Outbreaks of infectious diseases by new pathogenic microorganisms through water utilization have been reported in recent years. Especially, Legionnaires' disease has been recognized as a serious problem in modern societies since a high concentration of Legionella pneumophila often exist in water environment (such as cooling tower, bath water, recreational water) close to human activities. In this study, the quantitative detection method (colony-hybridization) for L. pneumophila was developed by combining the hybridization with the plate culture method. The developed detection method enabled L. pneumophila to be enumerated in various water samples. It was possible to quantify L. pneumophila without interferences of other bacteria by this method in case that the number of total coliforms on the plate was less than 10³ CFU.

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Road sediment is collected by road sweepers, however, it will be flushed because of rainfall. We investigated to determine the collected amount of road sediment and the harm substances attached on the sediment originated from mobile exhaust gases. The correlation analysis was conducted between the environmental factors, such as traffic numbers, species, amount of precipitation and sunny period.
TOC attached on the sediment has the positive correlation with the total traffic numbers, especially Large Freight Vehicles and Large-sized Special Motor Vehicles. On the other hands, the amount of precipitation has the negative correlation with TOC. It will be assumed that the organic carbon originated from exhaust gas can be washed by rainfall and move to road run-off. Some of poly aromatic hydrocarbons are found to have same correlation with environmental factors. Ferric compound has the relation with traffic number because the metal will come from car bodies. Zinc and cadmium have also correlation with the numbers.

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In order to develop the model for predicting the concentrations of toxic chemicals in natural aquatic systems, their relationship between water and sediment were investigated statistically with the data of “Chemicals in the Environment” published by Japan Environmental Agency. As to both the relationship at each sampling station and the relationship between sampling stations, almost all of the relationships for hydrophobic substances were significantly positive, but less significant correlations (sometimes negative) were observed for hydrophilic substances. In the case of high logKow (Octanol-water partition coefficient) (>2) substances, the calculated logKom (the ratio of concentration in mass of sediment organic matter to that in water) agreed closely with the reported ones for aromatic compounds, chlorinated hydrocarbon etc. by the sorption isotherm. In contrast, there observed from two to five degrees of magnitude differences between them in the case of low logKow (<2) substances. Ionic sorption and chemical reaction on sediment surface were most likely to be taken into consideration in order to explain the discrepancy observed for hydrophilic substances.

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Regeneration of the natural zeolite adsorbed by NH₄⁺ by use of saturated sodium chloride solution was examined. The following results were obtained.
1) The regeneration rate of zeolite was not dependent on their place of occurrence and crystal structures.
An empirical formula to predict regeneration rate by the particle size and the solution temperature was obtaind.
2) The space velocity of saturated sodium chloride solution in the regeneration column was determind in order to make the retention time in the column equal to the regeneration time given by the obtained empirical formula.
The volume of the regeneration solution used to obtain 90% regeneration ratio was 1.7ml · meq^-1 for Clinoptilolite and 0.8ml · meq^-1 for Mordenite regardless of NH₄⁺ exchange capacity.
3) The regeneration solution was reused after NH₄⁺ was removed. The regeneration capacity of the reused solution was almost the same as the new solution although K⁺, Ca⁺⁺ and Mg⁺⁺ accumulated in the solution. The sodium chloride used treat one cubic meter of the model wast water by the presented process was 104 grams for Clinoptilolite and 81 grams for Mordenite.

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Production of nitrous oxide was examined in nitrogen removal process treating domestic wastewater from combined sewerage system. Laboratory scale experimental units were set up to simulate circulated process consisting of denitrifying reactor and nitrifying reactor, and intermittent process employing time sequencing of anoxic and aerobic condition. Nitrogen removal was satisfactory and nitrogen conversion from influent total nitrogen to nitrous oxide gas was no more than 0.1% at solid retention time of 10 or 20 days. Continuous monitoring of nitrous oxide revealed that its emission has significant variation. Nitrous oxide emission from nitrification step was greater than that from denitrification in usual situation. However, there were a few days lasting events of abrupt emission of nitrous oxide from denitrification. Such events of high emission contributed to overall nitrous oxide emission to some extent. There was almost no difference in nitrous oxide production between the circulated process and the intermittent process. Hypothetical comparison of greenhouse effect between reduction of nitrous oxide and increased aeration and addition of methanol to reduce nitrous oxide emission indicates that such control methods are justified from the viewpoint of net greenhouse effect when nitrous oxide conversion from wastewater nitrogen is in the order of one percent.

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