In recent years, the frequent detection of micro-pollutants in surface, ground and even drinking water posed a serious risk to human health. Vacuum-UV/UV (VUV/UV) emitted by ozone-generating low pressure Hg lamps can be an effective and convenient treatment for the degradation of trace organic contaminants in water without additional chemical reagents. However, the low VUV emission efficiency of conventional UV lamps and the short transmission distance of VUV light in water greatly limited its practical application in a large extent. With optimized reactor design and understanding of degradation performance of typical organic contaminants, VUV/UV technology will be a good choice for small-scale water treatment.
      In this study, a novel mini-fluidic VUV/UV photo-reactor was built. The fluence rate of UV and VUV was determined by chemical actinometry as 5.76 and 0.586 mW cm?2 respectively. The performance of the photo-reactor was first examined by degrading a model compound, methylene blue (MB). The results showed that VUV/UV enhanced the degradation than UV and UV/H2O2 treatment due to the large amount of generated hydroxyl radical (?OH). The degradation of MB in the presence of tert-butanol under VUV/UV irradiation became much slower, which confirmed that ?OH oxidation was dominant in the VUV/UV process. In addition, the effects of VUV transmission gas media, flow rate, pH and initial concentration in the VUV/UV degradation were investigated in this study.
      The photo-degradation of eight sulfonamide (SA) antibiotics under UV, UV/H2O2, VUV, and VUV/UV/H2O2 treatment processes was studied using the specially designed VUV/UV photo-reactor. Results indicated that VUV/UV obviously enhanced the removal of target micro-pollutants without adding any chemical reagents than UV/H2O2 and UV. The removal rate of each SA could reach more than 99% with UV fluence of 180 mJ cm?2. The addition of H2O2 under VUV/UV irradiation did not enhanced the degradtaion compared to VUV/UV. The degradation kinetics and mechanisms of a representative SA, sulfamethazine (SMN), were studied in detail. SMN was found to be resistant to direct UV photolysis but readily degradable under VUV/UV irradiation. ?OH oxidation dominated in the VUV/UV treatment process. The degradation of SMN was the fastest in the pH range of 6.0?9.0, while other pH conditions would decrease the reaction rate by affecting SMN speciation and ?OH concentration. Six byproducts were identified using UPLC-Q-TOF-MS, and the potential degradation pathways of SMN including hydroxylation and SO2 extrusion were proposed. The antibacterial activity of the SMN solution, assessed by the growth inhibition of Escherichia coli, decreased by about 80% after VUV/UV treatment for 20 min.
       Three pilot VUV/UV reactors were designed and their degradation performance were examined by MB. Results indicated that the removal rate of MB was higher in a reactor with smaller inner diameter. The removal of seven SAs mixed in aqueous solution by UV and VUV/UV treatments was comparatively investigated in the reactor with the smallest inner diameter (35 mm). The results showed that under the experimental conditions of initial SA concentration = 20 μg L?1 (each), flow rate = 0.18 m3 h?1, and lamp input power = 120 W, VUV/UV treatment could achieve an almost complete removal of all studied SAs. Meanwhile, the electrical energy per order (EEO) values of VUV/UV under these conditions for all studied SAs ranged from 0.55 to 0.80, considerably less than those of UV treatment (1.02?5.09). The study demonstrates that VUV/UV requires less energy than UV to achieve the same treatment efficiency.