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A new upgraded biogas production process: Coupling microbial electrolysis cell and anaerobic digestion in single-chamber, barrel-shape stainless steel reactor
... As Energy source, hydrogen is an element which is the most abundant in the universe, the richest in energy per unit of mass, and can be used in many processes like biogas upgrading [2,3]. Biogas which is another gas form of energy storage is mainly made of a flammable component CH 4 , and CO 2 which should be cleaned to enhance the heating value of biogas [4]. So, this upgrading with hydrogen concerned in priority the conversion of carbon dioxide by combining it with molecules of hydrogen to produce molecules of methane, and this is done in combination with the action of a certain microorganisms named hydrogenotrophic methanogens [5,6]. ...
... As Energy source, hydrogen is an element which is the most abundant in the universe, the richest in energy per unit of mass, and can be used in many processes like biogas upgrading [2,3]. Biogas which is another gas form of energy storage is mainly made of a flammable component CH 4 , and CO 2 which should be cleaned to enhance the heating value of biogas [4]. So, this upgrading with hydrogen concerned in priority the conversion of carbon dioxide by combining it with molecules of hydrogen to produce molecules of methane, and this is done in combination with the action of a certain microorganisms named hydrogenotrophic methanogens [5,6]. ...
... Proof have been shown that with in-situ way, the methane production rate is higher, cheaper and less cumbersome than in ex-situ way [8]. Some previous studies have shown that with this in-situ upgrading, a final percentage of CO 2 less than 10 % of the biogas volume is observed [8], the increase of the final CH 4 percentage until 98 % of biogas volume and increasing its energy efficiency by 2.3 times [4]. The major concern in this study was the use of clean and safety hydrogen generation technique like solar photovoltaic energy [9], for biogas upgrading and its behaviour when using different substrates characteristics. ...
Hydrogen is the richest element in energy per unit of mass that exist. The challenge nowadays is its handling for different usages, as biogas upgrading. This research aims to study the behaviour of biogas upgrading with photovoltaic in-situ hydrogen generation with different type of substrates. It operates into batch reactors with 85 % of humidity of the mixture, with stainless steel electrodes at a controlled direct current voltage of 1.2 V at 38 • C, using pig slurry, chicken dung and rabbit poop (p > 0.05). Results showed a hydrogen generation during the process of 0.13 mol, 0.21 mol and 0.192 mol for pig slurry, chicken dung and rabbit poop, respectively. Leading to energy balance and energy recovery efficiency of 302.24 Wh.kg − 1 and 12.45 %, 596.53 Wh.kg − 1 and 19.99 %, and 1158.84 Wh.kg − 1 and 30.33 % for pig slurry, chicken dung and rabbit poop, respectively. This upgrading technique improved biomethanization, but varied depending on substrate chemical characteristics involved.
... As Energy source, hydrogen is an element which is the most abundant in the universe, the richest in energy per unit of mass, and can be used in many processes like biogas upgrading [2,3]. Biogas which is another gas form of energy storage is mainly made of a flammable component CH 4 , and CO 2 which should be cleaned to enhance the heating value of biogas [4]. So, this upgrading with hydrogen concerned in priority the conversion of carbon dioxide by combining it with molecules of hydrogen to produce molecules of methane, and this is done in combination with the action of a certain microorganisms named hydrogenotrophic methanogens [5,6]. ...
... As Energy source, hydrogen is an element which is the most abundant in the universe, the richest in energy per unit of mass, and can be used in many processes like biogas upgrading [2,3]. Biogas which is another gas form of energy storage is mainly made of a flammable component CH 4 , and CO 2 which should be cleaned to enhance the heating value of biogas [4]. So, this upgrading with hydrogen concerned in priority the conversion of carbon dioxide by combining it with molecules of hydrogen to produce molecules of methane, and this is done in combination with the action of a certain microorganisms named hydrogenotrophic methanogens [5,6]. ...
... Proof have been shown that with in-situ way, the methane production rate is higher, cheaper and less cumbersome than in ex-situ way [8]. Some previous studies have shown that with this in-situ upgrading, a final percentage of CO 2 less than 10 % of the biogas volume is observed [8], the increase of the final CH 4 percentage until 98 % of biogas volume and increasing its energy efficiency by 2.3 times [4]. The major concern in this study was the use of clean and safety hydrogen generation technique like solar photovoltaic energy [9], for biogas upgrading and its behaviour when using different substrates characteristics. ...
... Implementation of bioelectrochemistry into an AD reactor design is an alternative way of in situ biogas upgrading. A single-chamber stainless steel reactor combining a microbial electrolysis cell and AD was developed by Bo et al. (2014). The inner surface of a stainless steel reactor served as cathode through small voltage addition (1.0 V) and generated H 2 , while a carbon felt served as anode. ...
... The inner surface of a stainless steel reactor served as cathode through small voltage addition (1.0 V) and generated H 2 , while a carbon felt served as anode. In comparison to a reference reactor, the CH 4 yield doubled, resulting in 98% CH 4 content in the biogas, while the COD removal rate was increased three times (Bo et al. 2014). Biogas upgrading was demonstrated in the cathode compartment of a membraneless microbial electrosynthesis cell, which significantly reduced the required biogas retention time as well as energy consumption for biogas upgrading compared to injection of H 2 through sparging or a biofilter approach (Tartakovsky et al. 2021). ...
Power-to-X (P2X) technologies will play a more important role in the conversion of electric power to storable energy carriers, commodity chemicals and even food and feed. Among the different P2X technologies, microbial components form cornerstones of individual process steps. This review comprehensively presents the state-of-the-art of different P2X technologies from a microbiological standpoint. We are focusing on microbial conversions of hydrogen from water electrolysis to methane, other chemicals and proteins. We present the microbial toolbox needed to gain access to these products of interest, assess its current status and research needs, and discuss potential future developments that are needed to turn todays P2X concepts into tomorrow's technologies.
... The unleashing research and reviews are fundamental to implementing feasible MEC-AD reactor operations in the future (Nelabhotla and Dinamarca, 2018;Ning et al., 2021;Park et al., 2020). The prevalent investigative directions can be summarized as followings: (i) to explore whether employing cheaper electrode materials to treat wastewater and upgrade biogas CH 4 content (Bo et al., 2014;Feng et al., 2015;Lee et al., 2017;Ren et al., 2019); (ii) to elucidate the principal mechanisms of electron transfer in MECs and better understand bioelectrochemical contributions to organic conversion or CH 4 promotion (Liu et al., 2016b;Zhen et al., 2015); (iii) to assess the performance of the MEC-AD integrated systems at different scales and identify/understand susceptible factors of the stability, such as pH, temperature, and organic loading rates (substrate concentrations) (Cerrillo et al., 2017;De Vrieze et al., 2014;Lee et al., 2019;Park et al., 2019;Sangeetha et al., 2017;Zhang et al., 2013), or to elucidate the energy recovery efficiencies in MEC-AD (Gajaraj et al., 2016); (iv) to process different wastes or design reactors and structures (Zhao et al., 2021, Zhao et al., 2014. Nonetheless, there are only few systematic reviews that strived to unravel the microbial fingerprints (i.e., diversity, composition, and function) of methanation in MEC-AD, addressing the predominant presence of eubacteria and archaea in the biomass and the metabolically active populations. ...
... However, the CH 4 production rate increased first and then decreased with the increase in applied cell voltages (from 0.5 to 1.5 V), whereas COD removal efficiency always kept rising (Fig. 1f, Table S2), which used the 1 to 1 mixture of glucose and AD effluent as a substrate (Type II reactor) (Choi et al., 2017). Several studies concerning the fixed voltage applied in the coupling system have also similar confirmations tested with various substrates (Bo et al., 2014;Feng et al., 2015). Of note, the optimal external voltages for MEC-AD are essential to achieve high removal rates of pollutants, maximum biogas production, and supreme energy recovery. ...
Biomethane as a sustainable, alternative, and carbon-neutral renewable energy source to fossil fuels is highly needed to alleviate the global energy crisis and climate change. The conventional anaerobic digestion (AD) process for biomethane production from waste(water) streams has been widely employed while struggling with a low production rate, low biogas qualities, and frequent instability. The electric-biologically hybrid microbial electrochemical anaerobic digestion system (MEC-AD) prospects more stable and robust biomethane generation, which facilitates complex organic substrates degradation and mediates functional microbial populations by giving a small input power (commonly voltages < 1.0 V), mainly enhancing the communication between electroactive microorganisms and (electro)methanogens. Despite numerous bioreactor tests and studies that have been conducted, based on the MEC-AD systems, the integrated microbial fingerprints, and cooperation, accelerating substrate degradation, and biomethane production, have not been fully summarized. Herein, we present a comprehensive review of this novel developing biotechnology, beginning with the principles of MEC-AD. First, we examine the fundamentals, configurations, classifications, and influential factors of the whole system's performances (reactor types, applied voltages, temperatures, conductive materials, etc.,). Second, extracellular electron transfer either between diverse microbes or between microbes and electrodes for enhanced biomethane production are analyzed. Third, we further conclude (electro)methanogenesis, and microbial interactions, and construct ecological networks of microbial consortia in MEC-AD. Finally, future development and perspectives on MEC-AD for biomethane production are proposed.
