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Effects of carbon nanotube on denitrification performance of Alcaligenes sp. TB: Promotion of electron generation, transportation and consumption

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Abstract

Multi-walled carbon nanotubes (MWCNTs) promote biodegradation in water treatment, but the effect of MWCNT on denitrification under aerobic conditions is still unclear. This investigation focused on the denitrification performance of MWCNT and its toxic effects on Alcaligenes sp. TB which showed that 30 mg/L MWCNTs increased NO3- removal efficiency from 84% to 100% and decreased the NO2-and N2O accumulation rates by 36% and 17.5%, respectively. Nitrite reductase and nitrous oxide reductase activities were further increased by 19.5% and 7.5%, respectively. The mechanism demonstrated that electron generation (NADH yield) and electron transportation system activity increased by 14.5% and 104%, respectively. Cell membrane analysis found that MWCNT caused an increase in polyunsaturated fatty acids, which had positive effects on electron transportation and membrane fluidity at a low concentration of 96 mg/kg but caused membrane lipid peroxidation and impaired membrane integrity at a high concentration of 115 mg/L. These findings confirmed that MWCNT affects the activity of Alcaligenes sp. TB and consequently enhances denitrification performance.

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Multi-walled carbon nanotubes (MWCNTs) have widespread use in industrial and consumer products and great potential in biomedical applications. This leads to inevitably their release into the environment and the formation of their toxic effects on organisms. These effects can change depending on their physicochemical characteristics. Therefore, the toxicological findings of MWCNTs are inconsistent. Their toxicities related to surface modification have not been elucidated in a holistic manner. Hence, this study was conducted to clarify their potential toxic effects on zebrafish embryos/larvae in a comprehensive approach using morphologic, biochemical and molecular parameters. Zebrafish embryos were exposed to 5, 10, 20 mg/L doses of MWCNTs-COOH at 4 h after fertilization and grown until 96 hpf. Physiological findings demonstrated that they induced a concentration-dependent increase in the mortality rate, delayed hatching and decrease in the heartbeat rate. Moreover, it caused abnormalities including yolk sac edema, pericardial edema, head, tail malformations, and vertebral deformities. These effects may be due to the alterations in antioxidant and immune system related gene expressions after their entry into zebrafish embryo/larvae. The entry was confirmed from the evaluation of Raman spectra collected from the head, yolk sac, and tail of control and the nanotube treated groups. The gene expression analysis indicated the changes in the expression of oxidative stress (mtf-1, hsp70, and nfkb) and innate immune system (il-1β, tlr-4, tlr-22, trf, and cebp) related genes, especially an increased in the expression of the hsp70 and il-1β. These findings proved the developmental toxicities of MWCNTs-COOH on the zebrafish embryos/larvae.
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Manure application and crop residue returning have been performed to enhance crop yield and reduce soil reactive nitrogen (N r ) gas (N 2 O and NO x ) emissions. However, the dynamic characteristics of soil nitrogen-cycling (N-cycling) enzyme activities, and the relationship among N-cycling enzyme activities, N r contents and Nr gas emissions are not clearly understood. Six fertilization regimes, including control (CK-no fertilizer), synthetic N fertilizer alone (N), synthetic nitrogen, phosphorus and potassium fertilizer (NPK), pig manure (OM), pig manure (30% of N rate) with synthetic NPK (70% of N rate) (OMNPK), and crop residues (20% of N rate) with synthetic NPK (80% of N rate) (CRNPK), were used for 11 years to form stable soil conditions. The total N application rate in each fertilization regime, except CK, is the same (130 kg N ha ⁻¹ ) in the winter wheat season. The results showed that the cumulative emissions of N 2 O plus NO x in OM increased significantly by 43.7%, while those in OMNPK and CRNPK decreased by 8.2 and 15.3% compared to conventional fertilization regimes of NPK. The long-term application of manure or returning crop residues to partly replace synthetic N fertilizer may significantly enhance soil hydrolase activities compared with NPK at most stages of wheat growth. In contrast to OM, OMNPK and CRNPK primarily inhibited the activities of nitrate reductase (NR) and nitrite reductase (NiR) but increased hydroxylamine reductase (HyR) activity. Redundancy analysis (RDA) and stepwise multiple linear regression showed positive NR and NiR activities, while PRO activity is negative for N 2 O emission. NO x emissions were mainly controlled by HyR activities. Thus, soil reactive nitrogen (N r ) gas emissions may be mitigated by different fertilization regimes through the regulation of soil enzyme activities. Fertilization regimes, such as manure application and returning crop residues with synthetic NPK, could be recommended as optimal N fertilization strategies in Regosols to mitigate N r gas emissions.
