RESUMO
Recently, hydroxylamine (HAm) was introduced to drive advanced oxidation processes (AOPs) for removing organic contaminants. However, we found that HAm-driven Cu(II)/peroxymonosulfate oxidation of phenol produced p-nitrosophenol, 2-nitrophenol and 4-nitrophenol. The total nitro(so) products accounted for approximately 25.0 % of the phenol transformation at certain condition. SO4â¢- and â¢OH were identified as the primary and second significant oxidants, respectively. Reactive nitrogen species (RNS) were involved in phenol transformation. The pathway and mechanism of HAm transformation in HAm-driven transition metal ion-catalyzed AOPs were proposed for the first time in this study. The product of HAm via twice single-electron oxidation by Cu(II) is nitroxyl (HNO/NO-), which is a critical oxidation intermediate of HAm. Further oxidation of HNO by SO4â¢- or â¢OH is the initial step in propagating radical chain reactions, leading to nitric oxide radical (â¢NO) and nitrogen dioxide radical (â¢NO2) as the primary RNS. HAm is a critical intermediate in natural nitrogen cycle, suggesting that HAm can drive the oxidation processes of pollutants in natural environments. Nitro(so) products will be readily produced when AOPs are applied for ecological remediation. This study highlights the formation of toxic nitrosated and nitrated products in HAm-driven AOPs, and the requirement of risk assessments to evaluate the possible health and ecological impacts.
Assuntos
Nitratos , Poluentes Químicos da Água , Hidroxilamina , Oxirredução , Óxido Nítrico , Fenol , Hidroxilaminas , Poluentes Químicos da Água/análiseRESUMO
Sustainable sludge management has significance due to the great potential of recovering energy and resources, potentially achieving carbon neutrality and energy positivity in the process. However, whether the sludge reduction strategy really benefits the aim of a sustainable sludge management process requires a holistic analysis. In this study, nine scenarios involving different sludge management strategies with or without sludge reduction methods were environmentally and economically assessed to clarify the necessity of adopting a sludge reduction or not. Results reveal that direct sludge incineration without prior in-plant sludge reduction generates the least environmental impacts (less than 25-120 %), but it increases operation costs by 103-110 % compared to landfilling with prior in-plant sludge reduction. Chemical Oxygen Demand flows indicate that direct sludge incineration is superior in converting organic matter into energy compared to employing sludge reduction followed by landfilling or land application. This converted energy offsets environmental impacts from electricity consumption, but these electricity benefits are insignificant in the overall cost. Case studies suggest that direct sludge incineration could facilitate potential nutrient and energy recovery, especially for metropolis. While sludge reduction strategies are more suited for developing regions relying on landfills or land application, to lower the economic burdens. The findings of this study tend to shed light on the decision-making of adopting sludge reduction strategies and sustainable sludge management.
Assuntos
Incineração , Esgotos , Meio Ambiente , Incineração/métodos , Instalações de Eliminação de ResíduosRESUMO
Iopamidol (IPM) is widely used in medical clinical examination and treatment and has immeasurable harm to the ecological environment. The combination of UV and sulfite (UV/sulfite) process was developed to degrade IPM in this study. In contrast to that almost no removal of IPM was observed under sulfite reduction alone, the UV/sulfite process could efficiently reductively degrade IPM with the observed rate constant (kobs) of 2.08â¯min-1, which was nearly 4 times that of UV irradiation alone. The major active species in the UV/sulfite process were identified as hydrated electrons (eaq-) by employing active species scavengers. The influence of the initial pH, sulfite dosage, IPM concentration, UV intensity and common water matrix were evaluated. The degradation of IPM reached nearly 100% within only 2.5â¯min at pH 9, and kobs increased at higher initial sulfite dosages and greater UV intensities. HCO3- had a limited effect on the degradation of IPM, while humic acid (HA) was found to be a strong inhibitor in the UV/sulfite process. With the synergistic action of UV/sulfite, most of the iodine in IPM was found to release in the form of iodide ions (up to approximately 98%), and a few formed iodide-containing organic compounds, reducing significantly the toxicity of degradation products. Under direct UV irradiation and free radical reduction (mainly eaq-), 15 transformation intermediates of IPM were produced by amide hydrolysis, deiodination, hydroxyl radical addition and hydrogen abstraction reactions, in which free radical attack accounted for the main part. Consequently, the UV/sulfite process has a strong potential for IPM degradation in aquatic environments.
