The integration of ZVI-dehalogenation and electrochemical oxidation for the treatment of complex effluents polluted with iodinated compounds

Abstract

This work evaluates the integration of dehalogenation with Zero Valent Iron (ZVI) and electrochemical oxidation (EO) for the treatment of urines polluted with iodinated X-ray contrast media (ICM). To do this, different strategies were evaluated: pretreatment with ZVI followed by EO (ZVI-EO) or electrolysis enhanced with ZVI-dehalogenation (EO/ZVI). For comparison purposes, single electrolysis was also performed to check the best treatment strategy. Results showed that EO was less efficient than EO/ZVI and ZVI-EO processes. Removal percentages of 74.9%, 87.6% and 99.5% were reached after passing 13.8 Ah dm−3 at 10 mA cm−2 during EO, EO/ZVI and ZVI-EO, respectively. EO/ZVI process favored the production of large amounts of hydroxyl radicals in the effluent through Fenton´s reaction, enhancing the degradation rate of iopamidol (IPM). The pretreatment with ZVI allowed to transform up to 95% of IPM to C17H25N3O8. Then, electrolysis attained the almost complete removal of the raw pollutant (ZVI-EO). The different iodine species formed at the end of the treatment were also monitored, finding similar proportions of organic iodine species for EO and EO/ZVI processes, although single EO promoted the formation of the stable inorganic iodine (IO3-) and EO/ZVI favored the release of I-. Total organic carbon removal percentages lower than 20% were achieved, suggesting that the technologies employed were selective for the removal of the target pollutant under the operating conditions studied. Finally, the organic IPM by-products were also identified by LC-MS and the chromatographic area profiles showed higher values for EO/ZVI followed by ZVI-EO and EO.