Select persulfate activation processes were demonstrated to initiate oxidation not reliant on sulfate radicals, although the underlying mechanism has yet to be identified. This study explored singlet ...oxygenation and mediated electron transfer as plausible nonradical mechanisms for organic degradation by carbon nanotube (CNT)-activated peroxymonosulfate (PMS). The degradation of furfuryl alcohol (FFA) as a singlet oxygen (1O2) indicator and the kinetic retardation of FFA oxidation in the presence of l-histidine and azide as 1O2 quenchers apparently supported a role of 1O2 in the CNT/PMS system. However, the 1O2 scavenging effect was ascribed to a rapid PMS depletion by l-histidine and azide. A comparison of CNT/PMS and photoexcited Rose Bengal (RB) excluded the possibility of singlet oxygenation during heterogeneous persulfate activation. In contrast to the case of excited RB, solvent exchange (H2O to D2O) did not enhance FFA degradation by CNT/PMS and the pH- and substrate-dependent reactivity of CNT/PMS did not reflect the selective nature of 1O2. Alternatively, concomitant PMS reduction and trichlorophenol oxidation were achieved when PMS and trichlorophenol were physically separated in two chambers using a conductive vertically aligned CNT membrane. This result suggested that CNT-mediated electron transfer from organics to persulfate was primarily responsible for the nonradical degradative route.
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•DIET via conductive materials is a promising technology for anaerobic digestion.•Critical reviews on current understanding of DIET were conducted.•Relevant studies published to date ...were systematically analyzed.•Future perspectives for practical applications are proposed.
Anaerobic digestion (AD) is a microbial process that produces renewable energy in the form of methane by treating organic waste and high-strength wastewater. Recent studies have demonstrated that conductive materials can promote direct interspecies electron transfer (DIET) between exoelectrogenic bacteria and methanogenic archaea. DIET via conductive materials is more effective for methane production than interspecies electron transfer using electron carriers such as hydrogen, a principal route of methane production in conventional AD. This critical review presents the current understanding of DIET via conductive materials for methane production, summarizes the relevant studies published to date, and analyzes these studies with regard to conductive materials, substrates, inocula, performance, and microorganisms. Based on this analysis, possible future directions are suggested for practical DIET applications via conductive materials in AD.
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•GAC supplementation significantly increased methane production.•Increased methane production was mainly due to biomass attached to GAC.•Geobacter, Methanospirillum, and Methanolinea ...were enriched on GAC.•Direct interspecies electron transfer via GAC was generated.
Direct interspecies electron transfer (DIET) via conductive materials can provide significant benefits to anaerobic methane formation in terms of production amount and rate. Although granular activated carbon (GAC) demonstrated its applicability in facilitating DIET in methanogenesis, DIET in continuous flow anaerobic reactors has not been verified. Here, evidences of DIET via GAC were explored. The reactor supplemented with GAC showed 1.8-fold higher methane production rate than that without GAC (35.7 versus 20.1±7.1mL-CH4/d). Around 34% of methane formation was attributed to the biomass attached to GAC. Pyrosequencing of 16S rRNA gene demonstrated the enrichment of exoelectrogens (e.g. Geobacter) and hydrogenotrophic methanogens (e.g. Methanospirillum and Methanolinea) from the biomass attached to GAC. Furthermore, anodic and cathodic currents generation was observed in an electrochemical cell containing GAC biomass. Taken together, GAC supplementation created an environment for enriching the microorganisms involved in DIET, which increased the methane production rate.
The antimicrobial properties of graphene‐based membranes such as single‐layer graphene oxide (GO) and modified graphene oxide (rGO) on top of cellulose ester membrane are reported in this study. rGO ...membranes are made from GO by hydriodic acid (HI) vapor treatment. The antibacterial properties are tested after 3 h contact time with selected model bacteria. Complete bacterial cell inactivation is found only after contact with rGO membranes, while no significant bacterial inactivation is found for the control i) GO membrane, ii) the mixed cellulose ester support, and the iii) rGO membrane after additional washing that removes the remaining HI. This indicates that the antimicrobial effect is neither caused by the graphene nor the membrane support. The antimicrobial effect is found to be conclusively linked to the HI eliminating microbial growth, at concentrations from 0.005%. These findings emphasize the importance of caution in the reporting of antimicrobial properties of graphene‐based surfaces.
