Improvement of Power Generation Using Shewanella Putrefaciens
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Bioresource Technology 166 (2014) 451–457 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Improvement of power generation using Shewanella putrefaciens mediated bioanode in a single chambered microbial fuel cell: Effect of different anodic operating conditions ⇑ Soumya Pandit a, Santimoy Khilari b, Shantonu Roy a, Debabrata Pradhan b, Debabrata Das a, a Department of Biotechnology, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India b Materials Science Centre, Indian Institute of Technology, Kharagpur, Kharagpur 721302, India highlights Taguchi design to find out the key anodic process parameter. Impedance study to evaluate the influence of riboflavin addition to anolyte. Cyclic voltammetry to find out the effect of nano hematite modified anode. Microscopic study of biofilm formation using different nano hematite loaded anode. article info abstract Article history: Three different approaches were employed to improve single chambered microbial fuel cell (sMFC) Received 8 March 2014 performance using Shewanella putrefaciens as biocatalyst. Taguchi design was used to identify the key Received in revised form 18 May 2014 process parameter (anolyte concentration, CaCl2 and initial anolyte pH) for maximization of volumetric Accepted 21 May 2014 power. Supplementation of CaCl was found most significant and maximum power density of 4.92 Available online 29 May 2014 2 W/m3 was achieved. In subsequent approaches, effect on power output by riboflavin supplementation to anolyte and anode surface modification using nano-hematite (Fe2O3) was observed. Volumetric power Keywords: density was increased by 44% with addition of 100 nM riboflavin to anolyte while with 0.8 mg/cm2 Single chambered MFC nano-Fe O impregnated anode power density and columbic efficiency increased by 40% and 33% Riboflavin 2 3 Shewanella putrefaciens respectively. Cyclic voltammetry revealed improvement in electrochemical activity of Shewanella with Taguchi optimization nano-Fe2O3 loading and electrochemical impedance depicted inverse relationship between charge Nano hematite transfer resistance and nano-Fe2O3 loading. This study suggests anodic improvement strategies for maximization of power output. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction promising technology, MFC suffers from limitations such as low power density, high cost etc. MFCs will be a viable option for power Microbial fuel cell (MFC) uses electrochemically active bacteria generation if the current production of this device is improved (EAB) as biocatalyst to convert biodegradable waste into electricity (Kim et al., 2007). The electrochemical performance of the (Yang et al., 2012). EABs are gaining importance because of their bio-anode is one of the major factors that affect the bioelectricity electron donating ability to the electrodes in MFC. Microorganisms generation process therefore identification of key operational fac- such as members of the Geobacter family, Shewanella putrefaciens tors and their optimization is of utmost important for the maximi- and Shewanella oneidensis, Rhodoferax ferrireducens, Pseudomonas zation of the power output (Pham et al., 2009). Electrode aeruginosa, Clostridium butyrium and Aeromonas hydrophila have modification is another strategy to improve the performance of been reported to oxidize organic matter at anode to complete their an MFC (Wei et al., 2011). Thus the present study endeavored in metabolism process (Logan and Regan, 2006). In spite of being a this direction and was focused in improving power generation using Shewanella sp. as anodic biocatalyst in a single chambered MFC (sMFC). ⇑ Corresponding author. Tel.: +91 3222 283758/9434717424; fax: +91 3222 Many MFCs operation were reported with Shewanella sp. as a 255303. E-mail address: [email protected] (D. Das). model organism (Kim et al., 2002; Sharma and Kundu, 2010) which http://dx.doi.org/10.1016/j.biortech.2014.05.075 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. 452 S. Pandit et al. / Bioresource Technology 166 (2014) 451–457 is a facultative anaerobic bacteria that can use a wide range of elec- (60% v/v); 0.425 g KCl; 2.028 g anhydride Na2SO4; 0.19 g CaCl2Á2H2O; tron acceptors and are classified in the group of dissimilatory 0.105 g MgSO4Á7H2O and 1.004 g yeast extract (Difco) were taken. metal-reducing bacteria (DMRB) (Lovley et al., 2004). Intact cells The anolyte pH was adjusted to 7 (unless stated otherwise) of anaerobically grown S. putrefaciens are electrochemically active (Khilari et al., 2014) with 1.0 M carbonate/bicarbonate buffer. and can grow in a MFC using anode as its terminal electron Desirable chemical oxygen demand (COD) was maintained by acceptor. The anode performance in Shewanella inoculated MFC is altering the Na-lactate concentration in the medium. Since the influenced largely by factors such as anolyte pH; inoculum age; unmodified lactate medium contained 0.19 g CaCl2, all concentra- concentration of electron donor: Calcium chloride (CaCl2) ribofla- tions of CaCl2 added for