Electrodeposited polyaniline-carbon felt anode promotes electroactive biofilm for the improved energy recovery in microbial fuel cells using phenol containing wastewater

Electrodeposited polyaniline-carbon felt anode promotes electroactive biofilm for the improved energy recovery in microbial fuel cells using phenol containing wastewater | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrodeposited polyaniline-carbon felt anode promotes electroactive biofilm for the improved energy recovery in microbial fuel cells using phenol containing wastewater Subhendu Bhandari, Soumya Pandit, Chetan Pandit, Nishant Ranjan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4599921/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In the present study, Polyaniline (PANI)/ Carbon Felt (CF) composite electrodes were developed to be used as an anode in a Microbial Fuel Cell (MFC) for the enrichment of specific electroactive organisms on the anode. Comparative analysis of two approaches of Phenol degradation namely adsorption & biodegradation and for simultaneous generation of bio-electricity. Sulfuric acid-doped PANI was electrochemically synthesized in aqueous medium and deposited in-situ on the carbon felt anode followed by its characterization using SEM, XRD, and CV. To use these in MFC, different concentrations of PANI ranging from 0.25 mg/cm 2 to 1.25 mg/cm 2 , was deposited onto CF via potentiostatic electrodeposition technique and compared. The morphological analysis using FESEM of the anode revealed homogenous deposition of nanostructured PANI onto the surface of CF. Further characterization of PANI/CF composite shows that PANI has improved the surface area of the anode, thereby, increasing the conductivity of the anode and promoting biofilm attachment to the anode. The PANI/ CF composite anode with loading rate of 1.0 mg/cm 2 showed the best results with maximum power density of 584.2 mW m -2 and lowest charge transfer resistance of 49.6 Ω. The reduction of COD and total phenol of wastewater were 73% and 88% respectively. The obtained results from this study show that the power production and efficiency of the MFCs can be improved greatly by using Sulphate containing PANI/ CF composite as an anode material. The CLSM results indicated that PANI facilitates in promoting EAB biofilm which in turn helps in achieving enhanced power output. Electro catalyst Bioelectrochemical system Nyquist plots Capacitive Bioanode Power density SRB Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction Depleting fossil fuels and clean water sources has increased the need for sustainable energy production and wastewater recycling. Phenolic compounds are present in industrial effluents, including wastewaters from various sectors such as petroleum refineries, coal processing plants, paper manufacturing facilities, resins and coke making, steel industries, plastic and varnish industries, pharmaceutical industries, and numerous other industrial sectors. The conventional methods of wastewater recycling are expensive and energy-intensive. Hence, it has become crucial to find alternative sources of energy production and wastewater recycling (Epstein et al. 1987 ). Nowadays, research has been focused on utilizing wastewater as a source of energy in various energy-efficient technologies such as Anaerobic digestion, Microbial Fuel Cells (MFC), etc(Hidalgo et al. 2016 ; Fontmorin et al. 2021 ). Among these technologies, MFC is one of the promising technologies that produce power while simultaneously treating wastewater. MFCs are bio-electrochemical systems that utilize microorganisms as bio-catalysts. A typical dual-chambered MFC reactor consists of an anaerobic anode compartment, consisting of microorganisms at the anode, an aerobic cathode compartment consisting of a cathode, and a membrane separating the anode and cathode compartment (Vempaty and Mathuriya 2022 ). The microorganisms present at the anode oxidize the organic content present in the anolyte (typically, wastewater) and convert it into electrons and protons. The electrons flow to the cathode via an electric circuit. The electrons at the cathode react with the oxygen and protons that diffuse from the anode compartment to the cathode compartment through the membrane and form water(Hou et al. 2013 ; Hu et al. 2013 ; Huang et al. 2016 ; Hindatu et al. 2017 ). The electron production at the anode and consumption at the cathode are the defining characteristics of the MFC(Huang et al. 2011 ). It has already been proved that carbon felt is a useful adsorbent for phenol removal. Pseudomonas is a potent microorganism for phenol biodegradation, it was hypothesized that improved phenol wastewater treatment can be achieved using carbon felt anode with Pseudomonas as a biocatalyst in MFC. Phenol is a hazardous contaminant that exhibits resistance to natural degradation, resulting in its persistence throughout the environment. The removal of these substances from aquatic environments is necessary due to their significant toxicity levels. The existence of phenol poses a potential hazard to both human and aquatic life. The phenol concentration in wastewater has a range of 10 to 300 mg/l, with the potential to escalate to 4.5 g/l in instances of severe wastewater pollution. Moreover, the presence of hazardous polychlorinated phenols, which are produced as a result of the chlorination process in water containing phenol, poses a significant threat to both soil environments and aquatic ecosystems. The process of removing phenols by using the bioelectrochemical system with concomitant electricity generation has been studied by a few researchers; however, the majority of the previous research was done using different anode materials. Various methodologies were employed to eliminate phenol, including activated carbon adsorption, ion exchange, liquid-liquid extraction, and chemical oxidation. Nevertheless, the primary constraint is in the capital expenditure associated with the treatment process. The duration of the treatment was prolonged to reach the required level. In addition, the performance of MFCs was not compared with adsorption using the same size of carbon felt and Pseudomonas in aerobic growth. Therefore, the main objective of this study is to determine the efficiency of the MFC using carbon felt as anode. The effect of phenol concentration, external resistance, and anode surface area was investigated in terms of power output. Further, the performance of MFCs was compared with the adsorption technique and aerobic biodegradation in terms of phenol removal. Despite the many advantages and simplicity of MFC, it has still not been commercialized due to its low efficiency. One of the major factors that play a role in the performance of the MFC is its anode. Ideal anode material for an MFC should promote microbial attachment to its surface and promote electron transfer. Poor microbial attachment limits the electron transfer from the microorganism to the anode, resulting in low power production(Lai et al. 2011a ; Kazemi et al. 2021 ). Sulfur-reducing bacteria (SRB) were tested in MFCs and were confirmed to have the ability to perform extracellular electron transfer. Therefore, MFCs enriched with SRB can be highly efficient due to moderate operating conditions and high power production(Li et al. 2011 ). The interaction between microorganisms and electrodes in terms of biofilm development and electron transfer is one of the vital factors that limit power production in MFC. Electrode surface modification is widely studied to improve these interactions to increase power production in MFC(Li et al. 2014 ; Lin et al. 2019 ). Polyaniline (PANI) is an electrically conductive polymer that is relatively easy to synthesize and highly stable. It also has simple, reversible acid/ base doping/de-doping chemistry(Liu et al. 2004 ; Logan 2010 ). PANI has been used for the improvement of supercapacitors(Logan et al. 2006a ; Logan and Regan 2006 ), biosensors(Miran et al. 2017 ; Narayanasamy and Jayaprakash 2021 ), and anode modifiers in MFC(Pillalamarri et al. 2005 ; Qiao et al. 2008 ). (Qiao et al. 2007 ) studied the electrocatalytic property of carbon nanotube (CNT)/ PANI composite as an anode material for MFC. 20 wt. % CNT/ PANI composite showed a maximum power density of 42 mW m − 2 with Escherichia coli being used as a bio-catalyst. (Rahimnejad et al. 2015 ) synthesized PANI/ mesoporous titanium dioxide (TiO 2 ) composite to use as an anode in MFC utilizing Escherichia coli as a bio-catalyst. The 30 wt. % PANI/ TiO 2 composite anode exhibits a high power density of 1495 mW m − 2 . (Silvestre et al. 2015 ) modified carbon felt anode with PANI, which exhibited a high-power density of 27.4 W m − 2 . Anode biofilm analysis showed that a larger amount of bacteria and greater biodiversity were found on the modified anode than the unmodified anode. (Song et al. 2015 ) synthesized and studied the use of PANI hybridized three-dimensional (3D) graphene as an anode in MFC. The 3D graphene/ PANI anode showed a maximum power density of 768 mW m − 2 and a charge transfer resistance of 100 Ω. (Syed and Dinesan 1991 ) developed a Graphene/ PANI/ Carbon cloth anode that exhibited a maximum power density of 1390 mW m − 2 , which is 3 times greater than the MFC with an unmodified carbon cloth anode. (Vinodh et al. 2022 ) used PANI/graphene-modified oxidized carbon cloth as an anode in MFC and compared it against an unmodified carbon cloth anode. The PANI/graphene-modified carbon cloth anode showed a maximum power density of 884 mW m − 2 , which is 1.9 times higher than that of the unmodified carbon cloth anode. The protonic acid doping of the emeraldine base form of PANI results in the transition into a metallic state which increases the conductivity of PANI (Wang et al. 2015 ). (Yellappa et al. 2021 ) improved the performance of the MFC by using a carbon cloth modified with HSO 4 − doped PANI. The MFC showed a maximum power density of 5.16 W m − 2 and an internal resistance of 90 Ω which was 2.66 times higher and 66.5% lower respectively than the MFC with unmodified anode. (Yong et al. 2012 ) developed gas diffusion electrodes (GDE) modified with PANI binary doped with H 2 SO 4 and Ammonium lauryl sulfate. The increased hydrophilicity and conductivity of the PANI modified GDE resulted in increased biocompatibility of the anode. The PANI modified GDE showed faster started up of CO 2 conversion (6 days vs 12 days of unmodified GDE) and high acetate and butyrate production rate. The present study developed an anode using PANI electrodeposited onto the surface of carbon felt (CF) for enhanced power production in MFC. Further, the study compared the different concentrations of PANI/ CF composites ranging from 0.25 mg/cm 2 to 1.0 mg/cm 2 in terms of power production and internal resistance. The study suggests that the PANI/ CF is an excellent cost-effective replacement to conventional anodes by promoting biofilm formation onto the anode and increasing power production. 2. Methodology 2.1 Reagents used Sulfuric acid and aniline were obtained from Merck, India, and used as received without further purification. Nonwoven carbon felt (CF) with an average fiber diameter of 8.858 µm was purchased from Zoltek, MO. Deionized water was used for the preparation of the electrolyte medium. 