Treatment of VOCs with a wet scrubbing - catalytic ozonation process: Efficiency, mechanism and pilot-scale application

A wet scrubbing - catalytic ozonation (WCO) process with activated carbon (AC) loaded MnOx (MnOx/AC) as the catalyst was developed, based on volatile organic compounds (VOCs) can be efficiently removed. The mineralization efficiency, degradation pathway and mechanism, and effects of the process operating parameters were investigated in detail using toluene as the target pollutant. The results show that the average removal efficiency of toluene reached 71.82 % within 90 min under optimal conditions (C-Toluene = 100 mg/m(3); C-O3 = 1 mg/L; catalyst loading = 5 g/L; pH = 7; gas flow = 500 mL/min), which outperformed that of the gaseous system. Quenching experiments and electron spin resonance spectroscopy indicate that( center dot)OH and O-center dot(2)- are the two main reactive oxygen species (ROSs) in the system, which facilitate the opening of the benzene ring and significantly reduce by-products. The intermediates of toluene degradation were identified by proton-transfer reaction time-of-flight mass spectroscopy (PTR-TOF-MS). The results indicate that most of the intermediates generated in the system are captured in water rather than being emitted into the atmosphere. In the pilot-scale experiments, the WCO process exhibited a stable VOC removal efficiency (>= 61.05 %) for 10 d in the treatment of actual low-concentration VOCs. Therefore, in this study, an effective process for the removal of low-concentration VOCs is proposed, which can be used for multiple VOC treatments.