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1.
Water Res ; 179: 115904, 2020 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-32413615

RESUMO

Involvements of quorum sensing (QS) in the formation of aerobic granules for wastewater treatment have been well recognized. In previous studies the evolution of the QS-related activities and communities during bioreactor start-up period has been extensively studied, while the variation of QS in long-term reactor operation remains unrevealed. Furthermore, information about the roles of quorum quenching (QQ) in bioreactors is very limited. In this work, both QS and QQ during the start-up and successive long-term operation period of an aerobic granule bioreactor were explored. The QS activity and communities increased in the start-up but gradually decreased in the long-term operation, while the QQ activity and communities remained stable. These results indicate the longer persistence of QQ than QS in the granules and the minor contribution of QS in the long-term operation. This work provides a new insight into the roles of QQ and QS in wastewater treatment bioreactors.

2.
Biotechnol Bioeng ; 2020 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-32356906

RESUMO

Shewanella oneidensis MR-1, a model strain of exoelectrogenic bacteria (EEB), plays a key role in environmental bioremediation and bioelectrochemical systems because of its unique respiration capacity. However, only a narrow range of substrates can be utilized by S. oneidensis MR-1 as carbon sources, resulting in its limited applications. In this study, a rapid, highly efficient, and easily manipulated base-editing system pCBEso was developed by fusing a Cas9 nickase (Cas9n (D10A)) with the cytidine deaminase rAPOBEC1 in S. oneidensis MR-1. The C-to-T conversion of suitable C within the base-editing window could be readily and efficiently achieved by the pCBEso system without requiring double-strand break or repair templates. Moreover, double-locus simultaneous editing was successfully accomplished with an efficiency of 87.5%. With this tool, the key genes involving in N-acetylglucosamine (GlcNAc) or glucose metabolism in S. oneidensis MR-1 were identified. Furthermore, an engineered strain with expanded carbon source utilization spectra was constructed and exhibited a higher degradation rate for multiple organic pollutants (i.e., azo dyes and organoarsenic compounds) than the wild-type when glucose or GlcNAc was used as the sole carbon source. Such a base-editing system could be readily applied to other EEB. This study not only enhances the substrate utilization and pollutant degradation capacities of S. oneidensis MR-1 but also accelerates the robust construction of engineered strains for environmental bioremediation.

3.
Water Res ; 178: 115834, 2020 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-32339865

RESUMO

Bioactivity and settleability of activated sludge are essential for the operation of activated sludge systems in wastewater treatment. In this work, the fractal dimension of sludge image is proposed as a tool to evaluate these two factors. The specific endogenous respiration rate (SOURe) and the specific quasi-endogenous respiration rate (SOURq) are found to be more dependent on the 3D structure of sludge than the specific total respiration rate (SOURt). The relationship between the fractal structure and bioactivity suggests that the bioactivity governs the acceptable upper bound of the fractal dimension (Df), as at its theoretical maximum of 2.0, the non-porous compact flocs are predominant. The settleability or the biomass concentration determines the acceptable lower bound of Df, as at its theoretical minimum of 1.0, the free-swimming microbes are predominant. Our data reveal that the activated sludge has an acceptable fractal dimension Df in a range of 1.07-1.68. In practice, the fractal dimension should be controlled at a reasonable value as there is a trade-off between the bioactivity and physical structure to achieve better performance. A decrease or increase in the fractal dimension can serve as a signal for the change of the operational status, and this is further elucidated from the perspective of settling tanks using state point analysis. Compared with respirogram measurement, measuring fractal dimension is a complex process and its online implementation is challenging. Also, the measured value varies with the methods used. In addition, the difference in their theoretical values depends on the homogeneity of the sludge structure. Since the fractal dimension Df reflects both bioactivity and settleability of the sludge but is difficult to measure, in this work a relationship between Df and the easily measurable respirogram is established, and a method using the respirogram as a proxy of Df is proposed to control the bioactivity and settleability simultaneously. This respiration-based method is able to simultaneously control aeration and settling tanks, and could serve as an efficient tool for the management of wastewater treatment plants.

