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We investigated the effect of coagulant basicity on bacteriophage removal from river water by polyferric chloride (PFC). PFC at three basicities (basicity 0.9–2.1) was prepared by means of base titration (NaOH was added to ferric chloride (FeCl3) solution) and the virus removal efficiencies of those PFCs were compared with that of FeCl3 (basicity 0). The virus removal efficiencies of the PFCs were equal to or less than that of FeCl3 at both pH 6 and pH 8. This suggests that, unlike aluminum-based coagulants, increasing the basicity of iron-based coagulants does not improve virus removal efficiency. Furthermore, the relative abundance of monomeric iron(III) species in the PFCs decreased, whereas that of precipitated iron(III) species increased with increasing basicity, as assessed with a ferron method. Colloid charge density also decreased with increasing basicity. Therefore, it is likely that the reduction in the abundance of monomeric iron(III) species led to the reduction in colloid charge density, which then reduced virus removal efficiency. Thus, the development of novel iron-based coagulants with increased virus removal efficiency may not be possible by simply increasing the basicity of the coagulant.

Noroviruses (NVs) are one of the leading causes of epidemic gastroenteritis around the world. Water treatment technologies using membrane filtration for virus removal are becoming increasingly important. However, experiments to test removal of NVs from water have been hampered because NVs do not grow in cell culture or in small-animal models and therefore cannot be easily artificially propagated. Expression of the NV genome in a baculovirus-silkworm expression system has produced recombinant NV virus-like particles (rNV-VLPs) that are morphologically and antigenically similar to native NV. Here, we characterized these rNV-VLPs and evaluated their potential use in assessing NV removal. Electron microscopic analysis and peptide mass fingerprinting showed that the rNV-VLPs were morphologically identical to native NV. In addition, surface charge and particle size distribution, which are important factors for explaining virus particle behavior during membrane filtration, were successfully evaluated by using rNV-VLPs. The rNV-VLPs were easy to quantify with a commercially available enzyme-linked immunosorbent assay kit, they remained stable for several days at 4 °C after dilution in river water, and they were easy to concentrate with the ultrafiltration entrapment method used. Thus, rNV-VLPs can be used to facilitate our understanding of the behavior of NVs during membrane filtration processes.

The ability of in-line coagulation pretreatment with high-basicity polyaluminum chloride (PACl) coagulants to enhance virus removal by ceramic microfiltration (MF) was examined by comparing virus removal efficiencies from water pretreated with PACl-2.2 (basicity 2.2) and PACl-2.5 (basicity 2.5) versus alum, a synthetic aluminum chloride (AlCl3) solution, and two commercially available PACls, PACl-1.5 and PACl-1.8. The virus removal ratios for AlCl3, alum, PACl-1.5, and PACl-1.8 decreased markedly when the pH of the treated water shifted from 6.8 to 7.8, but was high at both pHs for PACl-2.2 and PACl-2.5. PACl-2.5 contains Al13 species and possibly Al30 species, and has a high colloid charge density. It removed viruses more efficiently than the other aluminum-based coagulants, not only at neutral pH, but also under weakly alkaline conditions. Moreover, the in-line coagulation–ceramic MF process with PACl-2.5 pretreatment removed not only viruses but also dissolved organic carbon and UV260-absorbing natural organic matter more efficiently and resulted in a lower residual aluminum concentration than did commercially available PACls, especially under weakly alkaline conditions. A combination of coagulation pretreatment with a high-basicity PACl and ceramic MF can provide effective treatment of drinking water over a broader pH range than is possible with commercially available aluminum-based coagulants.

The feasibility of in-line coagulation as a pretreatment for ceramic microfiltration (MF) was verified by comparing its efficiency in the removal of viruses with that of the traditional mechanical mixing approach for coagulation, and by examining the effect of coagulant dose and coagulation time on virus removal. The in-line coagulation–ceramic MF system efficiently removed bacteriophage Qβ and MS2: removal ratios were >8.2 log for infectious viruses and >5.4 log for total (infectious + inactivated) virus particles. These values were similar to those of the mechanical coagulation–ceramic MF system. The in-line coagulation system has potential as a useful pretreatment for the removal of viruses as an alternative to the mechanical mixing system, because the former efficiently removes viruses and has a smaller footprint in treatment plants. For the in-line coagulation–ceramic MF system, a coagulant dose of 1.08 mg-Al/L and a coagulation time of 1 min were required to achieve a high level of virus removal. Infectious Qβ and MS2 were removed to similar levels by the two precoagulation methods tested, but the removal of total MS2 particles was higher than that of Qβ particles, possibly because of the selective interaction with the cake layer.

We evaluated the removal of virus (bacteriophage Qβ) after hydraulic backwashing and the effects of reversible and irreversible membrane fouling on virus removal by a coagulation–microfiltration (MF) system. The rate of virus removal in the coagulation–MF system was low at the beginning of filtration but increased with filtration time, owing to the accumulation of foulant on the membrane. The rate of virus removal thereafter remained high, even after hydraulic backwashing of the membrane to remove reversible membrane foulant. The presence of irreversible, rather than reversible, membrane foulant contributed to the increase in virus removal rate observed at the beginning of filtration. The irreversible membrane fouling maintained a high virus removal rate even after hydraulic backwashing. Moreover, irreversible fouling of the membrane during long-term filtration (1 month) improved virus removal in the coagulation–MF system, and the membrane excluded virus particles even in the absence of coagulation pretreatment. Therefore, the accumulation of irreversible membrane foulant with filtration time played an important role in virus removal by the coagulation–MF system.

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.