emf were measured and
calculated according to Venkata Mohan et al. (2008a,b). COD
(closed refluxing method), VFA (volatile fatty acids) and pH were
determined according to the standard methods (APHA, 1998). Car-
bohydrates were analyzed by anthrone method (Morris, 1948).
Dehydrogenase and phosphatase enzymes activities of mixed cul-
ture were estimated by a method described elsewhere (Venkate-
swar Reddy et al., 2010). Toxicity of the wastewater before and
after treatment was analyzed using TOXTRAK toxicity test kit
(HACH instruments) with both the estrogens at 1000 lg/L of estro-
gens concentration. This test provides close approximates of the
inhibitory effects of toxicity experienced by Escherichia coli.
2.5.1. Estrogens estimation
Residual concentration of estrogens in aqueous phase was esti-
mated by employing direct competitive enzymatic-immunoassay
(EIA) using kits (E3-Accu-Bind Microwells, Monobind; EE2-Ecolog-
iena, Japan Envirochemicals Ltd.) (Kiran Kumar et al., 2009, 2011).
Upon addition of E3 (antigen) in the sample along with biotinyla-
ted antibody and E3-enzyme conjugate for binding onto the lim-
ited number of anti E3 (antibody) sites on the microplates. After
incubation (60 min; at room temperature), the micro-plates were
subjected to solid-phase washing followed by addition of enzyme
substrates (15 min; at room temperature). In the case of EE2,
EE2-antigen in the sample and EE2-enzyme conjugate binds onto
the limited number of anti EE2 (antibody) sites on the microplates.
After incubation (60 min; at room temperature), the micro-plates
were subjected to solid-phase washing followed by the addition
of enzyme substrates. The absorbance (color development) was
determined at 450 nm employing ELISA reader (BIOTEK). Total
estrogens concentrations were calculated based on the prepared
calibration curve using a series of standards (E3, Accu-Bind micro-
wells; EE2-Ecologiena), where, color intensity is inversely propor-
tional to the total estrogens concentration in the sample
(R2= 0.9912 (E3); 0.9914 (EE2)].
2.5.2. Bio-electrochemical evaluation
Bio-electrochemical behavior of BET was studied by cyclic vol-
tammetry (CV) using potentiostat–glavanostat system (Autolab,
PGSTAT12, Ecochemie) during the stabilized phase of operation.
CV was performed by applying a potential ramp at a scan rate of
30 mV/s over the range from +0.5 V to ?0.5 V to working electrode
(anode) to gradually change the potential and then reversing the
scan returns to the initial potential. Bio-anode was polarized
employing linear sweep voltammetry at applied voltage between
0.5 V and 0.1 V. All the electrochemical assays were performed
in situ in BET by considering anode (graphite) as working electrode
and cathode (graphite) as counter electrode, against saturated Ag/
AgCl reference electrode.
Phosphatase enzyme activity of mixed culture was estimated by
a method based on the reaction of disodium phenyl phosphate
(Venkateswar Reddy et al., 2010). Ten milliliters anodic mixed cul-
ture was added with 2 mL of methyl benzene, 10 mL disodium
phenyl phosphate, 10 mL citrate buffer (pH 7) in a sequence in
100 mL volumetric flask. After shaking at 200 rpm for 20 min the
flask was incubated at 37 ?C for 24 h and made up to 100 mL with
distilled water. The mixture was then filtered with compact filter
papers. The filtrate was then transferred into 100 mL volumetric
flask and 5 mL borate sodium hydroxide buffer (pH 9.6), 19 mL dis-
tilled water, 1 mL of Gibbs reagent (0.2%) were added sequentially,
and the solution in the flask was made up to 100 mL with distilled
water (37 ?C). The mixture was gently stirred and incubated at
room temperature for 20 min to develop color and the absorbance
was measured at 578 nm.
