Membrane-free Microbial Electrolysis Cells Research Articles

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.

Hydrogen production in single-chamber microbial electrolysis cells using Ponceau S dye.

In this study, Ponceau S dye, which is one of the hazardous dyes found in industrial wastewater, was examined for hydrogen production in single chamber-free membrane-free microbial electrolysis cells at different concentrations (10-40mg L-1). A gas content analysis (hydrogen, carbon dioxide, and methane) was measured daily using gas chromatography to determine the effects of the Ponceau S on hydrogen production levels. Hydrogen was successfully produced in the presence of Ponceau S dye, but the gas production levels were affected by the concentrations of Ponceau S. The maximum hydrogen production was measured as 18mL at a concentration level of 20mg L-1. Decolorization ratios of Ponceau S were in the range of 85-100%. Hydrogen production rates increased in the presence of Ponceau S (20mg L-1); however, yield (%) of the production decreased when compared to the control group. The percentage of COD removal was 94.78% in the presence of 40mg L-1 of Ponceau S. In conclusion, hydrogen can be generated using wastewaters contaminated with azo dyes such as Ponceau S, and decolorization of the dye can be achieved, simultaneously.

Experimental study on volatile sulfur compound inhibition using a single-chamber membrane-free microbial electrolysis cell

Odor emissions from sewer systems and wastewater treatment plants have attracted much attention due to the potential negative effects on human health. A single-chamber membrane-free microbial electrolysis cell was proposed for the removal of sulfides in a sewer system. The feasibility of the use of volatile sulfur compounds and their removal efficiency in liquid and headspace gas phases were investigated using synthetic wastewater with real sewer sediment and Ru/Ir-coated titanium electrodes. The results indicate that hydrogen sulfide and volatile organic sulfur compounds were effectively inhibited in the liquid phase upon electrochemical treatment at current densities of 1.55, 2.06, and 2.58mA/cm2, and their removal rates reached up to 86.2-100%, except for dimethyl trisulfide, the amount of which increased greatly at 1.55mA/cm2. In addition, the amount of volatile sulfur compounds in the headspace decreased greatly; however, the total theoretical odor concentration was still high, and methanethiol and ethanethiol greatly contributed to the total strength of the odor concentration due to their low odor threshold concentrations. The major pathway for sulfide removal in the single-chamber membrane-free microbial electrolysis cell is biotic oxidation, the removal rate of which was 0.4-0.5mg/min, 4-5 times that of indirect electrochemical oxidation.

Enhancement of Congo red decolorization by membrane-free structure and bio-cathode in a microbial electrolysis cell

A membrane-free microbial electrolysis cells (MFMEC) with bio-cathode was applied to enhance azo dye Congo red decolorization by the improvement of cathodic action and membrane abandon. To reveal the advantages of MFMEC, a membrane-free electrolysis cell (MFEC) without microorganism and a microbial electrolysis cell (MEC) with membrane were set as comparisons. The electrochemical characteristics of MFMEC and its relation with decolorization were analyzed by measuring cathode potential, EIS and current change. The results showed that MFMEC with bio-cathode acquired lower cathode potential than MFEC. The charge transfer resistance of MFMEC was 5.2 Ω which was lower than MEC (43.6 Ω). The decolorization efficiency of MFMEC with different voltages (0.3 V, 0.6 V and 0.9 V) were nearly identical and stable at 87.9%, 85.1%, and 86.7% respectively in 24 h. In batch tests without solution renewal, the decolorization had a remarkable increasing (25%) in cycle 2 and 3, then it had declined since cycle 4. The main degradation product was benzidine which produced by azo bond cleavage. More CH4 was produced with 0.9 V as a side reaction that restricted further increase of decolorization rate. The result demonstrated that both the act of co-substrates and accepting electrons from cathode were the main decolorization approaches of MFMEC.

A NEW DESIGN ENHANCES HYDROGEN PRODUCTION BY G. SULFURREDUCENS PCA STRAIN IN A SINGLE-CHAMBER MICROBIAL ELECTROLYSIS CELL (MEC)

