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1.
Chemosphere ; 239: 124773, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31518919

RESUMO

Hyporheic zone (HZ) sediments in river systems are often contaminated with heavy metals as a legacy of natural processes and anthropogenic activities. The geochemical behaviors of heavy metals in the HZ sediments at the laboratory scale have been extensively studied. However, the watershed-scale distributions of heavy metals in the HZ sediments and the processes controlling their distributions have not been well studied. Here, we report a watershed-scale study of heavy metals (i.e., Cr, Ni, Cu, Zn, Cd, and Pb) distributions in the HZ of the Maozhou River watershed, a heavily polluted area within the Pearl River Delta, southern China. Statistical analysis revealed that the spatial distribution of studied heavy metal concentrations was highly correlated with that of the sediment-associated sulfide at the watershed-scale. Metal extraction analysis and double-spherical aberration-corrected scanning transmission electron microscope imaging (Cs-STEM) further confirmed the strong association of heavy metals with sulfur. These observations demonstrated that the formation of metals-sulfide precipitates was the key process controlling the watershed-scale distributions of heavy metals (especially for Cr, Ni and Zn) in the HZ sediments. Additionally, high permeability of the HZ sediments may prevent Ni, Zn, Cd and Pb accumulation in sediments. Specially, Cu distribution was mainly affected by organic-Cu complexation. In the estuary area, salinity input likely affected the distributions of Ni, Zn and Cd through cation exchange processes. The findings improved our understanding of the distributions of heavy metals and the processes controlling their distributions at the watershed-scale, and have implications for remediating and managing contaminated HZ sediments.


Assuntos
Sedimentos Geológicos/análise , Metais Pesados/análise , Poluentes Químicos da Água/análise , China , Monitoramento Ambiental/métodos , Estuários , Sedimentos Geológicos/química , Metais Pesados/química , Metais Pesados/isolamento & purificação , Microscopia Eletrônica de Transmissão e Varredura , Rios , Salinidade , Sulfetos/análise , Sulfetos/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
2.
Sensors (Basel) ; 19(18)2019 Sep 09.
Artigo em Inglês | MEDLINE | ID: mdl-31505879

RESUMO

This paper proposed an optimal spectral resolution for diagnosing cadmium-lead (Cd-Pb) cross contamination with different pollution levels based on the hyperspectral reflectance of rice canopy. Feature bands were sequentially selected by two-way analysis of variance (ANOVA2) and random forests from the high-dimensional hyperspectral data after preprocessing. Then Support Vector Machine (SVM) was applied to diagnose the pollution levels using different feature bands combination with different spectral resolutions and cross validation was conducted to evaluate the distinguishing accuracies. Finally, the optimal spectral resolution could be determined by comparing the diagnosing accuracies of the optimal feature bands combination in each spectral resolution. In the experiments, the hyperspectral reflectance data of rice canopy with ten different spectral resolutions was captured, covering 16 pretreatments of Cd and Pb pollution. The experimental results showed the optimal spectral resolution was 9 nm with the highest average accuracy of 0.71 and relatively standard deviation of 0.07 for diagnosing the categories and levels of Cd-Pb cross contamination. The useful exploration provided an evidence for optimal spectral resolution selection to reduce the cost of heavy metal pollution diagnose.


Assuntos
Cádmio/isolamento & purificação , Poluição Ambiental , Chumbo/isolamento & purificação , Metais Pesados/isolamento & purificação , Cádmio/toxicidade , Chumbo/toxicidade , Metais Pesados/toxicidade , Oryza/efeitos dos fármacos
3.
Chemosphere ; 236: 124416, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31545207

