Iodinated contrast media oxidation by nonthermal plasma: The role of iodine as a tracer

Abstract

The oxidation of trace pharmaceutical compounds in wastewater desalination streams by nonthermal plasma (NTP) was evaluated. Brines from a two stage-RO pilot plant process as well as two sources of tertiary effluents, ultrafiltrated secondary effluents and membrane biological reactor effluents, were comparatively tested with ultra-pure water. The non-ionic and ionic iodinated contrast media (ICM) compounds, iopromide (IOPr) and diatrizoate (DTZ), respectively, were used as model compounds. The neurostabilizer drug carbamazepine (CBZ) was used for reference purposes. Based on deiodination profiles, two distinct patterns of initial oxidation could be established for the ICM. The time profile of deiodination and transformation paralleled for DTZ, indicating that transformation of the aromatic ring is the main initial pattern of transformation. For IOPr, a considerable lag phase of deiodination was observed, suggesting that oxidation of the alkyl chains rather than ring oxidation is the main pattern of initial transformation. Although transformation rate of IOPr was higher compared to DTZ, the rate and degree of deiodination was higher for DTZ than IOPr. Both ICM displayed a markedly lower susceptibility to NTP oxidation compared to CBZ. However, the kinetics of IOPr transformation seems to be less affected by the water matrixes, compared to DTZ and CBZ. Whereas NTP mediated oxidation of ICM followed first-order kinetics, a better fit to Harris model was found for CBZ. As a result of the NTP oxidation, treated brines and effluents displayed a substantial increase in biodegradability (measured as BOD). To conclude, NTP displayed a high potential for treating reluctant pharmaceuticals active compounds such as ICM, even at the background of relatively high DOC concentrations, as can be found in treated effluents and desalination brines, and with no need for chemical additives.