| Combination of UV photolysis and biofiltration is evaluated as an novel treatment strategy for the enhanced degradation of hardly biodegradable volatile organic compounds (VOCs) in recent years. In this paper, a custom-made integrated system composed of an UV reactor and a biotrickling filter was established to treat VOCs. Chlorobenzene, one of the halogenated aromatic compounds, was selected as a model compound since it's a typical recalcitrant VOC. UV degradation and BTF for treatment of chlorobenzene was studied respectively. The couple mechanism was studied using the coupling system operated under different conditions.Using separately of two UV sources of dominant wavelength 365nm (500w) high pressure mercury lamp and 185nm (18W) of low-pressure mercury lamp , effects of operation factors, including UV wavelength, inlet mass concentration of chlorobenzene, retention time and reaction medium, on the photooxidation rate of chlorobenzene and its transmission into intermediate products were investigated, respectively. The results showed that, under the conditions of 365nm wave length and low inlet chlorobenzene concentration, chlorobenzene removal was increased in linear mode with the extension of rentention time until maximum value of 87% was attained; and UV photodegradation of chlorobenzene followed second-order kinetics. O2 and H2O in air media could be transformed into active groups after exposure in UV irradiation, which therefore enhanced the photo-induced degradation. And it also supply the explanation for the lower remval efficiency of 61% using nitrogen gas as reaction medium. On the other hand, high inlet chlorobenzene concentration(8.47,10.95g/m3) led to decreased photon amounts that was utilized for per molecular pollutant, and it thus resulted in the declination of removal efficiency. Lower removal efficency was obtained when 185nm 18W low pressure mercury lamp was used as light source, and maximum efficiencies were only 31% and 7%, respectively, in the medium of air and nitrogen gas.Biotrickling filter (BTF) with ether-based polyurethane foam (PU-foam) as biofilm carrier was employed for purification of gaseous chlorobenzene , and results showed that inlet concentration, inlet load, spray volume, empty bed retention time all affected the removal efficiency of chlorobenzene. At EBRT75s, with the inlet concentration increasing slowly from 1.4 to 9.0g/m3, chlorobenzene removal rate was first improved and then presented a declining trend (62.8%→75.2%→ 58.6%). Prolongnation of EBRT (30,45,60,75,90 s) was favorable for the mass transfer and reaction of gaseous pollutants among the gas, liquid, microbial phases. Under the lower inter loading, removed chlorobenzene was increased in the linear relationship with the inter loading, and the removal efficiency was remained over 75% in most period of the experiment. The removal capacity for chlorobenzene was close to the maximum when the inter load was greater than 250g/m3·h, where poor mass transfer between gas-liquid phases became the rate-limiting factor for chlorobenzene biodegradation in BTF, and the significant drop in removal efficiency was observed thereafter.Therefore, UV oxidation using 185nm was coupled with BTF to purify the chlorobenzene gas. And the results showed that UV pretreatment could significantly reduce the start-up time and improve its operation performance and reliability of BTF, since part of chlorobenzene was degraded and transformed into more water soluble and biodegradable by-products. Although perfoemance was affected by reducing the EBRT or elevating inlet concentration, less significant fluctuation was observed in removing chlorobenzene, which was attributed to the cooperation effect between these two process. Under the conditions of EBRT 45s and UV RT 20s, excellent removal efficiency of 95% was achieved in the UV-BTF coupled system, and it was 21% higher that the plus of respective efficiency by single UV photooxidation and BTF unit. And it therefore layed a foundation for application of this combined system in treating recalcitrant VOCs.
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