Search

• 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]

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]