Zeta potential of clay-size particles in urban rainfall–runoff during hydrologic transport

Urban rainfall–runoff transports a wide spectrum of anthropogenic aqueous complexes and particulate matter (PM). Zeta potential (ξ) as an electrostatic parameter provides an index of destabilization for clay-size particles (<2 μm) transported during hydrologic processes including passage of the runoff hydrograph. However, ξ of PM in urban rainfall–runoff has rarely been studied due to the dynamic and complex hydrologic, physical and chemical nature of rainfall–runoff systems. This study examined a series of rainfall–runoff events captured from a paved source area catchment in Baton Rouge, LA to characterize ξ of clay-size particles. The ξ of clay-size particles was also examined as a function of hydrologic transport with coupled water chemistry variables. Study results indicated that ξ varied from approximately −15 to −30 mV across the hydrograph of each event and generally mimicked the runoff intensity during hydrologic transport. Hydrologic transport results indicate while ξ was inversely correlated to the hydrograph flow rate, this inverse correlation was a function of variations in water chemistry parameters (pH and ionic strength); parameters that were driven by hydrologic flow rate. For each event ξ exhibited hysteretic trends as a function of rainfall–runoff ionic strength and pH during the passage of the hydrograph. Results demonstrate that hydrologic transport played an important role driving both water chemistry and ξ trends for clay-size particles; as well as treatment behavior of rainfall–runoff unit operations and processes.