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Modeling the production process of organic compounds using reverse microbial fuel cell system

Number of pages: 85 File Format: word File Code: 31770
Year: 2013 University Degree: Master's degree Category: Biology - Environment
Tags/Keywords: biomass - Cathode - Electro fuel - Fossil fuels - Fuel cell system - Microbial electrosynthesis - Modeling - Process modeling - Renewable energy - Reverse microbial fuel cell
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  • Summary of Modeling the production process of organic compounds using reverse microbial fuel cell system

    Master's thesis in the field of Chemical-Biotechnology Engineering

    Abstract

    Deteriorating energy sources of fossil fuels will make the developing human society suffer from fuel shortage in the not too distant future. As a result, the concerns of the continuous and increasing release of carbon dioxide into the atmosphere, as well as the extent of pollution caused by fossil fuels that have made life on the planet difficult, increase the need for energy sources from renewable sources with minimal negative environmental impact. Reverse microbial fuel cells with a function in the opposite direction of microbial fuel cells, bacteria convert water and carbon dioxide into organic compounds using electrons that are transferred to the cathode in the anode or an external electrical source, in a process similar to photosynthesis. These organic compounds can be converted into fuel. In the present research, a model based on the direct conduction of electrons in biofilm is presented. The outputs of the present model include the profile of changes in substrate concentration, electric potential, distribution of active bacteria within the biofilm, temporal changes in current density and biofilm thickness. In order to investigate the effect of different factors compared to a control state, a reference state was created using the available parameter values ??for the carbon dioxide substrate and the pure Spermosa ovala microbial community. Coulombic efficiency in this model is a function of substrate concentration and cathode potential. For the carbon dioxide substrate and with the presence of Sporomosa ovata microbial species, if the concentration increased, the coulombic efficiency and current density decreased, but the thickness of the biofilm increased. Since the electrical conductivity coefficient of Sporomosa ovata biofilm is very high, most of the resistances of the microbial fuel cell with this microbial community and the carbon dioxide substrate are caused by mass transfer resistances. Despite the concentration of 0.025 mmol/cm3 of the substrate in the catholyte, the maximum consumption current density will be 0.3 ampere/square meter and the coulombic efficiency will be 75%. Since the coulombic efficiency is a function of the electric potential and the concentration of the substrate in the catholyte, and the maximum coulombic efficiency was shown at a concentration of 0.025 mmol/cm3, 75% and at an electric potential of 1.13, 55%, as a result, by creating an optimal state at this concentration and at this potential, a high production efficiency of acetate can be achieved.

    Key words: reverse microbial fuel cell, microbial electrosynthesis, electro-fuel, cathode and modeling.

    1-1 Introduction

    Deteriorating energy sources of fossil fuels will make the developing human society suffer from fuel shortage in the not too distant future. With the rapid growth of the population and reaching the limit of 10 billion people, the need for inexhaustible sources of fuel will increase in 50 years [1]. Based on an estimate of population growth and economic growth along with it and taking into account the growth trend of energy demand, the amount of energy demand will be 27 terawatts in 2050 AD and 43 terawatts in 2100 AD [2]. Therefore, although oil, natural gas, and coal can meet energy needs in the short term, in the coming decades, with the demand for oil exceeding its supply, they cannot be considered as a suitable option. As a result, due to the fact that fossil fuel sources are gradually decreasing, even if new sources of oil are found or the exploitation of existing reservoirs is increased, the important problem of climate change will not only not be solved, but will also be aggravated. Undoubtedly, the release of carbon stored in fossil fuels increases the concentration of carbon dioxide in the atmosphere; The accumulation of greenhouse gases in recent years has caused the global average temperature to exceed prehistoric temperatures and lead to the melting of natural ice and the rise of sea levels [2]. Therefore, even replacing oil and gas with other fuels such as coal, methane hydrate and coal tar also leads to the release of more carbon dioxide gas into the atmosphere, intensifying environmental damage and accelerating climate change. Therefore, from this point of view, we need a way to produce energy that does not introduce carbon dioxide gas into the atmosphere at a rate of more than 1% per century.. The biggest challenge ahead is that in addition to meeting the growing need for energy, the issue of greenhouse gas emissions should also be resolved at the same time. It increases energy from renewable sources with minimal negative environmental impact [3]. In this regard, stricter environmental laws have been established and high financial credits have been approved for research in the field of new energy exploitation [1].

