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1.
Environ Sci Technol ; 2020 Mar 23.
Artigo em Inglês | MEDLINE | ID: mdl-32182042

RESUMO

Surface functional groups play a dominating role in determining the adsorption performance of metal oxide particles. The ability to manipulate the surface functional groups is vital in designing an effective adsorbent for water decontamination. In this study, a facile method is proposed for tuning the amount of the surface hydroxyl groups of CeO2 particles. The volume of water added during the ethylene glycol-mediated solvothermal synthesis of CeO2 particles can be used to adjust the amount of surface hydroxyl groups. By simple reduction in the volume of water, the number of surface hydroxyl groups of CeO2 particles can be increased and the phosphate adsorption capacity can be greatly improved. Our results show that the obtained CeO2 particles have high phosphate adsorption capacity at low phosphate concentrations, fast adsorption kinetics, and the ability to achieve an ultralow phosphate concentration in the real sewage effluent. This study provides an effective strategy for designing highly effective metal oxide adsorbents through surface functional group engineering.

2.
Water Res ; 170: 115356, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31816569

RESUMO

The ability of the TiO2-based photocatalysis process to mineralize organic pollutants has attracted attention worldwide for the degradation of recalcitrant pharmaceuticals and personal care products (PPCPs). Nevertheless, (1) the limited exploitation of the solar spectrum, i.e., activation under UV light (only 2-3% of solar spectrum), and (2) the high recombination rate of photo-generated charge carriers, i.e., electrons and holes, have limited its application which can, however, be improved by developing a TiO2-based heterojunction. The objective of this critical review paper is to discuss the recent developments (2009-2019) in visible-light-driven (VLD) TiO2-based heterojunctions for PPCP degradation and their degradation mechanisms. Compared to the conventional heterojunctions, Schottky and Z-scheme heterojunctions, which are non-conventional heterojunctions, are found to be more effective for PPCP degradation due to their more efficient separation of charge carriers and the occurrence of redox reactions at a relatively higher redox potential. Furthermore, the enhancement strategies for the development of a VLD TiO2-based heterojunction are also explored which can be achieved by selecting the (1) highly photocatalytically active {001} facet of anatase TiO2, (2) synthesis methods governing the structural changes at the junction interface, and (3) heterojunction components which can efficiently generate the powerful •OH radicals. The challenges in practical applications are also discussed which include factors, viz., cost reduction, recycling, stability, byproducts analysis, evaluation of the environmental effectiveness, and reactor design and scale-up of the VLD TiO2-based heterojunctions. Accordingly, the prospects of VLD TiO2-based heterojunctions for PPCP degradation in real environmental applications are discussed.


Assuntos
Luz , Catálise , Oxirredução
3.
Water Res ; 168: 115166, 2020 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-31634707

RESUMO

This study describes the photoelectrochemical (PEC) treatment of authentic sewage from Hong Kong for H2 production and degradation of emerging pollutants (EP's) simultaneously, and disinfection of E. coli. The g-C3N4/Ag/AgCl/BiVO4 (CAB-1) coated thin film acted as the photoanode in a three-electrode configuration PEC cell and real sewage as the electrolyte. Electrochemical studies revealed the near reversible, diffusion-controlled and high electron transfer reaction at the electrode-electrolyte surface. For CAB-1, the achieved photocurrent density was 0.1-0.2 mA cm-2 at 1.23 V vs. RHE exhibiting the highest PEC degradation efficiency (11.15% h-1 cm-2) compared to other base materials like g-C3N4/BiVO4 (6.88% h-1 cm-2) or Ag/AgCl/BiVO4 (4.06% h-1 cm-2). During the same reaction, the evolved 118 µmol of H2 gas corresponds to a Faradic efficiency of 69.38%. The composition of sewage was found to influence the overall PEC efficiency. The higher amount of total suspended solids, turbidity, and anionic species decreased the efficiency while as the other parameters like alkaline pH increased the PEC efficiency. Photo-electrochemically, the CAB-1 also effectively disinfected the E. coli present in the sewage with a final discharge of ≤1000 CFU/mL which is within the permissible discharge limits (≤1500 CFU/mL), in Hong Kong.


