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Catalytic oxidative removal of Mn2+ on activated-carbon surfaces by free chlorine was recently discovered and found to be potentially practicable for water treatment when using micrometer-sized activated carbon. Herein, we newly derived a kinetic model for trace-substance removal by catalytic reaction and applied it to the Mn2+ removal. External-film mass transfer, adsorption, and oxidation/desorption contributed similarly to the Mn2+ removal rate under actual practical conditions. The low removal rate in natural water was attributed to decreases in available adsorption sites: e.g., a 50% decrease in available sites in water with 0.26 mmol-Ca2+/L caused a 15% reduction in removal rate. Low temperature greatly reduced the removal rate by both enhancing the decrease in available sites and hindering mass transfer through increased viscosity. While adsorption sites differed 8-fold between different carbon particles, causing a 2.2-fold difference in removal rates, carbon particle size was more influential, with a >10-fold difference between 2- and 30-μm sizes.

Pesticides released into the environment may pose both ecological and human health risks. Governments set the regulations and guidelines for the allowable levels of active components of pesticides in various exposure sources, including drinking water. Several pesticide risk indicators have been developed using various methodologies, but such indicators are seldom used for the selection of pesticides to be included in national regulations and guidelines. The aim of the current study was to use risk indicators for the selection of pesticides to be included in regulations and guidelines. Twenty-four risk indicators were created, and a detection rate was defined to judge which indicators were the best for selection. The combination of two indicators (local sales of a pesticide for the purposes of either rice farming or other farming, divided by the guideline value and annual precipitation, and amended with the scores from the physical and chemical properties of the pesticide) gave the highest detection rates. In this case study, this procedure was used to evaluate 134 pesticides that are currently unregulated in the Japanese Drinking Water Quality Guidelines, from which 44 were selected as pesticides to be added to the primary group in the guidelines. The detection probability of the 44 pesticides was more than 72%. Among the 102 pesticides currently in the primary group, 17 were selected for withdrawal from the group. Keywords: Drinking water quality standards, Ranking, Risk assessment, Index

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 aluminumbased 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 ironbased coagulants with increased virus removal efficiency may not be possible by simply increasing the basicity of the coagulant. [ABSTRACT FROM AUTHOR]