Microbial Competition in Bioelectrochemical Systems

Bioelectrochemical systems(BESs)/ microbial fuel fells (MFCs) are a well-studied potential technology for bioremediation and decentralized wastewater treatment. However, progress has been somewhat stalled at the bench-scale. In well controlled experiments electron recovery is high. In natural environments, wastewaters are complex and anode-respiring bacteria can be outcompeted in the presence of competing microorganisms, leading to a loss in electron-recovery and power production. Furthermore, the cathode of the MFC plays a vital role in providing flexibility for treatment options but is an understudied part of MFCs. Modelling Intracellular Competition in a Denitrifying Biocathode: One potential MFC configuration uses an organic-oxidizing anode biofilm and a denitrifying cathode biofilm. However nitrite, a denitrification intermediate with environmental and public health impacts, has been reported to accumulate. In this study, before complete denitrification was achieved in a bench-scale, batch denitrifying cathode, nitrite concentrations reached 66.4 % ± 7.5 % of the initial nitrogen. Common environmental inhibitors such as insufficient electron donor, dissolved oxygen, insufficient carbon source, and pH, were considered as a cause of the accumulation. Improvement in these conditions did not mitigate nitrite accumulation. We present an activated sludge model with an integration of the Nernst-Monod model and indirect coupling of electrons (ASM-NICE) that effectively simulated the observed batch data, including nitrite-accumulation by coupling biocathodic electron transfer to intracellular electron mediators. The simulated half-saturation constants for mediated intracellular transfer of electrons during nitrate and nitrite reduction suggested a greater affinity for nitrate reduction when electrons are not limiting. The results imply that longer hydraulic retention times (HRTs) may be necessary for a denitrifying biocathode to ensure complete denitrification. These findings could play a role in designing full-scale MFC wastewater treatment systems to maximize total nitrogen removal. Experimental Evaluation of Responses of Anode-Respiring Communities to Nitrate: A poorly understood phenomenon with a potentially significant impact on electron recovery in MFCs is the role of competition between anode-respiring bacteria and microorganisms that use other electron acceptors. Nitrogen species are a major constituent of wastewater and nitrate can act as a competing electron acceptor in the anode. Studies investigating the impact of competition on population dynamics in mixed communities in the anode are lacking. Here, we investigated the impact of nitrate at different C/N ratios, 1.8, 3.7 and 7.4 mg-C/mg-N, on the electrochemical performance and the biofilm community in mixed-culture chemostat MFCs. The electrochemical performance of the MFC was not affected under electron donor non-limiting conditions, 7.4 mg-C/mg-N. At lower C/N ratios, electron donor limiting, electron recovery was significantly lower. The electrochemical performance recovered upon removal of nitrate at 3.7 mg-C/mg-N. Microbial community analysis showed a decrease of Deltaproteobacteria accompanied by an increase in Betaproteobacteria in response to nitrate at low C/N ratios, and no significant changes at 7.4 mg-C/mg-N. Transcriptional analysis showed increased transcription of nirK and nirS genes during nitrate flux suggesting that denitrification to N2 (and not facultative nitrate reduction by Geobacter spp.) might be the primary response to perturbation with nitrate. Modelling Interspecies Competition in the Anode of a Microbial Fuel Cell: MFCs offer great promise for simultaneous treatment of wastewater and energy recovery. Even though there have been extensive experimental studies of multi-species anode-respiring biofilms, models and process optimization studies have been scarce. The formulation and evaluation of models is a critical step in the application of MFCs to wastewater treatment and bioremediation. The purpose of this study was to formulate a model that could simulate the effect of influx of a competing electron acceptor such as nitrate on the anode biofilm community. A model was formulated considering two distinct communities of bacteria: an anode-respiring community (not capable of nitrate reduction) and a denitrifying community (not capable of anode-respiration). A competitive scenario involving the influx of acetate and nitrate at a C/N ratio of 1.8 mg-C/mg-N was used to calibrate the model using experimental data. Calibration results indicate that facultative reduction of nitrate by facultative anode-respiring bacteria could be an important factor playing a role in the robustness and resilience of the anode-biofilms to fluxes of nitrate. Sensitivity analyses revealed that the biofilm retention coefficient (biofilm detachment rate) and species-specific growth kinetic parameters could play a significant role in the robustness of anode communities to influx of nitrate. Further investigation of change in detachment rate in response to the presence of nitrate in bulk solution is required