RESUMO

The objective of this study was to develop a novel graphene oxide (GO)-based adsorbent by loading the cationic surfactant hexadecyltrimethylammonium bromide (HDTMA) to simultaneously scavenge copper ion, a charged species, and bisphenol A, an uncharged organic compound, from water. The HDTMA modification process was studied and the GO/HDTMA composites characterized using SEM (scanning electron microscopy), XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier Transform Infrared) spectroscopy. Within the concentration range of 6.4-11.5%, HDTMA caused the 2D GO sheets to form into solid 3D networks by reducing the repulsive forces and increasing the hydrophobic interactions between the adjacent GO sheets. The unique feature of this material is the simultaneous uptake of charged heavy metal ions and uncharged organic contaminants. The negative charges on GO results in the retention of heavy metal ions, while the hydrophobic phase created by the alkyl chain in HDTMA enables the adsorption of organic contaminants. The adsorption capacity of Cu2+ and bisphenol A reached 59.7 mg/g and 141.0 mg/g, respectively. The adsorption processes for both Cu2+ and bisphenol A were rapid, attaining ∼100% removal in 1 h and 2 h, respectively. Increasing the pH favored the adsorption of the two solutes. The presence of NaCl reduced the retention of Cu2+, but was beneficial for the adsorption of bisphenol A. The results demonstrate that the 3D structure and the adsorption of the target species can be achieved by tailoring the surface coverage of HDTMA on GO.


Assuntos
Compostos Benzidrílicos/isolamento & purificação , Cobre/isolamento & purificação , Grafite/química , Fenóis/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Adsorção , Cobre/química , Interações Hidrofóbicas e Hidrofílicas , Íons , Metais Pesados/isolamento & purificação , Espectroscopia Fotoeletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Tensoativos/química , Poluentes Químicos da Água/análise
4.
Environ Monit Assess ; 191(10): 615, 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31493036

RESUMO

Silica gel chitosan composite was prepared to perform adsorptive experiment of different heavy metal ion solutions. The characterization of chitosan + silica gel (Ch + Sg) composite was done by FTIR and SEM-EDS to understand the presence of active sites and to have an insight on the surface morphology. The adsorption study of heavy metal ions by Ch + Sg composite gives maximum removal percent for Cu, Pb and Ni which were obtained at pH 5 and for Hg at pH 6.The trend of removal by Ch + Sg signifies that maximum removal percent was attained at 120 min. The surface of Ch + Sg is heterogeneous for the adsorption of Hg, Ni and Cu and homogeneous for Pb adsorption. The values obtained for Pb signify that its adsorption best fitted to pseudo first order with the R2 value of 0.986, whereas pseudo second order best fitted to the experimental data of Cu, Ni and Hg as R2 values which are 0.983, 0.819 and 0.957 respectively. The values of change in entropy (⊿S) obtained for Pb, Cu, Ni and Hg are - 69.33, - 118, - 63.33 and - 98.52 J/mol K respectively. Negative values of change in enthalpy, ⊿H in (kJ/mol) are in the range of - 18.2 to - 37.66 which indicates both physical and chemical adsorption involves in the process of adsorption.


Assuntos
Quitosana/química , Metais Pesados/química , Metais Pesados/isolamento & purificação , Sílica Gel/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Entropia , Íons/química , Íons/isolamento & purificação , Cinética , Termodinâmica
5.
Environ Sci Pollut Res Int ; 26(29): 30365-30373, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31435909

RESUMO

Environmental benefits of biochar require a simple and effective method for preparation of functional N-doped biochar. In this study, urea/ZnCl2 was developed to prepare N-doped biochar via in situ hydrothermal carbonization (HTC) of Camellia sinensis waste at 120-280 °C for 2 h under 1.0-9.8 MPa. Physicochemical and structural properties of the N-doped biochar were investigated by Raman spectra, elemental analysis, BET surface area, SEM, TEM, XRD, and XPS. The results showed that the N content in biochar could reach up to 7.79% at 280 °C. Surface chemistry suggested that pyridinic N, pyrollic N, and graphitic N were the major N species on the biochar. Moreover, the N-doped biochar was successfully employed to remove metal ions Cu2+, Pb2+, Zn2+, and Cr6+. Adsorption data fit closely to the pseudo-second-order kinetic equation and the Langmuir adsorption isotherm model for all metal ions.


