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1.
PLoS One ; 15(8): e0238386, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32853235

RESUMO

Moving Bed Biofilm Reactors (MBBRs) can efficiently treat wastewater by incorporating suspended biocarriers that provide attachment surfaces for active microorganisms. The performance of MBBRs for wastewater treatment is, among other factors, contingent upon the characteristics of the surface area of the biocarriers. Thus, novel biocarrier topology designs can potentially increase MBBR performance in a significant manner. The goal of this work is to assess the performance of 3-D-printed biofilter media biocarriers with varying surface area designs for use in nitrifying MBBRs for wastewater treatment. Mathematical models, rendering, and 3D printing were used to design and fabricate gyroid-shaped biocarriers with a high degree of complexity at three different levels of specific surface area (SSA), generally providing greater specific surface areas than currently available commercial designs. The biocarriers were inoculated with a nitrifying bacteria community, and tested in a series of batch reactors for ammonia conversion to nitrate, in three different experimental configurations: constant fill ratio, constant total surface area, and constant biocarrier media count. Results showed that large and medium SSA gyroid biocarriers delivered the best ammonia conversion performance of all designs, and significantly better than that of a standard commercial design. The percentage of ammonia nitrogen conversion at 8 hours for the best performing biocarrier design was: 99.33% (large SSA gyroid, constant fill ratio), 94.74% (medium SSA gyroid, constant total surface area), and 92.73% (large SSA gyroid, constant biocarrier media count). Additionally, it is shown that the ammonia conversion performance was correlated to the specific surface area of the biocarrier, with the greatest rates of ammonia conversion (99.33%) and nitrate production (2.7 mg/L) for manufactured gyroid biocarriers with a specific surface area greater than 1980.5 m2/m3. The results suggest that the performance of commercial MBBRs for wastewater treatment can be greatly improved by manipulation of media design through topology optimization.


Assuntos
Biofilmes/crescimento & desenvolvimento , Reatores Biológicos/microbiologia , Águas Residuárias/análise , Águas Residuárias/microbiologia , Amônia/química , Bactérias/crescimento & desenvolvimento , Meios de Comunicação de Massa , Nitratos/química , Nitrificação/fisiologia , Nitrogênio/química , Impressão Tridimensional , Eliminação de Resíduos Líquidos/métodos
2.
PLoS One ; 15(8): e0238154, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32853236

RESUMO

Black soldier fly (BSF) (Hermetia illucens L.) is one of the most efficient bio-waste recyclers. Although, waste substrate amendments with biochar or gypsum during composting process are known to enhance nutrient retention, their impact on agro-industrial waste have not been documented. Hence, this study focuses on a comparative effect of agro-industrial waste amended with biochar and gypsum on BSF larval performance, waste degradation, and nitrogen (N) and potassium retention in frass fertilizer. Brewery spent grain was amended with biochar or gypsum at 0, 5, 10, 15 and 20% to determine the most effective rates of inclusion. Amending feedstock with 20% biochar significantly increased wet (89%) and dried (86%) larval yields than the control (unamended feedstock). However, amendment with 15% gypsum caused decrease in wet (34%) and dried (30%) larval yields but conserved the highest amount of N in frass. Furthermore, the inclusion of 20% biochar recorded the highest frass fertilizer yield and gave a 21% increase in N retention in frass fertilizer, while biomass conversion rate was increased by 195% compared to the control. Feedstock amendment with 5% biochar had the highest waste degradation efficiency. Potassium content in frass fertilizer was also significantly enhanced with biochar amendment. At maturity, frass compost with more than 10% inclusion rate of biochar had the highest cabbage seed germination indices (>100%). The findings of this study revealed that initial composting of biochar amended feedstocks using BSF larvae can significantly shorten compost maturity time to 5 weeks with enhanced nutrient recycling compared to the conventional composting methods.


