Degradation Pathways Of Atrazine Research Articles

Atrazine Degradation Pathway and Genes of <i>Arthrobacter</i> sp. FM326

Atrazine Degradation Pathway and Genes of <i>Arthrobacter</i> sp. FM326

Atrazine Removal from Municipal Wastewater Using a Membrane Bioreactor.

As the demand for potable water increases, direct potable reuse of wastewater is an attractive alternative method to produce potable water. However, implementation of such a process will require the removal of emerging contaminants which could accumulate in the drinking water supply. Here, the removal of atrazine, a commonly used herbicide, has been investigated. Using real and synthetic wastewater, as well as sludge from two wastewater treatment facilities in the United States in Norman, Oklahoma and Fayetteville, Arkansas, atrazine removal has been investigated. Our results indicate that about 20% of the atrazine is removed by adsorption onto the particulate matter present. Significant biodegradation of atrazine was only observed under aerobic conditions for sludge from Norman, Oklahoma. Next-generation sequencing of the activated sludge revealed the abundance of Noncardiac with known atrazine degradation pathways in the Norman aerobic sludge, which is believed to be responsible for atrazine biodegradation in our study. The detection of these bacteria could also be used to determine the likelihood of biodegradation of atrazine for a given wastewater treatment facility.

Removal of atrazine by biochar-supported zero-valent iron catalyzed persulfate oxidation: Reactivity, radical production and transformation pathway

Atrazine is a widely used herbicide whose presence poses a potential threat to agriculture and human living environment. This work studied the degradation performances and mechanisms of zero-valent iron and biochar composite (ZVI/BC) activated persulfate (PS) for atrazine. The results showed that the removal percentage of atrazine reached 73.47% within 30 min. Furthermore, the optimal parameters (175 mg/L ZVI/BC, 2 mM PS and initial pH of 3) were obtained through response surface methodology. Meanwhile, the high atrazine removal percentage (83.77%) was obtained under the optimal conditions. Radical quenching studies and electron spin resonance revealed that active substances produced during PS activation, as well as that SO4·− and HO· were dominant active species for the atrazine degradation. According to iron corrosion products and XPS analysis, the reaction mechanism of ZVI/BC-PS system was proposed as that ZVI loaded on the composites further activated PS to produce SO4·− and HO· which accompany with the valent changing of iron and finally causing degradation of atrazine. In addition, the degradation pathways of atrazine in ZVI/BC-PS system included dealkylation, alkyl oxidation and dechlorination-hydroxylation by the results of GC-MS and LC-MS. These findings demonstrated that ZVI/BC activated persulfate may be an efficient technique for the degradation of atrazine.

Activation of peroxydisulfate by natural titanomagnetite for atrazine removal via free radicals and high-valent iron-oxo species

Natural titanomagnetite, a potential catalyst, was used as a peroxydisulfate (PDS) activator for the removal of atrazine (ATZ) in water for the first time. The surface Fe(Ⅱ) and Fe(III) of titanomagnetite was certified as the active components by XRD and XPS analyses. ATZ removal showed a strong dependence on the titanomagnetite concentration (0–10 g/L), PDS concentration (0–10 mM) and the initial pH (3.0–11.0) under experimental conditions. Quite different from the traditional heterogeneous PDS-activated processes, titanomagnetite/PDS system could remove ATZ via both radical and nonradical pathways. Here, both free radicals (SO4− and HO) and high-valent iron-oxo species were proved to be the main reactive oxygen species (ROS) by quenching experiments, EPR tests and UPLC/ESI–MS/MS analysis. The high-valent iron-oxo species, FeⅣO and FeⅤO, could be generated from the Fe(Ⅱ) and Fe(III) of the titanomagnetite via a nonradical pathway. In addition, the generated passivation layer after reaction was found via XPS analysis, which could block the function of Fe(Ⅱ) and Fe(III), hindering the generation of ROS. However, the catalytic activity of titanomagnetite could recover if passivation layer was removed by ultrasonic cleaning. Finally, ten intermediates of ATZ were measured by UPLC-QTOF-MS/MS and the degradation pathways of ATZ in titanomagnetite/PDS system were proposed with the Gaussian 09 results. This work helps to better understand the generation of high-valent iron-oxo species and re-evaluate the effect of high-valent iron-oxo species in the heterogeneous iron-based PDS-activated processes.