Assuntos
Desinfecção , Poluentes Ambientais , Escherichia coli , Hong Kong , Hidrogênio , Esgotos , Prata
4.
J Hazard Mater ; 381: 121000, 2020 01 05.
Artigo em Inglês | MEDLINE | ID: mdl-31422344

RESUMO

A novel magnetic anionic hydrogel (nFeMAH), synthesized via a facile method, was characterized by XRD, VSM, SEM, TEM, FTIR, XPS, and ζ-potential measurement. Over the tested range of pH 2 to 12, the surface of the nFeMAH was permanently negative with a ζ-potential of -35 to -45 mV. The adsorption kinetics and capacity of nFeMAH were studied. Within 60 min, equilibrium was achieved with maximum adsorption capacities of 102 mg Cu(II)/g and 93 mg Ni(II)/g. The pseudo-second-order kinetics model was well-matched with the experimental data, whereas the Langmuir isotherm model agreed well with the isotherm data. The magnetic separation efficiency of nFeMAH remained above 90% after 20 cycles of adsorption-desorption, whereas the Ni(II) removal efficiency dropped from 92 to about 75% after the first cycle. The magnetic separation efficiency of nFeMAH was consistently high (99%). The major mechanism of metal removal by nFeMAH was ion exchange but there also was evidence for formation of metal oxides. Therefore, the application of nFeMAH for treating electroplating wastewater can be a desirable option when considering its superior performance in the adsorptive treatment, i.e., pH insensitivity, fast adsorption kinetics, high reusability, and consistency in magnetic separation.

5.
Environ Sci Technol ; 2019 Dec 24.
Artigo em Inglês | MEDLINE | ID: mdl-31804806

RESUMO

Eutrophication of water bodies is a serious and widespread environmental problem. Achieving low levels of phosphate concentration to prevent eutrophication is one of the important goals of the wastewater engineering and surface water management. Meeting the increasingly stringent standards is feasible in using a phosphate-selective sorption system. This critical review discusses the most fundamental aspects of selective phosphate removal processes and highlights gains from the latest developments of phosphate-selective sorbents. Selective sorption of phosphate over other competing anions can be achieved based on their differences in acid-base properties, geometric shapes, and metal complexing abilities. Correspondingly, interaction mechanisms between the phosphate and sorbent are categorized as hydrogen bonding, shape complementarity, and inner-sphere complexation, and their representative sorbents are organic-functionalized materials, molecularly imprinted polymers, and metal-based materials, respectively. Dominating factors affecting the phosphate sorption performance of these sorbents are critically examined, along with a discussion of some overlooked facts regarding the development of high-performance sorbents for selective phosphate removal from water and wastewater.

6.
Sci Total Environ ; 686: 878-887, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-31200308

RESUMO

Despite numerous developments in the field of heterogeneous photocatalysis, particularly its environmental applications, there remain fundamental uncertainties regarding the key properties which primarily govern the performance of a photocatalyst. In this study, four visible-light-driven magnetic photocatalysts, viz., Ag/Fe,N-TiO2/Fe3O4@SiO2, g-C3N4/TiO2/Fe3O4@SiO2, BiOBr/Fe3O4@SiO2, and BiOBr0.9I0.1/Fe3O4@SiO2, were synthesized and comparatively studied in terms of their material characteristics, charge transfer efficiency, and photocatalytic performance in the degradation of two model pharmaceuticals and personal care products (PPCPs), ibuprofen and benzophenone-3. Amongst the tested photocatalysts, the g-C3N4/TiO2/Fe3O4@SiO2 exhibited the fastest degradation kinetics for both the PPCPs. Property-performance relationships were evaluated in which the dependence of the photocatalytic performance on various adsorption-related, electronic band-structure-related, reactive species-related, and charge carriers-related properties was examined. The strongest performance relationship was found to be with photocurrent density-an indicator of charge transfer efficiency-for both PPCPs, indicating its influential role in governing the photocatalytic performance. The findings unfold a potential research direction towards exploration of factors which can enhance the charge transfer efficiency, thereby possibly enabling the rational design of highly efficient photocatalysts for PPCPs removal.

