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• Fe 3 O 4 NPs supported on sepiolite was applied as persulfate activator. • Small size and good dispersion of Fe 3 O 4 NPs were observed by FESEM and TEM. • 71.6% of ATZ and 20% of solution TOC can be removed by Fe 3 O 4 -Sep/PS after 60 min. • The structure stability and catalytic activity were proved during recycle runs. • Pathways included dealkylation, chain oxidation and dechlorination-hydroxylation. In this study, with sepiolite as a support, a novel magnetic Fe 3 O 4 -sepiolite composite was fabricated by coprecipitation method. The characterization results reveal that the sepiolite support could anchor Fe 3 O 4 nanoparticles with good dispersion. The composite was used as a catalyst to activate persulfate (PS) for atrazine (ATZ) degradation. 71.6% of ATZ and 20.9% of solution TOC could be removed after 60 min with 92 mmol/L of PS ([ATZ] 0 = 10 mmol/L). Due to the good adsorption capacity of Fe 3 O 4 -sepiolite composite toward ATZ, the degradation was considered to be facilitated by an adsorption process, since the adsorbed ATZ can be more easily transported to the active sites and be degraded in situ. Operation factors, including PS dose and solution pH, were investigated and found to be influential for the ATZ removal. The Fe 3 O 4 -sepiolite composite maintained its catalytic activity and structural stability with negligible Fe leaching during the recycling batch experiments. The intermediate products were further identified and the possible transformation pathway was then proposed based on the results. The findings of this research promote the application of Fe 3 O 4 -sepiolite composite as efficient and recyclable heterogeneous catalyst for organic degradation, and provide insights into the development of alternative catalysts with good adsorptive properties. [ABSTRACT FROM AUTHOR]

• O 3 /H 2 O 2 and MW/PS processes for the MBR effluent are systematically compared. • MW/PS process has a better treatment effect on refractory organics in MBR effluent. • Ozone plays a major role in the degradation of aromatic organic compounds in the O 3 /H 2 O 2 process. • Hydroxyl and sulfate radicals are the main reactive oxygen species in the MW/PS process. • Chemical oxidation (i.e. O 3 /H 2 O 2 , MW/PS) is a viable technology to eliminate organics in leachate. In this study, refractory organics in a membrane bioreactor (MBR) effluent were investigated following the treatment of landfill leachate by the ozone combined hydrogen peroxide (O 3 /H 2 O 2) and microwave-activated persulfate (MW/PS) processes. The treatment efficiency and the transformation characteristics of refractory organics and reactive oxygen species were determined. It was found that an acidic environment and an increase in the O 3 dosage improved the organic removal efficiency in the O 3 /H 2 O 2 process, and the use of H 2 O 2 improved the treatment efficiency, while excessive H 2 O 2 inhibited it. In the MW/PS process, an increase in the PS dosage and MW power greatly improved the treatment efficiency, while an alkaline environment inhibited it. Under the optimized reaction parameters, the O 3 /H 2 O 2 and MW/PS processes effectively degraded refractory organics (i.e., humic acid and fulvic acid) into components with a smaller molecular weight and simpler structure. The humification, aromaticity, and conjugation of organics in wastewater were greatly reduced. Compared to the O 3 /H 2 O 2 process, the MW/PS process had a better treatment effect on refractory organics, and there were more low molecular weight organics (<1 kDa) in the treated wastewater. Because O 3 is the main selective oxidant in the O 3 /H 2 O 2 process, a large amount of organic acids were accumulated. A large amount of hydroxyl radicals and sulfate radicals with strong oxidation ability were produced in the MW/PS process, and therefore the combined action of hydroxyl and sulfate radicals can efficiently decompose humus and intermediate organics. Overall, the MW/PS process was more effective in treating the MBR effluent than the O 3 /H 2 O 2 process. The results of this study provide a reference for the selection of an advanced oxidation process to eliminate refractory organics in landfill leachate. [ABSTRACT FROM AUTHOR]

• Refractory organics are degraded by the synergistic effects of MW with PS and H 2 O 2. • The MW/PS process degrades organics better than the MW/H 2 O 2 process. • Differences in DOM degradation mechanisms were revealed at the molecular level. • Humus is better degraded in the MW/PS process due to the major contribution of SO 4 -. This study investigated the degradation of organics in mature leachate treated by microwave radiation-activated persulfate (MW/PS) and hydrogen peroxide (MW/H 2 O 2) processes. Obvious synergistic effects existed in both the MW/PS and MW/H 2 O 2 processes, but were significantly higher in the MW/PS process. Refractory organics were better degraded by the MW/PS process than the MW/H 2 O 2 process due to the major contribution of SO 4 –. Moreover, according to Fourier transform-ion cyclotron resonance mass spectrometry coupled with electrospray ionization analysis results, the refractory organics (e.g. polycyclic aromatics (AI > 0.66), polyphenols (0.66 ≥ AI > 0.50)) were greatly degraded by both the MW/H 2 O 2 and MW/PS processes, but the MW/PS process degraded dissolved organic matter (DOM) over a wider range than the MW/H 2 O 2 process due to the different dominant radicals in the two processes. In addition, after reaction in the MW/PS process, the O/C ratio of DOM in the treated effluent showed an obvious increase, which can be mainly attributed to the reaction of sulfate radicals with the N- and S- containing compounds via single electron transfer. [ABSTRACT FROM AUTHOR]