Kinetics and pathway of atrazine degradation by a novel method: Persulfate coupled with dithionite

Efficient and environmentally friendly activation methods of persulfate (PS) have gained growing attention in the remediation of water or soil polluted by organic contaminants. Among all, the exploration of effective and applicable method for the PS activation becomes one of the hottest topics in the field of organic degradation. Dithionite (DTN) was employed in this study to activate PS and applied to degrade Atrazine (ATZ) without secondary pollution. ATZ could be completely degraded within 90 min by PS/DTN system. ATZ degradation by PS obeyed the pseudo-first-order kinetics and the rate constant values increased from (4.71–5.05) × 10−3 min−1 to (4.59–5.09) × 10−2 min−1 with the addition of DTN. Sulfate radicals were verified to be the dominant reactive species through the radical scavenging experiment. PS/DTN system can remain a strong oxidative ability in the range of pH below 9.0. The presence of Cl−, natural organic matter (NOM), and high concentration of HCO3− may inhibit the removal of ATZ while the low concentration of HCO3− can slightly promote the degradation. It was found that the degradation pathways of ATZ by PS/DTN involved de-chlorination and hydroxylation, de-alkylation, and de-amination by the reactive species. The study reveals that PS/DTN system has the broad application prospect in the treatment of refractory pollutants.

Efficient degradation of atrazine by LaCoO3/Al2O3 catalyzed peroxymonosulfate: Performance, degradation intermediates and mechanism

In this study, LaCoO3/Al2O3 (LCA) was utilized as a heterogeneous catalyst to activate peroxymonosulfate (PMS) to degrade atrazine (ATZ). The structural properties of the catalysts were characterized by SEM, EDS, XRD, XPS and TPD. The effects of some key parameters (i.e., loadings of LCA, ATZ concentration, catalyst dosage, PMS concentration, initial pH and coexisting ions) were optimized. In addition, under the optimal conditions of 100 mg/L 23LCA, 100 mg/L PMS and initial solution pH 6.8, the removal rate and mineralization efficiency of ATZ (5 mg/L) reached 100% and 30.8%, respectively. The superiority of the 23LCA/PMS system was verified by two controlled experiments. After three cycles of experiments, the degradation effect of ATZ was within an acceptable range. The degradation intermediates of ATZ were detected by UPLC-QTOF-MS/MS, and the possible degradation pathway of ATZ was proposed. In addition, the presence of SO4− and HO was identified by quenching experiments and SO4− was verified as the predominant radical. Finally, based on the comprehensive analysis, a reasonable reaction mechanism of the 23LCA/PMS system was proposed. In a word, these results indicate that LCA can act as a highly efficient heterogeneous catalyst to activate PMS to degrade ATZ in water.

Unraveling different mechanisms of persulfate activation by graphite felt anode and cathode to destruct contaminants of emerging concern

