Virus removal in a hybrid coagulation–microfiltration system–Investigating mechanisms of virus removal by a combination of PCR and PFU methods

Virus removal performance and mechanisms were investigated in a hybrid coagulation–microfiltration (MF) system by using river water spiked with bacteriophage Qβ. Virus removal increased with filtration time: the rate of virus removal was 4 log at the beginning of filtration and gradually increased to 6 log over 5 h, probably because of the growth of a cake layer that accumulated on the membrane surface. Quantification of the virus particles in the MF compartment by a combination of a polymerase chain reaction (PCR) method and a plaque forming unit (PFU) method revealed that most of the virus (>99.999%) in the MF compartment was entrapped in the aluminium floc and then located in the solid phase; most of the virus (>99.9%) in the solid phase was inactivated. The rate of recovery of virus particles from the MF compartment decreased with filtration time: after 3 h of filtration approximately half of the virus particles in the MF compartment were not recovered by hydraulic backwashing, indicating that the virus might have been retained on the MF membrane as part of an irreversible foulant.