Peroxymonosulfate Dosage Research Articles

Oxidative degradation of tetracycline using peroxymonosulfate activated by cobalt-doped pomelo peel carbon composite.

Tetracycline (TC) is a typical ecotoxic antibiotic, which easily causes bacterial resistance. Therefore, it is necessary to remove TC from the water environment. In recent years, advanced oxidation processes (AOPs) rely on the use of highly reactive oxidizing sulfate radical which is turning into an increasingly popular as a tool of the removal of TC. In this study, cobalt-doped pomelo peel carbon composite (Co-PPCC) was prepared by the impregnation coprecipitation method to activate peroxymonosulfate (PMS) to remove TC. SEM, BET, XRD, FTIR, XPS, TGA, and other analytical techniques indicated that a carbon composite catalyst with excellent performance has been successfully prepared. TC was removed by the synergistic effect of adsorption and catalytic degradation processes. The adsorption capacity was limited (only approximately 20% within 60 min) and tending to saturation, which indicated that the removal of TC in the Co-PPCC/PMS system was mainly due to oxidative degradation. The influence of the Co-PPCC and PMS dosage, initial TC concentration, initial pH values, and coexisting anions on the removal efficiency of TC was investigated. When the Co-PPCC catalyst dosage was 1 g/L, PMS concentration was 2 g/L, and pH value was 11, the removal efficiency of TC with a concentration of 50 mg/L reached 99% within 60 min. Free radical quenching experiment and electron paramagnetic resonance (EPR) analysis indicated that the free radical and non-radical degradation processes exist in the Co-PPCC/PMS/TC system. The main degradation products and the possible transformation pathways of TC were explored by LC-MS. In addition, after four cycles of Co-PPCC tests, the removal efficiency of TC can reach 64%. This study provides a new method to reuse abandoned pomelo peels and synthesize an economical and environmentally friendly catalyst for activating peroxymonosulfate to remove TC antibiotics in water.

Bicarbonate-enhanced iron-based Prussian blue analogs catalyze the Fenton-like degradation of p-nitrophenol

P-nitrophenol (PNP), a widely used compound, is harmful to the environment and human health. In this study, four iron-based Prussian blue analogs (PBAs) were prepared by coprecipitation (Co-Fe PBA, Mn-Fe PBA, Cu-Fe PBA and Fe-Fe PBA). The Co-Fe PBA exhibited high peroxymonosulfate (PMS) activation performance for PNP degradation, removing over 90% of PNP in 60 min at an optimal pH of 7, temperature at 30 ℃, initial concentration of 20 mg/L, PBA dose of 0.2 g/L and PMS dose of 1 g/L. The physicochemical properties of the Co-Fe PBA were investigated by various characterization methods. The catalytic activity of PBA and the influence of various process parameters and water quality on the catalytic reaction were investigated to elucidate the mechanism of p-nitrophenol degradation by PBA-activated persulfate. Moreover, the mechanism of accelerated degradation of PNP under HCO3– conditions and the role of major reactive oxides were determined by EPR measurement methods and free radical trapping experiments. HCO3– was found to directly activate PMS to produce reactive oxygen species, and 1O2, ∙OH and SO4∙- were all greatly increased. This work presents a promising green heterogeneous catalyst for the degradation of emerging contaminants (ECs) in real wastewater with natural organic matter and coexisting anions by PMS activation.

Activation of peroxymonosulfate by CuCo2O4 nano-particles towards long-lasting removal of atrazine

Abstract The effect of peroxymonosulfate (PMS) activated by nanocrystalline CuCo2O4 (NPS) on removal of atrazine (ATZ) was studied. First, the main experimental parameters were studied, including CuCo2O4 dose, PMS dose, initial pH value, and co-existing ion. The removal of ATZ (>99%) was attained under the optimal conditions (i.e., 150 mg/L CuCo2O4, 0.2 mM PMS, 5 mg/L ATZ, initial pH value of 6.8, and reaction time of 30 min). However, the removal of ATZ only reached 20.9% in the PMS alone system and there was no significant ATZ removal when adding CuCo2O4 alone into the solution, proving the good performance of the CuCo2O4/PMS system. Furthermore, reusability of CuCo2O4 was tested through five consecutive runs. To confirm which main active radicals were responsible in the system, two radical quenching experiments were carried out and electron paramagnetic resonance (EPR) was tested. In addition, the characterization of fresh and reacted CuCo2O4 NPs was tested by SEM, TEM, EDS, XRD, and XPS. Subsequently, based on the characterization of CuCo2O4 NPs and identification of radicals, ≡Cu2+/ ≡ Cu+ and ≡Co3+/ ≡ Co2+ were considered to be the main catalytic species, while the synergistic effect of Cu and Co played a crucial role. Finally, the degradation pathway of ATZ was proposed.

