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1.
J Contemp Dent Pract ; 21(2): 119-123, 2020 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-32381813

RESUMO

AIM: The aim of this study is to compare the efficacy of dipotassium oxalate and potassium nitrate to occlude dentinal tubules. MATERIALS AND METHODS: This study utilized Parkinson model of longitudinal dentin tubule occluding properties of dentifrices under a 4-day acid challenge. Dentin disks of approximately 1.5 mm thick were sectioned from the crowns of the freshly extracted molars. The disks were randomized into three sets of 15 and treated with dipotassium oxalate, potassium nitrate, or used as a control. The disks were then subjected to a 4-day acid challenge and evaluated by scanning electron microscopy (SEM). RESULTS: On days 1, 2, and 3, dipotassium oxalate showed significant occlusion of dentinal tubules. On day 4, no significant difference was observed between dipotassium oxalate and potassium nitrate. Both test groups showed better occlusion properties in comparison to the control. CONCLUSION: Through the use of a 4-day acid challenge, this study demonstrates that both agents can indeed occlude dentinal tubules. Initially, dipotassium oxalate does occlude dentinal tubules faster than potassium nitrate. However, at the conclusion of the acid challenge, minimal differences were observed in occlusion rate among the two agents. Further studies should be conducted to determine the efficacy of these two agents. CLINICAL SIGNIFICANCE: Both dipotassium oxalate and potassium nitrate can help treat patients with dentinal hypersensitivity.


Assuntos
Permeabilidade da Dentina , Ácido Oxálico , Dentina , Humanos , Nitratos , Compostos de Potássio
2.
J Environ Manage ; 265: 110576, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32421564

RESUMO

Phosphate rock (PR) and ferric salts have been frequently used to immobilize heavy metal(loid)s in soils, but in varied efficiencies referring to different metal(loid) pollutants. This study explored the effective application of plant ash (PA) to the previous formula of phosphate rock (PR) and ferric salts (Fe(NO3)3) (PR + Fe3++PA), compared to only PR, on the bioavailability and immobility of multi-metal(loid)s of selected arsenic (As), lead (Pb) and cadmium (Cd) in soils. Results from NaHCO3- extraction and toxicity characteristic leaching procedure (TCLP) implied the increase of the As mobility in soils by 7.0% and 2.6% using PR only, but the significant reduction of the As mobility by 24.2% and 82.4% jointly using PR + Fe3++PA. Meanwhile, the application of either PR alone or PR + Fe3++PA in soil significantly decreased Pb and Cd extracting in diethylene triamine pentacetate acid (DTPA) and TCLP, particularly, the immobilization effect of PR + Fe3++PA was better than that of PR. The leaching column test further confirmed the high durability of PR + Fe3++PA on the immobilization of As and Pb under the continuous acid exposure, but likely slightly increased the mobility of Cd (the accumulated concentration of Cd, 5.88 µg/L) compared to that (3.16 µg/L) in the untreated column (UN-column), which were both much lower than the level V (100 µg/L) of the Chinese National Quality Standard for Surface Water (GB 3838-2002). Therefore, PR + Fe3++PA exhibited the significant enhancement on the immobilization of As, Pb and Cd under simulated acid rain (SAR) leaching.


Assuntos
Arsênico , Metais Pesados , Poluentes do Solo , Cádmio , Compostos Férricos , Chumbo , Nitratos , Fosfatos , Solo
3.
Water Res ; 178: 115848, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32361288

