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Electro-fermentation (EF) has been extensively studied for recovering hydrogen and phosphorus from waste activated sludge (WAS), while was limited for the further application due to the low hydrogen yield and phosphorus recovery efficiency. This study proposed an efficient strategy for hydrogen and vivianite recovery from the simulated sludge fermentation liquid by sacrificial iron anode in EF. The optimum hydrogen productivity and the utilization efficiency of short chain fatty acids (SCFAs) reached 45.2 mmol/g COD and 77.6% at 5 d in pH 8. Phosphate removal efficiency achieved at 90.8% at 2 d and the high crystallinity and weight percentage of vivianite (84.8%) was obtained. The functional microbes, i.e., anaerobic fermentative bacteria, electrochemical active bacteria, homo-acetogens and iron-reducing bacteria were highly enriched and the inherent interaction between the microbial consortia and environmental variables was thoroughly explored. This work may provide a theoretical basis for energy/resource recovery from WAS in the further implementation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Hydrogen-entangled electron transfer has been verified as an important extracellular pathway of sharing reducing equivalents to regulate biofilm activities within a diversely anaerobic environment, especially in microbial electrosynthesis systems. However, with a lack of useful methods for in situ hydrogen detection in cathodic biofilms, the role of hydrogen involvement in electron transfer is still debatable. Here, a cathodic biofilm was constructed in CH 4 -produced microbial electrosynthesis reactors, in which the hydrogen evolution dynamic was analyzed to confirm the presence of hydrogen-associated electron transfer near the cathode within a micrometer scale. Fluorescent in situ hybridization images indicated that a colocalized community of archaea and bacteria developed within a 58.10-μm-thick biofilm at the cathode, suggesting that the hydrogen gradient detected by the microsensor was consumed by the collaboration of bacteria and archaea. Coupling of a microsensor and cyclic voltammetry test further provided semiquantitative results of the hydrogen-associated contribution to methane generation (around 21.20% ± 1.57% at a potential of -0.5 V to -0.69 V). This finding provides deep insight into the mechanism of electron transfer in biofilm on conductive materials. IMPORTANCE Electron transfer from an electrode to biofilm is of great interest to the fields of microbial electrochemical technology, bioremediation, and methanogenesis. It has a promising potential application to boost more value-added products or pollutant degradation. Importantly, the ability of microbes to obtain electrons from electrodes and utilize them brings new insight into direct interspecies electron transfer during methanogenesis. Previous studies verified the direct pathway of electron transfer from the electrode to a pure-culture bacterium, but it was rarely reported how the methanogenic biofilm of mixed cultures shares electrons by a hydrogen-associated or hydrogen-free pathway. In the current study, a combination method of microsensor and cyclic voltammetry successfully semiquantified the role of hydrogen in electron transfer from an electrode to methanogenic biofilm., (Copyright © 2020 American Society for Microbiology.)

In comparison to precious metal catalyst especially Platinum (Pt), nickel foam (NF) owned cheap cost and unique three-dimensional (3D) structure, however, it was scarcely applied as cathode material in microbial electrolysis cell (MEC) as the intrinsic laggard electrochemical activity for hydrogen recovery. In this study, a self-assembly 3D nickel foam-graphene (NF-G) cathode was fabricated by facile hydrothermal approach for hydrogen evolution in MECs. Electrochemical analysis (linear scan voltammetry and electrochemical impedance spectroscopy) revealed the improved electrochemical activity and effective mass diffusion after coating with graphene. NF-G as cathode in MEC showed a significant enhancement in hydrogen production rate compared with nickel foam at a variety of biases. Noticeably, NF-G showed a comparable averaged hydrogen production rate (1.31 ± 0.07 mL H2 mL(-1) reactor d(-1)) to Platinum/carbon (Pt/C) (1.32 ± 0.07 mL H2 mL(-1) reactor d(-1)) at 0.8 V. Profitable energy recovery could be achieved by NF-G cathode at higher applied voltage, which performed the best hydrogen yield of 3.27 ± 0.16 mol H2 mol(-1) acetate at 0.8 V and highest energy efficiency of 185.92 ± 6.48% at 0.6 V., (Copyright © 2016 Elsevier B.V. All rights reserved.)