The electro-activation of persulfate (PS) by graphite felt (GF) electrode is a novel advanced oxidation process applied for the degradation of contaminants of emerging concern (CECs). Both GF anode and cathode can electro-activate PS to degrade CECs, including atrazine (ATZ), bisphenol S, ethinylestradiol, and ibuprofen. The study examines the removal performance of ATZ in sulfate, nitrate, and perchlorate electrolyte. The degradation of ATZ followed the order of sulfate (36.3 L (Ah)−1) > perchlorate (22.2 L (Ah)−1) > nitrate (5.8 L (Ah)−1) in GF anode/PS system, while electrolytes had little influence on the degradation of ATZ (15.8–21.3 L (Ah)−1) in GF cathode/PS system. The mechanisms of PS electro-activation by GF anode and GF cathode were compared and investigated for the first time, through kinetic experiments, radical identification, and products analysis. Quenching experiments demonstrated that O2− and 1O2 were generated in GF cathode/PS and GF anode/PS systems respectively, besides HO and SO4−. Degradation pathways of ATZ in these two systems showed slight difference, and a total of eight transformation products of ATZ were identified. Acute toxicity of the treated ATZ solution decreased at the beginning and then increased in both systems at electric charge of 0.11 Ah L−1. Furthermore, both GF electrodes/PS systems exhibited satisfactory performance for actual effluent from wastewater treatment plants in the presence of 30 mM perchlorate (with ATZ removal of 78% at electric charge of 0.11 Ah L−1), leaving a potential possibility for its practical application.

Efficient degradation of atrazine by CoMgAl layered double oxides catalyzed peroxymonosulfate: Optimization, degradation pathways and mechanism

Ternary CoMgAl-LDOs were synthesized by co-precipitation and employed in the activation of peroxymonosulfate (PMS) for atrazine (ATZ) removal. A series of catalysts with different Co: Mg: Al ratios were obtained and characterized by XRD, SEM, EDS and XPS. Several key parameters such as Co: Mg: Al ratios, catalyst dosage, PMS dosage, initial pH and initial ATZ concentration were optimized. The results show that Co1Mg2Al1-LDO/PMS system exhibited better degradation performance and the maximum ATZ removal (98.7%) and TOC removal (26.5%) were obtained under the optimal conditions (Co1Mg2Al1-LDO = 75 mg/L, PMS = 0.4 mM and ATZ concentration = 10 mg/L at initial pH = 6.3). To verify the excellent performance in the Co1Mg2Al1-LDO/PMS system, three control experiments (i.e., PMS alone system, Co1Mg2Al1-LDO alone system and Mg3Al1-LDO/PMS system) and reusability tests were carried out. Furthermore, a total of eight intermediates were detected by UPLC-QTOF-MS/MS and the degradation pathways of ATZ were proposed. Besides, quenching experiments demonstrated that SO4− acted as the dominant active radicals and the amount of SO4− was quantified indirectly by HPLC. Finally, a reasonable reaction mechanism of Co1Mg2Al1-LDO/PMS system for ATZ removal was put forward according to the comprehensive analysis.

Degradation of atrazine by catalytic ozonation in the presence of iron scraps: performance, transformation pathway, and acute toxicity

Degradation of atrazine by catalytic ozonation in the presence of iron scraps (ZVI/O3) was carried out. The key operational parameters (i.e., initial pH, ZVI dosage, and ozone dosage) were optimized by the batch experiments, respectively. This ZVI/O3 system exhibited much higher degradation efficiency of atrazine than the single ozonation, ZVI, and traditional ZVI/O2 systems. The result shows that the pseudo-first-order constant (0.0927 min−1) and TOC removal rate (86.6%) obtained by the ZVI/O3 process were much higher than those of the three control experiments. In addition, X-ray diffraction (XRD) analysis indicates that slight of γ-FeOOH and Fe2O3 were formed on the surface of iron scrap after ZVI/O3 treatment. These corrosion products exhibit high catalytic ability for ozone decomposition, which could generate more hydroxyl radical (HO•) to degrade atrazine. Six transformation intermediates were identified by liquid chromatography-mass spectrometry (LC-MS) analysis in ZVI/O3 system, and the degradation pathway of atrazine was proposed. Toxicity tests based on the inhibition of the luminescence emitted by Photobacterium phosphoreum and Vibrio fischeri indicate the detoxification of atrazine by ZVI/O3 system. Finally, reused experiments indicate the approving recyclability of iron scraps. Consequently, the ZVI/O3 system could be as an effective and promising technology for pesticide wastewater treatment.