4.
Environ Sci Technol ; 2020 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-32243759

RESUMO

Accurate, rapid, and reliable quantification of saccharides is essential for understanding their behaviors and roles in environmental processes. However, the conventional colorimetric method for saccharide quantification fails to discriminate between fructose and glucose, resulting in the misestimation of total saccharides. To solve this problem, a fluorescence approach, that is, parallel factor framework-linear regression analysis, was developed in this work to quantify the specific fluorescence signatures of the fluorescent products generated from the reaction between saccharides and sulfuric acid. The fluorescent derivatives of saccharides were recognized and the simultaneous quantification of glucose and fructose was achieved with a detection limit of 2.9 µg/mL and 1.3 µg/mL, respectively. Furthermore, 200 µg/mL of the treated sorbitol and gluconic acid only, respectively, equaled to 6 µg/mL and 3 µg/mL of the treated glucose, indicating their negligible interference for the saccharide quantification using this method. In addition, the feasibility and robustness of this method in environmental applications were validated with the recovery tests using spiked real water samples. This fluorescence-based approach offers a new tool to monitor saccharides in complex environments.

5.
Analyst ; 2020 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-32307505

RESUMO

Oxidative stress may result in different modes of cell death, such as necrosis, apoptosis and necroptosis. Currently, researchers are still striving to develop efficient tools/methods to distinguish the cell death modes in direct and label-free ways. In this study, we attempted to employ Raman micro-spectroscopy to observe the molecular changes in Candida utilis cells under oxidative stress induced by low-temperature plasma (LTP) and explore the spectroscopic biomarkers for the modes of cell death under oxidative stress. In this research, we confirmed that LTP could impose oxidative stress on the yeast cells, and recorded the changes of Raman signals of cytochrome c in the cells under LTP oxidative stress. Subsequently, we identified the biochemical and morphological characteristic features corresponding to different modes of cell death. Interestingly, we found that LTP under certain conditions could induce oxidative stress which caused the yeast cell death mainly by means of necroptosis, which was verified by Annexin V/PI, HMGB1 location assay and immunoprecipitation assay of the RIP1/RIP3 necrosome. Correspondingly, we also showed that the LTP induced necroptosis, associated with the increase of cytoplasmic Ca2+ and mitochondrial ROS, the decrease of mitochondrial membrane potential, the release of oxidized cytochrome c from the mitochondrion to the cytoplasm, and the destruction of mitochondria in yeast cells. This work has therefore demonstrated that monitoring the redox state of cytochrome c using Raman micro-spectroscopy is very useful for distinguishing the modes of cell death and particularly may unveil the unique necroptosis process of cells under extrinsic oxidative stress.

6.
Biosens Bioelectron ; 156: 112136, 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32174561

RESUMO

Shewanella oneidensis MR-1, a model species of exoelectrogenic bacteria (EEB), has been widely applied in bioelectrochemical systems. Biofilms of EEB grown on electrodes are essential in governing the current output and power density of bioelectrochemical systems. The MR-1 genome is exceptionally dynamic due to the existence of a large number of insertion sequence (IS) elements. However, to date, the impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems remain unrevealed. Herein, we isolated a non-motile mutant (NMM) with biofilm-deficient phenotype from MR-1. We found that the insertion of an ISSod2 element into the flrA (encoding the master regulator for flagella synthesis and assembly) of MR-1 resulted in the non-motile and biofilm-deficient phenotypes in NMM cells. Notably, such a variant was readily confused with the wild-type strain because there were no obvious differences in growth rates and colonial morphologies between the two strains. However, the reduced biofilm formation on the electrodes and the deteriorated performances of bioelectrochemical systems and Cr(VI) immobilization for the strain NMM were observed. Given the wide distribution of IS elements in EEB, appropriate cultivation and preservation conditions should be adopted to reduce the likelihood that IS elements-mediated mutation occurs in EEB. These findings reveal the negative impacts of IS elements on the biofilm-forming capacity of EEB and performance of bioelectrochemical systems and suggest that great attention should be given to the actual physiological states of EEB before their applications.

