The objective of this study is to estimate the purification capacity for organic matter (carbon) in natural and man-made tidal flats. In this study, we measured respiration rates and biomass for diatom+bacteria+meiobenthos and macrobenthos in the permeable layer of soil in tidal flats. Furthermore, the role of these tidal flats for the purification of organic matter in Hiroshima Bay was studied.
The man-made tidal flats had deeper permeable layer for purification of sea water compared to the natural tidal flats. The carbon biomass of bacteria and macrobenthos were not significantly different between the natural and the man-made tidal flats. The respiration rates by diatom+bacteria+ meiobenthos and macrobenthos were not significantly different between the natural and the man-made tidal flats. However, the purification capacity by diatom+bacteria+meiobenthos and macrobenthos in man-made tidal flats was higher than that in natural ones. It is most probable that permeable layer of soil for purification capacity in man-made tidal flats was deeper compared to the natural ones. Purification capacity of natural and man-made tidal flats was compared with external and internal organic loading into Hiroshima Bay. The percent contribution of tidal flats was only about 0.5n%. Even if there were restoration of the area as in 1940s, the constribution will be 1.6%. The purification capacity of organic matter in tidal flats is not large as expected compared with pollution loading in Hiroshima Bay.

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Practical performance of ten individual type gappei-shori johkasous, on-site treatment facilities for household wastewater, were surveyed during a one year period. Effluent BOD and COD were below 20mg·l^-1 with a cumulative frequency of 70% and 80%, respectively. Mixed liquor in the contact aeration tank was recycled to the first chamber of the anaerobic filter tank in the five facilities of which their airlift type pumps could be used to transfer sloughed biofilm. Only one notch type system could easily regulate the amount of the recycled water as 3-4Q where Q was the influent water amount per day, while the amount of recycle changed frequently in the other four facilities. The effluent BOD, N-BOD, T-N, NO₃-N and DKN concentrations were reduced during the recycle operation. Their average values in the recycle mode were 12mg·l^-1, 4.5mg·l^-1, 10mg·l^-1, 4.9mg·l^-1 and 4.3mg·l^-1, respectively. It was clear that the biological denitrification took place during the recycle operation resulting in the decrease not only in T-N and NO₃-N but also in N-BOD which also caused the decrease of BOD. A number of operations in different recycle ratio suggested that effluent T-N could be around 10mg·l^-1 with the recycle ratio below 10Q, and it would be over 20mg·l^-1 with the recycle ratio near to 20Q.

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Coagulant dosed and DO controlled intermittent aeration activated sludge process, which treated domestic wastewater, was investigated so as to examine its ability of nitrogen removal and suppression of the emission of N₂0, one of the greenhouse effect gases. In respect to the N₂O emission into the air, that during aerobic period amounted to about 4 times as large as that during anoxic period. N₂O emission dissolved into the effluent was about 1/3 of that into the air. DO controlled intermittent aeration activated sludge process could achieve high nitrogen removal and restraint of N₂O emission under control of aeration and stirring by measuring DO and water temperature. N₂O conversion ratio from the nitrogen influent and that from the removed nitrogen could be reduced to about 0.05 and 0.06%, respectively, under the nitrogen loading of less than 0.021kg-T-N·kg-MLSS^-1·day^-1. However, each value increased drastically to 0.66 and 1.13%, respectively, under the nitrogen loading of 0.035kg-T-N·kg-MLSS^-1·day^-1. N₂O emission rate was raised over the range of nitrogen loading, at which the influence of higher-nitrogen loading on both the nitrogen removal efficiency and the nitrification ratio came to arise. Consequently, making the treatment under appropriate influent loading, at which satisfactory nitrogen removal efficiency could be obtained, could also restrain N₂O emission simultaneously.

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The objective of this study is to obtain the knowledge about the chemical changes of trichloroethylene (TCE) or tetrachloroethylene (PCE) in the processes of activated carbon adsorption and extraction by supercritical carbon dioxide.
TCE was extracted from 3 kinds of TCE loaded activated carbon samples -adsorbed from 100 ppm of aqueous solution, adsorbed from N2 gas blown through TCE saturated aqueous solution and adsorbed directly-. The infrared spectra of the fluids filtered by zeolite for dehydration after extraction showed normal TCE spectra. So, TCE did not change chemically in these processes.
The infrared spectra of some fluids for the activated carbon samples adsorbed from 50 ppm of PCE aqueous solution revealed the presence of not only PCE, but of TCE also. The dechlorination of PCE to TCE was found to occur in activated carbon fixed bed with adsorption from PCE aqueous solution. Produced TCE was able to be separated from PCE in the activated carbon fixed bed by “chromatographic effect”. In the process of extraction by supercritical carbon dioxide, PCE was found not to change chemically.
So, using the process of “activated carbon adsorption-supercritical carbon dioxide extraction”, TCE or PCE were able to be recovered witiout contaminations of water or products by decompositions, such as hydrolysis.

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A sensitive analytical method using multi-dimensional high performance liquid chromatography (MD-HPLC) has been developed to characterize the cyanobacteria toxins including microcystins RR, YR and LR, known to be hepatotoxic and act as tumor promoters, in lake water. The MD HPLC system was composed of two different columns, i.e., SUPELCOSIL DIOL as a pre-column and Develosil ODS as an analytical column, two 6-port column switching valves and a photodiode array detector.
One liter aliquots of lake water were treated with a Waters Sep-Pak® Vac tC₁₈ cartridge, and 250 μl of the treated solution was injected into the MD-HPLC. Only two fractions on the pre-column, i.e., one fraction including microcystins LR and YR, and the other fraction includ-ing microcystin RR, were passed to the analytical column.
The added standards were recovered in the range from 91.3 to 106.8% at the 0.1 μg·l^-1 level, and from 71.1 to 88.6% at the 0.02μg·l^-1 level. The detection limit of the microcystins in the lake water was 0.01 μg·l^-1.
The proposed method allows the simple, rapid and accurate determination of microcystins in lake water, and is suitable as a routine analysis technique.

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The relationship between meteorological conditions and lake water quality was investigated on the basis of 17-years monitoring data on lake and influent river water quality and meteorological data obtained for a shallow eutrophic lake, Lake Kasumigaura. In order to neglect the yearly trend in watershed environment, the availability of the comparison method between successive 2 years was validated with the correlation method between meteorological conditions and lake water quality after excluding the change in water quality of influent rivers. Using this comparison method, we are able to predict quantitatively the water quality change due to change in meteorological conditions and then have confirmed that an increase in air temperature possibly caused by global warming will result in the deterioration of lake water quality such as increase in COD, decrease in transparency.

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