Article
Soils are the main source of nitrous oxide (N 2 O) emissions, with 60–70% of global N 2 O production due to the enhanced denitrification activity with elevated nitrogen (N) availability associated with agricultural intensification. The amendment of agricultural soils with biosolids, the residual product of wastewater treatment, has been used for several decades as an inexpensive source of organic matter and N. Biosolids also contain elevated levels of trace elements such as copper (Cu), which influence the activity of the bacterial enzyme nitrous oxide reductase (N 2 OR). We extracted DNA from a pasture soil 20 years after application of biosolid and Cu salts and used an environmental genomics approach (GeoChip) to evaluate broad changes in the abundance and structure of families of N-cycling genes. We then focussed on abundances of individual bacterial genes involved in sequential N-reduction (nirS, nirK, and nosZ). There was no relationship between total soil Cu concentrations and the different N-cycling gene families (GeoChip; P > 0.1). However, increasing Zn was associated with decreased nitrification (amoA) and dissimilatory N-reduction (napA and nrfA) gene-family abundances (P < 0.1). When focused on individual bacterial denification pathway genes (qPCR), nosZ (nitrous oxide reductase) was found to be sensitive to Cu concentrations. Moreover, the activity of the Cu-dependent enzyme N 2 OR is potentially affected by historical Cu concentrations found in these pasture soils. The results highlight the sensitivity of a few key functional taxa (nosZ type denitrifying bacteria) to long-term Cu exposure in soil, and how these effects can translate into alteration of wider N-cycling processes such as those affecting net N 2 O emissions.
Article
The effect of pH on nitrous oxide (N2O) production rates was quantified in an intermittently-fed lab-scale sequencing batch reactor performing high-rate nitritation. N2O and other nitrogen (N) species (e.g. ammonium (NH4+), nitrite, hydroxylamine and nitric oxide) were monitored to identify in-cycle dynamics and determine N conversion rates at controlled pH set-points (6.5, 7, 7.5, 8 and 8.5). Operational conditions and microbial compositions remained similar during long-term reactor-scale pH campaigns. The specific ammonium removal rates and nitrite accumulation rates varied little with varying pH levels (p > 0.05). The specific net N2O production rates and net N2O yield of NH4+ removed (ΔN2O/ΔNH4+) increased up to seven-fold from pH 6.5 to 8, and decreased slightly with further pH increase to 8.5 (p < 0.05). Best-fit model simulations predicted nitrifier denitrification as the dominant N2O production pathway (≥87% of total net N2O production) at all examined pH. Our study highlights the effect of pH on biologically mediated N2O emissions in nitrogen removal systems and its importance in the design of N2O mitigation strategies.
Article
Partial denitrification (PD, nitrate → nitrite) using carbon sources in domestic wastewater with waste-activated sludge as inoculum was firstly achieved in this study. Through controlling influent pH at about 9.0 and anoxic reaction time of 1 h in the start-up, the nitrite (NO 2⁻ -N) production reached as high as 25.2 mg/L, with influent nitrate (NO 3⁻ -N) of about 30 mg/L and chemical oxygen demand (COD) to NO 3⁻ -N ratio of 5.9. Furthermore, PD performance remained stable without pH control during subsequent operations. Efficient NO 2⁻ -N production was closely related to the consumed amount of readily biodegradable COD (Ss) fraction, with optimal Ss/NO 3⁻ -N ratio of about 3.5. Thauera (19.1%), norank_f__Xanthomonadaceae (5.2%), and Thiobacillus (5.0%) were enriched during the 208-day operation, which may be responsible for high NO 2⁻ -N production. These findings provided a novel strategy for promoting mainstream PD/Anammox application, without additional nitrite-accumulating denitrifying sludge and external carbon sources.
Article
Effects of electron acceptors and free nitrous acid (FNA) concentrations on the denitrification performance and nitrous oxide (N2O) generation were investigated in denitrifying systems acclimated with nitrate (SBRA) and nitrite (SBRI). Denitrifying genes and functional microbial communities were also analyzed. Under the same influent organic carbon to nitrogen ratio, the nitrate removal percentage in SBRA was 75.2%, while that of nitrite was 99.8% in SBRI. The highest N2O conversion ratio of 89.9% was obtained when nitrite was applied to SBRA due to the insufficient electrons for N2O reductase (Nos). Higher N2O generation was attributed to the severe FNA inhibition on Nos when NO2N was used as the electron acceptor, rather than the relative abundance of gene nos. The dominant denitrifier was Acidovorax with the abundance of 21.9% in SBRA, while Thauera of 11.3% in SBRI.
