Degradation of diphenylamine by persulfate: Performance optimization, kinetics and mechanism

N-nitrosamines in electroplating and printing/dyeing industrial wastewater treatment plants: Removal efficiency, environmental emission, and the influence on drinking water

The discharge of industrial wastewater containing high concentrations of N-nitrosamines to the aquatic environment can impair downstream source waters and pose potential risks to human health. However, the transport and fate of N-nitrosamines in typical industrial wastewater treatment plants (IWWTPs) and the influence of these effluents on source water and drinking water are still unclear. This study investigated nine N-nitrosamines in four full-scale electroplating (E-) and printing/dyeing (PD-) IWWTPs, two drinking water treatment plants (DWTPs) in the lower reaches of these IWWTPs, and the corresponding tap water in South China. The total concentrations of N-nitrosamines (∑NAs) were 382-10,600, 480-1920, 494-789, and 27.9-427 ng/L in influents, effluents, source water, and tap water, respectively. The compositions of N-nitrosamine species in different influents varied a lot, while N-nitrosodi-n-butylamine (NDBA) and N-nitrosodimethylamine (NDMA) dominated in most of the effluents, source water, and tap water. More than 70 % N-nitrosamines were removed by wastewater treatment processes used in E-IWWTPs such as ferric-carbon micro-electrolysis (Fe/C-ME), while only about 50 % of N-nitrosamines were removed in PD-IWWTPs due to the use of chlorine reagent or other inefficient conventional processes such as flocculation by cationic amine-based polymers or bio-contact oxidation. Therefore, the mass fluxes of N-nitrosamines discharged from these industrial wastewaters to the environment in the selected two industrial towns were up to 14,700 mg/day. The results based on correlation and principal component analysis significantly demonstrated correlations between E-and PD-effluents and source water and tap water, suggesting that these effluents can serve as sources of N-nitrosamines to local drinking water systems. This study suggests that N-nitrosamines are prevalent in typical IWWTPs, which may infect drinking water systems. The findings of this study provide a basis data for the scientific evaluation of environmental processes of N-nitrosamines.

Degradation of 1,2,3-trichloropropane by unactivated persulfate and the implications for groundwater remediation

Persulfate (PS) is widely used as an in situ chemical oxidation (ISCO) technology for groundwater and soil remediation. While conventional theory generally assumes that PS needs to be "activated" to produce reactive radicals for pollutant degradation, herein, PS without explicit activation system was discovered for the degradation of 1,2,3-TCP with the generation of reactive oxidation species (ROS). Comparison of five common ISCO oxidants (PS, peroxymonosulfate, hydrogen peroxide, potassium permanganate, and sodium percarbonate) indicated that only unactivated PS was able to degrade 1,2,3-TCP in both pure water and 12 natural water samples. 50 μM 1,2,3-TCP degradation can be continued as long as there is enough PS (50 mM). The degradation rate of 1,2,3-TCP increased 450 % when the PS concentration increased from 10 mM to 50 mM and 500 % when the temperature increased from 25 °C to 45 °C. Electron paramagnetic resonance (EPR) analyzes, hydroxyl radicals (·OH) probe reaction and radical quenching experiments confirmed the involvement of both sulfate radicals (SO₄·-) and ·OH that were responsible for 1,2,3-TCP degradation and ·OH played a more important role. HCO₃^-, Cl^- and NOM are three groundwater matrix species that are most likely to inhibit PS oxidation of 1,2,3-TCP. Compared to activated PS, unactivated PS is more promising and more practical for groundwater remediation, since it has several advantages: (1) longer lifetime and better long-term availability; (2) ability of enduring contaminant degradation; (3) applicable for low-permeability zones remediation and potential to alleviate contaminant rebound or tailing problems; (4) environmental friendly; and (5) lower cost. Overall, results of this study show that unactivated PS is a promising in situ remediation technology that may be a good candidate for the most challenging low permeable zone remediation.

Degradation of benzothiazole pollutant by sulfate radical-based advanced oxidation process

Benzothiazole (BTH) is an aromatic heterocyclic compound with wide industrial applications. In view of its toxicity and wide environmental presence, previous efforts have been made to decompose BTH via different degradation pathways. However, due to its recalcitrant nature, conventional biological treatment methods cannot completely degrade BTH in the wastewater. In this study, sulfate radical-based advanced oxidation process (AOP) technique has been adopted to degrade BTH in aqueous phase. Persulfate (PS) was employed as radical promotor to generate sulfate radical via heat activation. Degradation of BTH by thermally activated persulfate via AOP has been experimentally evaluated in a systematic manner. Laboratory efforts have been made to examine the impact of a number of physiochemical parameters including the type of oxidants, reaction temperature, initial concentrations of PS and BTH, solution pH, and the presence of anionic species. It shows that a higher BTH degradation rate can be achieved by lowering BTH initial concentration or increasing PS concentration. Increasing solution pH or the presence of 10 mM of Cl^-, Br^-, CO32-, or HCO3- species can decrease BTH degradation rate. Furthermore, the primary radical(s) responsible for BTH degradation have been identified as sulfate radical at an acidic aqueous condition, and hydroxyl radical and sulfate radical combined at a basic condition. This study provides the necessary theoretical and technical foundations for BTH degradation via sulfate radical-based AOP technique. The conclusions from this study can substantially promote the field application of AOP, especially sulfate radical-based AOP technique, for BTH degradation in wastewater treatment process.

