Application of silver nanoparticles (nAg) or silver nitrate (AgNO3) has been shown to improve the microbiological efficacy of ceramic water filters used for household water treatment. Silver release, however, can lead to undesirable health effects and reduced filter effectiveness over time. The objectives of this study were to evaluate the contribution of nanoparticle detachment, dissolution, and cation exchange to silver elution, and to estimate silver retention under different influent water chemistries. Dissolved silver (Ag(+)) and nAg release from filter disks painted with 0.03 mg/g casein-coated nAg or AgNO3 were measured as a function of pH (5-9), ionic strength (1-50 mM), and cation species (Na(+), Ca(2+), Mg(2+)). Silver elution was controlled by dissolution as Ag(+) and subsequent cation exchange reactions regardless of the applied silver form. Effluent silver levels fell below the drinking water standard (0.1 mg/L) after flushing with 30-42 pore volumes of pH 7, 10 mM NaNO3 at pH 7. When the influent water was at pH 5, contained divalent cations or 50 mM NaNO3, silver concentrations were 5-10 times above the standard. Our findings support regular filter replacement and indicate that saline, hard, or acidic waters should be avoided to minimize effluent silver concentrations and preserve silver treatment integrity.

Nanomaterials are subject to various physical, chemical, and biological transformations, necessitating a better understanding of the impact of “aging” processes on nanoparticle fate and transport in engineered and natural porous media.

A one-dimensional mathematical model is developed and implemented to describe the coupled transport of citrate-stabilized silver nanoparticles (nAg) and dissolved silver ions in porous media. This hybrid numerical simulator employs an Eulerian finite difference (FD) method to model the reactive transport of dissolved constituents and a Lagrangian (random-walk particle-tracking (RWPT)) approach to capture the transport and differential aging of nanoparticles. Model performance is demonstrated by comparison of simulations with data obtained from a series of nAg transport and dissolution column experiments. A three pore volume pulse of a citrate-stabilized nAg suspension (ca. 3 mg/L) was introduced into a 12 or 16 cm long column packed with water-saturated quartz sand at a pore-water velocity of ca. 7.6 m/day and pH 4 or 7. While low retention levels (ca.17%) and no dissolution were observed for the pH 7 column, analysis of column effluent samples for pH 4 conditions indicated that ca. 88% of the injected silver mass was retained in the column, while 6% was eluted as particles (nAg) and 6% as dissolved ions (Ag(+)). Hybrid model simulations, employing a lumped nAg dissolution coefficient of (3.45 ± 0.35) × 10(-2)/h, are shown to accurately capture measured nAg transport and Ag(+) release behavior. A model sensitivity analysis explores the influence of flow velocity and particle size on nAg transport and fate, indicating that as velocity and particle size decrease, nAg dissolution and Ag(+) transport processes increasingly dominate silver mobility.