HUNGARIAN JOURNAL OF INDUSTRY AND CHEMISTRY Vol. 48(2) pp. 51–53 (2020) hjic.mk.uni-pannon.hu DOI: 10.33927/hjic-2020-27 CONSIDERATIONS TO APPROACH MEMBRANE BIOFOULING IN MICRO- BIAL FUEL CELLS SZABOLCS SZAKÁCS *1 AND PÉTER BAKONYI1 1Research Institute on Bioengineering, Membrane Technology and Energetics, University of Pannonia, Egyetem u. 10, 8200 Veszprém, HUNGARY Among bioelectrochemical systems, those referred to as microbial fuel cells (MFCs) are widely implemented for wastew- ater management and simultaneous recovery of electrical energy. MFCs are fundamentally assisted by bacterial popu- lations, mostly mixed cultures to be more exact that, after oxidizing the substrate, are capable of facilitating the passage of electrons to an electron acceptor, usually the anode. However, certain undesired bacterial strains often colonize not only the electrode but the membrane separator over time and cause severe biofouling. The membrane is an architectural element of many MFCs and determines the efficiency of the system. In this paper, this issue is overviewed briefly and some considerations concerning how to approach the problem are presented. Keywords: microbial fuel cell, membrane, oxygen mass transfer, biofouling 1. Introduction Bioelectrochemical systems, including Microbial Fuel Cells (MFCs), are often installed with a physical sepa- rator such as a membrane as illustrated in Fig. 1 [1]. The membrane, which separates the anode from the cathode, should enable the adequate migration of ions (in this case, cations such as protons) between the elec- trodes to ensure the MFC continues to produce electricity [2]. Furthermore, the membrane should function as a bar- rier against the crossover effect of substances to avoid the loss of the substrate (which normally is injected into the anode chamber in order to feed the species of electroac- tive bacteria shown in Table 1 living on a biofilm on the electrically-conductive anode surface) and penetration of dissolved oxygen from the aerated cathode chamber to the anaerobic anode chamber [3]. In addition to these requirements which are associ- ated with the physical and chemical properties of the material, the membranes should be relatively affordable. Another point that needs to be addressed is the stability of the membrane, which can be influenced by the com- plex chemical environment of the bulk phases (anolyte in the anode chamber, catholyte in the cathode chamber) in an MFC and microbiological phenomena [5]. Altogether, these effects may cause fouling of the membrane during its operation, moreover, when the underlying mechanism is associated with the metabolism and/or growth of mi- croorganisms, the term “biofouling” is more appropriate [6]. In summary, various membranes can be evaluated *Correspondence: szakacs.szabolcs@mk.uni-pannon.hu Figure 1: Scheme of an MFC and ranked based on the characteristics of the membrane materials (typically but not exclusively fabricated from polymers) and their observed behavior during MFC op- eration which can be monitored by various electrochemi- cal measurements, e.g., recording the cell voltage, as pre- sented in Fig. 2. 2. Membranes and biofouling in MFCs – The potential role of oxygen mass trans- fer In accordance with the previous section, the membrane separator divides the anaerobic anode chamber from the aerobic cathode chamber [7]. Therefore, it is reasonable to assume that the actual microbial communities develop- ing on the anode and the membrane have completely dif- ferent structures and relationships with gaseous oxygen. From the literature, it can be concluded with a good de- gree of certainty that the electrochemically active bacteria https://doi.org/10.33927/hjic-2020-27 mailto:szakacs.szabolcs@mk.uni-pannon.hu 52 SZAKÁCS, AND BAKONYI Table 1: Electroactive species of bacteria and their oxygen tolerance [4] Species Oxygen tolerance E. coli facultatively anaerobic https://bacdive.dsmz.de/strain/4907 Shewanella oneidensis facultatively anaerobic https://img.jgi.doe.gov/cgi-bin/m/main.cgi?section= TaxonDetail&page=taxonDetail&taxon_oid=637000258 Geobacter sulfurreducens strict anaerobe https://bacdive.dsmz.de/strain/5792 Geobacter metallireducens