Dehydrogenase enzyme activity of mixed culture was estimated
by a method based on the reduction of 2,3,5-triphenyltetrazolium
chloride (TTC) (Venkata Mohan et al., 2010a; Venkateswar Reddy
et al., 2010). Five milliliters TTC (5 g/L) and 2 mL of glucose solu-
tion (0.1 mol/L) were added to 5 mL of sample and the resulting
solution was stirred continuously for 20 min at 200 rpm prior to
incubation at 37 ?C for 12 h. To this 1 mL of concentrated sulfuric
acid was added to stop the deoxidization followed by 5 mL of
methylbenzene to extract the triphenyl formazan (TF) formed in
the reaction mixture, and agitated at 200 rpm for 30 min. After
keeping ideal for 3 min, the reaction mixture was then centrifuged
at 4000 rpm for 5 min and the supernatant absorbance was mea-
sured at 492 nm using spectrophotometer.
3. Results and discussion
3.1. Remediation through microbial electrogenesis
3.1.1. Estrogens removal
Both the E3 and EE2 showed removal under electrogenesis,
however, E3 showed higher removal efficiency. Removal of E3
showed a decreasing pattern with increasing concentration from
C1 to C3 supporting the toxic effects of estrogens on the biocatalyst
at higher concentrations (Fig. 1a). E3C1 showed higher removal
(50.28%) followed by E3C2 (41.04%) and E3C3 (16.25%). Subse-
quently, BET was operated at C2 concentration of E3 under poised
potential which showed a marginal increment in the E3 removal
(48.48%). However, the marginal increment in the removal was
not observed to be economically viable and hence the EE2 removal
was evaluated without poising the potential at C2 concentration
(44.60%). When the results were evaluated with time, E3 showed
a gradual removal pattern throughout the operation time (48 h),
while EE2 showed lower removal pattern initially and increased
Consolidated data representing the maximum values of power generation and substrate utilization along with EDCs removal during BET operation under varying experimental
Description of the experiment Maximum
E3 spiked at 500 lg/L concentration
E3 spiked at 1000 lg/L concentration
E3 spiked at 2000 lg/L concentration
E3 spiked at 1000 lg/L concentration and
poised potential of 2 V for initial 2 h
EE2 spiked at 1000 lg/L concentration
1.85 ? 1019
2.87 ? 1019
4.96 ? 1019
9.98 ? 1019
5.34 ? 1019
EE2C241451.0561.7792.1644.609.62 ? 1019
aDerived from charge obtained during voltammetric analysis at 30 mV/s scan rate.
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
with time (Fig. 1b). Both the estrogens (E3C2 and EE2C2) showed
reduction in toxicity levels after treatment in BET. EE2 bearing
wastewater showed higher initial toxicity levels (% I, 17%) com-
pared to E3 (8%). After treatment, complete reduction in toxicity le-
vel was observed in E3 bearing wastewater (0%), while negligible
reduction in toxicity levels (15%) was observed with EE2 bearing
wastewater. The simultaneous bio-electrochemical reactions hap-
pened during initial phase might have induced the electrochemical
oxidation favoring the break down of EE2 into simpler form sup-
porting its removal during the later phase. Estrogens function in
electron transfer as shuttler between anode and biocatalyst was
depicted in Fig. 2.
3.1.2. Substrate removal
COD removal efficiency decreased with increasing estrogens
concentration (C: 78.01%; E3C1: 79.5%; E3C2: 75.87%; E3C3:
73.03%) which might be due to the inhibitory effect of EDCs on bac-
terial metabolic activities (Fig. 1c). However, the application of
poised potential showed an increase in COD removal efficiency
(79%). On the contrary, carbohydrate removal was observed to in-
crease with increasing estrogens concentration (C: 85.78%; E3C1:
87.3%; E3C2: 90.64%; E3C3: 74.6%; E3C2-PP: 91.98%). This might
be due to the requirement of electrons to induce the bio-electro-
chemical treatment which can be generated from the glucose oxi-
dation. The EE2 spiked anodic fuel showed marginally higher
carbohydrate removal (92.16%) over E3 spiked fuel (90.64%). How-
ever the COD removal efficiency was comparatively less (61.77%)
in the case of EE2 bearing wastewater. This might be due to the ra-
pid conversion of carbon to its intermediary metabolites in the due
course of generating electrons. The generated electrons might not
be further converted to their respective end products due to the
complex nature of EE2 over E3.
