Single-chamber Microbial Electrolysis Cell Research Articles

Efficient hydrogen production from food waste leachate using single-chamber microbial electrolysis cell

The aim of this study was to develop an efficient strategy for enhancing H2 production in the single-chamber microbial electrolysis cell (MEC) using food waste leachate as a substrate. Different pH (8.5, 9.5, 10.5, and 11.2), applied voltage (0.8, 1.2, 1.5, 1.8, 2.0, 2.2, 2.3, and 2.4 V) and negative pressure control (−50 kPa) were tested in the single-chamber MEC. Suitable pH adjustment could greatly promote electricity generation and H2 production rather than negative pressure control. Under pH of 11.5 and 2.4 V, the maximum current density reached 121.9 ± 10.9 A/m³ with an average H2 concentration of 91.9 ± 3.2% in a 1.2-L single-chamber MEC within 30 continuous cycles of operation (∼607 h), which was constructed with carbon brushes as the anode and stainless steel brushes as the cathode. The maximum H2 production rate reached 853.2 ± 70.3 L/m³•d with an H2 yield of 26.3 mmol•H2/g•COD. The COD removal of 68.3 ± 6.8% and three-dimensional excitation-emission matrix spectra of the effluent in the MEC within 21 ± 3h indicated efficient organics degradation in the leachate. Our results should provide a promising way to enhance the H2 production of MEC during leachate treatment.

High-Efficiency Hydrogen Recovery from Corn Straw Hydrolysate Using Functional Bacteria and Negative Pressure with Microbial Electrolysis Cells

This study attempts to overcome the challenges associated with the degradation of complex organic substances like corn straw hydrolysate in hydrogen recovery by strategically enriching functional microbial communities in single-chamber cubic microbial electrolysis cells (MECs). We applied negative pressure, using acetate or xylose as electron donors, to mitigate the hydrogen sink issues caused by methanogens. This innovative method significantly enhanced MEC performance. MECs enriched with xylose demonstrated superior performance, achieving a hydrogen production rate 3.5 times higher than that achieved by those enriched with acetate. Under negative pressure, hydrogen production in N-XyHy10 reached 0.912 ± 0.08 LH2/L MEC/D, which was 6.7 times higher than in the passive-pressure MECs (XyHy10). This advancement also resulted in substantial increases in current density (73%), energy efficiency (800%), and overall energy efficiency (540%) compared with MECs operated under passive pressure with 10% hydrolysate feed. The enrichment of polysaccharide-degrading bacteria such as Citrobacter and Pseudomonas under negative pressure underscores the potential for their industrial application in harnessing complex organic substrates for bioenergy production in single-chamber MECs. This is a promising approach to scaling up bioenergy recovery processes. The findings of this research study contribute significantly to the field by demonstrating the efficacy of negative pressure in enhancing microbial activity and energy recovery, thereby offering a promising strategy for improving bioenergy production efficiency in industries.

Hydrogen production from wastewater using interdigitated printed electrode-based Single-Chamber microbial electrolysis cells

In the ever-increasing quest for alternative energy sources, hydrogen emerged as a promising green option, but efficient and economical production and management have been the primary constraints. Converting wastewater into H2 and other forms of energy attracted significant attention in terms of simultaneously and sustainably managing both the wastewater and the energy generation problems. Microbial Electrolysis Cells (MEC) evolved recently as promising options for converting wastewater into H2 and electricity but with serious constraints on scalability. The current research aims to explore design and manufacturing solutions to build structurally strong and electrochemically effective electrodes that can also lead to scalable MEC. Two designs based on the interdigitated and spiral electrode architectures are proposed and evaluated. The added design freedom with additive manufacturing by selective laser melting of specific alloys of choice is effectively utilised in physically prototyping the interdigitated and spiral electrode forms designed with controlled porosity constraints. Microstructural, electrochemical, and cell performance characterisations led to the understanding that the spiral electrode configuration with polypyrrole-coated stainless steel 316L anode is a promising design option for both longitudinal and lateral scale-up of the MEC.

