Microbial fuel cells (MFCs) are a promising technology to recover electrical energy from different types of waste. However, the power density of MFCs for practical applications is limited by the ...anode performance, mainly resulting from low bacterial loading capacity and low extracellular electron transfer (EET) efficiency. In this study, an open three-dimensional (3D) structured electrode was fabricated using a natural loofah sponge as the precursor material. The loofah sponge was directly converted into a continuous 3D macroporous carbon material via a simple carbonization procedure. The loofah sponge carbon (LSC) was decorated with nitrogen-enriched carbon nanoparticles by cocarbonizing polyaniline-hybridized loofah sponges to improve their microscopic structures. The macroscale porous structure of the LSCs greatly increased the bacterial loading capacity. The microscale coating of carbon nanoparticles favored EET due to the enhanced interaction between the bacteria and the anode. By using a single-chamber MFC equipped with the fabricated anode, a power density of 1090 ± 72 mW m–2 was achieved, which is much greater than that obtained by similarly sized traditional 3D anodes. This study introduces a promising method for the fabrication of high-performance anodes from low-cost, sustainable natural materials.
The reductive dechlorination of pentachlorophenol (PCP) by Geobacter sulfurreducens in the presence of different biochars was investigated to understand how biochars affect the bioreduction of ...environmental contaminants. The results indicated that biochars significantly accelerate electron transfer from cells to PCP, thus enhancing reductive dechlorination. The promotion effects of biochar (as high as 24-fold) in this process depend on its electron exchange capacity (EEC) and electrical conductivity (EC). A kinetic model revealed that the surface redox-active moieties (RAMs) and EC of biochar (900 °C) contributed to 56% and 41% of the biodegradation rate, respectively. This work demonstrates that biochars are efficient electron mediators for the dechlorination of PCP and that both the EC and RAMs of biochars play important roles in the electron transfer process.
Three-dimensional (3D) electrodes have been intensively investigated as alternatives to conventional plate electrodes in the development of high-performance microbial fuel cells (MFCs). However, the ...energy output of the MFCs with the 3D anodes is still limited for practical applications. In this study, a 3D anode modified with a nano-structured capacitive layer is prepared to improve the performance of an microbial fuel cell (MFC). The capacitive layer composes of titanium dioxide (TiO sub(2)) and egg white protein (EWP)-derived carbon assembled core-shell nanoparticles, which are integrated into loofah sponge carbon (LSC) to obtain a high-capacitive 3D electrode. The as-prepared 3D anode produces a power density of 2.59 + or - 0.12 W m super(-2), which is 63% and 201% higher than that of the original LSC and graphite anodes, respectively. The increased energy output is contributed to the enhanced electrochemical capacitance of the 3D anodes as well as the synergetic effects between TiO sub(2) and EWP-derived carbon due to their unique properties, such as relatively high surface area, good biocompatibility, and favorable surface functionalization for interfacial microbial electron transfer. The results obtained in this study will benefit the optimized design of new 3D materials to achieve enhanced performance in MFCs.
The impacts of exogenous or endogenous quorum sensing (QS) signaling molecules on mixed-culture electroactive biofilms (EABs), especially extracellular polymeric substances (EPS) and exoelectrogens ...using direct electron transfer mechanism inside EABs are poorly understood. This research focuses on the influence of acylhomoserine lactones (AHLs), the most common QS signaling molecules for gram negative bacteria, on mixed-culture EABs. Results indicated that both exogenous and endogenous AHLs played the role as regulators to improve the electrochemical activities of EABs. The energy recovery of MFCs increased from 20.5% ± 3.9% to 28.3% ± 4.1% with endogenous AHLs and further rose to 36.2% ± 5.1% with exogenous AHLs, and the start-up period of MFCs shortened from 13 days to 10 days with endogenous AHLs and further reduced to 4 days in the presence of exogenous AHLs. The influences of exogenous and endogenous AHLs were non-instantaneous. They improved some intrinsic properties, i.e. the electrode-associated biomass, the biofilm compactness and the ratio of live/dead cells to obtain superior EABs. Meanwhile, both endogenous and exogenous AHLs increased the concentration and redox activities of EPS. Besides, endogenous AHLs enhanced the diversity of EPS components. Noteworthily, the relative abundance of Geoboacter sp. which is the typical microbe using direct electron transfer mechanism is raised by exogenous AHLs, though so far neither known chemical QS-related gene nor protein has been reported in this genus. These findings will increase the current understanding of QS in EABs and open up an opportunity for regulating mixed-culture MFCs via QS.