Assuntos
Camellia sinensis/química , Carvão Vegetal/química , Metais Pesados/isolamento & purificação , Ureia/química , Adsorção , Carbono/química , Cloretos/química , Cinética , Microscopia Eletrônica de Varredura , Nitrogênio/química , Espectroscopia Fotoeletrônica , Análise Espectral Raman , Resíduos , Poluentes Químicos da Água/isolamento & purificação , Difração de Raios X , Compostos de Zinco/química
6.
Chemosphere ; 237: 124286, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-31349960

RESUMO

It is cost effective and thermodynamically feasible to recover EDTA and remove potential toxic elements (PTEs) with sulfide precipitation from soil-washing wastewater produced from EDTA washing PTEs-contaminated soil. However, poor solid-liquid separation and EDTA recovery restrict its application due to a large number of fine particles formed during the precipitation process. This study investigated the effect of single factor on PTEs (Cu, Pb, Cd, and Zn) removal and solid-liquid separation from wastewater. The results showed that Zn was the most difficult to remove compared with Cu, Pb, and Cd; with the aid of Ca(OH)2, Zn removal efficiency was improved from 22.16% to 92.45%, and over 70.98 min, its average rate was 4.2 times that obtained without Ca(OH)2 dosage; undissolved Ca(OH)2 adsorbed suspended particles, acted as condensation nucleus, and promoted similar flocculation effect (self-flocculation); dissolved Ca(OH)2 modified the charge on the surface of suspended particles by changing the zeta potential from -36.77 ±â€¯1.2 mV to -25.39 ±â€¯3.06 mV and weakened the electrostatic repulsion between the suspended particles, and promoted their adsorption and flocculation precipitation, thereby improving the solid-liquid separation. The acid-recovered EDTA was analyzed in the protonated form (H4EDTA) using Fourier transform infrared (FT-IR) spectroscopy, and it maintained the same ability to extract PTEs from the soil as that of fresh EDTA over several cycles. This indicates that Ca(OH)2-enhanced sulfide precipitation can effectively treat soil-washing wastewater and recover EDTA and potentially reduce the cost of remediation techniques for PTEs-contaminated soil with EDTA-enhanced soil washing.


Assuntos
Ácido Edético/isolamento & purificação , Recuperação e Remediação Ambiental/métodos , Poluentes do Solo/isolamento & purificação , Sulfetos/química , Águas Residuárias/química , Hidróxido de Cálcio/química , Precipitação Química , Ácido Edético/química , Metais Pesados/isolamento & purificação , Reciclagem , Poluentes do Solo/análise , Eletricidade Estática , Purificação da Água/métodos
7.
Biomed Res Int ; 2019: 2403718, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31317024

RESUMO

This study investigated the phytochemical characteristics and antioxidant activity in leaves, roots, stem, flower, and seed parts of Datura alba (D. alba). The study also assessed the heavy metal (Cr, Mn, Zn, and Cu) accumulation in each part of the plant. Among the phytochemicals, alkaloids were found only in leaves while tannins, flavonoids, and phenols were present in all parts of the plant. For antioxidant activity, free radical scavenging assay for 2,2-diphenyl-1-picrylhydrazyl (DPPH) was performed using ascorbic acid as the standard. Higher activity was shown by stem extract in methanol and leaf extract in n-hexane, ethyl acetate, and chloroform. Furthermore, all the target heavy metals were detected in all plant sections with the highest concentration of Zn in leaves and Cu in stem, root, flower, and seed. Due to stronger antioxidant potential and phytochemical composition, D. alba could prove as valuable prospect in pharmaceutical formulations by taking part in the antioxidant defense system against generation of free radicals.


Assuntos
Antioxidantes/química , Datura/química , Radicais Livres/antagonistas & inibidores , Metais Pesados/isolamento & purificação , Compostos Fitoquímicos/isolamento & purificação , Alcaloides/química , Alcaloides/isolamento & purificação , Antioxidantes/farmacologia , Flavonoides/química , Flavonoides/isolamento & purificação , Metais Pesados/química , Metais Pesados/classificação , Fenóis/química , Fenóis/isolamento & purificação , Compostos Fitoquímicos/química , Compostos Fitoquímicos/classificação , Extratos Vegetais/química , Extratos Vegetais/farmacologia , Folhas de Planta/química , Sementes/química , Taninos/química , Taninos/classificação , Taninos/isolamento & purificação
8.
Carbohydr Polym ; 222: 115016, 2019 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-31320089

RESUMO

In this research, an innovative biomass derived spongy adsorbent was fabricated by adopting dialdehyde cellulose nanocrystals (DCNC) as crosslinking and reinforcing building block, which showed high mechanical strength, satisfying adsorption performance and good recyclability. The improved shape integrity and specific surface area resulted from DCNC incorporation contribute to high adsorption performance of this sponge. Adsorption behaviors of the adsorbent were comprehensively studied. The qe for Pb2+ and Cd2+ by the adsorbent could reach as high as 767 and 517 mg/g, respectively. Also, this adsorbent showed excellent recyclability. In addition, the adsorbent exhibited satisfying fixed-bed column adsorption performance. Thus, it could be considered as promising high efficiency adsorbent.