... The photocathode is similar to the photo bioanode concept (semiconductor), which takes a photon from the light and converts it to electrons and holes in its conduction band and valence band, respectively Zheng et al., 2020b). The electrons in the photocathode conduction band are utilized for H + reduction, while the bio-electrons in the anode are transferred to fill the holes in the valence band of the photocathode (He et al., 2014). One of the photocatalytic materials is titanium dioxide (TiO 2 ), which has garnered significant interest as an excellent photocatalyst for H 2 production in a variety of systems due to its high photocatalytic activity, chemical stability, and low cost of TiO 2 . ...
... By adding a small voltage at the MEC within an AD-MEC system, hydrogenotrophic, electromethanogens, and acetoclastic methanogenesis can capture the electrons or H 2 formed at the cathode to turn the CO 2 into CH 4 directly (Cheng et al., 2009;Van Eerten-Jansen et al., 2012). Bioelectrochemical systems create CO 2 during bacterial metabolism on anode, with in-situ CO 2 capture and reduction on the cathode, thus, providing additional CH 4 formation in integrated AD-MEC systems (Bo et al., 2014;Rotaru et al., 2014b). However, there is a need to better understand the relationship between the electrochemical technology in AD systems and the organic conversion rates, species diversity, nutrient balance, and heavy metal concentrations on MEC efficiency and degradation rates when using a mixed feedstock. ...
This chapter presents various aspects of industrial hemp valorization with a focus on biorefinery and bioproducts applications. In the biorefinery pathway, the fractionation of hurd is presented first, followed by thermochemical and biochemical conversions of industrial hemp for biofuels and bio-chemicals. The chapter has discussed various industrial applications of hemp bast fiber, including construction and insulation material, biocomposite, and paper production. Besides, the chapter includes high-value bioproducts development from industrial hemp hurd, including building materials, bioplastics, carbonaceous materials, and paper products. In addition to the valorization, the economic feasibility of industrial hemp biomass for biofuel (ethanol, biodiesel, and biogas) has been highlighted. Considering the present challenges associated with the biorefinery of industrial hemp, future research approaches are also summarized at the end of the chapter.
... Research trends are represented in various areas of research, including wastewater treatment with increased methane production in anaerobic reactors equipped with electrodes (Tartakovsky et al. (2011), Rani et al. (2022) [3,4]); the improvement of design features of unit combinations to produce more hydrogen and methane (Rader et al. (2010), Bo et al. (2014) [5,6]); the influence of inoculum origin on the development of microbial associations in microbial electrolysis cell bioreactors (Cerrillo et al. (2017) [7]); and microbial associations that determine the biochemical parameters of anaerobic waste processing to obtain biofuel (Shulipa et al. (2017) [8]). ...
... Research trends are represented in various areas of research, including wastewater treatment with increased methane production in anaerobic reactors equipped with electrodes (Tartakovsky et al. (2011), Rani et al. (2022) [3,4]); the improvement of design features of unit combinations to produce more hydrogen and methane (Rader et al. (2010), Bo et al. (2014) [5,6]); the influence of inoculum origin on the development of microbial associations in microbial electrolysis cell bioreactors (Cerrillo et al. (2017) [7]); and microbial associations that determine the biochemical parameters of anaerobic waste processing to obtain biofuel (Shulipa et al. (2017) [8]). ...
This paper focuses on the study of the effect of electrolysis on activated sludge in a microbial electrolysis cell (MEC) under the anaerobic digestion of poultry manure. This study was conducted using a bioreactor design with and without electrodes (conventional condition). Measurements of pH, redox potential (ORP), and total dissolved solids were carried out, as was the microscopy of activated sludge during treatment and gasometry. There was an increase in the yields of CH4 and CO2 compared to conventional conditions. Thus, on the 14th day, there was an increase in the CH4 yield to 35.1% compared with the conventional conditions—31.6%—as well as in the CO2 yield to 53.5% compared with the cell without electrodes—37.7%. Visually, the microscopy of anaerobic activated sludge showed changes in the aggregation process itself, with the formation of cells of clusters of microorganism colonies with branches of a delineated shape. ORP fluctuations were related to the process of the dissociation into ions during the passage of an electric current through the electrodes, and were observed before and after the inclusion of a current into the system. A model of the effect of electrolysis during anaerobic digestion was developed, taking into account the influencing factors on the condition of the activated sludge.
... High current levels indicated that bacteria adhering to the anode were actively involved in anodic electron transfer. Consistent with our observation is a previous report that observed a similar peak at 0.15 V, representing the electrochemical activity of methanogens [42]. These peaks most likely show that the consortium's microorganisms have the electrochemical capacity to take electrons from the anode or extracellular electron transfer components. ...
Citation: Bhatt, P.; Poudyal, P.; Dhungana, P.; Prajapati, B.; Bajracharya, S.; Yadav, A.P.; Bhattarai, T.; Sreerama, L.; Joshi, J. Enhancement of Biogas (Methane) Production from Cow Dung Using a Microbial Electrochemical Cell and Molecular Characterization of Isolated Methanogenic Bacteria. Biomass 2024, 4, 455-471. https://doi. Abstract: Biogas has long been used as a household cooking fuel in many tropical counties, and it has the potential to be a significant energy source beyond household cooking fuel. In this study, we describe the use of low electrical energy input in an anaerobic digestion process using a microbial electrochemical cell (MEC) to promote methane content in biogas at 18, 28, and 37 • C. Although the maximum amount of biogas production was at 37 • C (25 cm 3), biogas could be effectively produced at lower temperatures, i.e., 18 (13 cm 3) and 28 • C (19 cm 3), with an external 2 V power input. The biogas production of 13 cm 3 obtained at 18 • C was~65-fold higher than the biogas produced without an external power supply (0.2 cm 3). This was further enhanced by 23% using carbon-nanotubes-treated (CNT) graphite electrodes. This suggests that the MEC can be operated at as low as 18 • C and still produce significant amounts of biogas. The share of CH 4 in biogas produced in the controls was 30%, whereas the biogas produced in an MEC had 80% CH 4. The MEC effectively reduced COD to 42%, whereas it consumed 98% of reducing sugars. Accordingly, it is a suitable method for waste/manure treatment. Molecular characterization using 16s rRNA sequencing confirmed the presence of methanogenic bacteria, viz., Serratia liquefaciens and Zoballella taiwanensis, in the inoculum used for the fermentation. Consistent with recent studies, we believe that electromethanogenesis will play a significant role in the production of value-added products and improve the management of waste by converting it to energy.
... When the modified graphite cathode was applied in group (3), the highest methane yield of 371 L/kg VS was achieved, corresponding to an increase of 72.6 % as compared to group (5) (conventional AD). Previous studies reported methane production enhancement (from 50 % to 300 %) could be achieved in the MEC-AD reactors when digesting glucose, acetate or waste activated sludge [18,47,48]. In addition, the positive effect of introducing conductive material was evident, as the methane yield increased by 15.3 % with biochar addition (group (4) compared to that of group (5) (conventional AD). ...
Integrating microbial electrolysis cells and anaerobic digestion (MEC-AD) improves upon conventional anaerobic digestion for biomethane production due to the in-situ provision of electrochemically produced reducing power (such as hydrogen). However, the electron transfer behaviour at the microbe-electrode interface remains unclear. This study assessed the micro-scale interface modification of a carbonaceous bioelectrode, leading to an enhanced local electric field, which was postulated to stimulate electro-methanogenesis. The effectiveness of incorporating electro-conductive biochar to enhance interspecies electron transfer was also evaluated for its potential to boost biomethane production. The findings revealed a notable increase in biomethane yield and methane content within the biogas of the MEC-AD system, with improvements of 96.8 % and 32.5 %, respectively, compared to conventional anaerobic digestion when co-digesting grass silage and cattle slurry. The enhancement was ascribed to the accumulation of charges and an intensified local electric field on the surface of the etched biocathode, thereby facilitating interfacial electron transfer. Incorporating 10 g/L of biochar to conventional anaerobic digestion resulted in a 7.9 % increase in biomethane yield compared to conventional anaerobic digestion. Overall, the heightened energy yield of biomethane by the MEC-AD system (featuring the modified graphite cathode) resulted in a 6.5-fold increase compared to the additional electrical energy input. This underscores the catalytic significance of the electricity in AD system.