Assuntos
Carvão Vegetal/química , Larva/crescimento & desenvolvimento , Simuliidae/crescimento & desenvolvimento , Animais , Biomassa , Compostagem/métodos , Fertilizantes , Resíduos Industriais , Nitrogênio/química , Solo/química
3.
Ecotoxicol Environ Saf ; 204: 111066, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32781344

RESUMO

In this study, an iron-doped metal-organic framework (MOF) Fe/ZIF-8 was synthesized from ZIF-8 at room temperature. Direct carbonization of Fe/ZIF-8 under a nitrogen atmosphere produced nanoporous nitrogen doped carbon nanoparticles decorated with Fe component (Fe/NC). The Fe/NC exhibited a large surface area (1221.185 m2 g-1) and narrow pore-size distribution (3-5 nm). The nanoporous Fe/NC components along with Nafion were used to modify a glassy carbon electrode for the electrochemical determination of chloramphenicol and metronidazole via linear sweep voltammetry. Under optimal conditions, the reduction peak currents (observed at -0.237 V and -0.071 V vs. Ag/AgCl) of these analytes increased linearly with increasing chloramphenicol and metronidazole concentrations in the range of 0.1-100 µM and 0.5-30 µM, with the detection limits estimated to be 31 nM and 165 nM, respectively. This result was attributed to the large surface area, porous structure, high nitrogen content, and as well as the electrocatalytic effect of Fe atoms embeded in the carbon support. The proposed sensor was used for chloramphenicol and metronidazole analysis in samples, providing satisfactory results.


Assuntos
Carbono/química , Cloranfenicol/análise , Técnicas Eletroquímicas/métodos , Ferro/química , Estruturas Metalorgânicas/química , Metronidazol/análise , Nitrogênio/química , Animais , Cloranfenicol/urina , Eletrodos , Humanos , Limite de Detecção , Metronidazol/urina , Leite/química , Nanoporos , Soluções Oftálmicas/química , Porosidade , Comprimidos/química
4.
J Chromatogr A ; 1627: 461393, 2020 Sep 13.
Artigo em Inglês | MEDLINE | ID: mdl-32823098

RESUMO

The selective extraction and column separation rear earth elements (REEs) were investigated in the present work. Herein, the functional ligand of N, N-dioctyldiglycolic acid (DODGA) was synthesized and chemically grafted on the silica gel (SG) particles to give the novel material SG@DODGA. The obtained SG@DODGA was fully characterized by NMR, BET (Brunauer-Emmett-Teller) N2 physisorption analysis, atom force microscopy (AFM), scanning electronic microscopy (SEM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). After investigating the adsorption capability of the SG@DODGA towards 16 kinds of REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Td, Dy, Ho, Er, Tm, Yb, Lu, Y and Sc), the results showed that the adsorption kinetic data was better fitted with pseudo-second-order model and Elovich model, the adsorption isotherms data was suitable for Freundlich model. The above result also indicated that the adsorption mechanism between the SG@DODGA and REEs was chemical ion exchange. Moreover, choose SG@DODGA as the column chromatography stationary phase and packed in a glass column for the column studies to obtain breakthroughs profile of each REEs. Furthermore, the column was used to try to separate the mixed 16 kinds of REEs. The first attempt to preliminary separate REEs result showed that this column could be applied for simply separating REEs. The light REEs La, Ce, Pr, Nd exhibited better separation effect than the other REEs.


Assuntos
Glicolatos/química , Metais Terras Raras/isolamento & purificação , Sílica Gel/química , Adsorção , Concentração de Íons de Hidrogênio , Íons , Cinética , Ligantes , Nitrogênio/química , Espectroscopia Fotoeletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Temperatura , Termogravimetria
5.
PLoS One ; 15(7): e0235225, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32649660

RESUMO

Freshwater wetlands of the temperate north are exposed to a range of pollutants that may alter their function, including nitrogen (N)-rich agricultural and urban runoff, seawater intrusion, and road salt contamination, though it is largely unknown how these drivers of change interact with the vegetation to affect wetland carbon (C) fluxes and microbial communities. We implemented a full factorial mesocosm (378.5 L tanks) experiment investigating C-related responses to three common wetland plants of eastern North America (Phragmites australis, Spartina pectinata, Typha latifolia), and four water quality treatments (fresh water control, N, road salt, sea salt). During the 2017 growing season, we quantified carbon dioxide (CO2) and methane (CH4) fluxes, above- and below-ground biomass, root porosity, light penetration, pore water chemistry (NH4+, NO3-, SO4-2, Cl-, DOC), soil C mineralization, as well as sediment microbial communities via 16S rRNA gene sequencing. Relative to freshwater controls, N enrichment stimulated plant biomass, which in turn increased CO2 uptake and reduced light penetration, especially in Spartina stands. Root porosity was not affected by water quality, but was positively correlated with CH4 emissions, suggesting that plants can be important conduits for CH4 from anoxic sediment to the atmosphere. Sediment microbial composition was largely unaffected by N addition, whereas salt amendments induced structural shifts, reduced sediment community diversity, and reduced C mineralization rates, presumably due to osmotic stress. Methane emissions were suppressed by sea salt, but not road salt, providing evidence for the additional chemical control (SO4-2 availability) on this microbial-mediated process. Thus, N may have stimulated plant activity while salting treatments preferentially enriched specific microbial populations. Together our findings underpin the utility of combining plant and microbial responses, and highlight the need for more integrative studies to predict the consequences of a changing environment on freshwater wetlands.


