Membrane-less Microbial Electrolysis Cell Research Articles

Scalable membrane-less microbial electrolysis cell with multiple compact electrode assemblies for high performance hydrogen production

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) is a promising method for sustainable energy production and decarbonization of energy systems. However, the application of MECs is limited by the electrochemical performance, scalability, and the cost associated with expensive materials. In this study, a scalable MEC (500 mL) with novel compact electrode assemblies and high electrode surface area to volume ratio (160 m2/m3) was designed and constructed. The use of membranes, precious metal catalyst, and current collectors with high costs was avoided. A high current density at the steady state of 49.5 ± 5.3 A/m2 was achieved using acetate as the substrate with phosphate buffer under the applied voltage of 1.01 V. The corresponding volumetric current density was 3948 ± 422 A/m3. The compact electrode assembly design limited methane production rate to 3.9 ± 0.2 L/L/D, while achieving a hydrogen production rate of 33.7 ± 1.7 L/L/D. With the suppression of microbial hydrogen consumption, the hydrogen production rate was 39.8 ± 1.9 L/L/D, higher by almost one order of magnitude than those of MECs with scaling up attempts. The compact electrode configuration reduced internal resistance to 88.5 ± 4.4 Ω cm2. The energy efficiency based on input electricity was 146 ± 7 % to 189 ± 9 % within the applied voltage range of 0.71 to 1.05 V. The results in this study demonstrated successful scaling up of high performance small MECs and offered a new possible approach of scaling up MECs by stacking high-performance subunits, with no trade-offs on electrochemical performance.

Evaluation of a bioelectrochemical reductive/oxidative sequential process for chlorinated aliphatic hydrocarbons (CAHs) removal from a real contaminated groundwater

In the present study, the sequential reductive/oxidative bioelectrochemical process has been tested with real groundwater from a contaminated site in Northern Italy for chlorinated aliphatic hydrocarbons (CAHs) removal. The sequential system was developed by connecting in series two membrane-less microbial electrolysis cells (MECs) equipped with an internal graphite counter electrode. The first MEC aimed at the CAHs reductive dechlorination (RD) and was constituted of a granular graphite working electrode. In the second MEC, a mixed metal oxide working electrode stimulated the oxidative dechlorination of the low chlorinated RD's by-products through oxygen production. The sequential process allowed complete mineralization of the CAHs contained in the real groundwater. A complete reduction of the perchloroethylene into vinyl chloride (VC) was observed in the first MEC polarized at −450 mV vs SHE, while the resulting VC was oxidized with a 92 ± 2 % efficiency in the second MEC due to the HRT increment from 0.7 to 1.7 days. Biomarkers of the reductive (Dehalococcoides mccartyi 16S rRNA and reductive dehalogenase genes) and oxidative (etnE, etnC genes) dechlorination have been monitored in the two MECs along with the ecotoxicity tests. Overall, they provide information on the efficiency of the applied technology and allow to assess the potential adverse effects. According to the Tetrahymena pyriformis reproduction inhibition test and Panagrellus redivivus mortality tests, showed a significant ecotoxicity reduction with respect its initial inhibitory effect at the tested concentrations.

Feasibility assessment of oil sands process water treatment in a flow‐through microbial electrolysis cell

This study examines the feasibility of oil sands process water (OSPW) treatment in a gravitational flow-through membraneless microbial electrolysis cell (MEC) using crushed metallurgical coke as an electrode material. Synthetic OSPW was composed of the water soluble fraction (WSF) of diesel, naphthenic acids (NAs), and metals with a total chemical oxygen demand (COD) concentration of 200 mg L − 1 and total NA concentration of 9.4 mg L − 1. OSPW treatment under bioelectrochemical conditions (1.4 V applied voltage) was compared with a control system operated at 0 V. Furthermore, in an additional set of experiments, microaerobic conditions were applied to both MEC and control setups to facilitate NA biodegradation. Highest NA and COD removal rates were observed in the MEC with microaeration in electrode compartments, where total NA concentration decreased to 4.2 mg L − 1 at a hydraulic retention time of 4 days. Furthermore, microtox and microalgae toxicological assays showed substantial toxicity decrease in this MEC.

