Study On The Transformation Characteristics Of Typical Phenylurea Herbicides By UV-activated Sulfate Radical Systems

The increasing demand for food has prompted the development of pesticides and herbicides,and the sharp increase in usage has led to pollution of the water environment.The aqueous solution containing herbicide will produce disinfection by-products（DBPs）,which harmful to human body after disinfection treatment.Therefore,it is of great significance to develop a technology that can effectively remove herbicides in water and control the formation of DBPs.The advanced oxidation process based on sulfate radical(SO₄^·-)are effective in removing organic pollutants.Ultraviolet（UV）activated persulfate（PS）and peroxymonosulfate（PMS）can effectively produce SO₄^·-,which has a good application prospect in drinking water treatment.In this study,isoproturon（ISO）and chlorotoluron（CHL）were taken as the research objects.The degradation characteristics and cost-effectiveness of PUHs in UV/PS and UV/PMS process were investigated.The formation potential of DBPs in subsequent disinfection oxidation and degradation pathways of these herbicides were compared between the UV photolysis,UV/PS and UV/H₂O₂ process.Finally,a quantitative structure-activity relationship（QSAR）model was established to estimate the UV/PS reactivity of structure-related phenylurea herbicides.PUHs could be degraded effectively by using UV/PS process,and SO₄^·-accounted for the main contribution.By the competition kinetics,the second-order rate constants of ISO with HO^·and SO₄^·-were calculated to be 8.87×10⁹ and 9.40×10⁹ M^-1s^-1,respectively.The corresponding k_app of CHL with HO^·and SO₄^·-were 5.80×10⁹ M^-1s^-1and 6.60×10⁹ M^-1s^-1,respectively.Increasing PS dosage and UV intensity can accelerate the removal of herbicides.It is notable that UV/PS degradation was resistant to p H,while coexistent ions and NOM depressed the process.Comparing the pathways under the three processes,it could be found that the greatest difference was whether there was breakage of-CON（CH₃）₂.QSAR model found that the reactivity of PUHs was related to the substituents on the benzene ring,the sensitivity of these oxidants to substitution effects for their reaction with PUHs decreased in the following order:O₃>>SO₄^·->HO^·.The degradation of phenylurea herbicides in UV/PS includes hydroxylation and scissions of bond between substituent and phenyl group.The pretreatment of UV and UV/H₂O₂greatly enhanced the DBPs-related toxicity in post-disinfection while UV/PS showed absolute superiority in controlling the water toxicity.UV/PMS could also effectively degrade PUHs,but the reaction rate was lower than that of UV/PS system.Increasing PS dosage and UV intensity linearly enhanced the k_obs of herbicides and the removal efficiency increased under alkaline conditions.Coexistent ions and NOM were the most vital reasons for the inhibition of PUHs removal,while HCO₃^-showed a positive effect.Based on the total cost of electricity and chemicals,UV/PS was more cost-effective than UV/PMS.From aforementioned results and discussions,as an emerging AOPs technology,SR-AOPs could not only effectively degrade many refractory pollutants,but also show inhibitive consequence on DBPs generation in subsequent disinfection,which had more obvious superiority than HR-AOPs.This study provides a theoretical basis for the practical application of water treatment process through in-depth exploration of SR-AOPs system through multiple aspects such as removal efficiency,degradation mechanism,economic benefits,and DBPs-related toxicity evaluation.From the perspective of ensuring the safety of drinking water,it is of great significance to improve the operation and management level of existing drinking water treatment.