Assuntos
Poluentes Químicos da Água , Purificação da Água , Radicais Livres , Iodetos , Iopamidol/química , Oxirredução , Sulfitos/química , Raios Ultravioleta , Poluentes Químicos da Água/análiseRESUMO
Recently, the combination of peroxymonosulfate (PMS) and hydroxylamine (HA) has been proposed as a green and efficient sulfate radical ()-based advanced oxidation process (AOP) for eliminating organic contaminants. However, we found that toxic nitrosated and nitrated aromatic compounds were generated during the treatment of phenolic compounds by PMS/HA system, indicating the involvement of reactive nitrogen species (RNS) during the interaction of PMS with HA. Specifically, considerable production of p-nitrosophenol (p-NSP) and mononitrophenol were obtained when phenol was oxidized by PMS/HA system under various conditions. At the molar ratio between HA and PMS of 1.0 and pH 5.0, sum of the yields of p-NSP and nitrophenols reached their maxima (around 50%). Moreover, production of p-NSP was inhibited while that of nitrophenols was promoted when applied NH2OH1/2H2SO4 was replaced by NH2OHHCl, which was possibly related to the formation of secondary reactive species induced by the reaction of with chloride ion. Further, formation of undesirable nitrosated and nitrated aromatic products was obtained in the treatment of other phenolic compounds including acetaminophen, bisphenol A, and bisphenol S by PMS/HA system. Considering the toxicity of nitrosated and nitrated aromatic compounds, practical application of PMS/HA system for environmental decontamination should be scrutinized.
Assuntos
Nitratos , Poluentes Químicos da Água , Hidroxilamina , Hidroxilaminas , Oxirredução , Peróxidos , Fenóis , Poluentes Químicos da Água/análiseRESUMO
In this work, we found that the distribution of two specific atrazine (ATZ) oxidation products (desethyl-atrazine (DEA) and desisopropyl-atrazine (DIA)) was different in oxidation processes involving aqueous ferryl ion (Fe(IV)) species and â¢OH. Specifically, the molar ratio of produced DEA to DIA (i.e., [DEA]/[DIA]) increased from 7.5 to 13 with increasing pH from 3 to 6 when ATZ was oxidized by Fe(IV), while the treatment of ATZ by â¢OH led to the [DEA]/[DIA] value of 2 which was independent of pH. Moreover, ATZ showed high reactivity towards Fe(IV) over a wide pH range, especially at near-neutral pH, at which ATZ oxidation in Fe(II)/peroxydisulfate system was even much faster than another well-defined Fe(IV) scavenger, the sulfoxides. By using this approach, it was obtained that the [DEA]/[DIA] value remained at 2 during ATZ transformation by the nitrilotriacetic acid (NTA) assisted Fenton-like (Fe(III)/H2O2) system, which was independent of solution pH and reactants dosage. This result clarified that â¢OH was the primary reactive intermediate formed in the NTA assisted Fe(III)/H2O2 system. This study not only developed a novel sensitive diagnostic tool for distinguishing Fe(IV) from â¢OH, but also provided more credible evidence to the nature of reactive intermediate in a commonly controversial system.
Assuntos
Atrazina , Compostos Férricos , Peróxido de Hidrogênio , Ácido Nitrilotriacético , OxirreduçãoRESUMO
Metal-organic frameworks (MOFs) constitute new class of materials recently used by researchers in the field of controlling cyanobacteria. However, the use of MOFs in combination with allelochemicals for cyanobacteria inhibition had not been investigated before. The present study is aimed towards the investigation of the effect and mechanism of cyanobacteria inhibition by combining MOF with allelochemical (ferulic acid, FA) for the first time. In this study, the results showed that the synergistic effect of Zn2+ and FA from Zn-MOF-FA could inhibit cyanobacteria to a greater extent than the corresponding dosage of Zn2+ and FA. The inhibition ratio of Microcystis aeruginosa has been found to be more than 50% when the Zn-MOF-FA concentration exceeds 2 mg·L-1 after four days exposure. Zn-MOF-FA at 1 mg·L-1 did not completely inhibit M. aeruginosa, and the inhibition effect has been of only temporary type. The inhibitory effect of Zn-MOF-FA on algae has mainly been attributed to the hindrance of electron transfer and energy capture in the photosynthetic system and the oxidative damage caused by reactive oxygen species (ROS).