Highly efficient activation of peroxymonosulfate by natural negatively-charged kaolinite with abundant hydroxyl groups for the degradation of atrazine

In this study, natural kaolinite, an abundant, low cost, thermally and chemically stable, and easily recyclable material was evaluated for the performance to activate peroxymonosulfate (PMS) by the degradation of atrazine. Based on radical quenching experiments and electron spinning resonance (ESR) spectra, hydroxyl radical (OH) and sulfate radical (SO4−) were identified to be the primary reactive species. The effects of catalyst loading, initial reaction pH, PMS dosage, initial atrazine concentration, and the presence of inorganic ions (Cl−, NO3−, HCO3− and H2PO4−) were also investigated in this work. Interestingly, the presence of H2PO4− enhanced the degradation efficiency of atrazine via promoting the decomposition of PMS. The transformation products were detected on a quadrupole time-of-flight liquid chromatography/mass spectrometer (Q-TOF-LC-MS) and the possible degradation pathway of atrazine was proposed. Based on comprehensive characterizations of crystal phase and crystallinity, porosity and pore structure, surface morphology, functional groups, and valence state of specific elements, the catalytic ability of natural kaolinite towards PMS is attributed to the abundant surface-bonded and structural hydroxyl groups. This study provides new insights of PMS activation by natural minerals for the degradation of refractory and deleterious contaminants in wastewater treatment.

Influence of solution pH on degradation of atrazine during UV and UV/H2O2 oxidation: kinetics, mechanism, and degradation pathways.

The kinetics, degradation mechanism and degradation pathways of atrazine (ATZ) during sole-UV and UV/H2O2 processes under various pH conditions were investigated; the effects of UV irradiation time and H2O2 dose were also evaluated. A higher reaction rate was observed under neutral pH conditions in the UV only process. For the UV/H2O2 process, a higher reaction rate was observed in acidic solution and the degradation rate of ATZ firstly increased with the increase of concentration of H2O2 and then decreased when H2O2 concentration exceeded 5 mg L−1. In addition, qualitative and quantitative analyses of oxidation intermediates of ATZ in aqueous solution during the sole-UV and UV/H2O2 processes were conducted using UPLC-ESI-MS/MS. Ten kinds of dechlorinated intermediates were detected during sole-UV treatment under all five pH conditions. In contrast, the speciation of intermediates in the UV/H2O2 process varied dramatically with solution pH. Based on the analysis of ATZ oxidation intermediates, ATZ degradation pathways under different pH conditions were proposed for the sole-UV and UV/H2O2 processes. The results showed that the main degradation reactions of ATZ included dechlorination-hydroxylation, dechlorination-dealkylation, de-alkylation, deamination-hydroxylation, alkylic-oxidation of lateral chains, dehydrogenation-olefination, dechlorination-hydrogenation, dechlorination-methoxylation and dehydroxylation.

Efficient degradation of atrazine by Co-NZ catalyst prepared by electroless plating in the presence of peroxymonosulfate: Characterization, performance and mechanistic consideration

A heterogeneous catalyst, cobalt-modified natural zeolite prepared by electroless plating technique (ECM-Co-NZ), was fabricated as a peroxymonosulfate (PMS) activator for enhancing the oxidative degradation of atrazine (ATZ) in aqueous media. SEM, EDS, BET, XRD, Py-DRIFT, H2-TPR and XPS techniques were applied to characterize the features of the synthesized catalyst and conventional impregnation sample for comparison. Then, the catalytic activity and recyclability of two materials were investigated comparatively. The results show that ECM-Co-NZ has a better catalytic performance as well as a longer operational life, and complete removal of ATZ can be achieved in 14 min in ECM-Co-NZ/PMS system. Further, the effects of key factors including Co mass loading, calcination temperature, catalyst dosage, PMS dosage, initial pH and ATZ concentration on ATZ removal and Co leaching in ECM-Co-NZ/PMS system were elucidated in details. In addition, reactive oxygen species generated in the oxidation process were identified by radical scavenging test, byproduct detection and fluorescent probe technique. The results reveal that both hydroxyl and sulfate radicals were contributed to the degradation of ATZ, but sulfate radical had dominant role in controlling the ECM-Co-NZ/PMS oxidation system. Finally, the reaction mechanism and possible ATZ degradation pathways were discussed based on the experiment results and previous literature.

