Modeling the transport of titanium dioxide nanomaterials from combined sewer overflows in an urban river

Combined sewer overflows (CSOs) occur frequently in the United States, discharging an estimated 3.2 billion cubic meters of untreated sewage into receiving waters every year. These discharges contain a variety of contaminants including engineered nanomaterials (ENMs), yet ENMs discharged through CSOs have not been taken into account in ENM fate and transport models. This study fills this knowledge gap by developing a new integrated model that links an urban hydrologic-hydraulic model, using the Storm Water Management Model (SWMM), with a three-dimensional hydrodynamic and water quality model of rivers, using the Environmental Fluid Dynamics Code (EFDC). The modeling framework was applied to predict the concentrations of titanium dioxide (TiO₂) ENMs in the Buffalo River in Buffalo, New York, as a result of CSO events. CSOs are shown to have a potential for transient high concentrations of ENMs and thus potentially high localized risk near the CSO outfalls and deposition zones in the river. The present approach provides a promising modeling framework to simulate ENM fate and transport in urban waterways. The model presented in this study can help build a management tool to predict temporally and spatially varying concentrations of ENMs introduced into receiving waters through CSOs.