strict anaerobe https://bacdive.dsmz.de/strain/5791 Desulfobulbus propionicus strict anaerobe https://bacdive.dsmz.de/strain/4004 Geothrix fermentans strict anaerobe https://bacdive.dsmz.de/strain/17672 Paracoccus pantotrophus facultatively anaerobic https://bacdive.dsmz.de/strain/13703 Rhodopseudomonas palustris DX-1 strict anaerobe https://bacdive.dsmz.de/strain/1819 on the anode are either strict or facultative anaerobes as shown in Table 1 [4]. However, a considerable knowledge gap seems to exist concerning the populations attached to the surface of the membrane and the occurrence of bio- fouling. In contrast, it is reasonable to suppose that these membrane-bound colonies and biofilms are more toler- ant of dissolved oxygen due to the technically direct and long-lasting contact with this substance. In general, the oxygen flux across a membrane in MFCs is described by the oxygen transfer coefficient which can be calculated by [8, 9] kO = − V At ln [ (C0 − C) C0 ] (1) where kO denotes the oxygen transfer coefficient (cm3/cm2s), V stands for the volume of liquid (cm3), A represents the surface area of the membrane (cm2), C0 refers to the saturation oxygen concentration (mol/dm3), C is the actual oxygen concentration mea- sured (mol/dm3) and t denotes the time of the measure- ment (s); and kO = DO L (2) where DO stands for the oxygen diffusion coefficient (cm2/s) and L represents the thickness of the membrane (cm). Figure 2: Schematic diagram of the MFC Therefore, it is worth examining which strains col- onize the membrane and how these mixed communi- ties vary depending on ko. Even though some previ- ous papers have demonstrated the use of various micro- scopic imaging techniques based on visual observations to study these biofouling layers on the surface of mem- branes [10–12], qualitative and quantitative feedback to highlight “what type of” and “how many” microbes can coexist is scarce. As a result, experimental methodology involving the apparatus of modern molecular biology, e.g. DNA-based identification, should be encouraged and im- plemented to answer such questions [13]. 3. Conclusions The capability of membranes to permeate dissolved oxy- gen in microbial fuel cells is key. On the one hand, re- duced oxygen transport membranes (OTMs) are likely to maintain the typically less oxygen tolerant, electroactive bacteria located on the surface of the anode in a good con- dition. On the other hand, oxygen mass transfer through the membrane is expected to affect the biofouling of the separator and thus, how microbial communities respond to changes in material properties, in particular ko, needs to be understood. The assessment of membranes with different values of ko should be carried out relative to Nafion, which is by far the most broadly employed poly- mer for benchmarking studies [14]. Acknowledgement This work was supported by the National Research, De- velopment and Innovation Office (NKFIH, Hungary) un- der grant number FK 131409 and GINOP-2.3.2-15-2016- 00016 Excellence of strategic R+D workshops, entitled “Development of modular, mobile water treatment sys- tems and waste water treatment technologies based on University of Pannonia to enhance growing dynamic ex- port of Hungary” (2016-2020) Hungarian Journal of Industry and Chemistry https://bacdive.dsmz.de/strain/4907 https://img.jgi.doe.gov/cgi-bin/m/main.cgi?section=TaxonDetail&page=taxonDetail&taxon_oid=637000258 https://img.jgi.doe.gov/cgi-bin/m/main.cgi?section=TaxonDetail&page=taxonDetail&taxon_oid=637000258 https://bacdive.dsmz.de/strain/5792 https://bacdive.dsmz.de/strain/5791 https://bacdive.dsmz.de/strain/4004 https://bacdive.dsmz.de/strain/17672 https://bacdive.dsmz.de/strain/13703 https://bacdive.dsmz.de/strain/1819 MEMBRANE BIOFOULING IN MICROBIAL FUEL CELLS 53 REFERENCES [1] Leong, J. X.; Daud, W. R. W.; Ghasemi, M.; Liew, K. B.; Ismail, M.: Ion exchange membranes separa- tors in microbial fuel cells for bioenergy conversion: A comprehensive review. Renew. Sustain. Energy Rev., 2013, 28, 575–587 DOI: 10.1016/j.rser.2013.08.052 [2] Daud, S. M.; Kim, B. H.; Ghasemi, M.; Daud, W. R. W.: Separators used in microbial electro- chemical technologies: Current status and future