Iodometric spectrophotometric determination of peroxydisulfate in hydroxylamine-involved AOPs: 15 min or 15 s for oxidative coloration?

In this study, iodometric spectrophotometry, the most-used method for detecting peroxydisulfate (PDS), was modified by increasing the concentration of potassium iodide (KI) for realizing the immediate PDS determination and avoiding the interference of hydroxylamine. Kinetic studies showed that the reaction between PDS and I^- to generate the yellow-colored I₃^- followed the kinetic equation as [Formula: see text] . Detection time of the iodometric spectrophotometry was shortened from 15 min to 15 s when KI concentration was increased from 0.6 M to 4.8 M. Different with the previous iodometric spectrophotometry, the modified method using 4.8 M KI as the indicator was well tolerable to the interference of hydroxylamine at acidic pH conditions. The calibration curve of the modified method showed a well linear relationship (R² = 0.999) between the absorbance of I₃^- at 352 nm and PDS concentration in the range of 0-80 μM. The modified method was highly sensitive with the absorptivity of 2.5 × 10⁴ M^-1 cm^-1 and the limit of detection of 0.11 μM. Moreover, the modified method was successfully applied for monitoring the change of PDS concentration during the degradation of diclofenac with four different PDS-based AOPs, the calculated reaction stoichiometric efficiency (RSE(%)=DiclofenacdegradedPDSconsumed×100%) followed the order as heat/PDS system > hydroxylamine/Fe²⁺/PDS system > hydroxylamine/Cu²⁺/PDS system > Fe²⁺/PDS system.

Degradation of aniline by ferrous ions activated persulfate: Impacts, mechanisms, and by-products

Wastewater contains a large number of anions and organics which can scavenge reactive radicals and limit the application of sulfate radical-based advanced oxidation processes (SR-AOPs) in practical engineering. Here, we studied the removal rate and mechanism of aniline by SR-AOPs in different influencing factors, such as sodium persulfate dosage, ferrous ions dosage, solution pH, Cl^-, HCO₃^-, NO₃^-, and other organic matter. By recognizing and analyzing free radicals, we concluded that SO₄^•- plays a major role in aniline degradation. The aniline removal rate increased with the initial concentrations of persulfate and ferrous ions, but aniline degradation was inhibited by excessive dosage. The aniline removal rate by ferrous-ions-catalyzed persulfate was higher under acidic conditions and could be improved under alkaline conditions if no ferrous ions were added. The addition of bicarbonate ions inhibited aniline removal, and the addition of nitrate ions barely caused the effect. While the addition of chloride ions promoted aniline degradation, which was confirmed that HClO generated from the reacting of Cl^- and persulfate played a key role. However, TOC indicated that aniline was not completely mineralized in the process. Further analysis of the products from GC-MS demonstrated that chloride-ion additions produced some harmful halogenated by-products. Our results can act as a basis for developing processes for the aniline degradation in wastewater.

The Roles of Sono-induced Nitrosation and Nitration in the Sono-degradation of Diphenylamine in Water: Mechanisms, Kinetics and Impact Factors

The potential risks of sono-induced nitrosation and nitration side reactions and consequent toxic nitrogenous byproducts were first investigated via sono-degradation of diphenylamine (DPhA) in this study. The kinetic models for overall DPhA degradation and the formation of nitrosation byproduct (N-nitrosodiphenylamine, NDPhA) and nitration byproducts (2-nitro-DPhA and 4-nitro-DPhA) were well established and fitted (R² > 0.98). Nitrosation contributed much more than nitration (namely, 43.3 - 47.3 times) to the sono-degradation of DPhA. The contribution of sono-induced nitrosation ranged from 0.4 to 56.6% at different conditions. The maximum NDPhA formation rate and the contribution of sono-induced nitrosation were obtained at 600 and 200 kHz, respectively, as ultrasonic frequencies at 200 to 800 kHz. Both NDPhA formation rate and the contribution of sono-induced nitrosation increased with increasing power density, while decreased with increasing initial pH and DPhA concentration. PO₄^3-, HCO₃^-, NH₄⁺ and Fe²⁺ presented negative impacts on sono-induced nitrosation in order of HCO₃^- >> Fe²⁺ > PO₄^3- > NH₄⁺, while Br^- exhibited a promoting effect. The mechanism of NDPhA formation via sono-induced nitrosation was first proposed.