Assuntos
Microbiota/fisiologia , Nitrogênio/química , Plantas/metabolismo , Cloreto de Sódio/química , Solo/química , Ciclo do Carbono , Connecticut , Água Doce/química , Sedimentos Geológicos/microbiologia , Nitrogênio/análise , Cloreto de Sódio/análise , Microbiologia do Solo , Qualidade da Água , Áreas Alagadas
6.
Science ; 368(6497): 1381-1385, 2020 06 19.
Artigo em Inglês | MEDLINE | ID: mdl-32554596

RESUMO

The enzyme nitrogenase uses a suite of complex metallocofactors to reduce dinitrogen (N2) to ammonia. Mechanistic details of this reaction remain sparse. We report a 1.83-angstrom crystal structure of the nitrogenase molybdenum-iron (MoFe) protein captured under physiological N2 turnover conditions. This structure reveals asymmetric displacements of the cofactor belt sulfurs (S2B or S3A and S5A) with distinct dinitrogen species in the two αß dimers of the protein. The sulfur-displaced sites are distinct in the ability of protein ligands to donate protons to the bound dinitrogen species, as well as the elongation of either the Mo-O5 (carboxyl) or Mo-O7 (hydroxyl) distance that switches the Mo-homocitrate ligation from bidentate to monodentate. These results highlight the dynamic nature of the cofactor during catalysis and provide evidence for participation of all belt-sulfur sites in this process.


Assuntos
Azotobacter vinelandii/enzimologia , Molibdoferredoxina/química , Nitrogênio/química , Biocatálise , Cristalografia por Raios X , Ligantes , Oxirredução , Multimerização Proteica , Enxofre/química
7.
Nat Commun ; 11(1): 3188, 2020 06 24.
Artigo em Inglês | MEDLINE | ID: mdl-32581225

RESUMO

Nitric oxide (NO) has been implicated in a variety of physiological and pathological processes. Monitoring cellular levels of NO requires a sensor to feature adequate sensitivity, transient recording ability and biocompatibility. Herein we report a single-atom catalysts (SACs)-based electrochemical sensor for the detection of NO in live cellular environment. The system employs nickel single atoms anchored on N-doped hollow carbon spheres (Ni SACs/N-C) that act as an excellent catalyst for electrochemical oxidation of NO. Notably, Ni SACs/N-C shows superior electrocatalytic performance to the commonly used Ni based nanomaterials, attributing from the greatly reduced Gibbs free energy that are required for Ni SACs/N-C in activating NO oxidation. Moreover, Ni SACs-based flexible and stretchable sensor shows high biocompatibility and low nanomolar sensitivity, enabling the real-time monitoring of NO release from cells upon drug and stretch stimulation. Our results demonstrate a promising means of using SACs for electrochemical sensing applications.


Assuntos
Técnicas Biossensoriais/métodos , Níquel/química , Óxido Nítrico/análise , Nitrogênio/química , Técnicas Biossensoriais/instrumentação , Carbono/química , Catálise , Eletroquímica , Células Endoteliais da Veia Umbilical Humana/metabolismo , Humanos , Nanoestruturas/química , Nanoestruturas/ultraestrutura , Óxido Nítrico/metabolismo , Oxirredução
8.
Nat Commun ; 11(1): 3072, 2020 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-32555185

