Photo and photocatalytic degradation of simetryn, prometryn, metolachlor, sulfometuron methyl, glyphosate, and glufosinate

Ultraviolet (UV) irradiation and photocatalytic treatments were investigated for the degradation of UV-sensitive herbicides (simetryn, prometryn, metolachlor, and sulfometuron methyl) and UV-insensitive herbicides (glyphosate and glufosinate) in both pure and river water. Rapid photodegradation was observed for UV-sensitive herbicides under UV irradiation, whereas degradation of UV-insensitive herbicides was negligible due to the lack of direct UV absorption. In contrast, photocatalytic treatment enabled the degradation of both UV-sensitive and UV-insensitive herbicides. In photocatalytic treatment, rate constants in river water were 7∼9 times lower than those in pure water, reflecting the inhibitory effects of coexisting constituents (water matrix effect). By contrast, UVC irradiation exhibited comparable degradation rate constants in river water and pure water, demonstrating its robustness toward water matrix effects. For practical application, the UVC irradiation was further evaluated in a continuous-flow system. More than 96% of metolachlor could be removed at a flow rate of 0.24 tonnes per hour using a 14 L reactor equipped with a 360 W mercury lamp. Furthermore, coating photocatalysts on the inner wall of the reactor enabled effective treatment of UV-insensitive herbicides. These results demonstrate that a UVC-centered treatment strategy, complemented by photocatalysis, offers a practical, scalable, and water-matrix-tolerant approach for the removal of herbicides from water sources.