2.2 Electrodeposition of PANI on CF and characterization Electrodeposition of PANI on CF was carried out via the potentiostatic method in presence of 0.1 M aqueous solution of aniline sulfate mixed with 1 M H 2 SO 4 solution as the electrolyte medium. A square-shaped sample of CF of dimension 4 cm x 4 cm was used as the working electrode and Pt wire was used as the counter electrode. A constant potential of 2V vs. Ag/AgCl reference electrode was applied to the working electrode for 3 min. A CF sample of similar dimensions was also analyzed in similar conditions in the absence of the acid solution for comparison. PANI was evenly deposited onto the surface of CF during potentiostatic synthesis. However, a drastic reduction of current by ca. 85% at the end of 3 min duration was observed for CF without acid solution which might be because the acid solution plays a role in enhancing the properties of CF. In contrast, a significantly lesser reduction of current response by ca. 12% was observed during electrodeposition using an acid solution which might be due to the presence of PANI nanoparticles protecting the exterior of CF from an acidic electrolyte medium. After the initial decrease of current response by 7 mA in 5 seconds, it reaches a plateau and starts decreasing slowly. Aniline sulfate is highly soluble in an aqueous medium and dissociates into ions very fast [31] which starts the formation of PANI and gets deposited onto the exterior of CF. The initial reduction of current response indicates the exposure time of bare CF to the electrolyte medium; whereas, the subsequent plateau range signifies the starting phase of electrodeposition, where the PANI starts covering the outer surface of CF. Since the conductivity of PANI is significantly less than CF, the current response of the working electrode starts decreasing slowly with the deposition of more PANI nanoparticles. Therefore, the slower reduction of the current response of the working electrode is indicative of controlled electrodeposition of PANI with retention of the much higher level of conductivity which is expected to be beneficial for improved electrochemical performances of CF-PANI composite. The morphology of CF and PANI/CF composite was studied using Field Emission Scanning Electron Microscopy (FE-SEM) (Nova nano FE-SEM 450). Energy dispersive X-ray spectroscopy was also used to analyze the elemental composition of the PANI/CF composite. The structure of the PANI/CF composite was studied using an X-ray Diffractometer (Shimadzu 6000 XRD) with Cu-Kα as a radiation source operated at a potential of 40 kV and current of 30 mA. Cyclic voltammetry (CV) was performed for CF and PANI/CF composite over a potential range of + 1 to -1V at a scan rate of 20 mV/s. Galvanostatic charge-discharge experiments were conducted for PANI/ CF composite within a voltage range of 0.6–0.0V at a current load of 10 A m 2 (Xu et al. 2018 ). 2.3 MFC test and operation A 0.6 cm thick polyacrylic plastic was used to build six identical single-chambered cuboidal MFCs. The operational volume of anodic chambers was 110 mL. The electrode terminal and reference electrode (Ag/AgCl, saturated KCl; +197mV, Equiptronics, India) for the sample were situated at the top of the anode chamber. Different concentration of PANI/CF composite ranging from 0.25 to 1.25 mg/cm 2 of predicted surface area of 32 cm 2 were used as an anode. Composite membranes were developed consisting of graphene oxide (GO) blended with polyvinyl alcohol (PVA), and silico tungstic acid (STA) polymer and used as proton-conducting membranes in the MFC (Khilari et al. 2013 ). The membrane cathode assembly (MCA) was created by effectively bonding the membrane (PVA-STA-GO) to a flexible carbon felt cathode containing 0.1 mg/cm 2 of manganese oxide nanotube (MnO2 -NTs) as an ORR catalyst using a Hydraulic Press for 10 minutes at 60°C (Moore Max Ton Hydraulic Press-800 kPa). The side treated with a catalyst coating was kept facing the membrane. The MFC reactors were provided with a window on one of its sides, where the MCA (16 cm 2 ) was installed using epoxy resin. In the anode chamber, provisions were created for inlet and outlet, sampling, wire input points (top), gas output, and so on. The circuit was joined using tin-coated copper wire. Leak-proof joint sealing was used to keep the anaerobic microenvironment in place in the anode compartment. Sample ports, wire input points (on top), inlet and output ports, and other components have previously been set up in the MFC. All MFCs were operated in fed-batch mode at a fixed external resistance of 100Ω and were recharged 36 hours later. A mixed anaerobic sludge (5% w/v) taken from a local wastewater treatment plant was inoculated into the MFC reactors. Wastewater was used as anolyte under Fed-batch conditions. When a voltage drop was observed, the exhausted feed was replaced with a fresh anolyte. All the MFCs were operated at room temperature. The polarization curve was obtained by varying external resistance (10 kΩ to 10Ω) and measuring the corresponding voltage drop (Mehrotra et al. 2022 ). The power and current produced were calculated according to Ohm’s law and were normalized to the surface area of the anode (Logan et al. 2006b ). Electrochemical Impedance Spectrometry (EIS) was used to measure the internal resistance of the MFC. EIS was performed using a potentiostat (BioLogic, France). A three-electrode configuration was used for the experiment – anode (working electrode), cathode (counter electrode), and Ag/ AgCl electrode (reference electrode). EIS was recorded by applying alternating current of frequency 100 KHz to 100 mHz with an amplitude of 10 mV (Rajesh et al. 2018 ). A Nyquist plot was plotted over the above frequency range using EClab software. CV of the MFCs was performed using potentiostat over a potential range (E range ) of + 1V to -1V over a scan rate of 20 mV/s. 2.4 Biofilm formation studies on graphite and biochar-coated graphite electrodes Following washing, the bacterial suspension was injected into the anode chamber of MFCs with various electrodes coated with graphite and charcoal. The bacterial growth medium (acetate wastewater) was injected for 6 batch cycles. The average biovolume of dead cells, living cells, and EPS for each kind of sheet was calculated and plotted for evaluation using five different types of biochar-coated graphite sheets (graphite as control, and biochar impregnated in graphite at varied ratios (1, 0.75, 0.5, and 0.25 mg/cm2). After the biofilm development experiment in MFCs, the various anodes were carefully removed and cut into pieces of around 5 mm by 5 mm from a consistent location for all of the runs. a PBS solution containing 0.1 mg/mL, 3 mM propidium iodide (PI). The biofilms were incubated in the stain solution for 30 minutes in the dark, till stained. We used a confocal laser scanning microscope (CLSM; ZeissMeta510; Carl ZEISS, Inc., USA) equipped with a Zeiss dry objective LCI Plan-Neo Fluor to observe the stained biofilm samples (20 x magnification and numerical aperture of 0.5). Ten different places on each surface were used to stack photos, which were then stitched together. The same process as previously described was used for picture capture and processing. [31]. To examine the photos and calculate the precise biovolume (m3/m2) in the biofouling layer using the COMSTAT, an image-processing program83 that was created as a script in Matlab 6.5 (The Math Works, Inc., Natick, MA). [32]. Every sample had 10 places on each graphite electrode that were chosen for microscopical observation and analysis. The CLSM image stacks were 3-dimensionally rebuilt using the Imaris program (Imaris Bitplane, Zurich, Switzerland). For five different types of varied concentrations of biochar including graphite electrodes, an average of the biovolume of cells attached was determined and analyzed. 2.5 Phenol Estimation Using Colorimetric Method 1 ml of the sample to be analyzed was taken and mixed with 0.1 ml of 0.1 M glycine buffer (pH 9.7) containing 5% potassium ferricyanide. This mixture was then added to 1 ml of 0.1M glycine buffer containing 0.25% of 4-aminopantipyrine. A red color was developed and the absorbance was measured at the filter of 505 nm. 3. Results and discussion 3.1 PANI/CF composite characterization FESEM images of CF (Figure 2a, b) reveal a smooth surface with an average diameter of 8.9 μm. Homogeneous deposition of PANI onto the surface of CF is evident from the magnified image (6,500 x) as illustrated in Figure 2c. However, some parts of the outer surface of CF are found still uncoated by PANI. A further magnified (50,000 x) image reveals the existence of bar-shaped PANI nanoparticles as shown in Figure 2d. The distribution of length, diameter, and aspect ratio (length: diameter) of PANI nanostructures was analyzed and illustrated in Figure 3 based on 20 nanoparticles identified in Figure 2d. The mean values of length, diameter, and aspect ratio were found to be 316 nm, 97 nm, and 3.3 respectively. It is noteworthy that apart from the electrodeposited nanoparticles, no other macro- or nanostructures of PANI exist in the CF/PANI composite. Therefore, further characterizations of PANI involve only the characteristics of PANI-coated CF. The presence of sulfur in electrodeposited PANI has been evident from the EDX spectrum (Figure 4) which signifies doping of as-synthesized PANI by sulfate ions generated from the dissociation of H 2 SO 4 as well as aniline sulfate in potentiostatic condition. X-ray diffractogram (XRD) (figure 5) of CF exhibits a prominent and sharper peak near 2θ=24.1° which corresponds to the (002) plane of its graphitic structure consisting of the crystalline component with differences in basal plane alignment [32][33]. Apart from that, a weaker shoulder appears near 42.8°. However, no additional peak arises after electrodeposition; rather, the sharper peak slightly shifts to 25° owing to the presence of PANI particles deposited over the exterior of CF. Since the signature of PANI near 25° [34] coincides with the peaks of CF, therefore, the peaks appearing near 25° and 42.1° are beyond the scope of distinguishing each other from the diffractogram. Therefore, the peaks of CF-PANI may be ascribed to the presence of both CF and PANI. The cyclic voltammogram of CF/PANI (Figure 6a) exhibits multiple reversible redox behavior as the signature of PANI existing on the surface of CF. The anodic peak in the forward anodic cycle (i.e., oxidation) appearing near 0.34 V may be ascribed to the transformation of the fully reduced leucoemeraldine form of PANI to the partially reduced and partially oxidized emeraldine form, whereas an additional peak near 0.63 V confirms its further oxidation to form fully oxidized pernigraniline form of PANI. The reversible reductions of pernigraniline to emeraldine and its further reduction into the leucoemeraldine form of PANI are evident from the reverse cathodic cycle (i.e., reduction) exhibiting peaks near 0.36 V and 0.14 V respectively. The enclosed area of the voltammogram of CF-PANI is indicative of its electrochemical pseudocapacitive nature exhibiting a specific capacitance of 70.4 F/cm 2 at the current density of 10 mA/cm 2 . In contrast to the electrodeposited counterpart, the enclosed area for CF was found to be negligible because of its very high electrically conductive nature which exhibited a specific capacitance of 0.3 F/cm 2 at the same current density. Further analysis of electrochemically capacitive performance was analyzed through the galvanostatic charge-discharge method. The charge-discharge profile of CF-PANI (Figure 4b) exhibits an approximately linear trend along with an internal resistance drop of 0.24 V and coulombic efficiency of 76%. The specific capacitance of CF-PANI was found to be 59.5 Fg -1 at the discharge rate of 1 Ag -1 . 3.2 Polarization studies with MFCs having a different concentration of PANI-coated anode The performance of the electrode half-cell system is frequently shown by the polarization-power density curve of the electrode half-cell. The relationship between the cell's current density and its voltage and power density is shown in the polarization curve. These curves can be used to describe the characteristics of the electrode, electrolyte, and various contact reactions. Using a stabilized cathodic half-cell with various sulfate-doped PANI concentrations made up of composite anodes under various circumstances, it was discovered what the anodic half-cell potential was. The power output of PANI/CF composite anode at concentrations of 0.25, 0.5, 0.75, 1.0, and 1.25 mg/cm 2 to see how it affected the MFC's PANI/CF anode power output (Figure 7). The anodic half-cell potential showed a statistically significant variation with the amount of sulfate-doped PANI utilized in the MFC. The anode with unmodified CF anode generated a maximum normalized power density (Pd max ) of 175.6 mW/m 2 (results not shown). The Pd max of MFCs increased to 224.7, 410.93, 506.3, 560.77, and 584.2 mW/m 2 respectively, upon impregnating CF anode with 0.25, 0.5, 0.75, 1.0, and 1.25 mg/cm 2 loading of PANI. By increasing the amount of PANI in the CF anode from 0.25 to 0.5 mg/cm 2 , it was evident that the Pd max had significantly improved (nearly twice as much). However, improvement in Pd max was only by 3.9% when the PANI concentration was increased from 1.0 to 1.25 mg/cm 2 . With increasing concentration of PANI in the anode from 0.25 to 1.0 mg/cm 2 , the maximum open circuit potential (OCP), Columbic efficiency (CE), and COD removal efficiency were all improving. However, as the concentration was further increased from 1.0 to 1.25 mg/cm 2 , it was observed that the MFC showed little to no increase in the OCP, CE, and COD removal efficiency. However, it was found that the internal resistance was decreasing with an increase in the concentration of PANI in the anode. It may be said that the composite anode's PANI concentration significantly affects the MFC's power output. The pattern of the internal resistance's decline with increasing PANI loading rate may be related to the increased growth of electroactive biofilms (EAB) on the anode surface. When the EAB breathes onto the anode surface, it may acquire a negative charge. The oxidation kinetics finally get more rapid when EAB gradually grows on an anode that contains PANI. The use of sustainable PANI could help to boost power output while also considerably lowering the cost of the anode. 