Assuntos
Celulose/análogos & derivados , Plumas/química , Queratinas/química , Metais Pesados/isolamento & purificação , Nanopartículas/química , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Animais , Biomassa , Celulose/química , Reagentes para Ligações Cruzadas/química , Reutilização de Equipamento , Metais Pesados/química , Porosidade , Poluentes Químicos da Água/química , Purificação da Água/instrumentação , Purificação da Água/métodos
9.
Environ Sci Pollut Res Int ; 26(26): 26696-26705, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31292878

RESUMO

Washing of contaminated soils or sediments using humic substances (HS) extracted either from source-rich materials or compost has been tested effective to remove various heavy metals. Nevertheless, the remaining chemical fractionation of metals and post-washing biological responses were not discussed in previous research. In this study, we used a HS extracted from green waste compost to wash off Cd, As, and Ni from a contaminated sediment, and evaluated the washing effect on sediment microbes by measuring a series of indexes with regard to microbial biomass and enzyme activities. Results showed that HS washing was more effective in removing the cationic metals Cd and Ni than the anionic metal As. The highest HS dose of 2000 mg L-1 resulted in 24.5-, 33.1-, and 12-fold increases of removal for Cd, Ni, and As, respectively. The remaining Cd and As were found to migrate to less stable fractions, whereas the remaining Ni was dominantly found in the residual fraction. Increases of metal removal efficiency, microbial biomass, and dehydrogenase activity were found to correlate with the increase of HS concentrations. Increasing doses of HS slightly altered sediment pH to the lower range but did not cause any significant effect on microbial activities. The study proves that HS washing is indeed a more environmental-friendly strategy than many existing washing agents which have exerted various side effects on soil properties.


Assuntos
Recuperação e Remediação Ambiental/métodos , Sedimentos Geológicos/química , Substâncias Húmicas , Metais Pesados/isolamento & purificação , Poluentes do Solo/isolamento & purificação , Solo/química , Biomassa , China , Compostagem , Sedimentos Geológicos/microbiologia , Metais Pesados/análise , Metais Pesados/química , Microbiologia do Solo , Poluentes do Solo/análise , Poluentes do Solo/química , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
10.
Chemosphere ; 234: 346-355, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31228836

RESUMO

Land application of sewage sludge has received significant attention in recent years but the presence of elevated heavy metals in the sludge limits its land application. The purposes of this study were to investigate the effects of sulfur dosage and inoculum size on the thermophilic bioleaching of heavy metals from sewage sludge in a pilot-scale bioreactor. The microbial communities in this thermophilic bioleaching process were also identified using real-time polymerase chain reaction (real-time PCR). The results showed that the oxidation of sulfur and metal solubilization decreased with the increasing sulfur dosage. When the sulfur dosage was greater than 2% (w/v), the sulfur oxidation and metal solubilization rates decreased, indicating that the thermophilic bioleaching was hindered by high levels of substrate. However, it was found that the efficiency of metal solubilization and solid degradation was increased with the increase of inoculum size in the range from 5% to 20%. At the end of bioleaching, the efficiency of Mn, Zn, Ni, Cu and Cr from the sewage sludge reached 73-100%, 51-60%, 38-52%, 17-43% and 1-38%, respectively, while SS and VSS were degraded by 33-48% and 47-67%, respectively. Based on the analysis of real-time PCR, Sulfobacillus acidophilus was observed to be the predominant species (13-67% of total bacteria), whereas the populations of Sulfobacillus thermosulfidooxidans and Acidithiobacillus caldus were accounted relatively low (<1%).