Control of Sulfate and Nitrate Reduction by Setting Hydraulic Retention Time and Applied Potential on a Membraneless Microbial Electrolysis Cell for Perchloroethylene Removal.

A membraneless microbial electrolysis cell (MEC) has been developed for perchloroethylene (PCE) removal through the reductive dechlorination reaction. The MEC consists of a tubular reactor of 8.24 L equipped with a graphite-granule working electrode which stimulates dechlorinating microorganisms while a graphite-granule cylindrical envelopment contained in a plastic mesh constituted the counter electrode of the MEC. Synthetic PCE-contaminated groundwater has been used as the feeding solution to test the nitrate and sulfate reduction reactions on the MEC performance at different hydraulic retention times (HRTs) (4.1, 1.8, and 1.2) and different cathodic potentials [−350, −450, and −650 mV vs standard hydrogen electrode (SHE)]. The HRT decrease from 4.1 to 1.8 d promoted a considerable increase in sulfate removal from 38 ± 11 to 113 ± 26 mg/Ld with a consequent current increase, while a shorter HRT of 1.2 d caused a partial inhibition of sulfate reduction with a consequent current decrease from −99 ± 3 to −52 ± 6 mA. Similarly, the cathodic potential investigation showed a direct correlation of current generation and sulfate removal in which the utilization of a cathodic potential of −350 mV versus SHE allowed for an 80% decrease in the sulfate removal rate with a consequent current decrease from −163 ± 7 to 41 ± 5 mA. The study showed the possibility to mitigate the energy consumption of the process by avoiding side reactions and current generation, through the selection of an appropriate HRT and applied cathodic potential.

Enhancing the electrochemical performance of Fe3O4 nanoparticles layered carbon electrodes in microbial electrolysis cell

The present study assesses the performance of microbial electrolysis cell (MEC) to generate electric current using (I) uncoated/untreated electrodes and (II) Fe3O4 nanoparticles (FNPs) coated electrodes. The cyclic voltammetry (CV) reports highest conductivity of 58 Sm−1 in (II) while lowest (0.18 Sm−1) in (I) electrodes. The impedance spectroscopy confirms bulk resistivity of 375 kΩ in (I) electrodes while relatively lowest resistivity of 0.4 kΩ in (II) electrodes. Two sets of single chamber membraneless MECs is operated simultaneously at different applied voltage (300 mV, 500 mV and 700 mV): RI (uncoated electrodes) and RII, (FNP coated electrodes). The RII attains maximum current density and power density of 15.2 mAcm−1 and 10.6 mWcm−2 respectively at 0.7 V while RI achieves the maximum current density and power density of 4.03 mAcm−2 and 2.8 mWcm−2 respectively at same voltage. Moreover, the current density recorded in electrodes (II) is significantly higher compared to electrodes (I) measured using CV. The result suggests FNP to be an excellent catalyst which improves biosynthesis of electric current. The biologically active environment consisting of anaerobic electrogenic microbes supported biosynthesis/generation of high electric current along with other metabolites produced from the microbes mediated redox reaction.

Sequential Reductive/oxidative Bioelectrochemical Process for Groundwater Perchloroethylene Removal

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants, microbial communities naturally present in groundwater can reduce CAHs as perchloroethylene (PCE) and trichloroethylene (TCE) to ethylene through reductive dechlorination (RD) reaction while low chlorinated CAHs like cis-dichloroethylene (cis DCE) and vinyl chloride (VC) can be oxidized by aerobic pathways. A combination of reductive and oxidative dechlorination results an effective strategy for the complete mineralization of CAHs. Bioelectrochemical systems (BES) are innovative processes which can be adopted to stimulate both reductive and oxidative dechlorination biomass through polarized electrodes. The present study describes the performances of a an oxidative bioelectrochemical reactor composed by a membrane-less microbial electrolysis cell (MEC) equipped with an internal graphite counterelectrode. In the oxidative reactor the oxygen provided by a mixed metal oxides (MMO) anode stimulated the oxidative dechlorination of the cisDCE contained in synthetic groundwater. Throughout the experimental period, both reductive and oxidative dechlorination pathways were identified due to presence of an internal counter electrode that acted as electron donor. Reductive and oxidative bioelectrochemical reactions, including anions reduction were determined and their relative contribution to the overall flowing current has been quantified in terms of oxidative and reductive coulombic efficiencies.