3.3 Effect of phenol concentration on power generation and coulombic efficiency Synthetic phenolic wastewater was used to study its suitability as anolyte in Pseudomonas Sp. mediated MFCs for further energy recovery. Phenol was used as sole carbon source in MFC. The COD was adjusted to around 3 g L-1 and 100 mL of that was used as anolyte for each cycle. The pH of the spent medium was adjusted near to 7.5 for electrogenesis for all the MFCs; however, the concentration of Phenol was varied in three reactors. 3 different concentration was taken- 250 mg/L; 100 mg/L and 400 mg/L .The reactors were denoted as MFC-1; MFC-2 and MFC-3 respectively. All three sMFCs were operated at multiple fed-batch cycle mode with a close circuit (100 Ω Rext) after the addition of different phenol concentration in anolyte. During start-up, a consistent increase in voltage output was observed with time using Pseudomonas inoculum. Operating voltage (OV) reached a maximum value after 2 weeks of continuous operation in all the MFCs except in MFC with 400 mg/L. A slightly longer start-up time was required for MFCs where phenol concentration was 400 mg/L. The steady-state condition was delayed by 2–3 days in these MFCs than acid pretreatment. The highest OV production of 192 ± 4 mV was observed in MFChaving phenol concentration of 250 mg/L. The OV of MFC with untreated inoculum was found to be 128 ± 7 MV at 100 Ω Rext during polarization study. . Polarization was conducted by changing external load in the external circuit. Once stabilized performance of MFC was observed, the maximum volumetric power density of about 3.42 W/m3 was obtained in the MFC withphenol concentration of250 mg/L in anolyte (Fig. 1). This power density was about 1.5 times higher than the power density obtained in the MFC inoculated with heat treated sludge, and about two times higher than the power obtained in the MFChaving phenol concentration of250 mg/L. The volumetric power density obtained in MFC with phenol concentration of 100 mg/Lwas found to be 2.72 W/m 3 . 3.4 Electrochemical impedance spectroscopy (EIS) studies EIS is mostly used to evaluate the caliber of electrode materials, biofilm development, and chemical reaction kinetics because it can detect certain features like ohmic resistance, charge transfer resistance, and diffusion transfer resistance. EIS is preferred over the slope technique and current interruption. A potentiostat (BioLogic SP 150, France) is used in this method to measure a wide frequency range of 100kHz to 1mHz. The results of this method are displayed as Nyquist or Bode graphs. The Nyquist plot is plotted against imaginary impedance with real impedance. The Nyquist plot consists of a semicircle and a linear line. The diameter of the semicircle represents the charge transfer resistance (Rct) [6]. During the study, a significant change in the diameter of the semicircle region of the PANI/CF’s impedance plot was observed (Figure 8). The following order was reached by the Rct value of MFCs: MFC-with 0.25 mg/cm 2 PANI anode (134.8 Ω) > MFC-with 0.5 mg/cm 2 PANI anode (84.5 Ω) > MFC- with 0.75 mg/cm 2 PANI anode (66.4 Ω) > MFC with 1.0 mg/cm 2 PANI anode (51.2 Ω) > MFC with 1.25 mg/cm 2 (49.6 Ω). The Rct value of CF anode with PANI was lower than Rct value of CF anode without PANI (174.5 Ω) (Results not shown). The highest electron transport caused by significant substrate oxidation, which increased the anodic voltage losses and enhanced current production, was shown by the minimum Rct value seen in the anode in the presence of 1.25 mg/cm 2 PANI/CF composite anode in MFC. The findings of the EIS concur with those of the half-cell polarization study. The findings show that the absence of EAB biofilm on the anode surface, resulting in low electron transport, is the primary cause of increased internal resistance in MFCs without PANI. 3.5 Cyclic voltammetry studies of different PANI/CF composite anode. Figure 9 shows the characteristic CV curve of a PANI/CF composite anode for different loading rates ranging from 0.25 to 1.25 mg/cm 2 at a fixed scan rate of 20 mV/s and potential windows of 0.8 V. CV was performed against the Ag/AgCl reference electrode. The quasi-rectangular shape of the CV curve demonstrates the behavior of the PANI/CF composite anode. From the CV plots, it can be observed that 1.25 mg/cm 2 showed the maximum anodic and cathode peak currents. This may be due to the large surface area attributed to the deposition of PANI onto the surface of CF, promotes the growth of EAB, enhances extracellular electron transfer (EET) and minimizes electron losses. Increasing the concentration of PANI on CF from 0.25 to 1.25 mg/cm 2 , resulted in increase in the EET, which improved the power production in MFC. Electron mediators, shuttles or carriers are responsible for the EET of the reactors. Significant redox peaks were observed at 0.16V, 0.28V and -0.124V, -0.06V which might indicate the presence of cytochrome-b complex as electron carriers. The CV of PANI/CF composite anode of loading rate 1.25 mg/cm 2 showed almost four times increase from the CV of unmodified CF anode (results not shown). This shows the role played by PANI in promoting biofilm formation on the anode and increase in the EET. 3.6 Evaluation of biofilm formation Using CLSM, the biofilm development and its constituent parts on the various PANI impregnated carbon felt anode surfaces were studied. Figures 10 and 10 display the quantifiable outcomes of electroactive microbial biofilm formation on various PANI impregnated carbon felt at the end of MFC studies. The data in Figure 10 were computed using the COMSTAT program. In compared to the 0.75 and 0.5 mg/cm2 biochar coated graphite electrode, a noticeably higher biomass of cells was seen on the 1 mg/cm2 biochar coated graphite electrode. The minimum and maximum biovolume of the attached microbial cell biomass for the 1 mg/cm2, 0.75, 0.5, and 0.25 mg/cm2 PANI impregnated carbon felt anodes were measured to be 15.69 m3/m 2 , 11.19 m3/m2 (1.84), and 10.74 m (0.95), respectively. The biovolume of cells between various 0.75 and 1 mg/cm2 biochar coated graphite electrodes did not significantly change. It is interesting to note that, in contrast to pure graphite, the biovolume of living cells was found to be larger, at 1 mg/cm2, and at 0.75 mg/cm2 for the biochar-coated electrode In the absence of PANI, less number of cells was found on the bare carbon felt anode, demonstrating a lack of microbe anode interaction. The IMARIS 3D pictures confirm the findings of the COMSTAT analysis. From the IMARIS picture (11A-11F), the 1 mg/cm2 biochar coated graphite anode had a substantial amount of cells present; in contrast, the 0.25 mg/cm2 PANI impregnated on CF had less cells (Figure 11B). 3.7 Phenolic wastewater treatment The wastewater treatment performance of all the MFCs was observed in terms of COD removal at different operating cycles. The results showed that the average COD removal efficiency of MFC-1 and MFC-2 was in the range of 72-80 %, which demonstrates the effective treatment efficiency of this system. Coulombic efficiency (CE) is the key parameter used to evaluate the recovery of the electron through the external circuit against theoretically that present in the organic matter of MFCs. An average CE observed in MFC-1 and MFC-2 was 8.2 % and 6.8 % respectively after 2 week (Fig. 4). MFC-1 has shown higher value because of better metabolic activity of EAB in the reactor compared to MFC-2. The Columbic efficiency of the MFCs were very less indicating there was a substantial COD that was not associated with power generation. MFC-1 shows higher columbic efficiency during all operating cycles. However, CE was slightly improved in MFC-2 at later might be because of better development of bio-film on the anode, because of reduction in methanogen than electrogen in the inoculum at slightly lower pH of nearly 6, as a result COD removal decreased and therefore CE increased. 3.9 Adsorption Study of phenol on Carbon felt Note that all samples were taken in duplicates for data accuracy and consistency. Thus, carbon felt adsorption takes around 22 hours to remove around 88% of phenol from aqueous solution with initial phenol concentration of 500 ppm. Thus, maximum adsorption capacity is found to be 8.33 mg per gram of adsorbent (carbon felt). 3.8 Discussion In an effort to improve the inoculum’s ability to adhere to the anode surface and increase its electrochemical conductivity, a variety of nanometals or metal oxides, including manganese oxide, iron oxide, and titanium oxide, are being used for anode surface modification as indicated in Tab. 1. Nanomaterials such as graphene, polymers, CNT form porous structures on the surface of the anode, which promotes bacterial adhesion to the anode surface by establishing redox active sites on the anode surface and also increase EET process. Carbon blacks are another excellent material for anode because it promotes biological interactions on their surface and are frequently utilized as anode to synthesize enzymes. Several different types of conductive polymers are used for anodic modification to improve the EET rate in MFCs. One of these conductive poymers is Polyaniline (PANI). Previous studies reported that the use of PANI to modify the surface of the anode, resulted in the enhancement of the power in MFC (Lai et al. 2011b; Rajesh et al. 2020; Mashkour et al. 2020). Polypyrrole (Ppy) is also a conductive polymer used in one of the studies to modify the surface of the anode which resulted in a greater power production, as well as increased stability and cell viability (Zhao et al. 2019). According to Li et al. (Li et al. 2011), the use of poly (aniline-co-aminophenol) (PAOA) in conjunction with carbon felt on the anodic surface could result in 118% higher performance than the unmodified anode. Other literature surveys also suggest that treating PANI with nitric acid and ethylenediamine, increases the nitrogen carbon ratio which is favorable for microbial adhesion (Savla et al. 2020). This study explores the development of an anode using PANI electrodeposited onto the surface of carbon felt (CF) for enhanced power production in MFC. The morphological characterization of PANI/CF composite states that deposition of PANI homogenously onto the surface of CF increases the surface area of the anode and establishes redox active sites on the anode. FE-SEM micrographs show the electrodeposited PANI onto to the surface of the CF. The EDX analysis of PANI/CF composite shows peaks at C, S and O which confirms the presence of sulphate ions on the surface of the anode. These Sulphate ions are responsible for the presence of active sites for microbial adhesion onto the surface of the anode. These active sites act as a “bait” for the electroactive microorganisms, which attach themselves to the anode. This promotes the growth of EAB and increase the transfer of electrons, which results in the enhancement of power production. The XRD and CV of PANI/CF composites also confirm the conductive nature of the anode. Other literature surveys such as Yellappa et al., (Yellappa et al. 2019) also confirm that PANI is responsible for the increase of surface area of the anode, which improves the adhesion of EAB and enhances electrocatalytic properties. The phenol rich wastewater was found suitable as substrate for bioelectricity generation using Pseudomonas mediated MFC. The reduction of COD and total phenol of wastewater were 73% and 88% respectively. This study demonstrates that, additional renewable bio-energy with simultaneous recalcitrant wastewater treatment can be achieved by Pseudomonas biocatalyzed MFC without any external power consumption. Different concentrations of PANI ranging from 0.25 mg/cm 2 to 1.25 mg/cm 2 was deposited onto the CF anode. The Polarization study showed steady increase in the PD max of PANI/CF composite of 0.25 mg/cm 2 to 1.0 mg/cm 2 . However, little increase was observed in the PD max of PANI/CF composite