Article
Ocean acidification events are recognized as important drivers of change in biological systems. Particularly, the impacts of acidification are more severe in estuarine systems than in surface ocean due to their shallowness, low buffering capacity, low salinity and high organic matter from land drainage. Moreover, because they are transitional areas, estuaries can be seriously impacted by a vast number of anthropogenic activities and in the last decades, carbon nanomaterials (CNMs) are considered as emerging contaminants in these ecosystems. Considering all these evidences, chronic experiment was carried out, trying to understand the possible alteration on the chemical behaviour of two different CNMs (functionalized and pristine) in predicted climate change scenarios and consequently, how these alterations could modify the sensitivity of one the most common marine and estuarine organisms (the polychaeta Hediste diversicolor) assessing a set of biomarkers related to polychaetes oxidative status as well as the metabolic performance and neurotoxicity. Our results demonstrated that all enzymes worked together to counteract seawater acidification and CNMs, however oxidative stress in the exposed polychaetes to both CNMs, especially under ocean acidification conditions, was enhanced. In fact, although the antioxidant enzymes tried to cope as compensatory response of cellular defense systems against oxidative stress, the synergistic interactive effects of pH and functionalized CNMs indicated that acidified pH significantly increased the oxidative damage (in terms of lipid peroxidation) in the cotaminated organisms. Different responses were observed in organisms submitted to pristine CNMs under pH control, where the lipid peroxidation did not increase along with the increasing exposure concentrations. The present results further demonstrated neurotoxicity caused by both CNMs, especially noticeable at acidified conditions. The mechanism of enhanced toxicity could be attributed to slighter aggregation and more suspended NMs in acidified seawater (as demonstrated by the DLS analysis). Therefore, ocean acidification may cause a higher risk of CNMs to marine ecosystems.
Article
Autotrophic denitrification (AuDen) is an efficient, convenient and eco-friendly biological process for the treatment of nitrate-contaminated organic-deficient waters. AuDen can be applied as a unique process or complement the conventional denitrification with organics, reducing the risk of organic carbon breakthrough in the effluent and formation of undesirable byproducts downstream (e.g. trihalomethanes). A wide range of inorganic compounds can act as electron donors for AuDen. The most used electron donors include hydrogen gas and reduced sulfur compounds, i.e. elemental sulfur, sulfide and thiosulfate. Recently, the denitrification potential of certain contaminants (such as sulfite, thiocyanate, arsenite and manganese) and inorganic wastes (such as biogenic elemental sulfur from biogas upgrading) has been revealed and attracted interest for developing technologies that combine nitrate removal with water detoxification. This paper critically reviews the state of the art of the most used electron donors for AuDen and highlights recent advances on the application of novel inorganic compounds, reactor configurations and microorganisms to support denitrification. Criteria and guidelines for the selection of a suitable electron donor are provided.
Article
This study of Cu(II)'s impact on aerobic denitrification of Paracoccus sp. YF1 revealed that the denitrification rate decreased markedly from 99.8%, 98.0%, 68.7% to 16.3% when the concentrations of Cu(II) rose from 0, 0.01 mM, 0.05 mM to 0.1 mM, respectively. This outcome was confirmed by the successful test of OD600, total protein and enzyme activities. As the concentration of Cu(II) increased from 0 to 0.1 mM, the total protein contents declined over a period of 48 h, and the activities of nitrate reductase (NR) and nitrite reductase (NIR) decreased remarkably during the first 24 h in a NO3⁻ sufficient state. Meanwhile, the reduction of NO3⁻ and NO2⁻ was positively correlated with the expression level of NR and NIR. The removal rate of nitrate in the control treatment and different concentration of Cu(II) treatment fitted approximately to the zero-order model. Scanning electron microscopy (SEM) confirmed that the cell surfaces of Paracoccus sp. YF1 were disrupted when exposed to 0.1 mM Cu(II). The adsorption of Cu(II) onto the cells’ surface was confirmed by Energy dispersive spectrometer (EDS), Fourier transform infrared spectra (FTIR), and X-ray photoelectron spectroscopy analysis (XPS). The insights obtained here regarding the influence of Cu(II) on aerobic denitrification will be of great significance for the treatment of heavy metals and nitrite co-existing sewage.
Article
The aim of this work was to study the effects of non-ionic surfactant on the accumulation of total microbial lipids and extracellular lipid by Cryptococcus curvatus MUCL 29819 with acetic acid as carbon source. Compared with Brij 58 and Triton X-100, Brij 58 most increased the total lipids, with a yield up to 2.84 g/L (extracellular lipid up to 47%). Brij 58 also increased the metabolic flow of acetic acid to lipid accumulation (maximum conversion of 0.54 g/g at 1.0 g/L Brij 58) and limited its conversion to non-lipid biomass (minimum conversion 0.12 g/g at 0.5 g/L Brij 58). The improvement in the proportion of extracellular lipid by tea saponin and Brij 58 was due to changes in cell membrane permeability and improvement of cell membrane fluidity. Triton X-100, having weaker surface activity, promoted release of extracellular lipid and also increased the proportion of polyunsaturated fatty acid (C22:6, docosahexaenoic acid).