7.
Anal Chem ; 92(5): 3990-3997, 2020 Mar 03.
Artigo em Inglês | MEDLINE | ID: mdl-32020800

RESUMO

Mercury (Hg), as a highly harmful environmental pollutant, poses severe ecological and health risks even at low concentrations. Accurate and sensitive methods for detecting Hg2+ ions in aquatic environments are highly needed. In this work, we developed a highly sensitive fluorescence sensor for Hg2+ detection with an integrated use of biosynthetic CdSe/CdS quantum dots (QDs) and liposome carrier signal amplification. To construct such a sensor, three single-stranded DNA probes were rationally designed based on the thymine-Hg2+-thymine (T-Hg2+-T) coordination chemical principles and by taking advantage of the biocompatibility and facile-modification properties of the biosynthetic QDs. Hg2+ could be determined in a range from 0.25 to 100 nM with a detection limit of 0.01 nM, which met the requirements of environmental sample detection. The sensor also exhibited a high selectivity for Hg2+ detection in the presence of other high-level metal ions. A satisfactory capacity of the sensor for detecting environmental samples including tap water, river water, and landfill leachate was also demonstrated. This work opens up a new application scenario for biosynthetic QDs and holds a great potential for environmental monitoring applications.

8.
Biotechnol Bioeng ; 117(5): 1294-1303, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32048726

RESUMO

The bioreduction capacity of Cr(VI) by Shewanella is mainly governed by its bidirectional extracellular electron transfer (EET). However, the low bidirectional EET efficiency restricts its wider applications in remediation of the environments contaminated by Cr(VI). Cyclic adenosine 3',5'-monophosphate (cAMP) commonly exists in Shewanella strains and cAMP-cyclic adenosine 3',5'-monophosphate receptor protein (CRP) system regulates multiple bidirectional EET-related pathways. This inspires us to strengthen the bidirectional EET through elevating the intracellular cAMP level in Shewanella strains. In this study, an exogenous gene encoding adenylate cyclase from the soil bacterium Beggiatoa sp. PS is functionally expressed in Shewanella oneidensis MR-1 (the strain MR-1/pbPAC) and a MR-1 mutant lacking all endogenous adenylate cyclase encoding genes (the strain Δca/pbPAC). The engineered strains exhibit the enhanced bidirectional EET capacities in microbial electrochemical systems compared with their counterparts. Meanwhile, a three times more rapid reduction rate of Cr(VI) is achieved by the strain MR-1/pbPAC than the control in batch experiments. Furthermore, a higher Cr(VI) reduction efficiency is also achieved by the strain MR-1/pbPAC in the Cr(VI)-reducing biocathode experiments. Such a bidirectional enhancement is attributed to the improved production of cAMP-CRP complex, which upregulates the expression levels of the genes encoding the c-type cytochromes and flavins synthetic pathways. Specially, this strategy could be used as a broad-spectrum approach for the other Shewanella strains. Our results demonstrate that elevating the intracellular cAMP levels could be an efficient strategy to enhance the bidirectional EET of Shewanella strains and improve their pollutant transformation capacity.

9.
Water Res ; 173: 115559, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32028250

RESUMO

Peroxymonosulfate (PMS) is extensively used as an oxidant to develop the sulfate radical-based advanced oxidation processes in the decontamination of organic pollutants and various PMS activation methods have been explored. Visible-light-assisted PMS activation to construct a Fenton-like process has shown a great potential for pollution control. In our work, BiVO4 nanosheets were prepared using a hydrothermal process and used to activate PMS under visible light. A rapid degradation of ciprofloxacin (CIP) was achieved by dosing PMS (0.96 g/L), BiVO4 (0.32 g/L) under visible light with a reaction rate constant of 77.72-fold higher than that in the BiVO4/visible light process. The electron spin resonance and free radical quenching experiments indicate that reactive species of •O2-, h+, •OH and SO4•- all worked, where h+, •OH and SO4•- were found as the dominant contributors to the CIP degradation. The spectroscopic analyses further demonstrate that the photoinduced electrons were directly involved in the PMS activation process. The generated •O2- was partially utilized to activate PMS and more •OH was produced because of the chain reactions between SO4•- and H2O/OH-. In this process, PMS acted as an electron acceptor to transfer the photo-induced charges from the conduction band of BiVO4 and PMS was successfully activated to yield the high-powered oxidative species. From the degradation intermediates of CIP detected by a liquid-chromatography-mass spectrometer, the possible degradation pathways were proposed. The substantially decreased toxicity of CIP after the reaction was also observed. This work might provide new insights into the visible-light-assisted PMS activation mechanisms and is useful to construct environmentally-friendly catalytic processes for the efficient degradation of organic pollutants.


