This study was undertaken to obtain basic data related to the community composition and metabolic functions of estuarine microbes. Water and sediment samples were collected in 2014－2015 from Juso Lagoon (brackish area) and Shirokita Wando (freshwater area) along the Yodo River flowing to Osaka Bay. The genotypes and phenotypes of the estuarine microbes were evaluated, respectively, using eubacterial 16S rRNA genes based on terminal-restriction fragment length polymorphism (T-RFLP) and on carbon-utilization tests using Biolog GN2 plates containing 95 separate carbon sources. The microbial community structure and carbon utilization profiles of the brackish sediment differed greatly from those of freshwater sediment. Canonical correlation analysis revealed that the estuarine microbes could be characterized by conductivity (salinity) and temperature of their habitats. Deltaproteobacteria including sulfate-reducing bacteria were possibly dominant in the brackish sediment, suggesting effects of the high sulfate concentration in seawater on the microbial community. The heterotrophic population and the diversity index calculated from the T-RFLP analysis and the carbon source utilization tests in summer and autumn in vegetation zones were higher than those in non-vegetation zones of both brackish and freshwater areas, suggesting that river vegetation can stimulate microbial activity in the rhizosphere.

The objective of this study is to develop a disinfection system independent of chlorine and energy, that is, electricity or light. Thus a filtration bed immobilized with nanosilver which can generate active oxygen, a sterilization agent, independent of light was proposed. Among seven kinds of filtration media immobilized with nanosilver, pumice, charcoal and zeolite gave the best three high disinfection efficiency, suggesting a microporous filtration media is suitable to exhibit disinfection effect of nanosilver. The effect of tidal flow condition, that is unsaturated and saturated time, on disinfection efficiency was investigated by continuous disinfection tests using a packed bed column with pumice immobilized with nanosilver. It was found that unsaturated time needed to generate active oxygen was more important than saturated time needed for disinfection by filtration media immobilized with nanosilver and a longer unsaturated time gave higher disinfection efficiency. Since the disinfection efficiency was maintained after the total number of times of disinfection treatment reached one hundred, persistence of disinfection effect of nanosiliver immobilize on pumice was confirmed. These results demonstrated enough possibility of the disinfection system independent of chlorine and energy with a filtration bed immobilized with nanosilver.