Nonradical Oxidation of Pollutants with Single-Atom-Fe(III)-Activated Persulfate: Fe(V) Being the Possible Intermediate Oxidant

When applied for the remediation of polluted water/soil, peroxydisulfate (PDS) usually needs to be effectively activated to generate sulfate radical as the working oxidant. However, a significant part of the oxidation capacity of PDS is lost in this way because sulfate radical unselectively reacts with most of the substances in water/soil. PDS activation without generating radicals is preferred to maximize its oxidation capacity for targeted pollutants. Here, we report that single-atom Fe(III)- and nitrogen-doped carbon (Fe-N-C) can efficiently activate PDS to selectively remove some organic pollutants following an unreported nonradical pathway. The single-atom Fe(III) coordinated with pyridinic N atoms was confirmed to be the active site for the catalytic decomposition of PDS. However, the PDS decomposition did not produce radicals or reactive oxygen species. It is very likely that the coordinated Fe(III) is readily converted to Fe(V) through two-electron abstraction by PDS, and Fe(V) is responsible for the selective degradation of organic pollutants. The PDS/Fe-N-C-coupled process utilizes more oxidation capacity of PDS than both radical oxidation and other reported nonradical oxidation like PDS/CuO under the same experimental conditions. This process provides a new approach to selectively degrade some organic pollutants through PDS activation.

Photochemical transformations of tetracycline antibiotics influenced by natural colloidal particles: Kinetics, factor effects and mechanisms

Natural colloidal particles (NCPs), ubiquitous in seawater and important carriers for most environmental contaminants, could affect the transportation and transformation of contaminants in the aquatic environment. This research focused on the photochemical transformation behaviors and mechanisms of tetracycline (TC) and oxytetracycline (OTC) in the presence of NCPs from the surface water in the intertidal zones of Yellow River Delta. Results showed that TCs could undergo the direct and indirect photochemical transformations, and were well fitted pseudo-first-order degradation kinetics. Compared with pure water, the photochemical transformations of TCs were enhanced by 1-3 times by NCPs. The photochemical transformations of TCs were accelerated with increasing pH (2.0-11.0) in pure water, but the presence of NCPs slightly depressed the effect of pH. At the low salinity, NCPs accelerated the photochemical transformations, however, there was no influence at the high salinity. Under light irradiation, TC mainly underwent indirect photolysis through the excited state colloidal organic matter (³COM*), while direct photolysis mainly occurred for OTC. NCPs affected both pathways and yields of TC transformations, but they only affected intermediates yields of OTC. This paper has revealed that NCPs play a significant role in photochemical transformations of tetracycline antibiotics.

Electrochemical degradation of Mordant Blue 13 azo dye using boron-doped diamond and dimensionally stable anodes: influence of experimental parameters and water matrix

In this work, the electrooxidation as environmentally clean technology has been studied to the degradation of Mordant Blue 13 azo dye (MB13) using boron-doped diamond (p-Si/BDD) and oxide ruthenium titanium (Ti/Ru_0.3Ti_0.7O₂ (DSA)) anodes in various water matrices: distilled water (DW), hot tap water (HTW), and simulated wastewaters with (SWS) and without surfactant (SW). The influence of experimental parameters, such as current density, initial dye concentration, electrolysis time/specific charge, and pH on the MB13 degradation rate, current efficiency, and energy consumption, has been determined. The enhanced rate of both color and chemical oxygen demand (COD) removal in sulfate aqueous solutions with BDD was observed, which indicates that sulfate (SO₄^-•) radicals along with ^•OH ones might be responsible for the degradation process. The MB13 decolorization process obeyed a pseudo-first-order reaction kinetics with the apparent rate constant from 7.36 × 10^-2 min^-1 to 4.39 × 10^-1 min^-1 for BDD and from 9.2 × 10^-3 min^-1 to 2.11 × 10^-2 min^-1 for DSA depending on the electrolysis conditions. The effect of water matrix on the decolorization and COD removal efficiency has been evaluated. Inorganic ions, mordant salt, and surfactant contained in simulated effluents decelerated the COD decay compared to DW and HTW for the both anodes; meanwhile, they differently affected the discoloration process. A comparison of the specific energy consumption for each electrocatalytic material under different experiment conditions has been made. The BDD electrode was more efficient than the DSA to oxidize the MB13 dye in all kinds of water.