RESUMO

Micro-aerobic enhancement technology has been developed as an effective tool to enhance simultaneous removal of sulfide, nitrate and organic carbon during the integrated autotrophic-heterotrophic denitrification (IAHD) process under high loading; however, its mechanism of enhancement for functional bacteria remains ambiguous. In this study, we discovered that heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) are responsible for enhancing IAHD performance under micro-aerobic conditions with high sulfide loading. In a continuous IAHD bioreactor, aeration rate of 2.6 mL min-1·L-1 promoted 2 to 4 times higher removal efficiencies of sulfide, nitrate and acetate with an influent sulfide concentration of 18.75 mmol/L. Metagenomic analysis revealed that trace oxygen stimulated the abundance of genes responsible for sulfide oxidation (sqr, glpE, pdo, sox and cysK), which were upregulated by 15.2%-129.9%, and the genes encoding nitrate reductase were up-regulated by 67.4%. The increased acetate removal efficiency was attributed to upregulation of ack, pta and TCA cycle related genes. The h-NRB Pseudomonas, Azoarcus, Thauera and Halomonas were detected and regarded as h-soNRB in our bioreactor. According to Illumina MiSeq sequencing, these genera were absolutely dominant in the micro-aerobic microbial community at relative abundances ranging from 82.72% to 90.84%. The sulfide, nitrate and acetate removal rates of Pseudomonas C27, a typical h-soNRB, were at least 10 times higher under micro-aerobic conditions than under anaerobic conditions. Besides, the sulfur, nitrogen and carbon metabolic network was constructed based on the Pseudomonas C27 genome. The pdo and cysK genes found in this strain may be the most advantageous for autotrophic sulfide oxidizing nitrate reducing bacteria (a-soNRB), which are closely related to the high-efficiency sulfide, nitrate and acetate removal performance under high sulfide concentrations and a limited oxygen supply. In addition, after micro-aerobic cultivation, the anaerobic sulfide loading tolerance of the IAHD bioreactor increased from 18.75 to 37.5 mmol/L with sulfide, nitrate and acetate removal efficiencies increasing 1.5 to 3 times, which suggests that intermittent micro-aeration might be a more economical and efficient regime for high-sulfide IAHD regulation.


Assuntos
Processos Autotróficos , Desnitrificação , Bactérias , Reatores Biológicos , Nitratos , Oxirredução , Sulfetos
4.
Bioresour Technol ; 310: 123465, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32388206

RESUMO

Nitrogen removal from saline wastewater is challenging due to adverse effects of salinity on biological processes. A novel sulfur-autotrophic cyclic denitrification filter (CDF) was tested for marine recirculating aquaculture systems (RAS) under varying conditions. Low ammonia, nitrite and sulfide concentrations were maintained at residence times between 4 and 12 h. After introduction of Poecilia sphenops, concentrations of NH4+-N, NO2--N, NO3--N were maintained below 1, 1, and 60 mg/L, respectively. Fish waste inputs to the CDF contributed to mixotrophic denitrification and low sulfate production. A mass balance showed that 7% of the feed nitrogen was assimilated by fish, 6% was removed by passive denitrification (e.g., in anoxic zones in filters), 60% in the CDF and 27% was discharged during sampling and solids removal. Daily fresh water addition was <2% of fish tank volumes. The results are promising as a low cost alternative for saline wastewater denitrification.


Assuntos
Reatores Biológicos , Desnitrificação , Animais , Aquicultura , Processos Autotróficos , Nitratos , Nitrogênio , Enxofre , Águas Residuárias
5.
Bioresour Technol ; 309: 123451, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32361619

RESUMO

Micro-aeration is an effective tool that helps integrated autotrophic and heterotrophic denitrification process to withstand high sulfide concentration by making heterotrophic sulfide-oxidizing nitrate-reducing bacteria (h-soNRB) prevail. For further understanding of the dominance of h-soNRB, Pseudomonas C27 was selected as the typical bacterium and its metabolic characteristics responding to sulfide and oxygen stimulation were studied. Under high sulfide concentration condition, addition of trace oxygen led to a two-stage sulfide oxidation process, and sulfide oxidation rate in the first stage was 1.4 times more than that under anaerobic condition. According to transcriptome analysis, the pdo gene significantly up-regulated 2.36 and 2.57 times with and without oxygen under stimulation of high sulfide concentration. Additionally, two possible enhanced sulfide removal pathways coping with high sulfide concentration, namely sqr-cysI-gpx-gor-glpE and cysK-gshA-gshB-pdo-glpE, caused by oxygen were proposed in Pseudomonas C27. These findings provide a theoretical basis for locating high-efficiency sulfur oxidase in h-soNRB.


