Although nitric oxide (NO) emissions from anaerobic ammonium oxidation (anammox)-based processes were reported previously, the NO production pathways are poorly understood. Here, we investigated the ...NO production pathways in anammox granules in detail by combining 15N-stable isotope tracer experiments with various inhibitors, microsensor measurements, and transcriptome analysis for key genes of NO2 – reduction. NO was emitted from the anammox granules, which account for 0.07% of the N2 emission. 15N-stable isotope-tracer experiments indicated that most of the N2 was produced by anammox bacteria, whereas NO was produced from NO2 – reduction by anammox and denitrifying bacteria. The NO emission rate was highest at pH 8.0 and accelerated by increasing NH4 + and NO2 – concentrations in the culture media. The microsensor analyses showed the in situ NO production rate was highest in the outer layer of the anammox granule where anammox activity was also highest. The detected in situ NO concentrations of up to 2.7 μM were significantly above physiological thresholds known to affect a wide range of microorganisms present in wastewater. Hence, NO likely plays pivotal roles in the microbial interactions in anammox granules, which needs to be further investigated.
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IJS, KILJ, NUK, PNG, UL, UM
Nitrous oxide (N2O) production pathway in a signal-stage nitritation-anammox sequencing batch reactor (SBR) was investigated based on a multilateral approach including real-time N2O monitoring, N2O ...isotopic composition analysis, and in-situ analyses of spatial distribution of N2O production rate and microbial populations in granular biomass. N2O emission rate was high in the initial phase of the operation cycle and gradually decreased with decreasing NH4+ concentration. The average emission of N2O was 0.98 ± 0.42% and 1.35 ± 0.72% of the incoming nitrogen load and removed nitrogen, respectively. The N2O isotopic composition analysis revealed that N2O was produced via NH2OH oxidation and NO2− reduction pathways equally, although there is an unknown influence from N2O reduction and/or anammox N2O production. However, the N2O isotopomer analysis could not discriminate the relative contribution of nitrifier denitrification and heterotrophic denitrification in the NO2− reduction pathway. Various in-situ techniques (e.g. microsensor measurements and FISH (fluorescent in-situ hybridization) analysis) were therefore applied to further identify N2O producers. Microsensor measurements revealed that approximately 70% of N2O was produced in the oxic surface zone, where nitrifiers were predominantly localized. Thus, NH2OH oxidation and NO2 reduction by nitrifiers (nitrifier-denitrification) could be responsible for the N2O production in the oxic zone. The rest of N2O (ca. 30%) was produced in the anammox bacteria-dominated anoxic zone, probably suggesting that NO2− reduction by coexisting putative heterotrophic denitrifiers and some other unknown pathway(s) including the possibility of anammox process account for the anaerobic N2O production. Further study is required to identify the anaerobic N2O production pathways. Our multilateral approach can be useful to quantitatively examine the relative contributions of N2O production pathways. Good understanding of the key N2O production pathways is essential to establish a strategy to mitigate N2O emission from biological nitrogen removal processes.
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•N2O production pathways were studied by N2O isotopic, FISH, and microsensor analyses.•Ca. 70% of N2O was produced in nitrifiers-dominated oxic surface zone of granules.•The rest of N2O (30%) was produced in the anammox bacteria-dominated anoxic zone.•Overall, N2O was produced via NH2OH oxidation and NO2− reduction pathways equally.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
An autotrophic partial nitrification granule. Display omitted
•The detection frequency of clones related to Nitrosomonas AOB was 62%.•Hydroxylamine oxidation was a key N2O production pathway in PN ...granules.•AOB were dominant and N2O was produced in the upper 200μm of PN granules.•N2O emission increased with increasing DO concentration.•In situ analyses explained N2O emission mechanisms in the PN process.