... In this context, although concrete has been a widely used material in the manufacture of biodigesters, the reduction or even the elimination of corrosion in these tanks is difficult even when special coating is applied. In order to solve these disadvantages, stainless steel has become a suitable option for this application due to its great corrosion resistance, among other factors [7,8]. ...
The main objective established in this work was to develop a model based on artificial neural networks (ANNs) to predict the corrosion status of stainless steel involved in biogas production, analyzing the influence of the material composition and the breakdown potential value. To achieve this objective, an ANN model capable of predicting the corrosion status of the material without the need to perform microscopic analysis on the material surface was proposed. The applicability of the corrosion models was verified via the experimental data considering different factors such as stainless steel composition, biogas environments simulated by artificial solution, temperature, surface finish, and the breakdown potential of the passive layer of stainless steel obtained from electrochemical tests. The optimal prediction performance shown by the model in terms of specificity and sensitivity values were 0.969 and 0.971, respectively, obtaining an accuracy of 0.966. Furthermore, analyzing the influence of the breakdown potential on corrosion modelling, an alternative model was presented capable of predicting the corrosion status automatically, without the need to resort to electrochemical tests for new conditions. The results demonstrated the utility of this technique to be considered in design and maintenance planning tasks for stainless steel structures subjected to localized corrosion in biogas production.
... consortia for methane yield [70] and enrich exoelectrogens to overcome thermodynamic barriers of methane production [71]. Therefore, the more diverse anaerobic metabolism of methanogenic microorganisms, particularly hydrogenotrophic methanogens, was responsible for methane yield rate increase in electro-AnMBRs [72]. It should be noted that no accumulation of hydrogen in electro-AnMBR systems has been reported, even though there are more hydrogen generation pathways in these systems, including hydrogen generation in acetogenesis stage of anaerobic digestion and HER process on the cathode. ...
In the face of the growing water shortage and energy crisis, anerobic membrane bioreactor (AnMBR) as a promising technology of wastewater treatment and bioenergy recovery has drawn extensive attention. Recently, electrochemical processes have been integrated into AnMBR systems (electro-AnMBRs) to address the critical issue of membrane fouling in AnMBRs, as well as improve biogas recovery. In this review, we systematically summarized the recent advances of electro-AnMBRs, which would provide useful information and recommendations for the scalable application of electro-AnMBRs. The configuration of electro-AnMBRs and electrode materials are summarized in detail. Furthermore, comparisons of AnMBR performances with/without electrostimulation, including pollutants removal, membrane fouling mitigation and energy recovery, have been conducted based on the available literature. In general, electrostimulation in AnMBRs can not only enhance pollutants removal, but also lower transmembrane pressure increasing rate (10% ~ 84.4%). Also, electro-AnMBRs operated under the same condition can increase biogas generation rate and methane yield rate, which are 60.0% and 42.1% higher than that of control, respectively. Thereafter, the challenges and future perspective of electro-AnMBR in research and applications are also discussed. This review highlights the potential and challenges that should be solved to facilitate the scalable application of electro-AnMBR in wastewater treatment and energy recovery.
... During electrolysis treatment, the lysis of accumulated microbial biomass and insoluble organic compounds occurs, which we assume could help maintain the productivity of the system producing biogas yields during the anaerobic digestion period, and which is consistent with the studies using an MEC [42] и в MEC-AD coupled system [43]. As can be observed from Figure 4, the electro-fermentation process produces a significant biogas yield on days 20-24, compared to the control and the application of stimulant additives. ...
This study aims to evaluate the process of biogas production from the droppings of Clarias gariepinus under intensification of methanogenesis using electrolysis pretreatment and electro-fermentation in comparison with the addition of stimulating substances (humates and zeolites). For the realization of a series of experiments, laboratory installations of electrolysis and electro-fermentation were developed. The following parameters were monitored: biogas composition, chemical oxygen demand, redox potential, hydrogen potential, nitrates, ammonia–ammonium, and nitrites. A taxonomic classification and review of the metabolic pathways were performed using the KEGG, MetaCyc, and EzTaxon databases. The stimulation of biomethanogenesis in the utilization of catfish droppings by the introduction of additional electron donors—exogenous hydrogen (electro-fermentation)—was confirmed. The electro-fermentation process released 4.3 times more methane compared to conventional conditions and stimulant additives and released 1.7 times more with electrolysis pretreatment. The main metabolic pathways of electron acceptor recruitment using bioinformatic databases are highlighted, and models of CO2 transformation involving exogenous hydrogen along the chain of metabolic reactions of methanogenesis are generated. The summary model of metabolic pathways of methanogenesis are also proposed. Based on the results of the present and previous studies, two technological solutions are proposed to implement the process of anaerobic treatment intensification of excreta of the clariid catfish. Additional studies should include the optimization of the operation mode of electro-fermentation and electrolysis pretreatment of the substrate during the aquacultivation process.
... Before commencing the power interruption tests, the biofilms population was dominated by bacteria (Test 0 in Figure 7 top), although the single most abundant genus in both reactors was the archaea Methanobacterium (29 and 28% for D1 and D2 respectively) (Figure 7 bottom). Methanobacterium species live on the reduction of CO₂ with H₂ to produce CH₄, which is coherent with the hypothesis that H₂ is the main intermediary in the electron transfer between the electrodes and CO₂ [6,7,29,30]. ...
The need to accommodate power fluctuations intrinsic to high-renewable systems will demand in the future the implementation of large quantities of energy storage capacity. Microbial electromethanogenesis (EM) can potentially absorb the excess of renewable energy and store it as CH₄. However, it is still unknown how power fluctuations impact on the performance of EM systems. In this study, power gaps from 24 to 96 h were applied to two 0.5 L EM reactors to assess the effect of power interruptions on current density, methane production and current conversion efficiency. In addition, the cathodes were operated with and without external H₂ supplementation during the power-off periods to analyse how power outages affect the two main metabolic stages of the EM (i.e.: the hydrogenic and methanogenic steps).
Methane production rates kept around 1000 mL per m² of electrode and per day regardless of the duration of the power interruptions and of the supplementation of hydrogen. Interestingly, current density increased in the absence of hydrogen (averaged current density during hydrogen supplementation was 0.36 A·m⁻², increasing up to 0.58 A·m⁻² without hydrogen). However current was less efficiently used in the production of methane with no hydrogen supplementation. Nevertheless, when the electrical power was restored after the power interruption experiments, performance parameters were similar to those observed before. These results indicate that EM is resilient to power fluctuations, which reinforces the opportunity of using EM as a technology for renewable energy storage.
... In small-scale experiments, such electrodes may require chemical pre-treatments to improve initial wettability and permit contact with the culture [23]. Stainless steel electrodes are occasionally used for biogas and H 2 evolution [20,24] but are more often integrated with carbon electrodes to improve current collection or provision due to higher conductivity [25]. While platinum-coated electrodes are often used as counter-electrodes [21] the cost of platinum makes industrial applications in working electrodes unfeasible. ...
Microbial electrosynthesis is the process of supplying electrons to microorganisms to reduce CO2 and yield industrially relevant products. Such systems are limited by their requirement for high currents, resulting in challenges to cell survival. Electrofermentation is an electron-efficient form of microbial electrosynthesis in which a small cathodic or anodic current is provided to a culture to alter the oxidation–reduction potential of the medium and, in turn, alter microbial metabolism. This approach has been successfully utilised to increase yields of diverse products including biogas, butanediol and lactate. Biomass conversion to lactate is frequently facilitated by ensiling plant biomass with homofermentative lactic acid bacteria. Although most commonly used as a preservative in ensiled animal feed, lactate has diverse industrial applications as a precursor for the production of probiotics, biofuels, bioplastics and platform chemicals. Lactate yields by lactic acid bacteria (LAB) are constrained by a number of redox limitations which must be overcome while maintaining profitability and sustainability. To date, electrofermentation has not been scaled past laboratory- or pilot-stage reactions. The increasing ease of genetic modification in a wide range of LAB species may prove key to overcoming some of the pitfalls of electrofermentation at commercial scale. This review explores the history of electrofermentation as a tool for controlling redox balance within bacterial biocatalysts, and the potential for electrofermentation to increase lactate production from low-value plant biomass.
... Furthermore, treatment with high voltage electric pulses in a liquid medium makes it possible to achieve inactivation of microorganisms at lower temperatures and in a shorter exposure time than traditional thermal pasteurization methods, contributing to better preservation of the products of thermolabile components. Therefore, the impact of high voltage electrical pulses on liquid medium can be positioned as a promising method to inactivate the microflora of liquid medium with minimal thermal destruction of the products [14][15][16]. ...