Phosphatase (PT) function is to deactivate the carbon source by
removing phosphate (PO3?) group without which cannot enter in
to any metabolic pathway. PT synthesised and excreted by bacteria
also involves in the transformation of organic and inorganic phos-
phorus compounds in the environments (Venkateswar Reddy et al.,
2010). Initial PT activity was 2.8 lg/mL and with time the activity
was changed with respect to the experimental variations studied
(Fig. 3a). PT activity showed an increasing trend with time in all
the experimental variations studied except E3C3 and EE2C2, where
the PT activity was dropped after certain time of operation after
reaching the maximum activity. Maximum PT activity was de-
creased with increasing estrogens concentration (C: 6.9 lg/mL;
E3C1: 6.8 lg/mL; E3C2: 5.4 lg/mL; E3C3: 4.9 lg/mL) suggesting
higher substrate utilization. Even at C2 concentration, PT activity
was higher for E3, while it was lower for EE2 supporting higher
glucose oxidation in presence of EE2. Bio-electrochemical break
down of estrogens requires electrons, which are generated during
substrate degradation. Higher carbon utilization was observed
with higher estrogens concentration. Moreover, EE2 was relatively
stable when compared to E3 which also enhanced the carbon uti-
lization. The lowering of PT activity with increasing estrogens con-
centration strongly supports the same.
3.1.4. Dehydrogenase catalyzed redox reactions
Dehydrogenase (DH) is an intracellular enzyme involved in the
redox reactions during the substrate metabolism. DH involves in
the transfer of protons (H+) between metabolic intermediates
using several mediators (NAD+, FAD+, etc.) availing H+and e?in
the cell leading to the generation of potential difference which is
essential for power generation. The transfer of H+in between the
substrates causes the potential difference in the system which in-
creases the e?flow showing higher current output (Venkata
Mohan et al., 2010a). Initial DH activity was 3.2 lg/mL and varied
with time as a function of estrogens concentration and nature dur-
ing the experimental study (Fig. 3a). On the contrary to PT activity,
ControlE3C1E3C2E3C3 E3C2-PP EE2C2
EDC removal efficiency (%)
0 1020 3040 50
Power density (mW/m2)
EDC removal (μ μg/L)
Removal eficiency (%)
Fig. 1. (a) Variation in the estrogen removal pattern with the function of
experimental conditions studied; (b) EDC removal and power generation efficiency
against time with the function of experimental conditions studied; (c) COD and
carbohydrate removal efficiency against experimental variations studied.
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
DH activity showed an increasing trend with time in all the exper-
imental variations except E3C3, where the DH activity was
dropped after reaching maximum value at 24th h. Higher DH activ-
ity with time indicates higher H+shuttling between metabolic
intermediates and continuous redox reactions supporting the
bio-electrochemical remediation of estrogens. EE2C2 showed max-
imum DH activity (7.6 lg/mL) indicating higher redox reactions
providing reducing powers from the substrate metabolism. Poised
potential also showed marginal increment in the DH activity
(6.4 lg/mL) compared to the control (5.9 lg/mL) supporting the
marginal improvement in the estrogens removal.
3.1.5. Change in redox state and acid metabolites
VFA and pH are integral expressions of the redox conditions of
any anaerobic process as well as intrinsic index of the microbial
group. VFA production is associated with the conversion of organic
fraction to acid metabolites in the acidogenic microenvironment.