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•N-acylhomoserine lactones (AHLs) promote energy recovery of mixed-culture MFC.•Both exogenous and endogenous AHLs improve electrochemical activity of biofilms.•Endogenous AHLs enhanced the diversity of extracellular polymeric substances (EPS).•AHLs result in higher concentration and redox activities of EPS.•AHLs raise proportions of live cells and Geobacter sp. to obtain superior biofilms.
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•Paddy soil contaminated with benzoate incubated with hematite and magnetite.•Iron oxides addition enhanced methanogenic benzoate degradation by 25–53%.•The facilitated syntrophy ...might involve direct interspecies electron transfer.•Bacillaceae, Peptococcaceae, and Methanobacterium are potentially involved.
Recent studies have suggested that conductive iron oxide minerals can facilitate syntrophic metabolism of the methanogenic degradation of organic matter, such as ethanol, propionate and butyrate, in natural and engineered microbial ecosystems. This enhanced syntrophy involves direct interspecies electron transfer (DIET) powered by microorganisms exchanging metabolic electrons through electrically conductive minerals. Here, we evaluated the possibility that conductive iron oxides (hematite and magnetite) can stimulate the methanogenic degradation of benzoate, which is a common intermediate in the anaerobic metabolism of aromatic compounds. The results showed that 89–94% of the electrons released from benzoate oxidation were recovered in CH4 production, and acetate was identified as the only carbon-bearing intermediate during benzoate degradation. Compared with the iron-free controls, the rates of methanogenic benzoate degradation were enhanced by 25% and 53% in the presence of hematite and magnetite, respectively. This stimulatory effect probably resulted from DIET-mediated methanogenesis in which electrons transfer between syntrophic partners via conductive iron minerals. Phylogenetic analyses revealed that Bacillaceae, Peptococcaceae, and Methanobacterium are potentially involved in the functioning of syntrophic DIET. Considering the ubiquitous presence of iron minerals within soils and sediments, the findings of this study will increase the current understanding of the natural biological attenuation of aromatic hydrocarbons in anaerobic environments.
The extracellular electron transfer (EET) efficiency in bioelectrochemical systems has been proven to be dependent on anode potentials. To explore the underlying mechanism, previous studies have ...mainly focused on EET conduit and bacterial biomass but rarely concerned with the role of extracellular polymeric substances (EPS) surrounding electroactive cells. In this study, the response of Geobacter biofilms to anode potentials was investigated with a special emphasis on the mechanistic role of EPS. The electrochemical activities and cell viabilities of Geobacter soli biofilms were simultaneously attenuated at 0.4 and 0.6 V compared to −0.2 and 0 V. It was found that the biofilms (especially the biofilm region closer to electrode surface) grown at −0.2 and 0 V produced relatively more extracellular redox-active proteins and less extracellular polysaccharides, which conferred higher electron accepting/donating capacities to EPS and consequently facilitated EET. Meanwhile, electrically nonconductive extracellular polysaccharide-dominated interior layers were formed in the biofilms grown at 0.4 and 0.6 V, which limited direct EET but might serve as physical barriers for protecting cells in these biofilms from the increasing stress by poised electrodes. These results demonstrated that the production of EPS under different anode potentials might be finely regulated by cells to keep balance between EET efficiency and cell-protection. This study provides a new insight to investigate the Geobacter biofilms coping with various environments, and is useful for optimizing electrochemical activity of anode biofilms.
