Formation of emerging iodinated disinfection by-products during ballast water treatment based on ozonation processes

Disinfection by-products (DBPs) generated by ballast water treatment pose a potential threat to marine environment which aroused widespread concern. In recent years, emerging iodinated DBPs have attracted widespread attention because of their stronger cytotoxicity and genotoxicity than brominated/chlorinated DBPs. In this study, the effects of different natural organic matter species, total residual oxidant (TRO) concentrations, storage time, temperature, pH, bromide and iodide concentrations on the generation of iodinated trihalomethanes (I-THMs) during ozonation process of ballast water were investigated. The results showed that bromochloroiodomethane and diiodochloromethane (DICM) were not detected under all conditions during ozonation of humaic acid (HA). Different kinds of precursors had a significantly effect on the formation of I-THMs. For algal cells as precursor, DICM were detected (1.22 μg/L), while DICM were not detected from oxidation of 1,3-etonedicarboxylic acid, fulvic acid (FA), phenol, resorcinol, hydroquinone and HA as precursors. The yields of I-THMs from oxidation of algal cells, FA and phenol were higher than other precursors. Linear relationships were observed between the formation of I-THMs and TRO concentrations. The yields of I-THMs reached a peak at 48 h (180 μg/L) after ozonation treatment of ballast water, and then decreased with storage time extension. An increase in temperature enhanced the formation of dibromoiodomethane and bromodiiodomethane, while wakened the formation of iodoform and dichloroiodomethane. The formation of I-THMs was complicatedly affected by different pH values in the range from 4 to 9. The more bromide concentrations, the more brominated I-THMs were formed. The concentrations of I-THMs increased with increasing iodide concentrations, and low concentrations of iodide had greater effect on the production of I-THMs than high concentrations of iodide.