This article presents future trends in research using microbiological methods to intensify bioprocesses for biogas production. The pretreatment by combinations of physical and chemical methods, such as cavitation and electrolysis, is considered. The approach of the article involved reviewing the residual area on the intensification technologies of anaerobic digestion with current methods to improve the quality and quantity of biogas. The most valuable reported positive results of the pretreatment of biological raw materials in the cavitation process were reviewed and are presented here. A model of the effect of electrolysis on the species diversity of bacteria in anaerobic digestion was developed, and changes in the dominance of the ecological and trophic systems were revealed on the basis of previous studies. The stimulating effect on biogas yield, reduction in the stabilization period of the reactor, and inactivation of microorganisms at lower temperatures is associated with different pretreatment methods that intensify anaerobic digestion. More research is recommended to focus on the electrolysis treatment of different types of waste and their ratios with optimization of regime parameters, as well as in combination with other pretreatments to produce biomethane and biohydrogen in larger quantities and in better qualities.
... Anaerobic digestion (AD) is a biological process that can reduce the volumetric and stabilization of organic matter in sewage sludge and is the most widely employed method [1][2][3]. Biogas derived from organic wastes in AD is primarily a mixture of methane (CH 4 , 50-75%) and carbon dioxide (CO 2 , 25-50%) [4]. Among different waste-to-energy technologies, AD has been highlighted to have lower global warming potential and acidification potential [5]. ...
Anaerobic digestion (AD) can produce renewable energy and reduce carbon emissions, but the energy conversion efficiency is still limited in some waste streams. This study tested the effect of applied voltage removal for microbial electrolysis cells (MECs) treating primary sewage sludge. Two MECs were operated in parallel: a MEC-0.3 V with an applied voltage of 0.3 V and a MEC-OCV with open circuit voltage. Both reactors were inoculated with seed sludge originating from a MEC at 0.3 V applied voltage, and three batch cycles were operated for 36 d. The methane production of the MEC-OCV was 3759 mL/L in the first cycle and 2759 mL/L in the second cycle, which was similar (105% and 103%, respectively) to that of the MEC-0.3 V. However, in the third cycle, the methane production of the MEC-OCV (1762 mL/L) was 38.8% lower than that of the MEC-0.3 V (4545 mL/L). The methane contents in the biogas were 68.6–74.2% from the MEC-OCV, comparable to those from the MEC-0.3 V (66.6–71.1%). These results indicate that not only the MEC-0.3V but also the MEC-OCV outperformed AD in terms of methane yield and productivity, and the promotion using MEC-derived inoculum persisted equally with the MEC-OCV for two batch cycles after removing the applied voltage. Therefore, a MEC operation with cycled power supply may be beneficial in reducing the electric energy usage and improving the biogas production performance, compared to conventional AD.
... These dominating microbes utilized the H 2 gas generated inside the inner surface of the stainless AD reactor and acted as cathode of MEC when a small voltage (1.0 V) was applied. As a result, the overall energy efficiency reached upto 66.7% [81]. An up-flow single chamber MEC was designed for CH 4 production where hydrogenotrophic methanogenesis decreased the cathodic Content courtesy of Springer Nature, terms of use apply. ...
Hydrogenotrophic methanogens play a key role in methane (CH4) production during various wastes’ anaerobic digestion (AD). The metabolism of hydrogenotrophic methanogens involves Wolfe-cycle to reduce carbon dioxide (CO2) to CH4 using hydrogen as feed. Hydrogenotrophic methanogenesis is a potential process for up-gradation of biogas and renewable power intermittency. This review focuses on enhancing hydrogenotrophic methanogenesis for the up-gradation of biogas and, more importantly, a hybrid system that couples both in-situ and ex-situ approaches in one unit. Upgradation of biogas by hydrogenotrophic methanogenesis is advantageous for achieving a higher concentration of CH4 and removing trace elements and CO2 from biogas. This approach helps to decrease the cost of upgrading biogas to natural gas quality. Using microbial electrolysis cells coupled with AD could be a potential alternative to increase the CH4 production yield and remove CO2 from biogas. The exploitation of the hydrogen gas and integration of the available technologies on a large scale could be explored in future work and help in realizing the production of clean CH4 in an industrial set-up. This review summarizes the metabolic background of hydrogenotrophic methanogens and their efficient utilization towards methane production. Limited works are available in public domain covering this aspect and thus a review article is important for the readers to update their understanding and research work in light of recent findings.
Graphical Abstract
... The bioelectrode in the bioelectrochemical system showed higher biocathode-related biomass, which was proved from protein evaluation of biofilms produced at the biocathode. The hydrogenotrophic methanogens were the major leading species in the microbial population (Bo et al. 2014). Hence, the in situ hydrogen production by using the bioelectrochemical system could boost hydrogenotrophic methanogens' activity, thus altering the microbial dominance (Cerrillo et al. 2021;Gao et al. 2021). ...
The Ukraine conflict has put critical pressure on gas supplies and increased the price of fertilisers. As a consequence, biogas has gained remarkable attention as a local source of both gas for energy and biofertiliser for agriculture. Moreover, climate change-related damage incentivises all sectors to decarbonise and integrate sustainable practices. For instance, anaerobic digestion allows decarbonisation and optimal waste management. Incorporating a biogas system in each country would limit global warming to 2 °C. If suitable policies mechanisms are implemented, the biogas industry could reduce global greenhouse gas emissions by 3.29–4.36 gigatonnes carbon dioxide equivalent, which represent about 10–13% of global emissions. Here, we review the role of the biogas sector in capturing methane and mitigating carbon emissions associated with biogas outputs. Since biogas impurities can cause severe practical difficulties in biogas storing and gas grid delivering systems, we present upgrading technologies that remove or consume the carbon dioxide in raw biogas, to achieve a minimum of 95% methane content. We discuss the role of hydrogen-assisted biological biogas upgrading in carbon sequestration by converting carbon dioxide to biomethane via utilising hydrogen generated primarily through other renewable energy sources such as water electrolysis and photovoltaic solar facilities or wind turbines. This conceptual shift of 'power to gas' allows storing and utilising the excess of energy generated in grids. By converting carbon dioxide produced during anaerobic digestion into additional biomethane, biogas has the potential to meet 53% of the demand for fossil natural gas. We also evaluate the role of digestate from biogas systems in producing biochar, which can be used directly as a biofertiliser or indirectly as a biomethanation enhancement, upgrading, and cleaning material.
... By adding a small voltage at the MEC within an AD-MEC system, hydrogenotrophic, electromethanogens, and acetoclastic methanogenesis can capture the electrons or H 2 formed at the cathode to turn the CO 2 into CH 4 directly (Cheng et al., 2009;Van Eerten-Jansen et al., 2012). Bioelectrochemical systems create CO 2 during bacterial metabolism on anode, with in-situ CO 2 capture and reduction on the cathode, thus, providing additional CH 4 formation in integrated AD-MEC systems (Bo et al., 2014;Rotaru et al., 2014b). However, there is a need to better understand the relationship between the electrochemical technology in AD systems and the organic conversion rates, species diversity, nutrient balance, and heavy metal concentrations on MEC efficiency and degradation rates when using a mixed feedstock. ...
During dark fermentation, organic material is converted into H2. Dark fermentation is also part of the first steps of the anaerobic digestion (AD) process, where organic material is converted into H2 and CO2. Due to thermodynamic limitations, the quantity of H2 produced from organic materials during the dark fermentation stage are limited. To enhance the CH4 production in an AD system, a microbial electrolysis cell (MEC) can be incorporated with the AD reactor, which overcomes the positive Gibbs free energy (ΔGr) and efficiently converts more organic waste into H2. The produced H2 from the MEC combines with CO2 to produce more CH4, thus boosting the CH4 generation in the AD-MEC system. This book chapter discusses: (1) microbial electrolysis technology; (2) MEC configurations and process conditions; (3) microbial community shifts, CH4 production, and H2 production in the AD-MEC system; (4) the role of electro-conductive materials and biochemical pathways in AD-MECs; (5) substrates treated with AD-MECs; (6) scaling-up challenges of AD system with MEC incorporation; and (7) future perspectives of AD-MEC systems.
... However, the concentration of CO 2 can be due to VFA degradation with time. The carbon content of the substrate after the oxidation is recovered as CO 2 gas [31]. ...
The performance of Microbial electrolysis cell (MEC) is affected by several operating conditions. Therefore, in the present study, an optimization study was done to determine the working efficiency of MEC in terms of COD (chemical oxygen demand) removal, hydrogen and current generation. Optimization was carried out using a quadratic mathematical model of response surface methodology (RSM). Thirteen sets of experimental runs were performed to optimize the applied voltage and hydraulic retention time (HRT) of single chambered batch fed MEC operated with dairy industry wastewater. The operating conditions (i.e) an applied voltage of 0.8 V and HRT of 2 days that showed a maximum COD removal response was chosen for further studies. The MEC operated at optimized condition (HRT- 2 days and applied voltage- 0.8 V) showed a COD removal efficiency of 95 ± 2%, hydrogen generation of 32 ± 5 mL/L/d, Power density of 152 mW/cm² and current generation of 19 mA. The results of the study implied that RSM, with its high degree of accuracy can be a reliable tool for optimizing the process of wastewater treatment. Also, dairy industry wastewater can be considered to be a potential source to generate hydrogen and energy through MEC at short HRT.
