The Yodo River, which has a large discharge area, is a source of tap water for fourteen million citizens in the Kinki area. It is also an inflow river supplying the largest pollutant load into Osaka Bay. The flow of the Yodo River, which has the Lake Biwa basin and seven dams in its upper reaches, its flow is usually stable and large water quality changes occur only during flooding stages. During our highly frequent routine observation (once every three days) , eleven events of the ordinary flooding in 2005-2006 and one of the superflooding due to the 1318 typhoon were observed in our past observation period. For superflooding the highest concentrations of T-COD, TOC, and SS, and the largest loadings of all pollutants were observed during the observation period of 1995-2013. The results may be useful reference data for automation operation systems in water supply plants and for the estimation of the impact of inflow pollutants on Osaka Bay. The shares of loads, discharged during the superflooding stage to the annual total load in 2013 were estimated. The differences between the regression equations of total loads of pollutant for the six largest flooding events, included the superflooding event, and all twelve events were clarified. Annual total loads of pollutants were estimated using L-Q equations on the basis of the highly frequent observations in 2013 and ΣL-ΣQ equations for the six flooding events. The total loads in the Yodo River could be estimated with high precision using by the regression equations.

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In the present study, sediment microbial fuel cells (SMFCs) were applied for the amendment of a marine sediment core sample from Tokyo Bay to evaluate their efficacy for bioremediation and the effect of the depth of the anode in the sediment. SMFCs were operated for 55 days, and the maximum power density reached 8.5 mW m^-2. The sediment oxidoreduction potential (ORP) continuously increased from -197 mV to -17 mV during the SMFC operation, and the oxygen consumption rate of the sediment was reduced by 15％. The reduction in the oxygen consumption rate was observed from 16 to 32 days after SMFC installation, during which an increase in the current density of the SMFC was observed. The anode depth had a significant effect on the power generation performance of the SMFC. In particular, an SMFC using an anode placed at the surface of the sediment exhibited a very low power density of 3.0 mA m^-2 compared with an anode placed deep in the sediment (16.5 mA m^-2) . To promote the bioremediation of sediment, the anode must be set at the surface of the sediment as well as in a deeper layer.

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To elucidate the effects of suspended particles on UV disinfection of water, inactivation properties of Escherichia coli and coliphage MS2 were tested in the presence of particles including carbon black (CB) and polystyrene (PS) beads of different sizes and colors. The UV transmittance of samples was mostly dependent on the particle size, rather than the material and color of the particle. Meanwhile, the inactivation efficiency of microorganisms was affected by the particle material and color. Compared with the sample without particle addition, CB at the concentration of 10¹⁰ particles mL^-1 deteriorated the inactivation efficiency of E. coli and MS2, whereas white PS enhanced it, implying a contribution of scattered UV light in the inactivation. The inactivation rate of MS2 with particles was statistically similar to that observed in samples without particle addition (p>0.05) , in spite of the quality of particle-added samples showing turbidity of 0.6–1.5 degrees, color above 13 degrees, and UV transmittance of 56–70%. This study indicates that, in the experimental conditions adopted in this study using standard particles, suspended particles in water do not necessarily interfere with UV disinfection and some particles can even enhance the efficiency by scattering UV light under certain conditions.

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To establish an effective soy-sauce production wastewater treatment system, we designed a combined system consisting of a psychrophilic (20 ºC) up-flow anaerobic sludge blanket (UASB) reactor and a down-flow hanging sponge (DHS) reactor under ambient temperature. The COD removal rate of 87±7％ was achieved at a 26±3.6 kgCOD m^-3 d^-1 organic loading rate (6,500±900 mgCOD L^-1 as influent synthetic soy-sauce based wastewater) in the UASB reactor. 16S rRNA gene sequence analysis revealed that syntrophs belonging to class Deltaproteobacteria, phylum Firmicutes, and phylum Thermotogae, Bacteria belonging to phylum Synergistetes, and methanogens mainly degrade approximately 40％ of the COD of soy-sauce-based synthetic wastewater in the UASB reactor. Syntrophic associations require low hydrogen partial pressure because of the difficulty of this reaction. Therefore, this study revealed that the UASB-DHS system can be applied to real soy-sauce production wastewater containing high organics and sodium concentrations because syntrophic associations were well developed.

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A strainer is one means for preventing the invasion of golden mussels (Limnoperna fortunei) into water facilities. To prevent decreased strainer function as a result of adhesion of golden mussels to the filter element surface, we have studied the applicability of copper alloys as filter media with antifouling properties. Water flow experiments were conducted using an automatic backwash strainer (filter rating: 30 μm) made of cupronickel or brass alloy in Lake Ohshio, Gunma, Japan, which is a habitat of golden mussel. For both copper alloys, no invasion of juvenile mussels into the pipe downstream of the strainer was observed, and no adhesion of mussel was observed on the filter surface. As described above, the copper alloy was found to be effective as a filter material for countermeasures to golden mussel invasion. However, corrosion in the water flow section of the strainer was observed owing to the destruction of the oxide film. Hence, the use of copper alloy was found to require corrosion protection.

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Primary water quality factors influencing the long-term change of blue-green algal growth in Lake Kasumigaura were investigated using water quality data surveyed by the public sector. Blue-green algae tended to grow when the dissolved oxygen (DO) concentration at the sediment surface decreased and the dissolved Mn (D-Mn) concentration increased. With a statistical analysis of the water quality data, the influence of D-Mn released from the sediment on the growth of the blue-green algae was discussed. Furthermore, seawater intrusion was inferred to be the major environmental factor behind the decrease in the DO concentration at the sediment surface. For the clarification of the mechanisms of the changes in the growth of blue-green algae, surveys and research needed in the future were proposed.

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Modeling the processes by which dissolved inorganic nitrogen and phosphorus contribute to biological productivity would be of assistance in restoring the soundness of the material cycles and food web in semi-enclosed seas. In this study, field observations to investigate the biogeochemical cycle of nutrients and the spatial variations were conducted in Osaka Bay in August and November 2015 to obtain basic data for modeling. The observed results for a stable isotope of dissolved organic carbon showed that dissolved organic matter is generated in the bay in summer in addition to those supplied from rivers. The dissolved organic matter spreads along the conservative mixing line toward the shelf sea. These results suggested that dissolved inorganic nitrogen and phosphorus supplied from rivers were assimilated by phytoplankton and transformed into dissolved organic matter, a large part of which flowed out of the bay before degradation into inorganic matter. The abundance of heterotrophic bacteria and cyanobacteria, and the significant correlations between those and heterotrophic nanoflagellates suggested that a significant amount of nitrogen was taken into the microbial loop by heterotrophic bacteria feeding on dissolved organic matter and cyanobacteria consuming the nutrients.

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