Insights into naphthalene degradation in aqueous solution and soil slurry medium: Performance and mechanisms

The performance of naphthalene (NAP) degradation in peroxodisulfate (PDS) and peroxymonosulfate (PMS) oxidation systems by nano zero valent iron (nZVI) combined with citric acid (CA) activation was reported in aqueous solution and soil slurry medium. The results in aqueous solution tests indicated that 98.1% and 98.9% of NAP were individually degraded in PDS/nZVI/CA and PMS/nZVI/CA systems within 2 h when the dosages of PDS, PMS, nZVI and CA were 1.0 mM, 0.1 mM, 0.2 mM and 0.1 mM, respectively. The consequences of scavenging tests and electron paramagnetic resonance detection demonstrated that HO• and SO4−• were the key factors on NAP removal. The presence of surfactants could consume ROSs and inhibit NAP removal. In addition, GC-MS was applied for the determination of NAP degradation intermediates, and three possible NAP degradation pathways were proposed in PDS oxidation process and two pathways in PMS oxidation process, respectively. The results in soil slurry medium showed that the presence of CA could promote the dissolution of soil minerals and the desorption of NAP from soil medium. 93.5% and 96.8% degradation of NAP were obtained in PDS/nZVI/CA and PMS/nZVI/CA systems within 24 h. Besides, the existence of DOM in soil could promote Fe(II)/Fe(III) cycle and NAP degradation through electron transfer. Based on the NAP degradation performance in the actual groundwater and soil medium, the above findings could provide basis and strong support for the potential application of PDS/nZVI/CA and PMS/nZVI/CA systems in the remediation of NAP contaminated sites.

Visible light assisted activation of peroxymonosulfate by bimetallic MOF based heterojunction MIL-53(Fe/Co)/CeO2 for atrazine degradation: Pivotal roles of dual redox cycle for reactive species generation

The present study illustrates a synthesis method for preparation of bimetallic metal organic framework (MOF) based heterojunction photocatalyst MIL-53(Fe/Co)/CeO2 (MIL-CO) and its potential towards activation of peroxymonosulfate (PMS) in water, under visible light irradiation. The catalyst/PMS system was employed to degrade and mineralize Atrazine (ATZ) in aqueous medium. 0.01 g/L of binary composite with 10 wt% CeO2 (MIL-CO(10)) and 0.25 g/L of PMS could achieve 99% ATZ degradation, for 10 mg/L ATZ concentration, within 60 min visible light exposure. The binary catalyst was characterized thoroughly using various techniques. Influences of different process parameters, like, catalyst and PMS dose, initial ATZ concentration, initial solution pH, process temperature, coexisting ions and organics, etc., were investigated. Applications of different radical scavengers and in-depth EPR investigation established the existence of degradation mechanisms involving the dominance of radical SO4∙-,OH∙,O2∙-,h+,O21 based process. Moreover, the applicability of MIL-CO/PMS/Vis system was studied in different real-life water matrixes. Various intermediates and byproducts were identified and probable degradation pathways were suggested. Detailed toxicity analysis was carried out to determine the elimination efficiency of harmful contaminants by the catalytic system. The binary composite showed excellent catalytic activity over six consecutive cycles with negligible metal leaching and remarkable structural stability. Surface bound redox interconversions of transition metal ions, coupled with efficient charge separation through heterojunction formation, result activation of PMS and ATZ molecules and generation of reactive species. Overall, the MIL-CO/PMS/Vis system has demonstrated extraordinary potential of binary MOF based heterojunction photocatalysts towards visible light driven mineralization of refractory pollutants.

CoFe-LDO nanoparticles as a novel catalyst of peroxymonosulfate (PMS) for histidine removal.