Strong promoted catalytic ozonation of atrazine at low temperature using tourmaline as catalyst: Influencing factors, reaction mechanisms and pathways

Tourmaline, an economical and eco-friendly natural mineral, has been widely used during the water treatment processes. In this investigation, the raw tourmaline has been found to be effective as a catalyst for ozonation in the degradation of atrazine (ATZ) under low temperature (278 K). Within typical experimental conditions (tourmaline dosage = 1 g L−1, [ATZ]0 = 5 μM, [O3]0 = 3 mg L−1, at pH 7.0 and 278 K), the removal efficiency of ATZ in catalytic ozonation was 98% after 10 min, compared with only 27% ATZ removal in the absence of catalyst. Surface properties and components of tourmaline were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectra (FTIR), pyridine-FTIR and energy dispersive X-ray (EDX). The characterization studies showed that metal attached hydroxyl groups (MOH, M = Fe, Al and Si) were the main active sites for ozone adsorption and decomposition. The formation of hydroxyl radicals (OH) as well as hydrogen peroxide (H2O2) led to fast ATZ degradation and 31 kinds of intermediates; meanwhile, possible degradation pathways of ATZ were detected and proposed. The mechanisms of reaction were proposed for tourmaline-catalyzed ozonation based on all the experimental results and material characterizations.

Silver vanadium oxide materials: Controlled synthesis by hydrothermal method and efficient photocatalytic degradation of atrazine and CV dye

Abstract Silver vanadium oxides have received remarkable attention in recent years because of their stability, suitable band gaps, and relatively superior photocatalytic abilities. This study reports the synthesis of silver vanadates by the hydrothermal method and the investigation of their photocatalytic abilities for removing crystal violet (CV) and atrazine pollutants under visible-light irradiation. The as-prepared silver vanadates are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS). Crystal violet and atrazine could be successfully degraded in the presence of the silver vanadate catalyst under visible-light irradiation. The obtained results show complete degradation of crystal violet after 24 h of treatment and over 97% degradation of atrazine after 72 h. The as-prepared silver vanadate materials show extremely high catalytic stability and maintain stable activity after three catalytic cycles. The scavenger studies indicate that O2− radicals are the main active species in the degradations of CV and atrazine, while OH and h+ play an assistant role in these processes. Liquid chromatography coupled with electrospray ionization mass spectrometry is used to analyze the samples obtained from the photocatalytic degradation of CV and atrazine. The degradation pathways of atrazine are evaluated suggesting two different routes including dechlorination–hydroxylation and alkylic-oxidation–de-alkylation. On the other hand, the degradation of the CV takes place via N-de-methylation in a stepwise manner generating the various N-de-methylated intermediate CV species. The excellent activity and photostability reveal that silver vanadates (including Ag4V2O7) are promising visible-light-responsive photocatalysts for water and wastewater treatment.

Enhancement of the degradation of atrazine through CoFe2O4 activated peroxymonosulfate (PMS) process: Kinetic, degradation intermediates, and toxicity evaluation