RESUMO

Biodiversity on the Earth is changing at an unprecedented rate due to a variety of global change factors (GCFs). However, the effects of GCFs on microbial diversity is unclear despite that soil microorganisms play a critical role in biogeochemical cycling. Here, we synthesize 1235 GCF observations worldwide and show that microbial rare species are more sensitive to GCFs than common species, while GCFs do not always lead to a reduction in microbial diversity. GCFs-induced shifts in microbial alpha diversity can be predominately explained by the changed soil pH. In addition, GCF impacts on soil functionality are explained by microbial community structure and biomass rather than the alpha diversity. Altogether, our findings of GCF impacts on microbial diversity are fundamentally different from previous knowledge for well-studied plant and animal communities, and are crucial to policy-making for the conservation of microbial diversity hotspots under global changes.


Assuntos
Biodiversidade , Mudança Climática , Microbiologia do Solo , Solo/química , Biomassa , Carbono/química , Clima , Pradaria , Concentração de Íons de Hidrogênio , Nitrogênio/química , Plantas
9.
PLoS One ; 15(6): e0234544, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32555670

RESUMO

Controlled-release and slow-release fertilizers can effectively supply nitrogen (N) while mitigating N loss. To determine the suitability of these fertilizers for plants in semi-arid environments, these fertilizers need to be evaluated under varying placement and temperature conditions. Several urea fertilizers were evaluated, including: uncoated, sulfur-coated (SCU), polymer-coated-sulfur-coated (PCSCU), and polymer-coated (PCU) with projected release timings between 45 and 180 d. Nitrogen release was measured under daily fluctuating or static temperatures applied either to the surface or buried in the soil. A second experiment consisted of two PCU sources and added a hanging bag placement comparison and low and high soil moisture treatments. For the first Experiment, the N in uncoated urea released shortly after application. The SCU and PCSCU treatments released > 80% of the N before the first sampling date. With fluctuating temperatures, the PCU 45, 75, 120, and 180 incorporated into the soil released N within +9, +9, -22, and -68 d of their expected timing. However, they released their N within 35 d when surface applied. Conversely, with static temperatures, PCU products released slowly, releasing under 80% for the entire study. The second experiment verified these results and showed no difference between low and high moisture and minimal release with fertilizer not in contact with soil. Each coated fertilizer in these studies exhibited slow/control release properties, but the PCU (surface applied) and SCU/PCSCU (surface applied or incorporated in soil) release was much more rapid than expected. Our research suggests that, although the SCU and PCSCU showed minimal slow-release properties (regardless of placement), the PCU fertilizers incorporated in the soil do have a controlled release approximate to what is expected, but have a much more rapid release when surface applied.


Assuntos
Agricultura , Preparações de Ação Retardada/farmacologia , Fertilizantes , Nitrogênio/farmacologia , Preparações de Ação Retardada/química , Nitrogênio/química , Polímeros/química , Solo/química , Enxofre/química , Temperatura , Ureia/química , Ureia/farmacologia
10.
Chemosphere ; 253: 126896, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32402467

RESUMO

High concentrations of manganese (Mn2+) and ammonia nitrogen (NH4+-N) in electrolytic manganese residue (EMR) have seriously hindered the sustainable development of electrolytic manganese industry. In this study, an innovative basic burning raw material (BRM) was used to stabilize/solidify Mn2+ and NH4+-N in EMR. The characteristics of EMR and BRM, stabilize mechanism of NH4+-N and Mn2+, and leaching test were investigated. The concentrations of NH4+-N and Mn2+ were 12.8 mg/L and 0.1 mg/L, respectively, when the solid liquid ratio was 1.5:1, and the mass ratio of EMR and BRM was 100:10, at the temperature of 20 °C reacting for 12 h Mn2+ was mostly solidified as bustamite ((Mn,Ca)Si2O6), groutite (MnOOH) and ramsdellite (MnO2). NH4+-N was mostly recycled by (NH4)2SO4 and (NH4)3H(SO4)2. Leaching test results indicated that the concentrations of heavy metals were within the permitted level for the integrated wastewater discharge standard (GB8978-1996). Economic evaluation revealed that the cost of EMR treatment was $ 10.15/t by BRM. This study provided a new research idea for EMR harmless disposal.