... Hybrid BES systems, though still at the very initial stages of development, combine BES with other conventional types of treatments (e.g., adsorption, filtration, algae, and constructed wetland), which offers a good solution for processing large quantities of wastewater. Previously tested hybrid BES systems, including MFC-membrane bioreactor (MFC-MBR), BES-anaerobic digestion (BES-AD), constructed wetland-BES (CW-BES), BES-fluidized bed reactor (BES-FBR), and BES-FBR coupled with electrocoagulation (EC + BES-FBR), have shown advanced performance in the production of biogas and the removal of COD, nitrogen, phosphorous, total suspended solids, azo dyes, antibiotics, etc. [201][202][203][204][205][206][207][208]. In terms of applications, conventional wastewater treatment methods have been developed and applied at much larger scales than BES approaches. ...
Bioelectrochemical system (BES) is an emerging technology for wastewater treatment. The urgent requirement for dealing with water shortage, wastewater treatment and reuse, energy generation, and resources recovery has promoted intensive research in BES during the last decade. This review summarizes the latest typical BES configurations based on specific functions, including microbial fuel cells (MFC), microbial electrolysis cells (MEC), microbial electrosynthesis systems (MSS), microbial desalination cells (MDC), microbial recycling cells (MRC), microbial solar cells (MSC), and microbial electrochemical snorkel (MES). The removal of contaminants, particularly emerging organic, non-metallic, metallic, and metalloid contaminants, and the recovery of resources in the form of bioenergy, biofuel, nutrients, metals, and metalloids in wastewater treatment using BES technology have been reviewed in this work. Limitations of BES technology in terms of reactor performance, scale-up, and construction costs for real-world wastewater treatment applications are discussed and future research directions needed for the successful deployment of BES technology are proposed.
... The integration of an anaerobic digester (AD) with MEC increases the efficiency of methane production. This case was revealed by the investigation done by Bo et al. (2014). They integrated AD with MEC fed on anaerobic sludge-acetate. ...
Microbial desalination cell (MDC) is a type of bioelectrochemical reactors that integrates microbial fuel cell (MFC) process for wastewater treatment with electrodialysis process for desalinating saline water while recovering electricity. Microbial-based technologies produce electricity by utilizing the organic waste found in wastewater as a substrate through a microbial catalyzed electrochemical reaction. This creates a potential gradient between the anode and the cathode that stimulates the ions’ transfer through an ion-exchange membrane. Microbial Electrolysis Cell (MEC) works in the same principle of MDC. Unlike the conventional MFC, it lacks a terminal acceptor of the electrons that results in the production of hydrogen at the cathode compartment. This chapter discussed the current progress of MDC in terms of treating different types of wastewater, while desalinating seawater, removing different pollutants, and generating electricity. Moreover, it provided the available integrated technologies for the production of biohydrogen, biomethane, and other fuels using a MEC. In addition, current challenges from these technologies were highlighted. Finally, it provided an effective future perspective for overcoming these challenges and paths for success.
Anaerobic electrochemical membrane bioreactor (AnEMBR) is to combine anaerobic membrane bioreactor with electrochemical technology. Elucidating the mechanisms of methane production kinetics and membrane fouling under electric field has been an area of intense research interest in AnEMBR. In wastewater treatment and resource recovery, the AnEMBR has been proven as a promising technology especially to overcome technical limitations confronted by conventional AnMBR system. For example, the methane production rate can be 20–50% faster under the external voltage less than 1.0 V into the AnEMBR than that without electric field. Efficient mitigation of membrane fouling can also be achieved by using the concepts of electrostatic interactions between foulants and conductive membrane or electrode materials. In this review, the fundamental aspects of methane production rate and fouling control by AnEMBR systems are discussed by critical review emphasizing reactor configurations, selection of electrode/membrane materials, and operating parameters. Furthermore, the impacts of electrochemical processes on microbial activity and the underlying mechanism occurring in the AnEMBR systems are discussed. The effects of alterations in the microbial community on reactor performance and energy recovery from the AnEMBRs are examined. Finally, suggestions to overcome current limitations faced by the AnEMBR are provided. Cutting-edge data presented in this study has the great potential to broaden the focus of translational and transdisciplinary studies on the AnEMBR as an innovative technology for sustainable wastewater treatment and resource recovery.
Waste is considered as a useful resource. Microbial electrolysis cells (MECs) as a novel carbon–neutral technology have replaced the conventional methods in treating industrial wastewater loaded with organic matters that could be converted to value-added products. MEC has proved to have diverse applications in industrial effluent treatment, biosynthesis of compounds such as hydrogen peroxide, methane, hydrogen, nutrient recovery, pollutant removal, and biosensing. However, this technology to be used in the circular industrial wastewater treatment for meeting the huge global energy demand is still in its infancy. The various parameters such as architectural design of the reactor and optimizing its working parameters such as feedstock, inoculum, electrode material and design, pH, temperature, and applied potential need to be standardized for the best output. Designing reactors operated using solar power or less electricity would be a real breakthrough. Similarly, choosing the apt electrode materials and its size to volume ratio of the reactor, reducing internal resistance, and experimenting with the inoculum type and time may reduce the current hindrances in the progression of this technology for industrial applications. The huge capital cost is an impediment, which if addressed with less capital expenditure and improved treatment efficiency and thereby an increased energy yield, then this fascinating technology may serve as a futuristic technology to solve the universal pollution problem and energy requirements and thereby ensuring sustainability.
The widespread application of anaerobic digestion technologies faces significant challenges, including low processing efficiency, poor stability, and low methane yield. The bioelectrochemical system, such as microbial fuel cell and microbial electrolysis cell, is proposed to integrate with anaerobic digestion for performance enhancement by provision of exogenous electrons. Bioelectrochemical system-anaerobic digestion (BES-AD) enhances the electron transfer activity between microorganisms and their resistance to toxic and hazardous substances by means of electrical currents. By optimizing key factors, such as reactor configurations, electrode materials, pH, organic loading rate, and temperature, the BES-AD performance can be improved. BES-AD has shown excellent performance in the removal of highly concentrated organic compounds and refractory substances in wastewater. BES-AD has great potential to break through bottlenecks of anaerobic digestion, and further application of the coupled system is conducive to the development of green, low-carbon, and circular economy.
Anaerobic digestion (AD) is a proven technology widely adopted to treat diverse organic wastes and produce energy in the form of heat, electricity and/or transportation fuels. The application of AD systems still faces challenges due to process stability, digestate management, high costs, and regulatory concerns and requirements among others. In many cases, it is often difficult for a traditional AD system to be economically viable because of all the related costs (e.g., capital, operating, disposal). These issues can be addressed via the following strategies: (1) improving conversion efficiency from waste feedstocks to final products; (2) producing higher-value products, including co-products, to offset the costs; (3) reducing the cost of digestate disposal, and (4) developing integrated systems by combining the above strategies. In addition to general operational approaches, pretreatment such as thermal hydrolysis and advanced reactor designs can increase conversion efficiency. Combining microbial electrochemical technologies (MET) with AD can enhance methane (CH4) production rates and CH4 contents beyond traditional AD systems. An alternative emerging concept is arrested methanogenesis, in which methanogens are inhibited or suppressed to produce volatile fatty acids (VFAs), which can be utilized as precursors for higher-value products, such as polyhydroxyalkanoates (PHA) polymer and sustainable aviation fuels (SAF). Tuning of AD microbial communities via proper control of operating conditions/parameters is essential for maximizing the production of desired products such as VFAs. Advanced microbial management strategies depend on a better understanding of microbiomes’ roles and functions in digesters and their interactions. The conversion of biogas to transportation fuels and bioproducts via biogas upgrading provides an alternative to fossil fuels and promotes wider adoption of AD technologies. Finally, improved digestate management technologies, beyond land applications, are emerging that combine beneficial use with a reduction in pollutants. This paper systematically reviews emerging technologies to improve the AD process and digestate management, including pretreatment and digester design, MET, arrested methanogenesis, PHA production, biogas upgrading, and digestate handling. Current challenges and technological gaps, and future research and development needs are also discussed.
Bioelectrochemical systems (BESs) have great potential in renewable energy production technologies. BES can generate electricity via Microbial Fuel Cell (MFC) or use electric current to synthesize valuable commodities in Microbial Electrolysis Cells (MECs). Various reactor configurations and operational protocols are increasing rapidly, although industrial-scale operation still faces difficulties. This article reviews the recent BES related to literature, with special attention to electrosynthesis and the most promising reactor configurations. We also attempted to clarify the numerous definitions proposed for BESs. The main components of BES are highlighted. Although the comparison of the various fermentation systems is, we collected useful and generally applicable operational parameters to be used for comparative studies. A brief overview links the appropriate microbes to the optimal reactor design.