• MW-PS-H 2 O 2 binary-oxidant process was firstly used to treat DDNP wastewater. • The oxidant utilization rate considerably increased with the binary oxidant process. • Both S O 4 · - and · O H were major contributions to organics degradation. Microwave (MW) irradiation is a superior approach to a warm-up system than conventional heating, and persulfate (PS) and hydrogen peroxide (H 2 O 2) can be efficiently activated to produce a reactive oxygen species for organic degradation. However, shortcomings remain regarding whether to use a low oxidant or the low treatment efficiency of a single oxidant process. In this study, a PS-H 2 O 2 binary oxidant process induced by MW was developed to treat dinitrodiazophenol industrial wastewater. The best chemical oxygen demand (COD) (73.5%) and color number (CN) (98.1%) removal efficiencies were obtained for the MW-PS-H 2 O 2 process under conditions of a total oxidant dose = 7.4 mM and n(PS)/n(H 2 O 2) = 3.7/3.7. In the MW-PS-H 2 O 2 process, the combination of ·OH and SO 4 − better degrades organics in DDNP industrial wastewater with the advantages of lower residual salinity (sulfate ions) and less invalid decomposition of excessive H 2 O 2. In addition, benzene ring substances and functional group substances were greatly degraded, and the molecular weight of the organics considerably decreased as a result of the MW-PS-H 2 O 2 process. Overall, the results demonstrate that the MW-PS-H 2 O 2 process is a promising treatment method for dinitrodiazophenol industrial wastewater with high treatment efficacy and high oxidant utilization. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Degradation of BPA was investigated by · OH - and SO 4 · - - AOPs. • The TOC removal rate achieved 36% and 24% for the catalyzed H 2 O 2 and persulfate. • BPA followed different transformation pathways in two systems. • The less radical scavenging may led to the higher removal of BPA by catalyzed H 2 O 2. • The magnetic fly ash presented good structural stability during the recycle runs. Abstract In this study, H 2 O 2 and persulfate (PS) were both proved to be heterogeneously catalyzed by the Fe 3 O 4 nanoparticle supported on coal fly ash for reactive oxidation species (ROS). The two heterogeneous advanced oxidation processes (AOPs) were systematically investigated, and the system with H 2 O 2 exhibited higher reactivity for Bisphenol A (BPA) elimination and total organic carbon (TOC) reduction. The two systems were comprehensively compared in terms of degradation kinetics, transformation way, water matrix species and catalyst stability. Systems with H 2 O 2 and PS can remove 100% and 80.2% of the BPA after 120 min (0.22 mmol/L), respectively([H 2 O 2 ] = 22 mmol/L, [PS] = 22 mmol/L). The oxidant efficiency in system with H 2 O 2 was obviously higher probably due to the less radical scavenging. A mechanism was proposed that the interface interactions between solid and liquid phase will affect the collision among molecular of oxidants and catalyst, as well as the lifetime of radicals during the their diffusion process. The quenching experiments demonstrated that the primary radical species in two systems were · OH and SO 4 · - / · OH , respectively, thus causing the different BPA degradation pathways and by-products. The catalyst presented good structural stability and relatively low Fe leaching in both systems during the recycle. The valence state transformation from Fe2+ to Fe3+ after the reaction explained the gradual catalytic activity loss. In the tap water and municipal wastewater, the system with PS was less influenced by the real water matrix due to the lower university of SO 4 · - toward organics. [ABSTRACT FROM AUTHOR]

Biochar is a carbon-rich material that can be obtained from pyrolysis of solid waste (e.g., agricultural solid waste and sludge from wastewater treatment plants). Biochar features low cost, large specific surface area, and strong adsorption capacity. New biochar composites can be produced via modification and loading of nano particles onto biochar. Biochar can contribute to the dispersion and stabilization of nano particles. In addition, nano particles can increase the number of surface-active sites, which improves the physicochemical properties of the material. Biochar and biochar composites have been applied widely in wastewater treatment, and have significantly enhanced the treatment performance of Fenton-like processes (activation of hydrogen peroxide and persulfate) as an advanced oxidation process for organics removal and wastewater decontamination. This paper reviews the preparation methods for biochar and biochar composites to systematically analyze the influential factors on the preparation process. The paper also comprehensively reviews the mechanisms by which biochar removes different organic pollutants. However, due to the vast number of different biochar feedstocks and their preparation methods, it is difficult to compare the properties of one biochar to another. Guidance if provided for the application of biochar and biochar composites for wastewater decontamination. Unlabelled Image • Performance of biochar is determined by preparation factors and loading processes. • The mechanism by which biochar adsorbs pollutants in water was analyzed. • Activation mechanisms for H 2 O 2 , PS, and PMS by biochar were determined. • Biochar shows great promise for the removal of pollutants from water. [ABSTRACT FROM AUTHOR]