prospects. Bioresour. Technol., 2015, 195, 170–179 DOI: 10.1016/j.biortech.2015.06.105 [3] Bakonyi, P.; Koók, L.; Kumar, G.; Tóth, G.; Rózsen- berszki, T.; Nguyen, D. D.; Chang, S. W.; Zhen, G.; Bélafi-Bakó, K.; Nemestóthy, N.: Architectural en- gineering of bioelectrochemical systems from the perspective of polymeric membrane separators: A comprehensive update on recent progress and fu- ture prospects. J. Memb. Sci., 2018, 564, 508–522 DOI: 10.1016/j.memsci.2018.07.051 [4] Sharma, V.; Kundu, P. P.: Biocatalysts in microbial fuel cells. Enzyme Microb. Technol., 2010, 47(5), 179–188 DOI: 10.1016/j.enzmictec.2010.07.001 [5] Koók, L.; Bakonyi, P.; Harnisch, F.; Kretzschmar, J.; Chae, K.-J.; Zhen, G.; Kumar, G.; Rózsenber- szki, T.; Tóth, G.; Nemestóthy, N.; Bélafi-Bakó, K.: Biofouling of membranes in microbial electrochem- ical technologies: Causes, characterization methods and mitigation strategies. Bioresour. Technol., 2019, 279, 327–338 DOI: 10.1016/j.biortech.2019.02.001 [6] Noori, Md. T.; Ghangrekar, M. M.; Mukherjee, C. K.; Min, B.: Biofouling effects on the perfor- mance of microbial fuel cells and recent advances in biotechnological and chemical strategies for mit- igation. Biotechnol. Adv., 2019, 37(8), 107420 DOI: 10.1016/j.biotechadv.2019.107420 [7] Patil, S. A.; Gildemyn, S.; Pant, D.; Zengler, K.; Lo- gan, B. E.; Rabaey, K.: A logical data representation framework for electricity-driven bioproduction pro- cesses. Biotechnol. Adv., 2015, 33(6), 736–744 DOI: 10.1016/j.biotechadv.2015.03.002 [8] Chae, K. J.; Choi, M.; Ajayi, F. F.; Park, W.; Chang, I. S.; Kim, I. S.: Mass transport through a pro- ton exchange membrane (Nafion) in microbial fuel cells. Energy and Fuels, 2008, 22(1), 169–176 DOI: 10.1021/ef700308u [9] Kim, J. R.; Cheng, S.; Oh, S.-E.; Logan, B. E.: Power generation using different cation, anion, and ultrafiltration membranes in microbial fuel cells. Environ. Sci. Technol., 2007, 41(3), 1004–1009 DOI: 10.1021/es062202m [10] Venkatesan, P. N.; Dharmalingam, S.: Effect of cation transport of SPEEK - Rutile TiO2 electrolyte on microbial fuel cell performance. J. Memb. Sci., 2015, 492, 518–527 DOI: 10.1016/j.memsci.2015.06.025 [11] Angioni, S.; Millia, L.; Bruni, G.; Tealdi, C.; Mustarelli, P.; Quartarone, E.: Improving the performances of NafionTM-based mem- branes for microbial fuel cells with silica-based, organically-functionalized mesostructured fillers. J. Power Sources, 2016, 334, 120–127 DOI: 10.1016/j.jpowsour.2016.10.014 [12] Mokhtarian, N.; Ghasemi, M.; Daud, W. W. R.; Is- mail, M.; Najafpour, G.; Alam, J.: Improvement of microbial fuel cell performance by using nafion polyaniline composite membranes as a separator. J. Fuel Cell Sci. Technol., 2013, 10(4), 041008 DOI: 10.1115/1.4024866 [13] Saratale, R. G.; Saratale, G. D.; Pugazhendhi, A.; Zhen, G.; Kumar, G.; Kadier, A.; Sivagurunathan, P.: Microbiome involved in microbial electrochemi- cal systems (MESs): A review. Chemosphere, 2017, 177, 176–188 DOI: 10.1016/j.chemosphere.2017.02.143 [14] Rahimnejad, M.; Bakeri, G.; Ghasemi, M.; Zire- pour, A.: A review on the role of proton exchange membrane on the performance of microbial fuel cell. Polym. Adv. Technol., 2014, 25(12), 1426–1432 DOI: 10.1002/pat.3383 48(2) pp. 51–53 (2020) https://doi.org/10.1016/j.rser.2013.08.052 https://doi.org/10.1016/j.biortech.2015.06.105 https://doi.org/10.1016/j.memsci.2018.07.051 https://doi.org/10.1016/j.enzmictec.2010.07.001 https://doi.org/10.1016/j.biortech.2019.02.001 https://doi.org/10.1016/j.biotechadv.2019.107420 https://doi.org/10.1016/j.biotechadv.2019.107420 https://doi.org/10.1016/j.biotechadv.2015.03.002 https://doi.org/10.1016/j.biotechadv.2015.03.002 https://doi.org/10.1021/ef700308u https://doi.org/10.1021/ef700308u https://doi.org/10.1021/es062202m https://doi.org/10.1021/es062202m https://doi.org/10.1016/j.memsci.2015.06.025 https://doi.org/10.1016/j.jpowsour.2016.10.014 https://doi.org/10.1016/j.jpowsour.2016.10.014 https://doi.org/10.1115/1.4024866 https://doi.org/10.1115/1.4024866 https://doi.org/10.1016/j.chemosphere.2017.02.143 https://doi.org/10.1002/pat.3383 Introduction Membranes and biofouling in MFCs – The potential role of oxygen mass transfer Conclusions