Article
Pesticide residues in riparian zones have attracted much attention in recent decades. Their accumulations potentially deteriorate microbial activity and disturb nitrogen cycle in riparian sediments. In this study, the short-term effects of chlorothalonil (CTN, a common pesticide) on microbial denitrification were explored in riparian sediments at three levels (5, 10 and 25 mg kg⁻¹). No significant differences were observed between control and 5 mg kg⁻¹ treatment; however, CTN in 10 and 25 mg kg⁻¹ treatments deteriorated sediment health condition and microbial activity. High concentrations of CTN also significantly decreased denitrification rates (¹⁵N pairing method) by 37–62%, but increased N2O emission in riparian sediments by 100–285%. Our data further revealed that CTN inhibited key enzyme activities responsible for microbial metabolism, and declined electron donor (NADH) and energy source (ATP) levels during denitrification. Key denitrifying enzyme activities were also suppressed by CTN, which explained the declined denitrification process and the elevated N2O emission. Additionally, high-throughput sequencing and quantitative-PCR analysis showed that CTN didn't remarkably change microbial community structures and denitrifying gene abundances after short-term exposure. Overall, this study highlights that riparian pesticides could impact nitrogen cycle of the interface between terrestrial and aquatic ecosystems, potentially accelerating water pollution and global climate change.
Article
Tungsten oxide/titanium oxide nanocomposites (nWO3-TiO2) with three different WO3-TiO2 mass ratios (n = 1%, 3% and 5%) were synthesized and used as a photo-anode to fabricate dye sensitized solar cells (DSSC), in conjunction with multiwall carbon nanotube (MWCNTs) as a platinum free (Pt-free) counter electrode. It was observed that [1%WO3-TiO2/N719/MWCNT] DSSC exhibited an efficiency enhancement of about 40% as compared to the conventional TiO2/dye/Pt solar cell, and 18% efficiency enhancement compared to [1%WO3-TiO2/N719/Pt] solar cell. The reduced electron-hole (e, h⁺) recombination in the nWO3-TiO2 nanocomposite due to reduced surface trap states, the increased accumulation of electrons at the photo-anode mediated by the photo-excitation of the dye, the efficient electron transportation and increased light absorption can be attributed to the superior performance of [nWO3-TiO2/N719/MWCNT] DSSCs in general. Also nWO3-TiO2 nanocomposite, when used as a photo-catalyst in the presence of UV radiation for the photo-catalytic degradation of Methylene blue (MB) dye, demonstrated the dye degradation efficiency as high as 99.99%. The enhanced degradation of MB dye further confirms the reduced charge (e, h⁺) recombination and enhanced light absorption, the features essential for a good DSSC. In addition to the photovoltaic and photo-catalytic studies, the morphological and optical characterization of nWO3-TiO2 nanocomposite photo-anodes films, the catalytic, electrochemical and electrical characterization of counter electrode and the fabricated DSSCs were carried out.
Article
In this study, magnetic multi-walled carbon nanotube (MMWCNT) composites were prepared via surface reversible addition fragmentation chain transfer (RAFT) co-polymerization of acrylic acid (AA) and N-isopropyl acrylamide (NIPAM) in the presence of Fe3O4 nanoparticles. First, a novel RAFT agent (RA) was prepared and then immobilized onto the surface of MWCNT to fabricate RA-g-MWCNT. Then, Fe3O4 nanoparticles were attached onto the surface of RA-g-MWCNT. Finally, RAFT co-polymerization of AA and NIPAM monomers was carried out via Fe3O4-g-RA-g-MWCNT RAFT agent. The structure and morphology of the prepared polymer-coated MWCNT was examined by FTIR, SEM, TEM, XRD, VSM, and TGA. The adsorption behaviours of the cationic dyes were studied. The equilibrium isotherm and kinetics of cationic dyes were investigated. Thermodynamics investigations also depicted that the adsorptions of cationic dyes were spontaneous and endothermic in nature. The synthesized dye adsorbent with high adsorption capacities, reusability, and easy recovery makes it as a good candidate for wastewater treatment.