Effects of the Feeding Solution Composition on a Reductive/Oxidative Sequential Bioelectrochemical Process for Perchloroethylene Removal

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to their improper use in several industrial activities. Specialized microorganisms are able to perform the reductive dechlorination (RD) of high-chlorinated CAHs such as perchloroethylene (PCE), while the low-chlorinated ethenes such as vinyl chloride (VC) are more susceptible to oxidative mechanisms performed by aerobic dechlorinating microorganisms. Bioelectrochemical systems can be used as an effective strategy for the stimulation of both anaerobic and aerobic microbial dechlorination, i.e., a biocathode can be used as an electron donor to perform the RD, while a bioanode can provide the oxygen necessary for the aerobic dechlorination reaction. In this study, a sequential bioelectrochemical process constituted by two membrane-less microbial electrolysis cells connected in series has been, for the first time, operated with synthetic groundwater, also containing sulphate and nitrate, to simulate more realistic process conditions due to the possible establishment of competitive processes for the reducing power, with respect to previous research made with a PCE-contaminated mineral medium (with neither sulphate nor nitrate). The shift from mineral medium to synthetic groundwater showed the establishment of sulphate and nitrate reduction and caused the temporary decrease of the PCE removal efficiency from 100% to 85%. The analysis of the RD biomarkers (i.e., Dehalococcoides mccartyi 16S rRNA and tceA, bvcA, vcrA genes) confirmed the decrement of reductive dechlorination performances after the introduction of the synthetic groundwater, also characterized by a lower ionic strength and nutrients content. On the other hand, the system self-adapted the flowing current to the increased demand for the sulphate and nitrate reduction, so that reducing power was not in defect for the RD, although RD coulombic efficiency was less.

Batch fed single chambered microbial electrolysis cell for the treatment of landfill leachate

A fed batch membraneless microbial electrolysis cell (MEC) was investigated for treating combined leachate and dairy wastewater at an applied voltage 0.8 V and hydraulic retention time (HRT) of 48 h. The COD (chemical oxygen demand) removal and energy recovery was tested by running several cycles of MEC with increasing ratios of leachate to dairy wastewater. With an increase in percentage of simulated leachate, MEC performance in terms of current generation, COD removal efficiency and hydrogen production showed a gradual decrease. A sudden drop in reactor performance was noticed when the concentration of leachate was increased from 14 to 16% corresponding to an increase in Organic Load Rate (OLR) from 23.89gCOD/m3/d to 24gCOD/m3/d. A continued operation of MEC at an OLR of 24gCOD/m3/d for ten continuous cycles resulted in COD removal efficiency of 73% and hydrogen production of 15 mL/L/d with current density of 10 A/m2 and a power density of 80 mW/cm2.

Hydrogen gas production with Ni, Ni–Co and Ni–Co–P electrodeposits as potential cathode catalyst by microbial electrolysis cells

The development of efficient and economical cathode, operating at ambient temperature and neutral pH is a crucial challenge for microbial electrolysis cell (MEC) to become commercialize hydrogen production technology. In the present work, eight different electrodes are prepared by the electroplating of Ni, Ni–Co and Ni–Co–P on two base metals i.e., Stainless Steel 316 and Copper separately to use as cathode in MEC. Electrodeposited cathode materials have been characterized by XRD, XPS, FESEM, EDX and linear voltammetry. The fabricated cathodes show higher corrosion stability with improved electro-catalytic performance for the hydrogen production in the MECs as compared to the bare cathodes (SS316 and Cu). Data obtained from linear voltammetry and MEC experiments show that developed cathode possess four times higher intrinsic catalytic activity in comparison to bare cathode. Electrodeposited cathodes are intensively examined in membrane-less MEC, operating under applied voltage of 0.6 V in batch mode at 30 ± 2 °C temperature, in neutral pH with acetate as substrate and activated sludge as inoculum. Ni–Co–P electrodeposit on Stainless Steel 316 cathode gives maximum hydrogen production rate of 4.2 ± 0.5 m3(H2)m−3d−1, columbic efficiencies 96.9 ± 2%, overall hydrogen recovery 90.3 ± 4%, overall energy efficiency 241.2 ± 5%, volumetric current density 310 ± 5 Am−3. The net energy recovery and COD removal are 4.25 kJ/gCOD and 61%, respectively. Prepared cathodes show stable performance for continuous 5 batch cycle operations in MEC.