Niche construction in a bioelectrochemical system with 3D-electrodes for efficient and thorough biodechlorination

The design of bioelectrochemical system based on the principle of niche construction, offers a prospective pathway for achieving efficient and thorough biodechlorination in groundwater. This study designed a single-chamber microbial electrolysis cell, with porous three-dimensional (3D) electrodes introduced, to accelerate the niche construction process of functional communities. This approach allowed the growth of various bacteria capable of simultaneously degrading 2,4-dichlorophenol (DCP) and its refractory intermediates, 4-chlorophenol (4CP). The 3D-electrodes provided abundant attachment sites for diverse microbes with a high initial Shannon index (3.4), and along the degradation progress, functional bacteria (Hydrogenoanaerobacterium and Rhodococcus erythropolis for DCP-degrading, Sphingobacterium hotanense for 4CP-degrading and Delftia tsuruhatensis for phenol-degrading) constructed their niches. Applying an external voltage (0.6 V) further increased the selective pressure and niche construction pace, as well as provided ‘micro-oxidation’ site on the electrode surface, thereby achieving the degradation of 4CP and mineralization of phenol. The porous electrodes could also adsorb contaminants and narrow their interaction distance with microbes, which benefited the degradation efficiency. Thus a 10-fold increase in the overall mineralization of DCP was achieved. This study constructed a novel bioelectrochemical system for achieving efficient and thorough biodechlorination, which was suitable for in situ bioremediation of groundwater.

Combined effect of temperature and illumination on treatment of etching terminal wastewater in single-chamber microbial electrolysis cells

Temperatures and illumination/darkness conditions influenced etching terminal wastewater (ETW) treatment using Serratia marcescens-inoculated single-chamber microbial electrolysis cells (MECs), achieving recalcitrant organics mineralization (6.0 − 12.2 mg/L/h) and complete heavy metals removal at 4 − 60 ℃ during 24 h operation. A favorable 6 h operation for heavy metals removal and the preferable 24 h for recalcitrant organics mineralization, demonstrated nonsynchronous removal/mineralization of these different components in the ETW. Temperature and illumination combinedly regulated S. marcescens release of more cathodic than anodic extracellular polymer substances (EPS) with a compositional diversity and the more functional cathodic triplet 3EPS* than active radical HO•, converse to the HO• over 3EPS* in darkness, for efficient recalcitrant organics mineralization. These results illustrated the combined influential temperature and illumination via regulating S. marcescens release of different EPS for ETW treatment, providing a new regulating strategy towards efficient treatment of actual industrial wastewaters in single-chamber MECs.

Micro-oxygen supply combined with applied voltage enhance ammonium oxidation and denitrification in a single-chamber microbial electrolysis cell: Performance and mechanism

Anodic ammonium oxidation catalyzed by microorganisms holds great potential as an effective anaerobic approach for ammonium and total nitrogen removal. However, the application of this approach is constrained by a low rate of ammonium oxidation, limiting the efficiency of total nitrogen removal. To overcome this limitation, a small amount of oxygen was introduced into a single-chamber microbial electrolysis cell to initiate the production of hydroxylamine through ammonium oxidation. Enhanced efficiency of overall nitrogen removal was obtained by the combined regulation of micro-oxygen and microbial electrode catalysis for ammonium oxidation and denitrification. According to the ammonium oxidation amount, the total oxidized nitrogen removal efficiency reached 67.87 ± 0.25 % and total nitrogen removal amount was 202.9 ± 0.5 mg/L, showing a high performance for treating high ammonium-contained wastewater. The oxidation peaks of hydroxylamine were determined at 0.43 V (vs. Ag/AgCl) for revealing the possible process of anodic hydroxylamine oxidation coupling to cathodic denitrification. In addition, microbial community analysis revealed that increasing the applied voltage regulated the abundance of nitrifying and denitrifying functional microbial communities both in the solution and on electrodes, and the key functional genes including hydroxylamine oxidation (hao), nitrate reduction (narG, narH, narI, napA, napB), nitrite reduce (nirK, nirS), and nitric oxide reduce (norB, norC), increased significantly at the applied voltage of 0.9 V, which accompanied by an obvious enhancement of enzyme activity compared to anaerobic and open circuit voltage. This work revealed the enhanced performance and mechanism on synergistic regulation by micro-oxygen and applied voltage for ammonium oxidation and denitrification, and provided new insights and feasible enhancing measures for treating high ammonium-nitrogen wastewater with low C/N ratio.