7.
Sci Total Environ ; 684: 351-359, 2019 Sep 20.
Artigo em Inglês | MEDLINE | ID: mdl-31153081

RESUMO

In the advanced oxidation processes, using persulfate (PS) as a radical precursor for pollutant degradation in groundwater has received increasing attention. In this study, zeolite supported nZVI composites (Z/nZVI) were synthesized through an ion exchange and borohydride reduction method to investigate their ability to activate PS for the TCE degradation. Based on preliminary screening of the PS activation by the Z/nZVI (PS-Z/nZVI) system in terms of TCE degradation, Z/nZVI composite with a zeolite to nZVI mass ratio of 1:1 (Z/nZVI (1)) was optimized as the best composition and chosen for further characterization and examination. Especially, for this PS-Z/nZVI system, PS concentration, solution matrix effects (i.e., solution pH, coexisting anions and natural organic matter) were studied. Characterization results revealed that the aggregation of nZVI particles was alleviated and they were good dispersed on the zeolite sheet with a large SSA (159.49 m2/g) compared to the unsupported nZVI (8.77 m2/g). The synthesized Z/nZVI (1) composite exhibited excellent activated ability towards PS (1.5 mM) and effectively degraded 98.8% of TCE at pH 7 within 120 min. The PS-Z/nZVI system was observed to operate effectively over a wide range of pH (i.e., 4-7) for TCE degradation. Moreover, the presence of nitrates (1 mM) and bicarbonates (10 mM) decreased the TCE degradation efficiency to 91.5% and 59.6%, respectively. Scavenger tests demonstrated that both sulfate and hydroxyl radicals participated in the TCE degradation. The ion chromatography analysis suggested the formation of oxalic acid and formic acid as the reaction intermediates during the TCE degradation process in the PS-Z/nZVI system.

8.
Chemosphere ; 224: 658-667, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30849627

RESUMO

Information on the environmental impact of magnetic TiO2-based nanophotocatalysts is scarce. This study evaluated the potential effects of an innovative magnetic nanophotocatalyst N-TiO2/Fe3O4@SiO2 (NTFS) on plants using Arabidopsis thaliana grown in a hydroponic system. NTFS was detected in the vascular tissues and mesophyll of plants, thus confirming the uptake and upwards transport of NTFS from roots to leaves. Fourier transform infrared spectroscopy was applied to determine compositional and structural alterations in plant tissues exposed to NTFS, or its two main components (N-TiO2 and Fe3O4@SiO2), at concentrations ranging from 0 to 1000 mg/L, but no changes were detected in the lipids, pectins, proteins, cellulose, hemicellulose, and carbohydrates. The morphology and biomass of the plants were not affected by the NTFS or its components either. Biosensors for inorganic phosphate (Pi) and MgATP2- were used to monitor the in vivo Pi and MgATP2- levels in the plant cells. The results showed that NTFS and its components did not induce any adverse effects on the cytosolic Pi level or ATP synthesis, indicating the energy physiology of Arabidopsis was unaffected. In general, NTFS has inconsequential toxic effects on Arabidopsis, but can be taken up by plants, enter the food chain, and cause potential exposure and bioaccumulation in animals and human beings.


Assuntos
Arabidopsis/efeitos dos fármacos , Titânio/farmacocinética , Arabidopsis/metabolismo , Transporte Biológico , Catálise , Compostos Férricos/metabolismo , Compostos Férricos/farmacocinética , Magnetismo , Fosfatos/análise , Processos Fotoquímicos , Folhas de Planta/química , Folhas de Planta/metabolismo , Raízes de Plantas/metabolismo , Dióxido de Silício/metabolismo , Dióxido de Silício/farmacocinética
9.
Chemosphere ; 217: 869-878, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30458422

RESUMO

A visible-light-driven and magnetic photocatalyst Ag/Fe,N-TiO2/Fe3O4@SiO2 (AgFeNTFS) was synthesized through a multi-step method. AgFeNTFS was tested for the photocatalytic disinfection of Escherichia coli (E. coli) and degradation of bisphenol A (BPA) under visible light irradiation, separately and simultaneously. The results showed that a 6.3-log reduction in cell density of E. coli was achieved and BPA (2 mg/L) was completely removed by AgFeNTFS in the separated photocatalytic processes within 120 min. In the simultaneous process, the photocatalytic disinfection of E. coli was not influenced in the presence of BPA, but the efficiency of BPA degradation was dropped by 10%. This was likely due to the competition for the same dominant reactive species of O2- and H2O2 between E. coli and BPA in the simultaneous process, as evidenced by the scavenger study and the interactions between the pollutants and AgFeNTFS. Moreover, the simultaneous photocatalytic activity of E. coli disinfection and BPA degradation by AgFeNTFS was investigated in the sewage obtained from a local wastewater treatment plant. The photocatalysis treated sewage could meet with the local disinfection discharge standard with a 3-log reduction of E. coli after 90 min, and a complete removal of BPA was achieved simultaneously after 360 min. Moreover, AgFeNTFS showed high magnetic separation efficiency and had a good reusability over three cycles for the simultaneous photocatalytic disinfection and degradation of BPA in both synthetic water and sewage. This study provides insights on the application of a reusable magnetic photocatalyst for simultaneous disinfection and degradation of BPA in sewage.


