Factors affecting formation of deethyl and deisopropyl products from atrazine degradation in UV/H₂O₂ and UV/PDS

摘要

In this study, the formation of deethyl products (DEPs) (i.e., atrazine amide (Atra-imine) and deethylatrazine (DEA)) and deisopropyl product (i.e., deisopropylatrazine (DIA)) from parent atrazine (ATZ) degraded in UV/H₂O₂ and UV/PDS processes under various conditions was monitored. It was found that SO₄˙? displayed a more distinctive preference to the ethyl function group of ATZ than HO˙, leading to the higher ratio of DEPs/DIA in UV/PDS system than that in UV/H₂O₂ system in pure water. The effects of water matrices (i.e., natural organic matter (NOM), carbonate/bicarbonate (HCO₃?/CO₃2?), and chloride ions (Cl?)) on ATZ degradation as well as formation of DEPs and DIA were evaluated in detail. The degradation of ATZ by UV/PDS was significantly inhibited in the presence of NOM, HCO₃?/CO₃2? or Cl?, because these components could competitively react with SO₄˙? and/or HO˙ to generate lower reactive secondary radicals (i.e., organic radicals, carbonate radicals (CO₃˙?) or reactive chlorine radicals (RCs)). The yields of these DEPs and DIA products from ATZ degradation were not impacted by NOM or HCO₃?/CO₃2?, possibly due to the low reactivity of organic radicals and CO₃˙? toward the side groups of ATZ. Howbeit, the increase of DIA yield companied with the decrease of DEPs yield was interestingly observed in the presence of Cl?, which was attributed to the promotion of Cl? at moderate concentration (mM range) for the conversion of SO₄˙? into HO˙. Comparatively, in the UV/H₂O₂ process, NOM and HCO₃?/CO₃2? exhibited a similar inhibitory effect on ATZ degradation, while the influence of Cl? was negligible. Differing from UV/PDS system, all these factors did not change DEPs and DIA yields in UV/H₂O₂ process. Moreover, it was confirmed that RCs had a greater selectivity but a lower reactivity on attacking the ethyl function group than that of SO₄˙?. These findings were also confirmed by monitoring the degradation of ATZ as well as the formation of DEPs and DIA in three natural waters.