anode of 1.0 mg/cm 2 to 1.25 mg/cm 2 . The highest PD max of 584.2 mW/m 2 was observed in PANI/CF of concentration 1.25 mg/cm 2 , which showed an increase of almost 230% when compared to unmodified CF anode. Similar trend was observed in the OCP, CE and COD removal efficiency of the MFC. However, the opposite trend was observed for the internal resistance of the MFC reactors. With increasing concentrations of PANI, it was observed that the internal resistance of the system was lowered. The lowest internal resistance was observed in MFC with 1.25 mg/cm 2 PANI/CF composite. With increasing concentration of PANI/CF composite anode, the growth of EAB also increases on the anode, which results in increase in the EET and power production. Hence, this might be responsible for the decreasing Rct values, for increasing concentration of PANI/CF composite anodes as observed in the EIS analysis. The CV of the MFCs at a fixed scan rate of 20 mV/s also confirms that with increasing concentration of PANI/CF composite, increase in the EET process and power production was observed. Table 1: Composite material as anode used in MFC with biocatalyst and their power density Sr. no Electrode Material Biocatalyst Power Density ( mW/m 2 ) Substrate Reference 1 CNT/Polyaniline composites E. coli 42 Glucose [115] 2 Nitrogen-doped/CNT/rGO E. coli 1137 - [116] 3 3D CNT/Chitosan Geobacter sulfurreducens 2.87 Acetate [117] 4 Nano-molybdenum carbide (Mo2 C)/CNT E. coli 170 Glucose [118] 5 Graphene oxide/Nanofibers modified carbon paper Shewanella MR- 1 34.2 Lactate [119] 6 Polypyrrole/Graphite oxide Shewanella oneidensis 1326 - [120] 7 Graphene-modified stainless-steel mesh E. coli Lactate [119] 4. Conclusions In summary, sulfate-doped PANI/CF electrode was developed to increase the biocompatibility of the anode. This study findings confirmed that electrodepositing the sulphate doped nanostructured PANI onto the surface of the CF increased the surface area of the anode, promoting the attachment of biofilm to the anode, which resulted in the enhancement of power production by the MFC. This study compared different concentrations of sulphate doped PANI ranging from 0.25 mg/cm2 to 1.0 mg/cm 2 . Out of these, it was found that sulphate doped PANI/ CF composite anode with a loading of 1.0 mg/cm 2 showed the best results. The wastewater exhibited a reduction of 73% in chemical oxygen demand (COD) and 88% in total phenol content. This study provides evidence that Pseudomonas biocatalyzed microbial fuel cells (MFCs) can meet the dual objectives of generating additional renewable bio-energy and treating refractory wastewater without the need for external power usage. The study also observed that the increased biofilm formation in the sulphate doped PANI/CF composite anode resulted in lower internal resistance when compared to the anode with unmodified CF. These findings show that the modification of CF with sulphate doped PANI enhanced the biofilm formation and electron transfer, which resulted in minimizing energy losses and increased efficiency of the MFC. Declarations Author Contributions: Conceptualization, S.B. and S.P.; methodology, C.P. and S.P.; data curation, C.P.; writing—original draft preparation, C.P., S.P and N.R.; writing—review and editing, S.B. and S.P.; visualization, S.B. and S.P.; supervision, S.P and S.B; funding acquisition, S.P. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. 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Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4599921","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":316373908,"identity":"bd0df174-ff10-499f-998e-843eb18859ee","order_by":0,"name":"Subhendu Bhandari","email":"","orcid":"","institution":"Maharashtra Institute of Technology - Art, Design and Technology University","correspondingAuthor":false,"prefix":"","firstName":"Subhendu","middleName":"","lastName":"Bhandari","suffix":""},{"id":316373910,"identity":"b1e88e20-304c-4b56-a924-10ee4faba7c5","order_by":1,"name":"Soumya 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University","correspondingAuthor":false,"prefix":"","firstName":"Nishant","middleName":"","lastName":"Ranjan","suffix":""}],"badges":[],"createdAt":"2024-06-18 12:17:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4599921/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4599921/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":59695690,"identity":"19d23b73-bd66-482a-8ba9-ab5d637b8eea","added_by":"auto","created_at":"2024-07-05 02:50:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":121269,"visible":true,"origin":"","legend":"\u003cp\u003eTime-dependent current response during potentiostatic electrodeposition of PANI onto the surface of CF.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/3ef68e0e457b31b23b692f06.png"},{"id":59695693,"identity":"d922a30c-46da-4cde-b660-ffc9702296a7","added_by":"auto","created_at":"2024-07-05 02:50:24","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":390196,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM images of (a) CF, (b) magnified (20,000 x) part of CF, (c) CF-PANI, (d) magnified (6,500 x) part of CF-PANI and (e) CF-PANI at higher magnification (50,000 x) revealing nanostructured PANI electrodeposited on to the surface of CF.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/5c548b3da276ba3aff281b72.png"},{"id":59695691,"identity":"53da1e87-1311-412e-932c-f821b229f2e9","added_by":"auto","created_at":"2024-07-05 02:50:24","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":110794,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of (a) length, (b) diameter, and (c) aspect ratio of PANI particles electrodeposited onto the surface of CF.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/105577dcfdaf61021a22bd0a.png"},{"id":59696274,"identity":"fd167fc2-4e8d-43f8-b527-564b8a091f64","added_by":"auto","created_at":"2024-07-05 02:58:24","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":146543,"visible":true,"origin":"","legend":"\u003cp\u003eEDX spectrum corroborates the presence of sulfur and oxygen as sulfate ions as a dopant of deposited PANI.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/0a6668e4c11a39fc19687951.png"},{"id":59695697,"identity":"92f965db-ba38-43bd-9142-e2ee39f15f1d","added_by":"auto","created_at":"2024-07-05 02:50:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":224608,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractogram of CF and CF/PANI.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/5ca6df4daabc1b4ad299fa0b.png"},{"id":59696275,"identity":"e2b0b1f9-99a7-413b-b7d0-34f9535512a9","added_by":"auto","created_at":"2024-07-05 02:58:24","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":125765,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cyclic voltammograms and (b) galvanostatic charge-discharge profiles of CF-PANI.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/aa0f628d2c583cddef00a4ce.png"},{"id":59695700,"identity":"a1c29319-1a0c-4872-acdb-ff251021e7db","added_by":"auto","created_at":"2024-07-05 02:50:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":81279,"visible":true,"origin":"","legend":"\u003cp\u003ePolarization graphs with various MFC, including Sulphate doped PANI -free and Sulphate doped PANI -free at varying concentrations in the graphite composite anodes. On the graph, the data points for power density and voltage are shown as solid and open symbols, respectively. A fixed amount of binder was applied to several Sulphate doped PANI supports for the purposes of comparability.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/b42bf03f102c1327e989c3d8.png"},{"id":59695694,"identity":"68f52861-ca06-4a41-b234-a57d3672dfec","added_by":"auto","created_at":"2024-07-05 02:50:24","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":31639,"visible":true,"origin":"","legend":"\u003cp\u003ePolarization study of phenol concentration\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/08ea983d87065e938e4f2f9a.png"},{"id":59695695,"identity":"6949d19c-0996-4ee7-a008-84dc7a620a6b","added_by":"auto","created_at":"2024-07-05 02:50:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":34264,"visible":true,"origin":"","legend":"\u003cp\u003eNyquist plots of several PANI with MFC anodes\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/81ee1133213ae3f755d4b34b.png"},{"id":59695698,"identity":"3adad76f-cb1d-4ab8-b9ba-9aaad32bbf4f","added_by":"auto","created_at":"2024-07-05 02:50:25","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":39506,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammetry utilizing PANI at a constant scan rate of 20 mV/s at room temperature\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/2a864eda91d111af611f6471.png"},{"id":59695699,"identity":"f5dd4588-e2f4-4ad8-951d-6ba4845a3630","added_by":"auto","created_at":"2024-07-05 02:50:25","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":826385,"visible":true,"origin":"","legend":"\u003cp\u003eIMARIS 3-D photos of biofilms on various biochar concentrations with graphite anodes A. untreated graphite; B. graphite anode impregnated with 0.25 mg/cm2 biochar; C. graphite anode impregnated with 0.5 mg/cm2 biochar; D. graphite anode impregnated with 0.5 mg/cm2 biochar; and E. graphite anode impregnated with 1.0 mg/cm2 biochar following the fourth batch cycle of an MFC experiment using a Dead cells, living cells, and anodes made of EPS biochar are depicted in the red, green, and blue clusters, respectively. Oranges and browns denote an area where living and dead cells overlap. Every picture is a viewpoint that measures several 600 m by 600 m.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/efa5542fbf0e19ebb7c262c0.png"},{"id":59696276,"identity":"02b9e0d1-4080-4021-934c-762abf3effd4","added_by":"auto","created_at":"2024-07-05 02:58:25","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":18810,"visible":true,"origin":"","legend":"\u003cp\u003eCoulombic efficiency of different Pseudomonas mediated MFC\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/590899353b443a0d3ddea9f8.png"},{"id":59695701,"identity":"8e742c3c-ece9-46a9-a08c-501a593e1568","added_by":"auto","created_at":"2024-07-05 02:50:25","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":91808,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e. Adsorption Capacity of Carbon felt\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eB\u003c/strong\u003e. Langmuir Adsorption Isotherm\u003c/p\u003e\n\u003cp\u003eQ max = 8.33 mg/g K = 0.133\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eC.\u003c/strong\u003e As clearly seen from the graph, P. aeruginosa was able to completely degrade the Sample-2 ( 200 ppm initial concentration ) within 12-15 hours ,where as it took about 22-25 hours for complete removal for sample-1(250 ppm initial concentration).Also, at the end of day 1,sample-3 shows only 50% phenol removal which indicates growth inhibition by phenol.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/c227f6940705dacaf852d9a7.png"},{"id":61076652,"identity":"481d1bca-9de4-4d56-9c26-fb546f0e1279","added_by":"auto","created_at":"2024-07-25 09:37:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2653480,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4599921/v1/322dfe4b-38c5-44dd-89b6-6364ce01e9cd.