Assuntos
Compostos Benzidrílicos/química , Desinfecção/métodos , Escherichia coli/efeitos da radiação , Luz , Fenóis/química , Esgotos/química , Dióxido de Silício/química , Titânio/química , Catálise , Compostos Férricos/química , Ferro/química , Magnetismo , Prata/química
10.
J Hazard Mater ; 365: 733-743, 2019 03 05.
Artigo em Inglês | MEDLINE | ID: mdl-30472459

RESUMO

The increasingly ubiquitous release of emerging refractory pollutants into water is a serious concern due to associated risks. In this study, mesoporous hierarchical BiOBr/Fe3O4@SiO2-a solvothermally synthesized visible-light-driven magnetic photocatalyst-not only exhibited fast kinetics (t1/2 = 8.7 min) in the photocatalytic degradation of ibuprofen in water but also achieved almost complete mineralization over a prolonged irradiation of 6 h. Various reactive species, including O2¯, OH, and H2O2, were detected, while the scavenging experiments revealed that eCB--mediated reactions and direct-hole oxidation are the major degradation routes. The magnetically recycled BiOBr/Fe3O4@SiO2 maintained ∼80% of its initial photocatalytic activity even after five consecutive cycles. The typically copresent wastewater constituents, including NOM and anions, inhibited the photocatalytic performance to varying extents, and hence necessitated an increase in the photocatalyst dosage to achieve complete ibuprofen degradation in real sewage. Based on the findings of batch experiments, the process was scaled up by developing a 5 L prototype photocatalytic reactor integrated with an electromagnetic separation unit. The results of prototype photocatalytic experiments were comparable to those of batch experiments, and an electromagnetic separation efficiency of ∼99% was achievable in 5 min.

11.
Chemosphere ; 216: 428-436, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30384313

RESUMO

In this study, the effects of surface modification of nZVI and arsenic (As) loading on the mobility of the three types of As-loaded nZVI (As-loaded pristine, chitosan-modified and polyaniline-modified nZVI) in quartz sand-packed columns were investigated. Breakthrough curves and retention profiles for the three types of As-loaded nZVI were analyzed by the Tufenkji-Elimelech equations and the HYDRUS-1D model. The mobility of both types of As-loaded modified nZVI was higher than the As-loaded pristine nZVI at both low and high As loadings. Compared to low As loading, the mobility of the three types of As-loaded nZVI was higher at high As loading. The values of the calculated and the fitted retention parameters of the three As-loaded nZVI were lower when As loading was higher or nZVI was modified, which were in line with the experimental column findings. The mechanisms of As-loaded nZVI transport were probably due to ripening and sedimentation. The As in the effluent was mainly from the As-loaded nZVI particles when nZVI was detected and was from the As release when no nZVI was detectable. It was evident that the mobility of the three types of As-loaded nZVI particles were severely limited (the maximum transport distance was less than 60 cm), regardless of surface modification and As loading. Therefore, the As release from the As-loaded nZVI could cause potentially wide pollution and should be paid more attention regarding to the application of nZVI in As remediation.


Assuntos
Arsênico/química , Recuperação e Remediação Ambiental/métodos , Água Subterrânea/química , Ferro/química , Nanopartículas Metálicas/química
12.
J Hazard Mater ; 370: 108-116, 2019 05 15.
Artigo em Inglês | MEDLINE | ID: mdl-28789808

