Degradation of Trichloroethylene and Tetrachloroethylene in Simulated Groundwater in a Flow-Through Photosono Reactor

Simulated groundwater solutions contaminated with trichloroethylene (TCE) and tetrachloroethylene (PCE) were treated in a flow-through reactor equipped with ultrasound (US) and ultraviolet light (UV) sources. The treatment process was operated using UV or US individually, and UV and US concurrently (UVUS). The solutions contaminated with TCE or PCE were exposed to UV light emitted from Hg-arc lamps surrounding the quartz reactor vessel, and to acoustic waves from a US horn located at the bottom of the reactor vessel. The rate constants ($k$) of photolysis by UV, sonolysis by US, and photosonolysis by UVUS were evaluated using a mathematical model in conjunction with a nonlinear regression analysis. The removal efficiencies ($E$) for the UV, US, and UVUS treatments were also determined. For TCE, the US rate constant ($k_{\mathrm{us}}=0.016\pm 0.010{\min }^{-1}$) and the UV rate constant ($k_{\mathrm{uv}}=0.076\pm 0.004{\min }^{-1}$) yield the theoretical additive rate constant ($k_{\mathrm{ad}}$) of $0.092{\min }^{-1}$, whereas the observed UVUS rate constant ($k_{\mathrm{uvus}}$) is $0.110\pm 0.002{\min }^{-1}$. Furthermore, the efficiency of the US treatment ($E_{\mathrm{us}}=0.299$) and of the UV treatment ($E_{\mathrm{uv}}=0.664$) gives the theoretical additive efficiency ($E_{\mathrm{ad}}$) of 0.706, whereas the observed UVUS efficiency ($E_{\mathrm{uvus}}$) is 0.741. For PCE, $k_{\mathrm{ad}}$ and $k_{\mathrm{uvus}}$ are 0.324 and $0.698{\min }^{\mathrm{-1}}$, respectively, whereas $E_{\mathrm{ad}}$ and $E_{\mathrm{uvus}}$ are 0.894 and 0.948, respectively. The results suggest that the combined effect of UV and US on the decomposition of TCE and PCE is likely synergistic.