Dissolved organic nitrogen (DON) has been aresearch subject due to its potential to form nitrogenous disinfection byproducts (N-DBPs) in drinking water treatment. In our study, CoFe layered double oxide (CoFe-LDO) was selected as an effective catalyst for the removal of histidine by activation of peroxymonosulfate (PMS). The results investigated that the removal of DON and histidine within 1h in the CoFe-LDO/PMS system were up to 61% and 72%, respectively. The influences of CoFe-LDO dosage, PMS dosage, and pH value for DON removal were alsoelucidated. The optimum pH was 8, and the optimal dosage of CoFe-LDO and PMS were 0.04g/L and 0.5mmol/L. It was found that SO4•- and •OH induced by the transformation of Co2+-Co3+ and Fe2+-Fe3+ on the catalyst surface were responsible for the degradation by ESR detection, in which SO4•- played a more important role. The degradation pathway of histidine indicated that it was partly oxidized to NH4+-N in the 60min and no evident generation of N2 during the whole process. Furthermore, degradation products of histidine have also been revealed by the analysis of HPLC-MS. In addition, the generation potentials of two typical N-DBPs were also clarified. The formation potential of dichloroacetonitrile (DCAN) decreased, while that of dichloroacetamide (DCAcAm) increased firstly before declining.

Assembling g-C3N4 nanosheets on rod-like CoFe2O4 nanocrystals to boost photocatalytic degradation of ciprofloxacin with peroxymonosulfate activation

Water pollution caused by organic pollutants seriously threatens the ecological balance. Photocatalytic oxidation technology with green, environment-friendly characteristics can effectively dispose of organic pollutants in water, is the potential replacement of the traditional sewage treatment technology. In this work, CoFe2O4/g-C3N4 heterojunction with nanosheets-on microrods structure was designed and prepared by a simple solvothermal-calcination synthetic method, which was applied for the degradation of cyprofloxacin (CIP) through the combination of peroxymonosulfate (PMS) and photocatalysis. The results reveal that the optimal photocatalytic degradation efficiency of CIP (20 mg/L) in the prepared CoFe2O4/g-C3N4-10/PMS system reached 97% within 60 min, and the degradation rate at a high level during the four cycles. The effects of different environmental factors (catalyst dose, PMS dose and initial CIP concentration) on the degradation of the system were studied. The enhancement of photocatalytic activity in the CoFe2O4/g-C3N4 composite can be mainly attributed to accelerated separation and transfer of electrons and holes through the formation of heterojunctions, which is beneficial to stimulate PMS to produce more SO4•- and •OH.

Co2+/PMS based sulfate-radical treatment for effective mineralization of spent ion exchange resin

Sulfate radical advance oxidation processes (SR-AOPs) have attracted a greater attention as a suitable alternative of the hydroxyl radical based advance oxidation process (HR-AOPs). In this study, for the first time we report liquid phase mineralization of nuclear grade cationic IRN-77 resin in Co2+/peroxymonosulfate (PMS) based SR-AOPs. After the dissolution of cationic IRN-77 resin, 30 volatile and 15 semi-volatile organic compounds were analyzed/detected using non-targeted GC-MS analysis. The optimal reaction parameters for the highest chemical oxygen demand (COD) removal (%) of IRN-77 resin were determined, and the initial pH, PMS dosage, and reaction temperature were found to be the most influential parameters for the resin degradation. We successfully achieved ∼90% COD removal (1000 mg/L; 1000 ppm) of dissolved spent resin for SR-AOPs by optimizing the reaction parameters as initial pH = 9, Co2+ = 4 mM (catalyst), PMS = 60 mM (as oxidant) at 60 °C temperature for 60 min reaction. The electron spin resonance spectroscopy (ESR) spectra confirmed the presence of SO4∙- and OH∙ as main reactive species in the Co2+/PMS resin system. In addition, Fourier transform infrared spectroscopy (FT-IR) analyses were used for structural characterization of solid and liquid phase resin samples. We believe that this work will offer a robust approach for the effective treatment of spent resin generated from nuclear industry.