Microbial electrolysis cell (MEC) is an innovative and green technology to generate hydrogen from a wide range of renewable energy sources and wastewater. At current stage, the performance of these systems is still far from real-world applications. The most likely limiting factors for successful commercialization of this technology are the large internal resistance, high fabrication and operational costs. The aim of the present study was to enhance hydrogen production, reduce the construction and operational costs in MECs via development of a novel MEC design. A single-chamber membrane-free MEC was designed and successfully produced hydrogen from organic substrate using a pure culture: Geobacter sulfurreducens PCA. The MEC system was operated with Platinum (Pt) cathode at applied voltage range of 0.6 V to 1.1 V. Geobacter sulfurreducens PCA strain and sodium acetate used as inoculum and a fuel sources, respectively. The conductivity of electrolyte solution in the MEC was 4.5 mS/cm. Due to an improved the MEC reactor architecture, the maximum hydrogen production rate (HPR) of 3.67 ± 0.03 m3 H2 /m3 d with volumetric current density (IV) of 293.73 ± 1.18 A/m3 was achieved under an external applied voltage (Eap): 1.1 V. The highest overall hydrogen recovery ( ) and overall energy efficiency ( ) were 91.80 ± 1.06% and 66.97 ± 0.09%, respectively.

Continuous hydrogen production from cassava starch processing wastewater by two-stage thermophilic dark fermentation and microbial electrolysis

Hydrogen production from cassava starch processing wastewater by two-stage thermophilic dark fermentation and microbial electrolysis was investigated. Single-chamber membrane-free microbial electrolysis cell with applied voltage of 0.6 V was optimum for hydrogen production with hydrogen yield of 245 ml H2 gCOD−1. Continuous microbial electrolysis reactor has a maximum hydrogen yield of 182 ml H2 gCOD−1 at HRT of 48 h with energy recovery efficiency of 217%. The continuous integrated two-stage dark fermentation and microbial electrolysis have hydrogen yield of 465 ml H2 gCOD−1 with 2 times hydrogen yield improving compared with a single stage and a maximum COD removal of 58% was achieved. Dominated bacteria at an anode of microbial electrolysis cell were exoelectrogens belong to Brevibacillus sp. Caloranaerobacter sp. and Geobacillus sp. Continuous two-stage thermophilic dark hydrogen fermentation and microbial electrolysis were efficient processes for hydrogen production from cassava starch processing wastewater.

Bioelectrochemical enhancement of the anaerobic digestion of thermal-alkaline pretreated sludge in microbial electrolysis cells

Batch experiments were conducted to study bioelectrochemical enhancement of the anaerobic digestion of thermal-alkaline-pretreated sludge in single-chamber membrane-free microbial electrolysis cells (MECs) with different applied voltage. Experimental results showed bioelectrochemical method could be combined with thermal-alkaline pretreatment to enhance anaerobic digestion of sludge. The methane productions of thermal-alkaline pretreated sludge increased by 20.0%–79.3% when applied voltage was 0.6–1.8 V. The optimal applied voltage was determined as 1.8 V. Water electrolysis did not occur during test under these applied voltages. The removal rates of SCOD and sludge VSS were increased by the applied voltages, with enhanced rates of 2.6–27.6% and 17.1–51.3%, respectively. These applied voltages could enhance the growth of hydrogenotrophic methanogens and inhibit a portion of acetoclastic methanogens. High voltage (up to 1.8 V) was required to produce more methane and reduce more sludge in anaerobic digestion of thermal-alkaline-pretreated sludge when the electrodes of MECs were constructed with special material (Ti/Ru alloy) with a large distance (2 cm).

Hydrogen production profiles using furans in microbial electrolysis cells.

Microbial electrochemical cells including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are novel biotechnological tools that can convert organic substances in wastewater or biomass into electricity or hydrogen. Electroactive microbial biofilms used in this technology have ability to transfer electrons from organic compounds to anodes. Evaluation of biofilm formation on anode is crucial for enhancing our understanding of hydrogen generation in terms of substrate utilization by microorganisms. In this study, furfural and hydroxymethylfurfural (HMF) were analyzed for hydrogen generation using single chamber membrane-free MECs (17mL), and anode biofilms were also examined. MECs were inoculated with mixed bacterial culture enriched using chloroethane sulphonate. Hydrogen was succesfully produced in the presence of HMF, but not furfural. MECs generated similar current densities (5.9 and 6mA/cm2 furfural and HMF, respectively). Biofilm samples obtained on the 24th and 40th day of cultivation using aromatic compounds were evaluated by using epi-fluorescent microscope. Our results show a correlation between biofilm density and hydrogen generation in single chamber MECs.