Efficient methane production from petrochemical wastewater in a single membrane-less microbial electrolysis cell: the effect of the operational parameters in batch and continuous mode on bioenergy recovery.

The main objective of this study is to evaluate the treatment and simultaneous production of methane from low-strength petrochemical wastewater by single membrane-less microbial electrolysis cells. To achieve this objective, the influence of variables such as applied voltage, operation mode, and hydraulic retention time (HRT) on the performance of the MEC system was investigated over a period of 110days. According to the obtained results, the maximum COD removal efficiency in the batch mode was higher than which in the continuous mode (i.e. 85.9% vs 75.3%). However, the maximum methane production in the continuous mode was almost 1.6 times higher than which in the batch mode. The results show, COD removal, methane content, and methane production in both operation modes, were enhanced as applied voltage increased from 0.6 to 0.8-1V. The proportion of methane, methane production rate, and COD removal were increased as HRT decreased from 72 to 48h, while these values were decreased as the HRT decreased from 48 to 12h. In continues mode, the energy efficiency had a range of 94.7% to 97.9% with an average of 96.6% in phase III, which almost recovered all of the electrical energy input into the system. These results suggest that single membrane-less microbial electrolysis cell is a promising process in order to the treatment of low-strength wastewater and methane production.

Real-time monitoring of a microbial electrolysis cell using an electrical equivalent circuit model.

Efforts in developing microbial electrolysis cells (MECs) resulted in several novel approachesfor wastewater treatment and bioelectrosynthesis. Practical implementation of these approaches necessitates the development of an adequate system for real-time (on-line) monitoring and diagnostics of MEC performance. This study describes a simple MEC equivalent electrical circuit (EEC) model and a parameter estimation procedure, which enable such real-time monitoring. The proposed approach involves MEC voltage and current measurements during its operation with periodic power supply connection/disconnection (on/off operation) followed by parameter estimation using either numerical or analytical solution of the model. The proposed monitoring approach is demonstrated using a membraneless MEC with flow-through porous electrodes. Laboratory tests showed that changes in the influent carbon source concentration and composition significantly affect MEC total internal resistance and capacitance estimated by the model. Fast response of these EEC model parameters to changes in operating conditions enables the development of a model-based approach for real-time monitoring and fault detection.

Computational and experimental analysis of organic degradation positively regulated by bioelectrochemistry in an anaerobic bioreactor system

Methane production was tested in membrane-less microbial electrolysis cells (MECs) under closed-circuit (RCC) and open-circuit (ROC) conditions, using glucose as a substrate, to understand the regulatory effects of bioelectrochemistry in anaerobic digestion systems. A dynamic model was built to simulate methane productions and microbial dynamics of functional populations, which were colonized in groups RCC and ROC during the start-up stage. The experiment results showed significantly greater methane production in RCC than ROC, the average methane production of RCC was 0.131 m3/m3/d, which was 1.4 times higher than that of ROC (0.055 m3/m3/d). The simulation results revealed that bioelectrochemistry had a significant influence on the abundance of microorganisms involved in acidogenesis and methanogenesis. The abundance of glucose-uptaking microorganisms was 87% of the total biomass in ROC without applied voltage, which was 20% higher than that in RCC (67%) when external voltages were applied between the anode and cathode. The abundance of hydrogenotrophic methanogens in RCC was 6% higher than that in ROC. The simulation results were verified through 16S rDNA high-throughput sequencing analysis. An electron balance analysis revealed that alteration of the acidogenesis type led to more acetate and hydrogen production from glucose fermentation, compared with the situation without bioelectrochemistry. An additional pathway from acetate to hydrogen was introduced by bioelectrolysis. These two factors resulted in significant enhancement of methane production in RCC. Bioelectrolysis process directly contributed to 26% of the total methane production after the start-up stage. When the applied voltages were cut down or decreased, RCC could maintain considerable methane productions, because the microbial communities and electron transfer pathways were already formed. Starting-up with high voltage, but operating under low voltage, could be an energy-favorable strategy for accelerating biogas production in bioelectro-anaerobic bioreactors.

