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Transport and Retention of Sulfidized Silver Nanoparticles in Porous Media: The Role of Air‐Water Interfaces, Flow Velocity, and Natural Organic Matter
Author(s) -
Leuther Frederic,
Köhne John Maximilian,
Metreveli George,
Vogel HansJörg
Publication year - 2020
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2020wr027074
Subject(s) - porous medium , saturation (graph theory) , water flow , porosity , dispersion (optics) , materials science , sink (geography) , flux (metallurgy) , adsorption , environmental chemistry , chemistry , chemical engineering , environmental engineering , environmental science , metallurgy , composite material , mathematics , physics , cartography , organic chemistry , engineering , combinatorics , optics , geography
The sulfidation and aging of silver nanoparticles (Ag‐NPs) with natural organic matter (NOM) are major transformation processes along their pathway in wastewater treatment plants and surface waters. Although soils appear to be a sink for disposed Ag‐NPs, the impact of variable saturation on the transport and retention behavior in porous media is still not fully understood. We studied the behavior of sulfidized silver nanoparticles (S‐Ag‐NPs, 1 mg L −1 ) in saturated and unsaturated sand columns regarding the effects of (i) the presence of NOM (5 mg L −1 ) in the aquatic phase on retention, transport, and remobilization of S‐Ag‐NPs and (ii) the distribution and quantity of air‐water and solid‐water interfaces for different flow velocities determined via X‐ray microtomography (X‐ray μCT). Unsaturated transport experiments were conducted under controlled conditions with unit gradients in water potential and constant water content along the flow direction for each applied flux. It was shown that (i) NOM in S‐Ag‐NP dispersion highly increased the NP‐mobility; (ii) differences between saturated and unsaturated transport were increasing with decreasing flux and, consequently, decreasing water contents; (iii) both, solid‐water and air‐water interfaces were involved in retention of S‐Ag‐NPs aged by NOM. Using numerical model simulations and X‐ray μCT of flow experiments, the breakthrough of Ag‐NP could be explained by a disproportional increase in air‐water interfaces and an increasing attachment efficiency with decreasing water content and flow velocity.