Single-chamber Microbial Electrolysis Cell Research Articles

Bio-Electrochemical Enhancement of Hydrogen and Methane Production in a Combined Anaerobic Digester (AD) and Microbial Electrolysis Cell (MEC) from Dairy Manure

Anaerobic digestion (AD) is a biological-based technology that generates methane-enriched biogas. A microbial electrolysis cell (MEC) uses electricity to initiate bacterial oxidization of organic matter to produce hydrogen. This study determined the effect of energy production and waste treatment when using dairy manure in a combined AD and MEC (AD-MEC) system compared to AD without MEC (AD-only). In the AD-MEC system, a single chamber MEC (150 mL) was placed inside a 10 L digester on day 20 of the digestion process and run for 272 h (11 days) to determine residual treatment and energy capacity with an MEC included. Cumulative H2 and CH4 production in the AD-MEC (2.43 L H2 and 23.6 L CH4) was higher than AD-only (0.00 L H2 and 10.9 L CH4). Hydrogen concentration during the first 24 h of MEC introduction constituted 20% of the produced biogas, after which time the H2 decreased as the CH4 concentration increased from 50% to 63%. The efficiency of electrical energy recovery (ηE) in the MEC was 73% (ηE min.) to 324% (ηE max.), with an average increase of 170% in total energy compared to AD-only. Chemical oxygen demand (COD) removal was higher in the AD-MEC (7.09 kJ/g COD removed) system compared to AD-only (6.19 kJ/g COD removed). This study showed that adding an MEC during the digestion process could increase overall energy production and organic removal from dairy manure.

Electroactive biofilms on surface functionalized anodes: The anode respiring behavior of a novel electroactive bacterium, Desulfuromonas acetexigens

Surface chemistry is known to influence the formation, composition, and electroactivity of electron-conducting biofilms. However, understanding of the evolution of microbial composition during biofilm development and its impact on the electrochemical response is limited. Here we present voltammetric, microscopic and microbial community analysis of biofilms formed under fixed applied potential for modified graphite electrodes during early (90 h) and mature (340 h) growth phases. Electrodes modified to introduce hydrophilic groups (-NH2, -COOH and -OH) enhance early-stage biofilm formation compared to unmodified or electrodes modified with hydrophobic groups (-C2H5). In addition, early-stage films formed on hydrophilic electrodes are dominated by the gram-negative sulfur-reducing bacterium Desulfuromonas acetexigens while Geobacter sp. dominates on -C2H5 and unmodified electrodes. As biofilms mature, current generation becomes similar, and D. acetexigens dominates in all biofilms irrespective of surface chemistry. Electrochemistry of pure culture D. acetexigens biofilms reveal that this microbe is capable of forming electroactive biofilms producing considerable current density of > 9 A/m2 in a short period of potential-induced growth (~19 h following inoculation) using acetate as an electron donor. The inability of D. acetexigens biofilms to use H2 as a sole source electron donor for current generation shows promise for maximizing H2 recovery in single-chambered microbial electrolysis cell systems treating wastewaters.

Ammonia oxidation and denitrification in a bio-anode single-chambered microbial electrolysis cell

In this study, anodic ammonia oxidation and denitrification were performed in single-chamber bioelectrochemical systems at a wide range of anodic potentials (−400 to +400 mV) versus Ag/AgCl. The low coulombic efficiencies (~30.84%) in reactors were mainly due to electrons being transferred to atmospheric oxygen through the electrode and reversal of the electrode. The removal efficiencies of acetate, ammonia, and total nitrogen were 100%, 100%, and 40.44% at +200 mV and 100%, 100%, and 50.24% at −200 mV, respectively. The nitrogen-removal mechanisms were nitrogen respiration/nitrate reduction at +200 mV and denitrification at −200 mV, and ammonia oxidation occurred by coupling with sulfate-reducing at −300 and −400 mV. Thauera, Comamonas, Alicycliphilus, Nitrosomonas, Desulforhabdus, Dethiosulfatibacter, and Desulfomicrobium were the dominant genera at the anode which participated in the nitrification/denitrification or sulfate-reducing processes. In summary, ammonia oxidation and denitrification could be coupled with carbon-removal or sulfur-reduction using a bio-anode with a suitable anodic potential.

