Performance Of Microbial Electrolysis Cell Research Articles

Impact of reactor architecture and design parameters on the performance of microbial electrolysis cells revealed by the electrode potential slope analysis

Microbial electrolysis cells (MECs) are appealing for recovering the chemical energy contained in domestic and industrial liquid wastes as hydrogen gas. Despite several years of research in the field, there is still a lack of critical analysis of how the reactor architecture dictates the electrochemical performance of the cell. In this study, internal resistance and onset voltage from the electrode potential slope analysis (EPS) were used in combination with current density, hydrogen production rate, reactor packing density, electrode spacing, membrane type and composition from 23 different studies to identify the reactor design parameters that primarily govern electrochemical performance of MECs. Using anion exchange membranes resulted in smaller internal resistances (AEM Rint= 41± 40 mΩ m2) and larger current density (18 ± 14 A m−2) compared to single chamber reactors (SC Rint= 68 ± 58 mΩ m2; 22 ± 16 A m−2) or MECs with cation exchange membranes (CEM Rint= 376 ± 280 mΩ m2; 3.0 ± 2.1 A m−2). Higher electrochemical performance for AEM- and SC-MECs translated in larger hydrogen gas production rates (0.122 mLH2 C−1 for AEM vs 0.117 mLH2 C−1 for SC), but only when inhibitors against hydrogen scavengers were added in single chamber systems (0.080 mLH2 C−1 for SC without inhibitors). Following membrane type and composition, maintaining a small electrode spacing was the most critical parameter to improve MEC performance, indicating that the low conductivity of the media primarily limit performance by increasing ohmic resistance. Reactor volume and electrode surface area negatively correlated with internal resistance and current density, indicating that better performance of scaled-up reactors can likely be obtained by stacking multiple smaller units rather than just increasing reactor size. Although challenges remain in the implementation of MECs for hydrogen production from liquid wastes, advances in electrochemical engineering of the reactors can facilitate scale up and performance prediction at scale.

Microbial Electrolysis Cell Exergy Evaluation

Bio-electrochemical systems have increasingly become the focus of research due to their potential in environmental biotechnology, particularly in the domains of waste utilization and energy recovery. A prominent method within this domain is the transformation of organic matter into hydrogen via microbial electrolysis cells (MECs). This study offers a thorough analysis of MEC performance, employing exergy analysis and incorporating relevant data from the existing literature. The findings of this research indicate a relationship between process efficiency and effective electron transfer originating from biological oxidation to the cathode reaction, facilitating hydrogen generation. The assessment performed revealed that the exergy efficiency of the process varies by a wide range, depending on conditions such as substrate type and concentration, applied external voltage, and the presence of specific inhibitors. This interplay between substrate concentration, overall efficiency, and energy requirement underlines the complex dynamics of optimizing MEC performance. Our insights provide understanding of the challenges in bio-electrochemical systems, offering implications for their sustainable and efficient use in environmental biotechnology. The theoretical analysis involved assessing the utilization of glucose and glycerol, along with the evaluation of electrical energy consumption and hydrogen yield. Our results demonstrate that a higher applied voltage is associated with greater exergy efficiency. Furthermore, after comparing the use of glucose and glycerol as substrates, our study supports the preferential application of glucose for enhanced efficiency.

A study of electron source preference and its impact on hydrogen production in microbial electrolysis cells fed with synthetic fermentation effluent

ABSTRACTFermentation effluents from organic wastes contain simple organic acids and ethanol, which are good electron sources for exoelectrogenic bacteria, and hence are considered a promising substrate for hydrogen production in microbial electrolysis cells (MECs). These fermentation products have different mechanisms and thermodynamics for their anaerobic oxidation, and therefore the composition of fermentation effluent significantly influences MEC performance. This study examined the microbial electrolysis of a synthetic fermentation effluent (containing acetate, propionate, butyrate, lactate, and ethanol) in two-chamber MECs fitted with either a proton exchange membrane (PEM) or an anion exchange membrane (AEM), with a focus on the utilization preference between the electron sources present in the effluent. Throughout the eight cycles of repeated batch operation with an applied voltage of 0.8 V, the AEM-MECs consistently outperformed the PEM-MECs in terms of organic removal, current generation, and hydrogen production. The highest hydrogen yield achieved for AEM-MECs was 1.26 L/g chemical oxygen demand (COD) fed (approximately 90% of the theoretical maximum), which was nearly double the yield for PEM-MECs (0.68 L/g COD fed). The superior performance of AEM-MECs was attributed to the greater pH imbalance and more acidic anodic pH in PEM-MECs (5.5–6.0), disrupting anodic respiration. Although butyrate is more thermodynamically favorable than propionate for anaerobic oxidation, butyrate was the least favored electron source, followed by propionate, in both AEM- and PEM-MECs, while ethanol and lactate were completely consumed. Further research is needed to better comprehend the preferences for different electron sources in fermentation effluents and enhance their microbial electrolysis.

