Chengchun Jiang

A new insight into Fenton and Fenton-like processes for water treatment.

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.

A new insight into Fenton and Fenton-like processes for water treatment: Part II. Influence of organic compounds on Fe(III)/Fe(II) interconversion and the course of reactions

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.

Transformation of Iodide by Carbon Nanotube Activated Peroxydisulfate and Formation of Iodoorganic Compounds in the Presence of Natural Organic Matter

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.

Chlorination of bisphenol S: Kinetics, products, and effect of humic acid

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 7.6-435.3 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.

Dominating role of ionic strength in the sedimentation of nano-TiO 2 in aquatic environments

Various factors affect the sedimentation behavior of nanotitanium dioxide (n-TiO2) in water. Accordingly, this study aimed to select the dominating factor. An index of sedimentation efficiency related to n-TiO2 concentration was applied to precisely describe the n-TiO 2 sedimentation behavior. Ionic strength (IS), natural organic matter (NOM) content, and pH were evaluated in sedimentation experiments. An orthogonal experimental design was used to sequence the affecting ability of these factors. Furthermore, simulative sedimentation experiments were performed. The n-TiO2 sedimentation behavior was only affected by pH and NOMcontent at low levels of IS. Moreover, divalent cations can efficiently influence the n-TiO2 sedimentation behavior compared with monovalent cations at fixed IS. Seven different environmental water samples were also used to investigate the n-TiO2 sedimentation behavior in aquatic environments. Results confirmed that IS, in which divalent cations may play an important role, was the dominating factor influencing the n-TiO2 sedimentation behavior in aquatic environments.

Transformation of Methylparaben by aqueous permanganate in the presence of iodide: Kinetics, modeling, and formation of iodinated aromatic products

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 ± 0.0071 to 1.0 ± 0.1 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 μM) treated by KMnO4 (50-150 μM) in the presence of I- (5-15 μM) suggested that higher I- or moderate KMnO4 concentration or neutral pH promoted their formation. A similar enhancing effect of I- (1 μM) on the transformation of MeP (1 μM) by KMnO4 (12.6 μM) 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.

Alternative assessment of nano-TiO2 sedimentation under different conditions based on sedimentation efficiency at quasi-stable state

The predictable significant increase in manufacture and use of engineered nanoparticles (ENPs) will cause their inevitable release into environment, and the potential harmful effects of ENPs have been confirmed. As representative ENPs, sedimentation behavior of nano-titanium dioxide (n-TiO2) should be better understood to control its environmental risk. In this study, an experimental methodology was established to set the sampling area and sampling time of n-TiO2 sedimentation. In addition, we defined a quasi-stable state and a precise index, i.e., sedimentation efficiency (SE) at this state, to describe the n-TiO2 sedimentation behavior. Both alternative concentration determination and conventional size measurement were applied to evaluate the sedimentation behavior of n-TiO2 with fulvic acid. Results showed that the sedimentation behavior described by SE was more precise and in disagreement with those predicted by particle size. Moreover, sedimentation experiments with salicylic acid (SA), under an electric field and different water temperatures or with sulfosalicylic acid under light irradiation were also performed. When the total organic carbon concentration of SA, the voltage of working electrodes, and water temperature increased, or the wavelength of light source decreased, the SE of n-TiO2 increased and n-TiO2 showed a tendency to settle in water. These findings might be important for deepening the understanding of n-TiO2 environmental behavior and exploring sedimentation behavior of other ENPs.

A Trickle Bed Electrochemical Reactor for Generation of Hydrogen Peroxide and Degradation of an Azo Dye in Water

Abstract A trickle bed electrochemical reactor was used to generate hydrogen peroxide in dilute electrolyte and then degrade an azo dye, i.e. reactive brilliant red X-3B in water by electro-Fenton process. The trickle bed reactor was composed of carbon black-polytetrafluoroethylene coated graphite chips. During the preparation of coated graphite chips, coating times and surfactant dosage were optimized to improve electro-generation of H2O2. In addition, the optimal electrolysis conditions for H2O2 electro-generation were obtained as follows, cell voltage of 4.5 V, air flow rate of 0.1 m3/h, electrolyte flow rate of 15 mL/min, and initial pH of 3. Under the given conditions, H2O2 concentration, production rate and current efficiency were 5.01 mmol/L, 134 μmol/(h·cm2) and 63.7%, respectively, after 1 h of electrolysis. With addition of 0.1 mmol/L Fe2+, 123 mg/L X-3B was completely removed from water after 30 min of electro-Fenton treatment, whereas total organic carbon dropped slowly from 17.8 mg/L to 2.28 mg/L (87% mineralization) after 3 h. The trickle bed reactor was sufficient to treat low-strength wastewater or be used in tandem with other treatment units.

Quantitatively assessing the role played by carbonate radicals in bromate formation by ozonation

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.

Is Sulfate Radical Really Generated from Peroxydisulfate Activated by Iron(II) for Environmental Decontamination

It is well documented that the traditional Fenton reagent (i.e., the combination of Fe(II) and H2O2) produces hydroxyl radical (•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 •OH-induced products. However, it remains unclear whether Fe(IV) is generated in the Fe(II) activated peroxydisulfate (PDS) process, where sulfate radical (SO4•-) is long recognized as the dominant intermediate in literature. Here we demonstrated that SO4•- 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 ∼100% 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 SO4•- and/or •OH.