Assuntos
Cianobactérias , Microcystis , Antioxidantes , Fotossíntese , Zinco/toxicidadeRESUMO
Transition metal catalyzed sulfite auto-oxidation is a promising technology used in water and wastewater treatment for the elimination of contaminants. In the literature, this process has been reported to be efficient only in the presence of oxygen. However, in this study, we unexpectedly found that the degradation of diatrizoate (DTZ) by a system based on the combination of copper ion and sulfite (Cu(II)/S(IV)) reached over 95% under anaerobic conditions, but was considerably retarded under aerobic conditions at pH 7. Furthermore, it was found that Cu(I), generated from the cleavage of the CuSO3 complex, was the main reactive species responsible for the degradation of DTZ by the Cu(II)/S(IV) system under anaerobic conditions. In fact, the absence of oxygen promoted the accumulation of Cu(I). The concomitant release of the iodide ion with the degradation of DTZ indicated that the anaerobic degradation of DTZ by the Cu(II)/S(IV) system mainly proceeded through the deiodination pathway, which was also confirmed by the detection of deiodinated products. The anaerobic degradation of DTZ was favored at higher initial concentrations of Cu(II) or sulfite in this system. Since the CuSO3 complex, the precursor of Cu(I), was formed mainly at pH 7, the highest anaerobic degradation of DTZ was achieved at pH 7. An increase in reaction temperature considerably enhanced the degradation of DTZ by the Cu(II)/S(IV) system with an apparent activation energy of 119.4 kJ/mol. The presence of chloride, bicarbonate and humic acid slightly influenced the anaerobic degradation of DTZ. The experiments with real water samples also demonstrated the effectiveness of the degradation of DTZ by the Cu(II)/S(IV) system under anaerobic conditions.
Assuntos
Cobre , Diatrizoato , Anaerobiose , Oxirredução , SulfitosRESUMO
Iodinated contrast media (ICM), which was widely used in medical imaging and was difficult to remove by conventional wastewater treatment methods, attained much attention due to its potential environmental impacts. Herein, iopamidol (IPM), one typical compound of ICM, was found to be rapidly degraded by ferrous activated persulfate oxidation (Fe(II)/PS) as compared with PS or Fe(II) alone. With a persulfate concentration of 1 mmol L-1, n(Fe(II))/n(PS) of 1:10, and a pH of 3.0, 78% IPM was degraded within 60 min, with a degradation rate of 0.1266 min-1. It was demonstrated that IPM degradation and deiodination were favored by a high temperature, while affected positively by acidic and neutral conditions. Radical quenching experiments and Electron Paramagnetic Resonace (EPR) spectra showed that the combined effects of SO4-· and ·OH contributed dominantly to degrade IPM, while the ·OH played an essential role during the degradation reaction. Through the Discrete Fourier Transform quantum chemical calculation, the possible reaction pathways for the oxidation of IPM by ·OH are as follows: IPM-TP651-TP667-TP541-TP557, IPM-TP651-TP525-TP557, IPM-TP705-TP631-TP661, and IPM-TP705-TP735. The obtained results showed that IPM could be degraded effectively by Fe(II)/PS system, giving a promising technique for IPM removal from water.
RESUMO
Chemical oxidation processes have been extensively utilized in disinfection and removal of emerging organic contaminants in recent decades. Some undesired byproducts, however, are produced in these processes. Of them, bromate has attracted the most intensive attention. It was previously regarded as a byproduct that typically occurred in ozone-based oxidation processes. However, for the past decade, bromate formation has been detected in other oxidation processes such as CuO-catalyzed chlorination, SO4--based oxidation, and ferrate oxidation processes. This review summarizes the occurrences, mechanisms, influencing factors, risk assessment, and control strategies of bromate formation in the four oxidation processes, i.e., ozone-based oxidation, chlorine-based oxidation, SO4--based oxidation, and ferrate oxidation. Besides, some unresolved issues for future studies are provided: (1) Clarification of the relative contributions of SO4- and Br to the oxidation of bromine for bromate formation in SO4--based oxidation processes; (2) evaluation of the role of different reactive species in the bromate formation in the process of UV/HOCl; (3) quantification of the dual role of alkalinity in bromate formation during ozonation; (4) assessment of the risks of bromate formation in SO4--based oxidation processes for practical applications; and (5) exploration of strategies for inhibiting bromate formation in SO4--based oxidation, UV/chlorine, and metal oxide-catalyzed chlorination processes.
