Comparative Degradation Of Phenytoin Sodium In Aqueous Solution By Ultraviolet And Ultraviolet/Persulfate

Pharmaceuticals and personal care products（PPCPs）have received growing attention in recent years with the development of the pharmaceutical industry and the increased concern of its problem in water pollution.As a typical PPCPs,phenytoin sodium（DPH）is a widely used anti-epileptic drug and itsstable chemical structure makes it is difficult to be removed by conventional water treatment processes.Advanced oxidation processes（AOPs）is one of the most effective strategies in removing PPCPs,while the complex operation conditions and secondary pollution of most AOPs limite their practical use.UV-based advanced oxidation process is widely concerned AOP because UV has simple operating conditions and low possibility in causing secondary pollution.UV can photolysis some organic-pollutants directly and efficiently produce some reactive radicals such as sulfated radicals(SO₄^·-)in the presence of persulfate.In this study,a typial UV based AOP,ultraviolet/persulfate（UV/PS）was used to remove DPH.The efficiency and reaction mechanism of the degradation of DPH in aqueous solution is of great significance for exploring UV-based water treatment technology.The degradation performance of DPH in UV and UV/PS systems was compared in this paper.When initial DPH was 20μM,pH=7.0（10 mM phosphate buffer）,the reaction temperature was 25°C,the PS dosage is 500μM:the removal rates of DPH in UV（reaction90 min）and UV/PS（reaction 30 min）systems were 85.4%and 94.7%,respectively.UV photolysis playsimportant roles in both kinds of UV systems（i.e.,UV and UV/PS systems）.In addition to UV direct photolysis of DPH in UV/PS system,there is also oxidative degradation of DPH by SO₄^·-,and the contribution of UV and SO₄^·-is 55.8%and 38.8%,respectively.We found that the UV removal efficiency of DPH was higher under alkaline conditions,while the different pH conditions in UV/PS had no significant effect on the degradation of DPH.The temperature can promote the degradation efficiency of DPH in both systems to some extent;inorganic anions such as Cl^-,NO₃^-and HCO₃^-have unobvious effect on the degradation efficiency of DPH in the two systems,humic acid（HA）can significantly inhibit the degradation efficiency of DPH in both systems.The results also show that the removal rate of DPH in UV/PS system was remarkably enhanced with the increase of PS dosage,and its pseudo first-order reaction rate constants(k_obs)are linearly positively correlated with the change in PS dosage.It was found that the mineralization degree of DPH was lower than the degradation efficiency in UV and UV/PS systems.The mineralization rate under the same conditions was less than 10%in thses systems.UV direct photolysis of DPH produce six kinds of intermediate products including benzophenone imine,benzophenone and 2,2-biphenylacetaldehyde,and two other intermediates such as hydroxyphenytoin were detected in UV/PS system.Based on thedetected products in UV and UV/PS systems,the degradation pathways of DPH were proposed.The biological toxicity of DPH remained a relatively high level in the UV system,but UV/PS system can significantly reduce the toxicity of the solution.Degradation of DPH by UV/PS system had a better inhibitory effect on the formation of disinfection by-products in the subsequent chlorination process,which was obviously superior to the UV system.