Microbial Electrolysis Cell Technology Research Articles

Treatment of two-phase olive mill waste and degradation of phenolic compounds with simultaneous bio-electrochemical conversion of CO2 to CH4 using a microbial electrolysis cell

This study deals with the treatment of a two-phase olive mill waste (TPOMW), with simultaneous bio-electrochemical reduction of CO2 to CH4 using a Microbial Electrolysis Cell (MEC). For this purpose, a dual-chamber MEC was constructed using carbon felt as anodic and cathodic electrodes. The performance was assessed in terms of COD removal, the degradation of the phenolic compounds as well as the electromethanosynthesis potential of the MEC bio-cathode. The MEC operated for 120 days and the results showed that increasing the concentration from 3 to 7 and 38 gCOD/L led to an increase of the COD removal from 74%, to 77% and to 87%, respectively, of the total phenolic content removal from 73%, to 76% and to 79%, respectively, as well as of the produced CH4 from 0.04, to 0.09 and to 0.07 mmols/gCODconsumed, respectively. Increasing the applied potential from 0.5 V to 1 V, while the TPOMW was employed in the anode with no dilution, resulted in further increase of both the COD and the total phenolic content removal from 87% to 79%, respectively, to 91%, while the produced CH4 further increased from 0.07 to 0.08 mmols/gCODconsumed. The results indicate that the MEC technology can be potentially exploited for the treatment of the TPOMW and produce CH4 as a waste-to-energy source.

Electrochemical process for petroleum refinery wastewater treatment to produce power and hydrogen using microbial electrolysis cell.

This research aims to assess the microbial electrolysis cell (MEC) fed with petroleum refinery wastewater (PRW) to produce power density and bio-electrochemical hydrogen. The MEC produces a maximum bio-electricity of 21.4mA and a power density of 1200123.90 W/m2 with a loading of chemical oxygen demand (COD) of 17000mg/L. Due to catalyzed oxidation of complex compounds in PRW with a maintained microbial biofilm growth was observed after 90 d of operation of MEC. Results showed that the oxidation of organic substances in PRW enhanced the size in the growth of microbial film which further increased the generation of electrons leading to current density of 5890mA/m2. The COD removal efficiency of MEC was found to be 89.9%. The bio-electricity and hydrogen production of the MEC was estimated to be 24.5mA and 19.2 L respectively when loaded with PRW having a COD of 17500mg/L after 130 d. Present experiments demonstrate the efficiency of MEC technology efficiency in treating petroleum wastewater with the help of microbial biofilm.

Scale-up and techno-economic analysis of microbial electrolysis cells for hydrogen production from wastewater

Microbial electrolysis cells (MECs) have demonstrated high-rate H2 production while concurrently treating wastewater, but the transition in scale from laboratory research to systems that can be practically applied has encountered challenges. It has been more than a decade since the first pilot-scale MEC was reported, and in recent years, many attempts have been made to overcome the barriers and move the technology to the market. This study provided a detailed analysis of MEC scale-up efforts and summarized the key factors that should be considered to further develop the technology. We compared the major scale-up configurations and systematically evaluated their performance from both technical and economic perspectives. We characterized how system scale-up impacts the key performance metrics such as volumetric current density and H2 production rate, and we proposed methods to evaluate and optimize system design and fabrication. In addition, preliminary techno-economic analysis indicates that MECs can be profitable in many different market scenarios with or without subsidies. We also provide perspectives on future development needed to transition MEC technology to the marketplace.