Microbial electrolysis cell as an effective tool for mitigating the toxic effects of Cu2+ on microorganisms in the acid mine drainage treatment: Efficacy and mechanisms

It is poorly understood how the mechanism of heavy metals affect sulfate-reducing bacteria (SRB) in microbial electrolysis cell (MEC) system, however, this is essential to improve the effectiveness of sulfate reduction in acid mine drainage (AMD). This study evaluated the impact of Cu2+ on MEC performance using SRBs enriched biocathode. The sulfate reduction rate and pathway, the fate of Cu, as well as the succession of microbial community were investigated. Results showed that MEC performance was optimized at influent Cu2+ concentration of 20 mg/L, while slight inhibition was observed at 40 mg/L. The removal of Cu2+ was accomplished through bioprecipitation and biosorption, forming CuS and Cu(OH)2. However, MEC performance was inhibited at higher Cu2+ concentrations (60 mg/L) due to damaged cell structure, increased charge transfer internal resistance, and altered microbial communities. Specifically, the relative abundance of Firmicutes and Bacteroidota decreased, and functional genes related to sulfate reduction metabolism were reduced, leading to impairment of the assimilatory and dissimilatory sulfate reduction pathways. This knowledge provides revealing insights and theoretical support for developing a feasible approach to realize the treatment of wastewater containing multiple pollutants.

Effects of the applied voltage on electroactive microbial biofilm viability and hydrogen production in a recalcitrant organic waste-fed single-chamber membrane-free microbial electrolysis cell performance

The microbial electrolysis cell (MEC) is a future clean technology with a wide range of applications in energy recycling fields, particularly for hydrogen production. Applied voltage governs the electrochemically active microbial activities in MEC and further affects hydrogen production. Therefore, this study investigated the impacts of the applied voltages on MEC performance and anodic biofilm viability during the biotransformation of straw waste biomass into green hydrogen energy in an anaerobic environment. The results revealed that the COD removal efficiency and bioH2 yield increased with the augmentation of the applied voltage and beyond 0.8 V started decreasing. Among the performed protocols MEC0.8 depicted the best performance with a maximum H2 production of 6.017 mmoles H2/g-COD which was ∼28.2 % and ∼9.8 % higher than that of MEC0.5 and MEC1.0 respectively. Moreover, it also achieved a maximum COD removal of 73.4% and a coulombic efficiency (CE) of 68.4%. Consistently, the anodic biofilm viability and bacterial cell shape in the MECs performed with 0.5 V and 0.8 V were less affected but largely damaged in a high potential operated protocol (MEC1.0), suggesting that the mixed electroactive consortia were so sensitive to high potentials. Furthermore, MEC1.0 displayed a high charge transfer resistance of 16.06 Ω which was ∼22.1 %, and ∼73.7 % higher than that of MEC0.8, and MEC0.5 respectively. Based on our novel study’s results, the optimal applied voltage for the best performance of MEC was 0.8 V; and this information will be a pillar for future MEC operations prior to maintaining its industrial practice.

Tofu Wastewater (TWW) Treatment and Hydrogen (H2) Production by Using A Microbial Electrolysis Cell (MEC) System

High organic pollutant in tofu wastewater (TWW) raises a negative impact on environmental sustainability and health. Therefore, the TWW must be treated before it is discharged into the environment. Microbial electrolysis cell (MEC) is one of the green technologies that can be used to treat wastewater and generate hydrogen as well. This work tries to investigate the performance of MEC based on the decrement of organic pollutants in TWW. Some important parameters of organic pollutants in TWW such as chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), total dissolved solids (TDS), total solid (TS), and pH were evaluated before and after MEC operation. The results showed that the COD and BOD levels decreased around 56% and 35% while pH increased from 7.90 to 7.16. Additionally, the TSS, TDS, and TS decreased by around 35.0%, 45.5%, and 33.2%. In addition, the optimum hydrogen yield (YH2) and hydrogen production rate (QH2) were obtained at 114 ± 0.1 mL H2/g COD 360 ± 20 mL H2/L/d. Overall, the MEC system could be used to reduce the level of organic pollutants in TWW and generated H2 at the same time.

