HYDRODYNAMIC AND ELECTRODE ORIENTATION EFFECTS ON SINGLE CHAMBER MEMBRANELESS MICROBIAL FUEL CELL
XXVI Congresso Nazionale della Società Chimica Italiana
Vicari Fabrizio *, Alessandro Galia , Onofrio Scialdone Dipartimento dell’Innovazione Industriale e Digitale – DIID – Ingegneria Chimica, Meccanica, Informatica, Gestionale. Università degli Studi di Palermo, Viale delle Scienze Ed. 6, 90128 Palermo,Italy;
*
[email protected]
Introduction Municipal, domestic, animal and food processing wastewater have a theoretical carbon content sufficient to energetically sustain the whole water infrastructure. However, it is a common practice to use additional energy to remove it instead of trying to convert it (1). It is possible, indeed, to directly convert this organic content into electricity thanks to microbial fuel cells (MFCs), bio-electrochemical devices in which particular bacterial strains oxidize the organic matter using electrodes as final electron acceptor (2). What has been mainly adopted in this work, is usually reported as Single Chamber Membraneless (SCML) MFC. SCML-MFC were developed without any physical delimitation between the anodic and cathodic environments. With regards to a conventional MFC, SCML have reduced cost, both investment and exercise, avoiding the usage of membranes (3). In some SCML-MFC work, an horizontal cathode is used, lying at the interface between the liquid and the gas phase (4), circumstance that inspired our work (5). Other authors have changed electrode distance in order to asses this parameter influence (6), deducing that a closer distance could increase aeration of the anodic biofilm, lowering the performance. Thus, researchers concern designing SCMLMFC is to limit as much as possible anode oxygenation (8). In the present work, this very same path was followed. The possibilities given by the usage of Shewanella putrefaciens to catalyze both anodic and cathodic (9) reactions are used to explore the effect of the increased aeration obtained placing the cathode horizontally. Hydrodynamic regimen effect was also evaluated changing the stirring rate.
References: 1. B.E. Logan, Microbial Fuel Cells, in: Microb. Fuel Cells, 1st ed., John Wiley & Sons, Inc., Hoboken, NJ, USA, 2007: pp. 1–11. doi:10.1002/9780470258590.ch1. 2. R. Kumar, L. Singh, Z.A. Wahid, M.F.M. Din, Exoelectrogens in microbial fuel cells toward bioelectricity generation: a review, Int. J. Energy Res. 39 (2015) 1048–1067. doi:10.1002/er.3305. 3. F.J. Hernández-Fernández, A. Pérez de los Ríos, M.J. Salar-García, V.M. Ortiz-Martínez, L.J. Lozano-Blanco, C. Godínez, F. Tomás-Alonso, J. Quesada-Medina, Recent progress and perspectives in microbial fuel cells for bioenergy generation and wastewater treatment, Fuel Process. Technol. 138 (2015) 284–297. doi:10.1016/j.fuproc.2015.05.022. 4. Z. Liu, X. Li, B. Jia, Y. Zheng, L. Fang, Q. Yang, D. Wang, G. Zeng, Production of electricity from surplus sludge using a single chamber floating-cathode microbial fuel cell, Water Sci. Technol. 60 (2009) 2399. doi:10.2166/wst.2009.313. 5. F. Vicari, A. D’Angelo, A. Galia, P. Quatrini, O. Scialdone, A single-chamber membraneless microbial fuel cell exposed to air using Shewanella putrefaciens, J. Electroanal. Chem. (2016). doi:10.1016/j.jelechem.2016.11.010. 6. D. Jiang, B. Li, Granular activated carbon single-chamber microbial fuel cells (GAC-SCMFCs): A design suitable for large-scale wastewater treatment processes, Biochem. Eng. J. 47 (2009) 31–37. doi:10.1016/j.bej.2009.06.013. 7. Y. Ahn, B.E. Logan, Domestic wastewater treatment using multi-electrode continuous flow MFCs with a separator electrode assembly design, Appl. Microbiol. Biotechnol. 97 (2013) 409–416. doi:10.1007/s00253-012-4455-8. 8. F. Zhu, W. Wang, X. Zhang, G. Tao, Electricity generation in a membrane-less microbial fuel cell with down-flow feeding onto the cathode, Bioresour. Technol. 102 (2011) 7324–7328. doi:10.1016/j.biortech.2011.04.062 9. F. Vicari, A. D’Angelo, A. Galia, P. Quatrini, and O. Scialdone, “A single-chamber membraneless microbial fuel cell exposed to air using Shewanella putrefaciens,” J. Electroanal. Chem., vol. 783, pp. 268–273, 2016.