Article
The fungicide chlorothalonil (CHT) has been widely used in the tea orchard due to its high-efficiency and sterilization. It has been reported that repeated application of CHT inhibits soil nitrification process. However, the acute impact of CHT on soil denitrification and associated N2O emissions is unclear. This study evaluated nitrate (NO3⁻) removal, denitrifying gene abundance and denitrifying enzyme activity of tea orchard soil after a 72-h-exposure to CHT. It was found that increasing CHT from 5 to 25 mg kg⁻¹ suppressed the NO3⁻ removal efficiency from 74.6% to 54.1%, but increased N2O emissions from 23.1% to 94.8%. Following treatment with 25 mg kg⁻¹ of CHT, the abundances of the nirK, nirS and nosZ genes were reduced by 31.6%, 22.1%, and 50.7%, respectively. Alternatively, the declines of the electron transport system activity (ETSA) value and adenosine triphosphate (ATP) content suggested that CHT had an inhibitory effect on microbial metabolism. Enzyme activity studies further revealed that the decrease of nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR) activities was the main reason for the suppression of denitrification by CHT. Furthermore, positive correlations were observed between denitrifying reductase activity and the intracellular metabolism, indicating that the decrease in microbial metabolism should also be responsible for the inhibitory effect of CHT on the denitrifying process. Overall, it was found that the acute exposure of soil to CHT could inhibit the denitrification process and significantly increase N2O emissions, which might result in destruction of the soil nitrogen cycle and exacerbation of global warming.
Article
In this research, the nitrate reduction rate increased 2-3 fold in the presence of five different porphyrin compounds (0.25 mM), among which hemin expressed the best accelerating effectiveness. Therefore, hemin was used to explore the catalytic characteristics and mechanisms during denitrification. The relationship between hemin concentrations (Chemin) and nitrate reduction rates (k) could be best described by the equation k = 8.7463 + 0.44528ln (Chemin-0.00993) (R2 = 0.9908). Furthermore, the activation energy decreased 87% compared to the hemin-free system. Two active centers of hemin, the Fe3+ atom and the porphyrin ligand, might be involved in catalyzing the denitrification process. Additionally, the accelerating site of hemin in the denitrification electron transfer chain was elucidated by different metabolic inhibitors. This study provides a better understanding of porphyrin compounds in bio-multistage redox reactions and is a promising strategy for its practice application.
Article
Nanomaterials for facilitating the microbial extracellular electron transfer (EET) process have drawn increasing attention due to their specific physical, chemical and electrical properties. This review summarizes the research advances of nanomaterials for accelerating the EET process. Nanostructured materials, including oligomer, carbon nanotube (CNT), graphene, metal, metal oxides, and polymer, exhibit numerous admirable properties such as large surface area, high electrical conductivity, and excellent catalytic activity. In this review, depending on the exact site where the nanomaterials work, the nanomaterials are classified into four groups: inside-membrane, interface, inside-biofilm and interspecies. Synthesis of the nanomaterials, EET enhancement performance, and corresponding enhancement mechanisms are also discussed. In spite of the challenges, nanomaterials will be extremely promising for promoting the EET process application in the future.
Article
Despite of the large array of available carbon nanotube (CNT) configurations that allow different industrial and scientific applications of these nanoparticles, their impacts on aquatic organisms, especially on invertebrate species, are still limited. To our knowledge, no information is available on how surface chemistry alteration (functionalization) of CNTs may impact the toxicity of these NPs to bivalve species after a chronic exposure. For this reason, the impacts induced by chronic exposure (28days) to unfunctionalized MWCNTs (Nf-MWCNTs) in comparison with functionalized MWCNTs (f-MWCNTs), were evaluated in R. philippinarum, by measuring alterations induced in clams' oxidative status, neurotoxicity and metabolic capacity. The results obtained revealed that exposure to both MWCNT materials altered energy-related responses, with higher metabolic capacity and lower glycogen, protein and lipid concentrations in clams exposed to these CNTs. Moreover, R. philippinarum exposed to Nf-MWCNTs and f-MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defense mechanisms (superoxide-dismutase, glutathione peroxidase and glutathione S-transferases) in exposed clams. Additionally, neurotoxicity was observed by inhibition of Cholinesterases activity in organisms exposed to both MWCNTs.
Article
The efficiency of wastewater denitrification was determined in batch cultures at low temperatures (10°C and 15°C) by adding different redox mediators (RMs; anthraquinone-2,6-disulphonate [AQDS], 2-hydroxy-1,4-naphthoquinone [LAW] and 1,2-naphthoquinone-4-sulphonate [NQS]). The denitrification rate and nitrogen removal efficiency were found to increase with the addition of RMs at low temperatures compared with the control. At 10°C, the highest nitrogen removal efficiency was 11% (control: 5%) and maximum denitrification rate of 2.06 mgNOx⁻–N/g volatile suspended solid [VSS]·h was achieved with addition of NQS (control: 1.15 mgNOx⁻–N/g VSS·h). At 15°C, the maximum denitrification efficiency increased to 18.7% with addition of LAW (control: 10.7%) and the denitrification rate improved to 5.63 mgNOx⁻–N/g VSS·h with addition of NQS (control: 3.53 mgNOx⁻–N/g VSS·h). Investigation of the underlying mechanism revealed a typical redox reaction. Addition of different RMs improved the oxidation–reduction potential, sludge dehydrogenase activity, and electron transport system to some extent compared with the control. Furthermore, the high-throughput sequencing revealed the presence of denitrifying bacteria such as Thauera spp., Pseudomonas spp., and Dechloromonas spp. in the acclimated sludge.