Assuntos
Oxigênio , Pseudomonas , Bactérias , Reatores Biológicos , Desnitrificação , Nitratos , Oxirredução , Sulfetos
6.
Bioresour Technol ; 308: 123302, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32276204

RESUMO

Pyrrhotite-sulfur autotrophic denitrification (PSAD) system, using mixture of pyrrhotite and sulfur particle as electron donor, was studied through batch, column and pilot experiments. Treating synthetic secondary effluent at HRT 3 h, the PSAD system obtained the effluent with NO3--N 0.28 ± 0.14 mg·L-1 and without PO43--P to be detected. Thiobacillus was the most abundant autotrophic denitrification bacteria; autotrophic, heterotrophic and sulfate-reducing bacteria coexisted in the PSAD system; phosphate was mainly removed in forms of graftonite, dufrenite, ardealite. The H+ produced in the SAD could accelerate the PAD through promoting pyrrhotite dissolution, and iron ions produced in the PAD could accelerate the SAD through Fe3+/Fe2+ shuttle. Because of the synergistic effects between the pyrrhotite and sulfur, the PSAD system removed nitrate and phosphate deeply and efficiently. It is a promising way to meet the stringent nitrogen and phosphorus discharge standards and to recover phosphorus resources from wastewater.


Assuntos
Desnitrificação , Microbiota , Processos Autotróficos , Reatores Biológicos , Minerais , Nitratos , Nitrogênio , Fosfatos , Enxofre
7.
Bioresour Technol ; 308: 123301, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32299051

RESUMO

The intracellular carbon metabolic flux pathways of denitrifying bacteria under aerobic conditions remain unclear. Here, a newly strain LSL251 was identified as Paracoccus thiophilus. Strain LSL251 removed 94.79% and 98.78% of total organic carbon and nitrate. 74.66% of nitrogen in culture system was lost as gaseous nitrogen. Moreover, 13C stable isotopic labeling and metabolic flux analyses revealed that the primary intracellular carbon metabolic pathways were the Entner-Doudoroff pathway and the tricarboxylic acid (TCA) cycle. Electrons are primarily donated as direct electron donor-NADH through the TCA cycle. Furthermore, response surface methodology modeled that the highest total nitrogen removal efficiency was 98.43%, where the optimal parameters were C/N ratio of 8.00, 32.98 °C, 50.18 rpm, and initial pH of 7.73. All together, these results have shed new lights on intracellular central carbon metabolic distribution and flux pathways of aerobic denitrifying bacteria.


Assuntos
Paracoccus , Aerobiose , Carbono , Ciclo do Carbono , Desnitrificação , Nitratos , Nitrogênio
8.
Bioresour Technol ; 309: 123345, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32305844

RESUMO

Aerobic denitrification is attracting increasing attention since its advantage of complete nitrogen removal in a single aerobic reactor with simplified configurations. This study investigated the nitrate kinetic affinity (half-saturation index, Km) by an isolated aerobic denitrifier named P. balearica strain RAD-17. It turned out that strain RAD-17 had a high Km of 162.5 mg-N/L and maximum nitrate reduction rate of 21.7 mg-N/(L•h), enabling it to treat high-strength nitrogen wastewater with high efficiency. Further analysis illustrated that Km was the critical value for the change of growth yield rate along initial nitrate concentrations. Nitrogen balance results elucidated an opposite nitrogen flux to cell synthesis and nitrogen loss during aerobic denitrification. Moreover, the expression of functional genes provided proofs for these phenotypic results at transcriptional level. Consequently, Km could be an indicator for nitrate flux division directing to respiration and assimilation in aerobic denitrifiers, shedding light on its regulation for wastewater treatment.


Assuntos
Desnitrificação , Nitratos , Aerobiose , Nitrificação , Nitrogênio , Águas Residuárias
9.
Bioresour Technol ; 310: 123404, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32334362

RESUMO

Cobalt(II)-histidine [Co(II)His] is potentially a better alternative to ferrous complexes in the chemical absorption-biological reduction (CABR) flue gas denitrification process in view of its higher oxygenation reversibility. Though with excellent O2-resistant ability, Co(II)His was still gradually oxidized into Co(III)His, losing NO binding capacity. Thus, Co(III)His biological reduction is an indispensable step in CABR process. Co(III)His reduction by Paracoccus versutus LYM under aerobic condition in the presence of nitrate or nitrite was investigated. Results indicated that simultaneous Co(III)His reduction and aerobic denitrification were achieved by strain LYM. Co(III)His reduction was significantly promoted by denitrification process, but dramatically inhibited by 5-15 mM sulfite. Co(II)His absorbent regeneration could be facilitated by adjusting O2 supply properly or adding nitrogen and carbon source regularly. These findings provide a basis for the application of Co(II)His as the absorbent in the CABR process and qualify P. versutus LYM as an applicable and competitive strain for this process.