Effect of start-up strategies with functionally redundant and efficient acetoclastic electroactive bacteria on the performance of microbial electrolysis cells fed with domestic wastewater

Different start-up strategies were investigated for enriching efficient acetoclastic electroactive bacteria (EAB) in wastewater-fed microbial electrolysis cells (MECs). Wastewater-fed MECs bioaugmented (B-MECs) at time zero with pure cultures of Geobacter sulfurreducens and Desulfuromonas acetexigens or pre-enriched anode biofilm (PEA-MECs) with G. sulfurreducens and D. acetexigens performed better than wastewater-fed MECs started with wastewater (WW-MECs) as the sole inoculum. The highest peak current (1575 ± 157 mA/m2), coulombic efficiency (70.3 ± 9 %), and CH4 production (0.27 ± 0.02 L/g-COD) was observed in PEA-MECs. The relative abundance of acetoclastic EAB was influenced by start-up strategies (Geobacter: 23.9 ± 2.6 % and Desulfuromonas: 13.7 ± 6 % for B-MECs; Geobacter: 29.6 % ± 5.1 % and Desulfuromonas: 0.45 ± 0.2 % for PEA-MECs; Geobacter: 7.9 ± 0.5 % for WW-MECs). These results provide a novel insight for enriching the anode with functionally redundant and efficient acetoclastic EAB, which is crucial for resource recovery from wastewater.

Biohydrogen Production in Microbial Electrolysis Cell Operating on Designed Consortium of Denitrifying Bacteria.

This study provides insight into the use of a designed microbial community to produce biohydrogen in simple, single-chamber microbial electrolysis cells (MECs). The ability of MECs to stably produce biohydrogen relies heavily on the setup and microorganisms working inside the system. Despite having the most straightforward configuration and effectively avoiding costly membranes, single-chamber MECs are prone to competing metabolic pathways. We present in this study one possible way of avoiding this problem using characteristically defined, designed microbial consortium. Here, we compare the performance of MECs inoculated with a designed consortium to MECs operating with a naturally occurring soil consortium. We adapted a cost-effective and simple single-chamber MEC design. The MEC was gastight, 100 mL in volume, and equipped with continuous monitoring for electrical output using a digital multimeter. Microorganisms were sourced from Indonesian environmental samples, either as denitrifying bacterial isolates grouped as a designed consortium or natural soil microbiome used in its entirety. The designed consortium consisted of five species from the Pseudomonas and Acinetobacter genera. The headspace gas profile was monitored periodically with a gas chromatograph. At the end of the culture, the composition of the natural soil consortium was characterized by next generation sequencing and the growth of the bacteria on the surface of the anodes by field emission scanning electron microscopy. We found that MEC using a designed consortium presented a better H2 production profile, with the ability of the system to maintain headspace H2 concentration relatively stable for a long time after reaching stationary growth period. In contrast, MECs inoculated with soil microbiome exhibited a strong decline in headspace H2 profile within the same time frame. This work utilizes a designed, denitrifying bacterial consortium isolated from Indonesian environmental samples that can survive in a nitrate-rich environment. Here we propose using a designed consortium as a biological approach to avoid methanogenesis in MECs, as a simple and environmentally friendly alternative to current chemical/physical methods. Our findings offer an alternative solution to avoid the problem of H2 loss in single-chamber MECs along with optimizing biohydrogen production through bioelectrochemical routes.

Evidence of competition between electrogens shaping electroactive microbial communities in microbial electrolysis cells.

In single-chamber microbial electrolysis cells (MECs), organic compounds are oxidized at the anode, liberating electrons that are used for hydrogen evolution at the cathode. Microbial communities on the anode and cathode surfaces and in the bulk liquid determine the function of the MEC. The communities are complex, and their assembly processes are poorly understood. We investigated MEC performance and community composition in nine MECs with a carbon cloth anode and a cathode of carbon nanoparticles, titanium, or stainless steel. Differences in lag time during the startup of replicate MECs suggested that the initial colonization by electrogenic bacteria was stochastic. A network analysis revealed negative correlations between different putatively electrogenic Deltaproteobacteria on the anode. Proximity to the conductive anode surface is important for electrogens, so the competition for space could explain the observed negative correlations. The cathode communities were dominated by hydrogen-utilizing taxa such as Methanobacterium and had a much lower proportion of negative correlations than the anodes. This could be explained by the diffusion of hydrogen throughout the cathode biofilms, reducing the need to compete for space.