Assuntos
Ciprofloxacino , Peróxidos , Catálise , Luz
10.
Environ Sci Technol ; 54(6): 3599-3608, 2020 03 17.
Artigo em Inglês | MEDLINE | ID: mdl-32062962

RESUMO

Pursuing efficient approaches to promote the extracellular electron transfer (EET) of extracellular respiratory bacteria is essential to their application in environmental remediation and waste treatment. Here, we report a new strategy of tuning electron flux by clustered regularly interspaced short palindromic repeat (CRISPR)-ddAsCpf1-based rediverting (namely STAR) to enhance the EET capacity of Shewanella oneidensis MR-1, a model extracellular respiratory bacterium widely present in the environment. The developed CRISPR-ddAsCpf1 system enabled approximately 100% gene repression with the green fluorescent protein (GFP) as a reporter. Using a WO3 probe, 10 representative genes encoding for putative competitive electron transfer proteins were screened, among which 7 genes were identified as valid targets for EET enhancement. Repressing the valid genes not only increased the transcription level of the l-lactate metabolism genes but also affected the genes involved in direct and indirect EET. Increased riboflavin production was also observed. The feasibility of this strategy to enhance the bioreduction of methyl orange, an organic pollutant, and chromium, a typical heavy metal, was demonstrated. This work implies a great potential of the STAR strategy with the CIRPSR-ddAsCpf1 system for enhancing bacterial EET to favor more efficient environmental remediation applications.


Assuntos
Poluentes Ambientais , Shewanella , Repetições Palindrômicas Curtas Agrupadas e Regularmente Espaçadas , Transporte de Elétrons , Elétrons
11.
Nat Commun ; 11(1): 265, 2020 01 14.
Artigo em Inglês | MEDLINE | ID: mdl-31937783

RESUMO

Glucose electrolysis offers a prospect of value-added glucaric acid synthesis and energy-saving hydrogen production from the biomass-based platform molecules. Here we report that nanostructured NiFe oxide (NiFeOx) and nitride (NiFeNx) catalysts, synthesized from NiFe layered double hydroxide nanosheet arrays on three-dimensional Ni foams, demonstrate a high activity and selectivity towards anodic glucose oxidation. The electrolytic cell assembled with these two catalysts can deliver 100 mA cm-2 at 1.39 V. A faradaic efficiency of 87% and glucaric acid yield of 83% are obtained from the glucose electrolysis, which takes place via a guluronic acid pathway evidenced by in-situ infrared spectroscopy. A rigorous process model combined with a techno-economic analysis shows that the electrochemical reduction of glucose produces glucaric acid at a 54% lower cost than the current chemical approach. This work suggests that glucose electrolysis is an energy-saving and cost-effective approach for H2 production and biomass valorization.


Assuntos
Ácido Glucárico/análise , Glucose/química , Hidrogênio/análise , Biomassa , Catálise , Cloretos/química , Conservação de Recursos Energéticos , Eletrodos , Eletrólise , Compostos Férricos/química , Ácido Glucárico/química , Hidrogênio/química , Hidróxidos/química , Nanoestruturas/química , Níquel/química , Oxirredução , Ureia/química
12.
Sci Adv ; 6(1): eaay0748, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31922006

RESUMO

Development of renewable energy is essential to mitigating the fossil fuel shortage and climate change issues. Here, we propose to produce a new type of energy, bio-coal, via a fast pyrolysis coupled with atmospheric distillation process. The high heating values of the as-prepared bio-coals from the representative biomass are within 25.4 to 28.2 MJ kg-1, which are comparable to that of the commercial coals. Life cycle assessment further shows that the bio-coal production process could achieve net positive energy, financial, and environmental benefits. By using available biomass wastes as feedstock, China is expected to have a total bio-coal production of 402 million tons of standard coal equivalent, which is equal to 13% of national coal consumption. It would grant China an opportunity to additionally cut 738 million tons of CO2 emission by substituting an equal amount of coal with bio-coal in 2030.

