Handa Notebook Thesis

[Audio] Hello Everyone, I am Jasreen Kaur from the Department of Environment and Energy Engineering. First and foremost, I would like to thank Professor Jung Sokhee for allowing me to present this very interesting paper entitled a kinetic perspective on extracellular electron transfer by anode-respiring bacteria. Without further a due let's get started..

[Audio] This presentation is divided into four section which are the introduction and objectives, anode potential losses, EET mechanisms types used by ARB and last but not least the conclusion. At the end of the slides there will also be a section on appendix.

[Audio] This presentation is divided into four section which are the introduction and objectives, anode potential losses, EET mechanisms types used by ARB and last but not least the conclusion. At the end of the slides there will also be a section on appendix.

[Audio] Diving into part 1 which is the Introduction. In microbial fuel cells and electrolysis cells , anode-respiring bacteria oxidize organic substrates to produce electrical current. In order to develop an electrical current, A R B must transfer electrons to a solid anode through extracellular electron transfer. A R B use various EET mechanisms to transfer electrons to the anode. The first mechanism is the direct electron transfer. Direct Electron Transfer between electron carriers in the bacteria and the solid electron acceptor. This mechanism is supported by the presence of outer-membrane cytochromes that can interact directly with the solid surface to carry out respiration. Bacteria using this mechanism require direct contact with the solid electron acceptor and, thus, cannot form a biofilm. The second EET mechanism is the soluble electron shuttle. Soluble Electron Shuttle: a compound that carries electrons from the bacteria by diffusive transport to the surface of the metal oxide and is able to react with it, discharging its electrons. Then, this compound, in its oxidized state, diffuses back to the cells, which should be able to use the same compound repeatedly .hence the name shuttle. The third EET mechanism is the solid component. Solid Component that is part of the extracellular biofilm matrix and is conductive for electron transfer from the bacteria to the solid surface. This mechanism is supported by the recent discovery of the possible role of cellular pili as nanowires, which are being characterized for their capability to conduct electrons. Other components may also be conductive and contribute in EET, such as extracellular cytochromes or bound electron mediators.

[Audio] Diving into part 1 which is the Introduction. In microbial fuel cells and electrolysis cells , anode-respiring bacteria oxidize organic substrates to produce electrical current. In order to develop an electrical current, ARB must transfer electrons to a solid anode through extracellular electron transfer. ARB use various EET mechanisms to transfer electrons to the anode. The first mechanism is the direct electron transfer. Direct Electron Transfer between electron carriers in the bacteria and the solid electron acceptor. This mechanism is supported by the presence of outer-membrane cytochromes that can interact directly with the solid surface to carry out respiration. Bacteria using this mechanism require direct contact with the solid electron acceptor and, thus, cannot form a biofilm. The second EET mechanism is the soluble electron shuttle. Soluble Electron Shuttle: a compound that carries electrons from the bacteria by diffusive transport to the surface of the metal oxide and is able to react with it, discharging its electrons. Then, this compound, in its oxidized state, diffuses back to the cells, which should be able to use the same compound repeatedly .hence the name shuttle. The third EET mechanism is the solid component. Solid Component that is part of the extracellular biofilm matrix and is conductive for electron transfer from the bacteria to the solid surface. This mechanism is supported by the recent discovery of the possible role of cellular pili as nanowires, which are being characterized for their capability to conduct electrons. Other components may also be conductive and contribute in EET, such as extracellular cytochromes or bound electron mediators.

[Audio] Thus, coming to the objectives of this review paper. There are two main objective whereby the first one is that ARB must be able to perform a twofold task which are A to produce a high current density that minimizes anode materials and reactor size and B at a low anode potential or can be defined as being as close as possible to the redox potential of the substrate being oxidized, which translates into minimal anode potential losses and high energy output. The second objective is to evaluate how well each EET mechanism can produce a high current density more than 10Ampere per meter square without a large anode potential loss.