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrodeposited polyaniline-carbon felt anode promotes electroactive biofilm for the improved energy recovery in microbial fuel cells using phenol containing wastewater","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eDepleting fossil fuels and clean water sources has increased the need for sustainable energy production and wastewater recycling. Phenolic compounds are present in industrial effluents, including wastewaters from various sectors such as petroleum refineries, coal processing plants, paper manufacturing facilities, resins and coke making, steel industries, plastic and varnish industries, pharmaceutical industries, and numerous other industrial sectors. The conventional methods of wastewater recycling are expensive and energy-intensive. Hence, it has become crucial to find alternative sources of energy production and wastewater recycling (Epstein et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1987\u003c/span\u003e). Nowadays, research has been focused on utilizing wastewater as a source of energy in various energy-efficient technologies such as Anaerobic digestion, Microbial Fuel Cells (MFC), etc(Hidalgo et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Fontmorin et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Among these technologies, MFC is one of the promising technologies that produce power while simultaneously treating wastewater. MFCs are bio-electrochemical systems that utilize microorganisms as bio-catalysts. A typical dual-chambered MFC reactor consists of an anaerobic anode compartment, consisting of microorganisms at the anode, an aerobic cathode compartment consisting of a cathode, and a membrane separating the anode and cathode compartment (Vempaty and Mathuriya \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The microorganisms present at the anode oxidize the organic content present in the anolyte (typically, wastewater) and convert it into electrons and protons. The electrons flow to the cathode via an electric circuit. The electrons at the cathode react with the oxygen and protons that diffuse from the anode compartment to the cathode compartment through the membrane and form water(Hou et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Hu et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Huang et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Hindatu et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The electron production at the anode and consumption at the cathode are the defining characteristics of the MFC(Huang et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt has already been proved that carbon felt is a useful adsorbent for phenol removal. Pseudomonas is a potent microorganism for phenol biodegradation, it was hypothesized that improved phenol wastewater treatment can be achieved using carbon felt anode with Pseudomonas as a biocatalyst in MFC. Phenol is a hazardous contaminant that exhibits resistance to natural degradation, resulting in its persistence throughout the environment. The removal of these substances from aquatic environments is necessary due to their significant toxicity levels. The existence of phenol poses a potential hazard to both human and aquatic life. The phenol concentration in wastewater has a range of 10 to 300 mg/l, with the potential to escalate to 4.5 g/l in instances of severe wastewater pollution. Moreover, the presence of hazardous polychlorinated phenols, which are produced as a result of the chlorination process in water containing phenol, poses a significant threat to both soil environments and aquatic ecosystems. The process of removing phenols by using the bioelectrochemical system with concomitant electricity generation has been studied by a few researchers; however, the majority of the previous research was done using different anode materials. Various methodologies were employed to eliminate phenol, including activated carbon adsorption, ion exchange, liquid-liquid extraction, and chemical oxidation. Nevertheless, the primary constraint is in the capital expenditure associated with the treatment process. The duration of the treatment was prolonged to reach the required level. In addition, the performance of MFCs was not compared with adsorption using the same size of carbon felt and Pseudomonas in aerobic growth. Therefore, the main objective of this study is to determine the efficiency of the MFC using carbon felt as anode. The effect of phenol concentration, external resistance, and anode surface area was investigated in terms of power output. Further, the performance of MFCs was compared with the adsorption technique and aerobic biodegradation in terms of phenol removal.\u003c/p\u003e \u003cp\u003eDespite the many advantages and simplicity of MFC, it has still not been commercialized due to its low efficiency. One of the major factors that play a role in the performance of the MFC is its anode. Ideal anode material for an MFC should promote microbial attachment to its surface and promote electron transfer. Poor microbial attachment limits the electron transfer from the microorganism to the anode, resulting in low power production(Lai et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011a\u003c/span\u003e; Kazemi et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSulfur-reducing bacteria (SRB) were tested in MFCs and were confirmed to have the ability to perform extracellular electron transfer. Therefore, MFCs enriched with SRB can be highly efficient due to moderate operating conditions and high power production(Li et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The interaction between microorganisms and electrodes in terms of biofilm development and electron transfer is one of the vital factors that limit power production in MFC. Electrode surface modification is widely studied to improve these interactions to increase power production in MFC(Li et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Lin et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Polyaniline (PANI) is an electrically conductive polymer that is relatively easy to synthesize and highly stable. It also has simple, reversible acid/ base doping/de-doping chemistry(Liu et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Logan \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). PANI has been used for the improvement of supercapacitors(Logan et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2006a\u003c/span\u003e; Logan and Regan \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), biosensors(Miran et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Narayanasamy and Jayaprakash \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and anode modifiers in MFC(Pillalamarri et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Qiao et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). (Qiao et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2007\u003c/span\u003e) studied the electrocatalytic property of carbon nanotube (CNT)/ PANI composite as an anode material for MFC. 20 wt. % CNT/ PANI composite showed a maximum power density of 42 mW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e with \u003cem\u003eEscherichia coli\u003c/em\u003e being used as a bio-catalyst. (Rahimnejad et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) synthesized PANI/ mesoporous titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) composite to use as an anode in MFC utilizing \u003cem\u003eEscherichia coli\u003c/em\u003e as a bio-catalyst. The 30 wt. % PANI/ TiO\u003csub\u003e2\u003c/sub\u003e composite anode exhibits a high power density of 1495 mW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. (Silvestre et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) modified carbon felt anode with PANI, which exhibited a high-power density of 27.4 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Anode biofilm analysis showed that a larger amount of bacteria and greater biodiversity were found on the modified anode than the unmodified anode. (Song et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) synthesized and studied the use of PANI hybridized three-dimensional (3D) graphene as an anode in MFC. The 3D graphene/ PANI anode showed a maximum power density of 768 mW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and a charge transfer resistance of 100 Ω. (Syed and Dinesan \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e1991\u003c/span\u003e) developed a Graphene/ PANI/ Carbon cloth anode that exhibited a maximum power density of 1390 mW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which is 3 times greater than the MFC with an unmodified carbon cloth anode. (Vinodh et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e) used PANI/graphene-modified oxidized carbon cloth as an anode in MFC and compared it against an unmodified carbon cloth anode. The PANI/graphene-modified carbon cloth anode showed a maximum power density of 884 mW m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which is 1.9 times higher than that of the unmodified carbon cloth anode. The protonic acid doping of the emeraldine base form of PANI results in the transition into a metallic state which increases the conductivity of PANI (Wang et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). (Yellappa et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) improved the performance of the MFC by using a carbon cloth modified with HSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e doped PANI. The MFC showed a maximum power density of 5.16 W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and an internal resistance of 90 Ω which was 2.66 times higher and 66.5% lower respectively than the MFC with unmodified anode. (Yong et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2012\u003c/span\u003e) developed gas diffusion electrodes (GDE) modified with PANI binary doped with H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e and Ammonium lauryl sulfate. The increased hydrophilicity and conductivity of the PANI modified GDE resulted in increased biocompatibility of the anode. The PANI modified GDE showed faster started up of CO\u003csub\u003e2\u003c/sub\u003e conversion (6 days vs 12 days of unmodified GDE) and high acetate and butyrate production rate.\u003c/p\u003e \u003cp\u003eThe present study developed an anode using PANI electrodeposited onto the surface of carbon felt (CF) for enhanced power production in MFC. Further, the study compared the different concentrations of PANI/ CF composites ranging from 0.25 mg/cm\u003csup\u003e2\u003c/sup\u003e to 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e in terms of power production and internal resistance. The study suggests that the PANI/ CF is an excellent cost-effective replacement to conventional anodes by promoting biofilm formation onto the anode and increasing power production.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e"},{"header":"2. Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Reagents used\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eSulfuric acid and aniline were obtained from Merck, India, and used as received without further purification. Nonwoven carbon felt (CF) with an average fiber diameter of 8.858 \u0026micro;m was purchased from Zoltek, MO. Deionized water was used for the preparation of the electrolyte medium.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Electrodeposition of PANI on CF and characterization\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eElectrodeposition of PANI on CF was carried out via the potentiostatic method in presence of 0.1 M aqueous solution of aniline sulfate mixed with 1 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution as the electrolyte medium. A square-shaped sample of CF of dimension 4 cm x 4 cm was used as the working electrode and Pt wire was used as the counter electrode. A constant potential of 2V vs. Ag/AgCl reference electrode was applied to the working electrode for 3 min. A CF sample of similar dimensions was also analyzed in similar conditions in the absence of the acid solution for comparison. PANI was evenly deposited onto the surface of CF during potentiostatic synthesis. However, a drastic reduction of current by ca. 85% at the end of 3 min duration was observed for CF without acid solution which might be because the acid solution plays a role in enhancing the properties of CF. In contrast, a significantly lesser reduction of current response by ca. 12% was observed during electrodeposition using an acid solution which might be due to the presence of PANI nanoparticles protecting the exterior of CF from an acidic electrolyte medium. After the initial decrease of current response by 7 mA in 5 seconds, it reaches a plateau and starts decreasing slowly. Aniline sulfate is highly soluble in an aqueous medium and dissociates into ions very fast [31] which starts the formation of PANI and gets deposited onto the exterior of CF. The initial reduction of current response indicates the exposure time of bare CF to the electrolyte medium; whereas, the subsequent plateau range signifies the starting phase of electrodeposition, where the PANI starts covering the outer surface of CF. Since the conductivity of PANI is significantly less than CF, the current response of the working electrode starts decreasing slowly with the deposition of more PANI nanoparticles. Therefore, the slower reduction of the current response of the working electrode is indicative of controlled electrodeposition of PANI with retention of the much higher level of conductivity which is expected to be beneficial for improved electrochemical performances of CF-PANI composite.