Degradation of bisphenol A through Ti–BiOI/ZIF-8/peroxymonosulfate (PMS): Catalyst preparation, experimental design and catalytic mechanism

In this work, zeolitic imidazolate framework-8 (ZIF-8) was loaded onto Ti-modified BiOI (Ti–BiOI) by in-situ synthesis to prepare novel binary photocatalytic materials (Ti–BiOI/ZIF-8), its physical parameters, chemical parameters, crystal structure and electrochemical properties were characterized. A novel photocatalytic oxidation system (Ti–BiOI/ZIF-8/PMS/Vis) consisting of Ti–BiOI/ZIF-8 and peroxymonosulfate (PMS) could efficiently remove BPA under visible light. In the first 2 ​min of the photocatalytic reaction, Ti–BiOI/ZIF-8 and PMS were excited to generate a large number of active groups (•O2−, •OH, •SO4− and h+), more than 90% of BPA was removed, and the degradation rate of Ti–BiOI/ZIF-8/PMS/Vis was 3.5 times higher that of monomer BiOI, and the removal rate of total-organic-carbon reached about 60%. In addition, the effects of PMS dosage and catalyst dosage on the removal of BPA were also investigated. The stability and reusability of the Ti–BiOI/ZIF-8 were verified through four cycles of degradation of BPA.

Biochar/iron oxide composite as an efficient peroxymonosulfate catalyst for the degradation of model naphthenic acids compounds

Naphthenic acids (NAs) are a mixture of aliphatic and alicyclic carboxylic acids which are persistent in the environment. In this study, a sludge-based biochar/iron oxide (B-FeOx) catalyst with 3D flower-like shaped structure was prepared through a facile hydrothermal method. For the first time, the B-FeOx catalyst was employed to activate peroxymonosulfate (PMS) for the removal of two model NA compounds (1-adamantanecarboxylic acid (ACA) and 4-methylheptanoic acid) at pH 8.50. Compared to biochar or FeOx alone, a higher degradation efficiency (96.1%) and faster degradation rate (k = 0.100 min−1) of ACA were obtained by the B-FeOx composite at a catalyst dose of 2.0 g/L and PMS dose of 2.5 mM. The higher degradation efficiency of B-FeOx was attributed to the improved surface area and pore volume as well as the abundant reactive sites induced by the flower-like structure. Furthermore, the hydroxyl radical (•OH) generated in the B-FeOx/PMS system was the dominant radical for both ACA and 4-methylheptanoic acid degradation as demonstrated through radical quenching experiments. The presence of chloride ions in the B-FeOx/PMS system showed a suppression effect on the degradation of ACA and 4-methylheptanoic acid at Cl− concentrations between 5 and 20 mM. No significant difference in the degradation rates of ACA and 4-methylheptanoic acid was observed at different Cl− concentrations. Overall, the results of this study showed that the sludge (waste material)-based B-FeOx composite may have the potential to be utilized as PMS catalyst for the removal of NAs that are especially abundant in oil sands process water.

Enhanced catalytic sulfamethoxazole degradation via peroxymonosulfate activation over amorphous CoSx@SiO2 nanocages derived from ZIF-67

In this work, the amorphous CoSx@SiO2 nanocages were hydrothermally synthesized by sulfurizing ZIF-67@SiO2 in the presence of thioacetamide (TAA). The catalytic performances of CoSx@SiO2 nanocages as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the sulfamethoxazole (SMX) degradation were systematically investigated. 100% SMX was degraded within 6 min in CoSx@SiO2/PMS system, indicating that the amorphous CoSx@SiO2 nanocages exhibited outstanding sulfate radical-advanced oxidation process (SR-AOP) activity toward SMX degradation due to the regeneration of Co2+ by surficial sulfur species like S2−/S22−. The effects of PMS dosages, initial pH, SMX concentrations and co-existing ions on SMX degradation efficiency were explored in detail. The SMX removal efficiency was obviously improved in the simulated wastewater containing chloride ions (Cl−) and low-concentration bicarbonate ions (HCO3−). The residual PMS and the generated sulfate radical (SO4·−) were determined quantitatively in CoSx@SiO2/PMS system. A possible mechanism in CoSx@SiO2/PMS system was proposed based on the results of quenching experiments, X-ray photoelectron spectroscopy (XPS) analysis, electrochemical tests, and electron spin resonance (ESR). The CoSx@SiO2 exhibited good stability and reusability, in which 100% SMX removal was achieved even after five consecutive cycles. This work provided a strategy for regulating the stability of cobalt-based catalyst for efficient pollutant degradation by PMS activation.