[Audio] Second part is the anode potential losses. In this section is it divided into 4 parts which are the intracellular potential losses, rate of substrate utilization by ARB, rate of electron production by ARB and the extracellular potential losses and its mechanisms..

. How to characterize anode potential losses?. .

[Audio] Coming into Part 1 of section 2 the intracellular potential losses Two kinetic processes are involved in intracellular potential losses from Edonor minus EOM these processes are common in all respiratory bacteria and are depicted in Figure. 5. From Figure. 5.1 First, bacteria oxidize the electron donor, producing intracellular reducing power in the form of an electron carrier such as NADH. To generate energy for the cells, the electron carrier is oxidized by transferring its electrons into the membrane associated proteins that are part of the electron transport chain, which ultimately leads to the external electron acceptor. From Figure. 5.2 In the case of ARB, the electrons are transferred to OM proteins that initiate the EET process..

[Audio] Part 2 of section 2 is the rate of substrate utilization by ARB. The rate of substrate utilization in microbial processes are frequently modeled using the Monod relationship. This relationship explicitly describes the rate at which bacteria oxidize the substrate and produce the reduced intracellular electron carrier. When the substrate is rate-limiting for the entire process of metabolism and EET, the current density generated by ARB can be written as equation. ( 1) for a biofilm setting where j is current density obtained by ARB, jmax is maximum current density of the ARB biofilm, S is substrate concentration in the liquid, Ks,apparent is the apparent half-saturation substrate concentration in a biofilm..

[Audio] Part 3 is rate of electron production by ARB Once ARB have produced the reduced intracellular carrier, they initiate electron flow through the electron transport chain until the electrons reach membrane-bound cytochromes that, in turn, initiate EET. The rate of reduction of electron shuttles can be modeled by the Monod relationship expressed in terms of the concentration of the soluble shuttle The problem is that Because the electron acceptor for ARB is a solid anode, we cannot use the Monod relationship, because we cannot define an anode concentration. Thus, we transform the concentration of an electron acceptor into the anode potential, which is achieved using the Nernst–Monod relationship developed by Marcus et al. ( 2007) to express the current density in an ARB biofilm. The formula is defined as below where R is the ideal gas constant, F is the Faraday constant, T is the temperature in kelvin and Eka is the potential at which the current density one over two maximum current density.

[Audio] The Nernst– Monod relationship combines the Monod relationship typically used to calculate the rate of electron acceptor utilization with the Nernst equation for describing the anode potential availability as the electron acceptor for ARB Because enzyme electrode and bacteria electrode systems have similar kinetic processes, we can analyze the potential losses in the ARB biofilm depicted in Figure. 6 in a similar manner as is performed in enzyme electrochemistry. Nernst– Monod equation as the baseline to distinguish intracellular potential losses from n anode. Thus, deviations from the Nernst–Monod equation will help us determine extracellular potential losses due to EET and interface electron transfer..

[Audio] Moving to Part 4 which is the extracellular potential losses. Two kinetic processes are involved in extracellular potential losses. First, electrons are transported from the ARB's OM proteins example cytochromes to the surface of the anode by either electron shuttles Figure. 6.3a or by a solid conductive matrix Figure 6.3 b This reduces the electron energy from E OM to E interface Then, electrons are transferred to the electrode by interface electrode transfer Figure 6.4,reducing the electron energy from E interface to E anode Given that these potential losses occur on the outside of the cell, it is unlikely that these losses are associated with ARB energy conservation and growth The underlying mechanisms involved in these kinetic processes includes diffusive transport, conduction, and electrochemical reactions are known to dissipate energy as heat or as an increase in entropy, thus strengthening our assumption that ARB cannot recover this energy for growth In order to maximize their growth by capturing as much energy as they can, ARB must minimize extracellular potential losses. Hence, the next section will be talking about the first mechanism which is the direct contact mechanism.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.

Extracellular potential losses -EET Mechanisms used by ARB.