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eThe morphology of CF and PANI/CF composite was studied using Field Emission Scanning Electron Microscopy (FE-SEM) (Nova nano FE-SEM 450). Energy dispersive X-ray spectroscopy was also used to analyze the elemental composition of the PANI/CF composite. The structure of the PANI/CF composite was studied using an X-ray Diffractometer (Shimadzu 6000 XRD) with Cu-Kα as a radiation source operated at a potential of 40 kV and current of 30 mA. Cyclic voltammetry (CV) was performed for CF and PANI/CF composite over a potential range of +\u0026thinsp;1 to -1V at a scan rate of 20 mV/s. Galvanostatic charge-discharge experiments were conducted for PANI/ CF composite within a voltage range of 0.6\u0026ndash;0.0V at a current load of 10 A m\u003csup\u003e2\u003c/sup\u003e (Xu et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 MFC test and operation\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eA 0.6 cm thick polyacrylic plastic was used to build six identical single-chambered cuboidal MFCs. The operational volume of anodic chambers was 110 mL. The electrode terminal and reference electrode (Ag/AgCl, saturated KCl; +197mV, Equiptronics, India) for the sample were situated at the top of the anode chamber. Different concentration of PANI/CF composite ranging from 0.25 to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e of predicted surface area of 32 cm\u003csup\u003e2\u003c/sup\u003e were used as an anode. Composite membranes were developed consisting of graphene oxide (GO) blended with polyvinyl alcohol (PVA), and silico tungstic acid (STA) polymer and used as proton-conducting membranes in the MFC (Khilari et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). The membrane cathode assembly (MCA) was created by effectively bonding the membrane (PVA-STA-GO) to a flexible carbon felt cathode containing 0.1 mg/cm\u003csup\u003e2\u003c/sup\u003e of manganese oxide nanotube (MnO2 -NTs) as an ORR catalyst using a Hydraulic Press for 10 minutes at 60\u0026deg;C (Moore Max Ton Hydraulic Press-800 kPa). The side treated with a catalyst coating was kept facing the membrane.\u003c/p\u003e \u003cp\u003eThe MFC reactors were provided with a window on one of its sides, where the MCA (16 cm\u003csup\u003e2\u003c/sup\u003e) was installed using epoxy resin. In the anode chamber, provisions were created for inlet and outlet, sampling, wire input points (top), gas output, and so on. The circuit was joined using tin-coated copper wire. Leak-proof joint sealing was used to keep the anaerobic microenvironment in place in the anode compartment. Sample ports, wire input points (on top), inlet and output ports, and other components have previously been set up in the MFC. All MFCs were operated in fed-batch mode at a fixed external resistance of 100Ω and were recharged 36 hours later. A mixed anaerobic sludge (5% w/v) taken from a local wastewater treatment plant was inoculated into the MFC reactors. Wastewater was used as anolyte under Fed-batch conditions. When a voltage drop was observed, the exhausted feed was replaced with a fresh anolyte. All the MFCs were operated at room temperature.\u003c/p\u003e \u003cp\u003eThe polarization curve was obtained by varying external resistance (10 kΩ to 10Ω) and measuring the corresponding voltage drop (Mehrotra et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The power and current produced were calculated according to Ohm\u0026rsquo;s law and were normalized to the surface area of the anode (Logan et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2006b\u003c/span\u003e). Electrochemical Impedance Spectrometry (EIS) was used to measure the internal resistance of the MFC. EIS was performed using a potentiostat (BioLogic, France). A three-electrode configuration was used for the experiment \u0026ndash; anode (working electrode), cathode (counter electrode), and Ag/ AgCl electrode (reference electrode). EIS was recorded by applying alternating current of frequency 100 KHz to 100 mHz with an amplitude of 10 mV (Rajesh et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). A Nyquist plot was plotted over the above frequency range using EClab software. CV of the MFCs was performed using potentiostat over a potential range (E\u003csub\u003erange\u003c/sub\u003e) of +\u0026thinsp;1V to -1V over a scan rate of 20 mV/s.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Biofilm formation studies on graphite and biochar-coated graphite electrodes\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003eFollowing washing, the bacterial suspension was injected into the anode chamber of MFCs with various electrodes coated with graphite and charcoal. The bacterial growth medium (acetate wastewater) was injected for 6 batch cycles. The average biovolume of dead cells, living cells, and EPS for each kind of sheet was calculated and plotted for evaluation using five different types of biochar-coated graphite sheets (graphite as control, and biochar impregnated in graphite at varied ratios (1, 0.75, 0.5, and 0.25 mg/cm2).\u003c/p\u003e \u003cp\u003eAfter the biofilm development experiment in MFCs, the various anodes were carefully removed and cut into pieces of around 5 mm by 5 mm from a consistent location for all of the runs. a PBS solution containing 0.1 mg/mL, 3 mM propidium iodide (PI). The biofilms were incubated in the stain solution for 30 minutes in the dark, till stained. We used a confocal laser scanning microscope (CLSM; ZeissMeta510; Carl ZEISS, Inc., USA) equipped with a Zeiss dry objective LCI Plan-Neo Fluor to observe the stained biofilm samples (20 x magnification and numerical aperture of 0.5). Ten different places on each surface were used to stack photos, which were then stitched together. The same process as previously described was used for picture capture and processing. [31]. To examine the photos and calculate the precise biovolume (m3/m2) in the biofouling layer using the COMSTAT, an image-processing program83 that was created as a script in Matlab 6.5 (The Math Works, Inc., Natick, MA). [32]. Every sample had 10 places on each graphite electrode that were chosen for microscopical observation and analysis. The CLSM image stacks were 3-dimensionally rebuilt using the Imaris program (Imaris Bitplane, Zurich, Switzerland). For five different types of varied concentrations of biochar including graphite electrodes, an average of the biovolume of cells attached was determined and analyzed.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Phenol Estimation Using Colorimetric Method\u003c/h2\u003e \u003cp\u003e \u003cdiv class=\"BlockQuote\"\u003e \u003cp\u003e1 ml of the sample to be analyzed was taken and mixed with 0.1 ml of 0.1 M glycine buffer (pH 9.7) containing 5% potassium ferricyanide. This mixture was then added to 1 ml of 0.1M glycine buffer containing 0.25% of 4-aminopantipyrine. A red color was developed and the absorbance was measured at the filter of 505 nm.\u003c/p\u003e \u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 PANI/CF composite characterization\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFESEM images of CF (Figure 2a, b) reveal a smooth surface with an average diameter of 8.9 \u0026mu;m. Homogeneous deposition of PANI onto the surface of CF is evident from the magnified image (6,500 x) as illustrated in Figure 2c. However, some parts of the outer surface of CF are found still uncoated by PANI. A further magnified (50,000 x) image reveals the existence of bar-shaped PANI nanoparticles as shown in Figure 2d. The distribution of length, diameter, and aspect ratio (length: diameter) of PANI nanostructures was analyzed and illustrated in Figure 3 based on 20 nanoparticles identified in Figure 2d. The mean values of length, diameter, and aspect ratio were found to be 316 nm, 97 nm, and 3.3 respectively. It is noteworthy that apart from the electrodeposited nanoparticles, no other macro- or nanostructures of PANI exist in the CF/PANI composite. Therefore, further characterizations of PANI involve only the characteristics of PANI-coated CF. The presence of sulfur in electrodeposited PANI has been evident from the EDX spectrum (Figure 4) which signifies doping of as-synthesized PANI by sulfate ions generated from the dissociation of H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e as well as aniline sulfate in potentiostatic condition.\u003c/p\u003e\n\u003cp\u003eX-ray diffractogram (XRD) (figure 5) of CF exhibits a prominent and sharper peak near 2\u0026theta;=24.1\u0026deg; which corresponds to the (002) plane of its graphitic structure consisting of the crystalline component with differences in basal plane alignment [32][33]. Apart from that, a weaker shoulder appears near 42.8\u0026deg;. However, no additional peak arises after electrodeposition; rather, the sharper peak slightly shifts to 25\u0026deg; owing to the presence of PANI particles deposited over the exterior of CF. Since the signature of PANI near 25\u0026deg; [34] coincides with the peaks of CF, therefore, the peaks appearing near 25\u0026deg; and 42.1\u0026deg; are beyond the scope of distinguishing each other from the diffractogram. Therefore, the peaks of CF-PANI may be ascribed to the presence of both CF and PANI.\u003c/p\u003e\n\u003cp\u003eThe cyclic voltammogram of CF/PANI (Figure 6a) exhibits multiple reversible redox behavior as the signature of PANI existing on the surface of CF. The anodic peak in the forward anodic cycle (i.e., oxidation) appearing near 0.34 V may be ascribed to the transformation of the fully reduced leucoemeraldine form of PANI to the partially reduced and partially oxidized emeraldine form, whereas an additional peak near 0.63 V confirms its further oxidation to form fully oxidized pernigraniline form of PANI. The reversible reductions of pernigraniline to emeraldine and its further reduction into the leucoemeraldine form of PANI are evident from the reverse cathodic cycle (i.e., reduction) exhibiting peaks near 0.36 V and 0.14 V respectively. The enclosed area of the voltammogram of CF-PANI is indicative of its electrochemical pseudocapacitive nature exhibiting a specific capacitance of 70.4 F/cm\u003csup\u003e2\u003c/sup\u003e at the current density of 10 mA/cm\u003csup\u003e2\u003c/sup\u003e. In contrast to the electrodeposited counterpart, the enclosed area for CF was found to be negligible because of its very high electrically conductive nature which exhibited a specific capacitance of 0.3 F/cm\u003csup\u003e2\u003c/sup\u003e at the same current density. Further analysis of electrochemically capacitive performance was analyzed through the galvanostatic charge-discharge method. The charge-discharge profile of CF-PANI (Figure 4b) exhibits an approximately linear trend along with an internal resistance drop of 0.24 V and coulombic efficiency of 76%. The specific capacitance of CF-PANI was found to be 59.5 Fg\u003csup\u003e-1\u003c/sup\u003e at the discharge rate of 1 Ag\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Polarization studies with MFCs having a different concentration of PANI-coated anode\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe performance of the electrode half-cell system is frequently shown by the polarization-power density curve of the electrode half-cell. The relationship between the cell\u0026apos;s current density and its voltage and power density is shown in the polarization curve. These curves can be used to describe the characteristics of the electrode, electrolyte, and various contact reactions. Using a stabilized cathodic half-cell with various sulfate-doped PANI concentrations made up of composite anodes under various circumstances, it was discovered what the anodic half-cell potential was. The power output of PANI/CF composite anode at concentrations of 0.25, 0.5, 0.75, 1.0, and 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e to see how it affected the MFC\u0026apos;s PANI/CF anode power output (Figure 7). The anodic half-cell potential showed a statistically significant variation with the amount of sulfate-doped PANI utilized in the MFC. The anode with unmodified CF anode generated a maximum normalized power density (Pd\u003csub\u003emax\u003c/sub\u003e) of 175.6 mW/m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003e(results not shown). The Pd\u003csub\u003emax\u003c/sub\u003e of MFCs increased to 224.7, 410.93, 506.3, 560.77, and 584.2 mW/m\u003csup\u003e2\u003c/sup\u003e respectively, upon impregnating CF anode with 0.25, 0.5, 0.75, 1.0, and 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e loading of PANI. By increasing the amount of PANI in the CF anode from 0.25 to 0.5 mg/cm\u003csup\u003e2\u003c/sup\u003e, it was evident that the Pd\u003csub\u003emax\u003c/sub\u003e had significantly improved (nearly twice as much). However, improvement in Pd\u003csub\u003emax\u003c/sub\u003e was only by 3.9% when the PANI concentration was increased from 1.0 to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e. With increasing concentration of PANI in the anode from 0.25 to 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e, the maximum open circuit potential (OCP), Columbic efficiency (CE), and COD removal efficiency were all improving. However, as the concentration was further increased from 1.0 to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e, it was observed that the MFC showed little to no increase in the OCP, CE, and COD removal efficiency.