Biohydrogen Production in Microbial Electrolysis Cells Utilizing Organic Residue Feedstock: A Review

The need for renewable and sustainable fuel and energy storage sources is pressing. Biohydrogen has the potential to be a storable energy carrier, a direct fuel and a diverse building block for various downstream products. Utilizing microbial electrolysis cells (MECs) to produce biohydrogen from residue streams, such as the organic fraction of municipal solid waste (OFMSW), agricultural residues and wastewater facilitate utilization and energy recovery from these streams, paving the path for a circular economy. The advantages of using hydrogen include high gravimetric energy density and, given the MEC pathway, the ability to capture heavy metals, ammonia and phosphates from waste streams, thereby allowing for multiple revenue streams emanating from MECs. A review of the MEC technology and its application was carried out to investigate the use of MEC in sustainable biohydrogen production. This review summarizes different MEC designs of varying scales, including anode materials, cathode materials, and configuration possibilities. This review highlights the accomplishments and challenges of small-scale to large-scale MECs. Suggestions for improving the successful upscaling of MECs are listed, thus emphasizing the areas for continued research.

Trends and perspectives of microbial electrolysis cell technology for ultimate green hydrogen production

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.

Nonconductive anode-associated biocarrier achieved differentiated functional bacteria enrichment and relieved the competitive pressure on anodic biofilm of microbial electrolysis cells

Microbial electrolysis cell (MEC) was an emerging technology for efficiently converting multifarious organic wastes to biogases (e.g. hydrogen and methane) with positive energy yield. The anode respiring process mediated by electrochemical active bacteria (EAB) in electrode biofilm was the key reaction in MECs. Yet, the anode has the trend to selectively enrich EAB (e.g. Geobacter sp.), which preferred simple organics. Feeding with relatively complex substrates, the EAB and fermentative bacteria competed on anode surface and formed biofilm stratification, which was adverse to the adjustment and synergistic interaction of those two functional bacteria. In this work, compensatory nonconductive biocarriers were equipped into MECs fed with sucrose to relieve the competitive pressure on anode by enriching differentiated functional bacteria on anode and nonconductive biocarriers, thus improving the overall organic degradation rate and current density. The addition of biocarrier reduced the cycle time by 35 % and improve the current density from 3.6 ± 0.3 to 5.3 ± 0.4 A/m−2 with non-fermented sucrose influent, while the COD removal and volatile fatty acids' utilization were also accelerated. With relatively complex substrates (fermented sucrose) in MECs, the fermentative bacteria were enriched on biocarriers, while the anode biofilm was domesticated for electrochemical activity with a much higher abundance of obligate EAB of 45.2 %. The nonconductive biocarriers in MECs could achieve biofilm differentiation and improve the synergistic interaction between EAB and fermentative bacteria. Achievements in this work provided a feasible method to improve the applicability of MEC technology in wastewater treatment of complex organics.

Recent Application of Nanomaterials to Overcome Technological Challenges of Microbial Electrolysis Cells.

Microbial electrolysis cells (MECs) have attracted significant interest as sustainable green hydrogen production devices because they utilize the environmentally friendly biocatalytic oxidation of organic wastes and electrochemical proton reduction with the support of relatively lower external power compared to that used by water electrolysis. However, the commercialization of MEC technology has stagnated owing to several critical technological challenges. Recently, many attempts have been made to utilize nanomaterials in MECs owing to the unique physicochemical properties of nanomaterials originating from their extremely small size (at least <100 nm in one dimension). The extraordinary properties of nanomaterials have provided great clues to overcome the technological hurdles in MECs. Nanomaterials are believed to play a crucial role in the commercialization of MECs. Thus, understanding the technological challenges of MECs, the characteristics of nanomaterials, and the employment of nanomaterials in MECs could be helpful in realizing commercial MEC technologies. Herein, the critical challenges that need to be addressed for MECs are highlighted, and then previous studies that used nanomaterials to overcome the technological difficulties of MECs are reviewed.

