Degradation Pathways Of Atrazine Research Articles

Insight into the role of charge carrier mediation zone for singlet oxygen production over rod-shape graphitic carbon nitride: Batch and continuous-flow reactor

As a new approach of creating the photo-exited electron (e-) and hole (h+) mediation zone for highly selective singlet oxygen (1O2) production, the rod-type graphitic carbon nitride (NCN) has been synthesized from the nitric acid-modified melamine followed by the calcination. The NCN exhibited a higher surface area and surface oxygen adsorption ability than bulk graphitic carbon nitride (BCN). The increment of CO and NHx groups on NCN corresponded to e- and h+ mediation groups, respectively, resulting in higher production of 1O2 than BCN. Moreover, those mediation groups on NCN result in higher recombination efficiency and longer e- decay time. As a result, the optimized NCN-0.5 (derived from 0.5 M of nitric acid-modified melamine) displayed 5.8 times higher kinetic rate constant of atrazine (ATZ) removal under UVA-LED irradiation compared to BCN. This study also evaluated the ATZ degradation pathways and toxicity effect of by-products. In addition, continuous flow experiments using NCN-0.5 showed superior ATZ removal performance with a hybrid concept between a slurry photocatalysis and a continuous stirred tank reactor system using actual effluent obtained from a wastewater treatment plant. Thus, this work provides an insight into the strategy for highly selective 1O2 production and the potential for water purification application.

Evaluation of nZVI for the degradation of atrazine in heterogeneous Fenton-like systems at circumneutral pH

The requirement of acidification for the successful of the Fenton processes in water treatment has promoted the search for new strategies to work at pH close to neutrality. With this objective, in this work the use of nZVI has been evaluated for the oxidative elimination of 10 mg L−1 of atrazine at circumneutral pH with nZVI/UVA, nZVI/H2O2, and nZVI/H2O2/UVA systems. While UVA irradiation of sole nZVI was ineffective for degrading the herbicide, the addition of H2O2 boosted up the reaction, with the nZVI/H2O2/UVA system attaining the highest degradation rate. The inhibition of the reaction upon addition of tert-butanol as scavenger pointed out the significant role of hydroxyl radicals in the atrazine oxidation. The characterization of fresh and spent samples, carried out by XRD, SEM, TEM, and nitrogen adsorption-desorption experiments, confirmed the presence of ferric oxidized compounds responsible of the heterogeneous photo-Fenton-like reactions. On the basis of the degradation products determined by high performance liquid chromatography (HPLC), a scheme of atrazine degradation pathways in the ZVI/H2O2/UVA system was proposed in which the reaction is mainly initiated by alkylic oxidation rather than dechlorination. Finally, the effect on the atrazine oxidation rate of the water constituent species was analyzed in different water matrices (pure, supply, simulated and secondary effluent real water). Considered individually, Cl−, SO42−, HCO3−, and DOC, showed a moderate inhibitory effect on atrazine degradation kinetics, but their combination could explain the significant decrease of efficiency detected in the real secondary effluent water compared to less complex matrices.

Intrinsic mechanisms of calcium sulfite activation by siderite for atrazine degradation

Employing sulfite to produce SO4−has drawn increasing interests. However, the excess amount of aqueous SO32−quenches the SO4−when utilizing Na2SO3 as the sulfite resources. The present study evaluated the degradation performance with atrazine (ATZ) as a model substance in the siderite/sulfite process by replacement of Na2SO3 with CaSO3. The results show that the present system works effectively towards ATZ degradation at an initial pH of 6, and the siderite/CaSO3 system performs much better than the siderite/Na2SO3 system due to the low solubility of CaSO3. An increase in siderite concentration slightly increases the degradation rate constant for ATZ. However, the change in CaSO3 dosage from 2 to 10 mM greatly decreases the ATZ degradation rate constant from 0.067 ± 0.003 min−1 to 0.021 ± 0.002 min−1. Based on the identified intermediate products, the possible ATZ degradation pathways were proposed. In addition, natural siderite can be used in the present system. Based on the facts that lots of research were performed with Na2SO3 to generate reactive species and the Ca2+ ion possesses some unique functions such as promoting the dewatering of activated sludge, the present research into CaSO3 activation can greatly advance our understanding of the mechanisms involved in sulfite activation and its further applications in wastewater treatment.

