Hydrophilic Organic Compound Migration in Biochar-Amended Stormwater Filters with Dynamic Conditions and Varied Background Dissolved Organic Carbon Contents

Urban stormwater runoff carries dissolved, hydrophilic urban pollutants into surface waters and aquifers, impairing human and aquatic health and threatening beneficial stormwater uses, such as augmentation of drinking water supplies. Black carbon-amended stormwater filters have been shown to remove dissolved metal and organic contaminants from urban stormwater runoff, and 1-dimensional intraparticle pore diffusion limited-sorption models have been validated for predicting filter performance under constant flow and influent conditions. However, as stormwater runoff is quite variable, it is important to understand how dynamic conditions and varied background dissolved organic carbon (DOC) affect the filter performance. This study investigates how dynamic flow and influent contaminant loading and variable background DOC conditions affect compound migration and transport modeling in biochar-amended stormwater filters through a series of four column experiments. Dynamic flow and influent contaminant loading conditions substantially affect contaminant migration, which is predicted by using a previously validated transport model with previously determined sorption and apparent intraparticle tortuosity parameters. Increased background DOC (from 3 mg C L^-1 to 18 mg C L^-1) accelerated contaminant migration. Fitting the transport model to observed breakthrough curves and equilibrium batch isotherm experiments reveals that increasing the DOC increases the intraparticle diffusion hindrance, reduces the sorption capacity of the carbon, and increases the linearity of the isotherms. Kinetic limitations of contaminant removal are shown to be exaggerated at higher DOC conditions by quantifying the impacts of DOC and contact time on filter performance. This study provides confidence in the robustness of the contaminant transport model predictions for simulating dynamic conditions and offers insight into the impact of dynamic conditions and background DOC on contaminant removal in biochar-amended stormwater filters.