Competing acetate consumption and production inside a microbial electrolysis cell

During dark fermentative biological hydrogen (H2) production acetate is the main metabolic end product. The subsequent anaerobic conversion of acetate to H2 is thermodynamically not favorable. In microbial electrolysis cells (MECs), these thermodynamic limits can be overcome by electroactive bacteria, using the anode as electron acceptor. In mixed culture MECs homoacetogenic bacteria can cause an unwanted decrease in H2 yield as they consume the produced H2 for acetate production, thus reversing the desired reaction. This study reveals the influence of H2 partial pressure on MEC processes and shows how to inhibit homoacetogenesis. Single chamber MECs were inoculated with mixed cultures and fed with acetate at a voltage of 0.8 V. One set was purged with a mixture of H2 and CO2, the other one with nitrogen (N2) in order to adjust the H2 partial pressure. An increase in acetate concentration was observed in MECs with high H2 partial pressure. N2 sparging inhibited homoacetogenic activity and facilitated microbial electrolysis. DNA sequencing results show that the most abundant classes were Deltaproteobacteria and Clostridia in MECs purged with N2 and H2/CO2, respectively. The results reveal the dual influence of the H2 partial pressure during MEC operation and provide new insights regarding the construction and operation of bioelectrochemical systems.

Rapid degradation of 2,4-dichloronitrobenzene in single-chamber microbial electrolysis cell with pre-acclimated bioanode: A comprehensive assessment

2,4-dichloronitrobenzene (DClNB) as a typical refractory pollutant, exists in multifarious industrial wastewater widely and poses a serious threat to the environment. An ion exchange membrane (IEM)-free microbial electrolysis cell (MEC) with pre-acclimated bioanode was built and evaluated systematically for treatment of DClNB containing wastewater. Results showed that compared with the non-acclimated or IEM-equipped MECs, the pre-acclimated IEM-free MECs had the best DClNB removal efficiency of 91.3% under COD and DClNB loading rates of nearly 1000 kg m−3 d−1 and 100 g m−3 d−1. Both of anode pre-acclimation and IEM removal reduced the electron transfer resistance by 71.1 and 194.5 Ω, respectively. Compared to the pre-acclimated IEM-equipped MEC, the cathode current efficiency of pre-acclimated IEM-free MEC increased by 13.7%. Analysis of live/dead cell staining indicated that a higher proportion of live cells was observed in the acclimated anode biofilm (66.1% vs. 47.3%), and the detoxification of DClNB in the pre-acclimated IEM-free MECs was significantly better (p < 0.05) than those of non-acclimated or IEM-equipped MECs. This study contributes to the performance improvement of the MEC process for treatment of toxic industrial wastewater.

Breaking the loop: Tackling homoacetogenesis by chloroform to halt hydrogen production-consumption loop in single chamber microbial electrolysis cells

The presence of homoacetogenesis and hydrogen production-consumption loop significantly hinders the efficient hydrogen recovery in single chamber microbial electrolysis cells (MECs). However, no effective inhibition method has been proposed against homoacetogens hitherto. In this study, we demonstrated the effectiveness of chloroform as a homoacetogen inhibitor in MECs. In small MECs (320 mL) operated in batch mode, chloroform with concentrations of 0.02% (v/v) and 0.03% (v/v) ceased homoacetogenesis with non-fermentable substrate (acetate), enhancing hydrogen yield and cathodic hydrogen recovery from 21% and 14% to 94% and 90%, respectively. Electrochemical performance was not significantly affected as current density (based on anode surface area) only decreased from 18 A/m2 to 13 A/m2 with chloroform concentration increased from 0% (v/v) to 0.03% (v/v). However, when using a fermentable substrate (glucose), the inhibition against homoacetogens by 0.01% (v/v) chloroform led to a significant decrease in current density possibly due to the decreased production of acetate, which reduced the substrate concentration for exoelectrogenesis. Nevertheless, in a larger MEC (10 L), using an immobilized sludge culture and higher glucose concentration (56 mM), 0.02% (v/v) chloroform enhanced hydrogen production rate from 0 L/L/D to 4.9 L/L/D and current density from 12-16 A/m2 to 18–21 A/m2. Microbial community analysis revealed that the homoacetogenic Acetobacterium spp. was eliminated in the cathodic biofilms and planktonic cells by chloroform. Future improvement of this method, through reducing the residual chloroform concentration and developing more environment-friendly inhibitor using similar mechanisms, may lead to the practical application in MECs.