Hydrothermal deposition of CoFe2O4 nanoparticles on activated carbon fibers promotes atrazine removal via physical adsorption and photo-Fenton degradation

Magnetic CoFe2O4 serves as a promising photo-Fenton reagent, but its low adsorption ability and catalytic activity inhibit the effective removal of atrazine (ATZ). Herein, activated carbon fiber/cobalt ferrite (ACF/CoFe2O4) composites were fabricated by hydrothermal deposition of CoFe2O4 nanoparticles around ACFs. As compared with CoFe2O4 nanoparticles, the ACF/CoFe2O4 composites showed better adsorption ability due to the synergistic effect between CoFe2O4 nanoparticles and ACF felts. The ATZ adsorption trend over the ACF/CoFe2O4 composites matched well with pseudo-first-order and pseudo-second-order kinetics model, suggesting that the diffusion and adsorption reaction played equal contribution to the ATZ adsorption. Notably, the ACFs in the ACF/CoFe2O4 composites decreased the band gap of CoFe2O4 nanoparticles from 1.82 eV to 1.62 eV, facilitating the enhanced photocatalytic activity. In the reaction system of ATZ, H2O2 and ACF/CoFe2O4 composites, the remarkable changes of Co and Fe valence states demonstrated that both Co3+/Co2+ and Fe3+/Fe2+ circulations took part in the Fenton-like reaction. The hydroxyl radicals that were generated in the photo-Fenton system effectively induced the oxidative degradation of ATZ. Moreover, the photo-Fenton degradation pathway of ATZ was proposed according to LC-MS analyses. Hence, the ACF/CoFe2O4 composite was a promising photo-Fenton catalyst to remove pesticide pollutants via physical adsorption and photo-Fenton degradation.

Citrate iron complex induced dramatically enhanced oxidation of atrazine with bimetallic Bi/Fe0: Reactivity, oxidation and mechanism

The oxidative degradation of atrazine (ATR) using bimetallic Bi/Fe0 nanoparticles cooperated with citric acid (CA) and sodium citrate (NaCA) without extra addition of H2O2 or another oxidant was conducted. Almost 73% of ATR was removed in Bi/Fe0+NaCA + CA buffer system in 3 h, and the bimetallic Bi/Fe0 performs high stability and long service life in the buffer system according to the results of cyclic degradation experiments. The citrate iron complex of Fe(II)[Cit]- played the key role for the degradation process since it could quickly react with the generated H2O2 to produce free radicals in the Bi/Fe0+NaCA + CA system, which broadened the applicable pH range of the traditional Fenton reaction and promoted the oxidative degradation process of ATR. The possible degradation pathways of ATR were also investigated. In the Bi/Fe0+NaCA + CA buffer system, twelve kinds of ATR intermediate products were detected, of which the main products were dechlorination products and alkyl oxidative products. Due to the pH controllable of the Bi/Fe0+NaCA + CA system, it could reduce the acidity impact on the environment and makes the additional impact on the environment lower. Therefore, this work provides a new strategy for the degradation of ATR.

Soil bacterial community dynamics following bioaugmentation with Paenarthrobacter sp. W11 in atrazine-contaminated soil

Atrazine is one of the most widely used herbicides, however it and its metabolites cause widespread contamination in soil and ground water. Bioaugmentation is an effective method for remediation of environmental organic pollutants. High-throughput sequencing provides an important tool for understanding the changes of microbial community and function in response to pollutants degradation based on bioaugmentation. In this study, the effect of biodegradation with Paenarthrobacter sp. W11 and the change of microbial community during atrazine degradation were investigated. The results showed that bioaugmentation significantly accelerated the degradation rate of atrazine in soil and reduced the toxic effect of atrazine residues on wheat growth. The extra available NH4+ through atrazine mineralization could serve as a nitrogen source to increase microbial numbers. High-throughput sequencing further revealed that the microbial community restored a new balance. The function of microbial community predicted by PICRUSt2 suggested that the biodegradation process of atrazine affected not only the atrazine degradation pathway, but also the nitrogen metabolism pathway. Methylobacillus and Pseudomonas were considered as the most important indigenous atrazine-degrading microorganisms, because their relative abundances were positively correlated with the relative abundance of Paenarthrobacter and atrazine degradation pathway. This study provides insight into the cooperation between indigenous microorganisms and external inoculums on atrazine degradation process.