Assuntos
Amônia/química , Materiais de Construção/análise , Eletrólitos/química , Compostos de Manganês/química , Nitrogênio/química , Reciclagem , Gerenciamento de Resíduos/métodos , China , Metais Pesados/análise , Águas Residuárias/química , Poluentes Químicos da Água/análise
11.
J Biosci Bioeng ; 130(2): 179-186, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32381439

RESUMO

The sediment-water interface is not only an important location for substrate conversion in a mariculture system, but also a major source of eutrophication. This study aimed to clarify the characteristics of inorganic nitrogen (ammonia, nitrite and nitrate) removal by Marichromatium gracile YL28 in the presence of both organic nitrogen and inorganic nitrogen. The results showed that, in the presence of peptone or urea, seaweed oligosaccharides (SOS) effectively enhanced the ammonia removal capacity of YL28 (6.42 mmol/L) and decreased the residual rate by 54.04% or 8.17%, respectively. With increasing peptone or urea concentrations, the removal of both ammonia and nitrate was gradually inhibited, and the residual rates of ammonia and nitrate reached 22.56-34.36% and 12.03-15.64% in the peptone system and 20.65-24.03% and 12.20-13.21% in the urea system, respectively. However, in the control group the residual rates of ammonia and nitrate reached 11.97% and 5.12%, respectively. In addition, the concentrations of peptone and urea did not affect nitrite removal, and YL28 displayed better cell growth and nitrogen removal activity in the presence of bait and SOS. Overall, the ability of YL28 to remove inorganic nitrogen was enhanced in the presence of organic nitrogen.


Assuntos
Aquicultura , Chromatiaceae/metabolismo , Nitrogênio/química , Nitrogênio/isolamento & purificação , Peptonas/farmacologia , Ureia/farmacologia , Água/química , Amônia/isolamento & purificação , Amônia/metabolismo , Desnitrificação/efeitos dos fármacos , Nitratos/isolamento & purificação , Nitratos/metabolismo , Nitritos/isolamento & purificação , Nitritos/metabolismo
12.
Chemosphere ; 255: 126976, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32402890

RESUMO

Bentonite was modified by introducing humic acid (HA) into interlayer space of bentonite. The structural and physicochemical properties of modified bentonite were determined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray powder diffraction (XRD) and thermogravimetric analysis (TGA). The results showed that HA could enter the bentonite interlayer and increase the interlayer distance. Moreover, we were also investigated the high adsorption capacity and thermodynamics of modified bentonite to NH4+ cations in solutions. Under the same conditions, the NH4+ adsorption efficiency of modified bentonite (96.4%) was 69.2% higher compared with the natural bentonite (57.0%). The pseudo-second order kinetic model well fit the adsorption kinetics of NH4+ on modified bentonite, indicating that the adsorption type was chemical adsorption or chemisorptions. The isotherms fit well with Langmuir model, and the separation factor revealed that NH4+ on modified bentonite belonged to favorable adsorption. Compared with the natural bentonite, the modified bentonite exhibited a much lower leaching loss of NH4+-N and NO3--N in soil. Meanwhile, the loss of nitrogen caused by NH3 volatilization and N2O emission from soil could also be significantly attenuated by the combined application of modified bentonite and urea. The slower nitrogen release in the treatment combining modified bentonite and urea resulted in a greater yield and nitrogen uptake of wheat. Collectively, the modified bentonite could be used as nitrogen fertilizer synergist to enhance the nitrogen use efficiency.


Assuntos
Bentonita/química , Substâncias Húmicas , Nitrogênio/química , Adsorção , Fertilizantes , Concentração de Íons de Hidrogênio , Cinética , Solo/química , Espectroscopia de Infravermelho com Transformada de Fourier , Ureia/química
13.
Chemosphere ; 255: 126970, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32408128