Article
Electron transport system activity (ETSa) and particulate organic matter (POM) concentrations and composition were measured in three areas of the continental shelf of the Ross Sea during summer 2014, in the framework of the Ross Sea Mesoscale Experiment (ROME) project. We aimed at testing whether in the epipelagic layer (0–200 m) ETS showed different activity depending on the geographical position and on the different hydrological structures that characterised each area, as eddy and fronts, and whether the ETSa of the microplanktonic fraction depended on POM quantitative and qualitative features. ETSa showed differences between the three areas, but within each of them the different hydrological conditions did not influence significantly the respiration activity. ETSa displayed significant correlations with POM, especially in the offshore areas characterised by residual ice influence and by a mesoscale eddy structure. In these zones ETSa was enhanced by good trophic value of POM, i.e. showing dominance of proteins and PON over structural carbohydrates and POC, respectively. The role of the phytoplanktonic fraction in ETSa was higher in the eddy-influenced area, that showed significantly higher chlorophyll-a concentrations. On the other hand, in the area placed coastward, the relationships between ETSa and POM changed. High ETSa were found in the subsurface layer and down to 100 m depth and were related to more refractory POM, whose utilization would require higher energy. Different ETSa-POM relationships were consistent with the anomalous phytoplanktonic bloom detected in the coastward area, characterised by Phaeocystis. Thus, the anomalies of the primary producers are reflected by changes in POM respiration and potential C utilization.
Article
In the present study we describe a simple method to immobilize the redox mediator anthraquinone-2,6-disulfonate (AQDS) at the surface of graphite electrodes, by means of a commercial anion exchange membrane. Cyclic voltammetry experiments confirmed the efficacy of the immobilization protocol and the long-term (over 70 days) electrochemical stability of the AQDS-functionalized electrode. Potentiostatic (–300 mV vs. SHE) batch experiments proved the capability of the electrode in accelerating the bioelectrochemical reductive dechlorination of the groundwater contaminant 1,2-dichloroethane (1,2-DCA) to harmless ethene by a mixed microbial culture, by serving as electron donor in the process. Considering the reported broad range of anodic and cathodic reactions catalyzed by AQDS, the herein described functionalized electrode has a remarkable potential for application in the environmental and industrial sector.
Article
Composites made with engineered nanomaterials (nanocomposites) have a wide range of applications, from use in basic consumer goods to critical national defense technologies. Carbon nanotubes (CNTs) are a popular addition in nanocomposites because of their enhanced mechanical, thermal, and electrical properties. Concerns have been raised, though, regarding potential exposure and health risks from nanocomposites containing CNTs because of comparisons to other high aspect ratio fibers. Assessing the factors affecting CNT release from composites is therefore paramount for understanding potential exposure scenarios that may occur during product handling and manipulation. Standardized methods for detecting and quantifying released CNTs, however, have not yet been developed. We therefore evaluated experimental approaches deployed by various researchers, with an emphasis on characterizing free versus composite bound CNTs. From our analysis of published studies characterizing CNT releases from nanocomposites, we found that the qualitative and quantitative methods used across studies varied greatly, thus limiting the ability for objective comparison and evaluation of various release factors. Nonetheless, qualitative results indicated that factors such as composite type, CNT functionalization, and energy input during manipulation (i.e., grinding) may affect CNT release. Based on our findings, we offer several recommendations for future product testing and assessment of potential exposure and health risks associated with CNT nanocomposites.Journal of Exposure Science and Environmental Epidemiology advance online publication, 31 May 2017; doi:10.1038/jes.2017.6.
Article
MWCNTs (Multi-walled carbon nanotubes) can be used for the fabrication of mixed matrix polymeric membranes that can enhance filtration perfomances of the membranes by modifying membrane surface properties. In this study, detailed characterization and filtration performances of MWCNTs functionalized with COOH group, blended into polymeric flat-sheet membranes were investigated using different polymer types. Morphological characterization was carried out using AFM, SEM and contact angle measurements. For filtration performance tests, protein, dextran, E. coli suspension, Xanthan Gum and real activated sludge solutions were used. Experimental data and analyses revealed that Polyethersulfone (PES) + MWCNT-COOH mixed matrix membranes have superior performane abilities compared to other tested membranes.
