Virus removal and transport in saturated and unsaturated sand columns

The purpose of this research was to determine the role that unsaturated flow conditions play in virus sorption and inactivation during transport through sand columns. Column flow experiments were conducted in Ottawa sand under both saturated and unsaturated flow conditions using two bacteriophages, MS2 and φX174. Input solution containing bromide (Br−) tracer and the viruses was applied to the column as a step function and samples were collected at the effluent end using a fraction collector. The convection–dispersion equation, partially calibrated with the transport parameters measured from the Br− signal, was used to evaluate the sorption and inactivation characteristics of the viruses. We found that, while removal of both MS2 and φX174 increased significantly under unsaturated flow conditions, the mechanisms responsible for removing the two viruses seemed to be different. The results from elution experiments using beef extract solution revealed that the increased removal of φX174 in the Ottawa sand under unsaturated conditions appeared to be caused by increased sorption whereas the increased removal of MS2 was due to inactivation. The difference in virus removal and transport behavior between saturated and unsaturated conditions was likely caused by additional sorption at the solid surfaces and the presence of the air–water interface (AWI) in the unsaturated system.