Hydrogen Production from Makgeolli Wastewater Using a Single‐Chamber Microbial Electrolysis Cell

Domestic and industrial wastewaters are subject to the biological treatment process before discharged to environment. In that process, organic substances contained in the wastewater are degraded by microorganisms. Microbial electrolysis cells (MECs) are suitable technology for wastewater treatment, simultaneously producing hydrogen. In most case, however, a significant amount of methane instead of hydrogen is produced when the wastewater is used for MECs. Here we show that hydrogen is the main product when Makgeolli wastewater (MW) is used as a substrate in a single‐chamber MEC which was operated using acetate and MW. Although current generation profiles vary according to the substrate type and the applied voltage, hydrogen portions were maintained over 90% at −0.6 V and −0.8 V with production rates of 0.95 and 1.55 m3H2/m3/d, respectively. This result shows a possibility of implementing MECs in the real wastewater treatment and hydrogen production.

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

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

Process kinetics for the electrocatalytic hydrogen evolution reaction on carbon-based Ni/NiO nanocomposite in a single-chamber microbial electrolysis cell

To explore the process kinetics of hydrogen evolution reaction (HER) on carbon-based Ni/NiO nanocomposite in the microbial electrolysis cells (MECs), the performance was systematically studied by different time-course sampling of five parallel single-chamber MECs operated under identical operating conditions, which included the electrochemical performance of anodes and cathodes, and the mechanism and kinetics of HER. It was hypothesized that the decreased performance of the nickel cathodes was due to corrosion and Ni dissolution. These results provide valuable insights into the effects of long-term operation on MEC performance.

Maximizing biohydrogen production from water hyacinth by coupling dark fermentation and electrohydrogenesis

Biohydrogen production via dark fermentation has shown immense potential for simultaneous energy generation and waste remediation. However, the low substrate conversion rates limit its practical feasibility. Therefore, the present work attempts to develop a single chamber microbial electrolysis cell (MEC) as an additional means for biohydrogen production. Different organic substrates including simple sugars and volatile fatty acids were demonstrated as potential substrates for H2 production in MEC. The use of water hyacinth as sole substrate for H2 production was examined. Furthermore, the feasibility of using MEC for second stage energy recovery after dark fermentation was explored. The two-stage process exhibited improved performance as compared to single stage MEC process with overall hydrogen yield of 67.69 L H2/kg CODconsumed, COD removal of 70.33% and energy recovery of 46%. These results suggest that coupled dark fermentation-MEC process can be a promising means for obtaining high yield biohydrogen from water hyacinth.

Effects of applied voltage on the anode biofilm formation and extracellular polymers substances in a single chamber microbial electrolysis cell

Effects of applied voltage on the anode biofilm formation and extracellular polymers substances in a single chamber microbial electrolysis cell

Improved hydrogen production in the single-chamber microbial electrolysis cell with inhibition of methanogenesis under alkaline conditions.

The aim of this study was to investigate hydrogen production enhanced by methanogenesis inhibition in the single-chamber microbial electrolysis cell (MEC) under alkaline conditions. With 50 mM bicarbonate buffer and 1 g L−1 acetate, the MEC was tested at pH = 8.5, 9.5, 10.5, and 11.2, respectively, within 124 d operation. Effective methanogenesis inhibition in the MEC increased with pH from 8.5 to 11.2. At pH 11.2, Methanobacteriaceae reached the lowest absolute quantity (i.e., biomass and mcrA gene copy number of methanogens) within the microbial community in the cathodic biofilm among the pH values. Under the alkaline conditions, a hydrogen percentage of 85–90% and a methane percentage < 15% were achieved within 25 cycles (50 d) of operation. The maximum current density in the MEC reached 83.7 ± 1.5 A m−3 with the average electrical recovery of 171 ± 18% and overall energy recovery of 72 ± 3%. The excellent performance of the MEC at pH = 11.2 was attributed to the low abundance of methanogens within the cathodic biofilm (2.23 ± 0.46 copy per cm2), low cathodic biomass (0.12 ± 0.01 mg protein per g), and low anode potential (−0.228 mV vs. saturated calomel electrode). Results from this study should be valuable to expand applications of the MEC with methanogenesis inhibition in alkaline wastewater treatment.