Simultaneous nitrification/denitrification in a single-chamber stainless steel bioelectrochemical reactor

The removal of nitrogen from wastewater with a low C/N ratio often requires additional carbon sources to address the shortage of electron donors, which increases the cost. We explored a simple and energy effecient means for treating wastewater with a high concentration of ammonia nitrogen under anoxic conditions without the addition of carbon sources. We constructed a stainless steel tube as an anaerobic single-chamber microbial electrolysis cell (MEC) for investigating autotrophic simultaneous nitrification/denitrification (SND). Two different structures (carbon brush vs. stainless-steel) were used to construct biocathodes and compared their performances under different voltages (1.8 V, 1.5 V, 1.2 V) applied by DC power. When voltage was applied at 1.5 V, the removal rates of TN and NH4+-N reached 19.68 ± 0.02 mg L−1 d−1 and 21.04 ± 0.17 mg L−1 d−1, respectively. Simultaneously, it achieved maximum TN and NH4+-N removal over 14 days (44.97 ± 0.28 %, 48.16 ± 0.32 %). These rates were 1.8 and 5 times of that obtained with the conventional carbon brush electrode and open-circuit control. Furthermore, microbial community and SEM analysis indicate that species of Thermomonas, Thibacillus and Thauera were the predominant autotrophic electroactive denitrifying bacteria in the reactors. Overall, we achieved a high rate of nitrogen removal, electron utilization and energy recovery in a single-chamber stainless steel MEC.

Overcoming hydrogen loss in single-chamber microbial electrolysis cells by urine amendment

The effective hydrogen production in single-chamber microbial electrolysis cells (MECs) has been seriously challenged by various hydrogen consumers resulting in substantial hydrogen loss. In previous studies, the total ammonia nitrogen (TAN) has been used to inhibit certain hydrogen-consuming microorganisms to enhance hydrogen production in fermentation. In this study, we explored the feasibility of using source-separated urine to overcome hydrogen loss in the MEC, with the primary component responsible being TAN generated via urea hydrolysis. Experimental results revealed that the optimal TAN concentration ranged from 1.17 g N/L to 1.75 g N/L. Within this range, the hydrogen production rate substantially improved from less than 100 L/(m3·d) up to 520 L/(m3·d), and cathode recovery efficiency and energy recovery efficiency were greatly enhanced, with the hydrogen percentage achieved over 95 % of the total gas volume, while maintaining uninterrupted electroactivity in the anode. Compared to using chemically added TAN, using source separated urine as the source of ammonia also showed the effect of overcoming hydrogen loss but with lower Coulombic efficiency due to the complex organic components. Pre-adaptation of the reactor with urea enhanced hydrogen production by nearly 60 %. This study demonstrated the effectiveness of TAN and urine in suppressing hydrogen loss, and the results are highly relevant to MECs treating real wastewater with high TAN concentrations, particularly human fecal and urine wastewater.

The aggregated biofilm dominated by Delftia tsuruhatensis enhances the removal efficiency of 2,4-dichlorophenol in a bioelectrochemical system

Bioelectrochemical system is a prospective strategy in organic-contaminated groundwater treatment, while few studies clearly distinguish the mechanisms of adsorption or biodegradation in this process, especially when dense biofilm is formed. This study employed a single chamber microbial electrolysis cell (MEC) with two three-dimensional electrodes for removing a typical organic contaminant, 2,4-dichlorophenol (DCP) from groundwater, which inoculated with anaerobic bacteria derived from sewage treatment plant. Compared with the single biodegradation system without electrodes, the three-dimensional electrodes with a high surface enabled an increase of alpha diversity of the microbial community (increased by 52.6% in Shannon index), and provided adaptive ecological niche for more bacteria. The application of weak voltage (0.6 V) furtherly optimized the microbial community structure, and promoted the aggregation of microorganisms with the formation of dense biofilm. Desorption experiment proved that the contaminants were removed from the groundwater mainly via adsorption by the biofilm rather than biodegradation, and compared with the reactor without electricity, the bioelectrochemical system increased the adsorption capacity from 50.0% to 74.5%. The aggregated bacteria on the surface of electrodes were mainly dominated by Delftia tsuruhatensis (85.0%), which could secrete extracellular polymers and has a high adsorption capacity (0.30 mg/g electrode material) for the contaminants. We found that a bioelectrochemical system with a three-dimensional electrode could stimulate the formation of dense biofilm and remove the organic contaminants as well as their possible more toxic degradation intermediates via adsorption. This study provides important guidance for applying bioelectrochemical system in groundwater or wastewater treatment.