Assuntos
Inoculantes Agrícolas , Metais Pesados/isolamento & purificação , Esgotos/química , Enxofre/farmacologia , Acidithiobacillus/metabolismo , Bactérias/metabolismo , Reatores Biológicos , Concentração de Íons de Hidrogênio , Metais Pesados/análise , Oxirredução , Projetos Piloto , Esgotos/microbiologia , Enxofre/análise , Eliminação de Resíduos Líquidos/métodos
11.
Chemosphere ; 234: 488-495, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31229709

RESUMO

Heavy metals present in industrial wastewater contribute to human and ecosystem health risk when discharged without proper treatment. Low-cost biosorbents with high metal-binding capacity are increasingly being utilized for the removal of heavy metals. Inherent physico-chemical properties of biosorbents significantly influence their adsorption capacity. Studies quantifying the influence exerted by these properties on adsorption capacity are scarce. This study quantifies the influence and relative importance of selected physico-chemical properties on the adsorption capacity of three divalent heavy metals; Cu2+, Cd2+ and Pb2+ using multivariate analysis. Twenty one biosorbent mixtures were created, systematically varying their physico-chemical properties using tea factory waste and coconut shell biochar. Their adsorption capacities were measured using batch sorption studies. The influence of physico-chemical properties on the adsorption capacity is comparable for all three metal cations. Regression models were developed to quantify the influence of physico-chemical parameters on the adsorption capacity based on regression coefficients. All models were found to have high reliability with R2 values above 0.98. Acidic surface functional groups were found to act as the key property that governs the adsorption capacity of Pb2+, Cu2+ and Cd2+. Carboxylic groups played a major role in the adsorption of Cu2+ and Pb2+, while lactonic groups were more important in providing binding sites to Cd2+. SSA failed to demonstrate a significant impact on the adsorption capacity of these three metals on its own when the biosorbent had a low surface functional group density.


Assuntos
Carvão Vegetal/química , Metais Pesados/isolamento & purificação , Purificação da Água/métodos , Adsorção , Cocos , Metais Pesados/análise , Metais Pesados/química , Propriedades de Superfície , Águas Residuárias/química , Poluentes Químicos da Água/análise , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/normas
12.
Appl Microbiol Biotechnol ; 103(13): 5411-5420, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31065755

RESUMO

Heavy metals, being toxic in nature, are one of the most persistent problems in wastewater. Unabated discharge of large amount of heavy metals into water bodies are known to cause several environmental and health impacts. Biological remediation processes like microbial remediation and phytoremediation are proved to be very effective in the reduction of heavy metal pollutants in wastewater. To circumvent the issues involved several peptides and proteins are being explored. Metal-binding capacity, accumulation, and tolerance of heavy metals in bacteria can be upsurge by overexpressing the genes which code for metal-binding proteins. In the present study, an attempt has been made to bioremediate heavy metal toxicity by overexpressing metal-binding proteins. Two expression cassettes harboring top4 metal-binding protein (T4MBP) and human metallothionein 3 (HMP3) were designed under the control of constitutive CaMV 35S promoter and transformed into E.coli TBI cells. E.coli over expressing HMP3 and T4MBP were immobilized in biobeads which were explored for the detoxification of water contaminated with copper and cadmium. Effects on the concentration of heavy metal before and after treatment with beads were estimated with the help of ICP-OES. Noteworthy results were obtained in the case of copper with 87.2% decrease in its concentration after treatment with biobeads. Significant decrement of 32.8% and 27.3% was found in case of zinc and cadmium, respectively. Mechanisms of binding of proteins with heavy metals were further validated by molecular modeling and metal-binding analysis. HMP3 protein was found to be more efficient in metal accumulation as compared with T4MBP. The fabricated biobeads in this study definitely offer an easy and user-handy approach towards the treatment of toxic wastewater.