Nitrogen vacancies induce sustainable redox of iron-cobalt bimetals for efficient peroxymonosulfate activation: Dual-path electron transfer

The construction of surface defect was a promising modification strategy to accelerate peroxymonosulfate (PMS) activation mediated by metal for water purification, but intrinsic impact on electron transfer path has been unclear. In this study, nitrogen vacancies (Vn) were introduced into graphite carbon nitride and coupled with iron-cobalt bimetals (FeCoOx/CN-Vn). Experimental and theoretical results confirmed that Vn not only provided abundant electrons to reduce Fe(III)/Co(III) into Fe(II)/Co(II), but also induced the extraction of electrons from pollutant to electron-poor Co(III) for a faster Co(III)/Co(II) cycle. The sustainable dual-path electron transfer effectively overcame the obstacle of low-valence metal regeneration in conventional PMS-based oxidation, increasing the degradation rate constant of tetracycline hydrochloride, a typical refractory pollutant, from 0.2479 to 0.6674 min−1 in the first 2 min. The impacts of environmental factors (pH, PMS dosage, types of oxidants, water matrix) were investigated. Also, the effect of co-existing inorganics and organics was explored using a response surface quadratic model. The evaluation of electrical energy consumption and stability confirmed the outstanding practical application prospect of FeCoOx/CN-Vn. Finally, degradation pathways of TCH were elucidated and toxicity of the products was evaluated using quantitative structure activity relationship (QSAR). This study not only furnished a novel insight into the defect-assisted PMS activation, but also achieved in-situ utilization of contaminant for efficient wastewater treatment.

Enhanced catalytic degradation of aqueous doxycycline (DOX) in Mg-Fe-LDH@biochar composite-activated peroxymonosulfate system: Performances, degradation pathways, mechanisms and environmental implications

In this study, the Mg-Fe-LDH@biochar composite was firstly fabricated and applied for effectively activation peroxymonosulfate (PMS) for aqueous doxycycline (DOX) degradation. The physiochemical properties of the as-synthesized composite were thoroughly characterized. In the developed Mg-Fe-LDH@biochar/PMS system, the catalytic DOX degradations were evaluated under different conditions. Under the optimal condition (0.75 g/L catalyst loading, 0.75 g/L PMS dosage, pH = 7.0), about 88.76% DOX (35 mg/L) was removed within 120 mins. The results of quenching test and electron paramagnetic resonance (EPR) illustrated that the •OH, SO4•- and •O2– radicals all contributed to the DOX degradation in the Mg-Fe-LDH@biochar/PMS system, whereas the 1O2-based non-radical degradation played the dominant role in DOX removal. The developed system was almost not adversely affected by the high-strength anions and exhibited high DOX decomposition rates in a wide pH range from 3.0 to 9.0, indicating the great potential in the practical application. The satisfactory reusability of the composite catalyst was demonstrated in the recycling test, with the DOX removal efficiency slightly declined from 90.08 to 84.42% after five runs. Based on the generation of reactive oxidative species and the transformation intermediates identified by HPLC-MS, the possible degradation pathways and reaction mechanism of DOX degradation in Mg-Fe-LDH@biochar/PMS system were proposed.

Catalytic degradation of acid red B in the system of ultrasound/peroxymonosulfate/Fe3O4

The wastewater containing azodyeswastewater features high chroma, difficult degradation and great harm to the environment. It is difficult to meet the increasingly stringent requirements for industrial wastewater discharge using traditional water treatment methods. In this paper, degradation of Acid Red B in the system of ultrasound/peroxymonosulfate/Fe3O4 was investigated. The effects of Fe3O4 dosage, peroxymonosulfate dosage, ultrasonic power, ultrasonic frequency, initial azo dye concentration and initial pH value on degradation were studied through orthogonal experiments. Besides, through single factor experiment, the influence of various factors on the degradation was determined in the system of ultrasound/peroxymonosulfate/Fe3O4. Ethanol and tert-Butanol were used to study the dominant radicals in the system. NaH2PO4, NaHCO3 and NaCl were added to study the degradation effect of inorganic anions on acid red B. Finally, ultraviolet–visible spectrophotometer was used to scan the spectrum to analyze the degradation path of acid red B in the system of ultrasound/ peroxymonosulfate/Fe3O4. The results indicate that proposed method is of great potential application value in removal of organic pollution and environmental purification.

