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Bioelectrochemical Enhancement and Intensification of Methane Production from Anaerobic Digestion
Published in Sonia M. Tiquia-Arashiro, Deepak Pant, Microbial Electrochemical Technologies, 2020
Christy M. Dykstra, Spyros G. Pavlostathis
In a typical methanogenic BES, a bioanode that oxidizes organics is separated from a biocathode that reduces CO2 to CH4 (Figure 1). A bioanode may oxidize acetate, releasing electrons to the anode surface and protons into the surrounding anolyte. With a low applied voltage to the system, electrons from the anode travel through the circuit to the cathode where they are used by methanogens for CO2 reduction to CH4 (Equation 4). The modes of electron transfer from the microbial surface to the anode and from the cathode surface to methanogens are discussed further in Section 5. At the cathode surface, various reduction reactions may occur, including those described in Equations 4–5. Methanogens may receive electrons directly from a cathode electrode surface for the reduction of CO2 to CH4 in a process termed ‘electromethanogenesis’ (Cheng et al. 2009; Lohner et al. 2014). If electron equivalents are not directly used, as illustrated in Equation 4, H2 produced from Equation 5 may be used for hydrogenotrophic methanogenesis, as shown in Equation 3. Theoretically, the electromethanogenesis reaction is more efficient than the H2-mediated biocathode methanogenesis because energy losses occur at each electron transfer. Thus, the electromethanogenesis reaction is desired over H2-mediated methanogenesis in methanogenic biocathodes because lower energy loss results in less required external energy input, increasing the overall energy efficiency of the BES.
Microbial Electrochemical Technologies and Their Applications
Published in Debabrata Das, Jhansi L. Varanasi, Fundamentals of Biofuel Production Processes, 2019
Debabrata Das, Jhansi L. Varanasi
It was observed that methane can be produced in MECs by using a biocathode comprised of methanogenic bacteria. Methanogens generate methane in MECs either through direct electron transfer or by using the evolved hydrogen (Siegert et al. 2014). Producing methane has an added advantage of CO2 capture along with methane generation. It is estimated that electrochemical reduction of CO2 using electromethanogenesis has an electron capture efficiency of 96% (Cheng et al. 2009). Compared to the traditional anaerobic digestion process, the electromethanogenesis process offers higher methane productivities (Booth 2009). Moreover, this technology can be integrated easily into the existing anaerobic digestion infrastructure, thereby reducing the capital investments.
A research challenge vision regarding management of agricultural waste in a circular bio-based economy
Published in Critical Reviews in Environmental Science and Technology, 2018
Nathalie Gontard, Ulf Sonesson, Morten Birkved, Mauro Majone, David Bolzonella, Annamaria Celli, Hélène Angellier-Coussy, Guang-Way Jang, Anne Verniquet, Jan Broeze, Burkhard Schaer, Ana Paula Batista, András Sebok
Microbial electrolysis cells (MEC) is an emerging eco-efficient and low-cost technology which can generate biomethane or hydrogen from organic material by applying an external electric potential or a current. In a MEC, “electro-active” microorganisms, or electro-trophes, are attached to the anode and oxidise organic waste substrates to carbon dioxide by using the electrodic material (usually graphite based) as final electron acceptor of their metabolism. The electrons produced by the anodic oxidation reaction, flowing across the external circuit, are used to (bio)catalyse the production of reduced target molecules such as H2, CH3COOH or CH4 (Zhen et al., 2017; Zeppilli et al., 2016a). This enables coupling waste treatment with the generation of energy carriers and chemicals. If a MEC is configured for “electromethanogenesis”, i.e. for reduction of CO2 to CH4 catalysed by electro-trophes attached to the cathode, the wastewater treatment (COD) oxidation in the anode can be coupled with the biogas upgrading to biomethane (Figure 3) (Villano et al., 2013; Blasco-Gómez et al., 2017).
Evaluation of methanogenic microbial electrolysis cells under closed/open circuit operations
Published in Environmental Technology, 2018
Liwen Luo, Suyun Xu, Yueqing Jin, Runqi Han, Hongbo Liu, Fan Lü
The methane yields from the three reactors followed the sequence R2 > R1 > R3, which is different from the sequence of substrate degradation rates (R2 > R3 > R1). First, the higher methane production of R2 than R1 confirmed the positive effect of biofilm enriched on bioelectrode [23]. However, the higher methane yield of R1 should be related to the electromethanogenesis which converts hydrogen and carbon dioxide into methane. In MECs, methane was theoretically produced from two pathways in the presence of acetate, carbon dioxide and hydrogen gas, which are aceticlastic methanogenesis and hydrogenotrophic methanogenesis. Based on thermodynamic calculation, under CC operation, methane could also be produced electrochemically through CO2 reduction at a voltage of 0.169 V under standard conditions by the reaction of Equation (2) [31]. In this study, the results of methane production between the CC and OC model were in accord with the fact that proper electric stimulation can accelerate the growth of microbes via promoting microbial metabolism, which was likely to enhance anaerobic methane production:The energy consumption within MECs is an important parameter for evaluating process performance. To evaluate energy recovery from different scenarios, energy balance was calculated and compared between R2 and R3 fed with acetate. Ivanov et al. have established a quantitative method to evaluate MEC effectiveness for energy recovery and wastewater treatment [18]. One of the variables was the energy used for COD removal, i.e. WEL (kWh/kg COD):where mCOD is the mass of removed COD, U is the applied voltage and I is the current density.
Methane, a renewable biofuel: from organic waste to bioenergy
Published in Biofuels, 2022
Mixtli J. Torres-Sebastián, Juan G. Colli-Mull, Lourdes Escobedo-Sánchez, Daniel Martínez-Fong, Leonardo Rios-Solis, María E. Gutiérrez-Castillo, Gloria López-Jiménez, María L. Moreno-Rivera, Luis R. Tovar-Gálvez, Armando J. Espadas-Álvarez
An alternative to producing methane is electromethanogenesis, which can be defined as the bioreduction of carbon dioxide to methane using an electrode as an electron donor [76], being a promising application of chemical systems offering a novel approach to waste treatment, carbon dioxide fixation, renewable energy storage into a chemical compound like methane [77], and therefore, sustainable electricity conversion [78]. Three metabolic pathways have been proposed to carry out this process [77]. The voltage supplied by the electrode and the electrode material are variables that affect the amount of methane produced [79]. There is a significant amount of microorganisms that are present in the process as a consortium, but electromethanogenesis itself is carried out by methanogens [77], being the composition of the microorganisms, another variable to consider. There are several relevant patents in the field of electromethanogenesis. For example, Knipe et al. [80] applied for a patent for an electromethanogenesis cell in which the cathode is porous and is constructed using 3 D printing, allowing it to absorb microorganisms and/or enzymes. There are three outstanding advantages in this patent: 1) The pore size of the electrode can be regulated when 3 D printing, allowing the electric current to be maximized. 2) Enzymes adsorbed in the electrode's pores allow improving charge transfer than only microbial cultures. 3) 3 D printing volumetrically maximizes space and reduces diffusion limitations. Another important request patent to mention is the one asked by Spoorman and Wahnschafft [81], consisting of three sections connected one after the other. The first is the electromethanogenesis chamber, the second section is methane storage, and the third is a combustion chamber, where the methane produced in the first is consumed. Furthermore, the CO2 obtained in the third chamber is recirculated to the first, where it can serve as a substrate to synthesize methane. The metabolic pathway in which CO2 is used as a substrate to produce methane is not described in this review.