Assuntos
Biodegradação Ambiental , Metais Pesados/isolamento & purificação , Proteínas do Tecido Nervoso/metabolismo , Águas Residuárias , Purificação da Água/métodos , Cádmio/isolamento & purificação , Quelantes , Cobre/isolamento & purificação , Escherichia coli/genética , Humanos , Regiões Promotoras Genéticas , Ligação Proteica , Zinco/isolamento & purificação
13.
Chemosphere ; 229: 142-159, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31078029

RESUMO

Heavy metal contamination is a growing concern in the developing world. Inadequate water and wastewater treatment, coupled with increased industrial activity, have led to increased heavy metal contamination in rivers, lakes, and other water sources in developing countries. However, common methods for removing heavy metals from water sources, including membrane filtration, activated carbon adsorption, and electrocoagulation, are not feasible for developing countries. As a result, a significant amount of research has been conducted on low-cost adsorbents to evaluate their ability to remove heavy metals. In this review article, we summarize the current state of research on the removal of heavy metals with an emphasis on low-cost adsorbents that are feasible in the context of the developing world. This review evaluates the use of adsorbents from four major categories: agricultural waste; naturally-occurring soil and mineral deposits; aquatic and terrestrial biomass; and other locally-available waste materials. Along with a summary of the use of these adsorbents in the removal of heavy metals, this article provides a summary of the influence of various water-quality parameters on heavy metals and these adsorbents. The proposed adsorption mechanisms for heavy metal removal are also discussed.


Assuntos
Custos e Análise de Custo , Países em Desenvolvimento , Metais Pesados/isolamento & purificação , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/economia , Água/química , Metais Pesados/química , Poluentes Químicos da Água/química
14.
Top Curr Chem (Cham) ; 377(3): 16, 2019 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-31111247

RESUMO

Elemental sulfur is an abundant and inexpensive chemical feedstock, yet it is underused as a starting material in chemical synthesis. Recently, a process coined inverse vulcanization was introduced in which elemental sulfur is converted into polymers by ring-opening polymerization, followed by cross-linking with an unsaturated organic molecule such as a polyene. The resulting materials have high sulfur content (typically 50-90% sulfur by mass) and display a range of interesting properties such as dynamic S-S bonds, redox activity, high refractive indices, mid-wave IR transparency, and heavy metal affinity. These properties have led to a swell of applications of these polymers in repairable materials, energy generation and storage, optical devices, and environmental remediation. This article will discuss the synthesis of polymers by inverse vulcanization and review case studies on their diverse applications. An outlook is also presented to discuss future opportunities and challenges for further advancement of polymers made by inverse vulcanization.


Assuntos
Técnicas de Química Sintética/métodos , Polimerização , Polímeros/síntese química , Compostos de Enxofre/síntese química , Enxofre/química , Reagentes para Ligações Cruzadas/química , Eletrodos , Recuperação e Remediação Ambiental/métodos , Metais Pesados/isolamento & purificação , Dispositivos Ópticos , Polímeros/química , Compostos de Enxofre/química
15.
Aquat Toxicol ; 212: 1-10, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31022608

RESUMO

Heavy metal pollution is one of the major environmental concerns worldwide. Toxic heavy metals when untreated get accumulated in environment and can pose severe threats to living organisms. It is well known that metals play a major role either directly or indirectly in different metabolic processes of bacteria. This allows bacterial cells to grow even in the presence of some toxic heavy metals. Microbial biotechnology has thus emerged as an effective and eco friendly solution in recent years for bioremediation of heavy metals. Therefore, this review is focused on summarising bacterial adaptation mechanisms for various heavy metals. It also shares some applications of have metal tolerant bacteria in bioremediation. Bacteria have evolved a number of processes for heavy metal tolerance viz., transportation across cell membrane, accumulation on cell wall, intra as well as extracellular entrapment, formation of complexes and redox reactions which form the basis of different bioremediation strategies. The genetic determinants for most of these resistances are located on plasmids however some may be chromosomal as well. Bacterial cells can uptake heavy by both ATP dependent and ATP independent processes. Bacterial cell wall also plays a very important role in accumulating heavy metals by bacterial cells. Gram-positive bacteria accumulate much higher concentrations of heavy metals on their cell walls than that of metals gram -ve bacteria. The role of bacterial metallothioneins (MTs) in heavy metal has also been reported. Thus, heavy metal tolerant bacteria are important for bioremediation of heavy metal pollutants from areas containing high concentrations of particular heavy metals.