Highly efficient degradation of sulfamethoxazole (SMX) by activating peroxymonosulfate (PMS) with CoFe2O4 in a wide pH range

The cobalt ferrite materials (CoxFe3−xO4) with different molar ratios of Co:Fe (1:16, 1:8, 1:4, 1:2, and 3:4) were synthesized by simple co-precipitation method, and used for catalyzing activation of peroxymonosulfate (PMS) to degrade sulfamethoxazole (SMX). The effects of catalyst dose, PMS dose, pH value, and inorganic ions on the degradation of SMX were investigated. Particularly, the degradation efficiency of SMX reached 91% within 10 min in CoFe2O4/PMS, and the removal rate of SMX achieved 81% at first 1 min. Meanwhile, the CoFe2O4/PMS reaction system exhibited excellent catalytic performance at a wide pH range from 3.00 to 11.00. The CoFe2O4 catalyst could be easily magnetically separated and exhibited high stability in cycle experiments. EPR and quenching experiments showed that 1O2, SO4−, and OH species were produced in the CoFe2O4/PMS system, especially OH and 1O2 played dominant roles during the degradation of SMX. The catalytic degradation mechanism of SMX in the CoFe2O4/SMX system was proposed, involving radical process and non-radical process. This work will provide a new way for the efficient treatment of wastewater especially those containing SMX compounds.

Nonprecious bimetallic Fe, Mo-embedded N-enriched porous biochar for efficient oxidation of aqueous organic contaminants

Bimetallic Fe- and Mo-embedded N-enriched porous biochar (Fe-Mo@N-BC) is developed and serves as a cost-effective and highly efficient catalyst for mineralization of non-biodegradation organic contaminants. Fe-Mo@N-BC was prepared by pyrolysis of complex Fe/Mo -containing precursors. Transmission electron microscopy and elemental mapping suggested that Fe and Mo are uniformly dispersed in nitrogen-doped biochar with hierarchical mesopores. In comparison to Fe@N-BC and Mo@N-BC, Fe-Mo@N-BC exhibited a superior activity for activating peroxymonosulfate (PMS). The stable activity was ascribed to N-doping and synergistic effect of Fe and Mo species, where both Fe-Nx and Mo-Nx can simultaneously serve as the active sites and N-BC can act as a carrier and an activator as well as an electron mediator. Electron paramagnetic resonance and quenching experiments indicated that HO•, O2•− and 1O2 were responsible for organic degradation. The effects of PMS dosage, initial Orange II concentration, temperature, solution pH, coexisting anions and humic acids on organic degradation were also investigated. With the assistance of an external magnet, Fe-Mo@N-BC can be easily separated after reaction and remains stable in the reusability tests. This work demonstrates a feasible strategy towards the fabrication of Fe, Mo-embedded N-enriched porous biochar catalysts for the detoxification of organic contaminants.

Efficient removal of organic pollutants by a Co/N/S-doped yolk-shell carbon catalyst via peroxymonosulfate activation

Carbon-based catalysts with heteroatom doping and hollow structures are desired for advanced oxidation processes (AOPs). Herein, dual-shelled Co, N, and S codoped hollow carbon nanocages were developed by wrapping zeolitic imidazolate framework-67 (ZIF-67) with trithiocyanuric acid (TCA) and performing subsequent carbonization. The optimal composite catalyst (Co-NC-CoS) exhibited excellent catalytic performance toward different organic pollutants. Almost complete removal of 4-NP (60 mg/L−1) was achieved within 20 min by 10 mg of catalyst and 0.2 g/L−1 peroxymonosulfate (PMS). Moreover, the catalyst showed good stability and reusability. The effects of catalyst and PMS dose, pollutant concentration, pH and common anions were investigated, and reactive oxygen species (ROS) were studied by scavenger experiments and electron paramagnetic resonance (EPR) tests. The results show that multidoped atoms S, Co and N all contributed to the degradation system. Several lines of evidence suggested that S could change the catalytic process from Co3+/Co2+ to Co3+/Co2+/Co0 reduction due to its low redox potential. Degradation was achieved through both radical and nonradical pathways, where sulfate radicals (SO4·̶), hydroxyl radicals (·OH) and singlet oxygen (1O2) were primary reactive species. Overall, this work may suggest that the novel multi heteroatom-doped catalysts with complex structures can be developed for environmental remediation.