Present State and Future Directions of Digital Payments System: A Historical and Bibliographic Examination

Purpose: The purpose of this research is to conduct a bibliographic analysis of digital payment systems.   Theoretical framework:  The digital payments system is a technologically advanced payment system that enables individuals, businesses, and nations to become self-sufficient, contactless, and tap-less when conducting transactions. Understanding the significance of the digital payment system is crucial.  There remains much to investigate and discover.   Design/methodology/approach:  The using of an academic search method on the Scopus database, a bibliometric study of 714 publications on digital payment systems from the year 2000 to 2022 was conducted. For this experiment, we made use of Biblioshiny, an R-based web application available in the Bibliometrix package. We were able to identify significant publications, authors, nations, and article themes by using the software's automatic technique. We studied the citations, co-citations, and social networks.   Findings:  The results were able to identify significant publications, authors, nations, and article themes by using the software's automatic technique. We studied the citations, co-citations, and social networks. The statistics revealed that the number of publications increased gradually in the early years, followed by a sharp rise between the years 2005 and 2022. These years correspond to the political attempts to recover from the 2008 global financial crisis. India conducts the most significant scientific research in this field, followed by United States and China.   Research, Practical & Social implications:  This study not only identifies the research fields in digital payment systems, but also identifies the central key themes with possible research directions, in the area of electronic money, mobile money, authentication, security, Internet of things, blockchain, FinTech, mobile banking and Covid – 19.   Originality/value:  The findings of this study may be used by policymakers to inform the design of digital payment systems, policy initiatives, and other policy measures. Banking, financial planning, and investment management professionals would understand the rising concerns completely. Therefore, researchers, practitioners, and policymakers will use the current literature while doing fresh research on the Payments system's strengths and weaknesses

Analyzing Inter-modal Competition between High Speed Rail and Conventional Transport Systems: A Game Theoretic Approach

AbstractA methodology is developed in order to assess the viability of transport infrastructure investment in the form of High Speed Rail (HSR). Public transportation mode operators such as HSR, conventional trains and buses, maximize their profits by varying prices and frequency for a given demand and infrastructure cost. In this study, the price competition between different operators is taken into consideration and the change in the existing market equilibrium due to the entry of the new mode is studied using the game theoretic approach. Hypothetical data for a particular route is used for game-based analysis. In this multiplayer game, the effect of introducing the new mode of transport on the Nash equilibrium is studied taking into account the competition between the other modes of transportation. The analysis of market share for the modes has been carried out using heterogeneity of the passengers based on the concept of Value-of-Time (VOT). The passengers are assumed to be intelligent and rational in choosing the mode that minimizes their generalized travel cost, which is a function of travel time weighted by the individual VOT and the monetary cost associated with the mode of travel. Thus, different combinations of entry and response strategies are studied for HSR and existing modes, and the impact of introduction of HSR is assessed in terms of profit, thus, reflecting on the sustainability and financial viability of the transport infrastructure investment

The role of inorganic nitrogen in successful formation of granular biofilms for wastewater treatment that support cyanobacteria and bacteria

Recently, the use of phototrophs for wastewater treatment has been revisited because of new approaches to separate them from effluent streams. One manifestation uses oxygenic photogranules (OPGs) which are dense, easily-settleable granular biofilms of cyanobacteria, which surrounding populations of heterotrophs, autotrophs, and microalgae. OPGs can remove COD and nitrogenous compounds without external aeration. To better grow and maintain biomass in the proposed wastewater process, this study seeks to understand the factors that contribute to successful granulation. Availability of initial inorganic nitrogen, particularly ammonium, was associated with successful cultivation of OPGs. In the first days of granulation, a decrease in ammonium coupled with an increase in a cyanobacterial-specific 16S rRNA gene, may suggest that ammonium was assimilated in cyanobacteria offering a competitive environment for growth. Though both successful and unsuccessful OPG formation demonstrated a shift from non-phototrophic bacterial dominated communities on day 0 to cyanobacterial dominated communities on day 42, the successful community had a greater relative abundance (46%) of OTUs associated with genera Oscillatoria and Geitlernema than the unsuccessful community (27%), supporting that filamentous cyanobacteria are essential for successful OPG formation. A greater concentration of chlorophyll b in the unsuccessful OPG formation suggested a greater abundance of algal species. This study offers indicators of granulation success, notably availability of inorganic nitrogen and chlorophyll a and b concentrations for monitoring the health and growth of biomass for a potential OPG process

