Uncontrolled dumping of discarded tires is hazardous to our ecosystem. Globally, disposal of tire waste to landfills is mostly restricted. Consequently, their reuse in engineering fills as tire derived aggregates is slowly gaining acceptance. During shredding of tires to manufacture tire derived aggregates (TDA), a new waste byproduct is generated which has a high iron content. In preliminary batch studies, it was observed that the TDA byproducts can remove greater than 99% of influent phosphorous concentration present in stormwater. In this study, role of biofilms in a TDA based treatment system is investigated, in terms of phosphorous removal and potential leachability of different toxic metals. Synthetic stormwater, river water and synthetic stormwater was applied as influent to different reactors containing TDA and TDA byproducts. Synthetic stormwater without nutrients was also applied to different reactors to serve as control units without biofilms. The influent applied to the reactors was flushed after every 72 hours and replaced with a new influent. The control units were compared with the reactors receiving synthetic stormwater and river water as influents. After 72 flushes, corresponding to roughly 6 years, it was observed that phosphorous removal capacity was higher in the reactors with biofilms, whereas, leachability of different metals was comparatively minimal in the reactors with biofilms. Reduced leachability and increased phosphorus removal could be attributed to the adsorption of leached metals and incorporation of phosphorous into biofilms. Thereby, it can be said that the presence of biofilms makes the TDA waste product a viable stormwater treatment system