13.
Bioresour Technol ; 299: 122686, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-31902635

RESUMO

Denitrification with non-organic electron donors for treating low C/N ratio wastewater has attracted growing interests. Hydrogen, reduced sulfur compounds and ferrous ions are mainly used in autotrophic denitrification, holding promise for achieving practical applications. Recently, the development of autotrophic denitrification-based processes, such as bioelectrochemically-supported hydrogenotrophic denitrification and sulfur-/iron-based denitrification assisted multi-contaminant removal, provide opportunities for applying these processes in wastewater treatment. Exploration of the autotrophic denitrification process in terms of contaminant removal mechanism, interaction among functional microorganisms, and potential full-scale applications is thus of great importance. Here, an overview of the commonly used non-organic electron donors, e.g., hydrogen, reduced sulfur compounds and ferrous ions, in denitrification for treating low C/N ratio wastewater is provided. Also, the feasibility of applying the combined processes based on autotrophic denitrification with the compounds is discussed. Furthermore, challenges and future possibilities as well as concerns about the practical applications are envisaged in this review.


Assuntos
Desnitrificação , Águas Residuárias , Processos Autotróficos , Reatores Biológicos , Elétrons , Nitratos , Nitrogênio
14.
Water Res ; 170: 115300, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31756614

RESUMO

Autotrophic iron-dependent denitrification (AIDD) is arising as a promising process for nitrogen removal from wastewater with a low carbon to nitrogen ratio. However, there is still a debate about the existence of such a process in activated sludge systems. This work provides evidence and elucidated the feasibility of autotrophic Fe(II)-oxidizing nitrate-reducing culture for nitrogen removal by long-term reactor operation, batch experimental verification, unstructured kinetic modeling and microbial community analyses. A relatively stable nitrate removal rate was achieved coupled with the oxidation of ferrous ions in 3-month operation of reactor. The kinetic modeling suggests that the iron oxidation was a growth-associated process in AIDD. Utilization of extracellular polymeric substances (and/or soluble microbial products) as electron donor for denitrification by heterotrophic denitrifiers was not mainly responsible for nitrogen removal in the reactor. After long-term operation of the reactor with activated sludge as inoculum, the enrichment culture KS-like consortium, dominated by Fe(II) oxidizer, Gallionellaceae, was successfully acclimated for autotrophic Fe(II)-oxidizing nitrate reduction. This work extents our understanding about the existence of such an autotrophic Fe(II)-oxidizing nitrate-reducing culture in both natural and engineered systems, and opens a door for its potential application in wastewater treatment.


Assuntos
Desnitrificação , Esgotos , Processos Autotróficos , Reatores Biológicos , Ferro , Nitratos , Nitrogênio
15.
Anal Chem ; 92(1): 707-715, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-31762256

RESUMO

Biofilms are microbial aggregates of microorganisms surrounded by a hydrogel-like matrix formed by extracellular polymeric substances (EPS). The formation of biofilms is intrinsically complex, from the attachment of microbial cells to the dispersion of the biofilm. Meanwhile, the three-dimensional framework built up by EPS changes with time and protects the microorganisms against environmental stress. Simultaneously acquiring chemical and structural information within the biofilm matrix is vital for the cognition and regulation of biofilms, yet it remains a great challenge due to the sample complexity and the limited approaches. In this study, confocal Raman microscopy and non-negative matrix factorization (NMF) analysis were combined to investigate spatiotemporal organization of Escherichia coli biofilms during development at molecular-level detail. The alternating non-negative least-squares (ANLS) approach was incorporated with the sequential coordinate-wise descent (SCD) algorithm to realize the NMF analysis for the large-scale hyperspectral data set. As a result, three components, including bacteria, protein, and polyhydroxybutyrate (PHB), were successfully resolved from the spectra of E. coli biofilm. Furthermore, the structural changes of biofilms could be visualized and quantified by their abundances derived from the NMF analysis, which might be related to the nutrient and oxygen gradient and physiological functions. This methodology provides a comprehensive understanding of the chemical constituents and their spatiotemporal distribution within the biofilm matrix. Furthermore, it also shows great potential for the analysis of unknown and complex biological samples with 3D Raman mapping.