Mechanochemically synthesized S-ZVIbm composites for the activation of persulfate in the pH-independent degradation of atrazine: Effects of sulfur dose and ball-milling conditions

Surface passivation and an increase in pH may restrain the efficiency and capacity of the zero-valent iron (ZVI) activated persulfate (PS) process. Mechanochemically sulfidated ZVI (S-ZVIbm) shows an extraordinary increase in the activation of PS. Ball-milling avoids the complex liquid reactions of traditional methods of activation and is easier to upscale. However, the effects of the sulfur dose and milling conditions have not been sufficiently investigated in the application of S-ZVIbm to the PS activation process. S-ZVIbm was pH-independent compared with similar catalysts. The best performance was obtained for S-ZVIbm with 25% sulfur synthesized at 300 rev min−1 for 5 h. Almost complete degradation of 50 μM ATZ was obtained after 40 min reaction with 6 mM PS and 0.3 g L-1 S-ZVIbm. Structural and species characterizations revealed the effects of the milling conditions and showed that sulfide (S2−) might be the predominant sulfur species. The primary facilitation mechanisms of S-ZVIbm were the mitigation of passivation, an increase in hydrophobicity, an increase in electron transfer and the accelerated regeneration of Fe2+. 57Fe Mössbauer spectrum confirmed that the Fe0 left in S-ZVIbm was about two times higher than that in reacted ZVIbm. Fe0 acted as the predominant PS activator, but FeS2, FeS and SO32− also contributed to PS activation. The degradation pathway of atrazine was clarified based on the detection of intermediates and density functional theory calculations. S-ZVIbm is a promising catalyst for the activation of PS used to remediate refractory contaminants and is amenable to upscaling from the laboratory scale.

Coupling biological and photocatalytic treatment of atrazine and tebuthiuron in aqueous solution

Pollutants, such as pesticides, find their way into wastewater treatment plants (WWTPs). WWTPs have been reported to be unable to fully remove these pesticides from water. Hence, research has been conducted in the development of methods to degrade them in wastewater. This work reports the coupling of biological and photocatalytic processes to particularly treat two model pesticides (atrazine and tebuthiuron) in aqueous solution. Liquid chromatography-mass spectroscopy/mass spectroscopy (LC-MS/MS) was used as an advanced analytical technique for the identification of both atrazine and tebuthiuron, and their degradation by products. The LCMS/MS data showed that atrazine and tebuthiuron were only removed substantially during their first treatment days. Based on LCMS/MS results, biodegradation of atrazine in the biological treatment section was via dealkylation to yield deethylatrazine (m/z 198), (2) dechlorination to yield N-isopropylammelide (m/z 156), and (3) deamination to yield cyanuric acid (m/z 129). There were no identified metabolites of tebuthiuron which suggested its structural stability, but a decrease was observed at the beginning of the treatment of the pollutant probably due to adsorption on the sludge. Photocatalysis further reduced the concentration of atrazine, while there was no significant decrease in tebuthiuron. The atrazine degradation pathways that were identified during photocatalysis studies were (1) degradation of atrazine (CIET, m/z 216) through the formation of hydroxyatrazine (OEIT, m/z 197), desethylhydroxyatrazine (OIAT, m/z 155), ammeline (OAAT, m/z 127) and cyanuric acid (OOOT, m/z 129), and (2) the degradation of atrazine, after the formation hydroxyatrazine (OEIT, m/z 197), could also proceed to form deethylatrazine (CIAA, m/z 198), followed by the formation of N-isopropylammelide (IAT, 156) and finally cyanuric acid (OOOT, m/z 129). The bio-photodegradation treatment process was efficient for the removal of atrazine but not for the removal of tebuthiuron.

