||Chinese cooking fume is one of the sources of volatile organic compounds (VOCs) in the air. An innovative control technology combining photocatalytic degradation and ozone oxidation (UV/TiO2+O3) was developed to decompose VOCs in the cooking fume. Fiberglass filter (FGF) coated with TiO2 was prepared by an impregnation procedure. A continuous-flow reaction system was self-designed by combining photocatalysis with advanced ozone oxidation technique. By passing the simulated cooking fume through the FGF, the VOC decomposition efficiency in the cooking fume could be increased by about 10%. The decomposition efficiency of VOCs in the cooking fume increased and then decreased with the inlet VOC concentration. A maximum VOC decomposition efficiency of 64% was obtained at 100 ppm. Similar trend was observed for reaction temperature with the VOC decomposition efficiencies ranging from 64 to 68%. Moreover, injection ozone concentration had a positive effect on the decomposition of VOCs in the cooking fume for injection ozone concentration ≤1000 ppm and leveled off for injection ozone concentration >1000 ppm. About 34% of VOC decomposition efficiency could be achieved solely by ozone oxidation with or without near-UV irradiation. A maximum of 75% and 94% VOC decomposition efficiency could be achieved by O3+UV/TiO2 and UV/TiO2+O3 techniques, respectively. The maximum decomposition efficiencies of VOCs decreased to 79% for using UV/TiO2+O3 technique with adding water in the oil fume. Comparing the chromatographical species of VOCs in the oil fume before and after the decomposition of VOCs by using UV/TiO2+O3 technique, we found that both TVOC and VOC species in the oil fume were effectively decomposed.|
Bench-scale experiments using iron modified and unmodified photocatalysts (Fe/TiO2 and TiO2) were conducted to compare their decomposition efficiencies of formaldehyde. The effects of operating parameters on the decomposition efficiency of formaldehyde were further investigated. The grain size of iron doped photocatalysts ranged from 25 to 60 nm. The iron doped content of 1, 3, and 5% Fe/TiO2 photocatalysts were measured as 1.2, 3.1, and 4.7%, respectively. The UV-visible analytical results showed that a significant red shift was observed while the iron doping content of Fe/TiO2 increased from 0 to 5%. Two continuous-flow reaction systems, the ozonolytic and the photocatalytic reactors, were combined in series to investigate their capability to decompose formaldehyde by Fe/TiO2 photocatalysts with operating parameters. Six operating parameters investigated in this study included the influent formaldehyde concentrations (0.15, 0.30, and 0.45 ppm), the relative humiditues (5, 35, and 55%), the irradiation of lights (visible, near-UV, and UV), the reaction temperatures (25, 30, and 35°C), the iron doping contents (1, 3, and 5% Fe/TiO2), and the injection ozone concentrations (2000 and 3000 ppb). The optimal operating parameters obtained in this study were the influent formaldehyde concentration of 0.15 ppm, the relative humidity of 5 %, the irradiation of UV light, the reaction temperature of 35°C, the iron doping content of 5% Fe/TiO2, and the injection ozone concentration of 3000 ppb. Overall, the decomposition efficiencies of formaldehyde for different decomposition techniques were ordered as UV/TiO2+O3 > O3+UV/TiO2 > UV/O3 ≈ O3. A maximum formaldehyde decomposition efficiency of 92% was obtained by using the UV/TiO2+O3 technology.
The removal of VOCs in the cooking fume and formaldehyde decomposition efficiency are pseudo first order reaction. The kinetic model simulation results showed that the reaction rate of TVOC and formaldehyde increased with influent TVOC concentration. However, when the influent TVOC concentration increased gradually to a critical concentration, due to the limitation of active sites on the photocatalyst surface, too many pollutant molecules can not occupy the surface sites of the photocatalyst, and the photocatalytic reaction can not be carried out. Therefore, when TVOC and formaldehyde concentrations were too high, the reaction rate tended to be low.