Degradation of Penicillin G by heat activated persulfate in aqueous solution

We used Heat Activated of Persulfate (HAP) to decompose Penicillin G (PEN G) in aqueous solution. The effect of pH (3-11), temperature (313-353 K), and initial concentration of Sodium Persulfate (SPS) (0.05-0.5 mM) on the decomposition level of PEN G were investigated. The residue of PEN G was determined by spectrophotometry at the wavelength of 290 nm. Also, the Chemical Oxygen Demand (COD) was measured in each experiment. The Total Organic Carbon (TOC) analysis was utilized for surveying the mineralization of PEN G. In addition, based on Arrhenius equation, the activation energy of PEN G decomposition was calculated. The results indicated that the maximum PEN G removal rate was obtained at pH 5 and by increasing the doses of SPS from 0.05 to 0.5 mM, the PEN G decomposition was enhanced. It was found that an increase in temperature is accompanied by an increase in removal efficiency of PEN G. The activation energy of the studied process was determined to be 94.8 kJ mol^-1, suggesting that a moderate activation energy is required for PEN G decomposition. The TOC measurements indicate that the HAP can efficiently mineralize PEN G. Besides, the presence of the scavengers significantly suppressed the HAP process to remove the PEN G. Overall, the results of this study demonstrate that using HAP process can be a suitable method for decomposing of PEN G in aqueous solutions.

Treatment of landfill leachate biochemical effluent using the nano-Fe3O4/Na2S2O8 system: Oxidation performance, wastewater spectral analysis, and activator characterization

Nano-Fe₃O₄ was used as heterogeneous catalyst to activate Na₂S₂O₈ for the generation of the sulfate radicals (SO₄^-) to oxidize the residual pollutants in landfill leachate biochemical effluent. The oxidation performance, wastewater spectral analysis and activator characterization were discussed. Oxidation experimental result shows that nano-Fe₃O₄ has obvious catalytic effect on Na₂S₂O₈ and can significantly enhance the oxidation efficiencies of Na₂S₂O₈ on landfill leachate biochemical effluent, with COD and color removals above 63% and 95%, respectively. Based on the analyses of three-dimensional excitation emission matrix fluorescence spectrum (3DEEM), ultraviolet-visible spectra (UV-vis), and Fourier Transform infrared spectroscopy (FTIR) of wastewater samples before and after treatment, it can be concluded that the pollution level of dissolved organic matter (DOM) declined and that the humic acid (HA) fractions were efficiently degraded into small molecules of fulvic acid (FA) fractions with less weight and stable structure. Compared to the raw wastewater sample, the aromaticity and substituent groups of the DOM were lessened in the treated wastewater sample. Moreover, the main structure of the organics and functional groups were changed by the Fe₃O₄/Na₂S₂O₈ system, with substantial decrease of conjugated double bonds. The micro morphology of nano-Fe₃O₄ was characterized before and after reaction by the methods of scanning electron microscope spectra (SEM), X-ray diffraction pattern (XRD), and X-ray photoelectron spectroscopy (XPS). The XRD pattern analysis showed that nano-Fe₃O₄ was oxidized into r-Fe₂O₃ and that the particle size of it also became smaller after reaction. XPS was employed to analyze the content and iron valence on the nano-Fe₃O₄ surface, and it can be found that the ratio of Fe³⁺/Fe²⁺ decreased from 1.8 before reaction to 0.8 after reaction. From the SEM analysis after the treatment, it was determined that the spacing between nano-Fe₃O₄ was increased, but in turn, the particles decreased in diameter.

Phenol abatement using persulfate activated by nZVI, H2O2 and NaOH and development of a kinetic model for alkaline activation

Three persulfate (PS) activation methods (nanoparticles of zero-valent iron (nZVI), hydrogen peroxide and alkali) were compared using phenol as target pollutant. Firstly, four experiments were conducted at 25°C in a batch way using the same initial phenol and oxidant concentrations (10 mM and 420 mM, respectively), being the molar ratio activator/PS fixed to 0.005 with nZVI (mass ratio 0.0011 nZVI/PS), to 2 using hydrogen peroxide and to 2 and 4 with NaOH. Phenol and PS conversions and aromatic byproducts profiles during 168 h reaction time were measured and compared, as well as mineralization and ecotoxicity of the samples. It was found that both phenol and aromatic byproducts (catechol and hydroquinone) totally disappeared using PS activated by alkali before 24 h, while a significant amount of aromatic intermediates was obtained with nZVI and H₂O₂. Additional runs were carried out using shorter times (0-2 h) to discriminate the oxidation route and the kinetic model of phenol abatement by using PS activated by alkali. Different initial concentrations of phenol (5-15 mM), PS (210 and 420 mM) and molar ratio NaOH/PS (2 and 4) were employed. The kinetic model obtained predicts accurately the evolution of phenol, persulfate, hydroquinone and catechol.