Assuntos
Desnitrificação , Paracoccus , Cobalto , Histidina , Nitratos , Nitritos , Nitrogênio
10.
Bioresour Technol ; 310: 123244, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32339888

RESUMO

High-nitrate wastewaters are known pose substantial risks to human and environmental health, while their effective treatment remains difficult. The denitrification of saline, high-NO3- wastewaters was investigated at the laboratory- and pilot-scale experiment. Complete denitrification was achieved for three different realistic wastewaters, and the maximum influent [NO3-]0 and salinity were as high as 20,500 mg/L and 7.8%, respectively. The results of microbial community structure analyses revealed that the sequences of denitrifying functional bacteria accounted for 96.2% of all sequences, and the functional genes for denitrification in bacteria were enriched with elevated salinity and [NO3-]0. A significant difference was observed in the dominant bacterial genus between synthetic and realistic wastewaters. Thauera and Halomonas species evolved to be the most common dominant genera contributing to the processes of nitrate, nitrite, and nitrous oxide reductase. This study is practically valuable for the treatment of realistic, saline, high-NO3- wastewaters via denitrification by heterotrophic bacteria.


Assuntos
Microbiota , Esgotos , Reatores Biológicos , Desnitrificação , Nitratos , Nitrogênio , Águas Residuárias
11.
Bioresour Technol ; 307: 123229, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32247270

RESUMO

The inclusion of S0 hydrolysis in a kinetic model of autotrophic denitrification has been recently proposed; however the model has not been calibrated or validated yet. Thus, a new methodology was developed and applied to calibrate and validate this kinetic model for the first time. An inoculum adapted from a poultry wastewater treatment plant at stoichiometric S0/NO3- ratio was used. The model was calibrated with batch data (initial nitrate concentrations of 50 and 6.25 mg NO3--N/L) at an S0/N ratio = 2.29 mg S/mg N and validated with seven different batch data. The sensitivity analysis showed that the most sensitive parameters are related to S0 hydrolysis. The kinetic model was successfully calibrated with the new methodology and validated, with Theil inequality coefficient values lower than 0.21. Thus, the proposed model and methodology were proved to be well suited for the simulation of elemental sulfur-based autotrophic denitrification in batch systems.


Assuntos
Reatores Biológicos , Desnitrificação , Processos Autotróficos , Calibragem , Nitratos , Enxofre
12.
Science ; 368(6486)2020 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-32241923

RESUMO

As primary producers, plants rely on a large aboveground surface area to collect carbon dioxide and sunlight and a large underground surface area to collect the water and mineral nutrients needed to support their growth and development. Accessibility of the essential nutrients nitrogen (N) and phosphorus (P) in the soil is affected by many factors that create a variable spatiotemporal landscape of their availability both at the local and global scale. Plants optimize uptake of the N and P available through modifications to their growth and development and engagement with microorganisms that facilitate their capture. The sensing of these nutrients, as well as the perception of overall nutrient status, shapes the plant's response to its nutrient environment, coordinating its development with microbial engagement to optimize N and P capture and regulate overall plant growth.