Microbial electrolysis enhanced bioconversion of coal to methane compared with anaerobic digestion: Insights into differences in metabolic pathways

Coal seams are considered occurrence sites for coalbed methane (CBM) accumulation and bio-methanation and sequestration of CO2. Biological approaches for the enhancement of the methanation rate of CO2 for CBM production have attracted increasing attention. The microbial electrolysis cell (MEC) is a technology with strong potential to improve the performance of the traditional anaerobic digestion (AD) system. In this study, AD and MEC-AD systems were developed to produce biomethane from coal. The results showed that the cumulative methane production of MEC-AD was 6.05 mL/g coal, 39.08% higher compared to AD alone (4.35 mL/g coal). The CO2 concentration was lower in the MEC-AD reactor, suggesting that the CO2 from coal degradation was further converted to biomethane. Metagenomics sequencing results showed that Geobacter.sp and Methanosarcina.sp were enriched in the anodic biofilm to the greatest extent, implying that direct interspecies electron transfer at the anode may promote biomethanation. Moreover, there was significant upregulation in the gene abundances of key enzymes involved in the degradation of aromatic compounds and methanogenic metabolism in hydrolytic bacteria. In particular, the gene pilA, which controls conductive pili, was significantly upregulated. The key intermediate metabolites (benzoic acid, phenol, pentadecane, etc.) showed a higher concentration and conversion rate in MEC-AD hydrolysis compared to AD. These results suggest that the efficiency of hydrolysis and interspecies electron transfer during coal digestion are facilitated by MEC technology, achieving a significant increase in biomethane production. This study provides insights into the development of efficient and low or negative carbon technologies for enhancing biomethane production and CO2 emission reduction.

Microbial Electrolysis Cell as a Diverse Technology: Overview of Prospective Applications, Advancements, and Challenges

Microbial electrolysis cells (MECs) have been explored for various applications, including the removal of industrial pollutants, wastewater treatment chemical synthesis, and biosensing. On the other hand, MEC technology is still in its early stages and faces significant obstacles regarding practical large-scale implementations. MECs are used for energy generation and hydrogen peroxide, methane, hydrogen/biohydrogen production, and pollutant removal. This review aimed to investigate the aforementioned uses in order to better understand the different applications of MECs in the following scenarios: MECs for energy generation and recycling, such as hydrogen, methane, and hydrogen peroxide; contaminant removal, particularly complex organic and inorganic contaminants; and resource recovery. MEC technology was examined in terms of new concepts, configuration optimization, electron transfer pathways in biocathodes, and coupling with other technologies for value-added applications, such as MEC anaerobic digestion, combined MEC–MFC, and others. The goal of the review was to help researchers and engineers understand the most recent developments in MEC technologies and applications.

Recent Developments in Microbial Electrolysis Cell-Based Biohydrogen Production Utilizing Wastewater as a Feedstock

Carbon constraints, as well as the growing hazard of greenhouse gas emissions, have accelerated research into all possible renewable energy and fuel sources. Microbial electrolysis cells (MECs), a novel technology able to convert soluble organic matter into energy such as hydrogen gas, represent the most recent breakthrough. While research into energy recovery from wastewater using microbial electrolysis cells is fascinating and a carbon-neutral technology that is still mostly limited to lab-scale applications, much more work on improving the function of microbial electrolysis cells would be required to expand their use in many of these applications. The present limiting issues for effective scaling up of the manufacturing process include the high manufacturing costs of microbial electrolysis cells, their high internal resistance and methanogenesis, and membrane/cathode biofouling. This paper examines the evolution of microbial electrolysis cell technology in terms of hydrogen yield, operational aspects that impact total hydrogen output in optimization studies, and important information on the efficiency of the processes. Moreover, life-cycle assessment of MEC technology in comparison to other technologies has been discussed. According to the results, MEC is at technology readiness level (TRL) 5, which means that it is ready for industrial development, and, according to the techno-economics, it may be commercialized soon due to its carbon-neutral qualities.