Efficient hydrogen production in single-chamber microbial electrolysis cell with a fermentable substrate under hyperalkaline conditions

Hydrogen production from food waste is of great significance for energy conversion and pollution control. The aim of this study was to investigate the glucose fermentation from food waste and hydrogen (H2) production in the single-chamber microbial electrolysis cell (MEC) under hyperalkaline conditions. Single-chamber MECs were tested with 1 g/L glucose as substrate under different pH values (i.e., 7.0, 9.5, and 11.2) and applied voltages (i.e., 0.8, 1.2, and 1.6 V). With pH increase from 7.0 to 11.2, H2 production with methanogenesis inhibition was significantly improved in the MEC. At pH of 11.2, the maximum current density reached 180 ± 9 A/m3 with the H2 purity of 93.3 ± 1.2% and average H2 yield of 7.72 ± 0.23 mol H2/ mol glucose under 1.6 V. Acetate from glucose fermentation was the largest electron sink within 12 h. Methanobacterium alcaliphilum dominated the archaeal communities with the relative abundance of > 99.0% in the cathodic biofilms. The microbial communities and mcr A gene copy numbers analyses showed that high pH enhanced the acetate production from glucose fermentation, inhibited syntrophic acetate-oxidizing with hydrogenotrophic methanogenesis in the anodic biofilms, and inhibited hydrogenotrophic methanogenesis in the cathodic biofilms. Our results of hyperalkaline conditions provide a feasible way to harvest H2 efficiently from fermentable substrates in the single-chamber MEC.

Hydrogen production in microbial electrolysis cell and reactor digestate valorization for biochar – a noble attempt towards circular economy

The relevance of sustainability through circular economy has focused on exploring biomass for biofuels and subsequent reactor digestate waste valorization. This noble study has investigated the bio-hydrogen production from sugarcane bagasse fed membrane-less single-chambered microbial Electrolysis Cell (SC-MEC). Also, the consequent biochar production from the MEC reactor digestate to promote maximum energy extraction from waste was explored. The bagasse in MEC resulted in 0.25 m3 of hydrogen/m3/day at an externally applied voltage supply of 0.8 V, with coulombic efficiency (CE) of 82.87 ± 2% and electrical energy efficiency of 97.47 ± 2%. The cathode and the Shewanella sp. Enriched bioanode were arranged for overpotential reduction, resulting in a high current density of 62 A/m2. The bio-remediation efficiency of SC-MEC was estimated in terms of COD removal reported as 31.16 ± 0.5%, nitrate removal as 28.18 ± 0.2%, and sulphate removal as 41.2 ± 0.2%. The reactor digestate was pyrolyzed, and the biochar yield was calculated as 17.8 ± 0.2%, with BET surface area of 8.903 m2/g. The fixed carbon content of digested bagasse was reported as 22.9 ± 0.2, while the total carbon lost during microbial digestion in SC-MEC was around 32 ± 0.2%. This study paves a route for a circular economy by practicing clean renewable energy and using the reactor waste for subsequent biochar production.

Nanoporous oxide coating on carbon paper electrodes to enable bio-hydrogen production in microbial electrolysis cells

To counteract expensive cathodes, a single chamber microbial electrolysis cell (MEC) equipped with nanoporous oxide coating on a carbon paper electrode as a cathode was explored. The performance of the MEC was evaluated based on the chemical oxygen demand (COD) removal efficiency, catalytic activity, and hydrogen production. The obtained results indicated that nanoporous oxide coated carbon electrode with TiO2 achieved maximum H2 yield (3.0 mol H2 mol−1 acetate), followed by ZrO2 and SiO2. In contrast, the uncoated carbon electrode achieved lower hydrogen yield (0.08 mol H2 mol−1 acetate). A maximum COD removal of 82% was achieved from the carbon electrode coated with TiO2 followed by 80.5% from SiO2 and 79% from ZrO2. Additionally, based on linear sweep voltammetry, nanoporous oxide coated electrodes started H2 evolution at a lower potential than the uncoated electrode, thereby exhibiting a higher catalytic rate. This investigation showed that carbon electrodes with nanoporous coating can be one of the economical (low cost) and potential electrodes to be used as a cathode in the MEC for hydrogen production instead of expensive metallic electrodes.