Marked variation in VFA concentration was observed during BET
operation with the function of experimental variations studied
(Fig. 3b). VFA profile showed almost similar pattern in all the cases
except EE2C2, where high VFA generation was observed which sus-
tained for extended period and dropped at the end, while in all
other cases almost similar concentration of VFA (685 ± 20 mg/L)
was generated till 24th h and dropped thereafter. The higher car-
bon utilization observed in the case of EE2C2 supports the VFA
generation. The observed higher DH activity and drop in PT activity
also strongly supported the simultaneous redox reactions favoring
the availability of reducing powers required for bio-electrochemi-
cal remediation. System pH was observed to corroborate well with
the VFA profile. Initial operating pH was adjusted to acidophilic
(pH 6) because of the known fact that the power generation effi-
ciency will be higher under acidophilic operation (Raghavulu
et al., 2009). Moreover, the proton transfer and electron discharge
between metabolic intermediates will be higher under acidophilic
redox environment which facilitates higher availability of reducing
powers (Venkata Mohan et al., 2010a) and this will have positive
impact on the break down of pollutants (estrogens). Generation
and consumption of VFA was observed in all the experimental vari-
ations studied resulting in a drop in the pH till 24th h and also a
gradual increment thereafter. Whereas, in the case of EE2C2, a
gradual and continuous drop in pH was observed till the end of
experiment. This might be due to the high redox reactions cata-
lyzed by DH, inter converting the acid metabolites and generating
the H+and e?during operation. Increase in VFA concentration dur-
ing BET operation enumerated the effective functioning of the aci-
corresponding power production, substrate degradation and en-
3.2. Estrogens role in electron transfer
Variations in the OCV, current density and power density were
depicted in Fig. 4a. Control operation showed an OCV of
394 ± 2 mV and CD of 162 ± 2 mA/m2resulting in a PD of
19.5 ± 1 mW/m2. Addition of both the estrogens has shown the
increment in power generation efficiency of BET compared to con-
trol which strongly supports their positive role in electron trans-
port (Fig. 2). However, the power generation efficiency varied
with the function of nature and concentration of the estrogens.
The addition of E3 (1000 lg/L) to the anodic fuel enhanced the
power output (E3C1, 395 ± 2 mV and 42.50 ± 1 mW/m2; E3C2,
420 ± 1 mV and 44.52 ± 2 mW/m2). However, further increment
in theE3 concentrationshowed
19 ± 0.5 mW/m2) in the power output suggesting the inhibitory
effect of estrogens on anodic biocatalyst (Fig. 1b). Application of
external potential to the system at C2 concentration showed neg-
46.5 ± 2 mW/m2) which corroborated well with the observed
estrogens removal. The voltage output was almost similar to E3
when EE2 was added at C2 concentration (413 ± 1 mV). However,
a drop(281 ± 1 mV and
output (427 ± 1 mVand
Induced EO through DET
EDC as electron shuttler
Fig. 2. Schematic representation of hypothetical EDC break down to its end products through electrochemical oxidation and its function as mediator between anode and
biocatalyst (EO: electrochemical oxidation; EDC: endocrine disrupting compounds; e?: electron).
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
the electron discharge (current) was increased resulting in higher
power (51 ± 0.5 mW/m2). The time taken to reach the maximum
power output was higher with EE2 (around 30th h) than E3
(around 24th h). This might be attributed to the gradual break
down of the EE2 molecule into its metabolic intermediates under
microbial electrogenesis due to its stable structure than E3.
3.2.1. Fuel cell behavior in response to estrogen removal
Polarization curve is plotted with current density against poten-
tial and power density under varying resistances (30–0.05 kX) to
visualize the maximum power density and current density with re-
spect to the nature and concentration of estrogens after attaining
maximum voltage (Fig. 4b). Maximum power density was found
with EE2C2 (40.02 mW/m2) at cell design point (400 O) followed
by E3C2 (34.56 mW/m2at 500 O), E3C2-PP (31.84 mW/m2at
300 O), control (24.32 mW/m2at 500 O), E3C1 (22.26 mW/m2at
300 O) and E3C3 (20.19 mW/m2at 300 O). Polarization curve helps
to find the cell design point and is a usual practice to operate the
fuel cell at the left side of the power density peak, where high volt-
age or low current density is possible. Fuel cell operation at higher
power density means operation at lower voltages (lower cell effi-
ciency), while operation at peak power density can cause instabil-
ity because the system has a tendency to oscillate between lower
and higher current densities. According to this principle the BET
fed with estrogens can be operated beyond 300 O for all the exper-
