Kinetic study and modeling of the vacuum-UV photoinduced degradation of 2,4-D

Vacuum-UV (VUV) photoinduced degradation of a model micropollutant, herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), was studied using a flow-through VUV photoreactor, operating in batch mode under kinetic control. Fast degradation rates were obtained using the VUV process, with 2,4-D concentrations lower than 1.5 mg L−1 being degraded by 90% after receiving a total UV/VUV fluence of 938 mJ cm−2. Experimental results showed that the initial degradation rate of 2,4-D in ultrapure water was independent of the initial concentration of the contaminant. The presence of alkalinity and NOM reduced the degradation rate by up to 72% due to the hydroxyl radical scavenging effect of carbonates/bicarbonates and NOM as well as their absorption of VUV radiation. The kinetics of the VUV induced degradation of 2,4-D in ultrapure water was also investigated through a kinetic model developed in this study. This model took into account the propagation and absorption of radiative energy in the reactor, generation of hydroxyl radicals via water photolysis, and interaction between photogenerated radicals and 2,4-D.

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► VUV photoinduced degradation of 2,4-D was studied in a flow-through photoreactor.
► Effect of initial concentration of the pollutant, alkalinity and NOM was studied.
► The kinetic behaviour was analyzed using experimental results.
► A complete model to describe the VUV-induced degradation of 2,4-D was developed.
► Propagation and absorption of radiation and interaction of species were studied.