Assuntos
Bromatos/química , Poluentes Químicos da Água/química , Brometos , Bromo , Cloro , Desinfecção , Halogenação , Ferro , Oxirredução , Ozônio , Medição de Risco , Poluentes Químicos da Água/análise , Purificação da ÁguaRESUMO
It is well documented that invertebrates can ingest and transport pathogenic bacteria, thus protecting the bacteria against disinfection in the laboratory. However, the risk assessment of and corresponding disinfection methods for natural invertebrate-internalized bacteria in biological activated carbon (BAC) filtration systems remain poorly understood. In this study, the risk of natural invertebrate-internalized bacteria was comprehensively assessed and methods to inactivate these bacteria were compared in a pilot-scale BAC filtration column study lasting one year. Seven groups of invertebrates dominated by rotifers and crustaceans were detected in the filtration column, five of which were collected for quantitative/qualitative identification of the bacteria they internalized. The community composition of internalized bacteria was analyzed via polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) coupled with sequence analysis of 16S rRNA gene fragments. Results showed that the average numbers of internalized bacteria per organism ranged from 160 to 6000, which increased exponentially with invertebrate body length. Some of the invertebrate-internalized bacteria were identified as opportunistic human pathogens, but no direct human pathogens were detected. A model was developed to calculate the residual bacteria concentration. Using this model, it was determined that an average of 800-100,000â¯CFU/m3 internalized bacteria would be protected and then released into the distribution mains after chlorination of 50â¯mg/L·min, with rotifers and copepods the dominant sources. Ozonation was more effective than both chlorination and UV radiation for inactivating the invertebrate-internalized bacteria.
Assuntos
Filtração/métodos , Invertebrados/microbiologia , Purificação da Água/métodos , Animais , Bactérias , Carvão Vegetal/química , Desinfecção/métodos , Medição de Risco , Raios UltravioletaRESUMO
This work investigates the transformation of iodide (I-) by Fe(II)-activated peroxydisulfate (PDS). The transformation of I- into iodate (IO3-) is a two-step process, involving reactive iodine species, such as hypoiodous acid (HOI), as a key intermediate, and IO3- as the final product. In the first step, SO4â¢- produced by Fe(II)-activated PDS is mainly responsible for the transformation of I- into HOI. In the second step, Fe(IV) formed by the reaction of Fe(III) with PDS is required, to facilitate the further oxidation of HOI to IO3-. The disproportionation of HOI and the oxidation by PDS alone contribute negligibly to IO3- formation. The IO3- yield increases to a maximum, before decreasing gradually, with increased PDS and Fe(II) dosages. The transformation of I- into IO3- is favored by lower pH and higher temperature, due to the greater SO4â¢- production by the reaction of Fe(II) with PDS under these conditions. Humic acid, as a representative natural organic matter, scavenges the formed HOI to form iodinated disinfection byproducts, which largely inhibit the transformation of I- into IO3-. In addition, the transformation of I- into IO3- and iodinated disinfection byproducts by Fe(II) activated PDS was confirmed in the natural waters.
RESUMO
Bicarbonate scavenges OH to form CO3- that enhances the bromate formation by ozonation. However, the role of CO3- in the bromate formation during ozonation has never been quantitatively investigated. Herein, we establish a quantitative approach for evaluating the role played by CO3- based on the detection of CO3--involved bromate and CO3- exposure. Experiments demonstrated that the CO3--involved bromate was responsible for 33.7-69.9% of the total bromate formed with bicarbonate concentrations from 0.5 mM to 4 mM. The CO3- exposure was two orders of magnitude higher than the corresponding OH exposure during ozonation. These results demonstrate that CO3- plays a comparable or even more pronounced role in the oxidation of bromine during bromate formation than OH. A model was developed based on the ratio of bromine oxidized by CO3-, which could predict the CO3--involved bromate formation well. Modeled and experimental results illustrated that the contribution of the CO3--involved bromate to the total bromate decreased with increasing pH or initial bromide, but almost remained unchanged at different ozone dosages. Moreover, the presence of humic acid led to an increase in this contribution during ozonation. The results of this study provide a more in-depth understanding of the mechanism of bromate formation during ozonation.
