Removal Of Lodinated Contrast Media Using Nano Zero-Valent Iron

Iodine contrast media(ICM)are widely used in imaging of internal body structure(organ,vascular and soft tissue)during diagnostic tests,which usually enter into the municipal wastewater system through human urine.Traditional methods of treatment cannot effectively remove the contrast agents,resulting in their accumulation and assimilation in the environment to the biological system,causing long-term adverse effects to the environment and the human body.On the other hand,nano zero-valent iron(nZVI)has been widely adopted to treat different pollutant due to its specific properties.In this paper,the potential and mechanisms of Diatrizoate sodium(DTA)removal by nZVI were explored under anaerobic and aerobic conditions respectively.Sodium diatrizoate(DTA)was selected as the model ICM.The results of the study will further promote the removal of contrast agents and the application of nano zero-valent iron.The main contents and conclusions of this paper are as follows.1.The feasibility of nZVI for reductive dehalogenation of DTA under anaerobic conditions was investigated.The impacts of various parameters,including nZVI dosage,DTA concentration,solution pH,aging time of nZVI,the presence of natural organic matter,and the type of competitive anions,on the dehalogenation of DTA as well as the formation of its reductive product 5-diacetamidobenzoate(DABA)using nZVI were evaluated.DTA dehalogenation in terms of its removal and DABA formation was enhanced with the increase in nZVI dosage but deteriorated when increasing solution pH.nZVI aging time had a negative impact on DTA dehalogenation.Natural organic matter at much low level could improve DTA dehalogenation,while had a negative influence at high concentrations.Contrary to sulfate,the presence of nitrate and phosphate strongly inhibited DTA removal using nZVI.The results also showed that the reductive product DABA could be degraded by aerobic biological post-treatment,suggesting DTA dehalogenation with nZVI may be a vital procedure for its biodegradability improvement and consequently complete removal.2.The feasibility of nZVI DTA removal under aerobic conditions was investigated.The impacts of various parameters,including nZVI dosage,solution pH,and the type of competitive anions,on the removal of DTA using nZVI were evaluated.Moreover,the possible removal mechanisms of DTA by nZVI under aerobic conditions was explored.The results showed that DTA could be degraded by nZVI in the presence of oxygen.DTA removal efficiency was enhanced with the increase in nZVI dosage but deteriorated when increasing solution pH.Contrary to phosphate,the presence of nitrate strongly inhibited DTA removal using nZVI.The results also illustrated that the mineralization of DTA by nZVI in the presence of oxygen was slight.Products identification suggested that both dehalogenation reaction and advanced oxidation process were exist during the removal of DTA by nZVI under aerobic conditions.