RESUMO

In this work, a CuO-Co3O4/Ti composite was prepared via the coating-calcination method and employed as a cathode for the NO3--N reduction to increase the removal efficiency of total nitrogen (TN). SEM, EDS, and XRD characterization results indicated that CuO and Co3O4 were successfully introduced to the surface of Ti. The CuO-Co3O4/Ti electrode eventually removed NO3--N with the main products of N2, NH4+-N and NO2--N. In comparison to the Co3O4/Ti electrode, the better hydrogen evolution properties of the CuO-Co3O4/Ti electrode resulted in pH increase and NH3 gas release, so the TN removal for CuO-Co3O4/Ti electrode was improved approximately 20%. The presence of Cl- with the concentration up to 1000 mg L-1 greatly promoted the removal of TN from 40.1% to 94.0%, as a result of NH4+-N oxidation with free chlorine produced from the anode. Furthermore, the CuO-Co3O4/Ti electrode was applied to conduct three types of actual wastewater (biological effluent of municipal wastewater and industrial wastewater, and a regeneration concentrate from an anion exchange process) for nitrate removal. The highest TN removal efficiency (78.5%) and current efficiency (54.5%), and the lowest energy consumption (2 × 10-4 kWh mg-1 TN) were obtained for the regeneration concentrate, suggesting the feasibility of the CuO-Co3O4/Ti electrode to the water with high conductivity and high Cl- concentration for removing TN by the reduction of nitrate.


Assuntos
Nitratos/química , Nitrogênio/química , Eliminação de Resíduos Líquidos/métodos , Reatores Biológicos , Cobre , Desnitrificação , Eletrodos , Óxidos de Nitrogênio , Oxirredução , Titânio/química , Águas Residuárias
14.
Int J Nanomedicine ; 15: 2617-2631, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32368044

RESUMO

Introduction: As widely used chemotherapeutic agents, platinum compounds have several therapeutic challenges, such as drug resistance and adverse effects. Theranostic systems, macromolecular or colloidal therapeutics with companion diagnostics, not only address controlled drug delivery but also enable real-time monitoring of tumor sites. Methods: Synthesis of magnetic mesoporous silica nanoparticles (MMSNs) was performed for dual magnetic resonance imaging and drug delivery. MMSN surfaces were modified by imidazoline groups (MMSN-Imi) for cisplatin (Cis-Pt) conjugation via free N-termini to achieve well-controlled drug-release kinetics. Cis-Pt adsorption isotherms and drug-release profile at pH 5 and 7.4 were investigated using inductively coupled plasma atomic emission spectroscopy. Results: MMSN-Imi showed a specific surface area of 517.6 m2 g-1, mean pore diameter of 3.26 nm, and saturated magnetization of 53.63 emu/g. A relatively high r2/r1 relaxivity value was obtained for MMSN-Imi. The nanoparticles provided high Cis-Pt loading with acceptable loading capacity (~30% w:w). Sustained release of Cis-Pt under acidic conditions led to specific inhibitory effects on the growth of human epithelial ovarian carcinoma cells, determined using MTT assays. Dual acridine orange-propidium iodide staining was investigated, confirming induction of apoptosis and necrotic cell death. Conclusion: MMSN-Imi exhibited potential for applications in cancer chemotherapy and combined imaging.


Assuntos
Sistemas de Liberação de Medicamentos , Imidazolinas/química , Nanopartículas de Magnetita/química , Platina/administração & dosagem , Dióxido de Silício/química , Nanomedicina Teranóstica , Adsorção , Antineoplásicos/administração & dosagem , Antineoplásicos/farmacologia , Morte Celular , Linhagem Celular Tumoral , Cisplatino/administração & dosagem , Cisplatino/farmacologia , Liberação Controlada de Fármacos , Difusão Dinâmica da Luz , Hemólise , Humanos , Cinética , Imagem por Ressonância Magnética , Nanopartículas de Magnetita/ultraestrutura , Nitrogênio/química , Tamanho da Partícula , Espectroscopia de Infravermelho com Transformada de Fourier , Eletricidade Estática , Temperatura , Difração de Raios X
15.
Chemosphere ; 255: 126901, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32387904

RESUMO

Enhanced nitrate removal from the secondary effluent in municipal wastewater treatment plants (WWTPs) is essential for avoiding water eutrophication. To this end, a vertical baffled solid-phase denitrification reactor (VBSDR) was developed using a starch and polycaprolactone (PCL) blend plate (S-PCL) as a carbon source and biofilm carrier. In this study, we evaluated the denitrification performance and microbial diversity of the VBSDR. The results of the Fourier transform infrared spectroscopy (FTIR), carbon leaching experiment, and scanning electron microscopy (SEM) demonstrated that the S-PCL structure can be attached and degraded more rapidly. Furthermore, the denitrification performance under varied operational conditions, i.e., influent nitrate loading rate (NLR) and operating temperature, was also investigated. Herein, when treating low C/N ratio and low-strength wastewater, a high denitrification rate (DR) [0.33 gN/(L·d)] was achieved. The effect of temperature on DR can be described by the Arrhenius-type equation, which shows that low temperature has a negative influence on DR and nitrate removal efficiency. Furthermore, DR was simultaneously affected by the NLR and temperature. The microbial diversity and community structure were determined by Illumina high-throughput sequencing. The special carbon source led to Acidovorax (denitrifying bacteria) and Flavobacterium (hydrolysis acidifying bacteria) being the VBSDR biofilm's most predominant functional bacteria at the genus level.