RESUMO

TiO2-based photocatalysis offers certain advantages like rapid degradation and mineralization of organic compounds. However, the practical applicability of photocatalysts in degradation of pharmaceuticals and personal care products (PPCPs) is still restricted by challenges including their limited photocatalytic activity under visible light and difficulty in their separation from suspension. To overcome these challenges, a visible-light-driven magnetic N-TiO2@SiO2@Fe3O4 nanophotocatalyst was developed through fine-tuning the pertinent factors (calcination temperature, Fe3O4 loading, and nitrogen doping) involved during synthesis process, on the basis of degradation of ibuprofen (a typical PPCP). The TEM-EDX, XRD and XPS analyses confirmed the successful synthesis of nanophotocatalyst. By comparing nanophotocatalyst's performance on ibuprofen under two visible light sources, i.e., compact fluorescent lamps (CFLs) and light emitting diodes (LEDs) of similar irradiance, CFLs of irradiance 320µWcm-2 and peak emissive wavelength 543nm served as a better source, resulting in 94% degradation. Furthermore, 93% of benzophenone-3 within 5h and 71% of carbamazepine within 9h was degraded under visible light emitted by CFLs. The superparamagnetic behavior of the nanophotocatalyst enabled its successful magnetic separation (95% efficiency) from the suspension within 20-25min under an electromagnetic field of ∼200mT.

13.
Environ Sci Technol ; 52(7): 4385-4392, 2018 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-29554421

RESUMO

The use of nano zerovalent iron (nZVI) for arsenate (As(V)) remediation has proven effective, but full-scale injection of nZVI into the subsurface has aroused serious concerns for associated environmental risks. This study evaluated the efficacy of nZVI treatment for arsenate remediation and its potential hazards to plants using Arabidopsis thaliana grown in a hydroponic system. Biosensors for inorganic phosphate (Pi) and MgATP2- were used to monitor in vivo Pi and MgATP2- levels in plant cells. The results showed that nZVI could remove As(V) from growth media, decrease As uptake by plants, and mitigate As(V) toxicity to plants. However, excess nZVI could cause Pi starvation in plants leading to detrimental effects on plant growth. Due to the competitive adsorption of As(V) and Pi on nZVI, removing As(V) via nZVI treatment at an upstream site could relieve downstream plants from As(V) toxicity and Pi deprivation, in which case 100 mg/L of nZVI was the optimal dosage for remediation of As(V) at a concentration around 16.13 mg/L.


Assuntos
Arabidopsis , Recuperação e Remediação Ambiental , Trifosfato de Adenosina , Arseniatos , Ferro , Fosfatos
14.
J Hazard Mater ; 343: 266-275, 2018 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-28968561

RESUMO

The influence of weak magnetic field (WMF) and tartrate on the oxidation and sequestration of Sb(III) by zerovalent iron (ZVI) was investigated with batch and semi-continuous reactors. The species analysis of antinomy in aqueous solution and solid precipitates implied that both Sb(III) adsorption preceding its conversion to Sb(V) in solid phase and Sb(III) oxidation to Sb(V) preceding its adsorption in aqueous phase occurred in the process of Sb(III) sequestration by ZVI. The application of WMF greatly increased the rate constants of Sbtot (total Sb) and Sb(III) disappearance during Sb(III)-tartrate and uncomplexed-Sb(III) sequestration by ZVI. The enhancing effect of WMF was primarily due to the accelerated ZVI corrosion in the presence of WMF, as evidenced by the influence of WMF on the change of solution and solid properties with reaction. However, tartrate greatly retarded Sb removal by ZVI. It was because tartrate inhibited ZVI corrosion, competed with Sb(III) and Sb(V) for the active surface sites, increased the negative surface charge of the generated iron (hydr)oxides due to its adsorption, and formed soluble complexes with Fe(III). The positive effect of WMF on Sb(III)-tartrate and uncomplexed-Sb(III) removal by ZVI was also verified with a magnetic semi-continuous reactor.

15.
Chemosphere ; 192: 209-216, 2018 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-29102865

RESUMO

Lanthanum-based adsorbents are ideal candidates for phosphate removal because of their excellent affinity to phosphate. However, their application in the removal of trace-levels of phosphate from sewage is still unsatisfactory due to the limited adsorption capacity and inadequate optimization of the operational parameters. To overcome these drawbacks, we have developed a novel lanthanum hydroxide (LH), using a facile precipitation and hydrothermal process that involves a nanorod-like structure with the lengths ranging from 124 to 1700 nm, depending on the La/OH molar ratio. The phosphate adsorption capacity of the developed LH is up to 170.1 mg-P g-1 in synthetic water, while a slightly lower adsorption capacity of 111.1 mg-P g-1 is observed in a sewage sample. A polynominal model consisting of three variables (i.e. dosage, reaction time and initial phosphate concentration) for predicting efficiency of phosphate removal has been successfully developed using a face-centred central composite design (CCD)-based methodology. The results also suggest a strong interactive effect of the dosage with the phosphate concentration, and reaction time, which can significantly affect the optimization of the phosphate removal by LH. Both X-ray photoelectron spectroscopy and X-ray diffraction studies indicate that the inner sphere complexation of phosphate with LH is probably the major mechanism governing phosphate removal.


