N₂O is emitted through the wastewater treatment process, especially through biological nitrification and denitrification. Recently much attention has come to be paid to N₂O emission, because N₂O is one of the greenhouse effect gases, which is causing global warming. In this study, examination on the effectiveness of DO controlled intermittent aeration activated sludge process was made with respect to suppression of N₂O emission and improvement of nitrogen removal. The results obtained were as follows: DO control operation was superior to former timer control operation for the ability of both suppression of N₂O emission and nitrogen removal Judging from ORP in the aeration tank, DO control operation could change the surroundings in it periodically for the effective progress of nitrification and denitrification. At the pilot plant experiments, DO control operation was confirmed to be very effective way to suppress N₂O emission and to enhance nitrogen removal efficiency; The conversion ratio from removed nitrogen to N₂O-N was restrained to 0.05% and nitrogen removal efficiency reached over 80%. It was clarified that coagulant dosed and DO controlled intermittent aeration activated sludge process would be very promising way to prevent global warming and to improve water environment.

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Effects of sewage effluent on periphytic algae in the River Tsunaki were surveyed using artificial substrata in weekly during summer in 1996. The artificial substrata were settled at 2m upper and 2m downstream site of the discharging point. After two weeks they were exchanged to clarify the influence of sewage on the periphytic algal community succession. Water quality were surveyed at three stations, artificial substrata settling sites and discharging point.The average concentrations of BOD were 0.7 (downstream site), 0.8 (sewage effluent) and 1.1mg/l (upstream site) . The many nutrient concentrations were constantly high at downstream site by the sewage effluent.
Different algal communities were formed on artificial substrata at the upper and down site. Of fifty algae recorded, Nitzschia amphibia (at the upper site) and Stigeoclonium spp. (at the down site) were dominant.Nitzschia amphibia is eurysaprobic species and Stigeoclonium spp.is a tolerant species for pollution. It was found that after forming the stable periphytic algal communitiy the sewage didn't influence the algal succession on artificial substrata. The successions of algal periphytic community on artificial substrata exchanged between the upper and down sites after two weeks reflected the enviromnent before the exchange. But the diversity index of them were down by the sewage eflluent.

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This paper investigated effects of the abundance of total bacterial populations and of limiting resources for bacteria on the removal process of bacteria by predation in a microbial community. For this analysis, an experimental, continuous flow system of a column bed-reactor was employed, to which bacterial suspension containing three species was supplied. The column reactor contains fiber carrier seeded with activated sludge. Population dynamics of bacteria, protozoa, and metazoa in influent and in effluent were examined under several conditions with varying total bacterial density and concentration of limiting resources contained in influent. The experimental results showed the tendency that bacterial density in the effluent was not affected either by the influent total bacterial density or by the resource abundance, which is explained using a mathematical model of one resource, one prey and one predator species. Experimental results suggests that the higher influent abundance of bacteria and/or resources for bacteria raise the size of predacious populations sustained in the community and species richness as well, which keeps the bacterial density in the effluent constant.

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An experiment was carried out concernings wine wastewater treatment by aprocess consisted of the UASB reactor (20 cm in diameter, 300 cm in height) and an aerobic biological filter (9.6 cm in diameter, 200 cm in height) as a post treatment. Filter medium modules consisted of polyester non-woven cloth and polyvinyl chloride spacer sheet were packed in the biological filter.Swine waste discharged froma flat floor type swine barn was used as influent which average water quality was 535 mg/l for BOD and 72 mg/l for NH₄-N. Hydraulic retention time of UASB reactor was about 1 day.The average loading rate of BOD was 0.5 kg/m³⋅day for the UASB reactor and 1.4 kg/m³⋅day for the biological filter. The experiment was carried out from July to December at ambient water temperature. Forty to seventy percent of BOD removal rate was maintained for the UASB reactor at water temperature of 5-30°C.The removal rate of BOD by the biological filter was 30-80%. An average settled effluent BOD was 52 mg/l during 5 July and 5 November and increased to about 148 mg/l during 10 November and 22 December. Reduction rates of NH₄-N by the biological filter were about 30-50% at the water temperature of 25-30°C, and lO-25% at the water temperature of 5-10°C.

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浄水場のろ過池に入る流入水とろ過水中の微粒子の大きさと数を測定して、緩速ろ過池の浄化能について検討を行った。また、実際の家庭に供給されている45点の水道水についても微粒子数の測定を行った結果、以下のことが分かった。
1) 流入水中、ろ過水中には微粒子直径2～<3μm間の微粒子数が多かった。
2) ろ過水中の微粒子数はろ過池間でほとんど差がなかった。
3) 流入水が緩速ろ過池を通過すると93分の1に微粒子数が減少した。
4) 水道水中には、2～<15μm間の全粒子数が1ml当たり平均106個あった。緩速ろ過処理による水道水は全粒子数の変動の幅が小さかった。

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Nitrification characteristics of immobilized microorganisms and suspended sludge in a nitrified liquor recycling process were examined through plant operation tests using synthetic and real municipal wastewaters. Influence of factors was evaluated on nitrification performance of a nitrification tank using pellets with immobilized microorganisms, and contributions to overall nitrification of the tank were estimated on pellets and suspended sludge respectively from nitrification activities based on respiration rates. It was confirmed that the nitrification rate of the nitrification tank sensitively depended on the DO concentration in the tank and followed the Monod equation. As the half saturation constant for DO concentration in the equation, a value of around 9mg/l was obtained, which was higher than reported values of 0.5 to 2 mg/l for suspended sludge. The nitrification activity of pellets decreased to a great extent due to limitations by low NH₄-N concentrations (Ne) of less than around 0.3 mg/l in the nitrification tank, and shared the contribution ratio to overall nitrification of the tank with suspended sludge almost evenly. While, the nitrification activity of pellets increased significantly to cover nearly 90% of overall nitrification when Ne exceeded 0.3 mg/l at low water temperatures or high nitrogen loading rates. It is concluded from these results that monitoring and control of DO and NH₄-N concentrations are important in operating the nitrification tank using pellets.

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