Organic Pollutant Degradation in Water by the Vacuum-Ultraviolet/Ultraviolet/HO Process: Inhibition and Enhancement Roles of HO.

A vacuum-ultraviolet/ultraviolet (VUV/UV) mercury lamp was found to be a highly efficient radiation source for UV-based advanced oxidation processes (AOPs). If this lamp could enhance the UV/HO process, it would be very attractive. Hence, we have investigated sulfamethazine (SMN) degradation by the VUV/UV/HO process based on a bench-scale mini-fluidic VUV/UV photoreaction system (MVPS), a pilot reactor, and a model analysis. At high [SMN] in the MVPS, the apparent SMN degradation rate constant ( k') increased with increasing HO dose, while at low [SMN], k' decreased with increasing HO dose; this behavior was unexpected. Meanwhile, at low [SMN] in a pilot reactor, HO induced just a slight enhancement in the VUV/UV/HO process. A numerical simulation of the process suggested that for an integrated AOP (i.e., VUV/UV/HO) consisting of various component AOPs, HO could inhibit the component AOPs with HO* that did not originate from HO (e.g., VUV photolysis of water). The apparent HO role in the integrated AOPs was dependent on the contribution comparison between component AOPs that involved HO* that did or did not originate from HO. These results revealed important information regarding the application of the VUV/UV/HO process in water treatment.