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The aim of this work was to study biologically reduced graphene oxide (RGO) for engineering the surface architecture of the bioelectrodes to improve the performance of Bioelectrochemical System (BES). Gluconobacter roseus mediates the reduction of graphene oxide (GO). The RGO modified bioelectrodes produced a current density of 1 mA/cm2 and 0.69 mA/cm2 with ethanol and glucose as substrates, respectively. The current density of RGO modified electrodes was nearly 10-times higher than the controls. This study, for the first time, reports a new strategy to improve the yield as well as efficiency of the BES by wrapping and wiring the electroactive microorganisms to the electrode surfaces using RGO. This innovative wrapping approach will decrease the loss of electrons in the microbe-electrolyte interfaces as well as increase the electron transfer rates at the microorganism-electrode interfaces.
This chapter will introduce the basic concepts of bioelectrocatalysis and the advantages of extremophiles for bioelectrochemical systems. The chapter will discuss electrogenic activity and electron transfer characteristics of extremophiles and their applications in microbial fuel cells, microbial electrolytic cells, microbial desalination cells, and microbial electrosynthesis. The use of extremophilic bioprocesses for production of bioenergy and value-added products from lignocellulosic biomass will also be discussed.
In the recent years, considerable body of research has been carried out in the field of bioelectrochemical systems (BESs) for treatment of wastewater and generation of power. In these systems, different microbes are used for carrying out the transfer of electrons from medium to the anode electrode. The microbes employed are known as electrogens as they have the capacity to transfer electrons. Bacteria such as those belonging to the species such as Geobacter, Betaproteo, Deltaproteo and Desulfurnonas and of genus Shewanella are the commonly explored electrogens in BESs. In the past few years, a renewed interest in microbial fuel cell (MFC) research has developed, yet power generated from these devices has not significantly advanced. The primary reason for this non-advancement is that the research is more focused on improving power generation rather than on elementary understanding of the electron transfer processes. This review focuses on the methods used to study electron transfer processes in biofilms growing on the electrodes and presents several successful applications of MFCs. In this review, we have defined electrochemically active biofilms as biofilms that exchange electrons with conductive surfaces called electrodes.
The present study is focused on enhancing the rheological properties of the electrolyte and eliminating sedimentation of microorganisms/flocs without affecting the electron transfer kinetics for improved bioelectricity generation. Agar derived from polysaccharide agarose (0.05-0.2%, w/v) was chosen as a rheology modifying agent. Electroanalytical investigations showed that electrolytes modified with 0.15% agar display a nine-fold increase in current density (1.2 mA/cm²) by a thermophilic strain (Geobacillus sp. 44C, 60 °C) when compared with the control. Sodium phosphate buffer (0.1 M, pH 7) electrolyte with riboflavin (0.1mM) was used as the control. Electrolytes modified with 0.15% agar significantly improved chemical oxygen demand removal rates. This developed electrolyte will aid in improving bioelectricity generation in Bioelectrochemical Systems (BES). The developed strategy avoids the use of peristaltic pumps and magnetic stirrers, thereby improving the energy efficiency of the process.
Soak liquor is a primary effluent from tannery industry. It poses a threat to the environment and it is necessary
to treat the effluent. The predominant tannery effluent bacteria were isolated, identified and used
for the electricity generation. The present study investigates the use of soak liquor for the first time as a
substrate for electricity generation in Microbial Fuel Cell (MFC). The high salinity and rich organic content
of soak liquor increase the efficiency of MFC. Various electrochemical characterizations such as polarization
curve, cyclic voltammetry, chronoamperometry, electrochemical impedance spectrometry were performed
to analyse the efficacy of the soak liquor. MFC produced a maximum power density (Pmax) of
44.02 mW/m2 with a current density 140.34 mA/m2. The chemical oxygen demand (COD) reduction rate
was found to be 93% ± 4.7% in a cycle period of 168 h. The presence of humic acid was identified in soak
liquor, which might be involved in shuttling of electrons from the microorganisms to the electrode.
The present study evaluates relative functioning of microbial electrochemical systems (MES) for simultaneous wastewater treatment, desalination and resource recovery. Two MES were designed having abiotic cathode (MES-A) and algal biocathode (MES-B) which were investigated with synthetic feed and saline water as proxy of typical real-field wastewater. Comparative anodic and cathodic efficiencies revealed a distinct disparity in both the MES when operated in open circuit (OC) and closed circuit (CC). The maximum open circuit voltage (OCV) read in MES-A and MES-B was about 700 mV and 600 mV, respectively. Salinity and organic carbon removal efficiencies were noticed high during CC operation as 72% and 55% in MES-A and 60% and 63% in MES-B. These discrete observations evidenced ascribe to the influence of microbial electrochemical induced ion-migration over cathodic reduction reactions (CRR).
Extracellular electron transfer in microorganisms has been applied for bioelectrochemical synthesis utilizing microbes to catalyze anodic and/or cathodic biochemical reactions. Anodic reactions (electron transfer from microbe to anode) are used for current production and cathodic reactions (electron transfer from cathode to microbe) have recently been applied for current consumption for valuable biochemical production. The extensively studied exoelectrogenic bacteria Shewanella and Geobacter showed that both directions for electron transfer would be possible. It was proposed that gram-positive bacteria, in the absence of cytochrome C, would accept electrons using a cascade of membrane-bound complexes such as membrane-bound Fe-S proteins, oxidoreductase, and periplasmic enzymes. Modification of the cathode with the addition of positive charged species such as chitosan or with an increase of the interfacial area using a porous three-dimensional scaffold electrode led to increased current consumption. The extracellular electron transfer from the cathode to the microbe could catalyze various bioelectrochemical reductions. Electrofermentation used electrons from the cathode as reducing power to produce more reduced compounds such as alcohols than acids, shifting the metabolic pathway. Electrofuel could be generated through artificial photosynthesis using electrical energy instead of solar energy in the process of carbon fixation.