Photodegradative fate and potential phototoxic products of bromocarbazoles and chlorocarbazoles in water

Bromocarbazoles and chlorocarbazoles are emerging environmental contaminants that have been reported to be persistent and possessing dioxin-like toxicity; however, their photodegradative fate in water is unknown. The photodegradation of 3-bromocarbazole, 3-chlorocarbazole, and 3,6-dichlorocarbazole was determined in ultrapure water. They proceeded by direct photolysis and followed first-order kinetics. The rate constants (k) were 0.4838, 0.3454, and 0.4422 h^-1 corresponding to half-lives (t _1/2) 1.81, 2.01, and 1.62, while the quantum yields (Ф) were 0.232, 0.180, and 0.295 respectively. The maximum wavelengths of absorption (λ _max) were in the near ultraviolet region (295, 296, 299, and 301 nm) implying these compounds are likely to degrade slowly under sunlight in natural aquatic environment. The molar extinction coefficients (ε) determined in acetonitrile were 18,573, 17,028, 13,385, and 14,010 L mol^-1 cm^-1, respectively, the latter being 3,6-dibromocarbazole. A bathochromic shift was observed with halogen addition on their respective mono-substituted congeners. Bromocarbazoles were observed to degrade faster in water than chlorocarbazoles. In addition, photodegradation was estimated to proceed faster in summer than in winter, in natural water system at 50° N latitude. In the absence of light, hydrolytic degradation occurred but proceeded very slowly. Hexahydroxybenzene and trihydroxycarbazole were positively identified as the likely photoproducts with the former being a known toxic compound. Dehalogenation, oxidative cleavage, hydroxylation, and hydrolysis are suggested as the major photodegradation mechanisms in water, yielding phototoxic products that may be of enhanced toxicity than the parent compounds.

Efficiency evaluation of the membrane/AOPs for paper mill wastewater treatment

The treatment of pulp and paper mill wastewater by combining an ultrafiltration (UF) membrane and advanced oxidation processes (AOPs) was investigated at a bench scale. In the present study, the effects of impressive parameters on membrane fouling such as CaCl₂ (mg/L), pH, and temperature (°C) were studied using response surface methodology (RSM). According to the results yielded, at the temperature of 45°C, pH of 10 and CaCl₂ concentration of 400 mg/L, the fouling reached its minimum (32%). Therefore, scanning electron microscopy (SEM) analyses showed that the average thickness of cake layer on the UF surface decreased from approximately 75.37 µm to 11.38 µm by optimizing the operating conditions. The results showed the UF permeate quality is not sufficient. Thus, AOPs applied for permeate. In this way, the performance of sulfate and hydroxyl radicals, generated by the activation of oxidants, such as persulfate ([Formula: see text]) and H₂O₂, by Fe(II) for removal efficiencies was examined. Accordingly, under the optimum conditions of Filtration/Fenton ([H₂O₂] = 15 mM, [Fe(II)] = 6 mM, pH = 3), the removal efficiency of chemical oxygen demand (COD), UV₂₅₄, and UV₂₈₀ was 95.02%, 86.74%, and 87.08%, respectively. This is while, in the optimum conditions of Filtration/[Formula: see text]/Fe(II) ([[Formula: see text]] = 7 mM, [Fe(II)] = 2 mM and pH = 6), the removal efficiency of COD, UV₂₅₄, and UV₂₈₀ reached 94.96%, 92.04%, and 90.16%, respectively. This is indicative of the fact that the process of Filtration/[Formula: see text]/Fe(II), with a lower oxidant and catalyst concentration and pH close to the neutral range is more efficient than that of Filtration/Fenton.

Photodegradation of diclofenac in aqueous solution by simulated sunlight irradiation: kinetics, thermodynamics and pathways

Diclofenac (DCF) is one of the most frequently detected pharmaceuticals in various water samples. This paper studied the effects of aquatic environmental factors (pH, temperature and dissolved organic matter) on photodegradation of DCF under simulated sunlight. The results demonstrate that degradation pathways proceed via pseudo first-order kinetics in all cases and the photodegradation of DCF by simulated sunlight. Thermodynamic study indicated that the photodegradation course is spontaneous, exothermic and irreversible. The rate constant gradually increased when the pH increased from 3 to 5, then decreased when the pH increased from 5 to 8, and finally increased when the pH further increased from 8 to 12. Humic acid inhibited the photodegradation of DCF. Three kinds of main degradation products were observed by high performance liquid chromatography/mass spectrometry and the degradation pathways were suggested. A toxicity test using Photobacterium phosphoreum T₃ Sp indicated the generation of some more toxic products than DCF.