Assuntos
Nitratos/metabolismo , Fixação de Nitrogênio , Nutrientes/metabolismo , Plantas/metabolismo , Desenvolvimento Vegetal , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/metabolismo , Raízes de Plantas/microbiologia , Plantas/microbiologia , Simbiose
13.
J Environ Manage ; 262: 110307, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32250790

RESUMO

Stream and riparian zone networks embedded in agricultural landscapes provide a potential intervention point to ameliorate the negative effects of agricultural runoff by reducing transport of nitrate (NO3-) and suspended sediments (SS) downstream. However, our ability to support and promote NO3- and SS attenuation is limited by our understanding of vegetative and hydrogeomorphic controls in realistic management contexts. In addition, agricultural landscapes are heterogenous on multiple management scales, from farm field to regional water management scales, and the effect of these heterogeneities and how they interact across scales to affect vegetative and hydrogeomorphic controls is poorly explored in many settings. This is especially true in irrigated agricultural settings, where stream and riparian networks are entwined with and sensitive to water management systems. To fill these gaps, we related the vegetative and hydrogeomorphic features of 67 waterway reaches across two water management districts in the California Central Valley to reach-scale NO3- and turbidity attenuation and district-scale water quality patterns. We found that in-stream NO3- attenuation was rare, but, when it did occur, it was promoted by shallow and wide riparian banks, low flows, and high channel-edge denitrification potential. Nitrate concentrations were consistently higher in upstream reaches compared to water district outlets, suggesting that while exports from the district were low, agricultural runoff may impair within-district water resources. Turbidity attenuation was highly variable and unrelated to vegetative or hydrogeomorphic features, suggesting that onfield controls are crucial to managing suspended sediments. We conclude that waterway networks have the potential to mitigate the effects of agricultural NO3- runoff in this setting, but that more effective monitoring and adoption of NO3- attenuating features is needed. Using our findings, we make specific management and monitoring recommendations at both reach and water district scales.


Assuntos
Agricultura , Nitratos , California , Monitoramento Ambiental , Óxidos de Nitrogênio , Abastecimento de Água
14.
Bioresour Technol ; 306: 123174, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-32197955

RESUMO

The current work coupled simultaneous sulfide and nitrate removal in a Microbial Fuel Cell (MFC). The substrate removal and electricity generation were coupled at influent Sulfide to Nitrate molar ratios (S/N ratios) of 5:0, 5:1, 5:2 and 5:3. The sulfide concentrations used included: 60 mg S/L, 300 mg S/L, 540 mg S/L, 780 mg S/L and 1020 mg S/L. The effect of S/N ratio on the performance of substrate removal was greater at higher influent sulfide concentration. The electricity generation also varied at different influent sulfide concentrations and S/N ratios. The number of electrons generated at S/N ratio of 5:2 was the largest at any fixed influent sulfide concentration. The Pearson correlation showed that effluent sulfate concentration and nitrogen gas had significant positive correlations with steady state voltage (or electronic quantity). Moreover, the simulation models were developed to establish the relation between substrate removal and electricity generation at various S/N ratios.


Assuntos
Fontes de Energia Bioelétrica , Eletricidade , Nitratos , Óxidos de Nitrogênio , Sulfetos
15.
Chemosphere ; 250: 126223, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32113098

RESUMO

Air quality in large cities has worsened in recent years as a consequence people's health is directly affected. Among the toxic compounds released to environmental air are polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs (nitro-PAHs), and oxygenated PAHs (oxy-PAHs). Performant methods to analyze these compounds is necessary to enable adequate monitoring of air quality. Thus, this manuscript presents the development of a highly sensitive method to analyze PAHs, nitro-PAHs, and oxy-PAHs collected from ambient air (PM2.5) and the gas phase for a period of one year in the urban area of Belo Horizonte, Brazil. PAHs and their derivatives were extracted by cold fiber solid phase microextraction (CF-SPME) and analyzed by gas chromatography coupled to mass spectrometry (GC/MS). The proposed method allows simultaneous analysis of 16 PAHs, nitro-PAHs and oxy-PAHs, presenting very good limits of detection and quantification, as well as appropriate precision and recovery. The results obtained for the period of one year allowed different studies. The compounds collected simultaneously from gas and particulate phase showed that total concentration of 16 PAHs were higher in the gas phase than in the particulate. On the other hand, nitro-PAHs and oxy-PAHs presented similar concentration in gas and particulate phases. The potential carcinogenicity of PAHs relative to benzo[a]pyrene showed benzo[a]pyrene equivalents of 0.49 ng m-3. The estimated risk of lifetime lung cancer was 5 × 10-5. Principal component analysis and diagnostic ratio was applied for source distribution indicating that burning of gasoline, diesel and biomass accounted for the PAHs profile in ambient air samples.