imental variations except EE2C2 and E3C2 where cell design points
were obtained at 400 O and 500 O, respectively. Rapid voltage sta-
bilization was observed at higher resistances compared to lower
resistances in all the cases, especially in EE2C2 operation. Rela-
tively higher electron discharge observed at lower resistances
might be the probable reason for higher potential drop and slow
stabilization of the voltage. At lower resistances the electrons
move more easily through the circuit than at higher resistance, oxi-
dizing electron carriers at the anode. This also might have helped
in the oxidation of estrogens at lower resistances increasing the
The potential curve in the polarization helps to understand the
losses during electron transfer in fuel cells. Electron transfer (direct
or mediated) from the bacteria towards the electrode in the anode
chamber is generally hampered by anodic over-potentials, which
can be described as transfer resistances and they lower the energy
efficiency of the fuel cell. Activation overpotentials (AO), ohmic
losses (OL) and concentration polarization (CP) are crucial during
fuel cell operation (Rinaldi et al., 2008; Venkata Mohan and Chan-
drasekhar, 2011). Oxidation of a compound at the anode surface or
reduction of a compound at the bacterial surface or its interior re-
quires activation energy which incurs a potential loss, generally
described as AO. OL are caused by electrical resistances of elec-
trodes, electrolyte and membrane and they are especially impor-
tant at higher current levels. In the present study, the addition of
EDCs to the anodic fuel helped in overcoming the potential losses,
especially with EE2. However, at very high concentration the losses
were increased again depicting lower PD and CD. Poised potential
also helped in decreasing the losses which is visualized as incre-
ment in the current, however is negligible. CP occurs when sub-
strate oxidizes faster at the anode generating more electrons
than that can be transported to the anode surface and subse-
quently to the cathode. This enables a large oxidative force on
the anode which results in the drastic potential drop making the
fuel cell unstable. In the present study, the higher electrons
released during anodic oxidation might be used for the estrogens
oxidation, especially in the case of EE2 which helps to overcome
the CP. Supply of sufficient substrate to the anode at rates of at
least the equivalent of the current generation is crucial to sustain
the current generation. Limited mass transfer of substrate towards
the anode can result in concentration or mass transfer losses (Lee
et al., 2009).
3.2.2. Cell emf and anodic oxidation potential
The anode potential and cell emf (vs Ag/AgCl (S)) were mea-
sured across various resistances (30–0.05 kX) (Fig. 5a). Anode po-
tential was observed to varying with respect to external load
suggesting the dependency of current generation capacity on an-
ode. Increase in the EDCs concentration showed an increment in
the anode potential up to 1000 lg/L and showed a drop with fur-
ther increment. This might be attributed to the inhibitory effect
on electron discharge from the bacterial cell towards anode. Gen-
erally, lower anode potential means less energy transfer for micro-
bial growth and cell maintenance along with higher electron
discharge, while higher anode potential means the higher energy
transfer towards bacterial growth resulting in faster start up of
electron discharge. Lower anode potential observed at higher E3
concentration supports the high energy conservation towards cell
maintenance to withstand the toxic effects. However, lower con-
centrations of EDCs might have helped in transferring the electrons
from the bacterial interior to the anode resulting in lower anode
potential. The difference between anode and cathode potentials
also should be considered, where it should be as high as possible
(Aelterman et al., 2008; Srikanth et al., 2010). Increase in the cell
emf observed with increasing estrogen concentration till the toxic
activity (μg/mL of phenol)
activity (μg/mL of toulene)
Fig. 3. (a) Profiles of phosphatase and dehydrogenase enzyme activities against
time; (b) pH and VFA against operation time, with the function of experimental
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
levels might be supporting the large enough potential difference
for the cell growth as well as electron discharge. The optimal anode
potential satisfies both cell growth and energy output (Wang et al.,
2009; Srikanth et al., 2010). Anode potential can also be correlated
to metabolic pattern of biocatalyst and the energy dissipation.
Compared to E3, EE2 spiked anodic fuel showed higher anode po-
tential initially which dropped with decreasing resistance. How-
ever, the drop is lower at less resistance when compared to E3,
while the current generation is higher which is suggesting its high-
er involvement in carrying the electrons towards anode.