Hydrogen generation from bamboo biomass using enzymatic hydrolysis and subsequent microbial electrolysis in a single chamber microbial electrolysis cell

Sustainable, economical. and clean energy production technologies acutely needed abundant supply of raw materials (biomass) and superior process engineering techniques to deliver the desired throughput. In this endeavour, here we demonstrated the utilization of lignocellulose (Bambusa bambos) by successive enzymatic treatment and microbial electrolysis in a single chamber MEC for generating clean fuel-hydrogen. In addition, we studied MEC (V=400 mL) by modifying an anode (graphene with 100 cm2 area) with monodisperse iron oxide nanoparticles (IONPs). Enzymatically (10% w/w laccase) pretreated Bambusa bambos with 40.31% reduced lignin was subjected to batch hydrolysis (20% w/w enzyme-to-substrate ratio) using cellulase. The glucose produced (99.54 ± 4 mg/dL) after 96 h of incubation was further operated in single chamber MEC equipped with highly efficient IONPs coated electrodes for hydrogen production. Engineering parameters namely-applied voltage (0.6-1.0 V) and mixing characteristics (0–400 rpm) were also investigated to improve the system performance. The MEC with IONPs coated anode offered hydrogen production efficiency 1.14 times higher as compared to MEC with the uncoated anode. The maximum hydrogen production of 0.02 g (224 mL) per gram of biomass was obtained in MEC with the coated anode at an applied voltage of 0.8 V under the influence of moderate mixing (200 rpm).

Simultaneous removal of multiple heavy metals using single chamber microbial electrolysis cells with biocathode in the micro-aerobic environment

The simultaneous and efficient removal of various heavy metals from wastewater to satisfy the requirements of zero discharge has been a research hotspot and difficult point. In the laboratory scale (0.5 L), the biocathode microbial electrolytic cells (BCMECs) were constructed with the pre-screened heavy metal-tolerant electroactive bacterial, mainly of the Sphingomonas, Azospira and Cupriavidus. The BCMECs system showed a more satisfactory removal effect for multiple heavy metals and organic pollutants. At the auxiliary voltage of 0.9 V and initial concentration of 20 mg L−1, the removal efficiency of Cu, Pb, Zn, Cd and COD were 98.76 ± 0.32%, 98.01 ± 0.76%, 73.58 ± 4.83%, 84.39 ± 5.95%, 77.55 ± 1.51%, respectively. It was found by various characterization techniques (CV, EIS, XPS et al.) that the constructed biocathode has the function of electrocatalytic reduction of heavy metal ions in a micro-aerobic, film-free environment. The positive shift (0.030–0.229 V) of the initial potential for heavy metal reduction and the absence of a significant increase (＜ 10 Ω) in the interfacial resistance indicated a reduction in the total free energy of the reduction reaction, which promotes the reaction and improves the efficiency of heavy metal removal. Bacterial community analysis revealed that the Proteobacteria has been dominant in different heavy metal environments. With the increase of heavy metal concentration, Sphingomonas, Azospira and Cupriavidus showed stronger tolerance and became the dominant genus. This study emphasized the important performance of biocathodes and the effective treatment of heavy metal wastewaters by BCMECs and provided a reasonable way for industrial and mining enterprises to innovate the water treatment process.

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.

Efficient H2 production in a ZnFe2O4/g-C3N4 photo-cathode single-chamber microbial electrolysis cell.

Photo-assisted single-chamber microbial electrolysis cells (MECs) incorporating semiconductor cathodes are attractively promising for exclusive hydrogen without CH4 and CO2. However, the unsustainable, high cost, and unstable metal catalysts on the cathodes along with the intricacies behind the interplay of circuital current, light illumination, and bacterial communities on both electrodes are poorly understood. Herein, photo-assisted single-chamber MECs incorporating ZnFe2O4/g-C3N4 cathodes are demonstrated to achieve efficient production of exclusive hydrogen (0.11 ± 0.01 m3/m2/day; 1.70 ± 0.04 m3/m3/day) with a solar-to-hydrogen conversion efficiency of 4.08 ± 0.17% and an energy efficiency relative to electrical input of 233 ± 5%. The ZnFe2O4/g-C3N4 structured cathodes exhibited appreciable higher photocurrents than the controls (g-C3N4: 4.3-fold; ZnFe2O4: 3.3-fold), and negligible leaking of Fe and Zn after the 4th-cycle operation. Circuital current and light illumination were proven to varying degree shape both electrodes for building up functional bacterial communities with metabolic regulation at the prolonged operation of 12 batch cycles. Energy metabolism and carbohydrate metabolism along with membrane transport, signal transduction, and cell motility based on PICRUSt functional prediction further confirmed the photo-assisted single-chamber MECs for efficient hydrogen production. This study provided a sustainable, cost-effective, and efficient approach for achieving high rates of exclusive hydrogen production and offered new insights for ingenious interplay of circuital current, light illumination, and bacterial communities for efficient hydrogen production in the photo-assisted single-chamber MECs. KEY POINTS: • ZnFe2O4/g-C3N4 cathodes of single-chamber MECs achieve efficient H2 production. • Light irradiation and circuit current shape bacterial communities on both electrodes. • Circuital current contributes to less leaking of Fe and Zn, and thus system stability.