Ammonia Removal by Simultaneous Nitrification and Denitrification in a Single Dual-Chamber Microbial Electrolysis Cell

Ammonia removal from wastewater was successfully achieved by simultaneous nitrification and denitrification (SND) in a double-chamber microbial electrolysis cell (MEC). The MEC operations at different applied voltages (0.7 to 1.5 V) and initial ammonia concentrations (30 to 150 mg/L) were conducted in order to evaluate their effects on MEC performance in batch mode. The maximum nitrification efficiency of 96.8% was obtained in the anode at 1.5 V, followed by 94.11% at 1.0 V and 87.05% at 0.7. At 1.5 V, the initial ammonia concentration considerably affected the nitrification rate, and the highest nitrification rate constant of 0.1601/h was determined from a first-order linear regression at 30 mg/L ammonium nitrogen. The overall total nitrogen removal efficiency was noted to be 85% via the SND in the MEC operated at an initial ammonium concentration of 50 mg/L and an applied cell voltage of 1.5 V. The MEC operation in continuous mode could remove ammonia (50 mg/L) in a series of anode and cathode chambers at the nitrogen removal rate of 170 g-N/m3.d at an HRT of 15. This study suggests that a standalone dual-chamber MEC can efficiently remove ammonia via the SND process without needing additional organic substrate and aeration, which makes this system viable for field applications.

Maximizing performance of microbial electrolysis cell fed with dark fermentation effluent from water hyacinth

The performance of microbial electrolysis cell (MEC) fed with dark fermentation effluent (DEF) from water hyacinth (WH) was enhanced in this study. First, the single effects of the auxiliary processes, including centrifugation, dilution, buffering, and external power input, were investigated. Then, the interaction of these processes was further evaluated using response surface methodology (RSM) and a combination of artificial neural network (ANN) and particle swarm optimization (PSO). Statistical analysis results revealed that ANN-PSO outperformed RSM in predictability. Consequently, the ANN-PSO approach determined that a 2.2-fold dilution of centrifuged-DFE (∼1.64 g of soluble metabolite products per L), buffer concentration of 75 mM, and an applied voltage of 0.7 V were the optimal conditions for simultaneously maximizing H2 production yield and energy efficiency of DFE@WH-fed MEC. Under co-optimized conditions, H2 yield (560.8 ± 10.8 mL/g-VS) and electrical energy recovery (162.2 ± 4.7%) significantly improved compared to unoptimized conditions.

Tailoring a highly conductive and super-hydrophilic electrode for biocatalytic performance of microbial electrolysis cells

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) has attracted attention as the next generation of technology for the hydrogen economy. MECs work by electrochemically active bacteria reducing organic compounds at the anode. However, the hydrophobic nature of carbon-based anodes suppresses the release of the produced gas and water penetration, which significantly reduces the possibility of microbial attachment. Consequently, a limited surface area of the anode is used, which decreases hydrogen production efficiency. In this study, the bifunctional material poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) was applied to the surface of a three-dimensional carbon felt anode to enhance the hydrogen production efficiency of an MEC owing to the high conductivity of PEDOT and super-hydrophilicity of PSS. In experiments, the PEDOT:PSS-modified anode almost doubled the hydrogen production efficiency of the MEC compared with the control anode owing to the increased capacitance current (239.3 %) and biofilm formation (220.7 %). The modified anode reduced the time required for the MEC to reach a steady state of hydrogen production by 14 days compared to the control anode. Microbial community profiles demonstrated that the modified anode had a greater abundance of electrochemically active bacteria than the control anode. This simple method could be widely applied to various bioelectrochemical systems (e.g., microbial fuel cells and solar cells) and to scaling up MECs.

High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L–1) were fully investigated. The TC of 0 to 1 mg L–1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L–1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L–1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L–1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment.