The effects of dissolved oxygen (DO) and pH on nitrous oxide (N2O) production rates and pathways in autotrophic partial nitrification (PN) granules were investigated at the granular level. N2O was primarily produced by betaproteobacterial ammonia-oxidizing bacteria, mainly Nitrosomonas europaea, in the oxic surface layer (<200μm) of the autotrophic PN granules. N2O production increased with increasing bulk DO concentration owing to activation of the ammonia (i.e., hydroxylamine) oxidation in this layer. The highest N2O emissions were observed at pH 7.5, although the ammonia oxidation rate was unchanged between pH 6.5 and 8.5. Overall, the results of this study suggest that in situ analyses of PN granules are essential to gaining insight into N2O emission mechanisms in a granule.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
ABSTRACT
Cryoconite granules are naturally occurring microbial structures on glacier surfaces worldwide. They play a key role in carbon and nitrogen cycling in glacier ecosystems and can accelerate ...the melting of snow and ice. However, detailed mechanism of nitrogen cycling in cryoconite granules remains unclear. Here, we demonstrate that redox stratification affects the spatial distribution of N cycling processes in cryoconite granules. Based on microsensor measurements for O2, NH4+, NO2– and NO3–, we identified the presence of fine-scale redox stratification within cryoconite granules. Cyanobacteria at the surface layer of the granules created oxic conditions, whereas the inner core of the granules was anoxic. Metatranscriptomic analyses indicated the active occurrences of nitrification in the inner core, whereas denitrification actively occurred both in the inner core and the surface layer of the granules. Cyanobacteria in the inner core of the granules were inactive, and likely dead and being degraded, providing carbon and nitrogen to support nitrifiers and denitrifiers. Quantities of nitrification genes/transcripts were greater in large cryoconite granules than small ones, most likely because nitrogen substrates were more abundantly present in the inner core of large granules due to distinct redox stratification. Our results suggest that the development of a granular structure of cryoconite granules can largely affect carbon and nitrogen cycling on glaciers.
Development of layered microbial structure and resulting redox stratification influence the nitrogen cycling within cryoconite granules, naturally occurring microbial structures found in glacier environments.
An ionophore-doped sensing membrane phosphate (PO4) microsensor based on bis(dibromophenylstannyl)methane (Bis microsensor) is described. The Bis microsensor showed a Nernstian response. The response ...of the Bis microsensor was log-linear down to a monohydrogen phosphate ion (HPO42−) concentration of 0.5 μM (corresponding to 1.0 μM of orthophosphate at pH 7.2), whereas the detection limit of PO4-microsensors based on trialkyl/aryltin chloride was 50 μM of HPO42−. The Bis microsensor showed excellent selectivity for HPO42− against nitrite, nitrate, chloride, bicarbonate and sulfate, as compared with PO4 microsensors based on trialkyl/aryltin chloride. Dissolved oxygen, which is known to interfere with the response of a previously developed cobalt-based potentiometric solid-state PO4 microsensor, had no effect on the response of the ionophore-doped sensing membrane-type microsensors described herein. Only OH− (i.e., pH) interfered with the ionophore-doped sensing membrane-type microsensors.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Anaerobic ammonium oxidation (anammox) is a promising process for NH4+-rich wastewaters such as anaerobic digester liquids. In the present study, we investigated various properties of an up-flow ...column reactor containing anammox granules and fed with a real digester liquid at four different concentrations (Phases 1 to 4). The efficiencies of NH4+ and NO2− removal decreased by up to 32% and 42%, respectively, in the digester-liquid-fed reactor (reactor-DL). When the performance of reactor-DL deteriorated, the community structure, spatial distribution, and in situ anammox activity in the two reactors were further investigated using 16S rRNA gene-based phylogenetic analysis, fluorescence in situ hybridization (FISH), and microelectrode measurements. The phylogenetic analysis and FISH results showed that non-anammox bacteria were predominant in the granule outer layers in reactor-DL, whereas anammox bacteria still dominated the granule interiors. Microelectrode measurements showed clear evidence of NH4+ oxidation activity in the interiors of granules from reactor-DL. Batch experiments using anammox granules at different acetate concentrations indicated that concentrations up to 50 mM had no effects on the anammox activity, whereas inorganic carbon uptake decreased in the presence of acetate. The present study clearly shows that the anammox activity and anammox bacterial density in the granules were maintained after feeding the digester liquid to the reactor for 140 days.
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•Digester liquids were fed to an anammox reactor.•Anammox activity and bacterial density were lower in the outer layer of granules.•Number of coexisting non-anammox bacteria increased in the outer layer of granules.•Anammox activity in the inner part of the granules was maintained.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Bottom hypoxia and consequential hydrogen sulfide (H
S) release from sediment in eutrophic estuaries is a major global environmental issue. We investigated dissolved oxygen, pH and H
S concentration ...profiles with microsensors and by sectioning sediment cores followed by colorimetric analysis. The results of these analyses were then compared with the physicochemical properties of the bottom water and sediment samples to determine their relationships with H
S production in sediment. High organic matter and fine particle composition of the sediment reduced the oxidation-reduction potential, stimulating H
S production. Use of a microsensor enabled measurement of H
S concentration profiles with submillimetre resolution, whereas the conventional sediment-sectioning method gave H
S measurements with a spatial resolution of 10 mm. Furthermore, microsensor measurements revealed H
S consumption occurring at the sediment surface in both the microbial mat and the sediment anoxic layer, which were not observed with sectioning. This H
S consumption prevented H
S release into the overlying water. However, the microsensor measurements had the potential to underestimate H
S concentrations. We propose that a combination of several techniques to measure microbial activity and determine its relationships with physicochemical properties of the sediment is essential to understanding the sulfur cycle under hypoxic conditions in eutrophic sediments.