Article
Sulfamethoxazole (SMX), as a common sulfonamide antibiotic, was reported to affect conventional anaerobic denitrification. This study presented effects of SMX on aerobic denitrification by an aerobic denitrifier strain Pseudomonas stutzeri PCN-1. Results demonstrated serious inhibition of N2O reduction as SMX reached 4?g/L, leading to higher N2O emission ratio (251-fold). Increase of SMX (?8?g/L) would induce highest nitrite accumulation (95.3mg/L) without reduction, and severe inhibition of nitrate reduction resulted in lower nitrate removal rate (0.15mg/L/h) as SMX reached 20?g/L. Furthermore, corresponding inhibition of SMX on denitrifying genes expression (nosZ>nirS>cnorB>napA) was found with a time-lapse expression between nosZ and cnorB. Meanwhile, the decline in electron transport activity and active microbial biomass of strain PCN-1 was revealed. The insight into mechanism of SMX influence on aerobic denitrifier is of particular significance to upgrade nitrogen removal process in antibiotics-containing wastewater treatment plant.
Article
The denitrification enzyme activity assay (DEA) and other ex situ, incubation-based methods are widely used for measuring biogeochemical transformations. DEA does not provide direct measurements of denitrification rates in situ, but rather denitrification potential under laboratory conditions over the course of an incubation with resource limitations removed. Despite recognized limitations, DEA has several advantages. In particular, it is a relatively simple and low-cost method considered reliable for comparing relative differences in denitrification, for example between areas subjected to different management treatments. However, a critical but, to our knowledge, untested assumption of DEA is that bacterial composition remains static during the assay, i.e., the microbial community being assayed is equivalent to the original community collected from the field. If this assumption is violated, it could result in flawed estimates of relative differences between samples. We tested the static-community assumption using high-throughput sequencing to measure differences in bacterial community composition between samples from two different wetland vegetation types over the course of standard DEA incubations. We also compared samples that were or were not treated with a standard amendment solution to differentiate amendment effects from “bottle effects” of time spent under storage and laboratory conditions. We found that initially distinct bacterial communities became less similar to each other during short-term cold storage, but then became more similar during incubation, with a net result of samples converging in composition. Surprisingly, there were no effects of amendment solution; bottle effects alone accounted for these changes. This raises concern that potentially important differences in wetland denitrification, or other processes measured using ex situ methods, could be obscured by changes in bacterial community composition that arise as an artifact of laboratory incubations.
Article
Removal of nitrate ions, as a pollutant, from water using armchair boron nitride nanotubes (BNNTs) was investigated by molecular dynamics (MD) simulations. The investigated system included a BNNT embedded between two graphene sheets as a membrane. This membrane was immersed into a water box containing nitrate ions. For the removal of nitrates, an external pressure was applied to the system. Six types of armchair BNNTs with different diameter including (4,4), (5,5), (6,6), (7,7), (8,8) and (9,9) BNNTs were used. The simulation results showed that the BNNTs with different diameters acted differently relative to permeation of nitrate ions and water molecules. The permeation of nitrate ions through the BNNTs was dependent on the applied pressures and the diameter of nanotubes. The flow rate of water through BNNTs was increased by increasing the diameter of the nanotubes.
Article
In this study, an efficient heterotrophic nitrifying-aerobic denitrifying bacteria strain SLWX2 was screened from 7 strains isolated from Stichopus japonicus culture ponds, with removal rates of NH4⁺-N, NO2⁻-N and NO3⁻-N up to 100%, 99.5% and 85.6% within 24 h, respectively. Through morphologic observation, physiological characteristics and 16S rDNA sequence analysis, strain SLWX2 was identified as Bacillus hwajinpoensis. The results of nitrogen removal characterization experiments indicated that, when NH4⁺-N, NO2⁻-N and NO3⁻-N existed at the same time, SLWX2 utilized NH4⁺-N firstly, then utilized NO2⁻-N and NO3⁻-N, and removed almost all the inorganic nitrogen within 72 h, suggesting that it could achieve simultaneous nitrification and denitrification itself. The results of nitrogen tolerance examination indicated that strain SLWX2 showed perfect nitrogen removal ability when the ammonia load was not above 500 mg·L⁻¹, nitrite load was not above 100 mg·L⁻¹ and nitrate load was not above 200 mg·L⁻¹, the maximal removal of ammonia nitrogen, nitrite nitrogen and nitrate nitrogen withinn 96 h reached 180 mg, 30 mg and 120 mg, respectively. Moreover, there was no NO2⁻-N accumulation during nitrification. This strain showed great potential in biological nitrogen removal of wastewater with high salt and nitrogen from mariculture and industries.