Assessment of
● Hydrodynamic regimen influence; ● Electrodes orientation effect; ● Comparison with undivided cell.
Cathode orientation effect
Materials and methods
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Figure 3. The electrochemical cell used in this study. Anode: carbon felt 10.5 cm2. Cathode: Compact graphite 10.5 cm2. A) Configuration with both electrodes placed vertically. B) Configuration with the cathode lying horizontally at the interface between liquid and gas phase. 0.12
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A SCML-MFC with parallel vertical electrodes was feed with LB broth diluted 1/3 with de-ionized (DI) water. Dilution was done in order to reduce the length of a single cycle. The reactor was subjected to five different stirring rate, from 0 to 900 rpm. Every speed was explored during a single cycle and repeated 3 times. The entire test duration is 5 months. Averaged voltage drop was evaluated for every speed, the standard deviation obtained in every cycle.
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“Shewanella Putrefaciens CN32” SEM by EMSL (www.flickr.com/photos/em sl/4584517878 creativecommons.org/license s/by-nc-sa/2.0/)
In order to asses the influence of electrode orientation, a SCML-MFC was equipped with parallel vertical electrodes (Figure 3A) and fed with LB broth in tree different cycle. A second reactor (Figure 3B), was equipped with a horizontal cathode for the same period and the same number of cycle. Figure 3 shows that a greater amount of energy can be sustained by horizontal cathode for longer durations. SCML reactors were eventually subjected to polarization (see Figure 4). A comparison with a conventional divided MFC is also provided in the polarization test (see Figure 4).
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A single-chamber electrochemical cell was used, continuously stirred and operated in batch mode. Air entered the reactor through a plastic mesh of about 100 μm. V = 60 mL. Anode: Carbon felt (10.5 cm2) Cathode: Compact graphite (10.5 cm2) Rext = 1 kΩ. Polarization were carried out with an external variable resistors. A keithley 2700 voltmeter datalogger was used to acquire cell voltage in time. S. putrefaciens was bought from Libniz Institute (Braunschweig, GERMANY) and cultured on LB broth.
Work goals:
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Figure 2. Stirring rate effect from 0 to 900 rpm on cell voltage across a 1 Figure 1. Stirring rate effect from 0 to 900 rpm on kΩ external resistor. Bars: Standard cell voltage across a 1 kΩ external resistor. deviation.
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Figure 5. Power densities (A) and polarization (B) curves for: undivided cell equipped with horizontal (triangle), vertical cathode (circle) and an H-type two-chamber cell (square). MFC equipped with carbon felt anode and compact graphite cathode and LB broth for the undivided cells and the anodic compartment of the divided one. In this last reactor a solution of Na2SO4 (0.1 M) adjusted to pH 2 with H2SO4 was used as catholyte.
Conclusions • •
A complete assessment of the relation between reactor hydrodynamic and cell voltage has been provided in terms of stirring rate effect evaluation. Higher cell voltages were achieved at the intermediate condition of 300 rpm, which may imply the perfect match between the need for a high mass transport rate of the substrate and the stress of the bacterial community; In comparison with the vertical cathode SCML-MFC and the most similar divided reactor that was possible to implement, performance was increased by an horizontal cathode position.;
