Modeling volatilization and adsorption of disinfection byproducts in natural watersheds.

It is an emerging concern that a series of disinfection byproducts (DBPs) produced in wastewater effluent have adversely impacted the downstream aquatic system and drinking water resources. The occurrence, fate, and transport of DBPs on receiving waterbodies, however, are currently not well-documented. To fill the knowledge gap, this study simulated the effects of volatilization and adsorption processes on the removals of DBPs (THM, HAA, HAN, HNM, and NA) in different types of watersheds (lake, stream, river, and aquifer). The effects of a series of variables, including hydrogeological characteristics (e.g., water depth, flow rate, roughness), environmental conditions (e.g., temperature, wind velocity), and chemical properties (e.g., octanol-water partition coefficient, Henry's law constant, molecular weight, density) were evaluated and their relative importance were compared. The results indicate that volatilization mechanism was preferred in the stream-type watershed and effective in reducing THMs, but unlikely to reduce HAAs. Adsorption and removal of DBPs on settling suspended solid in surface waters appears insignificant, accounting for less than 8% of the DBP content. Adsorption of DBPs on aquifer soil does not reduce DBPs directly; nonetheless, it reduces the mobility of DBPs in the aquifer and provides a place for other mechanisms to degrade/transform DBPs. The results of this study therefore may help understand the occurrence, fate, and risk of wastewater-derived DBPs in downstream waterbodies, and trigger more laboratory tests in the future to dedicate to the mechanisms and DBPs with significant impact.