Assuntos
Poliésteres/química , Eliminação de Resíduos Líquidos/métodos , Biofilmes , Reatores Biológicos/microbiologia , Carbono/química , Comamonadaceae , Desnitrificação , Nitratos/química , Nitrogênio/química , Amido/química , Temperatura , Águas Residuárias/química
16.
Food Chem ; 326: 126976, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32413756

RESUMO

This study developed a novel electrochemical sensor containing nitrogen-doped ordered mesoporous carbon (NOMC) for the sensitive and selective quantification of l-tryptophan (Trp). The electro-oxidation mechanism of Trp on the NOMC/Nafion/glass carbon electrode (GCE) was first investigated, and was found to follow a two-electron/two-proton transfer mechanism. Subsequently, the analytical operation conditions were optimized. Under the optimum testing conditions, the oxidation current was found to increase linearly with Trp concentration in the ranges 0.5-70.0 µM and 70.0-200.0 µM (different slopes in each range), with the limit of detection determined to be 35.0 nM (S/N = 3). In addition, the sensor was highly selective for Trp and showed good repeatability and long-term stability. Studies of Trp in real world systems, such as an 18 amino acid mixture and an enzymatic protein hydrolysate, showed excellent recoveries (99.30-103.60%). Results suggest that NOMC/Nafion/GCE sensor has excellent performance characteristics for routine Trp analysis.


Assuntos
Carbono/química , Técnicas Eletroquímicas/métodos , Nitrogênio/química , Triptofano/análise , Polímeros de Fluorcarboneto/química , Limite de Detecção , Oxirredução , Porosidade , Proteínas/química , Triptofano/química
17.
Food Chem ; 326: 126935, 2020 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-32447160

RESUMO

Carbon dots (CDs) have been a new class of fascinating carbon-based fluorescent nanomaterials. In the present work, new N-doped CDs with highly crystalline graphite structures are prepared from renewable precursors, chitosan and tartaric acid, and are well characterized. The prepared CDs are applied as a biocompatible fluorescent sensor for the sequential detection of Fe3+ and AA. Among various transition metal ions, Fe3+ can selectively quench the fluorescence of CDs. Upon the further addition of AA, the quenched fluorescence of CDs is then restored as Fe3+ is reduced to Fe2+ by AA, which can be utilized for the fluorescent determination of AA. A good linear relationship in the range of 0-150 µM of AA concentration is established with a low detection limit of 0.02 µM. Moreover, the practical applications of this fluorescent sensing method in measurement of AA in food samples are successfully realized with satisfactory results.


Assuntos
Ácido Ascórbico/análise , Carbono/química , Compostos Férricos/análise , Nanoestruturas/análise , Espectrometria de Fluorescência/métodos , Fluorescência , Limite de Detecção , Nitrogênio/química , Pontos Quânticos/química , Espectrometria de Fluorescência/instrumentação
18.
Food Chem ; 321: 126628, 2020 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-32259731

RESUMO

We investigated the potential of front-face synchronous fluorescence spectroscopy (△λ = 75 nm) to non-destructively evaluate beef freshness and quality decline during chilled storage. The total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS) and total viable count (TVC) values were used as standard freshness indicators. The fluorescent substances, including amino acids, collagen and conjugated Schiff bases, were highly correlated with the chemical and microbial deterioration of the beef. Quantitative models for simultaneously predicting the three freshness indicators were built combined with partial least squares (PLS) algorithm and showed good reliability. For TVB-N and TBARS values, Rc2 and Rp2 were both above 0.900, and for TVC values Rc2 and Rp2 were 0.912 and 0.871, respectively. The qualitative model established by partial least squares discriminant analysis (PLS-DA) algorithm could accurately classify beef samples as fresh, acceptable or spoiled. The accuracy of the calibration and validation sets were 92.54% and 86.96%, respectively.


