Effect of coagulant basicity on virus removal from water by polyferric chloride

Abstract

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.