Bacterial population dynamics and nitrification characteristic of immobilized activated sludge have been investigated during acclimation procedure to inorganic synthetic wastewater (NH₄-N 20mg·l^-1). A 1.5 liter reactor was operated at 20 °C with a hydraulic retention time of 3 hours for the start-up and 1 to 3 hours after 2 years. Number of nitrifying bacteria in pellet entrapping activated sludge increased around 10³ times in the first 10 days and reached to a higher level of 10⁸ to 10⁹ cells·ml^-1-pellet. The higher level was still maintained after 2 years. At the same time heterotrophic bacteria existed 10⁸ to 10⁹ cells·ml^-1-pellet throughout the operation. Electron micrographs of cross sections of pellet, both in the start-up period and after 2 years, suggested the coexistence of nitrifiers and heterotrophes both of which formed respective colonies. It was confirmed that the nitrification activity increased 3 times when the number of nitrifying bacteria increased 10 times.

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In this study, the relations between the toxicity and chemical structure of phenol and 16 chlorophenols from mono-chlorophenols to penta-chlorophenol (PCP) were investigated by using two kind of toxicity (IC₅₀ value, RCR₅₀ value) and 6 physicochemical parameters (log P_OW, pKa, Σσ, MIC, ΣD, mp), respectively.
The increase of the chlorine atom number in chlorophenols enhanced the toxicity to activated sludge (IC₅₀ value) and mouse liver mitochondria (RCR₅₀ value). A good linear correlation of γ=0.964 (n=17) was observed between the log 1/IC₅₀ and the log 1/RCR₅₀.
From the viewpoint of sensitivity, RCR₅₀ value has proved superior to IC₅₀ value in the order of 4 to 87 times. However, IC₅₀ value surpassed than RCR₅₀ value in a simple, rapid and stable method of determining the toxicity.
The log 1/IC₅₀ was closely correlated with log P_OW (γ=0.970), Σσ (γ=0.928), MCI (γ=0.922) and ΣD (γ=0.955), but was correlated with pKa (γ=0.736) and mp (γ=0.515). Physicochemical properties of the log 1/RCR₅₀ were also similar to those of log 1/IC₅₀.
From these results, the close correlation was observed between toxicity of IC₅₀ value or RCR₅₀ value and structure-activity relations of chorophenols tested.

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Enteropathogenic(EPEC), enterotoxigenic(ETEC), enterohemorrhagic(EHEC) and enteroinvasive(EIEC) Escherichia coli were investigated for susceptibility to UV radiation at 254nm and photoreactivation. The conclusions obtained in this study can be summarized as follows. 1) The doses of UV light required for 90 and 99 % inactivation of tested pathogenic Escherichia coli ranged from 0.1 to 7.1 mW·sec·cm^-2 and from 0.2 to 9.8 mW·sec·cm^-2, respectively. 2) Apparent photoreactivation with visible light from a fluorescent lamp was observed in EHEC O26 (FK10), EHEC O26 (FK11), EIEC O124, EIEC O152, EPEC O55. ETEC O6, ETEC O25 (FK20) and ETEC O25 (FK21), but not EHEC O157:H7, EIEC O167, EPEC O44, EPEC O142, EPEC O127 and ETEC O6:H16.

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Omura Bay is located in the central part of Nagasaki Prefecture and is connected with the open sea through Sasebo Bay by two narrow straits. Therefore movement of the bay water is very stagnant and oxygen-deficient water masses are formed at the bottom layer in the central part of the bay every summer.
We have been measuring the concentrations of phosphorus in this bay for twelve years.
The concentrations of total phosphorus in the surface layer began to increase gradually after 1992.
The concentrations in the whole bay become about 10 μg·l^-1 higher after September than those in the earlier months every year. It is thought that orthophosphate in the bottom layer at the central part of the bay, which was released from the bottom sediment in summer, causes the increase of total phosphorus in the surface layer after September. This water mass which has been enriched by ortophosphate (as total phosphorus : 70-100 μg·l^-1) is diffused by circulation owing to the drop in water temperature of the surface layer and mixing by wind, and the concentration of total phosphorus in the surface layer will rise.

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Hydroponic biofilter method which is a kind of technique for constructed wetlands was applied to purification of hyper-eutrophic Lake Kasumigaura water during July to September in 1994. Several kind of plants, such as Chinese Puk-Bung, Water Cress, Water Funnel and Spearmint, were cultured using artificial channels, and removal rates of particulate and dissolved nutrients from lake water were surveyed.
Average removal rates (g·m^-2·d^-1) of organic carbon, total nitrogen and total phosphorus during the summer period were as following; Chinese Puk Bung, 13.1, 3.05 and 0.095 ; Water Cress, 12.7, 1.80 and 0.029 ; Water Funnel, 8.4, 0.66 and -0.013 ; Spearmint, 14.7, 1.75, and 0.045 ; Control (filamentous green algae), 10.3, 1.65 and 0.021, respectively. Chinese Puk Bung showed high removal rates.

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