The degradation performance of atrazine by peroxymonosulfate (PMS) activated by CoFe2O4 nanoparticles (NPs) in heterogeneous catalytic process was studied in our study. In this work, first of all, influences of vital parameters (i.e., CoFe2O4 dose, PMS dose, initial pH, co-existing anion, and atrazine (ATZ) concentration) on ATZ removal were investigated systematically. The removal of ATZ (>99%) and first order reaction kinetic rate constant (Kobs = 0.181 min−1) were achieved after 30 min reaction with 0.4 g/L CoFe2O4, 0.8 mM PMS, and 10 mg/L ATZ at initial pH 6.3. In contrast, only 10% and 6% ATZ removal were achieved with PMS and CoFe2O4, respectively, verifying the excellent performance in the CoFe2O4/PMS system. In addition, reusability of the CoFe2O4 NPs was investigated after five successive runs. Radical quenching experiments were done and SO4− was identified as the main radical species. The fresh and used CoFe2O4 NPs were characterized via SEM, EDS, XRD and XPS techniques. What’s more, the possible degradation intermediates in CoFe2O4/PMS system were determined by ultrahigh performance liquid chromatograph-mass spectrometry. Activated sludge inhibition experiment was carried out to evaluate the variation of toxicity of the ATZ and its degradation intermediates in the oxidation process. Based on the identified products, the degradation pathway of ATZ in CoFe2O4/PMS system was put forward. Finally, the believable reaction mechanism of CoFe2O4/PMS system was proposed according to the comprehensive analysis.

Changes in atrazine speciation and the degradation pathway in red soil during the vermiremediation process

Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is a triazine herbicide intensively used in agricultural production and is often detected in different environmental matrices at concentrations above the permitted limit. This study investigated the influence of two earthworm species (epigeic Eisenia foetida and endogeic Amynthas robustus) on atrazine speciation and the degradation pathway. Our results revealed that both earthworms significantly accelerated atrazine degradation in a 28-day vermiremediation, and the residual atrazine declined from 4.23 ± 0.21 mg/kg in bulk soils to 0.51 ± 0.29 mg/kg (E. foetida) and 0.43 ± 0.19 mg/kg (A. robustus). By consuming organic matter (from 40.37 ± 1.14 to 36.31 ± 1.55 and 34.59 ± 1.13 g/kg for E. foetida and A. robustus) and neutralizing the soil pH (from 5.37 ± 0.27 to 6.36 ± 0.11 and 6.61 ± 0.30 for E. foetida and A. robustus), both earthworms reduced humus-fixed atrazine and increased the available atrazine. The percentage of available atrazine increased from 8.80 ± 0.21% in bulk soil to 10.30 ± 0.29% and 16.42 ± 0.18% in the vermiremediation treatments. Both earthworms promoted the hydroxyatrazine pathway by consuming soil organic matter and encouraged the deethylatrazine/deisopropylatrazine pathway by neutralizing the soil pH. Our findings unravel a new mechanism of vermiremediation by improving the soil physical-chemical properties and altering the atrazine degradation pathway, providing new insights into the influential factors on atrazine bioremediation in red soil.

Degradation of atrazine in soil by dielectric barrier discharge plasma – Potential singlet oxygen mediation

Dielectric barrier discharge (DBD) was used for the first time to remediate atrazine-polluted soil in a plane-to-grid plasma reactor operating with air at atmospheric pressure. It was established that atrazine degradation efficiency is an increasing function of applied voltage and discharge frequency. The degradation efficiency of atrazine in dry soil reached as high as 86.9% and 98.1% after 60 min of plasma treatment, starting from initial pollutant concentrations of 100 and 10 mg/kg, respectively. Low soil moisture content (5–10%) was found to enhance atrazine degradation in the DBD reactor in comparison to dry soil conditions. Atrazine mineralization after 60 min of treatment was 65.5% as confirmed by total organic carbon (TOC) analysis. The degradation profile of atrazine under DBD treatment was assessed using Fourier transform infrared spectroscopy (FTIR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Several degradation pathways of atrazine were identified in addition to those previously reported with OH, H2O2, or O3 as the main oxidizing agents. The detected degradants included des-ethyl atrazine, hydroxy atrazine and de-ethylated oligomers of atrazine with the isopropyl group being largely preserved. An atrazine degradation mechanism under DBD conditions is proposed that is consistent with the intermediates identified and supports the dominant involvement of singlet oxygen in initiating the degradation under DBD conditions.

