Nitrification and denitrification in the semi-aerobic landfill of the circulatory type are experimentally studied. This landfill method is characterized by the circulation of leachate and has the advantage of the rapid decrease in the concentrations of organic matter and total-nitrogen with time.
Two dimensional model reactors of the semi-aerobic landfill were constructed, and experiments with incinerator residus as contents had been continued for about 3 years. Mass balance in the reactors based on the chemical analysis of leachate, supplied substrates, and the remaining materials in the reactors was discussed. As a result, it was found that both nitrification and denitrification are caused in the reactors and that 0.95g of organic carbon was consumed for the denitrification of 1g of nitrogen. From the counted numbers of microorganisms in the contents and leachate, the biological ecosystem in the landfill is expected to be as follows : First, oligotrophic bacteria are dominant species, and the denitrification observed in this study is caused by oligotrophic denitrifying bacteria ; Second, denitrifiers utilize the organic-carbon produced by proteolytic bacteria decomposing autotrophic organisms such as nitrifying bacteria.

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Vertical location profiles of carp (Cyprinus carpio) in a water tank having 0.055.0mg·l^-1 of CN^- as a chemical component model of acute toxic conditions were investigated in order to propose criteria for judging abnormal water quality based on analysis of fish movement patterns by means of image recognition.
The findings were summarized as follows.
1) Under normal conditions, the carp usually frequented the lower one third of the water tank. The carp was observed near the surface (to a depth of 70mm) less than 20% of the observed time.
2) An abnormal movement pattern of carp when CN^- was present could be distinguished from the movement pattern under normal conditions, based on the breathing index proposed herein.
3) Continuous image recognition of fish and the analysis of their movement patterns over a 10 minute period could successfully detect CN^- concentrations higher than 0.1mg·l^-1.

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The amounts of changes in loadings and concentrations of pollutant matters, during flowing down in an irrigation channel without influx and efflux to outside, were estimated from the view point of mass balances under the ordinary loading condition by three diurnal observations and a daily observation. The diurnal means of flowing down rates for the conservative dissolved matter were nearly about 1.0, but most particulate organic matters ranged from 0.7 to 1.0. In an urban river where the concentrations of P0₄-P and SS were high, dissolved P0₄-P became particulate phosphorus with the adsorption to the suspended solids. But in the channel where both concentrations and the ratio of P0₄-P/SS were lower than urban rivers such changes were small and inconspicuous. The inclusive self-purification coefficients of organic matter including sedimentation and adsorption became larger than that by the conventional method using impulse injection of refined organic matter of high concentration. In the regular rectangular channel where the discharge and the water quality were stable, the removal of organic matter with sedimentation and adsorption was made clear to play an important roll in the inclusive self-purification as well as a river.

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The freezing rate has an appreciable effect on the solid-liquid separation characteristics of excess activated sludge in freezing and thawing process, which is considered to be one of the effective preconditionings of sewage sludge dewatering. The freezing rate was controlled from 0.581 to 25.0 mm h^-1 under a constant freezing temperature, -16.5°C.
The dewatering characteristics were more improved by slower freezing rate except below 2mm·h^-1. Suspended solids were more concentrated at the central region of freezing column by slower freezing rate. Dissolved organic carbon concentration (DOC) increased after thawing of frozen sludge, and its increment did not depend upon freezing rate. The DOC of thawed sludge increased during standing in room temperature (30°C) for 2 hours, and the increment was higher with more slowly frozen sludge. This suggested that the sludge cell structure would be physically destroyed more appreciably with slower freezing rate.

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