Activation of persulfate by Fe(III) species: Implications for 4-tert-butylphenol degradation

In this study, the activation of persulfate induced by Fe(III) species, including 5 kinds of iron oxhydroxides (IOs) and dissolved Fe³⁺ under dark condition were investigated. Ferrihydrite (FH) and akaganeite (AK) showed the highest activity in 4-tert-butylphenol (4tBP) removal. The 4tBP degradation rate constant decreased as the solution pH increased from pH 3.2 to 7.8 in FH/S₂O₈^2- system. However, the pH value had no significant effect on the 4tBP degradation in AK/S₂O₈^2- system. The degradation of 4tBP in Fe³⁺/S₂O₈^2- system was also performed to investigate the role of ferric species in persulfate activation. The pH dependency of 4tBP degradation rate was closely related to the speciation of Fe^III, whereas the Fe(H₂O)₆³⁺ was found to be the most active soluble iron complex form in the activation of S₂O₈^2-. 4tBP degradation was mainly due to the SO₄^- in IOs/S₂O₈^2- system, while SO₄^- and HO₂ both had great contribution on 4tBP degradation in Fe³⁺/S₂O₈^2- system. Further investigations showed clearly that 4tBP degradation efficiency was decreased significantly due to the trapping of SO₄^- by chloride. This finding may have promising implications in developing a new technology for the treatment of contaminated waters and soils, especially where Fe³⁺ species are naturally occurring.

Degradation of flumequine in aqueous solution by persulfate activated with common methods and polyhydroquinone-coated magnetite/multi-walled carbon nanotubes catalysts

In recent years, flumequine (FLU) has been ubiquitously detected in surface waters and municipal wastewaters. In light of its potential negative impacts to aquatic species, growing concern has been arisen for the removal of this antibiotic from natural waters. In this study, the kinetics, degradation mechanisms and pathways of aqueous FLU by persulfate (PS) oxidation were systematically determined. Three common activation methods, including heat, Fe(2+) and Cu(2+), and a novel heterogeneous catalyst, namely, polyhydroquinone-coated magnetite/multi-walled carbon nanotubes (Fe3O4/MWCNTs/PHQ), were investigated to activate PS for FLU removal. It was found that these three common activators enhanced FLU degradation obviously, while several influencing factors, such as solution pH, inorganic ions (especially HCO3(-) at 5 mmol/L) and dissolved organic matter extracts, exerted their different effects on FLU removal. The catalysts were characterized, and an efficient catalytic degradation performance, high stability and excellent reusability were observed. The measured total organic carbon levels suggested that FLU can be effectively mineralized by using the catalysts. Radical mechanism was studied by combination of the quenching tests and electron paramagnetic resonance analysis. It was assumed that sulfate radicals predominated in the activation of PS with Fe3O4/MWCNTs/PHQ for FLU removal, while hydroxyl radicals also contributed to the catalytic oxidation process. In addition, a total of fifteen reaction intermediates of FLU were identified, from which two possible pathways were proposed involving hydroxylation, decarbonylation and ring opening. Overall, this study represented a systematical evaluation regarding the transformation process of FLU by PS, and showed that the heterogeneous catalysts can efficiently activate PS for FLU removal from the water environment.

Optimization of sonochemical degradation of tetracycline in aqueous solution using sono-activated persulfate process

BACKGROUND

In this study, a central composite design (CCD) was used for modeling and optimizing the operation parameters such as pH, initial tetracycline and persulfate concentration and reaction time on the tetracycline degradation using sono-activated persulfate process. The effect of temperature, degradation kinetics and mineralization, were also investigated.

RESULTS

The results from CCD indicated that a quadratic model was appropriate to fit the experimental data (p < 0.0001) and maximum degradation of 95.01 % was predicted at pH = 10, persulfate concentration = 4 mM, initial tetracycline concentration = 30.05 mg/L, and reaction time = 119.99 min. Analysis of response surface plots revealed a significant positive effect of pH, persulfate concentration and reaction time, a negative effect of tetracycline concentration. The degradation process followed the pseudo-first-order kinetic. The activation energy value of 32.01 kJ/mol was obtained for US/S2O8 (2-) process. Under the optimum condition, the removal efficiency of COD and TOC reached to 72.8 % and 59.7 %, respectively. The changes of UV-Vis spectra during the process was investigated. The possible degradation pathway of tetracycline based on loses of N-methyl, hydroxyl, and amino groups was proposed.

CONCLUSIONS

This study indicated that sono-activated persulfate process was found to be a promising method for the degradation of tetracycline.