Article
A green process to prepare the hydrophobic and transparent CNT-based surface was developed without using any toxic chemicals, solvents or gases. CNT brush (CNT-b) powder, which was prepared by the repeated CVD, was the main material to prepare the desired surface. An adhesive layer of ethyl cellulose (EC) was spin coated on the glass substrate, where EC formed a networked porous microstructure. A low concentration CNT-b suspension was obtained by sonication of the mixture of CNT-b powders, sodium dodecylbenzenesulfonate (SDBS) and deionized water. To obtain the stabilized CNT-b suspension, it was found that 40 min of sonication time and SDBS/CNT-b weight ratio being 0.1 were required. The target surface was then prepared by spin coating CNT-b suspension on the EC coated glass. The contact angle of the prepared surface was around 120o and the optical transmittance was around 93% for the visible light. Either increasing the number of spin coatings or increasing the concentration of CNT-b suspension could slightly increase the contact angle to around 130o but the optical transmittance significantly reduce to about 75%, leading to a semi-transparent sample.
Article
This study investigated the denitrification characteristics and practical applications of PET–CAs (chloroanthraquinones immobilised on polyethylene terephthalate), which are novel functional biocarriers. The PET–CAs were characterized using Fourier transform infrared spectroscopy (FT-IR) and energy dispersive spectrometry (EDS). Among the PET–CAs, PET-1,8-DCA (PET modified by 1,8-dichloroanthraquinone) was the best functional biocarrier for accelerating the denitrification process with approximately 0.14 mmol anthraquinone. The denitrification process was pseudo-zero order, with CNO3− = 175.64–19.28 t and R2 = 0.9715. The pH of the PET-1,8-DCA system increased and ultimately reached 9.7. The stabilized ORP value with PET-1,8-DCA was approximately 70 mV lower than that of the control with PET. This study explored a novel design concept for the immobilization of quinone.
Article
In this study, effects of four kinds of redox mediators on denitrification performance, nitrate and nitrite reductase activities were investigated, including anthraquinone (AQ), 2-methyl-1,4-naphthoquinone (ME), lawsone (LAW) and anthraquinone-2,6-disulphonate (AQDS). Experimental results demonstrated that the optimum dosing concentrations of AQ, ME and LAW were 75, 25 and 75 μM. The maximum total nitrogen removal rates increased to 26.02, 20.16 and 33.50 mg-N/g-VSS/h at each optimum dosing concentration, which were approximately 1.60, 1.25 and 2.08 times higher compared to that without redox mediator addition. Unlike AQ and ME, addition of LAW appeared to have suppressed the accumulation of nitrite with peak vales about 21.60 mg/L compared to that of 121.9 mg/L with AQ and 180 mg/L with ME addition. Among four kinds of redox mediators, ME increased the nitrate reductase activity about 1.97 folds, and AQDS enhanced the nitrite reductase activity about 2.08 folds compared to the controls. The unbalance of affected nitrate reductase and nitrite reductase activities by redox mediator was considered as the main reason for nitrite accumulation in this study.
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Cryoconites are microbial aggregates commonly found on glacier surfaces, where they tend to take spherical, granular forms. While it has been postulated that the microbes in cryoconite granules play an important role in glacier ecosystems, information on their community structure is still limited and their functions remain unclear. Here, we present evidence for the occurrence of nitrogen cycling in cryoconite granules on a glacier in Central Asia. We detected marker genes for nitrogen fixation, nitrification, and denitrification in cryoconite granules by digital PCR, while digital RT-PCR analysis revealed that only marker genes for nitrification and denitrification were abundantly transcribed. Analysis of isotope ratios also indicated the occurrence of nitrification; nitrate in the meltwater on the glacier surface was of biological origin, while nitrate in the snow was of atmospheric origin. The predominant nitrifiers on this glacier belonged to the order Nitrosomonadales, as suggested by amoA sequences and 16S rRNA pyrosequencing analysis. Our results suggest that the intense carbon and nitrogen cycles by nitrifiers, denitrifiers, and cyanobacteria support abundant and active microbes on the Asian glacier.
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This article contributes to the growing study on the interactions between science and technology with China’s evidence in the field of nanotechnology, based on the database of United States Patent and Trademark Office. The analysis is focused during the period of 1991–2008, a rapid increasing period for the development of nanotechnology. Using the non-patent references cited by patents, we first investigate the science–technology connections in the context of Chinese nanotechnology, especially in institutional sectors and its application fields. Those patents, produced by academic researchers and directed towards basic scientific knowledge, generally cite more scientific references with a higher proportion of self-citations. It is interesting to find that patents contributed by collaborations between public organizations and corporations seldom contain scientific references. Following an interesting path on matching the data of publications and patents, we establish the author-inventor links in this emerging field. Author-inventors, who are co-active in publishing and patenting, are at the very top of the most prolific and highly cited researchers. Finally, we employ social network analysis to explore the characteristics of scientific and technological networks generated by co-authorship and co-invention data, to investigate the position and the role of patenting–publishing scientists in these research networks.