This paper describes a pilot plant study on algae removal of a fluidized bed biofilm reactor system for lake water treatment. The system does not need backwashing because the fluidized bed suffers no clogging. Moreover, the system uses dissolved oxygen in influent water for aerobic biological treatment without aeration equipment. Thus, this system is a low energy and easy maintenance way to purify eutrophic lake water. The system was operated continuously at a flow rate of 1500 m³·d^-1 for 9 months at Tsuchiura Port in Lake Kasumigaura. In this study, chlorophyll-a and dissolved oxygen in both influent and effluent water were monitored continuously. In summer (August to September) when water bloom occurred, the average removal efficiency of chlorophyll-a was 64% at the average influent chlorophyll-a concentration of 137.8 μg·l^-1. During the total experimental period (9 months), the average daily amount of removed chlorophyll-a was 40.3g·d^-1 at the average influent chlorophyll-a concentration of 89.5 μg·l^-1. By analyzing the relationship between the removed chlorophyll-a and the consumption of dissolved oxygen, it was estimated that almost all of algae trapped in the reactor was degraded biologically.

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Biodegradation characteristics of cyanobacteria, Phormidium tenue and its metabolites, 2-methylisoborneol(MIB) by protozoan microflagellate, Monas guttula, and the effect of temperature on them were examined in batch culture experiment. The flagellate was found to predate on P.tenue favorably as a food source within a wide temperature range from 10°C to 30°C. Specific growth rate(μ) and generation time(t_d) of the flagellate were 4.6day^-1 and 3.5h^-1, respectively at 20°C and 30°C, whereas in the case of 10°C the lag values of μ and t_d were obtained by 1.9 fold in comparison with the removal ratio of 61% at the first cultivation day and that of 99% at the 2nd day at 30°C, while at 20°C the removal was only about 30% in the first day, but P.tenue could be perfectly reduced at the 2nd day. Although the reduction rate of the P.tenue was slow at the lower temperature of 10°C, the removal reached 98% in the 7th day. Removal rate of P.tenue by the flagellate increased with the increase in temperature and reached maximal value with 4.0h^-1 at 30°C. The flagellate could contribute to the degradation of MIB, although the degradation was lower than that of P.tenue. It was found that the microflagellate could favorably predate on P.tenue and degrade its metabolite, MIB emitting musty odor in a wide range of temperature.

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Grey water from 70 household and some factories in a region without sewer was treated by sequencing batch reactor activated sludge process. Intermittent aeration manner was applied in this study, and several screens were installed in the reactors to remove the massive solid like leaf from the wastewater with the flow rate 26 m³. BOD concentration of influent was more than about 20 mg·l^-1.
Under operation condition of 4 cycles in a day, removal efficiencies of BOD, T-N and T-P were about 92%, 78% and 87%, respectively. Moreover, effluent NH₄-N concentration was maintained about 0.5 mg·l^-1 by controlling the amount of aeration.
When the water tempareture was 11°C in winter, number of cycle in a day was reduced twice and aeration time increated for good effluent water quality. The results showed that good removal efficiencies were achieved under these conditions.

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The characteristics and the effecting factors of the nitrification in the media-added activated sludge process (M-AS) were studied using pilot-plants. The hydrophilic gels and sponges were used as the adhesion media for microorganisms. The nitrification rate of the hydrophilic gels showed 60-109 g-N·m^-3-media·h^-1, and the concentration of the attached microorganisms on the media were 1,500-6,900 mg·l^-1 as MLSS in the oxic reactor. Although the MLSS of the sponges was approximately equivalent to that of the hydrophilic gels, the nitrification rates of the sponges were lower than those of the hydrophilic gels because the principal place for the growth of the nitrifier was considered as the outer surface of the sponges. The media nitrification rate increased in proportion to the increase of the adhesion area of the added media. The DO dependency of the media nitrification was higher than that of the suspended activated sludge. The specific nitrification rate of the attached microorganisms showed 4-5 times higher than that of the suspended activated sludge. The authors considered that this was caused by the low BOD/NH₃-N ratio of the oxic reactor influent.

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Sediments contaminated with nutrients, metals, metalloids, organics, and oxygen-consuming substances etc. can be found in freshwater, estuarine, and marine system throughout the world. Concentrations have been used historically and are still being used to assess sediment quality as an index of chemical contaminants, but such chemical criteria do not always show the toxicity strengh of sediments. The purpose of this study is to evaluate sediments toxicity sampled from Kojima Lake basin using the yeast Saccharomyces cerevisiae. The lag-time at the yeast growth phase was found to be the most sensitive toxicity index among the growth characteristics. The mode of dose-effect curve of environmental samples was different from that of chemicals such as heavy metals when they were administered alone. The toxicity of sediment sampled in spring is higher than in the other three seasons. The toxicity of Kojima Lake samples is higher than those of the two rivers in the same basin. Toxicity of acetone extracts is higher than that of n-hexane extracts from sediments. The yeast S. cerevisiae can be a good biological species to assess sediment toxicity.

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Distribution, composition and possible sources of nitrate and ammonia nitrogen (N0₃-N, NH₄-N) in ground water in Osaka City area were studied. Osaka City has area been developed on the alluvial lowland, where the diluvial terrace extends nearly from north to south within the center of area. Ground water collected from the terrace showed the tendency : NO₃-N >> NH₄-N and vice versa in these from its surrounding plain.
The land-use distribution in city area is 1.1% for agricultural field, and 99% of city area was serviced by municipal sewerage. Therefore, the load of nitrogen from the use of chemical fertilizers, the inadequate disposal of human excreta and domestic sewage are small.
The main source of inorganic nitrogen may be the pore water involving NH₄-N squeezed out with self-compaction of holocence clay bed lying on the aquifer. Such could be seen in the land subsidence of coastal area due to vigorous pumping of ground water in the past. The terrace play a role of the recharge area for the related aquifers in the pain, and so infiltrated surface water has considerable amount of oxygen. NO₃-N was considered to result from the nitrification of NH₄-N from the clay bed or only maintained in water dissolving oxygen.

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