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• Persulfate combined wet air oxidation (PWAO) is proposed to deep remove benzothiazole. • OH is firstly detected by electron paramagnetic resonance in wet air oxidation process. • OH plays a very important role in the PWAO process. • High COD removal is achieved with a large amount of microsphere polymers recycling. • The PWAO process has a lower operating cost than WAO in COD removal. Wet air oxidation (WAO) has an obvious advantage in treating wastewater with high concentration of organics, but harsh reaction conditions are required and the treatment efficiency has not reached a satisfactory level. Herein, we developed a low dosage of persulfate promoted WAO process (PWAO) to remove a model heterocyclic pollutant benzothiazole (BTH). The addition of persulfate remarkably enhanced the elimination of benzothiazole (BTH) and COD from water via degradation and polymerization. Under optimized operation condition (with 11.1 mM K 2 S 2 O 8 addition into WAO), about 65.0% of BTH converted into microsphere polymers and more than 94.6% COD was eliminated from water after polymers separation. Electron paramagnetic resonance (EPR) analysis and quenching experiments revealed that OH was effectively generated in a wide range of reaction temperature and it played the key role in BTH degradation and polymerization, while SO 4 − was detected at low temperature for its fast decomposition at high temperature. Quantum chemical calculation together with ultra-performance liquid chromatography with electrospray ionization tandem mass spectrometry (UPLC-ESI-MS) analysis confirmed that the degradation and polymerization of BTH mainly started from the heterocyclic ring, followed by further oxidation or polymerization. Comparing with normal WAO process, the PWAO technology had an advantage in lower operating cost in removing per unit COD and carbon resource recycle, which indicates a promising prospect in treating wastewater with high concentration of heterocyclic compounds. [ABSTRACT FROM AUTHOR]

The nitrogen heterocyclic compounds (NHCs) are very toxic and widely used in many industries, while the treatment of NHCs in wastewater has not attracted enough concern till now. Here we studied the complete degradation of a typical NHCs, benzopyrazole (BP), in wet oxidation. The effects of different operation parameters, such as stirring speed, temperature, reaction time and initial pH, on BP degradation and chemical oxygen demand (COD) removal were studied. BP was totally degraded and the COD removal efficiency achieved 76.7%, after 120 min reaction at 220 °C with initial pH 6.5. Meanwhile, 81.7% of the nitrogen from BP was removed from the solution. The toxicity of the BP solution was reduced by 95.2% after wet oxidation at 240 °C for 180 min. The influences of coexisted NO 3 − , CO 3 2− , SO 4 2− and PO 4 3− ions were also investigated. With quantum chemical calculation and intermediates analysis by electrospray ionization mass spectrometry, a very detailed degradation pathway of BP in wet oxidation was proposed. [ABSTRACT FROM AUTHOR]

Three simple structured nitrogen heterocyclic compounds (NHCs), namely indole (ID), benzopyrazole (BP) and benzotriazole (BT), were degraded via wet air oxidation (WAO) in an autoclave-type reactor. The elimination of target pollutants became significant only above 220 °C. The reactivity order of the three substrates was ID > BP > BT. The chemical oxygen demand (COD) removal levels were lower than 70%. Many partial oxidation intermediates were produced, as detected by electrospray ionization–mass spectrometry (ESI-MS). The presence of different anions, such as CO 3 2− , SO 4 2− , and PO 4 3− , had a detrimental effect on the removal performances. On the other hand, Cl − and NO 3 − had a beneficial effect on the WAO of the target pollutants. By combining quantum chemistry calculations and ESI-MS analysis, detailed degradation pathways of ID, BP, and BT could be proposed. It was concluded that ring breakage occurred on both the benzene and heterocyclic ring in the initial stage of WAO for all three substrates. [ABSTRACT FROM AUTHOR]

Abstract Photocatalytic ozonation is an attractive advanced oxidation process for wastewater treatment, but highly active catalysts with strong response to visible light are urgently needed to push forward its practical application. In this study, a hierarchical biomimetic monoclinic bismuth vanadate (BiVO 4) with leaves morphology was synthesized by a hydrothermal method, and employed as catalyst for oxalic acid and penicillin degradation in photocatalytic ozonation. The results show that the organics degradation was more efficient using leaves shaped BiVO 4 as catalyst than the bulk shaped one in photocatalytic ozonation and the synergy index is ranged from 2.8 to 3.3, indicating a superior positive synergistic effect between photocatalysis and ozonation. The higher activity of the leaves shaped BiVO 4 was probably attributed to the distinctive biomimetic morphology and preferable band structure with more negative CB potential. Mechanism studies suggested that the main reactive species were h+ and OH for the degradation of persistent oxalic acid in photocatalytic ozonation. In addition, the effect of ozone concentration and inorganic ions and reusability of the material were also intensively investigated. Graphical abstract Image 1 Highlights • Hierarchical biomimetic BiVO 4 with leaves morphology is synthesized. • L-BiVO 4 exhibits high synergy in photocatalytic ozonation process. • The reactive oxidizing species in photocatalytic ozonation is h+ and OH. • The high CB position plays an important role. [ABSTRACT FROM AUTHOR]

• Global softness of the NHCs was employed to correlate with the ozonation efficiency. • Higher global softness of NHCs resulted in a greater degradation efficiency. • Fewer N atoms in heterocyclic ring generated more OH from ozone dissociation. • Reactive sites for both O 3 and radical attack were located by FO theory. • Combined DFT and TOF-MS results were used to identify the hydroxylation products. Nitrogen-containing heterocyclic contaminants (NHCs) have aroused intense environmental issues in waterbody because of their high toxicity and strong recalcitrance against natural degradation. In this study, ozonation degradation on four typical NHCs - benzotriazole (BTA), benzimidazole (BMZ), indazole (IDZ), and indole (IDO) was carried out to investigate the effects of N atoms on degradation efficiency. Global softness of the NHCs was calculated by density functional theory (DFT) and correlated with ozonation efficiency. It was discovered that higher global softness of the NHCs resulted in the greater degradation efficiency. Mineralization results together with the quenching tests results suggested that NHCs with ortho-positioned N atoms in heterocyclic ring are easier to be mineralized, while the presence of para-positioned N atoms increased the recalcitrance for destruction. Apart from hydroxyl radicals, superoxide radicals and singlet oxygens were also identified by electron paramagnetic resonance (EPR) spectra. Condensed Fukui index was employed to probe the potential active sites for both direct ozone oxidation and radical-based attack. Single point energies were further calculated among these active sites to seek the initial-stage hydroxylation intermediates. Combined the calculation results with the identified intermediates from time-of-flight mass spectroscopy (TOF-MS), degradation routes of the NHCs were proposed. This study discovered structure-dependent behavior of NHCs on ozonation efficiency and envisaged a more accurate strategy for establishing the degradation pathway. [ABSTRACT FROM AUTHOR]