RESUMO
It is well documented that the traditional Fenton reagent (i.e., the combination of Fe(II) and H2O2) produces hydroxyl radical (â¢OH) under acidic conditions, while at near-neutral pH the reactive intermediate converts to ferryl ion (Fe(IV)) that can oxidize sulfoxides to produce corresponding sulfones, markedly differing from their â¢OH-induced products. However, it remains unclear whether Fe(IV) is generated in the Fe(II) activated peroxydisulfate (PDS) process, where sulfate radical (SO4â¢-) is long recognized as the dominant intermediate in literature. Here we demonstrated that SO4â¢- oxidized methyl phenyl sulfoxide (PMSO, a model sulfoxide) to produce biphenyl compounds rather than methyl phenyl sulfone (PMSO2). Interestingly, the formation of PMSO2 was observed when PMSO was treated by the Fe(II)/PDS system over a wide pH range, and the yields of PMSO2 were quantified to be â¼100% at acidic pH 3-5. The identification of Fe(IV) in the Fe(II)/PDS system could also reasonably explain the literature results on alcohol scavenging effect and ESR spectra analysis. Further, a Fe(IV)-based kinetic model was shown to accurately simulate the experimental data. This work urges re-evaluation of the Fe(II)/PDS system for environmental decontamination, given that Fe(IV) would have different reactivity toward environmental contaminants compared with SO4â¢- and/or â¢OH.
Assuntos
Compostos Ferrosos , Peróxido de Hidrogênio , Descontaminação , Radical Hidroxila , Oxirredução , SulfatosRESUMO
In previous studies, we interestingly found that several ligands (e.g., pyrophosphate, nitrilotriacetate, and humic acid) could significantly accelerate the oxidation rates of triclosan (TCS; the most widely used antimicrobial) by aqueous permanganate (Mn(VII)) especially at acid pH, which was ascribed to the contribution of ligand-stabilized Mn(III) (defined Mn(III)L) formed in situ as a potent oxidant. In this work, it was found that the oxidation of TCS by Mn(III)L resulted in the formation of dimers, as well as hydroxylated and quinone-like products, where TCS phenoxy radical was likely involved. This transformation pathway distinctly differed from that involved in Mn(VII) oxidation of TCS, where 2,4-dichlorophenol (DCP) was the major product with a high yield of â¼80%. Surprisingly, we found that the presence of various complexing ligands including pyrophosphate, nitrilotriacetate, and humic acid, as well as bisulfite slightly affected the yields of DCP, although they greatly enhanced the oxidation kinetics of TCS by Mn(VII). This result could not be reasonably explained by taking the contribution of Mn(III)L into account. Comparatively, the degradation of TCS by manganese dioxide (MnO2) was also greatly enhanced in the presence of these ligands with negligible formation of DCP, which could be rationalized by the contribution of Mn(III)L. In addition, it was demonstrated that DCP could not be generated from Mn(VII) oxidation of unstable phenoxy radical intermediates and stable oxidation products formed from TCS by Mn(III)L. These findings indicate that manganese intermediates other than Mn(III) are likely involved in the Mn(VII)/TCS/ligand systems responsible for the high yields of DCP product.
Assuntos
Triclosan , Substâncias Húmicas , Ligantes , Oxidantes , OxirreduçãoRESUMO
This work investigated impacts of iodide (I-) on the transformation of the widely used phenolic preservative methylparaben (MeP) as well as 11 other phenolic compounds by potassium permanganate (KMnO4). It was found that KMnO4 showed a low reactivity towards MeP in the absence of I- with apparent second-order rate constants (kapp) ranging from 0.065⯱â¯0.0071 to 1.0⯱â¯0.1â¯M-1s-1 over the pH range of 5-9. The presence of I- remarkably enhanced the transformation rates of MeP by KMnO4 via the contribution of hypoiodous acid (HOI) in situ formed, which displayed several orders of magnitude higher reactivity towards MeP than KMnO4. This enhancing effect of I- was greatly influenced by solution conditions (e.g., I- or KMnO4 concentration or pH), which could be well simulated by a kinetic model involving competition reactions (i.e., KMnO4 with I-, KMnO4 with MeP, HOI with KMnO4, and HOI with MeP). Similar enhancing effect of I- on the transformation kinetics of 5 other selected phenols (i.e., p-hydroxybenzoic acid, phenol, and bromophenols) at pH 7 was also observed, but not in the cases of bisphenol A, triclosan, 4-n-nonylphenol, and cresols. This discrepancy could be well explained by the relative reactivity of KMnO4 towards phenols vs I-. Liquid chromatography-tandem mass spectrometry analysis showed that iodinated aromatic products and/or iodinated quinone-like product were generated in the cases where I- enhancing effect was observed. Evolution of iodinated aromatic products generated from MeP (10⯵M) treated by KMnO4 (50-150⯵M) in the presence of I- (5-15⯵M) suggested that higher I- or moderate KMnO4 concentration or neutral pH promoted their formation. A similar enhancing effect of I- (1⯵M) on the transformation of MeP (1⯵M) by KMnO4 (12.6⯵M) and formation of iodinated aromatic products were also observed in natural water. This work demonstrates an important role of I- in the transformation kinetics and product formation of phenolic compounds by KMnO4, which has great implications for future applications of KMnO4 in treatment of I--containing water.