Efficient Methane Production from Beer Wastewater in a Membraneless Microbial Electrolysis Cell with a Stacked Cathode: The Effect of the Cathode/Anode Ratio on Bioenergy Recovery

A methane-producing microbial electrolysis cell (MEC) is a promising energy-recovery technology, yet its performance is generally inhibited by the insufficient cathode/anode ratio. In this study, a novel stacked stainless-steel-mesh cathode was designed to investigate the effect of the cathode/anode ratio on methane production in semi-continuous MECs. Overall, energy recovery was significantly enhanced by increasing the cathode/anode ratio. The methane production rate in R3 (cathode/anode ratio of 4 cm2/cm3) reached 0.14 m3 m–3 day–1 with an applied voltage of 0.9 V, which increased by 56–180% compared to the methane production rates in R2 (2.5 cm2/cm3) and R1 (1 cm2/cm3). The overall energy efficiency in R3 was 66–94% higher than the overall energy efficiencies in R2 and R1. The cathode area was sufficient for obtaining and maintaining a maximum current when the cathode/anode ratio was higher than 2.5 cm2/cm3. According to electron balance analysis, when the cathode/anode ratio was less than 2.5 cm2/cm3,...

Domestic wastewater treatment in parallel with methane production in a microbial electrolysis cell

Microbial electrolysis cells (MECs) have great potential as a technology for wastewater treatment in parallel to energy production. In this study we explore the feasibility of using a low-cost, membraneless MEC for domestic wastewater treatment and methane production in both batch and continuous modes. Low-strength wastewater can be successfully treated by means of an MEC, obtaining significant amounts of methane. The results also suggest that hydrogenotrophic methanogenesis reduce the incidence of homoacetogenic activity, thus improving the overall MEC performance. However, gas production rates are low and important aspects such as methane solubility in water still remain a challenge. Overall, MECs can offer competitive advantages not only for low-strength wastewater treatment but also as an aid to anaerobic methane production by improving the chemical oxygen demand (COD) removal and methane production rates.

Microbial community analysis in a long-term membrane-less microbial electrolysis cell with hydrogen and methane production

A single-chamber microbial electrolysis cell (MEC) aiming at hydrogen production with acetate as sole carbon source failed due to methanogenesis build-up despite the significant amount of 2-bromoethanesulfonate (BES) dosage, 50mM. Specific batch experiments and a thorough microbial community analysis, pyrosequencing and qPCR, of cathode, anode and medium were performed to understand these observations. The experimental data rebuts different hypothesis and shows that methanogenesis at high BES concentration was likely due to the capacity of some Archaea (hydrogen-oxidizing genus Methanobrevibacter) to resist high BES concentration up to 200mM. Methanobrevibacter, of the Methanobacteriales order, represented almost the 98% of the total Archaea in the cathode whereas Geobacter was highly abundant in the anode (72% of bacteria). Moreover, at higher BES concentration (up to 200mM), methanogenesis activity decreased resulting in an increase of homoacetogenic activity, which challenged the performance of the MEC for H2 production.

Scaling-up of membraneless microbial electrolysis cells (MECs) for domestic wastewater treatment: Bottlenecks and limitations

Microbial electrolysis cells (MECs) have the potential to become a sustainable domestic wastewater (dWW) treatment system. However, new scale-up experiences are required to gain knowledge of critical issues in MEC designs. In this study we assess the ability of two twin membraneless MEC units (that are part of a modular pilot-scale MEC) to treat dWW. Batch tests yielded COD removal efficiencies as high as 92%, with most of the hydrogen (>80% of the total production) being produced during the first 48h. During the continuous tests, MECs performance deteriorated significantly (energy consumption was relatively high and COD removal efficiencies fell below 10% in many cases), which was attributed to an inadequate configuration of the anodic chamber, insufficient mixing inside this chamber, inefficient hydrogen management on the cathode side and finally to dWW in itself. Some alternatives to the current design are suggested.