The origin of large molecules in primordial autocatalytic reaction networks

Large molecules such as proteins and nucleic acids are crucial for life, yet their primordial origin remains a major puzzle. The production of large molecules, as we know it today, requires good catalysts, and the only good catalysts we know that can accomplish this task consist of large molecules. Thus the origin of large molecules is a chicken and egg problem in chemistry. Here we present a mechanism, based on autocatalytic sets (ACSs), that is a possible solution to this problem. We discuss a mathematical model describing the population dynamics of molecules in a stylized but prebiotically plausible chemistry. Large molecules can be produced in this chemistry by the coalescing of smaller ones, with the smallest molecules, the `food set', being buffered. Some of the reactions can be catalyzed by molecules within the chemistry with varying catalytic strengths. Normally the concentrations of large molecules in such a scenario are very small, diminishing exponentially with their size. ACSs, if present in the catalytic network, can focus the resources of the system into a sparse set of molecules. ACSs can produce a bistability in the population dynamics and, in particular, steady states wherein the ACS molecules dominate the population. However to reach these steady states from initial conditions that contain only the food set typically requires very large catalytic strengths, growing exponentially with the size of the catalyst molecule. We present a solution to this problem by studying `nested ACSs', a structure in which a small ACS is connected to a larger one and reinforces it. We show that when the network contains a cascade of nested ACSs with the catalytic strengths of molecules increasing gradually with their size (e.g., as a power law), a sparse subset of molecules including some very large molecules can come to dominate the system.Comment: 49 pages, 17 figures including supporting informatio

Quantum frequency conversion of a quantum dot single-photon source on a nanophotonic chip

A. Singh, Q. Li, and X. Lu acknowledge support under the Cooperative Research Agreement between the UMD and NIST-PML. C. Schneider and S. Höfling acknowledge support by the State of Bavaria and the BMBF within the project Q.Com-HL. C. Schneider acknowledges funding by the DFG.Single self-assembled InAs/GaAs quantum dots are promising bright sources of indistinguishable photons for quantum information science. However, their distribution in emission wavelength, due to inhomogeneous broadening inherent to their growth, has limited the ability to create multiple identical sources. Quantum frequency conversion can overcome this issue, particularly if implemented using scalable chip-integrated technologies. Here, we report the first demonstration to our knowledge of quantum frequency conversion of a quantum dot single-photon source on a silicon nanophotonic chip. Single photons from a quantum dot in a micropillar cavity are shifted in wavelength with an on-chip conversion efficiency ≈12%, limited by the linewidth of the quantum dot photons. The intensity autocorrelation function g(2)(0) for the frequency-converted light is antibunched with g(2)(0) = 0.290 ± 0.030, compared to the before-conversion value g(2)(0) = 0.080 ± 0.003. We demonstrate the suitability of our frequency-conversion interface as a resource for quantum dot sources by characterizing its effectiveness across a wide span of input wavelengths (840–980 nm) and its ability to achieve tunable wavelength shifts difficult to obtain by other approaches.Publisher PDFPeer reviewe

Efficient fiber-coupled single-photon source based on quantum dots in a photonic-crystal waveguide

Many photonic quantum information processing applications would benefit from a high brightness, fiber-coupled source of triggered single photons. Here, we present a fiber-coupled photonic-crystal waveguide single-photon source relying on evanescent coupling of the light field from a tapered out-coupler to an optical fiber. A two-step approach is taken where the performance of the tapered out-coupler is recorded first on an independent device containing an on-chip reflector. Reflection measurements establish that the chip-to-fiber coupling efficiency exceeds 80 %. The detailed characterization of a high-efficiency photonic-crystal waveguide extended with a tapered out-coupling section is then performed. The corresponding overall single-photon source efficiency is 10.9 % $\pm$ 2.3 %, which quantifies the success probability to prepare an exciton in the quantum dot, couple it out as a photon in the waveguide, and subsequently transfer it to the fiber. The applied out-coupling method is robust, stable over time, and broadband over several tens of nanometers, which makes it a highly promising pathway to increase the efficiency and reliability of planar chip-based single-photon sources.Comment: 9 pages, 3 figure