Research On The Multi-VOCs Removal Using The Biotrickling Filter Coupled With Dielectric Barrier Discharge Oxidation

Emissions of toxic volatile organic compounds (VOCs) and odorous compounds from oil refining and pharmaceutical industries have been a serious environmental and health concern in recent years. Aerobic biodegradation of gas-phase VOCs in large volumes and low concentrations is an effective and economical option in comparison with other different physico-chemical techniques. However, the performance of bioreactor system treating industrial VOCs with poorly soluble and recalcitrant pollutants is not satisfactory. For now, isolating highly-efficient VOC-degrading strains and enhancing biodegradation by innovative bioreactor systems have attracted great attention.In this study, bacterial strains Pandoraea sp. WL1 and Pseudomonas sp. WL2 that could efficiently degrade p-xylene and ethyl mercaptan were isolated from activated sludge of a pharmaceutical wastewater treatment plant. Degradation pathway and kinetics analysis of substrate degradation by these two isolates were presented. In addition, removal performance and substrate interactions for mixed VOCs were firstly studied in a biotrickling filter (BTF) system. Lastly, an innovative BTF system coupled with a dielectric barrier discharge (DBD) reactor for treating mixed recalcitrant compounds was studied.1)A novel Pandoraea sp. strain WL1 was isolated, showing an ability of efficiently mineralizing sole p-xylene to p-toluic acid through the bi-oxidation. Kinetic analysis of 0-200 mg·L-1 p-xylene degradation by strain WL1 proved that strain WL1 could grow well with a highly efficient p-xylene-degrading ability. Besides, substrate range studies of Pandoraea sp. WL1 were performed to test its ability to degrade other selected aromatic compounds (toluene, p-cresol, p-toluic acid, phenol and terephthalic acid).2) Strain Pseudomonas sp. WL2 isolated from the activated sludge of a pharmaceutical wastewater treatment plant was able to efficiently degrade ethyl mercaptan as the sole carbon and energy source. Substrate range studies of Pseudomonas sp. WL2 were performed to test its ability to degrade other sulfur compounds, aldehydes and methanol. Kinetic analysis for ethyl mercaptan degradation with different initial concentrations was proved to be more efficient than other pure cultures reported previously. Also, it was shown that strain WL2 could oxidize ethyl mercaptan to CO2, bacterial cells and transform SO42- to diethyl disulfide through enzymatic oxidation, indicating a novel pathway for ethyl mercaptan degradation.3) The BTF system inoculated with the mixed cultures dominanted with strain WL1 and strain WL2 was proved with great removal performance and high stability for mixed VOCs (ethyl mercaptan, propyl mercaptan, p-xylene and toluene). Key interactions identified include little inhibition of p-xylene degradation and obvious inhibition of ethyl mercaptan degradation for a paired mixture. Moreover, it showed a higher elimination capacity value (200 g·m-3·h-1) than those from previous studies.4) In this study, an innovative design of bioreactor system for removing recalcitrant compounds (dimethyl sulfide, propyl mercaptan and toluene) by coupling DBD reactor as pretreatment with a BTF system was studied. In this integrated process, chemical control unit (namely, water absorption) followed with the DBD reactor was designed to keep the stability of a biotrickling filter from the side-effect of overdose ozone, and to simultaneously enhance the absorption of target pollutants into liquid medium. Performance evaluation of the coupled BTF system for removing a mixture of VOCs and odorous compounds (dimethyl sulfide, propyl mercaptan and toluene) was conducted. The enhanced removal efficiency of 22.3%-24.6% and 29%～41.8% for 57～373 mg·m-3 dimethyl sulfide were obtained, respectively, while the coupled BTF system were operated under different voltage discharges of 8.36 kV and 11.13 kV by the DBD reactor. Moreover, the removal efficiency was 17.5%～20.2% higher for 356～762 mg·m-3 propyl mercaptan under 8.36 kV compared with that of sole BTF system. These indicate that this novel bioreactor could effectively achieve better and more stable removal performance for poorly soluble and recalcitrant pollutants in the industrial application.