    Choosing suitable, cheap and clean alternatives for fossil fuels is an obvious necessity. Renewable energies such as solar energy, wind, geothermal energy and biomass energy are suitable options. In the meantime, solar energy is a suitable and attractive source of energy, because in addition to being renewable, it is also widely available. But due to the existence of technical and economic problems, it is not possible to fully rely on this energy in the short term. About 200 terawatts of 170,000 terawatts of radiated solar energy are converted into wind energy; While of this amount, 67 terawatts are stored as water energy through water cycles and 100 terawatts are stored as biomass through photosynthesis [4]. An illustration of this is shown in Figure 1-1. Some of the technologies related to these energies, such as wind turbines, electric dams, solar panels, and ethanol and methane production processes from biomass, have been developed in recent years, however, with the growth of societies, the rate of growth and development of these technologies should also increase. They are a suitable solution to solve energy and environmental challenges in the long term. But this completely depends on how to receive and use this energy. The sun does not shine uniformly throughout the day and in all areas. Therefore, solar panels can increase the need for electricity during the day, but without a suitable method for storing this energy, it cannot be used as the main source of energy supply throughout the day and night.

    Biomass energy is a form of solar energy in which solar energy is stored in a compact form in biomass for easier processing and transportation. This storage is done through the process of photosynthesis and the absorption of sunlight energy in the bonding of organic molecules of biomass. In this form, microorganisms convert biomass into fuel. This cycle includes three main parts:

    Production of biomass by sunlight and photosynthesis

    Production of suitable biofuel

    Production of useful energy from biofuel

    In this cycle, Photosynthesis takes solar energy and creates biomass in the form of plants and algae during a reduction process with the presence of carbon dioxide [5]. In fact, at this stage, solar energy is stored in the form of molecular bond energy in the organic materials that make up plants and algae.

    In most cases, the biomass that is used as a source of biofuel is made of polymers including proteins, lipids, and polysaccharides. These complex polymers are usually not suitable for direct use in energy production [5]; Because they are difficult to break and decompose. Therefore, a series of microbiological reactions are needed to convert biomass into suitable biofuels such as methane, hydrogen and ethanol. Acetate is also considered a useful biofuel. These fuels have a simpler molecular structure and are easily oxidized. The process of converting biomass into biofuels includes a set of hydrolysis, fermentation, deacidification, and methanation processes, which will be discussed in the following sections. Microorganisms can be present in any of these processes.

  • Contents & References of Modeling the production process of organic compounds using reverse microbial fuel cell system

    List:

    List of Contents. 4

    1-4 hydrolysis and fermentation. 4

    1-5 need for water resources and wastewater treatment 6

    1-6 fuel cell. 7

    1-7 Definition of fuel cell. 8

    1-8 types of fuel cells. 8

    1-9 Microbial fuel cells. 9

                  1-9-1 Application of microbial fuel cell. 11

                      1-9-1-1 Power generation. 12

                     1-9-1-2 Wastewater treatment. 12

                     1-9-1-3 Hydrogen production. 13

                    1-9-1-4 Removal of chemicals. 13

                    1-9-1-5 Biosensors. 13

                  1-9-2 Comparison of microbial fuel cells with bioethanol and methanation processes. 14

                   1-9-2-1 Technologies of demethane and microbial fuel cell. 14

                   1-9-2-2 Bioethanol and microbial fuel cell technologies. 14

                1-9-3 Investigation of the microbial community and their respiratory chain. 15

               1-9-3-1 How to transfer electrons from the microbe surface to the fuel cell anode surface. 17

    1-10 reverse microbial fuel cells. 21

             1-10-1 Electron transfer mechanisms. 22 10-2 Cathode biofilms. 24

             1-10-3 cathode electrode. 24

            1-10-4 Solution chemistry. 25

    1-11 The aim of the upcoming research. 27

    Chapter Two: Review of Previous Researches

    2-1 An overview of fuel cells from the past to the present. 28

    2-2 History of microbial fuel cell. 29

    2-3 History of microbial fuel cell modeling. 29

    2-4 History of microbial electrosynthesis. 33

    Chapter three: Examining equations and model structure

    3-1 Assumptions made .. 36

    3-2 Speed ??equations.. 37

    3-2-1 Substrate consumption equations. 37

    3-2-2 equation of the rate of auto-oxidation phenomenon of active microbes. 40

    3-2-3 Equation of the rate of inactivation of active microbes. 41

    3-3 Substrate mass conservation equation in biofilm. 41

    3-4 Checking the external mass transfer coefficient. 43

    3-5 Substrate mass conservation equation in catholyte liquid volume. 44

    3-6 electric potential equation and Ohm's law. 45

    3-7 Examining ohmic resistances. 47

    3-8 biomass mass conservation equation 48

    3-9 half-reactions performed in the anode and cathode sections of the reverse microbial fuel cell. 51

    3-10 Examining the model used to estimate design parameters. 51

    3-11 Numerical solution method. 52

    3-11-1 Finite difference method. 53

    3-11-1-1 Leading differences. 53

    3-11-1-2 Regressive differences. 53

    3-11-1-3 central differences. 53

    Chapter Four: The results obtained and their analysis

    4-1 Review of reference conditions. 57

    4-2 Effect of changing cathode potential and substrate concentration in liquid volume. 61

    4-3 Comparison of real values ??with values ??obtained from modeling. 68

    4-4 Summary and conclusion. 69

    4-4 suggestions.. 71

    Sources and references.. 72

     

     

    Source:

     

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