Work

Modeling bacterial transport and fate: Insight into the cascading consequences of soil water repellency and contrasting hydraulic conditions

Year: 2024

Type: article

Abstract: The mechanisms governing bacteria transport and fate rely on their hydrophobicity and the wettability of porous media across a wide range of soil moisture conditions, extending from extreme dryness to highly saturated states. However, it largely remains unknown how transport, retention, and release mechanisms change in natural soil systems in such conditions. We thus optimized our previously published unique transport data for hydrophilic Escherichia coli ( E. coli ) and hydrophobic Rhodococcus erythropolis ( R. erythropolis ) bacteria, and bromide (Br − ) in two distinct wettable and water-repellent soils at column scale. The soils were initially dry, followed by injecting influents in two pulses followed by a flushing step under saturated flow conditions for six pore volumes. We conducted simulations for each pulse separately and simultaneously for soils. There were differences in hydraulic properties of the soils due to their contrasting wetting characteristic in separate and simultaneously modeling of each pulse affecting Br − and bacteria transport fate. Bacteria attachment was the dominant retention mechanism in both soils in these conditions. Notably, the 82.4 min −1 attachment rate in wettable soil was almost 10× greater than in the water-repellent soil and it governed optimization of bacteria die-off. Physicochemical detachment and physical release unraveled the effect of bacteria size and hydrophobicity interacting with soil wettability. The smaller and hydrophobic R. erythropolis detached more easily while hydrophilic E. coli released; the rates were enhanced by soil water repellency. Further research is needed to reveal the effects of surface wettability properties on bacteria survival especially at the nanoscale. • Modeling showed bacteria attached to natural soils rather than undergoing significant straining. • Greater bacteria attachment occurred in wettable soil than water-repellent soil. • Water-repellency caused selective bacteria physical release or physicochemical detachment. • Optimizations showed small hydrophobic Rhodococcus erythropolis detached, large hydrophilic Escherichia coli released. • Separate optimization of bacteria pulses highlighted physical straining and release roles.

Source: The Science of The Total Environment

DOI: 10.1016/j.scitotenv.2024.176196

Authors: Nasrollah Sepehrnia, Forough Abbasi Teshnizi, Paul Hallett, Mark Coyne, Nima Shokri, Stephan Peth