Expanded graphite (EG) has been shown to be able to store a significant amount of sodium ions. Understanding the alkali metal ion storage in EG is of importance for improving EG electrode ...performance. In this work, the effect of interlayer distance of pure EG on sodium ion storage was investigated using the density functional theory calculation method. EG structure models with interlayer distances ranging from 3.4 Å to 10.0 Å were simulated. It was found that EG can store a fairly large amount of sodium ions through an intercalation mechanism without any contributions from the co-intercalation mechanism or adsorption mechanism if the interlayer distance is larger than 4.4 Å and smaller than 6.0 Å. It was also found that an interlayer distance of 6.0 Å gives strong binding energy of sodium ions with EG forming thermodynamically stable sodium-graphite intercalation compound (Na-GIC). However, when the interlayer distance becomes larger than 6.0 Å, the binding energy between sodium ions and EG becomes weaker. Computational results have also shown that the enthalpy of formation of the Na-GIC of EG is energetically more favourable when the interlayer distance is increased. An optimal
d
-spacing of EG for sodium ion storage was identified in this work. These findings provide atomistic insights into sodium ion storage in EG, providing guidelines for the design of graphite-based anode materials for sodium-ion batteries.
Expanded graphite with an interlayer distance of 4.4 Å enables sodium ion intercalation and thermodynamically most stable sodium-graphite intercalation compound can be formed when the interlayer distance reaches 6.0 Å.
Diglyme co-intercalation with sodium ion (Na
+
) into graphite can enable the use of graphite as a potential anode for sodium-ion batteries (NIBs). However, the presence of diglyme molecules in Na
+
...intercalated graphite limits Na
+
storage capacity and increases volume changes. In this work, the effect of functionalising diglyme molecules with fluoro and hydroxy groups on Na
+
storage properties in graphite were computationally studied. It was found that the functionalisation can significantly alter the binding between sodium and the solvent ligand as well as between the sodium-solvent complex and the graphite. The hydroxy-functionalised diglyme exhibits the strongest binding to the graphite of the other functionalised diglyme compounds considered. The calculations also reveal that the graphene layer affects the electron distribution on the diglyme molecule and Na, so the diglyme complexed Na binds more strongly to the graphene layer than the Na alone. We also propose a mechanism for the early stages of the intercalation mechanism that involves a reorientation of the sodium-diglyme complex and suggest how the solvent can be designed to optimise the co-intercalation process.
Binding of F-diglyme and OH-diglyme derivatives could be effectively used to tune the co-intercalation of Na into graphite.
Assessing the environmental, health, and climate impacts of bioaerosols requires knowledge of their size and abundance. These two properties were assessed through daily measurements of chemical ...tracers for pollens (sucrose, fructose, and glucose), fungal spores (mannitol and glucans), and Gram-negative bacterial endotoxins in two particulate matter (PM) size modes: fine particles (< 2.5 µm) and coarse particles (2.5–10 µm) as determined by their aerodynamic diameter. Measurements were made during the spring tree pollen season (mid-April to early May) and late summer ragweed season (late August to early September) in the Midwestern US in 2013. Under dry conditions, pollen, and fungal spore tracers were primarily in coarse PM (> 75 %), as expected for particles greater than 2.5 µm. Rainfall on 2 May corresponded to maximum atmospheric pollen tracer levels and a redistribution of pollen tracers to the fine PM fraction (> 80 %). Both changes were attributed to the osmotic rupture of pollen grains that led to the suspension of fine-sized pollen fragments. Fungal spore tracers peaked in concentration following spring rain events and decreased in particle size, but to a lesser extent than pollens. A short, heavy thunderstorm in late summer corresponded to an increase in endotoxin and glucose levels, with a simultaneous shift to smaller particle sizes. Simultaneous increase in bioaerosol levels and decrease in their size have significant implications for population exposures to bioaerosols, particularly during rain events. Chemical mass balance (CMB) source apportionment modeling and regionally specific pollen profiles were used to apportion PM mass to pollens and fungal spores. Springtime pollen contributions to the mass of particles < 10 µm (PM10) ranged from 0.04 to 0.8 µg m−3 (0.2–38 %, averaging 4 %), with maxima occurring on rainy days. Fungal spore contributions to PM10 mass ranged from 0.1 to 1.5 µg m−3 (0.8–17 %, averaging 5 %), with maxima occurring after rain. Overall, this study defines changes to the fine- and coarse-mode distribution of PM, pollens, fungal spores, and endotoxins in response to rain in the Midwestern United States and advances the ability to apportion PM mass to pollens.
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