The effect of the reduction methods and degree using hydriodic acid (HI) on the antimicrobial property of graphene oxide (GO) membrane is studied. Stacked GO and reduced graphene oxide membranes display no significant antimicrobial property except when the membrane is reduced chemically by HI vapor. The antimicrobial property is linked to the HI residue rather than an intrinsic property of GO.
In this paper, the effect of the composition of a nonsolvent bath on the physicochemical properties of the polyvinylidene fluoride (PVDF) ultrafiltration membranes were comprehensively investigated ...using the nonsolvent‐induced phase separation method. Three additives (ethanol, glycerol, or NaCl) were added to the water coagulation bath respectively to obtain different membranes. It was found that the microstructure of the membranes changed from finger‐like structure to the sponge‐like structure with the increase of additives concentration, which successfully improved the retention and mechanical properties of the membranes. In addition, the membrane surface became smoother and more hydrophilic. The membrane fabricated in 30 wt% glycerol bath exhibited outstanding comprehensive properties of retention and anti‐fouling, with a water flux of 243.5 L/(m2 h), a bovine serum albumin rejection of more than 90%, and a flux recovery rate of 97%. From mechanism analysis, the addition of ethanol, glycerol, or NaCl to the coagulation bath altered the thermodynamic stability of the polymer system, and slowed down the rate of solvent and nonsolvent diffusion from a kinetic perspective. This research provides important clues for optimizing the membrane properties, such as flux, rejection, and strength.
The changes in the coagulation bath can adjust the microstructure of the membrane and can affect the performance of the membrane.
Air-cathode microbial fuel cells (MFCs) were operated with variation of interspatial distance (0, 3, 6, and 9 mm), and the electrochemical performance and microbial community were comparatively ...evaluated. In polarization analysis the highest power densities (325 mW/m2) was obtained with an electrode spacing of 6 mm showing high capacitance and low charge transfer resistance. The MFC with 0 mm spacing resulted in much lower power density (53 mW/m2) than the other distances possibly due to high oxygen diffusion from the cathode. To compare the anode bacterial community compositions between biomass attached on the anodic electrodes, high throughput sequencing was performed. The community analyses results revealed that the three different clusters of Geobacter belonging to the Deltaproteobacteria were specifically enriched. The cluster I and II of Geobacter were most abundantly distributed in the 0 mm distanced sample which was exposed to relatively higher dissolved oxygen conditions while that of the cluster III was enriched in the 3, 6, and 9 mm samples. These results suggested that the cluster I and II of Geobacter species might survive better under relatively higher oxygen conditions than the cluster III Geobacter. On the other hand, relatively higher voltage and max power density were generated in the 3, 6, and 9 mm distanced MFC systems, where the cluster III Geobacter was highly enriched conditions. These results also suggested that the cluster III Geobacter might efficiently generate higher voltage and maximum power density than the other Geobacter clusters under oxygen limited conditions in air-cathode MFC system.
Pseudomonas aeruginosa is a well-known pathogenic bacterium that forms biofilms and produces virulence factors via quorum sensing (QS). Interfering with normal QS interactions between signal ...molecules and their cognate receptors is a developing strategy for attenuating its virulence. Here we tested the hypothesis that 6-gingerol, a pungent oil of fresh ginger, reduces biofilm formation and virulence by antagonistically binding to P. aeruginosa QS receptors. In silico studies demonstrated molecular binding occurs between 6-gingerol and the QS receptor LasR through hydrogen bonding and hydrophobic interactions. Experimentally 6-gingerol reduced biofilm formation, several virulence factors (e.g., exoprotease, rhamnolipid, and pyocyanin), and mice mortality. Further transcriptome analyses demonstrated that 6-gingerol successfully repressed QS-induced genes, specifically those related to the production of virulence factors. These results strongly support our hypothesis and offer insight into the molecular mechanism that caused QS gene repression.
