Organic Pollutant Degradation in Water by the Vacuum-Ultraviolet/Ultraviolet/H2O2 Process: Inhibition and Enhancement Roles of H2O2.

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/H2O2 process, it would be very attractive. Hence, we have investigated sulfamethazine (SMN) degradation by the VUV/UV/H2O2 process based on a bench-scale mini-fluidic VUV/UV photoreaction system (MVPS), a pilot reactor, and a model analysis. At high [SMN]0 in the MVPS, the apparent SMN degradation rate constant ( k'app) increased with increasing H2O2 dose, while at low [SMN]0, k'app decreased with increasing H2O2 dose; this behavior was unexpected. Meanwhile, at low [SMN]0 in a pilot reactor, H2O2 induced just a slight enhancement in the VUV/UV/H2O process. A numerical simulation of the process suggested that for an integrated AOP (i.e., VUV/UV/H2O2) consisting of various component AOPs, H2O2 could inhibit the component AOPs with HO* that did not originate from H2O2 (e.g., VUV photolysis of water). The apparent H2O2 role in the integrated AOPs was dependent on the contribution comparison between component AOPs that involved HO* that did or did not originate from H2O2. These results revealed important information regarding the application of the VUV/UV/H2O2 process in water treatment.