Transport of Escherichia coli phage through saturated porous media considering managed aquifer recharge

Abstract

Virus is one of the most potentially harmful microorganisms in groundwater. In this paper, the effects of hydrodynamic and hydrogeochemical conditions on the transportation of the colloidal virus considering managed aquifer recharge were systematically investigated. Escherichia coli phage, vB_EcoM-ep3, has a broad host range and was able to lyse pathogenic Escherichia coli. Bacteriophage with low risk to infect human has been found extensively in the groundwater environment, so it is considered as a representative model of groundwater viruses. Laboratory studies were carried out to analyze the transport of the Escherichia coli phage under varying conditions of pH, ionic strength, cation valence, flow rate, porous media, and phosphate buffer concentration. The results indicated that decreasing the pH will increase the adsorption of Escherichia coli phage. Increasing the ionic strength, either Na or Ca, will form negative condition for the migration of Escherichia coli phage. A comparison of different cation valence tests indicated that changes in transport and deposition were more pronounced with divalent Ca than monovalent Na. As the flow rate increases, the release of Escherichia coli phage increases and the retention of Escherichia coli phage in the aquifer medium reduces. Changes in porous media had a significant effect on Escherichia coli phage migration. With increase of phosphate buffer concentration, the suspension stability and migration ability of Escherichia coli phage are both increased. Based on laboratory-scale column experiments, a one-dimensional transport model was established to quantitatively describe the virus transport in saturated porous medium.

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

“…Surface charge density of pathogens can also influence their interactions with porous media and affect the migration behaviour ( Baygents et al, 1998 ). A thinner double layer charge on the cell surface can increase isoelectric point and reduce the repulsive force between biocolloids and medium particles, benefiting pathogenic attachment on porous media and suppressing their migration ( Zhang et al, 2018 ). For most RNA viruses, surface charge distribution is uneven ( Jin and Flury, 2002 ).…”

“…pH together with pathogenic isoelectronic point determine pathogen migration in subsurface environment by changing the adsorption-desorption and diffusion process. Pathogen adsorption on porous media is enhanced at lower pH, which decrease their migration rates ( Zhang et al, 2018 ). At higher pH value, pathogenic surface is more negatively charged and is harder to be adsorbed by aquifer media.…”

“…Some experimental evidence shows that MS2 bacteriophage has a higher migration rate in slightly alkaline groundwater (1.13 m/s, pH=8.1) than acidic groundwater (0.90 m/s, pH=6.1) ( Schulze-Makuch et al, 2003 ), and the diffusion coefficients of viruses increase with pH value ( Langlet et al, 2008 ). Elevated solution pH is reported to increase bacterial migration ( Kim et al, 2009 ), whereas the declined pH enhanced virus attachment to aquifer media and colloids, resulting in more retarded virus migration with lower peak-concentration, longer peak-concentration time and higher apparent collision efficiency ( Walshe et al, 2010 , Zhang et al, 2018 ). More bacteriophages MS2 and Φ X174 are attached on the solid-water interface under low pH condition and their migration is slowed ( Torkzaban et al, 2006 ).…”

“…More bacteriophages MS2 and Φ X174 are attached on the solid-water interface under low pH condition and their migration is slowed ( Torkzaban et al, 2006 ). In addition, higher pH can also enhance pathogen migration by encouraging the deprotonation of functional groups on cell surface and increasing the electrostatic repulsion ( Schinner et al, 2010 , Zhang et al, 2018 ). It is also worth noting that, when pH is close to the isoelectric point of pathogens, viruses might aggregate due to the weak electrostatic repulsion interactions, possibly causing blockage and immobile ( Schinner et al, 2010 , He et al, 2014 ).…”

“…Considering these key environmental geochemical and hydrological variables, the risks of pathogen migration in subsurface can also be evaluated by our proposed assessment algorithm but with different indices, following a similar rating and weighting scheme of DRASTIC suggested by the United States Environmental Protection Agency (USEPA) ( Aller et al, 1987 , Barbulescu, 2020 ). Based on the results of previous studies ( Kortelainen and Karhu, 2009 , Zhang et al, 2018 , Zhang et al, 2021e , Arcega-Cabrera et al, 2021 , White et al, 2021 ), the five indices include moisture (25%), flow rate (25%), surface roughness of medium (25%), ionic strength (15%) and pH (10%) ( Table 3 ). Again, this assessment algorithm is only suitable for most subsurface environment, and the importance of these geochemical and hydrological factors depends on pathogenic physiological features and vary significantly across species.…”