Selective inhibition of methanogenesis by acetylene in single chamber microbial electrolysis cells

Microbial electrolysis cells (MECs) for hydrogen production exhibit great advantages over many other biohydrogen production techniques in terms of versatility of substrate and hydrogen yield. However, hydrogen and acetate scavenging by methanogens puts forward a great challenge to the application of single chamber MECs when using mixed culture. In this study, we investigated the feasibility of using acetylene, a low-cost fuel and chemical building block, to selectively inhibit methanogenesis in single chamber MECs. Results demonstrate that the periodical injection of low concentration acetylene (1% and 5%) can successfully inhibit methanogenesis in MECs using both acetate and glucose as substrates. Current generation by exoelectrogens and the syntrophy between fermentative bacteria and exoelectrogens, however, were not negatively affected. Compared with the classic methanogen inhibitor, 2-Bromoethanesulfonate (BES), the low concentration acetylene demonstrates superior effectiveness in MECs. These results demonstrate the great potential of using acetylene as a cost-effective inhibitor against methanogenesis in MECs.

Development of methanogens within cathodic biofilm in the single-chamber microbial electrolysis cell

The aim of this study was to investigate the development of cathodic biofilm and its effect on methane production in a single-chamber microbial electrolysis cell (MEC). The MEC with 1 g/L acetate was successfully operated within 31 cycles (∼2400 h). The maximum methane production rate and average current capture efficiency in the MEC reached 93 L/m3·d and 82%, respectively. Distinct stratification of Methanobacteriaceae within cathodic biofilm was observed after 9 cycles of operation. The relative abundance of Methanobacteriaceae in the microbial community increased from 45.3% (0–15 μm), 57.6% (15–30 μm), 66.9% (30–45 μm) to 77.2% (45–60 μm) within the cathodic biofilm. The methane production rates were positively correlated with the mcrA gene copy numbers in the cathodic biofilm. Our results should be useful to understand the mechanism of methane and hydrogen production in the MEC.

An effective method for hydrogen production in a single-chamber microbial electrolysis by negative pressure control

In this study, we construct a scalable tubular single-chamber microbial electrolysis cell that using negative pressure (40.52 kPa) to enhance the hydrogen production. The impact of negative pressure on current production, hydrogen recovery, and microbial community of microbial electrolysis cells are investigated. Negative pressure could effectively enhance the hydrogen recovery and inhibit the growth of methanogens. Consequently, the microbial electrolysis cell operated under negative pressure achieves a maximum hydrogen production rate of 7.72 ± 0.06 L L−1 d−1, which is more than four times higher that of reactor running under normal pressure (1.51 ± 0.41 L L−1 d−1). Energy quantification shows that the electrical energy recovery under negative pressure is 146.98%, which is much higher than 95.00% under normal pressure. Therefore, negative pressure control is as effective for increasing hydrogen production and energy recovery in the scalable MEC, and has a great practical application prospect. However, negative pressure cannot knick out methanogens. Once negative pressure is removed, methanogens will quickly take over and after that applying negative pressure again can only partly inhibit methane production.

Revealing the impact of hydrogen production-consumption loop against efficient hydrogen recovery in single chamber microbial electrolysis cells (MECs)

Microbial electrolysis for hydrogen production exhibited great advantages over many other biohydrogen production techniques in terms of hydrogen yield (HY) and energy efficiency (EE). With the elimination of methanogens, homoacetogens could thrive as the major hydrogen sink to impair HY and EE. However, the determination of hydrogen loss in microbial electrolysis cells (MECs) was rather controversial. In this study, we quantitatively investigated the negative impact of homoacetogens on hydrogen recovery in single chamber MECs. Hydrogen partial pressure (HPP) ranging from 0 to 40 kPa greatly affected the hydrogen consumption rate while acetate concentration ranging from 0 to 100 mM had little impact. HY base on consumed substrate was not significantly affected with less than 20 kPa HPP but decreased from 87% to 66% with 20–34 kPa HPP. And the EE based on input electricity was decreased from 160% to 48% accompanied with the increase of HPP from 7 to 34 kPa. Microbial community analysis revealed that Acetobacterium was the dominant homoacetogenic hydrogen scavenger in cathodic biofilm and planktonic cells in the single chamber MECs.

