Activated sludge processes coupled with membrane filters were operated at 10, 20 and 30°C to study the influences of the water temperature, and various kinds of the nitrogen load conditions on nitrification and emission of N₂O, known as the greenhouse gas. The results obtained were as follows: Lower temperature, higher nitrogen concentration in the influent and shorter HRT caused the decrease of the nitrification efficiency and the increase of N₂O conversion ratio. In addition, the effects of the nitrogen load was higher at low water temperature than high temperature. Under the same condition of the nitrogen load per MLSS, the runs with low MLSS concentration achieved high nitrification rate and low N₂O conversion ratio than those with high MLSS concentration. It was suggested that oxygen diffusion was insufficient in the runs with higher MLSS concentration because of the larger-sized flocculation of the microorganisms, and so that effective oxygen supply was very important to improve the nitrification efficiency under such operational condition.

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An effective removal of suspended solid (SS) by using settled sludge and porous carriers as a filter has been experimentally investigated in a sequencing batch reactor (SBR). In this process, filtration was started in a down-flow mode after the formation of the filter bed, comprising a stratified layer of activated sludge and porous carriers, in a short settling time.
The SS concentration decreased below 10 mg·l^-1 after a short recirculating filtration, indicating that this new solid/liquid separation method is more efficient compared to the conventional gravity settling. The SS removal occurred mainly through the sludge bed. Despite the thickness of the sludge bed change with MLSS concentration, the SS removal rate was nearly the same for the MLSS concentration ranging from 1200 to 4500 mg·l^-1. The experimental results also showed that there is likely a proper filtration rate range which lead to an efficient SS removal, meanwhile no collapse was observed on the sludge bed.

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To evaluate the toxicity existing in effluent water, three different bioassays, in vitro cytotoxicity tests using three human cell lines, bioluminescene inhibition test using luminescent bacteria and daphnia acute immobilization test, were applied to effluent water samples collected from solid-waste incineration plants. Results obtained from bioassays were compared with the results from chemical and physical analysis.
Toxicity observed with bioassays were not necessarily correlated with individual indices from chemical analysis, such as AOX (adsorbable organic halides), dioxins, heavy metal contents and pH. However, the toxicity to human cell lines and daphnia were well correlated with the osmolarity of the samples. Moreover the dose-response curves coincided well with those of standard osmolarity solutions made of sodium chloride or glucose, suggesting that the osmolarity plays a significant role in the toxic effects of these effluent water samples.
Therefore, for the application of bioassays to effluent water samples, especially in case of in vitro cytotoxicity tests and daphnia test, consideration of the osmolarity of the samples is essential for accurate assessment of their toxicity.

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Investigation was conducted on the outbreaks of bloom Gephyrocapsa oceanica KAMPTMER in Tokyo Bay during the first two weeks of May 1995. The bloom broke out in Tokyo Bay early in May, spread to Sagami Bay and died out around May 20. According to our investigation, the bloom was 0.4m transparency, 117μg·l^-1 chlorophyll, 1.5 X 10⁵ cells·ml^-1 of the total amount of plankton and 17.0 mg·l^-1 dissolved oxygen (218.9% saturation). Compared to the bloom of diatom which often breaks out in Tokyo Bay, G. oceanica was much higher in turbidity. Observed values of fluorescene intensity in water and DO have indicated that the outbreakes of the bloom reached the peak from May 8 through May 10. Although the cause and mechanism of the outbreaks of bloom have remained unknownm, it is assumed that G. oceanica was led to Tokyo Bay by the meandering Japan Current and that conditions for its multiplication were met by the bay environment

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