Sorption of viruses during flow through saturated sand columns

Viruses pathogenic to humans have been found in wells and drinking water doe to the improper placement of wastewater disposal operations (e.g., septic tanks, wastewater infiltration basins) and inadequate removal of the organisms as the wastewater percolated through the soil. In order to develop well head protection criteria that are protective of public health, it is necessary to understand the mechanisms that control virus retention and removal in porous media. In this study, we report the results of a series of experiments on virus transport through sand columns (9.2 cm in diameter and 10.5 or 20 cm long) under saturated-flow conditions. Two bacteriophages, MS-2 and phi X-174, were used in the experiments. Virus solution was applied to the lower end of the column as a constant input, and samples were collected at the effluent end. A virus transport and fate model, partially calibrated with the transport parameters obtained from Br- tracer experiments, was used to evaluate the retention and inactivation characteristics of the viruses. We found that, while MS-2 was not sorbed by the Ottawa sand, a significant amount of the applied phi X-174 was retained but not inactivated in the columns. This was probably due to the difference in their isoelectric points. Retention of phi X-174 exhibited trends consistent with first-order attenuation that increased with residence time; however, the sand was found to have a finite sorption capacity for phi X-174. This study also demonstrates that virus sorption can be evaluated more effectively with a well-controlled column flow system than by the commonly used batch equilibration method.