This work explored the feasibility of a method combining physical (sonication and base) and biological (partial fermentation) processes for sludge treatment and the effects of trehalose on the hydrogen generation of microbial electrolysis cell at 0 °C. The results demonstrated that the above pretreatment method was favorable, which promoted organics decomposing into lower molecular weight matter. The promotion of trehalose for MEC efficiency was obvious and the optimal concentration of trehalose was 50 mmol/L. With this concentration, the highest hydrogen recovery rate was 0.25 m(3)-H₂/-m(3)-reactor per day. Coulomb efficiency and energy recovery efficiency were 46.4% and 203%, respectively. Further, the consumption order of mixed substances was VFAs>proteins>carbohydrates. For microorganism community, SEM photographs illustrated that the selectivity of environmental temperature for the species of anode bacteria was strong and denaturing gradient gel electrophoresis indicated that Microbacterium and Proteobacteria were the two main species and Proteobacteria may be one of the species that produced electrons., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

High overpotential and soaring prices of the cathode electrode are the bottlenecks for the development of microbial electrolysis technology for hydrogen production. In this study, a novel one-step electrodeposition method has been attempted to fabricate electrodeposited cathodes in situ growth of Ni–Co–S, Ni–S, Co–S catalyst on nickel foam (NF) to reduce the overpotential of electrodes. Finally, a uniform nanosheet with a high specific surface area and more active sites is formed on the NF surface, resulting in a lower overpotential than plain NF. At 0.8 V, the Co–S/NF cathode produces a favorable 42% increase in hydrogen yield (0.68 m3·m−3·d−1), 40% upsurge in current density (10.6 mA/cm3) and 39% rise of cathodic recovery rate (58.0 ± 3.2%) than bare NF, followed by Ni–Co–S/NF and Ni–S/NF cathode. All the electrodeposited electrodes demonstrate enhanced current density and reduced electron losses, thereby achieving efficient hydrogen production. These innovative varieties of electrodes are highly advantageous as they are relatively inexpensive and easy to manufacture with great potential in reducing costs and further real time application in large scale. • The overpotential of nickel foam is greatly reduced by Ni/Co/S electrodeposition. • High hydrogen yield is achieved by Co–S/NF electrode in neutral condition. • Electrodeposited electrodes show high current density and low electron losses in MEC. [ABSTRACT FROM AUTHOR]

A cheap but efficient electrode material is required to explore and apply to microbial electrolysis cell (MEC) with high hydrogen evolution reaction (HER) efficiency and low over-potential loss. Pt coating carbon cloth (Pt/CC) was one of the most efficient catalyst for hydrogen production in current lab research, but it is difficult to be applied in practice because of expensive cost and week strength from the base material (carbon cloth). Thus a cheap and effective supporting base material is worth to evaluate on hydrogen recovery and loss to methane for the MEC future application. In this study, nickel foam (NF) was used as an alternative to expensive carbon cloth, and NF coated with Pt (Pt/NF) was applied and evaluated through catalytic performance, hydrogen production efficiency and economic assessment in comparison with Pt/CC. The Pt/NF showed a competitive HER performance to Pt/CC. The highest hydrogen yield was reached 0.71 ± 0.03 m 3 /m 3 ·d by Pt/NF under 0.8 V, which exceeded 6%, 10% over Pt/CC and NF, respectively. The energy efficiency relative to the electrical energy input was 127% for Pt/NF and 123%, 110% for Pt/CC and NF, respectively. For fifteen cycles, the methane content of Pt/NF got the lowest due to its higher hydrogen evolution activity. The economic analysis showed a 56% reduction when using Pt/NF as supporting base in place of carbon cloth to achieve similar performance. The linear sweep voltammetry (LSV) showed the possibility to further reduce input voltage in a long term operation. [ABSTRACT FROM AUTHOR]