Degradation of toluene-2,4-diamine by persulphate: kinetics, intermediates and degradation pathway

In this study, the degradation of toluene-2,4-diamine (TDA) by persulphate (PS) in an aqueous solution at near-neutral pH was examined. The result showed that the degradation rate of TDA increased with increasing PS concentrations. The optimal dosage of PS in the reaction system was determined by efficiency indicator (I) coupling in the consumption of PS and decay half-life of TDA. Calculation showed that 0.74 mM of PS was the most effective dosage for TDA degradation, at that level the maximum I of 24.51 was obtained. PS can oxidize TDA for an extended reaction time period. Under neutral condition without activation, four degradation intermediates, 2,4-diamino-3-hydroxy-5-sulfonicacidtoluene, 2,4-diaminobenzaldehyde, 2,4-bis(vinylamino)benzaldehyde and 3,5-diamino-4-hydroxy-2-pentene, were identified by high-performance liquid chromatography-mass spectrometry. The tentative degradation pathway of TDA was proposed as well. It was found that hydroxyl radical played an important role in degradation of TDA with the activation of Fe2+, whereas PS anion and sulphate radicals were responsible for the degradation without activation of Fe2+.

Efficient peroxydisulfate activation process not relying on sulfate radical generation for water pollutant degradation

Peroxydisulfate (PDS) is an appealing oxidant for contaminated groundwater and toxic industrial wastewaters. Activation of PDS is necessary for application because of its low reactivity. Present activation processes always generate sulfate radicals as actual oxidants which unselectively oxidize organics and halide anions reducing oxidation capacity of PDS and producing toxic halogenated products. Here we report that copper oxide (CuO) can efficiently activate PDS under mild conditions without producing sulfate radicals. The PDS/CuO coupled process is most efficient at neutral pH for decomposing a model compound, 2,4-dichlorophenol (2,4-DCP). In a continuous-flow reaction with an empty-bed contact time of 0.55 min, over 90% of 2,4-DCP (initially 20 μM) and 90% of adsorbable organic chlorine (AOCl) can be removed at the PDS/2,4-DCP molar ratio of 1 and 4, respectively. Based on kinetic study and surface characterization, PDS is proposed to be first activated by CuO through outer-sphere interaction, the rate-limiting step, followed by a rapid reaction with 2,4-DCP present in the solution. In the presence of ubiquitous chloride ions in groundwater/industrial wastewater, the PDS/CuO oxidation shows significant advantages over sulfate radical oxidation by achieving much higher 2,4-DCP degradation capacity and avoiding the formation of highly chlorinated degradation products. This work provides a new way of PDS activation for contaminant removal.

One-step synthesis of water-dispersible silicon nanoparticles and their use in fluorescence lifetime imaging of living cells

Fluorescence intensity (upper panel) and lifetime (bottom panel) images of KB cells stained with FITC (B), Si NPs (C) and unstained control (A).

Transformation of polychlorinated biphenyls by persulfate at ambient temperature

Increasing attention has been paid to persulfate due to its high efficiency in degrading organic pollutants. This paper investigated the transformation of a selected polychlorinated biphenyl (PCB) by sodium persulfate without activators at near ambient temperature (10-40°C). The results showed that 2,4,4'-CB was completely decomposed by persulfate at 30°C in 8 h. The products were identified by gas chromatography-mass spectrometry (GC-MS), and transformation pathways could be divided into two steps as dechlorination and hydroxylation. Electron paramagnetic resonance (EPR) technique was used to identify the generated radical species at different pH values at ambient temperature. The results showed that sulfate radicals (SO(4)(•-)) were predominant under acidic condition and hydroxyl radicals ((•)OH) were predominant under basic condition. This behavior was also confirmed by the quenching studies and kinetic model. Decreasing the solution pH resulted in increasing the degradation efficiency of 2,4,4'-CB. Moreover, the degradation of other PCBs such as 2-CB, 4-CB, 2,4-CB, 2,4'-CB, and 2,4,6-CB with persulfate was examined. The findings of this study can provide guidance in the remediation of PCBs contaminated soil and water with persulfate.

Degradation kinetics and mechanism of aniline by heat-assisted persulfate oxidation

Oxidation of aniline by persulfate in aqueous solutions was investigated and the reaction kinetic rates under different temperature, persulfate concentration and pH conditions were examined in batch experiments. The results showed that, the aniline degradation followed pseudo first-order reaction model. Aniline degradation rate increased with increasing temperature or persulfate concentration. In the pH range of 3 to 11, a low aniline degradation rate was obtained at strong acid system (pH 3), while a high degradation rate was achieved at strong alkalinity (pH 11). Maximum aniline degradation occurred at pH 7 when the solution was in a weak level of acid and alkalinity (pH 5, 7 and 9). Produced intermediates during the oxidation process were identified using liquid chromatography-mass spectrometry technology. And nitrobenzene, 4-4'-diaminodiphenyl and 1-hydroxy-1,2-diphenylhydrazine have been identified as the major intermediates of aniline oxidation by persulfate and the degradation mechanism of aniline was also tentatively proposed.

