Unraveling complexities of velocity dependent retention and release parameters for E. coli in saturated porous media

Authors: SASIDHARAN, S. - Flinders University; Bradford, Scott; TORKZABAN, SAEED - Commonwealth Scientific And Industrial Research Organisation (CSIRO); YE, XUEYAN - Jilin University; VANDERZALM, JOANNE - Commonwealth Scientific And Industrial Research Organisation (CSIRO); DU, XINQIANG - Jilin University; PAGE, DECLAN - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/11/2017
Publication Date: 6/11/2017
Citation: Sasidharan, S., Bradford, S.A., Torkzaban, S., Ye, X., Vanderzalm, J., Du, X., Page, D. 2017. Unraveling complexities of velocity dependent retention and release parameters for E. coli in saturated porous media. Science of the Total Environment. 603:406-415. doi: 10.1016/j.scitotenv.2017.06.091.

Interpretive Summary: An understanding of factors that influence the fate of bacteria in soils and groundwater are needed to design more efficient remediation strategies and to mitigate the risks of disease causing bacteria on human health. This study investigated the causes and complexities associated with the velocity dependency of bacteria retention and release parameters under different solution chemistry conditions. Results indicate that bacteria retention parameters are strong functions of water velocity due to changes in the adhesive interaction with time and differences in forces and torques that act on bacteria near solid surfaces. This information will be of interest to scientist and engineers, government regulators, and health care professionals concerned with predicting the fate of bacteria in soils and groundwater.

Technical Abstract: Escherichia coli transport and release experiments were conducted to investigate the pore-water velocity (v) dependency of the sticking efficiency (a), the fraction of the solid surface area that contributed to retention (Sf), the percentage of injected cells that were irreversibly retained (Mirr), and cell release under different ionic strength (IS) conditions. Values of a, Sf, and Mirr increased with increasing IS and decreasing v, but the dependency on v was greatest at intermediate IS (30 and 50 mM). Following the retention phase, successive increases in v up to 100 or 150 m d-1 and flow interruption of 24 hours produced negligible amounts of cell release. Conversely, excavation of the sand from the columns in excess electrolyte solution resulted in the release of more than 80% of the retained bacteria. These observations were explained by: (i) extended interaction energy calculations on a heterogeneous sand collector; (ii) an increase in adhesive strength with the residence time; and (iii) torque balance consideration on rough surfaces. In particular, a, Sf, and Mirr increased with IS due to lower energy barriers and stronger primary minima. The values of a, Sf, and Mirr also increased with decreasing v because the adhesive strength increased with the residence time (e.g., an increased probability to diffuse over the energy barrier) and lower hydrodynamic forces diminished cell removal. The controlling influence of lever arms at microscopic roughness locations and grain-grain contacts were used to explain negligible cell removal with large increases in v and large amounts of cell recovery following sand excavation. Results reveal the underlying causes and complexities of the velocity dependency of E. coli retention and release parameters.