Electrochemical treatment of nitrate (NO3−), nitrite (NO2−) and mixtures of nitrate and nitrite was evaluated with microbial catalysts on a cathode in three different bioelectrochemical ...denitrification systems (BEDS). The removal rates and removal percentage of nitrogen (N) compounds varied during biotic and abiotic operations. The biotic cathode using NO3−-N as an electron acceptor showed enhanced removal percentages (88%) compared to the operation with NO2−-N (85%). The simultaneous reduction of NO3−-N and NO2−-N occurred in the operation with a mixture of N compounds. The bacterial diversity from the initial inoculum (return sludge) changed at the end of bioelectrochemical denitrification operation after 55 days. The microbial community composition was different depending on the type of electron acceptor. BEDS operation with NO3−-N and NO2−-N was enriched with Proteobacteria and Firmicutes respectively. BEDS with a mixture of N electron acceptors showed enrichment with Proteobacteria. There was no clear, distinct microbial community between the cathode biofilm and suspended biomass.
•Nitrogen removal was enhanced with biocathode in comparison with abiotic cathode.•Simultaneous reduction of NO3 and NO2 was achieved by bioelectrochemical reduction.•Electron transport phenomenon of biocathode with different N ions was revealed.•Firmicutes and Proteobacteria were mostly enriched with NO3 and NO2, respectively.•Proteobacteria and Bacteroidetes were enriched with a mixture of NO3 and NO2 ions.
Bacterial biofilm formation can cause serious problems in clinical and industrial settings, which drives the development or screening of biofilm inhibitors. Some biofilm inhibitors have been screened ...from natural products or modified from natural compounds. Ginger has been used as a medicinal herb to treat infectious diseases for thousands of years, which leads to the hypothesis that it may contain chemicals inhibiting biofilm formation. To test this hypothesis, we evaluated ginger's ability to inhibit Pseudomonas aeruginosa PA14 biofilm formation. A static biofilm assay demonstrated that biofilm development was reduced by 39-56% when ginger extract was added to the culture. In addition, various phenotypes were altered after ginger addition of PA14. Ginger extract decreased production of extracellular polymeric substances. This finding was confirmed by chemical analysis and confocal laser scanning microscopy. Furthermore, ginger extract formed noticeably less rugose colonies on agar plates containing Congo red and facilitated swarming motility on soft agar plates. The inhibition of biofilm formation and the altered phenotypes appear to be linked to a reduced level of a second messenger, bis-(3'-5')-cyclic dimeric guanosine monophosphate. Importantly, ginger extract inhibited biofilm formation in both Gram-positive and Gram-negative bacteria. Also, surface biofilm cells formed with ginger extract detached more easily with surfactant than did those without ginger extract. Taken together, these findings provide a foundation for the possible discovery of a broad spectrum biofilm inhibitor.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Continuously feeding influent wastewater containing diverse bacterial species to a wastewater treatment activated sludge bioreactor may influence the activated sludge bacterial community temporal ...dynamics. To explore this possibility, this study tracked influent wastewater and activated sludge bacterial communities by pyrosequencing 16S rRNA genes from four full-scale wastewater treatment plants over a 9-month period. The activated sludge communities showed significantly higher richness and evenness than the influent wastewater communities. Furthermore, the two communities were different in composition and temporal dynamics. These results demonstrate that the impact of the influent wastewater communities on the activated sludge communities was weak. Nevertheless, 4.3–9.3% of the operational taxonomic units (OTUs) detected in the activated sludge were shared with the influent wastewater, implying contribution from influent wastewater communities to some extent. However, the relative OTU abundance of the influent wastewater was not maintained in the activated sludge communities (i.e., weak neutral assembly). In addition, the variability of the communities of the shared OTUs was moderately correlated with abiotic factors imposed to the bioreactors. Taken together, temporal dynamics of activated sludge communities appear to be predominantly explained by species sorting processes in response to influent wastewater communities.
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•The temporal variation of influent and bioreactor bacterial communities was evaluated.•The two communities differed in terms of diversity and composition.•Small portion of bioreactor community was shared with influent community.•The influent relative species abundance was not maintained in the bioreactor.•Species sorting processes explained a majority of the community temporal dynamics.
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