Assuntos
Iodetos/química , Parabenos/química , Fenóis/química , Compostos Benzidrílicos/química , Halogenação , Concentração de Íons de Hidrogênio , Compostos de Iodo/química , Cinética , Modelos Químicos , Permanganato de Potássio/química , Triclosan/química , Poluentes Químicos da Água/química , Purificação da Água/métodosRESUMO
This study investigated the use of Dracontomelon duperreanum leaf litter extract (DDLLE) in inhibiting the growth and photosynthesis of the algae Microcystis aeruginosa. The goal of the study was to evaluate a potential solution for cyanobacterial bloom prevention. M. aeruginosa was exposed to extract concentrations from 0.4 to 2.0 g L-1. Chlorophyll-a (Chl-a) content and photosynthesis levels were assessed using pulse amplitude modulated fluorimetry phytoplankton analyzer. Results suggested that the extract could efficiently suppress M. aeruginosa growth. The content of Chl-a was only 19.0 µg L-1 and achieved 96.0% inhibition rate when exposed to 2.0 g L-1 on day 15. Growth rate in response to different extract concentrations were consistent with changes in the photosynthesis efficiency (alpha), maximal relative electron transport rate and maximal photochemical efficiency of photosystem II (F v /F m ). Furthermore, several kinds of volatile chemicals and their concentrations in DDLLE had been identified by GC-MS, which of them play major role to suppress the growth of M. aeruginosa should be further studied.
Assuntos
Anacardiaceae/química , Microcystis/efeitos dos fármacos , Complexo de Proteína do Fotossistema II/efeitos dos fármacos , Extratos Vegetais/toxicidade , Poluição da Água/prevenção & controle , Clorofila/metabolismo , Clorofila A , Cianobactérias/metabolismo , Transporte de Elétrons , Microcystis/metabolismo , Microcystis/fisiologia , Fotossíntese/efeitos dos fármacos , Complexo de Proteína do Fotossistema II/metabolismo , Fitoplâncton/metabolismo , Folhas de Planta/metabolismoRESUMO
Bisphenol S (BPS), as a main alternative of bisphenol A for the production of industrial and consumer products, is now frequently detected in aquatic environments. In this work, it was found that free chlorine could effectively degrade BPS over a wide pH range from 5 to 10 with apparent second-order rate constants of 7.6-435.3â¯M-1s-1. A total of eleven products including chlorinated BPS (i.e., mono/di/tri/tetrachloro-BPS), 4-hydroxybenzenesulfonic acid (BSA), chlorinated BSA (mono/dichloro-BSA), 4-chlorophenol (4CP), and two polymeric products were detected by high performance liquid chromatography and electrospray ionization-tandem quadrupole time-of-flight mass spectrometry. Two parallel transformation pathways were tentatively proposed: (i) BPS was attacked by stepwise chlorine electrophilic substitution with the formation of chlorinated BPS. (ii) BPS was oxidized by chlorine via electron transfer leading to the formation of BSA, 4CP and polymeric products. Humic acid (HA) significantly suppressed the degradation rates of BPS even taking chlorine consumption into account, while negligibly affected the products species. The inhibitory effect of HA was reasonably explained by a two-channel kinetic model. It was proposed that HA negligibly influenced pathway i while appreciably inhibited the degradation of BPS through pathway ii, where HA reversed BPS phenoxyl radical (formed via pathway ii) back to parent BPS.