Abstract: GeoChip (II) and single strand conformation polymorphism (SSCP) were used to characterize anode microbial communities of a microbial electrolysis cell (MEC). Biofilm communities, enriched in a two-chamber MEC (R1, 0.6V applied) having a coulombic efficiency (CE) of 35±4% and a hydrogen yield of 31±3%, were used as the inoculum for a new reactor (R2). After three months R2 achieved stable performance with CE=38±4% and Few changes in the predominant populations were observed from R1 to R2. Unlike sludge inoculation process in R1 in the beginning, little further elimination was aroused by community competitions in anode biofilm reformation in R2. Functional genes detection of biofilm indicated that cytochrome genes enriched soon in new reactor R2, and four genera (Desulfovibrio, Rhodopseudomonas, Shewanella and Geobacter) were likely to contribute to exoelectrogenic activity. This work also implied that symbiosis of microbial communities (exoelectrogens and others) contribute to system performance and stability. [Copyright &y& Elsevier]

Abstract: Methane production occurs during hydrogen gas generation in microbial electrolysis cells (MECs), particularly when single chamber systems are used which do not keep gases, generated at the cathode, separate from the anode. Few studies have examined the factors contributing to methane gas generation or the main pathway in MECs. It is shown here that methane generation is primarily associated with current generation and hydrogenotrophic methanogenesis and not substrate (acetate). Little methane gas was generated in the initial reaction time (<12h) in a fed batch MEC when acetate concentrations were high. Most methane was produced at the end of a batch cycle when hydrogen and carbon dioxide gases were present at the greatest concentrations. Increasing the cycle time from 24 to 72h resulted in complete consumption of hydrogen gas in the headspace (applied voltage of 0.7V) with methane production. High applied voltages reduced methane production. Little methane (<4%) accumulated in the gas phase at an applied voltage of 0.6–0.9V over a typical 24h cycle. However, when the applied voltage was decreased to 0.4V, there was a greater production of methane than hydrogen gas due to low current densities and long cycle times. The lack of significant hydrogen production from acetate was also supported by Coulombic efficiencies that were all around 90%, indicating electron flow was not altered by changes in methane production. These results demonstrate that methane production in single chamber MECs is primarily associated with current generation and hydrogen gas production, and not acetoclastic methanogenesis. Methane generation will therefore be difficult to control in mixed culture MECs that produce high concentrations of hydrogen gas. By keeping cycle times short, and using higher applied voltages (≥0.6V), it is possible to reduce methane gas concentrations (<4%) but not eliminate methanogenesis in MECs. [Copyright &y& Elsevier]

Waste sludge lysate was produced by dehydration after pyrolysis of waste activated sludge. In addition to dominant components such as protein, polysaccharide, and volatile fatty acids (VFAs), it also contained melanoidins, which produced from Maillard reaction. The inclusion of melanoidins will lead to poor biological degradation in conventional anaerobic digestion (AD). While microbial electrolysis cell (MEC) was proved an enhanced degradation of complex organic matter for hydrogen production. The results showed that under high concentration conditions, conventional AD caused the accumulation of propionic acid and slowed down the use of acetic acid, but MEC overcame the defects and increased the chemical oxygen demand (COD) removal efficiency by 40.33%, and achieved average hydrogen production rate (0.15 ± 0.05 L L−1 day−1), which was 79 times that of AD system (0.0019 ± 0.0009 L L−1 day−1). Therefore, MEC can enhanced biodegradation of the waste sludge lysate for high hydrogen production. Unlabelled Image • MEC achieved higher COD removal than AD in high concentration sludge lysate. • MEC overcame the limit of AD on VFAs utilization to degrade sludge lysate. • H 2 production was enhanced significantly in MEC than AD. [ABSTRACT FROM AUTHOR]