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•Highest EET and cell viability observed in biofilms grown at −0.2 and 0 V.•Heterogeneity is elucidated in spatial distribution of both viable cells and EPS.•Electrochemical activity of biofilm is positively related to redox activity of EPS.•Polysaccharide-dominated interior layers of EPS in 0.4 and 0.6 V biofilms hinder EET.
Composting is an efficient way to convert organic waste into fertilizers. However, waste materials often contain large amounts of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) ...that can reduce the efficacy of antibiotic treatments when transmitted to humans. Because conventional composting often fails to remove these compounds, we evaluated if hyperthermophilic composting with elevated temperature is more efficient at removing ARGs and MGEs and explored the underlying mechanisms of ARG removal of the two composting methods. We found that hyperthermophilic composting removed ARGs and MGEs more efficiently than conventional composting (89% and 49%, respectively). Furthermore, the half-lives of ARGs and MGEs were lower in hyperthermophilic compositing compared to conventional composting (67% and 58%, respectively). More-efficient removal of ARGs and MGEs was associated with a higher reduction in bacterial abundance and diversity of potential ARG hosts. Partial least-squares path modeling suggested that reduction of MGEs played a key role in ARG removal in hyperthermophilic composting, while ARG reduction was mainly driven by changes in bacterial community composition under conventional composting. Together these results suggest that hyperthermophilic composting can significantly enhance the removal of ARGs and MGEs and that the mechanisms of ARG and MGE removal can depend on composting temperature.
Abstract
Iron oxides and humic substances (humics) have substantial effects on biochemical processes, such as methanogenesis, due to their redox reactivity and ubiquitous presence. This study aimed ...to investigate how methanogenesis is affected by the common occurrence of these compounds, which has not been considered to date. The experiment was conducted with anoxic paddy soil microcosms receiving a humics surrogate compound (anthraquinone-2,6-disulfonate, AQDS) and three iron(III) oxides (ferrihydrite, hematite, and magnetite) differing in crystallinity and conductivity. Ferrihydrite suppressed methanogenesis, whereas AQDS, hematite, and magnetite facilitated methanogenesis. CH4 production in co-occurring ferrihydrite + AQDS, hematite + AQDS, and magnetite + AQDS cultures was 4.1, 1.3, and 0.9 times greater than the corresponding cultures without AQDS, respectively. Syntrophic cooperation between Geobacter and Methanosarcina occurred in the methanogenesis-facilitated cultures. Experimental results suggested that the conductive characteristics of iron(III) oxides was an important factor determining the methanogenic response to the co-occurrence of iron(III) oxides and humics in anaerobic paddy soil. This work indicated that the type of iron(III) oxides may significantly affect carbon cycling under anoxic conditions in natural wetlands.
This study is the first attempt to investigate the methanogenic response to the co-occurrence of iron(III) oxides and humics in anoxic paddy soil.
Abstract
Integration of methanogens with semiconductors is an effective approach to sustainable solar-driven methanogenesis. However, the H
2
production rate by semiconductors largely exceeds that of ...methanogen metabolism, resulting in abundant H
2
as side product. Here, we report that binary metallic active sites (namely, NiCu alloys) are incorporated into the interface between CdS semiconductors and
Methanosarcina barkeri
. The self-assembled
Methanosarcina barkeri
-NiCu@CdS exhibits nearly 100% CH
4
selectivity with a quantum yield of 12.41 ± 0.16% under light illumination, which not only exceeds the reported biotic-abiotic hybrid systems but also is superior to most photocatalytic systems. Further investigation reveal that the Ni-Cu-Cu hollow sites in NiCu alloys can directly supply hydrogen atoms and electrons through photocatalysis to the
Methanosarcina barkeri
for methanogenesis via both extracellular and intracellular hydrogen cycles, effectively turning down the H
2
production. This work provides important insights into the biotic-abiotic hybrid interface, and offers an avenue for engineering the methanogenesis process.
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