Enhanced degradation of atrazine in water by VUV/UV/Fe process: Role of the in situ generated H2O2

Abstract

Vacuum ultraviolet/ultraviolet/Fe (VUV/UV/Fe) has been regarded as a new advanced oxidation process (AOP), but its kinetics and mechanism for pollutant degradation remain largely unknown. This work investigates the degradation of a typical pesticide, i.e. atrazine (ATZ), by VUV/UV/Fe. The results show that ATZ was efficiently degraded by VUV/UV/Fe and the pseudo first-order rate constant (ka) reached 1.01 min−1, which was 1.7 times as high as the sum of those by UV/Fe and VUV/UV. This synergistic effect observed during the VUV/UV/Fe process was attributed to effective utilization of the H2O2, which was generated in situ by VUV photolysis of water, via the Fenton-like reaction. The apparent production rate of H2O2 was 0.19 mM min−1 in VUV/UV process, but decreased dramatically to 0.07 mM min−1 with addition of 1.0 mM Fe3+, which confirms the consumption of H2O2 by the Fenton-like reaction. The addition of tert-butanol and 1,4-benzoquinone proves that HO2 generated via the Fenton-like reaction played an important role, albeit not as much as HO, in the degradation of ATZ by VUV/UV/Fe. The application of Fe3+ as the iron source was much more effective than that of Fe2+ for the degradation of ATZ by VUV/UV/Fe. ka was a concave function of the solution pH and reached the optimal value at pH 3.5. The four selected inorganic anions inhibited the ATZ degradation by VUV/UV/Fe in an order of SO42− < HCO3− < NO3− < Cl−. The release of Cl− caused by the substitute reaction of chlorine atom with reactive oxygen species accounted for only 17.8% of the removed ATZ. It demonstrates that VUV/UV/Fe is a promising treatment process for pollutant removal from water.