Nickel-based electrodeposits as potential cathode catalysts for hydrogen production by microbial electrolysis

Abstract The development of cost-effective cathodes, operating at neutral pH and ambient temperatures, is a crucial challenge for the practical application of microbial electrolysis cell (MEC) technology. In this study, NiW and NiMo co-deposits produced by electroplating on Ni-foam are explored as cathodes in MEC. The fabricated electrodes exhibit higher corrosion stability and enhanced electrocatalytic activity towards hydrogen evolution reaction in neutral electrolyte compared to the bare Ni-foam. NiW/Ni-foam electrodes possess six times higher intrinsic catalytic activity, estimated from data obtained by linear voltammetry and chronoamperometry. The newly developed electrodes are applied as cathodes in single-chamber membrane-free MEC reactors, inoculated with wastewater and activated sludge from a municipal wastewater treatment plant. Cathodic hydrogen recovery of 79% and 89% by using NiW and NiMo cathodes, respectively, is achieved at applied voltage of 0.6 V. The obtained results reveal potential for practical application of used catalysts in MEC.

Biomethane recovery from Egeria densa in a microbial electrolysis cell-assisted anaerobic system: Performance and stability assessment

Renewable energy recovery from submerged aquatic plants such as Egeria densa (E. densa) via continuous anaerobic digestion (AD) represents a bottleneck because of process instability. Here, a single-chamber membrane-free microbial electrolysis cell (MEC) equipped with a pair of Ti/RuO2 mesh electrodes (i.e. the combined MEC-AD system) was implemented at different applied voltages (0–1.0 V) to evaluate the potential effects of bioelectrochemical stimulation on methane production and process stability of E. densa fermentation. The application of MEC effectively stabilized E. densa fermentation and upgraded overall process performance, especially solid matters removal. E. densa AD process was operated steadily throughout bioelectrochemical process without any signs of imbalance. The solubilization-removal of solid matters and methane conversion efficiency gradually increased with increasing applied voltage, with an average methane yield of approximately 248.2 ± 21.0 mL L−1 d−1 at 1.0 V. Whereas, the stability of the process became worse immediately once the external power was removed, with weaken solid matters removal along with methane output, evidencing the favorable and indispensable role in maintaining process stability. The stabilizing effect was further quantitatively demonstrated by statistical analysis using standard deviation (SD), coefficient of variance (CV) and box-plots. The syntrophic and win–win interactions between fermenting bacteria and electroactive bacteria might have contributed to the improved process stability and bioenergy recovery.

Comparison of various carbohydrates for hydrogen production in microbial electrolysis cells

ABSTRACTThe direct production of hydrogen from various carbohydrates of lignocellulosic biomass is examined by using single-chamber membrane-free microbial electrolysis cells. The mixed microbial culture was enriched with 20 mmol L−1 2-chloroethane sulphonate and 10 mmol L−1 sodium acetate as a carbon source. Hydrogen was produced from all carbon sources used, including monosaccharides (glucose, galactose, mannose, xylose and arabinose) and disaccharides (maltose, saccharose and cellobiose). Hydrogen gas (18 mL) was produced using 3.33 mmol L−1 maltose and 20 mL of hydrogen was produced using cellobiose after 14 d of operation. Methane was not produced under any of the tested conditions. The effects of sugar concentration were also examined. Hydrogen production rates varied from 0.01 m3 d−1 m−3 to 0.09 m3 d−1 m−3. The maximum hydrogen yield ranged from 14% to 111%. Our results suggested that carbohydrates, such as maltose and cellobiose, are suitable carbon sources for hydrogen production, when methanogens are suppressed.

Hydrogen gas production with an electroformed Ni mesh cathode catalysts in a single-chamber microbial electrolysis cell (MEC)

Microbial electrolysis cells (MECs) are generally regarded as a promising future technology for manufacturing green hydrogen from organic material present in wastewaters and other renewable energy sources. However, the development of inexpensive and high-efficient cathode catalyst is the most critical challenge for MECs to become a commercialized H2 production technology. In this study, a non-noble metal electroformed Ni mesh cathode alternatives to typical cathode material (Pt/CC) was intensively examined in a single-chamber membrane-free MEC. To the best of our knowledge, the use of electroformed Ni mesh as the MEC cathode catalyst has not been reported so far. The MEC was operated in fed-batch mode and the performance of the Ni mesh cathode was compared with that of Pt/CC cathode in terms of columbic efficiencies (75 ± 4% vs. 72.7 ± 1%), overall hydrogen recovery (89.3 ± 4% vs. 90.9 ± 3%), overall energy efficiency (62.9 ± 5% vs. 69.1 ± 2%), the maximum volumetric hydrogen production rate (4.18 ± 1 m3 H2/m3 d vs. 4.25 ± 1 m3 H2/m3 d), volumetric current density (312 ± 9 A/m3 vs. 314 ± 5 A/m3). The obtained results in this study highlight the great potential of using the electroformed Ni mesh catalysts as a viable cathode material for hydrogen production in MECs.