Assuntos
Lantânio/química , Fosfatos/química , Esgotos/química , Poluentes Químicos da Água/química , Purificação da Água/métodos , Adsorção , Nanotubos , Espectroscopia Fotoeletrônica , Água/química , Difração de Raios X
16.
Environ Sci Technol ; 51(21): 12377-12384, 2017 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-29035555

RESUMO

Lanthanum-based materials are effective for sequestering phosphate in water, however, their removal mechanisms remain unclear, and the effects of environmentally relevant factors have not yet been studied. Hereby, this study explored the mechanisms of phosphate removal using La(OH)3 by employing extended X-ray absorption spectroscopy (EXAFS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), density functional theory (DFT) and chemical equilibrium modeling. The results showed that surface complexation was the primary mechanism for phosphate removal and in binary phosphate configurations, namely diprotonated bidentate mononuclear (BM-H2) and bidentate binuclear (BB-H2), coexisting on La(OH)3 in acidic conditions. By increasing the pH to 7, BM-H1 and BB-H2 were the two major configurations governing phosphate adsorption on La(OH)3, whereas BB-H1 was the dominant configuration of phosphate adsorption at pH 9. With increasing phosphate loading, the phosphate configuration of on La(OH)3 transforms from binary BM-H1 and BB-H2 to BB-H1. Amorphous Ca3(PO4)2 forms in the presence of Ca, leading to enhanced phosphate removal at alkaline conditions. The contributions of different mechanisms to the overall phosphate removal were successfully simulated by a chemical equilibrium model that was consistent with the spectroscopic results. This study provides new insights into the molecular-level mechanism of phosphate removal by La(OH)3.


Assuntos
Lantânio , Nanotubos , Adsorção , Fosfatos , Espectroscopia de Infravermelho com Transformada de Fourier
17.
Water Res ; 126: 179-188, 2017 12 01.
Artigo em Inglês | MEDLINE | ID: mdl-28950228

RESUMO

The use of lanthanum (La)-based materials for phosphate removal from water and wastewater has received increasing attention. However, challenges remain to enhance phosphate sorption capacities and recover La-based sorbents. In this study, magnetic La(OH)3/Fe3O4 nanocomposites with varied La-to-Fe mass ratios were synthesized through a precipitation and hydrothermal method. Based upon preliminary screening of synthesized La(OH)3/Fe3O4 nanocomposites in terms of phosphate sorption capacity and La content, La(OH)3/Fe3O4 nanocomposite with a La-to-Fe mass ratio of 4:1 was chosen for further characterization and evaluation. Specifically, for these materials, magnetic separation efficiency, phosphate sorption kinetics and isotherm behavior, and solution matrix effects (e.g., coexisting ions, solution pH, and ionic strength) are reported. The developed La(OH)3/Fe3O4 (4:1) nanocomposite has an excellent magnetic separation efficiency of >98%, fast sorption kinetics of 30 min, high sorption capacity of 83.5 mg P/g, and strong selectivity for phosphate in presence of competing ions. Phosphate uptake by La(OH)3/Fe3O4 (4:1) was pH-dependent with the highest sorption capacities observed over a pH range of 4-6. The ionic strength of the solution had little interference with phosphate sorption. Sorption-desorption cyclic experiments demonstrated the good reusability of the La(OH)3/Fe3O4 (4:1) nanocomposite. In a real treated wastewater effluent with phosphate concentration of 1.1 mg P/L, 0.1 g/L of La(OH)3/Fe3O4 (4:1) efficiently reduced the phosphate concentration to below 0.05 mg P/L. Electrostatic attraction and inner-sphere complexation between La(OH)3 and P via ligand exchange were identified as the sorption mechanisms of phosphate by La(OH)3/Fe3O4 (4:1).