Establishment of sulfate radical advanced oxidation process based on Fe2+/O2/dithionite for organic contaminants degradation

The sulfate radical advanced oxidation process is considered as one of the most effective technologies for refractory organic pollutant removal. However, the current sulfate radical generation source is very limited, and so far only peroxydisulfate, peroxymonosulfate and sulfite were reported as the generation sources. In this study, dithionite (DTN) was introduced as sulfate radical generation source for the first time. It was combined with Fe2+ and O2 to form a simple and effective oxidation system: Fe2+/O2/DTN. The established system was used to degrade atrazine (ATZ). The degradation pathways of ATZ and generation mechanism of dominant reactive species in Fe2+/O2/DTN system were investigated. The results showed that ATZ and the total organic carbon (TOC) have been significantly reduced in 20 min with the initial solution pH varying from 5.0 to 7.0 in Fe2+/O2/DTN system. Moreover, the possible degradation pathway of ATZ has been proposed involving dealkylation, dechlorination, carbonylation and hydroxylation. Primary radical identification through quenching experiments, ESR spectra and density functional theory (DFT) revealed the existence of sulfate radical (SO4·-) and hydroxyl radical (·OH) in the system. It is suspected that FeSO3+ is the possible precursor of SO3·- and SO4·-. Therefore, the generation of FeSO3+ and the possible formation pathways of SO3·- and SO4·- have been predicted based on the results of alternating reaction atmosphere test. The study indicates that Fe2+/O2/DTN system could generate SO4·- and has great potential for the remediation of organic micro-pollution water bodies and contaminated soil.

Iron-crosslinked alginate derived Fe/C composites for atrazine removal from water

Fe/C composite is emerging as a promising nanoscale zero-valent iron (nZVI) based material for wastewater treatment to counteract the limitations of nZVI, while its preparation method, structure-activity relationship, and working mechanisms and conditions still need to be studied. In this study, Fe/C composites derived from iron-crosslinked alginate was successfully achieved via high temperature pyrolysis. Ferric ions were only transformed into Fe3O4/γ-Fe2O3 at low pyrolysis temperature (≤500 °C), whereas Fe0/Fe3C became the primary Fe species with the formation of graphitic carbon at elevated pyrolysis temperature (≥700 °C). Fe/C composites from higher pyrolysis temperature presented better performance in atrazine (ATZ) removal, and the optimal pyrolysis temperature was 800 °C (Fe/C-800). Batch experiments showed that the removal kinetics of ATZ (10 mg L−1) by Fe/C-800 (0.2 g L−1) followed pseudo-second-order model, and 24-h ATZ removal efficiency maintained at 93.5 ± 1.0% within pH 3–9. The adsorption by the graphitic carbon phase of Fe/C-800 was the principal contributor to the pH-independent superior performance in ATZ removal, and the Langmuir model fitted adsorption capacity was 64.8 mg g−1 at pH 6. Although the carbon-phase adsorbed ATZ was basically unavailable for degradation, Fe0/Fe3C-mediated ATZ degradation contributed to the great reactivity of Fe/C-800 at pH 3. Fe0/Fe3C in Fe/C-800 was more efficient for ATZ degradation than commercial nZVI, and oxidative dealkylation by Fe0/Fe3C mediated Fenton reaction was the predominant ATZ degradation pathway rather than reductive dechlorination. Moreover, the produced ATZ degradation intermediates could be further adsorbed by Fe/C-800, mitigating potential secondary pollution. Thus, iron-crosslinked alginate derived Fe/C composites can be an excellent alternative for nZVI in organics-polluted water treatment with great reactivity and wide pH applicability.

Photooxidation of atrazine and its influence on disinfection byproducts formation during post-chlorination: effect of solution pH and mechanism

Partial photooxidation of micropollutants may lead to various degradation intermediates, obviously affecting disinfection byproducts (DBPs) formation during the post-chlorination process. The photooxidation of atrazine (ATZ) in aqueous solutions with low-pressure mercury UV lamps in UV, UV/H2O2 and UV/TiO2 treatment system and the formation of chlorinated disinfection byproducts (DBPs) during subsequent chlorination processes including dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were investigated in this study. The effect of solution pH on the oxidation pathway of ATZ in three UV photooxidation treatment process and the impact of photooxidation on the DBPs formations were assessed. Based on UPLC-ESI–MS/MS analyses, identification of main oxidation intermediates was performed and the plausible degradation pathways of ATZ in photooxidation system were proposed, indicating that photooxidation of ATZ in UV/H2O2 and UV/TiO2 process system was significantly pH-dependent processes. Dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were detected in photooxidized ATZ solutions. Compared to the other three DBPs, TCM and TCP were the main DBPs formed. The DBPs formations were greatly promoted in oxidized ATZ solutions. Solution pH and UV irradiation time exhibited obvious impact on the DBPs formation on the basis of DBP species. The variation tendency of DBPs observed relates to the combustion of ATZ in photooxidation system and the production oxidation intermediates.