Assuntos
Bactérias/efeitos dos fármacos , Metais Pesados/isolamento & purificação , Metais Pesados/toxicidade , Poluentes Químicos da Água/isolamento & purificação , Bactérias/genética , Biodegradação Ambiental , Parede Celular/efeitos dos fármacos , Parede Celular/metabolismo , Óperon/genética , Poluentes Químicos da Água/toxicidade
16.
Artigo em Inglês | MEDLINE | ID: mdl-30964379

RESUMO

Fe-Ni/kaolin catalyst was used for the production of carbon nanotubes (CNTs) via catalytic chemical vapour deposition followed by acid purification treatment and functionalization with polyethylene glycol to give purified carbon nanotubes (P-CNTs) and polyethylene glycol carbon nanotubes (PEG-CNTs), respectively. The as-synthesized CNTs, P-CNTs and PEG-CNTs were characterized by high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), Fourier transform infrared and Brunauer Emmett Teller (BET). The adsorption behaviour P-CNTs and PEG-CNTs to remove specifically Cr and Zn from battery wastewater were examined by the batch adsorption process as a function of different contact time, adsorbent dosage and temperature. The HRSEM/HRTEM/BET analysis confirmed that both nano-adsorbents were tube-like in nature, high porosity and crystalline, with PEG-CNTs possessing high surface area (970.81 m2/g) than P-CNTs (781.88 m2/g). The optimum contact time and adsorbent dosage to remove Cr and Zn by P-CNTs and PEG-CNTs were 90 and 50 min and 0.3 g, respectively. Under the applied conditions, PEG-CNTs exhibited high adsorption capacity than P-CNTs for the selected heavy metals. The adsorption equilibrium data were better fitted to the Freundlich model while the kinetic data conformed to the pseudo-second-order model. Thermodynamic studies demonstrated the feasibility and endothermic nature of the system. This study demonstrated that both nano-adsorbents purify battery wastewater and with better performance by PEG-CNTs.


Assuntos
Metais Pesados/isolamento & purificação , Nanotubos de Carbono/química , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Adsorção , Cinética , Metais Pesados/química , Polietilenoglicóis/química , Porosidade , Termodinâmica , Poluentes Químicos da Água/química
17.
Int J Biol Macromol ; 132: 278-288, 2019 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-30940581

RESUMO

N­N­N­triethylammonium chitosan (TEAC) and carboxymethyl chitosan (CMCh), the two water-soluble chitosan derivatives were utilized for the removal and recovery of heavy metals by size enhanced ultrafiltration (SEUF). The strong positive quaternary ammonium [-N+(C2H5)3] cation in TEAC interacts with Cr(VI), which exists as a strong chromate anion thereby enabling the efficient removal of chromate through ultrafiltration. CMCh consists of COOH and NH2 moieties, which facilitate interactions with heavy metals such as Cu(II) and Ni(II). FTIR, SEM, and EDAX were used to characterize the chitosan derivatives before and after the removal of metals. The experiments were designed with the central composite design (CCD) of response surface methodology (RSM). The metal ion removal experiments were conducted as per the statistical design to determine the optimum process conditions; initial pH of the feed solution, polymer to metal loading ratio (P/M), and initial concentration of the feed solution. The optimization study was conducted to maximize the heavy metal rejection and binding capacity of the chitosan derivatives. The analysis of variance (ANOVA) was performed to validate the developed regression models.


Assuntos
Quitosana/análogos & derivados , Metais Pesados/química , Metais Pesados/isolamento & purificação , Ultrafiltração/métodos , Quitosana/química , Concentração de Íons de Hidrogênio
18.
Food Chem ; 289: 26-32, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-30955611

RESUMO

A straightforward and efficient method was developed by ultrasound assisted emulsification microextraction (USAEME) combined with inductively coupled plasma optical emission spectroscopy (ICP/OES) to trace some toxic heavy metal ions in eight select farmed and four select imported rice samples. In this study, carbon tetrachloride (CCl4) and 1-(2-pyridylazo)2-naphthol (PAN) were used as the extraction solvent and complexing reagent, respectively. The extraction parameters were optimized by means of a central composite design (CCD). Detection and quantification limits were set to be between 0.02 and 0.08 µg L-1 and 0.07-0.30 µg L-1, respectively. The accuracy of our method was further verified against two certified reference materials namely NCS ZC73029 and NIES No 10-b. While no trace of contaminations was found in some rice samples (Tarom, Hashemi, Sadri, Khazar and one imported sample), others such as Kazemi, Jamshidi, Dom Siah, Guilanehand and three of the imported samples were considerably polluted.