Microbial electrolysis cells for hydrogen production

Microbial electrolysis cells (MECs) present an attractive route for energy-saving hydrogen (H2) production along with treatment of various wastewaters, which can convert organic matter into H2 with the assistance of microbial electrocatalysis. However, the development of such renewable technologies for H2 production still faces considerable challenges regarding how to enhance the H2 production rate and to lower the energy and the system cost. In this review, we will focus on the recent research progress of MEC for H2 production. First, we present a brief introduction of MEC technology and the operating mechanism for H2 production. Then, the electrode materials including some typical electrocatalysts for hydrogen production are summarized and discussed. We also highlight how various substrates used in MEC affect the associated performance of hydrogen generation. Finally we presents several key scientific challenges and our perspectives on how to enhance the electrochemical performance.

Improving hydrogen production in microbial electrolysis cells through hydraulic connection with thermoelectric generators

Using alternative power sources to drive hydrogen production in microbial electrolysis cells (MECs) is important to implementation of MEC technology. Herein, thermoelectric generators (TEG) were to power MECs using simulated waste heat. With the MEC anolyte as a cold source for TEG, current generation of the MEC increased to 2.46 ± 0.06 mA and hydrogen production reached 0.14 m3 m−3 d-1, higher than those of the TEG-MEC system without hydraulic connection (1.16 ± 0.07 mA and 0.07 ± 0.01 m3 m−3 d-1). A high recirculation rate of 30 mL min-1 doubled both current generation and hydrogen production with 10 mL min-1, benefited from a stronger cooling effect that increased the TEG voltage output. However, the optimal recirculation rate was determined as 20 mL min-1 because of comparable performance but potentially less energy requirement. Reducing anolyte hydraulic retention time to 4 h has increased hydrogen production to 0.25 ± 0.05 m3 m−3 d-1 but decreased organic removal efficiency to 69 ± 2%. Adding three more TEG units that captured more heat energy further enhanced hydrogen production to 0.36 m3 m−3 d-1. Those results have demonstrated a successful integration of TEG with MEC through both electrical and hydraulic connections for simultaneous wastewater treatment and energy recovery.

Continuous hydrogen production from food waste by anaerobic digestion (AD) coupled single-chamber microbial electrolysis cell (MEC) under negative pressure

Increased generation of food waste (FW) poses significant risks to the social environment, and therefore it is critical that efficient technology be developed for effective waste valorization. This study used an integrated reactor to combine single-chamber microbial electrolysis cell (MEC) treatment and anaerobic digestion (AD) to achieve efficient hydrogen recovery using FW as substrate. Hydrogen production during continuous AD-MEC operation (511.02 ml H2 g−1 VS) was higher than that achieved by AD (49.39 ml H2 g−1 VS). The hydrogen recovery and electrical energy recovery in AD-MEC were as high as 96% and 238.7 ± 5.8%, respectively. To explore the mechanism of hydrogen production increase, the main components of FW [lipids, volatile fatty acids (VFAs), carbohydrates, and protein] were analyzed to investigate the utilization of organic matter. Compared with AD treatment, the removal rates of carbohydrates and proteins in the soluble phase in AD-MEC were increased by 4 times and 2.3 times, respectively. The removal of VFAs by AD-MEC was increased by 4.7 times, which indicated that the AD reactor coupled with MEC technology improved the utilization of the main organic components and thus increased hydrogen production. This study demonstrates the possibilities of reducing FW quantities along with the production of bio-hydrogen.

Modified graphite electrodes as potential cathodic electrocatalysts for microbial electrolysis cells

Microbial electrolysis cell (MEC) is an ecologically clean and innovative technology for hydrogen production. The development of cost-effective cathodes with high catalytic activity for hydrogen evolution reaction (HER) in nearneutral electrolytes is the most critical challenge for the practical application of MEC technology. In this study, graphite electrodes, functionalized with non-noble metal oxides, were produced and after electrochemical pre-treatment investigated as potential cathodes for MEC. The morphology of the developed materials was analyzed by scanning electron microscopy (SEM). Their electrochemical performance in neutral phosphate buffer solution (PBS) was explored by means of linear sweep voltammetry (LSV) and chronoamperometry (CA). The results from both methods show that all modified electrodes exhibit higher electrocatalytic activity towards HER than that of bare graphite, which is a prerequisite for further evaluation of these materials as cathodes in real MEC.