N-doped macroporous carbon loading Mo2C as cathode electrocatalyst of hybrid neutral-alkaline microbial electrolysis cells for H2 generation

Microbial electrolysis cells (MECs) show promise in energy-effective hydrogen (H2) production by harvesting electric energy from wastewater, while the implementation of such a desirable technique faces challenges of expensive cathodic catalysts and unfavorable neutral electrolyte for hydrogen evolution reaction (HER). This work presents a simple and cost-effective pyrolysis route to fabricate hybrid electrocatalysts of Mo2C loaded nitrogen-doped porous carbon (Mo2C/NC). The Mo2C/NC-800 catalyst delivers impressively high activity and durability in pH-varied electrolyte from alkali, neutral and acid, particularly in alkali condition (e.g. 1.0 M KOH) where the overpotential@10 mA cm−2 is only 138 mV which is comparable to the commercial Pt/C catalysts. A hybrid neutral-alkaline MEC is therefore developed that uses Mo2C/NC as the cathode catalyst for H2 production. The system requires an applied voltage of 1.0 V to achieve current density of ∼20.0 A m−2 at H2 generation rate of 170.5 L m−2 d−1. This MEC performance is considerably higher than that of the traditional symmetric neutral counterpart that requires an applied voltage of 1.0 V to achieve current density of ∼18.0 A m−2 at H2 generation rate of 159.4 L m−2 d−1 indicating promising potential of Mo2C/NC electrocatalyst to be applied in MEC device for H2 generation.

Statistical optimization of operating parameters of microbial electrolysis cell treating dairy industry wastewater using quadratic model to enhance energy generation

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.

Redox mediator-regulated microbial electrolysis cell to boost coulombic efficiency and degradation activity during gaseous chlorobenzene abatement

Microbial electrolysis cell (MEC), a promising technology, is being developed for volatile organic compounds (VOCs) abatement. One of the critical issues to limit its industrial application is the poor electron transfer. In this work, anthraquinone-2,6-disulfonate (AQDS) and flavin mononucleotide (FMN) are dosed to MECs for the chlorobenzene (CB) removal, which are denoted as MEC-AQDS and MEC-FMN, respectively. The MEC performance is significantly promoted due to that RMs lower down the internal resistance. The CB removal efficiency in MEC-AQDS and MEC-FMN are increased by 40% and 20%, respectively, compared with neat MEC. Moreover, ECmax and Ks of MEC-AQDS are 26% and 75% higher than that of neat MEC, respectively. AQDS is a more suitable RM with 66% and 50% higher in dechlorination efficiency and coulombic efficiency, respectively, compared with FMN. The enhancement of dechlorination process in MEC-AQDS is ascribed to two reasons. The lower resistance accelerates the electron transfer rate during dechlorination; and the enhancing growth of dechlorinating bacterium leads to an abundant excretion of dechlorination enzymes. Additionally, electrochemical analysis and intermediate detection imply that RMs affect the electron transfer pathways but not the degradation mechanism, that is, CB converts into 2-chlorophenol and 3-chlorocatechol successively, then ring-opens and dechlorinates for mineralization.

Effect of Ultrasonic Pretreatment of Sewage Sludge on the Performance of Bioelectrochemical Anaerobic Digester

Objectives : This study examined the effect of ultrasonic pretreatment on primary sewage sludge (raw sludge) solubilization and its subsequent microbial electrolysis cells (MECs) operation performance.Methods : To compare the effect of ultrasound on raw sludge solubilization, ultrasonic pretreatment was conducted at 1~4 W/mL energy density for 5~30 min. In MECs operation, raw sludge was used as a control group, and ultrasound pretreated sludge was used as an experimental group. For comparing MECs performance, biogas production, and organic matter removal were analyzed.Results and Discussion : The optimal experimental condition for ultrasonic pretreatment were 30 min of sonication time at 3 W/mL. In methane production, MEC with ultrasound pretreatment (MEC 3W) produced 243 mL/L more methane than that of unpretreated MEC (MEC) by 4,970 mL/L at 1, 3 cycles. In the modified Gompertz model analysis, the lag phase of MEC 3W was 0.46 days, which was 0.12 days longer than MEC. The maximum methane production rate of MEC 3W by 938.5 mL/L/day was also higher than MEC. MEC 3W showed a 1.8% higher TS removal rate, 2.4% VS removal rate than MEC. COD removal rate also improved by 2.0% when ultrasound pretreatment was applied. The methane yield of MEC with ultrasound pretreatment (377.4 mL/g VSin.) was 0.4% higher than that of MEC without pretreatment.Conclusion Ultrasonic pretreatment of sewage sludge improved the methane production and organic removal in microbial electrolysis cells. It is necessary to find the optimal operating conditions to obtain the maximize the performance.

