Converting peracetic acid activation by Fe3O4 from nonradical to radical pathway via the incorporation of L-cysteine.

Recently, peracetic acid (PAA) based Fenton (-like) processes have received much attention in water treatment. However, these processes are limited by the sluggish Fe(III)/Fe(II) redox circulation efficiency. In this study, L-cysteine (L-Cys), an environmentally friendly electron donor, was applied to enhance the Fe3O4/PAA process for the sulfamethoxazole (SMX) abatement. Surprisingly, the L-Cys incorporation was found not only to enhance the SMX degradation rate constant by 3.2 times but also to switch the Fe(IV) dominated nonradical pathway into the •OH dominated radical pathway. Experiment and theoretical calculation result elucidated -NH2, -SH, and -COOH of L-Cys can increase Fe solubilization by binding to the Fe sites of Fe3O4, while -SH of L-Cys can promote the reduction of bounded/dissolved Fe(III). Similar SMX conversion pathways driven by the Fe3O4/PAA process with or without L-Cys were revealed. Excessive L-Cys or PAA, high pH and the coexisting HCO3-/H2PO4- exhibit inhibitory effects on SMX degradation, while Cl- and humic acid barely affect the SMX removal. This work advances the knowledge of the enhanced mechanism insights of L-Cys toward heterogeneous Fenton (-like) processes and provides experimental data for the efficient treatment of sulfonamide antibiotics in the water treatment.

Hydrogen sulfite promoted the activation of persulfate by µM Fe2+ for bisphenol A degradation.

This study evaluated the improvement of bisphenol A (BPA) elimination through hydrogen sulfite (HS) coupling with persulfate (PS) activated by low amounts of Fe2+. Under the optimum condition (10 µM Fe2+, 0.6 mM HS, 0.8 mM PS, pH = 4.0), 100% BPA (5 µM) was removed within 15 min. Sulfate radical (SO4•-) and singlet oxygen (1O2) were confirmed as the primary active species for BPA degradation in the Fe2+/HS/PS system, and the steady-state concentration of SO4•- and 1O2 was 2.43 × 10-9 M and 1.67 × 10-9 M, respectively. Besides, FeHSO3+ and FeOHSO3H+ were the main iron species in the Fe2+/HS/PS system. The removal potency of BPA depended on the operation parameters, such as chemical reagent dosages, reaction temperature, and the solution initial pH. The impact of NO3-, SO42-, and humic acid (HA) on BPA removal was negligible, whereas Cl-, HCO3-, and HPO42- restrained BPA decomposition. Two injections of HS could improve the limitation of BPA degradation efficiency due to the rapid consumption of HS in the reaction process. The lower removal efficiency of BPA was observed in real water matrices than that in ultrapure water. Whatever, up to 58.1%, 66.3%, 68.1%, and 88.1% of BPA were removed from domestic wastewater, lake water, river water, and tap water within 10 min, respectively. In addition, the BPA degradation process was characterized by the 3D fluorescence spectra technique, which indicated the BPA oxidation intermediates also have fluorescence characteristics. Moreover, 6 intermediate products were identified, and the possible degradation pathways of BPA were proposed. Additionally, the Fe2+/HS/PS system also exerted an excellent performance for the removal of other representative organic contaminants including enrofloxacin, acid orange 7, acetaminophen, and phenol. All results indicated that the Fe2+/HS/PS system could be a promising method for organic pollutant removal.

Remediation of sulfathiazole contaminated soil by peroxymonosulfate: Performance, mechanism and phytotoxicity.