Development of exoelectrogenic bioanode and study on feasibility of hydrogen production using abiotic VITO-CoRE™ and VITO-CASE™ electrodes in a single chamber microbial electrolysis cell (MEC) at low current densities

Single chamber membrane-free microbial electrolysis cell (MEC) was operated for the assessment of exoelectrogenic bacteria (EB) growth at carbon felt anode and resultant hydrogen (H2) production at abiotic cathodes, made using cold rolling (VITO-CoRE™) and casting (VITO-CASE™) methods. Progressive enrichment of EB was observed on anode during 70days of operation at an applied potential of +0.2V vs Ag/AgCl, and a maximum current density (CD) of 330.59mA/m2 (1.38mA) was recorded. H2 production at selected abiotic cathodes was observed, when the enriched bioanode was coupled to them in galvanostat mode between 0.1 and 1.0mA current range for 10min each. Higher H2 production of 114.46±3.75mL/m2 was documented with VITO-CoRE™ at 0.6mA, while 102.76±3.75mL/m2 was recorded with VITO-CASE™ at 0.8mA of current application. This study demonstrates the feasibility of H2 production on abiotic cathodes using enriched bioanode at low current densities.

Hydrogen production and wastewater treatment in a microbial electrolysis cell with a biocathode.

The broad application of microbial electrolysis cells (MECs) requires a system characterized by low cost and high operational sustainability. Biocathode MECs, which only require bacteria as the cathode catalysts, can satisfy these demands and have attracted considerable attention in recent years. In this study, we have examined biocathode alternatives to the typical platinum cathode in a single-chamber, membrane-free MEC. This biocathode MEC has been used for simultaneous hydrogen production and wastewater treatment. The results showed that hydrogen production rates increased in response to an increase in voltage. At an applied voltage of 0.9 V, the biocathode MEC achieved a hydrogen production rate of 0.39 m3 m(-3) d(-1), with a current density of 134 Am(-3), chemical oxygen demand (COD) removal of 90%, a coulombic efficiency of 63%, a cathodic hydrogen recovery of 37%, and an energy efficiency based on an electricity input of 67%. The biocathode demonstrated sufficient electrocatalytic activity and achieved a performance level comparable to that of the platinum cathode. Moreover, the substrate that was used to simulate wastewater in this study was efficiently treated by the MEC.

Bioelectrochemical enhancement of hydrogen and methane production from the anaerobic digestion of sewage sludge in single-chamber membrane-free microbial electrolysis cells

Batch tests were carried out to investigate the bioelectrochemical enhancement of hydrogen and methane production from the anaerobic digestion of sewage sludge in single-chamber membrane-free microbial electrolysis cells (MEC) and non-MECs. Hydrogen and methane were produced from the anaerobic digestion of sewage sludge in all reactors. Compared with controls, hydrogen production was enhanced 1.7–5.2-fold, and methane production 11.4–13.6-fold with Ti/Ru electrodes at applied voltages of 1.4 and 1.8 V, respectively. Most of hydrogen was produced in the first 5 days of digestion and most of methane was generated after 5 days. No oxygen was detected in the biogas and no hydrogen production was detected in the control test with water. The applied voltages can enhance the removal of suspended and volatile suspended solids, increase the transformation of soluble chemical oxygen demand, accelerate the conversion of volatile fatty acids and maintain an optimal pH range for methanogen growth.

Hydrogen production using single-chamber membrane-free microbial electrolysis cells

Microbial electrohydrogenesis provides a new approach for hydrogen generation from renewable biomass. Membranes were used in all the reported microbial electrolysis cells (MECs) to separate the anode and cathode chambers. To reduce the potential losses associated with membrane and increase the energy recovery of this process, single-chamber membrane-free MECs were designed and used to investigate hydrogen production by one mixed culture and one pure culture: Shewanella oneidensis MR-1. At an applied voltage of 0.6 V, this system with a mixed culture achieved a hydrogen production rate of 0.53 m 3/day/m 3 (0.11 m 3/day/m 2) with a current density of 9.3 A/m 2 at pH 7 and 0.69 m 3/day/m 3 (0.15 m 3/day/m 2) with a current density of 14 A/m 2 at pH 5.8. Stable hydrogen production from lactic acid by S. oneidensis was also observed. Methane was detected during the hydrogen production process with the mixed culture and negatively affected hydrogen production rate. However, by employing suitable approaches, such as exposure of cathodes to air, the hydrogenotrophic methanogens can be suppressed. The current density and volumetric hydrogen production rate of this system have potential to increase significantly by further reducing the electrode spacing and increasing the ratio of electrode surface area/cell volume.