Vapor-Fed Cathode Microbial Electrolysis Cells with Closely Spaced Electrodes Enables Greatly Improved Performance.

Hydrogen can be electrochemically produced in microbial electrolysis cells (MECs) by current generated from bacterial anodes with a small added voltage. MECs typically use a liquid catholyte containing a buffer or salts. However, anions in these catholytes result in charge being balanced predominantly by ions other than hydroxide or protons, leading to anode acidification. To enhance only hydroxide ion transport to the anode, we developed a novel vapor-fed MEC configuration lacking a catholyte with closely spaced electrodes and an anion exchange membrane to limit the acidification. This MEC design produced a record-high sustained current density of 43.1 ± 0.6 A/m2 and a H2 production rate of 72 ± 2 LH2/L-d (cell voltage of 0.79 ± 0.00 V). There was minimal impact on MEC performance of increased acetate concentrations, solution conductivity, or anolyte buffer capacity at applied voltages up to 1.1 V, as shown by a nearly constant internal resistance of only 6.8 ± 0.3 mΩ m2. At applied external voltages >1.1 V, the buffer capacity impacted performance, with current densities increasing from 28.5 ± 0.6 A/m2 (20 mM phosphate buffer solution (PBS)) to 51 ± 1 A/m2 (100 mM PBS). These results show that a vapor-fed MEC can produce higher and more stable performance than liquid-fed cathodes by enhancing transport of hydroxide ions to the anode.

Enhancing hydrogen production through anode fed-batch mode and controlled cell voltage in a microbial electrolysis cell fully catalysed by microorganisms

A microbial electrolysis cell (MEC) fully catalysed by microorganisms is an attractive technology because it incorporates the state-of-the-art concept of converting organic waste to hydrogen with less external energy input than conventional electrolysers. In this work, the impact of the anode feed mode on the production of hydrogen by the biocathode was studied. In the first part, three feed modes and MEC performance in terms of hydrogen production were evaluated. The results showed the highest hydrogen production under the continuous mode (14.6 ± 0.4), followed by the fed-batch (12.7 ± 0.4) and batch (0 L m−2 cathode day−1) modes. On one hand, the continuous mode only increased by 15% even though the hydraulic retention time (HRT) (2.78 h) was lower than the fed-batch mode (HRT 5 h). A total replacement (fed-batch) rather than a constant mix of existing anolyte and fresh medium (continuous) was preferable. On the other hand, no hydrogen was produced in batch mode due to the extensive HRT (24 h) and bioanode starvation. In the second part, the fed-batch mode was further evaluated using a chronoamperometry method under a range of applied cell voltages of 0.3–1.6 V. Based on the potential evolution at the electrodes, three main regions were identified depending on the applied cell voltages: the cathode activation (<0.8 V), transition (0.8–1.1 V), and anode limitation (>1.1 V) regions. The maximum hydrogen production recorded was 12.1 ± 2.1 L m−2 cathode day−1 at 1.0 V applied voltage when the oxidation and reduction reactions at the anode and cathode were optimal (2.38 ± 0.61 A m−2). Microbial community analysis of the biocathode revealed that Alpha-, and Deltaproteobacteria were dominant in the samples with >70% abundance. At the genus level, Desulfovibrio sp. was the most abundant in the samples, showing that these microbes may be responsible for hydrogen evolution.

Sustainable phosphorus recovery from wastewater and fertilizer production in microbial electrolysis cells using the biochar-based cathode

Reducing the energy consumption and electrode cost for electrochemical recovery of phosphorus (P) from wastewater is crucial for the large-scale application. In this study, biochar electrodes were investigated as the low-cost cathode in a microbial electrolysis cell (MEC) and this P-enriched biochar electrode was directly retrieved as P fertilizer after wastewater treatment. The Fe2+ salt modified biochar significantly increased the electrochemical performance of MECs due to the improved electrical conductivity and cathodic activity. Compared to the pristine biochar cathode, the current density of the MEC increased from 16.8 ± 0.2 A/m3 to 20.7 ± 0.8 A/m3, and the P removal increased from 28.8% ± 1% to 62.4% ± 3.5%. The power consumption was 0.25 ± 0.01 kWh/kg P which was more than one order of magnitude lower than the previous report. It was also demonstrated that the P enriched biochar amended soil improved the Pakchoi cultivation.