Performance and bacterial enrichment of bioelectrochemical systems during methane and acetate production

A number of studies suggested that anaerobic digestion processes can be enhanced by inserting electrodes in anaerobic digesters, however a thorough work with relation to the bacterial shifts, especially with regards to acetogenesis, is lacking. In our work we investigated the performance and the respective shifts in the bacterial composition of bioelectrochemical systems producing methane and acetate from synthetic wastewater. A membraneless microbial electrolysis cell (MEC) could produce net energy with methane as the main end-product, however a membrane system was promoting acetogenesis and failed to operate as an energy producer. Bacteria present in the effluent of the membraneless system could also produce acetate with cathodic efficiencies over 60% when the cathode potentials dropped below −1000 mV vs. SHE. Different bacterial species were enriched on the two electrodes of each MEC, despite the fact that the electrodes were hydraulically connected and within a close distance from each other. Acetobacterium spp. and Acetoanaerobium spp., which could be found on the cathode of the membrane system, can be considered responsible for acetate production and decreased energy efficiency.

Revealing the proliferation of hydrogen scavengers in a single-chamber microbial electrolysis cell using electron balances

The bioelectrochemical generation of hydrogen in microbial electrolysis cells (MECs) is a promising technology with many bottlenecks to be solved. Among them, the proliferation of hydrogen scavengers drastically reduces the cell efficiency leading to unrealistic coulombic efficiencies (CE) and cathodic gas recoveries (rCAT). This work provides a novel theoretical approach to understand, through electron equivalent balances, the fate of hydrogen in these systems. It was validated with a long term operated single-chamber membrane-less MEC. In the short term, H2-recycling (i.e. hydrogen being derived to the anode) resulted in rCAT of only 4% and in CE up to 463%. The 80.5% of the current intensity came from H2-recycling and only the 19.5% from substrate oxidation. In the long term, methane was produced from hydrogen, thus decreasing rCAT to 0 (rCAT = 94.5% when considering methane production). CE was 74.5% suggesting that H2-recycling only took place when methanogenic activity was marginal.

Microbial electrolysis cell scale-up for combined wastewater treatment and hydrogen production

This study demonstrates microbial electrolysis cell (MEC) scale-up from a 50mL to a 10L cell. Initially, a 50mL membraneless MEC with a gas diffusion cathode was operated on synthetic wastewater at different organic loads. It was concluded that process scale-up might be best accomplished using a “reactor-in-series” concept. Consequently, 855mL and 10L MECs were built and operated. By optimizing the hydraulic retention time (HRT) of the 855mL MEC and individually controlling the applied voltages of three anodic compartments with a real-time optimization algorithm, a COD removal of 5.7g LR-1d-1 and a hydrogen production of 1.0–2.6L LR-1d-1 was achieved. Furthermore, a two MECs in series 10L setup was constructed and operated on municipal wastewater. This test showed a COD removal rate of 0.5g LR-1d-1, a removal efficiency of 60–76%, and an energy consumption of 0.9Whperg of COD removed.

Dehydrogenase activity in association with poised potential during biohydrogen production in single chamber microbial electrolysis cell

Variation in the dehydrogenase (DH) activity and its simultaneous influence on hydrogen (H 2) production, substrate degradation rate (SDR) and volatile fatty acid (VFA) generation was investigated with respect to varying poised potential in single chambered membrane-less microbial electrolysis cell (MEC) using anaerobic consortia as biocatalyst. Poised potential showed significant influence on H 2 production and DH activity. Maximum H 2 production was observed at 1.0 V whereas the control system showed least H 2 production among the experimental variations studied. DH activity was observed maximum at 0.6 V followed by 0.8, 0.9 and 1.0 V, suggests the influence of poised potential on the microbial metabolism. Almost complete degradation of substrate was observed in all the experimental conditions studied irrespective of the applied potential. Experimental data was also analysed employing multiple regression analysis and 3D-surface plots to find out the best theoretical poised potential for maximum H 2 production and DH activity.