\u003c/p\u003e\n\u003cp\u003eHowever, it was found that the internal resistance was decreasing with an increase in the concentration of PANI in the anode. It may be said that the composite anode\u0026apos;s PANI concentration significantly affects the MFC\u0026apos;s power output. The pattern of the internal resistance\u0026apos;s decline with increasing PANI loading rate may be related to the increased growth of electroactive biofilms (EAB) on the anode surface. When the EAB breathes onto the anode surface, it may acquire a negative charge. The oxidation kinetics finally get more rapid when EAB gradually grows on an anode that contains PANI. The use of sustainable PANI could help to boost power output while also considerably lowering the cost of the anode.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Effect of phenol concentration on power generation and coulombic efficiency\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSynthetic phenolic wastewater was used to study its suitability as anolyte in Pseudomonas Sp. mediated MFCs for further energy recovery. Phenol was used as sole carbon source in MFC. The COD was adjusted to around 3 g L-1 and 100 mL of that was used as anolyte for each cycle. The pH of the spent medium was adjusted near to 7.5 for electrogenesis for all the MFCs; however, the concentration of Phenol was varied in three reactors. 3 different concentration was taken- 250 mg/L; 100 mg/L and 400 mg/L .The reactors were denoted as MFC-1; MFC-2 and MFC-3 respectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAll three sMFCs were operated at multiple fed-batch cycle mode with a close circuit \u0026nbsp;(100 Ω Rext) after the addition of different phenol concentration in anolyte. During start-up, a consistent increase in voltage output was observed with time using Pseudomonas inoculum. Operating voltage (OV) reached a maximum value after 2 weeks of continuous operation in all the MFCs except in \u0026nbsp;MFC with 400 mg/L. A slightly longer start-up time was required for MFCs where phenol concentration was 400 mg/L. The steady-state condition was delayed by 2\u0026ndash;3 days in these MFCs than acid pretreatment. The highest OV production of 192 \u0026plusmn; 4 mV was observed in MFChaving phenol concentration of 250 mg/L. The OV of MFC with untreated inoculum was found to be 128 \u0026plusmn; 7 MV at 100 Ω Rext during polarization study. . Polarization was conducted by changing external load in the external circuit. Once stabilized performance of MFC was observed, the maximum volumetric power density of about 3.42 W/m3 was obtained in the MFC withphenol concentration of250 mg/L in anolyte (Fig. 1). This power density was about 1.5 times higher than the power density obtained in the MFC inoculated with heat treated sludge, and about two times higher than the power obtained in the MFChaving phenol concentration of250 mg/L. The volumetric power density obtained in MFC with phenol concentration of 100 mg/Lwas found to be 2.72 W/m\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4 Electrochemical impedance spectroscopy (EIS) studies\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eEIS is mostly used to evaluate the caliber of electrode materials, biofilm development, and chemical reaction kinetics because it can detect certain features like ohmic resistance, charge transfer resistance, and diffusion transfer resistance. EIS is preferred over the slope technique and current interruption. A potentiostat (BioLogic SP 150, France) is used in this method to measure a wide frequency range of 100kHz to 1mHz. The results of this method are displayed as Nyquist or Bode graphs. The Nyquist plot is plotted against imaginary impedance with real impedance. The Nyquist plot consists of a semicircle and a linear line. The diameter of the semicircle represents the charge transfer resistance (Rct) [6]. During the study, a significant change in the diameter of the semicircle region of the PANI/CF\u0026rsquo;s impedance plot was observed (Figure 8). The following order was reached by the Rct value of MFCs: MFC-with 0.25 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI anode (134.8 \u0026Omega;) \u0026gt; MFC-with 0.5 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI anode (84.5 \u0026Omega;) \u0026gt; MFC- with 0.75 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI anode (66.4 \u0026Omega;) \u0026gt; MFC with 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI anode (51.2 \u0026Omega;) \u0026gt; MFC with 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e (49.6 \u0026Omega;). The Rct value of CF anode with PANI was lower than Rct value of CF anode without PANI (174.5 \u0026Omega;) (Results not shown). The highest electron transport caused by significant substrate oxidation, which increased the anodic voltage losses and enhanced current production, was shown by the minimum Rct value seen in the anode in the presence of 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI/CF composite anode in MFC. The findings of the EIS concur with those of the half-cell polarization study. The findings show that the absence of EAB biofilm on the anode surface, resulting in low electron transport, is the primary cause of increased internal resistance in MFCs without PANI.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.5 Cyclic voltammetry studies of different PANI/CF composite anode.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eFigure 9 shows the characteristic CV curve of a PANI/CF composite anode for different loading rates ranging from 0.25 to 1.25 mg/cm\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eat a fixed scan rate of 20 mV/s and potential windows of 0.8 V. CV was performed against the Ag/AgCl reference electrode. The quasi-rectangular shape of the CV curve demonstrates the behavior of the PANI/CF composite anode. From the CV plots, it can be observed that 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e showed the maximum anodic and cathode peak currents. This may be due to the large surface area attributed to the deposition of PANI onto the surface of CF, promotes the growth of EAB, enhances extracellular electron transfer (EET) and minimizes electron losses. Increasing the concentration of PANI on CF from 0.25 to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e, resulted in increase in the EET, which improved the power production in MFC. Electron mediators, shuttles or carriers are responsible for the EET of the reactors. Significant redox peaks were observed at 0.16V, 0.28V and -0.124V, -0.06V which might indicate the presence of cytochrome-b complex as electron carriers.\u0026nbsp;The CV of PANI/CF composite anode of loading rate 1.25 mg/cm\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eshowed almost four times increase from the CV of unmodified CF anode (results not shown). This shows the role played by PANI in promoting biofilm formation on the anode and increase in the EET.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.6 Evaluation of biofilm formation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUsing CLSM, the biofilm development and its constituent parts on the various PANI impregnated carbon felt anode surfaces were studied. Figures 10 and 10 display the quantifiable outcomes of electroactive microbial biofilm formation on various PANI impregnated carbon felt at the end of MFC studies.\u003c/p\u003e\n\u003cp\u003eThe data in Figure 10 were computed using the COMSTAT program. In compared to the 0.75 and 0.5 mg/cm2 biochar coated graphite electrode, a noticeably higher biomass of cells was seen on the 1 mg/cm2 biochar coated graphite electrode. The minimum and maximum biovolume of the attached microbial cell biomass for the 1 mg/cm2, 0.75, 0.5, and 0.25 mg/cm2 PANI impregnated carbon felt anodes were measured to be 15.69 m3/m\u003csup\u003e2\u003c/sup\u003e , 11.19 m3/m2 (1.84), and 10.74 m (0.95), respectively. The biovolume of cells between various 0.75 and 1 mg/cm2 biochar coated graphite electrodes did not significantly change. It is interesting to note that, in contrast to pure graphite, the biovolume of living cells was found to be larger, at 1 mg/cm2, and at 0.75 mg/cm2 for the biochar-coated electrode\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the absence of PANI, less number of cells was found on the bare carbon felt anode, demonstrating a lack of microbe anode interaction. The IMARIS 3D pictures confirm the findings of the COMSTAT analysis. From the IMARIS picture (11A-11F), the 1 mg/cm2 biochar coated graphite anode had a substantial amount of cells present; in contrast, the 0.25 mg/cm2 PANI impregnated on CF had less cells (Figure 11B).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.7 Phenolic wastewater treatment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe wastewater treatment performance of all the MFCs was observed in terms of COD removal at different operating cycles. The results showed that the average COD removal efficiency of MFC-1 and MFC-2 was in the range of 72-80 %, which demonstrates the effective treatment efficiency of this system. Coulombic efficiency (CE) is the key parameter used to evaluate the recovery of the electron through the external circuit against theoretically that present in the organic matter of MFCs. An average CE observed in MFC-1 and MFC-2 was 8.2 % and 6.8 % respectively after 2 week (Fig. 4). MFC-1 has shown higher value because of better metabolic activity of EAB in the reactor compared to MFC-2. The Columbic efficiency of the MFCs were very less indicating there was a substantial COD that was not associated with power generation. \u0026nbsp;MFC-1 shows higher columbic efficiency during all operating cycles. However, CE was slightly improved in MFC-2 at later might be because of better development of bio-film on the anode, because of reduction in methanogen than electrogen in the inoculum at slightly lower pH of nearly 6, as a result COD removal decreased and therefore CE increased.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.9 Adsorption Study of phenol on Carbon felt\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNote that all samples were taken in duplicates for data accuracy and consistency.\u003c/p\u003e\n\u003cp\u003eThus, carbon felt adsorption takes around 22 hours to remove around 88% of phenol from aqueous solution with initial phenol concentration of 500 ppm.\u003c/p\u003e\n\u003cp\u003eThus, maximum adsorption capacity is found to be 8.33 mg per gram of adsorbent (carbon felt).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.8 Discussion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn an effort to improve the inoculum\u0026rsquo;s ability to adhere to the anode surface and increase its electrochemical conductivity, a variety of nanometals or metal oxides, including manganese oxide, iron oxide, and titanium oxide, are being used for anode surface modification as indicated in Tab. 1. \u0026nbsp;Nanomaterials such as graphene, polymers, CNT form porous structures on the surface of the anode, which promotes bacterial adhesion to the anode surface by establishing redox active sites on the anode surface and also increase EET process. Carbon blacks are another excellent material for anode because it promotes biological interactions on their surface and are frequently utilized as anode to synthesize enzymes. Several different types of conductive polymers are used for anodic modification to improve the EET rate in MFCs. One of these conductive poymers is Polyaniline (PANI). Previous studies reported that the use of PANI to modify the surface of the anode, resulted in the enhancement of the power in MFC (Lai et al. 2011b; Rajesh et al. 2020; Mashkour et al. 2020). Polypyrrole (Ppy) is also a conductive polymer used in one of the studies to modify the surface of the anode which resulted in a greater power production, as well as increased stability and cell viability (Zhao et al. 2019). According to Li et al. (Li et al. 2011), the use of poly (aniline-co-aminophenol) (PAOA) in conjunction with carbon felt on the anodic surface could result in 118% higher performance than the unmodified anode. Other literature surveys also suggest that treating PANI with nitric acid and ethylenediamine, increases the nitrogen carbon ratio which is favorable for microbial adhesion (Savla et al. 2020).