Assuntos
Carne Vermelha/análise , Algoritmos , Animais , Calibragem , Bovinos , Análise Discriminante , Análise dos Mínimos Quadrados , Nitrogênio/química , Carne Vermelha/microbiologia , Reprodutibilidade dos Testes , Espectrometria de Fluorescência , Substâncias Reativas com Ácido Tiobarbitúrico/química
19.
PLoS One ; 15(3): e0230192, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32226036

RESUMO

While movement patterns of grazing ungulates are strongly dependent on forage quality their use of nutrient hotspots such as termite mounds or grazing lawns has rarely been quantified, especially in savanna ecosystems where soil-nutrient quality is low. Additionally, few experiments have been conducted to determine the role of termite mound- and grazing lawn-derived soils in improving forage quality in the field. We studied wild ungulate grazing activities around ten termite mounds, six grazing lawns and their respective control sites in a Miombo system of Issa Valley, western Tanzania, in the same system. We used indirect observations (i.e., dung, tracks) to identify seasonal and spatial variations in habitat use of various wild mammalian grazers. Grazer visitation rates were nine and three times higher on termite mounds and grazing lawns, respectively, compared to control sites. During the rainy season, termite mounds were more frequently used than grazing lawns while the latter were used more often during the dry season. In an additional pot experiment with soils derived from different areas, we found that Cynodon dactylon in termite mound-derived soils had twice as high Nitrogen and Phosphorous contents and biomass compared to grasses planted in grazing lawn soils and control site soils. We highlight that both termite mounds and grazing lawns play a significant role in influencing seasonal nutrient dynamics, forage nutrient quality, habitat selectivity, and, hence, grazing activities and movement patterns of wild ungulate grazers in savannas. We conclude that termite mounds and grazing lawns are important for habitat heterogeneity in otherwise nutrient-poor savanna systems.


Assuntos
Cynodon/química , Nutrientes/química , Poaceae/química , Animais , Biomassa , Ecossistema , Comportamento Alimentar/fisiologia , Pradaria , Isópteros/química , Mamíferos , Nitrogênio/química , Fósforo/química , Plantas/química , Estações do Ano , Solo/química , Tanzânia
20.
J Vis Exp ; (157)2020 03 19.
Artigo em Inglês | MEDLINE | ID: mdl-32250360

RESUMO

Chemical model complexes are prepared to represent the active site of an enzyme. In this protocol, a family of tridentate pincer ligand precursors (each possessing two sulfur and one nitrogen donor atom functionalities (SNS) and based on bis-imidazole or bis-triazole compounds) are metallated with CoCl2·6H2O to afford tridentate SNS pincer cobalt(II) complexes. Preparation of the cobalt(II) model complexes for liver alcohol dehydrogenase is facile. Based on a quick color change upon adding the CoCl2·6H2O to acetonitrile solution that contains the ligand precursor, the complex forms rapidly. Formation of the metal complex is complete after allowing the solution to reflux overnight. These cobalt(II) complexes serve as models for the zinc active site in liver alcohol dehydrogenase (LADH). The complexes are characterized using single crystal X-ray diffraction, electrospray mass spectrometry, ultra-violet visible spectroscopy, and elemental analysis. To accurately determine the structure of the complex, its single crystal structure must be determined. Single crystals of the complexes that are suitable for X-ray diffraction are then grown via slow vapor diffusion of diethyl ether into an acetonitrile solution that contains the cobalt(II) complex. For high quality crystals, recrystallization typically takes place over a 1 week period, or longer. The method can be applied to the preparation of other model coordination complexes and can be used in undergraduate teaching laboratories. Finally, it is believed that others may find this recrystallization method to obtain single crystals beneficial to their research.


Assuntos
Álcool Desidrogenase/química , Cobalto/química , Complexos de Coordenação/química , Fígado/enzimologia , Modelos Químicos , Cristalografia por Raios X , Imidazóis , Ligantes , Nitrogênio/química , Espectrometria de Massas por Ionização por Electrospray , Enxofre/química , Zinco/química
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