Microbial electrolysis cell (MEC): Reactor configurations, recent advances and strategies in biohydrogen production

• Microbial electrolysis cells (MECs) are widely used for biohydrogen production. • Mechanism, microbiology and thermodynamics of MEC for hydrogen was given. • Biological factors, cathodes and catalysts, Anode materials, substrates was discussed. • Single/dual chamber, centric tubular, Up-flow single chamber MEC was articulated. • Membrane free MEC for continual hydrogen production was elaborated in this review. Hydrogen gas has a lot of potential as an ecologically friendly and efficient vehicle fuel. Nearly all hydrogen gas is generated using non-renewable fossil fuels such as coal, oil, and natural gas. As a result of climate change and declining oil supplies linked to fossil fuel use, hydrogen production from renewable energy sources is becoming a viable option. Biohydrogen is produced from various biomasses and wastes through several methods. Hydrogen can be produced through multiple technologies, such as electrochemical, biochemical, photochemical, and thermochemical processes. Among these techniques, Microbial electrolysis cells (MECs) are plausible bioelectrochemical systems to produce hydrogen; wherein organic compounds are oxidized with the chemical evolution of hydrogen in the cathode chamber. MECs combine microbial and electrochemical processes and are progressively contemplated as a better option for biohydrogen production. Therefore, elaborated data on the MECs-based hydrogen production is signposted in this review. The reactor design is one of the most important variables affecting hydrogen and current production rates in MECs. Upscaling is also influenced by the reactor design. Initially, the mechanism, microbiology, and thermodynamics of MEC for hydrogen production are explained to comprehend the technology. The different types of MECs are articulated in this review using sundry literature. Further, the prerequisite factors for improving MECs efficacy, such as biological factors, cathodes, catalysts, anode materials, and substrates, are discussed.

Enhanced biohydrogen production in a membraneless single-chamber microbial electrolysis cell during high-strength wastewater treatment: Effect of electrode materials and configurations

The selection of better electrode material and studies of the electrocatalytic activities of the electrodes are crucial to increasing biohydrogen production in a microbial electrolysis cells (MEC). In the present work, we studied biohydrogen production and electrocatalytic activities using a membraneless single-chamber MEC fed with high-strength wastewater, using different electrode materials (metal and carbon electrode), configurations and electrode distance. The electro-fermentation (EF) process showed a significantly higher biohydrogen production and COD removal, compared to conventional dark fermentation reactor (DF). The maximum hydrogen production rate (HPR) obtained was 314 m3 H2/m3R.d with an overall biohydrogen recovery (rH2) of 340% using the electrode configuration stainless steel 304 pleated mesh 60 as anode and stainless steel 304 flat mesh 60 as cathode at 4 cm of electrode distance. The onset potential for the hydrogen evolution reaction (HER) with metal electrode was significantly lower than carbon electrode.

A novel pico-hydro power (PHP)-Microbial electrolysis cell (MEC) coupled system for sustainable hydrogen production during palm oil mill effluent (POME) wastewater treatment

Due to accelerating global efforts toward decarbonization, a clean hydrogen (H2) producing technology, Microbial Electrolysis Cell (MEC), has garnered considerable attention. However, MEC's external energy requirement has raised concerns about its sustainability, scalability and application costs. The objective of this research was to build a renewable energy generating system for MECs' performance enhancement during the treatment of Palm oil mill effluent (POME). A novel integration of a pico-hydro-power generator (PHP) with single-chambered MECs exceptionally improved its performance. The performance boost was observed as 1.16 m3-H2/m3d H2 and 113 A/m3current production in concomitant with 73% organics removal from Palm Oil Mill Effluent (POME) wastewater, which is higher than the previous single-chambered MECs studies. 78% H2 recovery rcat (H2) along with 57% coulombic efficiency (CE) corroborated the removal of a high percentage of electrons from POME organic materials to generate >96% pure H2. The MEC nourished POME wastewater degrading communities while stimulating growth of electroactive Geobacter in the anodic biofilm which produced H2. The overall H2 recovery, COD removal rate and energy efficiency of PHP-MEC are superior than other MECs powered by other external renewable energy sources reported to date. The PHP-MEC prototype paves the path of scale up studies to build a renewable energy dependent future.