Microbial electrolysis cells (MECs) use exoelectrogenic microorganisms to convert organic matter into H2, although yields can vary significantly with environmental conditions, likely due to variations in microbial communities. This study was undertaken to better understand how microbial communities affect reactor function. Using wastewater as inoculum, 15 MEC reactors were operated for >50 days and subsequently five reactors were selected for further analysis. Solution (26 mL) was collected every 3–4 days for DNA extraction. DNA was hybridized to GeoChip, a comprehensive functional gene array, to examine differences in the reactor microbial communities. A large variety of microbial functional genes were observed in all reactors. Performances ranged from poor (0.1 ± 0.1 mL) to high (12.2 ± 1.0 mL) H2 production, with a maximum yield of 5.01 ± 0.43 mol H2/molglucose. The best performance was associated with higher cytochrome c genes, considerably higher exoelectrogenic bacteria (such as Shewanella, Geobacter), less methanogens and less hydrogen-utilizing bacteria. The results confirmed the possibility to obtain an effective community for hydrogen production using wastewater as inoculum. Not like fermentation, hydrogen production was significantly controlled by electron transporting process in MECs. GeoChip findings suggested that biofilm formation can be highly stochastic and that presence of dissimilatory metal-reducing bacteria and antagonistic methanogens is critical for efficient hydrogen production in MEC reactors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe anode achieved 101–743% higher of hydrogen productivity than other iron sources. • Fe anode led complete removal of phosphate within 2 d (vs. 0–39.4% in other groups). • More crystalline vivianite particles were observed in EF system assisted by Fe anode. • Homo-acetogens (78.0%), EAB (8.0%) and DIRB (2.3%) were enriched in Fe anode group. • Correlation and syntrophy between functional microbes and metabolites were explored. Electro-fermentation (EF) is a promising technology for extracting valuable metabolites from waste biomass, while its effectiveness for phosphorus recovery has received little attention. In this study, we investigated the impact of different iron sources, i.e., FeCl 3 , FeOOH, Fe 2 O 3 , zero-valent iron (ZVI), a built-in Fe anode, and stainless-steel mesh (SSM), on concurrent biohydrogen and vivianite (Fe 3 (PO 4) 2 ·8H 2 O) recovery from sludge fermentation liquid (SFL) in an EF system. Results indicated that the Fe anode group achieved the highest hydrogen productivity of 17.7 mmol/g COD at 5 d, which was 101–743% higher than that of other iron sources. The utilization efficiency of short-chain fatty acids (SCFAs) peaked at 79.1% within 5 d, which was 1.2 folds higher than that of Control (without iron addition). Moreover, the phosphate removal efficiency reached 100% within 2 d and 5 d in Fe anode and SSM group, respectively, while the other groups achieved only 0–39.4% removal. SEM and XRD analyses demonstrated the existence of vivianite particles in the recovered products in the groups of FeCl 3 , FeOOH and Fe anode. Electrochemically active bacteria (EAB), e.g., Geobacter , Comamonas , and Desulfovibrio , accounted for 3.6–60.2% of all groups. Geobacter , Azospira , Comamonas , and Desulfovibrio , which are also considered dissimilatory iron reducing bacteria (DIRB), were enriched to 0.1–40.7% in all groups. Acetoanbacterium and Acetoaerobium , typical homo-acetogens, were enriched to 78.0% in the Fe anode group, while was only 9.0–29.3% in other groups. Correlation and molecular ecological network (MEN) analyses of the functional microbial consortia further indicated the intertrophic interaction. This study provides a theoretical basis for synchronous hydrogen and phosphorus recovery from WAS in the further industrial implementation. [ABSTRACT FROM AUTHOR]

The effects of chemosynthetic and biological surfactants on accelerating hydrogen generation from waste activated sludge (WAS) is investigated in a short-cut fermentation-bioelectrochemical system. The specific experiments are conducted in a series of completely stirred tank reactors (CSTRs) and single-chamber microbial electrolysis cells (MECs). Results shows that rhamnolipid (RL) lead to a VFAs yield 1.16-fold and 3.63-fold higher over with sodium dodecylsulphate (SDS) and sodium dodecyl benzene sulfonate (SDBS) treatments in CSTRs on 72 h. By contrast, the corresponding conversion efficiency of methanogenesis is inhibited (0.18 ± 0.03% versus 1.89 ± 0.15% (SDS) and 6.63 ± 0.77% (SDBS)), which is beneficial for subsequent hydrogen production in MECs. The distribution of the acidogenesis metabolites is also affected by the types of surfactants, reflected on cascade changing of hydrogen production. Highest hydrogen yield is 12.90 mg H 2 g −1 VSS in RL-MECs, which is larger than all values that have been reported for fermentation and single-chamber MECs. Current and electrochemical impedance spectroscopy clearly demonstrate the important role of RL treatment in electron/proton transfer and the internal resistance decrease. This study demonstrate the sustainability and attractiveness of WAS short-cut fermentation-elelctrohydrogenesis, providing a sound basis for sludge stabilization and bioenergy recovery. [ABSTRACT FROM AUTHOR]