\u003c/p\u003e\n\u003cp\u003eThis study explores the development of an anode using PANI electrodeposited onto the surface of carbon felt (CF) for enhanced power production in MFC. The morphological characterization of PANI/CF composite states that deposition of PANI homogenously onto the surface of CF increases the surface area of the anode and establishes redox active sites on the anode. FE-SEM micrographs show the electrodeposited PANI onto to the surface of the CF. The EDX analysis of PANI/CF composite shows peaks at C, S and O which confirms the presence of sulphate ions on the surface of the anode. These Sulphate ions are responsible for the presence of active sites for microbial adhesion onto the surface of the anode. These active sites act as a \u0026ldquo;bait\u0026rdquo; for the electroactive microorganisms, which attach themselves to the anode. This promotes the growth of EAB and increase the transfer of electrons, which results in the enhancement of power production. The XRD and CV of PANI/CF composites also confirm the conductive nature of the anode. Other literature surveys such as Yellappa et al.,\u0026nbsp;(Yellappa et al. 2019)\u0026nbsp;also confirm that PANI is responsible for the increase of surface area of the anode, which improves the adhesion of EAB and enhances electrocatalytic properties.\u003c/p\u003e\n\u003cp\u003eThe phenol rich wastewater was found suitable as substrate for bioelectricity generation using Pseudomonas mediated MFC. The reduction of COD and total phenol of wastewater were 73% and 88% respectively. This study demonstrates that, additional renewable bio-energy with simultaneous recalcitrant wastewater treatment can be achieved by Pseudomonas biocatalyzed MFC without any external power consumption. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eDifferent concentrations of PANI ranging from 0.25 mg/cm\u003csup\u003e2\u0026nbsp;\u003c/sup\u003eto 1.25 mg/cm\u003csup\u003e2\u0026nbsp;\u003c/sup\u003ewas deposited onto the CF anode. The Polarization study showed steady increase in the PD\u003csub\u003emax\u003c/sub\u003e of PANI/CF composite of 0.25 mg/cm\u003csup\u003e2\u003c/sup\u003e to 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e. However, little increase was observed in the PD\u003csub\u003emax\u003c/sub\u003e of PANI/CF composite anode of 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e. The highest\u0026nbsp;PD\u003csub\u003emax\u003c/sub\u003e of 584.2 mW/m\u003csup\u003e2\u003c/sup\u003e was observed in PANI/CF of concentration 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e, which showed an increase of almost 230% when compared to unmodified CF anode.\u0026nbsp;Similar trend was observed in the OCP, CE and COD removal efficiency of the MFC. However, the opposite trend was observed for the internal resistance of the MFC reactors. With increasing concentrations of PANI, it was observed that the internal resistance of the system was lowered. The lowest internal resistance was observed in MFC with 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e PANI/CF composite. With increasing concentration of PANI/CF composite anode, the growth of EAB also increases on the anode, which results in increase in the EET and power production. Hence, this might be responsible for the decreasing Rct values, for increasing concentration of PANI/CF composite anodes as observed in the EIS analysis. The CV of the MFCs at a fixed scan rate of 20 mV/s also confirms that with increasing concentration of PANI/CF composite, increase in the EET process and power production was observed.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTable 1: Composite material as anode used in MFC with biocatalyst and their power density\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003eSr. no \u0026nbsp;\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003eElectrode Material \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003eBiocatalyst\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003ePower Density\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cu\u003e(\u003c/u\u003e\u003cstrong\u003emW/m\u003csup\u003e2\u003c/sup\u003e)\u003cu\u003e\u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003eSubstrate\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cu\u003eReference\u003c/u\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eCNT/Polyaniline composites\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e42 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eGlucose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[115]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eNitrogen-doped/CNT/rGO \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e1137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[116]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e3D CNT/Chitosan \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eGeobacter sulfurreducens\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e2.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eAcetate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[117]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eNano-molybdenum carbide\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(Mo2 C)/CNT \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e170\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eGlucose\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[118]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eGraphene oxide/Nanofibers\u003c/p\u003e\n \u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; modified carbon paper \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eShewanella MR- 1\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e34.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eLactate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[119]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003ePolypyrrole/Graphite oxide \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eShewanella\u0026nbsp;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e\u003cem\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; oneidensis\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e1326\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[120]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003e7\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eGraphene-modified stainless-steel mesh \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u003cem\u003eE. coli\u003c/em\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eLactate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003e[119]\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn summary, sulfate-doped PANI/CF electrode was developed to increase the biocompatibility of the anode. This study findings confirmed that electrodepositing the sulphate doped nanostructured PANI onto the surface of the CF increased the surface area of the anode, promoting the attachment of biofilm to the anode, which resulted in the enhancement of power production by the MFC. This study compared different concentrations of sulphate doped PANI ranging from 0.25 mg/cm2 to 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e. Out of these, it was found that sulphate doped PANI/ CF composite anode with a loading of 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e showed the best results. The wastewater exhibited a reduction of 73% in chemical oxygen demand (COD) and 88% in total phenol content. This study provides evidence that Pseudomonas biocatalyzed microbial fuel cells (MFCs) can meet the dual objectives of generating additional renewable bio-energy and treating refractory wastewater without the need for external power usage. The study also observed that the increased biofilm formation in the sulphate doped PANI/CF composite anode resulted in lower internal resistance when compared to the anode with unmodified CF. These findings show that the modification of CF with sulphate doped PANI enhanced the biofilm formation and electron transfer, which resulted in minimizing energy losses and increased efficiency of the MFC.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u003c/strong\u003e Conceptualization, S.B. and S.P.; methodology, C.P. and S.P.; data curation, C.P.; writing\u0026mdash;original draft preparation, C.P., S.P and N.R.; writing\u0026mdash;review and editing, S.B. and S.P.; visualization, S.B. and S.P.; supervision, S.P and S.B; funding acquisition, S.P. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding:\u003c/strong\u003e This research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments:\u003c/strong\u003e The authors hereby acknowledge Prof. Dipak Khastgir of Rubber Technology Centre and Central Research Facility of Indian Institute of Technology Kharagpur, India for their assistance in characterization.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest:\u003c/strong\u003e \u0026quot;The authors declare no conflict of interest.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEpstein AJ, Ginder JM, Zuo F et al (1987) Insulator-to-metal transition in polyaniline: Effect of protonation in emeraldine. 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Electrochim Acta 296:69\u0026ndash;74. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.electacta.2018.11.039\u003c/span\u003e\u003cspan address=\"10.1016/j.electacta.2018.11.039\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Electro catalyst, Bioelectrochemical system, Nyquist plots, Capacitive Bioanode, Power density, SRB","lastPublishedDoi":"10.21203/rs.3.rs-4599921/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4599921/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn the present study, Polyaniline (PANI)/ Carbon Felt (CF) composite electrodes were developed to be used as an anode in a Microbial Fuel Cell (MFC) for the enrichment of specific electroactive organisms on the anode. Comparative analysis of two approaches of Phenol degradation namely adsorption \u0026amp; biodegradation and for simultaneous generation of bio-electricity. Sulfuric acid-doped PANI was electrochemically synthesized in aqueous medium and deposited \u003cem\u003ein-situ\u003c/em\u003e on the carbon felt anode followed by its characterization using SEM, XRD, and CV. To use these in MFC, different concentrations of PANI ranging from 0.25 mg/cm\u003csup\u003e2\u003c/sup\u003e to 1.25 mg/cm\u003csup\u003e2\u003c/sup\u003e, was deposited onto CF via potentiostatic electrodeposition technique and compared. The morphological analysis using FESEM of the anode revealed homogenous deposition of nanostructured PANI onto the surface of CF. Further characterization of PANI/CF composite shows that PANI has improved the surface area of the anode, thereby, increasing the conductivity of the anode and promoting biofilm attachment to the anode. The PANI/ CF composite anode with loading rate of 1.0 mg/cm\u003csup\u003e2\u003c/sup\u003e showed the best results with maximum power density of 584.2 mW m\u003csup\u003e-2\u003c/sup\u003e and lowest charge transfer resistance of 49.6 Ω. The reduction of COD and total phenol of wastewater were 73% and 88% respectively. The obtained results from this study show that the power production and efficiency of the MFCs can be improved greatly by using Sulphate containing PANI/ CF composite as an anode material.\u003cstrong\u003e \u003c/strong\u003eThe CLSM results indicated that PANI facilitates in promoting EAB biofilm which in turn helps in achieving enhanced power output.\u003c/p\u003e","manuscriptTitle":"Electrodeposited polyaniline-carbon felt anode promotes electroactive biofilm for the improved energy recovery in microbial fuel cells using phenol containing wastewater","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-05 02:50:20","doi":"10.21203/rs.3.rs-4599921/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"baf71518-da6a-4930-a03e-3d92fb61b1c5","owner":[],"postedDate":"July 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-07-25T09:29:12+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-05 02:50:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4599921","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4599921","identity":"rs-4599921","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}