Bioelectrochemical systems (BESs) have great potential in renewable energy production technologies. BES can generate electricity via Microbial Fuel Cell (MFC) or use the electric current for the synthesis of valuable commodities in Microbial Electrolysis Cells (MECs). The number of various reactor configurations and operational protocols increasing rapidly although, the industrial scale operation is still facing difficulties. This article reviews the recent BES related to literature, with special attention to electrosynthesis and the most promising reactor configurations. We also attempted to clarify the numerous definitions proposed for BESs. The main components of BES are highlighted. Although the comparison of the various fermentation systems is we collected useful and generally applicable operational parameters to be used for comparative studies. A brief overview to link the appropriate microbes to the optimal reactor design is given.
This study qualitatively assessed the impacts of different start-up strategies on the performance of methane (CH4) production from cattle manure (CM) in electromethanogenic reactors. Single chamber MECs were operated with an applied voltage of 0.7 V and the impact of electrode acclimatization with a simple substrate, acetate (ACE) vs a complex waste, CM, was compared. Upon biofilm formation on the sole carbon source (ACE or CM), several MECs (ACE_CM and CM_ACE) were subjected to cross-feeding (switching substrate to CM or ACE) during the test period to evaluate the impact of the primary substrate. Even though there was twice as much peak current density via feeding ACE during biofilm formation, this did not translate into higher CH4 production during the test period, when reactors were fed with CM. Higher or similar CH4 production was recorded in CM_CM reactors compared to ACE_CM at various soluble chemical oxygen demand (sCOD) concentrations. Additionally, feeding ACE as primary substrate did not significantly impact either COD removals or coulombic efficiencies. On the other hand, the use of anaerobic digester (AD) seed as an inoculum in CM-fed MECs (CM_CM), relative to no inoculum added MECs (Blank), increased the initial CH4 production rate by 45% and reduced the start-up time by 20%. In CM-fed MECs, Geobacter dominated bacterial communities of bioanodes and hydrogenotrophic methanogen Methanoculleus dominated archaeal communities of biocathodes. Community cluster analysis revealed the significance of primary substrate in shaping electrode biofilm; thus, it should be carefully selected for successful start-up of electromethanogenic reactors treating wastes.
Microbial electrolysis cell coupled with anaerobic digestion (MEC-AD) is currently encountering constraints on electromethanogenesis. The electrode configuration modification can be a simple yet efficient way to improve electromethanogenesis. This study evaluated two coaxial electrode configurations (large anode and small cathode: A10C1; small anode and large cathode: A1C10) using carbon felt as the electrode material. At an external voltage of 1.7 V, CH4 content was found exclusively higher in A1C10 (11 % and 13 % higher for acetate-fed and cow manure-fed, respectively) than that of the control reactors. Consequently, CH4 production was 13 % and 29 % higher in acetate-fed and CM-fed A1C10, respectively. The strengthened electromethanogenesis was attributed to the enrichment of interspecies hydrogen transfer microbes (i.e., Mesotoga and Bathyarchaeia). The coaxial configuration with a large cathode surface area demonstrated a viable stereotype in MEC-AD for improved waste treatment and energy recovery.
Currently, gray hydrogen and blue hydrogen are widely recognized as renewable energy, but in reality, they are made from fossil fuels. The most important task to achieve the hydrogen-based society is the development of economic green hydrogen production technology. Microbial electrolysis cell (MEC) is a next-generation energy-producing wastewater treatment technology that treats renewable organic wastewater and simultaneously produces the ultimate green hydrogen. For hydrogen production in MFC, it is necessary to input electrical energy into MEC. However, that energy is all covered by the energy produced by the MEC. Therefore, hydrogen production in MEC can be defined as the ultimate green hydrogen. This review contains an in-depth summary and analysis of the principles and feasibility of MEC technology, the composition and shape of MEC, electrode materials, and practical application cases in various types of wastewaters. Furthermore, compatibility and scalability with other environmental systems were reviewed at the pilot scale. Based on this, the technical limitations of MEC were diagnosed and future research directions for the practical application of MEC technology were suggested.
Stainless steel mesh, as the common cathode of microbial electrolytic cell-assisted anaerobic digestion (MEC-AD), has the disadvantages of low specific surface area, poor biocompatibility and low catalytic activity, which limits the production of methane. Metal-organic frameworks (MOFs) have attracted much attention due to their adjustable pores and specific catalytic properties. However, little attention was paid to the combination of MOF and stainless-steel mesh to improve the performance of MEC-AD cathode. In this study, we combined stainless steel mesh with bimetallic MOF catalyst (Fe/Ni–NH2BDC) to prepare a composite cathode, and verified its promoting effect on AD of swine wastewater. The experimental results showed that the reactor with the carbonized MOF composite cathode (FeNi2-PAN2) achieved the highest soluble chemical oxygen demand removal rate of 82.92% and a maximum cumulative methane yield of 213.47 mL CH4/g COD under an applied voltage of 0.8 V, which were 33.14% and 57.56% higher than those of an anaerobic digestion (AD) control reactor, respectively, and higher than those of a carbon paper (CP) cathode reactor. The enrichment of Methanobacterium and Methanoculleus on the surface of FeNi2-PAN2 cathode surface indicated that FeNi2-PAN2 cathode enhanced hydrogenotrophic methanogenesis and improved the stability of AD.
Food waste has become a global environmental concern over emissions of greenhouse gas and odorous pollutants. Anaerobic digestion is gaining increasing attention as an effective food waste disposal method combining waste minimization and bioenergy recovery. Solid-state anaerobic digestion can handle food waste containing high contents of solids and has the merits of higher disposal volumes and less parasitic energy input, however, the low energy/mass transfer impairs the treatment efficiency. This study incorporated bio-electrochemical treatment into solid-state anaerobic digestion of food waste to overcome these shortcomings for enhanced performances. Food waste liquid leachate was used as feedstock to validate the bio-electrochemical treatment effects under different conditions. At a low applied voltage of 0.7 V and initial pH of 8.13, the methane yield increased by 77.5% while the carbon dioxide yield decreased by 16.0% compared with the control without electrodes. Although higher voltages (1.1–2.0 V) contributed to higher methane and hydrogen yields, the fast consumption and breakages of anodes significantly decreased the treatment consistency and material lifespan. Thereby, 0.7 V was selected as the applied voltage when incorporating the bio-electrochemical unit into the solid-state digester treating food waste. Cathodic hydroxide generation increased the buffering capacity, thus contributing to a more stable start-up process. With an immersed electrode surface area of 25.2 cm²/L, the highest methane yield of 526.7 mL/gVS was recorded with lower carbon dioxide and hydrogen contents initially, and the peak gaseous hydrogen sulfide emission was significantly reduced by 71.5% mainly due to the ferrous ions release from low carbon steel anode for sulfide precipitation.
To better understand anaerobic digestion (AD) conditions during start-up, a series of batch and bench-scale studies were conducted to investigate conditions affecting the performance of the anaerobic reactors, including pH fluctuations, ammonia inhibition, and bioaugmentation. Capacitive soil moisture sensors were placed inside the AD reactors to provide near real-time microbial monitoring under experimental batch conditions and to create a microbial electrolysis cell (MEC) environment. After an eight-day digestion process at 40 °C, the capacitive soil moisture sensors performed as a rudimentary microbial activity tracking device. However, the electrodes had a statistically significant impact on biogas production with a small potential 0.8 V having a stabilizing effect on AD at 40 °C during start-up. Furthermore, electrode-assisted AD noted a biogas output 63.7% higher than the conventional AD without electrodes. Conversely, the bioaugmented electrode-assisted AD showed a 7% increase in biogas volume when compared to the non-bioaugmented batch.
The abilities of carbon cloth, graphite plate and stainless steel to form microbial anodes were compared under identical conditions. Each electrode was polarised at −0.2 V vs. SCE in soil leachate and fed by successive additions of 20 mM acetate. Under these conditions, the maximum current densities provided were on average 33.7 A m−2 for carbon cloth, 20.6 A m−2 for stainless steel, and 9.5 A m−2 for flat graphite. The high current density obtained with carbon cloth was obviously influenced by the three-dimensional electrode structure. Nevertheless, a fair comparison between flat electrodes demonstrated the great interest of stainless steel. The comparison was even more in favour of stainless steel at higher potential values. At +0.1 V vs. SCE stainless steel provided up to 35 A m−2, while graphite did not exceed 11 A m−2. This was the first demonstration that stainless steel offers a very promising ability to form microbial anodes. The surface topography of the stainless steel did not significantly affect the current provided. Analysis of the voltammetry curves allowed two groups of electrode materials to be distinguished by their kinetics. The division into two well-defined kinetics groups proved to be appropriate for a wide range of microbial anodes described in the literature.