Assuntos
Metais Pesados/análise , Oryza/química , Espectrofotometria Atômica/métodos , Tetracloreto de Carbono/química , Limite de Detecção , Microextração em Fase Líquida , Metais Pesados/isolamento & purificação , Naftóis/química , Oryza/metabolismo , Sonicação
19.
Chemosphere ; 225: 579-587, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30901653

RESUMO

Drinking water treatment residue (DWTR) and municipal waste incineration bottom ash (BA) have been traditionally considered as solid waste. With the development of urbanization, their subsequent treatment and resource regeneration need to be further researched. In this work, a composite geopolymer with BA and DWTR was successfully synthesized and applied in the immobilization of Cd, Pb and Zn. The analysis of the geopolymers with different ratios of BA and DWTR, curing times and heavy metals was performed through chemical analysis, SEM, FTIR, XRD, XPS, ICP-AES and compressive strength tests. The results show that the geopolymer samples based on BA and DWTR (BWG) presented higher compressive strength than the samples with single BA material. The sample with 20% DWTR and 80% BA (BWG20) possesses the highest compressive strength (24.10 MPa) among the materials ratios. Furthermore, the microstructure and characterization results indicate that the geopolymer matrix was successfully formed in BWG and was significantly changed by the ratio, curing time and addition of heavy metals. The immobilization efficiency for different categories and dosages of heavy metals by BWG20 were all higher than 99.43%. Moreover, the XPS results demonstrate that the heavy metals were immobilized in geopolymer mainly by divalent state forms.


Assuntos
Cinza de Carvão/química , Metais Pesados/isolamento & purificação , Polímeros/química , Purificação da Água/métodos , Força Compressiva , Incineração , Metais Pesados/análise , Polímeros/síntese química , Reciclagem
20.
Environ Sci Pollut Res Int ; 26(13): 12689-12697, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30877542

RESUMO

In this study, amine-terminated hyperbranched PAMAM (polyamidoamine) polymer (AT-HBP) was synthesized as a multifunctional chelating agent to remove two heavy metal ions (Cr(III) and Cu(II)) from the simulated wastewater solutions. The AT-HBP was characterized by Fourier transformed infrared (FTIR), dynamic light scattering (DLS), and proton nuclear magnetic resonance (1H NMR) analysis. The removal process was carried out in two different methods, centrifuged process and ultrafiltration. The concentration of heavy metal ions before and after removal was measured by inductively coupled plasma (ICP) instrument. The removal processes were evaluated by changing different parameters such as solution pH, AT-HBP dosage, and metal ion concentration. To evaluate the extend of binding of heavy metal ions in the presence of AT-HBP the presence of salt in the solution was also examined on the performance of the removal system. The overall results indicated that removal percentages higher than 98% for Cr(III) and 86% for Cu(II) were achieved for heavy metal concentrations of 100 mg/L for both removal process methods. Furthermore, the function of second generation of polypropylenimine (PPI) was compared to AT-HBP. The results reveal that the removal of Cr(III) and Cu(II) ions by AT-HBP were approximately 20% and 10% higher compared to PPI, respectively. Finally, hyperbranched dendritic polymer with lower expenses to synthesize compared to dendrimer underlined favorable properties as a multifunctional chelating agent and enhancement of ultrafiltration process for wastewater treatment. Graphical abstract.


Assuntos
Dendrímeros/química , Metais Pesados/isolamento & purificação , Eliminação de Resíduos Líquidos/métodos , Adsorção , Aminas/química , Quelantes/química , Difusão Dinâmica da Luz , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Membranas Artificiais , Metais Pesados/química , Poliaminas/química , Espectroscopia de Infravermelho com Transformada de Fourier , Eliminação de Resíduos Líquidos/instrumentação , Águas Residuárias/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/isolamento & purificação
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