Sulfate radical-advanced oxidation process (SR-AOP) for simultaneous removal of refractory organic contaminants and ammonia in landfill leachate

Typically, a mature landfill leachate contains high levels of non-biodegradable organics and ammonia nitrogen. Simultaneous removal of the both persistent leachate pollutants is a significant challenge. This paper reports the first scientific study to apply a sulfate radical (SO(4)(·-)) - based advanced oxidation process (SR-AOP) to treat a mature leachate, with an emphasis of concurrent removal of refractory organics and ammonia. In this study, all the experiments were run in a batch reactor with temperature control. In the thermal persulfate oxidation (TPO) process, persulfate (S(2)O(8)(2-)) was activated by heat to produce powerful oxidants, SO(4)(·-) (E(o) = 2.6 V). Three factors affecting the removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen were investigated, including initial solution pH (3-8.3), temperature (27-50 °C), and chemical dose (S(2)O(8)(2-):12COD(0) = 0.25-2.0). Typically, acidic pH (3-4), higher temperature, and higher dose favored the removal of COD and ammonia. At S(2)O(8)(2-):12COD(0) = 2 and 50 °C, the COD removal rates were 79% and 91% at pH 8.3 (no pH adjustment) and 4, respectively; and the ammonia nitrogen removal reached 100% at pH 8.3 or 4. SR-AOP appears to be more advantageous over hydroxyl radical (OH∙)-based advanced oxidation processes (HR-AOPs) because OH∙ almost does not oxidize ammonia. Furthermore, compared with Fenton treatment of the same batch leachate sample, the TPO could achieve a higher COD removal at an identical chemical dose. For example, COD removal was 40% at H(2)O(2):2.125COD(0) = 2 during Fenton treatment (pH 3), but 91% at S(2)O(8)(2-):12COD(0) = 2 during TPO (pH 4). These findings demonstrate that SR-AOP is a promising landfill leachate treatment method.

Degradation efficiencies of azo dye Acid Orange 7 by the interaction of heat, UV and anions with common oxidants: persulfate, peroxymonosulfate and hydrogen peroxide

In this paper, the degradation of azo dye Acid Orange 7 (AO7) by three common peroxides (persulfate (PS), peroxymonosulfate (PMS) or hydrogen peroxide (H(2)O(2))) under various activation conditions, i.e., heat (25-80 degrees C), UV light (254 nm), or anions (SO(4)(2-), NO(3)(-), CO(3)(2-), HCO(3)(-), HPO(4)(2-), and Cl(-)), was investigated. The order of AO7 degradation efficiencies by heat activation is PS>>PMS>H(2)O(2). PS oxidation activated by heat (>50 degrees C) is an effective degradation technology, while PMS and H(2)O(2) are hardly activated. When assisted by UV, peroxides could all be activated and degrade AO7 quickly. The order is PS>H(2)O(2)>PMS. We activated peroxides, for the first time, by using some anions and compared the subsequently degradation efficiencies of AO7. It was found that PMS could be activated by some anions, but PS and H(2)O(2) cannot. The activation efficiencies of PMS by SO(4)(2-) and NO(3)(-) are negligible, whereas remarkable by HCO(3)(-), HPO(4)(2-), Cl(-) and CO(3)(2-). For HCO(3)(-), HPO(4)(2-) and Cl(-), the activation efficiencies become higher with the increase of anion concentration. For CO(3)(2-), however, the activation efficiency is higher at lower concentration.

A novel advanced oxidation process to degrade organic pollutants in wastewater: microwave-activated persulfate oxidation

This article, for the first time, provides a novel advanced oxidation process based on sulfate radical (SO4*-) to degrade organic pollutants in wastewater: microwave (MW)-activated persulfate oxidation (APO) with or without active carbon (AC). Azo dye acid Orange 7 (AO7) is used as a model compound to investigate the high reactivity of MW-APO. It is found that AO7 (up to 1000 mg/L) is completely decolorized within 5-7 min under an 800 W MW furnace assisted-APO. In the presence of chloride ion (up to 0.50 mol/L), the decolorization is still 100% completed, though delayed for about 1-2 min. Experiments are made to examine the enhancement by AC. It is exciting to find that the 100% decolorization of AO7 (500 mg/L) is achieved within 3 min by MW-APO using 1.0 g/L AC as catalyst, while the degradation efficiency maintains at 50% by MW energy without persulfate after about 5 min. Besides the destruction of visible light chromophore band of AO7 (484 nm), during MW-APO, two bands in the ultraviolet region (228 nm and 310 nm) are rapidly broken down. The removal of COD is about 83%-95% for 500 mg/L AO7. SO4*- is identified with quenching studies using specific alcohols. Both SO4*- and *OH could degrade AO7, but SO4*- plays the dominant role. In a word, MW-APO AC is a new catalytic combustion technology for destruction of organic contamination even for high concentration.