DNA sequencing continues to decrease in cost with the Illumina HiSeq2000 generating up to 600 Gb of paired-end 100 base reads in a ten-day run. Here we present a protocol for community amplicon sequencing on the HiSeq2000 and MiSeq Illumina platforms, and apply that protocol to sequence 24 microbial communities from host-associated and free-living environments. A critical question as more sequencing platforms become available is whether biological conclusions derived on one platform are consistent with what would be derived on a different platform. We show that the protocol developed for these instruments successfully recaptures known biological results, and additionally that biological conclusions are consistent across sequencing platforms (the HiSeq2000 versus the MiSeq) and across the sequenced regions of amplicons.Keywords: illumine; barcoded sequencing; QIIME
Waste biomass is a cheap and relatively abundant source of electrons for microbes capable of producing electrical current outside the cell. Rapidly developing microbial electrochemical technologies, such as microbial fuel cells, are part of a diverse platform of future sustainable energy and chemical production technologies. We review the key advances that will enable the use of exoelectrogenic microorganisms to generate biofuels, hydrogen gas, methane, and other valuable inorganic and organic chemicals. Moreover, we examine the key challenges for implementing these systems and compare them to similar renewable energy technologies. Although commercial development is already underway in several different applications, ranging from wastewater treatment to industrial chemical production, further research is needed regarding efficiency, scalability, system lifetimes, and reliability.
Among different conversion processes for biomass, biological anaerobic digestion is one of the most economic ways to produce
biogas from various biomass substrates. In addition to hydrolysis of polymeric substances, the activity and performance of
the methanogenic bacteria is of paramount importance during methanogenesis. The aim of this paper is primarily to review the
recent literature about the occurrence of both acetotrophic and hydrogenotrophic methanogens during anaerobic conversion of
particulate biomass to methane (not wastewater treatment), while this review does not cover the activity of the acetate oxidizing
bacteria. Both acetotrophic and hydrogenotrophic methanogens are essential for the last step of methanogenesis, but the reports
about their roles during this phase of the process are very limited. Despite, some conclusions can still be drawn. At low
concentrations of acetate, normally filamentous Methanosaeta species dominate, e.g., often observed in sewage sludge. Apparently,
high concentrations of toxic ionic agents, like ammonia, hydrogen sulfide (H2S) and volatile fatty acids (VFA), inhibit preferably Methanosaetaceae and especially allow the growth of Methanosarcina species
consisting of irregular cell clumps, e.g., in cattle manure. Thermophilic conditions can favour rod like or coccoid hydrogenotrophic
methanogens. Thermophilic Methanosarcina species were also observed, but not thermophilic Methanosaetae. Other environmental
factors could favour hydrogentrophic bacteria, e.g., short or low retention times in a biomass reactor. However, no general
rules regarding process parameters could be derivated at the moment, which favours hydrogenotrophic methanogens. Presumably,
it depends only on the hydrogen concentration, which is generally not mentioned in the literature.
The ongoing revolution in high-throughput sequencing continues to democratize the ability of small groups of investigators to map the microbial component of the biosphere. In particular, the coevolution of new sequencing platforms and new software tools allows data acquisition and analysis on an unprecedented scale. Here we report the next stage in this coevolutionary arms race, using the Illumina GAIIx platform to sequence a diverse array of 25 environmental samples and three known "mock communities" at a depth averaging 3.1 million reads per sample. We demonstrate excellent consistency in taxonomic recovery and recapture diversity patterns that were previously reported on the basis of metaanalysis of many studies from the literature (notably, the saline/nonsaline split in environmental samples and the split between host-associated and free-living communities). We also demonstrate that 2,000 Illumina single-end reads are sufficient to recapture the same relationships among samples that we observe with the full dataset. The results thus open up the possibility of conducting large-scale studies analyzing thousands of samples simultaneously to survey microbial communities at an unprecedented spatial and temporal resolution.
During two-phase sludge anaerobic digestion, sludge is usually hydrolyzed and acidified in the first phase, then methane is produced in the second stage. To get more methane from sludge, most studies in literature focused on the increase of sludge hydrolysis. In this paper a different sludge pretreatment method, i.e., pretreating sludge at pH 10 for 8 d is reported, by which both waste activated sludge hydrolysis and acidification were increased, and the methane production was significantly improved. First, the effect of different sludge pretreatment methods on methane yield was compared. The pH 10 pretreated sludge showed the highest accumulative methane yield (398 mL per g of volatile suspended solids), which was 4.4-, 3.5-, 3.1-, and 2.3-fold of the blank (unpretreated), ultrasonic, thermal, and thermal-alkaline pretreated sludge, respectively. Nevertheless, its total time involved in the first (hydrolysis and acidification) and second (methanogenesis) stages was 17 (8 + 9) d, which was almost the same as other pretreatments. Then, the mechanisms for pH 10 pretreatment significantly improving methane yield were investigated. It was found that pretreating sludge at pH 10 caused the greatest sludge hydrolysis, acidification, soluble C:N and C:P ratios, and Fe(3+) concentration with a suitable short-chain fatty acids composition in the first stage, which resulted in the highest microorganism activity (ATP) and methane production in the second phase. Further investigation on the second phase microorganisms with fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) indicated that there were much greater active methanogenesis Archaea when methane was produced with the pH 10 pretreated sludge, and the predominant morphology of the microcolonies suggest a shift to Methanosarcina sp. like.
New sustainable methods are needed to produce renewable energy carriers that can be stored and used for transportation, heating, or chemical production. Here we demonstrate that methane can directly be produced using a biocathode containing methanogens in electrochemical systems (abiotic anode) or microbial electrolysis cells (MECs; biotic anode) by a process called electromethanogenesis. At a set potential of less than -0.7 V (vs Ag/AgCl), carbon dioxide was reduced to methane using a two-chamber electrochemical reactor containing an abiotic anode, a biocathode, and no precious metal catalysts. At -1.0 V, the current capture efficiency was 96%. Electrochemical measurements made using linear sweep voltammetry showed that the biocathode substantially increased current densities compared to a plain carbon cathode where only small amounts of hydrogen gas could be produced. Both increased current densities and very small hydrogen production rates by a plain cathode therefore support a mechanism of methane production directly from current and not from hydrogen gas. The biocathode was dominated by a single Archaeon, Methanobacterium palustre. When a current was generated by an exoelectrogenic biofilm on the anode growing on acetate in a single-chamber MEC, methane was produced at an overall energy efficiency of 80% (electrical energy and substrate heat of combustion). These results show that electromethanogenesis can be used to convert electrical current produced from renewable energy sources (such as wind, solar, or biomass) into a biofuel (methane) as well as serving as a method for the capture of carbon dioxide.
This study describes the performance of bioelectrochemical systems, based on electrochemically active mixed culture, capable of reducing CO2 to CH4 and CH3COOH via direct and/or indirect extracellular electron transfer. The metabolic pathway and end products of this mixed culture were highly dependent on the set cathode potentials. Only CH4 and H2 were produced when the cathode potentials were set in the range from −850 to −950 mV (vs. Ag/AgCl). At potentials more negative than −950 mV, CH4, H2 and CH3COOH were simultaneously produced. With a relatively large cathode surface area of 49 cm−2, CH4 and CH3COOH were produced at high rates of 129.32 mL d−1 and 94.73 mg d−1, respectively (at potential of −1150 mV). The highest current capture efficiency reached to 97% in batch potentiostatic experiments. These results presented here suggest that mixed culture show the ability to directly accept electrons from the electrode and abiotically produce H2 to convert CO2 into various organic compounds.
A methane-producing microbial electrolysis cell (MEC) is a technology to convert CO2 into methane, using electricity as an energy source and microorganisms as the catalyst. A methane-producing MEC provides the possibility to increase the fuel yield per hectare of land area, when the CO2 produced in biofuel production processes is converted to additional fuel methane. Besides increasing fuel yield per hectare of land area, this also results in more efficient use of land area, water, and nutrients. In this research, the performance of a methane-producing MEC was studied for 188 days in a flat-plate MEC design. Methane production rate and energy efficiency of the methane-producing MEC were investigated with time to elucidate the main bottlenecks limiting system performance. When using water as the electron donor at the anode during continuous operation, methane production rate was 0.006 m3/m3 per day at a cathode potential of −0.55 V vs. normal hydrogen electrode with a coulombic efficiency of 23.1%. External electrical energy input was 73.5 kWh/m3 methane, resulting in a voltage efficiency of 13.4%. Consequently, overall energy efficiency was 3.1%. The maximum achieved energy efficiency was obtained in a yield test and was 51.3%. Analysis of internal resistance showed that in the short term, cathode and anode losses were dominant, but with time, also pH gradient and transport losses became more important. The results obtained in this study are used to discuss the possible contribution of methane-producing MECs to increase the fuel yield per hectare of land area.
Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were considered two alternative pathways of dissimilatory nitrate reduction. In this study, we firstly reported that both denitrification and DNRA occurred in Pseudomonas alcaliphila strain MBR with an electrode as the sole electron donor in a double chamber bio-electrochemical system (BES). The initial concentration of nitrate appeared as a factor determining the type of nitrate reduction with electrode as the sole electron donor at the same potential (-500 mV). As the initial concentration of nitrate increased, the fraction of nitrate reduced through denitrification also increased. While nitrite (1.38 ± 0.04 mM) was used as electron acceptor instead of nitrate, the electrons recovery via DNRA and denitrification were 43.06 ± 1.02% and 50.51 ± 1.37%, respectively. The electrochemical activities and surface topography of the working electrode catalyzed by strain MBR were evaluated by cyclic voltammetry and scanning electron microscopy. The results suggested that cells of strain MBR were adhered to the electrode, playing the role of electron transfer media for nitrate and nitrite reduction. Thus, for the first time, the results that DNRA and denitrification occurred simultaneously were confirmed by powering the strain with electricity. The study further expanded the range of metabolic reactions and had potential value for the recognization of dissimilatory nitrate reduction in various ecosystems. Biotechnol. Bioeng. 2012; 109: 2904-2910. © 2012 Wiley Periodicals, Inc.
Autogenerative high pressure digestion (AHPD) is a novel configuration of anaerobic digestion, in which micro-organisms produce autogenerated biogas pressures up to 90 bar with >90% CH(4)-content in a single step reactor. (1) The less than 10% CO(2)-content was postulated to be resulting from proportionally more CO(2) dissolution relative to CH(4) at increasing pressure. However, at 90 bar of total pressure Henry's law also predicts dissolution of 81% of produced CH(4). Therefore, in the present research we studied whether CO(2) can be selectively retained in solution at moderately high pressures up to 20 bar, aiming to produce high-calorific biogas with >90% methane. Experiments were performed in an 8 L closed fed-batch pressure digester fed with acetate as the substrate. Experimental results confirmed CH(4) distribution over gas and liquid phase according to Henry's law, but the CO(2)-content of the biogas was only 1-2%, at pH 7, that is, much lower than expected. By varying the ratio between acid neutralizing capacity (ANC) and total inorganic carbon (TIC(produced)) of the substrate between 0 and 1, the biogas CO(2)-content could be controlled independently of pressure. However, by decreasing the ANC relative to the TIC(produced) CO(2) accumulation in the aqueous medium caused acidification to pH 5, but remarkably, acetic acid was still converted into CH(4) at a rate comparable to neutral conditions.
Hydrogen gas can be produced by electrohydrogenesis in microbial electrolysis cells (MECs) at greater yields than fermentation and at greater energy efficiencies than water electrolysis. It has been assumed that a membrane is needed in an MEC to avoid hydrogen losses due to bacterial consumption of the product gas. However, high cathodic hydrogen recoveries (78 +/- 1% to 96 +/- 1%) were achieved in an MEC despite the absence of a membrane between the electrodes (applied voltages of 0.3 < E(ap) < 0.8 V; 7.5 mS/cm solution conductivity). Through the use of a membrane-less system, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 +/- 0.02 m3 H2/m3 reactor per day (292 +/- 1 A/m3) at an applied voltage of E(ap) = 0.8 V. This production rate is more than double that obtained in previous MEC studies. The energy efficiency relative to the electrical input decreased with applied voltage from 406 +/- 6% (E(ap) = 0.3 V) to 194 +/- 2% (E(ap) = 0.8 V). Overall energy efficiency relative to both E(ap) and energy of the substrate averaged 78 +/- 4%, with a maximum of 86 +/- 2% (1.02 +/- 0.05 m3 H2/m3 day, E(ap) = 0.4 V). At E(ap) = 0.2 V, the hydrogen recovery substantially decreased, and methane concentrations increased from an average of 1.9 +/- 1.3% (E(ap) = 0.3-0.8 V) to 28 +/- 0% of the gas, due to the long cycle time of the reactor. Increasing the solution conductivity to 20 mS/ cm increased hydrogen production rates for E(ap) = 0.3-0.6 V, but consistent reactor performance could not be obtained in the high conductivity solution at E(ap) > 0.6 V. These results demonstrate that high hydrogen recovery and production rates are possible in a single chamber MEC without a membrane, potentially reducing the costs of these systems and allowing for new and simpler designs.
Microbial electrolysis cells (MECs) are an efficient technology for generating hydrogen gas from organic matter, but alternatives to precious metals are needed for cathode catalysts. We show here that high surface area stainless steel brush cathodes produce hydrogen at rates and efficiencies similar to those achieved with platinum-catalyzed carbon cloth cathodes in single-chamber MECs. Using a stainless steel brush cathode with a specific surface area of 810 m2/m3, hydrogen was produced at a rate of 1.7 +/- 0.1 m3-H2/m3-d (current density of 188 +/- 10 A/m3) at an applied voltage of 0.6 V. The energy efficiency relative to the electrical energy input was 221 +/- 8%, and the overall energy efficiency was 78 +/- 5% based on both electrical energy and substrate utilization. These values compare well to previous results obtained using platinum on flat carbon cathodes in a similar system. Reducing the cathode surface area by 75% decreased performance from 91 +/- 3 A/m3 to 78 +/- 4 A/m3. A brush cathode with graphite instead of stainless steel and a specific surface area of 4600 m2/m3 generated substantially less current (1.7 +/- 0.0 A/m3), and a flat stainless steel cathode (25 m2/m3) produced 64 +/- 1 A/m3, demonstrating that both the stainless steel and the large surface area contributed to high current densities. Linear sweep voltammetry showed that the stainless steel brush cathodes both reduced the overpotential needed for hydrogen evolution and exhibited a decrease in overpotential over time as a result of activation. These results demonstrate for the first time that hydrogen production can be achieved at rates comparable to those with precious metal catalysts in MECs without the need for expensive cathodes.
Microbial fuel cells (MFCs) are typically designed as a two-chamber system with the bacteria in the anode chamber separated from the cathode chamber by a polymeric proton exchange membrane (PEM). Most MFCs use aqueous cathodes where water is bubbled with air to provide dissolved oxygen to electrode. To increase energy output and reduce the cost of MFCs, we examined power generation in an air-cathode MFC containing carbon electrodes in the presence and absence of a polymeric proton exchange membrane (PEM). Bacteria present in domestic wastewater were used as the biocatalyst, and glucose and wastewater were tested as substrates. Power density was found to be much greater than typically reported for aqueous-cathode MFCs, reaching a maximum of 262 +/- 10 mW/m2 (6.6 +/- 0.3 mW/L; liquid volume) using glucose. Removing the PEM increased the maximum power density to 494 +/- 21 mW/m2 (12.5 +/- 0.5 mW/L). Coulombic efficiency was 40-55% with the PEM and 9-12% with the PEM removed, indicating substantial oxygen diffusion into the anode chamber in the absence of the PEM. Power output increased with glucose concentration according to saturation-type kinetics, with a half saturation constant of 79 mg/L with the PEM-MFC and 103 mg/L in the MFC without a PEM (1000 omega resistor). Similar results on the effect of the PEM on power density were found using wastewater, where 28 +/- 3 mW/m2 (0.7 +/- 0.1 mW/L) (28% Coulombic efficiency) was produced with the PEM, and 146 +/- 8 mW/m2 (3.7 +/- 0.2 mW/L) (20% Coulombic efficiency) was produced when the PEM was removed. The increase in power output when a PEM was removed was attributed to a higher cathode potential as shown by an increase in the open circuit potential. An analysis based on available anode surface area and maximum bacterial growth rates suggests that mediatorless MFCs may have an upper order-of-magnitude limit in power density of 10(3) mW/m2. A cost-effective approach to achieving power densities in this range will likely require systems that do not contain a polymeric PEM in the MFC and systems based on direct oxygen transfer to a carbon cathode.
Laboratory-scale experiments were performed in which the corrosion protection of stainless steels in seawater was afforded by cathodic protection. The method was implemented for the first time using the potential difference at the marine sediment/seawater interface as the only source of electric power. Graphite electrodes buried in marine sediment, developing a potential of -0.45 V versus a saturated calomel electrode (SCE), were used as anodes to cathodically polarize UNS S30403 stainless steel coupons that were exposed to seawater. The cathodic protection system was operated with low polarization of stainless steel, typically to -0.2 V (vs SCE) and was found to properly prevent material failure even in the presence of a well-developed biofilm. With voltammetry, the protection current was found to be related to the oxidation of reduced sulfur compounds in the sediments. Results demonstrate that this inexpensive and environmentally friendly method can, so far, extend the service life of stainless steels in seawater.
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