Biohydrogen production from sugar industry effluents using nickel based electrode materials in microbial electrolysis cell

Biohydrogen production from sugar industry effluents in a dual chamber microbial electrolysis cell (MEC) was investigated in this study. The MEC reactor was operated with different effluents as a substrate from cane sugar and raw sugar reprocessing units of sugar industry. The biohydrogen production was investigated using different cathode materials of Nickel plate, Nickel foam, Stainless Steel mesh. The performance of MEC was tested based on the production of hydrogen, coloumbic efficiency, hydrogen recovery and COD removal efficiency respectively. The MEC hydrogen productions revealed that cane sugar effluent was more effective as compared to raw sugar effluent. The experimental results showed that at an applied voltage of 1.0 V, Ni-foam exhibited maximum hydrogen production of 1.59 and 1.43 mmol/L/D in cane sugar and raw sugar effluents respectively, which was about twice than SS-mesh and 1.2 times Ni-plate. This study shows that Ni-foam is one of the potential candidate as low cost electrode for improving hydrogen production in MEC technology with the treatment of industrial effluents.

Selection of the best barrier solutions for liquid displacement gas collecting metre to prevent gas solubility in microbial electrolysis cells

Microbial electrolysis cells (MECs) are a novel technology aiming at producing hydrogen from biomass or wastewater. The collection and preservation of the gas generated in the MECs is the first and most important operation in gas measuring techniques. There are several techniques for the quantitative evaluation of gas production in MECs, such as Owen method, respirometre, and gas bag methods. However, the costs associated with these methods could make MEC technology scale-up expensive and impractical. This work describes evaluation of commonly used biogas measurement techniques and analyses potential errors associated with liquid displacement gas measurement. Inaccuracy mainly due to CO2, and CH4 dilution in displaceable liquids was evaluated by testing solubility of CO2 in 12 different barrier solutions. 95% saturated NaCl (pH 0.5) solution exhibited lower CO2 solubility among the tested solutions. These results indicate that gas production in MECs can be accurately tested using an inexpensive, simple gas metre.

Selection of the best barrier solutions for liquid displacement gas collecting meter to prevent gas solubility in microbial electrolysis cells (MECs)

Microbial electrolysis cells (MECs) are a novel technology aiming at producing hydrogen from biomass or wastewater. The collection and preservation of the gas generated in the MECs is the first and most important operation in gas measuring techniques. There are several techniques for the quantitative evaluation of gas production in MECs, such as Owen method, respirometre, and gas bag methods. However, the costs associated with these methods could make MEC technology scale-up expensive and impractical. This work describes evaluation of commonly used biogas measurement techniques and analyses potential errors associated with liquid displacement gas measurement. Inaccuracy mainly due to CO2, and CH4 dilution in displaceable liquids was evaluated by testing solubility of CO2 in 12 different barrier solutions. 95% saturated NaCl (pH 0.5) solution exhibited lower CO2 solubility among the tested solutions. These results indicate that gas production in MECs can be accurately tested using an inexpensive, simple gas metre.