Taguchi optimization process were vin, etc (Kim et al., 2002; Park and Zeikus, 2002). Previous studies normalized to the un-modified medium. were carried out to evaluate the individual effect of these operating parameters in the anode chamber that influenced the activity of 2.2. Synthesis of nano Fe2O3 Shewanella. However, the combined effects of these parameters have not yet been explored. A better understanding of interrela- Fe2O3 nano structure was prepared by a simple solvothermal tionship between the operational parameters is needed prior to method. In a typical synthesis, 30 mL 0.05 M ethanolic solution successful MFC application. The present study addressed the of FeCl3 was taken in a beaker and 360 mg urea was added to this individual as well as the combined effect of the above mentioned solution followed by stirring for 10 min. After stirring a clear solu- operating parameters. Taguchi method was adapted to evaluate tion was formed which was transferred to a 50 mL Teflon-line the influence of anolyte pH, CaCl2 and substrate concentration on stainless steel autoclave. Hydrothermal dwell temperature was volumetric power generation. set at 150 °C for 12 h. Then the autoclave was allowed to cool down Initially, it was assumed that outer most cytochrome C type naturally to room temperature and precipitate formed inside protein is involved in exocellular electron transfer (EET) and ribo- Teflon line container was collected by centrifugation. Subsequently flavin plays significant role in EET by donating electron to anode the product was washed with distilled water followed by ethanol (Kim et al., 2002). Recent work has shown that Shewanella species for several times. Finally the washed precipitate was dried in an secrete riboflavin that facilitates electron transfer to both insoluble oven at 60 °C for 6 h. metals and anodes. The removal of accumulated soluble flavins decreases the rate of electron transfer by Shewanella biofilm to 2.3. Physical characterizations of nano Fe2O3 electrodes over 80%. Commercial riboflavin is much cheaper con- sidering the requirement in anolyte of MFC (Marsili et al., 2008). The crystallographic phase and structure were evaluated from Thus, in our second approach, riboflavin was supplemented to ano- X-ray diffractogram. Powder X-ray diffraction was carried out in lyte to study the improvement in power output. Electrochemical a Rigaku Ultima III using Cu Ka (40 kV, 40 mA) radiation over a impedance spectroscopy was employed to estimate the reduction range of 20À80°. The surface morphology and composition was in internal resistance. studied with a Zeiss Supra scanning electron microscope at an In a third approach, the influence of anode modification accelerating voltage of 5 kV. (impregnated) with Nano Fe2O3 on power output was investigated. Anode activity of a MFC can be improved by introducing electroca- 2.4. Nano Fe2O3 decorated anode preparation pacitive component into it. It is well known that a capacitive anode can perform much efficiently than its noncapacitive counterpart. The anode was modified with nano Fe2O3 containing electrode So, incorporation of electrochemically charge storage materials modifier ink. In a typical ink preparation, requisite amount of nano 2 on anode surface is desirable. Now-a-days transitional metal Fe2O3 (0.2, 0.4, 0.8 mg/cm ) was dispersed in acetone-isopropyl oxides are extensively studied as electrode materials for electro- alcohol (1:1) solution with 5 wt% polytetrafluoroethylene (PTFE; chemical capacitors. Among these oxides Fe2O3 has gained much 60 wt%; Sigma Aldrich). The ink was subsequently sprayed on a attention for its low cost, non toxicity, high performance and long carbon cloth by a gravity spray gun. Then the modified carbon cycle life (Park et al., 2008). It was previously reported that Shewa- cloth was allowed to dry at 70 °C in an oven for 6 h. Finally the nella was attracted by hematite or Fe2O3 particles and it had a dried Fe2O3 loaded carbon cloth was used as anode in MFCs. tendency to reduce hematite (Bose, 2009). Thus hematite can be utilized as an anode modifier. In the present study, (hematite) 2.5. MFC assembly construction Fe2O3 nano structure was prepared, characterized and impreg- nated in the carbon cloth anode and its loading effect was evalu- Nine identical sMFCs were used for the experiments. The MFC ated on current output of sMFC. In addition, cyclic voltammetry consisted of an anode compartment and a membrane cathode was utilized to evaluate the capacitance of different nano Fe2O3 assembly (MCA) placed on opposite sides. The cuboidal anode loadings on anode of sMFC. chamber is made from transparent polyacrylic material with outer dimensions 7 Â 8 Â 3.5 cm3 of 110 mL capacity. The anode cham- ber had two ports at the top, one for electrode terminal and the 2. Methods other for reference electrode (Ag/AgCl, saturated KCl; +197 mV, Equiptronics, India) and sampling. The anode consisted of a carbon 2.1. Microbial strain, media and growth conditions cloth of working surface area 12 cm2 with a stainless steel wire welded to form the terminal. A low cost custom made KOH doped S.