Microbial Community and Atrazine-Degrading Genetic Potential in Deep Zones of a Hypersaline Lake-Aquifer System

The chemical composition of groundwater and related surface water ecosystems can be modified by intensive agricultural activities. This is the case of the Natural Reserve of Pétrola saline lake (Albacete, SE Spain), which constitutes the discharge area of an unconfined aquifer. The extended use of fertilizers and pesticides poses a threat to ecosystem sustainability. One of the most applied herbicides worldwide has been atrazine. Despite being prohibited in Spain since 2007 by European regulations, atrazine can still be detected due to its high persistence in the environment. Atrazine degradation pathways are mediated by biological processes performed by microorganisms with adapted metabolic mechanisms that make in situ bioremediation possible. To evaluate the presence of such microorganisms in the unconfined aquifer, groundwater was collected from a flowing 37.9 m deep piezometer. DNA was extracted, and the bacterial 16S rRNA gene was amplified and cloned. Later, 93 clones were sequenced, providing the first molecular assessment of bacterial community structure in the deep zones of the aquifer. Some of these bacteria have been previously described to be involved in atrazine degradation. In addition, 14 bacteria were isolated from the groundwater samples and identified by 16S rRNA gene sequencing. DNA from these bacteria was subjected to PCR assays with primers designed for the genes involved in the atrazine degradation pathway. Positive results in the amplification were found in at least three of these bacteria (Arthrobacter sp., Nocardioides sp. and Pseudomonas sp.). The atrazine-degrading genetic potential was shown to be dependent on the trzN and atzA,B,C gene combination. These results suggest for the first time the adaptation of the bacterial population present in deep aquifer zones to atrazine exposure, even after more than 15 years of its ban in Spain. In addition, this study provides the baseline data about the bacterial communities found in deep aquifer zones from the hypersaline lake-aquifer system.

Degradation of aqueous atrazine using persulfate activated by electrochemical plasma coupling with microbubbles: removal mechanisms and potential applications

Persulfate (PS) activated by dielectric barrier discharge (DBD) integrated with microbubbles (MBs) was designed to decompose atrazine (ATZ) from aqueous solutions. The degradation efficiency reached 89% at a discharge power of 85W, a PS concentration of 1mM, and a air flow rate of 30mL/min after 75min treatment. Heat caused by DBD favoured ATZ removal. Besides, the effect of PS dosage, discharge power and initial pH values on ATZ removal was evaluated. The calculated energy yield revealed that it was economical and promising to treat 1L of ATZ-wastewaters. The existence of SO42−, Cl−, CO32− and HCO3− lead to negative effects, while positive effect was observed when the presence of MBs and humic acid. The identification results of radicals and degradation intermediates suggested that multiple synergistic effects (such as heat, eaq− and H•) activated PS, and 1O2/reactive nitrogen species, •OH and SO4−• with contributions of 18%, 26%, and 29%, were main species attacking ATZ. ATZ degradation pathways including olefination, alkylic-oxidation, dealkylation, and dechlorination were proposed. An environment-friendly and a novel method for enhancing the PS-activation and ATZ-decomposition was provided, which fully utilised the electric-chemical conversion of DBD and high mass transfer efficiency of MBs.

Degradation of atrazine in aqueous solution through peroxymonosulfate activated by Co-modified nano-titanium dioxide.