Quasi-2D liquid cell for high density hydrogen storage

Hydrogen has been recognized as a future energy carrier that may allow a gradual transformation from a fossil fuel-based economy to a hydrogen economy. One of main obstacles to implement hydrogen economy is efficient storage of hydrogen. Up to present, none of proposed storage methods completely satisfy all department of energy (DOE) target criteria with gravimetric capacity ~5.5wt% and loss rate 0.1 (g/h)/kg for hydrogen storage yet. Here we demonstrate high density of hydrogen nano-bubble (HNB) up to ~3.4±0.18wt% can be efficiently generated and stored via an electron radiolysis assisted abstraction reaction (RAAR) in an encapsulated quasi-2D water reservoir containing organic molecules. The RAAR is a reaction between radiolytic water species and the surface groups of organic molecules. In our system, the long term stability of HNB comes from supersaturation of hydrogen molecules controllable by the electron dose rate and concentration of the organic molecule. The best gravimetric capacity and loss rate in our experiment are ~3.4±0.18wt% and 0.18(g/h)/kg, respectively, in 25°C and at 1bar which fall closely to the DOE targets. A TEM equipped with a continuous flow holder with a quasi-2D water reservoir is utilized for in-situ generation and storage of HNB. The regeneration time for HNB formation is in the order of a few ten seconds. This process can be linked with the microbial electrolysis cell technology that converts hydrogen from wastewater containing abundant organics.

Microbial electrolysis cells for hydrogen production and urban wastewater treatment: A case study of Saudi Arabia

This paper reviews the status of microbial electrolysis cells (MEC) as a mean for hydrogen (H2) production and urban wastewater treatment method. A case study of the Kingdom of Saudi Arabia (KSA) under MEC concept was developed. KSA is the world’s third largest per capita water user country with no lakes and rivers. Every year, around 1.17 and 0.38 billionm3 of domestic and industrial wastewater is generated respectively. The KSA government is seeking sustainable solutions for wastewater treatment and waste-to-energy (WTE) production to bridge the ever increasing water and energy demand-supply gap. However, there is no WTE facility exists to convert the wastewater into energy. Moreover, the potential of wastewater is not examined as an energy recovery substrate. This study, for the first time, estimated that a total electricity of 434 MWe can be produced in 2015 from the KSA’s wastewater if MEC technology is employed. Similarly, an estimated total electricity of 612 and 767 MWe can be produced for the years 2025 and 2035 from the domestic and industrial wastewater by using MEC technology. A surplus electricity of 508 and 637 MWe for the years 2025 and 2035 respectively can be added to the national grid after fulfilling the energy requirement of MEC wastewater treatment plants. Collectively, MEC will contribute 20.4% and 25.6% share of the KSA government’s WTE target of 3GW in 2025 and 2035 respectively. A number of challenges in MEC such as ohmic and concentration losses, saturation kinetics and competing reactions that lower the H2 production are discussed with their potential solutions including, the improvements in MEC design and the use of appropriate electrolytes, antibiotics and air or oxygen.

Potential Use of Microbial Electrolysis Cells in Domestic Wastewater Treatment Plants for Energy Recovery

Globally, large amounts of electrical energy are spent every year for domestic wastewater (dWW) treatment. In the future, energy prices are expected to rise as the demand for energy resources increases and fossil fuel reserves become depleted. By using appropriate technologies, the potential chemical energy contained in the organic compounds present in dWWs might help to improve the energy and economic balance of dWW treatment plants. Bioelectrochemical Systems (BESs) in general and microbial electrolysis cells (MECs) in particular represent an emerging technology capable of harvesting part of this energy. This study offers an overview of the potential of using MEC technology in dWW treatment plants (dWWTPs) to reduce the energy bill. It begins with a brief account of the basics of BESs, followed by an examination of how MECs can be integrated in dWW treatment plants (dWWTPs), identifying scaling-up bottlenecks and estimating potential energy savings. A simplified analysis showed that the use of MEC technology may help to reduce up to ~20% the energy consumption in a conventional dWWTP. The study concludes with a discussion of the future perspectives of MEC technology for dWW treatment. The growing rates of municipal water and wastewater treatment markets in Europe offer excellent business prospects and it is expected that the first generation of MECs could be ready within 1-4 years. However, before MEC technology may achieve practical implementation in dWWTPs, it needs not only to overcome important techno-economic challenges, but also to compete with other energy-producing technologies.