Assuntos
Cloro/química , Substâncias Húmicas , Fenóis/química , Sulfonas/química , Poluentes Químicos da Água/química , Cromatografia Líquida de Alta Pressão , Halogenação , Concentração de Íons de Hidrogênio , Cinética , Oxirredução , Espectrometria de Massas por Ionização por Electrospray , Purificação da Água/métodosRESUMO
In this study, we interestingly found that peroxydisulfate (PDS) could be activated by a commercial multiwalled carbon nanotube (CNT) material via a nonradical pathway. Iodide (I-) was quickly and almost completely oxidized to hypoiodous acid (HOI) in the PDS/CNT system over the pH range of 5-9, but the further transformation to iodate (IO3-) was negligible. A kinetic model was proposed, which involved the formation of reactive PDS-CNT complexes, and then their decomposition into sulfate anion (SO42-) via inner electron transfer within the complexes or by competitively reacting with I-. Several influencing factors (e.g., PDS and CNT dosages, and solution pH) on I- oxidation kinetics by this system were evaluated. Humic acid (HA) decreased the oxidation kinetics of I-, probably resulting from its inhibitory effect on the interaction between PDS and CNT to form the reactive complexes. Moreover, adsordable organic iodine compounds (AOI) as well as specific iodoform and iodoacetic acid were appreciably produced in the PDS/CNT/I- system with HA. These results demonstrate the potential risk of producing toxic iodinated organic compounds in the novel PDS/CNT oxidation process developed very recently, which should be taken into consideration before its practical application in water treatment.
Assuntos
Iodetos/química , Nanotubos de Carbono , Iodatos/química , Oxirredução , Poluentes Químicos da Água , Purificação da ÁguaRESUMO
The interconversion of Fe(III)/Fe(II) in Fenton (Fe(2+)/H2O2) and Fenton-like (Fe(3+)/H2O2) reactions has been studied to better understand their intrinsic mechanisms. The reactions were conducted at an initial pH of 3.0, with H2O2 in excess and iron in catalytic concentrations, and with nitrobenzene and atrazine as model organic compounds. The results of this study have shown that some intermediate species in the degradation of aromatic compounds can influence the interconversion of Fe(III)/Fe(II) in the Fenton and Fenton-like reactions, and hence influence the rate and course of the reactions. Thus, from the point of view of Fe(III)/Fe(II) interconversion, a Fenton-like reaction inevitably involves a classical Fenton reaction, and a Fenton reaction may also involve a Fenton-like reaction step. These two reactions may be somewhat interchangeable and proceed simultaneously. In the case of the degradation of aromatic compounds, the Fenton-like reactions display autocatalytic character, but no such effect is observed for non-aromatic compounds.
Assuntos
Peróxido de Hidrogênio/química , Ferro/química , Oxigênio/química , Poluentes Químicos da Água/isolamento & purificação , Purificação da Água/métodos , Atrazina/química , Catálise , Concentração de Íons de Hidrogênio , Radical Hidroxila , Cinética , Modelos Químicos , Nitrobenzenos/química , Compostos Orgânicos/química , Poluentes Químicos da Água/análiseRESUMO
In this study, two Fenton (Fe(2+)/H(2)O(2)) and Fenton-like (Fe(3+)/H(2)O(2)) reactions were compared to clarify their roles in phenol degradation under varying H(2)O(2) concentrations, iron dosages and pHs, as well as in the presence of radical scavenger. The results of this study showed that a Fenton-like reaction must proceed concurrently with a classic Fenton reaction, and the concurrent Fenton reaction played a major role in the degradation of pollutants. For the Fenton-like reaction, some oxidation intermediates of phenolic compounds may promote the conversion of Fe(III) to Fe(II) in addition to the uni-molecular decomposition of the Fe(III)-hydroperoxy complexes. The results also showed that varying H(2)O(2) concentrations exerted identical effects on the two reactions, and that phenol degradation in both reactions could be correlated to the decomposition of H(2)O(2). At low levels of iron concentration, the Fenton reaction appeared to be more efficient than the Fenton-like reaction in terms of the phenol degradation and H(2)O(2) decomposition. Additionally, the Fenton reaction had an effective pH range of 2.5-6.0, while the Fenton-like reaction was limited to a narrow pH range of 2.8-3.8. Although the Fenton-like reaction was much slower than that of the Fenton reaction, the overall extent of phenol degradation and H(2)O(2) decomposition at the optimal conditions was equivalent.