Assuntos
Nanocompostos/química , Fosfatos/isolamento & purificação , Eliminação de Resíduos Líquidos/métodos , Poluentes Químicos da Água/isolamento & purificação , Adsorção , Precipitação Química , Compostos Férricos/química , Concentração de Íons de Hidrogênio , Cinética , Lantânio/química , Magnetismo , Concentração Osmolar , Fosfatos/química , Espectroscopia Fotoeletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Águas Residuárias/química , Poluentes Químicos da Água/química
18.
Waste Manag ; 67: 315-323, 2017 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-28587803

RESUMO

In order to foster sustainable management of food waste, innovations in food waste valorization technologies are crucial. Black soldier fly (BSF) bioconversion is an emerging technology that can turn food waste into high-protein fish feed through the use of BSF larvae. The conventional method of BSF bioconversion is to feed BSF larvae with food waste directly without any moisture adjustment. However, it was reported that difficulty has been experienced in the separation of the residue (larval excreta and undigested material) from the insect biomass due to excessive moisture. In addition to the residue separation problem, the moisture content of the food waste may also affect the growth and survival aspects of BSF larvae. This study aims to determine the most suitable moisture content of food waste that can improve residue separation as well as evaluate the effects of the moisture content of food waste on larval growth and survival. In this study, pre-consumer and post-consumer food waste with different moisture content (70%, 75% and 80%) was fed to BSF larvae in a temperature-controlled rotary drum reactor. The results show that the residue can be effectively separated from the insect biomass by sieving using a 2.36mm sieve, for both types of food waste at 70% and 75% moisture content. However, sieving of the residue was not feasible for food waste at 80% moisture content. On the other hand, reduced moisture content of food waste was found to slow down larval growth. Hence, there is a trade-off between the sieving efficiency of the residue and the larval growth rate. Furthermore, the larval survival rate was not affected by the moisture content of food waste. A high larval survival rate of at least 95% was achieved using a temperature-controlled rotary drum reactor for all treatment groups. The study provides valuable insights for the waste management industry on understanding the effects of moisture content when employing BSF bioconversion for food waste recycling.


Assuntos
Reatores Biológicos , Alimentos , Reciclagem , Simuliidae , Resíduos Sólidos , Gerenciamento de Resíduos , Ração Animal , Animais , Larva
19.
J Hazard Mater ; 322(Pt A): 195-204, 2017 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-26857338

RESUMO

Acid dyes found in textile industrial effluents are hazardous aromatic pollutants which ionize in aqueous environments. Owing to their non-biodegradability, conventional wastewater treatment processes are not able to remove them and sorptive treatment systems can alternatively be employed. In this study, a nano γ-Fe2O3 based magnetic cationic hydrogel, synthesized through a facile method, was applied for the removal of two acid dyes (Acid Red 27 and Acid Orange 52). The sorption performance (e.g., capacity and kinetics) and solution matrix effects (e.g., pH and competing anions) were investigated. Furthermore, different regeneration conditions (e.g., composition, strength and amount) were tested to develop a suitable regeneration strategy, based on which, reusability of the material was investigated for 30 consecutive sorption-desorption cycles. The material exhibited a rapid sorption rate (99% dye removal within 5min) and sorption isotherm data agreed well with the Langmuir model with an estimated maximum capacity of 833mg/g and 1430mg/g for Acid Red 27 and Acid Orange 52, respectively. The high sorptive performance persisted not only over a wide pH range but also over 30 consecutive rounds of sorption-desorption. Moreover, the impregnated γ-Fe2O3 nanoparticles rendered the hydrogel superparamagnetic allowing its convenient magnetic separation.

20.
Water Res ; 106: 259-271, 2016 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-27728820

RESUMO

Due to the unique physical and chemical characteristics of hydrogels, such as hydrophilicity, swellability, and modifiability, there is increasing research interest in the development and application of novel hydrogels in water and wastewater treatment. Hydrogels have exhibited superior performance in the adsorptive removal of a wide range of aqueous pollutants including heavy metals, nutrients, and toxic dyes. However, there remain certain challenges which need to be addressed in order to evolve hydrogel based treatment systems from the lab-scale to practical applications. This review provides a coverage of the latest developments in the application of hydrogels for the adsorptive removal of aqueous pollutants. A holistic overview of different steps involved in the hydrogel based treatment systems is provided, and the influencing factors and mechanisms of pollutants removal are reviewed. Major challenges pertaining to adsorption kinetics, operational pH range, interference, and hydrogel recovery are examined. Important considerations such as stability and reusability of hydrogels and resource recovery are also discussed, for economic and sustainability concerns.


Assuntos
Hidrogel de Polietilenoglicol-Dimetacrilato , Poluentes Químicos da Água , Adsorção , Hidrogéis , Águas Residuárias
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