Assuntos
Poluentes Atmosféricos/análise , Poluição do Ar/estatística & dados numéricos , Monitoramento Ambiental , Hidrocarbonetos Policíclicos Aromáticos/análise , Poluição do Ar/análise , Benzo(a)pireno/análise , Brasil , Respiração Celular , Cidades , Poeira/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Gasolina/análise , Humanos , Nitratos/química , Óxidos de Nitrogênio/análise , Oxigênio/química , Material Particulado/análise , Microextração em Fase Sólida
16.
Chemosphere ; 250: 126256, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32114341

RESUMO

Nitrated phenols in particulate matters are among the major components of brown carbon, harm plant growth and human health. To understand the size distributions of nitrated phenols in the polluted coastal region and the factors influencing these distributions, size-resolved particulate matters were collected from a rural site in the coastal city of Qingdao, China, in January 2019, and analyzed for the presence of 11 nitrated phenols. The average concentrations of total nitrated phenols in fine- and coarse-mode particles were 123.6 and 37.2 ng m-3, respectively. 4-Nitrophenol was found to be the dominant nitrated phenol, followed by 3-methyl-6-nitrocatechol, 3-methyl-4-nitrophenol, and 4-nitrocatechol. On average, maximum concentrations of nitrated phenols were in condensation-mode particles, whereas a minor concentration peak of nitro-salicylic acids was present in droplet-mode particles. In addition, a minor concentration peak of 4-methyl-2,6-dinitrophenol was noticed in coarse-mode particles. Comparisons of the size distributions under different situations confirmed that both primary emissions and secondary formation had significant effects on the abundances and particle-sizes of nitrated phenols. Coal combustion in residential villages and firework burning during a festival led to a sharp increase of nitrated phenols in condensation-mode particles, whereas dust promoted their heterogeneous formation in coarse-mode particles, and high humidity in the coastal area facilitated their aqueous formation in droplet-mode particles.


Assuntos
Poluentes Atmosféricos/análise , Monitoramento Ambiental , Fenóis/análise , Aerossóis/análise , Carbono/análise , Catecóis , Cidades , Carvão Mineral , Poeira , Humanos , Nitratos , Nitrocompostos , Óxidos de Nitrogênio , Tamanho da Partícula , Material Particulado/análise , Estações do Ano
17.
Bioresour Technol ; 307: 123196, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32220820

RESUMO

A novel biomaterial FeCl3/CaCl2/KH2PO4 modified municipal sludge biochar (FCPC) was synthesized. And the impacts of critical factors such as HRT, temperature and C/N ratio on simultaneous denitrification, dephosphorization and Cd(II) removal were investigated. Results show that the highest nitrate removal efficiency reached 92.22% (8.49 mg·L-1·h-1) in test group A and approximately 100% (9.19 mg·L-1·h-1) in test group B. Very low phosphate concentrations (approximately 2.50 mg/L) were detected in the effluent. The average removal efficiency of Cd(II) reached 86.40% (4.42 mg·L-1·h-1) in experimental group A and 90.15% (4.61 mg·L-1·h-1) in experimental group B. Gas emissions and biological precipitation in the bioreactors were monitored, further to confirming contaminant removal mechanisms. Additionally, Cupriavidus H29 was found to contribute dominantly to the FCPC bioreactor activity.


Assuntos
Cádmio , Cupriavidus , Materiais Biocompatíveis , Reatores Biológicos , Desnitrificação , Nitratos , Nitrogênio , Fósforo , Proteobactérias
18.
Bioresour Technol ; 307: 123230, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32222687

RESUMO

Strain Z195 was isolated and identified as Paracoccus denitrificans. Z195 exhibited efficient aerobic denitrification and carbon removal abilities, and removed 93.74% of total nitrogen (TN) and 97.81% of total organic carbon.71.88% of nitrogen was lost as gaseous products.13C-metabolic flux analysis revealed that 95% and 132% of the carbon fluxes entered the Entner-Doudoroff (ED) pathway and tricarboxylic acid (TCA) cycle, respectively. Electrons produced by carbon metabolism markedly promoted the processes of nitrogen metabolism process and aerobic respiration. A response surface methodology model demonstrated that the optimal conditions for the maximum TN removal were a C/N ratio of 7.47, shaking speed of 108 rpm, temperature of 31 °C and initial pH of 8.02. Additionally, the average TN and chemical oxygen demand removal efficiencies of raw wastewater were 89% and 91%, respectively. The results give new insight for understanding metabolic flux analysis of aerobic denitrifying bacteria.