Efficient degradation of atrazine by BiOBr/UiO-66 composite photocatalyst under visible light irradiation: Environmental factors, mechanisms and degradation pathways

Atrazine, a typical herbicide, has caused extensive concern due to its wide application and persistance. In this work, a visible light responsive photocatalyst BiOBr/UiO-66 was synthesized and applied to the degradation of atrazine. The BiOBr/UiO-66 materials exhibited significantly enhanced photocatalytic performance on the degradation of atrazine under visible light irradiation compared to pure BiOBr. Moreover, the effects of typical environment factors (i.e. pH, common anions, inorganic cations and water matrix) on the degradation of atrazine were investigated extensively. Results showed that atrazine was degraded with the fastest rate at the strong acidity conditions of pH = 3.1 in the investigated pH region (3.1–9.4). The photocatalytic degradation of atrazine was obviously inhibited by HCO3− and SO42−. However, Cl− had negligible influence on the degradation of atrazine. Inorganic cations had little influence on the degradation of atrazine. Futhermore, the water matrix showed apparent impacts on the photocatalytic degradation of atrazine by BiOBr/UiO-66. In mineral water, tap water and river water, the removal efficiency of atrazine was evidently lower than that in pure water. The main active species that responsible for the degradation of atrazine by BiOBr/UiO-66 were determined to be ·O2− and h+. Ultimately, the degradation pathways of atrazine were proposed based on the intermediates detected by LC-MS/MS.

Activation of peroxymonosulfate using drinking water treatment residuals for the degradation of atrazine

Drinking water treatment residuals (WTRs) are safe byproducts of water treatment plants containing iron. This work studies the degradation of atrazine (ATZ) by WTR-catalyzed peroxymonosulfate (PMS) in aqueous solutions. Factors that affect the catalytic performance (the PMS concentration, catalyst dose, initial solution pH, reaction temperature and water matrix species) were investigated. The results show that the catalytic degradation efficiency of ATZ increases with the increase in PMS concentration and temperature, whereas a higher content of WTRs results in lower removal efficiency because of the quenching effect and negative effect of high pH. For an initial solution pH of 3 and 5, 94.1% and 87.4% of ATZ degradation can be achieved within 6h, whereas the value is only 26% for pH of 7. The production of sulfate radicals (SO4−) and hydroxyl radicals (OH) was confirmed by classic radical quenching and electron spin resonance (ESR) tests. Based on the GC–MS and LC–MS results, the main degradation pathways of ATZ may contain dealkylation, dechlorination-hydroxylation, and alkyl chain oxidation processes. In addition to the ATZ removal ability, the WTRs/PMS system can simultaneously remove phosphorus. This article provides a new idea for wastewater treatment and usage of WTRs as a resource.

Sulfite promoted photochemical cleavage of s-triazine ring: The case study of atrazine

Regarding the abundant solar energy on the earth, photochemical method is the most attractive approach for the decomposition of atrazine pollutant which is widely existed in surface water. In this study, we report that the presence of sulfite can alter the photochemical atrazine degradation pathway to cleave its s-triazine ring. Density functional theory calculation results first suggested that a reductive process might be highly possible to break the s-triazine ring of atrazine by comparing the highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap values of six possible atrazine degradation intermediates. The subsequent experimental results reveal that the presence of sulfite shifted a direct atrazine hydroxylated dechlorination pathway to an indirect photo-degradation route with the aid of hydrated electrons and hydrogen atoms, which were produced from the photolysis of sulfite solution under UV irradiation. This rational degradation pathway change increased the atrazine degradation and dechlorination rates by 4.3times, and also effectively cleaved s-triazine ring, as confirmed by the generation of ammonium ions and small molecule acids during the degradation of 2,4-diamino-1,3,5-triazine with this sulfite promoted photochemical reduction process. This study provides a mild strategy to completely mineralize atrazine, and also sheds light on how the degradation pathway could affect the s-triazine ring cleavage.