Enhancing Volatile Fatty Acid Production during Anaerobic Fermentation of Waste Activated Sludge with Persulfates: Peroxymonosulfate versus Peroxydisulfate

Persulfates ((peroxymonosulfate (PMS) and peroxydisulfate (PDS)) can disintegrate waste activated sludge (WAS), but their influence on volatile fatty acid (VFA) production during anaerobic fermentation is largely unclear. Particularly, it is unknown whether persulfates can improve fermentation without any preactivation. This study investigated how the direct addition of PMS and PDS into the fermenter influences VFA production from WAS, and uncovered possible mechanisms of improved VFA production. At the PMS dosage of 1.0 mM/gVS, maximum VFA yield (1025 ± 55 mg COD/L) was observed in 5 days of fermentation, which was 24% higher than that with an equimolar addition of PDS and 132% higher than that without persulfate addition. However, the cost-effectiveness of PMS in enhancing VFA production is lower than that of PDS. The in situ generated hydroxyl and sulfate radicals from persulfates in the fermenter enhanced not only WAS disintegration and solubilization but also the formation of biodegradable substances for acidification. Moreover, the direct addition of persulfates into the fermenter shifted the microbial community toward hydrolysis-acidification such as Clostridium_sensu_stricto_10 and Fonticella. Results of this study also suggest that preactivation is not necessary when persulfates are applied to improve WAS fermentation.

Highly efficient activation of peroxymonosulfate by bismuth oxybromide for sulfamethoxazole degradation under ambient conditions: Synthesis, performance, kinetics and mechanisms

A 3D flower-like bismuth oxybromide (BiOBr) was synthesized by a facile one-pot chemical precipitation method and its potential on sulfamethoxazole (SMX) degradation via peroxymonosulfate (PMS) activation was investigated for the first time. The physic-chemical properties of BiOBr were characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The key influencing factors in SMX degradation (including catalyst loading, PMS dosage, pH etc.) were discussed. The attack sites and degradation pathway were proposed via the identification of the reactive sites on SMX molecular together with the detection of intermediate degradation products. Furthermore, the toxicity of the intermediate products was evaluated via the ecological activity relationship (ECOSAR) program and the PMS activation mechanism over BiOBr was proposed via the determination of reactive species. Hydroxyl radical and singlet oxygen were identified as the main reactive species in the system and the enhanced catalytic efficiency of BiOBr was attributed to the active metal (Bi3+-Bi5+-Bi3+) redox cycles as well as the light effect. The enhancement on SMX degradation from light effect could be observed under visible light irradiation, even at ambient light condition. Finally, the robustness of the BiOBr/PMS system was further examined via multiple organics degradation as well as the performance comparison with other metal oxides. These findings provide an insight for BiOBr as a viable and superior alternative for PMS activation in organics degradation.

Activation of permonosulfate by Co-Fe3O4 composite catalyst for amino acid removal: Performance and mechanism of Co-Fe3O4 nanoparticles

Dissolved organic nitrogen (DON) derived from amino acids has been a major concern in drinking water treatment because of its potential to form nitrogenous disinfection byproducts (N-DBPs). The degradation performance of amino acids by peroxymonosulfate (PMS) activated by Co-Fe3O4 composite catalyst in heterogeneous catalytic process was elucidated in our study. The sole and combined catalytic performance of PMS and Co-Fe3O4 were evaluated for two amino acid species (i.e., histidine and phenylalanine) separately and validated under varying levels of PMS dose, Co-Fe3O4 dose, initial pH. The removal of histidine (62%) and phenylalanine (33%) was achieved with 0.1 g/L Co-Fe3O4, 1.5 mM PMS in the PMS/Co-Fe3O4 system. In contrast, only 19% and 16% histidine removal were obtained under individual application of PMS and Co-Fe3O4, respectively, confirming the preferable performance in the Co-Fe3O4/PMS system. Moreover, the reusability of the Co-Fe3O4 was elucidated after four successive runs. Radical quenching experiments revealed •OH and SO4•− were active while SO4•− was the dominant radical species. Examination of degradation intermediates and N-DBPs in Co-Fe3O4/PMS system showed that the increase of DCAN in histidine was attributed to histamine formation which produced more DCAN. Finally, the mechanism by the Co-Fe3O4/PMS system for the degradation of amino acids was proposed. The catalyst Co-Fe3O4 exhibited a unique adsorption of amino acids and the electron donor ability of Fe2+ enhanced the Co3+/Co2+ cycle which promoted the generation of free radicals according to the conversion of Fe and Co valence states.