Assuntos
Paracoccus denitrificans , Aerobiose , Bactérias , Desnitrificação , Redes e Vias Metabólicas , Nitratos , Nitrificação , Nitrogênio
19.
Water Res ; 175: 115688, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32171095

RESUMO

Ion exchange is widely used to treat nitrate-contaminated groundwater, but high salt usage for resin regeneration and management of waste brine residuals increase treatment costs and add environmental burdens. Development of palladium-based catalytic nitrate treatment systems for brine treatment and reuse has showed promising activity for nitrate reduction and selectivity towards the N2 over the alternative product ammonia, but this strategy overlooks the potential value of nitrogen resources. Here, we evaluated a hybrid catalytic hydrogenation/membrane distillation process for nitrogen resource recovery during treatment and reuse of nitrate-contaminated waste ion exchange brines. In the first step of the hybrid process, a Ru/C catalyst with high selectivity towards ammonia was found to be effective for nitrate hydrogenation under conditions representative of waste brines, including expected salt buildup that would occur with repeated brine reuse cycles. The apparent rate constants normalized to metal mass (0.30 ± 0.03 mM min-1 gRu-1 under baseline condition) were comparable to the state-of-the-art bimetallic Pd catalyst. In the second stage of the hybrid process, membrane distillation was applied to recover the ammonia product from the brine matrix, capturing nitrogen as ammonium sulfate, a commercial fertilizer product. Solution pH significantly influenced the rate of ammonia mass transfer through the gas-permeable membrane by controlling the fraction of free ammonia species (NH3) present in the solution. The rate of ammonia recovery was not affected by increasing salt levels in the brine, indicating the feasibility of membrane distillation for recovering ammonia over repeated reuse cycles. Finally, high rates of nitrate hydrogenation (apparent rate constant 1.80 ± 0.04 mM min-1 gRu-1) and ammonia recovery (overall mass transfer coefficient 0.20 m h-1) with the hybrid treatment process were demonstrated when treating a real waste ion exchange brine obtained from a drinking water utility. These findings introduce an innovative strategy for recycling waste ion exchange brine while simultaneously recovering potentially valuable nitrogen resources when treating contaminated groundwater.


Assuntos
Destilação , Nitrogênio , Hidrogenação , Troca Iônica , Nitratos , Sais
20.
Electron. j. biotechnol ; 44: 47-57, Mar. 2020. tab, ilus, graf
Artigo em Inglês | LILACS | ID: biblio-1087699

RESUMO

BACKGROUND: The determination of kinetic parameters and the development of mathematical models are of great interest to predict the growth of microalgae, the consumption of substrate and the design of photobioreactors focused on CO2 capture. However, most of the models in the literature have been developed for CO2 concentrations below 10%. RESULTS: A nonaxenic microalgal consortium was isolated from landfill leachate in order to study its kinetic behavior using a dynamic model. The model considered the CO2 mass transfer from the gas phase to the liquid phase and the effect of light intensity, assimilated nitrogen concentration, ammonium concentration and nitrate concentration. The proposed mathematical model was adjusted with 13 kinetic parameters and validated with a good fit obtained between experimental and simulated data. CONCLUSIONS: Good results were obtained, demonstrating the robustness of the proposed model. The assumption in the model of DIC inhibition in the ammonium and nitrate uptakes was correct, so this aspect should be considered when evaluating the kinetics with microalgae with high inlet CO2 concentrations.


Assuntos
Dióxido de Carbono/análise , Microalgas/efeitos da radiação , Microalgas/fisiologia , Cinética , Vertedores , Fótons , Microalgas/isolamento & purificação , Microalgas/crescimento & desenvolvimento , Fotobiorreatores , Águas Residuárias , Modelos Biológicos , Nitratos , Nitrogênio
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