Peroxymonosulfate (PMS) was successfully adopted to remove organic pollutants in water, but it was rarely applied to soil remediation. Sulfathiazole (STZ) is a widely used sulfonamide antibiotic, while its residues have negative impacts on soil. To the best of our knowledge, this is the first attempt to apply PMS for the treatment of STZ-contaminated soil. The results showed that 4 mM PMS can degrade 96.54% of STZ in the soil within 60 min. Quenching and probe experiments revealed that singlet oxygen rather than hydroxyl radical and sulfate radical was the predominant reactive oxygen species responsible for STZ removal. The presence of Cl-, SO42-, NO3-, Fe3+, and HA enhanced the degradation efficiency of STZ, while HCO3- and Mn2+ presented an obstructive effect on STZ elimination at high concentrations. Different chemical extraction procedures were used to determine the bioavailability of the heavy metals. PMS oxidation process caused an unnoticeable influence of the concentrations of heavy metals except for the increase of Mn concentration and the decrease of Ba concentration. Moreover, the germination rate and stem length of wheat and radish both increased, indicating PMS oxidation reduced the toxicity of STZ, and the increase of Mn concentration did not cause a negative impact on their growth. Besides, the results of XRD and FTIR tests showed oxidation processes have negligible impacts on soil structure and composition. Based on intermediates identified, STZ degradation pathways in the PMS system were proposed. According to the results of this study, using PMS alone to repair STZ-contaminated soil is a relatively feasible, safe, and environmentally friendly technology.

Minute Cu2+ coupling with HCO3- for efficient degradation of acetaminophen via H2O2 activation.

Homogeneous Cu2+-mediated activation of H2O2 has been widely applied for the removal of organic contaminants, but fairly high dosage of Cu2+ is generally required and may cause secondary pollution. In the present study, minute Cu2+ (2.5 µM) catalyzed H2O2 exhibited excellent efficiency in degradation of organic pollutants with the assistant of naturally occurring level HCO3- (1 mM). In a typical case, acetaminophen (ACE) was completely eliminated within 10 min which followed the pseudo-first-order kinetics. Singlet oxygen and superoxide radical rather than traditionally identified hydroxyl radical were the predominant reactive oxygen species (ROS) responsible for ACE degradation. Meanwhile, Cu3+ was deduced through Cu+ and p-hydroxybenzoic acid formation analysis. CuCO3(aq) was the main complex with high reactivity for the activation of H2O2 to form ROS and Cu3+. The removal efficiency of ACE depended on the operating parameters, such as Cu2+, HCO3- and H2O2 dosage, solution initial pH. The presence of Cl-, HPO42-, humic acid were found to retard ACE removal while other anions such as SO42- and NO3- had no obvious effect. ACE exhibited lower degradation efficiency in real water matrices than that in ultra-pure water. Nevertheless, 58-100% of ACE was removed from domestic wastewater, lake water and tap water within 60 min. Moreover, eight intermediate products were identified and the possible degradation pathways of ACE were proposed. Additionally, other typical organic pollutants including bisphenol A, norfloxacin, lomefloxacin hydrochloride and sulfadiazine, exhibited great removal efficiency in the Cu2+/H2O2/HCO3- system.

Ca(OH)2-mediated activation of peroxymonosulfate for the degradation of bisphenol S.

Alkaline substances could activate peroxymonosulfate (PMS) for the removal of organic pollutants, but relatively high alkali consumption is generally required, which can cause too high pH of the solution after the reaction and lead to secondary pollution. Within this study, PMS activated by a relatively low dosage of Ca(OH)2 (1 mM) exhibited excellent efficiency in the removal of bisphenol S (BPS). The pH of the solution declined to almost neutral (pH = 8.2) during the reaction period and conformed to the direct emission standards (pH = 6-9). In a typical case, BPS was completely degraded within 240 min and followed the kinetics of pseudo-first-order. The degradation efficiency of BPS depended on the operating parameters, such as the Ca(OH)2, PMS and BPS dosages, initial solution pH, reaction temperature, co-existing anions, humic acid (HA), and water matrices. Quenching experiments were performed to verify that singlet oxygen (1O2) and superoxide radicals (O2˙-) were the predominant ROS. Degradation of BPS has been significantly accelerated as the temperature increased. Furthermore, degradation of BPS could be maintained at a high level across a broad range of pH values (5.3-11.15). The SO4 -, NO3 - did not significantly impact the degradation of BPS, however, both HCO3 - and HA inhibited oxidation of BPS by the Ca(OH)2/PMS system, and Cl- had a dual-edged sword effect on BPS degradation. In addition, based on the 4 identified intermediates, 3 pathways of BPS degradation were proposed. The degradation of BPS was lower in domestic wastewater compared to other naturals waters and ultrapure; nevertheless, up to 75.86%, 77.94% and 81.48% of BPS was degraded in domestic wastewater, Yaohu Lake water and Poyang Lake water, respectively. Finally, phenolic chemicals and antibiotics, including bisphenol A, norfloxacin, lomefloxacin hydrochloride, and sulfadiazine could also be efficiently removed via the Ca(OH)2/PMS system.