16.
J Environ Sci (China) ; 88: 21-30, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31862063

RESUMO

Enhancing sludge dewatering is of importance in reducing environmental burden and disposal costs. In this work, a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), was combined with Fenton's reagent for sludge dewatering. Results show that the Fenton-CTAB conditioning significantly promotes the sludge dewatering. Using combined techniques of response surface methodology and uniform design, dosages of Fe2+, H2O2, and CTAB for water content response were optimized to be 89, 276, and 233 mg/g dry solids (DS), respectively. The water content of sludge decreased from 79.0% to 66.8% under the optimal conditions. Compared with cationic polyacrylamide, the Fenton-CTAB system exhibited superior sludge dewatering performance. To gain insights into the mechanisms involved in sludge dewatering, the effects of Fenton-CTAB conditioning on the composition of extracellular polymeric substances (EPS) and the morphology of the sludge flocs were investigated. The decomposition of EPS into some dissolved organics and the release of proteins in tightly bound EPS facilitated the conversion of bound water to free water and further reduced the water content of sludge cake. After conditioning, morphology of sludge showed aggregation. Overall, the enhanced sludge dewatering by Fenton-CTAB treatment provides an efficient way for management of sewage sludge.


Assuntos
Peróxido de Hidrogênio , Ferro , Esgotos , Eliminação de Resíduos Líquidos , Tensoativos , Água
17.
J Hazard Mater ; 382: 121090, 2020 01 15.
Artigo em Inglês | MEDLINE | ID: mdl-31476718

RESUMO

Fenton reaction is widely used for hazardous pollutant degradation. Reducing agents (RAs) have been proven to be efficient in promoting the generation of HO• in Fenton reaction by accelerating the redox cycle of Fe3+/Fe2+. However, the roles of different RAs in Fenton reaction remain unrevealed. In this work, the catalytic activity of three RAs, i.e., hydroxylamine (NH2OH), ascorbic acid (AA) and cysteine (Cys), on the degradation of benzoic acid (BA) and the hydroxyl radical formation in the Fenton-RAs system were investigated. Results show the catalytic performance of RAs in BA degradation by Fenton reaction followed an order of NH2OH > AA > Cys. Compared with the conventional Fenton system, the effective pH range in the Fenton-NH2OH system extended from 3.0 to 5.0, while the optimal pH in the Fenton-AA and Fenton-Cys systems ranged from 3.0 to 4.0. The Fenton-AA system exhibited a two-stage reaction toward BA degradation, which was different from the Fenton-NH2OH and Fenton-Cys systems. Furthermore, the dosing manner of AA was found to be a key factor governing its role in the Fenton-AA system. This observation suggests the different mechanisms behind the enhancement of the three RAs in Fenton system. Different from NH2OH and Cys, AA would inhibit the generation of HO•, especially at the fast stage of degradation process, where Fe3+ has not accumulated yet. In addition, the economic analysis using the electrical energy per order indicates Fenton-NH2OH system was economically feasible with the lowest energy input, compared to Fenton-AA and Fenton-Cys systems. These results are useful to better understand the roles of RAs in Fenton system, and also provide guidance about the selection and dosing manner of suitable RAs in the advanced oxidation processes.

18.
Environ Sci Technol ; 53(24): 14604-14611, 2019 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-31747260

RESUMO

Although arsenic at a high concentration imposes strong selective pressure on microbes, various microbes have been found to grow in As-rich environments. So far, little is known about how microbes can sense and move toward arsenate in the environment, and the underlying molecular mechanisms have not been revealed. Here, we report the chemotaxis response toward arsenate (As(V)) by Shewanella putrefaciens CN-32, a model dissimilatory metal-reducing bacterium (DMRB), and elucidate the mechanisms. We find that S. putrefaciens CN-32 exhibits a chemotactic behavior toward As(V) and diverse electron acceptors. To sense As(V), S. putrefaciens CN-32 requires functional arsenate respiratory reductase but does not depend on its metal-reducing-like respiratory pathway. We observe that such a sense is governed by an energy taxis mechanism and mediated by several methyl-accepting chemotaxis proteins (MCPs), rather than a specific MCP. Moreover, we reveal that the chemotactic signal transduction pathway is conserved in Shewanella, and histidine kinase and flagella-mediated motility are essential for taxis toward As(V). This work reverses the conventional view about arsenic as a chemotactic inhibitor to microbes by revealing the positive chemotaxis of Shewanella to As(V).

