Tracing the sources of iodine species in a non-saline wastewater

There are two types of wastewater in Hong Kong, non-saline and saline wastewaters. When it comes to disinfection, iodide is an important inorganic ion in concern because it may involve in the formation of iodinated disinfection byproducts, which show significantly higher toxicity than their brominated and chlorinated analogues. In this study, it was found that a non-saline wastewater in Hong Kong contained an unexpected high level of iodine. To trace the iodine sources of this non-saline wastewater, the information of the corresponding area was collected to find the possible iodine sources; then, the water samples from the possible iodine sources were collected; the concentrations of iodine species (iodide, iodate and organic iodine) in these collected water samples were determined; finally, the contribution percentages of iodine species from different sources were calculated. The results revealed that a specific domestic wastewater was the major iodine source, contributing to 68.6% of total iodine, 66.3% of iodide, 57.0% of iodate, and 112% of organic iodine in the non-saline wastewater, while landfill leachate, industrial and hospital wastewaters were the minor iodine sources, contributing to 6.6%, 3.1%, and 3.0% of total iodine in the non-saline wastewater, respectively. Furthermore, it was found that the extensive use of salt might result in high levels of iodine in the domestic wastewater and thus lead to the high level of iodine in the non-saline wastewater.