Degradation of organics extracted from dewatered sludge by alkaline pretreatment in microbial electrolysis cell.

Waste activated sludge in China are mostly subjected to dewatering process before final disposal without stabilization. This study investigated the feasibility of organics degradation and H2 production from non-stabilized dewatered sludge (DS) by microbial electrolysis cells (MECs). Alkaline pretreatment was used to disintegrate sludge matrix and solubilize organic matters in DS. Then, the treatment performance of DS supernatant in a single-chamber MEC at various applied voltages was investigated. The COD (chemical oxygen demand) removal rate increased with increasing voltage, which ranged from 26.35 to 44.92% at 0.5-0.9V. The average coulombic efficiency was 75.6%, while the cathodic hydrogen recovery was not satisfied (15.56-20.05%) with H2 production rates of 0.027-0.038m3 H2/(m3day). The reasons could be ascribed to the complexity of the substrate, H2 loss, and the confinement of configuration in scale-up. The organic matter degradation was influenced by the composition of DS. The carbohydrates could be readily used; meanwhile, the major component of the DS supernatant, i.e. proteins, was difficult to be utilized, which resulted from the low biodegradability of the transphilic fractions during the MEC operation.

Hydrogen consumption and methanogenic community evolution in anodophilic biofilms in single chamber microbial electrolysis cells under different startup modes

GeoChips based onmcrAand cytochrome genes to evaluate community structure variety of methanogens and electron transfer process.

Applied voltage optimization for denitrification process improvement by denitrifying species of Pseudomonas in microbial electrolysis cell (MEC)

Denitrification is the conversion process of nitrate to gaseous nitrogen forms carried out by bacteria commonly referred to as denitrifiers. Microbial Electrolysis Cell (MEC) is a type of bioelectrochemical system (BES) that is connected to external power source to aid the reactions. This research investigates the effect of applied voltage value on denitrification by nitrate removal efficiency of two model denitrifying species from the genus Pseudomonas in single-chambered MEC. Pseudomonas aeruginosa and Pseudomonas nitroreducens exhibited native removal efficiency at 70.62% and 68.20%, respectively. These values respectively reached up to 89.67% and 88.58% at 1.20 V, the upper limit of this study. Pseudomonas aeruginosa displayed better performance in MEC based off its produced current stability (mA) across the 0.35-1.20 V range. The effect of applied voltage on nitrate removal efficiency and setup performance was more prominent on known exoelectrogenic species of Pseudomonas such as Pseudomonas aeruginosa compared to Pseudomonas nitroreducens. Operating applied voltages of 0.35 V and 0.70 V was recommended for the application of the system based on technical and economical considerations. Further studies are needed to determine the response of the bacteria on wider range of applied voltages in MEC as well as elucidating these effects on autotrophic systems.

Electrical current generation in microbial electrolysis cells by hyperthermophilic archaea Ferroglobus placidus and Geoglobus ahangari

Few microorganisms have been examined for current generation under thermophilic (40–65°C) or hyperthermophilic temperatures (≥80°C) in microbial electrochemical systems. Two iron-reducing archaea from the family Archaeoglobaceae, Ferroglobus placidus and Geoglobus ahangari, showed electro-active behavior leading to current generation at hyperthermophilic temperatures in single-chamber microbial electrolysis cells (MECs). A current density (j) of 0.68±0.11A/m2 was attained in F. placidus MECs at 85°C, and 0.57±0.10A/m2 in G. ahangari MECs at 80°C, with an applied voltage of 0.7V. Cyclic voltammetry (CV) showed that both strains produced a sigmoidal catalytic wave, with a mid-point potential of −0.39V (vs. Ag/AgCl) for F. placidus and −0.37V for G. ahangari. The comparison of CVs using spent medium and turnover CVs, coupled with the detection of peaks at the same potentials in both turnover and non-turnover conditions, suggested that mediators were not used for electron transfer and that both archaea produced current through direct contact with the electrode. These two archaeal species, and other hyperthermophilic exoelectrogens, have the potential to broaden the applications of microbial electrochemical technologies for producing biofuels and other bioelectrochemical products under extreme environmental conditions.