19.
ACS Appl Mater Interfaces ; 11(46): 43180-43187, 2019 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-31660719

RESUMO

Carbon-based materials are recognized as promising candidates for pollutant degradation because of their environmental benignity. Massive and cost-effective production and efficient recovery of carbon-based catalysts are crucial to apply this technology. However, various nanostructured carbons with different dimensions are usually utilized as precursors while not considering their complex preparation procedures and the high costs of ingredients. Moreover, catalyst separation and recovery are not given sufficient attention. In this work, a calcium salt-assisted pyrolysis strategy is proposed to tune the catalytic site formation of carbon-based catalysts. Results show that blending equal amounts of Ca2+ (calcium chloride) and organic precursors could greatly improve the catalytic activity of the carbonated product to activate peroxymonosulfate for pollutant degradation. In addition, the proposed synthetic strategy is universal to most of the readily accessed and cost-effective organic precursors. Singlet oxygen is identified as the main reactive oxidant for pollutant removal in the catalytic reaction. By cross-linking calcium ions and alginate as a hydrogel to immobilize the catalyst, the carbon material could be readily recovered. Furthermore, a long-term continuous-flow reactor test is conducted to validate the effectiveness of applying the immobilized catalyst to treat a synthetic wastewater with 0.5 mM bisphenol A. As a result, a green synthesis and immobilization strategy for persulfate catalysts is successfully established, and the prepared catalyst might be applied for wastewater treatment through using calcium salt in two purposes.

20.
Environ Sci Technol ; 53(22): 13302-13311, 2019 Nov 19.
Artigo em Inglês | MEDLINE | ID: mdl-31621307

RESUMO

Composite magnetic aluminum hydroxide at iron oxide nanomaterials, Al(OH)3@Fe3O4, with a well-defined core-shell structure, were used as pretreatment adsorbents for the removal of silica in brackish water. The Al(OH)3 outer shell confers silica adsorption capacity, and the superparamagnetic Fe3O4 core allows material separation and magnetic recovery. The as-prepared nanomaterials (2 g L-1) remove ∼95 and ∼80% silica from Si-rich solutions with 0.5 and 2 mM initial silica concentrations, respectively. Regeneration under basic conditions was evaluated, and post-adsorption treatment with 0.05 M NaOH yielded optimal material reusability. After four regeneration cycles, the Al(OH)3@Fe3O4 nanomaterials retain their magnetic property while still being able to remove ∼40% silica from solutions at an adsorbent concentration of 2 g L-1. The mechanism of silica adsorption onto the surface of the nanomaterials was probed using several spectroscopic techniques. ATR-FTIR (attenuated total reflection-Fourier transform infrared) integrated with two-dimensional correlation analysis shows that silica species vary from Q2 to Q4 with adsorption time corresponding to silica polymerization. 29Si solid-state NMR spectra show an upfield chemical shift displacement of the Q2 signal, which indicates the formation of Q4 units, suggesting silica polymerization onto the Al(OH)3 shell. In addition, a laboratory-scale reverse osmosis setup was used to evaluate Al(OH)3@Fe3O4 as pretreatment materials for silica removal. Results show that silica scaling was significantly alleviated, and water recovery was enhanced when feed waters were pretreated with the magnetic nanomaterials. Taken together, our study highlights the promise of magnetic Al(OH)3@Fe3O4 nanomaterials in treating brackish water and achieving higher water recovery for inland desalination.


Assuntos
Dióxido de Silício , Poluentes Químicos da Água , Adsorção , Alumínio , Ferro , Osmose
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