Peroxymonosulfate (PMS) heterogeneous activation by Co3 O4 -modified catalyst has shown significant implications to generate free radicals for organic pollutants degradation in water. In this study, PMS heterogeneous activation was applied to degrade atrazine (ATZ) using Co3 O4 -mediated titanium dioxide nanoparticles (Co3 O4 /TiO2 NPs), which were synthesized by sol-gel method. Firstly, characteristics of the fresh and used Co3 O4 /TiO2 NPs were analyzed via SEM, TEM, XRD, EDS, and XPS techniques. Then, the influences of several key parameters (i.e., Co3 O4 /TiO2 NPs dose (0.02-0.3g/L), PMS dose (0-0.6mM), initial pH (3.0-11.0), and co-existing anions) on the ATZ degradation were investigated systematically. Besides, control systems were set up to verify the high efficiency of Co3 O4 /TiO2 NPs. In addition, the radical scavenging experiments revealed that sulfate and hydroxyl radicals were generated in the Co3 O4 /TiO2 -PMS system, while sulfate radicals were the dominant reactive species responsible for ATZ degradation. Furthermore, the stability and reusability of the Co3 O4 /TiO2 NPs were investigated after four consecutive experiments. Based on the identified products, possible degradation pathways of ATZ in the Co3 O4 /TiO2 -PMS system were proposed. Finally, the possible reaction mechanism of Co3 O4 /TiO2 -PMS system was proposed according to the comprehensive analysis. Findings of this study provided useful information for the application of Co3 O4 /TiO2 NPs in recalcitrant organic contaminants degradation. PRACTITIONER POINTS: Co3 O4 /TiO2 NPs were synthesized via the simple sol-gel method. Co3 O4 /TiO2 NPs possessed excellent catalytic performance for PMS to eliminate ATZ. Sulfate radicals play a dominant role in the degradation of ATZ. ATZ degradation pathways and reaction mechanism in the system were proposed.

Peroxydisulfate activation by in-situ synthesized Fe3O4 nanoparticles for degradation of atrazine: Performance and mechanism

Herein activation of persoxydisulfate (PDS) was achieved by in-situ synthesized Fe3O4 nanoparticles (NPs) from a sacrificial iron anode in an electrochemical (EC) cell. The as-synthesized Fe3O4 NPs were characterized to be in spherical and in the nano size. The performance of the process, EC-Fe3O4/PDS, was investigated in terms of atrazine (ATZ) degradation. Optimum process conditions were determined as initial pH of 5, electrolyte (Na2SO4) concentration of 1 mM, a current density of 1.67 A m−2, PDS concentration of 0.5 mM and initial ATZ concentration of 10 mg L–1. At optimum conditions, the EC-Fe3O4/PDS process could effectively degrade 80% of ATZ in an aqueous solution within a short reaction time of 20 min. The electrical energy consumption of the process was found to be quite low with 0.0307 kWh/m3. Based on the LC/MS analysis, the degradation pathway of ATZ with seven transformation products was proposed. Finally, a possible mechanism of the EC-Fe3O4/PDS process was put forward, which includes the activation of PDS and the role of radicals in the degradation of ATZ. In conclusion, the combination of Fe3O4 NPs catalyzed PDS oxidation with the EC process was very effective in the degradation of ATZ to dechlorinated final products. The strong synergistic effect makes this process superior to conventional methods due to the high degradation efficiency with low electrical energy and chemical consumption. Application of this method, with very low current density, may not only minimize the electrical energy consumption but also help reduce the sludge production due to the lower iron dissolution.

Activation of peroxymonosulfate by cobalt-impregnated biochar for atrazine degradation: The pivotal roles of persistent free radicals and ecotoxicity assessment

Cobalt-mediated activation of peroxymonosulfate (PMS) has been extensively investigated for the degradation of emerging organic pollutants. In this study, PMS activation via cobalt-impregnated biochar towards atrazine (ATZ) degradation was systematically examined, and the underlying reaction mechanism was explicated. It was found that persistent free radicals (PFRs) contained in biochar play a pivotal role in PMS activation process. The PFRs enabled an efficient transfer electron to both cobalt atom and O2, facilitating the recycle of Co(III)/Co(II), and thereby leaded to an excellent catalytic performance. In contrast to oxic condition, the elimination of dissolved oxygen significantly retarded the ATZ degradation efficiency from 0.76 to 0.36 min-1. Radical scavenging experiments and electron paramagnetic resonance (EPR) analysis confirmed that the ATZ degradation was primarily due to SO4·- and, to a lesser extent, ·OH. In addition, dual descriptor (DD) method was carried out to reveal reactive sites on ATZ for radicals attacking and predicted derivatives. Meanwhile, the possible ATZ degradation pathways were accordingly proposed, and the ecotoxicity evaluation of the oxidation intermediates was also conducted by ECOSAR. Consequently, the cobalt-impregnated biochar could be an efficient and environmentally friendly catalyst to activate PMS for abatement and detoxication of ATZ.

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.