3.2.3. Deviation in the anodic oxidation with load
Deviation in the anodic oxidation potential with respect to
external varying resistance was depicted in terms of relative de-
crease in the anode potential (RDAP) which is also useful in deter-
mining the maximum sustainable power. The fuel cell will be in
steady state if the power generated by the BET equals the power
consumption for an extended time and the power production is
said to be sustainable. Sustainable power calculations were made
considering the initial anodic potential (Eo
tial at each applied external resistance (Eanodic) after reaching a sta-
ble cell potential at respective experimental conditions (Venkata
Mohan et al., 2008b). Electron discharge (current) was started at
10 kX in the case of EE2C2 condition supporting its early response
to the external load compared to other conditions. E3C2 and E3C2-
PP conditions responded at 5 kX showing the current generation.
Though, they responded to a lower resistance, the variation in cur-
rent generation was negligible among these three conditions. All
the other experimental conditions showed electron discharge at
even lower resistances indicating their inefficiency. Among the
three efficient conditions, EE2C2 showed a gradual deviation in
the anodic oxidation till the least external resistance applied, while
E3C2 and E3C2-PP conditions showed a gradual drop till 500 X and
drastically dropped thereafter. This behavior indicates the concen-
anodic) and anodic poten-
0 2040 6080 100
E3C1 E3C2 E3C3 E3C2-PP EE2C2
Current density (mA/m2)
150 200 250300
3025 2015 1050
Resistance (kΩ Ω)
Fig. 4. (a) Open circuit voltage (OCV), current density and power density profiles measured during BET operation; (b) Fuel cell behavior in terms of polarization with the
function of experimental conditions studied at maximum performance of BET [measured across variable resistance (30 kX–50 X)].
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
tration losses occurred at very lower resistance in the case of E3C2
and E3C2-PP, while EE2C2 has overcome the concentration losses
resulting in higher power. This can also be correlated and sup-
ported by the oxidation of electron donor (glucose), where higher
oxidation was observed with EE2C2 compared to the other two
conditions but the electrons generated have been utilized for the
oxidation of estrogens. The linear fit drawn at high external resis-
tances represented the region in which the external resistance con-
trols the power, while, the linear fit drawn at low external
resistances represented the region in which the power is limited
by kinetics, mass transfer, or internal resistance (Venkata Mohan
et al., 2008a; Srikanth et al., 2010). When the external resistance
is high, the RDAP increases linearly with decreasing external resis-
tance because the electron delivery to the cathode is limited by
external resistance. However, when a low external resistance is ap-
plied, electron delivery to the cathode is limited by kinetic and/or
mass transfer resistances. RDAP increases linearly with decreased
external resistance, with different slopes, for external resistance
limited or internal resistance limited conditions. The conditions
where external and internal resistance limitations are equal must
be somewhere between these two lines. EE2C2 showed higher sus-
tainable resistance (?7.5 kX) followed by E3C2 and E3C2-PP
(?5 kX) (Sfig. 2). All the other three experimental conditions
showed very low sustainable resistance.
3.2.4. Cyclic and linear sweeps to understand the electron discharge
Electron discharge properties in terms of bio-electrochemical
behavior with respect to estrogens nature and concentration were
evaluated during BET operation by employing CV. CV measures
both redox activities of the components involved in biochemical
system in solution and redox activities of the components bound
to the bacteria and also reported to help in identifying electro-ac-
tive species (Jayarama Reddy, 1986; Venkata Mohan et al., 2010a;
Srikanth et al., 2010). Voltammograms (vs Ag/AgCl) recorded in situ
visualized marked variation in the electron discharge properties
and energy generation pattern with the function of experimental
conditions (Fig. 5b). Addition of estrogens has shown increment
in both the oxidation and reduction currents over control opera-
tion, which might be due to their function in electron transfer. This
behavior was strongly supported by the polarization behavior and
051015 20 2530
Resistance (kΩ Ω)
Cell emf (mV)
Anode potential (mV)
-0.750-0.500-0.250 00.250 0.500 0.750
E / V Vs. Ag/AgCl (S)
i / A
Black: Control; Red: E3C1;
Blue: E3C2; Wine: E3C3; Cyan:
E3C2-PP; Green: EE2C2
Fig. 5. (a) Electron motive force (emf) and anodic oxidation potential [measured across variable resistance (30 kX–50 X)]; (b) cyclic voltammetric profiles taken at maximum
performance of the system operation [anode and cathode as working and counter electrodes, respectively against Ag/AgCl (S) reference electrode; scan rate 30 mV/s].