Selective degradation of acetaminophen from hydrolyzed urine by peroxymonosulfate alone: performances and mechanisms.

Owing to the high concentration of pharmaceuticals in urine, the degradation of these organic pollutants before their environmental release is highly desired. Peroxymonosulfate (PMS) is a desirable oxidant that can be applied to environmental remediation; however, the performance and mechanism of PMS for the degradation of pharmaceuticals in the urine matrix have not been investigated. Herein, PMS was first discovered to efficiently degrade typical pharmaceuticals in hydrolyzed urine (HU) by selecting acetaminophen (ACE) as a target compound. Quenching experiments revealed that singlet oxygen (1O2) and hydroxyl radicals (HO˙) were observed in the HU/PMS system, but the principal reactive species (RS) responsible for ACE removal was 1O2. The major constituents of HU, including SO4 2- and organics (creatine, creatinine and hippuric acid), hardly affected the elimination of ACE, whereas Cl-, H2PO4 - and NH4 + would accelerate ACE degradation. Besides, HCO3 - slightly inhibited this process. The ACE degradation efficiency was enhanced using photo-irradiation, including sunlight and visible light, although increasing the reaction temperature could, interestingly, hardly accelerate the degradation rate of ACE. Three-dimensional excitation-emission matrices (3D-EEMs) have indicated that other intermediates that have a higher fluorescence intensity might be generated in the HU/PMS system. Finally, nine intermediate products were determined and the degradation pathways of ACE were proposed. Overall, the results of this study illustrated that PMS is an efficient oxidant for the degradation of ACE in HU.

Enhanced removal of organic contaminants in water by the combination of peroxymonosulfate and carbonate.

In this study, a favorable CO32-/PMS system for efficient degradation of organic contaminants (acid orange 7 (AO7), acetaminophen, para-aminobenzoic acid, phenol, methylene orange, methylene blue) in water was firstly reported. Under optimal conditions, the decolorization ration of AO7 was 100% within 40 min. Data fitting showed that the AO7 decolorization could be described by the pseudo-first-order kinetics, and the rates constant values ranging from 0.0006 to 0.2297 min-1 depending on the operating parameters (initial PMS, CO32-, AO7 concentrations). Radical scavenging studies revealed that superoxide anion radical (O2-) and singlet oxygen (1O2) rather than sulfate (SO4-) nor hydroxyl (HO) were the dominant oxidants might be responsible for AO7 degradation. The presence of NO3-, HPO42- and low concentration of Cl-, NO2-, HCO3-, H2PO4-, HA had no significantly effect on the decolorization of AO7. Adding a higher Cl- concentration displayed favorable effects on the removal efficiencies of AO7, but adding a higher NO2-, HCO3-, H2PO4- and HA concentration apparently inhibited this process. The decolorization of AO7 was lower in wastewater in comparison to other natural waters and ultrapure water, which was probably due to the presence of higher concentration of colloids in wastewater. Nevertheless, up to 94.8%, 97.0% and 85.1% of AO7 were degraded from the filtrate, permeate, and retentate phases of wastewater within 60 min, respectively. Consequently, CO32-/PMS would be promising for removal methodology for AO7 in wastewater containing considerable colloids. Finally, three intermediates were identified and degradation pathways of AO7 were proposed.