A. Kiran Kumar et al./Bioresource Technology 104 (2012) 547–556
anodic-oxidation potentials. However, EE2 addition showed higher
catalytic current compared to E3 addition during both oxidation
and reduction phases. The catalytic current was also observed to
increase with increasing E3 concentration up to 1000 lg/L and
showed drastic drop thereafter which might be due to the inhibi-
tory effect of estrogen on the metabolic activities at toxic loads. Re-
dox pairs corresponding to the electron carriers were not observed
on CV (vs Ag/AgCl) with any case of experimental variation might
be due to the usage of anode as working electrode instead of noble
metal electrodes which generally have higher electrochemical
properties. The capacitance was also observed to increase with
increasing estrogens concentration and was very higher with EE2
indicating higher electron holding capacity of BET when operated
Number of electrons transferred to the working electrode (an-
ode) with the function of experimental variation can be calculated
from the charge (Q) obtained against applied potential during vol-
tammetric analysis. Exo-electrogenic biocatalyst acts as driving
force to generate electrons from substrate degradation and these
electrons will transfer towards the working electrode and depicted
as current in the voltammetric signature. Marked improvement in
the electron transfer was observed after loading estrogens com-
pared to the control operation (1.85 ? 1019) (Table 1). The electron
transfer was increased with increment in the estrogens concentra-
tion (E3C1, 2.87 ? 1019; E3C2, 4.96 ? 1019; E3C3, 9.98 ? 1019)
which might be due to the higher electron discharge from the bio-
catalyst against increasing estrogens concentration. Significant
increment in electron transfer was observed with the EE2 bearing
wastewater (EE2C2, 9.62 ? 1019) compared to E3 bearing waste-
water (E3C2, 4.96 ? 1019) which is strongly supported by the ob-
served electrogenesis and carbon consumption. Application of
poised potential showed marginal improvement in the electron
transfer (E3C2-PP, 5.34 ? 1019) which is also supported by the
marginal variations observed in the electron discharge, estrogen
removal and substrate degradation efficiencies. Overall, the BET
performance illustrated variation in power generation and sub-
strate degradation with the function of concentration and nature
Anode was also polarized through linear sweep voltammetry
(LSV) between 0.5 V and 0.1 V using potentiostat–glavanostat sys-
tem at each experimental variation (not shown). LSV depicts the
maximum feasible current generation from the system at applied
voltage. Current generation from the anode varied with the range
of applied voltage irrespective of the experiment studied. Observed
catalytic current from LSV was directly proportional to the applied
voltage in all the cases studied. Marked improvement in catalytic
current was recorded with the addition of estrogen compounds
compared to the control supporting their role in electron transfer.
Catalytic current showed significant variation with the function of
estrogen compound. Addition of EE2 to the wastewater showed a
good increment in the catalytic current compared to the E3 bearing
wastewater. Increment of catalytic current was observed with
increasing E3 concentration up to 1000 lg/L. However, further
increment in E3 concentration showed a marked drop in the cata-
lytic current lower than the control operation supporting its inhib-
itory effect. Overall, the electrogenic activity of the system
sustained at lower concentrations of estrogens, while marked drop
in the activity was observed at higher estrogens concentration sug-
gesting their inhibitory effect on microbial metabolism.
Simultaneous bio-electrochemical reactions occurring in the
BET system resulted in the bioremediation of estrogen compounds.
Improved electrogenic activity was observed at lower concentra-
tion of estrogens, while operation at higher concentrations docu-
mented drop in the activity indicating their inhibitory effect on
the process performance.
Higher power generation was noticed with addition of estrogen
compounds along with wastewater which attributes their function
in the electron transfer. Generation and discharge pattern of elec-
trons showed good correlation with the power output and sub-
strate degradation. Dehydrogenase and phosphatase enzyme
activities also depicted good correlation with the substrate degra-
dation and bio-electrochemical activity.
The authors wish to thank Director, CSIR-IICT, Hyderabad for his
encouragement in carrying out this work. M.V.R, K.C. and S.S. wish
to thank the Council of Scientific and Industrial Research (CSIR) for
providing research fellowships.
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